Hepatic lipase (HL) is a lipolytic enzyme that contributes to the regulation of plasma triglyceride (TG) levels. Elevated TG levels may increase the risk of developing coronary heart disease, and studies suggest that mutations in the HL gene may be associated with elevated TG levels and increased risk of coronary heart disease. Hepatic lipase facilitates the clearance of TG from the very low density lipoprotein (VLDL) pool, and this function is governed by the composition and quality of high density lipoprotein (HDL) particles. In humans, HL is a liver resident enzyme regulated by factors that release it from the liver and activate it in the bloodstream. HDL regulates the release of HL from the liver and HDL structure controls HL transport and activation in the circulation. Alterations in HDL-apolipoprotein composition can perturb HL function by inhibiting the release and activation of the enzyme. HDL structure may therefore affect plasma TG levels and coronary heart disease risk.
Triglycerides and Heart DiseaseElevated plasma triglyceride (TG) levels have been viewed as a risk factor for coronary heart disease (CHD) for more than a decade.1,2 Plasma TG levels are regulated by both synthesis and degradation of both very low density lipoprotein (VLDL) and chylomicron particles. The clearance of TG-rich lipoproteins from the circulation is controlled by the actions of lipoprotein lipase (LPL) and hepatic lipase (HL) and by the interlipoprotein exchange of TG by cholesteryl ester transfer protein. Lipoprotein lipase is the predominant TG lipase and is responsible for hydrolyzing TG in chylomicrons and VLDL, whereas HL is both a phospholipase and a TG lipase and plays an important role in HDL metabolism and in the conversion of VLDL to LDL.3 Single nucleotide polymorphisms (SNPs) in the HL gene (LIPC) have been shown to associate with plasma lipid concentrations and increased CHD risk. 4,5 Hepatic lipase deficiency is a result of relatively rare LIPC mutations that give rise to a loss in circulating HL activity (due to impaired secretion or inactive enzyme) and cause an increase in TG-rich HDL and VLDL remnants and increased CHD risk.