1638-P: Oxidized Lipids Cause Ceramide Accumulation and Insulin Resistance in Skeletal Muscle

Accumulation of muscle lipids promotes insulin resistance and type 2 diabetes (T2D). Ceramides are important muscle lipids that decrease insulin sensitivity and it was previously shown that accumulation of ceramides in the sarcolemma negatively impacts insulin sensitivity in humans. The mechanisms explaining accumulation of lipids in specific compartments in skeletal muscle are unknown, but one possibility is through circulating oxidized lipids. POVPC, a major circulating oxidized phospholipid, was exposed to rat myotubes (1-50 μM) for 4h and the total cellular ceramide levels in myotubes measured by LC-MS/MS. Total ceramide content increased dose dependently at POVPC doses in the physiological range (5 μM, p <0.05). To determine the mechanism of POVPC induced ceramide accumulation, ceramide was measured in myotubes after treatment with POVPC (25 μM) in the presence of inhibitors of neutral and acid sphingomyelinase (GW4869 and ARC39), ceramide synthase (fumonisin B₁) and serine palmitoyltransferase (myriocin). The individually administered inhibitors in the presence of POVPC each showed a decrease (41-55%) in ceramide accumulation. When all of inhibitors were administered together along with POVPC, an almost complete inhibition of ceramide accumulation (95%) was observed indicating that the sphingomyelinase, de novo, and salvage pathways of ceramide synthesis are activated by POVPC. The role of oxidized lipids on insulin sensitivity was examined after treatment of rat myotubes with 1-25 μM POVPC. Increasing doses of POVPC at doses as low as 1 μM significantly decreased insulin sensitivity in vitro (p <0.05). These results reveal circulating oxidized lipids promote ceramide accumulation and insulin resistance in muscle cells and may help explain variability in total and localized muscle ceramide levels between individuals. These data also suggest that therapies designed to lower circulating oxidized lipids could be beneficial for the treatment and prevention of T2D.