Interrupting oral infection of Porphyromonas gingivalis with anti-FimA antibody attenuates bacterial dissemination to the arthritic joint and improves experimental arthritis

Identification of a new genetic variant (G231N, E232T, N235D) of peptidylarginine deiminase from P. gingivalis in advanced periodontitis

Chronic periodontitis (CP), an inflammatory disease of periodontal tissues driven by a dysbiotic subgingival bacterial biofilm, is also associated with several systemic diseases, including rheumatoid arthritis (RA). Porphyromonas gingivalis, one of the bacterial species implicated in CP as a keystone pathogen produces peptidyl arginine deiminase (PPAD) that citrullinates C-terminal arginine residues in proteins and peptides. Autoimmunity to citrullinated epitopes is crucial in RA, hence PPAD activity is considered a possible mechanistic link between CP and RA. Here we determined the PPAD enzymatic activity produced by clinical isolates of P. gingivalis, sequenced the ppad gene, and correlated the results with clinical determinants of CP in patients from whom the bacteria were isolated. The analysis revealed variations in PPAD activity and genetic diversity of the ppad gene in clinical P. gingivalis isolates. Interestingly, the severity of CP was correlated with a higher level of PPAD activity that was associated with the presence of a triple mutation (G231N, E232T, N235D) in PPAD in comparison to W83 and ATCC 33277 type strains. The relation between mutations and enhanced activity was verified by directed mutagenesis which showed that all three amino acid residue substitutions must be introduced into PPAD expressed by the type strains to obtain the super-active enzyme. Cumulatively, these results may lead to the development of novel prognostic tools to assess the progress of CP in the context of associated RA by analyzing the ppad genotype in CP patients infected with P. gingivalis.

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.

Microbial Imbalance and Intestinal Permeability in the Pathogenesis of Rheumatoid Arthritis: A Mechanism Review with a Focus on Bacterial Translocation, Citrullination, and Probiotic Intervention

This review aims to investigate the role of intestinal permeability (IP) in rheumatoid arthritis (RA), following the hypotheses that leakage of intestinal microbes can influence increased citrullination of peptides leading to anti-citrullinated protein antibody (ACPA) production and inflammation in RA; and that leaked microbes can migrate to the peripheral joints, leading to immune responses and synovitis in peripheral joints. This review explored the evidence for the link between microbial dysbiosis and increased IP in the inflammatory state in RA, as well as the role of increased citrullination and bacterial translocation in the link between microbiota and immune responses in RA. Furthermore, this research aims to evaluate the potential effect of probiotics on RA symptoms and pathogenesis via proposed mechanisms, including the support of microbial balance and suppression of inflammatory factors in RA. A systematic literature search was conducted in three tranches (review, mechanism, intervention). 71 peer-reviewed papers met the inclusions criteria and are summarized in a narrative analysis. Primary studies were critically appraised, synthesized and their relevance to clinical practice evaluated. Evidence found in this mechanism review consistently supported intestinal dysbiosis and increased IP in arthritis. An altered intestinal microbiome was demonstrated in RA with specific microbes such as Collinsella and Eggerthella correlating with increased IP, mucosal inflammation, and immune responses. Hypercitrullination and ACPA production correlated with arthritic symptoms and intestinal microbes were shown to influence hypercitrullination. Some in vitro and animal studies demonstrated a link between leakage of microbes and bacterial translocation, but further research is needed to elucidate the link between IP and citrullination. Probiotic intervention studies evidenced reductions in inflammatory markers IL-6 and TNFα, associated with proliferation of synovial tissue and pain perception in RA joint inflammation. Despite some conflict in the literature, probiotics may present a promising nutritional intervention in the suppression of both, disease activity and inflammatory markers.Key teaching pointsThere is evidence for a dysbiotic profile of the RA gut with specific RA-associated microbes.Increased intestinal permeability and leakage of PAD enzyme facilitates citrullination of peptides.Hypercitrullination and ACPA production correlate to arthritic signs.Microbial leakage and translocation plays a role in the pathogenesis of RA.Probiotics (e.g. L. Casei 01) may reduce inflammation and ameliorate RA symptoms.

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.

The oral microbiome in autoimmune diseases: friend or foe?

The human body is colonized by abundant and diverse microorganisms, collectively known as the microbiome. The oral cavity has more than 700 species of bacteria and consists of unique microbiome niches on mucosal surfaces, on tooth hard tissue, and in saliva. The homeostatic balance between the oral microbiota and the immune system plays an indispensable role in maintaining the well-being and health status of the human host. Growing evidence has demonstrated that oral microbiota dysbiosis is actively involved in regulating the initiation and progression of an array of autoimmune diseases.Oral microbiota dysbiosis is driven by multiple factors, such as host genetic factors, dietary habits, stress, smoking, administration of antibiotics, tissue injury and infection. The dysregulation in the oral microbiome plays a crucial role in triggering and promoting autoimmune diseases via several mechanisms, including microbial translocation, molecular mimicry, autoantigen overproduction, and amplification of autoimmune responses by cytokines. Good oral hygiene behaviors, low carbohydrate diets, healthy lifestyles, usage of prebiotics, probiotics or synbiotics, oral microbiota transplantation and nanomedicine-based therapeutics are promising avenues for maintaining a balanced oral microbiome and treating oral microbiota-mediated autoimmune diseases. Thus, a comprehensive understanding of the relationship between oral microbiota dysbiosis and autoimmune diseases is critical for providing novel insights into the development of oral microbiota-based therapeutic approaches for combating these refractory diseases.

Differential effects of periodontal microbiome on the rheumatoid factor induction during rheumatoid arthritis pathogenesis

Association between exposure to periodontal bacteria and development of autoantibodies related to rheumatoid arthritis (RA) has been widely accepted; however, direct causal relationship between periodontal bacteria and rheumatoid factor (RF) is currently not fully understood. We investigated whether periodontal bacteria could affect RF status. Patients with preclinical, new-onset, or chronic RA underwent periodontal examination, and investigation of subgingival microbiome via 16S rRNA sequencing. Degree of arthritis and RF induction was examined in collagen-induced arthritis (CIA) mice that were orally inoculated with different periodontal bacteria species. Subsequently, single-cell RNA sequencing analysis of the mouse spleen cells was performed. Patients with preclinical RA showed an increased abundance of the Porphyromonadacae family in the subgingival microbiome compared to those with new-onset or chronic RA, despite comparable periodontitis severity among them. Notably, a distinct subgingival microbial community was found between patients with high-positive RF and those with negative or low-positive RF (p=0.022). Oral infections with the periodontal pathogens P. gingivalis and Treponema denticola in CIA mice similarly enhanced arthritis score, but resulted in different levels of RF induction. Genes related to B cell receptor signaling, B cell proliferation, activation, and differentiation, and CD4⁺ T cell costimulation and cytokine production were involved in the differential induction of RF in mice exposed to different bacteria. In summary, periodontal microbiome might shape RF status by affecting the humoral immune response during RA pathogenesis.

Host and bacterial factors linking periodontitis and rheumatoid arthritis

Observations from numerous clinical, epidemiological and serological studies link periodontitis with severity and progression of rheumatoid arthritis. The strong association is observed despite totally different aetiology of these two diseases, periodontitis being driven by dysbiotic microbial flora on the tooth surface below the gum line, while rheumatoid arthritis being the autoimmune disease powered by anti-citrullinated protein antibodies (ACPAs). Here we discuss genetic and environmental risk factors underlying development of both diseases with special emphasis on bacteria implicated in pathogenicity of periodontitis. Individual periodontal pathogens and their virulence factors are argued as potentially contributing to putative causative link between periodontal infection and initiation of a chain of events leading to breakdown of immunotolerance and development of ACPAs. In this respect peptidylarginine deiminase, an enzyme unique among prokaryotes for Porphyromonas gingivalis, is elaborated as a potential mechanistic link between this major periodontal pathogen and initiation of rheumatoid arthritis development.

Dysbiotic relationship between arthritis and the oral-gut microbiome. A critical review

Arthritis and prosthetic joint infections (PJIs) overall are associated with reduced quality of life and limited work capacity. Multiple, overlapping factors contribute to these conditions. Some investigations have suggested a dysbiotic association between the oral-gut microbiome and pathogenesis of arthritis and PJIs. A better understanding of the role of the oral-gut microbiota in arthritis and PJI pathophysiology can shed light into how its disequilibrium can discharge a pro-inflammatory response, and impact the health of patients susceptible to arthritis or with established joint disease. A review of published in vivo and clinical data suggested that alterations in oral and gut microbiota can lead to a disturbance of immunoregulatory properties, and may be associated with joint infections and arthritis. This review brings new insights into the current status of the evidence on the potential molecules and inflammatory biomarkers disrupted by an oral-gut microbial dysbiosis. Normal commensals and pathogenic oral and gut microflora homeostasis are important not only to prevent infections per se but also its potential progression. Further experiments, especially controlled clinical trials, are needed to ascertain how microbiome manipulation and other microbiota-directed approaches can help control inflammation and effectively prevent and treat arthritic diseases. Additionally, studies on the effects of the long-term oral diseases, such as chronic periodontitis, on arthritis and PJIs need to be conducted.

Oral and Gut Microbial Dysbiosis and Non-alcoholic Fatty Liver Disease: The Central Role of Porphyromonas gingivalis

Gut microbiota play many important roles, such as the regulation of immunity and barrier function in the intestine, and are crucial for maintaining homeostasis in living organisms. The disruption in microbiota is called dysbiosis, which has been associated with various chronic inflammatory conditions, food allergies, colorectal cancer, etc. The gut microbiota is also affected by several other factors such as diet, antibiotics and other medications, or bacterial and viral infections. Moreover, there are some reports on the oral-gut-liver axis indicating that the disruption of oral microbiota affects the intestinal biota. Non-alcoholic fatty liver disease (NAFLD) is one of the systemic diseases caused due to the dysregulation of the oral-gut-liver axis. NAFLD is the most common liver disease reported in the developed countries. It includes liver damage ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), cirrhosis, and cancer. Recently, accumulating evidence supports an association between NAFLD and dysbiosis of oral and gut microbiota. Periodontopathic bacteria, especially Porphyromonas gingivalis, have been correlated with the pathogenesis and development of NAFLD based on the clinical and basic research, and immunology. P. gingivalis was detected in the liver, and lipopolysaccharide from this bacteria has been shown to be involved in the progression of NAFLD, thereby indicating a direct role of P. gingivalis in NAFLD. Moreover, P. gingivalis induces dysbiosis of gut microbiota, which promotes the progression of NAFLD, through disrupting both metabolic and immunologic pathways. Here, we review the roles of microbial dysbiosis in NAFLD. Focusing on P. gingivalis, we evaluate and summarize the most recent advances in our understanding of the relationship between oral-gut microbiome symbiosis and the pathogenesis and progression of non-alcoholic fatty liver disease, as well as discuss novel strategies targeting both P. gingivalis and microbial dysbiosis.

Haemophilus parasuis (Glaesserella parasuis) as a Potential Driver of Molecular Mimicry and Inflammation in Rheumatoid Arthritis

Background:Haemophilus parasuis (Hps; now Glaesserella parasuis) is an infectious agent that causes severe arthritis in swines and shares sequence similarity with residues 261–273 of collagen type 2 (Coll_261−273), a possible autoantigen in rheumatoid arthritis (RA).

Objectives/methods: We tested the presence of Hps sequencing 16S ribosomal RNA in crevicular fluid, synovial fluids, and tissues in patients with arthritis (RA and other peripheral arthritides) and in healthy controls. Moreover, we examined the cross-recognition of Hps by Coll_261−273-specific T cells in HLA-DRB1^*04^pos RA patients, by T-cell receptor (TCR) beta chain spectratyping and T-cell phenotyping.

Results:Hps DNA was present in 57.4% of the tooth crevicular fluids of RA patients and in 31.6% of controls. Anti-Hps IgM and IgG titers were detectable and correlated with disease duration and the age of the patients. Peripheral blood mononuclear cells (PBMCs) were stimulated with Hps virulence-associated trimeric autotransporter peptide (VtaA10_755−766), homologous to human Coll_261−273 or co-cultured with live Hps. In both conditions, the expanded TCR repertoire overlapped with Coll_261−273 and led to the production of IL-17.

Discussion: We show that the DNA of an infectious agent (Hps), not previously described as pathogen in humans, is present in most patients with RA and that an Hps peptide is able to activate T cells specific for Coll_261−273, likely inducing or maintaining a molecular mimicry mechanism.

Conclusion: The cross-reactivity between VtaA10_755−766 of a non-human infectious agent and human Coll_261−273 suggests an involvement in the pathogenesis of RA. This mechanism appears emphasized in predisposed individuals, such as patients with shared epitope.

S-Propargyl-Cysteine Remodels the Gut Microbiota to Alleviate Rheumatoid Arthritis by Regulating Bile Acid Metabolism

Background

Rheumatoid arthritis (RA) is a long-term autoimmune disorder characterized by chronic inflammation that results in swollen and painful joints and even cartilage and bone damage. The gut microbiota, a novel anti-inflammatory target, is considered an important environmental factor in the development of RA. S-propargyl-cysteine (SPRC), an amino acid analogue, exerts anti-inflammatory, cardioprotective effects, and neuroprotective effects on various diseases. In recent studies, an SPRC treatment exerted anti-inflammatory effects on RA. Meanwhile, gut microbiome dysbiosis in individuals with RA has also been reported by many researchers. However, the relationship between SPRC and gut microbiota in individuals with RA remains unclear.

Methods

Thirty male Sprague-Dawley (SD) rats were randomly divided into three groups of 10 each, including the Control, Model, and SPRC groups. Adjuvant-induced arthritis (AIA) rats in SPRC group were treated with SPRC. Measurement of paw volume and serum tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6) levels were applied to evaluate the inflammatory status. Fecal samples were collected on the 14^th day and 28^th day. Gut microbiota were analyzed using 16S ribosomal RNA (rRNA) gene amplicon sequencing. Untargeted metabolomics on plasma samples was applied to investigate the metabolic changes induced by the altered gut microbiota by using derivatization-UHPLC-Q-TOF/MS.

Findings

Using 16S rRNA amplicon sequencing, we found that SPRC significantly altered the gut microbiota structure in AIA rats. In particular, Bifidobacterium, a genus of BSH (Bile Salt Hydrolase)-producing microbes, was overrepresented in SPRC-treated AIA rats. Additionally, a subsequent metabolomics analysis indicated that bile acid metabolism was also altered by SPRC treatment. Interestingly, glycochenodeoxycholic acid (GCDCA) and glycocholic acid (GCA), which are formed with the participation of BSH-producing microbes in the intestine, were identified as crucial biomarkers responding to SPRC treatment with significantly lowered levels.

Interpretation

A mechanistic link between the gut microbiota and plasma metabolites was revealed in this study, which provides insights into the mechanism of SPRC treatment for RA from the perspective of the gut microbiota.

Molecular Strategies Underlying Porphyromonas gingivalis Virulence

The anaerobic Gram-negative bacterium Porphyromonas gingivalis is considered the keystone of periodontitis diseases, a set of inflammatory conditions that affects the tissues surrounding the teeth. In the recent years, the major virulence factors exploited by P. gingivalis have been identified and characterized, including a cocktail of toxins, mainly proteases called gingipains, which promote gingival tissue invasion. These effectors use the Sec pathway to cross the inner membrane and are then recruited and transported across the outer membrane by the type IX secretion system (T9SS). In P. gingivalis, most secreted effectors are attached to anionic lipopolysaccharides (A-LPS), and hence form a virulence coat at the cell surface. P. gingivalis produces additional virulence factors to evade host immune responses, such as capsular polysaccharide, fimbriae and outer membrane vesicles. In addition to periodontitis, it is proposed that this broad repertoire of virulence factors enable P. gingivalis to be involved in diverse human diseases such as rheumatoid arthritis, and neurodegenerative, Alzheimer, and cardiovascular disorders. Here, we review the major virulence determinants of P. gingivalis and discuss future directions to better understand their mechanisms of action.

Inhibition of Cathepsin K Alleviates Autophagy-Related Inflammation in Periodontitis-Aggravating Arthritis

Rheumatoid arthritis (RA) and periodontitis share many epidemiological and pathological features, with emerging studies reporting a relationship between the two diseases. Recently, RA and periodontitis have been associated with autophagy. In the present study, we investigated the effects of cathepsin K (CtsK) inhibition on RA with periodontitis in a mouse model and its immunological function affecting autophagy. To topically inhibit CtsK periodontitis with arthritis in the animal model, adeno-associated virus (AAV) transfection was performed in periodontal and knee joint regions. Transfection of small interfering RNA (siRNA) was performed to inhibit CtsK in RAW264.7 cells. The effects of CtsK inhibition on the autophagy pathway were then evaluated in both in vivo and in vitro experiments. RA and periodontitis aggravated destruction and inflammation in their respective lesion areas. Inhibition of CtsK had multiple effects: (i) reduced destruction of alveolar bone and articular tissue, (ii) decreased macrophage numbers and inflammatory cytokine expression in the synovium, and (iii) alleviated expression of the autophagy-related transcription factor EB (TFEB) and microtubule-associated protein 1A/1B-light chain 3 (LC3) at the protein level in knee joints. Inhibition of CtsK in vitro reduced the expression of autophagy-related proteins and related inflammatory factors. Our data revealed that the inhibition of CtsK resisted the destruction of articular tissues and relieved inflammation from RA with periodontitis. Furthermore, CtsK was implicated as an imperative regulator of the autophagy pathway in RA and macrophages.

Long-term antibacterial activity of a composite coating on titanium for dental implant application

Dental implants are the most innovative and superior treatment modality for tooth replacement. However, titanium implants still suffer from insufficient antibacterial capability and peri-implant diseases remain one of the most common and intractable complications. To prevent peri-implant diseases, a composite coating containing a new antibacterial agent, (Z-)-4-bromo-5-(bromomethylene)-2(5H)-furanone (BBF) was fabricated on titanium. This study was designed to investigate the antibacterial activity of the composite coating against two common peri-implant pathogens (Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans). The morphology of the composite coating showed that BBF-loaded poly(L-lactic acid) nanospheres were well-distributed in the pores of the microarc oxidation coating, and cross-linked with each other and the wall pores by gelatin. A release study indicated that the antibacterial coating could sustain the release of BBF for 60 d, with a slight initial burst release occurring during the first 4 h. The antibacterial rate of the composite coating for adhering bacteria was the highest (over 97%) after 1 d and over 90% throughout a 30-day incubation period. The total fluorescence intensity of the composite coating was the lowest, and the vast majority of the fluorescence was red (dead bacteria). Moreover, real-time polymerase chain reaction analysis confirmed that the relative gene expression of the adherent bacteria on the composite coating was down-regulated. It was therefore concluded that the composite coating fabricated on titanium, which showed excellent and relatively long-term antibacterial activity against Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans, is a potential and promising strategy to be applied on dental implants for the prevention of peri-implant diseases.

Porphyromonas gingivalis ligada a enfermedad periodontal y su relación con la artritis reumatoide: identificación de nuevos mecanismos biomoleculares

Objetivo: revisar la literatura científica existente con respecto a la patogenicidad de Porphyromonas gingivalis, ligada a enfermedad periodontal (EP) (disbiosis oral), y su asociación con la activación de mecanismos fisiopatológicos en la artritis reumatoide (AR), a fin de exponer los nuevos mecanismos biomoleculares implicados. Métodos: búsqueda sistemática en la base de datos del Medical Subject Headings (MeSH), PubMed, Science Direct, Nature y Google académico usando las palabras clave: Aggregatibacter actinomycetemcomitans; artritis reumatoide; citrulinación; disbiosis; odontología; periodontitis; Porphyromonas gingivalis y reumatología. De un total de 297 publicaciones, se seleccionaron 52, todas a partir del año 2018; la selección fue hecha a partir de los criterios de inclusión y exclusión establecidos por los autores. Resultados: la infección por Porphyromonas gingivalis, ligada a la EP, está fuertemente implicada en la patogénesis y desarrollo de AR. Su relación se vincula con el proceso de citrulinación y producción de anticuerpos antipéptidos citrulinados. Se han identificado asociaciones entre la virulencia microbiana de dicho agente y la expresión de múltiples genes, relacionados con la activación de la respuesta inmune y el inicio del proceso inflamatorio crónico. Conclusiones: existe una alta asociación entre la patogenia de ambas enfermedades, donde microorganismos ligados a la EP, como Porphyromonas gingivalis, tienen la capacidad de aumentar la citrulinación, galactosilación, fucosilación, así como la excesiva glicosilación de Fragmentos de unión al antígeno (Fab), y por lo tanto, la agresividad de la AR.

Troublesome friends within us: the role of gut microbiota on rheumatoid arthritis etiopathogenesis and its clinical and therapeutic relevance

The role of gut microbiota on immune regulation and the development of autoimmune diseases such as rheumatoid arthritis (RA) is an emerging research topic. Multiple studies have demonstrated alterations on gut microbiota composition and/or function (referred to as dysbiosis) both in early and established RA patients. Still, research delineating the molecular mechanisms by which gut microorganisms induce the loss of immune tolerance or contribute to disease progression is scarce. Available data indicate that gut microbiota alterations are involved in RA autoimmune response by several mechanisms including the post-translational modification of host proteins, molecular mimicry between bacterial and host epitopes, activation of immune system and polarization toward inflammatory phenotypes, as well as induction of intestinal permeability. Therefore, in this review we analyze recent clinical and molecular evidence linking gut microbiota with the etiopathogenesis of RA. The potential of the gut microbiota as a diagnostic or severity biomarker is discussed, as well as the opportunity areas for the development of complementary therapeutic strategies based on the modulation of gut microbiota in the rheumatic patient.

Porphyromonas gingivalis, a Long-Range Pathogen: Systemic Impact and Therapeutic Implications

Periodontitis is an inflammatory disease associated with a dysbiosis of the oral flora characterized by a chronic sustained inflammation leading to destruction of tooth-supporting tissues. Over the last decade, an association between periodontitis and systemic disorders such as cardiovascular diseases, rheumatoid arthritis and obesity has been demonstrated. The role of periodontal pathogens, notably Porphyromonas gingivalis (P. gingivalis), in the onset or exacerbation of systemic diseases has been proposed. P. gingivalis expresses several virulence factors that promote its survival, spreading, and sustaining systemic inflammation. Recently, the impact of periodontitis on gut dysbiosis has also been suggested as a potential mechanism underlying the systemic influence of periodontitis. New therapeutic strategies for periodontitis and other dysbiotic conditions, including the use of beneficial microbes to restore healthy microbial flora, may pave the way to improved therapeutic outcomes and more thorough patient management.

Gingimaps: Protein Localization in the Oral Pathogen Porphyromonas gingivalis

Porphyromonas gingivalis is an oral pathogen involved in the widespread disease periodontitis. In recent years, however, this bacterium has been implicated in the etiology of another common disorder, the autoimmune disease rheumatoid arthritis. Periodontitis and rheumatoid arthritis were known to correlate for decades, but only recently a possible molecular connection underlying this association has been unveiled. P. gingivalis possesses an enzyme that citrullinates certain host proteins and, potentially, elicits autoimmune antibodies against such citrullinated proteins. These autoantibodies are highly specific for rheumatoid arthritis and have been purported both as a symptom and a potential cause of the disease. The citrullinating enzyme and other major virulence factors of P. gingivalis, including some that were implicated in the etiology of rheumatoid arthritis, are targeted to the host tissue as secreted or outer-membrane-bound proteins. These targeting events play pivotal roles in the interactions between the pathogen and its human host. Accordingly, the overall protein sorting and secretion events in P. gingivalis are of prime relevance for understanding its full disease-causing potential and for developing preventive and therapeutic approaches. The aim of this review is therefore to offer a comprehensive overview of the subcellular and extracellular localization of all proteins in three reference strains and four clinical isolates of P. gingivalis, as well as the mechanisms employed to reach these destinations.

Association of periodontitis with radiographic knee osteoarthritis

BACKGROUND

To examine whether periodontitis is associated with the presence and severity of radiographic knee osteoarthritis (OA).

METHODS

Using data from the Korea National Health and Nutrition Examination Survey between 2010 and 2013, participants over the age of 50 were included in this study. Dental examinations and knee radiographs are performed in participants aged ≥50 years in this cohort. Periodontitis was defined using the community periodontal index, which was determined by measuring periodontal probing depth. The definition of radiographic knee OA was based on the Kellgren-Lawrence (K-L) grading system, which determined a K-L class ≥2 to be radiographic knee OA. The associations between periodontitis and presence and severity of radiographic knee OA were examined using logistic regression analyses.

RESULTS

Among 7969 total participants, 965 men and 2078 women had radiographic knee OA. Periodontitis was observed in 1,185 (39.4%) people among those who had radiographic knee OA. Periodontitis (adjusted odds radio [aOR] 1.21, 95% confidence interval 1.05 to 1.40) was associated with radiographic knee OA after adjusting for variables including age, sex, body mass index, socioeconomic status, diabetes, and dental status. Participants were more likely to have radiographic knee OA as the severity of periodontitis increased (non-severe periodontitis, aOR 1.14 [0.98 to 1.32]; severe periodontitis, aOR 1.47 [1.17 to 1.85]). Moreover, the presence of periodontitis significantly increased with an increasing K-L class (class 1, aOR 1.30 [1.09 to 1.54]; class 2, aOR 1.32 [1.08 to 1.60]; class 3, aOR 1.39 [1.14 to 1.70]; class 4, aOR 1.45 [1.11 to 1.90]).

CONCLUSION

Periodontitis is associated with the presence and severity of radiographic knee OA.

Inflammatory arthritis disrupts gut resolution mechanisms, promoting barrier breakdown by Porphyromonas gingivalis

Rheumatoid arthritis is linked with altered host immune responses and severe joint destruction. Recent evidence suggests that loss of gut homeostasis and barrier breach by pathobionts, including Porphyromonas gingivalis, may influence disease severity. The mechanism(s) leading to altered gut homeostasis and barrier breakdown in inflammatory arthritis are poorly understood. In the present study, we found a significant reduction in intestinal concentrations of several proresolving mediators during inflammatory arthritis, including downregulation of the gut-protective mediator resolvin D5n-3 DPA (RvD5n-3 DPA). This was linked with increased metabolism of RvD5n-3 DPA to its inactive 17-oxo metabolite. We also found downregulation of IL-10 expression in the gut of arthritic mice that was coupled with a reduction in IL-10 and IL-10 receptor (IL-10R) in lamina propria macrophages. These changes were linked with a decrease in the number of mucus-producing goblet cells and tight junction molecule expression in the intestinal epithelium of arthritic mice when compared with naive mice. P. gingivalis inoculation further downregulated intestinal RvD5n-3 DPA and Il-10 levels and the expression of gut tight junction proteins. RvD5n-3 DPA, but not its metabolite 17-oxo-RvD5n-3 DPA, increased the expression of both IL-10 and IL-10R in macrophages via the upregulation of the aryl hydrocarbon receptor agonist l-kynurenine. Administration of RvD5n-3 DPA to arthritic P. gingivalis-inoculated mice increased intestinal Il-10 expression, restored gut barrier function, and reduced joint inflammation. Together, these findings uncover mechanisms in the pathogenesis of rheumatoid arthritis, where disruption of the gut RvD5n-3 DPA-IL-10 axis weakens the gut barrier, which becomes permissive to the pathogenic actions of the pathobiont P. gingivalis.

A cross talk between dysbiosis and gut-associated immune system governs the development of inflammatory arthropathies

BACKGROUND

Emerging evidence suggests that dysbiosis, imbalanced gut microbial community, might be a key player in the development of various diseases, including inflammatory arthropathies, such as rheumatoid arthritis, spondyloarthritis (mainly, ankylosing spondylitis and psoriatic arthritis), and osteoarthritis. Yet, the underlying mechanisms and corresponding interactions remain poorly understood.

METHODS

We conducted a critical and extensive literature review to explore the association between dysbiosis and the development of inflammatory arthropathies. We also reviewed the literature to assess the perspectives that ameliorate inflammatory arthropathies by manipulating the microbiota with probiotics, prebiotics or fecal microbiota transplantation.

RESULTS

Some bacterial species (e.g. Prevotella, Citrobacter rodentium, Collinsella aerofaciens, Segmented filamentous bacteria) participate in the creation of the pro-inflammatory immune status, presumably via epitope mimicry, modification of self-antigens, enhanced cell apoptosis mechanisms, and destruction of tight junction proteins and intestinal barrier integrity, all leading to the development and maintainance of inflammatory arthropathies. Whether dysbiosis is an epiphenomenon or is an active driver of these disorders remains unclear, yet, recent observations clearly suggest that dysbiosis precedes and triggers their development implying a causative relationship between dysbiosis and inflammatory arthropathies. The underlying mechanisms include dysbiosis-mediated changes in the functional activity of the intestinal immune cell subsets, such as innate lymphoid cells, mucosa-associated invariant T cells, invariant natural killer T cells, T-follicular helper and T-regulatory cells. In turn, disturbed functionality of the gut-associated immune system is shown to promote the overgrowth of many bacteria, thus establishing a detrimental vicious circle of actively maintaining arthritis.

CONCLUSIONS

Analysis of the data described in the review supports the notion that a close, dynamic and tightly regulated cross talk between dysbiosis and the gut-associated immune system governs the development of inflammatory arthropathies.

Peptide-Based Inhibitors of Fimbrial Biogenesis in Porphyromonas gingivalis

Periodontitis is a progressive inflammatory disease that affects roughly half of American adults. Colonization of the oral cavity by the Gram-negative bacterial pathogen Porphyromonas gingivalis is a key event in the initiation and development of periodontal disease. Adhesive surface structures termed fimbriae (pili) mediate interactions of P. gingivalis with other bacteria and with host cells throughout the course of disease. The P. gingivalis fimbriae are assembled via a novel mechanism that involves proteolytic processing of lipidated precursor subunits and their subsequent polymerization on the bacterial surface. Given their extracellular assembly mechanism and central roles in pathogenesis, the P. gingivalis fimbriae are attractive targets for anti-infective therapeutics to prevent or treat periodontal disease. Here we confirm that conserved sequences in the N and C termini of the Mfa1 fimbrial subunit protein perform critical roles in subunit polymerization. We show that treatment of P. gingivalis with peptides corresponding to the conserved C-terminal region inhibits the extracellular assembly of Mfa fimbriae on the bacterial surface. We also show that peptide treatment interferes with the function of Mfa fimbriae by reducing P. gingivalis adhesion to Streptococcus gordonii in a dual-species biofilm model. Finally, we show that treatment of bacteria with similar peptides inhibits extracellular polymerization of the Fim fimbriae, which are also expressed by P. gingivalis These results support a donor strand-based assembly mechanism for the P. gingivalis fimbriae and demonstrate the feasibility of using extracellular peptides to disrupt the biogenesis and function of these critical periodontal disease virulence factors.

Talk to your gut: the oral-gut microbiome axis and its immunomodulatory role in the etiology of rheumatoid arthritis

Microbial communities inhabiting the human body, collectively called the microbiome, are critical modulators of immunity. This notion is underpinned by associations between changes in the microbiome and particular autoimmune disorders. Specifically, in rheumatoid arthritis, one of the most frequently occurring autoimmune disorders worldwide, changes in the oral and gut microbiomes have been implicated in the loss of tolerance against self-antigens and in increased inflammatory events promoting the damage of joints. In the present review, we highlight recently gained insights in the roles of microbes in the etiology of rheumatoid arthritis. In addition, we address important immunomodulatory processes, including biofilm formation and neutrophil function, which have been implicated in host-microbe interactions relevant for rheumatoid arthritis. Lastly, we present recent advances in the development and evaluation of emerging microbiome-based therapeutic approaches. Altogether, we conclude that the key to uncovering the etiopathogenesis of rheumatoid arthritis will lie in the immunomodulatory functions of the oral and gut microbiomes.