Effects of model organophosphorous pesticides on DNA damage and proliferation of HepG2 cells.

Organophosphorous compounds (OPs) are commonly used pesticides. The primary mechanism of OP toxicity is the inhibition of acetylcholine esterase in the nervous system leading to a variety of acute and chronic effects. Recent studies have revealed several other targets of OPs that disturb noncholinergic biological systems. We investigated whether low concentrations of model OPs-methyl parathion (PT), methyl paraoxon (PO), and dimefox (DF)-induce DNA damage and/or affect cell proliferation in human hepatoma HepG2 cells. Genotoxicity of OPs was evaluated using the comet assay. The effect on cell proliferation was tested using the MTT assay and proliferation marker Ki-67 immunocytochemistry. The effects of OPs on mRNA expression of the DNA damage responsivegenes p53, p21, GADD45alpha, and MDM2 were determined using qRT-PCR. PT induced DNA damage at lower concentrations (1 microg/mL) than PO (100 microg/mL), whereas DF did not induce DNA damage. PT and PO caused a reduction of cell proliferation at their highest concentrations (100 microg/mL), while DF increased cell proliferation at all concentrations used (0.01-100 microg/mL). PT and PO upregulated expression of DNA damage responsive genes, while DF upregulated expression of p53, downregulated expression of p21, and had no effect on the expression of MDM2 and GADD45alpha. We conclude that PT and PO are genotoxic, while DF shows mitogenic activity. An important finding of this study is that PT had higher genotoxic potential than PO, which warrants for further investigations to correctly evaluate the hazards of exposure to these chemicals. (c) 2008 Wiley-Liss, Inc.