[Disturbances of lipoprotein metabolism in metabolic syndrome]

Dyslipidemia in metabolic syndrome (MS), called the atherogenic triad, includes elevated levels of plasma triglycerides (TGs), low levels of HDL-cholesterol (HDL-CH), and the presence of small dense low-density lipoproteins (sdLDLs) with normal or slightly elevated LDL-CH levels. Insulin resistance drives the increase in the three main sources of TG for VLDL synthesis: fatty-acid flux from adipose tissue, de novo lipogenesis, and uptake of remnant lipoproteins. Overproduction of VLDL, predominantly triglyceride-rich large VLDL1 particles, induces the cascade of events which lead to abnormalities of other plasma lipoproteins. The accumulation of VLDL in plasma and decreased activity of lipoprotein lipase (LPL) impair the catabolism of chylomicrons. Moreover, hyperinsulinemia induces increased intestinal production of chylomicrons. These factors cause augmented postprandial lipemia. Hepatic overproduction of VLDL leads to an increased level of VLDL remnants in plasma. Highly atherogenic sdLDLs are generated from VLDL1 particles by the action of LPL, cholesterol ester transfer protein (CETP), and hepatic lipase (HL). In the presence of hypertriglyceridemia, accelerated CETP-mediated lipid transfer generates TG-enriched HDL particles. This enhances HDL catabolism mediated by HL and endothelial lipase (EL). The assessment of risk of atherosclerotic cardiovascular disease in MS related to low HDL-CH and the presence of sdLDL particles may be improved by the incorporation of measurements of apolipoproteins (apo)-B and apoA-I into clinical practice. In addition, the concentration of non-HDL-CH may be useful in quantifying apo-B-containing atherogenic lipoproteins.