Alteration of the NAD+/NADH ratio in CHO cells by stable transfection with human cytosolic glycerol-3-phosphate dehydrogenase: resistance to oxidative stress.

The intracellular level of the NAD+/NADH ratio plays a vital role in sustaining and coordinating the catabolic reaction of the cell, and reflects the redox state of cytosol. Antioxidants play a role to protect cytosol and membrane from free radicals. This role of antioxidants involves sustaining cell viability and the procedure is thought to be regulated by the equilibrium of the redox state of the cell. However, there is very little known about how the NAD+/NADH level is set and changed. To alter the ratio, human NAD-dependent glycerol-3-phosphate dehydrogenase (cGPDH) cDNA was transfected stably in CHO dhfr- cells. When compared to parental CHO cells, cGPDH activities of the transfected cells were increased 8-12 fold, but the NAD+/NADH ratio was decreased. Specific growth rate of the transfected cells was similar to or slight lower than that of wild type CHO cells. Cell viability of the stable transformants against H2O2 was increased without change of either catalase or glutathione peroxidase activity. However, the increase of cell viability was correlated with the decrease of NAD+/NADH ratio in transfectants. From these results, it is suggested that the overexpression of cGPDH changes the NAD+/NADH ratio toward a decrease, and by this change in the redox state the cell confers more resistance against H2O2.