Shikonin inhibits IgE-mediated histamine release by human basophils and Syk kinase activity.

OBJECTIVE: Shikonin, a component of the herbal medicine "Shikon", is known to suppress inflammatory reactions, but its molecular targets are not identified. This study examines the effect of shikonin on human basophil degranulation response and aims to identify its targets. MATERIALS: Human basophils in isolated leukocytes from healthy volunteers' peripheral blood; recombinant human Syk and Lyn tyrosine kinases. METHODS: Histamine release from basophils stimulated with anti-IgE antibody was analyzed fluorimetrically. Syk and Lyn kinase activities were tested in Vitro with recombinant proteins and analyzed by off-chip mobility shift assay. RESULTS: Shikonin dose-dependently inhibited the histamine release from basophils induced by anti-IgE antibody (IC50 = 2.6 +/- 1.0 microM; mean +/- SEM). A search for the target(s) of shikonin in the signal cascade of IgE-mediated activation showed that it strongly inhibits Syk (IC50 = 7.8 microM, in the recombinant kinase assay), which plays a pivotal role in the degranulation response. A less significant inhibition was found for Lyn, which phosphorylates FcepsilonRI-betagamma subunits and also Syk. CONCLUSIONS: These results indicate that the inhibition of Syk-dependent phosphorylation events might underlie the blocked histamine release from human basophils, thus contributing to the anti-inflammatory effects of shikonin.

IgG-mediated histamine release from canine mastocytoma-derived cells.

BACKGROUND: Recent data suggest that normal tissue mast cells can express functional receptors for IgG under certain conditions. However, little is known about IgG receptor expression and functional consequences in mast cell neoplasms. METHODS: In this study, neoplastic mast cells were obtained from a dog with cutaneous mastocytoma (CM-MC) and from a dog with visceral mastocytoma (VI-MC). Both cell populations were characterized morphologically and functionally. RESULTS: Most cells proliferated constantly in suspension without particular supplements. Doubling times of CM-MC and VI-MC were 52.2 and 27.5 h, respectively. Both cell types were sensitive to formalin fixation, did not contain heparin and were tryptase and chymase positive. Electron microscopy showed fine granules with electron-dense content in both cell populations. The total histamine content of CM-MC and VI-MC was 0.25 and 0.10 pg/cell, respectively. Calcium ionophore A23187 and substance P induced dose-dependent histamine release, whereas compound 48/80 had no effect. Most significantly, both cell types, when sensitized with monomeric dog IgG, released histamine upon stimulation by anti-dog IgG. CONCLUSIONS: Dog mastocytoma-derived cells may be useful to study the regulation of neoplastic mast cell growth and differentiation, as well as IgG receptor-mediated activation in neoplastic mast cells. Further research is required to clarify the pathophysiological significance of constitutive expression of IgG receptors in neoplastic (canine) mast cells.