Hydrogen peroxide (H(2)O(2)) is a major reactive oxygen species that has been implicated in various neurodegenerative diseases. Quercetin, one of the plant flavonoids, has been reported to harbor various physiological properties including antioxidant activity. In this study, we investigated the neuroprotective effects of quercetin against H(2)O(2)-induced apoptosis in human neuronal SH-SY5Y cells. H(2)O(2)-mediated cytotoxicity and lactate dehydrogenase release were suppressed in a quercetin concentration-dependent manner. In addition, quercetin repressed the expression of the pro-apoptotic Bax gene and enhanced that of the anti-apoptotic Bcl-2 gene in SH-SY5Y cells. Moreover, quercetin effectively inhibited the activation of the caspase cascade that leads to DNA fragmentation, a key feature of apoptosis, and subsequent cell death. These results indicate the importance of quercetin in protecting against H(2)O(2)-mediated neuronal cell death. Thus, quercetin might potentially serve as an agent for prevention of neurodegenerative diseases caused by oxidative stress and apoptosis.
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