Effect of 7 beta-hydroxycholesterol on astrocyte primary cultures and derived spontaneously transformed cell lines. Cytotoxicity and cholesterogenesis.

The correlation between the lethal effect of 7 beta-hydroxycholesterol (7 beta-OH-CH) on spontaneously transformed cell lines derived from rat astrocyte primary cultures (normal cells) and de novo cholesterogenesis was investigated. Both 7 beta-OH-CH and 7-keto-CH were not cytotoxic on normal cells but 7 beta-OH-CH affected markedly the viability of the transformed cells. The use of [14C]acetate or [14C]mevalonate indicated that 7-keto-CH inhibits de novo cholesterogenesis upstream of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) in both cell types whereas 7 beta-OH-CH also inhibits downstream of HMGR. The accumulation of two radiolabelled products X1 and X2 between mevalonate and CH was found in unsaponifiable neutral lipids extracted from 7 beta-OH-CH treated transformed cells. HPLC and GC-MS revealed that X1 and X2 are not lanosterol and 24,25-epoxylanosterol, respectively. Incubation of the transformed cells with X1 and X2 did not affect their viability. Our data demonstrate that, under our experimental conditions, 7 beta-OH-CH cytotoxicity is not linked to the inhibition of de novo cholesterogenesis in cultured glial transformed cells.