Laoxianghuang polysaccharide promotes the anti-inflammatory cytokine interleukin-10 in colitis via gut microbial linoleic acid.

Background: Our previous study found that the polysaccharide from Laoxianghuang (LP), fermented fruit of bergamot (traditional Chinese medicine and food), can alter gut microbiota and regulate short-chain fatty acids (SCFAs) in vitro. Nevertheless, there is a paucity of reports on the impact of LP on gut microbiota in vivo.

Purpose: To analyze the structures of LP, investigate the influence of LP on the damaged intestinal barrier in DSS-induced colitis mice, and further explore its potential mechanisms.

Methods: We analyzed the physicochemical properties of purified LP by HPLC, SEM, and FT-IR spectrum. Then, to assess the effect of LP in DSS-induced colitis mice, we observed the damage to the colon tissue, measured inflammatory cytokines and tight junction protein expression through RT-qPCR as well as immunofluorescent staining, and investigated the influence of LP on altering gut microbiota and metabolites using 16 s rRNA sequencing and HPLC-MS/MS. Ultimately, the impact of linoleic acid on inflammatory cytokines was confirmed by the LPS-induced RAW264.7 cells.

Results: LP, mainly galactoglucan, could inhibit weight loss and colon shortening, decrease levels of tumor necrosis factor-α (TNF-α), increase levels of interleukin-10 (IL-10) and the intestinal acetic acid and butyric acid, and promote the expression of tight junction proteins ZO-1 and Claudin-1. Meanwhile, LP enhanced the abundance of beneficial bacteria including Romboutsia, Eubacterium_coprostanoligenes_group, and Akkermansia, and regulated linoleic acid metabolism to increase the linoleic acid level. In vitro cell experiment proved that linoleic acid could elevate the level of IL-10 and inhibit inflammatory responses.

Conclusions: Our results suggested that LP effectively alleviated colitis by promoting the anti-inflammatory cytokine interleukin-10 via gut microbiota-mediated linoleic acid metabolism.