Suppressive effects of retinoids, carotenoids and antioxidant vitamins on heterocyclic amine-induced umu C gene expression in Salmonella typhimurium (TA 1535/pSK 1002)

Effects of retinoids, carotenoids and antioxidant vitamins were studied by mutagen-induced umu C gene expression system in Salmonella typhimurium (TA 1535/pSK 1002). Retinol (vitamin A), retinol acetate and retinoic acid showed remarkable inhibitory activities, whereas retinol palmitate exhibited significant but weak activity for umu C gene expression in tester bacteria induced by 3-amino-3,4-dimethyl-5H-pyrido[4,3-b]indol (Trp-P-1) in the presence of hepatic metabolizing enzymes (S9 mixture). Carotenoids having provitamin A activity (beta-carotene and canthaxanthin) exhibited moderate suppressive effects on the same experimental system. The ranks of suppressive activities were retinol > retinol acetate > retinoic acid > canthaxanthin > beta-carotene > retinol palmitate and their doses for inhibition by 50% (ID50) were estimated to be 1.2 x 10(-7), 3.0 x 10(-7), 5.4 x 10(-7), 1.5 x 10(-6), 4.0 x 10(-5) and 6.0 x 10(-5) M, respectively. However, they did not cause significant inhibition on umu C gene expression induced by direct-acting mutagen (adriamycin or mitomycin C) in the absence of S9 mixture. Inhibition of umu gene expression appears to be due to inhibition of P450-mediated metabolic activation of the heterocyclic amine Trp-P-1. Ascorbic acid (vitamin C) showed weak but significant suppressive activity at high-dose concentrations (3 x 10(-6)-10(-4)M). However, a-tocopherol did not exhibit significant suppression at all dose concentrations. The significance of the experimental results is discussed from the viewpoint of the chemoprevention against genotoxicity associated with carcinogenesis.