Fecal Microbiota Transplantation Improves Clinical Symptoms and Promotes Intestinal Microecological Remodeling in Patients with Constipation Complicated by Anxiety: A Multi-omics Study

Technical Summary: Fecal Microbiota Transplantation in Constipation Complicated by Anxiety

Problem Statement
Constipation is a heterogeneous functional bowel disorder frequently comorbid with anxiety and depressive symptoms, suggesting coordinated disturbances across the gut microbiota, intestinal metabolism, and the gut-brain axis. While Fecal Microbiota Transplantation (FMT) has shown promise in functional gastrointestinal disorders, its clinical efficacy and underlying multi-omics mechanisms in patients with constipation complicated by anxiety remain unclear. Specifically, it is unknown whether FMT can restore gut microbial composition, functional potential, and metabolic profiles toward a healthy state in this specific patient population, and whether baseline ecological features predict treatment response.

Methodology
This study employed a multi-omics approach integrating clinical phenotyping, shotgun metagenomics, and untargeted metabolomics.

• Cohort: Eighteen patients with constipation complicated by anxiety (diagnosed via clinical criteria and HAMA scores ≥14) received two cycles of oral FMT capsules. Ten healthy individuals served as controls.
• Intervention: Patients underwent two cycles of oral FMT (two capsules, twice daily, for six days per cycle, with a 7-day interval), preceded by a 3-day vancomycin course and bowel preparation.
• Clinical Assessment: Efficacy was evaluated using the Wexner constipation score, PAC-QOL (quality of life), ODS (obstructed defecation syndrome), SDS (depression), and HAMA (anxiety) scores. Patients were stratified into "Effective" (≥50% reduction in Wexner score) and "No_Effective" groups.
• Omics Profiling:
  • Metagenomics: Shotgun sequencing (DNBSEQ-T7, PE150) was performed on fecal samples (n=37). Taxonomic profiling used MetaPhlAn 4.0, and functional annotation utilized HUMAnN 3.6 mapped to MetaCyc pathways.
  • Metabolomics: Untargeted metabolomics (LC-Orbitrap) was conducted on fecal samples (n=36).
• Analysis: The study utilized differential abundance analysis, pattern classification (Reversible, Persistently Dysregulated, Induced Dysregulation, No change), and Spearman correlation network analysis to link microbial taxa, metabolites, and clinical phenotypes.

Key Results

1. Clinical Improvement: FMT significantly reduced scores across all clinical metrics. The Wexner score decreased from 20.78 to 14.17 (P=0.0017), PAC-QOL from 54.06 to 37.56 (P=0.0018), ODS from 15.94 to 9.89 (P=0.0022), SDS from 61.39 to 40.78 (P=0.0032), and HAMA from 24.56 to 15.72 (P=0.0218). The overall effective rate was 55.6%.
2. Microbial Remodeling:
   • Structure: Baseline patient microbiota was distinct from healthy controls. Post-FMT, the microbial structure shifted toward a healthy-like profile, though it did not fully normalize.
   • Species Recovery: While strict multiple-testing correction yielded no significant species changes in Pre vs. Post comparisons, unadjusted analysis (P < 0.05) identified 29 differential species. 52 species (28.7%) were classified as "Reversible," with Clostridium, Blautia, and Lachnospira showing the most significant recovery.
   • Efficacy Stratification: The "Effective" group exhibited a baseline microbiota closer to healthy controls, with higher abundance of Bifidobacterium longum. The "No_Effective" group showed enrichment of potentially dysbiotic species (Klebsiella pneumoniae, Synergistes jonesii, Prevotella intermedia) at baseline.
3. Functional Pathway Recovery:
   • Baseline functional pathways were predominantly downregulated. Post-FMT, pathways related to anaerobic fermentation (e.g., pyruvate to butanoate) and amino acid metabolism (e.g., L-serine/glycine biosynthesis) showed recovery toward healthy levels.
   • Pathways related to bacterial surface structures and polysaccharide biosynthesis (e.g., colanic acid, O-antigen construction) remained persistently dysregulated.
   • The "Effective" group showed a higher proportion of reversible pathways (34%) compared to the "No_Effective" group, where 52% of pathways remained unchanged.
4. Metabolic Remodeling:
   • Fecal metabolomics revealed a shift from a globally suppressed metabolic state to a more active profile. Baseline patients had predominantly decreased metabolites; post-FMT, the number of increased metabolites rose significantly.
   • The "Effective" group demonstrated more pronounced metabolic remodeling (21 differential metabolites Pre vs. Post) compared to the "No_Effective" group (6 metabolites).
   • Key metabolic shifts involved amino acids, lipids, and phenylpropanoids.
5. Correlation Networks: Integrated network analysis identified Butyricicoccus sp. AM29-23AC as a key node significantly negatively correlated with Wexner, PAC-QOL, ODS, SDS, and HAMA scores (rho = −0.799 for Wexner). This species was embedded in a short-chain fatty acid (SCFA)-related subnetwork involving Roseburia, Faecalibacterium, and Coprococcus.

Significance and Claims
The authors claim that oral FMT capsules are associated with the improvement of constipation symptoms, quality of life, and anxiety/depression-related scores in patients with constipation complicated by anxiety. This clinical improvement is accompanied by a coordinated remodeling of the gut ecosystem at the levels of microbial composition, functional potential, and fecal metabolic profiles.

The study posits that:

• Baseline Determinants: The recipient's baseline microbial composition, functional ecological niches, and metabolic background are critical determinants of FMT efficacy. Patients with a "healthier" baseline state (e.g., higher Bifidobacterium longum) are more likely to respond.
• Mechanistic Links: Butyricicoccus sp. AM29-23AC and SCFA-related microbiota-metabolite networks represent candidate mechanisms linking FMT-induced ecological remodeling to clinical symptom improvement.
• Partial Restoration: FMT promotes partial recovery of the gut microbiome and metabolome but does not fully normalize these systems in the short term, particularly regarding bacterial surface structure pathways.

The authors emphasize that these findings provide multi-omics evidence supporting further investigation into FMT for this condition and offer a basis for future precision selection of responsive patients, while acknowledging limitations such as the small sample size and lack of a placebo-controlled design.