Inhibitors of Complex I of the mitochondrial respiratory chain, such as rotenone, promote Parkinson disease-like symptoms and signs of oxidative stress. Dopamine (DA) oxidation products may be implicated in such a process. We show here that theo-quinone dopaminochrome (DACHR), a relatively stable DA oxidation product, promotes concentration (0.1–0.2 μm)- and respiration-dependent generation of H2O2at Complex I in brain mitochondria, with further stimulation by low concentrations of rotenone (5–30 nm). The rotenone effect required that contaminating Ca2+(8–10 μm) was not removed. DACHR apparently extracts an electron from the constitutively autoxidizable site in Complex I, producing a semiquinone, which then transfers an electron to O2, generating\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{{\bar{{\cdot}}}}\) \end{document}and then H2O2. Mitochondrial removal of H2O2monoamine, formed by either oxidase activity or DACHR, was performed largely by glutathione peroxidase and glutathione reductase, which were negatively regulated by low intramitochondrial Ca2+levels. Thus, the H2O2formed accumulated in the medium if contaminating Ca2+was present; in the absence of Ca2+, H2O2was completely removed if it originated from monoamine oxidase, but was less completely removed if it originated from DACHR. We propose that the primary action of rotenone is to promote extracellular\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{{\bar{{\cdot}}}}\) \end{document}release via activation of NADPH oxidase in the microglia. In turn,\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{{\bar{{\cdot}}}}\) \end{document}oxidizes DA to DACHR extracellularly. (The reaction is favored by the lack of GSH, which would otherwise preferably produce GSH adducts of dopaminoquinone.) Once formed, DACHR (which is resistant to GSH) enters neurons to activate the rotenone-stimulated redox cycle described.
Mechanistic insight from the crystal structure of mitochondrial complex I
