Elevated levels of osteoprotegerin (OPG) and hepatocyte growth factor (HGF) in rheumatoid arthritis

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Abstract
Rheumatic diseases are often associated with changes in bone metabolism. Excessive production and release of cytokines and other growth factors due to inflammation, e.g. tumor necrosis factor-α (TNF-α), receptor activator of NF-κB ligand (RANKL), interleukins such as IL-1and IL-6, may cause alterations in bone homeostasis leading to bone degradation. Other components such as osteoprotegerin (OPG) and possibly the ligand-receptor pair hepatocyte growth factor (HGF) and c-met may counteract this destruction. We have measured the levels of OPG, and HGF/c-met, in serum, synovial fluid (SF), and cartilage from patients with rheumatoid arthritis (RA) and other arthritides. We found a) elevated levels of both OPG and HGF in SF from RA patients relative to arthritides of other causes, b) increased levels of both OPG and HGF in SF from seropositive RA patients (RA+ ) compared to seronegative RA patients (RA-), c) elevated levels of both OPG and HGF in serum from RA patients compared to healthy controls, d) no correlation between severity of inflammation and levels of OPG or HGF, and e) presence of HGF/c-met in both cartilage and synovial tissue. The most significant elevations of OPG and HGF were found in patients with RA, the rheumatic disease most frequently associated with the development of secondary osteoporosis.