Rebamipide suppresses formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide production by inhibiting fMLP-receptor binding in human neutrophils.

The purpose of the present work was to investigate the mechanism underlying the inhibitory action of rebamipide on superoxide anion (O2) production induced by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) in human neutrophils. Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)), a product of phosphoinositide 3-OH-kinase (PI 3-kinase) accumulated in response to fMLP and this accumulation was well correlated with O2 production in human neutrophils. Rebamipide inhibited PIP(3) production in parallel with the inhibition of fMLP-induced O2 production. PI 3-kinase activity in anti-PI 3-kinase p85 immunoprecipitates was not affected by the presence of rebamipide, therefore rebamipide did not have a direct inhibitory action on PI 3-kinase activity. Since rebamipide had no inhibitory effect on O2 production induced by NaF, a direct activator of G protein, the target of the inhibitory action of rebamipide appears to be a component of the signal transduction pathway upstream of G protein. Scatchard analysis of [3H]fMLP binding to human neutrophil membrane revealed that rebamipide increased the K(D) value of [3H]fMLP without altering the number of [3H]fMLP binding sites, suggesting that rebamipide has a competitive antagonistic action against the fMLP-receptor. The competitive antagonistic action was further confirmed by the finding that rebamipide caused a parallel shift to the right in the dose-response curve of O2 production induced by fMLP. These results provide evidence that the competitive inhibitory action of rebamipide on the fMLP-receptor plays a main role in its inhibitory action on fMLP-induced O2 production.