Ascorbate as a "redox sensor" and protector against irradiation-induced oxidative stress in 32D CL 3 hematopoietic cells and subclones overexpressing human manganese superoxide dismutase.

Abstract

To determine whether increased expression of manganese superoxide dismutase (MnSOD) protects cells from irradiation by preventing the production of reactive oxygen species (ROS), a new approach to detecting free radical intermediates using ascorbate as an endogenous spin trap was used. Cells from the 32D cl 3 hematopoietic cell line or a subclone overexpressing MnSOD (2C6) were incubated with dehydroascorbate for 30 min and irradiated to doses from 0 to 50 Gy. Radical intermediates reacting with spin traps or ascorbate were measured by electron spin resonance spectroscopy. Results were compared to irradiation-induced changes in thiol levels, irradiation survival curves, and accumulation of 8-OHdG as a measurement of DNA oxidative damage. Manganese superoxide dismutase-overexpressing 2C6 cells maintained higher levels of ascorbate (5.4 +/- 0.5 and 2.6 +/- 0.5 nmol/10(6) cells, respectively) and thiols (14.0 +/- 0.1 and 11.1 +/- 0.2 nmol/10(6) cells) compared to 32D cl 3 parent cells. Cells overexpressing MnSOD produced lower levels of ROS than did the parental 32D cl 3 cells, as evidenced by lower expenditure of ascorbate and GSH after irradiation. Increased ascorbate levels protected both 32D cl 3 and 2C6 cells from irradiation killing, as demonstrated by an increased shoulder on survival curves and decreased DNA 8-OHdG accumulation. Manganese superoxide dismutase overexpression protects 2C6 cells from irradiation damage by scavenging ROS that readily interact with major endogenous antioxidants--ascorbate and GSH--in nontransfected hematopoietic 32D cl 3 cells.