title: The parkinsonism-inducing drug 1-methyl-4-phenylpyridinium triggers intracellular dopamine oxidation. A novel mechanism of toxicity.
abstract: Uptake of the Parkinsonism-inducing toxin, 1-methyl-4-phenylpyridinium (MPP(+)), into dopaminergic terminals is thought to block Complex I activity leading to ATP loss and overproduction of reactive oxygen species (ROS). The present study indicates that MPP(+)-induced ROS formation is not mitochondrial in origin but results from intracellular dopamine (DA) oxidation. Although a mean lethal dose of MPP(+) led to ROS production in identified dopaminergic neurons, toxic doses of the Complex I inhibitor rotenone did not. Concurrent with ROS formation, MPP(+) redistributed vesicular DA to the cytoplasm prior to its extrusion from the cell by reverse transport via the DA transporter. MPP(+)-induced DA redistribution was also associated with cell death. Depleting cells of newly synthesized and/or stored DA significantly attenuated both superoxide production and cell death, whereas enhancing intracellular DA content exacerbated dopaminergic sensitivity to MPP(+). Lastly, depleting cells of DA in the presence of succinate completely abolished MPP(+)-induced cell death. Thus, MPP(+) neurotoxicity is a multi-component process involving both mitochondrial dysfunction and ROS generated by vesicular DA displacement. These results suggest that in the presence of a Complex I defect, misregulation of DA storage could lead to the loss of nigrostriatal neurons in Parkinson's disease.
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: J
authors.initials: J
authors.lastname: Lotharius
authors.forename: K L
authors.initials: KL
authors.lastname: O'Malley
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000493:pharmacokinetics* / Q000633:toxicity*; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004298:Dopamine / Q000378:metabolism*; D007700:Kinetics; D008636:Mesencephalon / Q000166:cytology; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010084:Oxidation-Reduction; D020734:Parkinsonian Disorders / Q000139:chemically induced; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012402:Rotenone / Q000494:pharmacology
chemical_list: D017382:Reactive Oxygen Species; D012402:Rotenone; D015655:1-Methyl-4-phenylpyridinium; D004298:Dopamine