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-CULTURES ARE 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) 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 P388D(1) 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 competetively 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 P388D(1) cells strongly depended on the species of extracellular cholesterol carrier cautions against premature generalizations of conventional non-human cell culture data.