The effect of oral metformin on insulin sensitivity in insulin-resistant ponies

The effect of pre-dosing with metformin on the insulin response to oral sugar in insulin-dysregulated horses

BACKGROUND

A single dose of metformin administered 1 h prior to oral glucose challenge was previously shown to reduce insulinaemic responses in horses with experimentally-induced insulin dysregulation (ID). Targeted administration could be useful for controlling post-prandial hyperinsulinaemia in horses with naturally-occurring ID.

OBJECTIVES

The objective was to compare the insulinaemic and glycaemic responses to oral sugar testing (OST) performed at different intervals after a single dose of metformin in horses with naturally-occurring ID. We hypothesised that pre-treatment with one dose of metformin would significantly decrease the insulinaemic response to OST.

STUDY DESIGN

Randomised cross-over in vivo experiment.

METHODS

Eight university-owned adult horses with naturally-occurring ID underwent OST 1, 2 and 6 h following a single oral dose of metformin (30 mg/kg) or 1 h after placebo (240 mL water) with a 7-day washout between treatments over a period of 3 weeks. Plasma insulin, C-peptide and glucose concentrations were measured at 0, 60 and 90 min after 0.45 mL/kg light corn syrup and the effect of treatment (and the interval since dosing) examined using a mixed effects linear regression model.

RESULTS

Metformin treatment had no significant effect on plasma glucose, insulin or C-peptide concentrations at any time point compared with placebo (p > 0.05). For OST 1 h post metformin, median (IQR) plasma insulin was 91.3 (62.4-114.9) μIU/mL at 60 min versus 76.2 (59.1-134.5) for placebo (p = 0.8) and 62.7 (31.4-109.7) at 90 min versus 51.8 (29.2-126.3) for placebo (p = 0.9).

MAIN LIMITATIONS

Small sample size may limit identification of more subtle decreases in insulin concentration with metformin pre-dosing. The results of this study are relevant only for one pre-treatment dose (30 mg/kg) which limits extrapolation to predictions about the effects of longer-term metformin administration on insulin and glucose dynamics in the horse.

CONCLUSIONS AND CLINICAL IMPORTANCE

The results do not support the use of targeted metformin treatment to reduce post-prandial hyperinsulinaemia in horses with naturally-occurring ID.

Effect of 5'-adenosine monophosphate-activated protein kinase agonists on insulin and glucose dynamics in experimentally induced insulin dysregulation in horses

BACKGROUND

5'-adenosine monophosphate-activated protein kinase (AMPK) agonists, particularly resveratrol (RES), have not been extensively evaluated for their effect on insulin dysregulation (ID) in horses.

OBJECTIVES

Evaluate the effects of treatment with RES (10 mg/kg PO q12h), metformin (MET; 30 mg/kg PO q12h), and aspirin (ASP; 20 mg/kg PO q24h) on experimentally induced ID.

ANIMALS

Thirty-three healthy, adult, light-breed horses.

METHODS

Unblinded, placebo-controlled, experimental trial evaluating effects of AMPK agonists (RES, MET, and ASP) on experimentally induced ID. Horses were randomly assigned to a treatment group (RES, MET/ASP, RES/ASP, RES/MET/ASP, or placebo [CON]) after induction of ID with dexamethasone (0.08 mg/kg PO q24h for 7 days). Frequently sampled insulin-modified IV glucose tolerance tests (FSIGTT) and oral sugar tests (OST) were performed at baseline, 7 days after ID, and ID plus 7 days of treatment. Minimal model and OST variables were compared between (1-way ANOVA) and within (1-way ANOVA for repeated measures) groups over time to determine effects of treatment on ID.

RESULTS

Administration of dexamethasone for 14 days resulted in significantly altered insulin and glucose dynamics (SI, DI, basal [glucose], and [insulin]) and produced clinical signs of laminitis in 5 out of 33 (15%) of horses included in the study. Combination therapy with RES, MET, and ASP did not significantly improve insulin and glucose dynamics in horses with experimentally induced ID.

CONCLUSIONS AND CLINICAL IMPORTANCE

Metabolic testing before glucocorticoid administration should be considered in horses with clinical signs of metabolic syndrome.

Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse

BACKGROUND

Identifying intake levels of nonstructural carbohydrates (NSCs) that limit the postprandial insulinaemic response in the insulin dysregulated (ID) horse may help reduce hyperinsulinaemia-associated laminitis (HAL) risk.

OBJECTIVE

To determine if ID horses have thresholds for pure sources of starch and sugar, above which there is an augmented insulin response.

STUDY DESIGN

Randomised crossover experiment.

METHODS

Fourteen adult horses (6 ID and 8 noninsulin dysregulated, NID; matched for bodyweight) were randomly fed eight dietary treatments. Dietary treatments were formulated using a base of low-nonstructural carbohydrate pellet (LNSC; 0.04 g of water-soluble carbohydrates (WSCs)/kg bwt and 0.01 g of starch/kg bwt), to which pure sugar (dextrose) or starch (50:50 mix of waxy-maize and oat starch powder) sources were titrated to create diets with increasing amounts of either WSC (0.06-0.17 g WSC/kg bwt), or starch (0.03-0.1 g starch/kg bwt). Horses were fed each dietary treatment at a rate of 1 g/kg bwt once over 12 weeks. Serial blood samples were collected pre- and up to 240 min postprandially. Insulin was determined via RIA and diet analytes were determined via wet chemistry. Statistical analysis was performed with a mixed effect model. Positive incremental area under the curve for insulin (IAUCi) was calculated for all horses and dietary treatments.

RESULTS

There was no significant effect of diet in NID horses but diets with NSC >0.1 g/kg bwt produced an augmented response in ID horses compared with the LNSC (p < 0.05). ID horses IAUCi were also significantly different to all NID IAUCi for diets with NSC >0.1 g/kg (p < 0.04). Apparent thresholds for sugar and starch addition varied.

CONCLUSIONS

Based on this study, using supplemental pure starch and sugar sources, ID horses seem to have an apparent threshold for NSC of around 0.1 g/kg bwt/meal, above which significantly increased insulin responses are seen compared with NID horses.

Short-term effects of canagliflozin on glucose and insulin responses in insulin dysregulated horses: A randomized, placebo-controlled, double-blind, study

BACKGROUND

Decreasing hyperinsulinemia is crucial in preventing laminitis in insulin dysregulated (ID) horses. Complementary pharmacological treatments that efficiently decrease postprandial hyperinsulinemia in ID horses are needed.

OBJECTIVES

Compare short-term effects of canagliflozin vs placebo on glucose and insulin responses to an oral sugar test (OST) as well as the effects on body weight and triglyceride concentrations in horses with ID.

ANIMALS

Sixteen privately-owned ID horses.

METHODS

A single-center, randomized, double-blind, placebo-controlled, parallel design study. The horses were randomized (ratio 1:1) to either once daily PO treatment with 0.6 mg/kg canagliflozin or placebo. The study consisted of an initial 3-day period for obtaining baseline data, a 3-week double-blind treatment period at home, and a 3-day follow-up period similar to the initial baseline period but with continued double-blind treatment. Horses were subjected to an 8-sample OST in the morning of the third day on both visits.

RESULTS

Maximal geometric least square (LS) mean insulin concentration (95% confidence interval [CI]) during the OST decreased after 3 weeks of canagliflozin treatment compared with placebo (83.2; 55.4-125.0 vs 215.2; 143.2-323.2 μIU/mL). The geometric LS mean insulin response (insulin AUC0-180 ) for canagliflozin-treated horses was >66% lower compared with placebo. Least square mean body weight decreased by 11.1 (4-18.1) kg and LS mean triglyceride concentrations increased by 0.99 (0.47-1.5) mmol/L with canagliflozin treatment.

CONCLUSIONS AND CLINICAL IMPORTANCE

Canagliflozin is a promising drug for treatment of ID horses that requires future studies.

A one-health approach to identifying and mitigating the impact of endocrine disorders on human and equine athletes

Endocrinopathies affect multiple species in ever-increasing percentages of their populations, creating an opportunity to apply one-health approaches to determining creative preventative measures and therapies in athletes. Obesity and alterations in insulin and glucose dynamics are medical concerns that play a role in whole-body health and homeostasis in both horses and humans. The role and impact of endocrine disorders on the musculoskeletal, cardiovascular, and reproductive systems are of particular interest to the athlete. Elucidation of both physiologic and pathophysiologic mechanisms involved in disease processes, starting in utero, is important for development of prevention and treatment strategies for the health and well-being of all species. This review focuses on the unrecognized effects of endocrine disorders associated with the origins of metabolic disease; inflammation at the intersection of endocrine disease and related diseases in the musculoskeletal, cardiovascular, and reproductive systems; novel interventions; and diagnostics that are informed via multiomic and one-health approaches. Readers interested in further details on specific equine performance conditions associated with endocrine disease are invited to read the companion Currents in One Health by Manfredi et al, JAVMA, February 2023.

Two cases of suspected poisoning with goat's rue (Galega officinalis L.) in horses

The present report describes two novel cases of suspected intoxication with Galega officinalis in a 6- and 21-year-old Arabian mares displaying acute respiratory signs. Both animals showed signs of pulmonary edema at physical examination, with the oldest of the two also manifesting severe dyspnea and foamy nasal discharge. The mares were grazing on the same meadow with hay available ad libitum. Botanical analysis of the latter showed traces of the toxic plant Galega officinalis (L.), which has been daily ingested at a dose of around 14 g of dry matter for three days. Based on the respiratory signs and the presence of goat's rue in the mares' feed, a presumptive diagnosis of plant poisoning was assumed. Dietary change and treatment allowed the 6-year-old mare to fully recover in three days while a longer period of about two weeks was necessary for the older horse. Horses avoid eating fresh goat's rue as its palatability is low, yet poisoning may still happen in these species when the plant is found in dried and processed feed material.

Obesity-Related Metabolic Dysfunction in Dairy Cows and Horses: Comparison to Human Metabolic Syndrome

Obesity has become a serious health problem with frequent occurrence both in human and animal populations. It is estimated that it may affect over 85% of the human population and 70–80% of horses and cows by 2030. Fat cow syndrome (FCS) is a combination of metabolic, digestive, infectious, and reproductive disorders that affects obese periparturient dairy cows, and occurs most frequently in loose-housing systems, where periparturient and dry cows are fed and managed in one group disregarding the lactation stages. Equine metabolic syndrome (EMS) was named after human metabolic syndrome (MetS) and has insulin dysregulation as a central and consistent feature. It is often associated with obesity, although EMS may occur in a lean phenotype as well. Other inconsistent features of EMS are cardiovascular changes and adipose dysregulation. Laminitis is the main clinical consequence of EMS. MetS holds a 30-years old lead in research and represents a clustering of risk factors that comprise abdominal obesity, dyslipidemia, hypertension, and hyperglycemia (impaired fasting glucose or type 2 diabetes mellitus—T2DM), which are associated with doubled atherosclerotic cardiovascular disease risk, and a 5-fold increased risk for T2DM. The main aim of this review is to provide critical information for better understanding of the underlying mechanisms of obesity-related metabolic dysfunction in animals, especially in cows and horses, in comparison with MetS. Human medicine studies can offer suitable candidate mechanisms to fill the existing gap in the literature, which might be indispensable for owners to tackle FCS, EMS, and their consequences.

The Influence of Diet Change and Oral Metformin on Blood Glucose Regulation and the Fecal Microbiota of Healthy Horses

Simple Summary

Horses are susceptible to a condition known as Equine Metabolic Syndrome (EMS), which is somewhat similar to metabolic syndrome and type II diabetes in people, and is characterized by elevated insulin levels and increased susceptibility to other adverse health outcomes. Common treatments, including change to an all-hay diet and a drug called metformin, may provide benefits through modulation of intestinal bacteria, collectively known as the gut microbiota. In the studies reported here, horses undergoing such a diet change, regardless of the presence of metformin, showed a significant expansion in their fecal microbiota of a specific, poorly characterized group of bacteria. Notably, this phylum is distantly related to the bacteria found to expand in the fecal microbiota of mice and humans following metformin administration, suggesting removal from pasture to reduce the caloric intake may exert effects on the equine microbiota similar to those seen in other host species treated with metformin.

Abstract

Common treatments for Equine Metabolic Syndrome (EMS) and associated conditions include removal from pasture and adoption of an all-hay diet. Pharmacological treatments for EMS include metformin, a biguanide antihyperglycemic agent also administered to people to help improve glucose tolerance and insulin sensitivity. Both treatments may work, at least partially, through the gut microbiota, yet little is known regarding these effects in the equine host. To determine the influence on the fecal microbiota of this diet change and administration of metformin, six healthy horses were removed from pasture and switched to an all-hay diet, with four of those horses also receiving oral metformin for seven days. Control horses (n = 24) remaining on pasture and receiving no metformin were sampled at the beginning and end of one week. All samples were subjected to 16S rRNA sequencing, and horses undergoing the diet change were subjected to an oral sugar test twice, one week apart. Characteristic changes in the microbiota following diet change included the significant expansion of the phylum Kiritimatiellaeota. As Kiritimatiellaeota are related to Verrucomicrobia, found to expand in the microbiota of mice and humans in response to metformin, this taxon may represent the cognate microbes in equine hosts.

Investigation of the Effects of a Dietary Supplement on Insulin and Adipokine Concentrations in Equine Metabolic Syndrome/Insulin Dysregulation

High insulin concentrations are a common clinical feature of equine metabolic syndrome (EMS) and insulin dysregulation. Hyperinsulinemia can induce laminitis, so reduction of insulin concentrations in response to an oral challenge should decrease risk. In human studies, diets containing a polyphenol (resveratrol) led to improvements in insulin sensitivity. In rodents, the addition of leucine to a resveratrol supplement caused a decrease in the amount of resveratrol needed to achieve a clinical effect. We hypothesize a supplementation with a low dose of a synergistic polyphenol and amino acid blend including leucine (SPB+L) would improve metabolic health in EMS/insulin dysregulated horses. Fifteen EMS/ID horses received a high or low dose of SPB+ L daily for 6 weeks. Insulin during an oral sugar test (OST), body condition score, weight, baseline high-molecular-weight (HMW) adiponectin, triglycerides, nonesterified fatty acids, and tumor necrosis factor alpha were assessed before supplementation (PRE) and after supplementation (POST) via paired Student's t-tests and a repeated-measures mixed-model analysis of variance (significant at P < .05). There were no differences between doses. Horses in the POST group weighed significantly less, had significantly higher baseline HMW adiponectin concentrations, and had significantly lower insulin concentrations at 60- and 75-minute time points (P < .05). Insulin concentrations of the horsesin the POST group, but not in the PRE group, were lower and similar to results from the study conducted three years before the present study (PRIOR) for 0- and 60-minute time points (P < .002). An increased HMW adiponectin level supports increasing insulin sensitivity after supplementation. These results suggest that SPB + L supplementation at either dose leads to improvements in the clinical manifestations of EMS/insulin dysregulation, potentially reducing laminitis risk.

A review of recent developments in the pharmacological prevention and treatment of endocrinopathic laminitis

Despite the prevalence of endocrinopathic laminitis, the pharmacologic options for preventing and treating the disease are severely limited. The present review aims to discuss the spectrum of potential therapeutic agents for the condition, ranging from early experimental compounds to agents nearing registration. There are different pharmacologic targets for, and approaches to, managing laminitis. Reducing hyperinsulinaemia is central to diminishing endocrinopathic laminitis risk, and a detailed understanding of the pathophysiology of insulin dysregulation is necessary to identify pathways that can be targeted to minimise post-prandial insulin secretion and action. This area of research is advancing rapidly, with several exciting prospects, such as sodium-dependent glucose co-transporter-2 inhibitors, on the horizon for the treatment of equine metabolic dysfunction. Drugs that directly target the lamellae and aim to reduce the damage inflicted on the lamellae as part of this condition, are not yet available. Although progress in this area of laminitis therapy is slower, improved understanding of the events that lead to lamellar failure has enabled the investigation of novel drugs that aim to prevent laminitis at the site of the lesion. Finally, a brief review is included of the directions being taken in the management of the chronic and acute pain that accompanies laminitis. Medications for relieving the pain associated with laminitis are currently the most-prescribed drugs for the disease, and range from simple, affordable and thoroughly tested options, such as phenylbutazone, to newer, less-understood applications such as paracetamol and gabapentin. In the future, endocrinopathic laminitis management plans will likely take a multi-faceted approach that still hinge on effective dietary management and exercise, but also include drugs that address foot pathology, pain and underlying endocrine disturbances.

Pharmacodynamic Effects of Pioglitazone on High Molecular Weight Adiponectin Concentrations and Insulin Response After Oral Sugar in Equids

Chronic insulin dysregulation is challenging to manage with pharmaceuticals in horses. Pioglitazone improves insulin sensitivity in humans, and the pharmacokinetics of pioglitazone have been evaluated in horses. The objectives of this study were to assess the pharmacodynamic effects of oral pioglitazone on morphometric parameters, hepatic enzyme activity and function, adipokines, and enteroinsular response to oral sugar. A prospective pilot study was performed using fifteen adult equids (8 ponies, 7 horses) to evaluate the effects of short-term pioglitazone administration (2 mg/kg PO q 24 hours, 28 days). Oral sugar tests (OST) were performed before and after treatment. Adipokines were measured at day 0, 14, and 28 of administration. Plasma drug concentrations were measured at day 14 and 28 of administration. The subjects were grouped into horses, ponies, and insulin dysregulated (ID) animals. Baseline values for all parameters were compared with values obtained at day 14 and 28 using one-way or two-way analysis of variance. Mild changes were noted in morphometric parameters and hepatic enzymes. No differences were found in leptin concentrations or the blood glucose response to the OST. Significant decreases were found in the insulin response to OST at 90 and 120 minutes time points and the area under the curve after pioglitazone treatment in the pony and ID groups. High-molecular-weight (HMW) adiponectin concentrations were significantly increased in all groups after pioglitazone treatment. Decreased insulin concentrations in response to oral sugar and increased HMW adiponectin concentrations indicate positive effects of pioglitazone for treatment of metabolic derangements in equine metabolic syndrome, which warrant future clinical study.

Glucose and insulin response after intravenous and subcutaneous somatostatin administration in healthy horses

Equine metabolic syndrome (EMS) is prevalent in the equine population, and somatostatin analogs might be useful for diagnosis and/or treatment of EMS in horses. The purpose of this study was to evaluate the glucose and insulin responses to subcutaneous and intravenous administration of somatostatin. Six healthy research horses were included in this prospective study. An initial pilot study was performed to assess several different doses (10-22 µg/kg [4.5-10 µg/lb]) in two horses, then a final dosage of 22 µg/kg (10 µg/lb) was administered to six horses IV and SQ in a two-period randomized cross-over study performed over a 3-month study period. Blood samples were collected for measurement of plasma insulin and glucose concentrations during a 24-hr study period. Both IV and SQ somatostatin resulted in decreased insulin and increased glucose concentrations. SQ somatostatin resulted in a longer clinical effect, with return to baseline insulin occurring at 1.5 hr postadministration, versus 45 min for IV. Both IV and SQ administration of somatostatin to normal horses resulted in decreased insulin and increased glucose concentrations, likely due to suppression of insulin secretion by somatostatin. A more prolonged effect was seen following SQ administration as compared to IV administration, and no adverse effects were noted at varying doses. This study provides additional information regarding the effect of somatostatin administration on insulin and glucose concentrations in clinically healthy horses.

Diagnostic Testing for Equine Endocrine Diseases: Confirmation Versus Confusion

Despite there being only 2 common endocrine diseases in horses, pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS), diagnosis is still confusing. Failing to consider horse factors and treating based on laboratory results only have caused many animals to receive lifelong drug treatment unnecessarily. Increased plasma ACTH, baseline or TRH stimulated, supports a diagnosis of PPID; however, breed, age, thriftiness, illness, coat color, geography, diet, and season also affect ACTH concentration. Insulin dysregulation, the hallmark of EMS, can result from insulin resistance or excessive postprandial insulin release. Each requires a different diagnostic test to reach a diagnosis.

ECEIM consensus statement on equine metabolic syndrome

Equine metabolic syndrome (EMS) is a widely recognized collection of risk factors for endocrinopathic laminitis. The most important of these risk factors is insulin dysregulation (ID). Clinicians and horse owners must recognize the presence of these risk factors so that they can be targeted and controlled to reduce the risk of laminitis attacks. Diagnosis of EMS is based partly on the horse's history and clinical examination findings, and partly on laboratory testing. Several choices of test exist which examine different facets of ID and other related metabolic disturbances. EMS is controlled mainly by dietary strategies and exercise programs that aim to improve insulin regulation and decrease obesity where present. In some cases, pharmacologic aids might be useful. Management of an EMS case is a long‐term strategy requiring diligence and discipline by the horse's carer and support and guidance from their veterinarians.

Metformin Increases Proliferative Activity and Viability of Multipotent Stromal Stem Cells Isolated from Adipose Tissue Derived from Horses with Equine Metabolic Syndrome

In this study, we investigated the influence of metformin (MF) on proliferation and viability of adipose-derived stromal cells isolated from horses (EqASCs). We determined the effect of metformin on cell metabolism in terms of mitochondrial metabolism and oxidative status. Our purpose was to evaluate the metformin effect on cells derived from healthy horses (EqASCHE) and individuals affected by equine metabolic syndrome (EqASCEMS). The cells were treated with 0.5 μM MF for 72 h. The proliferative activity was evaluated based on the measurement of BrdU incorporation during DNA synthesis, as well as population doubling time rate (PDT) and distribution of EqASCs in the cell cycle. The influence of metformin on EqASC viability was determined in relation to apoptosis profile, mitochondrial membrane potential, oxidative stress markers and BAX/BCL-2 mRNA ratio. Further, we were interested in possibility of metformin affecting the Wnt3a signalling pathway and, thus, we determined mRNA and protein level of WNT3A and β-catenin. Finally, using a two-tailed RT-qPCR method, we investigated the expression of miR-16-5p, miR-21-5p, miR-29a-3p, miR-140-3p and miR-145-5p. Obtained results indicate pro-proliferative and anti-apoptotic effects of metformin on EqASCs. In this study, MF significantly improved proliferation of EqASCs, which manifested in increased synthesis of DNA and lowered PDT value. Additionally, metformin improved metabolism and viability of cells, which correlated with higher mitochondrial membrane potential, reduced apoptosis and increased WNT3A/β-catenin expression. Metformin modulates the miRNA expression differently in EqASCHE and EqASCEMS. Metformin may be used as a preconditioning agent which stimulates proliferative activity and viability of EqASCs.

Pharmacokinetics of Metformin in Combination With Sitagliptin in Adult Horses After Enteral Administration

Insulin dysregulation (ID) is a common metabolic disorder in horses. Recently, incretin hormone release has been suggested to be involved in ID in horses. In human medicine, metformin and sitagliptin are commonly used in combination for metabolic syndrome. This combination could be useful in treating ID in horses. However, no pharmacokinetics data have been reported in this species. The objective of the present study was to establish the plasma concentration-time profile and to derive pharmacokinetics data for a combination of metformin and sitagliptin in horses after enteral administration. Six healthy adult Purebred Spanish horses were used. A metformin (15 mg/kg) plus sitagliptin (1.5 mg/kg) preparation was administered by intragastric route (IG) as an enteral solution. Blood samples were collected from 0 to 48 hours after IG drug administration. Plasma concentrations of metformin and sitagliptin were measured using high performance liquid chromatography methods. The t_½λz for metformin was 2.9 hours and for sitagliptin 21 hours. The C_max was 442 ± 84 mg/L within 0.9 hours for metformin and 94 ± 14 mg/L within 1.3 hours for sitagliptin. No adverse effects were observed, and the combination of metformin and sitagliptin was well tolerated. Therefore, these results suggest that metformin plus sitagliptin might be a combination to consider in horses with ID. Additional studies are needed to establish the effectiveness and tolerance in equids affected by endocrine disorders.

Equine metabolic syndrome in Colombian creole horse: case report

ABSTRACT The equine metabolic syndrome is a condition that can be recognized because of obesity, insulin resistance and laminitis. Genetic factors could play a role in the occurrence of this syndrome. Certain breeds such as ponies (including the South American creole horses) have a lower sensibility to insulin and a higher prevalence of hyperinsulinemia. The environment and management conditions, such as overfeeding and lack of exercise are factors that bring a propensity for obesity. The adipose tissue works as an endocrine organ producing hormones (adipokines or adipocytokines) that affect the horse´s metabolism. The objective of this report is to describe the first case report of a Colombian creole mare with a metabolic syndrome, diagnosed by means of the combined test of glucose-insulin and clinical signs. Early diagnosis of this entity and an adequate treatment are useful for improving the life and the zootechnical conditions of the patient.

Genomewide association study reveals a risk locus for equine metabolic syndrome in the Arabian horse

Equine obesity can cause life-threatening secondary chronic conditions, similar to those in humans and other animal species. Equine metabolic syndrome (EMS), primarily characterized by hyperinsulinemia, is often present in obese horses and ponies. Due to clinical similarities to conditions such as pituitary pars intermedia dysfunction (formerly equine Cushing's disease), conclusive diagnosis of EMS often proves challenging. Aside from changes in diet and exercise, few targeted treatments are available for EMS, emphasizing the need for early identification of at-risk individuals to enable implementation of preventative measures. A genomewide association study (GWAS) using Arabian horses with a history of severe laminitis secondary to EMS revealed significant genetic markers near a single candidate gene () that may play a role in cholesterol homeostasis. The best marker, BIEC2-263524 (chr14:69276814 T > C), was correlated with elevated insulin values and increased frequency of laminitis ( = 0.0024 and = 9.663 × 10, respectively). In a second population of Arabian horses, the BIEC2-263524 marker maintained its associations with higher modified insulin-to-glucose ratio (MIRG) values ( = 0.0056) and BCS ( = 0.0063). Screening of the predicted coding regions by sequencing identified a polymorphic guanine homopolymer and 5 haplotypes in the 3' untranslated region (UTR). An 11 guanine (11-G) allele at was correlated with elevated insulin values in the GWAS population ( = 0.0008) and, in the second population, elevated MIRG and increased BCS > 6.5 ( = 0.0055 and = 0.0162, respectively). The BIEC2-263524-C and the 3' UTR -11(G) polymorphisms were correlated at a 98% frequency, indicating strong linkage disequilibrium across this 150-kb haplotype. Assays for these markers could diagnose horses with a genetic predisposition to develop obesity. Additionally, discovery of FAM174A function may improve our understanding of the etiology of this troubling illness in the horse and warrants investigation of this locus for a role in metabolic- and obesity-related disorders of other species.

How swimming affects plasma insulin and glucose concentration in Thoroughbreds: A pilot study

Low intensity exercise increases insulin-stimulated glucose uptake in skeletal muscle and decreases its plasma concentration. In this study, plasma insulin and glucose concentrations were evaluated 5min before and 5, 15, 25, 35, 45 and 60min after an IV bolus of glucose in 12 Thoroughbreds before and after 1 month of submaximal aquatraining exercise, monitored using heart rate and blood lactate. Plasma glucose concentrations were evaluated using a colorimetric enzymatic method, and plasma insulin concentrations with a solid-phase radioimmunoassay method. Pre-training plasma glucose concentrations at 15, 25 and 35min, area under the glucose curve and peak glucose concentration were significantly higher than post-training values (P<0.05). Baseline pre-training plasma insulin concentrations were significantly lower than in the post-training period, and plasma insulin was significantly higher at 45 and 60min in the pre-training period than the post-training period. These results indicate that aquatraining could improve insulin-glucose metabolism in horses.

Therapeutics for Equine Endocrine Disorders

Equine endocrine disease is commonly encountered by equine practitioners. Pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS) predominate. The most logical therapeutic approach in PPID uses dopamine agonists; pergolide mesylate is the most common. Bromocryptine and cabergoline are alternative drugs with similar actions. Drugs from other classes have a poor evidence basis, although cyproheptadine and trilostane might be considered. EMS requires management changes as the primary approach; reasonable justification for use of drugs such as levothyroxine and metformin may apply. Therapeutic options exist in rare cases of diabetes mellitus, diabetes insipidus, hyperthyroidism, and critical illness-related corticosteroid insufficiency.

Equine metabolic syndrome

Laminitis is one of the most common and frustrating clinical presentations in equine practice. While the principles of treatment for laminitis have not changed for several decades, there have been some important paradigm shifts in our understanding of laminitis. Most importantly, it is essential to consider laminitis as a clinical sign of disease and not as a disease in its own right. Once this shift in thinking has occurred, it is logical to then question what disease caused the laminitis. More than 90 per cent of horses presented with laminitis as their primary clinical sign will have developed it as a consequence of endocrine disease; most commonly equine metabolic syndrome (EMS). Given the fact that many horses will have painful protracted and/or chronic recurrent disease, a good understanding of the predisposing factors and how to diagnose and manage them is crucial. Current evidence suggests that early diagnosis and effective management of EMS should be a key aim for practising veterinary surgeons to prevent the devastating consequences of laminitis. This review will focus on EMS, its diagnosis and management.

Treatment of equine metabolic syndrome: A clinical case series

REASONS FOR PERFORMING STUDY

Treatment of equine metabolic syndrome (EMS) is essential to improve insulin sensitivity and reduce the risk of laminitis. Calorie restriction and increased exercise are the mainstays of treatment but there is potential for poor owner compliance.

OBJECTIVES

To determine whether significant weight loss accompanied by improvements in measures of insulin sensitivity can be achieved in horses and ponies with EMS managed by their owners in their normal environment under veterinary guidance.

STUDY DESIGN

Retrospective clinical case series.

METHODS

Horses and ponies attending 2 university hospitals for investigation and treatment of suspected EMS were eligible for inclusion in the study. Animals underwent a clinical examination, basal and dynamic endocrine testing; those with pituitary pars intermedia dysfunction (PPID) were excluded. Owners were given individually tailored diet and exercise programmes to follow for between 3 and 6 months. After the treatment period, clinical examination and endocrine tests were repeated and results compared to the initial assessment.

RESULTS

Nineteen animals were recruited to the study, 17 with a history of laminitis. All animals showed a reduction in body condition score (P<0.001) and 18/19 had a reduction in bodyweight (P<0.001) between assessments. There were significant (P<0.05) reductions in basal insulin, insulin at 45 min during a combined glucose insulin tolerance test (CGIT), time for blood glucose concentration to return to baseline during a CGIT and mean area under the glucose curve.

CONCLUSIONS

A diet and exercise programme tailored to the needs of the individual animal and implemented by the owner results in weight loss accompanied by improvements in insulin sensitivity.

AICAR administration affects glucose metabolism by upregulating the novel glucose transporter, GLUT8, in equine skeletal muscle

Equine metabolic syndrome is characterized by obesity and insulin resistance (IR). Currently, there is no effective pharmacological treatment for this insidious disease. Glucose uptake is mediated by a family of glucose transporters (GLUT), and is regulated by insulin-dependent and -independent pathways, including 5-AMP-activated protein kinase (AMPK). Importantly, the activation of AMPK, by 5-aminoimidazole-4-carboxamide-1-D-ribofuranoside (AICAR) stimulates glucose uptake in both healthy and diabetic humans. However, whether AICAR promotes glucose uptake in horses has not been established. It is hypothesized that AICAR administration would enhance glucose transport in equine skeletal muscle through AMPK activation. In this study, the effect of an intravenous AICAR infusion on blood glucose and insulin concentrations, as well as on GLUT expression and AMPK activation in equine skeletal muscle (quantified by Western blotting) was examined. Upon administration, plasma AICAR rapidly reached peak concentration. Treatment with AICAR resulted in a decrease (P <0.05) in blood glucose and an increase (P <0.05) in insulin concentration without a change in lactate concentration. The ratio of phosphorylated to total AMPK was increased (P <0.05) in skeletal muscle. While GLUT4 and GLUT1 protein expression remained unchanged, GLUT8 was increased (P <0.05) following AICAR treatment. Up-regulation of GLUT8 protein expression by AICAR suggests that this novel GLUT isoform plays an important role in equine muscle glucose transport. In addition, the data suggest that AMPK activation enhances pancreatic insulin secretion. Collectively, the findings suggest that AICAR acutely promotes muscle glucose uptake in healthy horses and thus its therapeutic potential for managing IR requires investigation.

Effect of dietary nonstructural carbohydrate content on activation of 5'-adenosine monophosphate-activated protein kinase in liver, skeletal muscle, and digital laminae of lean and obese ponies

Background

In EMS‐associated laminitis, laminar failure may occur in response to energy failure related to insulin resistance (IR) or to the effect of hyperinsulinemia on laminar tissue. 5′‐Adenosine‐monophosphate‐activated protein kinase (AMPK) is a marker of tissue energy deprivation, which may occur in IR.

Hypothesis/Objectives

To characterize tissue AMPK regulation in ponies subjected to a dietary carbohydrate (CHO) challenge.

Animals

Twenty‐two mixed‐breed ponies.

Methods

Immunohistochemistry and immunoblotting for total AMPK and phospho(P)‐AMPK and RT‐qPCR for AMPK‐responsive genes were performed on laminar, liver, and skeletal muscle samples collected after a 7‐day feeding protocol in which ponies stratified on body condition score (BCS; obese or lean) were fed either a low‐CHO diet (ESC + starch, approximately 7% DM; n = 5 obese, 5 lean) or a high‐CHO diet (ESC + starch, approximately 42% DM; n = 6 obese, 6 lean).

Results

5′‐Adenosine‐monophosphate‐activated protein kinase was immunolocalized to laminar keratinocytes, dermal constituents, and hepatocytes. A high‐CHO diet resulted in significantly decreased laminar [P‐AMPK] in lean ponies (P = .03), but no changes in skeletal muscle (lean, P = .33; obese, P = .43) or liver (lean, P = .84; obese, P = .13) [P‐AMPK]. An inverse correlation existed between [blood glucose] and laminar [P‐AMPK] in obese ponies on a high‐CHO diet.

Conclusions and Clinical Importance

Laminar tissue exhibited a normal response to a high‐CHO diet (decreased [P‐AMPK]), whereas this response was not observed in liver and skeletal muscle in both lean (skeletal muscle, P = .33; liver, P = .84) and obese (skeletal muscle, P = .43; liver, P = .13) ponies.

Insulin dysregulation

Abnormalities of insulin metabolism include hyperinsulinaemia and insulin resistance, and these problems are collectively referred to as insulin dysregulation in this review. Insulin dysregulation is a key component of equine metabolic syndrome: a collection of endocrine and metabolic abnormalities associated with the development of laminitis in horses, ponies and donkeys. Insulin dysregulation can also accompany prematurity and systemic illness in foals. Causes of insulin resistance are discussed, including pathological conditions of obesity, systemic inflammation and pituitary pars intermedia dysfunction, as well as the physiological responses to stress and pregnancy. Most of the discussion of insulin dysregulation to date has focused on insulin resistance, but there is increasing interest in hyperinsulinaemia itself and insulin responses to feeding. An oral sugar test or in-feed oral glucose tolerance test can be performed to assess insulin responses to dietary carbohydrates, and these tests are now recommended for use in clinical practice. Incretin hormones are likely to play an important role in postprandial hyperinsulinaemia and are the subject of current research. Insulin resistance exacerbates hyperinsulinaemia, and insulin sensitivity can be measured by performing a combined glucose-insulin test or i.v. insulin tolerance test. In both of these tests, exogenous insulin is administered and the rate of glucose uptake into tissues measured. Diagnosis and management of hyperinsulinaemia is recommended to reduce the risk of laminitis. The term insulin dysregulation is introduced here to refer collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome.

Effects of metformin hydrochloride on blood glucose and insulin responses to oral dextrose in horses

REASONS FOR PERFORMING STUDY

Metformin is a potential therapeutic agent for the treatment of insulin resistance (IR). In laboratory animals, orally administered metformin reduces intestinal glucose absorption and may therefore affect insulinaemic responses to oral carbohydrate ingestion.

OBJECTIVES

To determine whether pretreatment with metformin reduces plasma glucose concentration and insulin responses following consumption of dextrose in horses.

STUDY DESIGN

Therapeutic cross-over study.

METHODS

Seven healthy Standardbred and Thoroughbred geldings were subjected to an oral dextrose challenge test on 4 occasions: with and without metformin, before and after induction of IR with dexamethasone. Metformin was administered by nasogastric tube at 30 mg/kg bwt 1 h before administration of dextrose. Glucose and insulin concentrations in plasma/serum were measured at regular intervals during each test. Linear mixed models were specified for each predetermined outcome variable, and for each model the 'treatment' was included as a fixed effect with 4 categorical levels (none, metformin, dexamethasone and dexamethasone with metformin) and horse accounted for as a random effect.

RESULTS

In healthy horses, the administration of metformin resulted in a statistically significant reduction in peak glucose concentration (P = 0.002), area under the glucose curve (P<0.001) and insulin concentration 120 min after dextrose administration (P = 0.011). Following the induction of IR, administration of metformin was associated with significant differences in peak glucose concentration (P<0.001), the percentage increase in glucose concentration (P = 0.010), the area under the glucose curve (P<0.001) and insulin concentration at 120 min (P = 0.034) and 150 min after dextrose administration (P = 0.014).

CONCLUSIONS

Metformin resulted in reduced glycaemic and insulinaemic responses both in healthy horses and in horses with experimentally induced IR.

POTENTIAL RELEVANCE

Metformin may benefit horses with naturally acquired IR by reducing glycaemic and insulinaemic responses to dietary nonstructural carbohydrates. Further investigations into the mechanisms of action of metformin in horses and controlled clinical trials are warranted.

Dietary restriction in combination with a nutraceutical supplement for the management of equine metabolic syndrome in horses

Few studies have examined the effect of dietary restriction in horses with equine metabolic syndrome (EMS). This study aimed to determine improvements in insulin sensitivity following dietary restriction for 6 weeks, and to determine if the improvement would be greater in horses receiving short-chain fructo-oligosaccharides (sc-FOS). Dietary management involved feeding grass hay, restricted to 1.25% of body mass (BM) as daily dry matter intake and soaked in cold water prior to feeding, with the addition of a vitamin and mineral nutraceutical supplement with or without the addition of sc-FOS (10 g/100 kg). Soaking the hay resulted in a significant reduction in non-structural carbohydrates (38%, P = 0.01), digestible energy (6.78%, P = 0.01) and water soluble minerals. Following 6 weeks of dietary restriction with soaked grass hay and nutraceutical supplement, horses lost an average of 6.8% BM and showed reductions in body condition score (BCS) and belly circumference. Sensitivity to insulin improved overall, as determined by the total insulin response during the combined glucose insulin test. The magnitude of improvement in insulin sensitivity was associated with the degree of insulin resistance recorded at outset, and the extent of overall losses in BM and BCS, but was independent of the addition of sc-FOS. The nutraceutical supplement was highly palatable and no adverse effects were noted. From the findings of this study a strict dietary program in combination with a specifically designed vitamin and mineral nutraceutical supplement can be recommended to obtain rapid improvements in BM, BCS and insulin sensitivity of animals presenting with EMS.