Iridoid glycosides and phenolic glycosides from Gentiana rhodantha and their anti-inflammatory activities

Abstract

Seven previously undescribed glycosides, including four iridoid glycosides (1, 2, 4, and 5), three phenolic glucosides (18, 21, and 22), together with nineteen known compounds, were isolated from the ethanol extract of Gentiana rhodantha Franch. Their structures were determined by analysis of 1D and 2D NMR, HRESIMS, X-ray diffraction, NMR calculation, and electronic circular dichroism (ECD) calculation. Among them, compound 21 was a novel highly rearranged endo-phenolic analogue with a unique skeleton. Moreover, the absolute configuration of compound 3 was determined by a single-crystal X-ray diffraction experiment for the first time. These isolates were evaluated for their inhibitory activity against the LPS-induced NO production in the RAW 264.7 cell lines. As a result, compound 14 exhibited remarkable inhibitory activities against NO production with an IC₅₀ value of 6.89 ± 0.28 μM. Moreover, compound 14 significantly reduced LPS-stimulated pro-inflammatory cytokine and mediators (IL-6, iNOS and COX-2), while upregulating anti-inflammatory cytokine the IL-10 in RAW 264.7 macrophages. Further studies suggested that compound 14 exerted anti-inflammatory effects by regulating the TLR4/MyD88/NF-κB signaling pathway.