Nelumbo Nucifera Root Extract Containing Catechin Polyphenols Strengthens Innate Immunity in Vitro and Ameliorates Dexamethasone-Induced Immunosuppression Ex Vivo

The coronavirus disease 2019 pandemic has underscored the importance of a well-functioning immune system in protecting against pathogens. Therefore, in this study, we investigated the effects of Nelumbo nucifera root extract on innate immunity using in vitro and specific ex vivo models of dexamethasone-induced immunosuppression. Our findings demonstrated that Nelumbo nucifera root extract significantly enhances innate immune responses in both models. Mechanistic analyses revealed that Nelumbo nucifera root extract activates innate immune responses via the nuclear factor-kappa B signalling pathway. To identify bioactive compounds contributing to these effects of Nelumbo nucifera root extract, liquid chromatography - quadrupole time-of-flight mass spectrometry was employed. Among the four candidate compounds identified (tyrosine, tryptophan, catechin, and gallocatechin), catechin and gallocatechin significantly increased innate immune responses in vitro. This study highlights Nelumbo nucifera root extract, enriched with catechin-based functional compounds, as a promising natural material for the development of functional foods aimed at immune enhancement.