indole-3-acetonitrile and 4-chloroindole

4-chloro-methoxyindole is a naturally occurring compound in Vicia faba which can easily react with nitrite to form a N-nitroso compound. In this in vitro study, the potential genotoxic effects of nitrosated 4-chloro-6-methoxyindole and its structural analogue 4-chloroindole were evaluated for the first time by using both Salmonella and Chinese hamster V79 cells. Additionally, the inhibition of gap junctional intercellular communication in V79 cells by these compounds was determined; this is a validated parameter for tumor-promoting activity. Most assays were also performed with nitrosated indole-3-acetonitrile, a naturally occurring compound in brassicas. Both nitrosated chloroindoles were highly mutagenic to Salmonella typhimurium TA100 without the need of exogenous metabolic activation and were potent inducers of Sister Chromatid Exchanges. Nitrosated indole-3-acetonitrile generated the same effects, although at much higher concentrations. Equivocal results were obtained for the nitrosated chloroindoles in a forward mutation assay using the hypoxanthine guaninephosphoribosyltransferase locus. All nitrosated indole compounds significantly inhibited gap junctional intercellular communication. These results indicate that nitrosated chloroindoles and nitrosated indole-3-acetonitrile should be considered as mutagens and agents with potential tumor-promoting capacity.

Topics: Animals; Carcinogenicity Tests; Carcinogens; Cell Communication; Cell Line; Cricetinae; Cricetulus; Indoles; Mutagenicity Tests; Mutagens; Mutation; Nitrosation; Salmonella typhimurium; Sister Chromatid Exchange

The nitrosation rates of indole-3-acetonitrile, indole-3-carbinol, indole and 4-chloroindole and the stability of their nitrosated products were investigated. Each of the nitrosated indole compounds was directly mutagenic to Salmonella typhimurium TA100 in the following order of potency: 4-chloroindole much greater than indole-3-carbinol greater than or equal to indole greater than indole-3-acetonitrile. Total N-nitroso determinations, carried out according to a modified method of Walters et al. (Analyst, Lond. 1978, 103, 1127), and Ames test results revealed that each of the indole compounds immediately formed mutagenic N-nitroso products upon nitrite treatment under acidic conditions. However, the nitrosation rates of indole and 4-chloroindole were higher than those of indole-3-acetonitrile and indole-3-carbinol. For indole-3-carbinol, indole-3-acetonitrile and indole, no change in the amount of nitrosated products was observed at increasing incubation times from about 15 up to 60 min. For 4-chloroindole the amount of nitrosated products decreased with increasing incubation times. In all cases the responses in the Ames test paralleled the amounts of nitrosated products. The stabilities of the nitrosated products of the indole compounds were investigated at pH 2 and 8. Both mutagenicity data and measurements by high-performance liquid chromatography using a photohydrolysis detector indicated that the nitrosation products of indole-3-acetonitrile, indole-3-carbinol and indole were more stable at pH 8 than at pH 2. Conversely, nitrosated 4-chloroindole was stable at pH 2 but not at pH 8. The pH 8 chromatograms showed a large nitrite peak. From this we hypothesized that the presence of free nitrite might be responsible for the stability of nitrosated indole-3-acetonitrile, indole-3-carbinol and indole at pH 8. Experiments confirmed the existence of an equilibrium between the nitrosated indole compound and the free indole compound plus nitrite.

Topics: Biotransformation; Chemical Phenomena; Chemistry; Chromatography, High Pressure Liquid; Hydrolysis; Indoles; Mutagenicity Tests; Nitrosation; Photochemistry; Salmonella typhimurium; Spectrophotometry, Ultraviolet