The three major components of dyslipidemia associated with the metabolic syndrome are increased fasting and post-prandial triglyceride-rich lipoproteins (TRLs), decreased high-density lipoprotein (HDL), and increased small, dense low-density lipoprotein (LDL) particles. Insulin resistance and compensatory hyperinsulinemia lead to overproduction of very low-density lipoprotein particles. A relative deficiency of lipoprotein lipase, an insulin-sensitive enzyme, is partly responsible for the decreased clearance of fasting and postprandial TRLs, and the decreased production of HDL particles. The resulting increased concentration of cholesteryl ester-rich fasting and postprandial TRLs is the central lipoprotein abnormality of the metabolic syndrome. The increase of small, dense LDL particles, and decrease of large, buoyant HDL particles are consequential events. All these lipoprotein defects contribute largely to the increased cardiovascular disease risk in individuals with insulin resistance. Peroxisome proliferator-activated receptor (PPAR)α, PPARγ, and PPARδ agonists seem to improve dyslipidemia of the metabolic syndrome by regulating the expression of important genes involved in the deranged lipoprotein metabolism associated with insulin resistance.
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