Then 100 ml of DMSO were added to solubilize the formazan produced by healthy mitochondria

ing NF-kB and caspase-1 activation. EGCG is the main constituent of polyphenols and the most abundant and active polyphenolic compound with potent biological properties, including antioxidant, hepatoprotective, chemopreventive, and anticarcinogenic effects. It has been reported that the active site of EGCG can react with oxygen free radicals, supporting that EGCG possesses potent antioxidant properties. In addition, EGCG is a known inhibitor of the STAT1 transcription factor, which has been implicated in the production of ROS and the activation of caspase-3 in cisplatin-induced ototoxicity. However, the effects of EGCG on NO-induced ototoxicity have not yet been established. NO is a free radical that predominantly functions as a messenger and effector molecule. Many studies have suggested that free oxygen radicals can cause hearing impairment. Recent evidence suggests that excessive NO production plays an important role in pathological damage of the cochlea and elevated hearing thresholds. The induction of apoptotic cell death by NO depends on its concentration and the cell type involved. High concentrations of NO donors have been shown to generate toxic concentrations of NO and induce apoptosis. However, NO treatment at lower, more physiological levels may often have protective effect, preventing the onset of apoptosis in many mammalian cells. In the current study, we found that higher concentrations of SNAP induced auditory cell death, but low doses of SNAP did not affect cell viability. This finding is consistent with other studies that have RS-1 demonstrated the induction of Molt-4 cell death by high concentrations of SNAP. Many studies have shown that the ototoxicity of cisplatin can be mediated by increased NO production in the inner ear, leading to auditory cell destruction. L-NAME, a competitive inhibitor of NOS, was shown to reduce cisplatin-induced hearing disturbances. In this study, we confirmed that L-NAME suppressed cisplatin-induced hair cell destruction and iNOS expression in organ of Corti explants, and we investigated the direct effects of NO and protective effects of EGCG on hair cell death. NO destroyed the orderly arrangement of the 3 OHC rows and the IHC row in the basal, middle, and apical turns in Corti explants, and EGCG abrogated NO-induced destruction of hair cell arrays. Additionally, an NO scavenger effectively inhibited NO-induced hair cell destruction. These results imply that a high concentration of NO is involved in ototoxicity and that this phenomenon can be counteracted by antioxidants. In mammals, mitochondria act as the central checkpoint for many forms of apoptosis. The mitochondrial pathway is believed to be the main target for survival signaling pathways. NO has been reported to interfere with the mitochondrial respiratory chain at several sites, resulting in increased generation of ROS that subsequently react with NO to form peroxynitrite, which in turn damages cells and leads to cell death. Mitochondrial alterations leading to mitochondrial membrane depolarization induce apoptosis by reduction of MMP and release of cyt c. Thus, we investigated NO-induced cell death, MMP loss, ROS generation, and cyt c release in auditory HEI-OC1 cells. The results revealed that NO-induced ROS production may lead to a decrease in MMP, which in turn increases mitochondrial membrane permeability and releases mitochondrial apoptogenic factors, such as cyt c, into the cytosol. This indicated that NO-induced apoptosis may