Günter Steiner

Therapeutic strategies for rheumatoid arthritis.

Recent years have seen considerable advances in our understanding of both the clinical and basic-research aspects of rheumatoid arthritis. Clinical progress has come from a better recognition of the natural history of the disease, the development and validation of outcome measures for clinical trials and, consequently, innovative trial designs. In parallel, basic research has provided clues to the pathogenic events underlying rheumatoid arthritis, and advances in biotechnology have facilitated the development of new classes of therapeutics. Here, we summarize the fruits of these advances: innovative approaches to the use of existing, traditional disease-modifying antirheumatic drugs; novel agents approved very recently; and further avenues that are presently under investigation or which are of more distant promise.

Osteoclasts are essential for TNF-α–mediated joint destruction

The detailed cellular and molecular mechanisms leading to joint destruction in rheumatoid arthritis, a disease driven by proinflammatory cytokines, are still unknown. To address the question of whether osteoclasts play a pivotal role in this process, transgenic mice that express human TNF (hTNFtg) and that develop a severe and destructive arthritis were crossed with osteopetrotic, c-fos-deficient mice (c-fos(-/-)) completely lacking osteoclasts. The resulting mutant mice (c-fos(-/-)hTNFtg) developed a TNF-dependent arthritis in the absence of osteoclasts. All clinical features of arthritis, such as paw swelling and reduction of grip strength, progressed equally in both groups. Histological evaluation of joint sections revealed no difference in the extent of synovial inflammation, its cellular composition (except for the lack of osteoclasts), and the expression of matrix metalloprotein-ase-3 (MMP-3) and MMP-13. In addition, cartilage damage, proteoglycan loss, and MMP-3, -9, and -13 expression in chondrocytes were similar in hTNFtg and c-fos(-/-)hTNFtg mice. However, despite the presence of severe inflammatory changes, c-fos(-/-)hTNFtg mice were fully protected against bone destruction. These data reveal that TNF-dependent bone erosion is mediated by osteoclasts and that the absence of osteoclasts alters TNF-mediated arthritis from a destructive to a nondestructive arthritis. Therefore, in addition to the use of anti-inflammatory therapies, osteoclast inhibition could be beneficial for the treatment of rheumatoid arthritis.

Activation, differential localization, and regulation of the stress-activated protein kinases, extracellular signal–regulated kinase, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase, in synovial tissue and cells in rheumatoid arthritis

OBJECTIVE To investigate whether stress- and mitogen-activated protein kinases (SAPK/MAPK), such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, are significantly activated in rheumatoid arthritis (RA) synovial tissue compared with their activation in degenerative joint disease; to assess the localization of SAPK/MAPK activation in rheumatoid synovial tissue; and to search for the factors leading to stress kinase activation in human synovial cells. METHODS Immunoblotting and immunohistology by antibodies specific for the activated forms of SAPK/MAPK were performed on synovial tissue samples from patients with RA and osteoarthritis (OA). In addition, untreated and cytokine-treated human synovial cells were assessed for SAPK/MAPK activation and downstream signaling by various techniques. RESULTS ERK, JNK, and p38 MAPK activation were almost exclusively found in synovial tissue from RA, but not OA, patients. ERK activation was localized around synovial microvessels, JNK activation was localized around and within mononuclear cell infiltrates, and p38 MAPK activation was observed in the synovial lining layer and in synovial endothelial cells. Tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6 were the major inducers of ERK, JNK, and p38 MAPK activation in cultured human synovial cells. CONCLUSION Signaling through SAPK/MAPK pathways is a typical feature of chronic synovitis in RA, but not in degenerative joint disease. SAPK/MAPK signaling is found at distinct sites in the synovial tissue, is induced by proinflammatory cytokines, and could lead to the design of highly targeted therapies.

Repair of local bone erosions and reversal of systemic bone loss upon therapy with anti-tumor necrosis factor in combination with osteoprotegerin or parathyroid hormone in tumor necrosis factor-mediated arthritis.

Local bone erosion and systemic bone loss are hallmarks of rheumatoid arthritis and cause progressive disability. Tumor necrosis factor (TNF) is a key mediator of arthritis and acts catabolically on bone by stimulating bone resorption and inhibiting bone formation. We hypothesized that the concerted action of anti-TNF, which reduces inflammation and parathyroid hormone (PTH), which stimulates bone formation, or osteoprotegerin (OPG), which blocks bone resorption and could lead to repair of local bone erosions and reversal of systemic bone loss. To test this, human TNF-transgenic mice with established erosive arthritis and systemic bone loss were treated with PTH, OPG, and anti-TNF, alone or in combination. Local bone erosions almost fully regressed, on combined treatment with anti-TNF and PTH and/or OPG, suggesting repair of inflammatory skeletal lesions. In contrast, OPG and anti-TNF alone led to arrest of bone erosions but did not achieve repair. Treatment with PTH alone had no influence on the progression of bone erosions. Local bone erosions all showed signs of new bone formation such as the presence of osteoblasts, osteoid formation, and mineralization. Furthermore, systemic bone loss was completely reversed on combined treatment and this effect was mediated by osteoblast stimulation and osteoclast blockade. In summary, we conclude that local joint destruction and systemic inflammatory bone loss because of TNF can regress and that repair requires a combined approach by reducing inflammation, blocking bone resorption, or stimulating bone formation.

Anti-A2/RA33 autoantibodies are directed to the RNA binding region of the A2 protein of the heterogeneous nuclear ribonucleoprotein complex. Differential epitope recognition in rheumatoid arthritis, systemic lupus erythematosus, and mixed connective tissue disease.

The recently described anti-A2/RA33 autoantibodies occur in 20-40% of patients with RA, SLE, and mixed connective tissue disease (MCTD). They are directed to the A2 protein of the heterogeneous nuclear ribonucleoprotein complex (hnRNP-A2), an abundant nuclear protein associated with the spliceosome. The NH2-terminal half of the antigen contains two conserved RNA binding domains whereas its COOH-terminal part is extremely glycine-rich. The aim of this study was to characterize the autoepitopes of hnRNP-A2 and to investigate the effects of anti-A2/RA33 autoantibodies on possible functions of the antigen. Using bacterially expressed fragments, two major discontinuous epitopes were identified. One containing the complete second RNA binding domain was recognized by the majority of patients with RA and SLE but not by patients with MCTD. The second epitope contained sequences of both RNA binding domains and was preferentially targeted by patients with MCTD. When the RNA binding properties of the antigen were investigated, oligoribonucleotides containing the sequence motif r(UUAG) were found to bind to a site closely adjacent or overlapping with the epitope targeted by autoantibodies from patients with RA and SLE. Moreover, anti-A2/RA33 autoantibodies from patients with RA or SLE, but not from patients with MCTD, inhibited binding of RNA. Thus, anti-A2/RA33 autoantibodies recognize conformation-dependent epitopes located in a functionally important region of the antigen. Furthermore, the specific recognition of an epitope by MCTD patients may be used as another argument in favor of considering MCTD a distinct connective tissue disease.

Increased bioactive TNF in human systemic lupus erythematosus: associations with cell death

In systemic lupus erythematosus (SLE) serum TNF is increased and correlates with its soluble receptors and with disease activity. We therefore investigated (i) whether the TNF in SLE serum is bioactive, (ii) whether SLE cells react to TNF and (iii) whether there are associations with cell death, which is regarded as pathogenic in SLE. Sera from active SLE patients induced an increase in fibroblast CD54, which was abolished by blocking antibodies against TNF, suggesting TNF bioactivity. SLE lymphocytes had a similar surface expression of TNF-R I as healthy lymphocytes, their expression of TNF-R II was slightly increased. Recombinant TNF induced cell death in PBMC of SLE patients, suggesting functional receptors. Serum levels of sTNF-RII (as a surrogate marker for TNF activity) correlated with sTNF-RI and disease activity, as expected, and also correlated with the percentage of dying lymphocytes and with lymphocytic CD95. SLE sera contain increased amounts of biologically active TNF. Peripheral blood lymphocytes of SLE patients express functional TNF receptors. Finally, associations with cell death and CD95 receptors suggest that TNF may be pathogenic in SLE.

Purification and partial sequencing of the nuclear autoantigen RA33 shows that it is indistinguishable from the A2 protein of the heterogeneous nuclear ribonucleoprotein complex.

RA33 is a nuclear autoantigen with an apparent molecular mass of 33 kD. Autoantibodies against RA33 are found in about 30% of sera from RA patients, but only occasionally in sera from patients with other connective tissue diseases. To characterize RA33, the antigen was purified from HeLa cell nuclear extracts to more than 90% homogeneity by affinity chromatography on heparin-Sepharose and by chromatofocusing. Sequence analysis of five tryptic peptides revealed that their sequences matched corresponding sequences of the A2 protein of the heterogeneous nuclear ribonucleoprotein (hnRNP) complex. Furthermore, RA33 was shown to be present in the 40S hnRNP complex and to behave indistinguishably from A2 in binding to single stranded DNA. In summary, these data strongly indicate that RA33 and A2 are the same protein, and thus identify on a molecular level a new autoantigen.

Activation of the interferon‐γ signaling pathway in systemic lupus erythematosus peripheral blood mononuclear cells

OBJECTIVE To investigate interferon-gamma (IFNgamma) signaling in peripheral blood mononuclear cells (PBMCs) from patients with systemic lupus erythematosus (SLE) by analyzing IFNgamma receptor (IFNgammaR) expression, STAT-1 expression and phosphorylation, and the regulation of IFNgamma-inducible genes. METHODS Fluorocytometry was used to investigate expression of STAT-1, pSTAT-1, CD95, HLA-DR, class I major histocompatibility complex (MHC), IFNgamma-inducible 10-kd protein (IP-10), monokine induced by IFNgamma (Mig), and IFNgammaR in PBMCs from SLE patients and healthy individuals. STAT-1 phosphorylation was determined by fluorocytometry and Western blotting after stimulation with IFNalpha or IFNgamma. Quantitative polymerase chain reaction was used to assess messenger RNA (mRNA) expression of the IFNgamma-inducible genes IP-10 and Mig shortly after preparation or after stimulation with IFNgamma in monocytes. RESULTS STAT-1 expression was increased in PBMCs from SLE patients and correlated significantly with disease activity and with the IFN-inducible expression of CD95 and HLA-DR. STAT-1 expression also showed a trend toward association with class I MHC expression. In addition, the expression of other IFNgamma-inducible genes, such as IP-10 or Mig, was increased in SLE monocytes. While STAT-1 phosphorylation in SLE PBMCs and PBMCs from healthy individuals was similar after IFNalpha stimulation, incubation with IFNgamma induced STAT-1 phosphorylation only in SLE lymphocytes. Moreover, SLE monocytes showed a considerably higher increase in pSTAT-1 expression upon IFNgamma stimulation than monocytes from healthy individuals. Increased responsiveness of SLE monocytes to IFNgamma was also confirmed on the mRNA level, where expression of the IFN-inducible, STAT-1-dependent genes IP-10 and Mig was more efficiently increased in SLE cells. However, IFNgammaR was similarly expressed on SLE lymphocytes and monocytes and those from healthy individuals. CONCLUSION In addition to supporting the role of IFNs in SLE immunopathogenesis in general, the findings of the present study support a role of IFNgamma in this disease.

Avidity maturation of anti–citrullinated protein antibodies in rheumatoid arthritis

OBJECTIVE Anti-citrullinated protein antibodies (ACPAs) are highly specific for rheumatoid arthritis (RA) and are present years before the onset of symptoms. The avidity of autoantibodies can have a strong impact on their effector potency. This study was undertaken to analyze the avidity of ACPAs in serum samples obtained from ACPA-positive healthy individuals (predisease), patients with early disease, and patients with established RA as well as the avidity maturation over time in samples from healthy subjects who later developed RA. METHODS We measured ACPA avidity in serum samples from ACPA-positive healthy individuals, symptomatic individuals, and patients with established RA in 5 collections from The Netherlands, Canada, and Austria. We determined the dynamics of avidity maturation of ACPAs from the predisease stage to established disease in 1 case from the native North American population and in 10 cases from a Dutch blood donor cohort. RESULTS The overall ACPA response was characterized by low-avidity antibodies. Higher-avidity ACPAs were observed in symptomatic patients only, while low-avidity ACPAs were observed in both healthy subjects and patients. In longitudinal samples obtained from subjects prior to disease onset, ACPA avidity increased over time until disease onset. No further avidity maturation was observed after disease onset. CONCLUSION Our findings indicate that avidity maturation of the ACPA response takes place prior to disease onset.

The need for prognosticators in rheumatoid arthritis. Biological and clinical markers: where are we now?

Rheumatoid arthritis is a heterogeneous disease with respect to clinical manifestations, serologic abnormalities, joint damage and functional impairment. Predicting outcome in a reliable way to allow for strategic therapeutic decision-making as well as for prediction of the response to the various therapeutic modalities available today, especially biological agents, would provide means for optimization of care. In the present article, the current information on biological and clinical markers related to disease activity and joint damage as well as for predictive purposes is reviewed. It will be shown that the relationship of many biomarkers with disease characteristics is confounded by factors unrelated to the disease, and that only few biomarkers exist with some predictive value. Moreover, clinical markers appear of equal value as biomarkers for this purpose, although they likewise have limited capacity in these regards. The analysis suggests the search for better markers to predict outcomes and therapeutic responsiveness in rheumatoid arthritis needs to be intensified.