Tetrastigma hemsleyanum protects against sepsis-induced intestinal injury by suppressing TLR4/NF-κB signaling and macrophage polarization

Technical Summary: Tetrastigma hemsleyanum Protects Against Sepsis-Induced Intestinal Injury

Problem Statement
Sepsis-induced intestinal injury acts as a critical driver of systemic inflammation and multiple organ dysfunction syndrome (MODS). This injury is characterized by the breakdown of the epithelial barrier, depletion of mucus-secreting goblet cells, and the translocation of bacterial products (e.g., LPS) into circulation, which amplifies the cytokine storm. The underlying mechanisms involve the activation of the TLR4/NF-κB signaling pathway, leading to a shift in intestinal macrophages toward a pro-inflammatory M1 phenotype and severe dysbiosis of the gut microbiota. While Tetrastigma hemsleyanum (TH), known as "Sanyeqing" in Traditional Chinese Medicine, possesses documented anti-inflammatory and immunomodulatory properties, its specific efficacy and mechanistic role in mitigating sepsis-induced intestinal injury remain unexplored.

Methodology
The study utilized a rat cecal ligation and puncture (CLP) model to induce mid-grade sepsis in male Sprague–Dawley rats.

• Experimental Design: Rats were pre-treated with TH (2, 4, or 8 g/kg) via intragastric gavage for 14 consecutive days prior to CLP surgery. A sham group and a sepsis-only (vehicle) group served as controls.
• Assessment Metrics: At 72 hours post-surgery, the study evaluated:
  • Physiological/Histological: Survival rates, body weight changes, mucosal histopathology (H&E), goblet cell abundance (PAS staining), and mitochondrial ultrastructure (Transmission Electron Microscopy).
  • Molecular Signaling: Expression of TLR4, COX-2, and NF-κB (p65 and p-p65) via immunohistochemistry (IHC), Western blot, and qRT-PCR.
  • Barrier Integrity: Tight junction proteins (ZO-1 and occludin) assessed via immunofluorescence (IF).
  • Immune Response: Macrophage polarization (M1 vs. M2) in the distal ileum lamina propria using flow cytometry (CD11b, CD86, CD206 markers) and cytokine profiling (TNF-α, IL-6, IL-1β, IL-10) via ELISA.
  • Microbiome: 16S rRNA gene sequencing of intestinal contents to analyze microbial diversity, community composition, and co-occurrence networks.

Key Results

1. Protection of Intestinal Structure: TH pretreatment dose-dependently attenuated sepsis-induced weight loss and improved survival. Histologically, TH reversed villus shortening, epithelial disruption, and goblet cell loss. It also preserved mitochondrial ultrastructure and restored the expression of tight junction proteins ZO-1 and occludin.
2. Suppression of Inflammatory Signaling: TH significantly downregulated the TLR4/COX-2/NF-κB signaling pathway at both the mRNA and protein levels. This inhibition correlated with a reduction in pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) and an increase in the anti-inflammatory cytokine IL-10.
3. Modulation of Macrophage Polarization: Flow cytometry revealed that sepsis induced a shift toward the pro-inflammatory M1 phenotype (CD86⁺). TH treatment suppressed M1 polarization and promoted a shift toward the anti-inflammatory, reparative M2 phenotype (CD206⁺).
4. Restoration of Gut Microbiota: TH partially reversed sepsis-induced dysbiosis. It restored microbial diversity (alpha and beta diversity), suppressed the expansion of the Proteobacteria phylum (specifically Escherichia–Shigella), and enriched beneficial taxa associated with short-chain fatty acid (SCFA) production, such as Lachnospiraceae and Ruminococcaceae. Furthermore, TH rebuilt the complexity and stability of the microbial co-occurrence network.

Key Contributions
This study provides the first evidence that Tetrastigma hemsleyanum exerts a protective effect against sepsis-induced intestinal injury. The primary contributions include:

• Mechanistic Elucidation: Establishing that TH functions by modulating the "gut microbiota–macrophage–TLR4/NF-κB axis." Specifically, it links the restoration of beneficial microbial taxa to the suppression of TLR4/NF-κB signaling and the subsequent reprogramming of macrophages from M1 to M2.
• Multi-Targeted Therapy: Demonstrating that TH acts synergistically to preserve the physical intestinal barrier, dampen systemic inflammation, and restore ecological homeostasis in the gut.
• Microbiome Insights: Identifying that TH acts as a microbiota-targeted intervention that reverses the loss of diversity and the bloom of opportunistic pathogens characteristic of sepsis.

Significance and Claims
The authors claim that TH represents a promising candidate for adjunctive therapy in sepsis management. By simultaneously reinforcing the mucosal barrier, inhibiting the TLR4/NF-κB inflammatory cascade, and promoting macrophage M2 polarization, TH addresses multiple pathological drivers of sepsis. The study suggests that TH's ability to remodel the gut microbiota—specifically by enriching SCFA-producing bacteria—may be a critical upstream mechanism for its immunomodulatory effects.

Limitations and Future Directions
The authors modestly acknowledge several limitations:

• The study used a whole TH extract rather than isolated bioactive constituents, leaving the specific active compounds unidentified.
• While 16S sequencing suggested an enrichment of SCFA-producing bacteria, fecal SCFA levels were not directly quantified, preventing a definitive link between microbial metabolic output and barrier repair.
• Causality between microbiota remodeling and macrophage polarization was not established; the authors note that future studies using fecal microbiota transplantation or antibiotic-depletion models are required to confirm if the immunomodulatory effects are mediated directly by the microbiota.
• The regimen was preventive (pre-treatment); future research is needed to evaluate therapeutic efficacy when administered post-onset.