Human aldo-keto reductases (AKR1C1-AKR1C3) increase the mutagenicity of environmental nitroarenes in the mammalian HPRT forward gene mutagenicity assay

The diesel exhaust constituent 1-nitropyrene (1-NP) is classified as a probable human carcinogen and other constituents 1,8-dinitropyrene (1,8-DNP) and 3-nitrobenzanthrone (3-NBA) are classified as possible human carcinogens by the International Agency for Research on Cancer. These nitroarenes are activated by nitroreduction via nitroso- and hydroxylamino- intermediates on route to the corresponding amine product(s). Two types of DNA adduct can occur in this sequence. First, the hydroxylamino- intermediate can undergo sulphonation or acetylation giving rise to a strong leaving group so that stable covalent adducts can form. Second, back oxidation of these air sensitive intermediates can give rise to reactive oxygen species and nitrogen species (ROS, RNS) so that oxidatively damaged bases can form. Human aldo-keto reductases AKR1C1, AKR1C2 and AKR1C3 play prominent roles in the nitroreduction of these nitroarenes in human lung cell lines. We now report that when AKR1C1-AKR1C3 are transfected into V79–4 cells we observe a significant increase in HPRT gene mutation. The mutation is dependent on AKR1C enzyme activity since isoform specific inhibitors reduced the number of mutant colonies formed. ROS scavengers reduced the number of mutant colonies formed with 1-NP, 1–8-DNP and 3-NBA in the presence of transfected AKR1C1. Ethyl gallate and the superoxide dismutase mimetic (MnTBAP) reduced the number of mutant colonies formed. Nitric oxide scavengers, 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazoyl-1-oxy-3-oxide and uric acid, also reduced the number of mutant colonies formed. Our results suggest that both 8-oxo-dG and 8-nitro-dG lesions may contribute to the mutation observed. Since AKR1C1-AKR1C3 are potently induced by NRF2, its activation might increase the mutagenicity of nitroarenes in the context of diesel exhaust exposure.