BACTERIAL PHOTOMUTAGENICITY TESTING - DISTINCTION BETWEEN DIRECT, ENZYME-MEDIATED AND LIGHT-INDUCED EVENTS

A bacterial photomutagenicity test system has been established accordi ng to a predetermined protocol using a light source emitting multiple wave lengths, including W-A and UV-B, and the tester strains used for standard bacterial mutagenicity testing. 8-Methoxypsoralen (8-MOP) was used as a photomutagenic positive control showing no mutagenicity in the absence of light and borderline (Salmonella typhimurium TA1537) or clear (Salmonella typhimurium TA102 and Escherichia coli WP2) mutagen ic effects in the presence of light. Using the same experimental condi tions, the UV filters p-aminobenzoic acid (PABA), octyl dimethyl PABA (Eusolex(R) 6007), and 4-methylbenzylidene camphor (Eusolex(R) 6300) w ere non-mutagenic (in the absence of light) and non-photomutagenic (in the presence of light). Dihydroxyacetone (DHA), used as an active ing redient in self-tanning lotions, slightly increased the number of reve rtants in Salmonella typhimurium TA100 and TA102 in the absence of lig ht. However, the relevance of these effects is equivocal, since they o ccurred at very high, cytotoxic concentrations (5000 mu g/plate). Furt hermore, these increases were not potentiated by light, thus demonstra ting the non-photomutagenicity of DHA. In contrast, 7,12-dimethylbenz[ a]anthracene (DMBA), which is non-mutagenic per se and is activated by external metabolizing systems (e.g., S9-mix) in the absence of light, was clearly mutagenic in Salmonella typhimurium TA98 and TA1537 in th e presence of light (and the absence of S9-mix). Although the photomut agenic potency of DMBA, on a molar basis, was certainly lower than tha t of 8-MOP, the absolute mutagenic effects of DMBA in the respective b acterial strains were in a similar range under either S9-mix or photoa ctivation conditions. The strain specificity of the mutagenic effects were, however, different for either enzyme- or light-mediated mutageni city. This indicates that different reactive intermediates are respons ible for the mutagenicity in the tests using the two different activat ion systems. These results further suggest to use DMBA as a positive p hotomutagenic control compound alternatively to 8-MOP, since the latte r is non- or only weakly photomutagenic in Salmonella typhimurium TA98 and TA1537. Furthermore, the usefulness and application of this photo mutagenicity test system could be demonstrated for the testing of diff erent photoabsorbing chemicals and cosmetic ingredients.