(309h) Modulating Lipid Fate Controls Lipotoxicity in Palmitate-Treated Hepatic Cells

As the American waistline continues to expand so too does the burgeoning health crisis associated with obesity, diabetes and the all-encompassing metabolic syndrome. The pathogenesis of these now common conditions involves abnormal accumulation of lipids (steatosis) in non-adipose tissues due to elevated free fatty acid export from adipose tissue. In the liver, chronic steatosis and saturated fatty acids (SFA) overexposure can result in dysregulation of ER function and oxidative stress. However, the lipid metabolic pathways and mechanisms responsible for these deleterious alterations remain largely undefined. Our central hypothesis is that overexposure to SFAs (e.g., palmitate) leads to increased saturation of ER membrane phospholipids, which alters membrane stability and induces ER stress.

In order to better characterize the phenotypic response of hepatic cells to SFA overexposure, we have sought to systematically perturb the three main pathways of fatty acid utilization and disposal: (1) phospholipid (PL) synthesis and remodeling, (2) energy generation by beta-oxidation, and (3) triglyceride (TG) synthesis. Experimentally, we simulated hepatic lipotoxicity using palmitate-treated H4IIEC3 rat hepatocytes as an in vitromodel. This system demonstrated significantly higher levels of reactive oxygen species (ROS) accumulation, endoplasmic reticulum (ER) stress associated protein release (CHOP), and cell death as well as increased saturation of membrane phospholipid species. Using treatments designed to modulate specific lipid metabolic pathways, we have found that blocking phospholipid breakdown and turnover (using phospholipase inhibitors) or enhancing fatty acid disposal (using AICAR to stimulate beta-oxidation) can suppress the lipotoxic effects of palmitate.

 A detailed investigation is currently underway to elucidate the mechanisms by which these treatments are able to reverse the lipotoxic effects of SFA overexposure. We are applying isotopically labeled ¹³C-palmitate to trace the fate of exogenous fatty acids using metabolic flux analysis (MFA) and lipidomic profiling. This will enable us to identify pathways that are responsible for the observed metabolic phenotypes and develop a better understanding of the mechanisms leading to ROS accumulation and lipoapotosis in the presence of elevated SFAs. This understanding is expected to provide more effective and targeted therapies for treatment of fatty liver disease and related complications associated with diabetes and obesity.