Crude Polygalae Radix after boiling with licorice decoction alleviates intestinal mucosal barrier injury of rats by regulating TLR4/NF-κB signaling pathway.

Ethnopharmacological Relevance: Polygala tenuifolia Willd. (pharmacologically termed Polygalae Radix, PR), a nootropic botanical in traditional Chinese medicine, demonstrates anxiolytic and cognitive-enhancing properties with two millennia of documented therapeutic applications. Long-term or large-dose use of crude Polygalae Radix (CPR) causes intestinal injury, which could be reduced by use of Glycyrrhiza uralensis Fisch. (licorice) decoction-boiled Polygalae Radix. However, the effects of boiling CPR with licorice decoction on reducing intestinal mucosal barrier injury have not been studied.

Aim Of The Study: Our research mainly focused on the alleviating effects and underlying mechanism of CPR after boiling with licorice decoction on intestinal mucosal barrier injury in rats.

Methods And Materials: SD rats were orally administered CPR and licorice decoction-boiled PR (LPR) extracts respectively for 15 consecutive days. Subsequently, levels of pro-inflammatory cytokines and immunoglobulins were measured, and histopathological changes in intestinal tissues were examined. The mRNA expression levels of pro-inflammatory cytokines were evaluated by qRT-PCR. The expression difference of TLR4/NF-κB signaling pathway key protein and tight junction (TJ) protein were evaluated using Western blotting and immunohistochemistry.

Results: Processing PR with licorice decoction significantly ameliorated the downregulation of intestinal TJ proteins (occludin, claudin-1, and ZO-1) and elevated serum lipopolysaccharide levels induced by CPR. It alleviated the suppression of intestinal immunoglobulin A, serum immunoglobulin A and immunoglobulin G levels caused by CPR while mitigating intestinal mucosal injury and inflammatory responses. Additionally, processing PR with licorice decoction inhibited CPR-triggered upregulation of TLR4, NF-κB p65, p-NF-κB p65, and p-κBα proteins expression, while preventing IκBα downregulation in intestinal tissues. Furthermore, it significantly suppressed the upregulation of interleukin (IL)-6, IL-8, and tumor necrosis factor-α (TNF-α) mRNA expression while concurrently inhibiting the secretion levels of these pro-inflammatory cytokines in small intestine.

Conclusion: Our experimental data suggest that licorice decoction boiling effectively prevents CPR-induced reductions in TJ proteins and immunoglobulins expression, alleviates intestinal mucosal barrier injuries, and mediates these effects through suppression of TLR4/NF-κB signaling pathway activation and subsequent production of IL-6, IL-8, and TNF-α.