title: Effects of plasma apolipoproteins on lipoprotein lipase-mediated lipolysis of small and large lipid emulsions.
abstract: Large (ca. 120 nm) and small (ca. 35 nm) emulsions consisting of triolein (TO) and phosphatidylcholine (PC) were prepared as the primary protein-free models of chylomicrons and their remnants, respectively. Lipoprotein lipase (LPL)-mediated lipolysis of emulsion TO was retarded in chylomicron-free human plasma compared with the hydrolysis activated by isolated apolipoprotein C-II (apoC-II). In 30% plasma, free fatty acid (FFA) release rate was higher for large emulsions than for small ones, while both emulsions were hydrolyzed at similar rates in the presence of isolated apoC-II. Isolated apolipoprotein C-III (apoC-III) or apolipoprotein E (apoE) worked as LPL-inhibitor of the lipolysis activated by apoC-II. It was also observed that apolipoprotein A-I (apoA-I) showed distinct inhibitory effects on the lipolysis of large and small emulsions: more effective inhibition for small emulsions. Kinetic analyses showed that K(m)(app) and V(max)(app) for the lipolysis of emulsions were lower in the presence of 30% plasma than isolated apoC-II. ApoA-I also markedly decreased K(m)(app) and V(max)(app) for LPL-catalyzed hydrolysis of both emulsions. In chylomicron-free serum, the density of bound apoA-I at small emulsion surfaces was about three fold greater than large emulsion surfaces, but the binding densities of apoC-II, apoC-III and apoE were less for small emulsion surfaces than for large ones, suggesting that apoA-I preferentially binds to small particles and displaces other exchangeable apolipoproteins from particle surfaces. These results indicate that, in addition to the well known inhibitory effects of apoC-III and apoE, apoA-I in plasma regulates the lipolysis of triglyceride (TG)-rich emulsions and lipoproteins in a size-dependent manner.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Shin-ya
authors.initials: SY
authors.lastname: Morita
authors.forename: Michiko
authors.initials: M
authors.lastname: Kumon
authors.forename: Misa
authors.initials: M
authors.lastname: Kawabe
authors.forename: Kazuchika
authors.initials: K
authors.lastname: Nishitsuji
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Saito
authors.forename: Aline
authors.initials: A
authors.lastname: Vertut-Doï
authors.forename: Minoru
authors.initials: M
authors.lastname: Nakano
authors.forename: Tetsurou
authors.initials: T
authors.lastname: Handa
mesh_terms: D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism / Q000494:pharmacology; D053304:Apolipoprotein C-II; D053305:Apolipoprotein C-III; D001053:Apolipoproteins / Q000097:blood / Q000302:isolation & purification / Q000494:pharmacology*; D001056:Apolipoproteins C / Q000378:metabolism / Q000494:pharmacology; D001057:Apolipoproteins E / Q000378:metabolism / Q000494:pharmacology; D002417:Cattle; D004655:Emulsions; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D007700:Kinetics; D050356:Lipid Metabolism; D008066:Lipolysis / Q000187:drug effects*; D008071:Lipoprotein Lipase / Q000187:drug effects / Q000378:metabolism*; D008892:Milk / Q000201:enzymology; D010713:Phosphatidylcholines / Q000378:metabolism; D011485:Protein Binding; D014304:Triolein / Q000378:metabolism
chemical_list: D016632:Apolipoprotein A-I; D053304:Apolipoprotein C-II; D053305:Apolipoprotein C-III; D001053:Apolipoproteins; D001056:Apolipoproteins C; D001057:Apolipoproteins E; D004655:Emulsions; D010713:Phosphatidylcholines; D014304:Triolein; D008071:Lipoprotein Lipase