Probiotics and Biomarkers in Irritable Bowel Syndrome

The BIO-IBS study is a double-blind, randomized, placebo-controlled clinical trial investigating whether a combination probiotic improves symptoms in adults with irritable bowel syndrome (IBS). The trial also explores biological mechanisms and predictors of treatment response.

Background \& Rationale IBS is a common disorder of gut-brain interaction (\~4% prevalence in Sweden). Current treatments include dietary, pharmacological, and psychological approaches. Increasing evidence suggests the gut microbiome plays a key role, prompting interest in probiotics.

Aims

1\. Evaluate effect of probiotic combination on IBS symptoms. 2, Identify predictors of response. 3. Investigate IBS pathophysiology and biomarkers.

Study Design

Type: Double-blind, randomized, placebo-controlled, parallel-group Participants: 252 adults with IBS Randomization: 1:1 (probiotic vs placebo) Treatment duration: 12 weeks Follow-up: 3 months post-treatment Timeline: Recruitment starting April 2026 lasting \~3 years

Participants Inclusion Criteria

Adult (≥18 years), IBS (Rome IV criteria) IBS-SSS \> 75 BMI 18.5-35 Able to consent and complete Swedish questionnaires

Key Exclusion Criteria

Significant gastrointestinal or systemic disease Recent antibiotics (within 3 months) or probiotics (within 2 weeks) Opioid use Pregnancy/breastfeeding Significant lab abnormalities (e.g., high fecal calprotectin) Major lifestyle/treatment changes

Intervention

Active treatment: Tablet containing both L. reuteri strains Placebo: Identical without bacteria Dose: 1 tablet twice daily Duration: 12 weeks Compliance ≥80% required for per-protocol analysis.

Outcomes Primary Outcome

Change in IBS symptom severity (IBS-SSS) from baseline to 12 weeks (intervention vs placebo)

Secondary Outcomes

Proportion achieving ≥50 or ≥100 point IBS-SSS reduction Gastrointestinal symptoms (GSRS-IBS) Pain reduction Quality of life (IBSQOL) Work productivity (WPAI:IBS) Transit time (gut motility) Adverse events Sustainability of effects (3-month follow-up)

Exploratory Outcomes

Stool consistency/frequency Biomarkers (microbiome, immune, metabolomics, etc.) Psychological and lifestyle factors Dietary influences Mechanistic insights into IBS

Study Procedures Visits Screening (2-8 weeks before randomization Consent, questionnaires, biological samples, diaries

Randomization (Day 0) Baseline assessments and start of treatment

During intervention Regular symptom tracking Phone follow-up at week 6

End of treatment (12 weeks) Repeat assessments and samples

Follow-up (3 months later) Long-term outcomes

Optional (Facultative) Assessments Rectal sensitivity (barostat) Sigmoidoscopy ± confocal endomicroscopy MRI (motility and colonic volume)

Measurements

Questionnaires: IBS-SSS, GSRS-IBS, HADS, PHQ-15, IBSQOL, stress, work productivity Biological samples: blood, stool, urine, saliva Gut function: transit time (radiopaque markers and sweetcorn method) Diet: food frequency and recall diaries

Statistical Considerations Sample size: 252 participants (powered to detect clinically meaningful IBS-SSS difference)

Populations:

Intention-to-treat (all randomized) Per-protocol (≥80% compliance, no major deviations) Analysis plan: Defined in a Statistical Analysis Plan No interim analysis

Safety Probiotics considered safe with minimal risk (mainly transient flatulence). Adverse events will be recorded and classified by severity and causality. IBS symptom fluctuations are not counted as adverse events unless worsened.

Ethics \& Data Handling Conducted according to Declaration of Helsinki and ICH-GCP. Participants give informed consent and can withdraw anytime. Data are pseudonymized and securely stored (REDCap)

Risk-Benefit Assessment Low risk due to established safety of L. reuteri strains Moderate participant burden (questionnaires, sample collection) Optional procedures may cause discomfort but are controlled and voluntary Potential benefit: improved IBS symptoms and better understanding of disease mechanisms

Key Strengths Large sample size Rigorous randomized controlled design Comprehensive symptom, biological, and mechanistic assessment Long follow-up

Conclusion This study aims to determine whether a novel probiotic combination improves IBS symptoms and to identify biological and clinical predictors of response, contributing to more personalized treatment strategies in IBS.

• Gastrointestinal Symptom Rating Scale- IBS (GSRS-IBS) [Срок оценки: Screening (15-60 days pre-intervention), baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84), 3 month follow up post intervention]
• General global assessment: satisfactory adequate relief of symptoms from baseline to end of intervention between arms [Срок оценки: During intervention (days 14, 28, 42, 56, 70), end of intervention (day 84)]
• General global assessment: worst pain over the last 24 hours, intervention group vs placebo group reduced between baseline and end of intervention between arms [Срок оценки: During intervention (days 14, 28, 42, 56, 70), end of intervention (day 84)]
• IBS-quality of life (IBS-QoL) [Срок оценки: Baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84), 3 month follow up post intervention]
• Work Productivity and Activity Impairment:IBS (WPAI:IBS) [Срок оценки: Baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84), 3 month follow up post intervention]
• Change in oro-anal transit time from baseline to end of intervention between groups: Radiopaque markers [Срок оценки: Baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84)]
• Change in oro-anal transit time from baseline to end of intervention between groups: sweetcorn [Срок оценки: Baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84)]
• Hospital Anxiety and Depression Scale (HADS) [Срок оценки: Baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84), 3 month follow up post intervention]
• Patient Health Questionnaire (PHQ) [Срок оценки: Baseline (day 0 of intervention), during intervention (days 14, 28, 42, 56, 70), end of intervention (day 84), 3 month follow up post intervention]