Metabolomic Signatures of Insulin Resistance in Human Skeletal Muscle Are Exacerbated with Insulin Stimulation

Metabolomic profiling has identified signatures of insulin resistance in skeletal muscle; however, the direct effect of insulin stimulation on these metabolite signatures in humans remains largely unresolved. To address this, we investigated the effect of insulin stimulation on skeletal muscle metabolites in a well characterized cohort of humans spanning the spectrum of insulin sensitivity. Vastus lateralis muscle samples were obtained from endurance athletes, sedentary lean and obese adults, and individuals with type 2 diabetes (n=16,15,15,12, respectively) under basal conditions and 1-hour into a hyperinsulinemic-euglycemic clamp. Metabolomic analysis was performed using UPLC-MS/MS. Basal concentrations of TCA cycle intermediates, including citrate, alpha-ketoglutarate, succinate, fumarate, malate and oxaloacetate, were positively related to insulin sensitivity (steady-state clamp R_d glucose in mg/kg/min; all P<0.01). Most of these relationships strengthened during insulin stimulation, with the strongest relationships observed for malate (r² = 0.453, P<0.01) and fumarate (r² = 0.501, P<0.01) that reflected a blunted increase in TCA intermediates during insulin stimulation with insulin resistance. Insulin stimulation lowered most medium- and long-chain acyl-carnitines compared with basal levels; however, this effect was also attenuated as a function of insulin resistance, signaling impaired metabolic flexibility. Notably, basal levels of several acyl-carnitines, including C12:0, C14:0, C16:0 and C18:1, were increased in endurance athletes compared with other groups (all P<0.05). Several amino acids, including leucine, isoleucine and lysine, were negatively related to insulin sensitivity in the basal and insulin stimulated state (all P<0.01). Together these findings indicate that physiologic insulin stimulation exacerbates metabolic signatures of skeletal muscle insulin resistance in humans.