PREVENTION OF CHOLESTERYL ESTER ACCUMULATION IN P388D(1) MACROPHAGE-LIKE CELLS BY INCREASED CELLULAR VITAMIN-E DEPENDS ON SPECIES OF EXTRACELLULAR CHOLESTEROL - CONVENTIONAL HETEROLOGOUS NONHUMAN CELL-CULTURESARE POOR MODELS OF HUMAN ATHEROSCLEROTIC FOAM CELL-FORMATION

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 P388D(1) macr ophage-like cells on their cholesterol and cholesteryl ester levels an d their response to the exposure to different lipoproteins. alpha-Toco pherol loading, but not ascorbic acid loading, of P388D(1) cells stron gly reduced their cellular cholesteryl ester/cholesterol ratio (the cr ucial 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, howev er, did not reduce the cholesteryl ester/cholesterol ratio when human unmodified low-density lipoprotein (LDL) was added to culture medium c ontaining fetal calf serum. Thus, the uptake of fetal-calf-serum-deriv ed cholesterol was competetively reduced by human LDL, the uptake of w hich remained unaffected by alpha-tocopherol. Similarly, alpha-tocophe rol loading did not prevent cholesteryl ester formation induced by hum an LDL either oxidized with Cu2+, ultraviolet light or HOCl, or modifi ed by acetylation, aggregation or by malondialdehyde treatment. The pr esent experimental conditions lacked any pro-oxidative burden, since ( a) ascorbic acid, either alone or combined with alpha-tocopherol, did not affect cellular cholesteryl eater 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 modif ied LDL. Thus, the reduction of cellular cholesteryl esters by alpha-t ocopherol in the absence of human unmodified LDL was hardly due to com mon antioxidative properties of vitamin E. In conclusion, the present observation that a desirable alpha-tocopherol effect on the cholestery l ester balance in mouse-tumor-derived P388D(1) cells strongly depende d on the species of extracellular cholesterol carrier cautions against premature generalizations of conventional non-human cell culture data .