Evidence for modulation of hydrogen peroxide-induced endothelial barrier dysfunction by nitric oxide in vitro

Acute effects of the nitric oxide (NO) donors sodium nitroprusside and glyceryl trinitrate on hydrogen peroxide (H2O2)-induced increases in endothelial monolayer permeability to trypan blue-labelled bovine serum albumin have been investigated in vitro. Exposure of bovine pulmonary artery endothelial cell monolayers to 0.2 mM H2O2 for 20 min caused a significant increase in percentage trypan blue-labelled albumin transfer from the lumenal to the ablumenal compartment (basal 6.0 +/- 0.6 to 25.4 +/- 0.9%, n = 4, P < 0.0005). In separate experiments 100 mu M sodium nitroprusside significantly enhanced the effect of 0.2 mM H2O2 (from 7.4 +/- 1.4 to 11.9 +/- 1.5%, n = 9, P < 0.0001) but did not alter albumin transfer in the absence of H2O2. This additive effect appeared to be due to NO release from sodium nitroprusside, since nitrite concentration in the medium overlying cells treated with 100 mu M sodium nitroprusside was 19.9 +/- 1.8 mu M (n = 12). Significantly less nitrite (3.5 +/- 0.5 mu M, n = 12, P < 0.0001) was found in the medium overlying cells treated with 100 mu M glyceryl trinitrate, which in contrast to sodium nitroprusside, inhibited the permeability increase caused by H2O2 (from 15.6 +/- 3.3 to 13.8 +/- 3.1%, n = 6, P < 0.001). Furthermore 10 mu M sodium nitroprusside, which released comparable amount of nitrite (4.5 +/- 0.4 mu M, n = 6) to 100 mu M glyceryl trinitrate, also inhibited the permeability increase caused by H2O2 (from 20.7 +/- 0.4 to 19.4 +/- 0.3%, n = 9, P < 0.01). We conclude that relatively large amounts of NO released from 100 mu M sodium nitroprusside exacerbate the barrier dysfunction caused by H2O2, while lower amounts of NO give a small amount of cytoprotection.