Biomarkers of intestinal barrier function in multiple sclerosis are associated with disease activity

Background: Recent evidence suggests a role for the gut–brain axis in the pathophysiology of multiple sclerosis (MS). Materials and methods: We studied biomarkers of intestinal permeability in 126 people with MS (57 relapsing-remitting multiple sclerosis (RRMS) and 69 progressive MS) and in a group of healthy controls for comparison. Serum/plasma concentrations of zonulin (a regulator of enterocyte tight junctions), tight junction proteins (ZO-1 and occludin), intestinal fatty acid binding protein (IFABP)/ileal bile acid binding protein (IBABP), D-lactate, and lipopolysaccharide (LPS) binding protein were measured. Results: Zonulin concentrations were significantly higher when a concurrent magnetic resonance imaging (MRI) confirmed the presence of blood–brain barrier (BBB) disruption (Gad+ RRMS) and were correlated with tight junction proteins. IBABP and D-lactate were elevated in people with RRMS compared to controls, but did not discriminate between Gad+ and Gad– subgroups. Baseline zonulin concentrations were associated with 1-year disease progression in progressive MS. Conclusions: People with MS have altered biomarkers of intestinal barrier integrity. Zonulin concentrations are associated with 1-year disease progression in progressive MS and closely mirror BBB breakdown in RRMS. Zonulin may mediate breakdown of both the intestinal barrier and the BBB in gut dysbiosis through the regulation of tight junctions. This could explain how the gut–brain axis modulates neuroinflammation in MS.