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Circulating Dickkopf-1 and osteoprotegerin in patients with early and longstanding rheumatoid arthritis.

BACKGROUND
Rheumatoid arthritis (RA) is characterized by inflammation of the synovial membrane, leading to invasion of synovial tissue into the adjacent cartilage matrix with degradation of articular cartilage and bone as a consequence. Dickkopf-1 (DKK-1) and osteoprotegerin (OPG) have been demonstrated to be key molecules involved in bone erosion and bone remodeling. The aim of this study was to explore the potential role of DKK-1 and OPG in different stage of RA.


METHODS
The protein levels of DKK-1 and OPG were detected by ELISA. The serum samples were collected from 300 patients with RA and 60 healthy controls. Of which, 150 RA patients were defined as early RA (disease duration < or = 1 year), and other 150 RA patients were defined as longlasting RA (disease duration > or = 5 years). At the time of serum sampling, various clinical and laboratory parameters were assessed. The correlations of DKK-1 or OPG and clinical/laboratory parameters were analyzed.


RESULTS
The serum level of DKK-1 was elevated in patients with longstanding RA compared with healthy controls, while no significant difference was observed between the two groups in the level of OPG. In contrast, in early RA patients, the circulating OPG was elevated, while there was no significant difference between the two groups in expression of DKK-1. The serum DKK-1 was correlated with Sharp score and DAS28 in longstanding RA patients. In early RA, age was the only parameter that was significantly related to serum OPG.


CONCLUSIONS
There was a cross-talk between DKK-1 and OPG, which involved in bone destruction in RA. In different stage of RA, DKK-1 and OPG may play different roles in the pathogenesis of RA.