SOD1 and liver cancer: The effect of treatment with various concentrations of SOE (0, 30, 60, 120 μg/mL) on gene and protein expression of three different antioxidant enzymes, including catalase, glutathione peroxidase (GPx) and superoxide dismutase (SOD), in liver cancer cells (Hepa1-6 and HepG2) and non-cancerous cells (HaCaT stimulated with H2O2) were examined.