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.

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.