Nitrite-induced mutations in a forward mutation assay: influence of nitrite concentration and pH.

The mutagenicity of sodium nitrite at three pHs (7.4, 6.4 and 5.4) has been investigated by treating a shuttle vector plasmid in vitro and assaying for mutations within the supF target gene following replication of the damaged plasmid in human Ad293 cells. Mutation frequency increased with increasing nitrite concentration and decreasing pH. Among treatments from which a significant number of mutants could be collected, the most commonly induced mutations were GC-->AT transitions (44-56% of total mutations), followed by GC-->TA transversions (24-30%). The types of mutations induced at different nitrite concentrations and different pH's were similar, though some differences in their distribution throughout the supF gene were noted. These results provide information on the types of mutations that may be produced following the processing of nitrite-induced DNA damage in human cells.