Inhibition of retinoid toxicity by rat liver S9 fraction in cultured mammalian cells.

The effects of retinol (Rol), retinyl acetate (RAc) or retinoic acid (RA) on growth of Chinese hamster V79 cells were studied. In addition, the effect of Rol on cell growth in the human lymphoid cell line RPMI no. 1788 was examined. Cultures were treated with retinoid alone, with retinoid plus S9 mix and with retinoid plus the supernatant of S9 fraction. Treatment of Rol, RAc or RA alone inhibited the growth of both cell lines as evidenced by a dose-dependent decrease of viable cell counts. Concurrent treatment of a retinoid with the well-known metabolic activation system S9 mix containing the rat liver S9 fraction plus enzyme cofactors resulted in a total elimination of the toxic effect of a retinoid. For instance, V79 cells treated with Rol, RAc or RA alone at the highest dose of 32 micrograms/ml, and human lymphoid cells treated with Rol at the highest dose of 24 micrograms/ml resulted in killing of over 90% of the cells, while addition of S9 mix to the cultures treated with such high doses of a retinoid showed no reduction of viable cells as compared with the controls. The supernatant of S9 fraction after high speed centrifugation also had dose-dependent protective effects against the toxicity of retinol in V79 cells. Finally, experiments using sucrose gradient centrifugation and [3H] Rol suggests that binding of a retinoid to its specific binding protein in the S9 mixture and supernatant greatly decreases or abolished the toxicity of free retinoid in cultured mammalian cells.