Dopamine toxicity involves mitochondrial complex I inhibition: implications to dopamine-related neuropsychiatric disorders D. Ben-Shachar * , R. Zuk, H. Gazawi, P. Ljubuncic Research Lab of Psychobiology, Department of Psychiatry, Bruce Rappaport Faculty of Medicine, Rambam Medical Center, Technion ITT, P.O. Box 9649, Haifa, Israel Received 20 November 2003; accepted 9 February 2004 Abstract Dopamine, which is suggested as a prominent etiological factor in several neuropsychiatric disorders such as Parkinson’s disease and schizophrenia, demonstrates neurotoxic properties. In such dopamine-related diseases mitochondrial dysfunction has been reported. Dopamine oxidized metabolites were shown to inhibit the mitochondrial respiratory system both in vivo and in vitro. In the present study, we suggest an additional mechanism for dopamine toxicity, which involves mitochondrial complex I inhibition by dopamine. In human neuroblastoma SH-SY5Y cells dopamine induced a reduction in ATP concentrations, which was negatively correlated to intracellular dopamine levels (r ¼0:96, P ¼ 0:012), and was already evident at non-toxic dopamine doses. In disrupted mitochondria dopamine inhibited complex I activity with IC 50 ¼ 11:87  1:45 mM or 8:12  0:75 mM in the presence of CoQ or ferricyanide, respectively, with no effect on complexes IVand V activities. The catechol moiety, but not the amine group, of dopamine is essential for complex I inhibition, as is indicated by comparing the inhibitory potential of functionally and structurally dopamine-related compounds. In line with the latter is the finding that chelatable FeCl 2 prevented dopamine-induced inhibition of complex I. Monoamine oxidase A and B inhibitors, as well as the antioxidant butylated hydroxytoluene (BHT), did not prevent dopamine-induced inhibition, suggesting that dopamine oxidation was not involved in this process. The present study suggests that dopamine toxicity involves, or is initiated by, its interaction with the mitochondrial oxidative phosphorylation system. We further hypothesize that this interaction between dopamine and mitochondria is associated with mitochondrial dysfunction observed in dopamine-related neuropsychiatric disorders, such as schizophrenia and Parkinson’s disease. # 2004 Elsevier Inc. All rights reserved. Keywords: Dopamine; Brain mitochondria; Complex I; Neurotoxicity; Parkinson’s disease; Schizophrenia 1. Introduction Dopamine plays a key role in the pathophysiology of several psychiatric and neurological disorders such as schizophrenia, tardive dyskinesia, Parkinson’s disease, and Tourette’s syndrome. At physiological concentrations dopamine does not induce degenerative processes in brain, and has been shown to activate the expression of cell survival genes and proteins [1]. In contrast, at higher, pathological concentrations numerous studies have shown that dopamine can cause cell death both in vivo and in cell cultures. Thus, administration of dopamine into the stria- tum [2] results in pre- and postsynaptic damage, while intraventricular injection of dopamine to rats resulted in a dose-dependent death of the animal [3]. Further, toxins which can cause extensive release of dopamine, such as methamphetamine and 1-methyl-4 phenyl-1,2,3,6-tetra hydropyridine (MPTP), also cause degeneration of dopa- minergic neurons [4–7]. Dopamine-dependent cell death has been demonstrated in mesencephalic, cerebellar, stria- tal, and cortical primary neurons cultures [8–12]. It is widely believed that dopamine can induce neurotoxic effects by the formation of highly reactive oxygen species, quinones and semiquinones generated by dopamine auto- oxidation or by its enzymatic metabolism by monoamine oxidase (MAO) leading to a state of oxidative stress [2,10,13–17]. However, elevation of extracellular dopa- mine concentrations in rat brain in the absence of a neurotoxin did not induce any change in oxidative stress parameters such as lipid peroxidation, protein oxidation, glutathione, and glutathione reductase and peroxidase Biochemical Pharmacology 67 (2004) 1965–1974 0006-2952/$ – see front matter # 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.bcp.2004.02.015 * Corresponding author. Tel.: þ972-4-8295224; fax: þ972-4-8510941. E-mail address: shachar@tx.technion.ac.il (D. Ben-Shachar).