Rubiae Radix suppresses the activation of mast cells through the inhibition of Syk kinase for anti-allergic activity

The effect of extracts from various Oriental medicinal herbs on mast‐cell‐mediated allergic reactions was investigated in this study. Of these extracts, the medicinal herb Rubiae Radix exhibited the most potent activity in the cells, with an IC50 value (concentration necessary to obtain 50% inhibition of the response) of approximately 35±2.1 μg mL−1, and its inhibition of compound‐48/80‐induced systemic anaphylaxis by 48.6±8.5% at 300 mg kg−1 in mice. It also inhibited the expression of the pro‐inflammatory mediator tumour necrosis factor‐α (TNF‐α). As for its mechanism of action, Rubiae Radix suppressed the activating phosphorylation of Syk, a key enzyme in mast‐cell signalling processes, and that of Akt in a dose‐dependent manner. It also inhibited the MAP kinase ERK1/2, which is critical for the production of inflammatory cytokines in mast cells, as indicated by the suppression of the activating phosphorylation of ERK1/2. These results suggest that Rubiae Radix suppresses the activation of mast cells through the inhibition of Syk for antiallergic activity.