Project: Research project

Project Details


Chemicals are generally assumed to initiate carcinogenesis by binding to
cellular DNA, and thereby turning a critical gene(s) on or off. The
binding of nitrosamines is thought to be mediated by an unstable
Alpha-hydroxynitrosamine metabolite, which rapidly decomposes to the final
alkylating intermediate. We propose to study the metabolism of several
nitrosamines whose mechanism of action is not understood and for which the
alkylation pathway is not documented and perhaps not totally responsible
for the genotoxicity of these carcinogenic compounds. We are suggesting
that the cytochrome P-450 and NADPH-cytochrome-P-450-reductase dependent
denitrosation process, which has been historically considered a
detoxification pathway, may play a role in the genotoxicity of
nitrosamines. This hypothesis is based on the formation of nitric oxide in
the metabolism of nitrosamines. Nitric oxide itself, or by spontaneous in
vivo oxidation, may initiate genotoxicity. Using dimethylnitrosamine,
N-nitrosopyrrolidine, N-nitrosopiperidine and N-methyl-N-phenylnitrosamine
we are proposing to determine the relative significance of denitrosation
and Alpha-hydroxylation (DNA alkylation). This will be done by studying
their metabolism under a variety of conditions and determining how their
genotoxicity is altered as measured by five indicators of toxicity. The
five indicators are: a) formation of revertant colonies (Ames assay); b)
covalent binding of the nitrosamine to DNA; c) detection of promutagenic
lesions; d) deamination of DNA bases; and e) single strand breaks, alkali
labile lesions and DNA-cross-linking as measured by alkaline elution or
DNA-unwinding/hydroxylapatite chromatography. The Alpha-acetoxy
derivatives of the four nitrosamines will be studied using the same
indicators in order to assess the contribution of Alpha-oxidation
(Alpha-hydroxylation) to the genotoxicity exhibited by the parent
nitrosamines. All of the above studies will be done using S. typhimurium
TA1535 and/or TA102 as the DNA-containing substrate. Results of these
studies will allow us to relate a specific route of metabolism and specific
metabolites to particular indicators of genotoxicity. These relationships
and correlations should provide insight into the roles of dealkylation and
denitrosation in the carcinogenic activation of nitrosamines.
Effective start/end date1/1/8512/31/92


  • National Institutes of Health


  • Medicine(all)

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