Postprandial VLDL-triglyceride Metabolism in Type 2 Diabetes Patients With and Without NAFLD

Overview

Non-alcoholic fatty liver disease (NAFLD) covers a spectrum from simple reversible hepatic steatosis to inflammation and fibrosis termed steatohepatitis (NASH). The mechanisms behind why some subjects progress from NAFLD to NASH are not clear and the responsible mechanism for storage of excess amounts of liver fat in patients with NAFLD are poorly understood. Patients with type 2 diabetes mellitus (T2D) and abdominally obese subjects very often have accumulation of liver fat (NAFLD). T2D is also associated with abnormal lipid metabolism (dyslipidemia), including free fatty acids (FFA), hypertriglyceridemia and excessive postprandial hyperlipidemia which increases the risk of ischemic cardiovascular disease (CVD) and heart failure. In healthy, insulin sensitive subjects the postprandial increase in triglycerides (TG) is primarily caused by meal derived chylomicrons, whereas endogenously produced TG (VLDL-TG) and decreased peripheral TG clearance only becomes quantitatively important in insulin resistant subjects .Thus, postprandial lipidemia in T2D results from both chylomicronemia as well as a reduction in both insulin mediated suppression of VLDL-TG secretion and lipoprotein lipase (LPL) mediated peripheral clearance. A recent study demonstrated that the ability of insulin to suppress hepatic VLDL-TG after a fat-enriched meal and the duration of the postprandial hyperlipidemia was similar in patients with T2D compared with age- and BMI matched individuals without T2D, indicating that the degree of insulin mediated VLDL-TG secretion and hyperlipidemia primarily depends on insulin sensitivity and not the presence of T2D diabetes per se. In these studies, the investigators want to examine the effect of a fat enriched mixed-meal on hepatic VLDL-TG handling and adipose storage capacity in patients with T2D with and without NAFLD. Investigators will address these questions using carboxyl-14C triolein labeled VLDL-TG, magnetic resonance (MR) spectroscopy of liver, muscle and fat biopsies in combination with state-of-the art muscle and adipose tissue enzyme kinetics, gene- and protein expression. The overarching goals are to define abnormalities and differences between patients with T2D with and without NAFLD in terms of hepatic lipid metabolism.