Effect of reactive oxygen metabolites on endothelial permeability: role of nitric oxide and iron

We evaluated the effects of the xanthine oxidase (XO)-derived reactive oxygen metabolites on the permeability of bovine pulmonary artery-endothelial monolayers and examined how iron and nitric oxide (NO) participate in these changes in permeability.

Permeability was measured using a cell-column chromatographic method in which monolayers were exposed to combinations of agents.

Exposure of monolayers to a superoxide/peroxide generator, xanthine (X, 0.1 mM)/XO (25 mU/mL), increased solute permeability after 10 minutes, but the same dose of either X or XO alone did not. Exposure of monolayers to peroxide (0.1 mM) also increased permeability, but only after 70 minutes. This X/XO permeability was attenuated by either catalase, superoxide dismutase, methionine (1 mM), an oxy-radical scavenger, or desferrioxamine (0.1 mM), an iron chelator. Spermine NONOate (SNO), an NO donor, attenuated X/XO permeability at 0.1 mM, but this protection was not significant at 0.01 or 1 mM. Spermine NONOate (0.1 mM) did not alter the permeability produced by 0.1 mM peroxide. L-N5-(1-iminoethyl)-ornithine (10 microM), an NO synthase inhibitor, completely blocked peroxide-, and partially attenuated X/XO-mediated permeability. However, 3-morphosynodiomine (SIN-1, 1 mM) plus catalase (1,000 U/mL), a peroxynitrite generator, did not alter permeability.

Xanthine/Xanthine Oxidase permeability involves peroxide, superoxide, oxy-radicals, and iron. Endogenous NO may regulate peroxide-, but not superoxide-mediated permeability. The protective effects of exogenous NO on the X/XO permeability may represent interactions between superoxide, peroxide, and cell surface-bound iron.