Response of genes related to iron and porphyrin transport in Porphyromonas gingivalis to blue light

BACKGROUND

Antimicrobial blue light (aBL) kills a variety of bacteria, including Porphyromonas gingivalis. However, little is known about the transcriptomic response of P. gingivalis to aBL therapy. This study was designed to evaluate the selective cytotoxicity of aBL against P. gingivalis over human cells and to further investigate the genetic response of P. gingivalis to aBL at the transcriptome level.

METHODS

Colony forming unit (CFU) testing, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM) were used to investigate the antimicrobial effectiveness of blue light against P. gingivalis. The temperatures of the irradiated targets were measured to prevent overheating. Multiple fluorescent probes were used to quantify reactive oxygen species (ROS) generation after blue-light irradiation. RNA sequencing (RNA-seq) was used to investigate the changes in global gene expression. Following the screening of target genes, real-time quantitative polymerase chain reaction (RT-qPCR) was performed to confirm the regulation of gene expression.

RESULTS

A 405 nm aBL at 100 mW/cm² significantly killed P. gingivalis within 5 min while sparing human gingival fibroblasts (HGFs). No obvious temperature changes were detected in the irradiated surface under our experimental conditions. RNA-seq showed that the transcription of multiple genes was regulated, and RT-qPCR revealed that the expression levels of the genes RgpA and RgpB, which may promote heme uptake, as well as the genes Ftn and FetB, which are related to iron homeostasis, were significantly upregulated. The expression levels of the FeoB-2 and HmuR genes, which are related to hydroxyl radical scavenging, were significantly downregulated.

CONCLUSIONS

aBL strengthens the heme uptake and iron export gene pathways while reducing the ROS scavenging pathways in P. gingivalis, thus improving the accumulation of endogenous photosensitizers and enhancing oxidative damage to P. gingivalis.

Controllable acidophilic dual-emission fluorescent carbonized polymer dots for selective imaging of bacteria

Fluorescent materials can be powerful contrast agents in photoelectric devices and for bioimaging. As emerging fluorescent materials, carbonized polymer dots (CPDs) with high quantum yields (QYs), long-wavelength emission and multiple functions are highly desired. Despite great progress in the synthetic methods and QYs of CPDs, multiple emission of CPDs is challenging. Therefore, we developed CPDs with dual-emission fluorescence in terms of inherent blue and red emission. In addition, CPDs with sole blue emission (B-CPDs) and red emission (R-CPDs) were synthesized, respectively, by regulating the reaction conditions to control the quantitative structure and emission centers. The absolute QY of R-CPDs in water was 24.33%. These three types of CPDs with dual/sole emission could be used in optoelectronic and bioimaging applications. With different CPDs coated on a commercially available gallium nitride light-emitting diode chip as a color-conversion layer, LEDs with blue, yellow, and red emission were achieved. Benefiting from the different emission intensities and emission peaks of R/B-CPDs in different pH conditions, they were used (without further modification) to distinguish between Porphyromonas gingivalis, Streptococcus mutans, Escherichia coli and Staphylococcus aureus in dental plaque biofilms (the first time this has been demonstrated). These findings could enable a new development direction of CPDs based on the design of multi-emission centers.

[Molecular mechanism involved in adhesion of monocytes to endothelial cells induced by nicotine and Porphyromonas gingivalis-LPS]

OBJECTIVE

To investigate molecular mechanism involved in nicotine in combination with Porphyromonas gingivalis (P.g) caused monocyte-endothelial cell adhesion.

METHODS

The effect of nicotine, P.g-lipopolysaccharide (P.g-LPS) and their combination on the proliferation of U937 cells was determined by CCK-8 method. Interleukin-6 (IL-6) expression was investigated by real-time PCR after U937 cells were treated with nicotine, P.g-LPS and their combination. In human umbilical vein endothelial cells (HUVECs), the expressions of monocyte chemoattractant protein CCL-8 and adhesion molecules including vascular cell adhesion molecule 1 (Vcam-1), very late antigen 4 alpha (VLA4α), tumor necrosis factor receptor superfamily member 4 (OX40) and OX40 ligand (OX40L) were detected by real-time PCR or Western blotting assays after HUVEC cells were treated with nicotine, P.g-LPS and their combination. Adhesion of monocytes to endothelial cells was detected after the HUVECs and U937 cells were stimulated with nicotine, P.g-LPS and their combination, respectively.

RESULTS

P.g-LPS did not affect the proliferative ability of nicotine in U937 cells. However, the ability of P.g-LPS induced IL-6 expression was inhibited by 100 μmol/L nicotine in U937 cells. In HUVECs, the expressions of CCL-8, Vcam-1, VLA4α, OX40 and OX40L were significantly up-regulated by nicotine and P.g-LPS combination compared with nicotine alone, P.g-LPS alone and the untreated control. Adhesion of monocytes to HUVECs results showed that the two types of cells treated with nicotine in combination with P.g-LPS could markedly increase the adhesion ability of monocytes to HUVECs.

CONCLUSION

P.g-LPS in combination with nicotine could recruit monocytes to endothelial lesion through up-regulation of CCL-8, and promote adhesion of monocytes to endothelial cells through enhancement of Vcam-1/VLA4α and OX40/OX40L interactions, which could be involved in the initiation and development of atherosclerosis.

Anti-inflammatory activity of fisetin in human gingival fibroblasts treated with lipopolysaccharide

Fisetin is an anti-inflammatory flavonoid; however, its anti-inflammatory mechanism is not yet understood. In this study, we evaluated the anti-inflammatory effect of fisetin and its association with mitogen-activated protein kinase (MAPK) and nuclear factor kappa-beta pathways in human gingival fibroblasts (HGFs) treated with lipopolysaccharide (LPS) obtained from Porphyromonas gingivalis. The cell signaling, cell viability, and cyclooxygenase-2 (COX-2) expression of HGFs treated with various concentrations (0, 1, 5, 10, and 15 μM) of fisetin were measured by cell viability assay (MTT), Western blotting, and reverse transcriptase polymerase chain reaction analysis on COX-2. We found that fisetin significantly reduced the synthesis and expression of prostaglandin E2 in HGFs treated with LPS. Activation of extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 MAPK was suppressed consistently by fisetin in HGFs treated with LPS. The data indicate that fisetin inhibits MAPK activation and COX-2 expression without affecting cell viability. These findings may be valuable for understanding the mechanism of the effect of fisetin on periodontal disease.

Outer membrane vesicles of Porphyromonas gingivalis elicit a mucosal immune response

We previously reported that mutation of galE in Porphyromonas gingivalis has pleiotropic effects, including a truncated lipopolysaccharide (LPS) O-antigen and deglycosylation of the outer membrane protein OMP85 homolog. In the present study, further analysis of the galE mutant revealed that it produced little or no outer membrane vesicles (OMVs). Using three mouse antisera raised against whole cells of the P. gingivalis wild type strain, we performed ELISAs to examine the reactivity of these antisera with whole cells of the wild type or the galE mutant. All three antisera had significantly lower reactivity against the galE mutant compared to wild type. OMVs, but not LPS, retained the immunodominant determinant of P. gingivalis, as determined by ELISAs (with wild type LPS or OMVs as antigen) and absorption assays. In addition, we assessed the capacity of OMVs as a vaccine antigen by intranasal immunization to BALB/c mice. Synthetic double-stranded RNA polyriboinosinic polyribocytidylic acid [Poly (I∶C)], an agonist of Toll-like receptor 3 (TLR3), was used as the mucosal adjuvant. Vaccination with OMV elicited dramatically high levels of P. gingivalis-specific IgA in nasal washes and saliva, as well as serum IgG and IgA. In conclusion, the OMVs of P. gingivalis have an important role in mucosal immunogenicity as well as in antigenicity. We propose that P. gingivalis OMV is an intriguing immunogen for development of a periodontal disease vaccine.

Genetic transformation of an obligate anaerobe, P. gingivalis for FMN-green fluorescent protein expression in studying host-microbe interaction

The recent introduction of “oxygen-independent” flavin mononucleotide (FMN)-based fluorescent proteins (FbFPs) is of major interest to both eukaryotic and prokaryotic microbial biologists. Accordingly, we demonstrate for the first time that an obligate anaerobe, the successful opportunistic pathogen of the oral cavity, Porphyromonas gingivalis, can be genetically engineered for expression of the non-toxic green FbFP. The resulting transformants are functional for studying dynamic bacterial processes in living host cells. The visualization of the transformed P. gingivalis (PgFbFP) revealed strong fluorescence that reached a maximum emission at 495 nm as determined by fluorescence microscopy and spectrofluorometry. Human primary gingival epithelial cells (GECs) were infected with PgFbFP and the bacterial invasion of host cells was analyzed by a quantitative fluorescence microscopy and antibiotic protection assays. The results showed similar levels of intracellular bacteria for both wild type and PgFbFP strains. In conjunction with organelle specific fluorescent dyes, utilization of the transformed strain provided direct and accurate determination of the live/metabolically active P. gingivalis' trafficking in the GECs over time. Furthermore, the GECs were co-infected with PgFbFP and the ATP-dependent Clp serine protease-deficient mutant (ClpP-) to study the differential fates of the two strains within the same host cells. Quantitative co-localization analyses displayed the intracellular PgFbFP significantly associated with the endoplasmic reticulum network, whereas the majority of ClpP- organisms trafficked into the lysosomes. Hence, we have developed a novel and reliable method to characterize live host cell-microbe interactions and demonstrated the adaptability of FMN-green fluorescent protein for studying persistent host infections induced by obligate anaerobic organisms.

Detection of bacterial cells by impedance spectra via fluidic electrodes in a microfluidic device

In this study, a novel method for detecting bacterial cells in deionized (DI) water suspension is presented by using fluidic electrodes with a hydrodynamic focusing technique. KCl solution was utilized as both sheath flow and fluidic electrodes, and the bacterial suspension was squeezed to form three flowing layers with different conductivities on a microfluidic chip. An impedance analyzer was connected with the KCl solution through two Ag/AgCl wires to apply an AC voltage to fluidic layers within a certain frequency for impedance measurements. Porphyromonas gingivalis and Escherichia coli were detected and linear relationships were found between the impedance and the logarithmic value of the bacterial concentration in certain cell concentration ranges. It is demonstrated that bacterial detection using the microdevice is rapid and convenient, with a chip made of simple flow channels, and the detection sensitivity of cell counting can be tuned by varying the width of the sample flow layer through changing input velocities, showing a detection limit of 10(3) cells mL(-1).

Comparative anti-inflammatory activities of curcumin and tetrahydrocurcumin based on the phenolic O-H bond dissociation enthalpy, ionization potential and quantum chemical descriptor

Curcumin and its reduced derivative tetrahydrocurcumin have been shown to exhibit chemopreventive activity. Cyclooxygenase-2 (COX-2) inhibition in lipopolysaccharide (LPS)- or Porphyromonas gingivalis fimbria-stimulated RAW 264.7 cells was investigated using Northern blot analysis. The fimbria-stimulated expression of the COX-2 gene was inhibited by curcumin but not by tetrahydrocurcumin. LPS-stimulated COX-2 gene expression was completely inhibited by curcumin, but an increase in the concentration of tetrahydrocurcumin did not cause complete inhibition of COX-2 expression. The inhibitory effect of curcumin on nuclear factor kappa B (NF-kappaB) activation in the cells was clearly observed, but that of tetrahydrocurcumin was incomplete even at a concentration of 20 microM. To explain the difference in effect between the two compounds, analysis of the frontier orbital was performed using ab initio 6-31G* wave function. The calculated chemical hardness (eta) for curcumin was clearly smaller, whereas its electronegativity (chi) and electrophilicity (omega) were clearly greater than the corresponding values for the curcumin-related compounds tetrahydrocurcumin, isoeugenol and eugenol. This suggested that the anti-inflammatory activities of curcumin may be related to eta-, chi- and/or omega-controlled enzymes. In addition, the bond dissociation enthalpy (BDE) of the phenolic OH was calculated using the density function theory (DFT)/B3LY. The total BDE values of curcumin and tetrahydrocurcumin were almost identical, but the BDE of one-electron oxidation and ionization potential (IP) for curcumin were lower than those for tetrahydrocurcumin, suggesting the highly pro-oxidative activity of curcumin. Curcumin has both oxidant and antioxidant properties. A causal link between the anti-inflammatory activities and molecular properties of phenolic antioxidants is suggested.

Dense fimbrial meshwork enhances Porphyromonas gingivalis adhesiveness: a scanning electron microscopic study

BACKGROUND AND OBJECTIVE

The aim of this study was to determine how the fimbriae of Porphyromonas gingivalis function in plaque formation.

MATERIAL AND METHODS

We used scanning electron microscopy to examine aggregates and hemaggregates of fimbria-rich ATCC33277 (parent) and fimbra-poor OZ6301C (pgmA-knockout, mutant) strains of P. gingivalis. We also assessed the hemagglutination activity of the two strains as an indicator of P. gingivalis adhesiveness.

RESULTS

Aggregates of P. gingivalis were composed of bacterial chains and clusters. Rich fimbriae projecting from cells of the parent strain tended to bunch and form a dense meshwork among bacterial cells. In contrast, cells of the mutant strain projected fewer fimbriae and the meshwork was looser. Hemaggregates including cells of the parent strain contained a detached, dense fimbrial meshwork that adhered to erythrocytes. Hemaggregates comprising cells of the mutant strain included bacterial chains and clusters that adhered to erythrocytes by shorter fimbriae than those of the parent strain. The hemagglutination titer of the parent strain was 10-fold higher than that of the mutant strain, although the number of fimbriae per cell of the parent strain was only double that of the mutant strain.

CONCLUSION

The results indicate that P. gingivalis adhesiveness is prominently enhanced by the dense fimbrial meshwork. Thus, the virulence of P. gingivalis is increased by the presence of rich fimbriae.

Effect of acetylsalicylic acid on aggregation of human platelets by Porphyromonas gingivalis

This study investigated the effect of in vivo low-dose acetylsalicylic acid (ASA, aspirin) on human platelet aggregation induced in vitro by Porphyromonas gingivalis cells. Blood was collected from volunteers (n = 20), half of whom ingested 81 mg of aspirin 24 hours before donating blood. Low-dose aspirin inhibited P. gingivalis cell-induced platelet aggregation and produced an inverse correlation of inhibition to number of cells. At the higher concentration of cells used in this in vitro assay, aspirin inhibition was significant (P = 0.001); however, partial platelet activation was observed. The significance of partial platelet activation is discussed in this article, as is the relevance of platelet aggregation to the putative link between inflammatory periodontal disease and cardiovascular disease.

Differential interactions of fimbriae and lipopolysaccharide from Porphyromonas gingivalis with the Toll-like receptor 2-centred pattern recognition apparatus

The lipopolysaccharide (LPS) and fimbriae of Porphyromonas gingivalis play important roles in periodontal inflammation and pathogenesis. We investigated fimbriae and LPS from several P. gingivalis strains in terms of relative dependence on Toll-like receptor (TLR) signalling partners or accessory pattern-recognition molecules mediating ligand transfer to TLRs, and determined induced assembly of receptor complexes in lipid rafts. Fimbriae could utilize TLR1 or TLR6 for cooperative TLR2-dependent activation of transfected cell lines, in contrast to LPS and a mutant version of fimbriae which displayed preference for TLR1. Whether used to activate human cell lines or mouse macrophages, fimbriae exhibited strong dependence on membrane-expressed CD14 (mCD14), which could not be substituted for by soluble CD14 (sCD14). In contrast, sCD14 efficiently substituted for mCD14 in LPS-induced cellular activation. LPS-binding protein was more important for LPS- than for fimbria-induced cell activation, whereas the converse was true for CD11b/CD18. Cell activation by LPS or fimbriae required lipid raft function and formation of heterotypic receptor complexes (TLR1-2/CD14/CD11b/CD18), although wild-type fimbriae additionally recruited TLR6. In summary, TLR2 activation by P. gingivalis LPS or fimbriae involves differential dependence on accessory signalling or ligand-binding receptors, which may differentially influence innate immune responses.

Porphyromonas gingivalis-induced platelet aggregation in plasma depends on Hgp44 adhesin but not Rgp proteinase

Evidence from recent epidemiological studies suggests a link between periodontal infections and increased risk of atherosclerosis and related cardiovascular and cerebrovascular events in human subjects. One of the major pathogens of periodontitis, Porphyromonas gingivalis, has the ability to aggregate human platelets in platelet-rich plasma (PRP). Mechanism of P. gingivalis-induced platelet aggregation in PRP was investigated. Proteinase inhibitors toward Arg-gingipain (Rgp) and Lys-gingipain (Kgp) did not suppress P. gingivalis-induced platelet aggregation in PRP, whereas the Rgp inhibitor markedly inhibited P. gingivalis-induced platelet aggregation using washed platelets. Mutant analysis revealed that P. gingivalis-induced platelet aggregation in PRP depended on Rgp-, Kgp- and haemagglutinin A (HagA)-encoding genes that intragenically coded for adhesins such as Hgp44. Hgp44 adhesin on the bacterial cell surface, which was processed by Rgp and Kgp proteinases, was essential for P. gingivalis-induced platelet aggregation in PRP. P. gingivalis cell-reactive IgG in plasma, and FcgammaRIIa receptor and to a lesser extent GPIbalpha receptor on platelets were found to be a prerequisite for P. gingivalis-induced platelet aggregation in PRP. These results reveal a novel mechanism of platelet aggregation by P. gingivalis.

Intracellular signaling and cytokine induction upon interactions of Porphyromonas gingivalis fimbriae with pattern-recognition receptors

Toll-like receptors (TLRs) and other pattern-recognition receptors (PRRs) of the innate immune system form functional receptor complexes that recognize and respond to pathogen-associated molecular patterns (PAMPs). Porphyromonas gingivalis is an important pathogen in human periodontitis and has also been implicated in atherosclerosis. A major virulence factor of this pathogen is the fimbriae, which function as a surface adhesin. Here we present evidence that fimbriae also constitute a predominant P. gingivalis proinflammatory molecule which activates the TLR signaling pathway resulting in induction of proinflammatory cytokines (IL-1beta, IL-6, and TNF-alpha) and chemokines (IL-8) in monocytic cells. Although TLR2 and TLR4 mediate cellular activation in response to fimbriae, other PRRs, namely CD14 and CD11b/CD18, are involved in the recognition of fimbriae. We thus propose that fimbriae function as a PAMP which interacts with a PRR multi-receptor complex, where CD14 and CD11b/CD18 function as recruiting receptors and TLRs function as signaling receptors. In addition to cytokine induction, TLR activation by fimbriae also results in upregulation of the CD40, CD80, and CD86 costimulatory molecules in antigen-presenting cells, suggesting that fimbriae are sensed as a potential "danger" to the host immune system. Moreover, proinflammatory cytokine induction is attenuated upon repeated cellular stimulation with P. gingivalis fimbriae. This mechanism of tolerance induction which serves to mitigate excessive and potentially harmful inflammatory reactions appears to be due partly to fimbria-induced downregulation of the expression of interleukin-1 receptor-associated kinase-1 (IRAK-1), an important signaling intermediate of the TLR pathway. Understanding the molecular basis of how the host recognizes and responds to P. gingivalis fimbriae is essential for developing molecular approaches to control P. gingivalis-induced inflammatory responses in periodontal disease and perhaps atherosclerosis.

Fiber optic fluorescence microprobe for endodontic diagnosis

Successful endodontic therapy requires total debridement as well as complete obturation of the root canal to the cemento-dentinal junction. The goal of this study was to investigate the feasibility of using quantitative fluorescence spectroscopy for the detection and localization of pathological dentin, pulpal remnants, and microorganisms within the root canal. Specific aims were to identify: 1) characteristic excitation/emission spectra for healthy dentin, decayed dentin, enamel, and pulp; 2) the potential of specific spectral data for differentiating between these tissues; and 3) the potential of spectral data for detecting the presence and identifying four common endodontic pathogens. Fluorescence spectra were determined in the tissues of permanent human teeth, extirpated healthy and necrotic pulps, and four endodontic pathogens. Excitation/emission spectra were collected at 366 nm, 405 nm, and 440 nm excitation. Marked differences in spectral signatures between the different tissues under investigation were observed. We postulate that the differences in fluorescence spectra of decayed vs. healthy dentin are due to the loss of mineralized tissue components and increased organic presence and water in these tissues. Pulpal tissue showed distinctly different fluorescence spectra from healthy and decayed dentin, providing a basis for differentiating between tissue categories. Each bacterial species demonstrated distinct spectral emission patterns.

A regulation cascade controls expression of Porphyromonas gingivalis fimbriae via the FimR response regulator

Little is known about how Porphyromonas gingivalis, a Gram-negative oral anaerobe, senses environmental changes, and how such information is transmitted to the cell. The production of P. gingivalis surface fimbriae is regulated by FimS-FimR, a two component signal transduction system. Expression of fimA, encoding the fimbrilin protein subunit of fimbriae, is positively regulated by the FimR response regulator. In this study we investigated the molecular mechanisms of FimR regulation of fimA expression. Comparative transcription profiling of fimR wild-type and mutant strains shows that FimR controls the expression of several genes including five clustered around the fimA locus. Chromatin immunoprecipitation assays and electrophoretic mobility shift assays identify and confirm that FimR binds to the promoter region of the first gene in the fimA cluster. Gene expression analyses of mutant strains reveal a transcriptional cascade involving multiple steps, with FimR activating expression of the first gene of the cluster that encodes a key regulatory protein.

Light-induced modulation of Porphyromonas gingivalis growth

The bacterium Porphyromonas gingivalis is a clinically significant agent in periodontitis, a disease for which there is no definitive cure. Several groups have attempted to kill this bacterium using low levels of light in the absence of a photosensitizer, with conflicting results. We hypothesize that it is not possible to kill P. gingivalis by targeting endogenous porphyrins for a photochemical reaction. We demonstrated that irradiation of P. gingivalis with 455 or 625 nm light emitting diodes did not induce a photochemical killing of the cultures. Controlled temperature experiments indicate that irradiation at either wavelength did not significantly impact the growth of P. gingivalis cultures, as compared to non-irradiated controls. Rather, the irradiation caused a temperature increase in the growth medium, which altered the growth of the cultures. These results indicate that heat-induced killing of P. gingivalis could be the mechanism behind successful irradiation experiments with this bacterium.

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

OBJECTIVES

Porphyromonas gingivalis is a significant periodontal pathogen that has been shown in vitro to be able to invade gingival epithelial cells and grow intracellularly. The aim of the present study was to detect P. gingivalis in gingival tissues from chronic periodontitis (CP) patients.

MATERIALS AND METHODS

Monoclonal antibodies specific to a cell membrane-bound thiol proteinase of P. gingivalis were used to detect the microbe in gingival tissues of CP patients (n = 13) by immunohistochemistry. The presence of P. gingivalis was also analysed by polymerase chain reaction (PCR).

RESULTS

Immunohistochemical analysis of the periodontal tissues revealed positive staining for P. gingivalis thiol proteinase in 11 of the 13 patients. Positive staining was mainly located intracellularly in the perinuclear region of the cytoplasm in the periodontal epithelial cells and it could be detected throughout the whole depth of both pocket and oral epithelium. The sensitivity of immunohistochemistry was found to be comparable with that of PCR.

CONCLUSIONS

Our results provide in vivo evidence of the ability of P. gingivalis to enter human gingival epithelial cells. Intracellular localization of P. gingivalis contributes to its evasion of the host immune surveillance and eventually increases its resistance to conventional treatments of periodontal diseases.

The major structural components of two cell surface filaments of Porphyromonas gingivalis are matured through lipoprotein precursors

Bacterial cell surface filaments play significant roles in adherence to and invasion of host cells. They are generated by the chaperone/usher pathway system (class I fimbriae), the type II secretion system (type IV pili) and the nucleation-dependent polymerization system (Curli filaments) that are categorized by their modes of expression and assembly. In this study, we found that the periodontal pathogen Porphyromonas gingivalis expressed the major structural components of two cell surface filaments (fimbrilin and the 75 kDa protein) that had extremely long prosequences in their primary gene products. N-terminal amino acid sequencing of the prosequences, treatment of P. gingivalis cells with globomycin, an inhibitor for lipoprotein-specific signal peptidase, amino acid substitution of the cysteine residue of the prosequence of fimbrilin and [(3)H]-palmitic acid labelling implied that fimbrilin and the 75 kDa protein were matured through their lipoprotein precursor forms. Accumulation of precursor forms of fimbrilin and the 75 kDa protein on the cell surface of the gingipain-null mutant revealed that Arg-gingipain processed these precursors on the surface to yield their mature forms, which subsequently assembled into the filamentous structures, suggesting that the transport and assembly of the major component proteins appear to be novel.

A novel polymeric chlorhexidine delivery device for the treatment of periodontal disease

An implantable, anti-microbial delivery device for the treatment of periodontal disease has been developed. In this polymer-based delivery system, the encapsulation efficiency, release characteristics, and bioactivity of anti-microbial agent were controlled by the complexation of the drug with cyclodextrins of differing lipophilicity. Microparticles of poly(dl-lactic-co-glycolic acid) (PLGA) containing chlorhexidine (Chx) free base, chlorhexidine digluconate (Chx-Dg) and their association or inclusion complex with methylated-beta-cyclodextrin (MBCD) and hydroxypropyl-beta-cyclodextrin (HPBCD) were prepared by single emulsion, solvent evaporation technique. It was observed that encapsulation efficiency and release of the chlorhexidine derivatives from the microparticles was a function of the lipophilicity of the cyclodextrin. Complexation of the poorly water soluble Chx with the more hydrophilic HPBCD resulted in 62% higher encapsulation efficiency and longer duration of sustained release over a 2-week period than complexation with the more lipophilic MBCD. In contrast, the complexation of the more water-soluble derivative of chlorhexidine, Chx-Dg, with the more lipophilic MBCD improved encapsulation efficiency by 12% and prolonged its release in comparison to both the free Chx-Dg and its complex with HPBCD. Furthermore, it was observed that the initial burst effect could be diminished by complexation with CD. Preliminary studies have shown that the chlorhexidine released from PLGA chips is biologically active against bacterial population that is relevant in periodontitis (P. gingivalis and B. forsythus) and a healthy inhibition zone is maintained in agar plate assay over a period of at least a 1-week. The PLGA/CD delivery system described in this paper may prove useful for the localized delivery of chlorhexidine salts and other anti-microbial agents in the treatment of periodontal disease where prolonged-controlled delivery is desired.

NF-κB-dependent induction of osteoprotegerin by Porphyromonas gingivalis in endothelial cells

Porphyromonas gingivalis is a major etiological pathogen of adult periodontitis characterized by alveolar bone resorption. Vascular endothelial cells supply many inflammatory cytokines into periodontal tissue. However, whether the cells contribute to bone metabolism in periodontitis remains unknown. In this study, we investigated the effect of P. gingivalis on osteoprotegerin (OPG) and receptor activator of NF-kappaB ligand (RANKL) production, both of which are key regulators of bone metabolism, in human microvascular endothelial cells (HMVECs). We showed that P. gingivalis upregulated expression of OPG but not RANKL mRNA in HMVEC. P. gingivalis induced NF-kappaB activation, and the induction of OPG in HMVEC by the pathogen was blocked by the inhibitors of NF-kappaB. In addition, incubation of OPG with P. gingivalis supernatant resulted in loss of the protein. These results indicate that P. gingivalis-stimulated HMVEC secrete OPG via a NF-kappaB-dependent pathway, while the OPG is partly degraded by the bacteria. Thus, microvascular endothelial cells can act as a source of OPG and thereby may play an important role in regulating bone metabolism in periodontitis.

Phototoxic Effect of Visible Light on Porphyromonas gingivalis and Fusobacterium nucleatum: An In Vitro Study¶†

The antibacterial effect of visible light irradiation combined with photosensitizers has been reported. The objective of this was to test the effect of visible light irradiation without photosensitizers on the viability of oral microorganisms. Strains of Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus mutans and Streptococcus faecalis in suspension or grown on agar were exposed to visible light at wavelengths of 400-500 nm. These wavelengths are used to photopolymerize composite resins widely used for dental restoration. Three photocuring light sources, quartz-tungsten-halogen lamp, light-emitting diode and plasma-arc, at power densities between 260 and 1300 mW/cm2 were used for up to 3 min. Bacterial samples were also exposed to a near-infrared diode laser (wavelength, 830 nm), using identical irradiation parameters for comparison. The results show that blue light sources exert a phototoxic effect on P. gingivalis and F. nucleatum. The minimal inhibitory dose for P. gingivalis and F. nucleatum was 16-62 J/cm2, a value significantly lower than that for S. mutans and S. faecalis (159-212 J/cm2). Near-infrared diode laser irradiation did not affect any of the bacteria tested. Our results suggest that visible light sources without exogenous photosensitizers have a phototoxic effect mainly on Gram-negative periodontal pathogens.

Suppression of Virulence of Porphyromonas gingivalis by Potent Inhibitors Specific for Gingipains

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium that is implicated as a major etiologic agent of adult periodontal disease. This bacterium is asaccharolytic and possesses strong potency for proteolysis. It produces a novel class of cysteine proteinases, termed gingipains, in the cell-associated and secretory forms. Gingipains consist of arginine-X-specific cysteine proteinases (Arg-gingipains, Rgps) and lysine-X-specific cysteine proteinase (Lys-gingipain, Kgp). Previous studies using various P. gingivalis mutants deficient in Rgp- and/or Kgp-encoding genes have revealed that both enzymes are important for the bacterium both to exhibit its virulence and to survive in periodontal pockets. Mammalian internal proteinase inhibitors such as cystatins, a1-antichymotrypsin, and tissue inhibitor of metalloproteinases (TIMPs) have little or no effects on the proteolytic activities of these enzymes, suggesting the evasion of the bacterium from host defense mechanisms. Recent epidemiological reports have shown a significant relation between periodontal diseases and systemic diseases such as cardiovascular diseases and diabetes. Thus, the development of potent inhibitors specific for gingipains provides new therapeutic approaches to treat periodontal diseases and the related systemic diseases. More recently, we have developed novel synthetic inhibitors specific for Rgp and Kgp, based on the specificity and efficacy of cleavage of histatins by each enzyme. We have also isolated a novel and potent inhibitor of Rgp from the culture supernatant of Streptomyces species strain FA-70, now designated as FA-70C1. Here we summarized the usefulness of these new inhibitors in providing a broader application in studies of this important class of enzymes.

Binding ofPorphyromonas gingivalisfimbriae toTreponema denticoladentilisin

Treponema denticola has been reported to coaggregate with Porphyromonas gingivalis and localize closely together in matured subgingival plaque. In this study of the interaction of T. denticola with P. gingivalis, the P. gingivalis fimbria-binding protein of T. denticola was identified by two-dimensional electrophoresis followed by a ligand overlay assay with P. gingivalis fimbriae, and was determined to be dentilisin, a chymotrypsin-like proteinase of T. denticola. The binding was further demonstrated with a ligand overlay assay using an isolated GST fusion dentilisin construct. Our results suggest that P. gingivalis fimbriae and T. denticola dentilisin are implicated in the coaggregation of these bacteria.

Isolation and characterization of a novel and potent inhibitor of Arg-gingipain from Streptomyces sp. strain FA-70

Arg-gingipain (Rgp) is a major cysteine proteinase produced by the oral bacterium Porphyromonas gingivalis, which is a major pathogen of advanced periodontal diseases. This enzyme is important for the bacterium both to exhibit its virulence and to survive in periodontal pockets. The development of Rgp inhibitors thus provides new therapeutic approaches to periodontal diseases. In this study, we first isolated and purified a novel and potent inhibitor of Rgp from the culture supernatant of Streptomyces species strain FA-70, now designated as FA-70C1. This compound was found to be an antipain analog composed of phenylalanyl-ureido-citrullinyl-valinyl-cycloarginal (C27H43N9O7). The Ki value was calculated to be 4.5x10(-9) M when benzyloxycarbonyl-phenylalanyl-arginine-4-methly-coumaryl-7-amide was used as a substrate. This compound also inhibited cathepsins B, L, and H, though their Ki values were much higher than that of Rgp. FA-70C1 had little or no inhibitory activity on Lys-gingipain, another cysteine proteinase of P. gingivalis. The Rgp-induced degradation of various human proteins was completely blocked by this inhibitor. Disruption of both the bactericidal activity of polymorphonuclear leukocytes and the viability of human fibroblasts and umbilical vein endothelial cells induced by the culture supernatant of P. gingivalis was suppressed by the inhibitor in a dose-dependent manner. The enhancement of vascular permeability induced by in vivo administration of the culture supernatant of P. gingivalis was strongly inhibited by the inhibitor. Furthermore, the growth of P. gingivalis was suppressed by FA-70C1 in a dose-dependent manner. These results strongly suggest that FA-70C1 is a useful tool to prevent the virulence of P. gingivalis.

A conserved Ala320 in the FtsZ of Porphyromonas gingivalis is important for cell division

We have previously cloned the gene encoding the cell division protein FtsZ, designated PgFtsZ, from Porphyromonas gingivalis, an oral anaerobic bacterium implicated in advanced periodontal disease. In the present study, we have shown that overexpression of ZDeltaC02, a mutant form of PgFtsZ in which 128 amino acid residues have been removed from the C-terminus, caused an inhibition of cell division in E. coli cells. However, overexpression of ZDeltaC03, missing 177 residues from the C-terminus, did not inhibit cell division, suggesting that the 49 residues between 281 and 329 are required for cell division. Sequence comparison of the known prokaryotic FtsZs revealed that this region contained a highly conserved domain, designated A-domain, in which Ala320 of PgFtsZ was conserved throughout a broad variety of species. Therefore, we analyzed the role of Ala320 by site-directed mutagenesis. We found that overexpression of ZA320H and ZA320R resulted in the normal phenotype, unlike the wild type. Immunoblot analysis showed that these mutant proteins were expressed at similar levels. These results suggest that Ala320 is highly conserved and is crucial for cell division.

Kinetics of coaggregation of Porphyromonas gingivalis with Fusobacterium nucleatum using an automated microtiter plate assay

Coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum strains was previously studied using either a semi-quantitative macroscopic assay or radioactive tracer assays. A new automated microtiter plate assay is introduced, in which the plate reader (Vmax) was adapted to allow quantitative evaluation of the kinetics of coaggregation. F nucleatum PK 1594 coaggregated with P. gingivalis HG 405 with a maximal coaggregation rate of 1.05 mOD/min, which occurred at a P. gingivalis to F. nucleatum cell ratio of 1 to 2. F. nucleatum PK 1594 failed to do so with P. gingivalis strains A 7436 or ATCC 33277. Galactose inhibition of this coaggregation could be quantitatively measured over a wide range of concentrations to demonstrate its dose-dependent manner. P. gingivalis HG 405 failed to coaggregate with F. nucleatum strains ATCC 25586 and ATCC 49256. The assay used in the present study is a sensitive and efficient quantitative automated tool to study coaggregation and may replace tedious radioactive tracer assays.

Evaluation of co-aggregation among Streptococcus mitis, Fusobacterium nucleatum and Porphyromonas gingivalis

AIMS

To develop a semi-quantitative method for evaluating co-aggregation reactions among three bacterial species, and to examine the influence of Fusobacterium nucleatum on the adherence of Porphyromonas gingivalis.

METHODS AND RESULTS

The method involves coating hydroxyapatite (HAP) discs with streptococcal cells and treatment with radio-labelled bacterial cell suspensions. The sensitivity of the method was estimated by comparison with a turbidometric co-aggregation assay. Results from the two methods were in close agreement. Streptococcus mitis-coated HAP discs were immersed in a 3H-labelled Fus. nucleatum cell suspension and then a 14C-labelled P. gingivalis cell suspension. The discs were then pyrolysed to recover and quantify the released 3H and 14C radioactivity. The number of Fus. nucleatum cells on the discs increased with immersion time and this, in turn, resulted in elevated adherence of P. gingivalis.

CONCLUSION

The data indicate that the method closely reflects co-aggregation characters, and that Fus. nucleatum has a positive effect on the adherence of P. gingivalis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present method, which is designed to mimic the oral environment, should prove useful in the semi-quantitative evaluation of co-aggregation reactions.

Quantitative real-time PCR for Porphyromonas gingivalis and total bacteria

Accurate quantitation of the number of cells of individual bacterial species in dental plaque samples is needed for understanding the bacterial etiology of periodontitis. Real-time PCR offers a sensitive, efficient, and reliable approach to quantitation. Using the TaqMan system we were able to determine both the amount of Porphyromonas gingivalis and the total number of bacterial cells present in plaque samples. Using species-specific primers and a fluorescent probe, detection of DNA from serial dilutions of P. gingivalis cells was linear over a large range of DNA concentrations (correlation coefficient = 0.96). No difference was observed between P. gingivalis DNA alone and the same DNA mixed with DNA isolated from dental plaque, indicating that P. gingivalis levels can be determined accurately from clinical samples. The total number of cells of all bacterial species was determined using universal primers and a fluorescent probe. Standard curves using four different bacterial species gave similar results (correlation coefficient = 0.86). Levels of both P. gingivalis and total bacteria were determined from a series of human plaque samples. High levels of P. gingivalis were observed in several of the samples from subjects with periodontitis and none of those from healthy subjects. Real-time quantitative PCR provided a sensitive and reliable method for quantitating P. gingivalis. In addition, it allowed the determination of the total number of bacterial cells present in a complex sample so that the percentage of P. gingivalis cells could be determined.

Large-scale synthesis and functional elements for the antimicrobial activity of defensins

Human neutrophil defensins, and their analogues incorporating anionic, hydrophobic or cationic residues at the N- and C-termini, were synthesized by solid-phase procedures. The synthetic defensins were examined for their microbicidal activity against Candida albicans, two Gram-negative bacteria (Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis) and two Gram-positive bacteria (Streptococcus gordonii and Streptococcus mutans). The human neutrophil peptide 1 (HNP1) and HNP2 were found to be potent candidacidal agents. HNP3, which differs by one amino acid at the N-terminus of its sequence, was totally inactive. The Gram-negative bacteria A. actinomycetemcomitans and P. gingivalis and the Gram-positive bacteria S. gordonii and S. mutans were insensitive to human defensins. However, the insertion of two basic residues, such as arginine, at both the N-terminus and the C-terminus of HNP2 significantly enhanced antifungal and antibacterial activity. The addition of anionic residues, such as aspartic acid, at the N- and C-termini rendered the molecule totally inactive. The presence of two hydrophobic amino acids, such as valine, at the N-terminus of HNP2 and of two basic arginine residues at its C-terminus resulted in molecules that were optimally active against these oral pathogens. The results suggest that the N- and C-terminal residues in defensin peptides are the crucial functional elements that determine their microbicidal potency. The three-dimensional structure of all defensins constitutes the same amphiphilic beta-sheet structure, with the polar face formed by the N- and C-terminal residues playing an important role in defining microbicidal potency and the antimicrobial spectrum. The enhanced microbicidal activity observed for defensin peptides with two basic residues at both the N- and C-termini could be due to optimization of the amphiphilicity of the structure, which could facilitate specific interactions with the microbial membranes.

Infection of primary human gingival fibroblasts by Porphyromonas gingivalis and Prevotella intermedia

Adhesion and penetration of clinical isolates of Porphyromonas gingivalis and Prevotella intermedia in human gingival fibroblast monolayers were studied by transmission electron microscopy (TEM). Fibroblasts were cultured from biopsies of human healthy gingiva. Porphyromonas gingivalis and Prevotella intermedia were isolated from patients with periodontitis. Fibroblasts were incubated with microorganisms in an antibiotic-free medium for 24 h. Then cultures were washed to remove nonadherent bacteria. Consecutively, infected cultures were grown for another 24 h. Thereafter, the treated monolayers were prepared for TEM investigations. Internalized Porphyromonas gingivalis and Prevotella intermedia were visible after 24 h of incubation. Prevotella intermedia showed only division in cytoplasm of fibroblasts after 24 h and 48 h incubations. Infected fibroblasts revealed various morphological alterations such as extensive vacuolization and breakdown of mitochondria. These findings demonstrate that Porphyromonas gingivalis and Prevotella intermedia may invade human gingival fibroblasts and thus may damage these cells directly or due to the release of microbial cytotoxic components.

Histopathological investigation of gingival tissue from patients with rapidly progressive periodontitis

In this study, fine structural features of the pocket walls in rapidly progressive periodontitis (RPP) and adult periodontitis (AP) in 20 cases were compared using light and transmission electron microscopy. Gingiva was also obtained from a control group of periodontally healthy teeth. Clinical parameters were assessed in both RPP and AP patients and in controls. Bone destruction and attachment loss were more marked in RPP than in AP. Light microscopical observations of inflamed RPP tissue as compared to AP showed gross histological distortions in the pocket walls. Micro-ridges within the epithelium and large intercellular spaces between the epithelial cells were observed in most RPP biopsies. Epithelial cells surrounding the microclefts and adjacent keratinocytes were found to produce interleukin-1beta (IL-1beta). Prevotella intermedia and Porphyromonas gingivalis were identified in the RPP biopsies using immunohistological methods. These microorganisms were localized outside the epithelium and inside intercellular spaces. Furthermore, the effect of inflammation on the distribution of collagen types I, III, IV, V, and VI in the human gingiva was studied after staining them with antibodies to these proteins. In RPP and AP tissues, the staining was sparse in areas of inflammation and leukocytic infiltration. Collagen type I and III were almost entirely lost at sites of inflammation. Type V and VI collagen antibodies were retained in inflamed areas. Type IV collagen was restricted to basement membrane structures. These observations demonstrated numerous structural features indicative of more pronounced degenerative changes in RPP than in AP.

Cellular events concurrent with Porphyromonas gingivalis invasion of oral epithelium in vitro

The aim of the present study was to elucidate events related to receptor function, signal transmission and cytoskeletal rearrangements concurrent with Porphyromonas gingivalis invasion of oral epithelial cells in vitro. Porphyromonas gingivalis strain FDC 381 and the KB cell line (ATCC CCL 17) were used in a previously described antibiotic protection assay. The involvement of a receptor-mediated endocytosis pathway in the internalization process was demonstrated after treatment of the epithelial cells with monodansylcadaverine and ouabain, substances that inhibit formation of coated pits, resulting in reduction in the number of invading P. gingivalis: Treatment of the epithelial cells with the protein kinase (PK) inhibitor staurosporine and the tyrosine-specific PK inhibitor genistein was also found to significantly decrease the number of invading bacteria, suggesting involvement of tyrosine phosphorylation in signal transduction during invasion. This was further supported by the identification of a 43 kD protein acting as a substrate for tyrosine phosphorylation subsequent to the microbial-host cell interaction. Tyrosine phosphorylation of the 43 kD protein was strongly reduced by treatment with PK inhibitors. The decrease in invasion observed after treatment of epithelial cells with colchicine and nocodazole, inhibitors of microtubuli polymerization, suggested that the bacterial-receptor interaction and the phosphotyrosine-dependent intracellular signalling trigger an internalization process involving rearrangements of cytoskeletal microtubuli.

Porphyromonas gingivalis outer membrane vesicles promote bacterial resistance to chlorhexidine

Porphyromonas gingivalis has been frequently associated with some types of periodontal diseases and possesses various mechanisms favoring the pathogenic process. It has been recently observed that vesicles elaborated by P. gingivalis are able to protect bacteria from the bactericidal activity of human serum. The aim of the present investigation was to evaluate the ability of vesicles from P. gingivalis in protecting oral bacteria against chlorhexidine. Data indicate that vesicles released by P. gingivalis may bind chlorhexidine, thus allowing protection for itself and for other oral bacterial species. It has also been demonstrated that lipopolysaccharides are the major component involved in the binding of chlorhexidine by vesicles. The mechanism of resistance reported in this study indicates that bacterial interactions in the oral cavity may influence the sensitivity of microbes.

Demonstration of adherence properties of Porphyromonas gingivalis outer membrane vesicles using a new microassay

Vesicles made by Porphyromonas gingivalis possess several biological activities, including the ability to adhere to oral surfaces and to bacteria. In this study, a new and simple method was developed to measure the adherence capability of outer membrane vesicles from P. gingivalis. Vesicles were conjugated to fluorescent microspheres (0.7 micron) and added to wells of a Teflon-coated microscope slide previously covered with a variety of soluble ligands. After incubation and washes, the number of fluorescent microspheres per microscopic field were counted. Vesicle-coated microspheres attached best to gelatin (> 200 per field), whereas other compounds (such as fibronectin, fibrinogen, collagen and laminin) provided moderate attachment, and no attachment was observed to bovine serum albumin. Adherence to any of the tested ligands was not observed when fluorescent microspheres were conjugated to bovine serum albumin or lipopolysaccharides from P. gingivalis. The adherence of vesicle-coated microspheres to ligands was not significantly affected when the pH of the reaction mixture was between 4 and 10. None of the tested carbohydrates lowered the attachment capability of vesicle-coated microspheres to substrates. When vesicle-coated microspheres were treated with trypsin and chymotrypsin or heated, this resulted in a significant loss of attachment, suggesting a possible involvement of proteinaceous molecules in the process. The present study confirms that vesicles of P. gingivalis are capable of attachment to various molecules and indicate their potential role in colonization.

Cytotoxicity of Porphyromonas gingivalis toward cultured human gingival fibroblasts

Direct cytotoxicity of black-pigmented anaerobic rods was studied on the confluent monolayer of human gingival fibroblasts in vitro. Only strains of Porphyromonas gingivalis caused morphological alteration (cell-rounding) and notable depression of viability of fibroblasts. To determine the location of the cytotoxicity, bacterial surface components, i.e., outer membrane, lipopolysaccharide, fimbriae and outer membrane vesicles were prepared from P. gingivalis and their cytotoxicity was assessed. Among these preparations, only outer membrane vesicles are supposed to have high affinity to human gingival fibroblasts, and the cytotoxicity of outer membrane vesicles was found to be much stronger than that of the other constituents. This cytotoxic factor seemed to consist largely of protein and to be associated with the enzyme activity of outer membrane vesicles. The effects of some protease inhibitors and L-cysteine on the cytotoxicity of outer membrane vesicles suggest that the mechanism of cell-rounding is different from that of cell death.