Do anti-carbamylated protein antibodies in rheumatoid arthritis reflect local and systemic osteoporosis? A study of osteoprotegrin and receptor activator for nuclear factor kappa B ligand and radiological assessment

Background One of the most important and dangerous complications of rheumatoid arthritis (RA) is bone loss, which manifested by erosions and juxta-articular or systemic bone loss. Anti-carbamylated protein (anti-CarP) antibodies which are also called anti-homocitrulline antibodies have recently been found in RA. Increase anti-CarP antibody titres may lead to severe disease and increase the progression of bone loss. Osteoprotegrin and receptor activator for nuclear factor kappa B and its ligand (RANKL) are the main players in the pathogenesis of osteoporosis. Thus, we aimed to investigate and detect the presence and prevalence of anti-CarP in rheumatoid arthritis and their association with disease severity and osteoporosis, as well as with OPG/RANKL in 80 Egyptian RA patients to highlight this relationship which could be useful in managing RA patients with osteoporosis. Results Serum anti-CarP levels were significantly increased in the RA group compared with the control group ( P < 0.001). We found a negative association between anti-CarP and anti-CCP and disease activity ( r =−0.878, −0.534, respectively, P <0.001). We also found a positive correlation between anti-CarP and the Larsen score, DEXA score, RF, HAQ, and RANKL ( r =0.646, 0.287, 0.243, 0.892, 0.671, 0.869 [respectively], P <0.001) and there was negative correlation between anti-CarP and OPG ( r =−0.553, P <0.001). Conclusion Anti-CarP antibodies are associated with disease severity and disability in RA patients. They could play an important and significant role in the pathogenesis of osteoporosis in these patients.