Increased citrullination and expression of peptidylarginine deiminases independently of P. gingivalis and A. actinomycetemcomitans in gingival tissue of patients with periodontitis

Caspase-11 mediated inflammasome activation in macrophages by systemic infection of A. actinomycetemcomitans exacerbates arthritis

Clinical studies have shown that Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is associated with aggressive periodontitis and can potentially trigger or exacerbate rheumatoid arthritis (RA). However, the mechanism is poorly understood. Here, we show that systemic infection with A. actinomycetemcomitans triggers the progression of arthritis in mice anti-collagen antibody-induced arthritis (CAIA) model following IL-1β secretion and cell infiltration in paws in a manner that is dependent on caspase-11-mediated inflammasome activation in macrophages. The administration of polymyxin B (PMB), chloroquine, and anti-CD11b antibody suppressed inflammasome activation in macrophages and arthritis in mice, suggesting that the recognition of lipopolysaccharide (LPS) in the cytosol after bacterial degradation by lysosomes and invasion via CD11b are needed to trigger arthritis following inflammasome activation in macrophages. These data reveal that the inhibition of caspase-11-mediated inflammasome activation potentiates aggravation of RA induced by infection with A. actinomycetemcomitans. This work highlights how RA can be progressed by inflammasome activation as a result of periodontitis-associated bacterial infection and discusses the mechanism of inflammasome activation in response to infection with A. actinomycetemcomitans.

The peculiar features, diversity and impact of citrulline-reactive autoantibodies

Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations.

Comparative evaluation of semaphorin-4D, peptidylarginine deiminase-2, and matrix metalloproteinase-8 levels of gingival crevicular fluid in periodontally healthy and Stage III periodontitis smoker and non-smoker patients before and after non-surgical periodontal therapy

BACKGROUND

This study was designed to assess the influence of non-surgical periodontal therapy (NSPT) on gingival crevicular fluid (GCF) levels of semaphorin-4D (SEMA-4D), peptidylarginine deiminase-2 (PAD-2), and matrix metalloproteinase-8 (MMP-8) levels in periodontally healthy, Stage III periodontitis non-smoker and smoker patients.

METHODS

Sixty patients were equally divided into three groups, Group I: Periodontally healthy, Group II: Non-smokers with Stage III periodontitis, and Group III: Smokers with Stage III periodontitis. The patients underwent NSPT with clinical and biochemical parameters examined at baseline and 3 months post therapy. GCF was collected for levels of SEMA-4D, PAD-2, and MMP-8 through enzyme-linked immunosorbent assay (ELISA).

RESULTS

Greater values of PPD (8.06 ± 0.19 mm), CAL (8.94 ± 0.19 mm), PI (2.58 ± 0.19) while lower PBI (1.39 ± 0.19%) and GI (1.72 ± 0.19) scores were seen in Group III as compared to Group II, which reduced significantly from baseline to 3 months in both the groups after NSPT. Minimum values of SEMA-4D, PAD-2, and MMP-8 levels in GCF were seen for Group I, which increased incrementally to Group II and III. Also, among Group II and III the SEMA-4D, PAD-2, and MMP-8 levels in GCF reduced from baseline to 3 months indicating a favorable response within the tissues.

CONCLUSION

Greater levels in GCF of Levels of SEMA-4D, PAD-2, and MMP-8 in Group II and III, which reduced significantly post NSPT, implied that these biomarkers play a pivotal role in the inflammatory process and can be utilized for early diagnosis.

Protein Citrullination by Peptidyl Arginine Deiminase/Arginine Deiminase Homologs in Members of the Human Microbiota and Its Recognition by Anti-Citrullinated Protein Antibodies

The human microbiome exists throughout the body, and it is essential for maintaining various physiological processes, including immunity, and dysbiotic events, which are associated with autoimmunity. Peptidylarginine deiminase (PAD) enzymes can citrullinate self-proteins related to rheumatoid arthritis (RA) that induce the production of anti-citrullinated protein antibodies (ACPAs) and lead to inflammation and joint damage. The present investigation was carried out to demonstrate the expression of homologs of PADs or arginine deiminases (ADs) and citrullinated proteins in members of the human microbiota. To achieve the objective, we used 17 microbial strains and specific polyclonal antibodies (pAbs) of the synthetic peptide derived from residues 100-200 of human PAD2 (anti-PAD2 pAb), and the recombinant fragment of amino acids 326 and 611 of human PAD4 (anti-PAD4 pAb), a human anti-citrulline pAb, and affinity ACPAs of an RA patient. Western blot (WB), enzyme-linked immunosorbent assay (ELISA), elution, and a test with Griess reagent were used. This is a cross-sectional case-control study on patients diagnosed with RA and control subjects. Inferential statistics were applied using the non-parametric Kruskal-Wallis test and Mann-Whitney U test generated in the SPSS program. Some members of phyla Firmicutes and Proteobacteria harbor homologs of PADs/ADs and citrullinated antigens that are reactive to the ACPAs of RA patients. Microbial citrullinome and homolog enzymes of PADs/ADs are extensive in the human microbiome and are involved in the production of ACPAs. Our findings suggest a molecular link between microorganisms of a dysbiotic microbiota and RA pathogenesis.

Determination of serum and gingival crevicular fluid levels of omentin in healthy and rheumatoid arthritis subjects with and without periodontitis

OBJECTIVE

The aim of this study was to assess and correlate the serum and GCF levels of omentin with the periodontal status of rheumatoid arthritis (RA) patients with and without periodontitis.

METHODS

Forty-four patients were divided into four groups: group H: 11 systemically and periodontally healthy subjects; group P: 11 systemically healthy subjects with periodontitis; group RA: 11 periodontally healthy subjects with rheumatoid arthritis and group RA + P: 11 rheumatoid arthritis subjects with periodontitis. Periodontal parameters (plaque index, modified gingival index, probing depth, and clinical attachment level) were recorded and serum and GCF samples were collected for the estimation of omentin using ELISA.

RESULTS

The mean value of plaque index, modified gingival index, probing depth, and clinical attachment level were significantly higher whereas serum and GCF omentin levels were found to be decreased in group IV when compared to the other groups. The significant correlation was found between the serum and GCF omentin levels with all the periodontal parameters.

CONCLUSION

The omentin level in serum and GCF was found to be lower in RA patients with periodontitis. It is also inversely correlated with the periodontal parameters. Thus, omentin can serve as a significant diagnostic and therapeutic tool in both periodontal and rheumatoid disease.

Periodontitis and rheumatoid arthritis-Global efforts to untangle two complex diseases

Understanding the impact of oral health on rheumatoid arthritis (RA) will inform how best to manage patients with both periodontitis and RA. This review seeks to provide an update on interventional and mechanistic investigations, including a brief summary of European Research programs investigating the link between periodontitis and RA. Recent clinical studies are described that evaluate how the treatment of one disease impacts on the other, as are studies in both humans and animal models that have sought to identify the potential mechanisms linking the two diseases.

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.

Assessment of Epstein-Barr virus, Candida albicans, and some periodontal pathogens in rheumatoid arthritis patients with periodontitis

OBJECTIVE

To comparatively investigate the periodontal results and microbial load in subgingival biofilm samples (SBS) in rheumatoid arthritis subjects and healthy volunteers.

METHODS

One hundred twenty subjects were classified into different cohorts: healthy (H-C); periodontitis with good systemic health (H-P); rheumatoid arthritis (RA) and good periodontal health (RA-C); and periodontitis with RA (RA-P). The periodontal parameters were recorded, and SBS were collected to determine periodontal pathogens including Epstein-Barr Virus (EBV) and Candida albicans using reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Subjects that had greater disease course, determined by moderate or high disease activity scores 28 (DAS28), suffered from worse oral health conditions (higher plaque index, gingival index, bleeding on probing, probing depth, and excessive clinical attachment loss) than those with low DAS28 scores. A higher prevalence of Treponema denticola (T. denticola) was observed in the RA-P group. Cyclic citrullinated peptide was associated with the occurrence of T. denticola and Campylobacter rectus. DAS28 using C-reactive protein (DAS28-CRP) had a significant association with Capnocytophaga gingivalis and EBV. The duration of the RA disease was associated with the presence of T. denticola.

CONCLUSION

Subgingival microbial difference could reliably discriminate RA from healthy individuals. Especially, T. denticola and EBV may play a key role in periodontitis associated with RA.

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.

Factors associated with the composition of the gut microbiome in patients with established rheumatoid arthritis and its value for predicting treatment responses

BACKGROUND

We aimed to investigate the gut microbiota of patients with established rheumatoid arthritis (RA) who have been managed with disease-modifying anti-rheumatic drugs (DMARDs) for a long time. We focused on factors that might affect composition of the gut microbiota. Furthermore, we investigated whether gut microbiota composition predicts future clinical responses to conventional synthetic DMARDs (csDMARDs) in patients with an insufficient response to initial therapy.

METHODS

We recruited 94 patients with RA and 30 healthy participants. Fecal gut microbiome was analyzed by 16S rRNA amplificon sequencing; the resulting raw reads were processed based on QIIME2. Calypso online software was used for data visualization and to compare microbial composition between groups. For RA patients with moderate-to-high disease activity, treatment was changed after stool collection, and responses were observed 6 months later.

RESULTS

The composition of the gut microbiota in patients with established RA was different from that of healthy participants. Young RA patients (< 45 years) had reduced richness, evenness, and distinct gut microbial compositions when compared with older RA patients and healthy individuals. Disease activity and rheumatoid factor levels were not associated with microbiome composition. Overall, biological DMARDs and csDMARDs, except sulfasalazine and TNF inhibitors, respectively, were not associated with the gut microbial composition in patients with established RA. However, the combination of Subdoligranulum and Fusicatenibacter genera was associated with a future good response to second-line csDMARDs in patients who showed an insufficient response to first-line csDMARDs.

CONCLUSION

Gut microbial composition in patients with established RA is different from that in healthy individuals. Thus, the gut microbiome has the potential to predict responses of some RA patients to csDMARDs.

C-terminal citrullinated peptide alters antigen-specific APC:T cell interactions leading to breach of immune tolerance

In rheumatoid arthritis, the emergence of anti-citrullinated autoimmunity is associated with HLA-antigen-T cell receptor complexes. The precise mechanisms underpinning this breach of tolerance are not well understood. Porphyromonas gingivalis expresses an enzyme capable of non-endogenous C-terminal citrullination with potential to generate citrullinated autoantigens. Here we document how C-terminal citrullination of ovalbumin peptide^323-339 alters the interaction between antigen-presenting cells and OTII T cells to induce functional changes in responding T cells. These data reveal that C-terminal citrullination is sufficient to breach T cell peripheral tolerance in vivo and reveal the potential of C-terminal citrullination to lower the threshold for T cell activation. Finally, we demonstrate a role for the IL-2/STAT5/CD25 signalling axis in breach of tolerance. Together, our data identify a tractable mechanism and targetable pathways underpinning breach of tolerance in rheumatoid arthritis and provide new conceptual insight into the origins of anti-citrullinated autoimmunity.

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.

Oral Microbiome in Pre-Rheumatoid Arthritis: The Role of Aggregatibacter Actinomycetemcomitans in Bacterial Composition

Rheumatoid arthritis (RA) is a chronic autoimmune disease that symmetrically affects the joints, eventually leading to cartilage and tissue destruction. While there are multiple etiologies for RA, from environmental to genetic risk factors, periodontal disease (PD) may contribute to the acceleration of RA symptoms in pre-rheumatoid arthritis (pre-RA) and RA patients. While PD is caused by multiple oral bacteria, this review explains the role of Aggregatibacter actinomycetemcomitans (Aa) in the pathogenesis of pre-RA and RA based on 13 primary articles. This paper focuses on the Aa virulence factor leukotoxin A (LtxA) because it has been reported to cause cellular destruction and inflammation in the oral cavity that can accelerate the development of RA. Individuals who are classified as pre-RA may benefit from periodontal screening to further reduce their risk of developing advanced RA. Additionally, they may benefit from earlier pharmacological therapy for RA using disease-modifying anti-rheumatic drugs (DMARD) and antibacterial treatment.

Host mRNA Analysis of Periodontal Disease Patients Positive for Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Tannerella forsythia

Periodontal disease is a frequent pathology worldwide, with a constantly increasing prevalence. For the optimal management of periodontal disease, there is a need to take advantage of actual technology to understand the bacterial etiology correlated with the pathogenic mechanisms, risk factors and treatment protocols. We analyzed the scientific literature published in the last 5 years regarding the recent applications of mRNA analysis in periodontal disease for the main known bacterial species considered to be the etiological agents: Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Tannerella forsythia. We identified new pathogenic mechanisms, therapeutic target genes and possible pathways to prevent periodontal disease. The mRNA analysis, as well as the important technological progress in recent years, supports its implementation in the routine management of periodontal disease patients.

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.

Pros and cons of causative association between periodontitis and rheumatoid arthritis

Research in recent decades has brought significant advancements in understanding of the molecular basis of the etiology of autoimmune diseases, including rheumatoid arthritis, a common systemic disease in which an inappropriate or inadequate immune response to environmental challenges leads to joint destruction. Recent studies have indicated that the classical viewpoint of the immunological processes underpinning the pathobiology of rheumatoid arthritis is restricted and needs to be expanded to include a more holistic and interdisciplinary approach incorporating bacteria-induced inflammatory reactions as an important pathway in rheumatoid arthritis etiology. Here, we discuss in detail data showing the clinical and molecular association of rheumatoid arthritis development with periodontal diseases. We also describe the unique role of periopathogens, which have been proposed to be crucial in the initiation and progression of this autoimmune pathological disorder.

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.

Pleckstrin Levels Are Increased in Patients with Chronic Periodontitis and Regulated via the MAP Kinase-p38α Signaling Pathway in Gingival Fibroblasts

Chronic periodontitis (CP) is a bacteria-driven inflammatory disease characterized by the breakdown of gingival tissue, the periodontal ligament, and alveolar bone, leading ultimately to tooth loss. We previously reported the pleckstrin gene (PLEK) to be highly upregulated in gingival tissue of patients with CP and the only gene concurrently upregulated in other inflammatory diseases including rheumatoid arthritis and cardiovascular diseases. Using saliva from 169 individuals diagnosed with CP and healthy controls, we investigated whether pleckstrin could serve as a novel biomarker of periodontitis. Additionally, we explored signal pathways involved in the regulation of PLEK using human gingival fibroblasts (HGFs). Pleckstrin levels were significantly higher (p < 0.001) in the saliva samples of patients with CP compared to controls and closely associated with CP severity. Immunohistochemical analysis revealed the expression of pleckstrin in inflammatory cells and gingival fibroblasts of CP patients. To explore the signal pathways involved in pleckstrin regulation, we stimulated HGFs with either interleukin-1β (IL-1β) or lipopolysaccharides (LPS) alone, or in combination with inhibitors targeting c-Jun N-terminal kinase, tyrosine kinase, protein kinase C, or p38 MAP kinase. Results showed that IL-1β and LPS significantly increased PLEK mRNA and pleckstrin protein levels. VX-745, the p38 MAP kinase inhibitor significantly decreased IL-1β- and LPS-induced pleckstrin levels at both the mRNA and the protein level. Together, these findings show that pleckstrin could serve as a salivary biomarker for the chronic inflammatory disease periodontitis and a regulator of inflammation via the p38 MAP kinase pathway.

Post-translational Modifications in Oral Bacteria and Their Functional Impact

Oral bacteria colonize the oral cavity, surrounding complex and variable environments. Post-translational modifications (PTMs) are an efficient biochemical mechanism across all domains of life. Oral bacteria could depend on PTMs to quickly regulate their metabolic processes in the face of external stimuli. In recent years, thanks to advances in enrichment strategies, the number and variety of PTMs that have been identified and characterized in oral bacteria have increased. PTMs, covalently modified by diverse enzymes, occur in amino acid residues of the target substrate, altering the functions of proteins involved in different biological processes. For example, Ptk1 reciprocally phosphorylates Php1 on tyrosine residues 159 and 161, required for Porphyromonas gingivalis EPS production and community development with the antecedent oral biofilm constituent Streptococcus gordonii, and in turn Php1 dephosphorylates Ptk1 and rapidly causes the conversion of Ptk1 to a state of low tyrosine phosphorylation. Protein acetylation is also widespread in oral bacteria. In the acetylome of Streptococcus mutans, 973 acetylation sites were identified in 445 proteins, accounting for 22.7% of overall proteins involving virulence factors and pathogenic processes. Other PTMs in oral bacteria include serine or threonine glycosylation in Cnm involving intracerebral hemorrhage, arginine citrullination in peptidylarginine deiminases (PADs), leading to inflammation, lysine succinylation in P. gingivalis virulence factors (gingipains, fimbriae, RagB, and PorR), and cysteine glutathionylation in thioredoxin-like protein (Tlp) in response to oxidative stress in S. mutans. Here we review oral bacterial PTMs, focusing on acetylation, phosphorylation, glycosylation, citrullination, succinylation, and glutathionylation, and corresponding modifying enzymes. We describe different PTMs in association with some examples, discussing their potential role and function in oral bacteria physiological processes and regulatory networks. Identification and characterization of PTMs not only contribute to understanding their role in oral bacterial virulence, adaption, and resistance but will open new avenues to treat oral infectious diseases.

Role of protein deimination in cardiovascular diseases: potential new avenues for diagnostic and prognostic biomarkers

INTRODUCTION

Arginine deimination (citrullination) is a post-translational modification catalyzed by a family of peptidyl arginine deiminase (PAD) enzymes. Cell-based functional studies and animal models have manifested the key role of PADs in various cardiovascular diseases (CVDs).

AREA COVERED

This review summarizes the latest developments in the role of PADs in CVD pathogenesis. It focuses on the PAD functions and diverse citrullinated proteins in cardiovascular conditions like deep vein thrombosis, ischemia/reperfusion, and atherosclerosis. Identification of PAD isoforms and citrullinated targets are essential for directing diagnosis and clinical intervention. Finally, anti-citrullinated protein antibodies (ACPAs) are addressed as an independent risk factor for cardiovascular events. A search of PubMed biomedical literature from the past ten years was performed with a combination of the following keywords: PAD/PADI, deimination/citrullination, autoimmune, fibrosis, NET, neutrophil, macrophage, inflammation, inflammasome, cardiovascular, heart disease, myocardial infarction, ischemia, atherosclerosis, thrombosis, and aging. Additional papers from retrieved articles were also considered.

EXPERT OPINION

PADs are unique family of enzymes that converts peptidyl-arginine to -citrulline in protein permanently. Overexpression or increased activity of PAD has been observed in various CVDs with acute and chronic inflammation as the background. Importantly, far beyond being simply involved in forming neutrophil extracellular traps (NETs), accumulating evidence indicated PAD activation as a trigger for numerous processes, such as transcriptional regulation, endothelial dysfunction, and thrombus formation. In summary, the findings so far have testified the important role of deimination in cardiovascular biology, while more basic and translational studies are essential to further exploration.

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.

Causal risk and protective factors in rheumatoid arthritis: A genetic update

The characterization of risk and protective factors in complex diseases such as rheumatoid arthritis (RA) has evolved from epidemiological studies, which test association, to the use of Mendelian randomization approaches, which test direct relationships. Indeed, direct associations with the mucosal origin of RA are retrieved with periodontal disease (Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans predominantly), interstitial lung involvement, tobacco smoking and air pollutants. Next, factors directly associated with an acquired immune response include genetic factors (HLA DRB1, PTPN22), capacity to produce anti-modified protein antibodies (AMPA), and relatives with a history of autoimmune diseases. Finally, factors can be also classified according to their direct capacity to interfere with the IL-6/CRP/sIL-IL6R proinflammatory pathway as risk factor (body fat, cardiometabolic factors, type 2 diabetes, depressive syndrome) or either as protective factors by controlling of sIL-6R levels (higher education level, and intelligence). Although some co-founders have been characterized (e.g. vitamin D, physical activity, cancer) the direct association with sex-discrepancy, pregnancy, and infections among other factors remains to be better explored.

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.

Past infections are associated with low levels of anti-citrullinated protein autoantibodies in rheumatoid arthritis

Background : Rheumatoid arthritis (RA), an autoimmune disease of unknown etiology, is believed to occur as the result of actions of genetic and environmental factors. In this study, we examined the relation of past histories about infectious diseases with the levels anti-citrullinated protein autoantibodies (ACPA) in RA. Methods : Results of a questionnaire about histories of infectious diseases were obtained from 85 patients with RA, and were analyzed. Results : Significantly lower level of ACPA was detected in patients with the history of tonsillitis, otitis media or urinary cystitis than in those without it. There was no difference in the level of ACPA in RA patients between with and without cold / influenza, rubella, chickenpox, herpes labialis or herpes zoster. When RA patients were divided into two groups, high-level and low-level ACPA, multiple logistic regression analysis revealed that the history of otitis media was a significantly independent factor for the low level of ACPA. There was no significant relation between the level of rheumatoid factor and histories of infectious diseases. Conclusion : This study clarified that the past history of otitis media is associated with the low level of ACPA in RA. J. Med. Invest. 67 : 182-188, February, 2020.

Interplay of Microbiota and Citrullination in the Immunopathogenesis of Rheumatoid Arthritis

Microbiota is a balanced ecosystem that has important functions to the host health including development, defense, digestion, and absorption of dietary fibers and minerals, vitamin synthesizes, protection, and training the host immune system. On the other hand, its dysbiosis is linked to many human diseases such as rheumatoid arthritis (RA). The RA is an inflammatory autoimmune disorder caused by genetic and environmental factors; microbiota may be considered as a risk environmental factor for it. Citrullination is a post-translation modification (PMT) that converts the amino acid arginine to amino acid citrulline in certain proteins. These citrullinated proteins are recognized as a foreign antigen by the immune system resulting in the upregulation of inflammatory action such as in RA. The current work highlights the effect of both gut and oral microbiota dysbiosis on the development of RA, as well as discusses how the alteration in microbiota composition leads to the overgrowth of some bacterial species that entangled in RA pathogenicity. The evidence suggested that some oral and gut microbial species such as Porphyromonas gingivalis and Prevotella copri, respectively, contribute to RA pathogenesis. During dysbiosis, these bacteria can mediate the citrullination of either human or bacteria proteins to trigger an immune response that leads to the generation of autoantibodies.

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.

IFN-γ or IL-4 polarization impacts the response of gingival fibroblasts to oral bacteria

BACKGROUND AND OBJECTIVE

We previously reported that gingival fibroblasts (GFs) can be polarized into functionally distinct subtypes, immune-activating but tissue-destructive or tissue-reparative, in response to T helper (Th1) and Th2 stimuli, respectively. The purpose of this study was to evaluate the effect of polarization on GFs responses to oral bacteria.

METHODS

Unprimed (GF(-)) and IFN-γ (GF(IFN-γ)) or IL-4 primed (GF(IL-4)) GFs were stimulated with live Fusobacterium nucleatum or Porphyromonas gingivalis. The mRNA expression of IL-1β, IL-4, LPS-recognizing components (Toll-like receptor (TLR) 4, CD14), molecules involved in antigen presentation (human leukocyte antigen (HLA)-ABC, HLA-DP, CD74, CD40), chemokines (C-X-C motif chemokine (CXCL)10, CXCL11, chemokine (C-C motif) ligand 20 (CCL20)), collagen type 1 alpha 1 (COL1A1), and matrix metalloproteinase (MMP)-1, and the protein levels of IL-1β, CD14, CXCL11, CCL20, and COL1A1 accumulated in supernatants were analyzed using real-time PCR and ELISA.

RESULTS

In response to oral bacteria, the GF(IFN-γ) significantly upregulated the expression of LPS-recognizing components, molecules involved in antigen presentation, CXCL10, and CXCL11, whereas the levels of IL-4 and COL1A1 were downregulated, compared with GF(-). The levels of IL-1β, CCL20, and MMP-1 from GF(IFN-γ) were differently regulated between both bacteria; F. nucleatum was synergistically upregulated, but P. gingivalis was downregulated. The GF(IL-4) stimulated with both bacteria upregulated the levels of IL-4, whereas the levels of TLR4 and chemokines were downregulated, compared with GF(-). The regulation of IL-1β, CD14, CXCL11, CCL20, and COL1A1 proteins showed a similar tendency with mRNA regulation.

CONCLUSION

Polarization of GFs with IFN-γ or IL-4 affected the way that GFs responded to oral bacteria through up or downregulation of inflammatory responses and extracellular matrix control.

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.

Effect of Porphyromonas gingivalis infection on gut dysbiosis and resultant arthritis exacerbation in mouse model

BACKGROUND

Porphyromonas gingivalis (Pg) infection causes periodontal disease and exacerbates rheumatoid arthritis (RA). It is reported that inoculation of periodontopathogenic bacteria (i.e., Pg) can alter gut microbiota composition in the animal models. Gut microbiota dysbiosis in human has shown strong associations with systemic diseases, including RA, diabetes mellitus, and inflammatory bowel disease. Therefore, this study investigated dysbiosis-mediated arthritis by Pg oral inoculation in an experimental arthritis model mouse.

METHODS

Pg inoculation in the oral cavity twice a week for 6 weeks was performed to induce periodontitis in SKG mice. Concomitantly, a single intraperitoneal (i.p.) injection of laminarin (LA) was administered to induce experimental arthritis (Pg-LA mouse). Citrullinated protein (CP) and IL-6 levels in serum as well as periodontal, intestinal, and joint tissues were measured by ELISA. Gut microbiota composition was determined by pyrosequencing the 16 s ribosomal RNA genes after DNA purification of mouse feces. Fecal microbiota transplantation (FMT) was performed by transferring Pg-LA-derived feces to normal SKG mice. The effects of Pg peptidylarginine deiminase (PgPAD) on the level of citrullinated proteins and arthritis progression were determined using a PgPAD knockout mutant.

RESULTS

Periodontal alveolar bone loss and IL-6 in gingival tissue were induced by Pg oral infection, as well as severe joint destruction, increased arthritis scores (AS), and both IL-6 and CP productions in serum, joint, and intestinal tissues. Distribution of Deferribacteres and S24-7 was decreased, while CP was significantly increased in gingiva, joint, and intestinal tissues of Pg-inoculated experimental arthritis mice compared to experimental arthritis mice without Pg inoculation. Further, FMT from Pg-inoculated experimental arthritis mice reproduced donor gut microbiota and resulted in severe joint destruction with increased IL-6 and CP production in joint and intestinal tissues. The average AS of FMT from Pg-inoculated experimental arthritis was much higher than that of donor mouse. However, inoculation of the PgPAD knockout mutant inhibited the elevation of arthritis scores and ACPA level in serum and reduced CP amount in gingival, joint, and intestinal tissues compared to Pg wild-type inoculation.

CONCLUSION

Pg oral infection affected gut microbiota dysbiosis and joint destruction via increased CP generation.

rs2476601 in PTPN22 gene in rheumatoid arthritis and periodontitis-a possible interface?

BACKGROUND

Rheumatoid arthritis (RA) and periodontitis (PD) are proven to share common risk markers, including genetic factors. In the present study we focused on genetic variants in PTPN22 (rs2476601), PADI4 (rs2240340), CTLA4 genes (rs3087243) and its impact on RA and PD.

MATERIALS AND METHODS

In the study 111 RA patients and 256 systemically healthy controls were involved. A subdivision of patients and controls was carried out according the severity of periodontitis (no/level 1 PD vs. level 2 PD).

RESULTS

I. Evaluating the genetic impact on the occurrence of RA the T allele of rs2476601 (PTPN22) (bivariate: p < 0.001; multivariate: p = 0.018) and T allele of rs2240340 (PADI4) (bivariate: p = 0.006; multivariate: p = 0.070) were associated with an increased vulnerability to RA. II. Investigating the genetic influence on level 2 PD the T allele of rs2476601 (PTPN22) was shown to be associated with a higher susceptibility to PD within the RA group (bivariate: p = 0.043; multivariate: p = 0.024). III. The T allele of rs2476601 (PTPN22) was proven to be a significant marker of RA and level 2 PD comorbidity (bivariate: p < 0.001; multivariate: p = 0.028).

CONCLUSIONS

These results support the thesis that genetic variations may represent a possible link between PD and RA. The study increases knowledge about disease-specific and cross-disease genetic pattern.

The relationship between periodontal status and rheumatoid arthritis - systematic review

There have been numerous publications investigating the relationship between periodontitis (PD) and rheumatoid arthritis (RA) so far.

This publication presents the common risk factors for the development of PD and RA. The major impact of the pathological bacterial factor and cigarette smoking with chronic inflammation playing the key role in both diseases has been confirmed by numerous studies in various populations over the years. More research focuses nowadays also on the role of improper diet and obesity. Pathophysiological pathways, such as increased concentration of proinflammatory cytokines, indirectly affecting the cardiovascular complications and coagulation disorders, which has an impact on function disorders of tissue metalloproteinase inhibitors and the plasminogen activation system, were also researched.

This systematic review of current literature has shown numerous discrepancies in previous analyses and the need for further detailed research on the relationship between periodontal status and RA.

Adipokines and periodontal markers as risk indicators of early rheumatoid arthritis: a cross-sectional study

OBJECTIVE

To establish the association between adipokine levels and markers of periodontal involvement as risk indicators of early stages of RA (eRA) and the interaction between the presence of markers of periodontal disease with adipokine in eRA individuals.

MATERIALS AND METHODS

Fifty-one patients with a diagnosis of eRA and 51 healthy controls matched for age and sex were studied. Clinical joint condition, clinical and serological markers of disease activity, serum adipokine levels (leptin, adiponectin, resistin, adipsin, vaspin, and IL-6), periodontal diagnosis, presence of Porphyromonas gingivalis, and related IgG1 and IgG2 antibodies were evaluated. Comparisons were made between eRA and healthy controls for periodontal indicators and adipokines. A subgroup analysis was realized with a non-conditional logistic regression to establish the association between the levels of leptin in individuals with eRA and controls according to the periodontal condition, presence of P. gingivalis, or high titers of IgG antibodies against P. gingivalis.

RESULTS

The condition of overweight or obesity is associated with the diagnosis of eRA (p = 0.05), and these individuals also have higher levels of leptin (p = 0.001) and vaspin (p = 0.007). Higher frequency of P. gingivalis (p = 0.001) was found in the eRa group. Individuals with eRA with higher IgG2 titers against P. gingivalis had higher levels of leptin (OR: 1.66 (CI 95% 1.01-2.73)); however, individuals with periodontitis or P. gingivalis with eRA were associated with highest levels of leptin (OR: 1.86, CI 95% 1.19-24.3; and OR: 2.04, CI 95% 1.37-3 respectively).

CONCLUSIONS

eRA individuals have high levels of leptin and vaspin. However, the presence of periodontitis and related-periodontal disease markers showed an effect only in leptin levels in eRA individuals.

CLINICAL RELEVANCE

Emphasizing in personalized medicine, monitoring serum leptin levels and periodontitis markers can improve the early diagnosis of RA.

Heritability of Oral Microbiota and Immune Responses to Oral Bacteria

Maintaining a symbiotic oral microbiota is essential for oral and dental health, and host genetic factors may affect the composition or function of the oral microbiota through a range of possible mechanisms, including immune pathways. The study included 836 Swedish twins divided into separate groups of adolescents (n = 418) and unrelated adults (n = 418). Oral microbiota composition and functions of non-enzymatically lysed oral bacteria samples were evaluated using 16S rRNA gene sequencing and functional bioinformatics tools in the adolescents. Adaptive immune responses were assessed by testing for serum IgG antibodies against a panel of common oral bacteria in adults. In the adolescents, host genetic factors were associated with both the detection and abundance of microbial species, but with considerable variation between species. Host genetic factors were associated with predicted microbiota functions, including several functions related to bacterial sucrose, fructose, and carbohydrate metabolism. In adults, genetic factors were associated with serum antibodies against oral bacteria. In conclusion, host genetic factors affect the composition of the oral microbiota at a species level, and host-governed adaptive immune responses, and also affect the concerted functions of the oral microbiota as a whole. This may help explain why some people are genetically predisposed to the major dental diseases of caries and periodontitis.

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.

Neutrophil Extracellular Traps in Periodontitis

Neutrophils are key cells of the immune system and have a decisive role in fighting foreign pathogens in infectious diseases. Neutrophil extracellular traps (NETs) consist of a mesh of DNA enclosing antimicrobial peptides and histones that are released into extracellular space following neutrophil response to a wide range of stimuli, such as pathogens, host-derived mediators and drugs. Neutrophils can remain functional after NET formation and are important for periodontal homeostasis. Periodontitis is an inflammatory multifactorial disease caused by a dysbiosis state between the gingival microbiome and the immune response of the host. The pathogenesis of periodontitis includes an immune-inflammatory component in which impaired NET formation and/or elimination can be involved, contributing to an exacerbated inflammatory reaction and to the destruction of gingival tissue. In this review, we summarize the current knowledge about the role of NETs in the pathogenesis of periodontitis.

Infectious Triggers in Periodontitis and the Gut in Rheumatoid Arthritis (RA): A Complex Story About Association and Causality

Rheumatoid arthritis (RA) is a systemic immune mediated inflammatory disease of unknown origin, which is predominantly affecting the joints. Antibodies against citrullinated peptides are a rather specific immunological hallmark of this heterogeneous entity. Furthermore, certain sequences of the third hypervariable region of human leukocyte antigen (HLA)-DR class II major histocompatibility (MHC) molecules, the so called "shared epitope" sequences, appear to promote autoantibody positive types of RA. However, MHC-II molecule and other genetic associations with RA could not be linked to immune responses against specific citrullinated peptides, nor do genetic factors fully explain the origin of RA. Consequently, non-genetic factors must play an important role in the complex interaction of endogenous and exogenous disease factors. Tobacco smoking was the first environmental factor that was associated with onset and severity of RA. Notably, smoking is also an established risk factor for oral diseases. Furthermore, smoking is associated with extra-articular RA manifestations such as interstitial lung disease in anatomical proximity to the airway mucosa, but also with subcutaneous rheumatoid nodules. In the mouth, Porphyromonas gingivalis is a periodontal pathogen with unique citrullinating capacity of foreign microbial antigens as well as candidate RA autoantigens. Although the original hypothesis that this single pathogen is causative for RA remained unproven, epidemiological as well as experimental evidence linking periodontitis (PD) with RA is rapidly accumulating. Other periopathogens such as Aggregatibacter actinomycetemcomitans and Prevotella intermedia were also proposed to play a specific immunodominant role in context of RA. However, demonstration of T cell reactivity against citrullinated, MHC-II presented autoantigens from RA synovium coinciding with immunity against Prevotella copri (Pc.), a gut microbe attracted attention to another mucosal site, the intestine. Pc. was accumulated in the feces of clinically healthy subjects with citrulline directed immune responses and was correlated with RA onset. In conclusion, we retrieved more than one line of evidence for mucosal sites and different microbial taxa to be potentially involved in the development of RA. This review gives an overview of infectious agents and mucosal pathologies, and discusses the current evidence for causality between different exogenous or mucosal factors and systemic inflammation in RA.

Microbial and Host Factors That Affect Bacterial Invasion of the Gingiva

Periodontitis is a chronic inflammation of the periodontium caused by the loss of homeostasis between subgingival biofilms and susceptible hosts. Bacterial invasion into the gingival tissue and persistent infection are major events that lead to chronic inflammation. The intratissue bacterial communities are as complex as the subgingival biofilms and can also form biofilm-like structures, which will serve as a reservoir for local and systemic infections. The epithelium forms physical, chemical, and immunological barriers against invading microbes. Nevertheless, many bacterial species can invade the gingival epithelium through transcellular and paracellular pathways. In addition, both genetic and environmental factors of the hosts can affect epithelial barrier functions and thus bacterial invasion of the gingiva. In this review, current evidence for the bacterial invasion of the gingival tissue in periodontitis has been summarized, and the microbial and host factors that determine bacterial invasion of the gingiva have been reviewed.

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 Impact of Cigarette Smoking on Risk of Rheumatoid Arthritis: A Narrative Review

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and subsequent proliferation of synovial tissues, which eventually leads to cartilage and bone destruction without effective treatments. Anti-citrullinated cyclic peptide/protein antibody (ACPA) and rheumatoid factor (RF) are two main characteristic autoantibodies found in RA patients and are associated with unfavorable disease outcomes. Although etiologies and causes of the disease have not been fully clarified yet, it is likely that interactive contributions of genetic and environmental factors play a main role in RA pathology. Previous works have demonstrated several genetic and environmental factors as risks of RA development and/or autoantibody productions. Among these, cigarette smoking and HLA-DRB1 are the well-established environmental and genetic risks, respectively. In this narrative review, we provide a recent update on genetic contributions to RA and the environmental risks of RA with a special focus on cigarette smoking and its impacts on RA pathology. We also describe gene–environmental interaction in RA pathogenesis with an emphasis on cigarette smoking and HLA-DRB1.

Non-surgical oral hygiene interventions on disease activity of Rheumatoid arthritis patients with periodontitis: A randomized controlled trial

Background. Periodontitis and rheumatoid arthritis have similar epidemiology and pathophysiology. Understanding the interaction between these two diseases is vital in our settings. We set out to assess the effect of oral hygiene interventions on disease activity of rheumatoid arthritis patients with periodontitis in Kampala, Uganda. Methods. Fifty-eight patients attending an arthritis clinic with rheumatoid arthritis and periodontitis were randomly assigned to either an intervention group or a control group. Patients diagnosed with rheumatoid arthritis at least two years before, who were on the same medication, dose, or formulation for RA treatment during the preceding three months, were included. The patients were >18 years of age, would be available for all the study visits in the next six months, had at least six natural teeth, had periodontal disease classified as Dutch Periodontal Index (DPSI) >3 and provided written informed consent. Those who had a chronic disorder requiring chronic or intermittent use of antibiotics, were pregnant, were lactating, or had intent to become pregnant were excluded. The primary outcome measure was a change in Disease Activity Score of 28 Joints (DAS28 score) in two 3-month follow-up periods after the intervention. The secondary outcome measure was a change in periodontal status. Results. There was a statistically significant improvement in the DAS-28 score in both the intervention and control arms during the follow-up period (P<0.01). The participants carrying more than one bacterial species had worse DAS-28 scores. Conclusion. Oral hygiene interventions given to RA patients could drastically improve their RA treatment outcomes, especially in resource-limited settings.

PtpA and PknG Proteins Secreted by Mycobacterium avium subsp. paratuberculosis are Recognized by Sera from Patients with Rheumatoid Arthritis: A Case-Control Study

Purpose

Rheumatoid arthritis (RA) can result from complex interactions between the affected person’s genetic background and environment. Viral and bacterial infections may play a pathogenetic role in RA through different mechanisms of action. We aimed to evaluate the presence of antibodies (Abs) directed against two proteins of Mycobacterium avium subsp. paratuberculosis (MAP) in sera of RA subjects, which are crucial for the survival of the pathogen within macrophages. Moreover, we analyzed the correlation of immune response to both proteins with the following homologous peptides: BOLF1_305–320, MAP_4027_18–32 and IRF5_424–434 to understand how the synergic role of Epstein–Barr virus (EBV) and MAP infection in genetically predisposed subjects may lead to a possible deregulation of interferon regulatory factor 5 (IRF5).

Materials and methods

The presence of Abs against protein tyrosine phosphatase A (PtpA) and protein kinase G (PknG) in sera from Sardinian RA patients (n=84) and healthy volunteers (HCs, n=79) was tested by indirect ELISA.

Results

RA sera showed a remarkably high frequency of reactivity against PtpA in comparison to HCs (48.8% vs 7.6%; p<0.001) and lower but statistically significant responses towards PknG (27.4% vs 10.1%; p=0.0054). We found a significant linear correlation between the number of swollen joints and the concentrations of antibodies against PtpA (p=0.018). Furthermore, a significant bivariate correlation between PtpA and MAP MAP_4027_18–32 peptide has been found, suggesting that MAP infection may induce a secondary immune response through cross-reaction with IRF5 (R²=0.5).

Conclusion

PtpA and PknG are strongly recognized in RA which supports the hypothesis that MAP infection may be involved in the pathogenesis of RA.

Linkage of Periodontitis and Rheumatoid Arthritis: Current Evidence and Potential Biological Interactions

The association between rheumatoid arthritis (RA) and periodontal disease (PD) has been the focus of numerous investigations driven by their common pathological features. RA is an autoimmune disease characterized by chronic inflammation, the production of anti-citrullinated proteins antibodies (ACPA) leading to synovial joint inflammation and destruction. PD is a chronic inflammatory condition associated with a dysbiotic microbial biofilm affecting the supporting tissues around the teeth leading to the destruction of mineralized and non-mineralized connective tissues. Chronic inflammation associated with both RA and PD is similar in the predominant adaptive immune phenotype, in the imbalance between pro- and anti-inflammatory cytokines and in the role of smoking and genetic background as risk factors. Structural damage that occurs in consequence of chronic inflammation is the ultimate cause of loss of function and disability observed with the progression of RA and PD. Interestingly, the periodontal pathogen Porphyromonas gingivalis has been implicated in the generation of ACPA in RA patients, suggesting a direct biological intersection between PD and RA. However, more studies are warranted to confirm this link, elucidate potential mechanisms involved, and ascertain temporal associations between RA and PD. This review is mainly focused on recent clinical and translational research intends to discuss and provide an overview of the relationship between RA and PD, exploring the similarities in the immune-pathological aspects and the possible mechanisms linking the development and progression of both diseases. In addition, the current available treatments targeting both RA and PD were revised.

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.