Genotoxicity of dichlorvos in strains of Drosophila melanogaster defective in DNA repair.

Dichlorvos (DDVP), an organophosphate pesticide, is reported to be genotoxic at high concentrations. However, the roles of DNA damage repair pathways in DDVP genotoxicity are not well characterized. To test whether pre- and post-replication pathways are involved, we measured changes in DNA migration (Comet assay) in the midgut cells of Drosophila melanogaster Oregon R+ larvae and in some mutants of pre- (mei-9, mus201, and mus207) and post- (mei-41 and mus209)replication DNA repair pathways. Insects were exposed to environmentally relevant concentrations of DDVP (up to 15ng/ml) for 48h. After insect exposure to 0.15ng/ml DDVP, we observed greater DNA damage in pre-replication repair mutants; effects on Oregon R+ and post-replication repair mutants were insignificant. In contrast, significant DNA damage was observed in the post-replication repair mutants after their exposure to 1.5 and 15ng/ml DDVP. The pre-replication repair mutant mus207 showed maximum sensitivity to DDVP, suggestive of alkylation damage to DNA. We also examined mutants (SOD- and urate-null) that are sensitive to oxidative stress and the results indicate that significant oxidative DNA damage occurs in DDVP-exposed mutants. This study suggests involvement of both pre- and post-replication repair pathways against DDVP-induced DNA damage in Drosophila, with oxidative DNA damage leading to genotoxicity.