Assessment of antioxidant potential of phytochemicals in human glioblastoma (U-87 MG) cells

Abstract

Imbalance between production of reactive oxygen/nitrogen species (ROS/RNS) leads to oxidative stress and has been well documented for mitochondrial dysfunction, a prime cause towards pathogenesis of neurological diseases and cancer. Glioblastoma Multiforme (GBM) is a highly aggressive, invasive and primary brain tumor which shows resistance to chemotherapy and radiotherapy. Superoxide dismutase (SOD) is an antioxidant enzyme that scavenges the production of superoxide radicals and dismutases into H?O? which is further converted into H?O and O? by catalase (CAT) enzyme. Apurinic/Apyrimidinic endonuclease (APE1) is a central enzyme of base excision repair (BER) pathway with two important functions; DNA repair and redox regulation of transcription factors (TFs) responsible for cell survival. In this study, it was seen that oxidative stress induced by endogenously found oxidants H?O? and glucose oxidase (GO) enhanced the activities of both CuZn-SOD and MnSOD in U-87 MG cells. In addition, CuZn-SOD levels were found to be increased in H?O?-induced oxidative stress and MnSOD levels were found to be increased in both H?O? and GO- induced oxidative stress. Further, pretreatment with phytochemicals Curcumin and Quercetin modulated the activities and expression of both forms of SOD studied. The BER-pathway enzyme, APE1 level was found to be decreased in mitochondria of oxidative stress induced U-87 MG cells by H?O? and GO, and in contrast APE1 level was found to be increased in cytosol, which indicates that oxidative stress affects the expression level and sub-cellular localization of APE1. Taken together, these results indicate that in GBM it is more likely that activated SOD a key player of antioxidant system and APE1 a key player in BER-pathway might be facilitating cancer cells to survive in oxidative stress environment.