Assessment of the relative cytotoxicity of Porphyromonas gingivalis cells, products, and components on human epithelial cell lines

Inhibition of SARS-CoV-2 infection by Porphyromonas gingivalis and the oral microbiome

The COVID-19 pandemic persists despite the availability of vaccines, and it is therefore crucial to develop new therapeutic and preventive approaches. In this study, we investigated the potential role of the oral microbiome in SARS-CoV-2 infection. Using an in vitro SARS-CoV-2 pseudovirus infection assay, we found a potent inhibitory effect exerted by Porphyromonas gingivalis on SARS-CoV-2 infection mediated by known P. gingivalis compounds such as phosphoglycerol dihydroceramide (PGDHC) and gingipains as well as by unknown bacterial factors. We found that the gingipain-mediated inhibition of infection is likely due to cytotoxicity, while PGDHC inhibited virus infection by an unknown mechanism. Unidentified factors present in P. gingivalis supernatant inhibited SARS-CoV-2 likely via the fusion step of the virus life cycle. We addressed the role of other oral bacteria and found certain periodontal pathogens capable of inhibiting SARS-CoV-2 pseudovirus infection by inducing cytotoxicity on target cells. In the human oral cavity, we observed the modulatory activity of oral microbial communities varied among individuals in that some saliva-based cultures were capable of inhibiting while others were enhancing infection. These findings contribute to our understanding of the complex relationship between the oral microbiome and viral infections, offering potential avenues for innovative therapeutic strategies in combating COVID-19.

The Role of Lactic Acid on Wound Healing, Cell Growth, Cell Cycle Kinetics, and Gene Expression of Cultured Junctional Epithelium Cells in the Pathophysiology of Periodontal Disease

Lactic acid (LA) is short-chain fatty acid, such as butyric acid and propionic acid, that is produced as a metabolite of lactic acid bacteria, including periodontopathic bacteria. These short-chain fatty acids have positive effects on human health but can also have negative effects, such as the promotion of periodontal disease (PD), which is caused by periodontal pathogens present in the gingival sulcus. PD is characterized by apical migration of junctional epithelium, deepening of pockets, and alveolar bone loss. Thus, the junctional epithelial cells that form the bottom of the gingival sulcus are extremely important in investigating the pathophysiology of PD. The aim of this study was to investigate the effect of LA on wound healing, cell growth, cell cycle kinetics, and gene expression of cultured junctional epithelium cells. The results showed that stimulation with 10 mM LA slowed wound healing of the junctional epithelial cell layer and arrested the cell cycle in the G0/G1 (early cell cycle) phase, thereby inhibiting cell growth. However, cell destruction was not observed. LA also enhanced mRNA expression of integrin α5, interleukin (IL)-6, IL-8, intercellular adhesion molecule-1, and receptor activator of nuclear factor kappa-B ligand. The results of this study suggest that stimulation of junctional epithelial cells with high concentrations of LA could exacerbate PD, similarly to butyric acid and propionic acid.

Effects of Short-Chain Fatty Acids on Human Oral Epithelial Cells and the Potential Impact on Periodontal Disease: A Systematic Review of In Vitro Studies

Short-chain fatty acids (SCFA), bacterial metabolites released from dental biofilm, are supposed to target the oral epithelium. There is, however, no consensus on how SCFA affect the oral epithelial cells. The objective of the present study was to systematically review the available in vitro evidence of the impact of SCFA on human oral epithelial cells in the context of periodontal disease. A comprehensive electronic search using five databases along with a grey literature search was performed. In vitro studies that evaluated the effects of SCFA on human oral epithelial cells were eligible for inclusion. Risk of bias was assessed by the University of Bristol's tool for assessing risk of bias in cell culture studies. Certainty in cumulative evidence was evaluated using GRADE criteria (grading of recommendations assessment, development, and evaluation). Of 3591 records identified, 10 were eligible for inclusion. A meta-analysis was not possible due to the heterogeneity between the studies. The risk of bias across the studies was considered "serious" due to the presence of methodological biases. Despite these limitations, this review showed that SCFA negatively affect the viability of oral epithelial cells by activating a series of cellular events that includes apoptosis, autophagy, and pyroptosis. SCFA impair the integrity and presumably the transmigration of leucocytes through the epithelial layer by changing junctional and adhesion protein expression, respectively. SCFA also affect the expression of chemokines and cytokines in oral epithelial cells. Future research needs to identify the underlying signaling cascades and to translate the in vitro findings into preclinical models.

Epithelial cell detachment by Porphyromonas gingivalis biofilm and planktonic cultures

Porphyromonas gingivalis is present as a biofilm at the sites of periodontal infections. The detachment of gingival epithelial cells induced by P. gingivalis biofilms was examined using planktonic cultures as a comparison. Exponentially grown planktonic cultures or 40-h biofilms were co-incubated with epithelial cells in a 24-well plate for 4 h. Epithelial cell detachment was assessed using imaging. The activity of arginine-gingipain (Rgp) and gene expression profiles of P. gingivalis cultures were examined using a gingipain assay and quantitative PCR, respectively. P. gingivalis biofilms induced significantly higher cell detachment and displayed higher Rgp activity compared to the planktonic cultures. The genes involved in gingipain post-translational modification, but not rgp genes, were significantly up-regulated in P. gingivalis biofilms. The results underline the importance of including biofilms in the study of bacterial and host cell interactions.

Identification of interspecies interactions affecting Porphyromonas gingivalis virulence phenotypes

Background

Periodontitis is recognized as a complex polymicrobial disease, however, the impact of the bacterial interactions among the 700–1,000 different species of the oral microbiota remains poorly understood. We conducted an in vitro screen for oral bacteria that mitigate selected virulence phenotypes of the important periodontal pathogen, Porphyromonas gingivalis.

Method

We isolated and identified oral anaerobic bacteria from subgingival plaque of dental patients. When cocultured with P. gingivalis W83, specific isolates reduced the cytopathogenic effects of P. gingivalis on oral epithelial cells.

Result

In an initial screen of 103 subgingival isolates, we identified 19 distinct strains from nine species of bacteria (including Actinomyces naeslundii, Streptococcus oralis, Streptococcus mitis, and Veilonella dispar) that protect oral epithelial cells from P. gingivalis-induced cytotoxicity. We found that some of these strains inhibited P. gingivalis growth in plate assays through the production of organic acids, whereas some decreased the gingipain activity of P. gingivalis in coculture or mixing experiments.

Conclusion

In summary, we identified 19 strains isolated from human subgingival plaque that interacted with P. gingivalis, resulting in mitigation of its cytotoxicity to oral epithelial cells, inhibition of growth, and/or reduction of gingipain activity. Understanding the mechanisms of interaction between bacteria in the oral microbial community may lead to the development of new probiotic agents and new strategies for interrupting the development of periodontal disease.

Gingipain-dependent interactions with the host are important for survival of Porphyromonas gingivalis

Porphyromonas gingivalis, a major periodontal pathogen, must acquire nutrients from host derived substrates, overcome oxidative stress and subvert the immune system. These activities can be coordinated via the gingipains which represent the most significant virulence factor produced by this organism. In the context of our contribution to this field, we will review the current understanding of gingipain biogenesis, glycosylation, and regulation, as well as discuss their role in oxidative stress resistance and apoptosis. We can postulate a model, in which gingipains may be part of the mechanism for P. gingivalis virulence.

Temporal activation of anti- and pro-apoptotic factors in human gingival fibroblasts infected with the periodontal pathogen, Porphyromonas gingivalis: potential role of bacterial proteases in host signalling

Background

Porphyromonas gingivalis is the foremost oral pathogen of adult periodontitis in humans. However, the mechanisms of bacterial invasion and the resultant destruction of the gingival tissue remain largely undefined.

Results

We report host-P. gingivalis interactions in primary human gingival fibroblast (HGF) cells. Quantitative immunostaining revealed the need for a high multiplicity of infection for optimal infection. Early in infection (2–12 h), P. gingivalis activated the proinflammatory transcription factor NF-kappa B, partly via the PI3 kinase/AKT pathway. This was accompanied by the induction of cellular anti-apoptotic genes, including Bfl-1, Boo, Bcl-XL, Bcl2, Mcl-1, Bcl-w and Survivin. Late in infection (24–36 h) the anti-apoptotic genes largely shut down and the pro-apoptotic genes, including Nip3, Hrk, Bak, Bik, Bok, Bax, Bad, Bim and Moap-1, were activated. Apoptosis was characterized by nuclear DNA degradation and activation of caspases-3, -6, -7 and -9 via the intrinsic mitochondrial pathway. Use of inhibitors revealed an anti-apoptotic function of NF-kappa B and PI3 kinase in P. gingivalis-infected HGF cells. Use of a triple protease mutant P. gingivalis lacking three major gingipains (rgpA rgpB kgp) suggested a role of some or all these proteases in myriad aspects of bacteria-gingival interaction.

Conclusion

The pathology of the gingival fibroblast in P. gingivalis infection is affected by a temporal shift from cellular survival response to apoptosis, regulated by a number of anti- and pro-apoptotic molecules. The gingipain group of proteases affects bacteria-host interactions and may directly promote apoptosis by intracellular proteolytic activation of caspase-3.

Gingipains from Porphyromonas gingivalis W83 induce cell adhesion molecule cleavage and apoptosis in endothelial cells

The presence of Porphyromonas gingivalis in the periodontal pocket and the high levels of gingipain activity detected in gingival crevicular fluid could implicate a role for gingipains in the destruction of the highly vascular periodontal tissue. To explore the effects of these proteases on endothelial cells, we exposed bovine coronary artery endothelial cells and human microvascular endothelial cells to gingipain-active extracellular protein preparations and/or purified gingipains from P. gingivalis. Treated cells exhibited a rapid loss of cell adhesion properties that was followed by apoptotic cell death. Cleavage of N- and VE-cadherin and integrin beta1 was observed in immunoblots of cell lysates. There was a direct correlation between the kinetics of cleavage of N- and VE-cadherin and loss of cell adhesion properties. Loss of cell adhesion, as well as N- and VE-cadherin and integrin beta1 cleavage, could be inhibited or significantly delayed by preincubation of P. gingivalis W83 gingipain-active extracellular extracts with the cysteine protease inhibitor Nalpha-p-tosyl-l-lysine chloromethylketone. Furthermore, purified gingipains also induced endothelial cell detachment and apoptosis. Apoptosis-associated events, including annexin V positivity, caspase-3 activation, and cleavage of the caspase substrates poly(ADP-ribose) polymerase and topoisomerase I (Topo I), were observed in endothelial cells after detachment. All of the effects observed were correlated with the different levels of cysteine-dependent proteolytic activity of the extracts tested. Taken together, these results indicate that gingipains from P. gingivalis can alter cell adhesion molecules and induce endothelial cell death, which could have implications for the pathogenicity of this organism.

In vitro evaluation of the biocompatibility of contaminated implant surfaces treated with an Er : YAG laser and an air powder system

Titanium platelets with a sand-blasted and acid-etched surface were coated with bovine serum albumin and incubated with a suspension of Porphyromonas gingivalis (ATCC 33277). Four groups with a total of 48 specimens were formed. Laser irradiation of the specimens (n = 12) was performed on a computer-controlled XY translation stage at pulse energy 60 mJ and frequency 10 pps. Twelve specimens were treated with an air powder system. After the respective treatment, human gingival fibroblasts were incubated on the specimens. The proliferation rate was determined by means of fluorescence activity of a redox indicator (Alamar Blue Assay) which is reduced by metabolic activity related to cellular growth. Proliferation was determined up to 72 h. Contaminated and non-treated as well as sterile specimens served as positive and negative controls. Proliferation activity was significantly (Mann-Whitney U-test, P < 0.05) reduced on contaminated and non-treated platelets when compared to sterile specimens. Both on laser as well as air powder-treated specimens, cell growth was not significantly different from that on sterile specimens. Air powder treatment led to microscopically visible alterations of the implant surface whereas laser-treated surfaces remained unchanged. Both air powder and Er : YAG laser irradiation have a good potential to remove cytotoxic bacterial components from implant surfaces. At the irradiation parameters investigated, the Er : YAG laser ensures a reliable decontamination of implants in vitro without altering surface morphology.

Lipopolysaccharide from the periodontal pathogen Porphyromonas gingivalis prevents apoptosis of HL60-derived neutrophils in vitro

Lipopolysaccharide (LPS) from Porphyromonas gingivalis prevented apoptosis of HL60-derived neutrophils, which could not be restored upon the addition of interleukin-10. Signaling of P. gingivalis LPS through Toll-like receptor 2 (TLR2), not TLR4, may account for the inhibiting effect of P. gingivalis LPS on apoptosis and provide a mechanism for the development of destructive periodontal inflammation.

Surface ultrastructure of intact and in situ chlorhexidine-treated human buccal cells. A method for scanning electron microscopy

Air-dried and ethanol-fixed buccal epithelial cell smears from five subjects were observed by scanning electron microscopy. The mucous pellicle was precipitated as a smooth haze covering the cells, and outlines of bacteria were found embedded within it. Rinsing the preparations under running water gradually diminished the mucous pellicle but not the cell-adherent bacteria. A more complete dissolution of the pellicle was accomplished by washing the buccal epithelial cells before smearing. After a chlorhexidine mouthrinse the buccal cells appeared distorted, with only a few adherent bacteria. Three days after the rinsing, the denatured appearance still persisted on many cells, however, simultaneously with the emergence of undenatured epithelial cells with adherent bacteria. The method introduced in this study is useful to investigate the bacteria-mucus-epithelial cell interactions. A possible mode of antibacterial activity of chlorhexidine in vivo may be that it destroys bacterial adhesins. The substantivity of chlorhexidine in the oral cavity may be linked to the turnover rate of the oral epithelial cells.

Effect of Porphyromonas gingivalis on epithelial cell MMP-9 type IV collagenase production

Porphyromonas gingivalis is reportedly capable of stimulating the expression of host cell matrix metalloproteinases (MMP), contributing to tissue destruction. However, the impact of this bacterium on specific molecules remains to be determined. In this study, we evaluate the effect of P. gingivalis on regulation of MMP-9 expression in human gingival epithelial cells (HGEC). Various inocula of P. gingivalis were added to cultures of HGEC. The effects of live bacteria, heat-killed bacteria, and outer membrane extract were analyzed. MMP-9 secretion by HGEC was evaluated by enzyme-linked immunosorbent assay. For inocula smaller than one bacterium per cell, the quantity of MMP-9 secreted by HGEC was increased in comparison to control conditions. For inocula from 2.5 to 250 bacteria per cell, an inhibition of MMP-9 secretion in a dose-response fashion was observed, with a maximum reduction (ranging from 80 to 95% in five experiments) at 50 bacteria per cell. Gelatin zymograms confirmed the decrease in MMP-9 secretion. A band of 83 kDa, corresponding to activated enzyme, was present for inocula of 0.5 to 50 bacteria. Inhibition took place without any alteration of epithelial cell viability. Heat-killed bacteria and outer membrane extract also provoked proenzyme activation but did not inhibit MMP-9 secretion. These results demonstrate a direct effect of P. gingivalis on HGEC, suggesting a specific action on the collagen renewal process at the interface between the epithelium and connective tissue.

Catalytic site targeted mutagenesis of the α-gingivain gene of Porphyromonas gingivalis using Tn-4351 to generate isogenic mutants

The extracellular proteinases of the anaerobe Porphyromonas gingivalis, are implicated in the destruction of host defence mechanisms in periodontitis. We have previously purified one of these enzymes, alpha-gingivain, and established that it belongs to the cysteine proteinase family of enzymes. In the present study, transposon Tn4351 was used to alter the open reading frame encoding a region that includes the catalytic site of alpha-gingivain by targeted mutagenesis. Escherichia coli HB101 which harbours R751 was used to introduce the transposon into P. gingivalis ATCC 33277 by conjugal transfer. E. coli was transformed using the altered plasmid with a Cla I site insertion of a sequence common to the catalytic site histidine or cysteine of many cysteine proteinases. The frequency of the transconjugation was 4.5 x 10(5) while the recipient viable counts comprised 60% of the original P. gingivalis. The result of this targeted mutagenesis was inactivation of gingivains such that some colonies on skimmed-milk agar plates showed no clear surrounding zones of hydrolysis and their normal catalytic activity towards L-BAPNA was destroyed.

Anti-inflammatory and analgesic activity of the bradykinin antagonist, icatibant (Hoe 140), against an extract from Porphyromonas gingivalis

1. Porphyromonas gingivalis is one of the bacteria likely to be related to pain in periodontitis. Several enzymes isolated from P. gingivalis have been reported to have kininogenase activity. Since kinin release could be held responsible for inflammatory symptoms and pain in periodontitis, we investigated whether the inflammatory and algesic effects of a sonic extract from P. gingivalis (PGSE) could be inhibited by the potent bradykinin B2 receptor antagonist, icatibant (Hoe 140). 2. In anaesthetized rats, the subplantar injection of PGSE (0.1 and 1.0 mg) caused a dose-dependent oedema of the hind paws. The net increase of the paw volume 60 min after the injection was 23 +/- 5% and 77 +/- 12%, respectively. The oedema was rich in plasma proteins as determined by the Evans blue method. Pretreatment with icatibant (300 nmol kg-1, s.c.) significantly reduced the effect of 1.0 mg of PGSE whereas the effects of 0.1 mg of PGSE remained unaffected. 3. The subplantar injection of 1.0 mg of PGSE in unanaesthetized rats caused nociceptive behavioural responses which started about 5 min after the injection and lasted for about 10-15 min. These responses were completely prevented by pretreatment with icatibant (300 nmol kg-1, s.c.). 4. The present results show that the plasma extravasation induced by non-algesic doses of a sonic extract from P. gingivalis are caused by mechanisms other than B2 kinin receptor activation whereas inflammatory effects of algesic doses are due to the action of kinins. The pain elicited by the extract is solely mediated by kinins and can be prevented by icatibant. The bradykinin antagonist could thus have a potential for a clinical use against pain associated with periodontal inflammation.