Induction of mutagenic activity of tetracycline by synergistic action with nitrite

Synergistic mutagenicity of tetracycline(TC) and nitrite was investigated by the bacterial mutation test in the Salmonella/microsome system by using the reaction products obtained under neutral condition as well as under acidic condition (in simulated gastric juice). Results from tests using Salmonella typhimurium TA 100 disclosed a significant increase in the appearance of histidine (+) (his+) revertants by the reaction product between TC and nitrite in the presence of the rat liver-microsomal enzyme system (S9 mix), while the mutagenic potency of the reaction product of the two compounds in simulated gastric juice was extremely weak. In the process of the reaction of TC with and without nitrite in the presence of S9 mix, formaldehyde was detected, indicating the demethylation of TC by demethylase in S9. To explain the induction mechanism of the synergistic mutagenicity of TC and nitrite, it was suggested that the alkylating reaction of nitroso compound formed by nitrosation of the 4-demethylated intermediate of TC by the aid of microsomal metabolism is more important than the well known nitrosation mechanism under acidic condition such as in gastric juice in rats and in simulated gastric juice.