Different reactivities of high density lipoprotein2 subfractions with hepatic lipase.
Human high density lipoproteins2 (HDL2) consist of particles that contain both apolipoprotein (apo) A-I and apoA-II (A-I/A-II-HDL2) and others that contain apoA-I but are devoid of apoA-II (A-I-HDL2). When postprandial lipemia is pronounced, a fraction of HDL2 is converted into HDL2-like particles. These HDL3 exhibit lower apoA-I/apoA-II ratios than the parent HDL2, suggesting preferential conversion of A-I/A-II-HDL2 into HDL3 (J. Clin. Invest. 1984. 74: 2017-2023). Triglyceride transfer from triglyceride-rich lipoproteins to HDL2 and subsequent lipolysis by hepatic lipase are thought to mediate the conversion of HDL2 into HDL3. To understand why A-I/A-II-HDL2 are preferentially converted into HDL3, we separated postprandial HDL2 into A-I-HDL2 and A-I/A-II-HDL2 species by immunoaffinity chromatography using a monoclonal antibody for apoA-II, and determined the ability of HDL2 species i) to participate in protein-mediated lipid transfer; and ii) to interact with hepatic lipase in vitro. Triglyceride transfer from/to triglyceride-rich lipoproteins was similar for the two HDL2 species. In contrast, A-I/A-II-HDL2 were twice as effective as A-I-HDL2 in liberating hepatic lipase immobilized on HDL3-Sepharose. Lipolysis of triglycerides by hepatic lipase was 60% higher in postprandial A-I/A-II-HDL2 than in postprandial A-I-HDL2. Hydrolysis of phosphatidylcholine by hepatic lipase was threefold higher in A-II-containing HDL2 when compared with HDL2 devoid of apoA-II. The different lipolytic rates in HDL2 subspecies correlated with the size reduction of substrate lipoproteins. Reconstitution of postprandial A-I-HDL2 with apoA-II enhanced the rate of lipolysis by hepatic lipase to that observed in A-I/A-II-HDL2. We conclude that it is the interaction with hepatic lipase rather than the rate of triglyceride transfer that results in the preferred conversion of postprandial A-II-containing HDL2 into HDL3, and that apoA-II exerts a crucial role in this process.
Mowri
H O
HO
Department of Medicine, Baylor College of Medicine, Houston, TX 77030.
Patsch
W
W
Smith
L C
LC
Gotto
A M
AM
Patsch
J R
JR
D016632:Apolipoprotein A-I / Q000032:analysis; D016633:Apolipoprotein A-II / Q000032:analysis; D006801:Humans; D007700:Kinetics; D008049:Lipase / Q000378:metabolism*; D008066:Lipolysis; D008075:Lipoproteins, HDL / Q000032:analysis / Q000378:metabolism*; D053439:Lipoproteins, HDL2; D053440:Lipoproteins, HDL3; D008099:Liver / Q000201:enzymology*; D014280:Triglycerides / Q000032:analysis / Q000378:metabolism
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D008075:Lipoproteins, HDL; D053439:Lipoproteins, HDL2; D053440:Lipoproteins, HDL3; D014280:Triglycerides; D008049:Lipase