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.