Complete and reversible inhibition of NADPH oxidase in human neutrophils by phenylarsine oxide at a step distal to membrane translocation of the enzyme subunits.

The effects of the trivalent arsenical phenylarsine oxide (PAO) on the activity of NADPH oxidase in human neutrophils were studied. PAO caused a rapid dose-dependent inhibition of superoxide generation which was maximal at a concentration of 1 microM, irrespective of the stimulating agent. This inhibitory effect was not due to impaired transduction of activation signals since neither degranulation nor phagocytosis were modified. When cytosolic and membrane fractions from resting neutrophils were combined to reconstitute the NADPH oxidase, O2-. generation was inhibited by PAO while translocation of the NADPH oxidase components to the plasma membrane fraction was not affected. The inhibition was completely and specifically reversed by 2,3-dimercaptopropanol, not by dithiothreitol or beta-mercaptoethanol, indicating that PAO binds covalently to spatially vicinal thiol groups. PAO inhibited the plasma membrane's capacity to initiate O2-. generation while it apparently did not affect the cytosol. When PAO was added subsequently to NADPH oxidase activation, no inhibition was observed, indicating that PAO cannot reach its target once the oxidase is functionally assembled. In conclusion, PAO is the first complete and reversible inhibitor of NADPH oxidase which could provide the basis for new therapeutical approaches in inflammatory diseases.