Effect of five triterpenoid compounds isolated from leaves of Diospyros kaki on stimulus-induced superoxide generation and tyrosyl phosphorylation in human polymorphonuclear leukocytes

Background: The crude drug “kaki-yô” is a traditional medicine used in Japan as a hypotensive drug. Methods: The effect of five triterpenoid compounds, isolated from leaves of Diospyros kaki on stimulus-induced superoxide generation and phosphorylation of tyrosine residues of protein in human neutrophils was investigated. The five compounds examined were α-amyrin (A), uvaol (UV), ursolic acid (UA), 19 α-hydroxy ursolic acid (HU) and 19 α,24-dihydroxy ursolic acid (DHU). Results: When the cells were preincubated with these compounds, the superoxide generation induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) was significantly suppressed in a concentration-dependent manner. These compounds also suppressed the superoxide generation induced by arachidonic acid (AA) in high concentrations. In the case of the superoxide generation induced by phorbol 12-myristate 13-acetate (PMA), UA, HU and DHU suppressed the superoxide generation but A and UV gave no effect. When the cells were incubated with fMLP in UA, HU and DHU, 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. Conclusions: Triterpenoid compounds suppress stimulus-induced superoxide generation and tyrosyl phosphorylation and may have pharmaceutical applications.