Abstract
IntroductionReceptor activator of nuclear factor kappa B ligand (RANKL) is a key regulator of bone metabolism. Anti-citrullinated protein antibodies (ACPA) have been suggested to cause bone destruction by osteoclast activation. We investigated the relationship between RANKL and ACPA in patients with early untreated rheumatoid arthritis (RA).MethodsPatients with newly diagnosed untreated RA (n = 183) were analyzed at baseline and 3 months after initiating methotrexate (MTX) treatment. Serum RANKL (total RANKL), ACPA (anti-CCP2) and ACPA specificities (anti-citrullinated (cit)-vimentin, anti-cit-enolase and anti-cit-fibrinogen) were determined by enzyme-linked immunosorbent assay (ELISA). Synovial RANKL expression was evaluated by immunohistochemistry in a small group of patients (n = 15). The relationship between anti-cit-vim antibodies and bone destruction was further validated in 1116 RA patients included in the EIRA cohort. Pearson’s chi-square test, Wilcoxon rank sum test, Wilcoxon signed rank test and linear regression models were used.ResultsSerum RANKL concentration was significantly higher (p <0.05) in ACPA-positive (median: 689 pmol/L, IQR 342–1253) compared with ACPA-negative (median: 159 pmol/L, IQR 96–243) patients and this difference was also seen for synovial RANKL expression. Serum RANKL associated with ACPA (p <0.05) and bone erosions in rheumatoid factor (RF)-negative patients (n = 59). Among ACPA specificites, anti-cit-vimentin (amino acids 60–75) was associated with higher RANKL concentration and higher prevalence of bone erosion (p <0.05). Significant reductions in both serum RANKL and ACPA levels were observed after 3 months of MTX treatment (p <0.05).ConclusionsRANKL was elevated in ACPA-positive and in anti-cit-vimentin-positive patients with early untreated RA and associated with bone erosions. These findings give further support for an early direct pathogenic link between ACPA and bone destruction in RA.
Highlights
Receptor activator of nuclear factor kappa B ligand (RANKL) is a key regulator of bone metabolism
Serum samples and disease activity score 28 (DAS28) based on the erythrocyte sedimentation rate (ESR) were obtained at baseline and at clinical follow-up, which occurred after a median of 14 weeks (interquartile range 25−75 % (IQR) 13−15)
To further investigate the relationship between RANKL and Anti-citrullinated protein antibodies (ACPA) independent of rheumatoid factor (RF), we performed a separate analysis of RF-negative patients
Summary
Receptor activator of nuclear factor kappa B ligand (RANKL) is a key regulator of bone metabolism. Anti-citrullinated protein antibodies (ACPA) have been suggested to cause bone destruction by osteoclast activation. Presence of systemic autoimmunity with rheumatoid factor (RF) and/or anti-citrullinated protein antibodies (ACPA) in RA is associated with an increased risk of bone damage [7,8,9,10]. In addition to ACPA, markers of inflammation and of high disease activity (e.g., C-reactive protein (CRP) and disease activity score (DAS) 28) have been shown to be associated with increased bone damage in patients with RA [8, 10]. Efficient treatment with diseasemodifying antirheumatic drugs (DMARD), including methotrexate (MTX), results in reduced disease activity and less bone destruction [12], while the effect on ACPA is still not completely elucidated [13, 14]
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