Inhibition of Histamine Synthesis by Glycyrrhetinic Acid in Mast Cells Cocultured with Swiss 3T3 Fibroblasts

The effect of glycyrrhetinic acid (18-O-β-glycyrrhetinic acid, GA) on histamine metabolism was investigated in cultured mast cells (CMCs) cocultured with Swiss 3T3 fibroblasts. GA strongly inhibited histamine synthesis in the cocultured CMCs. Since 50 µM GA inhibited about 80% of histidine decarboxylase (HDC) activity, the inhibitory activity of GA for histamine synthesis was considered to be derived from the inhibition of HDC activity. The number of berberine-sulfate-positive cells also decreased in the presence of GA, which indicated that maturation of CMCs was inhibited by GA. Furthermore, we examined the effect of GA on the mRNA expression of novel protein kinase C δ (nPKCδ), a major isoform of CMCs, by Northern blot analysis. The expression of nPKCδ mRNA in the presence of GA was significantly lower than in the absence of GA. These results suggest the possibility that the inhibition of histamine synthesis by GA is regulated by nPKCδ.