In vivo evidence for the role of lipoprotein lipase activity in the regulation of apolipoprotein AI metabolism : A kinetic study in control subjects and patients with type II diabetes mellitus

The aim of this study was to delineate the role of lipoprotein lipase (LPL) activity in the kinetic alterations of high density lipoprotein (HDL) metabolism in patients with type II diabetes mellitus compared with controls. The kinetics of HDL were studied by endogenous labeling of HDL apolipoprotein AI (HDL-apo AI) using a primed infusion of D(3)-leucine. The HDL-apo AI fractional catabolic rate (FCR) was significantly increased (0.32 +/- 0.07 vs. 0.23 +/- 0.05 pool/day; P < 0.01), and HDL composition was changed [HDL cholesterol, 0.77 +/- 0.16 vs. 1.19 +/- 0.37 mmol/L (P < 0.05); HDL triglycerides, 0.19 +/- 0.12 vs. 0.10 +/- 0.03 mmol/L (P < 0.05)] in diabetic patients compared with healthy subjects. HDL-apo AI FCR was correlated to plasma and HDL triglyceride concentrations (r = 0.82; P < 0.05 and r = 0.80; P < 0.05, respectively) and to homeostasis model assessment (r = 0.78; P < 0.05). Postheparin plasma LPL activity was decreased in type II diabetes (6.8 +/- 2.8 vs. 18.1 +/- 5.2 micromol/mL postheparin plasma.h; P < 0.005) compared with that in healthy subjects and was correlated to the FCR of HDL-apo AI (r = -0.63; P < 0.05). LPL activity was also correlated with HDL cholesterol (r = 0.78; P < 0.05), plasma and HDL triglycerides (r = -0.87; P < 0.005 and r = -0.83; P < 0.05, respectively), and homeostasis model assessment (r = -0.79; P < 0.05). In addition, the LPL to hepatic lipase ratio was correlated with the catabolic rate of HDL (r = -0.76; P < 0.06). These results suggest that a decrease in the LPL to hepatic lipase ratio in type II diabetes mellitus, mainly related to lowered LPL activity, could induce an increase in HDL catabolism. These alterations in HDL kinetics in type II diabetes proceed to some extent from changes in their composition, probably linked to an increase in triglyceride transfer from very low density lipoprotein particles, in close relationship with LPL activity and resistance to insulin.