THE CYTOPROTECTIVE ROLES OF ASCORBATE AND GLUTATHIONE AGAINST NITROGEN-DIOXIDE TOXICITY IN HUMAN ENDOTHELIAL-CELLS

The depletion of human umbilical vein endothelial (HUVE) cell glutathi one with buthionine sulfoximine or with sulfur amino acid-free medium potentiated the sub-lethal (H-3-deoxyglucose release) and lethal (lact ate dehydrogenase release) cytotoxicity responses of the cells to dire ct exposure to NO2 over the range 2-20 ppm. When control cells, or glu tathione-depleted cells, were either pre-loaded with ascorbate (intrac ellular ascorbate), or washed with ascorbate-containing medium just be fore exposure (extracellular ascorbate), the cells were fully protecte d from NO2-dependent toxicity, Concomitant with these exposures, NO2 c aused dose-dependent depletions of both glutathione and ascorbate. Fur ther, it was noted that the depletion of the intracellular ascorbate-p ool was accelerated in these glutathione depleted cells. Conversely, l oading ascorbate into the cells significantly diminished NO2-dependent depletion of intracellular GSH, In contrast to affecting the acute cy totoxicity response of the HUVE cells to NO2, ascorbate supplementatio n of the medium of cells exposed to NO2 at clonal density facilitated considerable protection to the colony-forming efficiency of the cells. We conclude that both ascorbate and glutathione play important protec tive roles in defending HUVE cells from the toxicity of NO2 under dire ct exposure conditions. The results also strengthen the premise that a scorbate and glutathione co-operate in the antioxidative protection of cellular viability.