Effects of anti-allergic drugs on human neutrophil superoxide-generating NADPH oxidase.

The effects of anti-allergic drugs with or without H1-receptor antagonism on the NADPH oxidase (EC 1.6.99.6) from human neutrophils in both whole-cell and fully soluble (cell-free) systems were investigated. Three anti-allergic drugs with H1-receptor antagonism, azelastine, ketotifen and oxatomide, were found to inhibit the superoxide generation of human neutrophils exposed to phorbol myristate acetate in a whole-cell system and the activation of superoxide-generating NADPH oxidase by sodium dodecyl sulfate in a cell-free system. The concentrations of these drugs required for 50% inhibition of the oxidase (IC50) were: azelastine--0.7 microM in the whole-cell system and 0.5 microM in the cell-free system; ketotifen--60 microM in the whole-cell system and 6.8 microM in the cell-free system; and oxatomide--25 microM in the whole-cell system and 9.7 microM in the cell-free system. In addition, in the cell-free system, these drugs did not change the Km values for the NADPH of the oxidase. However, these drugs did not inhibit the superoxide generation of NADPH oxidase after its activation in whole-cell and cell-free systems, suggesting that these drugs do not have superoxide-scavenger actions. Concentrations of less than 200 microM of anti-allergic drugs without H1-receptor antagonism, tranilast, repirinast and ibudilast, did not inhibit neutrophil NADPH oxidase in whole-cell and cell-free systems. The IC50 of hydrocortisone in the cell-free system was 60 microM. These results suggest that anti-allergic drugs with H1-receptor antagonism inhibit activation of the solubilized membrane-bound enzyme by sodium dodecyl sulfate in cell-free systems and that they have much stronger anti-inflammatory action than hydrocortisone.