title: Flavoenzyme-catalyzed redox cycling of hydroxylamino- and amino metabolites of 2,4,6-trinitrotoluene: implications for their cytotoxicity.
abstract: 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.
authors.affiliation: Institute of Biochemistry, Sector of Xenobiotics Biochemistry, MokslininkuSt. 12, Vilnius 2600, Lithuania.
authors.forename: Jonas
authors.initials: J
authors.lastname: Sarlauskas
authors.forename: Ausra
authors.initials: A
authors.lastname: Nemeikaite-Ceniene
authors.forename: Zilvinas
authors.initials: Z
authors.lastname: Anusevicius
authors.forename: Lina
authors.initials: L
authors.lastname: Miseviciene
authors.forename: Marta Martinez
authors.initials: MM
authors.lastname: Julvez
authors.forename: Milagros
authors.initials: M
authors.lastname: Medina
authors.forename: Carlos
authors.initials: C
authors.lastname: Gomez-Moreno
authors.forename: Narimantas
authors.initials: N
authors.lastname: Cenas
mesh_terms: D000588:Amines / Q000737:chemistry* / Q000493:pharmacokinetics; D000818:Animals; D002384:Catalysis; D002417:Cattle; D002460:Cell Line; D064420:Drug-Related Side Effects and Adverse Reactions; D044927:Electron-Transferring Flavoproteins / Q000737:chemistry* / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D014303:Trinitrotoluene / Q000737:chemistry* / Q000493:pharmacokinetics / Q000633:toxicity*
chemical_list: D000588:Amines; D044927:Electron-Transferring Flavoproteins; D014303:Trinitrotoluene; D010088:Oxidoreductases