Background: Rheumatoid arthritis (RA) is a chronic inflammatory disease that may result in debilitating joint deformities with destruction of bone and cartilage. Inflammation is still considered the pivotal inducer of both components of joint damage. A mechanism of bone destruction that could be dissociated from inflammation was proposed in which osteoclasts activation play a prominent role in bone resorption. RANKL and its natural decoy receptor, osteoprotegerin (OPG), play key roles in osteoclast activation.
Objective: To evaluate osteoprotegrin (OPG) and soluble RANKL (s-RANKL) level in serum of rheumatoid arthritis patients, and to correlate their levels in serum to disease activity and radiological findings (bone loss).
Patients and methods: Fifty five rheumatoid arthritis patients were included in the study. They were classified according to disease activity into 2 groups: The first group was active RA group, and the second was inactive RA group. In addition, RA group was classified according to bone erosions into 2 groups: The first group was RA group with bone erosions and the second group was RA group without bone erosions. The study included 25 healthy individuals of matched age and sex as a control group. All participants were exposed to complete clinical examination, radiological examination, and full laboratory evaluation including osteoclast activity markers (OPG/ RANKL ratio), inflammation markers (ESR, CRP and DAS-28 score), immunological markers (RF and anti-CCP), biochemical markers (calcium, phosphorus and alkaline phosphatase) and complete blood picture (CBC).
Results: OPG/ RANKL ratio was significantly lower in RA group compared to control group. OPG/RANKL ratio was significantly lower in active RA group compared to inactive RA group. OPG/ RANKL ratio was significantly lower in RA group with bone erosion compared to RA group without bone erosions. OPG/ RANKL ratio showed significant negative correlation with both disease duration (in all RA groups) and inflammatory markers (in some not all RA groups). OPG/ RANKL ratio did not correlate with biochemical markers in all RA groups.
Conclusion: OPG/ RANKL ratio could be used to monitor joint damage (bone erosions) progression in patients with RA. Progression of joint damage (bone erosions) due to osteoclast over activity could, at least in part, be dissociated from inflammation. Therefore, targeting OPG/ RANKL ratio may be effective in preventing bone damage in RA patients.