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Detection of PCB adducts by the 32P-postlabeling technique
M R McLean1, L W Robertson, R C Gupta
1Department of Preventive Medicine and Environmental Health, University of Kentucky, Lexington 40536-0305, USA.
Chemical Research in Toxicology
|January 1, 1996
Summary
Lower chlorinated biphenyls can be bioactivated to genotoxic metabolites. These compounds form DNA adducts through arene oxides and quinone/semiquinone species, potentially explaining carcinogenicity.
Area of Science:
- Environmental Chemistry
- Toxicology
- Biochemistry
Background:
- Polychlorinated biphenyls (PCBs) are environmental pollutants with known carcinogenicity.
- The bioactivation pathways of lower chlorinated biphenyls (LCBs) to genotoxic metabolites are not fully understood.
Purpose of the Study:
- To investigate the bioactivation of LCBs to electrophilic metabolites using microsomal systems alone or with peroxidase.
- To identify the types of metabolites formed and their potential genotoxicity.
Main Methods:
- Incubation of monochloro- and dichlorobiphenyls with rat liver microsomes and an NADPH-regenerating system.
- Analysis of DNA adducts using 32P-postlabeling after microsomal incubation and/or subsequent oxidation with horseradish peroxidase.
- UV/vis spectroscopy to characterize quinone/semiquinone metabolite formation.
Main Results:
- LCBs formed DNA adducts via microsomal activation alone, with increased adducts after peroxidase oxidation.
- Ascorbic acid significantly inhibited the formation of major adducts in oxidized samples.
- Metabolites of 4-monochlorobiphenyl (4-MCB) exhibited UV/vis spectra characteristic of quinones.
Conclusions:
- LCBs can be bioactivated to genotoxic electrophilic metabolites, likely via arene oxides and quinone/semiquinone intermediates.
- These findings suggest LCBs may be genotoxic and contribute to the carcinogenicity of commercial PCB mixtures.
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