2,6-and 3,5-dimethylaniline-induced mutagenesis in Chinese hamster ovary cells expressing human cytochrome P450 1A2 and sulfotransferase

Aim: The aim of this study was to test the hypothesis that human cytochrome P450 1A2 (CYP1A2) and sulfotransferase (SULT) contribute to the phase I and II bioactivation of 2,6-dimethylaniline (2,6-DMA) and 3,5-dimethylaniline (3,5-DMA) in affecting the incidence of genotoxicity.Methodology: 5P3H1 cells carrying cytochrome P450 1A2 (CYP1A2) and SULT cells were treated with various concentrations of 2,6-and 3,5-DMA for 48 hr or their N-hydroxyl and aminophenol metabolites for 1 hr in the absence or presence of 2,6-Dichloro-4-nitrophenol (DCNP). Cell lethality was assayed by trypan blue exclusion and induced mutagenesis of adenine phosphoribosyl transferase (aprt) gene was also evaluated. Results: A significant dose-dependent increase in cytotoxicity and mutant fraction was observed after treatment with 2,6- and 3,5-DMA, and their metabolites; N-hydroxy and aminophenol metabolites are more potent than the parent compounds. Addition of sulfotransferase inhibitor DCNP decreased the cytotoxic and mutagenic effects of 2,6- and 3,5-DMA, and their metabolites in a dose-dependent manner. Interpretation: This research indicate that 2,6 and 3,5-DMA are mutagenic, and their toxicity in model systems depend on metabolic activation. This activation is mediated by CYP1A2 and SULT enzymes

The role of nucleotide excision repair on 2,6- and 3,5-dimethylaniline-induced genotoxicity

Aim: To examine the possible role of nucleotide excision repair (NER) in affecting the ultimate mutagenic potency of 2,6- and 3,5-dimethylaniline (DMA) and their metabolites.Methodology: Two cell lines, nucleotide excision repair (NER)-proficient AA8 and deficient UV5 cells were treated with 50, 100, 250, 500 and 1000 μM of 2,6- and 3,5-DMA for 48 hr or their N-hydroxyl and aminophenol metabolites for 1 hr. Cell survival was determined by trypan blue exclusion assay, and 8-azaadenine-resistant mutants at adenine phosphoribosyltransferase (aprt) gene locus were evaluated.Results: A dose-dependent increase in cytotoxicity and mutant fraction was observed in AA8 and UV5 cells, treated with 2,6- and 3,5-DMA and their metabolites, but showed considerable variation in potency; N-hydroxyl and aminophenol metabolites of 2,6- and 3,5-DMA in serum-free α-minimal essential medium (MEM) having the highest potency, and 2,6- and 3,5-DMA in regular MEM at least. Repair-deficient UV5 cells were more sensitive to cytotoxic and mutagenic action than repair-proficient AA8 cells. Interpretation: These findings suggest that 2,6- and 3,5-DMA-induced DNA damage response may trigger cytotoxicity and mutagenicity when not completely repaired