3-amino-1-methyl-5h-pyrido(4-3-b)indole and Cell-Transformation--Neoplastic

Heterocyclic aromatic amines (HCA) are formed upon frying of poultry, fish or meat and have been shown to induce tumours in rodent bioassays. We investigated the transforming activity of HCA in an in vitro assay using the M2/C3H mouse fibroblast cell line. An external metabolic activation system (rat liver homogenate) was required in order to observe any HCA-induced cytotoxic effects or cell transforming activity. Trp-P-1 and Trp-P-2 are shown to be among the most potent transforming HCA that have been detected in food. Metabolic activation of HCA has been shown to proceed via N-hydroxylation of the exocyclic amino group. Therefore, we tested 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N(2)-OH-PhIP) the activated metabolite of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. N(2)-OH-PhIP proved to be one of the most powerful compounds with transforming activity observable at a concentration as low as 30 nM. Since 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the most abundant HCA formed in fried and grilled food and N-hydroxylation appears to be the predominant pathway of human metabolism, these data support the hypothesis that HCA are involved in the aetiology of human cancer.

Topics: Amines; Animals; Carbolines; Cell Transformation, Neoplastic; Cells, Cultured; Cooking; Heterocyclic Compounds; Imidazoles; Liver; Mice; Mice, Inbred C57BL; Mutagens; Pyridines

Three recombinant human P450 enzymes, forms 1A1, 1A2, and 1B1, were coexpressed with NADPH-cytochrome P450 reductase in an E. coli lacZ strain suitable for detection of the mutagenicity of heterocyclic and aromatic amines. The resulting strains expressed the recombinant P450 holoenzymes at high levels. MeIQ (2-amino-3,4-dimethylimidazo[4,5-f]quinoline) was activated effectively by P450 1A2, weakly by P450 1A1, and not detectably by P450 1B1. MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline) and Trp-P-2 (3-amino-1-methyl-5H-pyrido[4,3-b]indole) were activated by all three enzymes, with form 1A2 the most effective. These strains facilitate analysis of the substrate specificity of human P450 forms that participate in the metabolic activation of carcinogens.

Topics: Animals; Aryl Hydrocarbon Hydroxylases; Biotransformation; Carbolines; Catalysis; Cell Transformation, Neoplastic; COS Cells; Cytochrome P-450 CYP1A1; Cytochrome P-450 CYP1A2; Cytochrome P-450 CYP1B1; Cytochrome P-450 Enzyme System; Escherichia coli; Lac Operon; Quinolines; Quinoxalines; Substrate Specificity

Results from in vivo and in vitro studies showing that antioxidants may act as anticarcinogens support the role of active oxygen in carcinogenesis and provide impetus for exploring the functions of dietary antioxidants in cancer prevention by using in vitro models. We examined the single and combined effects of selenium, a component of glutathione peroxidase, and vitamin E, a known antioxidant, on cell transformation induced in C3H/10T-1/2 cells by x-rays, benzo[a]pyrene, or tryptophan pyrolysate and on the levels of cellular scavenging systems and peroxide destruction. Incubation of C3H/10T-1/2 cells with 2.5 microM Na2SeO3 (selenium) or with 7 microM alpha-tocopherol succinate (vitamin E) 24 hr prior to exposure to x-rays or the chemical carcinogens resulted in an inhibition of transformation by each of the antioxidants with an additive-inhibitory action when the two nutrients were combined. Cellular pretreatment with selenium resulted in increased levels of cellular glutathione peroxidase, catalase, and nonprotein thiols (glutathione) and in an enhanced destruction of peroxide. Cells pretreated with vitamin E did not show these biochemical effects, and the combined pretreatment with vitamin E and selenium did not augment the effect of selenium on these parameters. The results support our earlier studies showing that free radical-mediated events play a role in radiation and chemically induced transformation. They indicate that selenium and vitamin E act alone and in additive fashion as radioprotecting and chemopreventing agents. The results further suggest that selenium confers protection in part by inducing or activating cellular free-radical scavenging systems and by enhancing peroxide breakdown while vitamin E appears to confer its protection by an alternate complementary mechanism.

Topics: Animals; Benzo(a)pyrene; Carbolines; Catalase; Cell Transformation, Neoplastic; Cells, Cultured; Glutathione; Glutathione Peroxidase; Glutathione Transferase; Mice; Peroxides; Selenium; Vitamin E; X-Rays

Short term cultures of golden hamster embryo cells were exposed to X-irradiation and/or to 3-amino-1-methyl-5H-pyrido[4,3,-b]indole (Trp-P-2), a pyrolysis product of GL-tryptophan. Oncogenic transformation was scored following treatment with radiation and the pyrolysate, alone or in combination. Pre-treatment of the cells with 50 rad or 150 rad and subsequent exposure to 0.5 microgram/ml Trp-P-2, resulted in a higher transformation frequency as compared to that observed following exposure to the single agents. The enhanced frequency was related to the absorbed dose of radiation. The data suggest a synergistic interaction between X-rays and the pyrolysis product in their oncogenic action.

Topics: Animals; Carbolines; Carcinogens; Cell Transformation, Neoplastic; Cells, Cultured; Cricetinae; Indoles; Mesocricetus; Neoplasms, Radiation-Induced; Radiation, Ionizing; X-Rays