A number of epidemiological studies have demonstrated a strong association between the incidence of
Parkinson's disease and
pesticide exposure. Earlier it was demonstrated that exposure to the pesticides
endosulfan and
zineb, alone and in combination, caused neurodegeneration in vivo. It was hypothesized that these pesticides cause neurotoxicity, in part, by enhancing apoptotic cell death. SH-SY5Y human
neuroblastoma cells, which retain a catecholaminergic phenotype, were exposed to
endosulfan,
zineb or a combination of these chemicals, in vitro. For mixture studies, concentrations of pesticides (100 microM each) were chosen based on LC(25) (lethal concentration) that would result in minimum cell death. Exposure to a mixture of pesticides exhibited significantly (P < or = 0.05) higher toxicity than each one alone. Both pesticides were found to cause apoptotic cell death that was concentration (50-400 microM) dependent. A flow cytometric (7-aminoactinomycin D) assay was used to distinguish live, early apoptotic and late apoptotic/necrotic populations. Exposure to mixtures of the pesticides enhanced both early apoptosis and late apoptosis/
necrosis compared with either chemical alone. Visual evaluation using
a DNA ladder assay and a fluorescence
Annexin V/PI assay confirmed the contribution of both apoptotic and necrotic processes. These findings suggest that the cytotoxicity of
endosulfan and
zineb, both individually and in mixtures, is associated with the occurrence of early and late apoptotic/necrotic processes in SH-SY5Y human
neuroblastoma cells and support the contention that
pesticide-induced neuronal cell death leading to
neurodegenerative disease may, at least in part, be associated with early and late apoptosis of dopaminergic neurons.