Glycolipid-enriched fraction of Osmanthus fragrans inhibits LPS-induced expression of inflammatory genes, COX-2, E-selectin, and Interleukin-8

Osmanthus fragrans Lour. is a small ornamental tree native to the Southeastern parts of China. It is mainly cultivated because of its characteristic fragrance, and used in the food and perfume industry. Besides, its flowers are used in traditional Chinese medicine to treat a variety of diseases including those related to inflammation. The aim of the study was to investigate in more detail the anti-inflammatory properties of O. fragrans flowers, and to characterize their active principles and mechanisms of action. O. fragrans flowers were successively extracted with n-hexane, dichloromethane and methanol. The extracts were further fractionated by chromatographic separation. COX-2 mRNA expression in PMA-differentiated, LPS-stimulated THP-1 cells was used as lead assay for activity-guided fractionation. The most potent fraction was chemically analyzed by LC-HRMS. The pharmacological activity was also evaluated in other inflammation-related in-vitro models, such as analysis of IL-8 secretion and E-selectin expression in HUVECtert cells and selective inhibition of COX-isoenzymes. n-Hexane and dichloromethane extracts of O. fragrans flowers significantly inhibited COX-2 (PTGS2) mRNA expression. Additionally, both extracts inhibited COX-2 enzyme activity, whereas COX-1 enzyme activity was affected to a significantly lower extent. Fractionation of the extracts led to a highly active, glycolipid-containing fraction. In total, 10 glycolipids were tentatively annotated by LC-HRMS. This fraction also inhibited LPS-induced COX-2 mRNA expression, IL-8 secretion and E-selectin expression. The effects were limited to LPS-induced inflammation and not observed when inflammatory genes were induced by TNF-α, IL-1β or FSL-1. Since all these inducers of inflammation act via different receptors, it is likely that the fraction interferes with the binding of LPS to the TLR4-receptor, which mediates pro-inflammatory effects of LPS. Taken together, the results demonstrate the anti-inflammatory potential of O. fragrans flower extracts in general, and of the glycolipid-enriched fraction in particular. The effects of glycolipid-enriched fraction are potentially mediated via the inhibition of the TLR4 receptor complex. [Display omitted] •Lipophilic extracts of O. fragrans flowers inhibited COX-2 mRNA expression.•Purification led to a highly potent fraction mainly containing DGDGs and MGMGs.•Glycolipid-enriched fraction inhibits LPS-stimulated IL-8 and E-Selectin expression.•Also, COX-2