Intracellular localization of Porphyromonas gingivalis thiol proteinase in periodontal tissues of chronic periodontitis patients

Paradigm shift in the pathogenesis and treatment of oral cancer and other cancers focused on the oralome and antimicrobial-based therapeutics

The oral microbiome is a community of microorganisms, comprised of bacteria, fungi, viruses, archaea, and protozoa, that form a complex ecosystem within the oral cavity. Although minor perturbations in the environment are frequent and compensable, major shifts in the oral microbiome can promote an unbalanced state, known as dysbiosis. Dysbiosis can promote oral diseases, including periodontitis. In addition, oral dysbiosis has been associated with other systemic diseases, including cancer. The objective of this review is to evaluate the epidemiologic evidence linking periodontitis to oral, gastrointestinal, lung, breast, prostate, and uterine cancers, as well as describe new evidence and insights into the role of oral dysbiosis in the etiology and pathogenesis of the cancer types discussed. Finally, we discuss how antimicrobials, antimicrobial peptides, and probiotics may be promising tools to prevent and treat these cancers, targeting both the microbes and associated carcinogenesis processes. These findings represent a novel paradigm in the pathogenesis and treatment of cancer focused on the oral microbiome and antimicrobial‐based therapies.

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.

Inhibitory effect of 1,25-dihydroxyvitamin D3 on Porphyromonas gingivalis-induced inflammation and bone resorption in vivo

OBJECTIVE

To investigate whether intragastric administration of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) could inhibit the bone resorption and inflammation in a mouse calvarial model infected by Porphyromonas gingivalis (P. gingivalis).

DESIGN

Live P. gingivalis ATCC 33277 was injected once daily for 6days into the subcutaneous tissue overlying the calvaria in mice. At the same time, 1,25(OH)₂D₃ (50μg/kg per day) was administered by gavage for 9days, starting 3d before the infection. Mice were killed under ether anesthesia 8h after the last injection of P. gingivalis. Micro-computed tomography scanning was used to evaluate calvarial bone loss. Tartrate-resistant acid phosphatase was used to detect osteoclast activity. Real-time PCR was used to assess the mRNA expressions of OPG, RANKL, c-Fos, NFATc1, CTSK and TRAP in calvarial bone and IL-6, IL-10, IL-1β, IL-12p40 and TNF-α in soft tissue. The levels of serum IL-6, IL-10 were determined by ELISA.

RESULTS

1,25(OH)₂D₃ treatment apparently attenuated bone resorption in P. gingivalis-induced mouse calvarial model and markedly reduced the number of osteoclasts. The expression levels of RANKL and osteoclast-related genes such as c-Fos, NFATc1, CTSK and TRAP were also decreased by 1,25(OH)₂D₃. Besides, 1,25(OH)₂D₃ inhibited the expression of pro-inflammatory cytokines IL-6, IL-12p40 and TNF-α and enormously elevated the expression of anti-inflammatory cytokine IL-10.

CONCLUSION

1,25(OH)₂D₃ may decrease bone resorption in vivo via suppressing the expression of osteoclast-related genes and its anti-inflammatory properties.

Effects of 1,25-dihydroxyvitamin D3 on Macrophage Cytokine Secretion Stimulated by Porphyromonas gingivalis

Vitamin D is known to be closely associated with periodontitis; however, its exact mechanisms remain to be clarified. The present study aimed to investigate the influence of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on Porphyromonas gingivalis (Pg)-stimulated cytokine production and the involved signaling pathways in macrophages. The main observation was that 1,25(OH)₂D₃ inhibited Pg-induced interleukin (IL)-6 cytokine expression but up-regulated the expression of anti-inflammatory cytokine IL-10. Further analyses showed that 1,25(OH)₂D₃ decreased p38 mitogen-activated protein kinase (MAPK) and extracellular signal regulated kinase (ERK)1/2 phosphorylation. Inhibited phosphorylation of p38 MAPK and ERK1/2 was associated with decreased level of IL-6 expression, but was not related to increased level of IL-10 expression in macrophages stimulated with Pg. These results suggest that 1,25(OH)₂D₃ might exert its anti-inflammatory effects on Pg-stimulated macrophages partly through its inhibitory effect on the p38 MAPK and ERK1/2 signaling pathway.

Relationship between invasion of the periodontium by periodontal pathogens and periodontal disease: a systematic review

Bacterial invasion of the periodontal tissues has been suggested as a relevant step in the etiopathogenesis of periodontal disease. However, its exact importance remains to be defined. The present systematic review assessed the scientific evidence concerning the relationship between the quality or quantity of periodontal microbiota in periodontal tissues and development of periodontal disease. The databases Medline-PubMed, Cochrane-CENTRAL, ISI Web of Knowledge and SCOPUS were searched, up to January 2014. Studies that reported evaluation of periodontal pathogens invasion on human tissues were selected. The screening of 440 title/abstracts elected 26 papers for full-text reading. Twenty three papers were subsequently excluded because of insufficient data or a study protocol not related to the objectives of this systematic review. All included studies were case-control studies that evaluated intracellular or adherent bacteria to epithelial cells from periodontal pockets versus healthy sulci. Study protocols presented heterogeneity regarding case and control definitions and methodological approaches for microbial identification. No consistent significant differences were found related to the presence/absence or proportion of specific periopathogens across the studies, as only one study found statistically significant differences regarding the presence of A. actinomycetemcomitans (p = 0.043), T. forsythia (P < 0.001), P. intermedia (P < 0.001), C. ochracea (P < 0.001) and C. rectus (P = 0.003) in epithelial cells from periodontal pockets vs. healthy sulci. All studies reported a larger unspecific bacterial load in or on the epithelial cells taken from a diseased site compared to a healthy sulcus. The current available data is of low to moderate quality and inconsistent mainly due to study design, poor reporting and methodological diversity. As so, there is insufficient evidence to support or exclude the invasion by periodontal pathogens as a key step in the etiopathogenesis of periodontal disease. Further research is needed.

Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

Anaerobic bacteria far outnumber aerobes in many human niches such as the gut, mouth, and vagina. Furthermore, anaerobic infections are common and frequently of indigenous origin. The ability of some anaerobic pathogens to invade human cells gives them adaptive measures to escape innate immunity as well as to modulate host cell behavior. However, ensuring that the anaerobic bacteria are live during experimental investigation of the events may pose challenges. Porphyromonas gingivalis, a Gram-negative anaerobe, is capable of invading a variety of eukaryotic non-phagocytic cells. This article outlines how to successfully culture and assess the ability of P. gingivalis to invade human umbilical vein endothelial cells (HUVECs). Two protocols were developed: one to measure bacteria that can successfully invade and survive within the host, and the other to visualize bacteria interacting with host cells. These techniques necessitate the use of an anaerobic chamber to supply P. gingivalis with an anaerobic environment for optimal growth. The first protocol is based on the antibiotic protection assay, which is largely used to study the invasion of host cells by bacteria. However, the antibiotic protection assay is limited; only intracellular bacteria that are culturable following antibiotic treatment and host cell lysis are measured. To assess all bacteria interacting with host cells, both live and dead, we developed a protocol that uses fluorescent microscopy to examine host-pathogen interaction. Bacteria are fluorescently labeled with 2',7'-Bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) and used to infect eukaryotic cells under anaerobic conditions. Following fixing with paraformaldehyde and permeabilization with 0.2% Triton X-100, host cells are labeled with TRITC phalloidin and DAPI to label the cell cytoskeleton and nucleus, respectively. Multiple images taken at different focal points (Z-stack) are obtained for temporal-spatial visualization of bacteria. Methods used in this study can be applied to any cultivable anaerobe and any eukaryotic cell type.

Effect of gallium aluminium arsenide diode laser therapy on Porphyromonas gingivalis in chronic periodontitis: a randomized controlled trial

OBJECTIVES

The aim of this randomized, controlled trial was to evaluate the effects of 685-nm gallium aluminium arsenide (GaAlAs) diode laser therapy (1.6 J cm^-2 ) as an adjunct to scaling and root planing in the treatment of chronic periodontitis.

METHODS

Thirty-two patients aged 35-60 years old who had chronic periodontitis met the eligibility criteria. They were randomly assigned to two equal groups: scaling and root planing were performed in the SRP group, while scaling, root planing and laser irradiation of periodontal pockets were performed in the SRP + DL group. Subgingival plaque samples were subjected to polymerase chain reaction (PCR) to detect P. gingivalis-colonized sites, and common clinical indices were evaluated before and 2 months after treatment. Clinical examination included gingival index (GI), plaque index (PI), probing depth (PD), clinical attachment level (CAL) and gingival bleeding index (GBI), all of which were recorded.

RESULTS

Data from 30 patients [19 women and 11 men; mean age, 48.4 (5.4) years old] were analysed. There were statistically significant improvements in GI, PD, CAL and GBI for the SRP + DL group compared to SRP group but no significant difference in PI between the groups. Additionally, the percentage of P. gingivalis-positive sites in the SRP + DL group decreased from 80% (12/15) to 20% (3/15) after laser irradiation (P < 0.05). No significant changes were noted in the SRP group.

CONCLUSION

GaAlAs diode laser irradiation of diseased periodontal pockets at 685 nm and 1.6 J cm^-2 seemed to be an effective adjuvant to mechanical instrumentation to treat chronic periodontitis.

In Situ Detection of Bacteria within Paraffin-embedded Tissues Using a Digoxin-labeled DNA Probe Targeting 16S rRNA

The presence of bacteria within the pocket epithelium and underlying connective tissue in gingival biopsies from patients with periodontitis has been reported using various methods, including electron microscopy, immunohistochemistry or immunofluorescence using bacteria-specific antibodies, and fluorescent in situ hybridization (FISH) using a fluorescence-labeled oligonucleotide probe. Nevertheless, these methods are not widely used due to technical limitation or difficulties. Here a method to localize bacteria within paraffin-embedded tissues using DIG-labeled DNA probes has been introduced. The paraffin-embedded tissues are the most common form of biopsy tissues available from pathology banks. Bacteria can be detected either in a species-specific or universal manner. Bacterial signals are detected as either discrete forms (coccus, rod, fusiform, and hairy form) of bacteria or dispersed forms. The technique allows other histological information to be obtained: the epithelia, connective tissue, inflammatory infiltrates, and blood vessels are well distinguished. This method can be used to study the role of bacteria in various diseases, such as periodontitis, cancers, and inflammatory immune diseases.

Intracellular localization of Treponema denticola chymotrypsin-like proteinase in chronic periodontitis

Treponema denticola is an important periodontal pathogen capable of tissue invasion. Its chymotrypsin-like proteinase (CTLP) can degrade a number of basement membrane components in vitro, thus suggesting a contribution to tissue invasion by the spirochete. The aim of this study was to analyze the localization of CTLP in chronic periodontitis tissues ex vivo. A polyclonal antibody specific to T. denticola cell-bound CTLP was used to detect the spirochetes in the gingival tissues of patients with moderate to severe chronic periodontitis (n=25) by immunohistochemistry and periodic acid-Schiff staining (PAS). The presence of T. denticola in the periodontal tissue samples was analyzed by PCR. Periodontal tissue samples of 12 of the 25 patients were found to be positive for T. denticola by PCR. Moreover, CTLP could be detected in the periodontal tissues of all these patients by immunohistochemistry. In the epithelium, the CTLP was mostly intracellular. Typically, the positive staining could be seen throughout the whole depth of the epithelium. When detected extracellularly, CTLP was localized mainly as granular deposits. The connective tissue stained diffusely positive in four cases. The positive staining co-localized with the PAS stain in nine cases. T. denticola and its CTLP could be detected in diseased human periodontium both intra- and extracellularly. The granular staining pattern was suggestive of the presence of T. denticola bacteria, whereas the more diffused staining pattern was indicative of the recent presence of the bacterium and shedding of the cell-bound proteinase.

Characterisation and optimisation of organotypic oral mucosal models to study Porphyromonas gingivalis invasion

Porphyromonas gingivalis is a Gram-negative, keystone pathogen in periodontitis that leads to tissue destruction and ultimately tooth loss. The organism is able to infect oral epithelial cells and two-dimensional (monolayer) cultures have been used to investigate this process. However, recently there has been interest in the use of three-dimensional, organotypic mucosal models to analyse infection. These models are composed of collagen-embedded fibroblasts overlain with multilayers of oral epithelial cells. In this study we report for the first time significant differences in the response of oral mucosal models to P. gingivalis infection when compared to monolayer cultures of oral epithelial cells. Intracellular survival (3-fold) and bacterial release (4-fold) of P. gingivalis was significantly increased in mucosal models compared with monolayer cultures, which may be due to the multi-layered nature and exfoliation of epithelial cells in these organotypic models. Furthermore, marked differences in the cytokine profile between infected organotypic models and monolayer cultures were observed, particularly for CXCL8 and IL6, which suggested that degradation of cytokines by P. gingivalis may be less pronounced in organotypic compared to monolayer cultures. These data suggest that use of oral mucosal models may provide a greater understanding of the host responses to P. gingivalis invasion than simple monolayer cultures.

Periodontal inflammatory burden correlates with C-reactive protein serum level

OBJECTIVE

The aim of study was to present a new method for evaluation of the periodontal inflammatory burden, to apply the method to the adult population and to correlate it with serum levels of C-reactive protein (CRP).

MATERIALS AND METHODS

On 515 extracted teeth was measured the neck circumferences (NC). The average values of the NC were obtained for 16 male and 16 female individual tooth types. In the clinical part of this study 238 dentate subjects were included. The subgingival area, inflamed area and periodontal wound size were calculated from NC, probing depth and BOP. The sum of the inflamed and ulcerated subgingival areas of all teeth represented the total periodontal inflammatory burden of an individual. Serum levels of CRP were measured by immunochemical method.

RESULTS

The average subgingival area in 238 subjects was calculated to be 13.11 ± 6.35 cm(2) and inflammatory burden area 9.25 ± 5.57 cm(2). The periodontal bleeding wound (p < 0.05) was significantly larger in men. The increased serum levels of CRP correlated with periodontal inflammatory burden (p < 0.05).

CONCLUSIONS

This new method quantifies the inflammatory burden caused by periodontal disease. The size of the inflammatory burden is correlated with increased serum levels of CRP.

Comparative evaluation of the effects of different photoablative laser irradiation protocols on the gingiva of periodontopathic patients

OBJECTIVE

We aimed at quantifying the presence of periodontopathogens in gingival biopsies from periodontitis patients treated with different photoablative lasers (diode GaAs, Er:YAG, Nd:YAG, and CO(2) lasers) and histologically analyzing their effects on the gingiva.

BACKGROUND DATA

Substantial evidence indicates that intracellular location of periodontal bacteria in the gingival epithelium may contribute to chronic periodontitis.

METHODS

Sixteen adult subjects with chronic periodontitis were subjected to conventional scaling/root planing and topical chlorhexidine, and immediately laser-irradiated on the inner and outer free gingiva. Small gingival biopsies were subjected to real-time polymerase chain reaction and cytofluorescence to identify periodontopathogens; tissue damage and endothelial ICAM-1 expression were assessed by histological and immunofluorescence analyses.

RESULTS

High DNA levels of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Treponema denticola, Prevotella intermedia, and Ekenella corrodens, were detected in all samples. Nd:YAG and diode lasers were capable of eradicating periodontopathogenic bacteria endowed within gingival epithelial cells outside periodontal pockets, without causing connective tissue damage and microvessel rupture. They also reduced ICAM-1 immunolabelling by the vascular endothelium. Conversely, Er:YAG lasers induced marked microvessel rupture and bleeding and failed to completely and selectively ablate the infected gingival epithelium, whereas CO(2) laser caused heat-induced coagulation of the lamina propria.

CONCLUSIONS

This study indicates that periodontopathogens can persist within cells outside the pocket epithelium, despite conventional periodontal treatment. Nd:YAG and diode lasers are able to eradicate intra- and extracellular bacteria from these sites, suggesting that they can be considered suitable devices to improve the clinical outcome of periodontal disease.

Increased expression of C-reactive protein gene in inflamed gingival tissues could be derived from endothelial cells stimulated with interleukin-6

BACKGROUND

Epidemiological studies have suggested periodontitis as a risk factor for ischemic heart disease. High sensitive C-reactive protein (hs-CRP), a predictor of cardiovascular risk, is elevated in periodontitis patients. Therefore, local infection-induced elevation of systemic CRP could account for the relationship between the 2 diseases. However, the underlying mechanism of CRP production in the periodontal tissues has not been fully elucidated. Therefore, the aim of the present study was to clarify the mechanism of CRP production in periodontal tissues.

METHODS

Gene expression of CRP in gingival biopsies was analysed by quantitative PCR. Human gingival epithelial cells (HGECs), human gingival fibroblasts (HGFBs), and human coronary artery endothelial cells (HCAECs) were characterized for CRP-producing ability by incubating with interleukin (IL)-1β, IL-6, soluble IL-6 receptor (sIL-6R), and Porphyromonas gingivalis strain W83.

RESULTS

Gene expression of CRP is significantly elevated in periodontitis lesions compared with gingivitis lesions. HCAECs, but not HGECs and HGFBs, produced CRP in response to IL-6 and IL-1β in the presence of sIL-6R. In contrast to IL-6, the effect of IL-1β on CRP production was indirect via induction of IL-6. IL-1β was produced by HGECs and HGFBs with stimulation of P. gingivalis antigens.

CONCLUSION

These results suggest that CRP induced locally by periodontal infection may play another role in the pathogenesis of periodontal disease, and to a much lesser extent, has the potential to modulate systemic CRP level by extra-hepatic CRP production.

Role of Porphyromonas gingivalis phosphoserine phosphatase enzyme SerB in inflammation, immune response, and induction of alveolar bone resorption in rats

Porphyromonas gingivalis secretes a serine phosphatase enzyme, SerB, upon contact with gingival epithelial cells in vitro. The SerB protein plays a critical role in internalization and survival of the organism in epithelial cells. SerB is also responsible for the inhibition of interleukin-8 (IL-8) secretion from gingival epithelial cells infected with P. gingivalis. This study examined the ability of a P. gingivalis SerB mutant to colonize the oral cavity and induce gingival inflammation, immune responses, and alveolar bone resorption in a rat model of periodontal disease. Both P. gingivalis ATCC 33277 and an isogenic ΔSerB mutant colonized the oral cavities of rats during the 12-week experimental period. Both of the strains induced significant (P < 0.05) systemic levels of immunoglobulin G (IgG) and isotypes IgG1, IgG2a, and IgG2b, indicating the involvement of both T helper type 1 (Th1) and Th2 responses to infection. Both strains induced significantly (P < 0.05) higher levels of alveolar bone resorption in infected rats than in sham-infected control rats. However, horizontal and interproximal alveolar bone resorption induced by the SerB mutant was significantly (P < 0.05) lower than that induced by the parental strain. Rats infected with the ΔSerB mutant exhibited significantly higher levels of apical migration of the junctional epithelium (P < 0.01) and polymorphonuclear neutrophil (PMN) recruitment (P < 0.001) into the gingival tissues than rats infected with the wild type. In conclusion, in a rat model of periodontal disease, the SerB phosphatase of P. gingivalis is required for maximal alveolar bone resorption, and in the absence of SerB, more PMNs are recruited into the gingival tissues.

Synergistic effects of lipopolysaccharides from periodontopathic bacteria on pro-inflammatory cytokine production in an ex vivo whole blood model

Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia have been strongly associated with chronic periodontitis. This disease is characterized by an accumulation of inflammatory cells in periodontal tissue and subgingival sites. The secretion of high levels of inflammatory cytokines by those cells is believed to contribute to periodontal tissue destruction. The aim of this study was to investigate the inflammatory response of whole blood from periodontitis patients following challenges with whole cells of P. gingivalis, T. denticola, and T. forsythia or their lipopolysaccharides (LPS), individually and in combination. Whole blood collected from seven periodontitis patients was stimulated with whole cells or LPS and the production of interleukin (IL)-1beta, IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) were quantified by enzyme-linked immunosorbent assays. The mono and mixed challenges with whole bacterial cells or LPS induced the secretion of high amounts of IL-1beta, IL-6, IL-8, and TNF-alpha by the mixed leukocyte population from periodontitis patients. In addition, P. gingivalis LPS, T. denticola LPS, and T. forsythia LPS acted in synergy to induce high levels of IL-1beta and TNF-alpha. This study suggests that P. gingivalis, T. denticola, and T. forsythia may contribute to the immunodestructive host response characteristic of periodontitis through synergistic effects of their LPS on the inflammatory response induced by a mixed population of leukocytes.

Clathrin-dependent entry of a gingipain adhesin peptide and Porphyromonas gingivalis into host cells

Porphyromonas gingivalis, a Gram-negative oral anaerobe, is associated with periodontitis, a disease that in some form affects up to 80% of the adult population in the USA. The organism interacts with gingival epithelium and surrounding tissue, and in this study we analysed interactions initiated by P. gingivalis and by a peptide derived from the adhesin domain of arg-gingipain A, a member of a family of surface cysteine proteinases. Recombinant peptide A44 blocked adherence of bacteria to host cell monolayers, and bound to components of the cell membrane fraction. In pull-down assays A44 associated with proteins involved in a clathrin-dependent endocytosis pathway. Inhibitor studies confirmed a role for clathrin, and confocal microscopy demonstrated that both A44-coated beads and intact bacteria colocalized with GFP-clathrin in host cells. Finally, we used siRNA to determine whether clathrin or caveolin-1 was involved in association of peptide and intact bacteria with host cells. Again, the results of these assays indicated that association of both A44 and P. gingivalis depended on the presence of clathrin, and support a working model in which A44 initiates a clathrin-dependent pathway that potentially leads to internalization of peptide or bacteria by host epithelial cells.

Intracellular survival and vascular cell-to-cell transmission of Porphyromonas gingivalis

Background

Porphyromonas gingivalis is associated with periodontal disease and invades different cell types including epithelial, endothelial and smooth muscle cells. In addition to P. gingivalis DNA, we have previously identified live invasive bacteria in atheromatous tissue. However, the mechanism of persistence of this organism in vascular tissues remains unclear. Therefore, the objective of this study was to analyze the ability of intracellular P. gingivalis to persist for extended periods of time, transmit to and possibly replicate in different cell types.

Results

Using antibiotic protection assays, immunofluorescent and laser confocal microscopy, we found that after a prolonged intracellular phase, while P. gingivalis can still be detected by immunostaining, the intracellular organisms lose their ability to be recovered in vitro. Surprisingly however, intracellular P. gingivalis could be recovered in vitro upon co incubation with fresh vascular host cells. We then demonstrated that the organism was able to exit the initially infected host cells, then enter and multiply in new host cells. Further, we found that cell-to-cell contact increased the transmission rate but was not required for transmission. Finally, we found that the invasion of new host cells allowed P. gingivalis to increase its numbers.

Conclusion

Our results suggest that the persistence of vascular tissue-embedded P. gingivalis is due to its ability to transmit among different cell types. This is the first communication demonstrating the intercellular transmission as a likely mechanism converting latent intracellular bacteria from state of dormancy to a viable state allowing for persistence of an inflammatory pathogen in vascular tissue.

Oral infections and systemic disease--an emerging problem in medicine

The relationship between oral and general health has been increasingly recognised during the past two decades. Several epidemiological studies have linked poor oral health with cardiovascular disease, poor glycaemic control in diabetics, low birth-weight pre-term babies, and a number of other conditions, including rheumatoid arthritis and osteoporosis. Oral infections are also recognised as a problem for individuals suffering from a range of chronic conditions, including cancer and infection with human immunodeficiency virus, as well as patients with ventilator-associated pneumonia. This review considers the systemic consequences of odontogenic infections and the possible mechanisms by which oral infection and inflammation can contribute to cardiovascular disease, as well as the oral conditions associated with medically compromised patients. A large number of clinical studies have established the clinical efficacy of topical antimicrobial agents, e.g., chlorhexidine and triclosan, in the prevention and control of oral disease, especially gingivitis and dental plaque. The possible risks of antimicrobial resistance are a concern, and the benefits of long-term use of triclosan require further evaluation. Oral infections have become an increasingly common risk-factor for systemic disease, which clinicians should take into account. Clinicians should increase their knowledge of oral diseases, and dentists must strengthen their understanding of general medicine, in order to avoid unnecessary risks for infection that originate in the mouth.

Regulation of RANKL and OPG gene expression in human gingival fibroblasts and periodontal ligament cells by Porphyromonas gingivalis: a putative role of the Arg-gingipains

Porphyromonas gingivalis is highly implicated in the pathogenesis of periodontitis, which is characterized by the destruction of periodontal connective tissues and the supporting alveolar bone. Receptor Activator of NF-kappaB Ligand (RANKL) stimulates bone resorption, whereas osteoprotegerin (OPG) blocks its action, and this bi-molecular system is implicated in periodontitis. The aim of this work was (a) to investigate the regulation of RANKL and OPG gene expression in human periodontal ligament (PDL) cells and gingival fibroblasts (GF), in response to P. gingivalis culture supernatants, by quantitative real-time PCR and (b) to attempt to identify putative virulence factors involved in this process. The results indicated that P. gingivalis induced RANKL and reduced OPG mRNA expression by the studied cells, resulting in an increased RANKL/OPG expression ratio. Heat-inactivation of P. gingivalis resulted in significant reduction of RANKL mRNA expression. A Lys-gingipain mutant strain did not affect, whereas an Arg-gingipain mutant strain further enhanced RANKL mRNA expression, compared to their parental wild-type strain. In conclusion, P. gingivalis up-regulates the RANKL/OPG expression ratio in GF and PDL cells, denoting an enhanced osteoclastogenic potential by the cells. The component mainly responsible for RANKL induction appears to be proteinaceous, and it may be regulated by the Arg-gingipains.

IL-8 and IDO expression by human gingival fibroblasts via TLRs

Human gingival fibroblasts (HGFs), a predominant cell type in tooth-supporting structure, are presently recognized for their active role in the innate immune response. They produce a variety of inflammatory cytokines in response to microbial components such as LPS from the key periodontal pathogen, Porphyromonas gingivalis. In this study, we demonstrated that HGFs expressed mRNA of TLRs 1, 2, 3, 4, 5, 6, and 9, but not TLRs 7, 8, and 10. Stimulation of HGFs with highly purified TLR2 ligand (P. gingivalis LPS), TLR3 ligand (poly(I:C)), TLR4 ligand (Escherichia coli LPS), and TLR5 ligand (Salmonella typhimurium flagellin) led to expression of IL-8 and IDO. A potent TLR 9 ligand, CpG oligodeoxynucleotide 2006 had no effect, although HGFs showed a detectable TLR9 mRNA expression. No significant enhancement on IL-8 or IDO expression was observed when HGFs were stimulated with various combinations of TLR ligands. Surprisingly, the TLR9 ligand CpG oligodeoxynucleotide 2006 was able to specifically inhibit poly(I:C)-induced IL-8 and IDO expression. TNF-alpha enhanced TLR ligand-induced IL-8 production in HGFs, whereas IFN-gamma enhanced TLR ligand-induced IDO expression. HGF production of IDO in response to P. gingivalis LPS, IFN-gamma, or the two in combination inhibited T cell proliferation in MLRs. The observed T cell inhibition could be reversed by addition of either 1-methyl-dl-tryptophan or l-tryptophan. Our results suggest an important role of HGFs not only in orchestrating the innate immune response, but also in dampening potentially harmful hyperactive inflammation in periodontal tissue.

Porphyromonas gingivalis-epithelial cell interactions in periodontitis

Emerging data on the consequences of the interactions between invasive oral bacteria and host cells have provided new insights into the pathogenesis of periodontal disease. Indeed, modulation of the mucosal epithelial barrier by pathogenic bacteria appears to be a critical step in the initiation and progression of periodontal disease. Periodontopathogens such as Porphyromonas gingivalis have developed different strategies to perturb the structural and functional integrity of the gingival epithelium. P. gingivalis adheres to, invades, and replicates within human epithelial cells. Adhesion of P. gingivalis to host cells is multimodal and involves the interaction of bacterial cell-surface adhesins with receptors expressed on the surfaces of epithelial cells. Internalization of P. gingivalis within host cells is rapid and requires both bacterial contact-dependent components and host-induced signaling pathways. P. gingivalis also subverts host responses to bacterial challenges by inactivating immune cells and molecules and by activating host processes leading to tissue destruction. The adaptive ability of these pathogens that allows them to survive within host cells and degrade periodontal tissue constituents may contribute to the initiation and progression of periodontitis. In this paper, we review current knowledge on the molecular cross-talk between P. gingivalis and gingival epithelial cells in the development of periodontitis.

Porphyromonas gingivalis-induced inflammatory mediator profile in an ex vivo human whole blood model

Periodontitis is characterized by an accumulation of inflammatory cells in periodontal tissue and subgingival sites. Leukocytes play a major role in the host response to Porphyromonas gingivalis, a major aetiological agent of chronic periodontitis. Secretion of high levels of inflammatory mediators, including cytokines and prostaglandins, by leucocytes is believed to contribute to periodontal tissue destruction. The aim of this study was to investigate the inflammatory response of an ex vivo whole blood model to P. gingivalis stimulation. The production of interleukin-1 beta (IL-1beta), IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-13, tumour necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), IFN-gamma-inducible protein 10 (IP-10), monocyte chemoattractant protein-1 (MCP-1), Regulated on Activation Normal T cell Expressed and Secreted (RANTES) and prostaglandin E2 (PGE2) were quantified by enzyme-linked immunosorbent assays. P. gingivalis induced the secretion of the pro-inflammatory cytokines IL-1beta, TNF-alpha, IL-6 and IFN-gamma, the chemokines IL-8, RANTES and MCP-1 and the inflammatory mediator PGE2 in an ex vivo human whole blood model. The secretion levels were dependent on the strain and the infectious dose used. While the mediator profiles were comparable between six healthy subjects, a high interindividual variability in the levels of secreted mediators was observed. This study supports the view that P. gingivalis, by inducing high levels of inflammatory mediators from a mixed leucocyte population, can contribute to the progression of periodontitis.