Anti-inflammatory compounds of "Qin-Jiao", the roots of Gentiana dahurica (Gentianaceae)

Ethnopharmacological relevance: "Qin-Jiao" is a well-known traditional Chinese medicinal (TCM) herb having been used generally for fighting rheumatoid arthritis (RA) since ancient times. The root of Gentiana dahurica Fisch (Gentianaceae) is one of the four officially validated "Qin-Jiao" as listed in the Chinese Pharmacopoeia. In addition, it is a common Tibetan medicinal herb used for the treatment of tonsillitis, urticaria, and RA, while the flowers have been used as a Mongolian herb for curing cough sore throat and eliminating the phlegm due to its anti-inflammatory effect.

Aim of the study: The aim of the study was to characterize the anti-inflammatory compounds in "Qin-Jiao", on the basis of detailed investigation on not only the phytochemical study of Gentiana dahurica, but also the bioactive evaluation on compounds obtained presently and previously from different "Qin-Jiao" origins and Gentiana species.

Materials and methods: The ethanol extract of air-dried roots of Gentiana dahurica was suspended into H2O and extracted with EtOAc and n-BuOH, successively. Repeated column chromatography (CC) and semi-preparative HPLC were carried out on each of the fractions. The isolated compounds were determined by detailed spectroscopic analysis and acidic hydrolysis. Anti-inflammatory activities of 18 isolates, together with 12 typical compounds obtained previously by our group from the other "Qin-Jiao" origins (Gentiana crassicaulis, Gentiana straminea) and Gentiana rigescens, were tested by inhibitory effects on LPS-induced NO production in macrophage RAW264.7 cells and TPA-induced cyclooxygenases-2 and -1 (COXs-2/1) production on zebrafish model.

Results: A new lignan glycoside (1) was identified, together with 20 known compounds, including 10 iridoid glycosides (2-11), three steroids (12-14), four lignans (15-18), one phenylpropanoid (19) and two triterpenes (20-21). Anti-inflammatory bioassay showed that only compound 21 displayed potential inhibitory effect on NO production (IC50=16.85 μM), while 20 tested compounds had inhibitory activities on COXs-2/1. Among them, the triterpenoid 21 was the most active compound with an inhibitory value of 78% at a concentration of 30 μM. All the tested compounds showed no cytotoxicity on five human cancer cell lines (40μM) and zebrafish (30 μM), except for 21 displaying weak cytotoxicity on human myeloid leukemia HL-60 (IC50=16.43 μM).

Conclusion: Most of compounds particularly iridoid glycosides from "Qin-Jiao" display potential inhibitory effect on COXs-2/1. The results support the historical importance of the well-known TCM herb, "Qin-Jiao", having been commonly used for fighting RA. As major components, the bioactive iridoid glycosides should play important role in the anti-inflammatory effect of "Qin-Jiao". Although further research will be required to evaluate the selective activities of the COXs-2/1 inhibitors, this work validates the medicinal use of "Qin-Jiao" and provides information for different "Qin-Jiao" origins having different treating effects on RA.