Deoxysphingolipids—Novel Skeletal Muscle Lipids Related to Insulin Resistance in Humans That Decrease Insulin Sensitivity In Vitro

Abstract

Accumulation of sphingolipids are thought to promote skeletal muscle insulin resistance. Deoxysphingolipids (dSL) are a novel type of sphingolipid made by condensing palmitate with alanine (deoxydihydroceramide - dDHCer) or glycine (deoxymethylceramide - dMeCer) instead of serine. In plasma, dSL are increased in individuals with type 2 diabetes and cause beta cell dysfunction in vitro. However, their role in skeletal muscle is unknown. We evaluated skeletal muscle dSL content in endurance trained athletes (n=13), lean (n=14), obese (n=12), and type 2 diabetic (n=10) men and women. Muscle dSL content was measured from biopsies using LC/MS/MS, and insulin sensitivity using a hyperinsulinemic-euglycemic clamp. After adjusting for repeated measures, total and C18:0 muscle dDHCer were inversely related to insulin sensitivity (p=0.0008, and p=0.0003, respectively), while dMeCer were below the limit of detection. Total and C18:0 dDHCer were significantly greater in obese and T2D compared to athletes and lean (p<0.004). In primary myotubes, dSL content was increased to determine effects on insulin sensitivity by altering media amino acid content with 5x alanine/glycine (no serine) or 1x alanine/glycine/serine as a control, and replaced every 24 hours for 2 days. Alanine and glycine supplementation increased myotube dDHCer content by 3.6 fold, dMeCer content by 21 fold, and decreased ceramide content by 30% relative to control. Fluorescence lifetime imaging revealed decreased oxidative flux in enhanced dSL conditions. Insulin sensitivity, measured using the percent increase in insulin stimulated glycogen synthesis, decreased from 55±9.1% in control to 4±9% in enhanced dSL conditions. Combined, these data reveal that dSL accumulate in insulin resistant human muscle, and appear to cause insulin resistance in vitro. These data suggest decreasing skeletal muscle deoxysphingolipid content may prevent or treat skeletal muscle insulin resistance. Disclosure S. Zarini: None. L. Perreault: Advisory Panel; Self; Novo Nordisk A/S. Speaker's Bureau; Self; Novo Nordisk A/S. Advisory Panel; Self; Merck & Co., Inc.. Speaker's Bureau; Self; Merck & Co., Inc., AstraZeneca, Janssen Pharmaceuticals, Inc., Boehringer Ingelheim Pharmaceuticals, Inc.. Consultant; Self; Boehringer Ingelheim Pharmaceuticals, Inc.. Advisory Panel; Self; Sanofi. Speaker's Bureau; Self; Sanofi. S.A. Newsom: None. D.E. Kahn: None. A. Kerege: None. K.A. Harrison: None. B. Bergman: Research Support; Self; Eli Lilly and Company. Advisory Panel; Spouse/Partner; Novo Nordisk Inc., Merck & Co., Inc., AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company.