Down-regulation of Endogenous Antioxidant Enzymes Gene Expression by Supplement of Vitamin C in Cultured Pheochromocytoma Cells

Background: Reactive oxygen species (ROS) have been linked to a variety of pathophysiological changes. Epidemiological studies supported the beneficial effect of supplementation of antioxidants. Antioxidant enzymes including catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPX) are endogenous enzymes which can scavenge ROS. This study investigated the effect of supplementation of ascorbic acid (vitamin C) on the changes of catalase, SOD, and GPX gene expression in cultured pheochromocytoma cells. Methods: Pheochromocytoma cells were incubated with vitamin C and divided into 4 groups: a control group (without vitamin C) and 3 treatment groups with vitamin C at 40, 80 and 160 μmol/L, respectively. After short-term (2 days) and long-term (7 days) incubation, the catalase, SOD, and GPX mRNA levels were determined by Northern blot. Results: After 2 days of incubation, vitamin C (160 μmol/L) attenuated the GPX mRNA level (100% to 91.8 ± 3.8%, p <0.01), whereas the catalase and SOD mRNA remained unchanged. After 7 days' incubation with vitamin C, all the catalase, SOD, and GPX mRNA were decreased significantly. Conclusion: These results suggest that 2 and 7 days of incubation with relatively high concentrations of vitamin C may down-regulate gene expression of antioxidant enzymes in cultured pheochromocytoma cells. Whether this phenomenon implicates clinical benefit needs further evaluation.