Intestinal Barrier and Gut Microbiota in Patients with Overlapping Irritable Bowel Syndrome and Functional Dyspepsia

Background Disturbances in the intestinal barrier and gut dysbiosis have been observed in patients with functional bowel diseases. Aims To investigate the correlation between biomarkers of intestinal barrier disorders at different layers and the severity of symptoms in patients with overlapping diarrhea-predominant irritable bowel syndrome and functional dyspepsia (IDFO), as well as with gut microbiota taxa. Methods This study included 45 patients with IDFO and 16 healthy controls. Endoscopy with biopsy of the duodenum and sigmoid colon (SC) was performed to count intraepithelial lymphocytes (IELs) and mucosal eosinophils (subepithelial layer), assess fatty acid binding protein (FABP; epithelial layer) level, and stain for mucin-2 (MUC-2; pre-epithelial layer). Composition of the gut microbiota was evaluated using 16S rRNA gene sequencing. Results Patients with IDFO exhibited an increase in biomarkers of intestinal barrier disorders at all layers studied. IEL count in the duodenum was correlated with the severity of bloating ( r = 0.336; p = 0.024) and, in the SC, was correlated with tenesmus severity ( r = 0.303; p = 0.042). FABP-1 level in the SC was correlated with the severity of diarrhea ( r = 0.577; p = 0.001), and FABP-5 concentration in the SC was correlated with abdominal distension ( r = 0.477; p = 0.010). MUC-2 concentration in the duodenum was correlated with the severity of heartburn ( r = 0.572; p = 0.025) and burning sensation in the epigastrium ( r = 0.518; p = 0.048). All biomarkers of intestinal barrier permeability were correlated with the abundance of some gut microbiota taxa. Conclusion Patients with IDFO exhibited disrupted intestinal barrier function in all layers, which was associated with clinical symptom severity and changes in the gut microbiota. Graphical Abstract