Relation of the Serum Levels of DKK-1 and Osteoprotegerin with Bone Mass in Tightly Controlled Rheumatoid Arthritis

Objective: To analyze the association between serum levels of osteoprotegerin (OPG) and Dickkopf-related protein 1 (DKK-1) and the annual percent change (%) in bone mineral density (BMD) in patients with tightly controlled rheumatoid arthritis (RA).

Methods: Observational mixed-study. RA patients followed-up with a tight-control strategy were included. Bone densitometries were performed at baseline (T0) and follow-up (T1) and serum levels of OPG and DKK-1 were measured by ELISA also in T0 and T1; additional clinical variables included disease activity measures, and treatment for RA and osteoporosis. Descriptive bivariate and multivariate analyses, stratified by gender, were performed.

Results: We included 97 RA patients (70% female, with a mean age of 53 years, and 76% with low activity by DAS28); 95% were treated with DMARDs and 37% with anti-osteoporotic drugs. Mean time between T0 and T1 was 2.7 years. Most patients had their BMD improved. The mean %BMD was +0.42% for lumbar spine, +0.15% for femoral neck and +0.91% for total femur. In men, baseline OPG was significantly associated with higher BMD loss (β coefficient -0.64) at femoral neck. In women, DKK-1 was associated with higher BMD loss at femoral neck (β coefficient -0.09), and total femur (β coefficient -0.11); however, DKK-1 was associated with lower BMD loss at lumbar spine (β coefficient 0.06).

Conclusion: In tightly controlled RA patients, we have found no evidence of bone loss. The role of DKK1 and OPG seems small and might be related to sex and to location.

Keywords: DKK-1.; bone density; osteoporosis; osteoprotegerin; rheumatoid arthritis.