Inhibitors of p38 suppress cytokine production in rheumatoid arthritis synovial membranes: Does variable inhibition of interleukin‐6 production limit effectiveness in vivo?

Objective

The activity of p38 MAPK regulates lipopolysaccharide (LPS)–stimulated production of key proinflammatory cytokines such as tumor necrosis factor α (TNFα). Consequently, p38 MAPK inhibitors have attracted considerable interest as potential treatments of rheumatoid arthritis (RA), and studies in murine models of arthritis have yielded promising results. However, the performance of several compounds in human clinical trials has been disappointing. At present, the reason for this poor performance is unclear. The aim of this study was to examine the effects of p38 inhibitors on both diseased and normal human tissue and cells, in order to test whether this kinase still plays a critical role in cytokine production under conditions of chronic inflammation.

Methods

Proinflammatory and antiinflammatory cytokine production was monitored after treatment of primary human monocytes, macrophages, and RA synovial membrane cultures with p38 MAPK inhibitor compounds. The following 3 inhibitors were used in these studies: SB‐203580 (inhibits the α and β isoforms), BIRB‐796 (inhibits the α, β, γ, and δ isoforms), and a novel, structurally distinct p38 MAPK inhibitor, SB‐731445 (inhibits the α and β isoforms).

Results

SB‐731445 and SB‐203580 produced profound inhibition of spontaneous production of proinflammatory cytokines (TNFα and interleukin‐1 [IL‐1]) in both RA membrane cultures and LPS‐stimulated primary human monocytes. However, this and other p38 MAPK inhibitors produced a significant increase in IL‐6 production by LPS‐stimulated primary human macrophages and a decrease in IL‐10 production by all cell types examined.

Conclusion

The potentially proinflammatory consequences of these activities (decreased IL‐10 production and increased IL‐6 production) may offer some explanation for the inability of p38 MAPK inhibitors to provide the therapeutic benefit that had been hoped for in RA.

     

Prevention of the onset and progression of collagen‐induced arthritis in rats by the potent p38 mitogen‐activated protein kinase inhibitor FR167653

Objective

FR167653 is a potent inhibitor of p38 mitogen‐activated protein kinase (MAPK) and inhibits tumor necrosis factor α (TNFα) and interleukin‐1β (IL‐1β) production in inflammatory cells. In this study we investigated the effect of FR167653 on collagen‐induced arthritis (CIA).

Methods

Rats with CIA were subcutaneously injected with FR167653 (32 mg/kg/day) starting on the day of the booster injection (day 7) in the prophylactic treatment group and after the onset of arthritis (day 21) in the therapeutic treatment group. Hind‐paw swelling, body weight, radiographic and histologic scores, and osteoclast number were evaluated. Cytokine levels in the serum and tissue were assessed by enzyme‐linked immunosorbent assays. Flow cytometric analysis of T lymphocytes from bone marrow was performed. The effect of FR167653 on in vitro osteoclast formation induced by soluble receptor activator of nuclear factor κB ligand (sRANKL) and TNFα was examined.

Results

Swelling of hind paws and loss of weight occurred in the CIA rats, but this was not evident in the prophylactic treatment group. Therapeutic treatment also significantly reduced paw swelling. The mean radiographic and histologic scores as well as the osteoclast numbers were significantly lower in the treatment group than in the CIA rats without treatment. FR167653 treatment reduced the serum levels of TNFα and IL‐1β, lowered the IL‐1β concentration in the ankle joints, and decreased the CD4−,CD8a+ T cell population in bone marrow. Furthermore, FR167653 inhibited the osteoclast‐like cell differentiation induced by both sRANKL and TNFα in vitro.

Conclusion

FR167653 prevents the onset of arthritis in a prophylactic treatment model and suppresses the progression of joint destruction in a therapeutic treatment model, suggesting that p38 MAPK is a potential therapeutic target for rheumatoid arthritis.

     

Inflammation is preceded by tumor necrosis factor‐dependent infiltration of mesenchymal cells in experimental arthritis

Objective

To determine the involvement of mesenchymal progenitor cells in the induction of collagen‐induced arthritis (CIA).

Methods

DBA/1 mice were immunized with type II collagen in adjuvant or adjuvant alone, and the presence of mesenchymal cells in the joints of prearthritic mice was studied by immunohistochemistry.

Results

An analysis of the joints on day 10 postimmunization (at least 10 days before the onset of arthritis) revealed synovial hyperplasia without leukocytic infiltration. Large, round cells expressing bone morphogenetic protein receptors (BMPRs), which serve as markers for primitive mesenchymal cells, were present in increased numbers in the bone marrow adjacent to the joint, in the synovium itself, and within enlarged bone canals that connect the bone marrow to the synovium. Similar changes were observed in mice given adjuvant without collagen. Adjuvant‐induced infiltration of BMPR⁺ cells and enlargement of bone canals were abrogated by anti‐tumor necrosis factor (anti‐TNF) treatment and were absent in TNFR p55/p75^−/− mice. Increased numbers of bone marrow cells and enlarged bone canals were observed in nonimmunized TNF transgenic mice (which spontaneously develop arthritis).

Conclusion

These findings suggest that in CIA, there is an antigen‐independent (innate) prearthritic phase that prepares the joint for the subsequent immune‐mediated arthritis. The induction phase involves marrow‐derived mesenchymal cells and requires the presence of TNF.

     

Tumor necrosis factor–inhibiting therapy preferentially targets bone destruction but not synovial inflammation in a tumor necrosis factor–driven model of rheumatoid arthritis

Objective

To investigate how tumor necrosis factor (TNF)–inhibiting therapy affects bone destruction and inflammation in a TNF‐driven mouse model of rheumatoid arthritis.

Methods

In order to evaluate the influence of TNF on osteoclastogenesis in vitro, different concentrations of TNF were added to spleen cell–derived monocytes in the absence or presence of different concentrations of RANKL. In addition, the effects of TNF inhibition on osteoclast precursors as well as local bone destruction in vivo were assessed by treating TNF‐transgenic mice with different doses of adalimumab.

Results

TNF stimulated osteoclastogenesis mainly by increasing the number of osteoclast precursor cells in vitro. This TNF effect was independent of the presence of RANKL. In the hTNF‐transgenic mouse model of destructive arthritis, low‐dose TNF‐inhibiting therapy with adalimumab had no effect on synovial inflammation but significantly inhibited local bone destruction and the generation of osteoclasts. This inhibition was accompanied by a reduction in the number of c‐Fms–positive osteoclast precursor cells in the bone marrow and a reduction of the osteoclast precursor pools in the blood and inflamed synovial membrane of hTNF‐transgenic mice.

Conclusion

Low‐dose TNF‐inhibiting therapy significantly reduces bone erosions by reducing the number of circulating and joint‐invading osteoclast precursors. This effect is uncoupled from its antiinflammatory action.

     

Antiinflammatory functions of p38 in mouse models of rheumatoid arthritis: Advantages of targeting upstream kinases MKK‐3 or MKK‐6

Objective

Inhibitors of p38 demonstrate limited benefit in rheumatoid arthritis (RA), perhaps due to the antiinflammatory functions of p38α. This study was performed to determine if selective deletion of p38α in macrophages affects the severity of arthritis and whether blocking upstream kinases in the p38 pathway, such as MKK‐3 or MKK‐6, avoids some of the limitations of p38 blockade.

Methods

Wild‐type (WT) mice and mice with selective deletion of p38α in macrophages (p38α^ΔLysM) were injected with K/BxN sera. Antigen‐induced arthritis was also induced in p38α^ΔLysM mice. Mouse joint extracts were evaluated by enzyme‐linked immunosorbent assay, quantitative polymerase chain reaction (qPCR), and Western blot analysis. Bone marrow–derived macrophages (BMMs) were stimulated with lipopolysaccharide (LPS) and were evaluated by qPCR and Western blotting. Bone marrow chimeras were generated using MKK‐3^−/− and MKK‐6^−/− mice, and K/BxN serum was administered to induce arthritis.

Results

Compared to WT mice, p38α^ΔLysM mice had increased disease severity and delayed resolution of arthritis, which correlated with higher synovial inflammatory mediator expression and ERK phosphorylation. In contrast to WT BMMs cultured in the presence of a p38α/β inhibitor, LPS‐stimulated MKK‐6– and MKK‐3–deficient BMMs had suppressed LPS‐mediated interleukin‐6 (IL‐6) expression but had normal IL‐10 production, dual‐specificity phosphatase 1 expression, and MAPK phosphorylation. WT chimeric mice with MKK‐6– and MKK‐3–deficient bone marrow had markedly decreased passive K/BxN arthritis severity.

Conclusion

Inhibiting p38α in a disease that is dominated by macrophage cytokines, such as RA, could paradoxically suppress antiinflammatory functions and interfere with clinical efficacy. Targeting an upstream kinase that regulates p38 could be more effective by suppressing proinflammatory cytokines while preventing decreased IL‐10 expression and increased MAPK activation.

     

T cells regulate the expression of matrix metalloproteinase in human osteoblasts via a dual mitogen‐activated protein kinase mechanism

Objective

To investigate the role of T cell induction of matrix metalloproteinase 13 (MMP‐13) production by human osteoblasts in order to better understand the process of bone loss in rheumatoid arthritis (RA).

Methods

Activated T cell–conditioned medium (ACTTCM) was used to mimic the physiologic conditions of inflammation. MMP‐13 production by human osteoblasts was assessed using a specific enzyme‐linked immunosorbent assay. Specific inhibitors of the p38 mitogen‐activated protein (MAP) kinase and the extracellular signal–regulated kinase 1/2 (ERK‐1/2) MAP kinase signaling pathways were used to assess their roles in T cell–mediated MMP‐13 production. Finally, recombinant cytokines representative of the major components in ACTTCM were assessed for their ability to induce MMP‐13.

Results

ACTTCM powerfully induced MMP‐13 in human osteoblasts. Inhibition of p38 activity abolished, while inhibition of ERK‐1/2 activity enhanced, MMP‐13 production. We next investigated physiologic levels of the T cell cytokines tumor necrosis factor α (TNFα), transforming growth factor β (TGFβ), interferon‐γ (IFNγ), and interleukin‐17 (IL‐17) for their roles in MMP‐13 induction. Although individual cytokines had no significant effect, the combination of TNFα, TGFβ, IFNγ, and IL‐17 resulted in a dramatic p38‐dependent induction of MMP‐13 identical to that produced by ACTTCM.

Conclusion

These studies demonstrate for the first time that human osteoblasts produce MMP‐13. The results also show that under conditions of chronic inflammation, multiple T cell cytokines synergize to induce high levels of MMP‐13 via a mechanism that is dependent on activated p38 MAP kinase and is suppressed by activated ERK‐1/2. Selective inhibition of p38 activity may offer a target for pharmacologic inhibition of bone loss in RA.

     

A tumor necrosis factor receptor loop peptide mimic inhibits bone destruction to the same extent as anti–tumor necrosis factor monoclonal antibody in murine collagen‐induced arthritis

Objective

The cyclic peptide WP9QY (YCWSQYLCY) was designed to mimic the most critical tumor necrosis factor α (TNFα) recognition loop on TNF receptor I, and it prevents interactions of TNFα with its receptor. We undertook this study to compare the effects of the WP9QY peptide on collagen‐induced arthritis (CIA) in mice with those of anti‐TNFα monoclonal antibody.

Methods

CIA was induced by primary and secondary immunizations. Osmotic minipumps were implanted in the backs of all mice on the day of the booster injection (day 21), and vehicle, anti‐TNF antibody (4 mg/kg/day), or WP9QY peptide (2 mg/kg/day or 4 mg/kg/day) was continuously infused until the mice were killed (day 40). Thereafter, clinical, radiographic, and histologic assessments were performed.

Results

WP9QY treatment inhibited CIA‐induced increases in the arthritis score, but onset of disease was not delayed by the peptide. The inhibitory effect of WP9QY on inflammation was definitely weaker than that of anti‐TNF antibody. Microfocal computed tomography analyses, however, revealed that WP9QY blocked CIA‐induced bone destruction at the knee joints to the same extent as did anti‐TNF antibody. In addition, WP9QY inhibited synovial pannus infiltration and reduced osteoclast number. Furthermore, inhibition of CIA‐induced systemic bone loss by WP9QY was more apparent than that by anti‐TNF antibody.

Conclusion

The TNFα antagonist WP9QY would be a useful template for the development of small molecular inhibitors to prevent both inflammatory bone destruction and systemic bone loss in rheumatoid arthritis.

     

Differential tissue expression and activation of p38 MAPK α, β, γ, and δ isoforms in rheumatoid arthritis

Objective

Activation of p38 MAPK is a key signaling step in chronic inflammation. Inhibition of p38 MAPK is considered to be a promising future strategy to control inflammatory diseases, but studies of compounds to inhibit this kinase have so far been limited to investigation of their side effects. We undertook the present study to investigate which specific molecule, among 4 different isoforms of p38 MAPK (α, β, γ, and δ), is predominantly expressed and activated in inflammation. Such knowledge could allow more specific targeting of p38 MAPK in inflammatory disease.

Methods

Studies were performed on inflamed tissue from patients with rheumatoid arthritis, as a prototype of inflammatory disease. The expression and activation of the α, β, γ, and δ isoforms of p38 MAPK were examined by immunoblotting, immunoprecipitation, and immunohistochemistry.

Results

Immunoblot analysis revealed that α and γ were the predominantly expressed p38 MAPK isoforms, whereas the other 2 isoforms were less frequently present. By immunohistochemistry, the expression of all p38 MAPK isoforms was localized to the synovial lining layer as well as to blood vessels. Colabeling with cell‐specific markers revealed that macrophages expressed the α and γ isoforms, synovial fibroblasts the β and γ isoforms, and granulocytes the δ isoform, whereas T lymphocytes were rarely positive for any p38 MAPK isoform. Double‐labeling with isoform‐specific antibody and pan‐p38 antibody against the phosphorylated form of p38 MAPK showed activation of the α and γ isoforms. Occasional activation of the β isoform was also noted in the synovial lining and the endothelium, whereas the δ isoform, although expressed in pericytes around blood vessels, was not phosphorylated. This phosphorylation pattern was confirmed in immunoprecipitation studies in which activated p38 MAPK from synovial tissue extracts was identified as p38 MAPKα and ‐γ but not p38 MAPKβ or ‐δ.

Conclusion

These data show that the α and γ isoforms of p38 MAPK dominate in chronic inflammation. Effective strategies to inhibit p38 MAPK should therefore aim to specifically target either or both of these isoforms.

     

Tumor necrosis factor α and RANKL blockade cannot halt bony spur formation in experimental inflammatory arthritis

Objective

To investigate the kinetics of bony spur formation and the relationship of bony spur formation to synovial inflammation and bone erosion in 2 rat arthritis models, and to address whether bony spur formation depends on the expression of tumor necrosis factor α (TNFα) or RANKL.

Methods

Analysis of the kinetics of synovial inflammation, bone erosion, osteoclast formation, and growth of bony spurs was performed in rat collagen‐induced arthritis (CIA) and adjuvant‐induced arthritis (AIA). In addition, inhibition experiments were performed to assess whether inhibition of TNFα and RANKL by pegylated soluble TNF receptor type I (pegTNFRI) and osteoprotegerin (OPG), respectively, affected bony spur formation.

Results

Bony spurs emerged from the periosteal surface close to joints, and initial proliferation of mesenchymal cells was noted as early as 3 days and 5 days after onset of CIA and AIA, respectively. Initiation of bony spur formation occurred shortly after the onset of inflammation and bone erosion. Neither pegTNFRI nor OPG could significantly halt the osteophytic responses in CIA and AIA.

Conclusion

These results suggest that bony spur formation is triggered by inflammation and initial structural damage in these rat models of inflammatory arthritis. Moreover, emergence of bony spurs depends on periosteal proliferation and is not affected by inhibition of either TNFα or RANKL. Bony spur formation can thus be considered a process that occurs independent of TNFα and RANKL and is triggered by destructive arthritis.

     

Characterization of pristane‐induced arthritis,a murine model of chronic disease: Response to antirheumatic agents,expression of joint cytokines,and immunopathology

Objective

To characterize chronic murine pristane‐induced arthritis (PIA) with regard to the response to antirheumatic agents, expression levels of proinflammatory cytokines, and immunopathologic features.

Methods

Male DBA/1 mice were injected intraperitoneally with pristane oil to induce a chronic polyarthritis, which was monitored by visual scoring. Serum antibody and splenocyte responses to a panel of putative joint‐derived autoantigens were measured. Whole paws were evaluated postmortem for changes in the levels of proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin‐1β (IL‐1β), and IL‐6 by enzyme‐linked immunosorbent assay, and standard histopathology techniques were used to determine joint structural changes. Therapeutic studies were performed for up to 8 weeks of dosing with prednisolone, methotrexate, 3 nonsteroidal antiinflammatory drugs (celecoxib, diclofenac, and indomethacin), a p38 MAPK inhibitor, SB242235, and human soluble TNF receptor (sTNFR; etanercept) and murine sTNFR fusion proteins.

Results

Antibody and cellular responses to the putative joint autoantigens revealed a broad extent of autoimmunity in PIA. TNFα, IL‐1β, and IL‐6 were all persistently up‐regulated in PIA joints. Prednisolone, methotrexate, celecoxib, indomethacin, and SB242235 all significantly reduced the arthritis scores. Etanercept was ineffective in reducing the arthritis scores, whereas murine sTNFR produced a significant, but nonsustained, benefit. Only prednisolone significantly reduced the expression of TNFα, IL‐1β, and IL‐6 in the joints. Prednisolone and methotrexate demonstrated the most effective joint protection.

Conclusion

We have markedly extended the characterization of PIA as a murine model of chronic inflammatory arthritis by demonstrating cellular and humoral autoantigenicity, elevation of clinically precedented joint cytokines, and variation in the response to several antirheumatic therapies. PIA offers significant potential for the long‐term study of immunopathologic mechanisms and novel therapies in rheumatoid arthritis.

     

Inhibition of antigen‐presenting cell function and stimulation of human peripheral blood mononuclear cells to express an antiinflammatory cytokine profile by the stress protein BiP: Relevance to the treatment of inflammatory arthritis

Objective

The stress protein and endoplasmic reticulum chaperone, immunoglobulin binding protein (BiP), is an autoantigen in rheumatoid arthritis (RA). Stress proteins, however, may have extracellular functions, mediated via cell surface receptors, that may include immunomodulatory functions. We sought to determine whether cell‐free BiP is present in the synovial fluid (SF) of patients with RA and to further investigate the possible extracellular antiinflammatory and immunomodulatory properties of BiP in peripheral blood mononuclear cells (PBMCs) in vitro.

Methods

The presence of BiP in SF was established by Western blotting. PBMCs were stimulated with exogenous recombinant human BiP, and cytokine production and cell proliferation were measured in the presence and absence of cell signaling inhibitors or neutralizing anti–interleukin‐10 (anti–IL‐10) monoclonal antibody. Cytokine levels were quantified by enzyme‐linked immunosorbent assay, cell proliferation by tritiated thymidine uptake, and cell surface molecule expression by flow cytometry.

Results

PBMCs responded to BiP with secretion of an antiinflammatory profile of cytokines. Although BiP stimulated the early production of tumor necrosis factor α (TNFα), the major cytokine induced was IL‐10. Soluble TNF receptor II and IL‐1 receptor antagonist secretion was also increased. Addition of SB203580, the MAPK p38 pathway inhibitor, partially inhibited the production of IL‐10 and TNFα, whereas they were unaffected by the MAPK ERK‐1/2 inhibitor PD98059. BiP also inhibited the recall antigen response by PBMCs to tuberculin purified protein derivative. Further investigation showed that incubation of monocytes in the presence of either BiP or IL‐10 down‐regulated CD86 and HLA–DR expression. The effect observed with IL‐10 was transient compared with the long‐lasting reduction induced by BiP.

Conclusion

Extracellular BiP may stimulate immunomodulatory and antiinflammatory pathways, which are only partly due to the production of IL‐10. These properties may be of relevance for the treatment of diseases such as RA.

     

ERK‐1/2 and p38 in the regulation of hypertrophic changes of normal articular cartilage chondrocytes induced by osteoarthritic subchondral osteoblasts

Objective

Previous studies have shown the influence of subchondral bone osteoblasts (SBOs) on phenotypical changes of articular cartilage chondrocytes (ACCs) during the development of osteoarthritis (OA). The molecular mechanisms involved during this process remain elusive, in particular, the signal transduction pathways. The aim of this study was to investigate the in vitro effects of OA SBOs on the phenotypical changes in normal ACCs and to unveil the potential involvement of MAPK signaling pathways during this process.

Methods

Normal and arthritic cartilage and bone samples were collected for isolation of ACCs and SBOs. Direct and indirect coculture models were applied to study chondrocyte hypertrophy under the influence of OA SBOs. MAPKs in the regulation of the cell–cell interactions were monitored by phosphorylated antibodies and relevant inhibitors.

Results

OA SBOs led to increased hypertrophic gene expression and matrix calcification in ACCs by means of both direct and indirect cell–cell interactions. In this study, we demonstrated for the first time that OA SBOs suppressed p38 phosphorylation and induced ERK‐1/2 signal phosphorylation in cocultured ACCs. The ERK‐1/2 pathway inhibitor PD98059 significantly attenuated the hypertrophic changes induced by conditioned medium from OA SBOs, and the p38 inhibitor SB203580 resulted in the up‐regulation of hypertrophic genes in ACCs.

Conclusion

The findings of this study suggest that the pathologic interaction of OA SBOs and ACCs is mediated via the activation of ERK‐1/2 phosphorylation and deactivation of p38 phosphorylation, resulting in hypertrophic differentiation of ACCs.

     

Osteoprotegerin protects against generalized bone loss in tumor necrosis factor–transgenic mice

Objective

To investigate the role of tumor necrosis factor (TNF) in systemic bone loss of chronic inflammatory conditions, such as rheumatoid arthritis (RA), and to address the therapeutic potential of osteoclast blockade.

Methods

We investigated systemic bone changes in human TNF transgenic (hTNFtg) mice, which spontaneously developed severe inflammatory arthritis.

Results

Osteodensitometry revealed a significant decrease in trabecular bone mineral density (BMD) (−37%) in hTNFtg mice, and histomorphometry revealed a dramatic loss of bone volume (−85%) compared with wild‐type controls. Osteoclast‐covered bone surface and serum levels of deoxypyridinoline crosslinks were significantly elevated, suggesting increased osteoclast‐mediated bone resorption in hTNFtg mice. Osteoprotegerin (OPG) completely blocked TNF‐mediated bone loss by increasing BMD (+89%) and bone volume (+647%). Most strikingly, formation of primary spongiosa was dramatically increased (+563%) in hTNFtg mice after OPG treatment. Osteoclast‐covered bone surface and serum levels of deoxypyridinoline crosslinks were significantly decreased by OPG, suggesting effective blockade of osteoclast‐mediated bone resorption. OPG did not influence levels of hTNF, TNF receptor I (TNFRI), interleukin‐1β (IL‐1β), and IL‐6. However, OPG decreased bone formation parameters (osteoblast‐covered bone surface and serum osteocalcin levels), which were elevated in hTNFtg mice. In contrast to OPG, bisphosphonates and anti‐TNF treatment did not affect generalized bone loss in hTNFtg mice. Anti‐TNF, however, did not affect levels of TNF and TNFRI at the concentrations tested. These data indicate that generalized bone loss due to increased TNF can be blocked by OPG.

Conclusion

OPG may represent a potent tool for preventing generalized loss of bone mass in chronic inflammatory disorders, especially RA.

     

Inhibition of interleukin‐1 but not tumor necrosis factor suppresses neovascularization in rat models of corneal angiogenesis and adjuvant arthritis

Objective

To assess the capacities of the cytokine inhibitors interleukin‐1 receptor antagonist (IL‐1Ra; anakinra) and PEGylated soluble tumor necrosis factor receptor I (PEG sTNFRI; pegsunercept) to suppress neovascularization.

Methods

A corneal angiogenesis assay was performed by implanting nylon discs impregnated with an angiogenic stimulator (basic fibroblast growth factor or vascular endothelial growth factor) into one cornea of female Sprague‐Dawley rats. Animals were treated with IL‐1Ra or PEG sTNFRI for 7 days, after which new vessels were quantified. In a parallel study, male Lewis rats with mycobacteria‐induced adjuvant‐induced arthritis were treated with IL‐1Ra or PEG sTNFRI for 7 days beginning at disease onset, after which scores for inflammation and bone erosion as well as capillary counts were acquired from sections of arthritic hind paws.

Results

Treatment with IL‐1Ra yielded a dose‐dependent reduction in growth factor–induced corneal angiogenesis, while PEG sTNFRI did not. IL‐1Ra, but not PEG sTNFRI, significantly reduced the number of capillaries in arthritic paws, even though both anticytokines reduced inflammation and bone erosion to a similar degree.

Conclusion

These data support a major role for IL‐1, but not TNFα, in angiogenesis and suggest that an additional antiarthritic mechanism afforded by IL‐1 inhibitors, but not anti‐TNF agents, is the suppression of the angiogenic component of pannus.

     

Zoledronic acid protects against local and systemic bone loss in tumor necrosis factor–mediated arthritis

Objective

Increased osteoclast activity is a key factor in bone loss in rheumatoid arthritis (RA). This suggests that osteoclast‐targeted therapies could effectively prevent skeletal damage in patients with RA. Zoledronic acid (ZA) is one of the most potent agents for blocking osteoclast function. We therefore investigated whether ZA can inhibit the bone loss associated with chronic inflammatory conditions.

Methods

Human tumor necrosis factor (TNF)–transgenic (hTNFtg) mice, which develop severe destructive arthritis as well as osteoporosis, were treated with phosphate buffered saline, single or repeated doses of ZA, calcitonin, or anti‐TNF, at the onset of arthritis.

Results

Synovial inflammation was not affected by ZA. In contrast, bone erosion was retarded by a single dose of ZA (−60%) and was almost completely blocked by repeated administration of ZA (−95%). Cartilage damage was partly inhibited, and synovial osteoclast counts were significantly reduced with ZA treatment. Systemic bone mass dramatically increased in hTNFtg mice after administration of ZA, which was attributable to an increase in trabecular number and connectivity. In addition, bone resorption parameters were significantly lowered after administration of ZA. Calcitonin had no effect on synovial inflammation, bone erosion, cartilage damage, or systemic bone mass. Anti‐TNF entirely blocked synovial inflammation, bone erosion, synovial osteoclast formation, and cartilage damage but had only minor effects on systemic bone mass.

Conclusion

ZA appears to be an effective tool for protecting bone from arthritic damage. In addition to their role in antiinflammatory drug therapy, modern bisphosphonates are promising candidates for maintaining joint integrity and reversing systemic bone loss in patients with arthritis.