Equine insulin resistance: the quest for sensitivity.

This research article focuses on understanding insulin resistance (IR) in horses, its relationship with obesity and fatty metabolism, how it is related to a risk of laminitis, as well as the exploration of potential therapeutic interventions. It discusses potential herbal agents based on human and animal studies, and the lessons learned using metformin, a human diabetes medication.

Understanding Insulin Resistance in Horses

• The article highlights that insulin resistance in horses is related to obesity and altered fat metabolism. Insulin plays vital roles such as stimulating glucose uptake by cells, lipogenesis, reducing lipolysis, DNA synthesis, and cell replication. Any reduction in tissue sensitivity to this hormone disrupts metabolic and haemodynamic balance.
• In horses, just as in humans, insulin resistance could lead to conditions such as glucose intolerance, endothelial dysfunction, haemodynamic pathology, increased procoagulation factors, and elevated expression of inflammatory markers.
• Horses with insulin resistance often display hyperinsulinaemia but it’s usually associated with normal or slightly elevated glucose levels, in contrast to humans.

Insulin Resistance and Risk of Laminitis

• The study notes a correlation between insulin resistance and an increased risk of laminitis, a painful condition affecting the horse’s foot. This risk is higher especially in horses showing characteristics of ‘equine metabolic syndrome’ (EMS), characterized by obesity, regional fat deposition, hypertriglyceridaemia, hyperleptinaemia, and hypertension.
• Horses with insulin resistance have now been recognized to be at a higher risk of developing laminitis under certain pasture conditions. This condition is sometimes referred to as ‘pre-laminitic metabolic syndrome’ (PLMS). Furthermore, chronic insulin resistance has also been associated with early-onset pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease).

Potential Therapeutic Interventions

• The article mentions potential methods that could alleviate insulin resistance, including diet modifications and increased exercises, although these are often difficult to implement, hence the push for pharmacological solutions.
• Herbal therapies have been proposed as possible treatment avenues. According to the article, six main mechanisms were explored including activation of insulin receptors, stimulation of glucose uptake, rate reduction of carbohydrate absorption, activation of peroxisome proliferator-activated receptors, reductions in obesity and reductions in oxidative stress.
• The research identified 19 potential herbal agents for controlling insulin resistance, each with varying mechanisms of action. These agents are suggested as deserving of further research.

Lessons from Metformin

• The research also discusses metformin, an anti-diabetic medication in humans that is often prescribed as the first-line treatment for human type-2 diabetes associated with IR, as a possible treatment for horses.
• Though it was initially found to have statistically significant effects on improving insulin sensitivity in horses, subsequent studies showed its bioavailability in horses was lower than in humans, indicating it may not be as effective at previously recommended dose rates.