Flavoenzyme-catalyzed redox cycling of hydroxylamino- and amino metabolites of 2,4,6-trinitrotoluene: implications for their cytotoxicity

• DOI: 10.1016/j.abb.2004.02.043
• Publication Date: 2004-04-13T09:30:59Z
• Authors: Jonas Šarlauskas; Aušra Nemeikaite-...; Žilvinas Anusevičius; Lina Misevičien≐; Marta Martinez Ju...; Milagros Medina; Carlos Gomez-Moreno; Narimantas Č≐nas
• Keywords: 0303 health sciences; Drug-Related Side Effects and Adverse Reactions; Electron-Transferring Flavoproteins; Fibroblasts; Catalysis; Cell Line; 3. Good health; 03 medical and health sciences; Animals; Cattle; Amines; Oxidoreductases; Oxidation-Reduction; Trinitrotoluene

The toxicity of 2,4,6-trinitrotoluene (TNT), a widespread environmental contaminant, is exerted through its enzymatic redox cycling and/or covalent binding of its reduction products to proteins and DNA. In this study, we examined the possibility of another cytotoxicity mechanism of the amino- and hydroxylamino metabolites of TNT, their flavoenzyme-catalyzed redox cycling. The above compounds acted as redox-cycling substrates for single-electron transferring NADPH:cytochrome P-450 reductase (P-450R) and ferredoxin:NADP(+) reductase (FNR), as well as substrates for the two-electron transferring flavoenzymes rat liver NAD(P)H:quinone oxidoreductase (NQO1) and Enterobacter cloacae NAD(P)H:nitroreductase (NR). Their reactivity in P-450R-, FNR-, and NR-catalyzed reactions increased with an increase in their single-electron reduction potential (E(1)(7)) or the decrease in the enthalpy of free radical formation. The cytotoxicity of the amino- and hydroxylamino metabolites of TNT towards bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was partly prevented by the antioxidant N,N'-diphenyl-p-phenylene diamine and desferrioxamine, and potentiated by 1,3-bis-(2-chloroethyl)-1-nitrosourea, thus pointing to the involvement of oxidative stress. In general, their cytotoxicity increased with an increase in their electron accepting properties, or their reactivity towards the single-electron transferring FNR and P-450R. Thus, our data imply that the flavoenzyme-catalyzed redox cycling of amino and hydroxylamino metabolites of TNT may be an important factor in their cytotoxicity.