| Recent studies suggest that exposure to agrochemicals may contribute to the development of idiopathic Parkinson's disease. The Mn-ethylene-bis-dithiocarbamate (EBDC) fungicide, maneb (MB), inhibits complex III of the electron transport chain and has been implicated in selective dopaminergic (DAergic) neurodegeneration. In the present study, we examined the potential neurotoxicity of mancozeb (MZ), a Mn-Zn-EBDC fungicide structurally similar to MB, and its primary metabolite, ethylene thiourea (ETU), using an in vitro rat primary mesencephalic cell culture model. We hypothesized that MZ, like MB, is toxic to DAergic neurons and inhibits mitochondrial respiration, resulting in metabolic stress, ATP loss, and ultimately cell death. Findings from this study show that acute exposure to MZ and MB, but not ETU, produce equipotent toxic effects, including decreased uptake of dopamine and GABA and mitochondrial dysfunction via inhibition and uncoupling of the electron transport chain, in DAergic and GABAergic neurons. Moreover, both the organic and Mn metal components of the fungicides were found to contribute to toxicity. In addition to mitochondrial perturbations, MZ and MB produced robust ROS levels via redox cycling with extracellular and intracellular oxidases, as measured by H2O2 formation inside and outside the cell. More specifically, it was found that NADPH oxidase, localized in microglia and in neurons, plays a modest role in MZ-induced ROS generation. In correlation with these data, MZ was quantified in biological samples of mesencephalic cells via electron spray ioniziation/ion trap mass spectrometry. Our findings indicate that a small amount of a MZ organometallic moiety enters the cell and remains at detectable levels for at least 14 h, during which time it can interact with intracellular components and elicit toxic effects. Moreover, a large amount of MZ remains outside the cell where it can interact with extracellular constituents to generate ROS. Overall, these data suggest that the primary mechanism of MZ neurotoxicity is ROS generation whereas perturbations in mitochondrial respiration are most likely secondary effects that occur as a result of oxidative stress. Because EBDC exposure has been linked to neuronal toxicity and is of environmental concern, such data are essential in understanding the health nsks associated with pesticide use and/or exposure. |
