Intramyocellular Ceramides: Subcellular Concentrations and Fractional De Novo Synthesis in Postabsorptive Humans

We investigated the relationship between insulin resistance markers and subsarcolemmal (SS) and intramyofibrillar (IMF) ceramide concentrations, as well as the contribution of plasma palmitate (6.5-h infusion of [U-¹³C]palmitate) to intramyocellular ceramides. Seventy-six postabsorptive men and women had muscle biopsies 1.5, 6.5, and 24 h after starting the tracer infusion. Concentrations and enrichment of muscle ceramides were measured by liquid chromatography-tandem mass spectrometry. We found that HOMA of insulin resistance, plasma insulin, and triglyceride concentrations were positively correlated with SS C16:0 and C18:1 ceramide, but not SS C14:0-Cer, C20:0-Cer, C24:0-Cer, and C24:1-Cer concentrations; IMF ceramide concentrations were not correlated with any metabolic parameters. The fractional contribution of plasma palmitate to 16:0 ceramide was greater in SS than IMF (SS, 18.2% vs. IMF, 8.7%; P = 0.0006). Plasma insulin concentrations correlated positively with the fractional contribution of plasma palmitate to SS 16:0 ceramide. The fractional contribution of plasma palmitate to intramyocellular SS 16:0 ceramide was positively correlated with SS C16:0 ceramide concentrations (γ = 0.435; P = 0.002). We conclude that skeletal muscle SS ceramides, especially C16 to C18 chain lengths and the de novo synthesis of intramyocellular ceramide from plasma palmitate are associated with markers of insulin resistance.