More on testing for insulin sensitivity and some interesting findings

While the article’s main thrust is certainly interesting, I don’t think it is the headline grabber. The grabber appears in the last line of the Abstract:

Development of screening tools to identify insulin-dysregulated horses using only baseline blood sample appears promising.

I could not resist that so went and read the article and they found that there are significant difference in the resting blood levels of carnitine between hyper-insulinemic and normal horses. This will need further investigation but would make the diagnosis much easier.

This article covered a lot of ground and also found two possible mechanisms to relate insulin dysregulation to laminitis. One was the finding that the Oral Glucose Test induced a low grade systemic inflammation. If The OGT is a mirror of what happens when horses graze nonstructural carbohydrates (sugars and starches) then this could be a part of the mechanism that induces endocrinopathic laminitis. Two, lower levels of arginine were found in horses with hyperinsulinemia. Taken from the article:

Lower arginine concentrations in horses with high insulin response therefore could be associated with some form of endothelial dysfunction, potentially involved in the pathophysiology of endocrinopathic laminitis.

DrO

Metabolic changes induced by oral glucose tests in horses and their diagnostic use
J Vet Intern Med. 2020 Dec 5.
Authors
Julien Delarocque 1 , Florian Frers 1 , Karsten Feige 1 , Korinna Huber 2 , Klaus Jung 3 , Tobias Warnken 1
Affiliations

1 Clinic for Horses, University of Veterinary Medicine Hannover, Foundation, Hanover, Germany.
2 Institute of Animal Science, Faculty of Agricultural Sciences, University of Hohenheim, Stuttgart, Germany.
3 Institute for Animal Breeding and Genetics, University of Veterinary Medicine Hannover, Foundation, Hanover, Germany.

Abstract

Background: Little is known about the implications of hyperinsulinemia on energy metabolism, and such knowledge might help understand the pathophysiology of insulin dysregulation.

Objectives: Describe differences in the metabolic response to an oral glucose test, depending on the magnitude of the insulin response.

Animals: Twelve Icelandic horses in various metabolic states.

Methods: Horses were subjected to 3 oral glucose tests (OGT; 0.5 g/kg body weight glucose). Basal, 120 and 180 minutes samples were analyzed using a combined liquid chromatography tandem mass spectrometry and flow injection analysis tandem mass spectrometry metabolomic assay. Insulin concentrations were measured using an ELISA. Analysis was performed using linear models and partial least-squares regression.

Results: The kynurenine : tryptophan ratio increased over time during the OGT (adjusted P-value = .001). A high insulin response was associated with lower arginine (adjusted P-value = .02) and carnitine (adjusted P-value = .03) concentrations. A predictive model using only baseline samples performed well with as few as 7 distinct metabolites (sensitivity, 86%; 95% confidence interval [CI], 81%-90%; specificity, 88%; 95% CI, 84%-92%).

Conclusions and clinical importance: Our results suggest induction of low-grade inflammation during the OGT. Plasma arginine and carnitine concentrations were lower in horses with high insulin response and could constitute potential therapeutic targets. Development of screening tools to identify insulin-dysregulated horses using only baseline blood sample appears promising.