Associations of plasma sphingolipid profiles with insulin response during oral glucose testing in Icelandic horses

BACKGROUND: Sphingolipids modulate insulin sensitivity in mammals. Increased synthesis of ceramides is linked to decreased insulin sensitivity of tissues. Conversely, activation of the insulin signaling pathway can downregulate ceramide synthesis. Elucidating the association between sphingolipid metabolism and insulin response during oral glucose testing may help explain the pathophysiology of insulin dysregulation in horses. HYPOTHESES: Horses with insulin dysregulation will have a plasma sphingolipid profile characterized by increased ceramide concentrations. The plasma sphingolipid profile will have decreased ceramide concentrations after acute activation of the insulin signaling pathway by oral glucose testing. ANIMALS: Twelve Icelandic horses. METHODS: Horses were subjected to an oral glucose test (0.5 g/kg body weight glucose), with plasma insulin concentrations measured at 0, 30, 60, 120, 180, and 240 minutes postglucose administration. Plasma samples were collected at 0 and 120 minutes for sphingolipid profiling using a liquid chromatography‐mass spectrometry‐based metabolomics analysis. Eighty‐three species of sphingolipids were detected, including 3‐ketosphinganines, dihydroceramides, ceramides, dihydrosphingomyelins, sphingomyelins, galatosylceramides, glucosylceramides, lactosylceramides, and ceramide‐1‐phosphates. RESULTS: Glucose administration did not significantly alter plasma sphingolipid profiles. C22:0‐ceramide, C24:1‐ceramide, C23:0‐ceramide, C16:1‐sphingomyelin, C22:0‐dihydroceramide, and C24:0‐ceramide were positively correlated with the insulin response (area under the curve). CONCLUSION AND CLINICAL IMPORTANCE: Positive correlation between the insulin response and sphingolipid concentrations implies upregulated sphingolipid metabolism in insulin dysregulated horses. A high plasma ceramide concentration can indicate insulin dysregulation in horses.