Virulence factors of Porphyromonas gingivalis

Gene expression profiling and characterization under hemin limitation in Porphyromonas gingivalis

Hemin is an important nutrient for Porphyromonas gingivalis growth and pathogenicity. We examined the gene expression profile of P. gingivalis, including genes involved in its pathogenicity, at various growth stages under hemin-standard and limited conditions by using a custom-made microarray. The transcription of many genes decreased after late-log and mid-log phases under hemin-standard and limited conditions, respectively. We focused on two groups of genes while comparing gene expression profiles under hemin-standard and limited conditions by gene tree analysis. Genes belonging to group A maintained high transcriptional levels, whereas genes in group B were expressed at low levels under standard hemin conditions. However, group B genes increased remarkably under hemin-limited conditions. Groups A and B contained genes involved in regulatory functions and protein fate, respectively. Genes related to energy metabolism, transport, and protein binding were present in both groups. Our results suggest that P. gingivalis experienced severe stress under hemin-limited conditions, and growth phase-dependent changes in transcription levels were observed for many genes. Moreover, increased expression of genes involved in energy metabolism suggests that hemin is related not only to pathogenicity, but also energy metabolism.

Methods of detection of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis and Tannerella forsythensis in periodontal microbiology, with special emphasis on advanced molecular techniques: a review

BACKGROUND

Certain specific bacterial species from the subgingival biofilm have demonstrated aetiological relevance in the initiation and progression of periodontitis. Among all the bacteria studied, three have shown the highest association with destructive periodontal diseases: Actinobacillus actinomycetemcomitans (Aa), Porphyromonas gingivalis (Pg) and Tannerella forsythensis (Tf). Therefore, the relevance of having accurate microbiological diagnostic techniques for their identification and quantification is clearly justified.

AIM

To evaluate critically all scientific information on the currently available microbial diagnostic techniques aimed for the identification and quantification of Aa, Pg and Tf.

SUMMARY

Bacterial culturing has been the reference diagnostic technique for many years and, in fact, most of our current knowledge on periodontal microbiology derives from cultural data. However, the advent of new microbial diagnostics, mostly based on immune and molecular technologies, has not only highlighted some of the shortcomings of cultural techniques but has also allowed their introduction as easy and available adjunct diagnostic tools to be used in clinical research and practice. These technologies, mostly polymerase chain reaction (PCR), represent a field of continuous development; however, we still lack the ideal diagnostic to study the subgingival microflora. Qualitative PCR is still hampered by the limited information provided. Quantitative PCR is still in development; however, the promising early results reported are still hampered by the high cost and the equipment necessary for the processing.

CONCLUSION

Quantitative PCR technology may have a major role in the near future as an adjunctive diagnostic tool in both epidemiological and clinical studies in periodontology. However, culture techniques still hold some inherent capabilities, which makes this diagnostic tool the current reference standard in periodontal microbiology.

Inhibition ofPorphyromonas gingivalisHemagglutinating Activity by Synthetic Peptides Derived from Phage Display Selection Using MAb Against the Recombinant Outer Membrane Protein

Porphyromonas gingivalis has been implicated as an pathogen in the development of periodontitis, and hemagglutinins have been identified as an important adhesion onto the gingival tissue cells, and to attach and lyse erythrocytes to uptake Fe ion as an essential nutriant. The 40-kDa outer membrane protein (OMP) has been moleculary cloned from P. gingivalis 381. Since the antibody against recombinant (r) 40-kDa OMP inhibited the hemagglutinating activity, and the polymeric form of r40-kDa OMP itself expressed hemagglutinating activity, the 40-kDa OMP is thought to be one of the hemagglutinins. Moreover, we established MAbs against r40-kDa OMP which were capable of inhibiting hemagglutinating activity of P. gingivalis vesicles. In the present study, a phage-displayed epitope mapping system was used to identify the functional domain expressing hemagglutinating activity by biopanning using the neutralizing mAb, Pg-ompA1. The minimal epitope requirements of the MAb and the predicted amino acid sequences were identified in the region of (96)IALDQTLGIP(105) in 40-kDa OMP. Synthetic peptide, (87)WPRVGQLFIALDQTLGIPTFSVCRME(116), mapped the relevant molecule within a short stretch and is corresponding to residues of 40-kDa OMP. Chemically synthesized peptide was used to determine its inhibitory activity against hemagglutinating activity. The synthetic peptide significantly abolished hemagglutinating activity in a dose-dependent manner. These findings suggest that the synthetic peptide is an effective antagonist of erythrocyte binding, and this peptide may be a potent inhibitor of hemagglutination of P. gingivalis cells. The use of synthetic peptide neutralizing hemagglutinating activity of P. gingivalis represents a possible new therapeutic approach to P. gingivalis infected periodontitis.

Coordinate expression of the Porphyromonas gingivalis lysine-specific gingipain proteinase, Kgp, arginine-specific gingipain proteinase, RgpA, and the heme/hemoglobin receptor, HmuR

Heme utilization inPorphyromonas gingivalisrequires the participation of an outer membrane hemin/hemoglobin receptor, HmuR, the lysine-specific gingipain proteinase (Kgp) and arginine-specific gingipain proteinase (Rgp). In this study, the expression ofhmuR,kgpandrgpAgenes in response to growth with different heme sources was examined by reverse transcription-polymerase chain reaction and enzyme-linked immunoassay. Coordinate regulation ofhmuR,kgpandrgpAgene expression was evaluated through utilization ofP. gingivalis hmuRandkgpmutants or by selective inactivation of proteinases with Kgp- and Rgp-specific inhibitors. We observed that expression of thekgpandrgpAgenes was not tightly regulated by heme, but rather by the growth phase. In contrast, expression of thehmuRgene was negatively regulated by heme, while growth ofP. gingivaliswith human serum resulted in increasedhmuRexpression. AP. gingivalis kgpisogenic mutant demonstrated significantly increasedhmuRgene expression, and inactivation of Kgp and Rgp activity by specific inhibitors up-regulatedhmuRgene transcription. Moreover, inactivation of Kgp up-regulatedrgpAtranscription. Finally, aP. gingivalis hmuRmutant exhibited repressedkgpgene expression and lysine-specific proteinase activity. Collectively, these results indicate thatkgp,rgpAandhmuRgene transcription is coordinately regulated and may facilitate greater efficiency of heme utilization inP. gingivalis.

Structures and biological activity of phosphorylated dihydroceramides of Porphyromonas gingivalis

Porphyromonas gingivalis, a recognized periodontal pathogen, synthesizes free ceramides as well as other phosphorylated ceramide lipids. The purpose of this study was to separate complex lipids of P. gingivalis by high-performance liquid chromatography (HPLC) and determine the structures and biological activities of the major ceramide classes. Using gas chromatography-mass spectrometry, electrospray tandem mass spectrometry (ESI-MS/MS) and NMR analyses, three major classes of dihydroceramides were identified in specific HPLC fractions, with all classes containing the same dihydroceramide base structures (3-OH isoC(17:0) in amide linkage to saturated long-chain bases of 17, 18, or 19 carbons). The free dihydroceramide class recovered in HPLC fractions 7-8 revealed little biological activity. HPLC fraction 20 dihydroceramides, substituted with 1-O-phosphoglycerol and isoC(15:0) linked to the hydroxyl of 3-OH isoC(17:0), significantly potentiated interleukin-1beta (IL-1beta)-mediated prostaglandin secretion and produced marked alterations in fibroblast morphology. HPLC fraction 28 dihydroceramides, substituted with 1-O-phosphoethanolamine, demonstrated little capacity to potentiate IL-1beta-mediated prostaglandin secretion. The novel phosphorylated dihydroceramides synthesized by P. gingivalis demonstrate varying biological activities based on the phosphorylated head group substitution and/or the addition of esterified fatty acid. These results also demonstrate the strong virulence capacity of phosphoglycerol dihydroceramides of P. gingivalis to promote inflammatory factor secretion from IL-1beta-treated fibroblasts and to produce marked alterations in cell morphology in culture.

Comparative whole-genome analysis of virulent and avirulent strains of Porphyromonas gingivalis

We used Porphyromonas gingivalis gene microarrays to compare the total gene contents of the virulent strain W83 and the avirulent type strain, ATCC 33277. Signal ratios and scatter plots indicated that the chromosomes were very similar, with approximately 93% of the predicted genes in common, while at least 7% of them showed very low or no signals in ATCC 33277. Verification of the array results by PCR indicated that several of the disparate genes were either absent from or variant in ATCC 33277. Divergent features included already reported insertion sequences and ragB, as well as additional hypothetical and functionally assigned genes. Several of the latter were organized in a putative operon in W83 and encoded enzymes involved in capsular polysaccharide synthesis. Another cluster was associated with two paralogous regions of the chromosome with a low G+C content, at 41%, compared to that of the whole genome, at 48%. These regions also contained conserved and species-specific hypothetical genes, transposons, insertion sequences, and integrases and were located adjacent to tRNA genes; thus, they had several characteristics of pathogenicity islands. While this global comparative analysis showed the close relationship between W83 and ATCC 33277, the clustering of genes that are present in W83 but divergent in or absent from ATCC 33277 is suggestive of chromosomal islands that may have been acquired by lateral gene transfer.

Monitoring of dnaK gene expression in Porphyromonas gingivalis by oxygen stress using DNA microarray

Porphyromonas gingivalis, a Gram-negative anaerobe associated with adult periodontitis, expresses numerous potential virulence factors. dnaK, a member of the heat shock protein family, functions as a molecular chaperone and plays a role in microbial pathogenicity. However, little is known regarding its gene expression caused by oxygen stress in P. gingivalis. In the present study, a custom-made DNA microarray was designed and used to monitor dnaK gene expression in P. gingivalis caused by oxygen stress. The results demonstrated that dnaK mRNA was up-regulated in a short time, and the DNA microarray results were confirmed by real-time polymerase chain reaction analysis. These findings suggest that oxygen stress stimulates gene expression of dnaK and may have a relationship to the aerotolerance activity of this organism as well as its expression of pathogenesis.

Effect of enamel matrix derivative on periodontal ligament cells in vitro is diminished by Porphyromonas gingivalis

BACKGROUND

Enamel matrix derivative (EMD) has been shown to possess a mitogenic effect to induce effective periodontal regeneration, however, it is unclear whether periodontal pathogens can modulate the effect of EMD. The present study examined the influence of Porphyromonas gingivalis on EMD-stimulated periodontal ligament (PDL) cells.

METHODS

P. gingivalis ATCC33277 and its mutants deficient in fimbriae (delta fimA) or gingipains (delta rgpA delta rgpB, delta kgp, and delta rgpA delta rgpB delta kgp) were employed. PDL cells were grown on EMD-coated dishes and infected with P. gingivalis wild strain or a mutant. Cell migration and proliferation were then evaluated with an in vitro wound healing assay. The expression of transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor I (IGF-I) mRNA by PDL cells was examined. Further, the degradation and phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) as well as paxillin in infected PDL cells were estimated using Western blot analysis.

RESULTS

P. gingivalis ATCC33277 inhibited the migration and proliferation of PDL cells on EMD-coated dishes, and the mutants delta fimA, delta rgpA delta rgpB, and delta kgp showed the same effects. Further, each of these organisms diminished the expression of TGF-beta1 and IGF-I mRNA, as well as the phosphorylation of ERK1/2 from EMD-stimulated PDL cells. In addition, total paxillin protein was markedly degraded by both the wild-type strain and each of the mutants except for delta rgpA delta rgpB delta kgp, which showed a negligible effect in all of the assays with EMD-stimulated PDL cells.

CONCLUSION

These results suggest that P. gingivalis diminishes the effect of EMD on PDL cells in vitro through a cooperative action of gingipains.

Cleavage of human transferrin by Porphyromonas gingivalis gingipains promotes growth and formation of hydroxyl radicals

Porphyromonas gingivalis, a gram-negative anaerobic bacterium associated with active lesions of chronic periodontitis, produces several proteinases which are presumably involved in host colonization, perturbation of the immune system, and tissue destruction. The aims of this study were to investigate the degradation of human transferrin by gingipain cysteine proteinases of P. gingivalis and to demonstrate the production of toxic hydroxyl radicals (HO*) catalyzed by the iron-containing transferrin fragments generated or by release of iron itself. Analysis by polyacrylamide gel electrophoresis and Western immunoblotting showed that preparations of Arg- and Lys-gingipains of P. gingivalis cleave transferrin (iron-free and iron-saturated forms) into fragments of various sizes. Interestingly, gingival crevicular fluid samples from diseased periodontal sites but not samples from healthy periodontal sites contained fragments of transferrin. By using (55)Fe-transferrin, it was found that degradation by P. gingivalis gingipains resulted in the production of free iron, as well as iron bound to lower-molecular-mass fragments. Subsequent to the degradation of transferrin, bacterial cells assimilated intracellularly the radiolabeled iron. Growth of P. gingivalis ATCC 33277, but not growth of an Arg-gingipain- and Lys-gingipain-deficient mutant, was possible in a chemically defined medium containing 30% iron-saturated transferrin as the only source of iron and peptides, suggesting that gingipains play a critical role in the acquisition of essential growth nutrients. Finally, the transferrin degradation products generated by Arg-gingipains A and B were capable of catalyzing the formation of HO*, as determined by a hypoxanthine/xanthine oxidase system and spin trapping-electron paramagnetic resonance spectrometry. Our study indicates that P. gingivalis gingipains degrade human transferrin, providing sources of iron and peptides. The iron-containing transferrin fragments or the release of iron itself may contribute to tissue destruction by catalyzing the formation of toxic HO*.

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.

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.

Differential gene induction in macrophage-like human cells by two types of Porphyromonas gingivalis: a microarray study

Several studies have provided clinical evidence that FimA clonal variation may contribute to the periodontopathogenicity of Porphyromonas gingivalis (P.g.). We studied the gene expression profiling of the macrophage-like human cell line U937 after infection of two types of P.g. (fimA type I; Pg-I and fimA type II; Pg-II) using microarray. Of 1088 genes examined, 394 genes were detectable. Bioinformatics algorithms were used to analyze the detectable genes. Hierarchical clustering analysis showed that gene expression patterns of Pg-II and the control (no infection) were grouped together. K-means clustering grouped 79 genes into Pg-II dominance and 88 genes into Pg-I dominance. A large number of genes related to cell signaling, extracellular communication proteins, cell receptors (by ligands), protein turnover and cell adhesion receptors/proteins were grouped into clusters of Pg-I dominance. Our results indicate that compared with Pg-I, Pg-II induces a low host response as measured by its weak induction of gene expression.

Studies on NADH oxidase and alkyl hydroperoxide reductase produced by Porphyromonas gingivalis

Enzymes that detoxify oxygen or oxygen radicals are important to anaerobic microorganisms that inhabit oxygenated environments. In previous studies we have determined that Porphyromonas gingivalis W50 cell extracts possess NADH oxidase-like activity, which increases slightly under oxygenated conditions. The aim of this study was to characterize the protein responsible for this activity in order to establish whether it protects the microorganism from oxidative stress. Protein purification based on NADH oxidase activity did not isolate a conventional NADH oxidase. Instead, the NADH oxidase activity was found to be associated with a FAD-dependent enzyme identified as 4-hydroxybutyryl-CoA dehydratase (AbfD). The biological significance of this activity with respect to protection against oxidative stress is not clear; hydrogen peroxide (H2O2) was present after completion of the NADH oxidase assay with the purified protein. Northern blot analysis, examining the expression of other proteins likely to function as NADH oxidases/peroxidases in P. gingivalis, revealed the transcription of a protein similar to alkyl-hydroperoxide reductase (AhpF-C), which could serve as an NADH oxidase and H2O2-detoxification system. AhpF is transcribed in a polycystronic way with its neighboring gene, which encodes for the coupling protein AhpC. No transcript could be detected for the closest match to an NADH oxidase identified in the P. gingivalis genome sequence. In conclusion, P. gingivalis seems to lack a protective NADH oxidase but AhpF-C could contribute to its moderate tolerance to reactive oxygen species by metabolizing H2O2.

Loss of lipopolysaccharide receptor CD14 from the surface of human macrophage-like cells mediated by Porphyromonas gingivalis outer membrane vesicles

Porphyromonas gingivalis, the major etiologic agent of chronic periodontitis, produces a broad spectrum of virulence factors, including outer membrane vesicles. In this study, we investigated the capacity of P. gingivalis vesicles to promote the shedding or cleavage of the lipopolysaccharide (LPS) receptor CD14 from the surface of human U937 macrophage-like cells. SDS-PAGE/Western immunoblotting analysis of gingival crevicular fluid samples from patients affected by moderate or advanced periodontitis revealed the presence of soluble CD14 and CD14 fragments, thus supporting the hypothesis of an in vivo shedding and cleavage of CD14 receptors. Flow cytometry analysis of macrophage-like cells treated with a vesicle-containing culture supernatant of P. gingivalis showed a significant decrease in the binding of anti-human CD14 to the cell surface. However, no accumulation of soluble CD14 or immunoreactive CD14 fragments in the assay supernatant could be demonstrated by ELISA. Treatment of macrophage-like cells with various concentrations of P. gingivalis vesicles substantially suppressed TNF-alpha production triggered by Escherichia coli LPS. This suppressive effect was much less important using heat-treated vesicles or in the presence of leupeptin, a gingipain inhibitor, during the treatment. Recombinant human CD14 receptors were found to be susceptible to proteolytic degradation by P. gingivalis vesicles. A purified Arg-gingipain preparation produced much more degradation than a Lys-gingipain preparation. This study provides evidence that P. gingivalis outer membrane vesicles contribute to the loss of membrane-bound CD14 receptors and that gingipains degrade this LPS receptor. Such a phenomenon, which results in an hyporesponsiveness of macrophages to LPS stimulation, may contribute to an increased capacity of P. gingivalis, and other periodontopathogens, to evade the host immune system mechanisms.

Inhibition of Hemagglutinating Activity by Monoclonal Antibody againstPorphyromonas gingivalis40-kDa Outer Membrane Protein

Periodontitis is a chronic inflammatory disease of periodontal tissues that results in alveolar bone loss, and Porphyromonas gingivalis, which has a high hemagglutinating activity, has been implicated as an important pathogen in the development of periodontitis. This bacterium has a high hemagglutinating activity. We previously succeeded in gene cloning the 40-kDa outer membrane protein (OMP) from P. gingivalis 381. Although recombinant (r) 40-kDa OMP itself did not show hemagglutinating activity, its polymeric form, constructed with a cross-linking reagent, significantly expressed that activity. Furthermore, an affinity-purified antibody against r40-kDa OMP inhibited the hemagglutinating activity of P. gingivalis vesicles. In the present study, in order to clarify the pathological role of 40-kDa OMP and develop passive immunotherapy, we examined the inhibitory effect of monoclonal antibodies (MAbs) against r40-kDa OMP on the hemagglutinating activity of P. gingivalis vesicles. The MAbs reacted with r40-kDa OMP, the outer membrane fraction, vesicles, and P. gingivalis cell extracts, and significantly inhibited the hemagglutinating activities of the polymeric r40-kDa OMP as well as of P. gingivalis vesicles. These findings suggest that MAbs against 40-kDa OMP may be useful for the development of passive immunotherapy and for assessing treatment for periodontal diseases caused by P. gingivalis infection.

Human gingival epithelial cells produce chemotactic factors interleukin-8 and monocyte chemoattractant protein-1 after stimulation with Porphyromonas gingivalis via toll-like receptor 2

BACKGROUND

The mechanism of stimulation of human gingival epithelial cells (HGEC) by Porphyromonas gingivalis (Pg) has not been fully clarified yet. In order to investigate the possible activation of HGEC by Pg through Toll-like receptors (TLRs), we analyzed the production of chemotactic factors and the activated nuclear factor-kappa B (NF-kappaB).

METHODS

The mRNA expression of TLRs and the protein expression of TLR2 and TLR4 in HGEC and gingival tissue were assessed using reverse transcription-polymerase chain reaction (RT-PCR) assay and immunohistochemical staining. Primary cultured HGEC (nHGEC) and HGEC transformed by simian virus 40 T antigen (OBA-9) were activated by a sonic extract (SE) of Pg to examine cytokine production and NF-kappaB activation using enzyme-linked immunosorbant assay (ELISA). In addition, Pg mediated activation of NF-kappaB in a TLR2-transfectant was also investigated.

RESULTS

RT-PCR results revealed that HGEC expressed mRNA of TLR2, TLR4, TLR5, and TLR9, although the expression profiles of each cell line were slightly different. In addition, immunostaining revealed the prominent expression of TLR2 not only in nHGEC, but also in the gingival epithelium of the tissue specimen. Interestingly, nHGEC and OBA-9 secreted IL-8 and monocyte chemoattractant protein (MCP)-1 upon stimulation with Pg SE more efficiently than LPS and fimbriae of Pg. Furthermore, Pg SE increased the activated NF-kappaB not only in OBA-9, but also in 293T cells transfected with the human TLR2 gene.

CONCLUSION

TLR2 participates, at least partly, in the signaling pathway to induce chemokine production in gingival epithelium as a reaction against Pg component(s), probably other than lipopolysaccharide and fimbriae.

Porphyromonas gingivalis induces receptor activator of NF-kappaB ligand expression in osteoblasts through the activator protein 1 pathway

Porphyromonas gingivalis, an important periodontal pathogen, is closely associated with inflammatory alveolar bone resorption, and several components of the organism such as lipopolysaccharides have been reported to stimulate production of cytokines that promote inflammatory bone destruction. We investigated the effect of infection with viable P. gingivalis on cytokine production by osteoblasts. Reverse transcription-PCR and real-time PCR analyses revealed that infection with P. gingivalis induced receptor activator of nuclear factor kappaB (NF-kappaB) ligand (RANKL) mRNA expression in mouse primary osteoblasts. Production of interleukin-6 was also stimulated; however, osteoprotegerin was not. SB20350 (an inhibitor of p38 mitogen-activated protein kinase), PD98059 (an inhibitor of classic mitogen-activated protein kinase kinase, MEK1/2), wortmannin (an inhibitor of phosphatidylinositol 3 kinase), and carbobenzoxyl-leucinyl-leucinyl-leucinal (an inhibitor of NF-kappaB) did not prevent the RANKL expression induced by P. gingivalis. Degradation of inhibitor of NF-kappaB-alpha was not detectable; however, curcumin, an inhibitor of activator protein 1 (AP-1), prevented the RANKL production induced by P. gingivalis infection. Western blot analysis revealed that phosphorylation of c-Jun, a component of AP-1, occurred in the infected cells, and an analysis of c-Fos binding to an oligonucleotide containing an AP-1 consensus site also demonstrated AP-1 activation in infected osteoblasts. Infection with P. gingivalis KDP136, an isogenic deficient mutant of arginine- and lysine-specific cysteine proteinases, did not stimulate RANKL production. These results suggest that P. gingivalis infection induces RANKL expression in osteoblasts through AP-1 signaling pathways and cysteine proteases of the organism are involved in RANKL production.

Fimbriated Porphyromonas gingivalis is more efficient than fimbria-deficient P. gingivalis in entering human dendritic cells in vitro and induces an inflammatory Th1 effector response

Porphyromonas gingivalis is a fimbriated mucosal pathogen implicated in chronic periodontitis (CP). The fimbriae are required for invasion of the gingival mucosa and for induction of CP in animal models of periodontitis. CP is associated with infection of immature dendritic cells (DCs) by P. gingivalis in situ and with increased numbers of dermal DCs (DDCs) and mature DCs in the lamina propria. The role of fimbriae in gaining entry into human DCs and how this modulates the inflammatory and effector immune responses, however, have not been explored. To address this, we generated monocyte-derived DCs (MDDCs) in vitro which phenotypically and functionally resemble DDCs. We show here that virulent fimbriated P. gingivalis 381, in contrast to its fimbria-deficient mutant, P. gingivalis DPG3, efficiently gains entry to MDDCs in a manner dependent on active cell metabolism and cytoskeletal rearrangement. In addition, uptake of 381, unlike DPG3, induces DCs to undergo maturation, upregulate costimulatory molecules, and secrete inflammation cytokines interleukin-1beta (IL-1beta), IL-6, tumor necrosis factor alpha, IL-10, and IL-12. Moreover, MDDCs pulsed with 381 also stimulated a higher autologous mixed lymphocyte reaction and induced a Th1-type response, with gamma interferon (IFN-gamma) being the main cytokine. Monocytes used as controls demonstrated fimbria-dependent uptake of 381 as well but produced low levels of inflammatory cytokines compared to MDDCs. When MDDCs were pulsed with recombinant fimbrillin of P. gingivalis (10 micro g/ml), maturation of MDDCs was also induced; moreover, matured MDDCs induced proliferation of autologous CD4(+) T cells and release of IFN-gamma. Thus, these results establish the significance of P. gingivalis fimbriae in the uptake of P. gingivalis by MDDCs and in induction of immunostimulatory Th1 responses.

The effect of oxygen on the growth and physiology of Porphyromonas gingivalis

Oxygen constitutes a constant challenge for the survival of strict anaerobes in the oral environment. The aim of this study was to investigate the effect of oxygen on the physiology and growth of Porphyromonas gingivalis in a continuous culture system when grown under conditions of hemin limitation and excess. Results showed that, when grown in the presence of hemin at 0.5 mg/l, P. gingivalis could tolerate low levels of oxygen, being able to reach steady-state when 6% oxygen was present in the incoming gas mixture. When the hemin concentration was increased to 5 mg/l, the culture tolerated 10% oxygen. Anaerobically-grown cells were coccoid in shape, whereas those grown in the presence of oxygen were bacillary. Acetate was the predominant end-product in cultures grown in the presence of oxygen or in cultures hemin-limited. Despite some changes in the activity of Arg- and Lys-gingipain, most of the proteolytic activity was retained in the presence of oxygen. Activity of each of the three anti-oxidant enzymes tested (NADH oxidase, NADH peroxidase and SOD) was detected under all conditions and usually increased under oxygenated environments. Higher activities were also seen in the hemin-limited cultures. These results show some of the changes that occur in the physiology of P. gingivalis as a result of oxidative stress and confirm that hemin has a protective effect on the growth of the microorganism in the presence of oxygen.

Differential cytokine induction by two types of Porphyromonas gingivalis

The presence of Porphyromonas gingivalis with type II fimA is strongly associated with adult periodontitis. However, the importance of specific fimA types in the immune response is unknown. Two types of P. gingivalis (type I and type II) and Actinomyces naeslundii were assessed for their degree of cytokine induction in the macrophage-like human cell line U937. Real-time reverse transcriptase polymerase chain reaction was used to determine mRNA expression of 12 cytokines. Significant levels of interleukin (IL)-8 induction and a similar cytokine expression pattern were observed at 6 h postinfection for all three bacterial strains. However, type II P. gingivalis infection showed statistically higher levels of IL-1beta, IL-8, IL-12 and tumor necrosis factor-alpha mRNA induction than those of control at 24 h postinfection, whereas type I P. gingivalis and A. naeslundii showed no significant induction of these cytokines. These data suggest that compared with A. naeslundii and type I P. gingivalis, type II P. gingivalis prolongs the cytokine response. Although other factors may also be involved, the sustained cytokine response induced by type II P. gingivalis may play an important role in enhanced periodontal tissue inflammation and destruction.

Inhibitory effect of green tea catechins on cysteine proteinases in Porphyromonas gingivalis

The purpose of this study was to examine the effects of catechins and their derivatives on the activities of Arg-gingipain (Rgp) and Lys-gingipain (Kgp) in Porphyromonas gingivalis. Catechin derivatives, which included (-)-epigallocatechin gallate, (-)-epicatechin gallate, (-)-gallocatechin gallate, and (-)-catechin gallate, significantly inhibited the Rgp activity. The 50% inhibitory concentrations (IC50s) of these catechin derivatives for Rgp ranged from 3 to 5 microm. While (-)-epigallocatechin and (-)-gallocatechin moderately inhibited Rgp activity (IC50s, 20 microm), (-) -epicatechin, (+)-catechin, and gallic acid were not effective, with IC50s greater than 300 microm. Further, some of the catechin derivatives tested also inhibited the Kgp activity, though to a lesser extent than inhibition of the Rgp activity. These findings suggest that green tea catechins may have the potential to reduce periodontal breakdown resulting from the potent proteinase activity of P. gingivalis.

Mixed infections with Porphyromonas gingivalis and Treponema denticola cause excessive inflammatory responses in a mouse pneumonia model compared with monoinfections

Periodontopathic anaerobes such as Porphyromonas gingivalis are frequently found in aspiration pneumonia and lung abscesses. However, defense mechanisms and responses to these bacterial infections in the lung in vivo remain poorly understood. The coexistence of P. gingivalis with Treponema denticola has been found at higher levels and proportions in periodontally diseased sites. We hypothesized that mixed infections with P. gingivalis and T. denticola can cause severe respiratory disease. In the present study, inflammatory responses to mono- and mixed inoculations with P. gingivalis and T. denticola in the bronchoalveolar lavage (BAL) fluid were investigated. Acute pneumonia and lung abscesses in mice with the mixed infection resulted in a 40% mortality rate within 72 h, compared with only 10% mortality for the respective monoinfections. Pulmonary clearance of P. gingivalis was delayed in the mice with mixed infections with P. gingivalis and T. denticola. Tumor necrosis factor alpha (TNFalpha) interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) levels from BAL fluid of mice with mixed infections at 24 h after inoculation were significantly higher than those after P. gingivalis monoinfection (TNFalpha: P < 0.05, Il-1beta: P < 0.001, IL-6: P < 0.05). The chemokine KC level from BAL fluid of mice at 48 h (P < 0.05) and 72 h after mixed infection was also significantly increased when compared with that after P. gingivalis monoinfection (P < 0.001). The present study demonstrates that a mixed infection of P. gingivalis with T. denticola in mouse causes a marked bronchopneumonia and lung abscess in the mouse model.

Quantitative detection ofPorphyromonas gingivalis fimAgenotypes in dental plaque

We developed quantitative fimA genotype assays and applied them in a pilot study investigating the fimbrial genotype distribution of Porphyromonas gingivalis in European subjects with or without chronic periodontitis. P. gingivalis was found in 71% and 9% of the samples from patients and healthy subjects, respectively. Enumeration of total P. gingivalis cell numbers by polymerase chain reaction and immunofluorescence showed excellent correspondence (r = 0.964). 73% of positive samples contained multiple fimA genotypes, but generally one genotype predominated by one to three orders of magnitude. Genotype II predominated in 60% of the samples. Genotype IV occurred with similar prevalence (73%) as genotype II but predominated in only 20% of the samples. Genotypes I, III and V were of much lower prevalence and cell densities of the latter two remained sparse. Our results suggest marked differences among the fimA genotypes' ability to colonize host sites with high cell numbers.

Identification of T-cell epitopes of Porphyromonas gingivalis heat-shock-protein 60 in periodontitis

The heat shock proteins (hsp) of bacterial species are considered to be involved in regulating the autoimmune mechanism in human diseases due to the considerable homology of their sequences with human hsp. To elucidate how stress proteins contribute to the immunopathogenesis of periodontitis, mononuclear cells from gingival connective tissue of 10 periodontitis patients were simulated with Porphyromonas gingivalis hsp60. T-cell lines reactive to P. gingivalis hsp60 were established from each patient to define T-cell epitope specificities. Anti-P. gingivalis IgG antibody titres were elevated in all patients. We could establish P. gingivalis hsp-reactive T-cell lines from gingival mononuclear cells that were mixtures of CD4+ and CD8+ cells. Of 108 overlapping synthetic peptides spanning the whole P. gingivalis hsp60 molecule, 10 peptides with epitope specificities for T-cells were identified, and were identical to those reported be B-cell epitopes in periodontitis.

Porphyromonas gingivalis induces murine macrophage foam cell formation

Atherosclerosis is a complex pathologic process initialed by the formation of cholesterol-rich plaque. Macrophages play a central role in the development of atherosclerosis, specifically in the initial accumulation of cholesterol in the arterial wall. It has been suggested that infection and chronic inflammatory conditions such as periodontitis may influence the atherosclerosis process. Porphyromonas gingivalis, one of the major pathogens involved in periodontitis, has been detected in human atheromas, suggesting that P. gingivalis infection may be associated with atherosclerosis. However, a causal relationship between this pathogen and the disease process has not yet been established. The purpose of the present investigation was to determine whether P. gingivalis could induce macrophages to form foam cells using the murine macrophage cell line (J774) as a model system. For inocula smaller than one bacterium per ten cells, P. gingivalis 381, as well as its lipopolysaccharide (LPS), induced foam cell formation of macrophages when cultured in the presence of human low-density lipoprotein (LDL). Infection of macrophages with increasing doses of P. gingivalis resulted in higher levels of foam cell formation. More than 70% of the cultured macrophages form cholesterol ester droplet-rich cells in the presence of 100 mug/ml of LDL when the inocula was more than 10 bacteria per cell. Low concentrations of P. gingivalis outer membrane vesicles also induced foam cell formation in the presence of LDL. In addition, it was demonstrated that P. gingivalis LPS alone was able to induce macrophage foam cell formation. P. gingivalis and its vesicles not only promoted LDL binding to macrophages but also induced macrophages to modify native LDL, which plays an important role in foam cell formation and the pathogenesis of atherosclerosis. Therefore, P. gingivalis cells or its vesicles released from periodontal lesions into the circulation may deliver virulence factor(s) such as LPS to the arterial wall to initiate or promote foam cell formation in macrophages and contribute to atheroma development.

Prevalence of periodontopathic bacteria in aggressive periodontitis patients in a Japanese population

BACKGROUND

Actinobacillus actinomycetemcomitans is considered a major etiologic agent of aggressive periodontitis. Other periodontopathic bacteria such as Porphyromonas gingivalis are also suspected of participating in aggressive periodontitis, although the evidence is controversial. The aim of the present study was to investigate the prevalence of periodontopathic bacteria and to clarify the microbiological features of aggressive periodontitis in Japanese patients.

METHODS

Subgingival plaque was collected from 50 aggressive periodontitis (AgP) patients (localized 10, generalized 40). Samples from 35 generalized chronic periodontitis (CP) patients and 18 healthy subjects were examined as controls. Plaque samples were examined using culture and polymerase chain reaction (PCR) method.

RESULTS

The prevalence of A. actinomycetemcomitans was relatively low in the localized (20%) and generalized (17.5%) AgP patients, with no significant difference observed in detection frequencies between AgP and the control groups (CP 8.6%, healthy 0%). On the other hand, Tannerella forsythensis (formerly Bacteroides forsythus), Campylobacter rectus, P. gingivalis, and Treponema denticola were frequently detected in localized as well as generalized aggressive periodontitis patients. The prevalence and proportion of P. gingivalis correlated with severity of clinical attachment loss in both localized and generalized aggressive periodontitis.

CONCLUSIONS

T. forsythensis, C. rectus, P. gingivalis, and T. denticola were the predominant periodontopathic bacteria of aggressive periodontitis patients in Japan. Although A. actinomycetem- comitans was also detected in AgP patients, the prevalence of this bacterium was much lower than that of P. gingivalis.

Effects of various culture environments on expression of major outer membrane proteins fromPorphyromonas gingivalis

We examined the effects of various culture environments on major outer membrane proteins from Porphyromonas gingivalis ATCC 33277. Major outer membrane protein patterns on gel electrophoresis showed little difference over the culturable range of osmolarity and pH. With elevated temperature or prolonged culture, the intensities of the gingipain bands decreased; however, bands of RagA, RagB and the putative porins were relatively stable. Similar results were observed with several different culture media. Although the precise functions of RagA, RagB and the putative porins are unknown, these factors may be strongly related to the initiation and progression of adult periodontitis.

Subcloning of the 200-kDa Porphyromonas gingivalis antigen gene and inhibition of hemagglutination by an antibody against the recombinant protein

Porphyromonas gingivalis is a major etiologic agent of periodontitis and exhibits hemagglutinating and adherence activities. We previously succeeded in molecular cloning the 200-kDa cell-surface antigenic protein (200-k AP), designated pMD101, that is recognized in sera from periodontitis patients, and identified the 200-k AP as a hemagglutinin A (HagA) derivative. HagA is one of the hemagglutinins known to be a useful vaccine against periodontitis. HagA has four large, contiguous, direct repeats and the repeat unit is believed to contain the hemagglutinin domain. Because production of 200-k AP was low in the Escherichia coli host, it was difficult to obtain large amounts of recombinant protein. In this study, we attempt to subclone the gene encoding the useful antigen from pMD101 in an effort to obtain large quantities. A subclone, designated pMD160, encoding a fusion protein of 80-kDa HagA and maltose-binding protein was successfully constructed, and the novel clone produced relatively large amounts of recombinant protein. DNA nucleotide sequences of the pMD160 insert demonstrated that the 80-kDa protein contained a short hemagglutinin motif and a direct repeat unit region. The recombinant protein was purified to homogeneity and rabbit antiserum was raised. The antibody was capable of inhibiting the hemagglutinating activity of P. gingivalis. These findings suggest that novel 80-kDa HagA derivative proteins can be produced efficiently from E. coli hosts and these may be useful in developing immunotherapy against periodontitis infected by P. gingivalis.

Periodontitis as an infectious disease: specific features and their implications

Periodontitis may be viewed as an infectious disease with a number of specific characteristics. Pathogens of the subgingival microbiota can interact with host tissues even without direct tissue penetration. Hence, antimicrobial agents must be available at a sufficiently high concentration not only within the periodontal tissues, but also outside, in the environment of the periodontal pocket. The subgingival microbiota accumulate on the root surface to form an adherent layer of plaque with the characteristics of a biofilm. Several mechanisms, such as diffusion barriers, and selective inactivation of agents lead to an increased resistance of bacteria in biofilms. Mechanical supragingival plaque control is indispensable to prevent the re-emergence of periodontal pathogens and the re-establishment of a biofilm in treated sites. Since specific features have important implications for the use of antimicrobial agents in periodontal therapy, extrapolations from experiences made in the therapy of other infections are only partially valid. The ultimate evidence for the efficacy of systemic or local chemotherapy must be obtained from treatment studies in humans with adequate follow-up.

Sequence analysis of kgp in Porphyromonas gingivalis isolates from periodontitis patients

The aim of the present study was to determine sequence variation in the Lys-x-specific protease (Kgp) encoding gene kgp of Porphyromonas gingivalis and to analyze its association with periodontal disease severity. Pooled subgingival plaque samples were obtained from the six most severely affected sites of 102 patients with periodontitis. Sequence analysis of the kgp gene in 23 clinical P. gingivalis isolates resulted in the identification of two distinct kgp types (kgp-I and kgp-II) according to sequence differences in the region encoding the catalytic domain. Restriction analysis revealed that 59 of the 102 patients were colonized by kgp-I and 43 by kgp-II. Patients harboring kgp-I or kgp-II showed no significant difference in the severity of periodontal disease as assessed by pocket probing depth and bleeding on probing following adjustment for smoking habit and age. Moreover, no differences in proteolytic activity of Kgp-I and Kgp-II were detected. The results indicated that two kgp types are maintained in natural populations of P. gingivalis.

Mice lacking inducible nitric oxide synthase demonstrate impaired killing of Porphyromonas gingivalis

Porphyromonas gingivalis is a primary etiological agent of generalized severe periodontitis, and emerging data suggest the importance of reactive oxygen and nitrogen species in periodontal tissue damage, as well as in microbial killing. Since nitric oxide (NO) released from inducible NO synthase (iNOS) has been shown to possess immunomodulatory, cytotoxic, and antibacterial effects in experimental models, we challenged iNOS-deficient (iNOS(-/-)) mice with P. gingivalis by using a subcutaneous chamber model to study the specific contribution of NO to host defense during P. gingivalis infection. iNOS(-/-) mice inoculated with P. gingivalis developed skin lesions and chamber rejection with higher frequency and to a greater degree than similarly challenged C57BL/6 wild-type (WT) mice. Chamber fluid from iNOS(-/-) mice possessed significantly more P. gingivalis than that of WT mice. The immunoglobulin G responses to P. gingivalis in serum was similar in WT and iNOS(-/-) mice, and the inductions of tumor necrosis factor alpha, interleukin-1 beta and interleukin-6, and prostaglandin E(2) were comparable between the two mouse strains. Although no differences in total leukocyte counts in chamber fluids were observed between iNOS(-/-) and WT mice, the percentage of dead polymorphonuclear leukocytes (PMNs) was significantly greater in iNOS(-/-) mouse chamber fluids than that of WT samples. Interestingly, casein-elicited PMNs from iNOS(-/-) mice released more superoxide than did WT PMNs when stimulated with P. gingivalis. These results indicate that modulation of superoxide levels is a mechanism by which NO influences PMN function and that NO is an important element of the host defense against P. gingivalis.

Modulation ofPorphyromonas GingivalisProteinase Activity by Suboptimal Doses of Antimicrobial Agents

BACKGROUND

Antimicrobial agents are sometimes used as adjuncts for the treatment of aggressive and refractory forms of periodontitis. In this study, we used a culture plate assay to investigate the effect of suboptimal doses of antimicrobial agents on proteinase activity of Porphyromonas gingivalis.

METHODS

A culture plate assay using gelatin as the substrate, which allows a semiquantitative determination of proteinase activity, was developed. Suboptimal inhibitory concentrations of tetracycline, minocycline, doxycycline, metronidazole, penicillin G, or chlorhexidine were added to the medium, and proteolysis zones were determined following the growth of three strains of P. gingivalis. The effect of antimicrobials on outer membrane vesicle-associated gingipains also was determined.

RESULTS

The gelatin plate assay was a convenient, simple procedure for investigating the effect of suboptimal inhibitory concentrations of antimicrobial agents on proteinases produced by P. gingivalis. The largest reduction (> 75%) in the proteolysis zones produced by three strains of P. gingivalis was obtained with minocycline. Tetracycline and doxycycline also reduced the proteolysis zones. A suboptimal inhibitory concentration of chlorhexidine increased the proteolysis zones by up to 70%. Metronidazole and penicillin G produced no noticeable effect. The suboptimal inhibitory concentrations of minocycline, tetracycline, and doxycyline did not reduce the activity of outer membrane vesicle-associated Arg- and Lys-gingipains.

CONCLUSION

Results from this study suggest that sublethal concentrations of some antimicrobial agents in subgingival sites have the potential to affect the physiology of P. gingivalis, notably by increasing or decreasing the proteolytic activity of the bacteria.

In vitro environmental regulation of Porphyromonas gingivalis growth and virulence

Porphyromonas gingivalis appears to be a major contributor to periodontal disease, especially soft tissue destruction, which is reflected by the ability to cause invasive, spreading lesions, and tissue inflammation in a murine abscess model. This study investigated the role of hemin on the regulation of growth and virulence of P. gingivalis strains. P. gingivalis strains W50, A7A1-28, 3079, 381, W50/BEI, and NG4B19 were grown in broth and on blood agar plates. P. gingivalis cells grown under iron-depleted conditions for multiple passages showed significantly decreased lesion size in mice, in contrast to cells grown under iron-normal (5 microg/ml) and iron-elevated conditions. Statistically significant (P < 0.01) decreases in gingipain enzyme activity were found among the strains grown under iron-depleted conditions. P. gingivalis grown in the presence of blood induced significantly different lesion type, lesion size, lesion onset, and mortality. Elevated hemin resulted in increased cell-associated iron in P. gingivalis, which increased the capacity of the microorganism to survive at times of iron deprivation. These results indicate that hemin or iron availability regulates multiple aspects related to P. gingivalis virulence, including growth, survival, gingipain levels, and iron accumulation.

Immune responses to heat shock protein in Porphyromonas gingivalis-infected periodontitis and atherosclerosis patients

BACKGROUND

It has been widely thought that heat shock protein might be involved in autoimmune disease mechanisms in humans.

OBJECTIVES

The present study was performed to evaluate the recognition of Porphyromonas gingivalis heat shock protein 60 (hsp60) and human hsp60 by immune sera in P. gingivalis-infected periodontitis and atherosclerosis patients.

MATERIALS AND METHODS

Mononuclear cells from atheroma lesions were stimulated with P. gingivalis hsp and sera from periodontitis or atherosclerosis patients were subjected to Western immunoblotting to P. gingivalis hsp or human hsp, respectively.

RESULTS

Western immunoblot analysis demonstrated the dual reactivity of anti-P. gingivalis antisera with P. gingivalis hsp and human hsp. We could also establish P. gingivalis hsp-specific T cell lines from the atheroma lesions, a mixture of CD4+ and CD8+ cells producing the cytokines characteristic of both Th1 and Th2 subsets.

CONCLUSION

These observations suggest the modulating effect of P. gingivalis hsp60 in the immunopathogenesis of periodontitis and atherosclerosis.

Effect of inactivation of the Arg- and/or Lys-gingipain gene on selected virulence and physiological properties of Porphyromonas gingivalis

Proteolytic enzymes produced by Porphyromonas gingivalis are thought to play critical roles in the pathogenesis of periodontitis. The aim of this study was to investigate the effect of gingipain cysteine proteinase gene inactivation on selected pathological and physiological functions of P. gingivalis. Our results showed that Arg- and Lys-gingipain activities are critical components for the efficient growth of P. gingivalis in human serum. However, when the serum was supplemented with peptides provided as pancreatic casein hydrolysate, the gingipains did not appear to be essential for growth. The effect of gingipain gene inactivation on the susceptibility of P. gingivalis to serum bactericidal activity was investigated using standardized human serum. The wild-type strain, P. gingivalis ATCC 33277, was largely unaffected by the bactericidal activity of human serum complement. On the other hand, mutants lacking Arg-gingipain A, Arg-gingipain B, or Lys-gingipain activity were susceptible to complement. Since gingipains are mostly located on the outer membrane of P. gingivalis, inactivation of the genes for these enzymes may modify cell surface properties. We showed that gingipain-deficient mutants differed in their capacities to assimilate radiolabeled amino acids, cause hemolysis, express adhesins, hemagglutinate, and form biofilms. Lastly, the gingipains, more specifically Arg-gingipains, were responsible for causing major cell damage to human gingival fibroblasts. In conclusion, our study indicated that, in addition to being critical in the pathogenic process, gingipains may play a variety of physiological roles in P. gingivalis, including controlling the expression and/or processing of virulence factors. Mutations in gingipain genes thus give rise to pleiotropic effects.

Role of the phosphatidylinositol 3 kinase-Akt pathway in the regulation of IL-10 and IL-12 by Porphyromonas gingivalis lipopolysaccharide

Stimulation of the APC by Porphyromonas gingivalis LPS has been shown to result in the production of certain pro- and anti-inflammatory cytokines. However, the signaling pathways that regulate these processes are currently unknown. In the present study, the role of the phosphatidylinositol 3 kinase (PI3K)-Akt pathway in regulating P. gingivalis LPS-induced production of IL-10, IL-12 p40, and IL-12 p70 by human monocytes was investigated. P. gingivalis LPS selectively activates the PI3K-Akt pathway via Toll-like receptor 2, and inhibition of this pathway results in an abrogation of extracellular signal-regulated kinase 1/2 phosphorylation, whereas the activation of p38 and c-Jun N-terminal kinase 1/2 kinases were unaffected. Analysis of cytokine production following stimulation of monocytes with P. gingivalis LPS revealed that inhibition of the PI3K pathway differentially regulated IL-10 and IL-12 synthesis. IL-10 production was suppressed, whereas IL-12 levels were enhanced. Inhibition of P. gingivalis LPS-mediated activation of the PI3K-Akt pathway resulted in a pronounced augmentation of NF-kappaB p65 that was independent of IkappaB-alpha degradation. Furthermore, the ability of the PI3K-Akt pathway to modulate IL-10 and IL-12 production appears to be mediated by the selective suppression of extracellular signal-regulated kinase 1/2 activity, as the MEK1 inhibitor PD98059 closely mimicked the effects of wortmannin and LY294002 to differentially regulate IL-10 and IL-12 production by P. gingivalis LPS-stimulated monocytes. These studies provide new insight into how engagement of the PI3K-Akt pathway by P. gingivalis LPS affects the induction of key immunoregulatory cytokines that control both qualitative and quantitative aspects of innate and adaptive immunity.

Antibodies to periodontal pathogens are associated with coronary heart disease

OBJECTIVE

We analyzed the association of coronary heart disease (CHD) and serology of periodontitis in a random sample (n=1163) of men (aged 45 to 74 years) by determining serum IgG-antibodies to Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis.

METHODS AND RESULTS

CHD (n=159) was more prevalent among edentulous than dentate subjects (19.8% and 12.1%, P=0.003). In the dentate population, CHD was more common among subjects seropositive for P. gingivalis compared with those seronegative (14.0% and 9.7%, P=0.029). Accordingly, CHD was more prevalent in subjects with a high combined antibody response than those with a low response (17.4% and 11.1%, P=0.026). When adjusted for age and several CHD risk factors, the subjects with a high combined antibody response had an odds ratio of 1.5 (95% CI, 0.95 to 2.50, P=0.077) for prevalent CHD. In a linear regression model, the combined antibody response was directly associated with prevalent CHD (P=0.046) and inversely with serum HDL cholesterol concentration (P=0.050).

CONCLUSIONS

In conclusion, edentulousness and serum antibodies to major periodontal pathogens were associated with CHD. This suggests that periodontal infection or response of the host against the infection may play a role in the pathogenesis of CHD.

Genomics of oral bacteria

Advances in bacterial genetics came with the discovery of the genetic code, followed by the development of recombinant DNA technologies. Now the field is undergoing a new revolution because of investigators' ability to sequence and assemble complete bacterial genomes. Over 200 genome projects have been completed or are in progress, and the oral microbiology research community has benefited through projects for oral bacteria and their non-oral-pathogen relatives. This review describes features of several oral bacterial genomes, and emphasizes the themes of species relationships, comparative genomics, and lateral gene transfer. Genomics is having a broad impact on basic research in microbial pathogenesis, and will lead to new approaches in clinical research and therapeutics. The oral microbiota is a unique community especially suited for new challenges to sequence the metagenomes of microbial consortia, and the genomes of uncultivable bacteria.

The herpesvirus-Porphyromonas gingivalis-periodontitis axis

OBJECTIVES AND BACKGROUND

Members of the herpesvirus family have accumulated considerable support for a role in severe types of periodontitis. This study aimed to examine whether human cytomegalovirus (HCMV), Epstein-Barr virus type 1 (EBV-1) or herpes simplex virus (HSV) together with the major periodontopathic bacterium Porphyromonas gingivalis might interact in the pathogenesis of periodontal breakdown.

METHODS

Sixteen subjects each contributed paper point samples from two progressing and two stable periodontitis lesions, as determined by ongoing loss of probing attachment. Polymerase chain reaction methodology was used to identify subgingival herpesviruses, P. gingivalis and other bacterial pathogens. Chi-squared tests and multivariate logistic regression were employed to identify statistical associations between herpesviruses, periodontopathic bacteria and clinical variables.

RESULTS

HCMV and HSV were both significant predictors of the presence of subgingival P. gingivalis. In turn, P. gingivalis was positively associated with periodontitis active disease, probing attachment level, probing pocket depth, gingival bleeding upon probing and patient age. EBV-1 was not linked to P. gingivalis, although the virus was predictive of periodontitis active disease. The periodontitis disease risk associated with herpesvirus-P. gingivalis combinations depended on both site-specific and subject-specific factors.

CONCLUSION

The present data of aggressive periodontitis implicate HCMV, HSV and P. gingivalis as either cofactors in its etiology or triggers of relapses. Further studies are needed to determine the spectrum of periodontopathogenicity of herpesviruses and effective management of these viruses in periodontal sites.

Serum antibody reactivity against recombinant PrtC of Porphyromonas gingivalis following periodontal therapy

OBJECTIVES

In 34 patients with chronic periodontitis, the presence of IgA, IgG, and IgG subclass serum antibodies against recombinant PrtC (rPrtC) of Porphyromonas gingivalis was assessed by immunoblot analysis 24 months after therapy.

METHODS

rPrtC was produced from P. gingivalis ATTC 33277 using the plasmid pGEX-2T. In addition, intraoral colonization with P. gingivalis was detected by PCR in subgingival plaque and swab samples from buccal mucosae, tonsils and tongue at baseline, 10 d, and 3, 6, 9, 12, 18, and 24 months.

RESULTS

All patients were found to harbor P. gingivalis in the oral cavity at least once during the observation period. The identified antibody responses against the rPrtC of P. gingivalis were IgA (97%, i.e. 33/34 patients) and IgG (100%, i.e. 34/34), with an IgG subclass distribution of IgG2 (65%, i.e. 22/34 patients) > IgG3 (47%, i.e. 16/34) > IgG1 (38%, i.e. 13/34) > IgG4 (29%, i.e. 10/34). Anti-rPrtC IgA and IgG antibody reactivity was found in all but one patients (anti-rPrtC IgA negative), who tested negative for P. gingivalis at all of the assessed intraoral sites for at least 6 months before sera collection. There was no association between IgG subclass reactivity against the rPrtC of P. gingivalis and progression of periodontal attachment loss.

CONCLUSION

The results indicated that anti-rPrtC IgA and IgG antibodies may serve as an indicator for past or present intraoral colonization with P. gingivalis.

Herpesviral-bacterial interactions in aggressive periodontitis

BACKGROUND

Human cytomegalovirus, Epstein-Barr virus and herpesvirus co-infections occur with significantly higher frequency in actively progressing than in stable periodontitis sites of adolescents and young adults. Also, periodontal presence of cytomegalovirus and Epstein-Barr virus is associated with increased occurrence of subgingival Porphyromonas gingivalis, Bacteroides forsythus, Dialister pneumosintes, Prevotella intermedia, Prevotella nigrescens, Treponema denticola and Actinobacillus actinomycetemcomitans.

AIM

This article reviews the evidence linking herpesviruses to the development of aggressive periodontitis and suggests a potential mechanism for herpesviral acceleration of the periodontal disease process.

CONCLUSIONS

It seems to be a reasonable supposition that the etiopathogenesis of various types of aggressive periodontitis includes the combined action of herpesviruses and specific bacterial species. New vaccines and vaccination technologies that are being developed against herpesviruses warrant testing for their ability to induce a protective immune response against destructive periodontal disease. Clearly, the importance of combined herpesviral-bacterial infections and associated host responses in the development of periodontitis needs to be studied further.

The collagenase activity of Porphyromonas gingivalis is due to Arg-gingipain

Degradation of type I collagen by Porphyromonas gingivalis was monitored by fluorogenic, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and growth assays. All three assays showed that inactivation of both the rgpA and rgpB genes was necessary to completely eliminate the capacity of P. gingivalis to cleave type I collagen. Leupeptin, an Arg-gingipain-specific protease inhibitor, almost completely inhibited collagen degradation by P. gingivalis cells whereas cathepsin B inhibitor II, a Lys-gingipain inhibitor, did not. A purified preparation of Arg-gingipains A and B hydrolyzed gelatin but did not cleave type I collagen, suggesting that the enzymes must be attached to the cell surface to exert collagenase activity. A number of substances used as adjuncts in periodontal therapy were also tested for their capacity to inhibit collagenase activity of P. gingivalis. Tetracycline, doxycycline, and chlorhexidine strongly inhibited collagenase activity.

Immunization with Porphyromonas gingivalis capsular polysaccharide prevents P. gingivalis-elicited oral bone loss in a murine model

The capsular polysaccharide (CPS) of the periodontal pathogen Porphyromonas gingivalis is an important virulence factor for this organism. We purified P. gingivalis CPS, immunized mice with this antigen, and assessed the vaccine potential of P. gingivalis CPS by using the murine oral challenge model. Animals immunized with P. gingivalis CPS developed elevated levels of immunoglobulin M (IgM) and IgG in serum that reacted with whole P. gingivalis organisms. The mice immunized with P. gingivalis CPS were protected from P. gingivalis-elicited oral bone loss. These data demonstrate that P. gingivalis CPS is a vaccine candidate for prevention of P. gingivalis-elicited oral bone loss.

Purification, gene cloning, gene expression, and mutants of Dps from the obligate anaerobe Porphyromonas gingivalis

The periodontopathogen Porphyromonas gingivalis is an obligate anaerobe that is devoid of catalase but exhibits a relatively high degree of resistance to peroxide stress. In the present study, we demonstrate that P. gingivalis contains a Dps homologue that plays an important role in the protection of cells from peroxide stress. The Dps protein isolated from P. gingivalis displayed a ferritin-like spherical polymer consisting of 19-kDa subunits. Molecular cloning and sequencing of the gene encoding this protein revealed that it had a high similarity in nucleotide and amino acid sequences to Dps proteins from other species. The expression of Dps was significantly increased by exposure of P. gingivalis to atmospheric oxygen in an OxyR-dependent manner, indicating that it is regulated by the reactive oxygen species-regulating gene oxyR. The Dps-deficient mutants, including the dps single mutant and the ftn dps double mutant, showed no viability loss upon exposure to atmospheric oxygen for 6 h. In contrast to the wild type, however, these mutants exhibited the high susceptibility to hydrogen peroxide, thereby disrupting the viability. On the other hand, no significant difference in sensitivity to mitomycin C and metronidazole was observed between the wild type and the mutants. Furthermore, the dps single mutant, compared with the wild type, showed a lower viability in infected human umbilical vein endothelial cells.

Human monoclonal antibody inhibits Porphyromonas gingivalis hemagglutinin activity

BACKGROUND

Porphyromonas gingivalis has been implicated as an important pathogen in the development of chronic periodontitis, and its colonization of subgingival sites is critical in the pathogenic process. One potential virulence factor, hemagglutinin, may mediate bacteria attachment onto and penetration into host cells, as well as agglutinate and lyse erythrocytes to intake heme, an absolute requirement for growth. We previously cloned the gene encoding the 130 kDa hemagglutinin domain (130k HMGD) and identified its functional domain. The construction of a human monoclonal antibody that is capable of inhibiting the hemagglutinating ability is significant and important toward the development of passive immunotherapy.

METHODS

Human lymphocytes isolated from a donor, who had high antibody titer against the recombinant 130k HMGD (r130k HMGD), were immortalized by Epstein-Barr virus, and specific antibody-producing B cells were established by panning using the r130k HMGD.

RESULTS

The constructed HuMAb-HMGD1, IgG subclass, recognized the r130k HMGD as well as the 43 and 49 kDa major bands in P. gingivalis cells and vesicles. The HuMAb-HMGD1 significantly inhibited hemagglutinating activity of P. gingivalis vesicles in a dose-dependent manner. Furthermore, the HuMAb-HMGD1 recognized the synthetic peptide, EGSNEFAPVQNLTGSSVG, which contains the functional domain of 130k HMGD.

CONCLUSION

The newly constructed HuMAb-HMGD1 may prove to be useful for the development of passive immunization against periodontal diseases caused by P. gingivalis infection, pending the results of fertility study in disease mode.

Molecular interaction of Porphyromonas gingivalis with host cells: implication for the microbial pathogenesis of periodontal disease

Porphyromonas gingivalis is a predominant periodontal pathogen, which expresses a number of potential virulence factors involved in the pathogenesis of periodontitis. Among them, fimbriae are a critical factor to mediate the bacterial interaction with host tissues, which promotes the bacterial adhesion to and invasion of the targeted sites. Fimbriae are capable of binding to human salivary components, commensal bacteria, and a variety of host cells including macrophages, epithelial cells, and fibroblasts. Human extracellular matrix (ECM) proteins such as vitronectin and fibronectin play important roles in cellular signal transduction via binding to receptor integrins. Fimbriae showed significant binding affinity to ECM proteins and clearly inhibited the molecular interactions between vitronectin/fibronectin and their receptor alphavbeta3 and alpha5beta1 integrins overexpressed on Chinese hamster ovary (CHO) cell strain. P. gingivalis fimbriae are likely to interrupt the cellular signaling via ECM proteins/integrins in periodontal regions. Fimbriae are also thought to be critically important in invasive events of the organism to host cells. The fimA genes, encoding FimA (a subunit of fimbriae), of P. gingivalis strains are classified into 5 types, I to V. Recent clinical investigations demonstrated the close relationship between the organisms with type II fimA and periodontitis development. Recombinant FimA (rFimA) proteins of types I to V were generated to compare their adhesion/invasion abilities to human gingival fibroblasts (HGF) and a human epithelial cell line (HEp-2 cells), respectively. There were no significant differences in the adhesion ability of microspheres (MS) coated with these rFimAs to HGF; however, the adhesion of type II rFimA-MS to HEp-2 cells was significantly greater than that of other rFimA types. It was also observed that the type II rFimA-MS markedly invaded the epithelial cells and accumulated around the nuclei. Collectively, these findings suggest that fimbriae of P. gingivalis, especially type II, are involved in the initiation and progression of human periodontitis.