Megastigmanes isolated from Boehmeria nivea leaves and their immunomodulatory effect on IL-1β and IL-10 production in RAW264.7 macrophages

Abstract

With the aim of isolating immunomodulatory compounds from the n-butanol extract of Boehmeria nivea leaves, nine megastigmane compounds were identified. Among these, the structure of the new compound 1, namely, “boehmegaside A”, was established using NMR and HR-ESI-MS, and its absolute configurations were established through ECD calculations and DP4+ analysis using DFT-NMR chemical shift calculations. Furthermore, eight of these compounds were discovered for the first time in the Boehmeria genus, marking this the first report on megastigmane compounds isolated from this genus. Regarding their immunomodulatory activity, the isolated megastigmane compounds 3, 2, and 6 exhibited pro-inflammatory cytokine IL-1β secretion inhibitory activity. Compounds 3 and 6 significantly increased anti-inflammatory cytokine IL-10 secretion in LPS-activated RAW264.7 cells. Furthermore, the study on the mechanism of the immunomodulatory and other biological activities of megastigmane compounds through molecular docking simulations revealed that the planar structures of 3, 2, and 6 were critical in their ability to directly suppress TLR4 signalling. Instead, they attached to a nearby smooth area in TLR4. This interference likely disrupted the ability of TLR4 and MD-2 to form their primary contact interface and recognize LPS. These findings highlight the significant role of TLR4 in inflammation and immunity, indicating that these megastigmane compounds may be beneficial in treating various inflammatory disorders associated with immunological issues.