Reductive metabolism of 1-nitropyrene accompanies deamination of cytosine

Area of Science:

• Environmental Health
• Molecular Toxicology
• Carcinogenesis

Background:

• 1-Nitropyrene (1-NP) is an environmental pollutant known for its mutagenic and tumorigenic properties.
• Nitroreduction is a primary metabolic activation pathway for 1-NP.
• Understanding the specific mutations caused by activated 1-NP is critical for assessing its health risks.

Purpose of the Study:

• To investigate the mutational specificity of reductively activated 1-nitropyrene.
• To identify the major DNA adducts formed and the types of mutations induced.
• To elucidate the role of cytosine deamination in the mutagenic mechanism.

Main Methods:

• Treatment of single-stranded M13mp18 DNA with tritium-labeled 1-nitrosopyrene and ascorbic acid to generate N-hydroxy-1-aminopyrene.
• High-performance liquid chromatography (HPLC) analysis of enzymatically digested DNA to identify tritium-labeled adducts.
• Transfection of adducted M13 DNA into Escherichia coli to assess viability and mutagenesis.
• Mutation analysis, particularly C-->T transitions, in the lacZ gene fragment.

Main Results:

• A major DNA adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene, was identified, accounting for over 95% of tritium incorporation.
• Transfection of adducted DNA resulted in a dose-dependent decrease in bacterial viability and increased mutagenesis.
• The predominant mutation observed in the absence of SOS functions was C-->T transition (48%).
• Ascorbic acid-induced nitroreduction was found to cause significant cytosine deamination, explaining the C-->T transitions.

Conclusions:

• Reductive activation of 1-nitropyrene leads to the formation of specific DNA adducts that are mutagenic.
• Cytosine deamination during nitroreduction is a key mechanism responsible for C-->T transitions induced by 1-NP metabolites.
• Mammalian nitroreductases like xanthine oxidase can catalyze this deamination process, highlighting potential in vivo relevance.