High levels of osteoprotegerin and soluble receptor activator of nuclear factor κB ligand in serum of rheumatoid arthritis patients and their normalization after anti–tumor necrosis factor α treatment

Abstract

Objective. To test the hypotheses that 1) proinflammatory cytokines affect osteoprotegerin (OPG) and soluble receptor activator of nuclear factor B ligand (sRANKL) production and therefore the OPG and sRANKL levels differ in rheumatoid arthritis (RA) patients in comparison with healthy individuals; and 2) anti-tumor necrosis factor ␣ (anti-TNF␣) therapy influences OPG and sRANKL levels.Methods. Sera were obtained from healthy individuals or RA patients receiving the combination of infliximab and methotrexate. Peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) were isolated from RA patients. Fibroblast-like synoviocytes (FLS) were isolated from synovial tissue obtained at total knee replacement in RA patients. Supernatants from cells stimulated with cytokines were collected after culture in vitro. Concentrations of OPG and sRANKL were determined by enzymelinked immunosorbent assays.Results. A strong positive correlation between OPG concentration and age was observed in healthy individuals but not in RA patients. The OPG and sRANKL levels were higher in RA patients than in healthy controls. Cultured FLS spontaneously secreted much higher amounts of OPG than PBMCs or SFMCs. Proinflammatory cytokines enhanced OPG production. Anti-TNF␣ treatment resulted in the normalization of serum OPG and sRANKL levels in RA patients without influencing the OPG:sRANKL ratio.Conclusion. Although higher serum levels of OPG and sRANKL are present in RA patients than in healthy individuals, the ratio of OPG:sRANKL is similar. There is an age-dependent increase of OPG but not sRANKL levels in healthy subjects. Anti-TNF␣ treatment results in the normalization of elevated levels of OPG and sRANKL in RA patients.Bone remodeling and bone loss are controlled by a balance between tumor necrosis factor (TNF) superfamily molecules: osteoprotegerin/osteoclastogenesis inhibitory factor (OPG/OCIF), receptor activator of nuclear factor B ligand (RANKL), receptor activator of nuclear factor B (RANK), and TNF-related apoptosisinducing ligand (TRAIL) (1-4). RANKL plays a key role in the regulation of osteoclastogenesis, osteoclast activation, dendritic cell survival, lymphocyte development, and lymph node organogenesis (5). Recent data Presented in part at

TRAIL-R2 (DR5) Mediates Apoptosis of Synovial Fibroblasts in Rheumatoid Arthritis

“…Decoy receptors for TRAIL have been implicated as crucial anti-apoptosis mechanisms for TRAIL, although the parallel susceptibility of RA synovial cells to both TRAIL and anti-DR5 Ab suggests that this might not apply to RA synovial cells. Alternatively, the synovial levels of endogenous TRAIL apoptosis blockers, such as soluble DR4, DR5, or OPG, might be increased in RA patients (30,31). Blockade of TRAIL-mediated apoptosis with the soluble DR5 is known to increase susceptibility to the development of arthritis in mice (6).…”

Gene expression analysis of major lineage‐defining factors in human bone marrow cells: Effect of aging, gender, and age‐related disorders

“…In all experimental results of arthritis studied thus far, inhibition of RANKL completely prevented bone loss and partially protected cartilage. As for RA patients, high serum levels of soluble RANKL 58 and increased expression of RANKL mRNA in synovial tissues 59 were observed, suggesting that RANKL is the principal mediator of bone loss in human RA. As far as we know, our study is the first to clarify the high level of RANKL mRNA in human bone marrow cells from RA patients.…”

“…52 In line with our results, Cao et al 53 suggested that the changes in RANKL expression associated with aging may contribute, at least in part, to the gradual loss of bone that occurs with age and the development of agerelated osteoporosis. However, some studies found no age-dependent change in the RANKL serum level in healthy individuals 54 or decreased in the serum RANKL concentration with age. 55 One explanation for this discrepancy may be that serum RANKL levels do not consistently reflect the local microenvironment in the bone.…”

The RANK/RANKL/osteoprotegerin system in rheumatoid arthritis: New insights from animal models

“…RA patients exhibit high serum levels of OPG and soluble RANKL, which normalize after anti-TNF␣ treatment (55). RANKL mRNA is present in the synovial lining layer in patients with RA (56), and RANKL as well as RANK are also detected in the synovium of rats with collagen-induced arthritis (3).…”