AIM-IBD: A Microbiome-Targeted Supplement in Mild-to-Moderate Ulcerative Colitis

Ulcerative colitis is a chronic inflammatory disease of the colonic mucosa characterized by relapsing and remitting symptoms including rectal bleeding, increased stool frequency, urgency, and impaired quality of life. Although 5-aminosalicylic acid (5-ASA, mesalamine) is the foundation of treatment for mild-to-moderate disease, a meaningful proportion of patients have persistent symptoms or ongoing objective inflammation despite optimized therapy, and many wish to defer immunosuppressive or biologic therapy. The intestinal microbiota of patients with active ulcerative colitis differ from those of healthy individuals, with depletion of short-chain fatty acid-producing taxa, reduced diversity, and altered microbial metabolism. Food-grade microbiome-targeted interventions therefore offer a non-immunosuppressive option to modify intestinal microbial ecology and inflammatory activity in this gap. AIM-IBD is designed as a Phase 2b, randomized, double-blind, placebo-controlled, parallel-group, multicenter proof-of-concept trial. Randomization is centralized and stratified by study site and baseline 5-ASA status. Participants, investigators, site staff, outcome assessors, endoscopy readers, central laboratory personnel, microbiome and metabolomics analysts, and the primary trial statistician remain blinded to allocation until database lock, except where emergency unblinding is required for participant safety. Blinding integrity is formally assessed at Weeks 12 and 24 using participant and investigator treatment-guess questionnaires summarized with Bang's and James's blinding indices. The Week 24 endoscopic assessment is by protocol-mandated flexible sigmoidoscopy with dual independent blinded reading and adjudication of discordant scores. Fecal calprotectin and other biomarkers are measured in a central laboratory. Stool samples for microbiome and metabolomics analyses are collected at baseline, Week 12, and Week 24 under a harmonized study procedure. The planned sample size of 162 participants (81 per arm) provides approximately 90% power to detect a 23-percentage-point absolute difference in the Week 24 primary endpoint (placebo 12% vs active 35%), with two-sided alpha 0.05 and approximately 15% attrition. This ambitious effect size is defensible only because the trial is designed as a high-signal proof-of-concept study: the enrolled population is enriched for objectively active disease (fecal calprotectin ≥250 µg/g and rectal bleeding subscore ≥1 at screening), background therapy is held constant (stable 5-ASA at unchanged dose for ≥8 weeks, or no inflammatory bowel disease therapy), and patients with recent advanced-therapy exposure or current corticosteroids are excluded. Sensitivity analyses across a range of placebo and active response assumptions are prespecified in the Statistical Analysis Plan. The intention-to-treat population is the primary analysis population. The primary composite endpoint is analyzed using stratified Cochran-Mantel-Haenszel methodology adjusted for randomization stratification factors. Key secondary endpoints are tested in a fixed-sequence hierarchical procedure controlling the family-wise error rate at two-sided alpha 0.05. The estimand framework follows ICH E9(R1): treatment failures (rescue therapy, prohibited escalation, ulcerative colitis-related hospitalization, colectomy, discontinuation for lack of efficacy) are handled under a composite strategy, with a supplementary treatment-policy estimand and prespecified sensitivity analyses (multiple imputation, tipping-point analysis, pattern-mixture). An independent Data Safety Monitoring Board with a written charter oversees safety, with scheduled reviews after approximately 25%, 50%, and 75% of planned enrollment and ad hoc reviews for predefined safety signals. An independent Endpoint Adjudication Committee adjudicates ulcerative colitis-related hospitalizations, colectomies, and any deaths. Rescue therapy is permitted at any time when clinically necessary; participants requiring rescue therapy or any prohibited treatment escalation before Week 24 are classified as treatment failures for the primary endpoint and continue safety follow-up whenever feasible. The trial is conducted in accordance with the Declaration of Helsinki and ICH-GCP E6(R3). Reporting follows the CONSORT statement, the SPIRIT protocol framework, and the STORMS reporting checklist for the microbiome workstream.