Interaction of free apolipoproteins with macrophages. Formation of high density lipoprotein-like lipoproteins and reduction of cellular cholesterol.
Mouse peritoneal macrophages, loaded with cholesteryl ester by incubating with acetylated human low density lipoprotein containing [3H]cholesteryl oleate, were exposed to purified human apolipoproteins (apo) A-I, A-II, C-III, or E in aqueous solutions. Unesterified cholesterol was released into the medium in the presence of apoA-I, -A-II, or -E, accompanied by the decrease in intracellular cholesteryl ester. ApoC-III had no such effects. Apparent Km values of the cholesterol release were estimated as 0.11, 0.14, and 0.24 microM, and Vmax values 35, 11, and 14 micrograms of cholesterol/mg of cell protein/6 h, for apoA-I, -A-II, and -E, respectively. The products formed with apoA-I, -A-II, or -E in the media were analyzed by density gradient ultracentrifugation when the cells were preloaded with [3H]cholesteryl oleate-acetylated low density lipoproteins and [3H]choline. Free [3H]cholesterol, [3H]phosphatidylcholine, and [3H]sphingomyelin were detected coincidentally as a symmetric peak at the density of 1.1 in each case. In the complex of lipids and apoA-I or apoA-II, the weight ratios of apolipoprotein/cholesterol/phosphatidylcholine/sphingomyelin/lysophosphatidyl- choline were estimated as 2.2:1:0.6:0.2:0.07 and 4.0:1:0.5:0.3:0.07, respectively. Both of the products formed with apoA-I and -A-II migrated slower than plasma high density lipoprotein in electrophoresis on agarose gel. Because the Km values are as low as 1:340-400, 1:140-160, and 1:6-8 of plasma concentrations of apoA-I, -A-II, and -E, respectively, the results have physiological relevance for a function of the free apolipoproteins in interstitial fluid to form high density lipoprotein and to reduce cellular cholesterol.
Hara
H
H
Department of Medicine, University of Alberta, Edmonton, Canada.
Yokoyama
S
S
D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D004587:Electrophoresis, Agar Gel; D005260:Female; D006801:Humans; D006868:Hydrolysis; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D051379:Mice; D010743:Phospholipids / Q000378:metabolism; D014461:Ultracentrifugation
D001053:Apolipoproteins; D008075:Lipoproteins, HDL; D010743:Phospholipids; D002784:Cholesterol