Dopamine modulates mitochondrial function in viable SH-SY5Y cells possibly via its interaction with complex I: relevance to dopamine pathology in schizophrenia.

Deleterious effects of dopamine (DA) involving mitochondrial dysfunction have an important role in DA-associated neuronal disorders, including schizophrenia and Parkinson's disease. DA detrimental effects have been attributed to its ability to be auto-oxidized to toxic reactive oxygen species. Since, unlike Parkinson's disease, schizophrenia does not involve neurodegenerative processes, we suggest a novel mechanism by which DA impairs mitochondrial function without affecting cell viability. DA significantly dissipated mitochondrial membrane potential (delta psi m) in SH-SY5Y cells. Bypassing complex I prevented the DA-induced depolarization. Moreover, DA inhibited complex I but not complex II activity in disrupted mitochondria, suggesting complex I participation in DA-induced mitochondrial dysfunction. We further demonstrated that intact mitochondria can accumulate DA in a saturated manner, with an apparent Km=122.1+/-28.6 nM and Vmax=1.41+/-0.15 pmol/mg protein/min, thereby enabling the interaction between DA and complex I. DA accumulation was an energy and Na+-dependent process. The pharmacological profile of mitochondrial DA uptake differed from that of other characterized DA transporters. Finally, relevance to schizophrenia is demonstrated by an abnormal interaction between DA and complex I in schizophrenic patients. These results suggest a non-lethal interaction between DA and mitochondria possibly via complex I, which can better explain DA-related pathological processes observed in non-degenerative disorders, such as schizophrenia.

Increased mitochondrial complex I activity in platelets of schizophrenic patients.

It is believed that dopamine and alterations of energy metabolism in cortical and subcortical structures are involved in the pathophysiology of schizophrenia. Recently, we and others have shown that dopamine may affect energy metabolism by interacting with mitochondrial complex I activity in rats both in vivo and in vitro. In this study activity of complexes I and IV was assessed in mitochondria isolated from blood platelet of schizophrenic patients and compared to patients with affective disorders and healthy control subjects. Seventy-seven in-patients who met DSM-IV criteria for schizophrenia (in acute exacerbation), bipolar disorder depressed type (BP), or recurrent major depressive disorder (MDD) and 24 control subjects participated in the study. A highly significant increase (240%, p < 0.001) in complex I activity but not in complex IV, was detected in medicated and unmedicated schizophrenic patients compared to controls. No such change was observed in patients with affective disorders. The data demonstrate a specific and selective, alteration in platelet complex I activity in schizophrenic patients, which is not related to medication. If this abnormality in platelet mitochondria reflects brain alterations, it may further support the relevance of alterations in energy metabolism to the pathophysiology of schizophrenia. Finally in the lack of any clinically relevant biological marker for schizophrenia, complex I activity in platelets might become a useful peripheral marker for this disorder.