Mutagenicity and antimutagenicity of Thai medicinal plants.

Crude extracts and partially purified as well as purified fractions were prepared from three Thai medicinal plants, namely, Acanthus ebracteatus Vahl, Plumbago indica Linn, and Rhinacanthus nasuthus Kurz, and then tested for their mutagenic and antimutagenic potentials using the Salmonella/microsome mutagenicity test. All fractions tested were not mutagenic toward either strain TA98 or TA100 whether tested in the presence or absence of S-9 mix. Interestingly, however, various fractions--especially those extracted by organic solvents such as petroleum ether, hexane, and chloroform, as well as some purified compounds from these plants--could strongly inhibit the mutagenicity of aflatoxin B1 (AFB1), an indirect mutagen, when tested in the presence of S-9 mix but not that of 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), which does not require metabolic activation for its mutagenicity. Furthermore, these fractions could markedly inhibit the activity of rat liver aniline hydroxylase, which is one of the cytochrome-P450-mediated reactions. These results therefore suggest that these Thai medicinal plants contain an antimutagen(s) which inhibits chemical mutagenesis by inhibiting the enzyme activities necessary for activation of indirect mutagens/carcinogens. Identification as well as anticarcinogenicity of purified compounds of these plants are being investigated in our laboratory.