The capsule of Porphyromonas gingivalis leads to a reduction in the host inflammatory response, evasion of phagocytosis, and increase in virulence

Porphyromonas gingivalis interaction with Candida albicans allows for aerobic escape, virulence and adherence

In the oral cavity Candida albicans interacts with many oral bacteria, including Porphyromonas gingivalis, both physically and metabolically. The aim of this in vitro study was to characterize these interactions and study their effects on the survival of P. gingivalis. First, metabolic interactions were evaluated by counting the colony forming units (CFU) after co-culturing. The results indicated that the anaerobic bacterium P. gingivalis survives under aerobic conditions when co-cultured with C. albicans. This is due to the oxygen consumption by C. albicans as determined by a reduction in survival upon the addition of Antimycin A. By measuring the protease activity, it was found that the presence of C. albicans induced gingipain activity by P. gingivalis, which is an important virulence factor. Adherence of P. gingivalis to hyphae of C. albicans was observed with a dynamic flow system. Using various C. albicans mutants, it was shown that the mechanism of adhesion was mediated by the cell wall adhesins, members of the agglutinin-like sequence (Als) family: Als3 and Als1. Furthermore, the two microorganisms could be co-cultured into forming a biofilm in which P. gingivalis can survive under aerobic culturing conditions, which was imaged using scanning electron microscopy. This study has further elucidated mechanisms of interaction, virulence acquisition and survival of P. gingivalis when co-cultured with C. albicans. Such survival could be essential for the pathogenicity of P. gingivalis in the oxygen-rich niches of the oral cavity. This study has emphasized the importance of interaction between different microbes in promoting survival, virulence and attachment of pathogens, which could be essential in facilitating penetration into the environment of the host.

A pleiotropic role of sialidase in the pathogenicity of Porphyromonas gingivalis

As one of the keystone pathogens of periodontitis, the oral bacterium Porphyromonas gingivalis produces an array of virulence factors, including a recently identified sialidase (PG0352). Our previous report involving loss-of-function studies indicated that PG0352 plays an important role in the pathophysiology of P. gingivalis. However, this report had not been corroborated by gain-of-function studies or substantiated in different P. gingivalis strains. To fill these gaps, herein we first confirm the role of PG0352 in cell surface structures (e.g., capsule) and serum resistance using P. gingivalis W83 strain through genetic complementation and then recapitulate these studies using P. gingivalis ATCC33277 strain. We further investigate the role of PG0352 and its counterpart (PGN1608) in ATCC33277 in cell growth, biofilm formation, neutrophil killing, cell invasion, and P. gingivalis-induced inflammation. Our results indicate that PG0352 and PGN1608 are implicated in P. gingivalis cell surface structures, hydrophobicity, biofilm formation, resistance to complement and neutrophil killing, and host immune responses. Possible molecular mechanisms involved are also discussed. In summary, this report underscores the importance of sialidases in the pathophysiology of P. gingivalis and opens an avenue to elucidate their underlying molecular mechanisms.

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Human Coronary Artery Endothelial Cell Response to Porphyromonas gingivalis W83 in a Collagen Three-Dimensional Culture Model

P. gingivalis has been reported to be an endothelial cell inflammatory response inducer that can lead to endothelial dysfunction processes related to atherosclerosis; however, these studies have been carried out in vitro in cell culture models on two-dimensional (2D) plastic surfaces that do not simulate the natural environment where pathology develops. This work aimed to evaluate the pro-inflammatory response of human coronary artery endothelial cells (HCAECs) to P. gingivalis in a 3D cell culture model compared with a 2D cell culture. HCAECs were cultured for 7 days on type I collagen matrices in both cultures and were stimulated at an MOI of 1 or 100 with live P. gingivalis W83 for 24 h. The expression of the genes COX-2, eNOS, and vWF and the levels of the pro-inflammatory cytokines thromboxane A2 (TXA-2) and prostaglandin I2 (PGI2) were evaluated. P. gingivalis W83 in the 2D cell culture increased IL-8 levels at MOI 100 and decreased MCP-1 levels at both MOI 100 and MOI 1. In contrast, the 3D cell culture induced an increased gene expression of COX-2 at both MOIs and reduced MCP-1 levels at MOI 100, whereas the gene expression of eNOS, vWF, and IL-8 and the levels of TXA2 and PGI2 showed no significant changes. These data suggest that in the collagen 3D culture model, P. gingivalis W83 induces a weak endothelial inflammatory response.

Isolation, characterization, and fibroblast uptake of bacterial extracellular vesicles from Porphyromonas gingivalis strains

Periodontitis is an inflammatory condition caused by bacteria and represents a serious health problem worldwide as the inflammation damages the supporting tissues of the teeth and may predispose to systemic diseases. Porphyromonas gingivalis is considered a keystone periodontal pathogen that releases bacterial extracellular vesicles (bEVs) containing virulence factors, such as gingipains, that may contribute to the pathogenesis of periodontitis. This study aimed to isolate and characterize bEVs from three strains of P. gingivalis, investigate putative bEV uptake into human oral fibroblasts, and determine the gingipain activity of the bEVs. bEVs from three bacterial strains, ATCC 33277, A7A1-28, and W83, were isolated through ultrafiltration and size-exclusion chromatography. Vesicle size distribution was measured by nano-tracking analysis (NTA). Transmission electron microscopy was used for bEV visualization. Flow cytometry was used to detect bEVs and gingipain activity was measured with an enzyme assay using a substrate specific for arg-gingipain. The uptake of bEVs into oral fibroblasts was visualized using confocal microscopy. NTA showed bEV concentrations from 108 to 1011 particles/mL and bEV diameters from 42 to 356 nm. TEM pictures demonstrated vesicle-like structures. bEV-gingipains were detected both by flow cytometry and enzyme assay. Fibroblasts incubated with bEVs labeled with fluorescent dye displayed intracellular localization consistent with bEV internalization. In conclusion, bEVs from P. gingivalis were successfully isolated and characterized, and their uptake into human oral fibroblasts was documented. The bEVs displayed active gingipains demonstrating their origin from P. gingivalis and the potential role of bEVs in periodontitis.

Host insulin resistance caused by Porphyromonas gingivalis-review of recent progresses

Porphyromonas gingivalis (P. gingivalis) is a Gram-negative oral anaerobic bacterium that plays a key role in the pathogenesis of periodontitis. P. gingivalis expresses a variety of virulence factors that disrupt innate and adaptive immunity, allowing P. gingivalis to survive and multiply in the host and destroy periodontal tissue. In addition to periodontal disease, P.gingivalis is also associated with systemic diseases, of which insulin resistance is an important pathological basis. P. gingivalis causes a systemic inflammatory response, disrupts insulin signaling pathways, induces pancreatic β-cell hypofunction and reduced numbers, and causes decreased insulin sensitivity leading to insulin resistance (IR). In this paper, we systematically review the studies on the mechanism of insulin resistance induced by P. gingivalis, discuss the association between P. gingivalis and systemic diseases based on insulin resistance, and finally propose relevant therapeutic approaches. Overall, through a systematic review of the mechanisms related to systemic diseases caused by P. gingivalis through insulin resistance, we hope to provide new insights for future basic research and clinical interventions for related systemic diseases.

Sialidase facilitates Porphyromonas gingivalis immune evasion by reducing M1 polarization, antigen presentation, and phagocytosis of infected macrophages

Background

Porphyromonas gingivalis (P. gingivalis), a major pathogen of periodontitis, can evade host immune defenses. Previously, we found that P. gingivalis W83 sialidase gene mutant strain (ΔPG0352) was more easily cleared by macrophages. The aims of this study were to investigate the effects of sialidase in P. gingivalis on the polarization, antigen presentation, and phagocytosis of infected macrophages and to clarify the mechanism of P. gingivalis immune evasion.

Methods

Human monocytes U937 were differentiated to macrophages and infected with P. gingivalis W83, ΔPG0352, comΔPG0352, and Escherichia coli (E. coli). The phagocytosis of macrophages was observed by transmission electron microscopy and flow cytometry. ELISA or Griess reaction were used to examine the levels of interleukin-12 (IL-12), inducible nitric oxide synthase (iNOS) and interleukin-10 (IL-10), and the expressions of CD68, CD80 and CD206 were determined by flow cytometry. The expression of major histocompatibility complex-II (MHC-II) was detected by immunofluorescence. A rat periodontitis model was established to determine the M1 and M2 polarization of macrophages.

Results

Compare with P. gingivalis W83, ΔPG0352 increased the levels of IL-12, iNOS, CD80, and MHC-II and inhibited the levels of IL-10 and CD206. Macrophages phagocytosed 75.4% of ΔPG0352 and 59.5% of P. gingivalis W83. In the rat periodontitis model, the levels of M1 and M2 macrophages in P. gingivalis W83 group were both higher than those in ΔPG0352 group, while the ratio of M1/M2 was higher in the ΔPG0352 group. Alveolar bone absorption was lower in ΔPG0352 group.

Conclusion

Sialidase facilitates P. gingivalis immune evasion by reducing M1 polarization, antigen presentation, and phagocytosis of infected macrophages.

Illuminating the oral microbiome and its host interactions: animal models of disease

Periodontitis and caries are driven by complex interactions between the oral microbiome and host factors, i.e. inflammation and dietary sugars, respectively. Animal models have been instrumental in our mechanistic understanding of these oral diseases, although no single model can faithfully reproduce all aspects of a given human disease. This review discusses evidence that the utility of an animal model lies in its capacity to address a specific hypothesis and, therefore, different aspects of a disease can be investigated using distinct and complementary models. As in vitro systems cannot replicate the complexity of in vivo host-microbe interactions and human research is typically correlative, model organisms-their limitations notwithstanding-remain essential in proving causality, identifying therapeutic targets, and evaluating the safety and efficacy of novel treatments. To achieve broader and deeper insights into oral disease pathogenesis, animal model-derived findings can be synthesized with data from in vitro and clinical research. In the absence of better mechanistic alternatives, dismissal of animal models on fidelity issues would impede further progress to understand and treat oral disease.

Current concepts in the pathogenesis of periodontitis: from symbiosis to dysbiosis

The primary etiological agent for the initiation and progression of periodontal disease is the dental plaque biofilm which is an organized aggregation of microorganisms residing within a complex intercellular matrix. The non-specific plaque hypothesis was the first attempt to explain the role of the dental biofilm in the pathogenesis of periodontal diseases. However, the introduction of sophisticated diagnostic and laboratory assays has led to the realisation that the development of periodontitis requires more than a mere increase in the biomass of dental plaque. Indeed, multispecies biofilms exhibit complex interactions between the bacteria and the host. In addition, not all resident microorganisms within the biofilm are pathogenic, since beneficial bacteria exist that serve to maintain a symbiotic relationship between the plaque microbiome and the host's immune-inflammatory response, preventing the emergence of pathogenic microorganisms and the development of dysbiosis. This review aims to highlight the development and structure of the dental plaque biofilm and to explore current literature on the transition from a healthy (symbiotic) to a diseased (dysbiotic) biofilm in periodontitis and the associated immune-inflammatory responses that drive periodontal tissue destruction and form mechanistic pathways that impact other systemic non-communicable diseases.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Mechanisms of Porphyromonas gingivalis to translocate over the oral mucosa and other tissue barriers

Introduction

The oral pathogen Porphyromonas gingivalis is not only associated with periodontitis but also with systemic diseases elsewhere in the body. The mechanisms by which P. gingivalis travels from the oral cavity to other organs in the body are largely unknown. This review describes the four putative mechanisms supported by experimental evidence, which enable translocation of P. gingivalis over the oral mucosa, endothelial barriers and subsequent dissemination into the bloodstream.

Mechanisms

The first mechanism: proteolytic enzymes secreted by P. gingivalis degrade adhesion molecules between tissue cells, and the extracellular matrix. This weakens the structural integrity of the mucosa and allows P. gingivalis to penetrate the tissue. The second is transcytosis: bacteria actively enter tissue cells and transfer to the next layer or the extracellular space. By travelling from cell to cell, P. gingivalis reaches deeper structures. Thirdly, professional phagocytes take up P. gingivalis and travel to the bloodstream where P. gingivalis is released. Lastly, P. gingivalis can adhere to the hyphae forming Candida albicans. These hyphae can penetrate the mucosal tissue, which may allow P. gingivalis to reach deeper structures.

Conclusion

More research could elucidate targets to inhibit P. gingivalis dissemination and prevent the onset of various systemic diseases.

Modulatory Mechanisms of Pathogenicity in Porphyromonas gingivalis and Other Periodontal Pathobionts

The pathogenesis of periodontitis depends on a sustained feedback loop where bacterial virulence factors and immune responses both contribute to inflammation and tissue degradation. Periodontitis is a multifactorial disease that is associated with a pathogenic shift in the oral microbiome. Within this shift, low-abundance Gram-negative anaerobic pathobionts transition from harmless colonisers of the subgingival environment to a virulent state that drives evasion and subversion of innate and adaptive immune responses. This, in turn, drives the progression of inflammatory disease and the destruction of tooth-supporting structures. From an evolutionary perspective, bacteria have developed this phenotypic plasticity in order to respond and adapt to environmental stimuli or external stressors. This review summarises the available knowledge of genetic, transcriptional, and post-translational mechanisms which mediate the commensal-pathogen transition of periodontal bacteria. The review will focus primarily on Porphyromonas gingivalis.

Advances in novel therapeutic approaches for periodontal diseases

Periodontal diseases are pathological processes resulting from infections and inflammation affecting the periodontium or the tissue surrounding and supporting the teeth. Pathogenic bacteria living in complex biofilms initiate and perpetuate this disease in susceptible hosts. In some cases, broad-spectrum antibiotic therapy has been a treatment of choice to control bacterial infection. However, increasing antibiotic resistance among periodontal pathogens has become a significant challenge when treating periodontal diseases. Thanks to the improved understanding of the pathogenesis of periodontal disease, which involves the host immune response, and the importance of the human microbiome, the primary goal of periodontal therapy has shifted, in recent years, to the restoration of homeostasis in oral microbiota and its harmonious balance with the host periodontal tissues. This shift in therapeutic goals and the drug resistance challenge call for alternative approaches to antibiotic therapy that indiscriminately eliminate harmful or beneficial bacteria. In this review, we summarize the recent advancement of alternative methods and new compounds that offer promising potential for the treatment and prevention of periodontal disease. Agents that target biofilm formation, bacterial quorum-sensing systems and other virulence factors have been reviewed. New and exciting microbiome approaches, such as oral microbiota replacement therapy and probiotic therapy for periodontal disease, are also discussed.

Porphyromonas gingivalis Virulence Factors and Clinical Significance in Periodontal Disease and Coronary Artery Diseases

Porphyromonas gingivalis is a gram-negative, anaerobic bacterium that lives in the oral cavity. It is an integral part of the oral microbiome, which includes more than 500 types of bacteria. Under certain circumstances, as a consequence of virulence factors, it can become very destructive and proliferate to many cells in periodontal lesions. It is one of the causative agents present extremely often in dental plaque and is the main etiological factor in the development of periodontal disease. During various therapeutic procedures, P. gingivalis can enter the blood and disseminate through it to distant organs. This primarily refers to the influence of periodontal agents on the development of subacute endocarditis and can facilitate the development of coronary heart disease, atherosclerosis, and ischemic infarction. The action of P. gingivalis is facilitated by numerous factors of virulence and pathogenicity such as fimbriae, hemolysin, hemagglutinin, capsules, outer membrane vesicles, lipopolysaccharides, and gingipains. A special problem is the possibility of biofilm formation. P. gingivalis in a biofilm is 500 to 1000 times less sensitive to antimicrobial drugs than planktonic cells, which represents a significant problem in the treatment of infections caused by this pathogen.

How Porphyromonas gingivalis Navigate the Map: The Effect of Surface Topography on the Adhesion of Porphyromonas gingivalis on Biomaterials

The main purpose of this study is to develop an understanding of how Porphyromonas gingivalis responds to subperiosteal implant surface topography. A literature review was drawn from various electronic databases from 2000 to 2021. The two main keywords used were "Porphyromonas gingivalis" and "Surface Topography". We excluded all reviews and or meta-analysis articles, articles not published in English, and articles with no surface characterization process or average surface roughness (Ra) value. A total of 26 selected publications were then included in this study. All research included showed the effect of topography on Porphyromonas gingivalis to various degrees. It was found that topography features such as size and shape affected Porphyromonas gingivalis adhesion to subperiosteal implant materials. In general, a smaller Ra value reduces Porphyromonas gingivalis regardless of the type of materials, with a threshold of 0.3 µm for titanium.

Leuconostoc mesenteroides LVBH107 Antibacterial Activity against Porphyromonas gingivalis and Anti-Inflammatory Activity against P. gingivalis Lipopolysaccharide-Stimulated RAW 264.7 Cells

Probiotics, active microorganisms benefiting human health, currently serve as nutritional supplements and clinical treatments. Periodontitis, a chronic infectious oral disease caused by Porphyromonas gingivalis (P. gingivalis), activates the host immune response to release numerous proinflammatory cytokines. Here, we aimed to clarify Leuconostoc mesenterica (L. mesenteroides) LVBH107 probiotic effects based on the inhibition of P.gingivalis activities while also evaluating the effectiveness of an in vitro P.gingivalis lipopolysaccharide-stimulated RAW 264.7 cell-based inflammation mode. L. mesenteroides LVBH107 survived at acid, bile salts, lysozyme, and hydrogen peroxide conditions, auto-aggregated and co-aggregated with P. gingivalis, exhibited strong hydrophobicity and electrostatic action, and strongly adhered to gingival epithelial and HT-29 cells (thus exhibiting oral tissue adherence and colonization abilities). Moreover, L.mesenteroides LVBH107 exhibited sensitivity to antibiotics erythromycin, doxycycline, minocycline, ampicillin, and others (thus indicating it lacked antibiotic resistance plasmids), effectively inhibited P.gingivalis biofilm formation and inflammation (in vitro inflammation model), reduced the secretion of pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) and inflammatory mediators (NO and PGE₂), and decreased the expression levels of inflammation related genes. Thus, L.mesenterica LVBH107 holds promise as a probiotic that can inhibit P.gingivalis biofilm formation and exert anti-inflammatory activity to maintain oral health.

Characterization of a Bacterial Kinase That Phosphorylates Dihydrosphingosine to Form dhS1P

Like other members of the phylum Bacteroidetes, the oral anaerobe Porphyromonas gingivalis synthesizes a variety of sphingolipids, similar to its human host. Studies have shown that synthesis of these lipids (dihydroceramides [DHCs]) is involved in oxidative stress resistance, the survival of P. gingivalis during stationary phase, and immune modulation. Here, we constructed a deletion mutant of P. gingivalis strain W83 with a deletion of the gene encoding DhSphK1, a protein that shows high similarity to a eukaryotic sphingosine kinase, an enzyme that phosphorylates sphingosine to form sphingosine-1-phosphate. Our data show that deletion of the dhSphK1 gene results in a shift in the sphingolipid composition of P. gingivalis cells; specifically, the mutant synthesizes higher levels of phosphoglycerol DHCs (PG-DHCs) than the parent strain W83. Although PG1348 shows high similarity to the eukaryotic sphingosine kinase, we discovered that the PG1348 enzyme is unique, since it preferentially phosphorylates dihydrosphingosine, not sphingosine. Besides changes in lipid composition, the W83 ΔPG1348 mutant displayed a defect in cell division, the biogenesis of outer membrane vesicles (OMVs), and the amount of K antigen capsule. Taken together, we have identified the first bacterial dihydrosphingosine kinase whose activity regulates the lipid profile of P. gingivalis and underlies a regulatory mechanism of immune modulation. IMPORTANCE Sphingoid base phosphates, such as sphingosine-1-phosphate (S1P) and dihydrosphingosine-1-phosphate (dhS1P), act as ligands for S1P receptors, and this interaction is known to play a central role in mediating angiogenesis, vascular stability and permeability, and immune cell migration to sites of inflammation. Studies suggest that a shift in ratio to higher levels of dhS1P in relation to S1P alters downstream signaling cascades due to differential binding and activation of the various S1P receptor isoforms. Specifically, higher levels of dhS1P are thought to be anti-inflammatory. Here, we report on the characterization of a novel kinase in Porphyromonas gingivalis that phosphorylates dihydrosphingosine to form dhS1P.

Role of PG0192 and PG0193 in the modulation of pro-inflammatory cytokines in macrophages in response to Porphyromonas gingivalis

Porphyromonas gingivalis is the main pathogen of chronic periodontitis. However, the specific mechanisms through which P. gingivalis induces immune and inflammatory responses in periodontitis have not been completely elucidated. In this study, we investigated the effects of the P. gingivalis outer membrane protein OmpH (encoded by PG0192 and PG0193) on interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expression in macrophages to assess the pro-inflammatory cytokine responses. A PG0192-PG0193 deletion mutant strain and a com△PG0192-0193 strain were constructed. Furthermore, rOmpH-1 and rOmpH-2 encoded by PG0192 and PG0193, respectively, were cloned, expressed, and purified for subsequent experiments. Notably, the expression of IL-6 and TNF-α at mRNA and protein levels was downregulated upon treatment of macrophages with the PG0192-PG0193 deletion mutant strain, whereas treatment of macrophages with P. gingivalis W83 co-incubated with rOmpH-1 or rOmpH-2 upregulated IL-6 and TNF-α mRNA levels. The addition of C5aR antagonist blocked this induction. Overall, our findings provided important insights into the roles of PG0192 and PG0193 for promoting IL-6 and TNF-α expression in macrophages exposed to P. gingivalis and revealed the involvement of C5aR in the pro-inflammatory response.

Dysbiosis of the duodenal microbiota as a diagnostic marker for pancreaticobiliary cancer

BACKGROUND

Pancreaticobiliary cancer (PB Ca) is a lethal disease, and a useful diagnostic marker is urgently needed. A correlation between the human microbiota and malignant gastrointestinal diseases was recently reported.

AIM

To investigate the efficacy of the duodenal microbiota for diagnosing PB Ca.

METHODS

We recruited 22 patients with benign pancreaticobiliary diseases (benign group) and 12 patients with PB Ca (malignant group). The duodenal microbiota of each patient was analyzed by the 16S rDNA terminal restriction fragment length polymorphism method. Patient characteristics, tumor markers, and relative abundances of the duodenal microbiota were compared between the benign and malignant groups.

RESULTS

Cancer antigen 19-9 (CA19-9), Bifidobacterium, Clostridium cluster XVIII, and Prevotella levels differed significantly between the benign and malignant groups. Clostridium cluster XVIII had the greatest area under the receiver operating characteristic curve (AUC) among the four factors with respect to diagnosing PB Ca (cutoff value: 3.038%; sensitivity: 58.3%; specificity: 95.2%; AUC: 0.81). The combination of Clostridium cluster XVIII (cutoff value: 3.038%) and CA19-9 Levels (cutoff value: 18.8 U/mL) showed 91.7% sensitivity and 71.4% specificity for diagnosing PB Ca.

CONCLUSION

The duodenal microbiota may be useful for PB Ca screening.

Oral-Gut-Brain Axis in Experimental Models of Periodontitis: Associating Gut Dysbiosis With Neurodegenerative Diseases

Periodontitis is considered a non-communicable chronic disease caused by a dysbiotic microbiota, which generates a low-grade systemic inflammation that chronically damages the organism. Several studies have associated periodontitis with other chronic non-communicable diseases, such as cardiovascular or neurodegenerative diseases. Besides, the oral bacteria considered a keystone pathogen, Porphyromonas gingivalis, has been detected in the hippocampus and brain cortex. Likewise, gut microbiota dysbiosis triggers a low-grade systemic inflammation, which also favors the risk for both cardiovascular and neurodegenerative diseases. Recently, the existence of an axis of Oral-Gut communication has been proposed, whose possible involvement in the development of neurodegenerative diseases has not been uncovered yet. The present review aims to compile evidence that the dysbiosis of the oral microbiota triggers changes in the gut microbiota, which creates a higher predisposition for the development of neuroinflammatory or neurodegenerative diseases.The Oral-Gut-Brain axis could be defined based on anatomical communications, where the mouth and the intestine are in constant communication. The oral-brain axis is mainly established from the trigeminal nerve and the gut-brain axis from the vagus nerve. The oral-gut communication is defined from an anatomical relation and the constant swallowing of oral bacteria. The gut-brain communication is more complex and due to bacteria-cells, immune and nervous system interactions. Thus, the gut-brain and oral-brain axis are in a bi-directional relationship. Through the qualitative analysis of the selected papers, we conclude that experimental periodontitis could produce both neurodegenerative pathologies and intestinal dysbiosis, and that periodontitis is likely to induce both conditions simultaneously. The severity of the neurodegenerative disease could depend, at least in part, on the effects of periodontitis in the gut microbiota, which could strengthen the immune response and create an injurious inflammatory and dysbiotic cycle. Thus, dementias would have their onset in dysbiotic phenomena that affect the oral cavity or the intestine. The selected studies allow us to speculate that oral-gut-brain communication exists, and bacteria probably get to the brain via trigeminal and vagus nerves.

Porphyromonas gingivalis outside the oral cavity

Porphyromonas gingivalis, a Gram-negative anaerobic bacillus present in periodontal disease, is considered one of the major pathogens in periodontitis. A literature search for English original studies, case series and review articles published up to December 2019 was performed using the MEDLINE, PubMed and GoogleScholar databases, with the search terms "Porphyromonas gingivalis" AND the potentially associated condition or systemic disease Abstracts and full text articles were used to make a review of published research literature on P. gingivalis outside the oral cavity. The main points of interest of this narrative review were: (i) a potential direct action of the bacterium and not the systemic effects of the inflammatory acute-phase response induced by the periodontitis, (ii) the presence of the bacterium (viable or not) in the organ, or (iii) the presence of its virulence factors. Virulence factors (gingipains, capsule, fimbriae, hemagglutinins, lipopolysaccharide, hemolysin, iron uptake transporters, toxic outer membrane blebs/vesicles, and DNA) associated with P. gingivalis can deregulate certain functions in humans, particularly host immune systems, and cause various local and systemic pathologies. The most recent studies linking P. gingivalis to systemic diseases were discussed, remembering particularly the molecular mechanisms involved in different infections, including cerebral, cardiovascular, pulmonary, bone, digestive and peri-natal infections. Recent involvement of P. gingivalis in neurological diseases has been demonstrated. P. gingivalis modulates cellular homeostasis and increases markers of inflammation. It is also a factor in the oxidative stress involved in beta-amyloid production.

A Porphyromonas gingivalis Capsule-Conjugate Vaccine Protects From Experimental Oral Bone Loss

Periodontal diseases are chronic inflammatory diseases of the periodontium that result in progressive destruction of the soft and hard tissues supporting the teeth, and it is the most common cause of tooth loss among adults. In the US alone, over 100 million individuals are estimated to have periodontal disease. Subgingival bacteria initiate and sustain inflammation, and, although several bacteria have been associated with periodontitis, Porphyromonas gingivalis has emerged as the key etiological organism significantly contributing to the disease. Currently, intensive clinical maintenance strategies are deployed to mitigate the further progression of disease in afflicted individuals; however, these treatments often fail to stop disease progression, and, as such, the development of an effective vaccine for periodontal disease is highly desirable. We generated a conjugate vaccine, comprising of the purified capsular polysaccharide of P. gingivalis conjugated to eCRM®, a proprietary and enhanced version of the CRM197 carrier protein with predetermined conjugation sites (Pg-CV). Mice immunized with alum adjuvanted Pg-CV developed robust serum levels of whole organism-specific IgG in comparison to animals immunized with unconjugated capsular polysaccharide alone. Using the murine oral bone loss model, we observed that mice immunized with the capsule-conjugate vaccine were significantly protected from the effects of P. gingivalis-elicited oral bone loss. Employing a preclinical model of infection-elicited oral bone loss, our data support that a conjugate vaccine incorporating capsular polysaccharide antigen is effective in reducing the main clinical endpoint of periodontal disease-oral bone destruction. Further development of a P. gingivalis capsule-based conjugate vaccine for preventing periodontal diseases is supported.

Gemella haemolysans inhibits the growth of the periodontal pathogen Porphyromonas gingivalis

The oral microbiome plays an important role in the human microbial community and in maintaining the health of an individual. Imbalances in the oral microbiome may contribute to oral and systemic diseases. The progression of periodontal disease is closely related to the growth of bacteria, such as Porphyromonas gingivalis, in the oral cavity. However, the pathogen growth mechanism specific to periodontal disease remains unknown. This study aimed to identify bacteria associated with periodontal health by focusing on hemolytic bacteria. Unstimulated saliva samples were collected from ten periodontitis patients and five healthy subjects to detect and identify the presence of hemolytic bacteria. The saliva of healthy subjects contained a higher proportion of G. haemolysans than saliva samples from patients with periodontitis. Growth inhibition assays indicated that the protein components contained in the culture supernatant of G. haemolysans directly suppressed the growth of P. gingivalis. This study shows that the presence of G. haemolysans in saliva is associated with periodontal health and that it inhibits the growth of P. gingivalis in vitro.

Taxonomic and Gene Category Analyses of Subgingival Plaques from a Group of Japanese Individuals with and without Periodontitis

Periodontitis is an inflammation of tooth-supporting tissues, which is caused by bacteria in the subgingival plaque (biofilm) and the host immune response. Traditionally, subgingival pathogens have been investigated using methods such as culturing, DNA probes, or PCR. The development of next-generation sequencing made it possible to investigate the whole microbiome in the subgingival plaque. Previous studies have implicated dysbiosis of the subgingival microbiome in the etiology of periodontitis. However, details are still lacking. In this study, we conducted a metagenomic analysis of subgingival plaque samples from a group of Japanese individuals with and without periodontitis. In the taxonomic composition analysis, genus Bacteroides and Mycobacterium demonstrated significantly different compositions between healthy sites and sites with periodontal pockets. The results from the relative abundance of functional gene categories, carbohydrate metabolism, glycan biosynthesis and metabolism, amino acid metabolism, replication and repair showed significant differences between healthy sites and sites with periodontal pockets. These results provide important insights into the shift in the taxonomic and functional gene category abundance caused by dysbiosis, which occurs during the progression of periodontal disease.

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.

Epstein-Barr Virus-Oral Bacterial Link in the Development of Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is the most common type of oral cancer. Its development has been associated with diverse factors such as tobacco smoking and alcohol consumption. In addition, it has been suggested that microorganisms are risk factors for oral carcinogenesis. Epstein-Barr virus (EBV), which establishes lifelong persistent infections and is intermittently shed in the saliva, has been associated with several lymphomas and carcinomas that arise in the oral cavity. In particular, it has been detected in a subset of OSCCs. Moreover, its presence in patients with periodontitis has also been described. Porphyromonas gingivalis (P. gingivalis) is an oral bacterium in the development of periodontal diseases. As a keystone pathogen of periodontitis, P. gingivalis is known not only to damage local periodontal tissues but also to evade the host immune system and eventually affect systemic health. Persistent exposure to P. gingivalis promotes tumorigenic properties of oral epithelial cells, suggesting that chronic P. gingivalis infection is a potential risk factor for OSCC. Given that the oral cavity serves as the main site where EBV and P. gingivalis are harbored, and because of their oncogenic potential, we review here the current information about the participation of these microorganisms in oral carcinogenesis, describe the mechanisms by which EBV and P. gingivalis independently or synergistically can collaborate, and propose a model of interaction between both microorganisms.

Alzheimer's Disease-Like Pathology Triggered by Porphyromonas gingivalis in Wild Type Rats Is Serotype Dependent

Periodontal disease is a disease of tooth-supporting tissues. It is a chronic disease with inflammatory nature and infectious etiology produced by a dysbiotic subgingival microbiota that colonizes the gingivodental sulcus. Among several periodontal bacteria, Porphyromonas gingivalis (P. gingivalis) highlights as a keystone pathogen. Previous reports have implied that chronic inflammatory response and measurable bone resorption are observed in young mice, even after a short period of periodontal infection with P. gingivalis, which has been considered as a suitable model of experimental periodontitis. Also, encapsulated P. gingivalis strains are more virulent than capsular-defective mutants, causing an increased immune response, augmented osteoclastic activity, and accrued alveolar bone resorption in these rodent experimental models of periodontitis. Recently, P. gingivalis has been associated with Alzheimer’s disease (AD) pathogenesis, either by worsening brain pathology in AD-transgenic mice or by inducing memory impairment and age-dependent neuroinflammation middle-aged wild type animals. We hypothesized here that the more virulent encapsulated P. gingivalis strains could trigger the appearance of brain AD-markers, neuroinflammation, and cognitive decline even in young rats subjected to a short periodontal infection exposure, due to their higher capacity of activating brain inflammatory responses. To test this hypothesis, we periodontally inoculated 4-week-old male Sprague-Dawley rats with K1, K2, or K4 P. gingivalis serotypes and the K1-isogenic non-encapsulated mutant (GPA), used as a control. 45-days after periodontal inoculations with P. gingivalis serotypes, rat´s spatial memory was evaluated for six consecutive days in the Oasis maze task. Following functional testing, the animals were sacrificed, and various tissues were removed to analyze alveolar bone resorption, cytokine production, and detect AD-specific biomarkers. Strikingly, only K1 or K2 P. gingivalis-infected rats displayed memory deficits, increased alveolar bone resorption, pro-inflammatory cytokine production, changes in astrocytic morphology, increased Aβ1-42 levels, and Tau hyperphosphorylation in the hippocampus. None of these effects were observed in rats infected with the non-encapsulated bacterial strains. Based on these results, we propose that the bacterial virulence factors constituted by capsular polysaccharides play a central role in activating innate immunity and inflammation in the AD-like pathology triggered by P. gingivalis in young rats subjected to an acute experimental infection episode.

Inherently and Conditionally Essential Protein Catabolism Genes of Porphyromonas gingivalis

Proteases are critical virulence determinants of Porphyromonas gingivalis, an emerging Alzheimer's disease, cancer, and arthritis pathogen and established agent of periodontitis. Transposon sequencing has been employed to define the core essential genome of this bacterium and genes conditionally essential in multiple environments - abscess formation; epithelial colonization; and cigarette smoke toxin exposure; as well as to elucidate genes required for iron acquisition and a functional type 9 secretion system. Validated and predicted protein catabolism genes identified include a combination of established virulence factors and a larger set of seemingly more mundane proteolytic genes. The functions and relevance of genes that share essentiality in multiple disease-relevant conditions are examined. These common stress-related genes may represent particularly attractive therapeutic targets for the control of P. gingivalis infections.

Antibacterial activity of nitric oxide-releasing carboxymethylcellulose against periodontal pathogens

The prevalence of periodontal disease poses a significant global health burden. Treatments for these diseases, primarily focused on removal and eradication of dental plaque biofilms, are challenging due to limited access to periodontal pockets where these oral pathogens reside. Herein, we report on the development and characterization of nitric oxide (NO)-releasing carboxymethylcellulose (CMC) derivatives and evaluate their in vitro bactericidal efficacy against planktonic Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, two prominent periodontopathogens. Bactericidal exposure assays revealed that three of the synthesized NO-releasing polymers were capable of reducing bacterial viability of both species by 99.9% in 2 hr at concentrations of 4 mg ml^-1 or lower, reflecting NO's potent and rapid bactericidal action. The NO-releasing CMCs elicited minimal toxicity to human gingival fibroblasts at their bactericidal concentrations following 24-hr exposure.

Virulence mechanisms used in the pathogenesis of periodontal diseases caused by Porphyromonas gingivalis

Periodontal diseases are characterized by progressive inflammation that destroys the tooth-supporting tissues, leading to gum bleeding and tooth loss. Porphyromonas gingivalis is considered one of the main etiological agents responsible for the initiation and progression of chronic periodontitis. This gram-negative, anaerobic bacterium is a part of a multi-species oral biofilm. P. gingivalis does not have the full pathway of protoporphyrin IX synthesis, nor does it produce siderophores. Therefore, for survival and proliferation, it requires heme as a source of iron and protoporphyrin IX. In order to obtain heme, P. gingivalis uses a number of mechanisms that affect the ability of this bacterium to initiate a pathological condition. This review presents the current knowledge regarding the best-known and characterized systems involved in heme acquisition by P. gingivalis. We focused on processes occurring in the initial states of infection, where gingipain, hemagglutinins, and hemolysins play a crucial role. The mechanisms encoded by hmu, iht and hus operons, including proteins with hemophore-like properties, as well as TonB-dependent outer membrane receptors are described. We present their function and participation in the progression of the infection. In addition, we describe mechanisms produced by P. gingivalis and other periodontopathogens in synergistic processes promoting the growth and virulence of P. gingivalis. We also describe processes regulating iron and heme homeostasis, including the homolog of the Fur protein, the two-component system HaeSR, as well as the OxyR, SigH, and PgDps proteins.

Lactobacillus-Derived Bioactive Metabolites for the Regulation of Periodontal Health: Evidences to Clinical Setting

Background: Gut microbiota plays a pivotal role in regulating host metabolism that affects the systemic health. To date, several studies have confirmed the fact that microbiota interacts with host, modulating immunity, controlling the homeostasis environment, and maintaining systemic condition. Recent studies have focused on the protective function of poly unsaturated fatty acids, 10-oxo-trans-11-oxadecenoic acid (KetoC) and 10-hydroxy-cis-12-octadecenoic acid (HYA), generated by gut microbiota on periodontal disease. Nevertheless, the mechanism remains unclear as investigations are limited to in vivo and in vitro studies. In this present review, we found that the administration of metabolites, KetoC and HYA, by a probiotic gut microbiota Lactobacillus plantarum from linoleic acid is found to inhibit the oxidation process, possess an antimicrobial function, and prevent the inflammation. These findings suggest the promising use of functional lipids for human health. Conclusion: Protective modalities of bioactive metabolites may support periodontal therapy by suppressing bacterial dysbiosis and regulating periodontal homeostasis in the clinical setting.

Herpesvirus-bacteria synergistic interaction in periodontitis

The etiopathogenesis of severe periodontitis includes herpesvirus-bacteria coinfection. This article evaluates the pathogenicity of herpesviruses (cytomegalovirus and Epstein-Barr virus) and periodontopathic bacteria (Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis) and coinfection of these infectious agents in the initiation and progression of periodontitis. Cytomegalovirus and A. actinomycetemcomitans/P. gingivalis exercise synergistic pathogenicity in the development of localized ("aggressive") juvenile periodontitis. Cytomegalovirus and Epstein-Barr virus are associated with P. gingivalis in adult types of periodontitis. Periodontal herpesviruses that enter the general circulation may also contribute to disease development in various organ systems. A 2-way interaction is likely to occur between periodontal herpesviruses and periodontopathic bacteria, with herpesviruses promoting bacterial upgrowth, and bacterial factors reactivating latent herpesviruses. Bacterial-induced gingivitis may facilitate herpesvirus colonization of the periodontium, and herpesvirus infections may impede the antibacterial host defense and alter periodontal cells to predispose for bacterial adherence and invasion. Herpesvirus-bacteria synergistic interactions, are likely to comprise an important pathogenic determinant of aggressive periodontitis. However, mechanistic investigations into the molecular and cellular interaction between periodontal herpesviruses and bacteria are still scarce. Herpesvirus-bacteria coinfection studies may yield significant new discoveries of pathogenic determinants, and drug and vaccine targets to minimize or prevent periodontitis and periodontitis-related systemic diseases.

Roles of Porphyromonas gingivalis and its virulence factors in periodontitis

Periodontitis is an infection-driven inflammatory disease, which is characterized by gingival inflammation and bone loss. Periodontitis is associated with various systemic diseases, including cardiovascular, respiratory, musculoskeletal, and reproductive system related abnormalities. Recent theory attributes the pathogenesis of periodontitis to oral microbial dysbiosis, in which Porphyromonas gingivalis acts as a critical agent by disrupting host immune homeostasis. Lipopolysaccharide, proteases, fimbriae, and some other virulence factors are among the strategies exploited by P. gingivalis to promote the bacterial colonization and facilitate the outgrowth of the surrounding microbial community. Virulence factors promote the coaggregation of P. gingivalis with other bacteria and the formation of dental biofilm. These virulence factors also modulate a variety of host immune components and subvert the immune response to evade bacterial clearance or induce an inflammatory environment. In this chapter, our focus is to discuss the virulence factors of periodontal pathogens, especially P. gingivalis, and their roles in regulating immune responses during periodontitis progression.

Porphyromonas gingivalis Tyrosine Phosphatase Php1 Promotes Community Development and Pathogenicity

Protein-tyrosine phosphorylation in bacteria plays a significant role in multiple cellular functions, including those related to community development and virulence. Metal-dependent protein tyrosine phosphatases that belong to the polymerase and histindinol phosphatase (PHP) family are widespread in Gram-positive bacteria. Here, we show that Porphyromonas gingivalis, a Gram-negative periodontal pathogen, expresses a PHP protein, Php1, with divalent metal ion-dependent tyrosine phosphatase activity. Php1 tyrosine phosphatase activity was attenuated by mutation of conserved histidine residues that are important for the coordination of metal ions and by mutation of a conserved arginine residue, a key residue for catalysis in other bacterial PHPs. The php1 gene is located immediately downstream of the gene encoding the bacterial tyrosine (BY) kinase Ptk1, which was a substrate for Php1 in vitro Php1 rapidly caused the conversion of Ptk1 to a state of low tyrosine phosphorylation in the absence of discernible intermediate phosphoforms. Active Php1 was required for P. gingivalis exopolysaccharide production and for community development with the antecedent oral biofilm constituent Streptococcus gordonii under nutrient-depleted conditions. In contrast, the absence of Php1 had no effect on the ability of P. gingivalis to form monospecies biofilms. In vitro, Php1 enzymatic activity was resistant to the effects of the streptococcal secreted metabolites pABA and H2O2, which inhibited Ltp1, an enzyme in the low-molecular-weight (LMW) phosphotyrosine phosphatase family. Ptk1 reciprocally phosphorylated Php1 on tyrosine residues 159 and 161, which independently impacted phosphatase activity. Loss of Php1 rendered P. gingivalis nonvirulent in an animal model of periodontal disease. Collectively, these results demonstrate that P. gingivalis possesses active PHP and LMW tyrosine phosphatases, a unique configuration in Gram-negatives which may allow P. gingivalis to maintain phosphorylation/dephosphorylation homeostasis in multispecies communities. Moreover, Php1 contributes to the pathogenic potential of the organism.IMPORTANCE Periodontal diseases are among the most common infections of humans and are also associated with systemic inflammatory conditions. Colonization and pathogenicity of P. gingivalis are regulated by signal transduction pathways based on protein tyrosine phosphorylation and dephosphorylation. Here, we identify and characterize a novel component of the tyrosine (de)phosphorylation axis: a polymerase and histindinol phosphatase (PHP) family enzyme. This tyrosine phosphatase, designated Php1, was required for P. gingivalis community development with other oral bacteria, and in the absence of Php1 activity P. gingivalis was unable to cause disease in a mouse model of periodontitis. This work provides significant insights into the protein tyrosine (de)phosphorylation network in P. gingivalis, its adaptation to heterotypic communities, and its contribution to colonization and virulence.

Importance of Virulence Factors for the Persistence of Oral Bacteria in the Inflamed Gingival Crevice and in the Pathogenesis of Periodontal Disease

Periodontitis is a chronic inflammation that develops due to a destructive tissue response to prolonged inflammation and a disturbed homeostasis (dysbiosis) in the interplay between the microorganisms of the dental biofilm and the host. The infectious nature of the microbes associated with periodontitis is unclear, as is the role of specific bacterial species and virulence factors that interfere with the host defense and tissue repair. This review highlights the impact of classical virulence factors, such as exotoxins, endotoxins, fimbriae and capsule, but also aims to emphasize the often-neglected cascade of metabolic products (e.g., those generated by anaerobic and proteolytic metabolism) that are produced by the bacterial phenotypes that survive and thrive in deep, inflamed periodontal pockets. This metabolic activity of the microbes aggravates the inflammatory response from a low-grade physiologic (homeostatic) inflammation (i.e., gingivitis) into more destructive or tissue remodeling processes in periodontitis. That bacteria associated with periodontitis are linked with a number of systemic diseases of importance in clinical medicine is highlighted and exemplified with rheumatoid arthritis, The unclear significance of a number of potential "virulence factors" that contribute to the pathogenicity of specific bacterial species in the complex biofilm-host interaction clinically is discussed in this review.

Pathogenesis of Important Virulence Factors of Porphyromonas gingivalis via Toll-Like Receptors

Periodontitis is a common intraoral infection and is inextricably linked to systemic diseases. Recently, the regulation between host immunologic response and periodontal pathogens has become a hotspot to explain the mechanism of periodontitis and related systemic diseases. Since Porphyromonas gingivalis (P. gingivalis) was proved as critical periodontal pathogen above all, researches focusing on the mechanism of its virulence factors have received extensive attention. Studies have shown that in the development of periodontitis, in addition to the direct release of virulent factors by periodontal pathogens to destroy periodontal tissues, over-low or over-high intrinsic immune and inflammatory response mediated by Toll-like receptors (TLRs) can lead to more lasting destruction of periodontal tissues. It is very necessary to sort out how various cytopathic factors of P. gingivalis mediate inflammation and immune responses between the host through TLRs so as to help precisely prevent, diagnose, and treat periodontitis in clinic. This review summarizes the role of three most widely studied pathogenic factors produced by P. gingivalis (lipopolysaccharide, gingipains, pili) and their interactions with TLRs at the cellular and molecular level in the progress of periodontitis.

The Role of Exopolysaccharides in Oral Biofilms

The oral cavity contains a rich consortium of exopolysaccharide-producing microbes. These extracellular polysaccharides comprise a major component of the oral biofilm. Together with extracellular proteins, DNA, and lipids, they form the biofilm matrix, which contributes to bacterial colonization, biofilm formation and maintenance, and pathogenesis. While a number of oral microbes have been studied in detail with regard to biofilm formation and pathogenesis, the exopolysaccharides have been well characterized for only select organisms, namely Streptococcus mutans and Aggregatibacter actinomycetemcomitans. Studies on the exopolysaccharides of other oral organisms, however, are in their infancy. In this review, we present the current research on exopolysaccharides of oral microbes regarding their biosynthesis, regulation, contributions to biofilm formation and stability of the matrix, and immune evasion. In addition, insight into the role of exopolysaccharides in biofilms is highlighted through the evaluation of emerging techniques such as pH probing of biofilm colonies, solid-state nuclear magnetic resonance for macromolecular interactions within biofilms, and super-resolution microscopy analysis of biofilm development. Finally, exopolysaccharide as a potential nutrient source for species within a biofilm is discussed.

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.

Novel Assay To Characterize Neutrophil Responses to Oral Biofilms

Neutrophils, the most numerous leukocytes, play an important role in maintaining oral health through interactions with oral microbial biofilms. Both neutrophil hyperactivity and the bacterial subversion of neutrophil responses can cause inflammation-mediated tissue damage like that seen in periodontal disease. We describe here an assay that assesses neutrophil activation responses to monospecies biofilm bacteria in vitro based on the surface expression of cluster of differentiation (CD) markers associated with various neutrophil functions. Most of what we know about neutrophil responses to bacteria is based on in vitro assays that use planktonic bacteria and isolated/preactivated neutrophils, which makes interpretation of the neutrophil responses to bacteria a challenge. An understanding of how neutrophils differentially interact with and respond to commensal and pathogenic oral bacteria is necessary in order to further understand the neutrophil's role in maintaining oral health and the pathogenesis of periodontal disease. In this study, a flow cytometry-based in vitro assay was developed to characterize neutrophil activation states based on CD marker expressions in response to oral monospecies bacterial biofilms. Using this approach, changes in CD marker expressions in response to specific prominent oral commensal and pathogenic bacteria were assayed. Several functional assays, including assays for phagocytosis, production of reactive oxygen species, activation of the transcription factor Nrf2, neutrophil extracellular trap formation, and myeloperoxidase release, were also performed to correlate neutrophil function with CD marker expression. Our results demonstrate that neutrophils display bacterial species-specific responses. This assay can be used to characterize how specific biofilms alter specific neutrophil pathways associated with their activation.

Capsular-defective Porphyromonas gingivalis mutant strains induce less alveolar bone resorption than W50 wild-type strain due to a decreased Th1/Th17 immune response and less osteoclast activity

BACKGROUND

Encapsulation of Porphyromonas gingivalis has been demonstrated as responsible of several host immunological changes, which have been associated with the pathogenesis of periodontitis. Using a murine model of periodontitis and two isogenic non-capsulated mutants of P. gingivalis, this study aimed to analyze whether P. gingivalis encapsulation induces more severe alveolar bone resorption, and whether this bone loss is associated with a T-helper (Th)1 and Th17-pattern of immune response.

METHODS

Experimental periodontal infections were generated by oral inoculation with the encapsulated W50 wild-type strain or isogenic non-encapsulated ΔPG0116-PG0120 (GPA) and ΔPG0109-PG0118 (GPC) mutants of P. gingivalis. Periodontal infections induced with the encapsulated HG184 or non-encapsulated ATCC 33277 strains of P. gingivalis were used as controls. Alveolar bone resorption was analyzed using microcomputed tomography and scanning electron microscopy. The expression levels of Th1, Th2, Th17, or T regulatory-associated cytokines and RANKL, as well as the periodontal bacterial load, were quantified by quantitative polymerase chain reaction. The detection of Th1 and Th17 lymphocytes was analyzed by flow cytometry.

RESULTS

In the periodontal lesions, both capsular-defective knockout mutant strains of P. gingivalis induced less alveolar bone resorption than the encapsulated W50 wild-type strain. This decreased bone loss was associated with a dismissed RANKL expression, decreased Th1- and Th17-type of cytokine expression, reduced Th1 and Th17 lymphocyte detection, and low osteoclast finding.

CONCLUSION

These data demonstrate that encapsulation of P. gingivalis plays a key role in the alveolar bone resorption induced during periodontitis, and this bone loss is associated with a Th1- and Th17-pattern of immune response triggered in the periodontal lesions.

Gut microbiota-mediated inflammation in obesity: a link with gastrointestinal cancer

Overweight and obesity are associated with increased risk of developing metabolic disorders such as diabetes and cardiovascular diseases. However, besides these metabolic diseases, excess body weight is also associated with different cancers, including gastrointestinal cancers, such as liver, pancreatic and colon cancers. Inflammation is a common feature of both obesity and cancer; however, the origin of this inflammation has been largely debated. Over the past decade, growing evidence has shown that the composition of the gut microbiota and its activity might be associated not only with the onset of inflammation but also with metabolic disorders and cancer. Here, we review the links between the gut microbiota, gut barrier function and the onset of low-grade inflammation in the development of gastrointestinal cancer. We also describe the mechanisms by which specific microorganism-associated molecular patterns crosstalk with the immune system and how the metabolic activity of bacteria induces specific signalling pathways beyond the gut that eventually trigger carcinogenesis.

Prevalence of Anaerobic Bacteria (P.gingivalis) as Major Microbial Agent in the Incidence Periodontal Diseases by Meta-analysis

STATEMENT OF THE PROBLEM

Periodontal diseases are complex oral diseases characterized by bacterial-induced inflammatory destruction of tooth-supporting tissues. Porphyromonas gingivalis (P. gingivalis) is a common gram-negative anaerobic oral bacteria strongly associated with periodontal disease.

PURPOSE

The present study was conducted to estimate prevalence of P. gingivalis in patients with periodontal diseases by using meta-analysis method.

MARTIALS AND METHOD

Different databases including PubMed, EmBase, Scopus, the Institute for Scientific Information (ISI) Web of Science, and the Cochrane Library were searched to identify original English-language studies addressing prevalence of P. gingivalis in periodontal diseases up to December 2014. The random effects model was applied in the meta-analysis and the heterogeneity between studies was assessed using a Cochran test and the I² index. Funnel plots and Egger test were used to examine publication bias. Statistical analyses were performed using STATA version 12.

RESULTS

Forty-two eligible studies published during 1993- 2016 were selected for meta-analysis. Considering all the included studies, the total sample size was 5,884 individuals containing 2,576 healthy people with a mean age of 37.21±7.45 years and 3,308 periodontal patients with a mean age of 44.16±8.35 years. Overall, the prevalence of P. gingivalis was 78% [95% CI: 74-81] in periodontal diseases group and 34% [95% CI: 26-41] in healthy individuals. There was a significantly higher prevalence of P.gingivalis in individuals with periodontal diseases compared to healthy subjects [78% versus 34%, respectively].

CONCLUSION

This study indicates that P. gingivalis is highly present in subjects with periodontal diseases and it also appears in periodontally healthy people, although to a lesser extent. Thus, the presence of P. gingivalis increases the chance of periodontal disease and it can be considered as a main potential risk factor.

A bacterial metabolite ameliorates periodontal pathogen-induced gingival epithelial barrier disruption via GPR40 signaling

Several studies have demonstrated the remarkable properties of microbiota and their metabolites in the pathogenesis of several inflammatory diseases. 10-Hydroxy-cis-12-octadecenoic acid (HYA), a bioactive metabolite generated by probiotic microorganisms during the process of fatty acid metabolism, has been studied for its protective effects against epithelial barrier impairment in the intestines. Herein, we examined the effect of HYA on gingival epithelial barrier function and its possible application for the prevention and treatment of periodontal disease. We found that GPR40, a fatty acid receptor, was expressed on gingival epithelial cells; activation of GPR40 by HYA significantly inhibited barrier impairment induced by Porphyromonas gingivalis, a representative periodontopathic bacterium. The degradation of E-cadherin and beta-catenin, basic components of the epithelial barrier, was prevented in a GPR40-dependent manner in vitro. Oral inoculation of HYA in a mouse experimental periodontitis model suppressed the bacteria-induced degradation of E-cadherin and subsequent inflammatory cytokine production in the gingival tissue. Collectively, these results suggest that HYA exerts a protective function, through GPR40 signaling, against periodontopathic bacteria-induced gingival epithelial barrier impairment and contributes to the suppression of inflammatory responses in periodontal diseases.

Sialidase Deficiency in Porphyromonas gingivalis Increases IL-12 Secretion in Stimulated Macrophages Through Regulation of CR3, IncRNA GAS5 and miR-21

Porphyromonas gingivalis (P. gingivalis) is a major periodontal pathogen that can induce an immune response leading to a destructive inflammatory process. During the inflammatory process, interleukin-12 (IL-12) is secreted, correlating with bacterial clearance by macrophages. Bacterial sialidase has recently been shown to influence the synthesis and modification of the macromolecules on its surface, and is associated with the interaction between bacteria and host cells. We have previously constructed a P. gingivalis sialidase gene mutant strain in P. gingivalis W83 (ΔPG0352) and found that ΔPG0352 showed less pathogenicity than the wild-type strain. In this study, U937-differentiated macrophages were stimulated by P. gingivalis W83, ΔPG0352, or PG0352 complemented strain (comΔPG0352). Transmission electron microscopy showed that P. gingivalis caused a loss of membrane integrity in macrophages and the intracellular bacteria were enclosed within endocytic vacuoles. The expression of both IL-12p35 and IL-12p40 genes and the levels of IL-12p70 were significantly higher in U937 stimulated by ΔPG0352 than in those with P. gingivalis W83 and comΔPG0352. In order to explain why ΔPG0352 induced more IL-12 in macrophages, immunofluorescence assays, PCR arrays, and gene silence or overexpression experiments were carried out. Immunofluorescence assays showed that ΔPG0352 induced lower expression of CR3 in macrophages. After CR3 was suppressed, there were no significant differences in the IL-12p70 levels between macrophages stimulated by P. gingivalis W83, ΔPG0352 or comΔPG0352. PCR array experiments showed that miR-21 and lncRNA GAS5 were differentially expressed between macrophages stimulated by P. gingivalis W83 and ΔPG0352, which had been identified by real-time PCR. The results of CR3 blocking and lncRNA GAS5 gene silence or overexpression showed that the difference in IL-12 levels between P. gingivalis W83 and ΔPG0352 groups was associated with CR3, lncRNA GAS5 and miR-21. Thus it can be concluded that the sialidase-deficient strain is more easily cleared by attenuating CR3 activation, reducing the inhibition of lncRNA GAS5, inducing less miR-21 and more IL-12 in macrophages. These results indicate that inhibiting the activity of sialidase in P. gingivalis will cause rapid clearing by macrophages.

Genes Contributing to Porphyromonas gingivalis Fitness in Abscess and Epithelial Cell Colonization Environments

Porphyromonas gingivalis is an important cause of serious periodontal diseases, and is emerging as a pathogen in several systemic conditions including some forms of cancer. Initial colonization by P. gingivalis involves interaction with gingival epithelial cells, and the organism can also access host tissues and spread haematogenously. To better understand the mechanisms underlying these properties, we utilized a highly saturated transposon insertion library of P. gingivalis, and assessed the fitness of mutants during epithelial cell colonization and survival in a murine abscess model by high-throughput sequencing (Tn-Seq). Transposon insertions in many genes previously suspected as contributing to virulence showed significant fitness defects in both screening assays. In addition, a number of genes not previously associated with P. gingivalis virulence were identified as important for fitness. We further examined fitness defects of four such genes by generating defined mutations. Genes encoding a carbamoyl phosphate synthetase, a replication-associated recombination protein, a nitrosative stress responsive HcpR transcription regulator, and RNase Z, a zinc phosphodiesterase, showed a fitness phenotype in epithelial cell colonization and in a competitive abscess infection. This study verifies the importance of several well-characterized putative virulence factors of P. gingivalis and identifies novel fitness determinants of the organism.

Molecular mechanisms of Porphyromonas gingivalis-host cell interaction on periodontal diseases

Porphyromonas gingivalis (P. gingivalis) is a major oral pathogen and associated with periodontal diseases including periodontitis and alveolar bone loss. In this review, we indicate that two virulence factors, which are hemoglobin receptor protein (HbR) and cysteine proteases “gingipains”, expressed by P. gingivalis have novel functions on the pathogenicity of P. gingivalis. P. gingivalis produces three types of gingipains and concomitantly several adhesin domains. Among the adhesin domains, hemoglobin receptor protein (HbR), also called HGP15, has the function of induction of interleukin-8 (IL-8) expression in human gingival epithelial cells, indicating the possibility that HbR is associated with P. gingivalis-induced periodontal inflammation. On bacteria-host cells contact, P. gingivalis induces cellular signaling alteration in host cells. Phosphatidylinositol 3-kinase (PI3K) and Akt are well known to play a pivotal role in various cellular physiological functions including cell survival and glucose metabolism in mammalian cells. Recently, we demonstrated that gingipains attenuate the activity of PI3K and Akt, which might have a causal influence on periodontal diseases by chronic infection to the host cells from the speculation of molecular analysis. In this review, we discuss new molecular and biological characterization of the virulence factors from P. gingivalis.