Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse

Prevalence and Progression of Resting ACTH, Insulin and Adiponectin Values as Indicators of Suspected Endocrine Diseases in Sport Horses and Ponies Compared to Non-Sport Horses, Ponies and Donkeys

Prevalence of endocrine disease in sport horses has been sparsely reported. They often compete well into their teenage years; thus, diagnosis and control of endocrine disease could be important to maintain performance and optimise health and welfare. The aim was to compare the prevalence of pituitary pars intermedia dysfunction (PPID), insulin dysregulation (ID) and metabolic obesity between sport and non-sport type breeds and assess disease progression. Blood samples submitted for plasma adrenocorticotropic hormone (ACTH), serum insulin or adiponectin were included in this study. Horses were grouped according to their breed into sport horses, which are typically used for athletic purposes, and non-sport horses, which are less-athletic breeds typically used for leisure. Cases included 1365 non-sport horse initial samples with 1850 non-sport horse follow-up samples and 1022 sport horse initial samples with 1081 sport horse follow-up samples. PPID and metabolic obesity were found to be as prevalent in the sport horse population, but non-sport horses were more likely to have ID. Upon follow up examination PPID was more prevalent with higher median ACTH in sport horses. This was also true of metabolic obesity in sport horses at follow-up, although median adiponectin was higher, perhaps indicating that the population is less severely affected than non-sport horses. Screening for endocrinopathies should be considered in sport horses presenting with poor performance.

Current understanding of insulin dysregulation and its relationship with carbohydrate and protein metabolism in horses

Insulin dysregulation (ID) is a common metabolic disorder in horses, characterized by hyperinsulinemia and/or peripheral insulin resistance. The critical role of hyperinsulinemia in endocrinopathic laminitis has driven research into the insulinotropic effects of dietary nutrients and the reciprocal impact of ID on nutrient metabolism. The relationship between ID and carbohydrate metabolism has been extensively studied; however, the effects of ID on protein metabolism in horses remain largely unexplored. This review begins with an overview of the importance of insulin in the regulation of muscle protein synthesis and degradation and then examines the current understanding of the interplay between ID and protein and carbohydrate metabolism in horses. Horses with ID exhibit altered resting plasma amino acid concentrations and shifts in postprandial amino acid dynamics. Recent work illustrated that ID horses had higher levels of plasma amino acids following a protein meal and delayed postprandial clearance from the blood compared to non-ID horses. The postprandial muscle synthetic response does not seem to be diminished in ID horses, but alterations in key cellular signaling molecules have been reported. ID horses display a pronounced hyperinsulinemic response following the consumption of feeds providing a range of protein, non-structural carbohydrate, starch and water-soluble carbohydrate intakes. Recent studies have shown that ID horses have an increased postprandial incretin response, contributing to the observed hyperinsulinemia. To minimize the postprandial insulin response, thresholds for carbohydrate consumption have recently been proposed. Similar thresholds should be established for protein to aid in the refinement of nutritional strategies to manage ID horses.

Corticosteroid Administration Enhances the Glycemic, Insulinemic, and Incretin Responses to a High-Protein Mixed Meal in Adult Horses

BACKGROUND

Corticosteroids are used routinely in horses and induce insulin dysregulation (ID). Nutrition is important for ID management and includes low nonstructural carbohydrate (NSC) diets and, often, high-protein ration balancers (RB). Insulin and incretin secretion increase after high-protein meals; corticosteroids may influence these effects.

HYPOTHESIS

A high-protein mixed meal will induce hyperinsulinemia and increased concentrations of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) in horses with ID; dexamethasone (DEX) will amplify this effect.

ANIMALS

Five horses with naturally occurring ID.

METHODS

Horses underwent an IV glucose tolerance test and a feed challenge test (FCT; 1 kg RB). Tests were repeated after DEX administration (0.08 mg/kg PO q24h, 7 days). Insulin, glucose, and incretin dynamics were compared pre- and post-DEX.

RESULTS

Corticosteroids exacerbated post-prandial hyperinsulinemia and hyperglycemia after a high-protein meal. The FCT area under the curve for insulin (AUCINS) after DEX was significantly higher than baseline (558 ± 182 μIU/mL × min vs. 257 ± 93.9 μIU/mL × min; p = 0.03). The maximum concentration of GIP (CmaxGIP) after DEX (381 ± 70.6 pg/mL) was significantly higher than baseline (262 ± 13.7 pg/mL; p = 0.013). The AUC for GLP-1 (AUCGLP-1; 31.1 ± 15.2 vs. 50 ± 20.2 pg/mL; p = 0.19) and the Cmax of GLP-1 (CmaxGLP-1; 39.1 ± 25.3 vs. 29.6 ± 12.2 pg/mL; p = 0.32) did not differ between DEX and baseline.

CONCLUSIONS AND CLINICAL IMPORTANCE

Metabolic responses to a high-protein mixed meal were exacerbated by corticosteroids. Horses receiving corticosteroids had larger GIP responses, which may enhance post-prandial hyperinsulinemia.

Pharmacokinetics and Alterations in Glucose and Insulin Levels After a Single Dose of Canagliflozin in Healthy Icelandic Horses

Canagliflozin (CFZ) is a sodium-glucose cotransporter-2 inhibitor that has shown promising results as a drug for the treatment of insulin dysregulation in horses. Even though CFZ is used clinically, no pharmacokinetic data has previously been published. In this study, the pharmacokinetics of CFZ after administration of a single oral dose of 1.8 mg/kg in eight healthy Icelandic horses was examined. Additionally, the effect of treatment on glucose and insulin levels in response to a graded glucose infusion was investigated. Plasma samples for CFZ quantification were taken at 0, 0.33, 0.66, 1, 1.33, 1.66, 2, 2.33, 2.66, 3, 3.5, 4, 5, 6, 8, 12, 24, 32, and 48 h post administration. CFZ was quantified using UHPLC coupled to tandem quadrupole mass spectrometry (UHPLC-MS/MS). A non-compartmental analysis revealed key pharmacokinetic parameters, including a median Tmax of 7 h, a Cmax of 2350 ng/mL, and a t1/2Z of 28.5 h. CFZ treatment reduced glucose (AUCGLU, p = 0.001) and insulin (AUCINS, p = 0.04) response to a graded glucose infusion administered 5 h after treatment. This indicates a rapid onset of action following a single dose in healthy Icelandic horses. No obvious adverse effects related to the treatment were observed.

Nutraceutical Supplement Mitigates Insulin Resistance in Horses with a History of Insulin Dysregulation During a Challenge with a High-Starch Diet

Insulin dysregulation (ID) is associated with an increased risk of laminitis which often necessitates the need for clinical intervention. To test the contention that the prophylactic supplementation of nutraceuticals could mitigate ID in susceptible horses, 16 mature horses with a history of ID were supplemented with either the placebo (n = 8) or nutraceutical (n = 8) once daily. Horses were housed in dry lots with ad libitum access to grass hay and fed a concentrate twice daily to provide 0.5 g starch/kg BW/meal. A combined glucose-insulin tolerance test was performed on all horses before and after 4 weeks of treatment. Nutraceutical-supplemented horses had 61% greater (p = 0.05) glucose clearance rates compared to the placebo group. This resulted in a shorter time in the positive phase of glucose clearance (p = 0.03) for the nutraceutical group compared to the placebo group. Horses receiving the nutraceutical had lower (p = 0.003) insulin concentrations at 75 min and lower (p = 0.04) glucose concentrations at 45 min compared to the placebo. Prophylactic supplementation with nutraceuticals resulted in greater glucose clearance rates during a starch challenge, indicating that nutraceuticals can mitigate ID in susceptible horses consuming an excess of non-structural carbohydrate.

Effects of storage-handling methods on nutrient analysis of fresh-forage samples

Forage low in nonstructural carbohydrates (NSC) is recommended for insulin dysregulated (ID) horses, indicating the importance of an accurate forage analysis. However, it remains to be fully understood how handling forage samples pre-analysis impacts nutrient values. The objective of this study was to compare the effect of fresh-forage storage-handling methods: microwave-oven (MO; 9kw; 70s then stored at -20℃), room temperature (20℃), 3℃, -20℃, and -80℃. Subsamples collected from a mixed-grass pasture and a ryegrass plot were analyzed for crude protein (CP), water soluble carbohydrates (WSC), ethanol soluble carbohydrates (ESC), starch and NSC (starch and WSC). Forage samples were stored for two different time periods (24h vs 1wk) prior to being shipped on ice to a commercial laboratory for wet chemistry (WC) and near-infrared spectroscopy (NIR) analysis. Mixed grass stored at RT showed a reduction in WSC (P=0.009), ESC (P=0.001) and NSC (P=0.006) from 24h to 1wk. Similarly, ESC and starch of the ryegrass and CP of mixed grass decreased after 1wk, but only when stored at -80℃ (P=0.007; P=0.001; P=0.02). Additionally, over time, CP of ryegrass and ESC of mixed grass became higher when stored at -20℃ and MO, respectively (P=0.02; P=0.03). From this study, in order to limit metabolic changes and provide accurate nutrient composition results, practically fresh forage that cannot be quickly analyzed should be transported on ice post collection to a storage location then immediately refrigerated where it can be kept up to one week prior to being shipped on ice for analysis.

Intra-articular triamcinolone acetonide injection results in increases in systemic insulin and glucose concentrations in horses without insulin dysregulation

BACKGROUND

Corticosteroids are a commonly used, inexpensive intra-articular treatment for osteoarthritis which may increase the risk for laminitis in horses due, in part, to hyperinsulinaemia. Humans with metabolic syndrome experience increases in insulin and glucose concentrations post-injection, but responses in horses are unknown.

OBJECTIVES

To determine the effect of a single intra-articular (IA) dose of triamcinolone acetate (TA) on blood insulin and glucose concentrations.

STUDY DESIGN

Before-after study.

METHODS

Ten horses with normal insulin regulation as assessed by an oral sugar test received 18 mg of TA into one middle carpal joint. Insulin and glucose concentrations were evaluated at baseline and 4, 6, 8, 24, 48, and 72 h following IA corticosteroid injection. Differences from baseline were evaluated using a repeated measures ANOVA with Dunnett's multiple comparison testing or a Friedman test with Dunn's correction (significant at p < 0.05).

RESULTS

Mean ± SD blood insulin concentration post IA TA injection was increased at 6 h (15.8 ± 3.1 μIU/mL, p = 0.01), 24 h (23 ± 5.8 μIU/mL, p ≤ 0.001), and 48 h (29 ± 13 μIU/mL, p ≤ 0.01) compared to baseline (10 ± 12.3 μIU/mL), with the peak at 48 h. Median ± 95% CI blood glucose concentration post IA TA injection was increased at 6 h (112.7 ± 20.3 mg/dL, p = 0.006), 8 h (112.9 ± 21.4 mg/dL, p = 0.004), 24 h (122.6 ± 14.6, p ≤ 0.0001), and 48 h (123.5 ± 15.4 mg/dL, p ≤ 0.0001) compared to baseline (89.2 ± 6.6 mg/dL), with the peak at 48 h.

MAIN LIMITATIONS

Only horses with normal insulin regulation were evaluated.

CONCLUSIONS

Blood insulin and glucose concentrations modestly increased for 48 h following IA TA.

A glucagon-like peptide-1 receptor antagonist reduces the insulin response to a glycemic meal in ponies

High plasma concentrations of insulin can cause acute laminitis. Ponies and horses with insulin dysregulation (ID) exhibit marked hyperinsulinemia in response to dietary hydrolyzable carbohydrates. Glucagon-like peptide-1 (GLP-1), an incretin hormone released from the gastrointestinal tract, enhances insulin release, and is increased postprandially in ponies with ID. The aim of this study was to determine whether blocking the GLP-1 receptor reduces the insulin response to a high glycemic meal. Five adult ponies were adapted to a cereal meal and then given two feed challenges 24 h apart of a meal containing 3 g/kg BW micronized maize. Using a randomized cross-over design all ponies received both treatments, where one of the feeds was preceded by the IV administration of a GLP-1 receptor blocking peptide, Exendin-3 (9-39) amide (80 µg/kg), and the other feed by a sham treatment of peptide diluent only. Blood samples were taken before feeding and peptide administration, and then at 30-min intervals via a jugular catheter for 6 h for the measurement of insulin, glucose, and active GLP-1. The peptide and meal challenge caused no adverse effects, and the change in plasma glucose in response to the meal was not affected (P = 0.36) by treatment: peak concentration 9.24 ± 1.22 and 9.14 ± 1.08 mmol/L without and with the antagonist, respectively. Similarly, there was no effect (P = 0.35) on plasma active GLP-1 concentrations: peak concentration 14.3 ± 1.36 pM and 13.7 ± 1.97 pM without and with the antagonist, respectively. However, the antagonist caused a significant decrease in the area under the curve for insulin (P = 0.04), and weak evidence (P = 0.06) of a reduction in peak insulin concentration (456 ± 147 μIU/mL and 370 ± 146 μIU/mL without and with the antagonist, respectively). The lower overall insulin response to the maize meal after treatment with the antagonist demonstrates that blocking the GLP-1 receptor partially reduced insulin production in response to a high starch, high glycemic index, diet. Using a different methodological approach to published studies, this study also confirmed that GLP-1 does contribute to the excessive insulin production in ponies with ID.