Plasma FABP2, IL-10, and LPS in Microscopic Colitis: An Exploratory Study of Their Biomarker Potential

Background and Objectives: Microscopic colitis (MC) encompasses two chronic inflammatory disorders of the large intestine: collagenous colitis (CC) and lymphocytic colitis (LC). Both conditions are characterised by chronic watery diarrhoea and substantially impaired quality of life. Diagnosis relies on colonoscopy with multiple biopsies, and no reliable non-invasive biomarker currently exists. This exploratory study aimed to investigate circulating fatty acid-binding protein 2 (FABP2), interleukin-10 (IL-10), and lipopolysaccharides (LPSs) as potential biomarkers for MC and to compare their profiles with those in ulcerative colitis (UC). Materials and Methods: Plasma samples were obtained from 45 patients with active CC, 16 patients with active LC, 52 healthy controls, 43 patients with active UC, and 43 patients with inactive UC. Concentrations of FABP2, IL-10, and LPS were measured by enzyme-linked immunosorbent assay (ELISA). Results: Plasma FABP2 concentrations differed significantly across groups (Kruskal-Wallis p = 0.008). CC patients exhibited the highest levels (median 1719.0 pg/mL, IQR 1364.0-2240.0) compared with active UC (median 1272.0 pg/mL, IQR 861.7-1727.5; p = 0.005) and inactive UC (median 1334.0 pg/mL, IQR 854.2-1702.0; p = 0.001), but did not differ significantly from controls (median 1364.5 pg/mL, IQR 982.6-2160.5; p = 0.076) or LC (median 1421.5 pg/mL, IQR 1207.0-2002.2; p = 0.171). IL-10 concentrations also differed across groups (Kruskal-Wallis p = 0.029 after removal of one extreme outlier in active UC). Active UC patients had significantly lower levels (median 2.6 pg/mL, IQR 1.4-4.6) than CC (median 4.0 pg/mL, IQR 3.0-7.2; p = 0.009) and controls (median 4.8 pg/mL, IQR 2.6-7.4; p = 0.005). LPS concentrations showed no overall differences across groups (Kruskal-Wallis p = 0.55), although CC patients had numerically higher levels (median 73.7 pg/mL, IQR 45.6-104.9) compared with controls (median 56.4 pg/mL, IQR 33.7-87.1; p = 0.124). No significant differences were observed between LC and other groups for any biomarker. Conclusions: In this exploratory study, plasma FABP2 and IL-10 showed limited diagnostic accuracy in differentiating CC from UC but failed to distinguish MC from healthy controls. LPS levels were not significantly different among study groups. None of the biomarkers reliably separated LC from other groups, possibly reflecting the small LC sample size. These preliminary findings suggest subtle differences in circulating biomarker profiles between CC and UC that warrant validation in larger cohorts.