Possible dysmetabolic hyperferritinemia in hyperinsulinemic horses

Abstract

Background: Hyperinsulinemia associated with equine metabolic syndrome and pituitary pars intermedia dysfunction is a risk factor for laminitis. Research in other species has shown elevated body iron levels as both a predictor and consequence of insulin resistance. In humans, this is known as dysmetabolic hyperferritinemia.

Aim: To explore the relationship between equine hyperinsulinemia and body iron levels.

Methods: We reviewed case histories and laboratory results from an open access database maintained by the Equine Cushing's and Insulin Resistance Group Inc. (ECIR). We identified 33 horses with confirmed hyperinsulinemia and laboratory results for serum iron, total iron binding capacity, and ferritin. Pearson correlation was used to test the relationship between insulin and iron indices. Additionally, we performed a secondary analysis of a previously reported controlled trial that was originally designed to test the correlation between iron status and the insulin response in horses. Here, we used a t-test to compare the mean values of insulin and ferritin between horses we categorized as normal or hyperinsulinemic based on their response to an oral challenge.

Results: Serum ferritin exceeded published reference range in 100% of the horses identified from the ECIR database. There were no statistically significant associations between insulin indices (RISQI, log insulin) and iron indices (log serum iron, log TSI%, log ferritin). There were trends for a negative association between RISQI and log iron [r(31) = -0.33, p = 0.058] and a positive association between age and ferritin [r(30) = 0.34, p = 0.054]. From the secondary data analysis of published data, we found significantly elevated ferritin (p = 0.05) in horses considered hyperinsulinemic by dynamic insulin testing compared to horses with a normal response.

Conclusion: These results suggest the potential for iron overload in hyperinsulinemic horses, a feature documented in other species and should stimulate further study into the relationship between insulin and iron dysregulation in the horse.

Keywords: Equine; Ferritin; Hyperinsulinemia; Iron overload.

Fig. 1.. Raw (non-transformed) data from Nielsen et al. (2012). Mean (+/-) SE for peak insulin to pelleted corn feeding (top) and ferritin (bottom) after grouping animals as normoinsulinemic (NORM) versus hyperinsulinemic (HYP) (***p =< 0.0001, *p = 0.05).