# Investigating the mechanisms of Sini San in alleviating inflammatory responses via multi-omics and the BDNF/TrkB/PI3K/AKT signaling pathway in depressive model rats

## TL;DR

This study explores how Sini San, a traditional Chinese medicine, reduces inflammation and depressive symptoms in rats by modulating gut health and brain signaling pathways.

## Contribution

The study identifies the BDNF/TrkB/PI3K/AKT signaling pathway and gut microbiota as key mechanisms through which Sini San alleviates depression.

## Key findings

- Sini San reduced NLRP3 inflammasome-related inflammation and pro-inflammatory cytokines in depressive rats.
- Sini San restored intestinal barrier function and gut microbiota balance disrupted by chronic stress.
- Sini San activated the BDNF/TrkB/PI3K/AKT signaling pathway, potentially improving synaptic plasticity and depressive symptoms.

## Abstract

Sini San, from the traditional Chinese medicine classic Treatise on Exogenous Febrile Disease, has been reported to improve anxiety and depressive symptoms in clinical practice and exhibits certain anti-inflammatory effects. Studies have shown that the inflammatory response is not merely a concomitant feature of depression but actively contributes to its pathogenesis via neuroimmune mechanisms. However, the underlying mechanism remains unclear.

This study aimed to evaluate the antidepressant effect and inflammatory profile of Sini San in chronic unpredictable mild stress (CUMS)-induced rats and to explore its potential mechanism.

The primary active ingredients, targets, and pathways of Sini San in treating depression were determined through network pharmacology. The improvement of depression-like behaviors was assessed using behavioral experiments. Tissue inflammatory responses were evaluated through histopathological analysis (HE staining and Nissl staining) and quantitative measurement of inflammatory cytokines by ELISA. Western blotting (WB) was employed to quantify protein expression levels, while RT-qPCR was used to assess mRNA transcription levels. Gut microbial composition was analyzed by 16S rRNA gene amplicon sequencing, with taxonomic classification performed using the Greengenes database.

The data indicated that Sini San reduced inflammation related to the NLRP3 inflammasome pathway by inhibiting the expression of NLRP3, ASC, caspase-1, and downstream pro-inflammatory cytokines IL-18, IL-1β, and TNF-α. According to network pharmacology analysis, Sini San mitigated depression via modulation of the PI3K/AKT signaling pathway. Upstream and downstream proteins, including BDNF (brain-derived neurotrophic factor), TrkB (tropomyosin receptor kinase B), and p-CREB (phosphorylated cAMP response element-binding protein), which were decreased after CUMS induction, were regulated by Sini San. Furthermore, Sini San enhanced the expression of colonic tight junction and adhesion junction proteins ZO-1, claudin-1, and occludin-1 mRNA, while simultaneously restoring intestinal microbiota balance—indicating amelioration of CUMS-induced disruptions in intestinal barrier function and microbial composition.

Sini San modulates the gut–brain axis by inhibiting the NLRP3 inflammasome, thereby alleviating CUMS-induced inflammation and gut microbiota dysbiosis in rats. This effect may further contribute to the improvement of depressive symptoms via regulation of the BDNF/TrkB/PI3K/AKT signaling pathway.

Graph abstract Schematic representation of the proposed mechanism for Sini San improving CUMS-induced depression-like behavior of rats. Our results demonstrated that CUMS-stimulated rats exhibited intestinal flora dysbiosis, which further activated the NLRP3 inflammasome pathway, leading to the release of inflammatory factors such as IL-18, IL-1β, TNF-α, etc. Inflammatory factors enter into the bloodstream and subsequently cross the blood-brain barrier (BBB), triggering neuroinflammation and synaptic damage. Furthermore, CUMS induction also affects BDNF/TrkB and its downstream PI3K/AKT signaling pathway, resulting in synaptic damage and synaptic plasticity, which ultimately contributes to depression-like behaviors. These pathological changes are reversed following treatment with Sini San. Simultaneously, our studies suggested that Sini San exerts antidepressant effects by modulating intestinal flora balance, attenuating the inflammatory response, and activating the BDNF/TrkB/PI3K/AKT signaling pathways through enhanced the phosphorylation of downstream proteins.

Illustration depicting the effects of a treatment on CUMS-mice involving traditional herbs. The left section shows SNS herbs and treatment by gavage in mice. The right section details neuro-inflammation, peripheral inflammation, and intestinal inflammation, highlighting pathways involving cytokines, inflammasomes, and the gut microbiota. The diagram illustrates potential interactions between depression, inflammation, and the intestinal barrier.