Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Gary W. Winston

Abstract

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- $>$ 1,6- $>$ 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.

Pages

218

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