Cytoprotective and Cytotoxic Effects of Rice Bran Extracts in Rat H9c2(2-1) Cardiomyocytes

This study was aimed at preliminarily assessing the cytoprotective and antioxidative effects of rice bran extracts (RBEs) from a Sarawak local rice variety (local name: "BJLN") and a commercial rice variety, "MR219," on oxidative stress in rat H9c2(2-1) cardiomyocytes. The cardiomyocytes were incubated with different concentrations of RBE and hydrogen peroxide (H₂O₂), respectively, to identify their respective IC₅₀ values and safe dose ranges. Two nonlethal and close-to-IC₅₀ doses of RBE were selected to evaluate their respective effects on H₂O₂ induced oxidative stress in cardiomyocytes. Both RBEs showed dose-dependent cytotoxicity effects on cardiomyocytes. H₂O₂ induction of cardiomyocytes pretreated with RBE further revealed the dose-dependent cytoprotective and antioxidative effects of RBE via an increase in IC₅₀ values of H₂O₂. Preliminary analyses of induction effects of RBE and H₂O₂ on cellular antioxidant enzyme, catalase (CAT), also revealed their potential in regulating these activities and expression profile of related gene on oxidative stress in cardiomyocytes. Pretreated cardiomyocytes significantly upregulated the enzymatic activity and expression level of CAT under the exposure of H₂O₂ induced oxidative stress. This preliminary study has demonstrated the potential antioxidant effects of RBE in alleviating H₂O₂-mediated oxidative injuries via upregulation in enzymatic activities and expression levels of CAT.