Anti-proliferative and cytotoxic activity of surface-associated material from periodontopathogenic bacteria

The effect of IL-1α on the expression of matrix metalloproteinases, plasminogen activators, and their inhibitors in osteoblastic ROS 17/2.8 cells

Interleukin-1 (IL-1) plays key roles in altering bone matrix turnover. This turnover is regulated by matrix metalloproteinases (MMPs), tissue inhibitor of matrix metalloproteinases (TIMPs), and the plasminogen activation system, including tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) , and plasminogen activator inhibitor type-1 (PAI-1). In this study, we examined the effect of IL-1alpha on the expression of the MMPs, TIMPs, tPA, uPA, and PAI-1 genes in osteoblasts derived from the rat osteosarcoma cell line ROS 17/2.8. The cells were cultured in alpha-minimum essential medium containing 10% fetal bovine serum with 0 or 100 U/ml of IL-1alpha for up to 14 days. The levels of MMPs, TIMPs, uPA, tPA, and PAI-1 expression were estimated by determining the mRNA levels using real-time RT-PCR and by determining protein levels using ELISA. In IL-1alpha cultures, the expression levels of MMP-1, -2, -3, -13, and -14 exceeded that of the control through day 14 of culture, and the expression of MMPs increased markedly from the proliferative to the later stages of culture. The TIMP-1, -2, and -3 expression levels increased from the initial to the proliferative stages of culture. The expression of tPA increased greatly during the proliferative stage of culture, and uPA expression increased throughout the culture period, increasing markedly from the proliferative to the later stages of culture. In contrast, PAI-1 expression decreased in the presence of IL-1alpha through day 14. These results suggest that IL-1alpha stimulate bone matrix turnover by increasing MMPs, tPA, and uPA production and decreasing PAI-1 production by osteoblasts, and incline the turnover to the resolution.

Surface-associated material from Porphyromonas gingivalis stimulates the release of nitric oxide by inducing expression of inducible nitric oxide synthase

The purpose of this study was to examine the effects of surface-associated material (SAM) from Porphyromonas gingivalis, a major cause of inflammatory periodontal disease, on the production of nitric oxide (NO) and expression of inducible nitric oxide synthase (iNOS) in the murine macrophage cell line RAW264.7. We also attempted to throw light on the signaling mechanisms involved in P. gingivalis SAM-induced NO production. SAM from P. gingivalis 381 was obtained by saline extraction. NO production was assayed by measuring the accumulation of nitrite in culture supernatants. Western blot analysis of iNOS and analysis of reverse transcription-polymerase chain reaction (RT-PCR) products were carried out. We found that P. gingivalis SAM can induce iNOS expression and stimulate the release of NO without additional stimuli and demonstrated an important role of the transcription factor NF-kappaB and microtubule polymerization in NO production. The production of NO required L-arginine, protein tyrosine kinase, and protein kinase C. The ability of P. gingivalis SAM to promote the production of NO may be important in the pathogenesis of inflammatory periodontal disease.

IL-1α stimulates the formation of osteoclast-like cells by increasing M-CSF and PGE2 production and decreasing OPG production by osteoblasts

Interleukin-1alpha (IL-1alpha) is one of the most potent bone-resorbing factors involved in the bone loss that is associated with inflammation. We examined the effect of the inflammatory mediator IL-1alpha on the expression of macrophage colony-stimulating factor (M-CSF), osteoprotegerin (OPG), and prostaglandin E2 (PGE2) in rat osteoblasts, and the indirect effect of IL-1alpha on the formation of osteoclast-like cells. Osteoblasts were cultured in alpha-minimum essential medium containing 10% fetal bovine serum with or without 100 units/ml of IL-1alpha for up to 14 days. The gene and protein expression of M-CSF and OPG were estimated by determining mRNA levels using the real-time polymerase chain reaction and protein levels using Western blot analysis. PGE2 expression was determined using an enzyme-linked immunosorbent assay. The formation of osteoclast-like cells was estimated using tartrate-resistant acid phosphatase (TRAP) staining of osteoclast precursors in culture with conditioned medium from IL-1alpha-treated osteoblasts and the soluble receptor activator of NF-kappaB ligand (RANKL). M-CSF and PGE2 expression in osteoblasts increased markedly in cells cultured with IL-1alpha, whereas OPG expression decreased. The conditioned medium containing M-CSF and PGE2 produced by IL-1alpha-treated osteoblasts and soluble RANKL increased the TRAP staining of osteoclast precursors. These results suggest that IL-1alpha stimulated the formation of osteoclast-like cells via an increase in M-CSF and PGE2 production, and a decrease in OPG production by osteoblasts.

IL-1alpha affects mineralized nodule formation by rat osteoblasts

The present study was conducted to determine the effect of the inflammatory mediator interleukin 1alpha (IL-1alpha) on osteogenesis using rat osteoblasts. We examined the effect of IL-1alpha on cell proliferation, alkaline phosphatase (ALPase) activity, mineralized nodule formation, and the expression of extracellular matrix proteins in rat osteosarcoma cell lines. The cells were cultured with alpha-minimum essential medium containing 10% fetal bovine serum with and without 0, 1, 10, and 100 units/ml of IL-1alpha for up to 14 days. The mineralized nodule formation was examined by alizarin red staining, and the calcium content in mineralized nodules was determined using a Calcium C-Test kit. The expression of extracellular matrix proteins was estimated by determining levels of mRNAs using the semiquantitative reverse transcription-polymerase chain reaction. The mineralized nodule formation and the calcium content in mineralized nodules were remarkably suppressed by IL-1alpha after 5 days of culture. The ALPase activity decreased in a dose-dependent manner in the presence of IL-1alpha after 7 days of culture. The expression of type I collagen was decreased after 3 days of culture with IL-1alpha. The expression of bone sialoprotein was slightly decreased at days 3 and 5, and the expression of osteopontin was increased at days 3, 5, and 7 of culture with IL-1alpha. These results suggest that IL-1alpha suppresses osteogenesis through a decrease in ALPase and type I collagen production by osteoblasts.

Oral microbial heat-shock proteins and their potential contributions to infections

The oral cavity is a complex ecosystem in which several hundred microbial species normally cohabit harmoniously. However, under certain special conditions, the growth of some micro-organisms with a pathogenic potential is promoted, leading to infections such as dental caries, periodontal disease, and stomatitis. The physiology and pathogenic properties of micro-organisms are influenced by modifications in environmental conditions that lead to the synthesis of specific proteins known as the heat-shock proteins (HSPs). HSPs are families of highly conserved proteins whose main role is to allow micro-organisms to survive under stress conditions. HSPs act as molecular chaperones in the assembly and folding of proteins, and as proteases when damaged or toxic proteins have to be degraded. Several pathological functions have been associated with these proteins. Many HSPs of oral micro-organisms, particularly periodontopathogens, have been identified, and some of their properties-including location, cytotoxicity, and amino acid sequence homology with other HSPs-have been reported. Since these proteins are immunodominant antigens in many human pathogens, studies have recently focused on the potential contributions of HSPs to oral diseases. The cytotoxicity of some bacterial HSPs may contribute to tissue destruction, whereas the presence of common epitopes in host proteins and microbial HSPs may lead to autoimmune responses. Here, we review the current knowledge regarding HSPs produced by oral micro-organisms and discuss their possible contributions to the pathogenesis of oral infections.

Prevalence of cytolethal distending toxin production in periodontopathogenic bacteria

Cytolethal distending toxin (CDT) is a newly identified virulence factor produced by several pathogenic bacteria implicated in chronic infection. Seventy three strains of periodontopathogenic bacteria were examined for the production of CDT by a HeLa cell bioassay and for the presence of the cdt gene by PCR with degenerative oligonucleotide primers, which were designed based on various regions of the Escherichia coli and Campylobacter cdtB genes, which have been successfully used for the identification and cloning of cdtABC genes from Actinobacillus actinomycetemcomitans Y4 (M. Sugai et al., Infect. Immun. 66:5008-5019, 1998). CDT activity was found in culture supernatants of 40 of 45 tested A. actinomycetemcomintans strains, but the titer of the toxin varied considerably among these strains. PCR experiments indicated the presence of Y4-type cdt sequences in these strains, but the rest of A. actinomycetemcomitans were negative by PCR amplification and also by Southern blot analysis for the cdtABC gene. In the 40 CDT-positive strains, Southern hybridization with HindIII-digested genomic DNA revealed that there are at least 6 restriction fragment length polymorphism types. This suggests that the cdtABC flanking region is highly polymorphic, which may partly explain the variability of the CDT activity in the culture supernatants. The rest of tested strains of periodontopathogenic bacteria did not have detectable CDT production by the HeLa cell assay and for cdtB sequences by PCR analysis under our experimental conditions. These results strongly suggested that CDT is a unique toxin predominantly produced by A. actinomycetemcomitans among periodontopathogenic bacteria.

Inhibited proliferation of human periodontal ligament cells and gingival fibroblasts by Actinobacillus actinomycetemcomitans: involvement of the cytolethal distending toxin

Actinobacillus actinomycetemcomitans can inhibit fibroblast proliferation. The objective of this study was to characterize the early proliferative responses of human periodontal ligament cells (PDLC) and gingival fibroblasts (GF) to A. actinomycetemcomitans components and to investigate the possible involvement of the cytolethal distending toxin (cdt) produced by this bacterium. The PDLC and GF were challenged with surface components of A. actinomycetemcomitans. Both DNA and protein synthesis as well as cell lysis or apoptosis were assayed for a 6-h period after addition of the bacterial extract. Unlike the controls, inhibition of DNA synthesis had already occurred in the challenged cells at the end of the initial 3- to 6-h period. No lysis or apoptosis was detected, and the total protein synthesis remained unaffected. The persistence of the effect on cell growth was confirmed after a 72-h period of challenge, during which the cells remained viable but exhibited an elongated and distended cell body. No significant differences were observed between PDLC and GF. When a cdt-knockout strain of A. actinomycetemcomitans was used almost no inhibitory effect on cell proliferation was observed. It was concluded that A. actinomycetemcomitans causes a non-lethal inhibition of proliferation in PDLC and GF as a result of an early arrest of DNA synthesis. Cytolethal distending toxin is responsible for most of this effect. This bacterial property may compromise tissue homeostasis in the periodontium.

Protective humoral immunity induced by surface-associated material from Actinobacillus actinomycetemcomitans in mice

The aim of the present study was to determine the role of antibodies specific to anti-surface-associated material from Actinobacillus actinomycetemcomitans (anti-SAM-Aa) in an infection induced by this periodontopathogen in mice. When SAM-Aa obtained by saline extraction of A. actinomycetemcomitans Y4 was separated on one-dimensional gel electrophoresis, this constituent contained antigen fragments with molecular weights ranging from 14000 to 79000. Immunoblot analysis revealed that increased antigen dose/immunization resulted in increased numbers of antigen epitopes recognized by serum antibodies of the immunized mice. Rapid healing of the primary lesions and high levels of specific IgG antibodies after challenge with live A. actinomycetemcomitans were seen in the immunized mice, especially at the highest-dose level of 100 microg/immunization. Transfer of SAM-Aa-immunized, but not the SAM-Aa-immunized and adsorbed, serum prior to challenge with live bacteria led to rapid healing of the lesions in the recipient mice. Increased phagocytosis of A. actinomycetemcomitans by murine macrophages (RAW264.7 cells) was observed when this periodontopathogen was opsonized by the SAM-Aa-immunized, but not SAM-Aa-immunized and adsorbed, serum. These results suggest that in mice, SAM-Aa antigens may induce protective antibodies by acting, at least, as an opsonin against challenge with live A. actinomycetemcomitans.

Analysis of the effect of changing environmental conditions on the expression patterns of exported surface-associated proteins of the oral pathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans has been specifically implicated in the aetiology of one or more of the periodontal diseases, conditions in which inflammation of the gums is associated with destruction of the alveolar bone supporting the teeth. In these diseases there is loss of attachment of the gums (gingivae) to the teeth forming a periodontal pocket. The microenvironment of this pocket is extremely complex and it is likely that there will be substantial variation in the environmental conditions operating in this habitat. The aim of the current investigation was to study the effect of disease-relevant environmental factors on the production and release of secreted surface- associated proteins of A. actinomycetemcomitans. These secreted proteins contain many of the virulence determinants of this organism. A range of environmental conditions were investigated: growth in a CO(2)-enriched aerobic atmosphere vs anaerobic growth, presence of serum or blood, biofilm vs planktonic mode of growth and iron depletion. Differential expression of a number of the secreted surface-associated proteins was observed under different growth conditions and these included the glycolytic enzyme triose phosphate isomerase. An ability to adapt to prevailing environmental conditions may facilitate the survival of the organism in the changing microIenvironment of the periodontal pocket.

Large-scale early in vitro response to actinobacillus actinomycetemcomitans suggests superantigenic activation of T-cells

The mode of T-cell response to Actinobacillus actinomycetemcomitans is largely unknown. The present study sought to investigate the hypothesis that A. actinomycetemcomitans expresses superantigens, capable of antigen-non-specific T-cell activation. To that end, peripheral blood mononuclear cells were stimulated with A. actinomycetemcomitans, and T-cell expression of the early activation marker, CD69, was determined by flow cytometry. Results showed that A. actinomycetemcomitans activated a large number of T-cells with magnitude similar to that of staphylococcal enterotoxin superantigens. A. actinomycetemcomitans sonicate preferentially activated T-cells expressing Vbeta5.1 and Vbeta8, while the extracellular preparation activated Vbeta5.1+, Vbeta8+, and Vbeta12+ T-cells. T-cell response to A. actinomycetemcomitans was observed in the presence of autologous, as well as heterologous, antigen-presenting cells, suggesting a MHC-non-restricted response. Thus, the in vitro response to A. actinomycetemcomitans is characterized by large-scale T-cell activation in a Vbeta-specific and MHC-non-restricted manner, consistent with the involvement of superantigens.

Evidence for apoptosis of the majority of T cells activated in vitro with Actinobacillus actinomycetemcomitans

Our previous studies had demonstrated that nearly half of all T cells stimulated with Actinobacillus actinomycetemcomitans are activated within a few hours. However, it was not known whether all of these T cells survive. The aim of the present study was to determine whether the T cells activated in response to A. actinomycetemcomitans undergo apoptosis. To that end, peripheral blood mononuclear cells were cultured at different time points in the presence of A. actinomycetemcomitans. Flow cytometric analysis demonstrated that, following exposure to a preparation of A. actinomycetemcomitans, T cells progressively externalized their plasma membrane phosphatidylserine, as measured by annexin V binding. Approximately half of all T cells bound annexin V by 96 h. During this period, Annexin V-positive T cells also incorporated propidium iodide suggesting loss of membrane integrity. The externalization of phosphatidylserine occurred at a higher rate among activated (CD69+) T cells, where roughly two-thirds became Annexin V-positive. Flow cytometric analysis also demonstrated shrinkage of the Annexin V-positive and propidium iodide-positive T cells. The data presented here provides evidence for the induction of apoptosis among the majority of the T cells responding to A. actinomycetemcomitans.

Control of the human cell cycle by a bacterial protein, gapstatin

The oral gram-negative bacterium Actinobacillus actinomycetemcomitans is a major pathogen in human periodontal disease. Saline extraction releases a range of surface-associated components from this bacterium, including one which exhibits potent anti-proliferative activity as assessed by its capacity to inhibit DNA synthesis by human and other mammalian cells. Cultures incubated with this bacterial fraction for a prolonged period comprise a high proportion of cells containing a 4n level of DNA. Studies using hydroxyurea-synchronized cultures showed that cells treated with the surface-associated fraction were arrested in the G2 phase of the cell cycle and did not enter mitosis. This G2/M blockade was observed only when the bacterial fraction was added to the cells during early S phase. Our data also suggest that the active bacterial component binds to surface receptors expressed by the human cells and may act by a novel mechanism which involves down-regulation of cyclin B1 expression. The anti-proliferative activity of the bacterial fraction, purified by a combination of ammonium sulphate precipitation, HPLC anion exchange and gel filtration, has been shown to be an 8 kDa protein, which we have called gapstatin. Purified gapstatin was shown to be responsible for the the inhibitory effects of the surface-associated fraction on mammalian cells.

Subcellular localization and cytotoxic activity of the GroEL-like protein isolated from Actinobacillus actinomycetemcomitans

The subcellular locations, ultrastructure, and cytotoxic activity of the GroEL-like protein from Actinobacillus actinomycetemcomitans were investigated. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) clearly indicated that synthesis of the GroEL-like protein is substantially increased after a thermal shock. Analysis of the purified native GroEL-like protein by transmission electron microscopy revealed the typical 14-mer cylindrical molecule, which had a diameter of about 12 nm. A. actinomycetemcomitans cells grown at 35 degreesC and heat shocked at 43 degreesC were fractionated, and fractions were separated by SDS-PAGE and analyzed by Western immunoblotting using antibodies to GroEL- and DnaK-like proteins. The GroEL-like protein was found in both the soluble and membrane fractions, whereas the DnaK-like protein was mostly found in the cytoplasm. An increase in specific proteins, including the GroEL- and DnaK-like proteins, was found in heat-shocked cells. The subcellular localization of the GroEL-like protein was examined by immunoelectron microscopy of whole cells. More GroEL-like protein was detected in stressed cells than in unstressed cells, and most of it was found not directly associated with outer membranes but rather in extracellular material. The native GroEL-like protein was assessed for cytotoxic activities. The GroEL-like protein increased the proliferation of periodontal ligament epithelial cells at concentrations between 0.4 and 1.0 microgram/ml. The number of cells in the culture decreased significantly at higher concentrations. A cell viability assay using HaCaT epithelial cells indicated that the GroEL-like protein was strongly toxic for the cells. These studies suggest the extracellular nature of the GroEL-like protein and its putative role in disease initiation.

The cell cycle-specific growth-inhibitory factor produced by Actinobacillus actinomycetemcomitans is a cytolethal distending toxin

Actinobacillus actinomycetemcomitans has been shown to produce a soluble cytotoxic factor(s) distinct from leukotoxin. We have identified in A. actinomycetemcomitans Y4 a cluster of genes encoding a cytolethal distending toxin (CDT). This new member of the CDT family is similar to the CDT produced by Haemophilus ducreyi. The CDT from A. actinomycetemcomitans was produced in Escherichia coli and was able to induce cell distension, growth arrest in G2/M phase, nucleus swelling, and chromatin fragmentation in HeLa cells. The three proteins, CDTA, -B and -C, encoded by the cdt locus were all required for toxin activity. Antiserum raised against recombinant CDTC completely inhibited the cytotoxic activity of culture supernatant and cell homogenate fractions of A. actinomycetemcomitans Y4. These results strongly suggest that the CDT is responsible for the cytotoxic activity present in the culture supernatant and cell homogenate fractions of A. actinomycetemcomitans Y4. This CDT is a new putative virulence factor of A. actinomycetemcomitans and may play a role in the pathogenesis of periodontal diseases.

Porphyromonas gingivalis reduces mitogenic and chemotactic responses of human periodontal ligament cells to platelet-derived growth factor in vitro

The effects of a sonicated Porphyromonas gingivalis ATCC 33277 protein extract on the mitogenic and chemotactic responses of human periodontal ligament (PDL) cells to the recombinant human platelet-derived growth factor-BB homodimer (PDGF-BB) were examined in vitro. Proliferation of PDL cells was inhibited by P. gingivalis extract at concentrations higher than 10 micrograms/mL protein. At 100 micrograms/mL of P. gingivalis extract, cells did not proliferate. DNA synthesis in PDL cells, as revealed by [3H]-thymidine incorporation, was also inhibited by approximately 50% in the presence of 50 micrograms/mL P. gingivalis extract for 24 hours. In contrast, PDGF-BB at 1 ng/mL enhanced DNA synthesis in PDL cells, followed by maximum enhancement at concentrations higher than 10 ng/mL PDGF-BB. However, this mitogenic response to PDGF-BB was markedly reduced in the presence of 20 micrograms/mL of P. gingivalis extract and did not reach the maximum level even if PDGF-BB concentrations were increased to 250 ng/mL. PDL cells exhibited a chemotactic response to PDGF-BB at 1 ng/mL, which was also inhibited by pretreatment of the cells with P. gingivalis extract at 10 to 50 micrograms/mL. Scatchard analysis of a [125I]-PDGF binding assay demonstrated that PDL cells have both high and low PDGF binding affinity sites. Treatment of the cells with P. gingivalis extract decreased the number of PDGF-binding sites to approximately 35% of the control level, while it caused only a slight change in the affinities of both types of binding site. These results indicated that the P. gingivalis extract reduced mitogenic and chemotactic responses of human PDL cells, possibly through mechanisms involving a decrease in PDGF-binding capacity of these cells. Due to this inhibitory effect of P. gingivalis, the normal levels of PDGF in periodontal lesions may not be sufficient to promote periodontal regeneration through activation of PDL cell proliferation and migration. Therefore, the therapeutic use of PDGF-BB, as a supplement to pre-existing PDGF and as an adjunct, while also eliminating P. gingivalis from periodontal lesions, would help periodontal tissue regeneration.

Alterations in phagocyte function and periodontal infection

A review of phagocytic cells-polymorphonuclear leukocytes and monocytes-in the inflammatory process is presented. Examples of phagocyte defect-related pathology serve as a framework for understanding the role of these cells in periodontal infection. The role of alterations in neutrophil function in localized juvenile periodontitis is presented as a model system for understanding periodontal pathology as a result of host-related functional abnormalities. Two topical alternative hypotheses for periodontal breakdown are presented in which macrophage control of the chronic lesion is altered by an absence of T cells or the influence of bacterial superantigens.

Bacterially induced bone destruction: mechanisms and misconceptions

Normal bone remodelling requires the coordinated regulation of the genesis and activity of osteoblast and osteoclast lineages. Any interference with these integrated cellular systems can result in dysregulation of remodelling with the consequent loss of bone matrix. Bacteria are important causes of bone pathology in common conditions such as periodontitis, dental cysts, bacterial arthritis, and osteomyelitis. It is now established that many of the bacteria implicated in bone diseases contain or produce molecules with potent effects on bone cells. Some of these molecules, such as components of the gram-positive cell walls (lipoteichoic acids), are weak stimulators of bone resorption in vitro, while others (PMT, cpn60) are as active as the most active mammalian osteolytic factors such as cytokines like IL-1 and TNF. The complexity of the integration of bone cell lineage development means that there are still question marks over the mechanism of action of many well-known bone-modulatory molecules such as parathyroid hormone. The key questions which must be asked of the now-recognized bacterial bone-modulatory molecules are as follows: (i) what cell population do they bind to, (ii) what is the nature of the receptor and postreceptor events, and (iii) is their action direct or dependent on the induction of secondary extracellular bone-modulating factors such as cytokines, eicosanoids, etc. In the case of LPS, this ubiquitous gram-negative polymer probably binds to osteoblasts or other cells in bone through the CD14 receptor and stimulates them to release cytokines and eicosanoids which then induce the recruitment and activation of osteoclasts. This explains the inhibitor effects of nonsteroidal and anticytokine agents on LPS-induced bone resorption. However, other bacterial factors such as the potent toxin PMT may act by blocking the normal maturation pathway of the osteoblast lineage, thus inducing dysregulation in the tightly regulated process of resorption and replacement of bone matrix. At the present time, it is not possible to define a general mechanism by which bacteria promote loss of bone matrix. Many bacteria are capable of stimulating bone matrix loss, and the information available would suggest that each organism possesses different factors which interact with bone in different ways. With the rapid increase in antibiotic resistance, particularly with Staphylococcus aureus and M. tuberculosis, organisms responsible for much bone pathology in developed countries only two generations ago, we would urge that much greater attention should be focused on the problem of bacterially induced bone remodelling in order to define pathogenetic mechanisms which could be therapeutic targets for the development of new treatment modalities.

The role of endotoxin and cytokines in the pathogenesis of odontogenic cysts

Odontogenic cysts arise from tooth-forming epithelial residues. The stimulus for the formation of radicular cysts is thought to be endotoxin released from the infected necrotic tooth pulp. However, in keratocysts and follicular cysts, such a stimulus is not present. In order to investigate what drives the cyst epithelium to proliferate, explant media and fluids from 16 radicular cysts, eight keratocysts and seven follicular cysts and explant media from four specimens of non-inflamed gingival tissue were examined for the presence of endotoxin and cytokines. Cyst fluids were also cultured for 72 h in anaerobic and aerobic conditions to detect micro-organisms. Endotoxin from three different bacteria, cytokines [interleukin-(IL) 1 alpha, IL-1 beta and IL-6] as well as prostaglandin E2 (PGE2) were tested in an epithelial cell-proliferation assay. As the cyst epithelium is supported by a connective tissue capsule, the effect of fibroblast culture media on epithelial cell proliferation was also investigated. The results showed significantly higher concentrations of endotoxin in radicular cyst fluid than in the keratocyst or the follicular cyst. None of the cyst fluids contained micro-organisms. Immunoassays demonstrated the presence of IL-1 alpha and -6 in all fluids and explants tested; IL-1 beta was only found in the inflammatory radicular cysts. However, reverse transcriptase-polymerase chain reaction showed that mRNAs for IL-1 alpha, -1 beta and -6 were present in all cyst types. Proliferation studies indicated that endotoxin and the cytokines had a mitogenic effect on epithelia at low concentrations; PGE2 had very little effect at low concentrations, and had an inhibitory effect at high concentrations. Cyst fibroblast culture media had a mitogenic effect on the epithelia that was enhanced by the presence of endotoxin.

Comparison of the pro-inflammatory cytokine-stimulating activity of the surface-associated proteins of periodontopathic bacteria

Saline extraction of the periodontopathic bacterium, Actinobacillus actinomycetemcomitans, releases surface-associated material (SAM), a complex mixture of proteins and carbohydrates with potent biological actions on isolated bone and on various mammalian cell populations. In this study, the relative ability of the SAM from 5 organisms, implicated in the pathology of periodontal disease, to stimulate human mesenchymal and myelomonocytic cells to synthesize the proinflammatory cytokines - interleukin (IL)-1 beta, IL-6 and tumour necrosis factor (TNF)alpha has been investigated. The bacteria investigated were Actinobacillus actinomycetemcomitans, Eikenella corrodens, Porphyromonas gingivalis, Prevotella intermedia and Campylobacter rectus. Human cells were exposed to a four log order range of concentrations of the SAM, or of Escherichia coli lipopolysaccharide, to provide full agonist dose responses in order to allow comparison of the potency and efficacy of each SAM. All SAMs demonstrated the capacity to stimulate human gingival fibroblasts (HGFs), human peripheral blood mononuclear cells (PBMCs) or the myelomonocytic cell line - Mono-Mac-6 to release one or all of the cytokines assayed. Activity was heat- and trypsin-sensitive suggesting that the active components were proteinaceous. However, there were substantial differences in the potency and efficacy of each SAM when compared on a concentration basis (w/v). The most active SAM was from A. actinomycetemcomitans with those from E. corrodens and P. gingivalis being slightly less active. The least active cytokine-stimulating SAMs were from C. rectus and Pr. intermedia. One major difference between the SAMs and E. coli LPS was the inability of the former to stimulate HGFs to release IL-1 beta or TNF alpha although they could stimulate PBMCs to release these cytokines. This may have relevance to the pathology of the periodontal diseases.

Immunosuppressive factor from Actinobacillus actinomycetemcomitans down regulates cytokine production

A cytoplasmic soluble fraction of Actinobacillus actinomycetemcomitans Y4 was isolated and characterized as suppressing mitogen-stimulated proliferation of and cytokine production by C3H/HeN mouse splenic T cells. This factor, designated suppressive factor 1 (SF1), was isolated from the supernatant of sonicated whole bacteria and purified by Q-Sepharose Fast Flow column chromatography, DEAE-Sepharose Fast Flow column chromatography, hydroxyapatite high-pressure liquid chromatography (HPLC), and Protein Pack 300 & 125 gel filtration HPLC. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the purified SF1 migrated as a single band corresponding to a molecular mass of 14 kDa. This molecule was protease labile, heat resistant, and noncytotoxic. N'-terminal sequence analysis revealed no homology with any known peptides of periodontopathic bacteria or with any host-derived growth factors. Purified SF1 suppressed the proliferation of mouse splenic T cells which had been stimulated with concanavalin A, as well as suppressing the production of interleukin-2 (IL-2), gamma interferon, IL-4, and IL-5 from CD4+ T cells as 0.1 microgram/ml or more. These data suggest that SF1 produced by the periodontal pathogen A. actinomycetemcomitans functions as a virulence factor by down regulating T-cell proliferation and cytokine production at local defense sites.

Virulence factors of Actinobacillus actinomycetemcomitans relevant to the pathogenesis of inflammatory periodontal diseases

There is strong evidence implicating Actinobacillus actinomycetemcomitans as the causative agent of localised juvenile periodontitis (LJP), a disease characterised by rapid destruction of the tooth-supporting tissues. This organism possesses a large number of virulence factors with a wide range of activities which enable it to colonise the oral cavity, invade periodontal tissues, evade host defences, initiate connective tissue destruction and interfere with tissue repair. Adhesion to epithelial and tooth surfaces is dependent on the presence of surface proteins and structures such as microvesicles and fimbriae. Invasion has been demonstrated in vivo and in vitro although the mechanisms involved are poorly understood. The organism has a number of means of evading host defences which include: (i) inhibiting poloymorphonuclear leukocyte (PMN) chemotaxis; (ii) killing PMNs and monocytes; (iii) producing immunosuppressive factors; (iv) secreting proteases capable of cleaving IgG; and (v) producing Fc-binding proteins. Surface components of A. actinomycetemcomitans are potent stimulators of bone resorption and can induce the release of a range of cytokines which can initiate tissue destruction. A number of surface components can also inhibit the proliferation of fibroblasts and their production of components of the extracellular matrix. Little is known, however, regarding the way in which these factors operate in vivo to produce the pathological features of the disease.

The potent bone-resorbing mediator of Actinobacillus actinomycetemcomitans is homologous to the molecular chaperone GroEL

Actinobacillus actinomycetemcomitans is a Gram-negative bacterium implicated in the pathology of localized juvenile periodontitis, a condition involving rapid destruction of alveolar bone. We have established that gentle extraction of this bacterium in saline releases a proteinaceous fraction (which we have termed surface-associated material [SAM] which has potent osteolytic activity in the murine calvarial bone resorption assay. Fractionation of the SAM has now revealed that activity is associated with a 62-kD protein. This bone-resorbing activity can be blocked by a monoclonal antibody (raised to the whole bacterium) that is claimed to recognize a protein homologous to the Escherichia coli molecular chaperone GroEL. Purification of this bone-resorbing protein to homogeneity has been achieved by a combination of anion exchange, gel filtration, and ATP-affinity chromatography and the NH2-terminal sequence shows > 95% homology to E. coli GroEL. This GroEL homologue is found in the SAM of A. actinomycetemcomitans but is not found in the osteolytically active SAM from other Gram-negative or Gram-positive bacteria. The GroEL protein from E. coli, but not from Mycobacterium tuberculosis and Mycobacterium leprae, also showed activity in the bone resorption assay. We believe this to be the first observation that a molecular chaperone has the capacity to stimulate the breakdown of connective tissue.

Characterization of an antiproliferative surface-associated protein from Actinobacillus actinomycetemcomitans which can be neutralized by sera from a proportion of patients with localized juvenile periodontitis

The gentle agitation of suspensions of Actinobacillus actinomycetemcomitans serotype a, b, or c in saline resulted in the release of a proteinaceous surface-associated material (SAM) which produced a dose-dependent inhibition of tritiated thymidine incorporation by the osteoblast-like cell line MG63 in culture. This cell line was sensitive to low concentrations of SAM (50% inhibitory concentration, 200 ng/ml for serotype c). Immunoglobulin G antibodies to constituents of the SAM were found in the blood of patients with localized juvenile periodontitis (LJP). Sera from 9 of 16 patients with LJP significantly neutralized the antiproliferative activity of the SAM, while sera from 15 controls, with no evidence of periodontal disease, were unable to neutralize this activity. Neutralization was not directly related to the patient's antibody titer to the whole SAM. Characterization of the antiproliferative activity in the SAM demonstrated that it was not cytotoxic and was heat and trypsin sensitive. The active component separated in a well-defined peak in anion-exchange high-performance liquid chromatography (HPLC) which, when further analyzed by size exclusion HPLC, revealed a single active peak, which had an apparent molecular mass of approximately 8 kDa. The lipopolysaccharide from A. actinomycetemcomitans was only weakly active. SAM from Porphyromonas gingivalis W50 and Eikenella corrodens NCTC 10596 did not exhibit any antiproliferative activity with this cell line, even at concentrations as high as 10 micrograms/ml. This study has shown that SAM from A. actinomycetemcomitans contains a potent antiproliferative protein whose activity can be neutralized by antibodies in the sera from some patients with LJP.

Modulins: a new class of cytokine-inducing, pro-inflammatory bacterial virulence factor

Despite the fact that the inflammatory and immune responses have evolved to combat microorganisms, the present generation of inflammation researchers has evinced relatively little interest, with the exception of septic shock, in microbially-induced inflammation. This in spite of the fact that the Gram-negative cell wall constituent, lipopolysaccharide, has been widely used as a tool in inflammation research. The reason for such lack of interest has been due to the therapeutic efficacy of antibiotics which are the treatment of choice for infections and their inflammatory sequelae. However, this is likely to change within the next decade or so, with the relentless increase in the incidence of antibiotic-resistant strains of bacteria. This will return therapy to the stage where clinicians will have to treat the inflammatory symptoms of infection. Many of these symptoms are due to the stimulation of cytokine synthesis. The capacity of bacteria to induce cytokine synthesis has, until the past few years, centred exclusively on lipopolysaccharide. However, it has been established during the past 5-10 years that a range of other molecules, mainly associated with the surface of bacteria, have the capacity to induce cytokine production. Some of these are exquisitely potent stimulators of pro-inflammatory cytokine synthesis. The nature and mechanism of action of these various cytokine-inducing molecules, for which we have devised the name modulins, is the subject of this review. It is clear that bacteria still have many surprises for us, as exemplified by the recent discovery of the role played by Helicobacter pylori in gastritis, gastric ulceration and gastric cancer.

Lipid A-associated proteins from periodontopathogenic bacteria induce interleukin-6 production by human gingival fibroblasts and monocytes

The aim of this study was to determine whether lipid A-associated proteins (LAP) from two periodontopathogenic species of bacteria were able to stimulate interleukin-6 (IL-6) release from human gingival fibroblasts and myelomonocytic cells. LAP and lipopolysaccharide (LPS) were extracted from Porphyromonas gingivalis and Prevotella intermedia and added to cultures of human gingival fibroblasts and mono-mac-6 monocytic cells. Release of IL-6 into the culture supernatants was determined by ELISA. LAP and LPS from Por. gingivalis, but not from Prev. intermedia, stimulated IL-6 release from both cell types in a dose-dependent manner although LPS was less potent than LAP in inducing IL-6 release from the fibroblasts. IL-6 was detectable in cultures of both cell types following stimulation with LAP from Por. gingivalis at a concentration as low as 10 ng/ml. In response to LAP from Prev. intermedia, IL-6 was produced by mono-mac-6 cells but not by fibroblasts. Our results show that bacterial cell wall components other than LPS can induce IL-6 release from cells of the periodontium in vitro. The production of such potent immunomodulatory agents in vivo may contribute to the connective tissue breakdown characteristic of chronic periodontitis.

Comparison of the osteolytic activity of surface-associated proteins of bacteria implicated in periodontal disease

OBJECTIVES

To compare the osteolytic activity of surface-associated material (SAM) and lipid A-associated proteins (LAPs) from periodontopathogenic bacteria.

MATERIALS AND METHODS

Surface-associated material was extracted from the surface and LAPs from the cell walls of a range of periodontopathic bacteria including Actinobacillus actinomycetemcomitans and Eikenella corrodens. These bacterial fractions were assayed to determine their composition and their capacity to induce bone resorption was determined by use of the neonatal murine calvarial bone resorption assay.

RESULTS

The SAMs from E. corrodens and A. actinomycetemcomitans demonstrated bone-resorbing capacity at concentrations as low as 1 ng ml-1 which, given the molecular weights of the active components, is in the picomolar range of activity. In contrast, the SAMs from the other three bacteria were significantly less potent and showed a lower efficacy. The LAPs all showed significant, and similar, capacities to induce bone breakdown.

CONCLUSIONS

This is the first demonstration that LAP from periodontopathic bacteria can stimulate bone degradation. The LAPs from diverse bacteria all produced similar levels of bone-resorbing activity. In contrast, the SAM showed significant differences in potency and in efficacy (maximal stimulation). This may mean that in vivo certain periodontopathic bacteria have significantly more bone-resorbing capacity than others and should be therapeutic targets.

Serum antibody response to surface-associated material from periodontopathogenic bacteria

Saline extracts of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis and Eikenella corrodens contain surface-associated components of these bacteria. It has been shown that these extracts are potent stimulators of bone resorption in vitro. The possibility that the components of these surface-associated materials (SAM) could contribute to the serum immune response in patients with juvenile or adult onset forms of rapidly progressive periodontitis were investigated by direct binding ELISA. Very high titres of serum IgG antibodies to SAM from A. actinomycetemcomitans were detected in patients with localized juvenile periodontitis (LJP). Patients with adult onset rapidly progressive periodontitis (RPP) had significantly raised antibody levels to SAM from P. gingivalis. Both groups of patients had significantly raised levels of antibodies to SAM from E. corrodens compared with control sera. Thus, not only does solubilized SAM have the capacity to induce bone resorption, but it also contributes to the antigenic load on the immune system in LJP and RPP.

Influence of a single application of subgingival chlorhexidine gel or tetracycline paste on the clinical parameters of adult periodontitis patients

The clinical effects of subgingivally placed 1% chlorhexidine gel (w/w) and 40% tetracycline (w/w) paste in periodontal pockets of 22 adult periodontitis patients were studied. The 2 agents were applied following scaling and root planing in pockets exceeding 4 mm. The patients were randomly divided into 3 groups: (a) scaling and root planing (SCRP) only, the control group; (b) corsodyl gel+SCRP; (c) Tetracycline paste+SCRP. Gel or paste were gently applied using a syringe with a blunt needle until the selected pocket was overfilled. Evaluations were made of clinical parameters including the plaque index (PI), gingival index (GI), bleeding index (GI-S), probing pocket depths, probing attachment levels and position of the gingival margin. The results suggested that all the treatment modalities were effective in producing statistically significant improvements in clinical parameters. It was concluded that the conventional treatment modalities were essential in the treatment of periodontal diseases, but in view of the structure of the periodontal pocket and adjacent complex root surface, subgingival drug application in certain cases, might also provide adjunctive improvement.