In Vitro Measurement of Lipoprotein and Hepatic Lipases

Abstract

Two genetically related lipases perform the hydrolysis of fatty acids from triglycerides and phosphohpids in plasma lipoproteins; lipoprotein lipase (LPL) and hepatic lipase (HL) (1). The former catabolizes the hydrolysis of triglycerides in chylomicrons and very low-density lipoproteins (VLDL) producing the so-called remnant particles. The later, with higher affinity for phospholipids, may modify the conformation of lipoproteins acting on the surface of intermediate-density lipoproteins (IDL) and high-density lipoprotein (HDL) particles. Both enzymes have a high affinity for the proteoglycans that anchor the lipases to the endothelial surface, their resident site. LPL has a peripheral distribution being more abundant in tissues in which fatty acids are stored (adipose tissue) or predominantly used as metabolic fuel (muscle), whereas HL is confined to the endothelia of the liver. When an heparin bolus is injected into the blood stream, a release of lipases from their anchors to the circulation is observed because lipases have higher affinity for heparin than for proteoglycans. After heparin injection, the amount of LPL and HL circulating in plasma is increased several hundred folds and the amount of lipases in postheparin plasma is taken as an indirect measure of the lipase content in the individual (2).