Metabolism and Mutagenicity of Dinitropyrenes: Effect of Chronic Ethanol Ingestion and Aroclor 1254 Pretreatment.

The nitroreduction of three potently mutagenic dinitropyrene (DNP) isomers by liver cytosol from Aroclor-1254-pretreated rats was studied. NAD(P)H-quinone oxidoreductase (NQOR) is increased 12- to 24-fold by this treatment and resulted in up to 5-fold induction of cytosolic DNP-nitroreductase as compared to chow-fed controls. Upon purification, NQOR activity towards menadione coeluted with C-nitroso- and 1,6-DNP nitroreductase activity. Purified NQOR catalyzed NAD(P)H-dependent reduction of all DNP, displayed the same isomer specificity as did cytosol and increased the mutagenicity of all DNP in the Ames assay up to 3-fold. In TA98NR, a strain deficient in nitroreductase, only the mutagenicity of 1,3-DNP was markedly lowered. 1,6- and 1,8-DNP were activated to approximately equal extents by NQOR in TA98NR and TA98. NQOR potently increased the mutagenicity of 1,3-DNP in TA98NR to levels comparable to that obtained in TA98. NQOR increased the mutagenicity of 1,6- but not 1,3- and 1,8-DNP to mutagenic intermediates in TA98/1,8-DNP$\sb6$, a strain deficient in O-acetyltransferase activity. Ethanol ingestion caused a 3- to 5-fold increase in NQOR, but only a slight increase in DNP-nitroreductase activity. NQOR induction however, caused $\sim$ 2-fold increases in the NAD(P)H-dependent rate of reduction of p-nitrosophenol. Inhibitor studies indicate a cofactor-specific participation of NQOR and alcohol dehydrogenase in the cytosolic C-nitrosoreductase activity. The genotoxicity of DNP towards S. typhimurium TA1535/pSK1002 was studied in the presence of cytosolic and microsomal fractions from ethanol- and pair-fed rats. Microsomes attenuated the genotoxicity of 1,3-, 1,6- and 1,8-DNP in the umu-test, the order being 1,3- $\u3e$ 1,6- $\u3e$ 1,8-DNP. Cytosol was deactivating 1,8-DNP most strongly, less with 1,6-DNP and activated 1,3-DNP. AM1 calculations for DNP and their reduced derivatives indicate that the isomer selectivity displayed in the bioactivation of DNP is not solely based on chemical grounds