Introduction
Inflammatory bowel diseases (IBD)—ulcerative colitis (UC) and Crohn’s disease (CD)—are characterized by chronic intestinal inflammation with variable relapsing courses. Beyond immune dysregulation, a growing body of evidence implicates dysfunction of the intestinal epithelial barrier (IEB) in symptom persistence, disease chronicity and complications. Restoring the structure and function of this epithelial barrier is therefore an attractive therapeutic goal, potentially complementary to immunomodulation.\n\nUntil now, no large randomized clinical trials have been specifically designed to test therapies with the primary goal of reconstituting barrier integrity. Methods to measure barrier function vary widely across studies, and no standardized framework exists to define, quantify or adjudicate “barrier healing.” To address this gap, an international panel of 12 experts produced a consensus statement outlining recommendations for designing trials and selecting tools to evaluate therapies that aim to restore intestinal barrier integrity and function in IBD (Vieujean et al., Gut 2026). This article summarizes the consensus, highlights practical recommendations for trialists, and discusses implications for clinical practice and research.
Why this consensus matters now
– Increasing recognition that persistent symptoms and poor long-term outcomes can relate to barrier defects, even when inflammation appears controlled.
– Emergence of candidate therapies with mechanisms that may directly affect epithelial cells, tight junctions, mucosal restitution and epithelial metabolism.
– Need for standardized endpoints and validated tools to evaluate barrier-targeted interventions, enabling reproducible, comparable evidence across trials.
Key references underpinning the effort include the consensus itself (Vieujean et al., Gut 2026), prior treat-to-target efforts in IBD such as STRIDE-II (D’Haens et al., Gastroenterology 2021), and foundational work on mucosal barrier biology (Turner, Nat Rev Immunol 2009; Camilleri et al., Neurogastroenterol Motil 2012; Fasano, Physiol Rev 2011).
New Guideline Highlights
The international consensus produced 14 agreed statements covering trial design, endpoint selection, timing of assessments, required protocol elements and recommended measurement tools.
Major themes:
– Barrier assessment is appropriate as an exploratory or secondary endpoint in standard IBD trials and can be a primary endpoint in trials explicitly targeting epithelial repair.
– A multimodal approach (combining structural imaging, functional tests and endogenous biomarkers) is recommended rather than reliance on any single assay.
– Standardization, central reading and pre-specified timing windows are essential to reduce variability.
– Disease-specific considerations: protocols should adapt measures to UC and CD phenotypes (colonic vs small bowel involvement) because tools perform differently by location.
Key takeaways for clinicians and trialists
– Define the intent: is the therapy aimed at structural epithelial repair, functional permeability, or both? This choice drives endpoint selection.
– Use a core panel of assessments (imaging ± biopsies, functional permeability tests, and specified circulating/fecal biomarkers) with pre-specified analytic methods.
– Standardize patient preparation, confounder documentation (e.g., NSAID use, recent infections), and centralize analysis where possible.
Updated Recommendations and Key Changes
\nThis consensus is not a replacement for disease management guidelines (e.g., STRIDE-II) but represents the first international attempt to standardize barrier-focused trial methodology. Notable advances compared with prior practice include:
– Explicit endorsement of barrier endpoints as primary outcomes in dedicated barrier-restoration trials (previously uncommon).
– Clear recommendation to combine orthogonal methods (structure + function + biomarkers) rather than exploratory single-test approaches. \n- Protocol-level requirements for timing of reassessment and standardization of confounders (medications, infections, bowel prep).
Table: Summary of major consensus recommendations (simplified)\n- Role of barrier assessment: exploratory/secondary endpoint in general IBD trials; primary endpoint in barrier-targeted trials.
– Endpoint composition: multimodal (imaging / biopsy structural measures + functional permeability testing + endogenous biomarkers).
– Timing: baseline, early (4–12 weeks) for pharmacodynamic signals, and later (24–52 weeks) for durable barrier healing.
– Standardization: central reading, harmonized sample handling, and documented confounders.
– Disease-specific: select small-bowel-capable tests for ileal CD (e.g., sugar permeability), colonic imaging for UC (endomicroscopy, mucosal histology).
Evidence driving the updates: trial variability and lack of standardized endpoints have hampered interpretation of barrier effects in past studies. The panel used a systematic review to identify candidate tools and then applied a Delphi process to reach consensus on a pragmatic, implementable framework (Vieujean et al., 2026).
Topic-by-Topic Recommendations
Below are the consensus recommendations organized by topic with practical details.
1) When can barrier endpoints be used?
– Primary endpoint: permitted when the therapeutic mechanism is explicitly targeted to epithelial repair/function and safety/clinical efficacy data support proceeding to pivotal testing.
– Secondary/exploratory: in trials of systemic or immune-directed therapies to assess off-target or complementary effects on barrier integrity.
2) Which endpoints should be chosen?
A multimodal core set is recommended:
– Structural assessment (composition depends on disease location): high-definition endoscopy with mucosal biopsies; advanced endoscopic imaging such as confocal laser endomicroscopy (CLE) where available for in vivo microscopic assessment.
– Histology: standardized scoring of epithelial injury and epithelial cell polarity, tight junction protein expression where biopsies are taken. Central pathology reading is recommended.
– Functional permeability assays: sugar probe tests (e.g., lactulose/mannitol or sucralose probes) for small-bowel permeability; orally administered probes with timed urine or blood collection.
– Endogenous biomarkers: serum intestinal fatty acid–binding protein (I-FABP) for enterocyte damage, faecal calprotectin (for barrier-linked neutrophilic translocation in the colon), and LPS-binding protein or endotoxin-core antibodies for translocation/endotoxemia signals. Zonulin remains investigational and is not recommended as a sole marker.
3) Timing of assessments\n- Baseline: all barrier assessments should be performed pre-randomization. \n- Early signal: 4–12 weeks — useful for pharmacodynamic effects (e.g., rapid changes in permeability or I-FABP).
– Durability and healing: 24–52 weeks — structural restoration and meaningful clinical benefit are best assessed later.
4) Protocol and standardization requirements
– Patient preparation: standardized diet prior to permeability testing, withholding of potential confounders (NSAIDs, non-essential antibiotics) per protocol.
– Sample handling: detailed SOPs for stool/serum/urine collection and storage, and timing relative to dosing and endoscopy.
– Central reading: centralized pathology and imaging interpretation to limit interobserver variability.
– Pre-specified analytic plan: definitions for what constitutes barrier “improvement” or “healing” must be written into the statistical analysis plan (e.g., % change in permeability, normalization thresholds).
5) Disease-specific considerations
– Ulcerative colitis: emphasis on colonic imaging (endoscopy, CLE), mucosal histology, fecal biomarkers. Sugar permeability tests may be less sensitive when disease is limited to the colon.
– Crohn’s disease: for small-bowel involvement, functional permeability tests (e.g., lactulose/mannitol, sucralose) and small-bowel imaging/enteroscopy-inclusive strategies are necessary. For isolated colonic CD, approach as for UC.
6) Analytical and clinical endpoints
– The panel recommends reporting both absolute and relative changes, responder rates (proportion achieving pre-defined normalization thresholds), and correlations between barrier outcomes and clinical/biomarker outcomes (e.g., symptom scores, calprotectin, endoscopic remission).
Tools: Strengths and Limitations
The consensus emphasizes the complementary nature of modalities:
– Confocal laser endomicroscopy (CLE): offers in vivo microscopic assessment of mucosal integrity and immediate detection of fluorescein leakage. Strength: direct visualization of epithelial gaps. Limitation: limited availability, operator-dependent, invasive.
– Histology and immunostaining: gold standard for structural changes and tight junction protein assessment. Strength: high specificity. Limitation: focal biopsies may miss patchy lesions; invasive.
– Sugar permeability tests (lactulose/mannitol, sucralose): non-invasive functional measures of paracellular and transcellular permeability. Strength: suitable for small-bowel assessment. Limitation: variable patient compliance, influenced by transit time and renal function.
– Endogenous biomarkers (I-FABP, calprotectin, LBP): minimally invasive and repeatable. Strength: practical for multicenter trials. Limitation: many are not specific for barrier defects and need validation as surrogate endpoints. Zonulin is not recommended as a standalone marker given assay variability and biological controversies.
Expert Commentary, Controversies and Research Needs
Panel perspectives and unresolved issues
– Consensus panelists agreed on the conceptual importance of barrier endpoints but noted practical hurdles: access to specialized imaging (CLE), inter-lab variability in biomarker assays, and the challenge of defining clinically meaningful thresholds of barrier ‘‘healing.’’
– Some experts cautioned against over-reliance on a single biomarker and urged that improvements in barrier metrics be tied to clinical benefit in later-phase trials before being adopted as surrogate regulatory endpoints.
– A key controversy surrounds zonulin: although biologically plausible as a regulator of tight junctions, current assays lack sufficient reliability for trial use; hence, the consensus recommends against using zonulin as a primary marker until standardization improves.
Priority areas for future research\n- Prospective validation of combined barrier panels as surrogate markers for patient-centered outcomes.
– Standardization and inter-laboratory calibration of I-FABP, LPS-related assays, and permeability test protocols.
– Development and wider dissemination of imaging modalities (including non-invasive imaging) that can provide reproducible measures of epithelial integrity.
– Mechanistic trials linking molecular markers of junctional complexes to functional tests and clinical endpoints.
Practical Implications for Trialists and Clinicians
Operational recommendations
– If planning a barrier-targeted trial, include a multidisciplinary steering committee with gastroenterology, pathology, imaging and biomarker expertise.
– Budget for central laboratories and centralized image/pathology reading.
– Pre-specify the analytic plan for composite barrier endpoints and sensitivity analyses that consider location of disease and confounders.
For clinicians interpreting trial data
– Look for trials that used multimodal assessments and pre-specified definitions of barrier improvement.
– Consider whether reported changes in barrier metrics correlate with patient-reported outcomes, endoscopic remission and hard clinical outcomes (steroid-free remission, hospitalization, surgery).
Illustrative Patient Vignette
John is a 32-year-old man with moderate ileal Crohn’s disease who experiences persistent post-prandial cramping despite steroid-free clinical remission and near-normal CRP. His gastroenterologist enrolls him in a trial of a novel agent aimed at enhancing epithelial restitution. Baseline assessments include small-bowel permeability testing (lactulose/mannitol), serum I-FABP, and ileocolonoscopy with biopsies and CLE. At 8 weeks, his permeability ratio improves and I-FABP falls, suggesting an early pharmacodynamic effect; at 26 weeks, histology shows reduced epithelial gap density and the patient’s symptoms markedly improve. This multimodal concordance strengthens the case that the agent is producing meaningful barrier restoration linked to symptomatic benefit.\n\n
Conclusions
The international consensus on intestinal epithelial barrier assessment in IBD trials provides the first structured framework to standardize how researchers measure and interpret barrier-related outcomes. It recognizes barrier healing as a plausible therapeutic target and recommends a pragmatic, multimodal approach combining structural imaging, functional tests and endogenous biomarkers, with rigorous standardization and centralization. These recommendations aim to accelerate the development of barrier-directed therapies while ensuring that measures are robust, reproducible and clinically meaningful. Future work will need to validate composite panels as surrogates for patient-centered outcomes and expand assay standardization to support regulatory acceptance.\n\n
References
1) Vieujean S, Atreya R, Buda A, Citi S, Danese S, Dewit O, Friedrich M, Ghosh S, Iacucci M, Jairath V, Kaser A, Leong R, Neurath MF, Pierre N, Pohin M, Rath T, Rivière P, Travis S, Zeissig S, Peyrin-Biroulet L. International consensus on intestinal epithelial barrier assessment and therapeutic effects in inflammatory bowel diseases clinical trials. Gut. 2026 Jul 16:gutjnl-2026-339056. doi: 10.1136/gutjnl-2026-339056. Epub ahead of print. PMID: 42463422.
2) D’Haens G, et al. STRIDE-II: An update on therapeutic targets for treat‑to‑target strategies in inflammatory bowel disease. Gastroenterology. 2021;160(5):1570–1583. (Selecting Therapeutic Targets in IBD: STRIDE-II)
3) Turner JR. Intestinal mucosal barrier function in health and disease. Nat Rev Immunol. 2009 Nov;9(11):799–809.
4) Camilleri M, Madsen K, Spiller R, Greenwood‑Van Meerveld B, Verne GN. Intestinal barrier function in health and gastrointestinal disease. Neurogastroenterol Motil. 2012 Jun;24(6):503–512.
5) Fasano A. Zonulin, regulation of tight junctions, and autoimmune diseases. Physiol Rev. 2011 Jan;91(1):151–175.
