Lipoprotein Lipase and Hepatic Endothelial Lipase are Key Enzymes in the Metabolism of Plasma High Density Lipoproteins, Particularly of HDL2

Abstract

In spite of the close association of plasma high density lipoproteins (HDL) with atherosclerotic vascular disease there is still relatively little knowledge on the pathways of HDL synthesis and degradation and on the factors which regulate the concentration of HDL and of its subfractions HDL2 and HDL3. It is becoming increasingly evident that circulating HDL particles are formed by a stepwise assimilation of constituents derived from different sources (Nikkilä 1978a,b). The primary HDL particle (“nascent” HDL) is elaborated by intestine and liver but immediately after its delivery to the circulation it becomes associated with apoprotein A-I and is transformed to HDL3. Another step in HDL synthesis takes place during degradation of the triglyceride-rich lipoproteins (VLDL and chylomicrons) at peripheral capillary beds by the action of lipoprotein lipase (LPL). Recently, preliminary evidence has been obtained for a role of yet another endothelial lipolytic enzyme, hepatic lipase (HEL), in the metabolism of HDL. The present paper summarizes some of the data indicating that the two heparin-releasable endothelial enzymes are important in the regulation of plasma HDL (HDL2) levels.