Expression of peptidylarginine deiminase-2 and -4, citrullinated proteins and anti-citrullinated protein antibodies in human gingiva

Food-derived bioactive peptides potentiating therapeutic intervention in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that affects the joints of the human body and is projected to have a prevalence age-standardized rate of 1.5 million new cases worldwide by 2030. Several conventional and non-conventional preventive and therapeutic interventions have been suggested but they have their side effects including nausea, abdominal pain, liver damage, ulcers, heightened blood pressure, coagulation, and bleeding. Interestingly, several food-derived peptides (FDPs) from both plant and animal sources are increasingly gaining a reputation for their potential in the management or therapy of RA with little or no side effects. In this review, the concept of inflammation, its major types (acute and chronic), and RA identified as a chronic type were discussed based on its pathogenesis and pathophysiology. The conventional treatment options for RA were briefly outlined as the backdrop of introducing the FDPs that potentiate therapeutic effects in the management of RA.

Periodontitis and periodontopathic bacteria as risk factors for rheumatoid arthritis: A review of the last 10 years

Rheumatoid arthritis (RA) is characterized by chronic inflammatory destruction of joint tissue and is caused by an abnormal autoimmune response triggered by interactions between genetics, environmental factors, and epigenetic and posttranslational modifications. RA has been suggested to be interrelated with periodontitis, a serious form or stage of chronic inflammatory periodontal disease associated with periodontopathic bacterial infections, genetic predisposition, environmental factors, and epigenetic influences. Over the last decade, a number of animal and clinical studies have been conducted to assess whether or not periodontitis and associated periodontopathic bacteria constitute risk factors for RA. The present review introduces recent accumulating evidence to support the associations of periodontitis and periodontopathic bacteria with the risk of RA or the outcome of RA pharmacological treatment with disease-modifying antirheumatic drugs. In addition, the results from intervention studies have suggested an improvement in RA clinical parameters after nonsurgical periodontal treatment. Furthermore, the potential causal mechanisms underlying the link between periodontitis and periodontopathic bacteria and RA are summarized.

Effect of Chronic Rhinosinusitis on the Risk of Development of Rheumatoid Arthritis

PURPOSE

Several studies have reported a possible link between chronic rhinosinusitis (CRS) and rheumatoid arthritis (RA). However, it remains unclear whether CRS could influence the risk of developing RA. Therefore, in this study, we focused on examining the association between CRS and RA.

METHODS

A total of 14,867 individuals with CRS and 14,867 without CRS were enrolled after 1:1 propensity score match from a nationwide longitudinal cohort database in South Korea. RA incidence was assessed using person-years at risk, and the hazard ratio (HR) was examined using the Cox proportional hazards model.

RESULTS

The incidence of RA (per 1,000 person-years) was 6.51 for those with CRS, 6.55 for those with CRS without nasal polyps (CRSsNP), and 5.96 for those with CRS with nasal polyps (CRSwNP). We found that CRS individuals had a significantly increased risk of subsequent RA development with an adjusted HR of 1.41, regardless of the phenotype (adjusted HR was 1.42 in CRSsNP and 1.37 in CRSwNP patients). Moreover, the risk of developing RA over time was relatively higher within the first 4 years after the diagnosis of CRS.

CONCLUSIONS

Our nationwide population-based cohort study suggests that CRS may be associated with a subsequent increase in RA events, regardless of the phenotype. Therefore, physicians should consider RA risk when diagnosing and treating CRS patients.

The serum immunoglobulin G titres against Porphyromonas gingivalis as a predictor of clinical response to 1-year treatment with biological disease-modifying antirheumatic drugs in rheumatoid arthritis patients: A retrospective cohort study

OBJECTIVES

The aim is to evaluate the relevance of serum immunoglobulin G (IgG) titres against periodontopathic bacteria to predict the clinical response to 1-year treatment with biological disease-modifying antirheumatic drugs (bDMARDs) in rheumatoid arthritis (RA) patients.

METHODS

Data were collected from 50 RA patients who had received conventional synthetic DMARDs, corticosteroids, or non-steroidal anti-inflammatory drugs before (baseline) and after 1-year treatment with bDMARDs in a retrospective cohort study. Changes in rheumatologic conditions were compared between the two groups for low and high baseline IgG titres against Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans according to their median measurements.

RESULTS

Twenty-five patients with low anti-P. gingivalis IgG titres showed significantly greater decreases in changes in the Clinical Disease Activity Index and swollen joint count than 25 patients with high anti-P. gingivalis IgG titres (p = .04 for both). Bivariate and multivariate analyses revealed a significantly positive association of baseline anti-P. gingivalis IgG titres with Clinical Disease Activity Index changes (p = .02 and p = .002). However, post-treatment rheumatologic conditions were comparable between 25 patients each in the low and high baseline anti-A. actinomycetemcomitans IgG titre groups.

CONCLUSIONS

Baseline serum anti-P. gingivalis IgG titres are predictive of the clinical response to 1-year treatment with bDMARDs in RA patients.

New insights into inflammatory osteoclast precursors as therapeutic targets for rheumatoid arthritis and periodontitis

Rheumatoid arthritis (RA) and periodontitis are chronic inflammatory diseases leading to increased bone resorption. Preventing this inflammatory bone resorption is a major health challenge. Both diseases share immunopathogenic similarities and a common inflammatory environment. The autoimmune response or periodontal infection stimulates certain immune actors, leading in both cases to chronic inflammation that perpetuates bone resorption. Moreover, RA and periodontitis have a strong epidemiological association that could be explained by periodontal microbial dysbiosis. This dysbiosis is believed to be involved in the initiation of RA via three mechanisms. (i) The dissemination of periodontal pathogens triggers systemic inflammation. (ii) Periodontal pathogens can induce the generation of citrullinated neoepitopes, leading to the generation of anti-citrullinated peptide autoantibodies. (iii) Intracellular danger-associated molecular patterns accelerate local and systemic inflammation. Therefore, periodontal dysbiosis could promote or sustain bone resorption in distant inflamed joints. Interestingly, in inflammatory conditions, the existence of osteoclasts distinct from "classical osteoclasts" has recently been reported. They have proinflammatory origins and functions. Several populations of osteoclast precursors have been described in RA, such as classical monocytes, a dendritic cell subtype, and arthritis-associated osteoclastogenic macrophages. The aim of this review is to synthesize knowledge on osteoclasts and their precursors in inflammatory conditions, especially in RA and periodontitis. Special attention will be given to recent data related to RA that could be of potential value in periodontitis due to the immunopathogenic similarities between the two diseases. Improving our understanding of these pathogenic mechanisms should lead to the identification of new therapeutic targets involved in the pathological inflammatory bone resorption associated with these diseases.

Extracellular Release of Citrullinated Vimentin Directly Acts on Osteoclasts to Promote Bone Resorption in a Mouse Model of Periodontitis

Elevated osteoclast (OC)-mediated bone resorption, a common pathological feature between periodontitis and rheumatoid arthritis (RA), implicates a possible mutually shared pathogenesis. The autoantibody to citrullinated vimentin (CV), a representative biomarker of RA, is reported to promote osteoclastogenesis (OC-genesis). However, its effect on OC-genesis in the context of periodontitis remains to be elucidated. In an in vitro experiment, the addition of exogenous CV upregulated the development of Tartrate-resistant acid phosphatase (TRAP)-positive multinuclear OCs from mouse bone marrow cells and increased the formation of resorption pits. However, Cl-amidine, an irreversible pan-peptidyl arginine deiminase (PAD) inhibitor, suppressed the production and secretion of CV from RANKL-stimulated OC precursors, suggesting that the citrullination of vimentin occurs in OC precursors. On the other hand, the anti-vimentin neutralizing antibody suppressed in vitro Receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced OC-genesis. The CV-induced upregulation of OC-genesis was abrogated by the Protein kinase C (PKC)-δ inhibitor Rottlerin, accompanied by the downmodulation of OC-genesis-related genes, including Osteoclast stimulatory transmembrane protein (OC-STAMP), TRAP and Matrix Metallopeptidase 9 (MMP9) as well as extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP)-kinase phosphorylation. Elevated levels of soluble CV and vimentin-bearing mononuclear cells were found in the bone resorption lesions of periodontitis induced in mice in the absence of an anti-CV antibody. Finally, local injection of anti-vimentin neutralizing antibody suppressed the periodontal bone loss induced in mice. Collectively, these results indicated that the extracellular release of CV promoted OC-genesis and bone resorption in periodontitis.

Progression of pre-rheumatoid arthritis to clinical disease of joints: Potential role of mesenchymal stem cells

Rheumatoid arthritis (RA) related autoimmunity is developed at mucosal sites due to the interplay between genetic risk factors and environmental triggers. The pre-RA phase that leads to anti-citrullinated protein antibodies, rheumatoid factor, and other autoantibodies spread in the systemic circulation may not affect articular tissue for years until a mysterious second hit triggers the localization of RA-related autoimmunity in joints. Several players in the joint microenvironment mediate the synovial innate and adaptive immunological processes, eventually leading to clinical synovitis. There still exists a gap in the early phase of RA pathogenesis, i.e., the progression of diseases from the systemic circulation to joints. The lack of better understanding of these events results in the inability to answer questions about why only after a certain point of time the disease appears in joints and why in some cases, it simply remains latent and doesn't affect joints at all. In the current review, we focused on the immunomodulatory and regenerative role of mesenchymal stem cells and associated exosomes in RA pathology. We also highlighted the age-related dysregulations in activities of mesenchymal stem cells and how that might trigger homing of systemic autoimmunity to joints.

Hypercitrullination and anti-citrullinated protein antibodies in chronic apical periodontitis, a laboratory investigation. Does autoimmunity contribute to the pathogenesis?

AIM

The presence of Gram-negative anaerobic bacteria, in particular, Porphyromonas gingivalis (P. gingivalis) in periapical granulomas predicts the generation of citrullinated proteins in the lesion. Citrullination of proteins may lead to the formation of anti-citrullinated autoantibodies (ACPA-s) initiating the formation of an autoimmune loop which may contribute to the perpetuation of inflammatory reactions and tissue damage in chronic apical periodontitis. The objective of this study was to demonstrate the formation of citrullinated proteins in chronic apical periodontitis and whether they can act as autoantigens.

METHODOLOGY

Twenty-five periapical granulomas (n = 25) were investigated in the study. Healthy periodontal tissue samples served as normal control tissue (n = 6). The peptidyl-citrulline level was determined with the dot blot method. ACPA levels were analysed using anti-citrullinated cyclic peptide (anti-CCP) EDIA kit. Differences between periapical granuloma and control samples were assessed using Mann-Whitney U tests. p Values <.05 were considered as statistically significant.

RESULTS

Protein concentrations, peptidyl-citrulline levels and anti-CCP ratios were compared between periapical granuloma and healthy control groups. Multiple linear regression analysis revealed significant (p = .042) hypercitrullination in periapical granuloma samples. Moreover, there was a significant difference in the ACPA ratios between periapical granuloma (2.03 ± 0.30) and healthy control (0.63 ± 0.17) groups (p = .01). Seventeen of 25 periapical granuloma samples (17/25; 68%), whereas one out of six control samples (1/6; 17%) were shown to be positive for the presence of ACPA.

CONCLUSIONS

This is the first study detecting the presence of citrullinated peptides and APCA in periapical granuloma, suggesting the contribution of autoimmune reactions in the pathogenesis and perpetuation of chronic apical periodontitis.

Unmet need in rheumatology: reports from the Advances in Targeted Therapies meeting, 2022

To detail the unmet clinical and scientific needs in the field of rheumatology. After a 2-year hiatus due to the SARS-CoV-2 pandemic, the 22nd annual international Advances in Targeted Therapies meeting brought together more than 100 leading basic scientists and clinical researchers in rheumatology, immunology, epidemiology, molecular biology and other specialties. Breakout sessions were convened with experts in five rheumatological disease-specific groups including: rheumatoid arthritis (RA), psoriatic arthritis, axial spondyloarthritis, systemic lupus erythematosus and connective tissue diseases (CTDs). In each group, experts were asked to identify and prioritise current unmet needs in clinical and translational research, as well as highlight recent progress in meeting formerly identified unmet needs. Clinical trial design innovation was emphasised across all disease states. Within RA, developing therapies and trials for refractory disease patients remained among the most important identified unmet needs and within lupus and spondyloarthritis the need to account for disease endotypes was highlighted. The RA group also identified the need to better understand the natural history of RA, pre-RA states and the need ultimately for precision medicine. In CTD generally, experts focused on the need to better identify molecular, cellular and clinical signals of early and undifferentiated disease in order to identify novel drug targets. There remains a strong need to develop therapies and therapeutic strategies for those with treatment-refractory disease. Increasingly it is clear that we need to better understand the natural history of these diseases, including their 'predisease' states, and identify molecular signatures, including at a tissue level, which can facilitate disease diagnosis and treatment. As these unmet needs in the field of rheumatic diseases have been identified based on consensus of expert clinicians and scientists in the field, this document may serve individual researchers, institutions and industry to help prioritise their scientific activities.

Immune dysregulation and pathogenic pathways mediated by common infections in rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the world's most prevalent inflammatory autoimmune diseases, affecting between 0.4 and 1.3% of the population. The susceptibility to RA appears to be influenced by a complex interaction between a favorable genetic background and the existence of a specific immune reaction against a wide range of environmental variables. Among the known environmental variables, infections are believed to have a significant role in promoting the formation of autoimmune disorders, which are frequently caused by specific microorganisms. Infections have been linked to RA in recent medical studies. In this study, we selected the most prevalent infections associated with RA from the literature and described the data confirming their pathogenic role in RA. Our investigation included Mycobacterium, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Proteus mirabilis, Epstein-Barr virus, parvovirus, and Prevotella copri.

Role of the PADI family in inflammatory autoimmune diseases and cancers: A systematic review

The peptidyl arginine deiminase (PADI) family is a calcium ion-dependent group of isozymes with sequence similarity that catalyze the citrullination of proteins. Histones can serve as the target substrate of PADI family isozymes, and therefore, the PADI family is involved in NETosis and the secretion of inflammatory cytokines. Thus, the PADI family is associated with the development of inflammatory autoimmune diseases and cancer, reproductive development, and other related diseases. In this review, we systematically discuss the role of the PADI family in the pathogenesis of various diseases based on studies from the past decade to provide a reference for future research.

Peptidylarginine Deiminase 2 Gene Polymorphisms in Subjects with Periodontitis Predispose to Rheumatoid Arthritis

Epidemiologic studies have shown associations between periodontitis and rheumatoid arthritis (RA), but a causal relationship has not been established. Citrullination of gingival proteins by human peptidylarginine deiminases (PADs) or PAD from Porphyromonas gingivalis has been proposed to generate autoantigens in anti-CCP-positive RA. This study investigated whether the association between periodontitis and RA is influenced by single nucleotide polymorphisms (SNPs) in the genes encoding PAD2 and PAD4 that catalyze aberrant citrullination in RA and often are overexpressed in inflamed gingival connective tissue in subjects with periodontitis. The study included 137 RA patients and 161 controls with self-reported periodontitis. Periodontitis onset preceded RA onset by 13 years on average and was not associated with any of the SNPs investigated. In subjects with periodontitis, carriage of the minor alleles of rs2057094 and rs2235912 in PADI2 significantly increased the risk of RA (odds ratios 1.42 [p = 0.03] and 1.48 [p = 0.02], respectively), and this effect was driven by the anti-CCP-negative RA patients. The minor alleles of these SNPs only increased risk of anti-CCP-positive RA in individuals with periodontitis and a history of smoking. These data suggest that individuals with periodontitis carrying the minor alleles of SNPs rs2057094, rs2076616 and rs2235912 in PADI2 may be at increased risk of RA.

Disease mechanisms in preclinical rheumatoid arthritis: A narrative review

In the last decades, the concept of preclinical rheumatoid arthritis (RA) has become established. In fact, the discovery that disease mechanisms start years before the onset of clinical RA has been one of the major recent insights in the understanding of RA pathogenesis. In accordance with the complex nature of the disease, preclinical events extend over several sequential phases. In a genetically predisposed host, environmental factors will further increase susceptibility for incident RA. In the initial steps of preclinical disease, immune disturbance mechanisms take place outside the joint compartment, namely in mucosal surfaces, such as the lung, gums or gut. Herein, the persistent immunologic response to altered antigens will lead to breach of tolerance and trigger autoimmunity. In a second phase, the immune response matures and is amplified at a systemic level, with epitope spreading and widening of the autoantibody repertoire. Finally, the synovial and bone compartment are targeted by specific autoantibodies against modified antigens, initiating a local inflammatory response that will eventually culminate in clinically evident synovitis. In this review, we discuss the elaborate disease mechanisms in place during preclinical RA, providing a broad perspective in the light of current evidence.

Antibodies to a Citrullinated Porphyromonas gingivalis Epitope Are Increased in Early Rheumatoid Arthritis, and Can Be Produced by Gingival Tissue B Cells: Implications for a Bacterial Origin in RA Etiology

Based on the epidemiological link between periodontitis and rheumatoid arthritis (RA), and the unique feature of the periodontal bacterium Porphyromonas gingivalis to citrullinate proteins, it has been suggested that production of anti-citrullinated protein antibodies (ACPA), which are present in a majority of RA patients, may be triggered in the gum mucosa. To address this hypothesis, we investigated the antibody response to a citrullinated P. gingivalis peptide in relation to the autoimmune ACPA response in early RA, and examined citrulline-reactivity in monoclonal antibodies derived from human gingival B cells. Antibodies to a citrullinated peptide derived from P. gingivalis (denoted CPP3) and human citrullinated peptides were analyzed by multiplex array in 2,807 RA patients and 372 controls; associations with RA risk factors and clinical features were examined. B cells from inflamed gingival tissue were single-cell sorted, and immunoglobulin (Ig) genes were amplified, sequenced, cloned and expressed (n=63) as recombinant monoclonal antibodies, and assayed for citrulline-reactivities by enzyme-linked immunosorbent assay. Additionally, affinity-purified polyclonal anti-cyclic-citrullinated peptide (CCP2) IgG, and monoclonal antibodies derived from RA blood and synovial fluid B cells (n=175), were screened for CPP3-reactivity. Elevated anti-CPP3 antibody levels were detected in RA (11%), mainly CCP2+ RA, compared to controls (2%), p<0.0001, with a significant association to HLA-DRB1 shared epitope alleles, smoking and baseline pain, but with low correlation to autoimmune ACPA fine-specificities. Monoclonal antibodies derived from gingival B cells showed cross-reactivity between P. gingivalis CPP3 and human citrullinated peptides, and a CPP3+/CCP2+ clone, derived from an RA blood memory B cell, was identified. Our data support the possibility that immunity to P. gingivalis derived citrullinated antigens, triggered in the inflamed gum mucosa, may contribute to the presence of ACPA in RA patients, through mechanisms of molecular mimicry.

Periodontitis in First Degree-Relatives of Individuals With Rheumatoid Arthritis: A Short Narrative Review

Periodontal disease (PD) and rheumatoid arthritis (RA) are chronic inflammatory diseases with a bi-directional relationship. Both share common genetic and environmental risk factors and result in the progressive destruction of bone and connective tissue. First degree relatives of patients with RA (FDR-RA) are one of the at-risk populations for RA. The etiopathogenic mechanisms of their susceptibility are currently being explored, focusing mostly on the role of anti–cyclic citrullinated protein/ peptide antibodies (ACPA) in triggering RA. Oral microbiota and their relation with oral health has been suggested as a factor influencing the risk of the FDR-RA developing RA. In particular, compromised periodontal status often correlates with ACPA seropositivity in FDR-RA. The presence of periodontal pathogens such as Porphyromonas gingivalis, in oral microbiota has been proposed to increase the risk of developing RA through its uniquely expressed peptidyl arginine deiminase (PPAD), capable of citrullinating both host and bacterial peptides. Aggregatibacter actinomycetemcomitans and its leukotoxin A (LtxA), also induces hypercitrullination in host neutrophils. Common risk factors of periodontitis and RA such as genetic predisposition, smoking, higher local and systemic inflammatory burden, are discussed in the literature. Based on those mechanisms periodontal disease seems to be presented as one of the factors triggering RA in FDR-RA. Larger studies evaluating all the potential mechanisms linking RA and periodontitis are needed in FDR-RA to confirm that periodontal disease should be considered in the screening of FDR-RA.

The Citrullination-Neutrophil Extracellular Trap Axis in Chronic Diseases

Citrullination of proteins is crucial for the formation of neutrophil extracellular traps (NETs) − strands of nuclear DNA expulsed in the extracellular environment along with antimicrobial proteins in order to halt the spread of pathogens. Paradoxically, NETs may be immunogenic and contribute to inflammation. It is known that for the externalization of DNA, a group of enzymes called peptidyl arginine deiminases (PADs) is required. Current research often looks at citrullination, NET formation, PAD overexpression, and extracellular DNA (ecDNA) accumulation in chronic diseases as separate events. In contrast, we propose that citrullination can be viewed as the primary mechanism of autoimmunity, for instance by the formation of anti-citrullinated protein antibodies (ACPAs) but also as a process contributing to chronic inflammation. Therefore, citrullination could be at the center, connecting and impacting multiple inflammatory diseases in which ACPAs, NETs, or ecDNA have already been documented. In this review, we aimed to highlight the importance of citrullination in the etiopathogenesis of a number of chronic diseases and to explore the diagnostic, prognostic, and therapeutic potential of the citrullination-NET axis.

No Genetic Causal Association Between Periodontitis and Arthritis: A Bidirectional Two-Sample Mendelian Randomization Analysis

Objectives

Periodontitis (PD) has been linked to arthritis in previous epidemiological observational studies; however, the results are inconclusive. It remains unclear whether the association between PD and arthritis is causal. The purpose of this study was to investigate the causal association of PD with arthritis, including rheumatoid arthritis (RA) and osteoarthritis (OA).

Methods

We performed a two-sample bidirectional Mendelian randomization (MR) analysis using publicly released genome-wide association studies (GWAS) statistics. The inverse-variance weighted (IVW) method was used as the primary analysis. We applied four complementary methods, including weighted median, weighted mode, MR-Egger regression and MR pleiotropy residual sum and outlier (MR-PRESSO) to detect and correct for the effect of horizontal pleiotropy.

Results

Genetically determined PD did not have a causal effect on OA (OR = 1.06, 95% CI: 0.99-1.15, P = 0.09) and RA (OR = 0.99, 95% CI: 0.87-1.13, P = 0.89). Furthermore, we did not find a significant causal effect of arthritis on PD in the reverse MR analysis. The results of MR-Egger regression, Weighted Median, and Weighted Mode methods were consistent with those of the IVW method. Horizontal pleiotropy was unlikely to distort the causal estimates according to the sensitivity analysis.

Conclusions

Our MR analysis reveals non-causal association of PD with arthritis, despite observational studies reporting an association between PD and arthritis.

Antibodies to Porphyromonas gingivalis Are Increased in Patients with Severe Periodontitis, and Associate with Presence of Specific Autoantibodies and Myocardial Infarction

There is accumulating data suggesting that periodontitis is associated with increased risk of systemic and autoimmune diseases, including cardiovascular disease, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), and there is an unmet need to identify these individuals early. With the periodontal bacteria Porphyromonas gingivalis (Pg) as one of the key drivers of periodontitis, we set out to investigate whether antibodies to Pg virulence factor arginine gingipain (Rgp) could serve as a biomarker for periodontitis patients at increased risk of autoimmunity and systemic disease. We measured serum anti-Rgp IgG in three study populations: PAROKRANK (779 individuals with myocardial infarction (MI); 719 controls), where 557 had periodontitis, and 312 were positive for autoantibodies associated with RA/SLE; the PerioGene North pilot (41 periodontitis; 39 controls); and an SLE case/control study (101 SLE; 100 controls). Anti-Rgp IgG levels were increased in severe periodontitis compared to controls (p < 0.0001), in individuals positive for anti-citrullinated protein antibodies (p = 0.04) and anti-dsDNA antibodies (p = 0.035), compared to autoantibody-negative individuals; and in MI patients versus matched controls (p = 0.035). Our data support longitudinal studies addressing the role of anti-Rgp antibodies as biomarkers for periodontitis patients at increased risk of developing autoimmunity linked to RA and SLE, and mechanisms underpinning these associations.

Etiology and Risk Factors for Rheumatoid Arthritis: A State-of-the-Art Review

Rheumatoid arthritis (RA) is the most common systemic inflammatory rheumatic disease. It is associated with significant burden at the patient and societal level. Extensive efforts have been devoted to identifying a potential cause for the development of RA. Epidemiological studies have thoroughly investigated the association of several factors with the risk and course of RA. Although a precise etiology remains elusive, the current understanding is that RA is a multifactorial disease, wherein complex interactions between host and environmental factors determine the overall risk of disease susceptibility, persistence and severity. Risk factors related to the host that have been associated with RA development may be divided into genetic; epigenetic; hormonal, reproductive and neuroendocrine; and comorbid host factors. In turn, environmental risk factors include smoking and other airborne exposures; microbiota and infectious agents; diet; and socioeconomic factors. In the present narrative review, aimed at clinicians and researchers in the field of RA, we provide a state-of-the-art overview of the current knowledge on this topic, focusing on recent progresses that have improved our comprehension of disease risk and development.

Applicability of Small-Molecule Inhibitors in the Study of Peptidyl Arginine Deiminase 2 (PAD2) and PAD4

Citrullination, the conversion of peptidyl-arginine into peptidyl-citrulline, is involved in the breakage of self-tolerance in anti-CCP-positive rheumatoid arthritis. This reaction is catalyzed by peptidyl arginine deiminases (PADs), of which PAD2 and PAD4 are thought to play key pathogenic roles. Small-molecule PAD inhibitors such as the pan-PAD inhibitor BB-Cl-amidine, the PAD2-specific inhibitor AFM-30a, and the PAD4-specific inhibitor GSK199 hold therapeutic potential and are useful tools in studies of citrullination. Using an ELISA based on the citrullination of fibrinogen, we found that AFM-30a inhibited the catalytic activity of PADs derived from live PMNs or lysed PBMCs and PMNs and of PADs in cell-free synovial fluid samples from RA patients, while GSK199 had minor effects. In combination, AFM-30a and GSK199 inhibited total intracellular citrullination and citrullination of histone H3 in PBMCs, as determined by Western blotting. They were essentially nontoxic to CD4⁺ T cells, CD8⁺ T cells, B cells, NK cells, and monocytes at concentrations ranging from 1 to 20 μM, while BB-Cl-amidine was cytotoxic at concentrations above 1 μM, as assessed by flow cytometric viability staining and by measurement of lactate dehydrogenase released from dying cells. In conclusion, AFM-30a is an efficient inhibitor of PAD2 derived from PBMCs, PMNs, or synovial fluid. AFM-30a and GSK199 can be used in combination for inhibition of PAD activity associated with PBMCs but without the cytotoxic effect of BB-Cl-amidine. This suggests that AFM-30a and GSK199 may have fewer off-target effects than BB-Cl-amidine and therefore hold greater therapeutic potential.

Should We Be Screening for and Treating Periodontal Disease in Individuals Who Are at Risk of Rheumatoid Arthritis?

There is increasing evidence supporting an association between periodontal disease (PD) and rheumatoid arthritis (RA), both mechanistically and clinically. Trials have shown that treating PD in people with RA may improve RA disease activity. Patients with musculoskeletal symptoms without arthritis, who test positive for cyclic-citrullinated protein antibodies, are at risk of RA (CCP+ at-risk), with seropositivity preceding arthritis onset by months or years. Importantly, there is evidence to suggest that periodontal inflammation may precede joint inflammation in CCP+ at-risk and, therefore, this could be a trigger for RA. There has been increased research interest in RA prevention and the phenotyping of the pre-RA disease phase. This review will examine the merits of identifying individuals who are CCP+ at-risk and performing screening for PD. In addition, we discuss how PD should be treated once identified. Finally, the review will consider future research needed to advance our understanding of this disease association.

Periodontitis and rheumatoid arthritis: What have we learned about their connection and their treatment?

Rheumatoid arthritis and periodontitis are chronic inflammatory diseases defined respectively by the destruction of the articular cartilage and tooth-supporting periodontal tissues. Although the epidemiologic evidence for an association between these two diseases is still scarce, there is emerging scientific information linking specific bacterial periodontal pathogens, such as Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, in the citrullination process, leading to autoantibody formation and compromised immunotolerance of the susceptible patient to rheumatoid arthritis. In this review, we update the existing information on the evidence, not only regarding the epidemiologic association, but also the biologic mechanisms linking these two diseases. Finally, we review information emerging from intervention studies evaluating whether periodontal treatment could influence the initiation and progression of rheumatoid arthritis.

Antibodies against citrullinated proteins in relation to periodontitis with or without rheumatoid arthritis: a cross-sectional study

Background

Previous studies have reported conflicting findings between serum anti-citrullinated protein antibodies (ACPA) levels in rheumatoid arthritis (RA) participants with and without periodontitis (Pd). This study aimed to analyse possible correlations between serum ACPA levels and clinical parameters in Pd and RA participants.

Methods

Full mouth periodontal examination (probing pocket depth, clinical attachment levels, gingival bleeding index, visual plaque index) was conducted and serum samples obtained from 80 participants comprising RA, Pd, both RA and Pd (RAPd) and healthy individuals (HC). Erythrocyte sedimentation rates (ESR) and periodontal inflamed surface area (PISA) were obtained. Serum samples were analysed for ACPA quantification using enzyme-linked immunosorbent assay (ELISA).

Results

Median levels (IU/mL) of ACPA (interquartile range, IQR) in RAPd, RA, Pd and HC groups were 118.58(274.51), 102.02(252.89), 78.48(132.6) and 51.67(91.31) respectively. ACPA levels were significantly higher in RAPd and RA as compared to HC group (p < 0.05). However, ACPA levels of any of the groups were not correlated with any clinical periodontal and RA parameters within the respective groups.

Conclusions

At individual level, the amount of serum ACPA seem to have an increasing trend with the diseased condition in the order of RAPd > RA > Pd > HC. However, lack of any significant correlation between the serum ACPA levels with the clinical Pd and RA parameters warrants further studies to investigate the causal link between RA and Pd for such a trend. Further studies involving more inflammatory biomarkers might be useful to establish the causal link between Pd in the development and progression of RA or vice versa.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01712-y.

Evaluation of galectin-3, peptidylarginine deiminase-4 and tumor necrosis factor-α levels in gingival crevicular fluid for periodontal health, gingivitis and stage III grade C periodontitis: A pilot study

BACKGROUND

Comparing the gingival crevicular fluid (GCF) levels of galectin-3, peptidylarginine deiminase 4 (PAD4) and tumor necrosis factor-alpha (TNF-α) in individuals with stage III grade C periodontitis and gingivitis and with healthy periodontium was the purpose of this clinical research.

METHODS

Sixty systemically healthy and non-smoker individuals consisting of stage III grade C periodontitis (group S3P/n = 20), gingivitis (group G/n = 20), and periodontally healthy (group HP/n = 20) were recruited for this research. Clinical parameters such as probing depth, clinical attachment level, gingival index, plaque index, and bleeding on probing were recorded in periodontal charts. Enzyme-linked immunosorbent assay method was used in evaluating the GCF levels of galectin-3, PAD4, and TNF-α for study groups.

RESULTS

The GCF galectin-3 total amount was highest in group S3P compared with group G and group HP (P <0.05). Its total amount was also higher in group G compared with group HP (P <0.05). The GCF PAD4 total amount was higher in group S3P compared with group HP (P <0.05) but was similar with group G (P >0.05). Its total amounts were also similar in group G and group HP (P >0.05). The GCF TNF-α total amounts were similar in group S3P and group G (P >0.05) but significantly greater than the group HP (P ˂0.05). The GCF galectin-3, PAD4, and TNF-α concentrations were lower in the group S3P and group G compared with the group HP (P <0.05). There were significant positive correlations between GCF galectin-3 total amount and all clinical parameters (P ˂0.01) and also between GCF galectin-3 and TNF-α total amounts (P ˂0.01). There was no correlation between PAD4 and clinical parameters, or between PAD4 and TNF-α (P >0.05).

CONCLUSIONS

Galectin-3 and PAD4 may be involved in the periodontal disease pathogenesis considering the elevated levels of these molecules in periodontal disease. These biomarkers may be used in the diagnosis of periodontal diseases.

An assessment of anti-citrullinated protein antibody in systemically healthy individuals with or without chronic periodontitis: A case-control study

Background:

Periodontitis has been implicated as a risk factor for rheumatoid arthritis (RA).

Aim:

This study aimed to assess the relationship between RA and chronic periodontitis (CP) by evaluating the serum levels of the anti citrullinated protein antibody (ACPA) which is a marker of RA in systemically healthy individuals with and without CP.

Materials and Methods:

This case–control study enrolled 40 systemically healthy individuals. Participants were divided into two groups, i.e., CP group Systemically healthy chronic periodontitis (CPSH) (n = 20) and control group Systemically healthy (SH) (n = 20), matched for age and gender. The CP patients were evaluated for periodontal parameters, namely probing pocket depth, clinical attachment loss, percentage of the site involved with attachment loss, and number of teeth present. A volume of 5 ml of venous blood was collected from both the groups and centrifuged; the separated serum was stored at − 70°C before being analyzed. Later, serum samples were tested for levels of ACPA in both the groups and compared.

Results:

The mean serum ACPA levels were higher in CPSH patients compared to SH (131.38 RU/ml vs. 34.54 RU/ml, P = 0.001), which was statistically highly significant. In addition, we found a significant elevation of serum ACPA levels in severe generalized CP patients compared to moderate generalized CP patients (175.47 RU/ml vs. 95.31 RU/ml, P = 0.001), and the difference was statistically highly significant.

Conclusion:

The results of the study confirmed that CP can be a risk factor for RA. Moreover, the severity of periodontitis appeared to be related to elevated serum levels of ACPA.

Oral Dysbiosis and Autoimmunity: From Local Periodontal Responses to an Imbalanced Systemic Immunity. A Review

The current paradigm of onset and progression of periodontitis includes oral dysbiosis directed by inflammophilic bacteria, leading to altered resolution of inflammation and lack of regulation of the inflammatory responses. In the construction of explanatory models of the etiopathogenesis of periodontal disease, autoimmune mechanisms were among the first to be explored and historically, for more than five decades, they have been described in an isolated manner as part of the tissue damage process observed in periodontitis, however direct participation of these mechanisms in the tissue damage is still controversial. Autoimmunity is affected by genetic and environmental factors, leading to an imbalance between the effector and regulatory responses, mostly associated with failed resolution mechanisms. However, dysbiosis/infection and chronic inflammation could trigger autoimmunity by several mechanisms including bystander activation, dysregulation of toll-like receptors, amplification of autoimmunity by cytokines, epitope spreading, autoantigens complementarity, autoantigens overproduction, microbial translocation, molecular mimicry, superantigens, and activation or inhibition of receptors related to autoimmunity by microorganisms. Even though autoreactivity in periodontitis is biologically plausible, the associated mechanisms could be related to non-pathologic responses which could even explain non-recognized physiological functions. In this review we shall discuss from a descriptive point of view, the autoimmune mechanisms related to periodontitis physio-pathogenesis and the participation of oral dysbiosis on local periodontal autoimmune responses as well as on different systemic inflammatory diseases.

Presence of salivary IgA anti-citrullinated protein antibodies associate with higher disease activity in patients with rheumatoid arthritis

Background

Circulating IgA anti-citrullinated protein antibodies (ACPA) associate with more active disease, but a previous study implied that salivary IgA ACPA is related to a less severe disease. Therefore, we aimed to characterize the IgA ACPA response in the saliva and serum in relation to clinical picture and risk factors among patients with rheumatoid arthritis (RA).

Methods

RA patients (n = 196) and healthy blood donors (n = 101), included in the cross-sectional study “Secretory ACPA in Rheumatoid Arthritis” (SARA), were analyzed for ACPA of IgA isotype, and for subclasses IgA1 and IgA2 ACPA in paired saliva and serum samples using modified enzyme-linked immunosorbent assays (ELISA) targeting reactivity to a cyclic citrullinated peptide (anti-CCP). Cutoff levels for positive tests were set at the 99th percentile for blood donors. Antibody levels were related to clinical characteristics, radiographic damage, smoking habits, and carriage of HLA-DRB1/shared epitope (SE).

Results

IgA ACPA in the saliva was found in 12% of RA patients, IgA1 occurred in 10%, and IgA2 in 9%. In serum, IgA ACPA was found in 45% of the patients, IgA1 in 44%, and IgA2 in 39%. Levels of IgA ACPA in the saliva correlated significantly with serum levels of IgA (r = 0.455). The presence of salivary IgA ACPA was associated with a higher erythrocyte sedimentation rate (ESR), 28-joint disease activity score, tender joint count, and patient global assessment at the time of sampling. None of the antibodies was associated with smoking, SE, or radiographic damage.

Conclusion

Salivary IgA ACPAs were detected in a subset of RA patients in association with higher disease activity. This suggests that mucosal ACPA responses in the oral cavity may contribute to disease-promoting processes in RA.

Levels of Anti-Citrullinated Protein Antibodies and Rheumatoid Factor, Including IgA Isotypes, and Articular Manifestations in Ulcerative Colitis and Crohn's Disease

Systemic presence of arthritis autoantibodies (AAb) is specific for rheumatoid arthritis (RA). AAb initiation might be triggered by chronic mucosal inflammation, such as in inflammatory bowel disease (IBD). We assessed the prevalence of anti-citrullinated protein antibodies (ACPA) and rheumatoid factor (RF) in ulcerative colitis (UC) and Crohn’s disease (CD) patients, with regard to the prevalence of joint complaints in AAb+ versus AAb− IBD patients. RA patients and healthy subjects (HC) served as controls. Serum was collected from 226 UC, 165 CD and 86 RA patients, and 36 HCs. One-hundred-and-ten UC (48.7%) and 76 CD (46.1%) patients were seropositive for at least one autoantibody, compared to 4 (13.9%) HCs and 81 (94.2%) RA patients. Eighty-three (37%) UC and 52 (32%) CD patients were seropositive for the anti-cyclic citrullinated protein antibody (anti-CCP2) of the immunoglobulin A type (IgA anti-CCP2), compared to 1 (2.8%) HC and 64 (74%) RA patients. RF of the immunoglobulin G type (IgG RF) and IgA RF seropositivity in UC and CD patients was comparable to HCs and low compared to RA patients. Arthralgia was reported by 34 (18.7%) UC and 50 (33.1%) CD patients, but presence of arthralgia was not increased in AAb+ patients. AAbs are frequently present in IBD patients, supporting the hypothesis that inflammation of intestinal mucosa induces low systemic levels of ACPA.

Localisation of citrullinated and carbamylated proteins in inflamed gingival tissues from rheumatoid arthritis patients

OBJECTIVES

It has been proposed that citrullination and carbamylation occur in the inflamed periodontium and could be the plausible mechanisms for the generation of antigens involved in the development and progression of RA. The purpose of this study was to determine the presence and location of citrullinated and carbamylated proteins in the gingival tissues and compare their abundance in periodontitis (PD) patients with or without RA.

MATERIALS AND METHODS

Gingival tissue samples of healthy (n = 5), PD with RA (n = 5) and PD without RA (n = 5) were collected. Specimens were formalin fixed, paraffin embedded and sectioned at 4 μm. The tissue sections were analysed for the presence of citrullinated and carbamylated proteins by immunohistochemistry. Semi-quantitative analysis was performed to quantify and compare the protein abundance between groups.

RESULTS

The number of cells containing citrullinated and carbamylated proteins with higher intensity was markedly increased in gingival tissues from PD with or without RA in comparison with healthy controls.

CONCLUSION

Inflamed gingival tissue is a potential source of citrullinated and carbamylated proteins other than synovial tissues. The extent to which the local accumulation of these proteins contributes to the pathogenesis of RA needs further elucidation.

CLINICAL RELEVANCE

If PD is a potential source of post-translationally modified proteins, untreated PD should not be taken lightly in the context of RA. Hence, addressing gingival inflammation should be viewed as an important preventive measure in the general population not only for the progression of periodontal disease but also reducing the risk of developing extra-oral comorbidities.

Prevalence and severity of periodontitis in patients with established rheumatoid arthritis and osteoarthritis

Introduction

Periodontitis is associated with many chronic health conditions including diabetes, cardiovascular disease, and rheumatoid arthritis (RA). RA and periodontitis have similarities in inflammatory mechanism, morphology, and histopathology. Osteoarthritis (OA) is a chronic, multifactorial degenerative disease characterized by the deterioration of cartilage in joints.

Objective

The aim of this study was to evaluate the prevalence and severity of periodontal disease in patients with established RA and OA.

Materials and Methods

A total of 200 patients reporting to the Department of Orthopaedics, KIMSDU, Karad were included in the study. Patients were divided into two groups: Group 1 that included 100 patients with established RA diagnosed according to American College of Rheumatology (ACR) classification 1987 criteria and Group 2 that comprised 100 patients diagnosed with OA. Demographic profile, medical and dental history, oral hygiene practices, and smoking status of study participants were recorded. Periodontal status of the patients were evaluated using the simplified oral hygiene index (OHI-S), Loe and Silness gingival index (GI), probing pocket depth (PPD), and clinical attachment level (CAL). On the basis of the CAL score periodontitis severity was defined as slight, moderate, and severe. Rheumatoid Factor (RF) and C-reactive protein (CRP) were considered as a serological marker in RA. Serological tests were performed to measure RF and CRP. Periodontal parameters and serological tests were correlated.

Results

This study reported 45% severe periodontitis prevalence in RA compared to OA group, which was 33%. Severity of periodontitis is significantly greater in RF positive RA group with mean CAL 5.38 mm compared to RF negative RA group with mean CAL 2.81 mm (P = 0.001). There was moderate positive correlation found between RF titer and severity of periodontitis (r = 0.311).

Conclusion

The severity of periodontitis was significantly higher among the patients with established RA as compared to patients with OA. RF positive patients had higher periodontal disease compared to RF negative patients. There was an increase in the mean clinical attachment loss with increase in RF titer.

[Protein arginine deiminase of oral microbiome plays a causal role in the polyarthritis rheumatoid initiating]

In the last decade, the association between the periodontitis and rheumatoid arthritis (RA) has been established, suggesting that oral microbiome plays a causal role by initiating this chronic autoimmune inflammatory disease of articulation. Both pathogenesis are similar in term of chronic inflammation, tissue breakdown and bone resorption. Molecular aspects have also revealed that citrullination, a post-translational modification catalyzed by peptidyl-arginine deiminases (PADs), is involved in both diseases. For RA, citrullinated proteins production leads to the synthesis the of anti-citrullinated protein antibodies triggering the loss of immune tolerance. In humans, five PADs have been identified. Recently, studies have found that only Porphyromonas species possess PAD. Thus, a major periodontal pathogen, Porphyromonas gingivalis, is able to generate citrullinated epitopes, and could consequently induce anti-citrullinated protein antibodies. In this review, citrullination process, periodontitis and RA are described to put them in relation with molecular, clinical and epidemiological studies establishing the association between periodontitis and RA.

Targeting a cysteine protease from a pathobiont alleviates experimental arthritis

Background

Several lines of evidence suggest that the pathobiont Porphyromonas gingivalis is involved in the development and/or progression of auto-inflammatory diseases. This bacterium produces cysteine proteases, such as gingipain RgpA, endowed with the potential to induce significant bone loss in model systems and in patients.

Objective

We sought to gain further insight into the role of this pathobiont in rheumatoid arthritis (RA) and to identify novel therapeutic targets for auto-inflammatory diseases.

Methods

We profiled the antibody response to RgPA-specific domains in patient sera. We also tested the potential protective effects of RgpA domains in an experimental arthritis model.

Results

Pre-immunization of rats with purified recombinant RgpA domains alleviated arthritis in the joints of the rodents and reduced bone erosion. Using a functional genomics approach at both the mRNA and protein levels, we report that the pre-immunizations reduced arthritis severity by impacting a matrix metalloprotease characteristic of articular injury, a chemokine known to be involved in recruiting inflammatory cells, and three inflammatory cytokines. Finally, we identified an amino acid motif in the RgpA catalytic domain of P. gingivalis that shares sequence homology with type II collagen.

Conclusion

We conclude that pre-immunization against gingipain domains can reduce the severity of experimentally induced arthritis. We suggest that targeting gingipain domains by pre-immunization, or, possibly, by small-molecule inhibitors, could reduce the potential of P. gingivalis to translocate to remote tissues and instigate and/or exacerbate pathology in RA, but also in other chronic inflammatory diseases.

Preclinical rheumatoid arthritis and rheumatoid arthritis prevention

PURPOSE OF REVIEW

This review is to provide an update on the current understanding of rheumatoid arthritis (RA) development related to disease development prior to the onset clinically apparent synovitis (i.e. Pre-RA), and opportunities for disease prevention.

RECENT FINDINGS

A growing number of studies have demonstrated that serum elevations of autoantibodies rheumatoid factor, antibodies to citrullinated protein/peptide antigens (ACPAs) and antibodies to other posttranslationally modified proteins (e.g. carbamylated proteins) are highly predictive of future development of inflammatory arthritis/RA during a period that can be termed Pre-RA. Other factors including genetic, environmental, symptoms and imaging findings can also enhance prediction. Moreover, several novel biomarkers and changes in autoantibodies (e.g. glycosylation of variable domains) have been identified in Pre-RA. There has also been growing evidence that initiation and propagation of RA-related autoimmunity during the Pre-RA phase may be related to mucosal processes. The discovery of Pre-RA has also underpinned the development of several clinical prevention trials in RA; specifically, the PRAIRI study demonstrated that a single dose of rituximab can delay the onset of clinically apparent IA in at-risk individuals. Additional studies are evaluating the ability of drugs including abatacept, hydroxychloroquine and methotrexate to prevent or delay future RA.

SUMMARY

The results from ongoing natural history and prevention trials in RA should further inform several critical issues in RA prevention including identification and enrolment of individuals at high-risk of imminent RA, the efficacy, safety and cost-effectiveness of prevention, and potentially the identification of new targets for prevention.

Citrullination in periodontium is associated with Porphyromonas gingivalis

OBJECTIVE

To analyse the citrulline level in the periodontium in association with the presence of or antibody levels against Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis.

DESIGN

Gingival crevicular fluid (GCF), subgingival biofilm and blood serum were sampled from 98 subjects (26 with RA, 72 without RA (NoRA)). GCF was analyzed for the level of citrulline, for interleukin (IL)-1β, IL-17, IL-10 and monocyte-chemoattractant protein (MCP)-1. Microorganisms were identified in subgingival biofilms. Antibodies againstP. gingivalis, and Aggregatibacter actinomycetemcomitans were quantified in serum.

RESULTS

GCF citrulline level was the lowest (by trend) in NoRA group without periodontitis. In NoRA, but not in RA an association between GCF citrulline level and P. gingivalis antibody levels was found and the GCF citrulline levels were higher in P. gingivalis positive samples. Any association of A. actinomycetemcomitans with GCF citrulline level did not exist. A model of univariate variance analysis (p = 0.001) showed a dependence of GCF citrulline level from the number of sites with PD (probing depth) ≥5 mm (p = 0.003) and the GCF MCP-1/CCL2 level (p = 0.019). Compared with NoRA in RA the number of teeth was lower, the number of sites with PD ≥ 5 mm was less, GCF levels of interleukin-17 and MCP-1/CCL2 were higher and those of IL-10 lower. Yeasts were only cultured in 15 RA patients (p < 0.001).

CONCLUSION

Citrullination in periodontium might be associated with P. gingivalis supporting the potential role as a trigger in the development of RA. Pathogenesis of periodontal disease in RA patients seems to differ from that in NoRA and should be investigated further.

The microbiome and rheumatoid arthritis

Rheumatoid Arthritis (RA) is a severe, chronic autoimmune disease that affects 1% of the world's population. Familial risk contributes 50% of the risk of seropositive RA, with strongest risks seen in first-degree relatives. Smoking increases the risk of developing anti-citrullinated peptide antibody (ACPA)⁺ RA, particularly in individuals with high-risk RA-susceptibility alleles. Other contributory environmental risks including particulate exposure, periodontal disease, bronchiectasis, diet, obesity and the oral contraceptive impact respiratory, oral, intestinal and genital tract mucosal sites. Furthermore, the first signs of autoimmunity may appear at mucosal sites e.g. sputum ACPA-IgA and IgG. While oral and faecal dysbiosis are well described, there is no consistent single bacterial species that appears to drive RA. Animal and human data suggest a model in which multiple environmental influences impact mucosal immune function through the host genetics through enhanced mucosal permeability and the traffic of pro-inflammatory PAMPs and the amplification of autoimmune responses. In some cases, autoimmunity may be driven by cross-reactivity, or mimicry, to pathogen-specific antigens, particularly where the host immune system fails to support their rapid control and elimination.

Increased IgA anti-citrullinated protein antibodies in the periodontal inflammatory exudate of healthy individuals compared to rheumatoid arthritis patients

Aim

To assess rheumatoid arthritis (RA)‐associated autoantibodies in the gingivocrevicular fluid (GCF) of RA patients and healthy controls with or without periodontal disease, as chronic mucosal inflammation in periodontal disease is hypothesized to contribute to the formation of these autoantibodies.

Materials and methods

Anti‐citrullinated protein antibodies (ACPA), rheumatoid factor (RF), and their IgA isotypes were assessed in the serum and GCF of RA patients (n = 72) and healthy controls (HC, n = 151). The presence and levels of these antibodies were studied in relation to interleukin (IL)‐8 and periodontal disease.

Results

In contrast to the HC, the levels of ACPA and RF in the serum and GCF of the RA patients were strongly correlated (p < .0001). The HC with high levels of IgA‐ACPA (n = 27) also had significantly higher levels of total IgG, total IgA, and IL‐8 in the GCF than the HC with low levels of IgA‐ACPA in the GCF (n = 124). Periodontal inflammation and smoking were seen more frequently in the group with high levels of IgA‐ACPA compared to the group with low IgA‐ACPA.

Conclusion

The IgA‐ACPA in the GCF of HC may be associated with periodontal inflammation and smoking, and could be involved in the progression to RA.

Individuals at risk of seropositive rheumatoid arthritis: the evolving story

The aetiology of the autoimmune disease rheumatoid arthritis (RA) involves a complex interplay between genetic and environmental factors that initiate many years before the onset of clinical symptoms. These interactions likely include both protective and susceptibility factors which together determine the risk of developing RA. More than 100 susceptibility loci have been linked to RA. The strongest association is with HLA-DRB1 alleles encoding antigen presenting molecules containing a unique sequence in the peptide-binding grove called the 'shared epitope'. Female sex, infections during childhood, lifestyle habits (e.g. smoking and diet) and distinct microbial agents, amongst many others, are interacting risk factors thought to contribute to RA pathogenesis by dysregulating the immune system in individuals with genetic susceptibility. Interestingly, patients with RA develop autoantibodies many years before the clinical onset of disease, providing strong evidence that the lack of tolerance to arthritogenic antigens is amongst the earliest events in the initiation of seropositive RA. Here, we will discuss the clinical and mechanistic evidence surrounding the role of different environmental and genetic factors in the phases leading to the production of autoantibodies and the initiation of symptomatic RA. Understanding this complexity is critical in order to develop tools to identify drivers of disease initiation and propagation and to develop preventive therapeutics.

A cross-sectional investigation into the association between Porphyromonas gingivalis and autoantibodies to citrullinated proteins in a German population

Background

Porphyromonas gingivalis (P.g) is unique among pathogens due to its ability to generate citrullinated proteins in an inflammatory milieu, potentially mediating the loss of immune tolerance, the production of anticitrullinated protein antibodies (ACPAs), and subsequently the development of rheumatoid arthritis (RA). Based on this hypothesis, we set out to investigate whether P.g is linked to ACPAs in a well-characterized German population.

Participants and methods

A total of 600 participants (292 women and 308 men with a mean age of 67 years) of the European Prospective Investigation into Cancer and Nutrition-Potsdam study were selected in 2013, and paired saliva and serum samples were collected. Salivary P.g DNA and serum anticyclic citrullinated peptide (anti-CCP2) levels were quantified by real-time polymerase chain reaction and anti-CCP2 enzyme-linked immunosorbent assay, respectively. In selected participants, additional ACPA fine-specificities were also analysed on a custom-made multiplex peptide array.

Results

Among participants with C-reactive protein greater than 3.0 mg/l, a one-unit increase in P.g DNA was associated with an almost twofold increase in anti-CCP2 levels. Moreover, participants with high P.g DNA had on average approximately 2.8-times higher anti-CCP2 levels when compared with participants with low P.g DNA, (Holm-adjusted p value = 0.01). Furthermore, citrullinated epitopes on α-enolase and vimentin were common ACPA reactivities among participants who also had high P.g DNA and elevated C-reactive protein.

Conclusions

Our study suggests that in specific subgroups of individuals with systemic inflammation, higher salivary P.g DNA is associated with elevated serum ACPA. These data support a role for P.g in the development of anticitrulline immunity.

The periodontal inflamed surface area is associated with the clinical response to biological disease-modifying antirheumatic drugs in rheumatoid arthritis: a retrospective study

Objectives: We evaluated whether the periodontal inflamed surface area (PISA), a measure of the inflammatory burden posed by periodontitis, is associated with the clinical response to biological disease-modifying antirheumatic drugs (bDMARDs) in patients with rheumatoid arthritis (RA).Methods: We conducted a retrospective study that collected rheumatologic and periodontal data from 54 patients with RA who had received corticosteroid, conventional synthetic DMARDs, or non-steroidal anti-inflammatory drugs before (baseline) and after 6 months of bDMARD therapy. After the patients were divided into two groups based on high or low PISA according to the median measurements at baseline, the rheumatologic condition was compared between the groups.Results: The patients with a low PISA showed significantly lower values for the Clinical Disease Activity Index (CDAI) (p = .008), swollen joint count (p = .02), and patient's and evaluator's global assessment (p = .01 and p = .03) and significantly greater decreases in changes in the CDAI from baseline to 6 months than the patients with a high PISA (p = .01), although these values were comparable at baseline. Both univariate and multivariate analyses revealed a significantly positive correlation between the baseline PISA and changes in the CDAI (p = .04 and p < .001).Conclusion: The PISA is associated with the clinical response to bDMARDs in patients with RA.

Gums and joints: is there a connection? Part two: the biological link

Rheumatoid arthritis (RA) and periodontitis (PD) are inflammatory diseases characterised by an exacerbated immune-inflammatory reaction that leads to the destruction of bone and other connective tissues that share numerous similarities. Although a significant and independent association between these two conditions has been described, the pathophysiological processes that may explain this relationship remain unknown and multiple theories have been proposed. This review presents the most important theories currently proposed to explain the biological link between RA and PD.

Cytokines in gingivocrevicular fluid of rheumatoid arthritis patients: A review of the literature

OBJECTIVE

Rheumatoid arthritis (RA) and periodontitis share several pathological features including bone and soft tissue destruction and high levels of circulating inflammatory proteins. Studies related to cytokines in the periodontal inflammatory exudate (gingivocrevicular fluid, GCF) of RA patients might provide insight into the association between periodontitis and RA. The aim of our study was to review the literature on cytokines in GCF of RA patients including the effect of anti-rheumatic treatment with biological disease-modifying anti-rheumatic drugs (DMARDs) and periodontal treatment on these cytokines.

MATERIALS AND METHODS

MedLine/PubMed searches with different combinations of keywords "rheumatoid arthritis or RA" and "crevicular fluid or GCF" until June 2019 revealed 64 articles. Ten cross-sectional observational studies and nine treatment studies fulfilled the inclusion criteria.

RESULTS

Rheumatoid arthritis patients have increased circulating and GCF levels of pro-inflammatory cytokines and proteins, despite anti-rheumatic treatment with biological DMARDs. Presence of periodontitis was accompanied by higher cytokine and protein levels. Treatment of periodontitis resulted in a decrease of these levels.

CONCLUSION

Analysis of GCF of RA patients reveals that the relationship between periodontitis and RA is bidirectional, probably caused by a non-specific inflammatory burden. Data for a specific relationship are barely present in GCF.

Rheumatoid Arthritis-Associated Mechanisms of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans

Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology characterized by immune-mediated damage of synovial joints and antibodies to citrullinated antigens. Periodontal disease, a bacterial-induced inflammatory disease of the periodontium, is commonly observed in RA and has implicated periodontal pathogens as potential triggers of the disease. In particular, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans have gained interest as microbial candidates involved in RA pathogenesis by inducing the production of citrullinated antigens. Here, we will discuss the clinical and mechanistic evidence surrounding the role of these periodontal bacteria in RA pathogenesis, which highlights a key area for the treatment and preventive interventions in RA.

Mucosa-Environment Interactions in the Pathogenesis of Rheumatoid Arthritis

Mucosal surfaces play a central role in the pathogenesis of rheumatoid arthritis (RA). Several risk factors, such as cigarette smoking, environmental pollution, and periodontitis interact with the host at the mucosal level, triggering immune system activation. Moreover, the alteration of microbiota homeostasis is gaining increased attention for its involvement in the disease pathogenesis, modulating the immune cell response at a local and subsequently at a systemic level. Currently, the onset of the clinical manifest arthritis is thought to be the last step of a series of pathogenic events lasting years. The positivity for anti-citrullinated protein antibodies (ACPAs) and rheumatoid factor (RF), in absence of symptoms, characterizes a preclinical phase of RA-namely systemic autoimmune phase- which is at high risk for disease progression. Several immune abnormalities, such as local ACPA production, increased T cell polarization towards a pro-inflammatory phenotype, and innate immune cell activation can be documented in at-risk subjects. Many of these abnormalities are direct consequences of the interaction between the environment and the host, which takes place at the mucosal level. The purpose of this review is to describe the humoral and cellular immune abnormalities detected in subjects at risk of RA, highlighting their origin from the mucosa-environment interaction.

Mucosa Biology and the Development of Rheumatoid Arthritis: Potential for Prevention by Targeting Mucosal Processes

As the goal in rheumatoid arthritis (RA) management shifts toward the prevention of joint disease, it is important to consider the role of mucosal sites in the pathogenesis of RA because they may be potential targets for preventive interventions. Multiple mucosal sites demonstrate immune dysregulation and inflammation in individuals with classifiable RA as well as, importantly, in individuals with systemic autoimmunity related to RA. The lung, gingival, and gastrointestinal mucosae are most strongly implicated in RA pathogenesis and may be sites where autoimmunity in RA initially develops. Targeting the exact site where the initial immune dysregulation in RA occurs is an appealing approach to prevention because it could avoid unwanted side effects of systemic therapies. However, several challenges must be addressed before mucosa-targeted interventions are a readily available option for RA prevention. Studies are needed to determine whether all RA-related immune dysregulation at mucosal sites will progress to joint disease and whether one or multiple mucosal sites demonstrate dysregulation prior to the development of classifiable RA. These areas of future research are likely to provide crucial pieces in the understanding of RA pathogenesis and ultimately RA prevention.

Periodontal status correlates with anti-citrullinated protein antibodies in first-degree relatives of individuals with rheumatoid arthritis

AIM

To evaluate periodontal status in first-degree relatives of patients with rheumatoid arthritis (FDR-RA) and detect correlation with the presence of anti-citrullinated protein antibodies (ACPAs).

MATERIALS AND METHODS

Rheumatologic status and periodontal status were evaluated in a nested case-control study of FDR-RA with no diagnosis of RA at enrolment. The following parameters were assessed in 34 ACPA-positive (ACPA+) and 65 ACPA-negative (ACPA-) subjects: gingival index (GI), plaque index (PI), probing depth (PD), bleeding on probing (BOP) and clinical attachment level (CAL). We compared the two groups using conditional logistic regression.

RESULTS

In ACPA+ individuals, the mean, PD, BOP, CAL and number of sites per person with PD > 4 mm and BOP were significantly higher compared to the ACPA- group. All ACPA+ subjects had periodontitis: 44.1% presenting moderate and 47.1% severe periodontitis. ACPA- subjects had mainly mild (30.8%) and moderate (27%) periodontitis, differences being significantly different for both moderate periodontitis (p = 0.001) and severe periodontitis (p < 0.001). In multivariable analyses, ACPA status (p = 0.04) and age (p = 0.002) were significantly and independently associated with periodontal conditions.

CONCLUSION

High prevalence and severity of periodontitis in FDR-RA was associated with seropositivity to ACPAs. This further strengthens the hypothesis that periodontitis may be a risk factor in the development of RA.

Periodontitis and Rheumatoid Arthritis: The Same Inflammatory Mediators?

The strict link between periodontitis (PD) and rheumatoid arthritis (RA) has been widely demonstrated by several studies. PD is significantly more frequent in RA patients in comparison with healthy subjects: this prevalence is higher in individuals at the earliest stages of disease and in seropositive patients. This is probably related to the role of P. gingivalis in inducing citrullination and leading to the development of the new antigens. Despite the many studies conducted on this topic, there is very little data available concerning the possibility to use the same biomarkers to evaluate both RA and PD patients. The aim of the review is to summarize this issue. Starting from genetic factors, data from literature demonstrated the association between HLA-DRB1 alleles and PD susceptibility, similar to RA patients; moreover, SE-positive patients showed simultaneously structural damage to the wrist and periodontal sites. Contrasting results are available concerning other genetic polymorphisms. Moreover, the possible role of proinflammatory cytokines, such as TNF and IL6 and autoantibodies, specifically anticyclic citrullinated peptide antibodies, has been examined, suggesting the need to perform further studies to better define this issue.