Relationship of bone morphogenetic proteins to disease activity and radiographic damage in patients with ankylosing spondylitis

Objectives: To determine serum concentrations of bone morphogenetic proteins (BMPs) in patients with ankylosing spondylitis (AS) and to investigate their relationship to disease activity, spinal dysmobility, and spinal damage. Methods: Serum samples from 40 AS patients, 40 rheumatoid arthritis (RA) patients, and 40 healthy subjects were obtained, and serum BMP-2, -4, and -7 levels were determined by enzyme-linked immunosorbent assay (ELISA). Clinical measurements for AS patients included the Bath AS Disease Activity Index (BASDAI), Metrology Index (BASMI), and Radiographic Index (BASRI), and those for RA patients included the disease activity score (DAS) 28 and Larsen scores. Sample collections and clinical assessments were performed at baseline and after a mean follow-up of 51.7±19.7 months. Results: At baseline, both AS and RA patients demonstrated significantly elevated serum BMP-2 and BMP-7 levels compared with healthy controls (p<0.05). In AS patients, baseline BMP-2 levels correlated well with BASDAI (p<0.05), and BMP-7 levels correlated with BASRI-spine (p<0.05). However, no BMP levels showed significant correlation with DAS28 and Larsen scores in RA patients. The changes in BMP-7 levels from baseline to after the follow-up period showed a significant correlation with the changes of BASRI-spine, but the changes in other BMPs did not show any significant relationship to the changes in clinical parameters. Conclusion: Overproduction of BMP-2 and BMP-7 was noted in AS patients, and serum BMP-7 levels reflected radiographic damage observed in AS.