Virulence factors of Porphyromonas gingivalis

Regulation of cementoblast function by P. gingivalis lipopolysaccharide via TLR2

Although cementoblasts express Toll-like receptors (TLR)-2 and -4, little is known regarding the possible participation of cementoblasts in the inflammatory response. We investigated the effects of Porphyromonas gingivalis lipopolysaccharide (LPS), tetra- and penta-acylated lipid A species (designated PgLPS(1435/1449) and PgLPS(1690), respectively), on gene expression of osteoclastogenesis-associated molecules in murine cementoblasts. Real-time quantitative RT-PCR analysis revealed that receptor activator of NF-kappaB ligand (RANKL), interleukin-6, Regulated on activation, normal T-cell expressed, and secreted (RANTES), macrophage inflammatory protein-1alpha, and monocyte chemoattractant protein-1 were rapidly and dramatically induced upon stimulation with PgLPS(1690), but only slightly induced with PgLPS(1435/1449). Osteoprotegerin, which was expressed constitutively, was not altered significantly. ELISA demonstrated synthesis of corresponding proteins. PgLPS(1690) significantly induced transcripts for NF-kappaB, and this activation was inhibited by pre-treatment with anti-TLR-2 but not with TLR-4 antibodies. These results suggest that cementoblasts participate in the recruitment of osteoclastic precursor cells by up-regulation of chemokines/cytokines.

Protective and destructive immunity in the periodontium: Part 1--innate and humoral immunity and the periodontium

Based on the results of recent research in the field, the present paper will discuss the protective and destructive aspects of the innate vs. adaptive (humoral and cell-mediated) immunity associated with the bacterial virulent factors or antigenic determinants during periodontal pathogenesis. Attention will be focused on: (i) the Toll-like receptors (TLR), the innate immune repertoire for recognizing the unique molecular patterns of microbial components that trigger innate and adaptive immunity for effective host defenses, in some general non-oral vs. periodontal microbial infections; (ii) T-cell-mediated immunity, Th-cytokines, and osteoclastogenesis in periodontal disease progression; and (iii) some molecular techniques developed and used to identify critical microbial virulence factors or antigens associated with host immunity (using Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis as the model species). Therefore, further understanding of the molecular interactions and mechanisms associated with the host's innate and adaptive immune responses will facilitate the development of new and innovative therapeutics for future periodontal treatments.

Innate immune signaling and Porphyromonas gingivalis-accelerated atherosclerosis

Periodontal diseases are a group of diseases that lead to erosion of the hard and soft tissues of the periodontium, which, in severe cases, can result in tooth loss. Anecdotal clinical observations have suggested that poor oral health may be associated with poor systemic health; however, only recently have appropriate epidemiological studies been initiated, with defined clinical endpoints of periodontal disease, to address the association of periodontal disease with increased risk for cardiovascular and cerebrovascular disease. Although conflicting reports exist, these epidemiological studies support this connection. Paralleling these epidemiological studies, emerging basic scientific studies also support that infection may represent a risk factor for atherosclerosis. With P. gingivalis as a model pathogen, in vitro studies support that this organism can activate host innate immune responses associated with atherosclerosis, and in vivo studies demonstrate that this organism can accelerate atheroma deposition in animal models. In this review, we focus primarily on the basic scientific studies performed to date which support that infection with bacteria, most notably P. gingivalis, accelerates atherosclerosis. Furthermore, we attempt to bring together these studies to provide an up-to-date framework of emerging theories into the mechanisms underlying periodontal disease and increased risk for atherosclerosis, as well as identify intervention strategies to reduce the incidence of periodontal disease in humans, in an attempt to decrease risk for systemic complications of periodontal disease such as atherosclerotic cardiovascular disease.

Porphyromonas gingivalis galE is involved in lipopolysaccharide O-antigen synthesis and biofilm formation

Porphyromonas gingivalis is a crucial component of complex plaque biofilms that form in the oral cavity, resulting in the progression of periodontal disease. To elucidate the mechanism of periodontal biofilm formation, we analyzed the involvement of several genes related to the synthesis of polysaccharides in P. gingivalis. Gene knockout P. gingivalis mutants were constructed by insertion of an ermF-ermAM cassette; among these mutants, the galE mutant showed some characteristic phenotypes involved in the loss of GalE activity. As expected, the galE mutant accumulated intracellular carbohydrates in the presence of 0.1% galactose and did not grow in the presence of galactose at a concentration greater than 1%, in contrast to the parental strain. Lipopolysaccharide (LPS) analysis indicated that the length of the O-antigen chain of the galE mutant was shorter than that of the wild type. It was also demonstrated that biofilms generated by the galE mutant had an intensity 4.5-fold greater than those of the wild type. Further, the galE mutant was found to be significantly susceptible to some antibiotics in comparison with the wild type. In addition, complementation of the galE mutation led to a partial recovery of the parental phenotypes. We concluded that the galE gene plays a pivotal role in the modification of LPS O antigen and biofilm formation in P. gingivalis and considered that our findings of a relationship between the function of the P. gingivalis galE gene and virulence phenotypes such as biofilm formation may provide clues for understanding the mechanism of pathogenicity in periodontal disease.

Construction of a sIgA-enhancing anti-Porphyromonas gingivalis FimA vaccine and nasal immunization in mice

Porphyromonas gingivalis is implicated in the etiology of chronic periodontitis. Fimbriae are one of several critical surface virulence factors of P. gingivalis. Interleukin 15 (IL-15) is a critical important cytokine for the differentiation of B-1 cells into IgA-inducing cells in mucosal tissues and the proliferation of B cells. The present study constructed a co-expression plasmid pIRES-fimA:IL-15 encoding fimbrinllin (FimA), a subunit of fimbriae and IL-15 as a sIgA-enhancing anti-P. gingivalis FimA vaccine. The plasmid pIRES-fimA:IL-15 was transfected to CHO cells. The expressions of FimA and IL-15 in CHO cells were verified by Western blot and ELISA. Mice were immunized with pIRES-fimA:IL-15 via nasal or intramucusal route. The results showed that nasal immunization was capable of promoting Ag-specific immune responses in the oral region as well as systemic immunity. When immunized via nasal route, IL-15 expressed by the plasmid enhanced FimA-specific sIgA antibody response. In conclusion, a co-expression plasmid pIRES-fimA:IL-15 has been constructed, and when immunized via nasal route, antigen-specific sIgA antibody response could be modulated positively in immunized mice.

The K1 serotype capsular polysaccharide of Porphyromonas gingivalis elicits chemokine production from murine macrophages that facilitates cell migration

Porphyromonas gingivalis is the principal organism associated with aggressive forms of generalized periodontal disease. Previous reports have suggested that encapsulated P. gingivalis strains are more virulent than unencapsulated strains; however, the contribution of capsular polysaccharide (CPS) to the virulence of this organism is poorly understood. Since periodontal disease presents with a complex inflammatory cell lesion comprised of neutrophils and monocytes, we cultured murine peritoneal macrophages with heat-killed P. gingivalis W83, CPS purified from P. gingivalis strain W83, and the seven known serotype-specific P. gingivalis CPS and assessed the ability of supernatant fluids produced by challenged macrophages to attract naïve inflammatory cells. We also defined JE/MCP-1, KC, MIP-2, and RANTES production in response to the P. gingivalis CPS antigens. We observed that supernatant fluids collected from macrophages incubated with P. gingivalis W83 and serotype K1 CPS stimulated the migration of naïve murine bone marrow-derived polymorphonuclear leukocytes in an in vitro cell migration chamber. CPS from W83 and the K1 serotype elicited potent chemokine secretion patterns for macrophages, while those specific to serotypes K2 to K7 were significantly less stimulatory. Reverse transcription-PCR and enzyme-linked immunosorbent assay revealed JE/MCP-1, KC, MIP-2, and RANTES expression from murine macrophages which had been challenged with purified P. gingivalis W83 CPS. Chemokine production appeared to be dependent on both the dose of and time of exposure to P. gingivalis W83 CPS. These data demonstrate that the P. gingivalis serotype K1 CPS elicits chemokine production from phagocytic cells. Furthermore, these data suggest that the host response to this antigen may contribute to the formation of the inflammatory cell lesion observed during P. gingivalis-elicited periodontal disease.

Enhanced biofilm formation and loss of capsule synthesis: deletion of a putative glycosyltransferase in Porphyromonas gingivalis

Periodontitis is a biofilm-mediated disease. Porphyromonas gingivalis is an obligate anaerobe consistently associated with severe manifestations of this disease. As an opportunistic pathogen, the ability to proliferate within and disseminate from subgingival biofilm (plaque) is central to its virulence. Here, we report the isolation of a P. gingivalis transposon insertion mutant altered in biofilm development and the reconstruction and characterization of this mutation in three different wild-type strains. The mutation responsible for the altered biofilm phenotype was in a gene with high sequence similarity ( approximately 61%) to a glycosyltransferase gene. The gene is located in a region of the chromosome that includes up to 16 genes predicted to be involved in the synthesis and transport of capsular polysaccharide. The phenotype of the reconstructed mutation in all three wild-type backgrounds is that of enhanced biofilm formation. In addition, in strain W83, a strain that is encapsulated, the glycosyltransferase mutation resulted in a loss of capsule. Further experiments showed that the W83 mutant strain was more hydrophobic and exhibited increased auto-aggregation. Our results indicate that we have identified a gene involved in capsular-polysaccharide synthesis in P. gingivalis and that the production of capsule prevented attachment and the initiation of in vitro biofilm formation on polystyrene microtiter plates.

Risk ofPorphyromonas gingivalisRecolonization During the Early Period of Periodontal Maintenance in Initially Severe Periodontitis Sites

BACKGROUND

Porphyromonas gingivalis is considered a critical pathogen of periodontal diseases including recurrent periodontitis. The profound effects of active periodontal treatment (APT) on P. gingivalis elimination were previously demonstrated and revealed that the subsequent P. gingivalis-free or -suppressed status seems to be maintained during early periodontal maintenance (PMT). The aim of the present study was to show the occurrence of microbial recolonization during this early PMT period.

METHODS

In total, 128 sites from 11 generalized chronic periodontitis patients and one generalized aggressive periodontitis patient underwent clinical and microbiologic examination at baseline (Exam-I), after APT (Exam-II), and in PMT (Exam-III). Exam-III was carried out an average of 4.5 +/- 3.5 months after Exam-II. Detection and quantification of putative pathogens were performed using a polymerase chain reaction-based method.

RESULTS

The PMT used was effective in maintaining the clinical conditions improved by APT. However, in microbiological examinations, Exam-III showed higher detection frequency and levels of P. gingivalis than Exam-II. This suggests that a P. gingivalis recolonization started in the early PMT period. P. gingivalis-increased sites then showed significantly more severe signs of periodontitis in Exam-I than P. gingivalis-stable sites (bleeding on probing frequency: 76.7% versus 56.5%; suppuration frequency: 41.9% versus 12.9%). On the other hand, in Exam-II, no significant differences of clinical parameters were noted between P. gingivalis-increased and -stable sites.

CONCLUSION

Severe periodontitis sites before APT seemed to place them at risk of P. gingivalis recolonization in the early PMT period, and this microbial restoration could be a cause of recurrent periodontitis.

Transvascular dissemination of Porphyromonas gingivalis from a sequestered site is dependent upon activation of the kallikrein/kinin pathway

BACKGROUND AND OBJECTIVE

Epidemiological evidence implicates a connection between human periodontitis and systemic diseases. One possible mechanism involves the direct dissemination of periodontopathogens to the target organs through the circulation. The aim of this work was to define the mechanism used by Porphyromonas gingivalis for dissemination from a sequestered infection site.

MATERIAL AND METHODS

BALB/c mice were subcutaneously infected with P. gingivalis via use of a mouse chamber model. Tissue fluids from various sites were collected and cultured to determine the presence of P. gingivalis. Evans Blue dye was used to measure the dissemination ability of P. gingivalis. Kinin-associated molecules were introduced into mice, and their effects on bacterial dissemination and mouse pathology were monitored.

RESULTS

P. gingivalis strain A7436 caused remote lesions and septicemia with severe cachexia, resulting in animal death. Intrachamber challenge with A7436 resulted in vascular permeability enhancement (VPE), as measured by the systemic infiltration of Evans Blue dye into chamber fluids. VPE was blocked by kininase and kinin receptor antagonist and enhanced by exogenous bradykinin and kininase inhibitor. Live bacteria were recovered from the subcutaneous perichamber and abdominal spaces (spreading), and from the blood (disseminating) of infected mice. Both kininase and kinin receptor antagonist reduced animal mortality as a result of infection with strain A7436 and decreased the number of bacteria recoverable from the blood, but they were not associated with bacterial spreading.

CONCLUSIONS

The results suggest that activation of the kinin system is involved in the breach of the vascular barrier that permits dissemination of P. gingivalis.

Analysis of conserved glutamate residues in Porphyromonas gingivalis outer membrane receptor HmuR: toward a further understanding of heme uptake

The aim of this study was to broaden the current knowledge about the Porphyromonas gingivalis heme receptor HmuR. Site-directed mutagenesis was employed to replace Glu427, Glu448, Glu458 and Glu503 by alanines and to construct a triple Glu427Ala/Glu448Ala/Glu 458Ala mutant. All iron/heme-starved P. gingivalis mutants showed decreased growth recovery when human serum as the iron/heme source was used, hmuR::ermF, hmuR (E503A) and hmuR (E427A,E448A,E458A) mutant strains being the most affected. E. coli cells expressing HmuR with mutated glutamate residues bound hemin, hemoglobin and hemin-serum albumin complex with the same efficiency as did the wild-type recombinant protein, suggesting that the residues were not directly involved in heme binding. These data indicate that in addition to two conserved histidine residues (His95 and His434), NPDL and YRAP motifs, conserved glutamate residues are important for HmuR to utilize heme present in serum hemoproteins.

Effects of various growth conditions in a chemostat on expression of virulence factors in Porphyromonas gingivalis

Porphyromonas gingivalis, one of the gram-negative organisms associated with periodontal disease, possesses potential virulence factors, including fimbriae, proteases, and major outer membrane proteins (OMPs). In this study, P. gingivalis ATCC 33277 was cultured in a chemostat under hemin excess and presumably peptide-limiting conditions to better understand the mechanisms of expression of the virulence factors upon environmental changes. At higher growth rates, the amounts of FimA and the 75-kDa protein, forming long and short fimbriae, respectively, increased significantly, whereas gingipains decreased in amount and activity. In a nutrient-limited medium, lesser amounts of the above two fimbrial proteins were observed, whereas clear differences were not found in the amounts of gingipains. In addition, two-dimensional electrophoresis revealed that proteins in cells were generally fewer in number during nutrient-limited growth. Under aeration, a considerable reduction in gingipain activity was found, whereas several proteins associated with intact cells significantly increased. However, the expression of major OMPs, such as RagA, RagB, and the OmpA-like proteins, was almost constant under all conditions tested. These results suggest that P. gingivalis may actively control expression of several virulence factors to survive in the widely fluctuating oral environment.

Inhibitory effects of macrocarpals on the biological activity of Porphyromonas gingivalis and other periodontopathic bacteria

BACKGROUND/AIMS

Macrocarpals, which are phloroglucinol derivatives contained in eucalyptus leaves, exhibit antimicrobial activity against a variety of bacteria including oral bacteria. This study examined effects of macrocarpals A, B, and C on periodontopathic bacteria, especially Porphyromonas gingivalis.

METHODS

Macrocarpals A, B, and C were purified from a 60% ethanol-extract of Eucalyptus globules leaves. To investigate antibacterial activity, representative periodontopathic bacteria were cultured in media with or without various amounts of macrocarpals; subsequently, the optical density at 660 nm was measured. Macrocarpal inhibition of P. gingivalis Arg- and Lys-specific proteinases was assessed by spectrofluorophotometric assay and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The effect of macrocarpals on P. gingivalis binding to saliva-coated hydroxyapatite beads was examined with (3)H-labeled P. gingivalis.

RESULTS

Growth of P. gingivalis was inhibited more strongly than growth of Prevotella intermedia or Prevotella nigrescens and Treponema denticola by macrocarpals, however, Actinobacillus actinomycetemcomitans and Fusobacterium nucleatum were much more resistant. Macrocarpals inhibited P. gingivalis Arg- and Lys-specific proteinases in a dose-dependent manner. The enzyme-inhibitory effect of macrocarpals was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis in which hemoglobin degradation by P. gingivalis proteinase was inhibited by macrocarpals. P. gingivalis binding to saliva-coated hydroxyapatite beads was also strongly attenuated by macrocarpals.

CONCLUSIONS

Macrocarpals A, B and C demonstrated antibacterial activity against periodontopathic bacteria. Among tested bacteria, P. gingivalis displayed the greatest sensitivity to macrocarpals; additionally, its trypsin-like proteinase activity and binding to saliva-coated hydroxyapatite beads were inhibited by macrocarpals. These results indicate that eucalyptus leaf extracts may be useful as a potent preventative of periodontal disease.

Porphyromonas gingivalis-epithelial cell interactions in periodontitis

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

Gingipains of Porphyromonas gingivalis modulate leukocyte adhesion molecule expression induced in human endothelial cells by ligation of CD99

Porphyromonas gingivalis has been implicated as a key etiologic agent in the pathogenesis of destructive chronic periodontitis. Among virulence factors of this organism are cysteine proteinases, or gingipains, that have the capacity to modulate host inflammatory defenses. Intercellular adhesion molecule expression by vascular endothelium represents a crucial process for leukocyte transendothelial migration into inflamed tissue. Ligation of CD99 on endothelial cells was shown to induce expression of endothelial leukocyte adhesion molecule 1, vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and major histocompatibility complex class II molecules and to increase adhesion of leukocytes. CD99 ligation was also found to induce nuclear translocation of NF-kappaB. These results indicate that endothelial cell activation by CD99 ligation may lead to the up-regulation of adhesion molecule expression via NF-kappaB activation. However, pretreatment of endothelial cells with gingipains caused a dose-dependent reduction of adhesion molecule expression and leukocyte adhesion induced by ligation of CD99 on endothelial cells. The data provide evidence that the gingipains can reduce the functional expression of CD99 on endothelial cells, leading indirectly to the disruption of adhesion molecule expression and of leukocyte recruitment to inflammatory foci.

Colitogenic and non-colitogenic commensal bacteria differentially trigger DC maturation and Th cell polarization: An important role for IL-6

We investigated whether commensal bacteria modulate activation and maturation of bone marrow-derived DC and their ability to prime CD4(+) T cells. We used Escherichia coli mpk, which induces colitis in gnotobiotic IL-2-deficient (IL-2(-/-)) mice, and Bacteroides vulgatus mpk, which prevents E. coli-induced colitis. Stimulation of DC with E. coli induced TNF-alpha, IL-12 and IL-6 secretion and expression of activation markers. Moreover, stimulation of DC with E. coli increased T cell activation and led to Th1 polarization. Stimulation with B. vulgatus led only to secretion of IL-6, and DC were driven into a semi-mature state with low expression of activation markers and did not promote Th1 responses. B. vulgatus-induced semi-mature DC were non-responsive to stimulation by E. coli in terms of maturation, T cell priming and TNF-alpha but not IL-6 production. The non-responsiveness of B. vulgatus-stimulated DC was abrogated by addition of anti-IL-6 mAb or mimicked with rIL-6. These data suggest that B. vulgatus-induced IL-6 drives DC into a semi-mature state in which they are non-responsive to proinflammatory activation by E. coli. This in vitro mechanism might contribute to the prevention of E. coli-triggered colitis development by B. vulgatus in vivo; high IL-6 mRNA expression was consistently found in B. vulgatus-colonized or B. vulgatus/E. coli co-colonized IL-2(-/-) mice and was associated with absence of colitis.

The hemoglobin receptor protein of porphyromonas gingivalis inhibits receptor activator NF-kappaB ligand-induced osteoclastogenesis from bone marrow macrophages

Extracellular proteinaceous factors of Porphyromonas gingivalis, a periodontal pathogen, that influence receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL)-induced osteoclastogenesis from bone marrow macrophages were investigated. The culture supernatant of P. gingivalis had the ability to inhibit RANKL-induced in vitro osteoclastogenesis. A major protein of the culture supernatant, hemoglobin receptor protein (HbR), suppressed RANKL-induced osteoclastogenesis in a dose-dependent fashion. HbR markedly inhibited RANKL-induced osteoclastogenesis when present in the culture for the first 24 h after addition of RANKL, whereas no significant inhibition was observed when HbR was added after 24 h or later, implying that HbR might interfere with only the initial stage of RANKL-mediated differentiation. HbR tightly bound to bone marrow macrophages and had the ability to induce phosphorylation of ERK, p38, NF-kappaB, and Akt. RANKL-induced phosphorylation of ERK, p38, and NF-kappaB was not suppressed by HbR, but that of Akt was markedly suppressed. HbR inhibited RANKL-mediated induction of c-Fos and NFATc1. HbR could induce beta interferon (IFN-beta) from bone marrow macrophages, but the induction level of IFN-beta might not be sufficient to suppress RANKL-mediated osteoclastogenesis, implying presence of an IFN-beta-independent pathway in HbR-mediated inhibition of osteoclastogenesis. Since rapid and extensive destruction of the alveolar bone causes tooth loss, resulting in loss of the gingival crevice that is an anatomical niche for periodontal pathogens such as P. gingivalis, the suppressive effect of HbR on osteoclastogenesis may help the microorganism exist long in the niche.

Antibody responses to Porphyromonas gingivalis hemagglutinin A and outer membrane protein in chronic periodontitis

BACKGROUND

Hemagglutinin and outer membrane protein (OMP) are major virulence factors associated with colonization of Porphyromonas gingivalis in the gingival crevice. The genes for the 200-kDa antigenic protein (200-kDa AP) and 40-kDa OMP of P. gingivalis have been successfully cloned. Additionally, the 200-kDa AP gene has been shown to constitute the hemagglutinin A (hagA) gene of P. gingivalis. Therefore, this study was constructed to evaluate the distributions and serum levels of immnoglobulin G (IgG) antibodies specific for 200-kDa AP and 40-kDa OMP in periodontitis patients.

METHODS

Fifty patients with chronic periodontitis and 59 controls without periodontal destruction were enrolled in this study. We cloned the genes for 200-kDa AP and 40-kDa OMP from P. gingivalis and constructed the purified recombinant proteins. Serum levels of IgG subclass antibodies specific for both recombinant 200-kDa and 40-kDa OMP were determined in patients and controls by an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The serum IgG subclass distribution for patients and controls was IgG1>IgG4>IgG2>IgG3 in the anti-200-kDa AP response, which was almost identical to that in the anti-40-kDa OMP response. The patient group showed significantly higher serum IgG responses to the 40-kDa OMP than the control group (P<0.01). In contrast, IgG subclass responses to the 200-kDa AP were not different between the patients and controls. Serum levels of antibodies reactive with both 200-kDa and 40-kDa proteins did not have a significant association with mean probing depth.

CONCLUSION

These results suggested that serum IgG responses against P. gingivalis OMP rather than the hagA may be more active in chronic periodontitis.

Proinflammatory gene expression in mouse ST2 cell line in response to infection by Porphyromonas gingivalis

Porphyromonas gingivalis is a predominant periodontal pathogen, whose infection causes inflammatory responses in periodontal tissue and alveolar bone resorption. Various virulence factors of this pathogen modulate host innate immune responses. It has been reported that gingipains degrade a wide variety of host cell proteins, and fimbriae are involved in bacterial adhesion to and invasion of host cells. In the present study, we profiled ST2 stromal cell gene expression following infection with the viable P. gingivalis strain ATCC33277 as well as with its gingipain- and fimbriae-deficient mutants, using microarray technology and quantitative real-time polymerase chain reaction. Using a mouse array of about 20,000 genes, we found that infection with the wild strain elicited a significant upregulation (greater than 2-fold) of expression of about 360 genes in ST2 cells, which included the chemokines CCL2, CCL5, and CXCL10, and other proinflammatory proteins such as interleukin-6 (IL-6) and matrix metalloproteinase-13 (MMP-13). Further, infection with the gingipain-deficient mutant elicited a reduced expression of the CXCL10, IL-6 and MMP-13 genes, suggesting that gingipains play an important role in inducing the expression of those genes following P. gingivalis infection. On the other hand, the pattern of global gene expression induced by the fimbriae-deficient mutant was similar to that by the wild strain. These results suggest that P. gingivalis infection induces gene expression of a wide variety of proinflammatory proteins in stromal cells/osteoblasts, and gingipains may be involved in inducing several of the proinflammatory factors.

Proteomics-based analysis of a counter-oxidative stress system in Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic pathogen associated with chronic periodontitis. Although anaerobic, P. gingivalis exhibits a high degree of aerotolerance, which enables it to survive within periodontal pockets. The aim of the present study was to examine the effect of oxidative stress on protein expression in P. gingivalis to obtain a better understanding of the mechanism underlying its aerotolerance. To accomplish this, P. gingivalis cells were grown under conditions of hemin limitation (0.01 microg/mL) to avoid the oxygen protective effect of hemin on oxidative stress. The proteins were then extracted from cultures either left untreated or subjected to oxidative stress and separated by 2-DE. The resultant protein expression profiles were examined by image scanning, and those found to differ depending on the presence or absence of aeration were subjected to MALDI-MS and then analyzed using the ORF database of P. gingivalis W83 from The Institute of Genomic Research. Oxidative stress was found to affect the expression of numerous proteins in P. gingivalis cells. In particular, the levels of HtpG, GroEL, DnaK, AhpC, TPR domain protein, and trigger factor were substantially increased.

Identification of amino acid residues involved in heme binding and hemoprotein utilization in the Porphyromonas gingivalis heme receptor HmuR

We have previously identified and characterized a heme/hemoglobin receptor, HmuR, in Porphyromonas gingivalis. To analyze the conserved amino acid residues of HmuR that may be involved in hemin/hemoprotein binding and utilization, we constructed a series of P. gingivalis A7436 hmuR mutants with amino acid replacements and characterized the ability of these mutants to utilize hemin and hemoproteins. Site-directed mutagenesis was employed to introduce mutations H95A, H434A, H95A-H434A, YRAP420-423YAAA, and NPDL442-445NAAA into HmuR in both P. gingivalis and Escherichia coli. Point mutations at H95 and H434 and in the NPDL motif of HmuR resulted in decreased binding to hemin, hemoglobin, and human serum albumin-hemin complex. Notably, mutations of these conserved sites and motifs led to reduced growth of P. gingivalis when human serum was used as the heme source. Analysis using a three-dimensional homology model of HmuR indicated that H95, H434, and the NPDL motif are present on apical or extracellular loops of HmuR, while the YRAP motif is present on the barrel wall. Taken together, these results support a role for H95, H434, and the NPDL motif of the P. gingivalis HmuR protein in heme binding and utilization of serum hemoproteins and the HmuR YRAP motif in serum hemoprotein utilization.

Intercellular spreading of Porphyromonas gingivalis infection in primary gingival epithelial cells

Porphyromonas gingivalis, an important periodontal pathogen, is an effective colonizer of oral tissues. The organism successfully invades, multiplies in, and survives for extended periods in primary gingival epithelial cells (GECs). It is unknown whether P. gingivalis resides in the cytoplasm of infected cells throughout the infection or can spread to adjacent cells over time. We developed a technique based on flow cytofluorometry and fluorescence microscopy to study propagation of the organism at different stages of infection of GECs. Results showed that P. gingivalis spreads cell to cell and that the amount of spreading increases gradually over time. There was a very low level of propagation of bacteria to uninfected cells early in the infection (3 h postinfection), but there were 20-fold and 45-fold increases in the propagation rate after 24 h and 48 h, respectively, of infection. Immunofluorescence microscopy of infected cells suggested that intercellular translocation of P. gingivalis may be mediated through actin-based membrane protrusions, bypassing the need for release of bacteria into extracellular medium. Consistent with these observations, cytochalasin D treatment of infected cells resulted in significant inhibition of bacterial spreading. This study shows for the first time that P. gingivalis disseminates from cell to cell without passing through the extracellular space. This mechanism of spreading may allow P. gingivalis to colonize oral tissues without exposure to the humoral immune response.

Tissue destruction induced by Porphyromonas gingivalis infection in a mouse chamber model is associated with host tumor necrosis factor generation

Intrachamber challenge with Porphyromonas gingivalis strain 381 in a mouse subcutaneous chamber model results in a local infection that progresses to exfoliation of the chambers within 15 days. This study was designed to elucidate the contribution of host reactions to tissue destruction manifested by chamber exfoliation in animals infected with P. gingivalis. Chamber fluids showed increasing levels of prostaglandin E(2) with infection, and the levels of tumor necrosis factor (TNF) in chamber fluids peaked just before chamber exfoliation. Intraperitoneal injection of a TNF inhibitor, thalidomide (TH), reduced the number of exfoliated chambers, while indomethacin had no effect. Exogenous TNF in chambers without bacterial infection did not cause chamber exfoliation but induced neutrophil infiltration. In a dual-chamber model, two chambers were implanted in the same mouse. One chamber was infected with P. gingivalis, and 9 days later exogenous TNF was added to the other chamber. Altogether, 66.67% of uninfected chambers were exfoliated between day 11 and day 16, although no bacteria were recovered from uninfected chambers. TH treatment alleviated both infected and uninfected chamber exfoliation. In this study, tissue destruction caused by P. gingivalis 381 infection was due to the elevation of the TNF levels and not due to local bacterial activities. Our results further indicate that local infection by P. gingivalis 381, a nondisseminating strain, actually has systemic effects on the host pathological outcome.

In vitro attachment of osteoblasts on contaminated rough titanium surfaces treated by Er:YAG laser

Microbial contamination of implant surfaces inhibits formation of new osseous tissues. Biocompatibility of sandblasted large grid (SLA) surface, after previous in vitro cocultivation with Porphyromonas gingivalis and concomitant Er:YAG laser irradiation of microorganisms, was tested by attachment of newly cultured osteoblasts. A total of 36 customized titanium cubes with SLA surface were placed into human osteoblast culture for 14 days. After removal of 1 control cube, 35 other cubes were contaminated with precultured P. gingivalis (ATCC33277) and incubated in broth medium for 1 week. Ablation was carried out on 32 cubes. Each side was treated for 23.5 s with a pulsed, water-cooled laser beam. After irradiation, cubes were again placed into fresh osteoblast culture for 2 weeks. One randomly selected single side per cube was analyzed by scanning electron microscope in 22 cubes. On other 10 cubes, vitality of attached cells was tested with ethidiumbromide staining by fluorescence microscopy. Three negative controls revealed constantly adherent P. gingivalis, and no osteoblasts were detectable after P. gingivalis contamination on the surfaces. Laser-treated specimens showed newly attached osteoblasts, extending over 50-80% of the surface. Positive control cube (without bacterial contamination) showed over 80% cell coverage of the surface. Vitality of widely stretched osteoblasts was confirmed by FITC staining. Our results indicate that Er:YAG laser was effective in removing P. gingivalis and cell compounds, offering an acceptable surface for new osteoblast attachment.

Inhibition of Lipopolysaccharide Activity by a Bacterial Cyclic Lipopeptide Surfactin

Compounds that inactivate lipopolysaccharide (LPS) activity have the potential of being new anti-inflammatory agents. Therefore, we searched among microbial secondary metabolites for compounds that inhibited LPS-stimulated adhesion between human umbilical vein endothelial cells (HUVEC) and HL-60 cells. By this screening, we found a cyclic lipopeptide surfactin from the culture broth of Bacillus sp. BML752-121F2 to be inhibitory. The addition of the surfactin prior to the LPS stimulation decreased HL-60 cell-HUVEC adhesion without showing any cytotoxicity. We confirmed that surfactin inhibited LPS-induced expression of ICAM-1 and VCAM-1 in HUVEC. It also inhibited the cellular adhesion induced by lipid A, the active component of LPS; but it did not inhibit TNF-alpha or IL-1 beta-induced cell adhesion. Then, surfactin was shown to suppress the interaction of lipid A with LPS-binding protein (LBP) that mediates the transport of LPS to its receptors. Finally, surface plasmon resonance (SPR) analysis revealed the surfactin to interact reversibly with lipid A. Thus, this Bacillus surfactin was shown to be an inhibitor of LPS-induced signal transduction, directly interacting with LPS.

Subgingival microbiota in peri-implant mucosa lesions and adjacent teeth in partially edentulous patients

BACKGROUND

Osseointegrated dental implants have been shown to be a predictable approach to provide the adequate support for the replacement of missing teeth. It has been observed that implants showing signs of peri-implantitis contain subgingival microbiota similar to that around natural teeth with periodontal disease. This study identified the subgingival microbiota around implants with peri-implant lesions and natural teeth in partially edentulous patients.

METHODS

Clinical and radiographic parameters were recorded and microbial samples taken from 16 implants with signs of pocketing, 12 neighboring and 11 non-neighboring teeth to the affected implants in 11 patients and 15 stable implants in eight patients (controls). Samples were cultured using techniques for Enterobacteriaceae spp and facultative/anaerobic periodontal pathogens. Statistical analysis included Friedman test to establish differences between the subgingival microbiota cultured from implants and teeth and two-tailed Mann Whitney test and chi square to find differences in two separate samples (P < or = 0.05).

RESULTS

There were statistical differences between the subgingival microbiota in peri-implant lesions and stable implants for Gram-negative enteric rods (P <0.05). P. gingivalis (1.42%) was detected in peri-implant lesions but not in stable implants. A significant correlation between the subgingival microbiota from implants and neighboring teeth for Gram-negative enteric rods (P = 0.023) and implants and non-neighboring teeth for P. gingivalis (P = 0.042) was found. The frequency detection of Gram-negative enteric rods (75%) and P. intermedia/nigrescens (25%) was higher in peri-implant lesions (P <0.05).

CONCLUSIONS

The subgingival microbiota in peri-implant lesions showed high levels of periodontopathic bacteria and superinfecting bacteria compared to healthy stable implants. The role of superinfecting bacteria in the pathogenesis of peri-implant lesions needs further investigation.

Apple- and Hop-Polyphenols Protect Periodontal Ligament Cells Stimulated With Enamel Matrix Derivative FromPorphyromonas gingivalis

BACKGROUND

Enamel matrix derivative (EMD) is a tissue regenerative agent used clinically as an adjunct to periodontal surgery. It was previously demonstrated that Porphyromonas gingivalis, a periodontal pathogen, significantly diminished the efficacy of EMD with periodontal ligament (PDL) cells through the proteolytic actions of Arg- and Lys-gingipains (Rgp and Kgp). Thus, antiproteolytic supplements are considered clinically desirable for effective periodontal regenerative therapies. In the present study, we examined apple- (AP) and hop-polyphenols to determine their ability to protect EMD-stimulated PDL cells from P. gingivalis.

METHODS

AP, apple condensed tannin (ACT), hop bract polyphenol (HBP), high and low molecular weight fractions of HBP (HMW-HBP and LMW-HBP), and epigallocatechin gallate (EGCg) were used. PDL cells were grown on EMD-coated dishes and infected with P. gingivalis, and cellular migration and proliferation were evaluated with an in vitro assay of wound healing assay in the presence or absence of the polyphenols.

RESULTS

Each polyphenol significantly enhanced the viability of PDL cells infected with P. gingivalis, whereas only EGCg demonstrated cytotoxicity. Further, all polyphenols significantly inhibited Rgp activity, with AP, ACT, and HBP more effective toward Kgp. P. gingivalis markedly diminished the migration and proliferation of EMD-stimulated PDL cells, whereas the addition of AP, ACT, HBP, and HMW-HBP significantly protected the cells from bacterial cytotoxicity. In contrast, EGCg and LMW-HBP did not show protective effects.

CONCLUSION

These results suggest that AP, ACT, AP, HBP, and HMW-HBP protect EMD-stimulated PDL cells from P. gingivalis and may be therapeutically useful supplements for EMD therapy.

Transmission of periodontal bacteria and models of infection

BACKGROUND

Bacteria play an essential role in the aetiology of periodontitis. Most bacterial species isolated from subgingival plaque are indigenous to the oral cavity. Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis are detected infrequently in periodontal health, which makes these species prime candidates to study person-to-person transmission. The aim of the present study was to review the literature on transmission of these periodontal bacterial species.

METHOD

We review the literature on bacterial typing techniques and summarize the information on clonal distribution of A. actinomycetemcomitans and P. gingivalis in family units based on different typing techniques in order to establish the likelihood for person-to-person transmission of these periodontal pathogens.

RESULTS

Vertical transmission of A. actinomycetemcomitans is estimated to be between 30% and 60%, whereas vertical transmission of P. gingivalis has rarely been observed. Horizontal transmission between spouses ranges between 14% and 60% for A. actinomycetemcomitans and between 30% and 75% for P. gingivalis. There is some evidence to show that cohabitation with a periodontitis patient influences the periodontal status of the spouse; however, substantially more information is needed to prove this hypothesis.

CONCLUSIONS

Transmission of putative periodontal pathogens between family members has been shown. The clinical consequences of these events have been poorly documented. Based on the current knowledge, screening for and prevention of transmission of specific virulent clones of A. actinomycetemcomitans may be feasible and effective in preventing some forms of periodontal disease. P. gingivalis is usually recovered from diseased adult subjects, and transmission of this pathogens seems largely restricted to adult individuals. Horizontal transmission of P. gingivalis may therefore be controlled by periodontal treatment involving elimination or significant suppression of the pathogen in diseased individuals and by a high standard of oral hygiene.

Involvement ofPorphyromonas gingivalis fimAGenotype in Treatment Outcome Following Non-Surgical Periodontal Therapy

BACKGROUND

Porphyromonas gingivalis is considered a critical pathogen in periodontal diseases. It is classified into six genotypes based on diversity of the fimA gene encoding fimbrillin. The present study evaluated the involvement of the fimA genotype in treatment outcome following non-surgical periodontal therapy.

METHODS

Chronic periodontitis patients were enrolled in this study; all received clinical and microbiological examinations at baseline. The detection of subgingival species and identification of P. gingivalis fimA genotypes were performed using polymerase chain reaction based methods. In total, 160 P. gingivalis positive sites with bleeding on probing (BOP) and a probing depth of > or =4 mm were accepted. They were followed up after scaling and root planing.

RESULTS

Longitudinal investigation indicated that fimA type I positive sites at baseline were followed by a significantly higher frequency of persistent BOP after treatment than type I negative sites (51.6% versus 27.9%), while types Ib and II were not. Type I positive sites also showed more persistence of Tannerella forsythensis and P. gingivalis after treatment than type I negative sites. In post-treatment investigation, type I positive sites showed higher frequencies of BOP and T. forsythensis detection than type I negative sites (77.8% versus 43.5% and 100% versus 76.1%, respectively).

CONCLUSIONS

BOP in initially type I positive sites showed little improvement with treatment, and the combined persistence of fimA type I and T. forsythensis seemed to be involved in this poor treatment outcome. The present study demonstrated the potential of P. gingivalis fimA type I as a predictor of persistent BOP after treatment.

Gingipain-Specific IgG in the Sera of Patients With Periodontal Disease Is Necessary for Opsonophagocytosis ofPorphyromonas gingivalis

BACKGROUND

Porphyromonas gingivalis is a primary etiologic agent of generalized aggressive periodontitis (GAgP), and gingipains, a group of cysteine proteinases, are critical virulence factors expressed by this organism. GAgP patients develop specific antibodies to gingipains; however, the function of these antibodies in the clearance of P. gingivalis infection is poorly understood.

METHODS

In this study, we defined the levels of gingipain-specific antibodies in GAgP patient sera and examined the ability of gingipain-specific antibodies to facilitate opsonophagocytosis of P. gingivalis by human polymorphonuclear leukocytes (PMNs) using a fluorescent phagocytosis assay.

RESULTS

GAgP patient sera possessed elevated levels of P. gingivalis-, arginine-gingipain (Rgp)A-, RgpB-, and lysine-gingipain (Kgp)-specific IgG (Kgp > RgpA > P. gingivalis > RgpB). Adsorption of GAgP sera with P. gingivalis whole organisms, RgpA, RgpB, and Kgp conjugated to sepharose beads reduced opsonophagocytosis of P. gingivalis by PMNs.

CONCLUSIONS

Our studies demonstrate that GAgP patient sera possess elevated levels of P. gingivalis- and gingipain-specific IgG. Furthermore, we show that gingipain antibodies promote uptake of P. gingivalis by PMNs, and our data suggest that gingipain-specific antibodies may be important for the control of P. gingivalis infections.

Generation of inflammatory stimuli: how bacteria set up inflammatory responses in the gingiva

OBJECTIVES

The primary aetiologic factor of periodontal disease is the bacterial biofilm. Gram-positive and gram-negative bacteria possess a plethora of structural or secreted components that may cause direct destruction to periodontal tissues or stimulate host cells to activate a wide range of inflammatory responses. These responses are intended to eliminate the microbial challenge, but may often cause further tissue damage.

METHODS

This review has been divided into three parts: (a) bacterial virulence factors, which includes basic information on bacterial virulence factors, and the principle inflammatory responses that host cells elicit against these factors, (b) main receptors and signalling pathways, which includes basic information about the main receptors that interact with the bacterial virulence factors, the nature of these interactions, and the activated signalling pathways that lead to inflammatory responses, and (c) initiation of inflammation, which includes a model by which the virulence factors may interact with host cells and lead to inflammatory responses in the gingiva.

FINDINGS AND CONCLUSIONS

Bacterial components/virulence factors may be involved in modulating inflammatory responses and include: lipopolysaccharides (LPS), peptidoglycans, lipotechoic acids, fimbriae, proteases, heat-shock proteins, formyl-methionyl peptides, and toxins. Potential host cell receptors involved in recognizing bacterial components and initiating signalling pathways that lead to inflammatory responses include: Toll-like receptors (TLRs), CD14, nucleotide-binding oligomerization domain proteins (Nod) and G-protein-coupled receptors, including formyl-methionyl peptide receptors and protease-activated receptors. Of the above bacterial and host molecules, evidence from experimental animal studies implicate LPS, fimbriae, proteases, TLRs, and CD14 in periodontal tissue or alveolar bone destruction. However, evidence verifying the involvement of any of the above molecules in periodontal tissue destruction in humans does not exist.

Sequence variations in rgpA and rgpB of Porphyromonas gingivalis in periodontitis

OBJECTIVE

The aim of the present study was to determine sequence variations in the active centre of the Arg-X-specific protease encoding genes rgpA and rgpB of clinical Porphyromonas gingivalis isolates and to analyse their prevalence in periodontitis patients before and 3 months after mechanical periodontal therapy.

BACKGROUND

Genetic diversity at nucleotides 281, 283, 286 and 331 has been shown to result in amino acid substitutions in the catalytic domain of RgpA and RgpB that affect the substrate specificity and thus may influence the efficacy of Arg-X-protease specific inhibitors.

METHODS

Sequence analysis of rgpA and rgpB genes in clinical P. gingivalis strains isolated from subgingival plaque samples of 82 periodontitis patients before and 3 months after mechanical supra- and subgingival debridement was performed.

RESULTS

No specific variation within the rgpA sequence was observed. However, the rgpB sequence in the region of the active centre showed five different rgpB genotypes, which were named NYPN, NSSN, NSSK, NYPK and DYPN according to the derived amino acid substitution. Porphyromonas gingivalis genotype NYPN was detected in 27 patients (32.9%) before and in 8 patients (9.8%) after therapy, NSSN in 26 (31.7%) and 10 (12.2%), NSSK in 22 (26.8%) and 2 (2.4%), NYPK in 5 (6.2%) and 1 (1.2%), and DYPN in 1 patient (1.2%) and 0 patients (0%), respectively. Only one patient (1.2%) harboured two P. gingivalis rgpB genotypes (NSSK/NYPN) before treatment; these were no longer detected after therapy.

CONCLUSION

The results indicate that five rgpB genotypes are maintained in natural populations of P. gingivalis. These data may be of importance with regard to the development of specific rgpB inhibitors.

The effects of intra-amniotic injection of periodontopathic lipopolysaccharides in sheep

OBJECTIVE

Periodontal disease may cause several complications of pregnancy, including fetal death. The purpose of this study was to investigate in sheep the effects of the intra-amniotic injection of lipopolysaccharide from 3 periodontopathic organisms and to compare these effects with those resulting from similar injection of Escherichia coli lipopolysaccharide. The outcomes that were studied included the rates of fetal death and the features of inflammation and lung maturation in survivors.

STUDY DESIGN

At 118 days of pregnancy, ewes that were bearing single fetuses were allocated at random to receive intra-amniotic injections of saline solution (n = 13 fetuses), or lipopolysaccharide from Porphyromonas gingivalis (in doses from 0.1 to 10 mg [n = 22 fetuses]), Actinobacillus actinomycetemcomitans (10 mg [n = 6 fetuses]; 1 mg [n = 6 fetuses]), Fusobacterium nucleatum (10 mg [n = 6 fetuses]) or Escherichia coli (10 mg [n = 14 fetuses]; 1 mg [n = 7 fetuses]). Surviving fetuses were delivered abdominally at 125 days of gestation (term, 150 days).

RESULTS

When compared with Escherichia coli lipopolysaccharide at similar dosages, periodontopathic lipopolysaccharides had high rates of fetal lethality. Only 6 of 22 fetuses that were exposed to intra-amniotic Porphyromonas gingivalis lipopolysaccharide survived doses of 0.1 to 10 mg, and only 3 of 6 fetuses survived 10-mg Actinobacillus actinomycetemcomitans lipopolysaccharide. Escherichia coli lipopolysaccharide did not cause fetal loss when given at doses of 10 mg (n = 14 fetuses) or 1 mg (n = 7 fetuses). Fetuses that survived exposure to these lipopolysaccharides showed features of inflammation in amniotic fluid and cord blood at birth and enhanced lung maturation.

CONCLUSION

Lipopolysaccharides from these 3 periodontopathic organisms have much higher rates of fetal lethality than Escherichia coli lipopolysaccharide but can cause similar intrauterine inflammatory responses and improvements in lung volumes in survivors. Sources of inflammation that are distant from the uterus may underlie a proportion of unexplained stillbirth and other complications of pregnancy.

Novel stationary-phase-upregulated protein of Porphyromonas gingivalis influences production of superoxide dismutase, thiol peroxidase and thioredoxin

Porphyromonas gingivalis, an obligately anaerobic bacterium, is implicated as a major pathogen in the development and progression of chronic periodontitis. Although expression of several virulence factors of the bacterium has been found to be affected by environmental stress such as entrance into the stationary growth phase and heat, there is relatively little information on the mechanisms that may operate in the bacterium in response to environmental stress. In this study, a novel protein (UstA) was investigated that was initially identified following two-dimensional gel analysis. Expression of UstA was upregulated in stationary phase or by exposure to atmospheric oxygen. N-terminal sequencing and database analysis with the P. gingivalis genome sequence revealed that the UstA-encoding gene (ustA) was located upstream of a homologue of the usp gene encoding the universal stress protein on the chromosome. The ustA gene appeared to be transcribed in a monocistronic fashion, as revealed by primer extension and Northern blot analysis. To elucidate the role of UstA in the bacterium, chromosomal mutants carrying a disruption of the ustA gene were constructed. The ustA mutant grew slower than the wild-type parent strain in rich medium, resulting in a lower yield in stationary phase. Furthermore, in this mutant, expression levels of the P. gingivalis homologues of superoxide dismutase, thiol peroxidase and thioredoxin were markedly higher than those in the wild-type, especially in stationary phase. The ustA mutant was more resistant to diamide, a thiol-specific oxidant, than the wild-type. In addition, the ustA mutation suppressed hypersensitivities of the oxyR mutant to diamide, metronidazole and mitomycin C. These results suggest that UstA may play a significant role in oxidative stress responses in the bacterium.

Targeting of Porphyromonas gingivalis with a bispecific antibody directed to FcalphaRI (CD89) improves in vitro clearance by gingival crevicular neutrophils

Phagocytosis and killing of pathogens by polymorphonuclear neutrophils (PMN) from gingival crevicular fluid (GCF) is diminished in chronic periodontitis patients. As an approach to improve targeting of PMN toward a periodontopathogen, Porphyromonas gingivalis, the efficacy of a bispecific antibody (BsAb) directed against both recombinant 130 kDa hemagglutinin domain (r130k-HMGD) of P. gingivalis, and PMN Fc receptor (FcR) was evaluated. GCF PMN exhibited higher IgA FcR (FcalphaRI) levels, and lower IgG FcR (FcgammaRIIa and FcgammaRIIIb) levels than PB PMN. Functional studies revealed that GCF PMN exhibited a higher capacity to phagocytose and kill P. gingivalis opsonized with a BsAb targeting P. gingivalis r130k-HMGD to FcalphaRI as compared to an anti-r130k-HMGD antibody. However, phagocytosis and killing activity of PB PMN that were incubated with the two antibodies proved comparable. These data support targeting of pathogens toward FcalphaRI as an option to improve antibacterial immunity in chronic periodontitis patients.

The Trans-Chromosomic Mouse-Derived Human Monoclonal Antibody Promotes Phagocytosis ofPorphyromonas gingivalisby Neutrophils

BACKGROUND

As a safe immunotherapeutic approach, human monoclonal antibody (hMAb) may be effective in clearing periodontopathic bacteria. The trans-chromosomic (TC) technology has recently been applied to construction of the TC mouse, which enables us to incorporate entire human chromosome fragments containing immunoglobulin (Ig) gene cluster. The aim of this study is to establish TC mouse-derived hMAb, and to test the in vitro opsonophagocytic activity.

METHODS

Human Ig-producing TC mouse was immunized by recombinant 40-kDa outer membrane protein (r40-kDa OMP) of Porphyromonas gingivalis 381, and the spleen cells were fused with the mouse myeloma cell line. The specificity of antir40- kDa OMP hMAb was evaluated with the enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance assays. Flow cytometric analyses were performed to assess the opsonophagocytic activity.

RESULTS

We successfully constructed 99 IgG isotype clones (IgG1: 84; IgG2: 11; IgG4: four clones), which were specifically reactive with r40-kDa OMP. The anti-r40-kDa OMP IgG1 hMAbs promoted phagocytosis of P. gingivalis by neutrophils. Futhermore, an increased opsonophagocytic activitity of anti-r40-kDa OMP IgG1 hMAbs was observed not only in P. gingivalis 381, but also in the W50, W83, and Su63 strains.

CONCLUSION

Our results document the TC mouse-derived hMAb to promote neutrophil phagocytosis of P. gingivalis, suggesting an immunotherapeutic option for clearance of P. gingivalis.

Construction of novel human monoclonal antibodies neutralizing Porphyromonas gingivalis hemagglutination activity using transgenic mice expressing human Ig loci

Porphyromonas gingivalis has been implicated as an important pathogen in the development of adult 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 lyses erythrocytes to intake heme, an absolute requirement for growth. Toward the development of passive immunotherapy, the construction of a human type monoclonal antibody, which is capable of inhibiting the hemagglutinating ability, will be significant and important. The human mAbs, both exhibiting a high degree of specificity and affinity against the recombinant 130 kDa hemagglutinin domain protein have been prepared using XenoMouse technology. The constructed Xeno-mAbs, IgG2 subclass, significantly inhibited hemagglutination of P. gingivalis and its vesicles. The newly constructed Xeno-mAbs 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.

Lipopolysaccharide preparation extracted from Porphyromonas gingivalis lipoprotein-deficient mutant shows a marked decrease in toll-like receptor 2-mediated signaling

We recently demonstrated that a new PG1828-encoded lipoprotein (PG1828LP) was able to be separated from a Porphyromonas gingivalis lipopolysaccharide (LPS) preparation, and we found that it exhibited strong cell activation, similar to that of Escherichia coli LPS, through a Toll-like receptor 2 (TLR2)-dependent pathway. In order to determine the virulence of PG1828LP toward cell activation, we generated a PG1828-deficient mutant of P. gingivalis strain 381 by allelic exchange mutagenesis using an ermF-ermAM antibiotic resistance cassette. A highly purified preparation of LPS from a PG1828-deficient mutant (DeltaPG1828-LPS) showed nearly the same ladder-like patterns in silver-stained gels as a preparation of LPS from a wild-type strain (WT-LPS), as well as Limulus amoebocyte lysate activities that were similar to those of the WT-LPS preparation. However, the ability of the DeltaPG1828-LPS preparation to activate NF-kappaB in TLR2-expressing cells was markedly attenuated. Cytokine production by human gingival fibroblasts was also decreased in response to the DeltaPG1828-LPS preparation in comparison with the WT-LPS preparation, and the activity was comparable to the stimulation of highly purified lipid A of P. gingivalis by TLR4. Further, lethal toxicity was rarely observed following intraperitoneal injection of the PG1828-deficient mutant into mice compared to that with the wild-type strain, while the DeltaPG1828-LPS preparation showed no lethal toxicity. Taken together, these results clearly indicate that PG1828LP plays an essential role in inflammatory responses and may be a major virulence factor of P. gingivalis.

The prevalence and pathogenic differences of Porphyromonas gingivalis fimA genotypes in patients with aggressive periodontitis

BACKGROUND

The fimA gene, which encodes fimbrillin (FimA), is found in Porphyromonas gingivalis and has been classified into six genotypes based on nucleotide sequence. P. gingivalis that possesses the type II fimA gene is prevalent in adult periodontitis.

OBJECTIVES

The aim of this study was to investigate the prevalence of P. gingivalis fimA genotypes in Japanese aggressive periodontitis patients, and to examine their virulence.

METHODS

Subgingival plaque samples were obtained from 223 sites in 18 aggressive periodontitis patients and 95 sites in 22 periodontally healthy young adults. Actinobacillus actinomycetemcomitans, P. gingivalis and Tannerella forsythensis detection, determination of the fimA genotype in P. gingivalis, and the quantification of P. gingivalis were analyzed by polymerase chain reaction (PCR) methods. The proteolytic activities of the P. gingivalis fimA type I and fimA type II were also examined.

RESULTS

In aggressive periodontitis patients, the most prevalent fimA genotype was the type II (46.7%), followed by the type Ib and type I, whereas in healthy subjects, the type I fimA was the only genotype detected. The number of P. gingivalis pathogens was the greatest in the type I fimA positive sites, and the frequency of coexisting A. actinomycetemcomitans and T. forsythensis was highest in the type II fimA positive sites in the aggressive periodontitis patients. Both the arginine-specific cysteine proteinase (Arg-gingipain) and lysine-specific cysteine proteinase (Lys-gingipain) activity of the P. gingivalis fimA type I strain were significantly higher than those of the fimA type II strains.

CONCLUSIONS

These results suggest that differences in virulence exist among different fimA genotypes. Coadherence with other pathogens in P. gingivalis fimA type II-associated aggressive periodontitis and quantitative increases in P. gingivalis in fimA type I-associated aggressive periodontitis are related to this virulence.

Functional implication of the hydrolysis of platelet endothelial cell adhesion molecule 1 (CD31) by gingipains of Porphyromonas gingivalis for the pathology of periodontal disease

Periodontitis is a response of highly vascularized tissues to the adjacent microflora of dental plaque. Progressive disease has been related to consortia of anaerobic bacteria, with the gram-negative organism Porphyromonas gingivalis particularly implicated. The gingipains, comprising a group of cysteine proteinases and associated hemagglutinin domains, are major virulence determinants of this organism. As vascular expression of leukocyte adhesion molecules is a critical determinant of tissue response to microbial challenge, the objective of this study was to determine the capacity of gingipains to modulate the expression and function of these receptors. Given the potential multifunctional role of platelet endothelial cell adhesion molecule 1 (PECAM-1) in the vasculature, the effect of gingipains on PECAM-1 expression by endothelial cells was examined. Activated gingipains preferentially down-regulated PECAM-1 expression on endothelial cells compared with vascular cell adhesion molecule 1 and endothelial-leukocyte adhesion molecule 1, but the reduction in PECAM-1 expression was completely inhibited in the presence of the cysteine proteinase inhibitor TLCK (Nalpha-p-tosyl-l-lysine chloromethyl ketone). Endothelial monolayers treated with activated gingipains demonstrated progressive intercellular gap formation that correlated with reduced intercellular junctional PECAM-1 expression as determined by Western blotting and immunofluorescence microscopy. This was accompanied by enhanced transfer of both albumin and neutrophils across the monolayer. The results suggest that degradation of PECAM-1 by gingipains contributes to increased vascular permeability and neutrophil flux at disease sites.

Mechanisms ofPorphyromonas gingivalis-induced monocyte chemoattractant protein-1 expression in endothelial cells

Monocyte chemoattractant protein-1 (MCP-1) is expressed in vascular endothelial cells of inflamed gingival tissues and plays an important role in periodontal pathogenesis. Endothelial cells produce high levels of MCP-1 in response to Porphyromonas gingivalis, an important periodontal pathogen. The present study investigated the mechanisms involved in MCP-1 production by human umbilical vein endothelial cells (HUVEC) following infection with P. gingivalis. In contrast to P. gingivalis, Bacteroides forsythus only weakly stimulated MCP-1 production while Treponema denticola could not induce MCP-1 in HUVEC. The MCP-1 production was independent of endogenous interleukin (IL)-1alpha as IL-1 receptor antagonist treatment did not reduce MCP-1 production by P. gingivalis. Meanwhile, antioxidant treatment and inhibition of NAD(P)H oxidase significantly reduced MCP-1 production. Pharmacological inhibition of p38 mitogen-associated protein (MAP) kinase, c-Jun N-terminal kinase (JNK), nuclear factor-kappaB (NF-kappaB) or activator protein-1 (AP-1) also substantially attenuated P. gingivalis-induced MCP-1 expression by HUVEC. Indeed, activation of NF-kappaB and AP-1 was observed in P. gingivalis-infected HUVEC. These results suggest that MCP-1 expression is upregulated in P. gingivalis-infected endothelial cells via reactive oxygen species, p38 MAP kinase, JNK, NF-kappaB, and AP-1.

Altered gingipain maturation in vimA- and vimE-defective isogenic mutants of Porphyromonas gingivalis

We have previously shown that gingipain activity in Porphyromonas gingivalis is modulated by the unique vimA and vimE genes. To determine if these genes had a similar phenotypic effect on protease maturation and activation, isogenic mutants defective in those genes were further characterized. Western blot analyses with antigingipain antibodies showed RgpA-, RgpB-, and Kgp-immunoreactive bands in membrane fractions as well as the culture supernatant of both P. gingivalis W83 and FLL93, the vimE-defective mutant. In contrast, the membrane of P. gingivalis FLL92, the vimA-defective mutant, demonstrated immunoreactivity only with RgpB antibodies. With mass spectrometry or Western blots, full-length RgpA and RgpB were identified from extracellular fractions. In similar extracellular fractions from P. gingivalis FLL92 and FLL93, purified RgpB activated only arginine-specific activity. In addition, the lipopolysaccharide profiles of the vimA and vimE mutants were truncated in comparison to that of W83. While glycosylated proteins were detected in the membrane and extracellular fractions from the vimA- and vimE-defective mutants, a monoclonal antibody (1B5) that reacts with specific sugar moieties of the P. gingivalis cell surface polysaccharide and membrane-associated Rgp gingipain showed no immunoreactivity with these fractions. Taken together, these results indicate a possible defect in sugar biogenesis in both the vimA- and vimE-defective mutants. These modulating genes play a role in the secretion, processing, and/or anchorage of gingipains on the cell surface.

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.

Iron and heme utilization in Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium associated with the initiation and progression of adult periodontal disease. Iron is utilized by this pathogen in the form of heme and has been shown to play an essential role in its growth and virulence. Recently, considerable attention has been given to the characterization of various secreted and surface-associated proteins of P. gingivalis and their contribution to virulence. In particular, the properties of proteins involved in the uptake of iron and heme have been extensively studied. Unlike other Gram-negative bacteria, P. gingivalis does not produce siderophores. Instead it employs specific outer membrane receptors, proteases (particularly gingipains), and lipoproteins to acquire iron/heme. In this review, we will focus on the diverse mechanisms of iron and heme acquisition in P. gingivalis. Specific proteins involved in iron and heme capture will be described. In addition, we will discuss new genes for iron/heme utilization identified by nucleotide sequencing of the P. gingivalis W83 genome. Putative iron- and heme-responsive gene regulation in P. gingivalis will be discussed. We will also examine the significance of heme/hemoglobin acquisition for the virulence of this pathogen.

IL-1-induced receptor activator of NF-kappa B ligand in human periodontal ligament cells involves ERK-dependent PGE2 production

Periodontitis, an inflammatory disorder of the supporting tissue of teeth, is one of the most common infectious diseases in humans. Periodontal pathogens promote inflammatory cytokines such as interleukin-1 (IL-1) and prostaglandin E2 (PGE2), resulting in alveolar bone destruction. In the present study, we examined the cellular and molecular mechanisms of IL-1-induced osteoclastogenesis using a coculture system of human periodontal ligament (PDL) cells and mouse spleen cells. IL-1alpha induced tartrate-resistant acid phosphatase positive (TRAP+) cell formation in a dose-dependent manner. IL-1alpha up-regulated receptor activator of NF-kappaB ligand (RANKL) and down-regulated osteoprotegerin (OPG) mRNA expression in PDL cells. The addition of cell-permeable PKI, an inhibitor of the cAMP/PKA signaling pathway, to the cocultures 8 h after the IL-1alpha stimulation inhibited IL-1alpha-induced TRAP+ cell formation. IL-1alpha-induced TRAP+ cell formation was completely blocked by either NS398, a selective inhibitor of cyclooxygenase (COX)-2, or PD98059, a specific inhibitor of extracellular signal-regulated kinase (ERK). Pretreatment with NS398 and PD98059 also inhibited both the up-regulation of RANKL and the down-regulation of OPG expression by IL-1alpha in PDL cells. IL-1alpha activated ERK phosphorylation and PD98059 greatly inhibited both COX-2 mRNA expression and PGE(2) production induced by IL-1alpha in PDL cells. In contrast, NEMO binding domain (NBD) peptide, a specific inhibitor of NF-kappaB signaling, did not affect COX2, RANKL, or OPG mRNA expression induced by IL-1alpha. These results suggest that IL-1alpha stimulates osteoclast formation by increasing the expression level of RANKL versus OPG via ERK-dependent PGE2 production in PDL cells.

Identification of a new membrane-associated protein that influences transport/maturation of gingipains and adhesins of Porphyromonas gingivalis

The dual membrane envelopes of Gram-negative bacteria provide two barriers of unlike nature that regulate the transport of molecules into and out of organisms. Organisms have developed several systems for transport across the inner and outer membranes. The Gram-negative periodontopathogenic bacterium Porphyromonas gingivalis produces proteinase and adhesin complexes, gingipains/adhesins, on the cell surface and in the extracellular milieu as one of the major virulence factors. Gingipains and/or adhesins are encoded by kgp, rgpA, rgpB, and hagA on the chromosome. In this study, we isolated a P. gingivalis mutant (porT), which showed very weak activities of gingipains in the cell lysates and culture supernatants. Subcellular fractionation and immunoblot analysis demonstrated that precursor forms of gingipains and adhesins were accumulated in the periplasmic space of the porT mutant cells. Peptide mass fingerprinting and N-terminal amino acid sequencing of the precursor proteins and the kgp'-'rgpB chimera gene product in the porT mutant indicated that these proteins lacked the signal peptide regions, consistent with their accumulation in the periplasm. The PorT protein seemed to be membrane-associated and exposed to the periplasmic space, as revealed by subcellular fractionation and immunoblot analysis using anti-PorT antiserum. These results suggest that the membrane-associated protein PorT is essential for transport of the kgp, rgpA, rgpB, and hagA gene products across the outer membrane from the periplasm to the cell surface, where they are processed and matured.