Intracellular degradation of Fusobacterium nucleatum in human gingival epithelial cells

Outer Membrane Vesicles Derived From Fusobacterium nucleatum Trigger Periodontitis Through Host Overimmunity

The virulent bacteria-induced host immune response dominates the occurrence and progression of periodontal diseases because of the roles of individual virulence factors from these pathogens in the initiation and spread of inflammation. Outer membrane vesicles (OMVs) as a pathogenic entity have recently attracted great attention as messenger bridges between bacteria and host tissues. Herein, the novel role of OMVs derived from Fusobacterium nucleatum in the occurrence of periodontitis is dissected. In a rat periodontitis model, it is found that OMVs derived from F. nucleatum caused deterioration of periodontitis by enhancing inflammation of the periodontium and absorption of alveolar bone, which is almost equivalent to the effect of F. nucleatum itself. Furthermore, that OMVs can independently induce periodontitis is shown. The pathogenicity of OMVs is attributed to multiple pathogenic components identified by omics. After entering human periodontal ligament stem cells (hPDLSCs) by endocytosis, OMVs activated NLRP3 inflammasomes and impaired the mineralization of hPDLSCs through NF-κB (p65) signaling, leading to the final injury of the periodontium and damage of alveolar bone in periodontitis. These results provide a new understanding of OMVs derived from pathogens and cues for the prevention of periodontitis.

Association of neutrophil defects with oral ulcers but undetermined role of neutrophils in recurrent aphthous stomatitis

Objective

Recurrent oral ulcers and severe periodontal diseases in patients with quantitative or qualitative neutrophil defects highlight the important role of neutrophils in maintaining oral mucosal barrier homeostasis. Recurrent aphthous stomatitis (RAS) is a common oral mucosal disease affecting up to 25% of the population, yet its etiopathogenesis remains unclear, and management is unsatisfactory. This review aims to gain insight into the pathogenesis of RAS.

Design

This narrative review examines the characteristics of oral and blood neutrophils, the associations between neutrophil defects and the occurrence of oral ulcers, and the evidence for the involvement of neutrophils in RAS. To conduct the review, relevant literature was searched in PubMed and Google Scholar, which was then thoroughly reviewed and critically appraised.

Results

Neutropenia, specifically a decrease in the number of oral neutrophils, impaired extravasation, and defective ROS production appear to be associated with oral ulcers, while defects in granule enzymes or NETosis are unlikely to have a link to oral ulcers. The review of the histopathology of RAS shows that neutrophils are concentrated in the denuded area but are latecomers to the scene and early leavers. However, the evidence for the involvement of neutrophils in the pathogenesis of RAS is inconsistent, leading to the proposal of two different scenarios involving either impaired or hyperactive neutrophils in the pathogenesis of RAS.

Probing antibacterial drugs for Fusobacterium nucleatum subsp. nucleatum ATCC 25586 targeting UDP-N-acetylglucosamine 1-carboxyltransferase

Fusobacterium nucleatum is a Gram-negative anaerobic bacteria that is commonly found in oral cavities and is associated with connective tissue destruction in periodontitis. UDP-N-acetylglucosamine 1-carboxyltransferase with enzyme commission number 2.5.1.7 is a transferases enzyme that plays a role in bacterial pathogenesis. Inhibiting binding sites of UDP-N-acetylglucosamine 1-carboxyltransferase is needed to find potential antibiotic candidates for periodontitis treatment. Hence, the research aimed to present potential UDP-N-acetylglucosamine 1-carboxyltransferase inhibiting compounds through molecular docking simulation by in silico analysis. DrugBank database was used to obtain the antibacterial candidates, which were further screened computationally using the AutoDock Vina program on Google Colab Pro. The top nine compounds yielded binding affinity ranging from -12.1 to -12.8 kcal/mol, with conivaptan as one of the three compounds having the highest binding affinity. Molecular dynamic study revealed that the ligand-protein complex for conivaptan had root-mean-square deviation values of 0.05-1.1 nm, indicating likeliness for stable interaction. Our findings suggest that conivaptan is the potent UDP-N-acetylglucosamine 1-carboxyltransferase inhibitor, hence its efficacy against periodontitis-causing bacteria.

Study of the inflammatory activating process in the early stage of Fusobacterium nucleatum infected PDLSCs

Fusobacterium nucleatum (F. nucleatum) is an early pathogenic colonizer in periodontitis, but the host response to infection with this pathogen remains unclear. In this study, we built an F. nucleatum infectious model with human periodontal ligament stem cells (PDLSCs) and showed that F. nucleatum could inhibit proliferation, and facilitate apoptosis, ferroptosis, and inflammatory cytokine production in a dose-dependent manner. The F. nucleatum adhesin FadA acted as a proinflammatory virulence factor and increased the expression of interleukin(IL)-1β, IL-6 and IL-8. Further study showed that FadA could bind with PEBP1 to activate the Raf1-MAPK and IKK-NF-κB signaling pathways. Time-course RNA-sequencing analyses showed the cascade of gene activation process in PDLSCs with increasing durations of F. nucleatum infection. NFκB1 and NFκB2 upregulated after 3 h of F. nucleatum-infection, and the inflammatory-related genes in the NF-κB signaling pathway were serially elevated with time. Using computational drug repositioning analysis, we predicted and validated that two potential drugs (piperlongumine and fisetin) could attenuate the negative effects of F. nucleatum-infection. Collectively, this study unveils the potential pathogenic mechanisms of F. nucleatum and the host inflammatory response at the early stage of F. nucleatum infection.

Patients with mesenchymal tumours and high Fusobacteriales prevalence have worse prognosis in colorectal cancer (CRC)

OBJECTIVES

Transcriptomic-based subtyping, consensus molecular subtyping (CMS) and colorectal cancer intrinsic subtyping (CRIS) identify a patient subpopulation with mesenchymal traits (CMS4/CRIS-B) and poorer outcome. Here, we investigated the relationship between prevalence of Fusobacterium nucleatum (Fn) and Fusobacteriales, CMS/CRIS subtyping, cell type composition, immune infiltrates and host contexture to refine patient stratification and to identify druggable context-specific vulnerabilities.

DESIGN

We coupled cell culture experiments with characterisation of Fn/Fusobacteriales prevalence and host biology/microenviroment in tumours from two independent colorectal cancer patient cohorts (Taxonomy: n=140, colon and rectal cases of The Cancer Genome Atlas (TCGA-COAD-READ) cohort: n=605).

RESULTS

In vitro, Fn infection induced inflammation via nuclear factor kappa-light-chain-enhancer of activated B cells/tumour necrosis factor alpha in HCT116 and HT29 cancer cell lines. In patients, high Fn/Fusobacteriales were found in CMS1, microsatellite unstable () tumours, with infiltration of M1 macrophages, reduced M2 macrophages, and high interleukin (IL)-6/IL-8/IL-1β signalling. Analysis of the Taxonomy cohort suggested that Fn was prognostic for CMS4/CRIS-B patients, despite having lower Fn load than CMS1 patients. In the TCGA-COAD-READ cohort, we likewise identified a differential association between Fusobacteriales relative abundance and outcome when stratifying patients in mesenchymal (either CMS4 and/or CRIS-B) versus non-mesenchymal (neither CMS4 nor CRIS-B). Patients with mesenchymal tumours and high Fusobacteriales had approximately twofold higher risk of worse outcome. These associations were null in non-mesenchymal patients. Modelling the three-way association between Fusobacteriales prevalence, molecular subtyping and host contexture with logistic models with an interaction term disentangled the pathogen-host signalling relationship and identified aberrations (including NOTCH, CSF1-3 and IL-6/IL-8) as candidate targets.

CONCLUSION

This study identifies CMS4/CRIS-B patients with high Fn/Fusobacteriales prevalence as a high-risk subpopulation that may benefit from therapeutics targeting mesenchymal biology.

The Regulatory Effect of Coaggregation Between Fusobacterium nucleatum and Streptococcus gordonii on the Synergistic Virulence to Human Gingival Epithelial Cells

In subgingival plaque biofilms, Fusobacterium nucleatum is closely related to the occurrence and development of periodontitis. Streptococcus gordonii, as an accessory pathogen, can coaggregate with periodontal pathogens, facilitating the subgingival colonization of periodontal pathogens. Studies have shown that F. nucleatum can coaggregate with S. gordonii and colonize the subgingival plaque. However, most studies have focused on monocultures or coinfection of species and the potential impact of coaggregation between the two species on periodontal interactions to human gingival epithelial cells (hGECs) remains poorly understood. The present study explored the effect of coaggregation between F. nucleatum and S. gordonii on subgingival synergistic virulence to hGECs. The results showed that coaggregation inhibited the adhesion and invasion of F. nucleatum to hGECs compared with that in the F. nucleatum monoculture and coinfection group. Coaggregation and coinfection with F. nucleatum both enhanced S. gordonii adhesion to hGECs, but neither of the two groups affected S. gordonii invasion to hGECs compared with S. gordonii monoculture. The gene expression levels of TLR2 and TLR4 in hGECs in the coaggregation group were higher than those in the monoculture groups but lower than those in the coinfection group. Compared with coinfection, the coaggregation inhibited apoptosis of hGECs and promoted the secretion of the proinflammatory cytokines TNF-α and IL-6 by hGECs, showed a synergistic inflammatory effect, while coaggregation inhibited the secretion of the anti-inflammatory cytokine TGF-β1. Coaggregation enhanced the phosphorylation of p65, p38, and JNK proteins and therefore activated the NF-κB and MAPK signaling pathways. Pretreatment with a pathway antagonist/inhibitor decreased the phosphorylation levels of proteins and the secretion of TNF-α and IL-6. In conclusion, coaggregation inhibited the adhesion and invasion of F. nucleatum to hGECs. However, it enhanced the adhesion of S. gordonii to hGECs. Compared with coinfection, coaggregation inhibited the apoptosis of hGECs. The coaggregation coordinately promoted the secretion of TNF-α and IL-6 by hGECs through the TLR/NF-κB and TLR/MAPK signaling pathways while inhibiting the secretion of TGF-β1, thus aggravating the inflammatory response of hGECs.

Pathogenic Mechanisms of Fusobacterium nucleatum on Oral Epithelial Cells

Periodontitis is an oral chronic inflammatory disease and may cause tooth loss in adults. Oral epithelial cells provide a barrier for bacteria and participate in the immune response. Fusobacterium nucleatum (F. nucleatum) is one of the common inhabitants of the oral cavity and has been identified as a potential etiologic bacterial agent of oral diseases, such as periodontitis and oral carcinomas. F. nucleatum has been shown to be of importance in the development of diverse human cancers. In the dental biofilm, it exhibits a structural role as a bridging organism, connecting primary colonizers to the largely anaerobic secondary colonizers. It expresses adhesins and is able to induce host cell responses, including the upregulation of defensins and the release of chemokines and interleukins. Like other microorganisms, its detection is achieved through germline-encoded pattern-recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs). By identification of the pathogenic mechanisms of F. nucleatum it will be possible to develop effective methods for the diagnosis, prevention, and treatment of diseases in which a F. nucleatum infection is involved. This review summarizes the recent progress in research targeting F. nucleatum and its impact on oral epithelial cells.

Fusobacterium nucleatum Accelerates Atherosclerosis via Macrophage-Driven Aberrant Proinflammatory Response and Lipid Metabolism

Periodontitis, an oral chronic inflammatory disease, is reported to show an association with atherosclerotic vascular disease. Fusobacterium nucleatum is an oral commensal bacterium that is abundantly implicated in various forms of periodontal diseases; however, its role in the pathogenesis of atherosclerosis is unclear. This study aimed to elucidate the underlying pathogenic mechanisms of atherosclerosis induced by F. nucleatum to provide new insight on the prevention and treatment of atherosclerosis. We used an animal model, that is, ApoE^–/– mice were infected with F. nucleatum by oral gavage, and in vitro co-culture models to assess the pathogenicity of F. nucleatum. The results indicate that F. nucleatum ATCC 25586 invaded aortic tissues and substantially increased the progression of atherosclerotic lesions. In addition, F. nucleatum changed plaque composition into a less-stable phenotype, characterized with increased subcutaneous macrophage infiltration, M1 polarization, lipid deposition, cell apoptosis, and reduced extracellular matrix and collagen content. The serum levels of pro-atherosclerotic factors, such as interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, monocyte chemoattractant protein-1 (MCP-1), c-reactive protein, and oxidized low-density lipoprotein (ox-LDL) and microRNAs (miR-146a, miR-155, and miR-23b) were considerably increased after F. nucleatum stimulation, whereas HDL-c level was reduced. F. nucleatum induced in vitro macrophage apoptosis in a time- and dose-dependent manner. F. nucleatum facilitated ox-LDL–induced cholesterol phagocytosis and accumulation by regulating the expression of lipid metabolism-related genes (AR-A1, ACAT1, ABCA1, and ABCG1). F. nucleatum further worsened the atherosclerotic plaque microenvironment by considerably increasing the levels of IL-6; IL-1β; TNF-α; MCP-1; and MMP-2, 8, and 9 and by suppressing fibronectin (FN) 1 levels during foam cell formation. This study shows that F. nucleatum ATCC 25586 is implicated in atherosclerosis by causing aberrant activation and lipid metabolism in macrophage.

Porphyromonas gingivalis outer membrane vesicles inhibit the invasion of Fusobacterium nucleatum into oral epithelial cells by downregulating FadA and FomA

Background

Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) participate in the formation and progression of periodontitis. They can exert virulence by invading into host cells, but the interaction between them and their specific mechanisms remain unclear. The purpose of this study was to study the effect of P. gingivalis outer membrane vesicles (OMVs) on the ability of F. nucleatum to invade oral epithelial cells, and the reasons for the influence.

Methods

The invasion abilities of the two bacteria were detected separately after mixed infection of P. gingivalis and F. nucleatum. Next, P. gingivalis OMVs were extracted with the kit, and their influence on the invasion ability of F. nucleatum was tested. The effects of P. gingivalis OMVs on F. nucleatum were evaluated by assessment of bacterial morphology, growth curves, auto‐aggregation morphology, and the expression of adhesion‐related proteins FadA and FomA.

Results

Our results showed that P. gingivalis inhibited the invasion of F. nucleatum into oral epithelial cells but F. nucleatum promoted the invasion of P. gingivalis. In subsequent experiments, we extracted P. gingivalis OMVs successfully and revealed that proteases in P. gingivalis OMVs inhibited the invasion of F. nucleatum into oral epithelial cells. Furthermore, P. gingivalis OMVs did not affect the morphology and proliferation of F. nucleatum, but proteases inside decreased the auto‐aggregation of F. nucleatum. Additionally, proteases in P. gingivalis OMVs reduced the expression levels of F. nucleatum surface adhesion‐related proteins FadA and FomA.

Conclusion

Our study demonstrated that proteases in P. gingivalis OMVs inhibited the invasion of F. nucleatum into oral epithelial cells by downregulating FadA and FomA.

Omega-3 polyunsaturated fatty acids: a promising approach for the management of oral lichen planus

BACKGROUND

Oral lichen planus (OLP) is a T-cell-mediated inflammatory disease with a risk of malignant transformation. Although the etiology of OLP is still uncertain, growing evidence suggests that oral microbiota, antigen-specific, and non-specific mechanisms are involved in the pathogenesis of OLP. Antigen-specific mechanisms include antigen presentation, T-cell activation, nuclear factor-kappa B signaling pathway, and cytokine secretion, while non-specific mechanisms consist of matrix metalloproteinases (MMP)-9 upregulation, psychological pressure, oxidative damage, aberrant expression of microRNAs (miRNAs), and autophagy. Till now, there is no cure for OLP, and the main purpose of OLP therapy is symptomatic control.

FINDING

Seafood and its derivative omega-3 polyunsaturated fatty acids (n-3 PUFAs) can suppress antigen presentation, T-cell activation, and nuclear factor-kappa B signaling pathway, modulate the overexpressed inflammatory cytokines, inhibit the expression of MMP-9, as well as regulate the expression of miRNAs and autophagy. And they are possible agents for ameliorating psychological disorder and oxidative damage. Moreover, n-3 PUFAs supplementation has a beneficial effect on preventing tumorigenesis.

CONCLUSION

n-3 PUFAs consumption may provide a non-toxic, inexpensive administration for OLP.

Effect of Hydrogen Peroxide Photoactivated Decontamination Using 940 nm Diode Laser in Periodontal Treatment: A Pilot Study

Objective: The aim of this study was to compare the antimicrobial effects of hydroxyl radical generation by photoactivation of hydrogen peroxide (H₂O₂) with diode laser (λ = 940 nm) in combination with conventional nonsurgical periodontal therapy. Materials and methods: Thirty-eight patients and 114 teeth were included in this study. The test teeth were randomly assigned to one of the three treatment groups: Group 1 (control group): scaling and root planning (SRP); and the following experimental groups: Group 2: SRP +940 nm diode laser; Group 3: SRP+photoactivation of H₂O₂ with 940 nm diode laser. Clinical examinations, such as periodontal probing depth (PPD), clinical attachment level (CAL), and bleeding on probing (BoP) were performed before and after the treatment. The microbiological evaluation included nine periodontal bacterial species investigated by means of real-time polymerase chain reaction assay before and after the treatment. The clinical and bacterial differences were assessed between the investigated groups. Results: The total bacteria load was reduced for all three studied groups and all periodontal indexes (PPD, CAL, and BoP) were improved after each treatment. Group 3 showed significant bacterial reduction of the major periodontal bacteria such as Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Prevotella intermedia, Peptostreptococcus micros, Fusobacterium nucleatum, Eubacterium nodatum (p < 0.001) in contrast to the other two groups (p > 0.001). Differences between tested groups showed significant results with regard to Group 3. Conclusions: The synergistic effect of SRP and photoactivation of H₂O₂ with 940 nm diode laser offers an efficient and reliable antimicrobial effect in the nonsurgical periodontal treatment approach.

Microbial and Host Factors That Affect Bacterial Invasion of the Gingiva

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

Invasion of Human Retinal Pigment Epithelial Cells by Porphyromonas gingivalis leading to Vacuolar/Cytosolic localization and Autophagy dysfunction In-Vitro

Recent epidemiological  studies link Periodontal disease(PD) to age-related macular degeneration (AMD). We documented earlier that Porphyromonas gingivalis(Pg), keystone oral-pathobiont, causative of PD, efficiently invades human gingival epithelial and blood-dendritic cells. Here, we investigated the ability of dysbiotic Pg-strains to invade human-retinal pigment epithelial cells(ARPE-19), their survival, intracellular localization, and the pathological effects, as dysfunction of RPEs leads to AMD. We show that live, but not heat-killed Pg-strains adhere to and invade ARPEs. This involves early adhesion to ARPE cell membrane, internalization and localization of Pg within single-membrane vacuoles or cytosol, with some nuclear localization apparent. No degradation of Pg or localization inside double-membrane autophagosomes was evident, with dividing Pg suggesting a metabolically active state during invasion. We found significant downregulation of autophagy-related genes particularly, autophagosome complex. Antibiotic protection-based recovery assay further confirmed distinct processes of adhesion, invasion and amplification of Pg within ARPE cells. This is the first study to demonstrate invasion of human-RPEs, begin to characterize intracellular localization and survival of Pg within these cells. Collectively, invasion of RPE by Pg and its prolonged survival by autophagy evasion within these cells suggest a strong rationale for studying the link between oral infection and AMD pathogenesis in individuals with periodontitis.

Fusobacterium nucleatum, the communication with colorectal cancer

Colorectal cancer (CRC) is the fourth most common cancer in 2018 with poor prognosis. Fusobacterium nucleatum (F.n), an anaerobe, is found to be enriched in both stools and tumor tissues of CRC patients. As surveys show, tumor initiates before the collection of F.n. In return, F.n helps cancer cells to build up tumor microenvironment and benefit for their chemo-resistant. The elements constituted the tumor environment, including neutrophils, macrophages and lymphocytes, contribute to the existing of tumor cells respectively. However, the integrated and interactive roles of those elements are poorly investigated. The intracellular molecular alteration MSI is a result of F.n infection and the microbiology-molecular pathological epidemiology (MPE) has become a new trend to analysis F.n and tumorigenesis. Chemoresistance of tumor cells is also affected by F.n induced microenvironment, or F.n achieves it directly. Finally, F.n could be a biomarker of CRC. All in all, our review will lay a foundation for the therapy of CRC through the interference of F.n and perspective to follow-up studies.

NLRX1 modulates differentially NLRP3 inflammasome activation and NF-κB signaling during Fusobacterium nucleatum infection

NOD-like receptors (NLRs) play a large role in regulation of host innate immunity, yet their role in periodontitis remains to be defined. NLRX1, a member of the NLR family that localizes to mitochondria, enhances mitochondrial ROS (mROS) generation. mROS can activate the NLRP3 inflammasome, yet the role of NLRX1 in NLRP3 inflammasome activation has not been examined. In this study, we revealed the mechanism by which NLRX1 positively regulates ATP-induced NLRP3 inflammasome activation through mROS in gingival epithelial cells (GECs). We found that depletion of NLRX1 by shRNA attenuated ATP-induced mROS generation and redistribution of the NLRP3 inflammasome adaptor protein, ASC. Furthermore, depletion of NLRX1 inhibited Fusobacterium nucleatum infection-activated caspase-1, suggesting that it also inhibits the NLRP3 inflammasome. Conversely, NLRX1 also acted as a negative regulator of NF-κB signaling and IL-8 expression. Thus, NLRX1 stimulates detection of the pathogen F. nucleatum via the inflammasome, while dampening cytokine production. We expect that commensals should not activate the inflammasome, and NLRX1 should decrease their ability to stimulate expression of pro-inflammatory cytokines such as IL-8. Therefore, NLRX1 may act as a potential switch with regards to anti-microbial responses in healthy or diseased states in the oral cavity.

Porphyromonas gingivalis suppresses invasion of Fusobacterium nucleatum into gingival epithelial cells

Invasion of periodontal pathogens into periodontal tissues is an important step that can cause tissue destruction in periodontal diseases. Porphyromonas gingivalis is a keystone pathogen and its gingipains are key virulence factors. Fusobacterium nucleatum is a bridge organism that mediates coadhesion of disease-causing late colonizers such as P. gingivalis and early colonizers during the development of dental biofilms. The aim of this study was to investigate how P. gingivalis, in particular its gingipains, influences the invasion of coinfecting F. nucleatum into gingival epithelial cells. When invasion of F. nucleatum was analyzed after 4 h of infection, invasion of F. nucleatum was suppressed in the presence of P. gingivalis compared with during monoinfection. However, coinfection with a gingipain-null mutant of P. gingivalis did not affect invasion of F. nucleatum. Inhibition of PI3K reduced invasion of F. nucleatum. P. gingivalis inactivated the PI3K/AKT pathway, which was also dependent on gingipains. Survival of intracellular F. nucleatum was promoted by P. gingivalis with Arg gingipain mutation. The results suggest that P. gingivalis, in particular its gingipains, can affect the invasion of coinfecting F. nucleatum through modulating intracellular signaling of the host cells.

The presence of bacteria within tissue provides insights into the pathogenesis of oral lichen planus

Oral lichen planus (OLP) is a chronic T cell-mediated mucocutaneous disease of unknown etiopathogenesis. Although various antigens have been considered, what actually triggers the inflammatory response of T cells is unknown. In the present study, we propose that intracellular bacteria present within tissues trigger T cell infiltration and provide target antigens. Sections of OLP (n = 36) and normal (n = 10) oral mucosal tissues were subjected to in situ hybridization using a universal probe targeting the bacterial 16S rRNA gene and immunohistochemistry with anti-CD3, anti-CD4, anti-CD8, and anti-macrophage-specific antibodies. Bacteria were abundant throughout the epithelium and the lamina propria of OLP tissues, which exhibited positive correlations with the levels of infiltrated CD3(+), CD4(+), and CD8(+) cells. Furthermore, bacteria were detected within the infiltrated T cells. Pyrosequencing analysis of the mucosal microbiota from OLP patients (n = 13) and control subjects (n = 11) revealed a decrease in Streptococcus and increases in gingivitis/periodontitis-associated bacteria in OLP lesions. Using the selected bacterial species, we demonstrated that certain oral bacteria damage the epithelial physical barrier, are internalized into epithelial cells or T cells, and induce production of T cell chemokines CXCL10 and CCL5. Our findings provide insights into the pathogenesis of OLP.

Periodontal bacterial invasion and infection: contribution to atherosclerotic pathology

OBJECTIVE

The objective of this review was to perform a systematic evaluation of the literature reporting current scientific evidence for periodontal bacteria as contributors to atherosclerosis.

METHODS

Literature from epidemiological, clinical and experimental studies concerning periodontal bacteria and atherosclerosis were reviewed. Gathered data were categorized into seven "proofs" of evidence that periodontal bacteria: 1) disseminate from the oral cavity and reach systemic vascular tissues; 2) can be found in the affected tissues; 3) live within the affected site; 4) invade affected cell types in vitro; 5) induce atherosclerosis in animal models of disease; 6) non-invasive mutants of periodontal bacteria cause significantly reduced pathology in vitro and in vivo; and 7) periodontal isolates from human atheromas can cause disease in animal models of infection.

RESULTS

Substantial evidence for proofs 1 to 6 was found. However, proof 7 has not yet been fulfilled.

CONCLUSIONS

Despite the lack of evidence that periodontal bacteria obtained from human atheromas can cause atherosclerosis in animal models of infection, attainment of proofs 1 to 6 provides support that periodontal pathogens can contribute to atherosclerosis.

Periodontal bacterial invasion and infection: contribution to atherosclerotic pathology

OBJECTIVE

The objective of this review was to perform a systematic evaluation of the literature reporting current scientific evidence for periodontal bacteria as contributors to atherosclerosis.

METHODS

Literature from epidemiological, clinical and experimental studies concerning periodontal bacteria and atherosclerosis were reviewed. Gathered data were categorized into seven "proofs" of evidence that periodontal bacteria: 1) disseminate from the oral cavity and reach systemic vascular tissues; 2) can be found in the affected tissues; 3) live within the affected site; 4) invade affected cell types in vitro; 5) induce atherosclerosis in animal models of disease; 6) non-invasive mutants of periodontal bacteria cause significantly reduced pathology in vitro and in vivo; and 7) periodontal isolates from human atheromas can cause disease in animal models of infection.

RESULTS

Substantial evidence for proofs 1 to 6 was found. However, proof 7 has not yet been fulfilled.

CONCLUSIONS

Despite the lack of evidence that periodontal bacteria obtained from human atheromas can cause atherosclerosis in animal models of infection, attainment proofs 1 to 6 provides support that periodontal pathogens can contribute to atherosclerosis.

Treponema denticola invasion into human gingival epithelial cells

Host cell invasion is important for periodontal pathogens in evading host defenses and spreading into deeper areas of the periodontal tissue. Treponema denticola has been implicated in a number of potentially pathogenic processes, including periodontal tissue penetration. Here we tested the ability of T. denticola strains to invade human gingival epithelial cells (HGEC). After 2 h infection, intracellular location of T. denticola cells was confirmed by confocal laser scanning microscopy (CLSM). Results from an antibiotic protection assay following [(3)H]uridine labeling indicated that invasion efficiency reached a maximum at 2 h after infection. Internalized T. denticola cells were still observed in HGEC at 24 h by CLSM. A dentilisin deficient mutant exhibited significantly decreased invasion (p < 0.05) compared with the wild-type strain. In inhibition assays, phenylmethylsulfonyl fluoride and metabolic inhibitors such as methyl-β-cyclodextrin and staurosporine significantly reduced T. denticola invasion. Under CLSM, T. denticola colocalized with GM-1 ganglioside-containing membrane microdomains in a cholesterol-dependent manner. These results indicated that T. denticola has the ability to invade into and survive within HGECs. Dentilisin activity of T. denticola and lipid rafts on HGEC appear to play important roles in this process.

N-acetylcysteine and the human serum components that inhibit bacterial invasion of gingival epithelial cells prevent experimental periodontitis in mice

PURPOSE

We previously reported that human serum significantly reduces the invasion of various oral bacterial species into gingival epithelial cells in vitro. The aims of the present study were to characterize the serum component(s) responsible for the inhibition of bacterial invasion of epithelial cells and to examine their effect on periodontitis induced in mice.

METHODS

Immortalized human gingival epithelial (HOK-16B) cells were infected with various 5- (and 6-) carboxy-fluorescein diacetate succinimidyl ester-labeled oral bacteria, including Fusobacterium nucleatum, Provetella intermedia, Porphyromonas gingivalis, and Treponiema denticola, in the absence or presence of three major serum components (human serum albumin [HSA], pooled human IgG [phIgG] and α1-antitrypsin). Bacterial adhesion and invasion were determined by flow cytometry. The levels of intracellular reactive oxygen species (ROS) and activation of small GTPases were examined. Experimental periodontitis was induced by oral inoculation of P. gingivalis and T. denticola in Balb/c mice.

RESULTS

HSA and phIgG, but not α1-antitrypsin, efficiently inhibited the invasion of various oral bacterial species into HOK-16B cells. HSA but not phIgG decreased the adhesion of F. nucleatum onto host cells and the levels of intracellular ROS in HOK-16B cells. N-acetylcysteine (NAC), a ROS scavenger, decreased both the levels of intracellular ROS and invasion of F. nucleatum into HOK-16B cells, confirming the role of ROS in bacterial invasion. Infection with F. nucleatum activated Rac1, a regulator of actin cytoskeleton dynamics. Not only HSA and NAC but also phIgG decreased the F. nucleatum-induced activation of Rac1. Furthermore, both HSA plus phIgG and NAC significantly reduced the alveolar bone loss in the experimental periodontitis induced by P. gingivalis and T. denticola in mice.

CONCLUSIONS

NAC and the serum components HSA and phIgG, which inhibit bacterial invasion of oral epithelial cells in vitro, can successfully prevent experimental periodontitis.

DNA methylation differentially regulates cytokine secretion in gingival epithelia in response to bacterial challenges

Epigenetic modifications are changes in gene expression without altering DNA sequence. We previously reported that bacteria-specific innate immune responses are regulated by epigenetic modifications. Our hypothesis is that DNA methylation affects gingival cytokine secretion in response to bacterial stimulation. Gingival epithelial cells (GECs) were treated with DNMT-1 inhibitors prior to Porphyromonas gingivalis (Pg) or Fusobacterium nucleatum (Fn) exposure. Protein secretion was assessed using ELISA. Gene expression was quantified using qRT-PCR. The ability of bacteria to invade inhibitor pretreated GECs was assessed utilizing flow cytometry. Changes were compared to unstimulated GECs. GEC upregulation of IL-6 and CXCL1 by Pg or Fn stimulation was significantly diminished by inhibitor pretreatment. Pg stimulated IL-1α secretion and inhibitor pretreatment significantly enhanced this upregulation, while Fn alone or with inhibitor pretreatment had no effect on IL-1α expression. GEC upregulation of human beta-definsin-2 in response to Pg and Fn exposure was enhanced following the inhibitor pretreatment. GEC susceptibility to bacterial invasion was unaltered. These results suggest that DNA methylation differentially affects gingival cytokine secretion in response to Pg or Fn. Our data provide basis for better understanding of how epigenetic modifications, brought on by exposure to oral bacteria, will subsequently affect host susceptibility to oral diseases.

Epithelial antimicrobial peptides: guardian of the oral cavity

Gingival epithelium provides first line of defence from the microorganisms present in dental plaque. It not only provides a mechanical barrier but also has an active immune function too. Gingival epithelial cells participate in innate immunity by producing a range of antimicrobial peptides to protect the host against oral pathogens. These epithelial antimicrobial peptides (EAPs) include the β-defensin family, cathelicidin (LL-37), calprotectin, and adrenomedullin. While some are constitutively expressed in gingival epithelial cells, others are induced upon exposure to microbial insults. It is likely that these EAPs have a role in determining the initiation and progression of oral diseases. EAPs are broad spectrum antimicrobials with a different but overlapping range of activity. Apart from antimicrobial activity, they participate in several other crucial roles in host tissues. Some of these, for instance, β-defensins, are chemotactic to immune cells. Others, such as calprotectin are important for wound healing and cell proliferation. Adrenomedullin, a multifunctional peptide, has its biological action in a wide range of tissues. Not only is it a potent vasodilator but also it has several endocrine effects. Knowing in detail the various bioactions of these EAPs may provide us with useful information regarding their utility as therapeutic agents.

A periodontal pathogen Treponema denticola hijacks the Fusobacterium nucleatum-driven host response

Periodontitis is a polymicrobial disease that arises from the dysbiosis of the plaque biofilm. To study polymicrobial interactions with gingival epithelial cells, the oral commensal Fusobacterium nucleatum and the periodontal pathogen Treponema denticola were chosen due to their opposing effects on the expression of human beta-defensins (HBDs) and interleukin (IL)-8 in gingival epithelial cells. Immortalized gingival epithelial HOK-16B cells were infected with either F. nucleatum or T. denticola alone or together, and the expression of HBDs and IL-8 was investigated. Coinfection with F. nucleatum and T. denticola neutralized the stimulatory and suppressive effects on the expression of HBD-2 and -3, but the suppressive effect of T. denticola on IL-8 expression remained. In CHO/CD14/TLR2 reporter cells, T. denticola attenuated F. nucleatum-induced activation of TLR2, a receptor that mediates HBD induction. Although F. nucleatum facilitated the invasion of T. denticola into host cells, T. denticola interfered with the fusion of internalized F. nucleatum with lysosomes, which may avert TLR9-dependent IL-8 induction. Furthermore, T. denticola suppressed the F. nucleatum-stimulated accumulation of intracellular reactive oxygen species (ROS), a group of essential signaling molecules for the TLR2 and TLR9 pathways. The elimination of ROS using N-acetyl cysteine completely blocked the inductions of HBD-3 and IL-8 and significantly reduced HBD-2 induction by F. nucleatum, confirming the importance of ROS in the host response. In sum, T. denticola incapacitates the F. nucleatum-induced expression of HBDs and IL-8 in gingival epithelial cells by interrupting endo-lysosomal maturation and ROS-dependent TLR activation. These results may provide new insights into polymicrobial interactions in the gingival sulcus.

Antibody and T cell responses to Fusobacterium nucleatum and Treponema denticola in health and chronic periodontitis

The characteristics of the T cell response to the members of oral flora are poorly understood. We characterized the antibody and T cell responses to FadA and Td92, adhesins from Fusobacterium nucleatum, an oral commensal, and Treponema denticola, a periodontal pathogen, respectively. Peripheral blood and saliva were obtained from healthy individuals and patients with untreated chronic periodontitis (CP, n = 11 paris) and after successful treatment of the disease (n = 9). The levels of antigen-specific antibody were measured by ELISA. In plasma, IgG1 was the most abundant isotype of Ab for both Ags, followed by IgA and then IgG4. The levels of FadA-specific salivary IgA (sIgA) were higher than Td92-specific sIgA and the FadA-specific IgA levels observed in plasma. However, the periodontal health status of the individuals did not affect the levels of FadA- or Td92-specific antibody. Even healthy individuals contained FadA- and Td92-specific CD4⁺ T cells, as determined by the detection of intracytoplasmic CD154 after short-term in vitro stimulation of peripheral blood mononuclear cells (PBMCs) with the antigens. Patients with CP tended to possess increased numbers of FadA- and Td92-specific CD4⁺ T cells but reduced numbers of Td92-specific Foxp3⁺CD4⁺ Tregs than the healthy subjects. Both FadA and Td92 induced the production of IFNγ and IL-10 but inhibited the secretion of IL-4 by PBMCs. In conclusion, F. nucleatum induced Th3 (sIgA)- and Th1 (IFNγ and IgG1)-dominant immune responses, whereas T. denticola induced a Th1 (IFNγ and IgG1)-dominant response. This IFNγ-dominant cytokine response was impaired in CP patients, and the Td92-induced IFNγ levels were negatively associated with periodontal destruction in patients. These findings may provide new insights into the homeostatic interaction between the immune system and oral bacteria and the pathogenesis of periodontitis.

The fate of Treponema denticola within human gingival epithelial cells

Treponema denticola is one of the major pathogens associated with chronic periodontitis. Bacterial invasion into gingival tissues is a critical process in the pathogenesis of periodontal disease. We recently reported that T. denticola can invade gingival epithelial cells. The aim of this study is to determine the fate of internalized T. denticola in gingival epithelial cells. Immortalized human gingival epithelial HOK-16B cells were infected with 5- (and 6-) carboxy-fluorescein diacetate succinimidyl ester (CFSE)-labeled live or heat-killed T. denticola for 24 h, and the presence of bacteria inside the cells was confirmed by confocal microscopy. Live T. denticola, but not heat-killed bacteria, invaded HOK-16B cells. Confocal microscopy also revealed that internalized T. denticola rarely colocalized with either endosomes or lysosomes. Transmission electron microscopy of infected cells showed that intracellular T. denticola was localized inside endosome-like structures. Although a culture-based antibiotics protection assay could not detect viable intracellular T. denticola 12 h after infection, a substantial number of bacteria were observed by confocal microscopy and weak expression of bacterial 16S ribosomal RNA was detected 48 h after infection. In addition, flow cytometric analysis of HOK-16B cells infected with CFSE-labeled T. denticola showed no loss of fluorescence over 48 h. Collectively, T. denticola invades gingival epithelial cells and remains within the host cells for many hours by resisting endolysosomal degradation. These findings may provide new insight into the role of T. denticola in the pathogenesis of periodontitis.

Fusobacterium nucleatum: an emerging gut pathogen?

The Gram-negative, non-sporulating, obligately anaerobic species, Fusobacterium nucleatum, is rapidly gaining notoriety as a pathogen with a surprising number of associated diseases. Recently, we have found that F. nucleatum is a more common resident of the GI tract than originally thought, and thus, through several studies, we have attempted to determine its gut-relevant potential for virulence. We have found that F. nucleatum possesses a number of pathogenic traits with relevance to gut diseases such as inflammatory bowel disease (IBD), however, we have also documented strain-associated differences in virulence. An intriguing picture emerges that paints F. nucleatum as both conferring beneficial as well as detrimental effects on host cells; and we suggest that the ultimate effects of F. nucleatum infection in the gut are a consequence of the microbes with which this species aggregates.

Beta-defensins: what are they really doing in the oral cavity?

Initially identified as broad-spectrum antimicrobial peptides, the members of the β-defensin family have increasingly been observed to exhibit numerous other activities, both in vitro and in vivo, that do not always relate directly to host defense. Much research has been carried out in the oral cavity, where the presence of commensal bacteria further complicates the definition of their role. In addition to direct antimicrobial activity, β-defensins exhibit potent chemotactic activity for a variety of innate immune cells, as well as stimulating other cells to secrete cytokines. They can also inhibit the inflammatory response, however, by the specific binding of microbe-associated molecular patterns. These patterns are also able to induce the expression of β-defensins in gingival epithelial cells, although significant differences are observed between different species of bacteria. Together these results suggest a complex model of a host-defense related function in maintenance of bacterial homeostasis and response to pathogens. This model is complicated, however, by numerous other observations of β-defensin involvement in cell proliferation, wound healing and cancer. Together, the in vitro, in vivo and human studies suggest that these peptides are important in the biology of the oral cavity; exactly how is still subject to speculation.