Effect of five flavonoid compounds isolated from leaves of Diospyros kaki on stimulus-induced superoxide generation and tyrosyl phosphorylation of proteins in human neutrophils

Abstract

Background: The crude drug “kaki-yô” is a traditional medicine used in Japan as a hypotensive drug. Methods: The effect of five flavonoid compounds isolated from the leaves of Diospyros kaki was investigated on the stimulus-induced superoxide generation and phosphorylation of tyrosine residues of protein in human neutrophils. The five compounds examined were kaempferol 3- O-β- d-galactopyranoside (TR), kaempferol 3- O-β- d-glucopyranoside (AS), isorhamnetin 3- O-β- d-glucopyranoside (IS), quercetin 3- O-β- d-galactopyranoside (HY), quercetin 3- O-β- d-glucopyranosyl-(6→1)-α- l-rhamnopyranoside (RU). Results: When the cells were preincubated with these five compounds, the superoxide generation induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) was significantly suppressed in a concentration-dependent manner. The arachidonic acid (AA)-induced superoxide generation was suppressed by TR, AS, HY and RU. On the other hand, the superoxide generation was weakly enhanced by IS in low concentration (5–20 μmol/l), but was suppressed in high concentration (50 μmol/l). The superoxide generation induced by phorbol 12-myristate 13-acetate (PMA) suppressed the TR, IS, HY and RU, but AS gave no effect. When the cells were incubated with fMLP in the presence of TR, IS and RU, fMLP-induced tyrosyl phosphorylation of 45-kDa proteins of the cells was dose-dependently suppressed in parallel to the suppression of fMLP-induced superoxide generation. These five flavonoids showed almost no hemolytic effect even at a concentration of 500 μmol/l. Conclusion: Flavonoid compounds suppressed stimulus-induced superoxide generation and tyrosyl phosphorylation and may have pharmaceutical application.