NITRIC-OXIDE ENHANCES HYDROGEN PEROXIDE-MEDIATED ENDOTHELIAL PERMEABILITY IN-VITRO

The objective of this study was to evaluate the effects of nitric oxid e (NO) on H2O2-mediated endothelial permeability. H2O2 (0.1 mM) increa sed permeability at 90 min to 298% of baseline. Spermine NONOate (SNO) , an NO donor, at 0.1 or 1 mM did not alter permeability. However, 0.1 mM H2O2 + 1 mM SNO increased permeability to 764%, twice that of 0.1 mM H2O2 alone. These treatments were not directly toxic to endothelial cells. This NO effect was concentration dependent, inasmuch as 0.1 mM SNO did not significantly change H2O2-mediated permeability. The NO-e nhanced, H2O2-dependent permeability required the simultaneous presenc e of NO and H2O2, inasmuch as preincubation with SNO for 30 min follow ed by 0.1 mM H2O2 did not alter permeability. Staining of endothelial junctions showed widening of the intercellular space only in junctions of cells exposed to H2O2 (0.1 mM) + SNO (1 mM). Furthermore, NO did n ot affect H2O2 metabolism by endothelial cells but significantly deple ted intracellular glutathione. This reduction of cell glutathione prod uced by NO exposure recovered 15-30 min after removal of the NO donor. NO-enhanced permeability was completely blocked by methionine (1 mM), a scavenger of reactive oxygen species, and by the iron chelator desf errioxamine (0.1 mM). These results suggest that NO may exacerbate the effects of H2O2-dependent increase in endothelial monolayer permeabil ity via the iron-catalyzed formation of reactive oxygen metabolites.