An evaluation of the mutagenicity, metabolism, and DNA adduct formation of 5-nitrobenzo [b] naphtho [2,1-d] thiophene

L. C. King, M. J. Kohan, L. Brooks, G. B. Nelson, J. A. Ross, J. Allison, L. Adams, D. Desai, S. Amin, W. Padgett, G. R. Lambert, A. M. Richard, S. Nesnow

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Abstract

Thioarenes, sulfur-containing polycyclic aromatic compounds, are environmental contaminants suspected of posing human health risks. In this study, 5-nitrobenzo[b]naphtho[2,1-d]-thiophene (5-nitro-BNT), a nitrated-thioarene, was examined for its mutagenicity, metabolism and subsequent formation of DNA adducts. 5-Nitro-BNT was weakly mutagenic in Salmonella typhimurium strains TA98 and TA100 without Aroclor-1254-induced rat liver S9 (S9), and its activity was increased in the presence of S9. Anaerobic metabolism of 5-nitro-BNT by S9 or xanthine oxidase (XO) produced one major metabolite, identified as 5-amino-BNT by NMR, MS, and UV spectroscopy and by comparison with an authentic standard. Aerobic S9 metabolism of 5-nitro-BNT produced a major metabolite, identified as trans-9,10-dihydroxy-9,10-dihydro-5-nitro-BNT (5-nitro-BNT-9,10-diol). Also present was a minor amount of 5-amino-BNT and trans-9,10-dihydroxy-9,10-dihydro-5-amino-BNT (5-amino-BNT-9,10-diol). DNA adduct analyses were performed using the 32P-postlabeling assay and reversed-phase HPLC. Three major XO-derived calf thymus DNA adducts were detected. On the basis of their chromatographic mobilities, two adducts were identified as reaction products of 5-nitro-BNT with 2′-deoxyguanosine and one adduct with 2′-deoxyadenosine. Incorporation of allopurinol (a specific XO inhibitor) in the incubation mixture resulted in loss of all three adducts, confirming enzymatic mediation by XO. Aerobic S9 activation of 5-nitro-BNT with calf thymus DNA produced three adducts. On the basis of their chromatographic mobilities, two were identified as reaction products of 5-nitro-BNT with 2′-deoxyguanosine and one with 2′-deoxyadenosine. Incorporation of 1-aminobenzotriazole (a P450 inhibitor) in the incubation mixture resulted in a loss of these adducts, confirming enzymatic mediation by P450. Aerobic S9-catalyzed metabolism of 5-nitro-BNT-9,10-diol produced the same DNA adducts as observed with 5-nitro-BNT. Aerobic S9-catalyzed metabolism of 5-amino-BNT-9,10-diol produced the same deoxyadenosine-derived DNA adducts as observed with 5-nitro-BNT and 5-nitro-BNT-9,10-diol. These results provide additional information that both ring oxidation and nitroreduction are involved in the metabolism, DNA adduct formation and mutagenicity of 5-nitro-BNT.

Original languageEnglish (US)
Pages (from-to)661-671
Number of pages11
JournalChemical research in toxicology
Volume14
Issue number6
DOIs
StatePublished - Jan 1 2001

All Science Journal Classification (ASJC) codes

  • Toxicology

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    King, L. C., Kohan, M. J., Brooks, L., Nelson, G. B., Ross, J. A., Allison, J., Adams, L., Desai, D., Amin, S., Padgett, W., Lambert, G. R., Richard, A. M., & Nesnow, S. (2001). An evaluation of the mutagenicity, metabolism, and DNA adduct formation of 5-nitrobenzo [b] naphtho [2,1-d] thiophene. Chemical research in toxicology, 14(6), 661-671. https://doi.org/10.1021/tx0001373