Autoantibodies to glucose‐6‐phosphate isomerase are elevated in the synovial fluid of rheumatoid arthritis patients

Autoantibodies as Diagnostic Markers and Mediator of Joint Inflammation in Arthritis

Rheumatoid arthritis is a systemic, polygenic, and multifactorial syndrome characterized by erosive polyarthritis, damage to joint architecture, and presence of autoantibodies against several self-structures in the serum and synovial fluid. These autoantibodies (anticitrullinated protein/peptide antibodies (ACPAs), rheumatoid factors (RF), anticollagen type II antibodies, antiglucose-6 phosphate isomerase antibodies, anticarbamylated protein antibodies, and antiacetylated protein antibodies) have different characteristics, diagnostic/prognostic value, and pathological significance in RA patients. Some of these antibodies are present in the patients' serum several years before the onset of clinical disease. Various genetic and environmental factors are associated with autoantibody production against different autoantigenic targets. Both the activating and inhibitory FcγRs and the activation of different complement cascades contribute to the downstream effector functions in the antibody-mediated disease pathology. Interplay between several molecules (cytokines, chemokines, proteases, and inflammatory mediators) culminates in causing damage to the articular cartilage and bones. In addition, autoantibodies are proven to be useful disease markers for RA, and different diagnostic tools are being developed for early diagnosis of the clinical disease. Recently, a direct link was proposed between the presence of autoantibodies and bone erosion as well as in the induction of pain. In this review, the diagnostic value of autoantibodies, their synthesis and function as a mediator of joint inflammation, and the significance of IgG-Fc glycosylation are discussed.

Revisit of autoimmunity to glucose-6-phosphate isomerase in experimental and rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory disorder characterized by synovial inflammation in multiple joints. Autoantibodies (Abs) are the hallmark of RA, and as disease-specific and diagnostic markers, rheumatoid factor and anti-citrullinated protein antibody (ACPA) are produced pre-clinically, but their pathogenic roles in RA remain elusive. In this review, we focus on one of the candidate autoantigens in RA; glucose-6-phosphate isomerase (GPI). The arthritogenic role of GPI has been confirmed in two different mouse models: the K/BxN- and GPI-induced arthritis models. Both anti-GPI Abs and citrullinated-GPI peptide Abs have been detected in human RA. Studies conducted in these rodent models have confirmed that the pathogenesis of arthritis involves the localization of autoantigens not only in the joints but also in the circulation. In this review, we revisit and summarize the arthritogenic relevance of GPI in animal RA models and in human RA, and extend the discussion to joint-specific inflammation.

Immunosensors for Biomarker Detection in Autoimmune Diseases

Autoimmune diseases occur when the immune system generates proinflammatory molecules and autoantibodies that mistakenly attack their own body. Traditional diagnosis of autoimmune disease is primarily based on physician assessment combined with core laboratory tests. However, these tests are not sensitive enough to detect early molecular events, and quite often, it is too late to control these autoimmune diseases and reverse tissue damage when conventional tests show positivity for disease. It is fortunate that during the past decade, research in nanotechnology has provided enormous opportunities for the development of ultrasensitive biosensors in detecting early biomarkers with high sensitivity. Biosensors consist of a biorecognition element and a transducer which are able to facilitate an accurate detection of proinflammatory molecules, autoantibodies and other disease-causing molecules. Apparently, novel biosensors could be superior to traditional metrics in assessing the drug efficacy in clinical trials, especially when specific biomarkers are indicative of the pathogenesis of disease. Furthermore, the portability of a biosensor enables the development of point-of-care devices. In this review, various types of biomolecule sensing systems, including electrochemical, optical and mechanical sensors, and their applications and future potentials in autoimmune disease treatment were discussed.

[Autoimmunity to glycolytic enzyme in rheumatoid arthritis]

Prognosis of rheumatoid arthritis (RA) patients has significantly improved with the recent use of biologics targeting TNFα, IL-6, and co-stimulatory molecule. In US and Europe, clear therapeutic benefit of anti-CD20 antibodies is also confirmed. As a disease specific marker, rheumatoid factor and anti-citrullinated protein antibody are crucial in RA, although the pathology of them is not defined. Here we focus on glycolytic enzyme such as glucose-6-phospate isomerase, that is confirmed as arthritogenic in two different mouse models, and discuss about pathogenic relevance to RA.

The role of antibodies in inflammatory arthritis

Inflammatory arthritis presents in a variety of diseases, from rheumatoid arthritis to hepatitis. Antibodies to autoantigens or to microbial constituents are commonly associated with these conditions. In some cases, the antibodies have diagnostic and prognostic relevance. It cannot as yet be determined definitively that any of them mediate joint damage, although the evidence from animal models indicates that this mechanism is likely. The purpose of this article is to give an overview of the spectrum of antibodies found in a variety of inflammatory arthritides. The relevant animal models are also discussed.

The activity of exoglycosidases in the synovial membrane and knee fluid of patients with rheumatoid arthritis and juvenile idiopathic arthritis

OBJECTIVE

To determine the activities of the five exoglycosidases that catabolize glycoconjugates (proteoglycans, glycoproteins, and glycolipids) in the synovial membrane and knee joint fluid of patients with rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA).

METHODS

The following exoglycosidases were analysed with the p-nitrophenyl derivatives of appropriate sugars as substrates: hexosaminidase (HEX) and its isoenzymes A and B, beta-glucuronidase, beta-galactosidase, alpha-mannosidase, and alpha-fucosidase.

RESULTS

Our results show that the activity of all exoglycosidases tested in the synovial membrane of patients with RA and JIA was significantly higher than in synovial fluid. We demonstrated that only the enzymatic activity of HEX was significantly higher in the tissue of patients with inflammatory diseases in comparison to the activity in the control group.

CONCLUSION

These data support the concept that the synovial cells of patients with RA and JIA are the main source of exoglycosidases, which catabolize glycoconjugates of cartilage.

Administration of PDE4 inhibitors suppressed the pannus-like inflammation by inhibition of cytokine production by macrophages and synovial fibroblast proliferation

A marked proliferation of synovial fibroblasts in joints leads to pannus formation in rheumatoid arthritis (RA). Various kinds of cytokines are produced in the pannus. The purpose of this study is to elucidate the effects of phosphodiesterase 4 (PDE4) inhibitors in a new animal model for the evaluation of pannus formation and cytokine production in the pannus. Mice sensitized with methylated bovine serum albumin (mBSA) were challenged by subcutaneous implantation of a membrane filter soaked in mBSA solution in the back of the mice. Drugs were orally administered for 10 days. The granuloma formed around the filter was collected on day 11. It was chopped into pieces and cultured in vitro for 24 hr. The cytokines were measured in the supernatants. The type of cytokines produced in the granuloma was quite similar to those produced in pannus in RA. Both PDE4 inhibitors, KF66490 and SB207499, suppressed the production of IL-1beta, TNF-alpha, and IL-12, and the increase in myeloperoxidase activity, a marker enzyme for neutrophils and hydroxyproline content. Compared to leflunomide, PDE4 inhibitors more strongly suppressed IL-12 production and the increase in myeloperoxidase activity. PDE4 inhibitors also inhibited lipopolysaccharide-induced TNF-alpha and IL-12 production from thioglycolate-induced murine peritoneal macrophages and the proliferation of rat synovial fibroblasts. These results indicate this model makes it easy to evaluate the effect of drugs on various cytokine productions in a granuloma without any purification step and may be a relevant model for evaluating novel antirheumatic drugs on pannus formation in RA. PDE4 inhibitors could have therapeutic effects on pannus formation in RA by inhibition of cytokine production by macrophages and synovial fibroblast proliferation.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.

The role and clinical implications of G6PI in experimental models of rheumatoid arthritis

The antigens that trigger the pathogenic immune response in rheumatoid arthritis (RA) remain unknown. Until recently it was assumed that either viral or microbial antigens, or joint-specific antigens were the target of arthritogenic T and B lymphocytes in RA. Consequently, murine models of arthritis are induced by immunization with either joint-specific antigens such as type II collagen or microbial products such as streptococcal cell wall. In the K/B×N T-cell receptor transgenic mouse model arthritis is caused by a systemic autoimmune response to the ubiquitously expressed glycolytic enzyme glucose-6-phosphate isomerase (G6PI). The autoreactive transgenic T cells recognize G6PI and provide help for the production of arthritogenic IgG antibodies against G6PI. More recently it was shown that G6PI immunization induces severe symmetrical peripheral polyarthritis in genetically unaltered DBA/I mice. In that model CD4⁺ T cells are necessary not only for the induction but also for the effector phase of arthritis. Here we review the pathomechanisms that lead from systemic autoreactivity to arthritis in these models, consider the relevance of anti-G6PI immune reactivity for RA, and discuss the insights into the pathogenesis of RA and possibly other autoimmune conditions that can be gained from these models.