H2O2 causes endothelial barrier dysfunction without disrupting the arginine nitric oxide pathway

We have previously demonstrated that nitric oxide ((.)NO) donors attenuate and that inhibition of endogenous nitric oxide synthase (NOS) enhances hydrogen peroxide (H2O2)-mediated porcine pulmonary artery endothelial cell (PAEC) injury. The current study investigates the hypothesis that oxidant-mediated inhibition of NOS contributes to PAEC injury. PAEC barrier function, measured as the transmonolayer clearance of albumin, was significantly impaired by H2O2 (10-100 mu M) in the absence of cytotoxicity. Treatment with H2O2 did not alter NOS activity, measured as the conversion of [H-3]arginine to [H-3]citrulline in PAEC lysates, either immediately after treatment with 0-250 mu M H2O2 for 30 min or for up to 120 min after treatment with 100 mu M H2O2. H2O2 had little effect on NOS activity in intact PAECs, measured as 1) the formation of [H-3]citrulline in [H-3]arginine-loaded PAECs, 2) PAEC guanosine 3',5'-cyclic monophosphate content, and 3) PAEC.NO release to the culture media. These results indicate that the arginine-.NO pathway remains intact after exposure to oxidant conditions sufficient to promote functional derangements of vascular endothelial cells.