The Association Between Endocrine Disrupting Chemicals and Equine Metabolic Syndrome

Our group demonstrated that 49% of Equine Metabolic Syndrome (EMS) phenotype variability is explained by shared environment; however only 4-18% is explained by diet, exercise and season, suggesting other environmental factors play a role in EMS. Endocrine Disrupting Chemicals (EDCs) are associated with metabolic syndrome and other endocrine abnormalities in humans. Preliminary data demonstrated that horses from farms <31 miles of EDC disposal sites (SF) were more likely to have had laminitis and had higher post oral-sugar-challenge insulin concentrations (INS-OST) suggesting EDC exposure as an EMS risk factor.

We sought to determine if plasma EDC concentration is correlated with metabolic measurements in 301 horses from 32 farms with bioassays measuring aryl hydrocarbon receptor (AHR-EDC) and estrogen receptor (ER-EDC) activation by EDCs. Mean (range) AHR-EDC and ER-EDC concentrations were 0.223 (0.02-2.47) and 279.66 (4.35-15,000) pg/ml plasma. EDCs were below the detection limit in approximately half of the horses. AICc statistics were used to determine the best linear multivariable regression model for EDC association with 9 EMS phenotypic variables. AHR-EDC was associated with glucose (p=0.042), triglyceride (p=0.011), and leptin (p=0.047) concentrations. ER-EDC was associated with glucose after an oral sugar test (OST) (p=0.010), glucose (p=0.003), insulin (p=0.004), and insulin-OST (p=0.002. Nine SNPs within exons 9-11 of AHR are being genotyped to determine if a gene-by-environment interaction plays a role in EMS. Overall, the results suggest that some unexplained environmental variance in individuals with EMS is due to EDC exposure mediated through the AHR and ER.