Human glutathione S-transferase-expressing Salmonella typhimurium tester strains to study the activation/detoxification of mutagenic compounds: studies with halogenated compounds, aromatic amines and aflatoxin B1.

Abstract

We have developed Salmonella typhimurium strains expressing human glutathione S-transferases (GSTs) to establish the role of these enzymes in chemical activation and deactivation. Alpha and pi class GSTs, GSTA1-1 and GSTP1-1, were expressed in Salmonella TA100 using a regulatable tac promoter expression system. The ability of these GST to modulate the mutagenicity of a range of mutagens including ethylene dibromide, ethylene dichloride and methylene dichloride was then investigated. Ethylene dibromide, ethylene dichloride and methylene dichloride were directly mutagenic in the control TA100 strain. The mutagenicity of ethylene dibromide and ethylene dichloride was increased in cells expressing GSTA1-1, but not in cells expressing GSTP1-1. In contrast, methylene dichloride mutagenicity was unaffected by the presence of either GST. The mutagenicity of 2-aminofluorene, was not altered by the presence of either GST isozyme, while that of N-hydroxy-2-acetylaminofluorene was slightly reduced with both isozymes. The mutagenicity of aflatoxin B1 (AFB1) was marginally decreased in strains expressing GSTP1-1. When GSTA1-1 expression was maximally induced, however, a more pronounced reduction was observed suggesting a role for GSTA1-1 in AFB1 deactivation. The tester strains described here should be valuable in establishing the specificity of human GST isozymes towards chemical toxins and carcinogens, especially for compounds whose reactive intermediates are short lived.