Generation and degradation of the complement fragment C5a in human serum by Bacteroides gingivalis

The oral microbiome - friend or foe?

The microbiome and the human body constitute an integrated superorganism, which is the result of millions of years of coevolution with mutual adaptation and functional integration, and confers significant benefits for both parties. This evolutionary process has resulted in a highly diverse oral microbiome, which covers the full spectrum of acidogenic, aciduric, inflammatory, and anti-inflammatory properties. The relative proportions of members of the microbiome are affected by factors associated with modern life, such as general diet patterns, sugar consumption, tobacco smoking, oral hygiene, use of antibiotics and other antimicrobials, and vaccines. A perturbed balance in the oral microbiome may result in caries, periodontal disease, or candidiasis, and oral bacteria passively transferred to normally sterile parts of the body may cause extra-oral infections. Nevertheless, it should never be our goal to eliminate the oral microbiome, but rather we have to develop ways to re-establish a harmonious coexistence that is lost because of the modern lifestyle. With regard to oral diseases, this goal can normally be achieved by optimal oral hygiene, exposure to fluoride, reduction of sucrose consumption, stimulation of our innate immune defense, smoking cessation, and control of diabetes.

The RgpA-Kgp proteinase-adhesin complexes of Porphyromonas gingivalis Inactivate the Th2 cytokines interleukin-4 and interleukin-5

The RgpA-Kgp proteinase-adhesin complexes are a primary virulence factor of Porphyromonas gingivalis, a major pathogen in the development of chronic periodontitis. The RgpA-Kgp complexes have been suggested to bias the immune response to a Th2 phenotype in disease by hydrolysis of Th1 cytokines. Here, we show that the RgpA-Kgp complexes hydrolyze and inactivate interleukin-4 (IL-4) and IL-5 under physiologically relevant conditions. Using the IL-4/IL-5-dependent TF1.8 T-cell line, it was found that at equimolar ratios of cytokine to RgpA-Kgp complexes, IL-4 and IL-5 were inactivated in the culture medium. The inactivation of IL-4 and IL-5 was RgpA-Kgp concentration dependent, as at an enzyme-to-cytokine molar ratio of 1:8, the bioactivity of the cytokines was greater than at the higher concentration of RgpA-Kgp of 1:1. Furthermore, inactivation of the cytokines by the RgpA-Kgp complexes was time dependent, as longer preincubation times resulted in lower cytokine activity. IL-5 was found to be slightly more resistant to inactivation than IL-4. Mass spectrometric analyses of IL-4 and IL-5 showed that hydrolysis by RgpA-Kgp complexes was C terminal to Arg and Lys residues of the cytokines. The peptides released indicated that the regions of IL-4 and IL-5 important for bioactivity were being hydrolyzed in the first 15 min of incubation. The ability of the RgpA-Kgp complexes to degrade Th2 cytokines may contribute to immune dysregulation and may play a role in the pathology of chronic periodontitis.

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.

Inhibition of Actinobacillus actinomycetemcomitans leukotoxicity by bacteria from the subgingival flora

Actinobacillus actinomycetemcomitans produces a pore-forming leukotoxin that lyses human polymorphonuclear leukocytes and monocytes. Certain proteolytic bacteria may coexist with A. actinomycetemcomitans in periodontal pockets. We aimed therefore to examine whether oral bacteria can modify the leukotoxicity of A. actinomycetemcomitans. A total of 55 strains representing 45 bacterial species of the subgingival flora were tested. Each strain was incubated with the highly toxic strain of A. actinomycetemcomitans HK 1519 and the leukotoxic activity of the suspension against human polymorphonuclear leukocytes was determined from the activity of the lactate dehydrogenase released upon lysis of the leukocytes. Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Prevotella melaninogenica and Prevotella loeschii inhibited the leukotoxicity of A. actinomycetemcomitans cells as well as the activity of leukotoxin purified from the same strain. The bacterial strains without the ability to block leukotoxic activity also failed to destroy pure leukotoxin even after 5 h of incubation. The proteolytic degradation of leukotoxin by P. gingivalis was mainly dependent on the activity of the enzymes R- and K-gingipains. P. intermedia and P. nigrescens also degraded the leukotoxin by enzymes. The results imply a role of the periodontal microflora in modifying the virulence of A. actinomycetemcomitans by destroying its leukotoxin.

RgpA-Kgp peptide-based immunogens provide protection against Porphyromonas gingivalis challenge in a murine lesion model

Porphyromonas gingivalis, a gram-negative bacterium, has been linked to the onset and progression of periodontitis, a chronic inflammatory disease of the supporting tissues of the teeth. A major virulence factor of P. gingivalis is an extracellular complex of Arg- and Lys-specific proteinases and adhesins designated the RgpA-Kgp complex (formerly the PrtR-PrtK complex). In this study we show that the RgpA-Kgp complex, when used as an immunogen with incomplete Freund adjuvant (IFA), protects against challenge with invasive and noninvasive strains of P. gingivalis in the murine lesion model. We identified a variety of peptide vaccine candidates from the RgpA and Kgp polyprotein sequences that involved the putative active site histidine of both proteinases and five repeat motifs in the adhesin domains of both polyproteins implicated in aggregation and binding to host substrates, designated adhesin-binding motif (ABM) peptides. These peptides were synthesized using standard, solid-phase protocols for 9-fluorenylmethoxy carbonyl chemistry with S-acetylmercaptoacetic acid (SAMA) as the N-terminal residue. The SAMA-peptides were then conjugated to diphtheria toxoid and used with IFA to immunize BALB/c mice. Both active-site peptides and three of the five ABM peptides gave protection (P < 0.005) against challenge with P. gingivalis in the murine lesion model. The three ABM peptide sequences that conferred protection exist within a 100-residue span in the RgpA44 and Kgp39 adhesins of the RgpA-Kgp complex. Protective anti-RgpA-Kgp complex mouse antisera recognized the RgpA27, Kgp39, and RgpA44 adhesins in an immunoblot. Epitope mapping of the RgpA27 adhesin using the protective anti-RgpA-Kgp antisera identified a major protective epitope that mapped immediately N terminal to one of the protective ABM peptides in the 100-residue span in RgpA44 and Kgp39. This identified protective epitope contains clusters of basic residues spatially surrounded by hydrophobic amino acids, a finding which is characteristic of a heparin binding motif.

Porphyrin-mediated binding to hemoglobin by the HA2 domain of cysteine proteinases (gingipains) and hemagglutinins from the periodontal pathogen Porphyromonas gingivalis

Heme binding and uptake are considered fundamental to the growth and virulence of the gram-negative periodontal pathogen Porphyromonas gingivalis. We therefore examined the potential role of the dominant P. gingivalis cysteine proteinases (gingipains) in the acquisition of heme from the environment. A recombinant hemoglobin-binding domain that is conserved between two predominant gingipains (domain HA2) demonstrated tight binding to hemin (Kd = 16 nM), and binding was inhibited by iron-free protoporphyrin IX (Ki = 2.5 microM). Hemoglobin binding to the gingipains and the recombinant HA2 (rHA2) domain (Kd = 2.1 nM) was also inhibited by protoporphyrin IX (Ki = 10 microM), demonstrating an essential interaction between the HA2 domain and the heme moiety in hemoglobin binding. Binding of rHA2 with either hemin, protoporphyrin IX, or hematoporphyrin was abolished by establishing covalent linkage of the protoporphyrin propionic acid side chains to fixed amines, demonstrating specific and directed binding of rHA2 to these protoporphyrins. A monoclonal antibody which recognizes a peptide epitope within the HA2 domain was employed to demonstrate that HA2-associated hemoglobin-binding activity was expressed and released by P. gingivalis cells in a batch culture, in parallel with proteinase activity. Cysteine proteinases from P. gingivalis appear to be multidomain proteins with functions for hemagglutination, erythrocyte lysis, proteolysis, and heme binding, as demonstrated here. Detailed understanding of the biochemical pathways for heme acquisition in P. gingivalis may allow precise targeting of this critical metabolic aspect for periodontal disease prevention.

Involvement of a lysine-specific cysteine proteinase in hemoglobin adsorption and heme accumulation by Porphyromonas gingivalis

The oral anaerobic bacterium Porphyromonas gingivalis, a major pathogen of advanced adult periodontitis, produces a novel class of cysteine proteinases in both cell-associated and secretory forms. A lysine-specific cysteine proteinase (Lys-gingipain, KGP), as well as an arginine-specific cysteine proteinase (Arg-gingipain), is a major trypsin-like proteinase of the organism. Recent studies indicate that the secreted KGP is implicated in the destruction of periodontal tissue and the disruption of host defense mechanisms. In this study, we have constructed a KGP-deficient mutant to determine whether the cell-associated KGP is important for pathophysiology of the organism. Although the mutant retained the strong ability to disrupt the bactericidal activity of polymorphonuclear leukocytes, its hemagglutination activity was reduced to about one-half that observed with the wild-type strain. More important, the mutant did not form black-pigmented colonies on blood agar plates, indicating the defect of hemoglobin adsorption and heme accumulation. Immunoblot analysis showed that the expression of a 19-kDa hemoglobin receptor protein, which is thought to be responsible for hemoglobin binding by the organism, was greatly retarded in this mutant. The mutant also showed a marked decrease in the ability to degrade fibrinogen. These results suggest the possible involvement of KGP in the hemoglobin binding and heme accumulation of the organism and in the bleeding tendency in periodontal pockets.

Construction and characterization of arginine-specific cysteine proteinase (Arg-gingipain)-deficient mutants of Porphyromonas gingivalis. Evidence for significant contribution of Arg-gingipain to virulence

Arginine-specific cysteine proteinase (Arg-gingipain; formerly, argingipain) is one of the major extracellular proteinases produced by the oral anaerobic bacterium Porphyromonas gingivalis. To determine whether Arg-gingipain is important for periodontopathogenicity of the organism, Arg-gingipain-deficient mutants were constructed via gene disruption by use of suicide plasmid systems. First, Southern hybridization analyses suggested that two separate Arg-gingipain-encoding genes designated rgpA and rgpB existed on 12.5- and 7.8-kilobase pair HindIII chromosomal fragments of P. gingivalis ATCC33277, respectively. rgpA and rgpB single mutants were constructed by mobilization of a suicide plasmid. Then, an rgpA rgpB double mutant was isolated by electroporation with a second suicide plasmid. No proteolytic activity for Arg-gingipain was observed in either the cell extract or the culture supernatant of the rgpA rgpB mutant. The chemiluminescence response of polymorphonuclear leukocytes, which is closely related to their bactericidal function, was not inhibited by the culture supernatant of the rgpA rgpA mutant, while the wild type parent showed a significant inhibition of the response. The result suggests that Arg-gingipain is responsible for disruption of the function of polymorphonuclear leukocytes. In addition, the rgpA rgpB double mutations caused a marked decrease in the hemagglutination of P. gingivalis, indicating that a major part of the hemagglutinin activity of the organism is associated with the two genes. These findings demonstrate that Arg-gingipain makes a significant contribution to the virulence of P. gingivalis.

The multiple forms of trypsin-like activity present in various strains of Porphyromonas gingivalis are due to the presence of either Arg-gingipain or Lys-gingipain

Porphyromonas gingivalis contains high concentrations of numerous cysteine proteinases with trypsin-like activity which have been implicated as important virulence factors in adult-onset periodontitis. We have analyzed the subfractions of six P. gingivalis strains for the presence of arginine-X- and lysine-X-specific proteinases (Arg-gingipain [RGP] and Lys-gingipain [KGP]) previously purified from P. gingivalis H66. Western blot (immunoblot) analysis using antibodies produced against RGP and the N-terminal peptides of RGP or the catalytic subunit of KGP indicated that these enzymes are synthesized by the strains studied and exist as multiple molecular mass species. The major forms of RGP were identified as 110-, 95-, 70- to 90-, and 50-kDa proteins, the first two being a complex of the 50-kDa catalytic subunit with hemagglutinins, with or without an added membrane anchorage peptide. The other forms are single-chain enzymes. While the 95- and 50-kDa RGP were found predominantly in culture medium, the 110- and 70- to 90-kDa forms associated with membranous fractions of the bacteria. The predominant form of KGP in all strains was a complex of the 60-kDa catalytic domain with hemagglutinins, and vesicle- and membrane-associated KGP was about 15 kDa larger than the 105-kDa enzyme present in culture media. These data explain the apparent complexity of P. gingivalis proteinases and indicate that in all strains tested there are two identical enzymes, one with arginine-X specificity and the other with lysine-X specificity, which, working in concert, are responsible for the trypsin-like activity associated with this bacterium.

Molecular cloning and structural characterization of the Arg-gingipain proteinase of Porphyromonas gingivalis. Biosynthesis as a proteinase-adhesin polyprotein

The identification of proteinases of Porphyromonas gingivalis that act as virulence factors in periodontal disease has important implications in the study of host-pathogen interactions as well as in the discovery of potential therapeutic and immunoprophylactic agents. We have cloned and characterized a gene that encodes the 50-kDa cysteine proteinase gingipain or Arg-gingipain-1 (RGP-1) described previously (Chen, Z., Potempa, J., Polanowski, A., Wikstrom, M., and Travis, J. (1992) J. Biol. Chem. 267, 18896-18901). Analysis of the amino acid sequence of RGP-1 deduced from the cloned DNA sequence showed that the biosynthesis of this proteinase involves processing of a polyprotein that contains multiple adhesin molecules located at its carboxyl terminus. This finding corroborates previous evidence (Pike R., McGraw, W., Potempa, J., and Travis, J. (1994) J. Biol. Chem. 269, 406-411) that RGP-1 is closely associated with adhesin molecules, and that high molecular weight forms of the proteinase are involved in the binding of erythrocytes.

Pathogenesis of periodontitis: a major arginine-specific cysteine proteinase from Porphyromonas gingivalis induces vascular permeability enhancement through activation of the kallikrein/kinin pathway

To elucidate the mechanism of production of an inflammatory exudate, gingival crevicular fluid (GCF), from periodontal pockets in periodontitis, we examined the vascular permeability enhancement (VPE) activity induced by an arginine-specific cysteine proteinase, Arg-gingipain-1 (RGP-1), produced by a major periopathogenic bacterium, Porphyromonas gingivalis. Intradermal injections into guinea pigs of RGP-1 (> 10(-8) M), or human plasma incubated with RGP-1 (> 10(-9) M), induced VPE in a dose- and activity-dependent manner but with different time courses for the two routes of production. VPE activity induced by RGP-1 was augmented by kininase inhibitors, inhibited by a kallikrein inhibitor and unaffected by an antihistamine drug. The VPE activity in human plasma incubated with RGP-1 also correlated closely with generation of bradykinin (BK). RGP-1 induced 30-40% less VPE activity in Hageman factor-deficient plasma and no VPE in plasma deficient in either prekallikrein (PK) or high molecular weight kininogen (HMWK). After incubation with RGP-1, plasma deficient in PK or HMWK, reconstituted with each missing protein, caused VPE, as did a mixture of purified PK and HMWK, but RGP-1 induced no VPE from HMWK. The VPE of extracts of clinically isolated P. gingivalis were reduced to about 10% by anti-RGP-1-IgG, leupeptin, or tosyl-L-lysine chloromethyl ketone, which paralleled effects observed with RGP-1. These results indicate that RGP-1 is the major VPE factor of P. gingivalis, inducing this activity through PK activation and subsequent BK release, resulting in GCF production at sites of periodontitis caused by infection with this organism.

Activation of serum complement by polysaccharide-containing antigens of Porphyromonas gingivalis

We previously reported that hot aqueous phenol extraction of Porphyromonas gingivalis yields a preparation containing both lipopolysaccharide (LPS) and an antigenically distinct capsular polysaccharide (PS). In the present study, we examined the capacity of phenol-water extracts from a number of strains of P. gingivalis to activate human serum complement. Anticomplementary activity of extracts from two invasive and two noninvasive strains of P. gingivalis was assessed in a sheep erythrocyte hemolytic assay and in an alternative pathway-selective rabbit erythrocyte hemolytic assay. In the sheep erythrocyte assay, extracts from noninvasive strains were found to exhibit greater anticomplementary activity than extracts derived from invasive strains. A phenol-water extract from invasive strain ATCC 53977 was further resolved into its LPS and PS fractions. Whereas isolated LPS from this strain exhibited strong anticomplementary activity, the PS fraction was only weakly active. Phenol-water extracts from three of four strains were found to be potent activators of the alternative pathway, with extracts from the two noninvasive strains being most active. The extract from the remaining strain (ATCC 53977) was a poor activator of the alternative pathway. Further analysis of this extract revealed, however, that the LPS fraction was a potent activator of the alternative pathway, although the PS fraction exhibited negligible activity. The results of this study indicate that phenol-water extracts of invasive and noninvasive strains of P. gingivalis differ in their respective anticomplementary activities, with invasive strains being less active. Although extracts from both invasive and noninvasive strains activated the alternative pathway, this activity appears to be attributable to the LPS, rather than the PS, component.

Chemotaxis and degranulation of polymorphonuclear leukocytes in the presence of sulfide

In polymicrobial infections such as periodontal disease, the polymorphonuclear leukocytes (PMN) may have to work in the absence of oxygen and in the presence of significant levels of hydrogen sulfide. There are conflicting results reported on the chemotactic capacity of PMN under anaerobic conditions. It is not known whether PMN are able to migrate and release the contents of their granules in the presence of sulfide. PMN were exposed to various levels of sulfide and their chemotaxis and degranulation were studied when they were stimulated with N-formyl-methionyl-leucyl-phenylalanine or zymosan-activated serum. Chemotaxis was evaluated with the agarose method. The release of granule markers, lactoferrin and myeloperoxidase, was evaluated with enzyme-linked immunosorbent assay. PMN had similar capacity for chemotaxis under aerobic and anaerobic conditions. The migration of PMN was only to a minor extent inhibited by 1-2 mM sulfide. The release of lactoferrin and myeloperoxidase was the same under aerobic and anaerobic conditions and was not significantly influenced by sulfide. PMN seem to be very well suited to defend the tissue against bacteria under the harsh conditions prevailing in the periodontal pocket.

Comparative studies of three proteases of Porphyromonas gingivalis

Three thiol-activated proteases, designated Qa, Ra, and Sa, in the soluble fraction of the cell extract of Porphyromonas gingivalis ATCC 33277 were purified by combinations of gel filtration, ion exchange chromatography and electrophoresis, and characterized. The molecular weights estimated by gel filtration method were 43 kDa (Sa), 87 kDa (Ra), and 170 kDa (Qa). However, they were found to have the same molecular weight (43 kDa), when estimated by SDS-PAGE, indicating that Sa is a monomeric, Ra is a dimeric and Qa is a tetrameric form. The 3 enzymes showed quite similar biochemical properties, and they could degrade not only the synthetic substrates but immunoglobulins, fibrinogen and albumin.

Inactivation of human serum bactericidal activity by a trypsinlike protease isolated from Porphyromonas gingivalis

A protease was isolated from an outer membrane vesicle preparation of Porphyromonas gingivalis ATCC 33277 and assessed for its ability to inactivate the bactericidal activity of normal human serum. The enzyme, which was activated by reducing agents, was found to be a trypsinlike protease with a molecular mass of approximately 80 kDa. Prior to being tested in the bactericidal assay, pooled human serum was preincubated with the partially purified enzyme. Under conditions in which the trypsinlike protease was activated, a strong reduction of the serum bactericidal activity against Capnocytophaga ochracea was noted. On the other hand, no reduction of the bactericidal action of serum was observed when the serum-protease mixture was preincubated in the presence of an inhibitor of the enzyme. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the protease was shown to degrade immunoglobulins G and M as well as complement factor C3. This study confirms the previous hypothesis that the proteases of P. gingivalis can interfere with the protective action of human serum.

Protective effect of Porphyromonas gingivalis outer membrane vesicles against bactericidal activity of human serum

The present study was undertaken to evaluate the effect of Porphyromonas gingivalis outer membrane vesicles on the bactericidal activity of human serum. Human serum was pretreated with extracellular vesicles and then incubated with a cell suspension of Capnocytophaga ochracea. After 2 h at 37 degrees C, the percent viability of C. ochracea was determined by cultivation on blood agar plates. At a final concentration of 0.3 mg/ml, outer membrane vesicles completely inhibited the serum bactericidal activity against C. ochracea. Boiling the vesicles prevented this inhibition. However, partial inhibition of the serum lethal action was obtained when a higher concentration (1.5 mg/ml) of boiled vesicles was used, which indicates the involvement of both heat-labile and heat-stable components associated with vesicles. Combining vesicles at a suboptimal concentration (0.1 mg/ml) with a reducing agent brought back inhibition of the bactericidal activity, whereas combining vesicles at an optimal concentration (0.3 mg/ml) with a thiol-blocking reagent caused a restoration of the bactericidal activity. When a purified preparation of P. gingivalis lipopolysaccharides was used instead of vesicles, inhibition of the bactericidal activity was also observed. These results indicate that the lipopolysaccharides and the proteolytic enzyme(s) associated with P. gingivalis outer membrane vesicles are likely to represent the heat-stable and the heat-labile components, respectively. It is possible that outer membrane vesicles released by P. gingivalis protect other bacterial species from complement action, thus favoring the pathogenic process of periodontal disease.

The role of complement in periodontal diseases

The complement system has been implicated as both a pathogenic mechanism and a means of protection in periodontal diseases. It is well known that bacteria activate complement; such activation can initiate a number of events, including bacterial opsonization and killing, release of inflammatory agents, and modulation of other immune reactions. Cleavage of complement proteins has been observed in gingival fluids from individuals with periodontal disease and some investigators have observed complement deposition in diseased gingival tissues. Furthermore, a number of bacterial from individuals with periodontal diseases have been found to activate complement in vitro; some of these organisms appear to have the capacity to evade opsonization due to their proteolytic capacity. However, concrete evidence is not yet available that indicates that complement activation occurs in human periodontal disease and is important in either its pathogenesis or in protection against bacterial virulence factors.

Extensive bone loss associated with periapical infection with Bacteroides gingivalis: a case report

A case is presented in which rapid and extensive bone loss occurred around a maxillary molar with periapical infection by Bacteroides gingivalis (Porphyromonas gingivalis). The lesion failed to respond to conventional endodontic therapy. An adjacent vital molar was extracted and an unfavourable periodontal condition occurred despite microbiological investigation and surgery.