Mild Mitochondrial Depolarization is Involved in a Neuroprotective Mechanism of Citrus sunki Peel Extract

Mitochondrial membrane potential (m) contributes to determining a driving force for calcium to enter the mitochondria. It has been demonstrated that even a small mitochondrial depolarization is sufficient to prevent mitochondrial calcium overload and the subsequent apoptosis. Therefore, mild mitochondrial depolarization has been recently evaluated as a novel mechanism of neuroprotection via inhibiting neurotoxic mitochondrial calcium overload during neuronal insults. In the present study, using both real-time recording and flow cytometric analyses of m, we demonstrated that ethanolic peel extract of Citrus sunki Hort. ex Tanaka (CPE) and its active compounds are capable of inducing a mild mitochondrial depolarization. Polymethoxylated flavones such as nobiletin and tangeretin were found as the active compounds responsible for CPE effects on m. Neuronal viability was significantly increased in a dose-dependent manner by CPE treatment in H2O2-stimulated HT-22 cells as an in vitro neuronal insult model. CPE treatment significantly inhibited H2O2-induced apoptotic processes such as chromatin condensation, caspase 3 activation and anti-poly (ADP-ribose) polymerase (PARP) cleavage. CPE treatment significantly blocked mitochondrial calcium overload in H2O2-stimulated HT-22 neurons as indicated by rhod-2 acetoxymethyl ester. Taken together, our findings suggest that CPE and its active compounds may be considered as promising neuroprotective agents via inducing a mild mitochondrial depolarization. Copyright (c) 2012 John Wiley & Sons, Ltd.