Fecal Zonulin-Related Proteins in Inflammatory Bowel Disease: Associations with Clinical Disease Activity and Inflammatory Markers.

Background and Objectives: Intestinal barrier dysfunction is increasingly recognized as a contributor to inflammatory bowel disease (IBD) pathophysiology. Zonulin, a regulator of epithelial tight-junction permeability, has emerged as a potential non-invasive biomarker; however, its clinical relevance remains uncertain. This study evaluated whether fecal zonulin levels reflect clinical disease activity in inflammatory bowel disease and explored their association with ileal involvement in Crohn's disease (CD). Materials and Methods: Forty-six consecutive IBD patients (26 CD, 20 UC) were prospectively included. Fecal zonulin was measured using a commercially available ELISA. In this study, the term "fecal zonulin" refers to ELISA-detected zonulin-related proteins. Clinical disease activity was assessed using CDAI for CD and the Mayo score for UC. Standard blood and fecal inflammatory markers were obtained, and subgroup analyses were performed according to disease type and location. Results: Fecal zonulin levels were significantly higher in active IBD compared with remission (106.37 vs. 53.80 ng/mL, p = 0.002). Patients with CD had higher zonulin concentrations than those with UC (91.4 vs. 51.0 ng/mL, p = 0.001). Zonulin showed a moderate positive correlation with fecal calprotectin (r = 0.338; p = 0.021). In multivariable analysis, clinical disease activity remained independently associated with zonulin levels, whereas ileal involvement was no longer statistically significant. Conclusions: Fecal zonulin is associated with disease activity in IBD, suggesting that fecal zonulin-related proteins may represent a potential adjunctive marker of epithelial barrier dysfunction and clinical disease activity in IBD. However, these findings should be considered exploratory and require validation in larger, longitudinal multicenter studies using standardized assays and endoscopic correlation.