Biomarkers reflecting disturbed gut barrier under treatment with TNF inhibitors in radiographic axial spondyloarthritis.

Objectives: The objective of this study is to investigate lipopolysaccharid-binding protein (LBP), zonulin and calprotectin as markers of bacterial translocation, disturbed gut barrier and intestinal inflammation in patients with radiographic axial spondyloarthritis (r-axSpA) during tumour necrosis factor inhibitor (TNFi) therapy and to analyze the association between disease activity, response to treatment and biomarker levels.

Methods: Patients with active r-axSpA of the German Spondyloarthritis Inception Cohort starting TNFi were compared with controls with chronic back pain. Serum levels of LBP, zonulin and calprotectin were measured at baseline and after 1 year of TNFi therapy. We analysed the longitudinal association between biomarkers and disease activity, and the relationship between biomarkers and treatment response with regression analysis.

Results: 121 patients with r-axSpA were compared with 63 controls. At baseline, patients with r-axSpA had higher levels of LBP and calprotectin than controls, which decreased significantly during TNFi treatment. LBP showed a positive association in longitudinal analyses with Axial Spondyloarthritis Disease Activity Score (ASDAS) (ß=0.08, 95% CI 0.06 to 0.10), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (ß=0.08, 95% CI 0.04 to 0.12) and C reactive protein (CRP) (ß=1.69, 95% CI 1.04 to 2.34). Calprotectin was associated with ASDAS (ß=0.04, 95% CI 0.01 to 0.07) and CRP (ß=0.82, 95% CI 0.27 to 1.37). Furthermore, LBP and calprotectin levels at baseline showed an association with a subsequent change in BASDAI. Baseline zonulin levels were not significantly associated with disease activity or treatment response.

Conclusion: Serum levels of LBP and calprotectin are associated with disease activity in patients with r-axSpA and decrease with TNFi response. In contrast, serum zonulin levels showed no association with disease activity or treatment response, arguing against a strict correlation between intestinal permeability and disease activity in axSpA.