GSH-related enzyme activity and tumor relation: glutathione peroxidase and glutathione reductase status under hypoxia in HepG2 cells

Abstract

In hepatocellular carcinoma (HCC), tumorigenesis, hypoxia and reactive oxygen species (ROS) play a crucial role in altering the tumor microenvironment (TME). Until now, the time-dependent alteration of hypoxia-inducible factor-1α (HIF-1α), the antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase (GR) under hypoxic conditions in HCC were not clear. Consequently, our main target was to investigate the role of GPx and GR status in HCC cell line (HepG2) under hypoxic conditions. HIF-1α protein levels in cell lysates were determined by ELISA assay and protein expressions were identified using western blot. GPx and GR activity levels of the cell lysates were measured spectrophotometrically. HIF-1α protein levels were determined under normoxic and hypoxic conditions (p<0.001). Also, HIF-1α protein levels and expressions were observed under time-dependent hypoxic conditions, the HIF-1α protein level is found to be reached its peak point at 4 h in the HepG2 cell line. We also have detected decreased activity levels of GPx and increased GR activity levels under hypoxia for 4 h (p<0.001). More than 4 h of exposure to hypoxic environment reducted the HIF-1α levels in HCC cells. According to the results, we suggest the ideal exposure time to hypoxic conditions as 4 h for the HepG2 cell line. In addition, hypoxia also stimulated the activity levels of GPx and GR. Our results suggest that the activity levels of GPx and/or GR enzymes may be therapeutic targets in the hypoxia-dependent HCC tumorigenesis process.