Bioactivity-guided isolation of immunomodulatory compounds from the fruits of Ligustrum lucidum.

ETHNOPHARMACOLOGICAL RELEVANCE: The fruits of Ligustrum lucidum (FLL) W.T. Aiton (Oleaceae) is included in the 2020 "Chinese Pharmacopoeia" and is widely used in traditional Chinese medicine as a tonic. In recent years, FLL has been reported to improve immune function, but the bioactive compounds and mechanisms of FLL remain poorly characterized. AIM OF THE STUDY: To identify FFL compounds with strong immune activity and explore their molecular mechanisms. MATERIALS AND METHODS: The phagocytic activity of RAW264.7 macrophages and proliferation activity of spleen lymphocytes were used to guide the isolation of bioactive compounds from FLL extracts. Lymphocyte subpopulations, Ca2+ concentrations, and surface molecule expression were analyzed using flow cytometry. Cytokine secretion was examined using ELISA. FITC-OVA uptake was observed using fluorescence microscopy. NF-κB activation was analyzed using western blotting. RESULTS: The extraction and isolation produced ten compounds, namely oleuropeinic acid, nuezhenide, isonuezhenide, salidroside, isoligustrosidic acid, ligulucidumosides A, 8(E)-nuezhenide, hydroxytyrosol, oleuropein, and p-hydroxyphenethyl 7-ß-D-glucosideelenolic acid ester were isolated and identified from FLL-Bu-30%. Immunoactivity experiments showed that hydroxytyrosol had the strongest macrophage phagocytotic and lymphocyte proliferation-promoting activities. Further studies showed that hydroxytyrosol could significantly enhance lymphocyte subsets CD3+, CD4+/CD8+, and CD3+CD4-CD8-, promote IL-4, IFN-γ, and TNF-α secretion, and increase intracellular Ca2+ concentrations. In addition, the results from RAW264.7 macrophages showed that hydroxytyrosol increased FITC-OVA uptake, induced TNF-α and IL-1ß production, upregulated MHC-II, CD80, and CD86 expression, promoted cytoplasmic IκB-α degradation, and increased nuclear NF-κB p65 levels. CONCLUSION: Our study provides substantial evidence regarding the mechanism of the immunomodulatory effects of compounds from FLL.