In the present study, we investigated the protective mechanism of quercetin (QUE) and its glycosides, rutin (RUT) and quercitrin (QUI), on reactive oxygen species (ROS)-dependent (H 2O 2) and -independent (chemical anoxia) cell death in rat glioma C6 cells. Induction of HO-1 protein expression was detected in QUE- but not RUT- or QUI-treated C6 cells, and this was prevented by cycloheximide and actinomycin D. Incubation of C6 cells with QUE, but not RUT or QUI, protected C6 cells from H 2O 2- and chemical anoxia-induced cytotoxicity according to the MTT and LDH release assays. Apoptotic characteristics including chromatin condensation, DNA ladders, and hypodiploid cells appeared in H 2O 2-and chemical anoxia-treated C6 cells, and those events were significantly suppressed by adding QUE (but not RUT or QUI). Increases in caspase 3, 8, and 9 enzyme activities with decreases in pro-PARP and pro-caspase 3 protein levels and an increase in cleaved D4-GDI protein were identified in H 2O 2-and chemical anoxia-treated C6 cells, and these were blocked by the addition of QUE, but not by RUT or QUI. Intracellular peroxide levels increased with H 2O 2 and decreased with chemical anoxia, and the addition of QUE reduced the intracellular peroxide levels induced by H 2O 2. Results of an anti-DPPH radical assay showed that QUE, RUT, and QUI dose-dependently inhibited the production of DPPH radicals in vitro; however, QUE (but not RUT or QUI) prevention of DNA damage induced by OH radicals was identified with a plasmid digestion assay. Increases in phosphorylated ERK and p53 protein expressions were detected in H 2O 2- but not chemical anoxia-treated C6 cells, and the addition of QUE significantly blocked H 2O 2-induced phosphorylated ERK and p53 protein expressions. Adding the HO-1 inhibitors, SnPP, CoPP, and ZnPP, reversed the protective effect of QUE against H 2O 2- and chemical anoxia-induced cell death according to the MTT assay and morphological observations. Additionally, QUE exhibited inhibitory effects on LPS/TPA-induced transformation in accordance with a decrease in MMP-9 enzyme activity and iNOS protein expression in C6 cells. Taken together, the results of this study suggest that QUE exhibits an inhibitory effect on both ROS-dependent and -independent cell death, and induction of HO-1 protein expression is involved.
- Chemical anoxia
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