Sensitive mass spectrometric procedure for the detection of bacterial cell wall components in rheumatoid joints

Proteomics in rheumatology: a new direction for old diseases

OBJECTIVES

Completion of the human genome project has stimulated scientists to begin looking for the next step in unraveling normal and abnormal functions within biological systems. Consequently, there is new focus on the role of proteins in these processes. Proteomics is a rapidly growing field that may provide a valuable approach to evaluate the field of rheumatology. The objectives of this article is to provide an overview of biophysical techniques, as "re-invented" research tools, as applied to the investigation of rheumatoid arthritis and osteoarthritis.

METHODS

MEDLINE search of articles in English-language journals from 1966 to 2004. The index words "Rheumatoid/osteoarthritis/connective tissue disorders" and the following co-indexing terms were used: "mass spec," "NMR," "SPR" and "Proteomics." Papers identified were reviewed, abstracted, and summarized. The authors' own work in the field is also presented.

RESULTS

As we move into the postgenomics era, new and exciting tools are being developed to study protein expression and protein interactions and identify new biomarkers for disease diagnosis and prognosis. Proteomics is an emerging field with widespread potential applications to rheumatic disease.

CONCLUSIONS

In this review the biophysical techniques of nuclear magnetic resonance, mass spectroscopy, and surface plasmon resonance as proteomic tools in the study of rheumatoid and osteoarthritis were reviewed. What is emerging is the identification of new biomarkers with clinical and therapeutic relevance.

Enzyme degradation and proinflammatory activity in arthritogenic and nonarthritogenic Eubacterium aerofaciens cell walls

Two almost-identical strains of Eubacterium aerofaciens isolated from the normal human gut flora were used. The cell wall (CW) of one strain with a peptidoglycan (PG) type A4alpha induces chronic arthritis in the rat after a single intraperitoneal injection, whereas CW of the other with PG type A4beta induces only a transient acute arthritis. The CW of the arthritogenic E. aerofaciens was a twofold-more-potent stimulator of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and monocyte chemoattractant protein 1 (MCP-1) than the nonarthritogenic CW. After degradation with mutanolysin, the capacity of the arthritogenic PG to stimulate production of TNF-alpha and MCP-1 was significantly increased, whereas that of the nonarthritogenic PG was significantly decreased. In other words, after enzyme degradation the arthritogenic PG had a four- to fivefold-stronger stimulatory capacity than that of the enzyme-treated nonarthritogenic PG. These findings indicate that the arthritogenicity of CW or a PG is not dependent on the enzyme resistance alone but also on how the PG fragments released by enzyme degradation stimulate the production of proinflammatory cytokines.

Reiter's syndrome and reactive arthritis: a current view

This paper reviews advances in the understanding of the pathogenesis of reactive arthritis that have occurred over the last decade. Inflammatory aseptic joint disease has been linked with prior infection initiated by many different species of microorganisms. The presence of intra-articular bacterial antigens has now been firmly established with the demonstration of bacteria, bacterial fragments, DNA, RNA, and bacterial lipopolysaccharide in joints of patients with reactive arthritis. Chlamydia trachomatis, Salmonella enteritidis, and Shigella flexneri have all been detected in the joint by immunological techniques, although there is still some doubt as to the form in which they reach the joint and whether or not they persist. A number of phlogistic bacterial components could be acting as arthritogens. Negative joint culture results from patients with reactive arthritis make it unlikely that bacteria in the joint are viable, although chlamydial DNA has been shown in the joints of patients with sexually acquired reactive arthritis using the polymerase chain reaction. The use of antimicrobial therapy in the treatment of reactive arthritis is under review; data suggests that long-term antibiotic treatment warrants further study. The role of HLA-B27 in disease pathogenesis is discussed as are possible mechanisms of interplay between germ and gene. HLA-B27 might confer disease susceptibility by affecting immune mechanisms other than classical antigen presentation. The immunopathogenesis of joint inflammation in reactive arthritis is explored with reference to studies of humoral and cellular immune responses. Serological evidence to support the concept of molecular mimicry is far from conclusive; the results of relevant studies are summarized. Lymphocyte proliferation experiments suggest that antigen presenting cells play an important role. Finally, our views on reactive arthritis in the 1990s, and areas of new and potentially fruitful future research are presented.

Mass spectrometric quantitation of muramic acid, a bacterial cell wall component, in septic synovial fluids

This is the first report describing the use of gas chromatography-mass spectrometry for detection of muramic acid in infected synovial fluid (SF). Muramic acid is a ubiquitous component of bacterial cell walls, and it has been proposed that it could serve as a chemical marker for the presence of live bacteria or bacterial debris in rheumatoid joints. Our goal was to determine whether muramic acid was present at detectable levels in septic SF, since this would serve as a positive control for studies of reactive and rheumatoid arthritis. Muramic acid was found to be present at levels of less than 250-1,700 ng/ml in 12 septic SF samples (10 of which were culture positive for Staphylococcus aureus and 1 each for Escherichia coli and Streptococcus pneumoniae). Among these samples, those containing low bacterial colony counts did not contain detectable muramic acid. Muramic acid was also not detected in any SF samples from 20 control patients. We conclude that muramic acid can be used as a marker for the presence of bacterial peptidoglycan in SF. With further lowering of gas chromatography-mass spectrometry detection limits, determination of the quantities of bacterial debris present in joints of patients with rheumatoid or reactive arthritis will be attainable.

Etiology of rheumatoid arthritis

Definite genetic associations with immunological cooperative HLA-D(R) antigens have been demonstrated for rheumatoid arthritis (RA). Microbial etiology has not been proven, but some hope for the supporters of this view is still given by small viruses, plasmids of enteric bacteria or perhaps oncogen-like DNA-sequences. Yet, electrophoretical analysis of membrane proteins or surface glycoproteins of RA synovial cells does not show any differences compared to reference cells. Autoimmunity to several tissue elements has been demonstrated, but most of it is of secondary nature. Antigenicities of type II and III collagens are probably only contributory factors for HLA-DR4 positive individuals. Proteoglycans or minor cartilage collagens have not been extensively studied, so far. Endocrine, dietary or psychological influences might be triggering events for otherwise 'preloaded' individuals.

High incidence of spontaneous Ig-producing lymphocytes in peripheral blood and synovial fluid of patients with active seropositive rheumatoid arthritis

Numbers of in vitro spontaneous IgG, IgM and IgA plaque-forming cells (PFC) as assessed by a modification of the protein A haemolytic plaque assay were determined in the blood and synovial fluid of patients with seropositive rheumatoid arthritis (RA) and compared with those of control groups. The total numbers of PFC were significantly higher in the peripheral blood of patients with active seropositive RA than in that of normal controls. In addition, most B lymphocytes in the synovial fluid of patients with active seropositive RA were active immunoglobulin (Ig) producers, whereas synovial fluid lymphocytes from patients with inactive seropositive RA and seronegative arthritis were not. In general, IgA PFC were relatively high in blood, whereas IgG PFC dominated in the synovial fluid. IgM PFC appear to be relatively low in blood and synovial fluid. However, a relative increase of IgG PFC was noted in the peripheral blood of patients with active RA. To test for polyclonality of the increased Ig synthesis, we tested the sera of patients and controls for the presence of polyclonal antibodies against sheep erythrocytes (SRBC) and SRBC modified by fluorescein isothiocyanate (FITC) and trinitrophenyl (TNP). No differences were observed with SRBC and TNP-SRBC agglutinin titres between patients and controls, but patients with RA had higher titres of FITC-SRBC agglutinins than normal sera. This finding supports the concept of a polyclonal nature of antibody production in RA patients.

Distribution of lysozyme in synovial tissue of patients with osteoarthritis and rheumatoid arthritis demonstrated by different enzyme histochemical methods

Lysozyme-producing cells were analysed by enzyme histochemistry in paraffin sections of synovial tissue of 60 patients with rheumatoid arthritis (RA) and 20 patients with osteoarthritis (OA). For lysozyme detection three enzyme histochemical systems - peroxidase-anti-peroxidase, alkaline phosphatase and biotin-avidin - were used in parallel experiments. Lysozyme was found to be produced by polymorphonuclear cells, mononuclear phagocytes and part of synovial lining cells. All types of lysozyme-producing cells were increased in RA compared with OA. Subgrouping of RA synovitis according to histomorphological criteria allowed the demonstration of an inverse relationship between the number of lysozyme-producing cells and the grade of proliferation of fibroblasts, called mesenchymoid transformation by Fassbender [19]. The different methods of lysozyme detection differed in specificity and sensitivity. The immunoenzymatic staining of lysozyme allows specific and quantitative evaluation of phagocytizing cells in RA and OA.