Protective effects of Quercus salicina blume leaves aqueous extracts against cadmium-induced oxidative stress and cell cytotoxicity in HK-2 cells

Background: Quercus salicina Blume is an evergreen plant growing southern parts of Korea and Japan, and has been used for the treatment of dysentery, dermatitis, and hemorrhage from possible effects such as anti-inflammatory, anti-endemic and litholytic activities. We investigated the underlying mechanisms of Quercus salicina Blume extracts (QS) protection against cadmium treatment utilizing human kidney origin HK-2 cells. Methods: To ascertain the functional constituents of the hot water-extracted QS, we conducted analyses determine the total phenolic and flavonoid contents. Subsequently, the antioxidant activity was assessed using DPPH (2,2-diphenyl-1-picrylhydrazyl) and FRAP (ferric ion reducing antioxidant power) methods. After treating HK-2 cells with QS and Cd, we confirmed the production of reactive oxygen species (ROS) and the expression of related proteins through western blotting. This investigation aimed to assess the antioxidant and anti-apoptotic effects of QS against cadmium-induced oxidative stress. Results: QS exhibited strong antioxidative potential, since the samples exhibited significantly high DPPH and FRAP values. Upon exposure of HK-2 cells to cadmium, inducing oxidative stress, the application of QS effectively reinstated cellular antioxidative functions, leading to an augmentation in cell viability. Notably, the presence of attenuated the heightened expression of oxidative marker enzymes induced by cadmium treatment, including SOD (superoxide dismutase) 1, catalase, Nrf-2, and Heme-oxygenase. The apparent disappearance of the apoptotic bodies indicates a potential apoptosis controlling effect of QS. Furthermore, the considerable increase in sub-G1 phase with the addition of cadmium was diminished under QS treatment indicating the ability of QS to reduce the degree of apoptosis related cell cycle phase. The apoptotic quenching effects of QS were accompanied by the downregulation of pro-apoptotic protein Bax and up-regulation of pro-apoptotic Bcl-2. The examination of cleaved caspase-9 and caspase-3 has provided evidence that the pronounced anti-apoptotic activities observed in cadmium challenged HK-2 cells significantly diminished in the presence of QS. Conclusions: QS is a highly effective antioxidant and reduces cell cytotoxicity caused by cadmium through antioxidant functions and anti-apoptotic capabilities.