Effects of Porphyromonas gingivalis infection on human gingival epithelial barrier function in vitro

A Review of a Breakdown in the Barrier: Tight Junction Dysfunction in Dental Diseases

The tight junction (TJ), a type of cell-cell junction, regulates the permeability of solutes across epithelial and endothelial cellular sheets and is believed to maintain cell polarity. However, recent studies have provided conflicting views on the roles of TJs in epithelial polarity. Membrane proteins, including occludin, claudin, and the junction adhesion molecule, have been identified as TJ components. TJs are predominantly found at the stratum granulosum and stratum corneum. Although it remains unclear whether the disruption of TJs is the cause or consequence of certain dental diseases, evidence suggests that TJ dysfunction may be a crucial factor in gingival epithelial barrier impairment and the progression of oral diseases. Bacterial infection is among the most specific factors we found that may contribute to the breakdown of the epithelial barrier formed by TJs in dental diseases. Bacteria and their products may weaken the epithelial barrier by directly destroying intercellular junctions or altering the expression of junctional proteins. Additionally, they may induce the production of inflammatory cytokines, which could lead to the downregulation of TJ proteins and, consequently, impair the epithelial barrier. This review introduces a novel perspective by exploring, for the first time, the role of TJs dysfunction in the breakdown of the oral epithelial barrier and its potential link to the progression of dental diseases such as gingivitis, periodontitis, Sjӧgren syndrome, and oral squamous cell carcinoma.

Gingival crevicular fluid Bax, Bcl-xl, interleukin-22, and transforming growth factor beta 1 levels in stage III periodontitis

BACKGROUND

Intrinsic apoptosis plays a critical role in immune defense and inflammation. Its dysregulation is involved in various chronic diseases. The B-cell lymphoma 2 (Bcl-2) family primarily mediates this mitochondrial pathway. This study aimed to investigate the proapoptotic Bcl-2-associated X protein (Bax) and antiapoptotic B-cell lymphoma-extra large (Bcl-xl) levels and their association with interleukin-22 (IL-22) and transforming growth factor beta 1 (TGF-β1) in the gingival crevicular fluid (GCF) of patients with periodontitis.

METHODS

A total of 75 systemically healthy nonsmokers were enrolled, of whom 23 had stage III periodontitis, 26 had gingivitis, and 26 were periodontally healthy. Whole-mouth clinical periodontal measurements were recorded. Bax, Bcl-xl, IL-22, and TGF-β1 levels in the GCF were determined by enzyme-linked immunosorbent assay (ELISA). Data were analyzed using nonparametric statistical tests.

RESULTS

The periodontitis group had significantly lower GCF Bax levels than the gingivitis group (p < 0.05). The periodontitis and gingivitis groups had higher GCF Bcl-xl levels than the periodontally healthy group (p < 0.05). GCF IL-22 levels were similar in all groups (p > 0.05). The periodontitis group had lower GCF TGF-β1 levels than the gingivitis and periodontally healthy groups (p < 0.05). The diseased groups had a lower GCF Bax/Bcl-xl ratio than the healthy controls (p < 0.05). IL-22 was positively correlated with Bax (p < 0.05).

CONCLUSIONS

This is the first study investigating GCF Bax and Bcl-xl levels in periodontal health and disease. Increased GCF Bcl-xl levels and a decreased Bax/Bcl-xl ratio in stage III periodontitis implicate that those apoptotic proteins may be involved in the pathogenesis of periodontal disease. Further studies are needed to enlighten the possible role of Bax and Bcl-xl and their association with IL-22 and TGF-β1 in periodontal diseases.

PLAIN LANGUAGE SUMMARY

A type of cell death called intrinsic apoptosis plays an important role in the body's defense system, and its dysregulation is linked to different human diseases. The B-cell lymphoma 2-associated X protein (Bax) and B-cell lymphoma-extra large (Bcl-xl) are apoptosis-related proteins, which promote and inhibit cell death, respectively. This study aimed to investigate Bax and Bcl-xl levels and their association with the signaling proteins interleukin-22 (IL-22) and transforming growth factor beta 1 (TGF-β1) in the gingival crevicular fluid (GCF), which accumulates around the necks of the teeth of patients suffering from gum diseases such as gingivitis and periodontitis. Clinical parameters were recorded and GCF was collected. Bax, Bcl-xl, IL-22, and TGF-β1 levels were measured by biochemical assay in periodontally healthy individuals who had healthy gums (n = 26) and patients with periodontitis (n = 23) and gingivitis (n = 26). Periodontitis patients had lower Bax levels than gingivitis patients. Periodontitis and gingivitis patients had higher Bcl-xl levels and a lower Bax/Bcl-xl ratio than periodontally healthy individuals. IL-22 was positively correlated with Bax. The present findings suggest that the apoptotic regulatory molecules may be involved in the development of gum diseases, highlighting the need for further research in this area.

Revisiting Socransky's Complexes: A Review Suggesting Updated New Bacterial Clusters (GF-MoR Complexes) for Periodontal and Peri-Implant Diseases and Conditions

This review aimed to identify newly discovered bacteria from individuals with periodontal/peri-implant diseases and organize them into new clusters (GF-MoR complexes) to update Socransky's complexes (1998). For methodological development, the PCC (Population, Concept, Context) strategy was used for the focus question construction: "In patients with periodontal and/or peri-implant disease, what bacteria (microorganisms) were detected through laboratory assays?" The search strategy was applied to PubMed/MEDLINE, PubMed Central, and Embase. The search key terms, combined with Boolean markers, were (1) bacteria, (2) microbiome, (3) microorganisms, (4) biofilm, (5) niche, (6) native bacteria, (7) gingivitis), (8) periodontitis, (9) peri-implant mucositis, and (10) peri-implantitis. The search was restricted to the period 1998-2024 and the English language. The bacteria groups in the oral cavity obtained/found were retrieved and included in the GF-MoR complexes, which were based on the disease/condition, presenting six groups: (1) health, (2) gingivitis, (3) peri-implant mucositis, (4) periodontitis, (5) peri-implantitis, and (6) necrotizing and molar-incisor (M-O) pattern periodontitis. The percentual found per group refers to the number of times a specific bacterium was found to be associated with a particular disease. A total of 381 articles were found: 162 articles were eligible for full-text reading (k = 0.92). Of these articles, nine were excluded with justification, and 153 were included in this review (k = 0.98). Most of the studies reported results for the health condition, periodontitis, and peri-implantitis (3 out of 6 GF-MoR clusters), limiting the number of bacteria found in the other groups. Therefore, it became essential to understand that bacterial colonization is a dynamic process, and the bacteria present in one group could also be present in others, such as those observed with the bacteria found in all groups (Porphyromonas gingivalis, Tannarela forsythia, Treponema denticola, and Aggregatibacter actinomycetemcomitans) (GF-MoR's red triangle). The second most observed bacteria were grouped in GF-MoR's blue triangle: Porphyromonas spp., Prevotela spp., and Treponema spp., which were present in five of the six groups. The third most detected bacteria were clustered in the grey polygon (GF-MoR's grey polygon): Fusobacterium nucleatum, Prevotella intermedia, Campylobacter rectus, and Eikenella corrodens. These three geometric shapes had the most relevant bacteria to periodontal and peri-implant diseases. Specifically, per group, GF-MoR's health group had 58 species; GF-MoR's gingivitis group presented 16 bacteria; GF-MoR's peri-implant mucositis included 17 bacteria; GF-MoR's periodontitis group had 101 different bacteria; GF-MoR's peri-implantitis presented 61 bacteria; and the last group was a combination of necrotizing diseases and molar-incisor (M-I) pattern periodontitis, with seven bacteria. After observing the top seven bacteria of all groups, all of them were found to be gram-negative. Groups 4 and 5 (periodontitis and peri-implantitis) presented the same top seven bacteria. For the first time in the literature, GF-MoR's complexes were presented, gathering bacteria data according to the condition found and including more bacteria than in Socransky's complexes. Based on this understanding, this study could drive future research into treatment options for periodontal and peri-implant diseases, guiding future studies and collaborations to prevent and worsen systemic conditions. Moreover, it permits the debate about the evolution of bacterial clusters.

Periodontitis and risk of cancer: Mechanistic evidence

This review aims to critically analyze the pathways of interaction and the pathogenic mechanisms linking periodontitis and oral bacteria with the initiation/progression of cancer at different body compartments. A higher risk of head and neck cancer has been consistently associated with periodontitis. This relationship has been explained by the local promotion of dysbiosis, chronic inflammation, immune evasion, and direct (epi)genetic damage to epithelial cells by periodontal pathobionts and their toxins. Epidemiological reports have also studied a possible link between periodontitis and the incidence of other malignancies at distant sites, such as lung, breast, prostate, and digestive tract cancers. Mechanistically, different pathways have been involved, including the induction of a chronic systemic inflammatory state and the spreading of oral pathobionts with carcinogenic potential. Indeed, periodontitis may promote low-grade systemic inflammation and phenotypic changes in the mononuclear cells, leading to the release of free radicals and cytokines, as well as extracellular matrix degradation, which are all mechanisms involved in carcinogenic and metastatic processes. Moreover, the transient hematogenous spill out or micro-aspiration/swallowing of periodontal bacteria and their virulence factors (i.e., lipopolysaccharides, fimbriae), may lead to non-indigenous bacterial colonization of multiple microenvironments. These events may in turn replenish the tumor-associated microbiome and thus influence the molecular hallmarks of cancer. Particularly, specific strains of oral pathobionts (e.g., Porphyromonas gingivalis and Fusobacterium nucleatum) may translocate through the hematogenous and enteral routes, being implicated in esophageal, gastric, pancreatic, and colorectal tumorigenesis through the modulation of the gastrointestinal antitumor immune system (i.e., tumor-infiltrating T cells) and the increased expression of pro-inflammatory/oncogenic genes. Ultimately, the potential influence of common risk factors, relevant comorbidities, and upstream drivers, such as gerovulnerability to multiple diseases, in explaining the relationship cannot be disregarded. The evidence analyzed here emphasizes the possible relevance of periodontitis in cancer initiation/progression and stimulates future research endeavors.

Odontogenic Maxillary Sinusitis Microbiology Compared With Chronic Rhinosinusitis: A Meta-Analysis

BACKGROUND

Subtypes of sinusitis have different symptoms and prognoses due to different pathogens. Odontogenic maxillary sinusitis (OMS) mainly occurs unilaterally and is different from chronic rhinosinusitis (CRS) usually occurring bilaterally in terms of clinical characteristics. However, comprehensive microbiological comparisons between OMS and CRS have never been systematically conducted and most comparisons are methodologically biased. This study aims to provide a comprehensive analysis of the microbiology associated with OMS and CRS through a meta-analysis approach in order to provide evidence for differential diagnosis of OMS and CRS from a microbiological perspective.

METHODS

The databases PubMed and CNKI were searched from their inception to July 2023. A random-effects model was employed to derive the pooled prevalence estimates of the identified bacterial species or genera.

RESULTS

The 17 represented studies included 6 concerning OMS, 12 concerning CRS, and 4 concerning normal sinus, yielding 191, 610, and 92 samples, respectively. Though not statistically significant, the prevalence of Peptostreptococcus and Prevotella was generally higher in OMS compared to CRS. Notably, Fusobacterium was identified as the only genus with a significantly higher prevalence in OMS compared to CRS.

CONCLUSION

Fusobacterium was significantly more prevalent in OMS compared with CRS, while Staphylococcus aureus was more prevalent in CRS than in OMS. Such differences in bacterial profile may partly explain the distinct pathology observed and contribute to the development of novel strategies for diagnosis and therapeutic interventions in OMS.

Oral host-microbe interactions investigated in 3D organotypic models

The oral cavity is inhabited by abundant microbes which continuously interact with the host and influence the host's health. Such host-microbe interactions (HMI) are dynamic and complex processes involving e.g. oral tissues, microbial communities and saliva. Due to difficulties in mimicking the in vivo complexity, it is still unclear how exactly HMI influence the transition between healthy status and disease conditions in the oral cavity. As an advanced approach, three-dimensional (3D) organotypic oral tissues (epithelium and mucosa/gingiva) are being increasingly used to study underlying mechanisms. These in vitro models were designed with different complexity depending on the research questions to be answered. In this review, we summarised the existing 3D oral HMI models, comparing designs and readouts, discussing applications as well as future perspectives.

Expression of tight junction proteins in smokers and non-smokers with generalized Stage III periodontitis

OBJECTIVE

This study aims to evaluate the gingival crevicular fluid (GCF) levels of tumor necrosis factor-α (TNF-α), zonula occludens-1 (ZO-1), occludin (Occ), and tricellulin (Tric) in periodontitis, as well as their alterations due to smoking.

BACKGROUND

Tight junctions (TJ), which consist of transmembrane and cytoplasmic scaffolding proteins, connect the epithelial cells of the periodontium. Occ, claudins, junctional adhesion molecules, and Tric are transmembrane TJ proteins found at the cell membrane. The transmembrane TJ proteins and the intracellular cytoskeleton are directly linked by cytoplasmic scaffolding proteins such as ZO-1. Although the functions and locations of these molecules have been defined, their behavior in periodontal inflammation is unknown.

METHODS

The study included four groups: individuals with periodontal health without smoking (C; n = 31), individuals with generalized Stage III periodontitis without smoking (P; n = 28), individuals with periodontal health while smoking (CS; n = 22), and individuals with generalized Stage III periodontitis while smoking (PS; n = 18). Clinical periodontal parameters were recorded, and enzyme-linked immunosorbent assay (ELISA) was used to examine ZO-1, Occ, Tric, and TNF-α levels in GCF.

RESULTS

In the periodontitis groups, clinical parameters were significantly higher (p < .001). The site-specific levels of TNF-α, ZO-1, Tric, and Occ in the P group were statistically higher than those in the other groups (p < .05). TNF-α, probing pocket depth (PPD), and bleeding on probing (BOP) exhibited positive correlations with all TJ proteins (p < .005).

CONCLUSIONS

Smoking could potentially affect the levels of epithelial TJ proteins in the GCF, thereby potentially playing a significant role in the pathogenesis of the periodontal disease.

Interleukin-22 Inhibits Apoptosis of Gingival Epithelial Cells Through TGF-β Signaling Pathway During Periodontitis

Periodontitis is a chronic inflammatory disease characterized by the destruction of tooth-supporting tissues. The gingival epithelium is the first barrier of periodontal tissue against oral pathogens and harmful substances. The structure and function of epithelial lining are essential for maintaining the integrity of the epithelial barrier. Abnormal apoptosis can lead to the decrease of functional keratinocytes and break homeostasis in gingival epithelium. Interleukin-22 is a cytokine that plays an important role in epithelial homeostasis in intestinal epithelium, inducing proliferation and inhibiting apoptosis, but its role in gingival epithelium is poorly understood. In this study, we investigated the effect of interleukin-22 on apoptosis of gingival epithelial cells during periodontitis. Interleukin-22 topical injection and Il22 gene knockout were performed in experimental periodontitis mice. Human gingival epithelial cells were co-cultured with Porphyromonas gingivalis with interleukin-22 treatment. We found that interleukin-22 inhibited apoptosis of gingival epithelial cells during periodontitis in vivo and in vitro, decreasing Bax expression and increasing Bcl-xL expression. As for the underlying mechanisms, we found that interleukin-22 reduced the expression of TGF-β receptor type II and inhibited the phosphorylation of Smad2 in gingival epithelial cells during periodontitis. Blockage of TGF-β receptors attenuated apoptosis induced by Porphyromonas gingivalis and increased Bcl-xL expression stimulated by interleukin-22. These results confirmed the inhibitory effect of interleukin-22 on apoptosis of gingival epithelial cells and revealed the involvement of TGF-β signaling pathway in gingival epithelial cell apoptosis during periodontitis.

Effect of Hesperidin on Barrier Function and Reactive Oxygen Species Production in an Oral Epithelial Cell Model, and on Secretion of Macrophage-Derived Inflammatory Mediators during Porphyromonas gingivalis Infection

Porphyromonas gingivalis is a periodontopathogenic bacterium that can adhere to and colonize periodontal tissues, leading to an inflammatory process, and, consequently, tissue destruction. New therapies using flavonoids, such as hesperidin, are being studied, and their promising properties have been highlighted. The aim of this study was to evaluate the effect of hesperidin on the epithelial barrier function, reactive oxygen species (ROS) production, and on the inflammatory response caused by P. gingivalis in in vitro models. The integrity of the epithelial tight junctions challenged by P. gingivalis was determined by monitoring the transepithelial electrical resistance (TER). P. gingivalis adherence to a gingival keratinocyte monolayer and a basement membrane model were evaluated by a fluorescence assay. A fluorometric assay was used to determine the ROS production in gingival keratinocytes. The level of pro-inflammatory cytokines and matrix metalloproteinases (MMPs) secretion was evaluated by ELISA; to assess NF-κB activation, the U937-3xjB-LUC monocyte cell line transfected with a luciferase reporter gene was used. Hesperidin protected against gingival epithelial barrier dysfunction caused by P. gingivalis and reduced the adherence of P. gingivalis to the basement membrane model. Hesperidin dose-dependently inhibited P. gingivalis-mediated ROS production by oral epithelial cells as well as the secretion of IL-1β, TNF-α, IL-8, MMP-2, and MMP-9 by macrophages challenged with P. gingivalis. Additionally, it was able to attenuate NF-κB activation in macrophages stimulated with P. gingivalis. These findings suggest that hesperidin has a protective effect on the epithelial barrier function, in addition to reducing ROS production and attenuating the inflammatory response associated with periodontal disease.

Bacterial extracellular vesicles and their interplay with the immune system

The mammalian intestinal tract harbors trillions of microorganisms confined within this space by mucosal barriers. Despite these barriers, bacterial components may still be found elsewhere in the body, even in healthy subjects. Bacteria can release small lipid-bound particles, also named bacterial extracellular vesicles (bEV). While bacteria themselves cannot normally penetrate the mucosal defense, bEVs may infiltrate the barrier and disseminate throughout the body. The extremely diverse cargo that bEVs can carry, depending on their parent species, strain, and growth conditions, grant them an equally broad potential to interact with host cells and influence immune functions. Herein, we review the current knowledge of processes underlying the uptake of bEVs by mammalian cells, and their effect on the immune system. Furthermore, we discuss how bEVs could be targeted and manipulated for diverse therapeutic purposes.

Effects of a Berry Polyphenolic Fraction on the Pathogenic Properties of Porphyromonas gingivalis

Porphyromonas gingivalis expresses a broad array of virulence factors that enable it to play a central role in the etiopathogenesis of periodontitis. The objective of the present study was to assess the effects of a berry polyphenolic fraction (Orophenol®) composed of extracts from cranberry, wild blueberry, and strawberry on the main pathogenic determinants of P. gingivalis. Orophenol® attenuated the growth of P. gingivalis and decreased its hemolytic activity, its adherence to a basement membrane matrix model, and its proteinase activities. The berry polyphenolic fraction also impaired the production of reactive oxygen species (ROS) by oral keratinocytes stimulated with P. gingivalis. Lastly, using an in vitro model of oral keratinocyte barrier, the fraction exerted a protective effect against the damages mediated by P. gingivalis. In conclusion, the berry polyphenolic fraction investigated in the present study attenuated several pathogenic properties of P. gingivalis. Although future clinical investigations are required, our study provided evidence that the polyphenols contained in this fraction may represent bioactive molecules of high interest for the prevention and/or treatment of periodontal disease.

A Phenolic-rich Extract of Cocoa (Theobroma cacao L.) Beans Impairs the Pathogenic Properties of Porphyromonas gingivalis and Attenuates the Activation of Nuclear Factor Kappa B in a Monocyte Model

Periodontitis, an inflammatory disease that affects tooth-supporting tissues, is the result of a polymicrobial infection involving mainly Gram negative anaerobic bacteria. The aim of the present study was to investigate the effects of a phenolic-rich extract of cocoa (Theobroma cacao L.) beans on the pathogenic properties of Porphyromonas gingivalis, which is well-known as a keystone pathogen in the development of periodontitis. The effect of the cocoa extract on P. gingivalis-induced activation of the nuclear factor kappa B (NF-κB) transcription factor in a monocyte model was also assessed. The cocoa extract, whose major phenolic compound was epicatechin, inhibited the growth, hemolytic activity, proteolytic activities, and adherence properties (basement membrane matrix, erythrocytes) of P. gingivalis in a dose-dependent manner. It also protected the barrier function of a keratinocyte model against the deleterious effects mediated by P. gingivalis, and attenuated reactive oxygen species (ROS) production by oral keratinocytes treated with P. gingivalis. Lastly, the cocoa extract showed an anti-inflammatory property by preventing P. gingivalis-induced NF-κB activation in monocytes. In conclusion, this in vitro study highlighted the potential value of an epicatechin-rich extract of cocoa beans for preventing and/or treating periodontal diseases.

Oral, Tongue-Coating Microbiota, and Metabolic Disorders: A Novel Area of Interactive Research

Interactions between colonizing microbiota and the host have been fully confirmed, among which the tongue-coating microbiota have a moderate rate of renewal and disease sensitivity and are easily obtained, making them an ideal research subject. Oral microbiota disorders are related to diabetes, obesity, cardiovascular disease, cancer, and other systemic diseases. As an important part of the oral cavity, tongue-coating microbiota can promote gastritis and digestive system tumors, affecting the occurrence and development of multiple chronic diseases. Common risk factors include diet, age, and immune status, among others. Metabolic regulatory mechanisms may be similar between the tongue and gut microbiota. Tongue-coating microbiota can be transferred to the respiratory or digestive tract and create a new balance with local microorganisms, together with the host epithelial cells forming a biological barrier. This barrier is involved in the production and circulation of nitric oxide (NO) and the function of taste receptors, forming the oral-gut-brain axis (similar to the gut-brain axis). At present, the disease model and mechanism of tongue-coating microbiota affecting metabolism have not been widely studied, but they have tremendous potential.

A cocoa (Theobroma cacao L.) extract impairs the growth, virulence properties, and inflammatory potential of Fusobacterium nucleatum and improves oral epithelial barrier function

Fusobacterium nucleatum is associated with many conditions and diseases, including periodontal diseases that affect tooth-supporting tissues. The aim of the present study was to investigate the effects of a cocoa extract (Theobroma cacao L.) on F. nucleatum with respect to growth, biofilm formation, adherence, and hydrogen sulfide (H₂S) production. The anti-inflammatory properties and the effect on epithelial barrier function of the cocoa extract were also assessed. The cocoa extract, whose major phenolic compound is epicatechin, dose-dependently inhibited the growth, biofilm formation, adherence properties (basement membrane matrix, oral epithelial cells), and H₂S production of F. nucleatum. It also decreased IL-6 and IL-8 production by F. nucleatum-stimulated oral epithelial cells and inhibited F. nucleatum-induced NF-κB activation in monocytes. Lastly, the cocoa extract enhanced the barrier function of an oral epithelial model by increasing the transepithelial electrical resistance. We provide evidence that the beneficial properties of an epicatechin-rich cocoa extract may be useful for preventing and/or treating periodontal diseases.

A Dual Zinc plus Arginine formulation protects against tumor necrosis factor-alpha-induced barrier dysfunction and enhances cell proliferation and migration in an in vitro gingival keratinocyte model

OBJECTIVE

To investigate the effects of Dual Zinc plus Arginine formulations (aqueous solution and dentifrice) on tumor necrosis factor-alpha (TNF-α)-induced barrier dysfunction as well as on cell proliferation and migration in an in vitro gingival keratinocyte model.

DESIGN

Gingival keratinocytes were seeded onto the membrane of a double-chamber system in the absence and presence of recombinant TNF-α and the formulations under investigation. The barrier function was assessed by determination of transepithelial electrical resistance (TER) and paracellular transport of fluorescein isothiocyanate (FITC)-dextran. The distribution of zonula occludens-1 (ZO-1) and occludin was visualized by immunofluorescence microscopy. The effects of the formulations on keratinocyte cell proliferation were determined using a fluorescent cell tracker dye, while a migration assay kit was used to investigate their effects on cell migration.

RESULTS

Under conditions where TNF-α induces loss of keratinocyte barrier integrity, the Dual Zinc plus Arginine formulations (aqueous solution and dentifrice) protected the keratinocyte tight junction against the damages since they prevented the TNF-α-induced drop in TER and increase in FITC-dextran paracellular flux in the in vitro model. The treatment of keratinocytes with the formulations markedly mitigated the altered distribution of ZO-1 and occludin. Both formulations increased the proliferation of keratinocytes and alleviated the negative impact caused by TNF-α. Lastly, the formulations increased the migration capacity of keratinocytes.

CONCLUSIONS

The ability of the Dual Zinc plus Arginine formulations to protect the barrier integrity of gingival keratinocytes from TNF-α-induced damage and to promote their proliferation and migration suggests that they may offer benefits for oral health.

Effects of a tart cherry (Prunus cerasus L.) phenolic extract on Porphyromonas gingivalis and its ability to impair the oral epithelial barrier

Periodontal diseases, including gingivitis and periodontitis, are a global oral health problem. Porphyromonas gingivalis, a key pathogen involved in the onset of periodontitis, is able to colonize the subgingival epithelium and invade the underlying connective tissue due to the contribution of cysteine proteases known as gingipains. In this study, we investigated the effects of a phenolic extract prepared from tart cherry (Prunus cerasus L.) juice on the growth, adherence, and protease activity of P. gingivalis. We also assessed the protective effect of the tart cherry extract on the disruption of the oral epithelial barrier induced by P. gingivalis. The tart cherry extract that contains procyanidins and quercetin and its derivatives (rutinoside, glucoside) as the most important phenolic compounds attenuated P. gingivalis growth, reduced adherence to an experimental basement membrane matrix model, and decreased the protease activities of P. gingivalis. The tart cherry extract also exerted a protective effect on the integrity of the oral epithelial barrier in an in vitro model infected with P. gingivalis. More specifically, the extract prevented a decrease in transepithelial electrical resistance as well as the destruction of tight junction proteins (zonula occludens-1 and occludin). These results suggest that the tart cherry phenolic extract may be a promising natural product for the treatment of periodontitis through its ability to attenuate the virulence properties of P. gingivalis and curtail the ability of this pathogen to impair the oral epithelial barrier.

Highbush blueberry proanthocyanidins alleviate Porphyromonas gingivalis-induced deleterious effects on oral mucosal cells

Strong evidence points to Porphyromonas gingivalis, a Gram-negative anaerobic bacterium, as a keystone species in the development of the chronic form of periodontitis. The aim of the present study was to investigate the ability of highbush blueberry proanthocyanidins (PACs) to alleviate the P. gingivalis-induced deleterious effects on oral mucosal cells. We first showed that highbush blueberry PACs protect the integrity of the gingival keratinocyte barrier against P. gingivalis-mediated damage, as determined by measuring the transepithelial electrical resistance and paracellular flux of FITC-conjugated dextran. Moreover, the PACs prevented the translocation of P. gingivalis across the gingival keratinocyte barrier model. The proteinase activity of P. gingivalis was inhibited by the PACs suggesting that they may exert beneficial effects by reducing proteolytic degradation of the epithelial tight junctions. Regulation of gingival fibroblast inflammatory reactions may be one of the ways to prevent and control periodontal disease progression and severity. We showed that PACs significantly reduce IL-6 and IL-8 secretion by P. gingivalis-stimulated gingival fibroblasts. The present study showed the capacity of highbush blueberry PACs to protect the integrity of an in vitro model of gingival keratinocyte barrier against P. gingivalis, and to attenuate the secretion of pro-inflammatory cytokines by gingival fibroblasts infected with P. gingivalis. These results suggest beneficial effects of blueberry PACs thus supporting the need for future clinical trials on the potential of these bioactive molecules for periodontal disease prevention and/or treatment.

Maintaining barrier function of infected gingival epithelial cells by inhibition of DNA methylation

BACKGROUND

Infection and inflammation induce epigenetic changes that alter gene expression. In periodontal disease, inflammation, and microbial dysbiosis occur, which can lead to compromised barrier function of the gingival epithelia. Here, we tested the hypotheses that infection of cultured human gingival epithelial (HGEp) cells with Porphyromonas gingivalis disrupts barrier function by inducing epigenetic alterations and that these effects can be blocked by inhibitors of DNA methylation.

METHODS

Primary HGEp cells were infected with P. gingivalis either in the presence or absence of the non-nucleoside DNA methyltransferase (DNMT) inhibitors RG108, (-) epigallocatechin-3-gallate (EGCG), or curcumin. Barrier function was assessed as transepithelial electrical resistance (TEER). DNA methylation and mRNA abundance were quantified for genes encoding components of three cell-cell junction complexes, CDH1, PKP2, and TJP1. Cell morphology and the abundance of cell-cell junction proteins were evaluated by confocal microscopy.

RESULTS

Compared to non-infected cells, P. gingivalis infection decreased TEER (P < 0.0001) of HGEp cells; increased methylation of the CDH1, PKP2, and TJP1 (P < 0.0001); and reduced their expression (mRNA abundance) (P < 0.005). Pretreatment with DNMT inhibitors prevented these infection-induced changes in HGEp cells, as well as the altered morphology associated with infection.

CONCLUSION

Pathogenic infection induced changes in DNA methylation and impaired the barrier function of cultured primary gingival epithelial cells, which suggests a mechanism for systemic consequences of periodontal disease. Inhibition of these events by non-nucleoside DNMT inhibitors represents a potential strategy to treat periodontal disease.

A Dual Zinc plus Arginine formulation attenuates the pathogenic properties of Porphyromonas gingivalis and protects gingival keratinocyte barrier function in an in vitro model

Background and objectives

Porphyromonas gingivalis, a late colonizer of the periodontal biofilm, has been strongly associated with the chronic form of periodontitis. The aim of this study was to investigate the effects of a Dual Zinc plus Arginine formulation (aqueous solution and dentifrice) on the pathogenic properties of P. gingivalis and the barrier function of an in vitro gingival epithelium model.

Results

The Dual Zinc plus Arginine aqueous solution and dentifrice inhibited the hemolytic and proteolytic activities of P. gingivalis. The Dual Zinc plus Arginine aqueous solution and dentifrice enhanced the barrier function of an in vitro gingival epithelium model as determined by a time-dependent increase in transepithelial electrical resistance and decrease in paracellular permeability. This was associated with an increased immunolabeling of two important tight junction proteins: zonula occludens-1 and occludin. The deleterious effects of P. gingivalis on keratinocyte barrier function as well as the ability of the bacterium to translocate through a gingival epithelium model were attenuated in the presence of either Dual Zinc plus Arginine aqueous solution or dentifrice.

Conclusions

The Dual Zinc plus Arginine formulation may offer benefits for patients affected by periodontal disease through its ability to attenuate the pathogenic properties of P. gingivalis and promote keratinocyte barrier function.

Outer membrane vesicles derived from Porphyromonas gingivalis induced cell death with disruption of tight junctions in human lung epithelial cells

OBJECTIVE

Porphyromonas gingivalis (P. gingivalis) is a major bacterium responsible for the progression of periodontitis. P. gingivalis produces small vesicles called outer membrane vesicles (OMVs) containing virulence factors. Increasing evidence suggests a close relationship between periodontitis and respiratory system diseases, such as aspiration pneumonia. However, little is known about whether P. gingivalis OMVs give rise to the impediment of lung epithelial cells. We investigated the effect of the OMVs on cell viability and tight junctions of lung epithelial cells.

DESIGN

Human lung epithelial A549 cells were treated with P. gingivalis OMVs. Cell viability was evaluated, and cell morphology was examined using scanning electron and phase contrast microscopies. To detect apoptosis induced by P. gingivalis OMVs, activation of caspase-3 and poly ADP-ribose polymerase (PARP) cleavage was examined by using Western blotting. Immunocytochemistry was performed to stain tight junction proteins.

RESULTS

P. gingivalis OMVs decreased cell viability in A549 cells in a dose- and time-dependent manner. Microscopic analysis revealed that the OMVs induced morphological changes leading to irregular cell membrane structures. The OMVs caused cell shrinkage, membrane blebbing, and cytoplasmic expulsion in a dose-dependent manner. Western blot analysis showed the OMVs induced caspase-3 activation and PARP cleavage. Treatment with the OMVs disrupted the intact distributions of tight junction proteins.

CONCLUSIONS

These results indicate that P. gingivalis OMVs induced cell death by destroying the barrier system in lung epithelial cells. Our present study raises the possibility that P. gingivalis OMVs is an important factor in the engagement of periodontitis with respiratory system diseases.

IL-1β strengthens the physical barrier in gingival epithelial cells

Periodontitis is one of the most common oral diseases worldwide and is caused by a variety of interactions between oral bacteria and the host. Here, pathogens induce inflammatory host responses that cause the secretion of proinflammatory cytokines such as IL-1β, IL-6, and IL-8 by oral epithelial cells. In various systems, it has been shown that inflammation compromises physical barriers, which enables bacteria to invade the tissue. In this study, we investigated the barrier properties of the oral mucosa under physiological and inflamed conditions. For this purpose, we assessed the influence of IL-1β on the transepithelial electrical resistance and in particular on tight junctions in vitro in human stratified squamous epithelium models. Indirect immunofluorescence and western blot analyses were performed to investigate localization and expression of tight junction proteins in primary gingival cells, immortalized gingival cells and native gingiva. Furthermore, the TEER of gingival keratinocytes was assessed. The results showed that IL-1β led to strengthening of the gingival keratinocyte barrier. This was demonstrated by an increase in TEER, the upregulation of TJ proteins, and an increase in the formation of TJ strands. The IL-1β-mediated upregulation of occludin was prevented by the NF-κB inhibitor BAY 11-7085. These observations provide insights into host responses in the early stages of periodontal disease and offer information about TJ formation in human gingival epithelial cells under physiological and inflammatory conditions. Comprehensive knowledge of the physical barrier during inflammation may help in developing strategies to effectively target the inflammatory barrier to improve the bioavailability of drugs for the treatment of periodontitis.

Resveratrol attenuates the pathogenic and inflammatory properties of Porphyromonas gingivalis

Porphyromonas gingivalis has been strongly associated with chronic periodontitis, which affects tooth-supporting tissues. This Gram-negative anaerobic bacterium produces a repertoire of virulence factors that modulate tissue destruction directly or indirectly by the induction of inflammatory processes. The aim of this study was to investigate the effects of resveratrol, a major polyphenol found in grapes and wine, on the growth and virulence properties of P. gingivalis as well as on gingival keratinocyte tight junction integrity and the host inflammatory response. Resveratrol exhibited antibacterial activity that may result from damage to the bacterial cell membrane. Resveratrol also killed a pre-formed P. gingivalis biofilm and reduced bacterial adherence to matrix proteins. In addition, resveratrol had a protective effect on the integrity of the keratinocyte tight junctions by inhibiting its breakdown by P. gingivalis. This may be related to the ability of resveratrol to inhibit the protease activities of P. gingivalis. Lastly, resveratrol reduced P. gingivalis-mediated activation of the NF-κB signaling pathway and attenuated TREM-1 gene expression as well as soluble TREM-1 secretion in monocytes. The effect on NF-κB activation likely results from the ability of resveratrol to act as a PPAR-γ agonist. In summary, the antibacterial, anti-adherence, and antiprotease properties of resveratrol, as well as its ability to protect the gingival keratinocyte barrier and attenuate the inflammatory response in monocytes suggest that it may be a promising novel therapeutic agent for treating periodontal disease.

Epigenetic reprogramming in periodontal disease: Dynamic crosstalk with potential impact in oncogenesis

Periodontitis is a chronic multifactorial inflammatory disease associated with microbial dysbiosis and characterized by progressive destruction of the periodontal tissues. Such chronic infectious inflammatory disease is recognized as a major public health problem worldwide with measurable impact in systemic health. It has become evident that the periodontal disease phenotypes are not only determined by the microbiome effect, but the extent of the tissue response is also driven by the host genome and epigenome patterns responding to various environmental exposures. More recently there is mounting evidence indicating that epigenetic reprogramming in response to combined intrinsic and environmental exposures, might be particularly relevant due its plasticity and potential application towards precision health. The complex epigenetic crosstalk is reflected in the prognosis and progress of periodontal diseases and may also lead to a favorable landscape for cancer development. This review discusses epigenomics modifications focusing on the role of DNA methylation and pathways linking microbial infection and inflammatory pathways, which are also associated with carcinogenesis. There is a more clear vision whereas 'omics' technologies applied to unveil relevant epigenetic factors could play a significant role in the treatment of periodontal disease in a personalized mode, evidencing that public health approach should coexist with precision individualized treatment.

Three-Dimensional In Vitro Oral Mucosa Models of Fungal and Bacterial Infections

Oral mucosa is the target tissue for many microorganisms involved in periodontitis and other infectious diseases affecting the oral cavity. Three-dimensional (3D) in vitro and ex vivo oral mucosa equivalents have been used for oral disease modeling and investigation of the mechanisms of oral bacterial and fungal infections. This review was conducted to analyze different studies using 3D oral mucosa models for the evaluation of the interactions of different microorganisms with oral mucosa. In this study, based on our inclusion criteria, 43 articles were selected and analyzed. Different types of 3D oral mucosa models of bacterial and fungal infections were discussed in terms of the biological system used, culture conditions, method of infection, and the biological endpoints assessed in each study. The critical analysis revealed some contradictory reports in this field of research in the literature. Challenges in recovering bacteria from oral mucosa models were further discussed, suggesting possible future directions in microbiomics, including the use of oral mucosa-on-a-chip. The potential use of these 3D tissue models for the evaluation of the effects of antiseptic agents on bacteria and oral mucosa was also addressed. This review concluded that there were many aspects that would require optimization and standardization with regard to using oral mucosal models for infection by microorganisms. Using new technologies-such as microfluidics and bioreactors-could help to reproduce some of the physiologically relevant conditions and further simulate the clinical situation. Impact statement Tissue-engineered or commercial models of the oral mucosa are very useful for the study of diseases that involve the interaction of microorganisms and oral epithelium. In this review, challenges in recovering bacteria from oral mucosa models, the potential use of these three-dimensional tissue models for the evaluation of the effects of antiseptic agents, and future directions in microbiomics are discussed.

Characterization of intratissue bacterial communities and isolation of Escherichia coli from oral lichen planus lesions

Oral lichen planus (OLP) is a chronic T cell-mediated inflammatory disease of unknown etiology. We previously proposed that the intracellular bacteria detected in OLP lesions are important triggering factors for T cell infiltration. This study aimed to identify OLP-associated bacterial species through the characterization of intratissue bacterial communities of OLP lesions. Seven pairs of bacterial communities collected from the mucosal surface and biopsied tissues of OLP lesions were analyzed by high-throughput sequencing of the 16S rRNA gene. The intratissue bacterial communities were characterized by decreased alpha diversity but increased beta diversity compared with those on the mucosal surface. While the relative abundance of most taxa was decreased within the tissues, that of Escherichia coli was significantly increased. Four E. coli strains were isolated from additional OLP biopsies and verified as K12 strains by whole-genome sequencing. The distribution of E. coli in sections of control (n = 12) and OLP (n = 22) tissues was examined by in situ hybridization. E. coli was detected in most OLP tissues, suggesting its potential role in the pathogenesis of OLP. The oral E. coli strains isolated from OLP tissues will be useful to investigate their role as triggering factors for T cell infiltration.

Keratinocytes protect soft-tissue integration of dental implant materials against bacterial challenges in a 3D-tissue infection model

The soft-tissue seal around dental implants protects the osseo-integrated screw against bacterial challenges. Surface properties of the implant material are crucial for implant survival against bacterial challenges, but there is no adequate in vitro model mimicking the soft-tissue seal around dental implants. Here, we set up a 3D-tissue model of the soft-tissue seal, in order to establish the roles of oral keratinocytes, gingival fibroblasts and materials surface properties in the protective seal. To this end, keratinocytes were grown on membrane filters in a transwell system, while fibroblasts were adhering to TiO₂ surfaces underneath the membrane. In absence of keratinocytes on the membrane, fibroblasts growing on the TiO₂ surface could not withstand challenges by commensal streptococci or pathogenic staphylococci. Keratinocytes growing on the membrane filters could withstand bacterial challenges, but tight junctions widened to allow invasion of bacteria to the underlying fibroblast layer in lower numbers than in absence of keratinocytes. The challenge of this bacterial invasion to the fibroblast layer on the TiO₂ surface negatively affected tissue integration of the surface, demonstrating the protective barrier role of keratinocytes. Streptococci caused less damage to fibroblasts than staphylococci. Importantly, the protection offered by the soft-tissue seal appeared sensitive to surface properties of the implant material. Integration by fibroblasts of a hydrophobic silicone rubber surface was affected more upon bacterial challenges than integration of more hydrophilic hydroxyapatite or TiO₂ surfaces. This differential response to different surface-chemistries makes the 3D-tissue infection model presented a useful tool in the development of new infection-resistant dental implant materials. STATEMENT OF SIGNIFICANCE: Failure rates of dental implants due to infection are surprisingly low, considering their functioning in the highly un-sterile oral cavity. This is attributed to the soft-tissue seal, protecting the osseo-integrated implant part against bacterial invasion. The seal consists of a layer of keratinocytes covering gingival fibroblasts, integrating the implant. Implant failure involves high patient discomfort and costs of replacing an infected implant, which necessitates development of improved, infection-resistant dental implant materials. New materials are often evaluated in mono-culture, examining bacterial adhesion or tissue interactions separately and neglecting the 3D-structure of the tissue seal. A 3D-tissue model allows to study new materials in a more relevant way, in which interactions between keratinocytes, gingival fibroblast, bacteria and materials surfaces are accounted for.

Porphyromonas gingivalis Impairs Oral Epithelial Barrier through Targeting GRHL2

Oral mucosa provides the first line of defense against a diverse array of environmental and microbial irritants by forming the barrier of epithelial cells interconnected by multiprotein tight junctions (TJ), adherens junctions, desmosomes, and gap junction complexes. Grainyhead-like 2 (GRHL2), an epithelial-specific transcription factor, may play a role in the formation of the mucosal epithelial barrier, as it regulates the expression of the junction proteins. The current study investigated the role of GRHL2 in the Porphyromonas gingivalis (Pg)-induced impairment of epithelial barrier functions. Exposure of human oral keratinocytes (HOK-16B and OKF6 cells) to Pg or Pg-derived lipopolysaccharides (Pg LPSs) led to rapid loss of endogenous GRHL2 and the junction proteins (e.g., zonula occludens, E-cadherin, claudins, and occludin). GRHL2 directly regulated the expression levels of the junction proteins and the epithelial permeability for small molecules (e.g., dextrans and Pg bacteria). To explore the functional role of GRHL2 in oral mucosal barrier, we used a Grhl2 conditional knockout (KO) mouse model, which allows for epithelial tissue-specific Grhl2 KO in an inducible manner. Grhl2 KO impaired the expression of the junction proteins at the junctional epithelium and increased the alveolar bone loss in the ligature-induced periodontitis model. Fluorescence in situ hybridization revealed increased epithelial penetration of oral bacteria in Grhl2 KO mice compared with the wild-type mice. Also, blood loadings of oral bacteria (e.g., Bacteroides, Bacillus, Firmicutes, β-proteobacteria, and Spirochetes) were significantly elevated in Grhl2 KO mice compared to the wild-type littermates. These data indicate that Pg bacteria may enhance paracellular penetration through oral mucosa in part by targeting the expression of GRHL2 in the oral epithelial cells, which then impairs the epithelial barrier by inhibition of junction protein expression, resulting in increased alveolar tissue destruction and systemic bacteremia.

Effects of Actinobacillus pleuropneumoniae on barrier function and inflammatory response of pig tracheal epithelial cells

Actinobacillus pleuropneumoniae is a respiratory pathogen that causes porcine pleuropneumonia, a fatal respiratory disease responsible for high economic losses in the swine industry worldwide. With the objective to better understand the interactions between A. pleuropneumoniae and the porcine respiratory epithelium, we investigated the capacity of this pathogen to damage the epithelial barrier and induce an inflammatory response. We showed that A. pleuropneumoniae, even at a multiplicity of infection of 10, is able to break the tracheal epithelial barrier integrity as determined by monitoring the transepithelial electrical resistance and fluorescein-isothiocyanate-dextran transport. Immunofluorescence staining analysis suggested that A. pleuropneumoniae is affecting two important tight junction proteins (occludin, zonula occludens-1). As a consequence of the breakdown of the epithelial barrier integrity, A. pleuropneumoniae can translocate across a cell monolayer. We also showed that tracheal epithelial cells secrete pro-inflammatory cytokines (IL-8, IL-6, TNF-α) in response to a stimulation with this pathogen. In summary, A. pleuropneumoniae is able to induce damage to the porcine respiratory epithelial barrier. Challenging the epithelial cells with A. pleuropneumoniae was also associated with the secretion of pro-inflammatory cytokines. This better knowledge of the interactions between A. pleuropneumoniae and the epithelial cells may help to design novel strategies to prevent epithelium invasion by this bacterium along with other swine respiratory pathogens.

The maintenance of an oral epithelial barrier

Oral epithelial barrier consists of closely controlled structure of the stratified squamous epithelium, which is the gateway to human bodies and encounters a huge burden of microbial, airborne and dietary antigens, as well as masticatory damage. Once this barrier is destroyed, it will trigger bone loss, tissue damage and microbial dysbiosis and lead to diseases, such as periodontitis, oral mucosal diseases and oral cancer. Recently, increasing evidences showed that different factors including microorganism, saliva, proteins and immune components have been considered to play a critical role in the disruption of oral epithelial barrier. Herein, we discussed mechanisms governing the maintenance of oral epithelial barrier. Besides, the role of oral epithelial barrier failure in oral carcinogenesis will also be talked about.

Oral Mucosal Epithelial Cells

Cellular Phenotype and Apoptosis: The function of epithelial tissues is the protection of the organism from chemical, microbial, and physical challenges which is indispensable for viability. To fulfill this task, oral epithelial cells follow a strongly regulated scheme of differentiation that results in the formation of structural proteins that manage the integrity of epithelial tissues and operate as a barrier. Oral epithelial cells are connected by various transmembrane proteins with specialized structures and functions. Keratin filaments adhere to the plasma membrane by desmosomes building a three-dimensional matrix.

Cell-Cell Contacts and Bacterial Influence: It is known that pathogenic oral bacteria are able to affect the expression and configuration of cell-cell junctions. Human keratinocytes up-regulate immune-modulatory receptors upon stimulation with bacterial components. Periodontal pathogens including P. gingivalis are able to inhibit oral epithelial innate immune responses through various mechanisms and to escape from host immune reaction, which supports the persistence of periodontitis and furthermore is able to affect the epithelial barrier function by altering expression and distribution of cell-cell interactions including tight junctions (TJs) and adherens junctions (AJs).

In the pathogenesis of periodontitis a highly organized biofilm community shifts from symbiosis to dysbiosis which results in destructive local inflammatory reactions.

Cellular Receptors: Cell-surface located toll like receptors (TLRs) and cytoplasmatic nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) belong to the pattern recognition receptors (PRRs). PRRs recognize microbial parts that represent pathogen-associated molecular patterns (PAMPs).

A multimeric complex of proteins known as inflammasome, which is a subset of NLRs, assembles after activation and proceeds to pro-inflammatory cytokine release.

Cytokine Production and Release: Cytokines and bacterial products may lead to host cell mediated tissue destruction. Keratinocytes are able to produce diverse pro-inflammatory cytokines and chemokines, including interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF)-α. Infection by pathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) can induce a differentiated production of these cytokines.

Immuno-modulation, Bacterial Infection, and Cancer Cells: There is a known association between bacterial infection and cancer. Bacterial components are able to up-regulate immune-modulatory receptors on cancer cells. Interactions of bacteria with tumor cells could support malignant transformation an environment with deficient immune regulation.

The aim of this review is to present a set of molecular mechanisms of oral epithelial cells and their reactions to a number of toxic influences.

Treponema denticola Induces Epithelial Barrier Dysfunction in Polarized Epithelial Cells

Treponema denticola, an anaerobic spirochete found mainly in the oral cavity, is associated with periodontal disease and has a variety of virulence factors. Although in vitro studies have shown that T. denticola is able to penetrate epithelial cell monolayers, its effect on the epithelial barrier junction is not known. Human gingival epithelial cells are closely associated with adjacent membranes, forming barriers in the presence of tight junction proteins, including zonula occludens-1 (ZO-1), claudin-1, and occludin. Tight junction proteins are also expressed by Madin-Darby canine kidney (MDCK) cells in culture. In this study, the MDCK cell profile was investigated following infection with T. denticola (ATCC 35405) wild-type, as well as with its dentilisin-deficient mutant, K1. Basolateral exposure of MDCK cell monolayers to T. denticola at a multiplicity of infection (MOI) of 10₄ resulted in a decrease in transepithelial electrical resistance (TER). Transepithelial electrical resistance in MDCK cell monolayers also decreased following apical exposure to T. denticola (MOI=10₄), although this took longer with basolateral exposure. The effect on the TER was time-dependent and required the presence of live bacteria. Meanwhile, MDCK cell viability showed a decrease with either basolateral or apical exposure. Immunofluorescence analysis demonstrated decreases in the amounts of immunoreactive ZO-1 and claudin-1 in association with disruption of cell-cell junctions in MDCK cells exposed apically or basolaterally to T. denticola. Western blot analysis demonstrated degradation of ZO-1 and claudin-1 in culture lysates derived from T. denticola-exposed MDCK cells, suggesting a bacteria-induced protease capable of cleaving these tight junction proteins.

Porphyromonas gingivalis bypasses epithelial barrier and modulates fibroblastic inflammatory response in an in vitro 3D spheroid model

Porphyromonas gingivalis-induced inflammatory effects are mostly investigated in monolayer cultured cells. The aim of this study was to develop a 3D spheroid model of gingiva to take into account epithelio-fibroblastic interactions. Human gingival epithelial cells (ECs) and human oral fibroblasts (FBs) were cultured by hanging drop method to generate 3D microtissue (MT) whose structure was analyzed on histological sections and the cell-to-cell interactions were observed by scanning and transmission electron microscopy (SEM and TEM). MTs were infected by P. gingivalis and the impact on cell death (Apaf-1, caspase-3), inflammatory markers (TNF-α, IL-6, IL-8) and extracellular matrix components (Col-IV, E-cadherin, integrin β1) was evaluated by immunohistochemistry and RT-qPCR. Results were compared to those observed in situ in experimental periodontitis and in human gingival biopsies. MTs exhibited a well-defined spatial organization where ECs were organized in an external cellular multilayer, while, FBs constituted the core. The infection of MT demonstrated the ability of P. gingivalis to bypass the epithelial barrier in order to reach the fibroblastic core and induce disorganization of the spheroid structure. An increased cell death was observed in fibroblastic core. The development of such 3D model may be useful to define the role of EC–FB interactions on periodontal host-immune response and to assess the efficacy of new therapeutics.

Cell culture models of oral mucosal barriers: A review with a focus on applications, culture conditions and barrier properties

Understanding the function of oral mucosal epithelial barriers is essential for a plethora of research fields such as tumor biology, inflammation and infection diseases, microbiomics, pharmacology, drug delivery, dental and biomarker research. The barrier properties are comprised by a physical, a transport and a metabolic barrier, and all these barrier components play pivotal roles in the communication between saliva and blood. The sum of all epithelia of the oral cavity and salivary glands is defined as the blood-saliva barrier. The functionality of the barrier is regulated by its microenvironment and often altered during diseases. A huge array of cell culture models have been developed to mimic specific parts of the blood-saliva barrier, but no ultimate standard in vitro models have been established. This review provides a comprehensive overview about developed in vitro models of oral mucosal barriers, their applications, various cultivation protocols and corresponding barrier properties.

Oral mucosa-on-a-chip to assess layer-specific responses to bacteria and dental materials

The human oral mucosa hosts a diverse microbiome and is exposed to potentially toxic biomaterials from dental restoratives. Mucosal health is partly determined by cell and tissue responses to challenges such as dental materials and pathogenic bacteria. An in vitro model to rapidly determine potential layer-specific responses would lead to a better understanding of mucosal homeostasis and pathology. Therefore, this study aimed to develop a co-cultured microfluidic mucosal model on-a-chip to rapidly assess mucosal remodeling and the responses of epithelial and subepithelial layers to challenges typically found in the oral environment. A gingival fibroblast-laden collagen hydrogel was assembled in the central channel of a three-channel microfluidic chamber with interconnecting pores, followed by a keratinocyte layer attached to the collagen exposed in the pores. This configuration produced apical and subepithelial side channels capable of sustaining flow. Keratinocyte, fibroblast, and collagen densities were optimized to create a co-culture tissue-like construct stable over one week. Cells were stained and imaged with epifluorescence microscopy to confirm layer characteristics. As proof-of-concept, the mucosal construct was exposed separately to a dental monomer, 2-hydroxylethyl methacrylate (HEMA), and the oral bacteria Streptococcus mutans. Exposure to HEMA lowered mucosal cell viability, while exposure to the bacteria lowered trans-epithelial electrical resistance. These findings suggest that the oral mucosa-on-a-chip is useful for studying oral mucosal interactions with bacteria and biomaterials with a histology-like view of the tissue layers.

Quorum-sensing molecule dihydroxy-2,3-pentanedione and its analogs as regulators of epithelial integrity

BACKGROUND AND OBJECTIVE

Quorum-sensing molecules regulate the behavior of bacteria within biofilms and at the same time elicit an immune response in host tissues. Our aim was to investigate the regulatory role of dihydroxy-2,3-pentanedione (DPD), the precursor of universal autoinducer-2 (AI-2), and its analogs (ethyl-DPD, butyl-DPD and isobutyl-DPD) in the integrity of gingival epithelial cells.

MATERIAL AND METHODS

Human gingival keratinocytes were incubated with four concentrations (10 μmol L^-1 , 1 μmol L^-1 , 100 nmol L^-1 and 10 nmol L^-1 ) of DPD and its analogs for 24 hours. The numbers of viable cells were determined using a proliferation kit, matrix metalloproteinase (MMP)-2 and -9 activities were determined by gelatin zymography, and expression of occludin protein and occludin mRNA were determined by western blotting and RT-qPCR, respectively.

RESULTS

Increased cell proliferation was observed in gingival keratinocytes incubated with 100 nmol L^-1 of butyl-DPD. MMP-9 activity was elevated in cells incubated with 10 μmol L^-1 of ethyl-DPD. On the other hand, MMP-2 activity did not show any significant change when gingival keratinocytes were incubated with or without DPD or analogs. Western blot analyses demonstrated five forms (105, 61, 52.2, 44 and 37 kDa) of occludin. Incubation with 1 μmol L^-1 and 100 nmol L^-1 of DPD and with 10 nmol L^-1 of ethyl-DPD increased dimeric (105 kDa) forms of occludin, while incubation with 100 nmol L^-1 of isobutyl-DPD increased monomeric (61 kDa) forms. DPD and ethyl-DPD decreased, and 100 nmol L^-1 of isobutyl-DPD and 10 nmol L^-1 of butyl-DPD increased, the monomeric (52.2 kDa and 44 kDa) forms of occludin, whereas ethyl-DPD decreased and isobutyl-DPD increased, the low-molecular-weight (37 kDa) forms. According to RT-qPCR analysis, the exposure of gingival keratinocytes to 10 μmol L^-1 of isobutyl-DPD up-regulated expression of occludin.

CONCLUSION

The results indicate that isobutyl-DPD has the potential to enhance the integrity of the epithelium by stimulating the formation of occluding, without affecting the proliferation or gelatinolytic enzyme activities of the exposed cells. The modulatory effect of an AI-2 analog on the epithelial cell response is shown for the first time.

Dual action of highbush blueberry proanthocyanidins on Aggregatibacter actinomycetemcomitans and the host inflammatory response

Background

The highbush blueberry (Vaccinium corymbosum) has a beneficial effect on several aspects of human health. The present study investigated the effects of highbush blueberry proanthocyanidins (PACs) on the virulence properties of Aggregatibacter actinomycetemcomitans and macrophage-associated inflammatory responses.

Methods

PACs were isolated from frozen highbush blueberries using solid-phase chromatography. A microplate dilution assay was performed to determine the effect of highbush blueberry PACs on A. actinomycetemcomitans growth as well as biofilm formation stained with crystal violet. Tight junction integrity of oral keratinocytes was assessed by measuring the transepithelial electrical resistance (TER), while macrophage viability was determined with a colorimetric MTT assay. Pro-inflammatory cytokine and MMP secretion by A. actinomycetemcomitans-stimulated macrophages was quantified by ELISA. The U937-3xκB-LUC monocyte cell line transfected with a luciferase reporter gene was used to monitor NF-κB activation.

Results

Highbush blueberry PACs reduced the growth of A. actinomycetemcomitans and prevented biofilm formation at sub-inhibitory concentrations. The treatment of pre-formed biofilms with the PACs resulted in a loss of bacterial viability. The antibacterial activity of the PACs appeared to involve damage to the bacterial cell membrane. The PACs protected the oral keratinocytes barrier integrity from damage caused by A. actinomycetemcomitans. The PACs also protected macrophages from the deleterious effect of leukotoxin Ltx-A and dose-dependently inhibited the secretion of pro-inflammatory cytokines (IL-1β, IL-6, CXCL8, TNF-α), matrix metalloproteinases (MMP-3, MMP-9), and sTREM-1 by A. actinomycetemcomitans-treated macrophages. The PACs also inhibited the activation of the NF-κB signaling pathway.

Conclusion

The antibacterial and anti-inflammatory properties of highbush blueberry PACs as well as their ability to protect the oral keratinocyte barrier and neutralize leukotoxin activity suggest that they may be promising candidates as novel therapeutic agents.

The innate host response in caries and periodontitis

INTRODUCTION

Innate immunity rapidly defends the host against infectious insults. These reactions are of limited specificity and exhaust without providing long-term protection. Functional fluids and effector molecules contribute to the defence against infectious agents, drive the immune response, and direct the cellular players.

AIM

To review the literature and present a summary of current knowledge about the function of tissues, cellular players and soluble mediators of innate immunity relevant to caries and periodontitis.

METHODS

Historical and recent literature was critically reviewed based on publications in peer-reviewed scientific journals.

RESULTS

The innate immune response is vital to resistance against caries and periodontitis and rapidly attempts to protect against infectious agents in the dental hard and soft tissues. Soluble mediators include specialized proteins and lipids. They function to signal to immune and inflammatory cells, provide antimicrobial resistance, and also induce mechanisms for potential repair of damaged tissues.

CONCLUSIONS

Far less investigated than adaptive immunity, innate immune responses are an emerging scientific and therapeutic frontier. Soluble mediators of the innate response provide a network of signals to organize the near immediate molecular and cellular response to infection, including direct and immediate antimicrobial activity. Further studies in human disease and animal models are generally needed.

Potassium is a key signal in host-microbiome dysbiosis in periodontitis

Dysbiosis, or the imbalance in the structural and/or functional properties of the microbiome, is at the origin of important infectious inflammatory diseases such as inflammatory bowel disease (IBD) and periodontal disease. Periodontitis is a polymicrobial inflammatory disease that affects a large proportion of the world's population and has been associated with a wide variety of systemic health conditions, such as diabetes, cardiovascular and respiratory diseases. Dysbiosis has been identified as a key element in the development of the disease. However, the precise mechanisms and environmental signals that lead to the initiation of dysbiosis in the human microbiome are largely unknown. In a series of previous in vivo studies using metatranscriptomic analysis of periodontitis and its progression we identified several functional signatures that were highly associated with the disease. Among them, potassium ion transport appeared to be key in the process of pathogenesis. To confirm its importance we performed a series of in vitro experiments, in which we demonstrated that potassium levels a increased the virulence of the oral community as a whole and at the same time altering the immune response of gingival epithelium, increasing the production of TNF-α and reducing the expression of IL-6 and the antimicrobial peptide human β-defensin 3 (hBD-3). These results indicate that levels of potassium in the periodontal pocket could be an important element in of dysbiosis in the oral microbiome. They are a starting point for the identification of key environmental signals that modify the behavior of the oral microbiome from a symbiotic community to a dysbiotic one.

Homeostasis of the human microbiome plays a key role in maintaining the healthy status of the human body. Changes in composition and function of the human microbiome (dysbiosis) are at the origin of important infectious inflammatory diseases such as inflammatory bowel disease (IBD) and periodontal disease. However, the environmental elements that trigger the development of dysbiotic diseases are largely unknown. In previous studies, using community-wide transcriptome analysis, we identified ion potassium transport as one of the most important functions in the pathogenesis of periodontitis and its progression. Here, we confirm with a series of in vitro experiments that potassium can act as an important signal in the dysbiotic process inducing pathogenesis in the oral microbiome and altering the host response in front of the microbial challenge that could lead to microbial immune subversion. Our study provides new insights into the important role that ion potassium plays a signal in oral dysbiosis during periodontitis.

Epithelial barrier and oral bacterial infection

The oral epithelial barrier separates the host from the environment and provides the first line of defense against pathogens, exogenous substances and mechanical stress. It consists of underlying connective tissue and a stratified keratinized epithelium with a basement membrane, whose cells undergo terminal differentiation resulting in the formation of a mechanically resistant surface. Gingival keratinocytes are connected by various transmembrane proteins, such as tight junctions, adherens junctions and gap junctions, each of which has a specialized structure and specific functions. Periodontal pathogens are able to induce inflammatory responses that lead to attachment loss and periodontal destruction. A number of studies have demonstrated that the characteristics of pathogenic oral bacteria influence the expression and structural integrity of different cell-cell junctions. Tissue destruction can be mediated by host cells following stimulation with cytokines and bacterial products. Keratinocytes, the main cell type in gingival epithelial tissues, express a variety of proinflammatory cytokines and chemokines, including interleukin-1alpha, interleukin-1beta, interleukin-6, interleukin-8 and tumor necrosis factor-alpha. Furthermore, the inflammatory mediators that may be secreted by oral keratinocytes are vascular endothelial growth factor, prostaglandin E2 , interleukin-1 receptor antagonist and chemokine (C-C motif) ligand 2. The protein family of matrix metalloproteinases is able to degrade all types of extracellular matrix protein, and can process a number of bioactive molecules. Matrix metalloproteinase activities under inflammatory conditions are mostly deregulated and often increased, and those mainly relevant in periodontal disease are matrix metalloproteinases 1, 2, 3, 8, 9, 13 and 24. Viral infection may also influence the epithelial barrier. Studies show that the expression of HIV proteins in the mucosal epithelium is correlated with the disruption of epithelial tight junctions, suggesting a possible enhancement of human papilloma virus infection by HIV-associated disruption of tight junctions. Altered expression of matrix metalloproteinases was demonstrated in keratinocytes transformed with human papilloma virus-16 or papilloma virus-18,. To summarize, the oral epithelium is able to react to a variety of exogenous, possibly noxious influences.

Black tea theaflavins attenuate Porphyromonas gingivalis virulence properties, modulate gingival keratinocyte tight junction integrity and exert anti-inflammatory activity

BACKGROUND AND OBJECTIVE

Over the last 10 years, bioactive plant food compounds have received considerable attention in regard to their beneficial effects against periodontal disease. In this study, we investigated the effects of black tea theaflavins (TFs) on the virulence properties of Porphyromonas gingivalis and gingival keratinocyte tight junction integrity. In addition, the effects of black tea TFs on the nuclear factor-κB (NF-κB) signaling pathway and proinflammatory cytokine/matrix metalloproteinase (MMP) secretion by monocytes/macrophages were assessed.

MATERIAL AND METHODS

Virulence factor gene expression in P. gingivalis was investigated by quantitative real-time PCR. A fluorescence assay was used to determine P. gingivalis adherence to, and invasion of, a gingival keratinocyte monolayer. Tight junction integrity of gingival keratinocytes was assessed by determination of transepithelial electrical resistance. Proinflammatory cytokine and MMP secretion by P. gingivalis-stimulated macrophages was quantified by ELISA. The U937-3xκB-LUC monocyte cell line transfected with a luciferase reporter gene was used to monitor NF-κB activation. Gelatin degradation was monitored using a fluorogenic assay.

RESULTS

Black tea TFs dose-dependently inhibited the expression of genes encoding the major virulence factors of P. gingivalis and attenuated its adherence to gingival keratinocytes. A treatment of gingival keratinocytes with black tea TFs significantly enhanced tight junction integrity and prevented P. gingivalis-mediated tight junction damage as well as bacterial invasion. Black tea TFs reduced the secretion of interleukin (IL)-1β, tumor necrosis factor-α, IL-6, chemokine (C-X-C) ligand 8, MMP-3, MMP-8 and MMP-9 by P. gingivalis-stimulated macrophages and attenuated the P. gingivalis-mediated activation of the NF-κB signaling pathway. Lastly, black tea TFs inhibited gelatin degradation by MMP-9.

CONCLUSION

This study provides clear evidence that black tea TFs represent promising multifunctional therapeutic agents for prevention and treatment of periodontal disease.

Influence of Enamel Matrix Derivative on Human Epithelial Cells In Vitro

BACKGROUND

In periodontal therapy enamel matrix derivative (EMD) has been successfully used for tissue regeneration by altering activity of various cells involved in periodontal regeneration. Studies have focused primarily on clinical parameters and outcome. Effects of EMD on oral epithelial cells are of crucial importance in order to understand the biology of regeneration. Aims of this study are to investigate proliferative and cytotoxic effects of EMD on oral epithelial cells and their possible influences on epithelial barrier function.

METHODS

SCC-25 cells, a human squamous cell carcinoma cell line, and primary keratinocytes were either treated with EMD dissolved in culture medium or added to wells/inserts precoated with EMD. Cells were incubated for 24, 48, and 72 hours. Proliferation rate was analyzed measuring the 5-bromo-2'-deoxyuridine nucleotide uptake. Cytotoxic effects of EMD treatment were sampled by lactate dehydrogenase release. Alterations of the epithelial barrier function induced by EMD were investigated by analysis of transepithelial electrical resistance (TER).

RESULTS

Statistically significant inhibitory effects of both malignant and primary cell proliferation could be demonstrated by precoating culture plate wells with EMD. No cytotoxic effects caused by EMD were detected. Precoating of inserts with EMD induced a significant increase of TER and barrier function.

CONCLUSIONS

This investigation compares applying EMD in solution to cells with precoating of wells with EMD. When precoating of wells was used solely, inhibition of cell proliferation was evident. Precoating may represent more suitable clinical usage. Furthermore, prelayering EMD induced an increase of TER of primary cells. These results suggest EMD may enhance barrier function.

Influence of retinoic acid on human gingival epithelial barriers

BACKGROUND AND OBJECTIVES

The gingival epithelium plays an important role in the protection of oral tissues from microbial challenge. Oral keratinocytes form a barrier and show various cellular contacts, including tight junctions (TJ). To analyse the barrier function in vitro the transepithelial electrical resistance (TER) is commonly used. Retinoic acid (RA) is an important signalling molecule in most tissues, including epithelial differentiation. RA signalling is mediated through three RA receptors. The aim of the study was to investigate the influence of RA on human gingival barriers in vitro.

MATERIAL AND METHODS

Immortalized human gingival keratinocytes were seeded on culture plate inserts. The effect of RA with and without infection with Porphyromonas gingivalis W83 on the barrier was analysed by TER measurements. The expression of TJ proteins was investigated by western blot.

RESULTS

During differentiation, mean TER increased from 16 (1 h), 43 (4 h) to 62 (6 h) Ohm × cm² . Addition of 15 μm RA increased TER by +19 after 1 h, +25 after 4 h and +16 Ohm × cm² after 6 h. The pan-RA receptor inhibitor BMS 493 resulted in TER values comparable to the control. The mean established TER of the control was approximately 110 Ohm × cm² . Addition of 15 μm RA elevated TER to 127 Ohm × cm² after 1 h, 150 Ohm × cm² after 4 h and 189 Ohm × cm² after 6 h (p ≤ 0.01). RA plus infection with P. gingivalis W83 further increased the TER increasing effect but could not prevent the destruction of TER induced by bacterial infection. The protein expression of the TJ proteins claudin 4 and occludin was enhanced while ZO-1 was downregulated after 1 h of RA incubation.

CONCLUSION

RA provides barrier-positive elements to the gingival epithelial cell model that is accompanied by altered expression of TJ proteins.

CD24 activates the NLRP3 inflammasome through c-Src kinase activity in a model of the lining epithelium of inflamed periodontal tissues

Chronic periodontitis is characterized by perturbation of the epithelial attachment to the tooth with subsequent migration of the lining epithelium and formation of a cleft or pocket. This non-keratinized lining epithelium provides initial responses to bacterial products by signalling through receptors of innate immunity to activate inflammasome pathways. These comprise an intracellular network of regulatory and effector molecules leading to synthesis and activation of pro-inflammatory cytokines. Conversely, CD24 is characteristically strongly expressed by the pocket epithelium and is reported to function as an important negative regulator for danger signals, protecting tissues from excessive leukocyte activity. The objective of the study was to determine the impact of ligation of CD24 on expression of inflammasome components. An epithelial mimic of pocket epithelium was used to evaluate activation of the NLRP3 inflammasome pathway. Surprisingly, antibody ligation of CD24 enhanced expression of NLRP3 together with co-activators ASC and caspase-1 resulting in burst release of activated interleukin (IL)-18. Potent product inhibition was detected with IL-18 suppressing expression of NLRP3, ASC, and caspase-1. Scant distribution of these products within pocket epithelium compared with healthy gingival attachment provided indication of potential cycling of NLRP3 inflammasome expression. As subjects with mild chronic periodontitis have increased titres of serum antibodies auto-reactive with CD24 compared with those of subjects with severe periodontitis, a molecular mechanism for regulated expression of the NLRP3 inflammasome mediated by c-Src kinase activity, is proposed. This pathway could be regionally disrupted by products of pathogenic bacteria with profound downregulation in the dysbiosis associated with severe disease.