The mechanism of HDL lowering in hypertriglyceridemic, insulin-resistant states

Hypertriglyceridemia and reduced plasma levels of high-density lipoprotein cholesterol (HDL-c) are the most frequent forms of dyslipidemia observed in insulin-resistant states, such as obesity, impaired fasting glucose, and Type 2 diabetes, and are highly atherogenic in these settings. The hypertriglyceridemia of insulin resistance is primarily due to an overproduction of very low-density lipoproteins (VLDL), and in some instances, is also due to reduced VLDL clearance and postprandial accumulation of VLDL, chylomicrons, and their remnants [i.e., triglyceride (TG)-rich lipoproteins]. TG-rich lipoproteins actively exchange their core lipids with HDL in vivo, a process that is facilitated by cholesteryl ester (CE) transfer protein (CETP), and in hypertriglyceridemic states, this process is enhanced. This results in TG enrichment of HDL in hypertriglyceridemic states. There is accumulating evidence that TG enrichment of HDL plays an important role in determining the rate at which HDL particles are cleared from the circulation. Here, we review the evidence that TG-enriched HDL, when modulated by lipolytic enzymes in the circulation, are catabolized more rapidly than native HDL, and may ultimately explain the lowering of HDL-c in insulin-resistant, hypertriglyceridemic states. Since we have recently reviewed in detail the evidence by Lamarche et al. [Clin. Chim. Acta 286 (1999) 145; J. Clin. Invest. 103 (8) (1999) 1191.] to support this hypothesis, in the present brief review, we will focus predominantly on our own recent research in this area.