Maneb, a widely used fungicide, has been associated with
Parkinsonism in humans. In experimental models,
maneb and its major active
element,
manganese ethylene-bis-dithiocarbamate (
Mn-EBDC) cause selective nigrostriatal neurodegeneration in mice and in rats, respectively. To investigate the mechanisms underlying this neurodegeneration, we studied the effects of
Mn-EBDC on proteasomal function, which is decreased in patients with
Parkinson's disease (PD), in a dopaminergic neuronal cell line (MES 23.5 or MES). The results demonstrated that exposure of MES cells to 6 microM
Mn-EBDC for 7 days produced not only significant neurotoxicity but also inhibition of proteasomal
chymotrypsin-like and postglutamyl
peptidase activities. Proteasomal dysfunction was accompanied by formation of cytoplasmic inclusions that were positive for
alpha-synuclein immunostaining and significantly increased
sodium dodecyl sulfate-insoluble
alpha-synuclein aggregation seen by Western blot analysis. In addition, there was a significant increase in oxidative stress, evidenced by elevated total
protein carbonyl content, in cells treated with
Mn-EBDC. Manipulation of intracellular
reduced glutathione levels with
N-acetyl-L-cysteine or L-
buthionine sulfoximine pretreatment to modulate
Mn-EBDC-mediated oxidative stress altered
Mn-EBDC-mediated neurotoxicity, proteasomal dysfunction, and
alpha-synuclein aggregation in these cells. These data suggest that neurotoxicity-induced by
Mn-EBDC is at least partially attributable to
Mn-EBDC-mediated proteasomal inhibition, and that the
proteasome may be an important target by which environmental exposure modifies the risk for developing PD in vulnerable populations.