Identification and characterisation of the anti‐allergic compound from lotus root

ABSTRACT Aim Histamine H1 receptor (H1R) gene is up‐regulated in the nasal mucosa of patients with pollinosis, and its expression level is strongly correlated with the severity of allergic symptoms. However, suppression of H1R mRNA to the basal level by antihistamine failed to alleviate nasal symptoms completely, and nuclear factor of activated T‐cells (NFAT) signalling was demonstrated to be the additional signalling responsible for the pathogenesis of allergic rhinitis (AR). Lotus Root (LR) has been traditionally used to improve the allergic symptoms; however, the underlying mechanism of its anti‐allergic activity is unknown. Here, we show that the LR aequeous extract suppressed ionomycin‐induced NFAT signalling‐mediated IL‐9 mRNA up‐regulation in RBL‐2H3 cells and toluene‐2,4‐diisocyanate (TDI)‐sensitised rats. Methods An active compound from LR was purified by aequeous extraction and ethanol precipitation followed by column chromatography, and its structure was resolved using thiol degradation followed by 1H‐NMR (nuclear magnetic resonance) and 13C‐NMR. The mRNA levels of H1R and IL‐9 were measured using real‐time reverse transcription‐polymerase chain reaction (RT‐PCR). Results We isolated and identified proanthocyanidin containing gallocatechin tetramer as an active compound. LR‐derived proanthocyanidin (LRPC) suppressed IL‐9 mRNA up‐regulation both in RBL‐2H3 cells and TDI‐sensitised rats. Combination therapy of LRPC with antihistamine markedly alleviated allergic symptoms. Conclusion Data suggest that LRPC alleviated nasal symptoms through the inhibition of IL‐9 mRNA up‐regulation, possibly through the inhibition of NFAT signalling, and that combination therapy of LRPC with antihistamine could be effective in advanced treatment for AR.