High melatonin levels are related to spinal ossification in patients with ankylosing spondylitis

Objectives: To investigate associations of serum melatonin with spinal ossification and cytokines in ankylosing spondylitis (AS).Methods: Serum was obtained from 52 AS patients and 25 healthy controls. Melatonin was measured by ELISA kit; bone morphogenetic protein (BMP)-2, dickkopf-related protein (Dkk)-1, IL-1β, IL-6, IL-17 and TNF-α concentrations were assayed using Luminex multiplex bead system. Osteocalcin and β isomer of C-terminal telopeptide of type I collagen (β-CTX) were measured using electrochemiluminescence immunoassay. Spinal damages were assessed using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) on radiographs.Results: Serum melatonin was significantly increased in AS patients. Serum melatonin correlated positively with mSASSS after multivariate adjustment for age and disease duration (r = 0.70, p < .01). Patients with spinal bone bridge have higher levels of melatonin than those without spinal bone bridge [16.69 (4.65, 41.10) pg/ml vs. 7.43 (3.29, 15.30) pg/ml, p = .03]. The multiple linear regression analysis found that melatonin was a risk factor for spinal bone formation (β = 0.35, p < .05). Additionally, melatonin correlated positively with osteocalcin (r = 0.34, p = .04) and IL-1β (r = 0.39, p = .04) in AS.Conclusion: Melatonin is increased in AS patients, especially in patients with spinal bone bridge. It suggests that melatonin may play an important role in the pathological osteogenesis of AS.