Reactivity of HDL subfractions towards lecithin-cholesterol acyltransferase. Modulation by their content in free cholesterol.
(1) Human HDL2 (d 1.070-1.125) and HDL3 (d 1.125-1.21) labelled with unesterified [14C]cholesterol, were incubated with a source of lecithin-cholesterol acyltransferase. For optimal activity, the reaction required the addition of albumin in excess, at least 3-times greater than the concentration of HDL-free cholesterol. Under such conditions, the reaction appeared saturable. HDL3 was found the most efficient substrate and the Vmax values expressed for 1.5 IU LCAT/ml and with an albumin/free cholesterol ratio of 3, were 8.3 nmol free cholesterol esterified/ml per h and 4.1 nmol/ml per h for HDL3 and HDL2, respectively. (2) HDL3 were modified in the presence of VLDL by inducing triacylglycerol lipolysis with a semipurified lipoprotein lipase from bovine milk. The newly formed HDL had gained free cholesterol and phospholipids, so that about 50% of these modified HDL, referred to as light-LIP-HDL3, were reisolated in the HDL2 density range. Light-LIP-HDL3 were enriched mostly in free cholesterol (+ 160%) and in phospholipid (+ 40%). Their reactivity towards LCAT was half-reduced compared to parent HDL3, which correlated well with a decrease in their phospholipid/free cholesterol molar ratio. Moreover, HDL3 artificially enriched in free cholesterol and exhibiting a comparable PL/FC behaved like lipolysis-modified HDL in their reactivity towards LCAT. (3) HDL3 were also modified by co-incubation with VLDL (post-VLDL-HDL3), or with VLDL and a source of lipid transfer protein (CET-HDL3). The latter treatment greatly affected the lipid composition of the core particle (-25% esterified cholesterol, +190% TG). In both cases, the moderate decreasing LCAT reactivity observed could be related to the phospholipid/free cholesterol ratio. Thus, like in artificial substrates, the lipid composition of the HDL surface may control the rate of LCAT-mediated cholesterol esterification.
Simard
G
G
Laboratoire de Biochimie Médicale, C.H.U. d'Angers, France.
Loiseau
D
D
Girault
A
A
Perret
B
B
D000818:Animals; D002417:Cattle; D002784:Cholesterol / Q000097:blood*; D002788:Cholesterol Esters / Q000097:blood; D005260:Female; D006801:Humans; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000097:blood*; D053439:Lipoproteins, HDL2; D053440:Lipoproteins, HDL3; D008892:Milk / Q000201:enzymology; D019301:Oleic Acid; D009829:Oleic Acids / Q000494:pharmacology; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood*; D010743:Phospholipids / Q000097:blood; D012709:Serum Albumin; D013379:Substrate Specificity; D014280:Triglycerides / Q000097:blood
D002788:Cholesterol Esters; D008075:Lipoproteins, HDL; D053439:Lipoproteins, HDL2; D053440:Lipoproteins, HDL3; D009829:Oleic Acids; D010743:Phospholipids; D012709:Serum Albumin; D014280:Triglycerides; D019301:Oleic Acid; D002784:Cholesterol; D007862:Phosphatidylcholine-Sterol O-Acyltransferase; D008071:Lipoprotein Lipase