Cholesterol is poorly available for free apolipoprotein-mediated cellular lipid efflux from smooth muscle cells.
To study the mechanism for resistance of smooth muscle cells (SMC) to cholesterol efflux caused by lipid-free apolipoproteins [Komaba, A., et al. (1992) J. Biol. Chem. 267, 17560-17566], the efflux of phospholipids and cholesterol was induced from mouse peritoneal macrophages (MP) and rat aortic SMC by phospholipid/triglyceride microemulsion, by human plasma high- and low-density lipoproteins (HDLs and LDLs), and by lipid-free human apolipoprotein (apo) A-I. The efflux of both lipids by the lipid microemulsion showed essentially the same kinetic profile for these two types of cells except that the rate of phospholipid efflux was 5-6 times slower by weight than cholesterol in both cases. The same ratio of cholesterol to phospholipid was also found in the efflux to LDLs. Lipid-free apoA-I mediated cellular cholesterol efflux, but the rate was much slower from SMC than from MP. However, the rate of apoA-I-mediated phospholipid efflux was similar between these two cells generating HDL-like particles, resulting in a high phospholipid:cholesterol ratio, (4-5):1 by weight, in the lipid efflux from SMC, in contrast with (0.8-1):1 in the lipid efflux from MP. When standardized for the cellular free cholesterol, the Vmax of cholesterol efflux induced by lipid-free apoA-I was 10 times slower from SMC than from MP, but only by at most 2-fold slower when lipid microemulsion was the acceptor. Thus, free cholesterol of SMC is less available than that of MP for free apolipoprotein-mediated generation of HDLs with cellular lipids.(ABSTRACT TRUNCATED AT 250 WORDS)
Li
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Lipid and Lipoprotein Research Group, University of Alberta, Edmonton, Canada.
Komaba
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Yokoyama
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D000818:Animals; D016632:Apolipoprotein A-I / Q000494:pharmacology; D001053:Apolipoproteins / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism*; D004655:Emulsions; D006801:Humans; D007700:Kinetics; D050356:Lipid Metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D010529:Peritoneal Cavity / Q000166:cytology; D010713:Phosphatidylcholines / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology; D051381:Rats; D014280:Triglycerides / Q000494:pharmacology
D016632:Apolipoprotein A-I; D001053:Apolipoproteins; D004655:Emulsions; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D010713:Phosphatidylcholines; D010743:Phospholipids; D014280:Triglycerides; D002784:Cholesterol