All-trans beta-carotene enhances mitogenic responses and ornithine decarboxylase activity of BALB/c 3T3 fibroblast cells induced by tumor promoter and fetal bovine serum but suppresses mutagen-dependent umu C gene expression in Salmonella typhimurium (TA 1535/pSK 1002).

Although previous epidemiological studies have indicated that beta-carotene is an important agent for the chemical prevention against carcinogenesis, a recent prospective study has strikingly suggested that supplementation with beta-carotene significantly increased the incidence of some types of cancer (The alpha-Tocopherol and beta-Carotene Cancer Prevention Study Group, New Engl. J. Med., 330 (1994) 1031-1035). To analyze the discrepancy of this problem, the authors analyze the effects of beta-carotene on biochemical and biological events associated with carcinogenesis by in vitro experiments. (1) All-trans beta-carotene enhanced the proliferation and DNA synthesis of BALB/c 3T3 cells induced by a tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and fetal bovine serum, although beta-carotene itself did not show mitogenic activity. (2) All-trans beta-carotene caused a remarkable stimulation for the early induction of ornithine decarboxylase (ODC) activity after the stimulation of TPA and fetal bovine serum. (3) All-trans beta-carotene exhibited significant antimutagenic activity which suppresses umu C gene expression in Salmonella typhimurium (TA 1535/pSK 1002) induced by a typical mutagen, 2-aminoanthracene (2-AA). These experimental results suggest that all-trans beta-carotene might cause beneficial and harmful effects on different phases of carcinogenesis.