Bio-guided isolation of anti-inflammatory compounds from Tilia tuan Szyszyl. flowers via in vitro and in silico study

Abstract

Ethnopharmacological relevanceTilia tuan Szyszyl. is a perennial arboreal plant renowned for its medicinal and economic significance. All the roots, stems, leaves, flowers, and fruits have been used medicinally by the folk Bai and Yi people in Yunnan province, China, to treat inflammation, rheumatism and pain for a long time. The detailed chemical constituents and their anti-inflammatory mechanisms remain unexplored. Aim of the studyThe objective of this study was to investigate the main anti-inflammatory constituents of T. tuan flowers through bio-guided isolation and to evaluate their anti-inflammatory effects relevant to its traditional medicinal use. Material and methodsBio-guided isolation was conducted on the extract of T. tuan flowers using a combination of column chromatography and preparative HPLC. The structures were established by a combination of extensive spectroscopic analyses and single-crystal X-ray diffraction analysis. The anti-inflammatory activity in vitro was evaluated by measuring the inhibition of nitric oxide (NO) production in LPS-stimulated RAW 264.7 cells. TNF-α and IL-6 levels were evaluated by ELISA. The expression of COX-2 and NF-κB was assayed via western blotting, and in-silico molecular docking was conducted to explore the potential mechanism. ResultsTwenty-two compounds, including ten flavonoids (1−10), seven phenylpropanoids (11−17), three triterpenoids (19−21), one sterol glucoside 18, and one glyceride 22, were identified from T. tuan flowers for the first time. Among them, 1 is a new compound. It is noted that 1, 5, 7, 8, 10, 17, and 22 exhibited remarkable anti-inflammatory activity against NO production with a range of 5.2–34.5 μM, superior to the positive control L-NMMA. Moreover, the new compound 1 inhibited significantly inflammatory factors IL-6 and TNF-α. ConclusionThe results show that flavonoids including the new one and the phenyl-propanoid are the primary active constituents of T. tuan flowers, responsible for its ethno-pharmacological uses on osteoarthritis and rheumatism. T. tuan flowers could be a promising therapeutic agent to modulate inflammatory diseases.