I
Ice - see Cyrotherapy
IGF-1 (Insulin-like Growth Factor-1)
Immune system
Incretins (GLP-1 and GIP)
Inflammation
Insulin
Insulin - hyperinsulinaemia
Insulin testing
Insulin Dysregulation
Insulin Resistance
Insulin tolerance test (ITT)
Invokana - see Canagliflozin & SGLT2 inhibitors
Iron
IGF-1 (Insulin-like Growth Factor-1)
Immune system
Incretins (GLP-1 and GIP)
Inflammation
Insulin
Insulin - hyperinsulinaemia
Insulin testing
Insulin Dysregulation
Insulin Resistance
Insulin tolerance test (ITT)
Invokana - see Canagliflozin & SGLT2 inhibitors
Iron
Ice - see Cryotherapy
IGF-1 (Insulin-like Growth Factor-1)
Insulin-like Growth Factor-1 is a hormone with a similar molecular structure and functional homology to insulin. IGF-1 is involved in cell proliferation.
There are currently (2017) two theories about what causes endocrinopathic (EMS-Associated) laminitis:
1. high levels of insulin act on IGF-1 receptors causing laminar stretching and weakening;
2. high levels of insulin cause vascular resistance and endothelin-1 expression.
From Equine Laminitis 2017 Chapter 37 PPID by Dianne McFarlane, Philip J Johnson and Harold C Schott II.
1. The IGF-1 theory: "Heightened levels of circulating insulin (hyperinsulinemia) are thought to adversely affect the integrity of the digital lamellae by insulin-mediated activation of insulin-like growth factor 1 (IGF-1) receptors on basal epidermal cells in the hoof" (see de Laat et al. 2013 below).
2. The vascular resistance theory: "hyperinsulinemia may also cause increased vascular resistance and endothelin-1 expression in the equine digit, suggesting that the risk of endocrinopathic laminitis might also result from abnormalities of perfusion". (See Gauff et al. 2013 but note that Gauff's research is in vitro on dead severed limbs, and the authors state that "This model has several drawbacks, and results cannot be transferred to the in vivo situation without considering the major differences between the experimental set-up and the complex in vivo situation").
However, Nanayakkara et al. 2019 looked at hoof and liver samples from healthy (but dead) horses and their results did not support the hypothesis that insulin causes laminitis by binding to IGF-1 receptors in the lamella. Insulin (not equine) had low affinity for binding to equine IGF-1 receptors, much lower than IGF-1, and binding by insulin was only seen at very high concentrations that would be unlikely to occur in horses. Only a small population of insulin receptors, confined to the endothelial cells that penetrate the lamellae, was found. The authors suggested that high concentrations of insulin might possibly displace IGF-1 from its receptors, causing an increase in free IGF-1 and therefore increased IGF-1 bioactivity. Or that perhaps IGF-1 isn't involved after all, and that insulin might cause laminitis by binding to the small number of insulin receptors in the lamellae.
Nanayakkara SN, Rahnama S, Harris PA, Anderson ST, de Laat MA, Bailey S, Sillence MN
Characterization of insulin and IGF-1 receptor binding in equine liver and lamellar tissue: implications for endocrinopathic laminitis
Domestic Animal Endocrinology Volume 66, January 2019, Pages 21-26 Published online 07 June 2018
Linked to:
Nanayakkara, Sachith N
The role of IGF-1 and hormone binding proteins in understanding insulin associated equine laminitis
PhD thesis Queensland University of Technology 2018
Rahnama S, Vathsangam N, Spence R, Medina-Torres CE, Pollitt CC, de Laat MA, Bailey SR, Sillence MN.
Effects of an anti-IGF-1 receptor monoclonal antibody on laminitis induced by prolonged hyperinsulinaemia in Standardbred horses.
PLoS One. 2020 Sep 29;15(9):e0239261. doi: 10.1371/journal.pone.0239261. PMID: 32991593; PMCID: PMC7524003.
"This study has provided further evidence that IGF-1R may play a role in the pathogenesis of endocrinopathic laminitis."
Rahnama S, Spence R, Vathsangam N, Baskerville CL, Bailey SR, de Laat MA, Anderson ST, Pollitt CC, Sillence MN.
Effects of insulin on IGF-1 receptors in equine lamellar tissue in vitro.
Domest Anim Endocrinol. 2021 Jan;74:106530. doi: 10.1016/j.domaniend.2020.106530. Epub 2020 Jul 29. PMID: 32818904.
Keywords: Equine; Insulin dysregulation; Laminitis; Monoclonal antibody
"The results demonstrate that insulin acts directly on lamellar tissue and suggest that a therapeutic anti-IGF-1R mAb could be useful in treating or preventing endocrinopathic laminitis."
Rahnama S, Vathsangam N, Spence R, Anderson ST, de Laat MA, Bailey S, Sillence MN.
Identification of monoclonal antibodies suitable for blocking IGF-1 receptors in the horse.
Domest Anim Endocrinol. 2021 Jan;74:106510. doi: 10.1016/j.domaniend.2020.106510. Epub 2020 Jun 17. PMID: 32652390.
Keywords: Equine; Insulin dysregulation; Laminitis.
Lane HE, Burns TA, Hegedus OC, Watts MR, Weber PS, Woltman KA, Geor RJ, McCutcheon LJ, Eades SC, Mathes LE, Belknap JK
Lamellar events related to insulin-like growth factor-1 receptor signaling in two models relevant to endocrinopathic laminitis
Equine Veterinary Journal published online 11 January 2017
Lamellar phospho (P)-protein concentrations of signaling proteins important in growth factor-related signaling were assessed in a high v low NSC diet model and a euglycemic hyperinsulinemic clamp model. Obese ponies fed a high NSC diet had higher lamellar P-(Ser 240/244) RPS6 levels, and positive correlations existed between resting insulin concentrations and lamellar concentrations of P-p70S6K and P-(Ser 240/244) RPS6. In the euglycemic hyperinsulinemic clamp model, lamellar concentrations of P-Akt, P-p70S6K, P-ERK 1/2, P-p90RSK, and both P-(Ser 235/236) and P-(Ser 240/244) RPS6 were increased.
Burns TA PhD dissertation 2013 Ohio State University
The Equine Metabolic Syndrome: Studies on the Pathophysiology of Obesity, Insulin Resistance, and Laminitis in Equids
P 170 Discussion and Conclusions: "it is possible that local activation of laminar IGF- 1R by insulin in the digit may contribute to the pathophysiology of EMSAL" (EMS-Associated Laminitis).
Kullmann A, Weber PS, Bishop JB, Roux TM, Norby B, Burns TA, McCutcheon LJ, Belknap JK, Geor RJ
Equine insulin receptor and insulin-like growth factor-1 receptor expression in digital lamellar tissue and insulin target tissues
Equine Vet J Sept 2016, 48: 626–632. doi:10.1111/ev
Insulin has been shown to activate signaling through IGF-1R at supraphysiologic concentrations that are attainable in the IR equid (Varewijck and Janssen 2012)
Major Breakthrough in Understanding Insulin Form of Laminitis - Animal Health Foundation June 2011"Horses have a large number of IGF-1 receptors in their feet, but no insulin receptors. Pollitt’s team now theorizes that these IGF-1 receptors are being stimulated by insulin that mimics insulin-like growth factor 1 and is binding to these receptors.
When this happens, the laminar epitheleal cells start to proliferate. Normally these cells in the middle of the foot don’t multiply. The cells are made at the coronary band and migrate all the way down to the sole without multiplying. This type of proliferation causes the laminae to stretch and lengthen and the weight of the horse to ruin the bond between the external hoof wall and the bone. The bone changes position, and laminitis occurs."
Melody de Laat et al. found that the IGF system is involved in the pathogenesis of endocrinopathic laminitis - see chapter 6 (p42):
Insulin-Induced Laminitis - An investigation of the disease mechanism in horses
by Melody de Laat, Martin Sillence, Catherine McGowan and Christopher Pollitt - RIRDC December 2011 (choose "Download PDF").
Published as:
Vet J. 2013 Feb 8. pii: S1090-0233(13)00008-7 (PubMed)
A potential role for lamellar insulin-like growth factor-1 receptor in the pathogenesis of hyperinsulinaemic laminitis.
de Laat MA, Pollitt CC, Kyaw-Tanner MT, McGowan CM, Sillence MN
"Stimulation of the IGF-1R by insulin may lead to inappropriate lamellar epidermal cell proliferation and lamellar weakening, a potential mechanism for hyperinsulinaemic laminitis."
Metformin may reduce cell growth in response to IGF-1:
Reproduction. 2010 Feb;139(2):409-18.
Metformin decreases IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in culturedbovine granulosa cells.
Tosca L, Ramé C, Chabrolle C, Tesseraud S, Dupont J
Burns TA, Watts MR, Weber PS, McCutcheon LJ, Geor RJ, Belknap JK
Distribution of insulin receptor and insulin-like growth factor-1 receptor in the digital laminae of mixed-breed ponies: An immunohistochemical study
Equine Veterinary JournalVolume 45, Issue 3, pages 326–332, May 2013 July 2012 (PubMed)
"Conclusions: Increased dietary NSC results in increased laminar endothelial IRc expression. Laminar keratinocytes do not express IRc, suggesting that insulin signalling in laminar epithelial cells must be mediated through other receptors (such as IGF-1R). Potential relevance: Manipulation of signalling downstream of IRc and IGF-1R may aid in treatment and prevention of laminitis associated with hyperinsulinaemia."
Is IGF-1 analysis available for horses?
Melody de Laat et al. 2011 (above) states that an accurate assay for determining serum IFG-1 concentrations in horses is not available.
However, DRG has an IGF-1 equine ELISA kit
There are currently (2017) two theories about what causes endocrinopathic (EMS-Associated) laminitis:
1. high levels of insulin act on IGF-1 receptors causing laminar stretching and weakening;
2. high levels of insulin cause vascular resistance and endothelin-1 expression.
From Equine Laminitis 2017 Chapter 37 PPID by Dianne McFarlane, Philip J Johnson and Harold C Schott II.
1. The IGF-1 theory: "Heightened levels of circulating insulin (hyperinsulinemia) are thought to adversely affect the integrity of the digital lamellae by insulin-mediated activation of insulin-like growth factor 1 (IGF-1) receptors on basal epidermal cells in the hoof" (see de Laat et al. 2013 below).
2. The vascular resistance theory: "hyperinsulinemia may also cause increased vascular resistance and endothelin-1 expression in the equine digit, suggesting that the risk of endocrinopathic laminitis might also result from abnormalities of perfusion". (See Gauff et al. 2013 but note that Gauff's research is in vitro on dead severed limbs, and the authors state that "This model has several drawbacks, and results cannot be transferred to the in vivo situation without considering the major differences between the experimental set-up and the complex in vivo situation").
However, Nanayakkara et al. 2019 looked at hoof and liver samples from healthy (but dead) horses and their results did not support the hypothesis that insulin causes laminitis by binding to IGF-1 receptors in the lamella. Insulin (not equine) had low affinity for binding to equine IGF-1 receptors, much lower than IGF-1, and binding by insulin was only seen at very high concentrations that would be unlikely to occur in horses. Only a small population of insulin receptors, confined to the endothelial cells that penetrate the lamellae, was found. The authors suggested that high concentrations of insulin might possibly displace IGF-1 from its receptors, causing an increase in free IGF-1 and therefore increased IGF-1 bioactivity. Or that perhaps IGF-1 isn't involved after all, and that insulin might cause laminitis by binding to the small number of insulin receptors in the lamellae.
Nanayakkara SN, Rahnama S, Harris PA, Anderson ST, de Laat MA, Bailey S, Sillence MN
Characterization of insulin and IGF-1 receptor binding in equine liver and lamellar tissue: implications for endocrinopathic laminitis
Domestic Animal Endocrinology Volume 66, January 2019, Pages 21-26 Published online 07 June 2018
Linked to:
Nanayakkara, Sachith N
The role of IGF-1 and hormone binding proteins in understanding insulin associated equine laminitis
PhD thesis Queensland University of Technology 2018
Rahnama S, Vathsangam N, Spence R, Medina-Torres CE, Pollitt CC, de Laat MA, Bailey SR, Sillence MN.
Effects of an anti-IGF-1 receptor monoclonal antibody on laminitis induced by prolonged hyperinsulinaemia in Standardbred horses.
PLoS One. 2020 Sep 29;15(9):e0239261. doi: 10.1371/journal.pone.0239261. PMID: 32991593; PMCID: PMC7524003.
"This study has provided further evidence that IGF-1R may play a role in the pathogenesis of endocrinopathic laminitis."
Rahnama S, Spence R, Vathsangam N, Baskerville CL, Bailey SR, de Laat MA, Anderson ST, Pollitt CC, Sillence MN.
Effects of insulin on IGF-1 receptors in equine lamellar tissue in vitro.
Domest Anim Endocrinol. 2021 Jan;74:106530. doi: 10.1016/j.domaniend.2020.106530. Epub 2020 Jul 29. PMID: 32818904.
Keywords: Equine; Insulin dysregulation; Laminitis; Monoclonal antibody
"The results demonstrate that insulin acts directly on lamellar tissue and suggest that a therapeutic anti-IGF-1R mAb could be useful in treating or preventing endocrinopathic laminitis."
Rahnama S, Vathsangam N, Spence R, Anderson ST, de Laat MA, Bailey S, Sillence MN.
Identification of monoclonal antibodies suitable for blocking IGF-1 receptors in the horse.
Domest Anim Endocrinol. 2021 Jan;74:106510. doi: 10.1016/j.domaniend.2020.106510. Epub 2020 Jun 17. PMID: 32652390.
Keywords: Equine; Insulin dysregulation; Laminitis.
Lane HE, Burns TA, Hegedus OC, Watts MR, Weber PS, Woltman KA, Geor RJ, McCutcheon LJ, Eades SC, Mathes LE, Belknap JK
Lamellar events related to insulin-like growth factor-1 receptor signaling in two models relevant to endocrinopathic laminitis
Equine Veterinary Journal published online 11 January 2017
Lamellar phospho (P)-protein concentrations of signaling proteins important in growth factor-related signaling were assessed in a high v low NSC diet model and a euglycemic hyperinsulinemic clamp model. Obese ponies fed a high NSC diet had higher lamellar P-(Ser 240/244) RPS6 levels, and positive correlations existed between resting insulin concentrations and lamellar concentrations of P-p70S6K and P-(Ser 240/244) RPS6. In the euglycemic hyperinsulinemic clamp model, lamellar concentrations of P-Akt, P-p70S6K, P-ERK 1/2, P-p90RSK, and both P-(Ser 235/236) and P-(Ser 240/244) RPS6 were increased.
Burns TA PhD dissertation 2013 Ohio State University
The Equine Metabolic Syndrome: Studies on the Pathophysiology of Obesity, Insulin Resistance, and Laminitis in Equids
P 170 Discussion and Conclusions: "it is possible that local activation of laminar IGF- 1R by insulin in the digit may contribute to the pathophysiology of EMSAL" (EMS-Associated Laminitis).
Kullmann A, Weber PS, Bishop JB, Roux TM, Norby B, Burns TA, McCutcheon LJ, Belknap JK, Geor RJ
Equine insulin receptor and insulin-like growth factor-1 receptor expression in digital lamellar tissue and insulin target tissues
Equine Vet J Sept 2016, 48: 626–632. doi:10.1111/ev
Insulin has been shown to activate signaling through IGF-1R at supraphysiologic concentrations that are attainable in the IR equid (Varewijck and Janssen 2012)
Major Breakthrough in Understanding Insulin Form of Laminitis - Animal Health Foundation June 2011"Horses have a large number of IGF-1 receptors in their feet, but no insulin receptors. Pollitt’s team now theorizes that these IGF-1 receptors are being stimulated by insulin that mimics insulin-like growth factor 1 and is binding to these receptors.
When this happens, the laminar epitheleal cells start to proliferate. Normally these cells in the middle of the foot don’t multiply. The cells are made at the coronary band and migrate all the way down to the sole without multiplying. This type of proliferation causes the laminae to stretch and lengthen and the weight of the horse to ruin the bond between the external hoof wall and the bone. The bone changes position, and laminitis occurs."
Melody de Laat et al. found that the IGF system is involved in the pathogenesis of endocrinopathic laminitis - see chapter 6 (p42):
Insulin-Induced Laminitis - An investigation of the disease mechanism in horses
by Melody de Laat, Martin Sillence, Catherine McGowan and Christopher Pollitt - RIRDC December 2011 (choose "Download PDF").
Published as:
Vet J. 2013 Feb 8. pii: S1090-0233(13)00008-7 (PubMed)
A potential role for lamellar insulin-like growth factor-1 receptor in the pathogenesis of hyperinsulinaemic laminitis.
de Laat MA, Pollitt CC, Kyaw-Tanner MT, McGowan CM, Sillence MN
"Stimulation of the IGF-1R by insulin may lead to inappropriate lamellar epidermal cell proliferation and lamellar weakening, a potential mechanism for hyperinsulinaemic laminitis."
Metformin may reduce cell growth in response to IGF-1:
Reproduction. 2010 Feb;139(2):409-18.
Metformin decreases IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in culturedbovine granulosa cells.
Tosca L, Ramé C, Chabrolle C, Tesseraud S, Dupont J
Burns TA, Watts MR, Weber PS, McCutcheon LJ, Geor RJ, Belknap JK
Distribution of insulin receptor and insulin-like growth factor-1 receptor in the digital laminae of mixed-breed ponies: An immunohistochemical study
Equine Veterinary JournalVolume 45, Issue 3, pages 326–332, May 2013 July 2012 (PubMed)
"Conclusions: Increased dietary NSC results in increased laminar endothelial IRc expression. Laminar keratinocytes do not express IRc, suggesting that insulin signalling in laminar epithelial cells must be mediated through other receptors (such as IGF-1R). Potential relevance: Manipulation of signalling downstream of IRc and IGF-1R may aid in treatment and prevention of laminitis associated with hyperinsulinaemia."
Is IGF-1 analysis available for horses?
Melody de Laat et al. 2011 (above) states that an accurate assay for determining serum IFG-1 concentrations in horses is not available.
However, DRG has an IGF-1 equine ELISA kit
Immune system
Miller AB, Loynachan AT, Bush HM, Hart KA, Barker VD, Campana-Emard AG, Grubbs ST, Adams AA.
Effects of pituitary pars intermedia dysfunction and Prascend (pergolide tablets) treatment on endocrine and immune function in horses.
Domest Anim Endocrinol. 2021 Jan;74:106531. doi: 10.1016/j.domaniend.2020.106531. Epub 2020 Jul 29. PMID: 32942194.
ACTH; Cortisol; Equine; Immune; PPID; Pergolide.
Miller AB, Loynachan AT, Bush HM, Hart KA, Barker VD, Campana-Emard AG, Grubbs ST, Adams AA.
Effects of pituitary pars intermedia dysfunction and Prascend (pergolide tablets) treatment on endocrine and immune function in horses.
Domest Anim Endocrinol. 2021 Jan;74:106531. doi: 10.1016/j.domaniend.2020.106531. Epub 2020 Jul 29. PMID: 32942194.
ACTH; Cortisol; Equine; Immune; PPID; Pergolide.
Incretins (GLP-1 and GIP)
Incretins are hormones that are released from the GI tract when glucose (and fat) are ingested, which increase the amount of insulin produced by the pancreas, even before blood glucose levels become elevated. Incretins are therefore insulinotropic - they stimulate/affect the production/activity of insulin.
Two incretins have been identified:
GLP-1 - glucagon-like peptide 1
GIP - gastric inhibitory peptide
The use of oral glucose tests where a given amount of glucose is fed to the horse and blood collected a given time later and tested for insulin takes account of the "incretin effect", as oral glucose administration is thought to cause a greater insulin peak than IV glucose administration.
See New Hyperinsulinemia Screening Test Promising (AAEP 2012) - www.bloodhorse.com - Christy Corp-Minamiji - March 2013
Research into the role of incretin biology in equine metabolic syndrome is currently being carried out by the University of Minnesota.
Incretins
de Laat MA, Fitzgerald DM
Equine Metabolic Syndrome: Role of the enteroinsular axis in the insulin response to oral carbohydrate
The Veterinary Journal February 2023 (online) 105967. https://doi.org/10.1016.j.tvjl.2023.105967. Open Access
Meier AD, de Laat MA, Reiche DB, Sillence MN
Glucagon-like peptide-1, insulin-like growth factor-1, and adiponectin in insulin-dysregulated ponies: effects of feeding a high nonstructural carbohydrate diet and association with prospective laminitis
Domest Anim Endocrinol. published online Sept 2019 13;71:106397. doi: 10.1016/j.domaniend.2019.106397
Fitzgerald DM, Walsh DM, Sillence MN, Pollitt CC, de Laat MA
Insulin and incretin response to grazing in insulin-dysregulated and healthy ponies
Journal of Veterinary Internal Medicine Volume 33, Issue 1 January/February 2019 Pages 225-232 https://doi.org/10.1111/jvim.15363
Kheder, Murad Hasan
The role of the equine enteroinsular axis in insulin dysregulation: In vitro mechanistic insights for disease prevention
2018 PhD thesis, Queensland University of Technology
de Laat MA, Fitzgerald DM, Sillence MN, Spence RJ
Glucagon-like peptide-2: A potential role in equine insulin dysregulation
Equine Vet Journal published online 04 Mar 2018. doi: 10.1111/evj.12825
Kheder MH, Bailey SR, Dudley KJ, Sillence MN, de Laat MA
Equine glucagon-like peptide-1 receptor physiology
PeerJ 2018 6:e4316 https://doi.org/10.7717/peerj.4316
Kheder MH, Sillence MN, Bryant LM, de Laat MA
The equine glucose-dependent insulinotropic polypeptide receptor: A potential therapeutic target for insulin dysregulation
J Anim Sci. 2017 Jun;95(6):2509-2516. doi: 10.2527/jas.2017.1468
"Insulin release was also shown to be concentration-dependent with GIP up to 0.1µM.....eGIPR is a potential therapeutic target for insulin dysregulation and obesity in horses."
Chameroy KA, Frank N, Elliott SB
Comparison of plasma active glucagon-like peptide 1 concentrations in normal horses and those with Equine Metabolic Syndrome and in horses placed on a high-grain diet
JEVS published online Feb 2016
Bamford NJ, Baskerville CL, Harris PA, Bailey SR
Postprandial glucose, insulin, and glucagon-like peptide-1 responses of different equine breeds adapted to meals containing micronized maize
J Anim Sci. 2015 Jul;93(7):3377-83. doi: 10.2527/jas.2014-8736
"GLP-1 concentrations were found to be different between breed groups and were strongly correlated with insulin concentrations. Glucose concentrations were only weakly correlated with GLP-1, indicating that breed-related differences in GLP-1 may not be directly related to glycemic responses. These associations may be consistent with a potential role for incretin hormones in equine postprandial hyperinsulinemia."
Rapson JL MSc thesis Michigan State University 2015
Effects of age and diet on glucose and insulin dynamics in the horse
p 44
de Graaf-Roelfsema E
Glucose homeostasis and the enteroinsular axis in the horse: A possible role in equine metabolic syndrome
The Veterinary Journal Volume 199, Issue 1, January 2014, Pages 11-18
Frank N, Tadros EM
Insulin Dysregulation
Equine Vet J. 2013 Aug 28 (PubMed)
"Incretin hormones are likely to play an important role in postprandial hyperinsulinaemia and are the subject of current research."
Insulin & Incretins - Animal Health Foundation Nov 2015
de Laat MA, McGree JM, Sillence MN
Equine hyperinsulinemia: investigation of the enteroinsular axix during insulin dysregulation
American Journal of Physiology - Endocrinology and Metabolism Published 3 November 2015
Equine Incretins in Laminitis Research: Animal Health Foundation Leads the Way in New Investigations into Equine Insulin Resistance - Animal Health Foundation October 2013
Kim W and Egan JM
The Role of Incretins in Glucose Homeostasis and Diabetes Treatment (human)
Pharmacological ReviewsDecember 2008 vol. 60 no. 4 470-512
Incretins are hormones that are released from the GI tract when glucose (and fat) are ingested, which increase the amount of insulin produced by the pancreas, even before blood glucose levels become elevated. Incretins are therefore insulinotropic - they stimulate/affect the production/activity of insulin.
Two incretins have been identified:
GLP-1 - glucagon-like peptide 1
GIP - gastric inhibitory peptide
The use of oral glucose tests where a given amount of glucose is fed to the horse and blood collected a given time later and tested for insulin takes account of the "incretin effect", as oral glucose administration is thought to cause a greater insulin peak than IV glucose administration.
See New Hyperinsulinemia Screening Test Promising (AAEP 2012) - www.bloodhorse.com - Christy Corp-Minamiji - March 2013
Research into the role of incretin biology in equine metabolic syndrome is currently being carried out by the University of Minnesota.
Incretins
de Laat MA, Fitzgerald DM
Equine Metabolic Syndrome: Role of the enteroinsular axis in the insulin response to oral carbohydrate
The Veterinary Journal February 2023 (online) 105967. https://doi.org/10.1016.j.tvjl.2023.105967. Open Access
Meier AD, de Laat MA, Reiche DB, Sillence MN
Glucagon-like peptide-1, insulin-like growth factor-1, and adiponectin in insulin-dysregulated ponies: effects of feeding a high nonstructural carbohydrate diet and association with prospective laminitis
Domest Anim Endocrinol. published online Sept 2019 13;71:106397. doi: 10.1016/j.domaniend.2019.106397
Fitzgerald DM, Walsh DM, Sillence MN, Pollitt CC, de Laat MA
Insulin and incretin response to grazing in insulin-dysregulated and healthy ponies
Journal of Veterinary Internal Medicine Volume 33, Issue 1 January/February 2019 Pages 225-232 https://doi.org/10.1111/jvim.15363
Kheder, Murad Hasan
The role of the equine enteroinsular axis in insulin dysregulation: In vitro mechanistic insights for disease prevention
2018 PhD thesis, Queensland University of Technology
de Laat MA, Fitzgerald DM, Sillence MN, Spence RJ
Glucagon-like peptide-2: A potential role in equine insulin dysregulation
Equine Vet Journal published online 04 Mar 2018. doi: 10.1111/evj.12825
Kheder MH, Bailey SR, Dudley KJ, Sillence MN, de Laat MA
Equine glucagon-like peptide-1 receptor physiology
PeerJ 2018 6:e4316 https://doi.org/10.7717/peerj.4316
Kheder MH, Sillence MN, Bryant LM, de Laat MA
The equine glucose-dependent insulinotropic polypeptide receptor: A potential therapeutic target for insulin dysregulation
J Anim Sci. 2017 Jun;95(6):2509-2516. doi: 10.2527/jas.2017.1468
"Insulin release was also shown to be concentration-dependent with GIP up to 0.1µM.....eGIPR is a potential therapeutic target for insulin dysregulation and obesity in horses."
Chameroy KA, Frank N, Elliott SB
Comparison of plasma active glucagon-like peptide 1 concentrations in normal horses and those with Equine Metabolic Syndrome and in horses placed on a high-grain diet
JEVS published online Feb 2016
Bamford NJ, Baskerville CL, Harris PA, Bailey SR
Postprandial glucose, insulin, and glucagon-like peptide-1 responses of different equine breeds adapted to meals containing micronized maize
J Anim Sci. 2015 Jul;93(7):3377-83. doi: 10.2527/jas.2014-8736
"GLP-1 concentrations were found to be different between breed groups and were strongly correlated with insulin concentrations. Glucose concentrations were only weakly correlated with GLP-1, indicating that breed-related differences in GLP-1 may not be directly related to glycemic responses. These associations may be consistent with a potential role for incretin hormones in equine postprandial hyperinsulinemia."
Rapson JL MSc thesis Michigan State University 2015
Effects of age and diet on glucose and insulin dynamics in the horse
p 44
de Graaf-Roelfsema E
Glucose homeostasis and the enteroinsular axis in the horse: A possible role in equine metabolic syndrome
The Veterinary Journal Volume 199, Issue 1, January 2014, Pages 11-18
Frank N, Tadros EM
Insulin Dysregulation
Equine Vet J. 2013 Aug 28 (PubMed)
"Incretin hormones are likely to play an important role in postprandial hyperinsulinaemia and are the subject of current research."
Insulin & Incretins - Animal Health Foundation Nov 2015
de Laat MA, McGree JM, Sillence MN
Equine hyperinsulinemia: investigation of the enteroinsular axix during insulin dysregulation
American Journal of Physiology - Endocrinology and Metabolism Published 3 November 2015
Equine Incretins in Laminitis Research: Animal Health Foundation Leads the Way in New Investigations into Equine Insulin Resistance - Animal Health Foundation October 2013
Kim W and Egan JM
The Role of Incretins in Glucose Homeostasis and Diabetes Treatment (human)
Pharmacological ReviewsDecember 2008 vol. 60 no. 4 470-512
Inflammation
Toll-like receptor (TLR) activation causes up-regulation of inflammatory pathways and release of pro-inflammatory cytokines.
Pro-inflammatory cytokines include:
interleukin-6 (IL-6)
tumour necrosis factor-alpha (TNF-alpha)
What is the role of inflammation in endocrine/hyperinsulinaemic laminitis?
Zak A, Siwinska N, Elzinga S, Barker VD, Stefaniak T, Schanbacher BJ, Place NJ, Niedzwiedz A, Adams AA
Effects of equine metabolic syndrome (EMS) on inflammation and acute-phase markers in horses
Domestic Animal Endocrinology published online 14 February 2020 https://doi.org/10.1016/j.domaniend.2020.106448
Timpson AJ, de Mestre AM, Elliott J, Harris PA, Cheng Z, Mirczuk SM, Callan L, Rainbow L, Menzies-Gow NJ
Seasonal and dietary influences on adipose tissue and systemic gene expression in control and previously laminitic ponies
JEVS published online 22 June 2018 DOI: https://doi.org/10.1016/j.jevs.2018.06.009
Leise B
The role of neutrophils in equine laminitis
Cell Tissue Res. March 2018;371(3):541‐550. Published online 3 Feb 2018. doi:10.1007/s00441-018-2788-z
Vet Immunol Immunopathol. 2014 Jan 15;157(1-2):78-86 (published online 24 Oct 2013)
Toll-like receptor and pro-inflammatory cytokine expression during prolonged hyperinsulinaemia in horses: implications for laminitis
de Laat MA, Clement CK, McGowan CM, Sillence MN, Pollitt CC, Lacombe VA
As of Oct 2013 "the role of inflammation in hyperinsulinaemic laminitis has not been adequately defined".
Following marked or moderate hyperinsulinaemia and the development of clinical or sub-clinical laminitis respectively, lamellar protein expression of TLR4 and TNF-α but not IL-6 was increased in horses with marked hyperinsulinaemic/clinical laminitis. Moderate hyperinsulinaemia/sub-clinical laminitis did not result in any upregulation of measured inflammatory parameters.
"The results suggest that insulin-sensitive tissues may not accurately reflect lamellar pathology during hyperinsulinaemia. While TLR4 is present in the lamellae, its activation appears unlikely to contribute significantly to the developmental pathogenesis of hyperinsulinaemic laminitis. However, inflammation may have a role to play in the later stages (e.g., repair or remodelling) of the disease."
Karikoski NP, McGowan CM, Singer ER, Asplin KE, Tulamo RM, Patterson-Kane JC
Pathology of Natural Cases of Equine Endocrinopathic Laminitis Associated With Hyperinsulinemia
Vet Pathol. 2014 Sep 17
The lamellae of 14 laminitic and hyperinsulinaemic horses and ponies were compared to controls.
"Acute separation originated from the abaxial region, with minimal associated inflammation".
Leise BS, Faleiros RR, Burns TA, Gardner AK, Watts MA, Black SJ, Geor R, McCutcheon LJ, van Eps A, Pollitt CC, Eades S, Johnson PJ, Belknap JK
Inflammation in laminitis: the “itis” in laminitis may not pertain to all
JEVS October 2013 Volume 33, Issue 10, Page 860
There are 3 types of laminitis: Sepsis-Related Laminitis (SRL or SIRS laminitis), Supporting Limb Laminitis (SLL) and hyperinsulinaemic laminitis (sometimes called EMSAL - EMS-associated laminitis).
Laminar signaling was assessed in all 3 types of laminitis.
All SRL (oligo-fructose, starch and black walnut induced) models showed an early laminar inflammatory response - leukocyte infiltration, expression of inflammatory proteins (cytokines, chemokines, COX-2), and activation of central inflammatory signaling (phospho-p38 MAPK). Cryotherapy blocked inflammatory proteins in the oligo-fructose model. Inflammatory events had decreased in the laminae by the start of Obel grade 3 laminitis in the starch model.
The hyperinsulinaemic laminitis model showed minimal increases in laminar inflammatory gene expression, with increases only in COX-2, but there was activation of signaling related to cellular energy levels and growth factor signaling.
The SSL model also showed minimal evidence of laminar inflammatory signaling, although hypoxia-related signaling was detected.
Conclusions: inflammation is an early and major part of sepsis-related laminitis, but does not appear to play a major role in hyperinsulinaemic or supporting limb laminitis.
de Laat M, Sillence M, McGowan C, Pollitt C
Insulin-Induced Laminitis - An investigation of the disease mechanism in horses
RIRDC Dec 2011
"Insulin-induced laminitis also produces a less inflammatory lesion that other experimental models of the disease (de Laat et al., 2011c; Faleiros et al., 2009) when assessed with calprotectin immunohistochemistry. Further corroboration of this finding with lamellar analysis of inflammatory
mediators is required. However, if inflammation is a minor player in insulin-induced laminitis pathophysiology then anti-inflammatory medications may only be useful for their analgesic properties in this form of laminitis, and may not alter progression of the disease".
What is the role of inflammation in insulin resistance?
Wray H, Elliott J, Bailey SR, Harris PA, Menzies-Gow NJ
Plasma concentrations of inflammatory markers in previously laminitic ponies
Equine Vet J. 2013 Sep;45(5):546-51. Epub 2013 Feb 19 (PubMed)
The inflammatory profile of previously laminitic ponies was no different to never laminitic ponies:
"Conclusions: There were significant effects of season, gender and bodyweight on a number of proinflammatory mediators or markers of inflammation. The only marker influenced by laminitis status was adiponectin, and concentrations of this anti-inflammatory marker were lower in previously laminitic animals.
Potential relevance: Recurrent laminitis may be associated with reduced anti-inflammatory capacity rather than a proinflammatory state."
Waller AP, Huettner L, Kohler K, Lacombe VA
Novel link between inflammation and impaired glucose transport during equine insulin resistance
Vet Immunol Immunopathol. 2012 Oct 15;149(3-4):208-15
Inflammatory markers TLR-3, SOCS-3 (suppressor of cytokine signalling) and TNF-alpha were measured in visceral (VIS) and subcutaneous (SC) adipose tissue and skeletal muscle (SM) from insulin resistant (IR) and insulin sensitive (IS) horses.
IR horses had significantly increased TLR-4 and SOCS-3 in skeletal muscle and visceral adipose tissue, but not subcutaneous adipose tissue.
IR horses had increased TNF-alpha in visceral but not subcutaneous adipose tissue.
IRS-1 (insulin receptor substrate 1) was no different between IR and IS horses.
"Taken together, the data suggested a pro-inflammatory state in SM and VIS, but not SC, adipose depot during compensated IR. In addition, SOCS-3 appears to be a novel link between inflammation and dysregulated glucose metabolism and insulin sensitivity during the early pathogenesis of insulin resistance".
Burns TA, Watts MR, Weber PS, McCutcheon LJ, Geor RJ, Belknap JK
Laminar inflammatory events in lean and obese ponies subjected to high-carbohydrate feeding: implications for pasture-associated laminitis
Equine Vet J. 2014 Jun 25
Suagee JK, Splan RK, Swyers KL, Geor RJ, Corl BA
Effects of high sugar and starch diets on postprandial inflammatory protein concentrations in horses
JEVS published online 09 December 2014
A high starch and sugar diet increased postprandial IL1β concentrations (an inflammatory cytokine).
Suagee JK, Corl BA, Crisman MV, Pleasant RS, Thatcher CD, Geor RJ
Relationships between body condition score and plasma inflammatory cytokines, insulin, and lipids in a mixed population of light-breed horses
J Vet Intern Med. 2013 Jan-Feb;27(1):157-63
"Plasma TNF (P = .047) and IL-6 (P = .021) concentrations were higher in females than males, whereas IL-6 concentrations correlated (P = .001) with age. Plasma SAA concentrations correlated with both insulin (P < .001) and BCS (P = .007)."
"This study provides evidence for factors, including age and sex, that may be associated with plasma concentrations of inflammatory proteins. Concentrations of SAA correlated with BCS and insulin, independent of age or sex. Because BCS and insulin correlate with increased SAA, it is possible that SAA is a component of laminitis pathophysiology."
Holbrook TC, Tipton T, McFarlane D
Neutrophil and cytokine dysregulation in hyperinsulinemic obese horses
Veterinary Immunology and Immunopathology 145 (2012) 283– 289 (Full)
de la Rebière de Pouyade G, Riggs LM, Moore JN, Franck T, Deby-Dupont G, Hurley DJ, Serteyn D
Equine neutrophil elastase in plasma, laminar tissue, and skin of horses administered black walnut heartwood extract
Vet Immunol Immunopathol. 2010 Jun 15;135(3-4):181-7 (PubMed)
"The administration of BWHE thus results in significant increases in the concentration of neutrophil elastase in the circulation, skin and laminar tissue. These results confirm a role for neutrophils in the developmental phase of laminitis, and the systemic nature of the inflammatory process. Furthermore, neutrophil elastase may play a key role in the disintegration of the hoof basal membrane and be a target for the development of new treatments for laminitis."
TLS comment: NB the pathology of BWHE laminitis may be quite different to that of endocrine laminitis.
Treiber K, Carter R, Gay L, Williams C, Geor
Inflammatory and redox status of ponies with a history of pasture-associated laminitis
Vet Immunol Immunopathol. 2009 Jun 15;129(3-4):216-20 (PubMed)
Vet Immunol Immunopathol. 2009 Feb 15;127(3-4):286-94. Epub 2008 Oct 31 PubMed
Effect of body condition, body weight and adiposity on inflammatory cytokine responses in old horses
Adams AA, Katepalli MP, Kohler K, Reedy SE, Stilz JP, Vick MM, Fitzgerald BP, Lawrence LM, Horohov DW
Vick MM, Adams AA, Murphy BA, Sessions DR, Horohov DW, Cook RF, Shelton BJ, Fitzgerald BP
Relationships among inflammatory cytokines, obesity, and insulin sensitivity in the horse
J Anim Sci. 2007 May;85(5):1144-55. Epub 2007 Jan 30 (Full)
" these results provide the first evidence associating obesity with increased inflammatory factors in the horse. Furthermore, the results suggest that an interrelationship exists among obesity, inflammatory cytokines"
Inflammation and obesity/adipose tissue
Roth P, Stanley J, Chamoun-Emanuelli A, Whitfield-Cargile C, Coleman M
Fecal extract from obese horses induces inflammation in vitro
Proceedings 4th Global Equine Endcorine Symposium January 2020 page 47
The enteric microbiome in dung from obese (BCS 7+) horses induced a greater inflammatory response with increased levels of pro-inflammatory cytokines IL-1beta, TNF-alpha and IL-6 when compared to non-obese (BCS 3-5) horses, in vitro, suggesting that the microbiome mediates an inflammatory response in the GI tract.
Bruynsteen L, Erkens T, Peelman LJ, Ducatelle R, Janssens GPJ, Harris PA, Hesta M
Expression of inflammation-related genes is associated with adipose tissue location in horses
BMC Veterinary Research Dec 2013 9:240 https://doi.org/10.1186/1746-6148-9-240
Laminitis and inflammation
Steelman SM, Chowdhary BP
Plasma proteomics shows an elevation of the anti-inflammatory protein APOA-IV in chronic equine laminitis
BMC Veterinary Research 27 Sept 2012 8:179 https://doi.org/10.1186/1746-6148-8-179
Inflammation and age
Siard-Altman MH, Harris PA, Moffett-Krotky AD, Ireland JL, Betancourt A, Barker VD, McMurry KE, Reedy SE, Adams AA
Relationships of inflamm-aging with circulating nutrient levels, body composition, age, and pituitary pars intermedia dysfunction in a senior horse population
Vet Immunol Immunopathol. 2020 Mar;221:110013. doi: 10.1016/j.vetimm.2020.110013. Epub 2020 Jan 26
Siard, Melissa H
Lymphocyte-mediated inflamm-aging in the horse
PhD dissertation 2017 University of Kentucky
Zak A, Siwinska N, Elzinga S, Barker VD, Stefaniak T, Schanbacher BJ, Place NJ, Niedzwiedz A, Adams AA
Effects of equine metabolic syndrome (EMS) on inflammation and acute-phase markers in horses
Domestic Animal Endocrinology published online 14 February 2020 https://doi.org/10.1016/j.domaniend.2020.106448
Timpson AJ, de Mestre AM, Elliott J, Harris PA, Cheng Z, Mirczuk SM, Callan L, Rainbow L, Menzies-Gow NJ
Seasonal and dietary influences on adipose tissue and systemic gene expression in control and previously laminitic ponies
JEVS published online 22 June 2018 DOI: https://doi.org/10.1016/j.jevs.2018.06.009
Leise B
The role of neutrophils in equine laminitis
Cell Tissue Res. March 2018;371(3):541‐550. Published online 3 Feb 2018. doi:10.1007/s00441-018-2788-z
Vet Immunol Immunopathol. 2014 Jan 15;157(1-2):78-86 (published online 24 Oct 2013)
Toll-like receptor and pro-inflammatory cytokine expression during prolonged hyperinsulinaemia in horses: implications for laminitis
de Laat MA, Clement CK, McGowan CM, Sillence MN, Pollitt CC, Lacombe VA
As of Oct 2013 "the role of inflammation in hyperinsulinaemic laminitis has not been adequately defined".
Following marked or moderate hyperinsulinaemia and the development of clinical or sub-clinical laminitis respectively, lamellar protein expression of TLR4 and TNF-α but not IL-6 was increased in horses with marked hyperinsulinaemic/clinical laminitis. Moderate hyperinsulinaemia/sub-clinical laminitis did not result in any upregulation of measured inflammatory parameters.
"The results suggest that insulin-sensitive tissues may not accurately reflect lamellar pathology during hyperinsulinaemia. While TLR4 is present in the lamellae, its activation appears unlikely to contribute significantly to the developmental pathogenesis of hyperinsulinaemic laminitis. However, inflammation may have a role to play in the later stages (e.g., repair or remodelling) of the disease."
Karikoski NP, McGowan CM, Singer ER, Asplin KE, Tulamo RM, Patterson-Kane JC
Pathology of Natural Cases of Equine Endocrinopathic Laminitis Associated With Hyperinsulinemia
Vet Pathol. 2014 Sep 17
The lamellae of 14 laminitic and hyperinsulinaemic horses and ponies were compared to controls.
"Acute separation originated from the abaxial region, with minimal associated inflammation".
Leise BS, Faleiros RR, Burns TA, Gardner AK, Watts MA, Black SJ, Geor R, McCutcheon LJ, van Eps A, Pollitt CC, Eades S, Johnson PJ, Belknap JK
Inflammation in laminitis: the “itis” in laminitis may not pertain to all
JEVS October 2013 Volume 33, Issue 10, Page 860
There are 3 types of laminitis: Sepsis-Related Laminitis (SRL or SIRS laminitis), Supporting Limb Laminitis (SLL) and hyperinsulinaemic laminitis (sometimes called EMSAL - EMS-associated laminitis).
Laminar signaling was assessed in all 3 types of laminitis.
All SRL (oligo-fructose, starch and black walnut induced) models showed an early laminar inflammatory response - leukocyte infiltration, expression of inflammatory proteins (cytokines, chemokines, COX-2), and activation of central inflammatory signaling (phospho-p38 MAPK). Cryotherapy blocked inflammatory proteins in the oligo-fructose model. Inflammatory events had decreased in the laminae by the start of Obel grade 3 laminitis in the starch model.
The hyperinsulinaemic laminitis model showed minimal increases in laminar inflammatory gene expression, with increases only in COX-2, but there was activation of signaling related to cellular energy levels and growth factor signaling.
The SSL model also showed minimal evidence of laminar inflammatory signaling, although hypoxia-related signaling was detected.
Conclusions: inflammation is an early and major part of sepsis-related laminitis, but does not appear to play a major role in hyperinsulinaemic or supporting limb laminitis.
de Laat M, Sillence M, McGowan C, Pollitt C
Insulin-Induced Laminitis - An investigation of the disease mechanism in horses
RIRDC Dec 2011
"Insulin-induced laminitis also produces a less inflammatory lesion that other experimental models of the disease (de Laat et al., 2011c; Faleiros et al., 2009) when assessed with calprotectin immunohistochemistry. Further corroboration of this finding with lamellar analysis of inflammatory
mediators is required. However, if inflammation is a minor player in insulin-induced laminitis pathophysiology then anti-inflammatory medications may only be useful for their analgesic properties in this form of laminitis, and may not alter progression of the disease".
What is the role of inflammation in insulin resistance?
Wray H, Elliott J, Bailey SR, Harris PA, Menzies-Gow NJ
Plasma concentrations of inflammatory markers in previously laminitic ponies
Equine Vet J. 2013 Sep;45(5):546-51. Epub 2013 Feb 19 (PubMed)
The inflammatory profile of previously laminitic ponies was no different to never laminitic ponies:
"Conclusions: There were significant effects of season, gender and bodyweight on a number of proinflammatory mediators or markers of inflammation. The only marker influenced by laminitis status was adiponectin, and concentrations of this anti-inflammatory marker were lower in previously laminitic animals.
Potential relevance: Recurrent laminitis may be associated with reduced anti-inflammatory capacity rather than a proinflammatory state."
Waller AP, Huettner L, Kohler K, Lacombe VA
Novel link between inflammation and impaired glucose transport during equine insulin resistance
Vet Immunol Immunopathol. 2012 Oct 15;149(3-4):208-15
Inflammatory markers TLR-3, SOCS-3 (suppressor of cytokine signalling) and TNF-alpha were measured in visceral (VIS) and subcutaneous (SC) adipose tissue and skeletal muscle (SM) from insulin resistant (IR) and insulin sensitive (IS) horses.
IR horses had significantly increased TLR-4 and SOCS-3 in skeletal muscle and visceral adipose tissue, but not subcutaneous adipose tissue.
IR horses had increased TNF-alpha in visceral but not subcutaneous adipose tissue.
IRS-1 (insulin receptor substrate 1) was no different between IR and IS horses.
"Taken together, the data suggested a pro-inflammatory state in SM and VIS, but not SC, adipose depot during compensated IR. In addition, SOCS-3 appears to be a novel link between inflammation and dysregulated glucose metabolism and insulin sensitivity during the early pathogenesis of insulin resistance".
Burns TA, Watts MR, Weber PS, McCutcheon LJ, Geor RJ, Belknap JK
Laminar inflammatory events in lean and obese ponies subjected to high-carbohydrate feeding: implications for pasture-associated laminitis
Equine Vet J. 2014 Jun 25
Suagee JK, Splan RK, Swyers KL, Geor RJ, Corl BA
Effects of high sugar and starch diets on postprandial inflammatory protein concentrations in horses
JEVS published online 09 December 2014
A high starch and sugar diet increased postprandial IL1β concentrations (an inflammatory cytokine).
Suagee JK, Corl BA, Crisman MV, Pleasant RS, Thatcher CD, Geor RJ
Relationships between body condition score and plasma inflammatory cytokines, insulin, and lipids in a mixed population of light-breed horses
J Vet Intern Med. 2013 Jan-Feb;27(1):157-63
"Plasma TNF (P = .047) and IL-6 (P = .021) concentrations were higher in females than males, whereas IL-6 concentrations correlated (P = .001) with age. Plasma SAA concentrations correlated with both insulin (P < .001) and BCS (P = .007)."
"This study provides evidence for factors, including age and sex, that may be associated with plasma concentrations of inflammatory proteins. Concentrations of SAA correlated with BCS and insulin, independent of age or sex. Because BCS and insulin correlate with increased SAA, it is possible that SAA is a component of laminitis pathophysiology."
Holbrook TC, Tipton T, McFarlane D
Neutrophil and cytokine dysregulation in hyperinsulinemic obese horses
Veterinary Immunology and Immunopathology 145 (2012) 283– 289 (Full)
de la Rebière de Pouyade G, Riggs LM, Moore JN, Franck T, Deby-Dupont G, Hurley DJ, Serteyn D
Equine neutrophil elastase in plasma, laminar tissue, and skin of horses administered black walnut heartwood extract
Vet Immunol Immunopathol. 2010 Jun 15;135(3-4):181-7 (PubMed)
"The administration of BWHE thus results in significant increases in the concentration of neutrophil elastase in the circulation, skin and laminar tissue. These results confirm a role for neutrophils in the developmental phase of laminitis, and the systemic nature of the inflammatory process. Furthermore, neutrophil elastase may play a key role in the disintegration of the hoof basal membrane and be a target for the development of new treatments for laminitis."
TLS comment: NB the pathology of BWHE laminitis may be quite different to that of endocrine laminitis.
Treiber K, Carter R, Gay L, Williams C, Geor
Inflammatory and redox status of ponies with a history of pasture-associated laminitis
Vet Immunol Immunopathol. 2009 Jun 15;129(3-4):216-20 (PubMed)
Vet Immunol Immunopathol. 2009 Feb 15;127(3-4):286-94. Epub 2008 Oct 31 PubMed
Effect of body condition, body weight and adiposity on inflammatory cytokine responses in old horses
Adams AA, Katepalli MP, Kohler K, Reedy SE, Stilz JP, Vick MM, Fitzgerald BP, Lawrence LM, Horohov DW
Vick MM, Adams AA, Murphy BA, Sessions DR, Horohov DW, Cook RF, Shelton BJ, Fitzgerald BP
Relationships among inflammatory cytokines, obesity, and insulin sensitivity in the horse
J Anim Sci. 2007 May;85(5):1144-55. Epub 2007 Jan 30 (Full)
" these results provide the first evidence associating obesity with increased inflammatory factors in the horse. Furthermore, the results suggest that an interrelationship exists among obesity, inflammatory cytokines"
Inflammation and obesity/adipose tissue
Roth P, Stanley J, Chamoun-Emanuelli A, Whitfield-Cargile C, Coleman M
Fecal extract from obese horses induces inflammation in vitro
Proceedings 4th Global Equine Endcorine Symposium January 2020 page 47
The enteric microbiome in dung from obese (BCS 7+) horses induced a greater inflammatory response with increased levels of pro-inflammatory cytokines IL-1beta, TNF-alpha and IL-6 when compared to non-obese (BCS 3-5) horses, in vitro, suggesting that the microbiome mediates an inflammatory response in the GI tract.
Bruynsteen L, Erkens T, Peelman LJ, Ducatelle R, Janssens GPJ, Harris PA, Hesta M
Expression of inflammation-related genes is associated with adipose tissue location in horses
BMC Veterinary Research Dec 2013 9:240 https://doi.org/10.1186/1746-6148-9-240
Laminitis and inflammation
Steelman SM, Chowdhary BP
Plasma proteomics shows an elevation of the anti-inflammatory protein APOA-IV in chronic equine laminitis
BMC Veterinary Research 27 Sept 2012 8:179 https://doi.org/10.1186/1746-6148-8-179
Inflammation and age
Siard-Altman MH, Harris PA, Moffett-Krotky AD, Ireland JL, Betancourt A, Barker VD, McMurry KE, Reedy SE, Adams AA
Relationships of inflamm-aging with circulating nutrient levels, body composition, age, and pituitary pars intermedia dysfunction in a senior horse population
Vet Immunol Immunopathol. 2020 Mar;221:110013. doi: 10.1016/j.vetimm.2020.110013. Epub 2020 Jan 26
Siard, Melissa H
Lymphocyte-mediated inflamm-aging in the horse
PhD dissertation 2017 University of Kentucky
Insulin
Insulin is an enzyme that is secreted by beta-cells in the pancreas in response to glucose in the blood. Above normal levels of insulin, termed insulin dysregulation (ID), is the cause of endocrinopathic laminitis (by far the most common form of laminitis). Factors that influence insulin secretion include the degree of insulin sensitivity (IS)/insulin resistance (IR), the level of hyperinsulinaemia and incretin effects.
Insulin conversion pmol/L to µIU/ml:
Insulin in µIU/ml x 6.945 = insulin in pmol/L
Insulin in pmol/L x 0.144 = insulin in µIU/ml
SydPath Unit Conversion Table will do the conversion for you
Insulin Synthesis and Secretion - Colorado State University
Physiologic Effects of Insulin - Colorado State University
Insulin conversion pmol/L to µIU/ml:
Insulin in µIU/ml x 6.945 = insulin in pmol/L
Insulin in pmol/L x 0.144 = insulin in µIU/ml
SydPath Unit Conversion Table will do the conversion for you
Insulin Synthesis and Secretion - Colorado State University
Physiologic Effects of Insulin - Colorado State University
Do insulin levels change throughout the day/from day to day?
Noble GK, Sillence MN
Diurnal rhythm and effects of feeding, exercise and recombinant equine growth hormone on serum insulin concentrations in the horse
Equine Veterinary Journal online Jan 2013
This research found that insulin did not follow a diurnal rhythm, but peaked following feeding (horses were fed an identical meal of oats, wheat & lucerne chaff and oat hay twice a day). However, insulin peaks were considerably higher following the morning meal, which was given 15.5 hours after the afternoon meal, compared to the afternoon meal, which was given 8.5 hours after the morning meal.
The Journal of Nutrition 1987
Responses of Blood Glucose, Insulin and Cortisol Concentrations to Common Equine Diets
Stull C, Rodiek A
found no diurnal variation in insulin (or glucose) in fasting 2 year old horses.
Fitzgerald DM, Walsh DM, Sillence MN, Pollitt CC, de Laat MA
Insulin and incretin response to grazing in insulin-dysregulated and healthy ponies
Journal of Veterinary Internal Medicine Volume 33, Issue 1 January/February 2019 Pages 225-232 https://doi.org/10.1111/jvim.15363
Pratt SE, Siciliano PD, Walston L
Variation of Insulin Sensitivity Estimates in Horses
Journal of Equine Veterinary Science Volume 29, Issue 6 , Pages 507-512, June 2009
6 horses had glucose and insulin tested on 6 different days (2 blocks of 3 consecutive days), at noon, 6 hours after eating. Significant day to day variations were seen in their insulin results (the mean coefficient of variation for insulin was 33.7%, RISQI 18.6%, glucose 5.5%), suggesting that results from a single blood sample may not be reliable and it may be best to take at least 2 different samples on different days.
Pratt SE, Geor RJ, McCutcheon LJ
Repeatability of 2 Methods for Assessment of Insulin Sensitivity and Glucose Dynamics in Horses
Journal of Veterinary Internal Medicine, 19: 883–888. (2005)
Insulin levels can be decreased by:
Some sedatives e,g. Detomidine hydrochloride (Domosedan) and Xylazine - insulin release is inhibited (causing increased blood glucose levels)
J Vet Pharmacol Ther. 1982 Dec;5(4):241-5 (PubMed)
Xylazine hydrochloride-induced hyperglycemia and hypoinsulinemia in thoroughbred horses
Thurmon JC, Neff-Davis C, Davis LE, Stoker RA, Benson GJ, Lock TF
"The effects of intravenous xylazine (1.1 mg/kg) were studied in six thoroughbred horses (five mares and a stallion). Plasma glucose concentration increased to 168% of control at 45 min and decreased to 112% of control at 180 min. Insulin had decreased to 31% of control at 15 min. Thereafter, insulin concentration increased, reaching its highest concentration at 150 min."
Effect of insulin on vasodilation in humans:
Baron AD
Hemodynamic actions of insulin (Full)
Am J Physiol. 1994 Aug;267(2 Pt 1):E187-202 (PubMed)
"There is accumulating evidence that insulin has a physiological role to vasodilate skeletal muscle vasculature in humans. This effect occurs in a dose-dependent fashion within a half-maximal response of approximately 40 microU/ml. This vasodilating action is impaired in states of insulin resistance such as obesity, non-insulin-dependent diabetes, and elevated blood pressure. The precise physiological role of insulin-mediated vasodilation is not known. Data indicate that the degree of skeletal muscle perfusion can be an important determinant of insulin-mediated glucose uptake. Therefore, it is possible that insulin-mediated vasodilation is an integral aspect of insulin's overall action to stimulate glucose uptake; thus defective vasodilation could potentially contribute to insulin resistance. In addition, insulin-mediated vasodilation may play a role in the regulation of vascular tone. Data are provided to indicate that the pressor response to systemic norepinephrine infusions is increased in obese insulin-resistant subjects. Moreover, the normal effect of insulin to shift the norepinephrine pressor dose-response curve to the right is impaired in these patients. Therefore, impaired insulin-mediated vasodilation could further contribute to the increased prevalence of hypertension observed in states of insulin resistance. Finally, data are presented to indicate that, via a yet unknown interaction with the endothelium, insulin is able to increase nitric oxide synthesis and release and through this mechanism vasodilate. It is interesting to speculate that states of insulin resistance might also be associated with a defect in insulin's action to modulate the nitric oxide system."
Insulin sensitivity
Owens, Kellie Marie, MSc Thesis 2009
The Effect of Changes in Body Condition on Insulin Sensitivity, Leptin, and Adiponectin in Horses fed Forage-Only Diets
Quinn R
Effect of weight gain, diet and exercise on insulin sensitivity in thoroughbred geldings
PhD dissertation 2007
Do different breeds have different insulin sensitivity?
Bamford NJ, Potter SJ, Harris PA, Bailey SR
Breed differences in insulin sensitivity and insulinemic responses to oral glucose in horses and ponies of moderate body condition score
Domest Anim Endocrinol. 2014 Apr;47:101-7. Epub 2013 Nov 9
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8 Standardbreds, 8 mixed breed ponies and 7 Andalusian-cross horses, all with a BCS between 4.7 and 5.3 underwent an oral glucose challenge (1.5 g/kg bw glucose) and a FSIGT. There was little difference in glucose results between groups. "These results indicate that there are clear breed-related differences in the insulin responses of horses and ponies to oral and intravenous glucose. All animals were in moderate body condition, indicating that breed-related differences in insulin dynamics occurred independent of obesity".
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Other research involving insulin in horses
Newkirk KM, Ehrensing G, Odoi A, Boston RC, Frank N
Immunohistochemical expression of insulin, glucagon, and somatostatin in pancreatic islets of horses with and without insulin resistance
Am J Vet Res. 2018 Feb;79(2):191-198. doi: 10.2460/ajvr.79.2.191
"Results suggested that, in insulin-resistant horses, insulin secretion was not increased but glucagon production might be downregulated as a compensatory response to hyperinsulinemia."
Newkirk KM, Ehrensing G, Odoi A, Boston RC, Frank N
Immunohistochemical expression of insulin, glucagon, and somatostatin in pancreatic islets of horses with and without insulin resistance
Am J Vet Res. 2018 Feb;79(2):191-198. doi: 10.2460/ajvr.79.2.191
"Results suggested that, in insulin-resistant horses, insulin secretion was not increased but glucagon production might be downregulated as a compensatory response to hyperinsulinemia."
Insulin - hyperinsulinaemia
What are the effects of hyperinsulinaemia? How could it increase the risk of laminitis?
Campolo A, de Laat MA, Keith L, Gruntmeir KJ, Lacombe VA
Prolonged hyperinsulinemia affects metabolic signal transduction markers in a tissue specific manner
Domest Anim Endocrinol. 2016 Apr;55:41-5. doi: 10.1016/j.domaniend.2015.11.001. Epub 2015 Nov 19
Burns TA, Watts MR, Weber PS, McCutcheon LJ, Geor RJ, Belknap JK
Distribution of insulin receptor and insulin-like growth factor-1 receptor in the digital laminae of mixed-breed ponies: An immunohistochemical study
Equine Veterinary JournalVolume 45, Issue 3, pages 326–332, May 2013 July 2012 (PubMed)
"Reasons for performing study: Hyperinsulinaemia has been implicated in the pathogenesis of laminitis; however, laminar cell types responding to insulin remain poorly characterised. Objectives: To identify laminar cell types expressing insulin receptor (IRc) and/or insulin-like growth factor-1 receptor (IGF-1R); and to evaluate the effect of dietary nonstructural carbohydrate (NSC) on their expression. Methods: Mixed-breed ponies (n = 22) received a conditioning hay chop diet (NSC ∼6%); following acclimation, ponies were stratified into lean (n = 11, body condition score [BCS]≤4) or obese (n = 11, BCS ≥7) groups and each group further stratified to remain on the low NSC diet (n = 5 each for obese and lean) or receive a high NSC diet (total diet ∼42% NSC; n = 6 each for obese and lean) for 7 days. Laminar samples were collected at the end of the feeding protocol and stained immunohistochemically for IRc and IGF-1R. The number of IRc(+) cells was quantified; distribution of IGF-1R was qualitatively described. Laminar IRc content was assessed via immunoblotting. Results: The number of IRc(+) cells was greater in the laminae of high NSC ponies than low NSC ponies (P = 0.001); there was a positive correlation between the change in serum insulin concentration and number of IRc(+) cells (r(2) = 0.74; P<0.0001). No epithelial IRc(+) cells were observed; IRc(+) cells were absent from the deep dermis. Analysis of serial sections identified IRc(+) cells as endothelial cells. The distribution of IGF-1R was more extensive than that of IRc, with signal in vascular elements, epithelial cells and fibroblasts. Conclusions: Increased dietary NSC results in increased laminar endothelial IRc expression. Laminar keratinocytes do not express IRc, suggesting that insulin signalling in laminar epithelial cells must be mediated through other receptors (such as IGF-1R). Potential relevance: Manipulation of signalling downstream of IRc and IGF-1R may aid in treatment and prevention of laminitis associated with hyperinsulinaemia."
Gauff F, Patan-Zugaj B, Licka TF
Hyperinsulinaemia increases vascular resistance and endothelin-1 expression in the equine digit
Equine Vet J. 2013 Sep;45(5):613-8 (PubMed)
"Short-term hyperinsulinaemia leads to increased vascular resistance in the equine digit and increased expression of ET-1 in the laminar tissue."
Vet Immunol Immunopathol. 2011 Aug 15;142(3-4):141-6. Epub 2011 May 7.
Effects of acute hyperinsulinemia on inflammatory proteins in horses.
Suagee JK, Corl BA, Crisman MV, Hulver MW, McCutcheon LJ, Geor RJ
"Insulin may be involved in the production of inflammatory cytokines, and this could be a mechanism for insulin increasing the risk of laminitis."
Veterinary Immunology and Immunopathology 140 (2011) 275–281
The developmental and acute phases of insulin-induced laminitis involve minimal metalloproteinase activity
de Laat MA, Kyaw-Tanner MT, Nourian AR, McGowan CM, Sillence MN, Pollitt CC
"The increased expression of MMP-9 may be associated with the infiltration of inflammatory leukocytes, or may be a direct result of hyperinsulinaemia." "laminitis was induced in non-obese horses in the current study which suggests that insulin itself may have been pro-inflammatory."
Vet J. 2007 Nov;174(3):530-5
Induction of laminitis by prolonged hyperinsulinaemia in clinically normal ponies
Asplin KE, Sillence MN, Pollitt CC, McGowan CM
"Obel grade 1 laminitis (prominent, palpable digital pulses, heat over the dorsal hoof wall and weight shifting) (Obel, 1948) was evident in all treated ponies at 32.6 +/- 5.4 h after infusions (of insulin) started. The time to onset of Obel grade 2 laminitis was 55.4 +/- 5.5 h. "Mean respiratory rate increased from 18.7 +/- 1.0 to 36 +/- 3.1 breaths/min, and heart rate increased from 49 +/- 2.2 to 70 +/- 3.7 bpm at the onset of Obel grade 2 laminitis." Some ponies showed signs of agitation associated with the onset of laminitis, but all remained bright and alert and ate and drank normally, and rectal temperature remained normal. Phenylbutazone at 4.4mg/kg BW orally or IV reduced clinical signs by one Obel grade.
What concentration of serum insulin could cause laminitis?
Vet J. 2011 Aug 26
Continuous intravenous infusion of glucose induces endogenous hyperinsulinaemia and lamellar histopathology in Standardbred horses
de Laat M, Sillence M, McGowan C, Pollitt C
"Based on the histopathological data, the potential threshold for insulin toxicity (i.e. laminitis) in horses may be at or below a serum concentration of 200 µIU/mL."
Vet J. 2007 Nov;174(3):530-5
Induction of laminitis by prolonged hyperinsulinaemia in clinically normal ponies
Asplin KE, Sillence MN, Pollitt CC, McGowan CM
"Mean serum insulin concentration in treatment ponies was 1036 +/- 55 µU/mL vs. 14.6 µU/mL in controls. All ponies in the treatment group developed clinical and histological laminitis (Obel grade 2) in all four feet within 72 h (55.4 +/- 5.5 h)".
Insulin testing
There is currently no perfect test for insulin dysfunction/Equine Metabolic Syndrome, but tests used to help diagnose insulin dysregulation/Equine Metabolic Syndrome) include:
1. Resting/basal insulin (usually carried out after the horse has been eating forage, but may also be useful when the horse is fasted for ~6 hours before the blood draw to check for chronic hyperinsulinaemia).
2. Oral dynamic tests:
Oral Sugar Test (OST)
In-feed Glucose Test - also called the Oral Glucose Test or Oral Glucose Tolerance Test (OGTT)
3. Intravenous dynamic tests (usually carried out in a clinic):
Minimal model analysis of the Frequently Sampled intravenous Glucose Tolerance Test (FSIGTT) - evaluates the early beta-cell response to intravenous glucose administration (the acute insulin response to glucose or AIRg), and assesses insulin sensitivity.
Euglycemic-Hyperinsulinemic Clamp (EHC) - assesses insulin sensitivity
Insulin Tolerance Test (ITT)
There is currently no perfect test for insulin dysfunction/Equine Metabolic Syndrome, but tests used to help diagnose insulin dysregulation/Equine Metabolic Syndrome) include:
1. Resting/basal insulin (usually carried out after the horse has been eating forage, but may also be useful when the horse is fasted for ~6 hours before the blood draw to check for chronic hyperinsulinaemia).
2. Oral dynamic tests:
Oral Sugar Test (OST)
In-feed Glucose Test - also called the Oral Glucose Test or Oral Glucose Tolerance Test (OGTT)
3. Intravenous dynamic tests (usually carried out in a clinic):
Minimal model analysis of the Frequently Sampled intravenous Glucose Tolerance Test (FSIGTT) - evaluates the early beta-cell response to intravenous glucose administration (the acute insulin response to glucose or AIRg), and assesses insulin sensitivity.
Euglycemic-Hyperinsulinemic Clamp (EHC) - assesses insulin sensitivity
Insulin Tolerance Test (ITT)
EEG 2020 Recommendations for the Diagnosis and Treatment of EMS Table 3
|
EEG 2020 Recommendations for the Diagnosis and Treatment of EMS Table 4
|
Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome (EMS) Equine Endocrinology Group 2020
Diagnosis of the Equine Metabolic Syndrome - The Liphook Equine Hospital and Laboratory
Cornell (USA) - instructions for insulin testing
Research comparing insulin tests and methods (most recent listed first):
Van Den Wollenberg L, Vandendriessche V, van Maanen K, Counotte GHM
Comparison of Two Diagnostic Methods to Detect Insulin Dysregulation in Horses Under Field Conditions
J Equine Vet Sci. May 2020;88:102954. Published online 7 February 2020. doi:10.1016/j.jevs.2020.102954 (Full paper is available as .pdf online, search on Van Den Wollenberg & title or click here for cache).
Leschke DH, Muir GS, Hodgson JK, Coyle M, Horn R, Bertin F-R.
Immunoreactive insulin stability in horses at risk of insulin dysregulation.
J Vet Intern Med. September 2019;1–6. https://doi.org/10.1111/jvim.15629. Open Access.
Keywords: chemiluminescent assay, diagnostic testing, endocrinology, equine metabolic syndrome, laminitis, obesity
When insulin concentrations were tested using CIA Immulite 1000, insulin was lower in EDTA samples, therefore testing insulin in EDTA samples is not recommended. Serum and heparin samples stored at 4'C were stable for up to 8 days, stored at 20'C were stable for up to 3 days. After day 4 insulin samples in serum decreased significantly, and there was a variable effect on heparin samples.
Olley RB, Carslake HB, Ireland JL, McGowan CM
Comparison of fasted basal insulin with the combined glucose-insulin test in horses and ponies with suspected insulin dysregulation
The Veterinary Journal Volume 252, October 2019 (online 05 August 2019). https://doi.org/10.1016/j.tvjl.2019.105351
Olley RB, Carslake HB, McGowan CM
Sensitivity and Specificity Of Fasted Basal Insulin Compared With Dynamic Testing In Horses And Ponies With Suspected Endocrine Disease
Equine Veterinary Journal Volume 49, Issue S51 September 2017 Page 24
Frank N, Walsh DM
Repeatability of Oral Sugar Test Results, Glucagon-Like Peptide-1 Measurements, and Serum High-Molecular-Weight Adiponectin Concentrations in Horses
J Vet Intern Med. 2017 Jul;31(4):1178-1187. doi: 10.1111/jvim.14725. Epub 2017 May 24
Dunbar LK, Mielnicki KA, Dembek KA, Toribio RE, Burns TA
Evaluation of Four Diagnostic Tests for Insulin Dysregulation in Adult Light‐Breed Horses
Journal of Veterinary Internal Medicine. 2016;30(3):885-891. doi:10.1111/jvim.13934
"In conclusion, commonly used tests for insulin dysregulation appear to produce variable results in the assessment of insulin sensitivity in horses, in that the results of a single test often do not accurately classify horses as IR or IS. Additional studies are required to determine the most useful tests for insulin dysregulation and to identify appropriate cut‐off values for defining insulin resistance, postprandial hyperinsulinemia, and their association with risk of laminitis."
Pratt-Phillips SE, Geor RJ, McCutcheon LJ
Comparison among the euglycemic-hyperinsulinemic clamp, insulin-modified frequently sampled intravenous glucose tolerance test, and oral glucose tolerance test for assessment of insulin sensitivity in healthy Standardbreds
Am J Vet Res. 2015 Jan;76(1):84-91
Conclusion: "In healthy Standardbreds with moderate body condition score, insulin sensitivities from the EHC and FSIGTT were strongly correlated but not equivalent. Estimates derived from an OGTT also may be useful to estimate insulin sensitivity."
Bröjer J, Lindåse S, Hedenskog J, Alvarsson K, Nostell K
Repeatability of the combined glucose-insulin tolerance test and the effect of a stressor before testing in horses of 2 breeds
J Vet Intern Med. 2013 Nov-Dec;27(6):1543-50. doi: 10.1111/jvim.12172
Banse HE, McFarlane D
Comparison of three methods for evaluation of equine insulin regulation in horses of varied body condition score
JEVS published online 13 Jan 2014
Insulin sensitivity - p 52 Equine Applied and Clinical Nutrition - Geor, Harris and Coenen (2013)
Tinworth KD, Wynn PC, Boston RC, Harris PA, Sillence MN, Thevis M, Thomas A, Noble GK.
Evaluation of commercially available assays for the measurement of equine insulin.
Domest Anim Endocrinol. 2011 Aug;41(2):81-90. doi: 10.1016/j.domaniend.2011.05.001. Epub 2011 May 31. PMID: 21741576.
Pratt SE, Geor RJ, McCutcheon LJ
Repeatability of 2 Methods for Assessment of Insulin Sensitivity and Glucose Dynamics in Horses
Journal of Veterinary Internal Medicine, 2005 Nov-Dec 19(6): 883–888. doi:10.1111/j.1939-1676.2005.tb02782.x
"Insulin sensitivity measured by the EHC has lower interday variation when compared with the minimal model estimate derived from the FSIGT".
Different breeds may need different normal ranges:
Bamford NJ, Potter SJ, Harris PA, Bailey SR
Breed differences in insulin sensitivity and insulinemic responses to oral glucose in horses and ponies of moderate body condition score
Domest Anim Endocrinol. 2014 Apr;47:101-7. Epub 2013 Nov 9
"there are clear breed-related differences in the insulin responses of horses and ponies to oral and intravenous glucose."
As well as different tests, insulin can be tested using different assays - RIA and CIA are the commonly used commercial assays. ELISA and LC-MS are also used.
"liquid chromatography and high-resolution/high-accuracy mass spectrometry (LC-MS) provides absolute amounts of insulin and could be assessed as a gold standard to measure insulin concentrations in blood samples" Warnken et al 2016
Testing the same blood sample using different assays is likely to give different results, and may result in some results (from the same sample) indicating insulin dysregulation whilst others indicate normal insulin regulation:
Carslake HB, Pinchbeck GL, McGowan CM
Evaluation of a Chemiluminescent Immunoassay for Measurement of Equine Insulin
Journal of Veterinary Internal Medicine published online 26 January 2017
"The CLIA is a highly repeatable assay which is suitable for within- and between-horse comparisons....At concentrations commonly used for diagnosis of insulin dysregulation (≤100 μIU/mL), results from the CLIA tend to be lower than from the RIA and should be interpreted accordingly."
Warnken T, Huber K, Feige K
Comparison of three different methods for the quantification of equine insulin
BMC Vet Res. 2016; 12(1): 196 Published online 2016 Sep 9. doi: 10.1186/s12917-016-0828-z
"In conclusion, analyses of equine serum samples for insulin with three different immunoassay methods revealed three different results for the same sample. Adjustment of insulin measurements and methods is essential to allow the consistence of information of several studies and research approaches, enabling evidence-based criteria to compare insulin concentrations consistently between assays, studies and laboratories. Since harmonization is an interminable process, further assay comparison research studies would be helpful to allow the comparison of results and cut-off values determined with the use of one method to another. This study illustrates the importance of considering the insulin analysis method when results of different laboratories or studies are compared or interpreted for the diagnosis of insulin-related endocrine and metabolic pathologies."
Banse HE, McCann J, Yang F, Wagg C, McFarlane D
Comparison of two methods for measurement of equine insulin
J Vet Diagn Invest. 2014 Jun 13;26(4):527-530 (PubMed)
"Diagnosis of equine hyperinsulinemia requires an accurate method for quantification of equine insulin concentrations. The objectives of the current study were to compare 2 commercially available techniques for measurement of equine insulin, the radioimmunoassay (RIA) and chemiluminescent immunoassay (CIA). Recovery was poor for both assays, but worse for the CIA. Serial dilution of a high endogenous insulin sample yielded better linearity for the RIA (r 2 = 0.99, P < 0.001) than the CIA (r 2 = 0.92, P = 0.009). Bland-Altman analysis indicated that the CIA was, on average, 91 pmol/l higher than the RIA, with wide limits of agreement (95% limits of agreement: -508 to 691 pmol/l). These findings suggest that results between the assays should not be considered interchangeable."
(However, when 5 discordant samples from a total of 40 were removed from the data set, bias and total error were within acceptable limits).
The above paper is based on the following PhD dissertation:
Heidi Banse
Mechanisms of Equine Insulin Resistance
PhD dissertation 2013
Borer-Weir KE, Bailey SR, Menzies-Gow NJ, Harris PA, Elliott J
Evaluation of a commercially available radioimmunoassay and species-specific ELISAs for measurement of high concentrations of insulin in equine serum
Am J Vet Res. 2012 Oct;73(10):1596-602
Firshman AM, Valberg SJ
Factors affecting clinical assessment of insulin sensitivity in horses
Equine Vet J. 2007 Nov;39(6):567-75 (PubMed)
"it is clear that there is not one ideal test, in terms of both practicality and accuracy, for evaluating insulin sensitivity in horses and improved diagnostic techniques are required".
Kronfeld DS, Treiber KH, Geor RJ
Comparison of nonspecific indications and quantitative methods for the assessment of insulin resistance in horses and ponies
J Am Vet Med Assoc. 2005 Mar 1;226(5):712-9
Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome (EMS) Equine Endocrinology Group 2020
Diagnosis of the Equine Metabolic Syndrome - The Liphook Equine Hospital and Laboratory
Cornell (USA) - instructions for insulin testing
Research comparing insulin tests and methods (most recent listed first):
Van Den Wollenberg L, Vandendriessche V, van Maanen K, Counotte GHM
Comparison of Two Diagnostic Methods to Detect Insulin Dysregulation in Horses Under Field Conditions
J Equine Vet Sci. May 2020;88:102954. Published online 7 February 2020. doi:10.1016/j.jevs.2020.102954 (Full paper is available as .pdf online, search on Van Den Wollenberg & title or click here for cache).
Leschke DH, Muir GS, Hodgson JK, Coyle M, Horn R, Bertin F-R.
Immunoreactive insulin stability in horses at risk of insulin dysregulation.
J Vet Intern Med. September 2019;1–6. https://doi.org/10.1111/jvim.15629. Open Access.
Keywords: chemiluminescent assay, diagnostic testing, endocrinology, equine metabolic syndrome, laminitis, obesity
When insulin concentrations were tested using CIA Immulite 1000, insulin was lower in EDTA samples, therefore testing insulin in EDTA samples is not recommended. Serum and heparin samples stored at 4'C were stable for up to 8 days, stored at 20'C were stable for up to 3 days. After day 4 insulin samples in serum decreased significantly, and there was a variable effect on heparin samples.
Olley RB, Carslake HB, Ireland JL, McGowan CM
Comparison of fasted basal insulin with the combined glucose-insulin test in horses and ponies with suspected insulin dysregulation
The Veterinary Journal Volume 252, October 2019 (online 05 August 2019). https://doi.org/10.1016/j.tvjl.2019.105351
Olley RB, Carslake HB, McGowan CM
Sensitivity and Specificity Of Fasted Basal Insulin Compared With Dynamic Testing In Horses And Ponies With Suspected Endocrine Disease
Equine Veterinary Journal Volume 49, Issue S51 September 2017 Page 24
Frank N, Walsh DM
Repeatability of Oral Sugar Test Results, Glucagon-Like Peptide-1 Measurements, and Serum High-Molecular-Weight Adiponectin Concentrations in Horses
J Vet Intern Med. 2017 Jul;31(4):1178-1187. doi: 10.1111/jvim.14725. Epub 2017 May 24
Dunbar LK, Mielnicki KA, Dembek KA, Toribio RE, Burns TA
Evaluation of Four Diagnostic Tests for Insulin Dysregulation in Adult Light‐Breed Horses
Journal of Veterinary Internal Medicine. 2016;30(3):885-891. doi:10.1111/jvim.13934
"In conclusion, commonly used tests for insulin dysregulation appear to produce variable results in the assessment of insulin sensitivity in horses, in that the results of a single test often do not accurately classify horses as IR or IS. Additional studies are required to determine the most useful tests for insulin dysregulation and to identify appropriate cut‐off values for defining insulin resistance, postprandial hyperinsulinemia, and their association with risk of laminitis."
Pratt-Phillips SE, Geor RJ, McCutcheon LJ
Comparison among the euglycemic-hyperinsulinemic clamp, insulin-modified frequently sampled intravenous glucose tolerance test, and oral glucose tolerance test for assessment of insulin sensitivity in healthy Standardbreds
Am J Vet Res. 2015 Jan;76(1):84-91
Conclusion: "In healthy Standardbreds with moderate body condition score, insulin sensitivities from the EHC and FSIGTT were strongly correlated but not equivalent. Estimates derived from an OGTT also may be useful to estimate insulin sensitivity."
Bröjer J, Lindåse S, Hedenskog J, Alvarsson K, Nostell K
Repeatability of the combined glucose-insulin tolerance test and the effect of a stressor before testing in horses of 2 breeds
J Vet Intern Med. 2013 Nov-Dec;27(6):1543-50. doi: 10.1111/jvim.12172
Banse HE, McFarlane D
Comparison of three methods for evaluation of equine insulin regulation in horses of varied body condition score
JEVS published online 13 Jan 2014
Insulin sensitivity - p 52 Equine Applied and Clinical Nutrition - Geor, Harris and Coenen (2013)
Tinworth KD, Wynn PC, Boston RC, Harris PA, Sillence MN, Thevis M, Thomas A, Noble GK.
Evaluation of commercially available assays for the measurement of equine insulin.
Domest Anim Endocrinol. 2011 Aug;41(2):81-90. doi: 10.1016/j.domaniend.2011.05.001. Epub 2011 May 31. PMID: 21741576.
Pratt SE, Geor RJ, McCutcheon LJ
Repeatability of 2 Methods for Assessment of Insulin Sensitivity and Glucose Dynamics in Horses
Journal of Veterinary Internal Medicine, 2005 Nov-Dec 19(6): 883–888. doi:10.1111/j.1939-1676.2005.tb02782.x
"Insulin sensitivity measured by the EHC has lower interday variation when compared with the minimal model estimate derived from the FSIGT".
Different breeds may need different normal ranges:
Bamford NJ, Potter SJ, Harris PA, Bailey SR
Breed differences in insulin sensitivity and insulinemic responses to oral glucose in horses and ponies of moderate body condition score
Domest Anim Endocrinol. 2014 Apr;47:101-7. Epub 2013 Nov 9
"there are clear breed-related differences in the insulin responses of horses and ponies to oral and intravenous glucose."
As well as different tests, insulin can be tested using different assays - RIA and CIA are the commonly used commercial assays. ELISA and LC-MS are also used.
"liquid chromatography and high-resolution/high-accuracy mass spectrometry (LC-MS) provides absolute amounts of insulin and could be assessed as a gold standard to measure insulin concentrations in blood samples" Warnken et al 2016
Testing the same blood sample using different assays is likely to give different results, and may result in some results (from the same sample) indicating insulin dysregulation whilst others indicate normal insulin regulation:
Carslake HB, Pinchbeck GL, McGowan CM
Evaluation of a Chemiluminescent Immunoassay for Measurement of Equine Insulin
Journal of Veterinary Internal Medicine published online 26 January 2017
"The CLIA is a highly repeatable assay which is suitable for within- and between-horse comparisons....At concentrations commonly used for diagnosis of insulin dysregulation (≤100 μIU/mL), results from the CLIA tend to be lower than from the RIA and should be interpreted accordingly."
Warnken T, Huber K, Feige K
Comparison of three different methods for the quantification of equine insulin
BMC Vet Res. 2016; 12(1): 196 Published online 2016 Sep 9. doi: 10.1186/s12917-016-0828-z
"In conclusion, analyses of equine serum samples for insulin with three different immunoassay methods revealed three different results for the same sample. Adjustment of insulin measurements and methods is essential to allow the consistence of information of several studies and research approaches, enabling evidence-based criteria to compare insulin concentrations consistently between assays, studies and laboratories. Since harmonization is an interminable process, further assay comparison research studies would be helpful to allow the comparison of results and cut-off values determined with the use of one method to another. This study illustrates the importance of considering the insulin analysis method when results of different laboratories or studies are compared or interpreted for the diagnosis of insulin-related endocrine and metabolic pathologies."
Banse HE, McCann J, Yang F, Wagg C, McFarlane D
Comparison of two methods for measurement of equine insulin
J Vet Diagn Invest. 2014 Jun 13;26(4):527-530 (PubMed)
"Diagnosis of equine hyperinsulinemia requires an accurate method for quantification of equine insulin concentrations. The objectives of the current study were to compare 2 commercially available techniques for measurement of equine insulin, the radioimmunoassay (RIA) and chemiluminescent immunoassay (CIA). Recovery was poor for both assays, but worse for the CIA. Serial dilution of a high endogenous insulin sample yielded better linearity for the RIA (r 2 = 0.99, P < 0.001) than the CIA (r 2 = 0.92, P = 0.009). Bland-Altman analysis indicated that the CIA was, on average, 91 pmol/l higher than the RIA, with wide limits of agreement (95% limits of agreement: -508 to 691 pmol/l). These findings suggest that results between the assays should not be considered interchangeable."
(However, when 5 discordant samples from a total of 40 were removed from the data set, bias and total error were within acceptable limits).
The above paper is based on the following PhD dissertation:
Heidi Banse
Mechanisms of Equine Insulin Resistance
PhD dissertation 2013
Borer-Weir KE, Bailey SR, Menzies-Gow NJ, Harris PA, Elliott J
Evaluation of a commercially available radioimmunoassay and species-specific ELISAs for measurement of high concentrations of insulin in equine serum
Am J Vet Res. 2012 Oct;73(10):1596-602
Firshman AM, Valberg SJ
Factors affecting clinical assessment of insulin sensitivity in horses
Equine Vet J. 2007 Nov;39(6):567-75 (PubMed)
"it is clear that there is not one ideal test, in terms of both practicality and accuracy, for evaluating insulin sensitivity in horses and improved diagnostic techniques are required".
Kronfeld DS, Treiber KH, Geor RJ
Comparison of nonspecific indications and quantitative methods for the assessment of insulin resistance in horses and ponies
J Am Vet Med Assoc. 2005 Mar 1;226(5):712-9
Insulin Dysregulation (ID)
Insulin Dysregulation (ID) is a collective term for abnormalities of insulin metabolism that include any combination of basal hyperinsulinaemia, insulin resistance (IR) and excessive insulin response to feed/sugar and starch. These insulin abnormalities are often interlinked - insulin resistance exacerbates hyperinsulinaemia, and chronic hyperinsulinaemia leads to insulin resistance. Horses with insulin dysregulation are predisposed to laminitis.
Nicholas Frank and Elizabeth Tadros introduced the term insulin dysregulation in 2013 "to refer collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome."
Insulin dysregulation is the key feature of Equine Metabolic Syndrome (EMS). Generalized or regional adiposity is also usually a feature of EMS, but not all obese horses have ID, and not all horses with ID are obese.
Frank N, Tadros E M
Insulin dysregulation
Equine Veterinary Journal Volume 46, Issue 1, pages 103–112, January 2014 (published online Nov 2013)
In Equine Laminitis (Belknap 2017, chapter 37), Dianne McFarlane, Philip Johnson and Harold Schott II describe insulin dysregulation as "abnormal glucose and insulin homeostasis", suggesting that ID is the cause of laminitis in both EMS and PPID, and that ID is an important risk factor for endocrinopathic laminitis when present in PPID horses.
Elzinga, Sarah E
Inflammation and Insulin Dysregulation in the Horse
University of Kentucky PhD thesis 2017
Insulin Dysregulation (ID) is a collective term for abnormalities of insulin metabolism that include any combination of basal hyperinsulinaemia, insulin resistance (IR) and excessive insulin response to feed/sugar and starch. These insulin abnormalities are often interlinked - insulin resistance exacerbates hyperinsulinaemia, and chronic hyperinsulinaemia leads to insulin resistance. Horses with insulin dysregulation are predisposed to laminitis.
Nicholas Frank and Elizabeth Tadros introduced the term insulin dysregulation in 2013 "to refer collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome."
Insulin dysregulation is the key feature of Equine Metabolic Syndrome (EMS). Generalized or regional adiposity is also usually a feature of EMS, but not all obese horses have ID, and not all horses with ID are obese.
Frank N, Tadros E M
Insulin dysregulation
Equine Veterinary Journal Volume 46, Issue 1, pages 103–112, January 2014 (published online Nov 2013)
In Equine Laminitis (Belknap 2017, chapter 37), Dianne McFarlane, Philip Johnson and Harold Schott II describe insulin dysregulation as "abnormal glucose and insulin homeostasis", suggesting that ID is the cause of laminitis in both EMS and PPID, and that ID is an important risk factor for endocrinopathic laminitis when present in PPID horses.
Elzinga, Sarah E
Inflammation and Insulin Dysregulation in the Horse
University of Kentucky PhD thesis 2017
Insulin Resistance (IR)
IR calculator - enter your horse's glucose and insulin blood results and the G:I ratio, RISQI, MIRG and IR status is calculated for you.
Insulin resistance was suggested as a cause for laminitis as early as 1989:
Med Hypotheses. 1989 Nov;30(3):203-10. (PubMed)
Equine laminitis--another hypothesis for pathogenesis.
Field JR, Jeffcott LB.
"Laminitis is an important condition in horses and ponies, not just because of the seriousness of the clinical signs and systemic changes involved, but because of the potentially poor prognosis and likelihood of recurrence. Laminitis is particularly prevalent in ponies and involves a multiplicity of aetiological factors. Fat ponies and those having previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bwt) than normal ponies or Standardbred horses. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic ponies establishing the existence of an apparently innate insulin insensitivity in these animals. These findings are important in regulation of carbohydrate and lipid metabolism and play a role in the pathogenesis of laminitis. The reduction of insulin effectiveness leads to elevation in thromboxane A2 activity, predisposing the animal to peripheral vasoconstriction, compromisation of blood flow to the foot and the development of laminitis."
Insulin resistance was suggested as a cause for laminitis as early as 1989:
Med Hypotheses. 1989 Nov;30(3):203-10. (PubMed)
Equine laminitis--another hypothesis for pathogenesis.
Field JR, Jeffcott LB.
"Laminitis is an important condition in horses and ponies, not just because of the seriousness of the clinical signs and systemic changes involved, but because of the potentially poor prognosis and likelihood of recurrence. Laminitis is particularly prevalent in ponies and involves a multiplicity of aetiological factors. Fat ponies and those having previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bwt) than normal ponies or Standardbred horses. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic ponies establishing the existence of an apparently innate insulin insensitivity in these animals. These findings are important in regulation of carbohydrate and lipid metabolism and play a role in the pathogenesis of laminitis. The reduction of insulin effectiveness leads to elevation in thromboxane A2 activity, predisposing the animal to peripheral vasoconstriction, compromisation of blood flow to the foot and the development of laminitis."
Insulin Tolerance Test (ITT)
From Table 4 of the 2020 Equine Endocrinology Group's Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome.
Insulin Tolerance Test
Procedure: Do not fast before this test. The horse should have access to grass or hay before the test.
Collect blood at time 0, then administer 0.10 IU/kg regular (soluble) insulin.
Collect blood 30 minutes later and measure glucose.
Feed a meal to the horse immediately after taking the 30 minute (last) blood sample.
Interpretation: Try to minimize stress prior to testing. A <50% decrease in blood glucose concentrations from baseline is consistent with insulin resistance.
Alternative test: The combined glucose-insulin test (CGIT) is an alterative to the ITT.
Dangers: The ITT can cause hypoglycaemia. Feed the horse straight after collecting the 30 minute blood sample. In rare cases, dextrose solution has been administered intravenously to address hypoglycaemia.
Lestelle JD, Thompson DL, Hebert RC
Characterization of Glucose Response Curves after Insulin Injection in Sensitive versus Insensitive Mares
Journal of Equine Veterinary Science Nov 2013 Volume 33 Issue 11 937 - 941
Lestelle, Jeanne D
Insulin dose response curves and factors affecting insulin sensitivity in horses
MSc thesis Louisiana State University 2012
Lestelle JD, Earl LR,Thompson DL Jr., Hebert RC, Mitcham PB
Insulin-glucose dose response curves in insulin sensitive and insensitive mares and effect of overnight and long-term feeding regimen
Journal of Equine Veterinary Science May–June 2011 Volume 31 Issues 5-6 Pages 285–286
From Table 4 of the 2020 Equine Endocrinology Group's Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome.
Insulin Tolerance Test
Procedure: Do not fast before this test. The horse should have access to grass or hay before the test.
Collect blood at time 0, then administer 0.10 IU/kg regular (soluble) insulin.
Collect blood 30 minutes later and measure glucose.
Feed a meal to the horse immediately after taking the 30 minute (last) blood sample.
Interpretation: Try to minimize stress prior to testing. A <50% decrease in blood glucose concentrations from baseline is consistent with insulin resistance.
Alternative test: The combined glucose-insulin test (CGIT) is an alterative to the ITT.
Dangers: The ITT can cause hypoglycaemia. Feed the horse straight after collecting the 30 minute blood sample. In rare cases, dextrose solution has been administered intravenously to address hypoglycaemia.
Lestelle JD, Thompson DL, Hebert RC
Characterization of Glucose Response Curves after Insulin Injection in Sensitive versus Insensitive Mares
Journal of Equine Veterinary Science Nov 2013 Volume 33 Issue 11 937 - 941
Lestelle, Jeanne D
Insulin dose response curves and factors affecting insulin sensitivity in horses
MSc thesis Louisiana State University 2012
Lestelle JD, Earl LR,Thompson DL Jr., Hebert RC, Mitcham PB
Insulin-glucose dose response curves in insulin sensitive and insensitive mares and effect of overnight and long-term feeding regimen
Journal of Equine Veterinary Science May–June 2011 Volume 31 Issues 5-6 Pages 285–286
Iron
Iron can be tested in the blood as serum iron and TIBC (Total Iron Binding Capacity). Kansas State University also tests ferritin.
Kansas State University normal ranges:
Serum iron 75 - 228 mcg/dL (13 - 40.8 umol/L)
TIBC 231 - 455 mcg/dL
Ferritin 43 - 261 ng/mL
Iron is measured in μg/dL (conventional units) or μmol/L (SI units). To convert μg/dL to μmol/L: μg/dL x 0.179 = μmol/L
To convert serum iron blood results to different units: Iron (Fe) - Unitslab.com
Is iron associated with insulin dysregulation?
Evidence to date (2022) suggests that many horses have levels of iron in their diet that far exceed the NRC recommendations for iron, and that dietary iron is unlikely to cause insulin resistance/dysregulation. Nielsen et al. 2012 found that, of horses all receiving a similar diet, only horses with insulin resistance had increased serum ferritin concentrations, suggesting that insulin resistance may cause iron overload, rather than that iron overload causes insulin resistance. McLean et al. 2022 points out that serum ferritin is not necessarily indicative of iron overload. Serum ferritin is associated with inflammation, and elevated serum ferritin may be seen in response to inflammation associated with insulin resistance, regardless of whether iron overload is present. McLean et al. 2022 suggests that insulin resistance appears to be rare in horses and ponies kept at a healthy weight and given sufficient exercise.
McLean NL, McGilchrist N, Nielsen BD.
Dietary iron unlikely to cause insulin resistance in horses.
Animals September 2022, 12 (19), 2510. https://doi.org/10.3390/ani12192510.
Keywords: iron; insulin resistance; racehorse; metabolic disease; nutrition; equine; horse
"Conclusions: This study demonstrated that greatly exceeding recommended dietary amounts of Fe did not result in a single reported case of IR in 1978 Thoroughbreds, confirming the hypothesis that, in isolation, high dietary Fe does not increase the incidence of IR. While there are no reported benefits of feeding high amounts of Fe, there are also no reported negative health consequences of feeding extra Fe (within the range discussed in this paper) in horses. The normal diet a racehorse receives, without supplementation, typically exceeds the required amounts of Fe by several fold, and there is no justification for supplementing more Fe. However, there also is no good justification for trying to select feedstuffs for low Fe concentration. It is not known whether IO is associated as a part of a multi-factorial disease cascade with IR in horses. Until research can determine this, greater emphasis needs to be placed on maintaining a healthy bodyweight for horses and ensuring adequate exercise to maintain insulin sensitivity."
Kellon EM, Gustafson KM.
Possible dysmetabolic hyperferritinemia in hyperinsulinemic horses.
Open Vet J. 2020;9(4):287-293. doi:10.4314/ovj.v9i4.2
J Zoo Wildl Med. 2012 Sep;43(3 Suppl):S61-5.
A potential link between insulin resistance and iron overload disorder in browsing rhinoceroses investigated through the use of an equine model.
Nielsen BD, Vick MM, Dennis PM.
See comment on TLS forum
Borges AS, Divers TJ, Stokol T, Mohammed OH
Serum Iron and Plasma Fibrinogen Concentrations as Indicatorsr of Systemic Inflammatory Diseases in Horses
J Vet Intern Med 2007; 21: 489-494
Kansas State University is the only laboratory in the world that currently tests equine ferritin, used to estimate the total body stores of iron.
A full iron panel includes ferritin, serum iron and TIBC (Total Iron Binding Capacity)
Smith et al. developed an enzyme immunoassay to measure equine serum ferritin which correlated significantly with nonheme iron concentrations in the liver and spleen.
Serum ferritin of 28 normal horses averaged 152 ng/ml and ranged from 70.2 to 250 ng/ml (the range obtained from logarithmic conversion was 66 to 205 ng/ml).
In 103 horses at slaughter, serum ferritin averaged 223 ng/ml, with 29 horses having levels >305 ng/ml, 5 horses having levels <66 ng/ml, and the highest level being 742 ng/ml. Serum iron was 120 ug/dl, total iron-binding capacity 388 ug/dl; liver non-heme iron concentration 0.181 mg/g, spleen non-heme iron concentration 1.59 mg/g. Many of the horses sampled at slaughter appeared to have iron overload, perhaps due to being older and therefore accumulating iron for many years, or perhaps they had been supplemented with iron before slaughter - histories and ages were not available.
Serum iron correlated significantly with total iron-binding capacity, but neither correlated with serum ferritin.
Serum ferritin correlated more closely with non-heme iron concentrations in the liver and spleen (than serum iron and total iron-binding capacity).
Serum ferritin was highly correlated with non-heme iron concentrations, but not in all horses, most of whom had higher serum ferritin levels than expected, which the paper suggests could reflect inflammation, infection, liver disease or individual variation.
All horses with low serum ferritin also had low non-heme iron concentrations.
Serum iron correlated significantly with spleen, but not liver, non-heme iron concentration.
Serum total iron-binding capacity did not reflect non-heme iron concentration in either organ.
Serum ferritin increased following intravenous iron therapy (1 g iron as ferric hydroxide on days 0, 2, 4 and 6) from 162 ng/ml to 395 ng/ml and was still high 8 days after iron treatment. Serum iron and total iron-binding capacity also increased during iron therapy but returned to normal levels 4 days after iron treatment.
Serum ferritin decreased following phlebotomy (51.7 ng/ml 13 days after phlebotomy compared to 161 ng/ml in non-phlebotomized horses. Serum iron and total iron-binding capacity were also lower in phlebotomized horses.
PCV and hemoglobin have also been used to evaluate iron status, but are insensitive, particularly as PCV can increase by as much as 68% when horses are excited.
Serum iron is influenced by factors including inflammation, hypoproteinaemia (low total protein) and ineffective red blood cell production.
Conclusion: "serum ferritin provides a good index of hepatic and splenic iron and can be used to evaluate iron storage in horses".
Smith JE, Moore K, Cipriano JE, Morris PG
Serum ferritin as a measure of stored iron in horses
J Nutr. 1984 Apr;114(4):677-81 (Full paper on ResearchGate)
Osbaldiston GW, Griffith PR
Serum iron levels in normal and anemic horses
The Canadian Veterinary Journal Vol 13 No 5 May 1972
Iron Overload – A Growing Nutritional Disorder from Dietary Excess - Amberlee Ficociello March 2007
Confusion on a new treatment for laminitis used in France - Graham Duncanson - April 2012 - Westover Veterinary Centre
A pony with laminitis and high levels of haemosiderin found on liver biopsy was treated with weekly blood letting for 8 weeks, which reduced the haemosiderin. The pony recovered from laminitis - vets were unable to confirm whether the blood letting had directly helped the laminitis. The high levels of haemosiderin (a stored form of iron) were thought to be due to high levels of iron found in borehole water that the pony was drinking.
See Ferritins and Hemosiderin - R Bowen - Colorado State University - April 2001
Iron Status of Hyperinsulinemic/Insulin Resistant Horses - Eleanor M Kellon VMD
Iron – Nuclear Fuel - Eleanor M Kellon VMD for Uckele Equine Dec 2013
Is iron implicated in the development of PPID?
There is research that suggests that accumulation of iron is present at affected neurons and associated microglia in the substantia nigra of PD patients. This additional free-iron has the capacity to generate reactive oxygen species, promote the aggregation of α-synuclein protein, and exacerbate or even cause neurodegeneration.
Iron overload symptoms in humans
Iron overload - www.irondisorders.org
Am J Pathol. 2013 Jun;182(6):2254-63 (PubMed)
Dietary iron overload induces visceral adipose tissue insulin resistance
Dongiovanni P, Ruscica M, Rametta R, Recalcati S, Steffani L, Gatti S, Girelli D, Cairo G, Magni P, Fargion S, Valenti L"Increased iron stores associated with elevated levels of the iron hormone hepcidin are a frequent feature of the metabolic syndrome."
Mice were fed either a standard or an iron-enriched diet for 16 weeks. "Iron supplementation increased hepatic iron and serum hepcidin fivefold and led to a 40% increase in fasting glucose due to insulin resistance, as confirmed by the insulin tolerance test, and to threefold higher levels of triglycerides. Iron supplemented mice had lower visceral adipose tissue mass estimated by epididymal fat pad, associated with iron accumulation in adipocytes. Decreased insulin signaling, evaluated by the phospho-Akt/Akt ratio, was detected in the visceral adipose tissue of iron overloaded mice, and gene expression analysis of visceral adipose tissue showed that an iron-enriched diet up-regulated iron-responsive genes and adipokines, favoring insulin resistance, whereas lipoprotein lipase was down-regulated." "In conclusion, we characterized a model of dysmetabolic iron overload syndrome in which an iron-enriched diet induces insulin resistance and hypertriglyceridemia and affects visceral adipose tissue metabolism by a mechanism involving hepcidin up-regulation."
Metabolism. 2013 Jan;62(1):62-9 (PubMed)
High-fat, high-fructose diet induces hepatic iron overload via a hepcidin-independent mechanism prior to the onset of liver steatosis and insulin resistance in mice
Tsuchiya H, Ebata Y, Sakabe T, Hama S, Kogure K, Shiota G
"Objective: Excess iron deposition in tissues leads to increased oxidative stress. The clinical observation that non-alcoholic fatty liver disease (NAFLD) is frequently associated with hepatic iron overload (HIO) indicates that iron-induced oxidative stress may be related to NAFLD pathology. Decreased expression of hepcidin, a hepatic hormone that suppresses dietary iron absorption in the duodenum, is frequently observed in NAFLD patients and has been postulated to be a cause of HIO."
"Results: Within 4 weeks after the start of the experiment, the mice exhibited significant increases in hepatic free fatty acid (FFA) content, serum insulin levels, and the homeostasis model assessment of insulin resistance. Interestingly, hepatic iron content and oxidative stress significantly increased with the HFHFr diet 2 weeks earlier than hepatic FFA accumulation and decreased insulin sensitivity. Moreover, hepatic hepcidin expression was significantly downregulated, as is also observed in NAFLD patients, but much later than the onset of HIO."
Tuomainen TP, Nyyssönen K, Salonen R, Tervahauta A, Korpela H, Lakka T, Kaplan GA, Salonen JT.
Body iron stores are associated with serum insulin and blood glucose concentrations. Population study in 1,013 eastern Finnish men.
Diabetes Care. 1997 Mar;20(3):426-8. PubMed.
"RESEARCH DESIGN AND METHODS:A cross-sectional population study was conducted in 1,013 middle-aged men, and an association of serum ferritin with concentrations of serum insulin, blood glucose, and serum fructosamine was tested.
RESULTS:The mean concentration of fasting serum insulin was 21.6% higher (95% CI 7.3-37.9%, P < 0.001) in the 5th quintile of serum ferritin compared with the 1st quintile. The elevation in blood glucose was 6.1% (95% CI 2.3-9.9%, P < 0.001) and in serum fructosamine 3.9% (1.5-6.9%, P < 0.01).
CONCLUSIONS:Mildly elevated body iron stores are associated with statistically significant elevations in glucose homeostasis indexes.
Kansas State University normal ranges:
Serum iron 75 - 228 mcg/dL (13 - 40.8 umol/L)
TIBC 231 - 455 mcg/dL
Ferritin 43 - 261 ng/mL
Iron is measured in μg/dL (conventional units) or μmol/L (SI units). To convert μg/dL to μmol/L: μg/dL x 0.179 = μmol/L
To convert serum iron blood results to different units: Iron (Fe) - Unitslab.com
Is iron associated with insulin dysregulation?
Evidence to date (2022) suggests that many horses have levels of iron in their diet that far exceed the NRC recommendations for iron, and that dietary iron is unlikely to cause insulin resistance/dysregulation. Nielsen et al. 2012 found that, of horses all receiving a similar diet, only horses with insulin resistance had increased serum ferritin concentrations, suggesting that insulin resistance may cause iron overload, rather than that iron overload causes insulin resistance. McLean et al. 2022 points out that serum ferritin is not necessarily indicative of iron overload. Serum ferritin is associated with inflammation, and elevated serum ferritin may be seen in response to inflammation associated with insulin resistance, regardless of whether iron overload is present. McLean et al. 2022 suggests that insulin resistance appears to be rare in horses and ponies kept at a healthy weight and given sufficient exercise.
McLean NL, McGilchrist N, Nielsen BD.
Dietary iron unlikely to cause insulin resistance in horses.
Animals September 2022, 12 (19), 2510. https://doi.org/10.3390/ani12192510.
Keywords: iron; insulin resistance; racehorse; metabolic disease; nutrition; equine; horse
"Conclusions: This study demonstrated that greatly exceeding recommended dietary amounts of Fe did not result in a single reported case of IR in 1978 Thoroughbreds, confirming the hypothesis that, in isolation, high dietary Fe does not increase the incidence of IR. While there are no reported benefits of feeding high amounts of Fe, there are also no reported negative health consequences of feeding extra Fe (within the range discussed in this paper) in horses. The normal diet a racehorse receives, without supplementation, typically exceeds the required amounts of Fe by several fold, and there is no justification for supplementing more Fe. However, there also is no good justification for trying to select feedstuffs for low Fe concentration. It is not known whether IO is associated as a part of a multi-factorial disease cascade with IR in horses. Until research can determine this, greater emphasis needs to be placed on maintaining a healthy bodyweight for horses and ensuring adequate exercise to maintain insulin sensitivity."
Kellon EM, Gustafson KM.
Possible dysmetabolic hyperferritinemia in hyperinsulinemic horses.
Open Vet J. 2020;9(4):287-293. doi:10.4314/ovj.v9i4.2
J Zoo Wildl Med. 2012 Sep;43(3 Suppl):S61-5.
A potential link between insulin resistance and iron overload disorder in browsing rhinoceroses investigated through the use of an equine model.
Nielsen BD, Vick MM, Dennis PM.
See comment on TLS forum
Borges AS, Divers TJ, Stokol T, Mohammed OH
Serum Iron and Plasma Fibrinogen Concentrations as Indicatorsr of Systemic Inflammatory Diseases in Horses
J Vet Intern Med 2007; 21: 489-494
Kansas State University is the only laboratory in the world that currently tests equine ferritin, used to estimate the total body stores of iron.
A full iron panel includes ferritin, serum iron and TIBC (Total Iron Binding Capacity)
Smith et al. developed an enzyme immunoassay to measure equine serum ferritin which correlated significantly with nonheme iron concentrations in the liver and spleen.
Serum ferritin of 28 normal horses averaged 152 ng/ml and ranged from 70.2 to 250 ng/ml (the range obtained from logarithmic conversion was 66 to 205 ng/ml).
In 103 horses at slaughter, serum ferritin averaged 223 ng/ml, with 29 horses having levels >305 ng/ml, 5 horses having levels <66 ng/ml, and the highest level being 742 ng/ml. Serum iron was 120 ug/dl, total iron-binding capacity 388 ug/dl; liver non-heme iron concentration 0.181 mg/g, spleen non-heme iron concentration 1.59 mg/g. Many of the horses sampled at slaughter appeared to have iron overload, perhaps due to being older and therefore accumulating iron for many years, or perhaps they had been supplemented with iron before slaughter - histories and ages were not available.
Serum iron correlated significantly with total iron-binding capacity, but neither correlated with serum ferritin.
Serum ferritin correlated more closely with non-heme iron concentrations in the liver and spleen (than serum iron and total iron-binding capacity).
Serum ferritin was highly correlated with non-heme iron concentrations, but not in all horses, most of whom had higher serum ferritin levels than expected, which the paper suggests could reflect inflammation, infection, liver disease or individual variation.
All horses with low serum ferritin also had low non-heme iron concentrations.
Serum iron correlated significantly with spleen, but not liver, non-heme iron concentration.
Serum total iron-binding capacity did not reflect non-heme iron concentration in either organ.
Serum ferritin increased following intravenous iron therapy (1 g iron as ferric hydroxide on days 0, 2, 4 and 6) from 162 ng/ml to 395 ng/ml and was still high 8 days after iron treatment. Serum iron and total iron-binding capacity also increased during iron therapy but returned to normal levels 4 days after iron treatment.
Serum ferritin decreased following phlebotomy (51.7 ng/ml 13 days after phlebotomy compared to 161 ng/ml in non-phlebotomized horses. Serum iron and total iron-binding capacity were also lower in phlebotomized horses.
PCV and hemoglobin have also been used to evaluate iron status, but are insensitive, particularly as PCV can increase by as much as 68% when horses are excited.
Serum iron is influenced by factors including inflammation, hypoproteinaemia (low total protein) and ineffective red blood cell production.
Conclusion: "serum ferritin provides a good index of hepatic and splenic iron and can be used to evaluate iron storage in horses".
Smith JE, Moore K, Cipriano JE, Morris PG
Serum ferritin as a measure of stored iron in horses
J Nutr. 1984 Apr;114(4):677-81 (Full paper on ResearchGate)
Osbaldiston GW, Griffith PR
Serum iron levels in normal and anemic horses
The Canadian Veterinary Journal Vol 13 No 5 May 1972
Iron Overload – A Growing Nutritional Disorder from Dietary Excess - Amberlee Ficociello March 2007
Confusion on a new treatment for laminitis used in France - Graham Duncanson - April 2012 - Westover Veterinary Centre
A pony with laminitis and high levels of haemosiderin found on liver biopsy was treated with weekly blood letting for 8 weeks, which reduced the haemosiderin. The pony recovered from laminitis - vets were unable to confirm whether the blood letting had directly helped the laminitis. The high levels of haemosiderin (a stored form of iron) were thought to be due to high levels of iron found in borehole water that the pony was drinking.
See Ferritins and Hemosiderin - R Bowen - Colorado State University - April 2001
Iron Status of Hyperinsulinemic/Insulin Resistant Horses - Eleanor M Kellon VMD
Iron – Nuclear Fuel - Eleanor M Kellon VMD for Uckele Equine Dec 2013
Is iron implicated in the development of PPID?
There is research that suggests that accumulation of iron is present at affected neurons and associated microglia in the substantia nigra of PD patients. This additional free-iron has the capacity to generate reactive oxygen species, promote the aggregation of α-synuclein protein, and exacerbate or even cause neurodegeneration.
Iron overload symptoms in humans
Iron overload - www.irondisorders.org
Am J Pathol. 2013 Jun;182(6):2254-63 (PubMed)
Dietary iron overload induces visceral adipose tissue insulin resistance
Dongiovanni P, Ruscica M, Rametta R, Recalcati S, Steffani L, Gatti S, Girelli D, Cairo G, Magni P, Fargion S, Valenti L"Increased iron stores associated with elevated levels of the iron hormone hepcidin are a frequent feature of the metabolic syndrome."
Mice were fed either a standard or an iron-enriched diet for 16 weeks. "Iron supplementation increased hepatic iron and serum hepcidin fivefold and led to a 40% increase in fasting glucose due to insulin resistance, as confirmed by the insulin tolerance test, and to threefold higher levels of triglycerides. Iron supplemented mice had lower visceral adipose tissue mass estimated by epididymal fat pad, associated with iron accumulation in adipocytes. Decreased insulin signaling, evaluated by the phospho-Akt/Akt ratio, was detected in the visceral adipose tissue of iron overloaded mice, and gene expression analysis of visceral adipose tissue showed that an iron-enriched diet up-regulated iron-responsive genes and adipokines, favoring insulin resistance, whereas lipoprotein lipase was down-regulated." "In conclusion, we characterized a model of dysmetabolic iron overload syndrome in which an iron-enriched diet induces insulin resistance and hypertriglyceridemia and affects visceral adipose tissue metabolism by a mechanism involving hepcidin up-regulation."
Metabolism. 2013 Jan;62(1):62-9 (PubMed)
High-fat, high-fructose diet induces hepatic iron overload via a hepcidin-independent mechanism prior to the onset of liver steatosis and insulin resistance in mice
Tsuchiya H, Ebata Y, Sakabe T, Hama S, Kogure K, Shiota G
"Objective: Excess iron deposition in tissues leads to increased oxidative stress. The clinical observation that non-alcoholic fatty liver disease (NAFLD) is frequently associated with hepatic iron overload (HIO) indicates that iron-induced oxidative stress may be related to NAFLD pathology. Decreased expression of hepcidin, a hepatic hormone that suppresses dietary iron absorption in the duodenum, is frequently observed in NAFLD patients and has been postulated to be a cause of HIO."
"Results: Within 4 weeks after the start of the experiment, the mice exhibited significant increases in hepatic free fatty acid (FFA) content, serum insulin levels, and the homeostasis model assessment of insulin resistance. Interestingly, hepatic iron content and oxidative stress significantly increased with the HFHFr diet 2 weeks earlier than hepatic FFA accumulation and decreased insulin sensitivity. Moreover, hepatic hepcidin expression was significantly downregulated, as is also observed in NAFLD patients, but much later than the onset of HIO."
Tuomainen TP, Nyyssönen K, Salonen R, Tervahauta A, Korpela H, Lakka T, Kaplan GA, Salonen JT.
Body iron stores are associated with serum insulin and blood glucose concentrations. Population study in 1,013 eastern Finnish men.
Diabetes Care. 1997 Mar;20(3):426-8. PubMed.
"RESEARCH DESIGN AND METHODS:A cross-sectional population study was conducted in 1,013 middle-aged men, and an association of serum ferritin with concentrations of serum insulin, blood glucose, and serum fructosamine was tested.
RESULTS:The mean concentration of fasting serum insulin was 21.6% higher (95% CI 7.3-37.9%, P < 0.001) in the 5th quintile of serum ferritin compared with the 1st quintile. The elevation in blood glucose was 6.1% (95% CI 2.3-9.9%, P < 0.001) and in serum fructosamine 3.9% (1.5-6.9%, P < 0.01).
CONCLUSIONS:Mildly elevated body iron stores are associated with statistically significant elevations in glucose homeostasis indexes.