Abstract 650: Ceramide as a Mediator of Insulin Resistance--Associated Atherosclerosis

Abstract

Objectives: Insulin resistance-induced hyperlipidemia and hyperlipoproteinemia are risk factors of atherosclerosis. Spingolipid ceramide is involved in insulin resistance and lipoprotein metabolism, and sphingomyelin, a ceramide metabolite, is an independent risk factor for CVD. Here we studied the role of spingolipids in insulin resistance associated atherosclerosis. Methods: Low density lipoprotein receptors knockout (LDLR -/- ) mice, a diet induced mouse model of insulin resistance and atherosclerosis, were fed a standard chow diet or a western diet (high fat with 0.2% cholesterol) for 12 weeks with or without myriocin, an inhibitor of de novo ceramide synthesis. A targeted lipidomics approach was used for hepatic and plasma profiling of ceramides. Metabolic 2 H 2 O-labeling technique was applied to quantify turnover rates of hepatic and plasma lipids and lipoproteins, including ApoB and ApoAI - the principle proteins of VLDL/LDL and HDL. Hepatic and intestinal expression of genes and proteins involved in insulin signaling, lipid and lipoprotein metabolism were characterized. Results: A western diet caused insulin resistance, increased hepatic and serum triglycerides and the altered distribution of hepatic ceramides, i.e. hepatic levels of long chain ceramides (C16 & C18), involved in apoptosis, were increased by 80% and 27%, respectively, while a very-long chain ceramide C24 was reduced more than twice. A western diet also induced dyslipidemia, hepatic oxidative stress, inflammation, apoptosis, mild fibrosis, and atherosclerosis. The plasma ratio of ApoB/ApoA1 was increased >2 fold which was due to increased production of ApoB. HDL turnover was not affected. Pharmacologic inhibition of sphingolipid biosynthesis with myriocin improved insulin sensitivity, hepatic steatosis, fibrosis, apoptosis, and prevented atherosclerosis. These changes were associated with decreased lipogenesis and ApoB production. In addition, myriocin significantly increased both plasma levels and flux of HDL. Conclusions: Modulation of sphingolipid metabolism may lead to the development of novel therapeutic strategies for the treatment of insulin resistance and associated atherosclerosis.