Another Look at the Contribution of Oral Microbiota to the Pathogenesis of Rheumatoid Arthritis: A Narrative Review.

Although autoimmunity contributes to rheumatoid arthritis (RA), several lines of evidence challenge the dogma that it is mainly an autoimmune disorder. As RA-associated human leukocyte antigens shape microbiomes and increase the risk of dysbiosis in mucosae, RA might rather be induced by epigenetic changes in long-lived synovial presenting cells, stressed by excessive translocations into joints of bacteria from the poorly cultivable gut, lung, or oral microbiota (in the same way as more pathogenic bacteria can lead to "reactive arthritis"). This narrative review (i) lists evidence supporting this scenario, including the identification of DNA from oral and gut microbiota in the RA synovium (but in also healthy synovia), and the possibility of translocation through blood, from mucosae to joints, of microbiota, either directly from the oral cavity or from the gut, following an increase of gut permeability worsened by migration within the gut of oral bacteria such as Porphyromonas gingivalis; (ii) suggests other methodologies for future works other than cross-sectional studies of periodontal microbiota in cohorts of patients with RA versus controls, namely, longitudinal studies of oral, gut, blood, and synovial microbiota combined with transcriptomic analyses of immune cells in individual patients at risk of RA, and in overt RA, before, during, and following flares of RA.

Sodium (18)F-sodium fluoride PET failed to predict responses to TNFα antagonist therapy in 31 patients with possible spondyloarthritis not meeting ASAS criteria.

OBJECTIVES: To determine whether (18)F-NaF positron-emission tomography (PET) contributes to the diagnosis of spondyloarthritis and whether observed uptakes predict the response to TNFα antagonist therapy. METHODS: We studied patients who had suspected spondyloarthritis but did not meet ASAS criteria and who were referred for an assessment of eligibility for TNFα antagonist therapy. (18)F-NaF PET was offered instead of bone scintigraphy. TNFα antagonist therapy was given if the clinician's level of confidence in the diagnosis of spondyloarthritis based on (18)F-NaF PET findings was ≥50/100. RESULTS: Thirty-one patients accepted to undergo (18)F-NaF PET. Their mean age was 39.9±11.7 years; 22% were HLA-B27-positive and none had evidence of sacroiliitis by magnetic resonance imaging. Of the 31 patients, 30 had abnormal (18)F-NaF PET findings. However, of the 312 high-uptake foci, only 123 (39.4%) matched sites of pain. TNFα antagonist therapy was given to 16 patients. The treated group and untreated group (n=15) were not significantly different for the mean number of high-uptake foci per patient (11.7±8.1 vs. 8.3±5.1, respectively) or for the proportion of patients with high uptake by the sacroiliac joints (13/16 [81%] vs. 8/15 [53%], respectively). In the treated group, 5 patients met ASAS response criteria after 3 months. These 5 patients were among the 9 treated patients who met Amor's modified criteria (arthritis instead of asymmetrical oligoarthritis). In the 5 responders, the (18)F-NaF uptake scores were nonsignificantly lower than in the 11 nonresponders (9.0±8.5 vs. 13.0±6.4, respectively). In the patients for whom the (18)F-NaF PET findings increased the level of confidence in the diagnosis of spondyloarthritis, this effect was short-lived. DISCUSSION: The positive predictive value of (18)F-NaF PET for diagnosing spondyloarthritis or predicting a response to TNFα antagonist therapy seems very low. This finding is probably ascribable to poor specificity.

Pathogenesis of hyperostosis: a key role for mesenchymatous cells?

The similarities between diffuse idiopathic skeletal hyperostosis (DISH) and some forms of ankylosing spondylitis suggest shared pathogenic mechanisms. Entheseal ossification progresses at the same rate in the two conditions, and spondyloarthritis was the first diagnosis considered in several families with genetically determined early-onset DISH. However, DISH may be a heterogeneous condition, as the presence of peripheral calcifications in some families suggests pathogenic similarities with several animal models combining entheseal ossification and peripheral calcifications, as well as with X-linked familial hypophosphatemia and dentin-matrix-protein mutations. In the far more common presentation of hyperostosis without calcifications, entheseal ossification may be related to abnormal osteoblastic differentiation of mesenchymatous stem cells normally found around the intervertebral disks, in the vertebral periosteum, and in the anterior and posterior longitudinal ligaments. The many factors suspected of promoting this abnormal differentiation include bone morphogenetic proteins (BMPs), retinoids, and various hormonal factors; in addition, adipokines such as leptin are the focus of growing interest based on the well-documented association between DISH and obesity. Confirmation of the role for mesenchymatous cells in DISH should encourage investigations of mesenchymatous cells as possible pathogenic contributors to the entheseal abnormalities seen in spondyloarthritis. These cells normally exert immunosuppressive effects, which may be subverted in spondyloarthritis, notably by a T-cell population that homes specifically to the entheses.

Rheumatoid arthritis and periodontal disease.

The prevalence of periodontal disease has increased two-fold among patients with rheumatoid arthritis (RA) compared to the general population. This increased prevalence is unrelated to secondary Sjögren's syndrome but instead reflects shared pathogenic mechanisms, including an increased prevalence of the shared epitope HLA-DRB1-04; exacerbated T-cell responsiveness with high tissue levels of IL-17; exaggerated B-cell responses, with plasma cells being the predominant cell type found within gingival tissue affected with periodontitis and B cells being twice as numerous as T cells; RANK overexpression; and an increase in the ratio of RANK-L over osteoprotegerin with a high level of RANK-L expression on gingival B cells, most notably those capable of recognizing Porphyromonas gingivalis. Other factors conducive to periodontitis include smoking and infection with the Epstein-Barr virus or cytomegalovirus, which act by promoting the growth of organisms such as P. gingivalis, whose DNA is often found in synovial tissue from RA patients. P. gingivalis produces the enzyme peptidylarginine deiminase that induces citrullination of various autoantigens, and levels of anti-CCP antibodies are considerably higher in RA patients with than without periodontal disease, suggesting that periodontitis may contribute to the pathogenesis of RA. Further support for this hypothesis comes from evidence that other antigens involved in RA, such as HC-gp39, are also present in gingival tissue. TNFα antagonists slow alveolar resorption but may perpetuate infection of periodontal pockets. Therefore, rheumatology patients, including those taking biotherapies, are likely to benefit from increased referral to dental care (e.g., scaling, root planing and, if needed, dental surgery), particularly as periodontitis is also associated with an increased risk of premature atheroma.