title: Prevention of cholesteryl ester accumulation in P388D1 macrophage-like cells by increased cellular vitamin E depends on species of extracellular cholesterol. Conventional heterologous non-human cell cultures are poor models of human atherosclerotic foam cell formation.
abstract: Since the cellular role of the antioxidative vitamins in the formation of foam cells has not yet been studied in detail, we investigated the effect of alpha-tocopherol and ascorbic acid loading of P388D1 macrophage-like cells on their cholesterol and cholesteryl ester levels and their response to the exposure to different lipoproteins. alpha-Tocopherol loading, but not ascorbic acid loading, of P388D1 cells strongly reduced their cellular cholesteryl ester/cholesterol ratio (the crucial indicator of foam cell formation) when fetal calf serum was the only extracellular source of cholesterol. Balance studies suggest that this effect of alpha-tocopherol was mainly due to a reduced uptake of fetal-calf-serum-derived cholesterol. alpha-Tocopherol loading, however, did not reduce the cholesteryl ester/cholesterol ratio when human unmodified low-density lipoprotein (LDL) was added to culture medium containing fetal calf serum. Thus, the uptake of fetal-calf-serum-derived cholesterol was competitively reduced by human LDL, the uptake of which remained unaffected by alpha-tocopherol. Similarly, alpha-tocopherol loading did not prevent cholesteryl ester formation induced by human LDL either oxidized with Cu2+, ultraviolet light or HOCl, or modified by acetylation, aggregation or by malondialdehyde treatment. The present experimental conditions lacked any pro-oxidative burden, since (a) ascorbic acid, either alone or combined with alpha-tocopherol, did not affect cellular cholesteryl ester levels, (b) foam cell formation was not a linear function of the degree of oxidative LDL modification, and (c) alpha-tocopherol lacked specific effects on oxidatively modified LDL. Thus, the reduction of cellular cholesteryl esters by alpha-tocopherol in the absence of human unmodified LDL was hardly due to common antioxidative properties of vitamin E. In conclusion, the present observation that a desirable alpha-tocopherol effect on the cholesteryl ester balance in mouse-tumor-derived P388D1 cells strongly depended on the species of extracellular cholesterol carrier, cautions against premature generalizations of conventional non-human cell culture data.
authors.affiliation: Institute of Biochemistry and Molecular Biology, University of Berne, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Asmis
authors.forename: V C
authors.initials: VC
authors.lastname: Llorente
authors.forename: K F
authors.initials: KF
authors.lastname: Gey
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001161:Arteriosclerosis / Q000209:etiology; D001667:Binding, Competitive; D001693:Biological Transport, Active; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D005487:Foam Cells / Q000378:metabolism; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D014810:Vitamin E / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D002788:Cholesterol Esters; D008077:Lipoproteins, LDL; D014810:Vitamin E; D002784:Cholesterol