In vitro and in vivo generation of reactive oxygen species, DNA damage and lactate dehydrogenase leakage by selected pesticides

Abstract

Reactive oxygen species may be involved in the toxicity of various pesticides and we have, therefore, examined the in vivo effects of structurally dissimilar polyhalogenated cyclic hydrocarbons (PCH), such as endrin and chlordane, chlorinated acetamide herbicides (CAH), such as alachlor, and organophosphate pesticides (OPS), such as chlorpyrifos and fenthion, on the production of hepatic and brain lipid peroxidation and DNA-single strand breaks (SSB), two indices of oxidative stress and oxidative tissue damage. The selected pesticides were administered p.o. to female Sprague-Dawley rats in two 0.25 LD 50 doses at 0 h and 21 h and killed at 24 h. In a parallel set of experiments, we have determined the in vitro effects of these pesticides on the DNA-SSB and enhanced lactate dehydrogenase leakage (LDH) from neuroactive PC-12 cells in culture. In vitro production of reactive oxygen species by these pesticides was also assessed by determining the enhanced chemiluminescence responses of hepatic and brain homogenates. Following treatment of rats with endrin, chlordane, alachlor, chlorpyrifos and fenthion, increases of 2.8-, 3.0-, 4.2-, 4.3- and 4.8-fold were observed in hepatic lipid peroxidation, respectively, while at these same doses, increases in lipid peroxidation of 2.4-, 2.1-, 3.6-, 4.6- and 5.3-fold, respectively, were observed in brain homogenates. Increases of 4.4-, 3.9-, 1.6-, 3.0-and 3.5-fold were observed in hepatic DNA-SSB following treatment of the rats with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively, while at these same doses, increases of 1.9-, 1.7-, 2.2-, 1.4-, 1.4-fold, respectively, were observed in brain nuclear DNA-SSB. Following in vitro incubation of hepatic and brain tissues with 1 nmol/ml of each of the five pesticides, maximum increases in chemiluminescence occurred within 4–7 min of incubation and persisted for over 10 min. Increases of 3.0-, 2.7-, 3.6-, 4.9- and 4.4-fold were observed in chemiluminescence following in vitro incubation of the liver homogenates with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively, while increases of 1.7-, 1.8-, 2.0-, 3.4- and 3.7- fold, respectively, were observed in the brain homogenates. Increases of 2.2-, 2.3-, 2.9-, 2.9- and 3.4-fold were observed in the chemiluminescence responses in the liver homogenates of the animals treated with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively, while increases of 1.8-, 2.0-, 3.2-, 2.9- and 2.4-fold, respectively, were observed in the brain homogenates. Cultured neuroactive PC-12 cells were incubated with the pesticides and the release of the enzyme lactate dehydrogenase (LDH) into the media as an indicator of cellular damage and cytotoxicity was examined. Maximal release of LDH from cultured PC-12 cells was observed at 100 nM concentrations of the pesticides. Increases of 2.3-, 2.5-, 2.8-, 3.1 and 3.4-fold were observed in LDH leakage following incubation of the PC-12 cells with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively. Following incubation of the cultured PC-12 cells with 100 nM concentrations of these same pesticides, increases in DNA-SSB of 2.5-, 2.2-, 2.1-, 2.4- and 2.5-fold, respectively, were observed. The results clearly demonstrate that these different classes of pesticides induce production of reactive oxygen species and oxidative tissue damage which may contribute to the toxic manifestations of these xenobiotics. Reactive oxygen species may serve as common mediators of programmed cell death (apoptosis) in response to many toxicants and pathological conditions.