Role of High Serum Tenascin C Levels as Potential Biomarker of Persistent Inflammation in Patients with Ankylosing Spondylitis Despite Treatment with cs-DMARDS or Anti-TNF Agents

<b>Background/Objectives:</b> Ankylosing spondylitis (AS) is a severe chronic inflammatory rheumatic disease involving the spine, sacroiliacs, and peripheral joints. A lack of therapeutic response leads to severe sequelae. Currently, new markers are being tested to identify patients with poor outcomes. Tenascin C (TNC) is involved in triggering some relevant mechanisms of inflammation. Today, it remains unclear whether TNC levels might be useful as a biomarker of persistent activity. The aim of this study was to evaluate in AS whether serum levels of tenascin C are associated with persistent disease activity despite treatment. <b>Methods:</b> We included AS patients who had been treated with conventional synthetic disease-modifying antirheumatic drugs (cs-DMARDS) or anti-TNF agents for at least three months in a cross-sectional study. Response was assessed with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI); scores ≥ 4 indicate persistent disease activity, while scores < 4 indicate inactive disease. Serum TNC levels, C-reactive protein (CRP) levels, and Erythrocyte Sedimentation Rate (ESR) were determined through the ELISA technique, nephelometry, and the Westergren method, respectively. <b>Results:</b> We evaluated 58 patients with AS (62.1% men); of them, 33 (56.9%) had persistent active disease (BASDAI ≥ 4) despite treatment and 25 (43.1%) had inactive disease (BASDAI < 4). The median TNC level was 18.6 ng/mL. BASDAI correlated with TNC levels (rho: 0.528, <i>p</i> < 0.001), CRP (0.352, <i>p</i> = 0.007), and ESR (0.342, <i>p</i> = 0.009). Patients with persistently active AS had higher serum TNC levels than those with inactive AS (35.2 vs. 6 ng/mL, <i>p</i> < 0.001). No differences in TNC level were found in patients treated with cs-DMARDS vs. anti-TNF agents. The ROC curve for serum tenascin C in active AS patients had an area under the curve = 0.78 (CI 95%: 0.65-0.91) with optimal serum tenascin C cutoff (>13.85 ng/mL). Sensitivity for detecting active AS was higher with TNC compared to ESR and CRP. <b>Conclusions:</b> We suggest that an elevated TNC level may be a useful biomarker of persistent disease activity despite treatment in AS; further studies should investigate the role of TNC levels in predicting the progression of the disease.