Mutagenicity of nitrosamines in enhanced Ames tests: A review of strain, metabolism, and solvent effects.

We review the results of the 'Enhanced' Ames Test (EAT) for assessment of the mutagenicity of N-nitrosamines, integrating the data from six key studies. High (>98 %) purities of the nitrosamines were confirmed by LC-MS and glutathione co-incubation to avoid false-positive results. The most sensitive strains were Salmonella typhimurium TA1535 and Escherichia coli WP2 uvrA (pKM101), which detect primarily GC→AT transitions, typically induced by O6-alkylguanine DNA adducts. Strain TA100 gave variable responses and strains TA98 and TA1537 gave negative results. Bioactivation by hamster liver S9 (particularly at the 30 % v/v level), rich in cytochrome P450 (CYP) forms 2E1 and 2C19, was more effective than rat liver S9. N-Methyl-2-pyrrolidone and ethyl acetate inhibited metabolic activation but DMSO (up to 1.6 % v/v) and water did not. These findings support the use of a tiered EAT strategy with TA1535, WP2 uvrA, hamster S9, and validated solvents, in agreement with published guidelines, for the robust risk assessment of nitrosamine mutagenicity.