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DNA adduct formation by alachlor metabolites
M A Brown1, E C Kimmel, J E Casida
1Department of Entomological Sciences, University of California, Berkeley 94720.
Life Sciences
|January 1, 1988
Summary
Alachlor's potential carcinogenicity was investigated by examining DNA adduct formation from the herbicide and its metabolites. The N-CH2OCH2OH metabolite or formaldehyde were identified as likely proximate carcinogens responsible for DNA damage.
Area of Science:
- Environmental Chemistry
- Toxicology
- Molecular Biology
Background:
- Alachlor is a widely used herbicide, and understanding its carcinogenicity is crucial for public health.
- DNA adduct formation is a key mechanism in chemical carcinogenesis.
- Identifying the specific metabolites responsible for DNA damage is essential for risk assessment.
Purpose of the Study:
- To determine the extent of DNA adduct formation by alachlor and its metabolites.
- To identify the causal agents in alachlor's carcinogenicity.
- To compare the reactivity of different alachlor metabolites in forming DNA adducts.
Main Methods:
- In vitro and in vivo studies using radiolabeled alachlor and its metabolites ([14C-phenyl]alachlor, [14C-phenyl]2-chloro-N-(2,6-diethylphenyl)acetamide (CDEPA), [14C-phenyl]2,6-diethylaniline (DEA), and [14C-methoxy]alachlor).
- Incubation with calf thymus DNA in the presence of activating systems (horseradish peroxidase/hydrogen peroxide, mouse liver microsomes/NADPH).
- Analysis of DNA, protein, and hemoglobin labeling in vivo following intraperitoneal administration to mice.
Main Results:
- 2,6-diethylaniline (DEA) was activated by horseradish peroxidase and hydrogen peroxide to form DNA adducts, likely via a 2,6-diethylnitrosobenzene intermediate.
- Mouse liver microsomes and NADPH enhanced DNA binding from all labeled preparations, with [14C-methoxy]alachlor showing 4-fold higher labeling compared to [14C-phenyl]alachlor.
- In vivo studies in mice confirmed higher labeling of liver DNA, protein, and hemoglobin with [14C-methoxy]alachlor, and identified N-CH2OCH2OH metabolite or formaldehyde as potential reactive intermediates.
Conclusions:
- The N-CH2OCH2OH metabolite or formaldehyde are implicated as reactive intermediates in DNA adduct formation by alachlor.
- These findings suggest that formaldehyde or the N-CH2OCH2OH metabolite are candidate proximate carcinogens contributing to alachlor's toxicity.
- Differential labeling observed with the methoxy versus phenyl radiolabel highlights metabolic pathways and reactive species involved in alachlor-induced DNA damage.