Plasma Activin A concentrations are not a useful biomarker for detecting insulin dysregulation and predicting laminitis risk in ponies.

Abstract

BACKGROUND: Circulating insulin concentrations are used to quantify risk of laminitis in currently non-laminitic ponies. Basal serum activin A (AA) concentration has previously been positively correlated with serum insulin concentrations 60 minutes (T60) following an oral sugar test (OST) in ponies with equine metabolic syndrome. Therefore, circulating AA might be a useful marker for insulin dysregulation (ID) and laminitis risk. OBJECTIVES: To explore the relationship between circulating AA concentrations at baseline (T0) and T60 in ponies that developed laminitis within six months and non-laminitic ponies. METHODS: Case-control study. Forty-three ponies that developed laminitis (PLP) during a four-year surveillance period were selected from a larger cohort; 43 ponies from the same cohort that remained non-laminitic (NLP) were selected as controls. Plasma AA concentrations were measured using a validated ELISA at T0 and T60 and compared between groups at both time points using a Wilcoxon signed ranks test. Correlations with other previously measured metabolic markers were investigated using Spearman's rank correlation coefficients. RESULTS: There was a significant difference between T0 plasma AA (median 8.8; interquartile range [6.2, 13.1]ng/mL) and T60 (13.1; [8.8, 20.1]ng/mL) within the NLP group (P= <0.001) and between plasma AA at T0 (7.4 [5.5, 12.4]ng/mL) and T60 (12.3 [6.9, 16.6]ng/ml) in the PLP group (P= <0.001). There were no significant correlations between plasma AA (T0 or T60) and any other measured metabolic marker. Single timepoints and retrospective analysis were the main limitations. CONCLUSION: Plasma AA concentration is not a useful marker for ID or predicting laminitis development in ponies.