Ankylosing spondylitis is characterized by an increased turnover of several different metalloproteinase-derived collagen species: a cross-sectional study

Ankylosing spondylitis (AS) is characterized by gradual cementation of the vertebrae, a process that is described by excessive extracellular matrix remodeling. Specific matrix metalloproteinase (MMP)-derived collagen fragments are released to the circulation, and measurement of those might act as biomarkers of ankylosis. The aim of the study was to investigate the diagnostic value of five novel assays measuring different collagen species. Five newly developed ELISAs measuring MMP-degraded collagen fragments in serum of 40 AS patients and 40 age-matched controls were measured: collagen type I (C1M), type II (C2M), type III (C3M), type IV (C4M) and type VI (C6M) as well as the bone formation marker osteocalcin. The levels of the five collagen neoepitopes were significantly higher in AS patients, except for osteocalcin. Cartilage degradation (C2M) was only significantly correlated with the basement membrane (C4M) in the AS patients. In contrast, C3M was significantly correlated with all of the other collagen markers. The highest diagnostic value was achieved when combining the C2M, C3M and C6M markers, AUC 87% (P < 0.0001). Moreover, a combination of the markers correlated with the clinical mSASS score (P = 0.004, R = 0.44). Novel and unique biomarkers of tissue remodeling may provide diagnostic value and aid in understanding of the AS pathology. Each of the biomarkers tells a unique story, and by combining them in a panel there, we found a strong correlation with mSASSS. We speculate that such panel will be a valuable tool for monitoring patients as effect of treatment, for the prediction of responders and for diagnostic purposes.