Purification, characterization, and sequence analysis of a potential virulence factor from Porphyromonas gingivalis, peptidylarginine deiminase

The initiation and progression of adult-onset periodontitis has been associated with infection of the gingival sulcus by Porphyromonas gingivalis. This organism utilizes a multitude of virulence factors to evade host defenses as it establishes itself as one of the predominant pathogens in periodontal pockets. A feature common to many other oral pathogens is the production of ammonia due to its protective effect during acidic cleansing cycles in the mouth. Additionally, ammonia production by P. gingivalis has been proposed as a virulence factor due to its negative effects on neutrophil function. In this study, we describe the first purification of a peptidylarginine deiminase (PAD) from a prokaryote. PAD exhibits biochemical characteristics and properties that suggest that it may be a virulence agent. PAD deiminates the guanidino group of carboxyl-terminal arginine residues on a variety of peptides, including the vasoregulatory peptide-hormone bradykinin, to yield ammonia and a citrulline residue. The soluble protein has an apparent mass of 46 kDa, while the DNA sequence predicts a full-length protein of 61.7 kDa. PAD is optimally active at 55 degrees C, stable at low pH, and shows the greatest activity above pH 9.0. Interestingly, in the presence of stabilizing factors, PAD is resistant to limited proteolysis and retains significant activity after short-term boiling. We propose that PAD, acting in concert with arginine-specific proteinases from P. gingivalis, promotes the growth of the pathogen in the periodontal pocket, initially by enhancing its survivability and then by assisting the organism in its circumvention of host humoral defenses.

The role of gingipains in the pathogenesis of periodontal disease

Gingipains are trypsin-like cysteine proteinases produced by Porphyromonas gingivalis, a major causative bacterium of adult periodontitis. HRgpA (95 kDa) and RgpB (50 kDa), products of 2 distinct but related genes, rgpA and rgpB, respectively, are specific for Arg-Xaa peptide bonds. Kgp, a product of the kgp gene, is specific for Lys-Xaa bonds. HRgpA and Kgp are non-covalent complexes containing separate catalytic and adhesion/ hemagglutinin domains, while RgpB has only a catalytic domain with a primary structure essentially identical to that of the catalytic subunit of HRgp. HRgpA and RgpB induce vascular permeability enhancement through activation of the kallikrein/kinin pathway and activate the blood coagulation system, which, respectively, are potentially associated with gingival crevicular fluid production and progression of inflammation leading to alveolar bone loss in the periodontitis site. Kgp is the most potent fibrinogen/fibrin degrading enzyme of the 3 gingipains in human plasma and is involved in the bleeding tendency at the diseased gingiva. HRgpA activates coagulation factors and degrades fibrinogen/fibrin more efficiently than RgpB due to the adhesion/hemagglutinin domains, which have affinity for phospholipids and fibrinogen. Gingipains degrade macrophage CD14, thus inhibiting activation of the leukocytes through the lipopolysaccharide (LPS) receptor, and thereby facilitating sustained colonization of P. gingivalis. Gingipains play a role in bacterial housekeeping and infection, including amino acid uptake from host proteins and fimbriae maturation. Based on the important activities of gingipains in the bacterial infection and the pathogenesis of periodontitis, the bacterial proteinases can be targets for periodontal disease therapy. Immunization with RgpB, HRgpA, or a portion of HRgpA catalytic domain attenuated P. gingivalis induced disorders in mice. In addition, a trypsin-like proteinase inhibitor retarded P. gingivalis growth specifically. Gingipains are potent virulence factors of P. gingivalis, and are likely to be associated with the development of periodontitis. It is, therefore, suggested that gingipain inhibition by vaccination and gingipain-specific inhibitors is a useful therapy for adult periodontitis caused by P. gingivalis infection.

Activation of the phosphatidylinositol 3-kinase/Akt pathway contributes to survival of primary epithelial cells infected with the periodontal pathogen Porphyromonas gingivalis

Porphyromonas gingivalis, an important periodontal pathogen, infects primary gingival epithelial cells (GECs). Despite the large number of bacteria that replicate inside the GECs, the host cell remains viable. We demonstrate that P. gingivalis triggers rapid and reversible surface phosphatidylserine exposure through a mechanism requiring caspase activation. However, after 1 day of infection, the bacteria no longer induce phosphatidylserine externalization and instead protect infected cells against apoptosis. Infection exerts its effect at the level of mitochondria, as P. gingivalis also blocks depolarization of the mitochondrial transmembrane potential and cytochrome c release. Interestingly, protein kinase B/Akt is phosphorylated during infection, which can be blocked with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. Suppression of the PI3K/Akt pathway following staurosporine treatment results in mitochondrial-membrane depolarization, cytochrome c release, DNA fragmentation, and increased apoptosis of infected GECs. Thus, P. gingivalis stimulates early surface exposure of phosphatidylserine, which could downmodulate the inflammatory response, while also promoting host cell survival through the PI3K/Akt pathway.

Expression of cytokines and inducible nitric oxide synthase in inflamed gingival tissue

BACKGROUND

Periodontopathic bacteria induce inflammation of periodontal tissues. The cytokines and nitric oxide released in periodontal lesions have been reported to play a protective role in bacterial infection and to relate to the process of inflammation. To clarify the relationship between colonization of periodontopathic bacteria and cytokines, we evaluated profiles of inflammatory cytokines, chemokine, anti-inflammatory cytokines, and inducible nitric oxide synthase (iNOS) and colonization by Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans, which are major pathogens of periodontitis.

METHODS

mRNA expression of cytokines and iNOS in inflamed and healthy gingival tissue was determined using reverse transcription-polymerase chain reaction (RT-PCR), and the relationship between their profiles and the detection of specific bacteria was analyzed.

RESULTS

The relative expression of interleukin (IL)-6 and iNOS mRNAs in periodontal lesions was significantly higher than those in healthy individuals. IL-6 mRNA expression was also significantly higher at bleeding on probing (BOP)-positive sites than at BOP-negative sites. The expressions of IL-1alpha and IL-8 increased, but IL-10 expression decreased at sites where A. actinomycetemcomitans was detected. We found no correlation between the expression of cytokine and iNOS mRNA and infection by P. gingivalis.

CONCLUSIONS

The expression of IL-6 may reflect inflammation in gingival tissue, and iNOS may be involved in the inflammatory process in periodontitis. The presence of A. actinomycetemcomitans or P. gingivalis might relate to the different cytokine profiles of IL-1alpha, IL-8, and IL-10.

Binding of complement inhibitor C4b-binding protein contributes to serum resistance of Porphyromonas gingivalis

The periodontal pathogen Porphyromonas gingivalis is highly resistant to the bactericidal activity of human complement, which is present in the gingival crevicular fluid at 70% of serum concentration. All thirteen clinical and laboratory P. gingivalis strains tested were able to capture the human complement inhibitor C4b-binding protein (C4BP), which may contribute to their serum resistance. Accordingly, in serum deficient of C4BP, it was found that significantly more terminal complement component C9 was deposited on P. gingivalis. Moreover, using purified proteins and various isogenic mutants, we found that the cysteine protease high molecular weight arginine-gingipain A (HRgpA) is a crucial C4BP ligand on the bacterial surface. Binding of C4BP to P. gingivalis appears to be localized to two binding sites: on the complement control protein 1 domain and complement control protein 6 and 7 domains of the alpha-chains. Furthermore, the bacterial binding of C4BP was found to increase with time of culture and a particularly strong binding was observed for large aggregates of bacteria that formed during culture on solid blood agar medium. Taken together, gingipains appear to be a very significant virulence factor not only destroying complement due to proteolytic degradation as we have shown previously, but was also inhibiting complement activation due to their ability to bind the complement inhibitor C4BP.

Interleukin-8 and granulocyte elastase in gingival crevicular fluid in relation to periodontopathogens in untreated adult periodontitis

BACKGROUND

This study aimed to determine the relationships among interleukin (IL)-8 and granulocyte elastase levels in gingival crevicular fluid (GCF) and the concomitant presence of periodontopathogens in untreated adult periodontitis.

METHODS

GCF and subgingival plaque samples were collected from 16 patients with untreated adult periodontitis and 10 healthy control subjects. IL-8 levels were determined by enzyme-linked immunosorbent assay (ELISA). Granulocyte elastase was analyzed with a neutrophilic granulocyte-specific, low molecular weight and chromogenic substrate, L-pyroglutamyl-L-prolyl-L-valine-p-nitroanilide, and the maximal rate of elastase activity (MR-EA) was calculated. Five DNA probes were used to detect the presence of A. actinomycetemcomitans (A.a.), B. forsythus (B.f.), P. gingivalis (P.g.), P. intermedia (P.i.), and T. denticola (T.d.).

RESULTS

Lower IL-8 concentrations and higher granulocyte elastase activities were found in patients than in healthy controls as well as in diseased conditions co-infected with B.f., P.g., P.i., and T.d. as compared to healthy conditions without the target species (P <0.05). IL-8 concentrations were positively correlated with MR-EA levels in the periodontitis conditions co-infected with B.f., P.g., P.i., and T.d. (P <0.05). A wide range of IL-8 concentrations was found among 15 patients when the periodontitis condition was characterized by co-infection with B.f., P.g., P.i., and T.d. MR-EA levels in the high IL-8 group of subjects were significantly higher than those in the low IL-8 group of subjects (P <0.01).

CONCLUSIONS

The present study shows that the local host-bacteria interactions in untreated periodontitis are diverse in terms of the intensity of inflammatory responses measured by IL-8-related granulocyte elastase activity in GCF. This might reflect different phases of the inflammatory response due to shifts in host-bacteria interactions and therefore be indicative of a range of periodontal disease activity levels.

Inducible nitric oxide synthase mediates bone development and P. gingivalis-induced alveolar bone loss

The role of inducible nitric oxide synthase (iNOS) in bone development and bacterially induced periodontal bone loss was examined using mice with targeted mutation of the iNOS gene. Femurs of iNOS KO mice showed 30% and 9% higher bone mineral density compared to wild type (WT) at 4 and 9 weeks of age, respectively. Micro-computed tomography revealed that cortical thickness and cortical bone density is increased in the absence of iNOS, while trabecular bone thickness and bone density remains unchanged. Histochemical analysis using TRAP staining showed that osteoclast numbers are lower by 25% in iNOS KO femurs compared to WT femurs. When bone marrow cells were stimulated with M-CSF and RANKL in vitro, iNOS KO cultures developed 51% fewer TRAP-positive multinuclear cells compared to WT cultures. When similar cultures were grown on dentine discs, resorption pit area was decreased by 54% in iNOS KO cultures. Gene expression studies showed that iNOS expression is induced by M-CSF and RANKL in WT bone marrow cultures, while no iNOS transcript was detected in iNOS KO. No compensatory change was detected in the expression of neuronal or endothelial NOS isoforms. There was no difference in RANK and osteoprotegerin expression between iNOS KO and WT bone marrow cultures after M-CSF and RANKL-treatment, while Traf6 expression was significantly lower in the absence of iNOS. In the alveolar bone of the maxilla, the distance between the cementoenamel junction and the alveolar bone crest was larger in iNOS KO compared to WT mice from 6 to 14 weeks of age, indicating a developmental effect of iNOS in oral tissues. Oral administration of the periodontal pathogen Porphyromonas gingivalis caused alveolar bone loss in the maxilla of WT mice, but failed to do so in iNOS KO mice. Expression of the osteoclast marker cathepsin K was 25% lower in iNOS KO alveolar bone. These data indicate that iNOS promotes bone resorption during bone development as well as after bacterial infection, and that iNOS is an important signal for normal osteoclast differentiation.

A novel kinase function of a nucleoside-diphosphate-kinase homologue in Porphyromonas gingivalis is critical in subversion of host cell apoptosis by targeting heat-shock protein 27

We have previously shown that a homologue of a conserved nucleoside-diphosphate-kinase (Ndk) family of multifunctional enzymes and secreted molecule in Porphyromonas gingivalis can modulate select host molecular pathways including downregulation of reactive-oxygen-species generation to promote bacterial survival in human gingival epithelial cells (GECs). In this study, we describe a novel kinase function for bacterial effector, P. gingivalis-Ndk, in abrogating epithelial cell death by phosphorylating heat-shock protein 27 (HSP27) in GECs. Infection by P. gingivalis was recently suggested to increase phosphorylation of HSP27 in cancer-epithelial cells; however, the mechanism and biological significance of antiapoptotic phospho-HSP27 during infection has never been characterised. Interestingly, using glutathione S-transferase-rNdk pull-down analysed by mass spectrometry, we identified HSP27 in GECs as a strong binder of P. gingivalis-Ndk and further verified using confocal microscopy and ELISA. Therefore, we hypothesised P. gingivalis-Ndk can phosphorylate HSP27 for inhibition of apoptosis in GECs. We further employed P. gingivalis-Ndk protein constructs and an isogenic P. gingivalis-ndk-deficient-mutant strain for functional examination. P. gingivalis-infected GECs displayed significantly increased phospho-HSP27 compared with ndk-deficient-strain during 24 hr infection. Phospho-HSP27 was significantly increased by transfection of GFP-tagged-Ndk into uninfected-GECs, and in vitro phosphorylation assays revealed direct phosphorylation of HSP27 at serines 78 and 82 by P. gingivalis-Ndk. Depletion of HSP27 via siRNA significantly reversed resistance against staurosporine-mediated-apoptosis during infection. Transfection of recombinant P. gingivalis-Ndk protein into GECs substantially decreased staurosporine-induced-apoptosis. Finally, ndk-deficient-mutant strain was unable to inhibit staurosporine-induced Cytochrome C release/Caspase-9 activation. Thus, we show for the first time the phosphorylation of HSP27 by a bacterial effector-P. gingivalis-Ndk-and a novel function of Ndks that is directly involved in inhibition of host cell apoptosis and the subsequent bacterial survival.

Role of protease-activated receptor-2 in inflammation, and its possible implications as a putative mediator of periodontitis

Proteinase-activated receptor-2 (PAR2) belongs to a novel subfamily of G-protein-coupled receptors with seven-transmembrane domains. This receptor is widely distributed throughout the body and seems to be importantly involved in inflammatory processes. PAR2 can be activated by serine proteases such as trypsin, mast cell tryptase, and bacterial proteases, such as gingipain produced by Porphyromonas gingivalis. This review describes the current stage of knowledge of the possible mechanisms that link PAR2 activation with periodontal disease, and proposes future therapeutic strategies to modulate the host response in the treatment of periodontitis.

Effect of Porphyromonas gingivalis on epithelial cell MMP-9 type IV collagenase production

Porphyromonas gingivalis is reportedly capable of stimulating the expression of host cell matrix metalloproteinases (MMP), contributing to tissue destruction. However, the impact of this bacterium on specific molecules remains to be determined. In this study, we evaluate the effect of P. gingivalis on regulation of MMP-9 expression in human gingival epithelial cells (HGEC). Various inocula of P. gingivalis were added to cultures of HGEC. The effects of live bacteria, heat-killed bacteria, and outer membrane extract were analyzed. MMP-9 secretion by HGEC was evaluated by enzyme-linked immunosorbent assay. For inocula smaller than one bacterium per cell, the quantity of MMP-9 secreted by HGEC was increased in comparison to control conditions. For inocula from 2.5 to 250 bacteria per cell, an inhibition of MMP-9 secretion in a dose-response fashion was observed, with a maximum reduction (ranging from 80 to 95% in five experiments) at 50 bacteria per cell. Gelatin zymograms confirmed the decrease in MMP-9 secretion. A band of 83 kDa, corresponding to activated enzyme, was present for inocula of 0.5 to 50 bacteria. Inhibition took place without any alteration of epithelial cell viability. Heat-killed bacteria and outer membrane extract also provoked proenzyme activation but did not inhibit MMP-9 secretion. These results demonstrate a direct effect of P. gingivalis on HGEC, suggesting a specific action on the collagen renewal process at the interface between the epithelium and connective tissue.

The effect of chemical inhibition of matrix metalloproteinases on the size of experimentally induced apical periodontitis

AIM

To determine the effect of matrix metalloproteinase (MMP) inhibition on periapical lesion formation in a rat model.

METHODOLOGY

The pulp chambers of mandibular fist molars of adult SD rats were exposed to be infected by oral microbes. The experimental group was fed 20 mg kg(-1) MMP-inhibitor chemically modified tetracycline-3 (CMT-3) daily in an oral gavage and the controls were fed the vehicle. After 2 and 4 weeks, the mandibles (n = 10 in both groups at both times) were radiographed, decalcified and subjected to histological analysis. Extension of necrosis in first molar distal root canals was measured from the histological sections, and periapical lesion sizes in the same roots were determined from radiographs and histological sections. Mann-Whitney U-test was used for the statistical analysis.

RESULTS

There was a statistically significant difference in the extension of necrosis in root canals between 2 and 4 weeks in the control group (P < 0.05), but not with MMP inhibition. Radiographically, MMP inhibition increased the periapical lesion size by 70% and 34% after 2 and 4 weeks respectively (P < 0.05 in after 2 weeks). In histological measurements, lesion size increased with MMP inhibition by 26% and 8% after 2 and 4 weeks respectively.

CONCLUSIONS

MMP inhibition affects pulpal and periapical inflammation, increasing the rate of spreading of necrosis in root canals and the rate of periapical lesion formation.

Endogenous acid ceramidase protects epithelial cells from Porphyromonas gingivalis-induced inflammation in vitro

Ceramidases are a group of enzymes that degrade pro-inflammatory ceramide by cleaving a fatty acid to form anti-inflammatory sphingosine lipid. Thus far, acid, neutral and alkaline ceramidase isozymes have been described. However, the expression patterns of ceramidase isoforms as well as their role in periodontal disease pathogenesis remain unknown. In this study, expression patterns of ceramidase isoforms were quantified by real-time PCR and immunohistochemistry in gingival samples of patients with periodontitis and healthy subjects, as well as in EpiGingivalTM-3D culture and OBA-9 gingival epithelial cells both of which were stimulated with or without the presence of live Porphyromonas gingivalis (ATCC 33277 strain). A significantly lower level of acid ceramidase expression was detected in gingival tissues from periodontal patients compared to those from healthy subjects. In addition, acid-ceramidase expression in EpiGingival™ 3D culture and OBA-9 cells was suppressed by stimulation with P. gingivalis in vitro. No significant fluctuation was detected for neutral or alkaline ceramidases in either gingival samples or cell cultures. Next, to elucidate the role of acid ceramidase in P. gingivalis-induced inflammation in vitro, OBA-9 cells were transduced with adenoviral vector expressing the human acid ceramidase (Ad-ASAH1) gene or control adenoviral vector (Ad-control). In response to stimulation with P. gingivalis, ASAH1-over-expressing OBA-9 cells showed significantly lower mRNA expressions of caspase-3 as well as the percentage of Annexin V-positive cells, when compared with OBA-9 cells transduced with Ad-control vector. Furthermore, in response to stimulation with P. gingivalis, ASAH1-over-expressing OBA-9 cells produced less TNF-α, IL-6, and IL1β pro-inflammatory cytokines than observed in OBA-9 cells transduced with Ad-control vector. Collectively, our data show the novel discovery of anti-inflammatory and anti-apoptotic effects of acid ceramidase in host cells exposed to periodontal bacteria, and the attenuation of the expression of host-protective acid ceramidase in periodontal lesions.

The role of bacterial and host proteinases in periodontal disease

It is abundantly obvious that the uncontrolled degradation and/or activation of host defense pathways is the major pathway by which the periodontal pathogen P. gingivalis promotes its growth and proliferation. By being able to shed host receptors, degrade cytokines, and activate coagulation, complement, and kallikrein/kinin pathways it is clear that this organism has found a mechanism(s) to evade host defense and at the same time develop a system for cannibalizing host proteins for its own nutritional usage (Fig 2). Thus, it seems only logical that the development of inhibitors against these bacterial proteinases would be a useful method for negating their activities and making such pathogens more susceptible to attack by host phagocyte cells. In this respect, the structure of the truncated form of RGP has just been elucidated. Thus, it should only be a question of time before inhibitors to this enzyme will be developed and, hopefully, be used to reduce the pathologies associated with the development of periodontitis and/or eliminate the disease altogether.

Expression of Arg-Gingipain RgpB is required for correct glycosylation and stability of monomeric Arg-gingipain RgpA from Porphyromonas gingivalis W50

Arg-gingipains are extracellular cysteine proteases produced by the gram-negative periodontal pathogen Porphyromonas gingivalis and are encoded by rgpA and rgpB. Three Arg-gingipains, heterodimeric high-molecular-mass Arg-gingipain HRgpA comprising the alpha-catalytic chain and the beta-adhesin chain, the monomeric soluble Arg-gingipain comprising only the alpha-catalytic chain (RgpA(cat)), and the monomeric membrane-type heavily glycosylated Arg-gingipain comprising the alpha-catalytic chain (mt-RgPA(cat)), are derived from rgpA. The monomeric enzymes contain between 14 and 30% carbohydrate by weight. rgpB encodes two monomeric enzymes, RgpB and mt-RgpB. Earlier work indicated that rgpB is involved in the glycosylation process, since inactivation of rgpB results in the loss of not only RgpB and mt-RgpB but also mt-RgpA(cat). This work aims to confirm the role of RgpB in the posttranslational modification of RgpA(cat) and the effect of aberrant glycosylation on the properties of this enzyme. Two-dimensional gel electrophoresis of cellular proteins from W50 and an inactivated rgpB strain (D7) showed few differences, suggesting that loss of RgpB has a specific effect on RgpA maturation. Inactivation of genes immediately upstream and downstream of rgpB had no effect on rgpA-derived enzymes, suggesting that the phenotype of the rgpB mutant is not due to a polar effect on transcription at this locus. Matrix-assisted laser desorption ionization-time of flight analysis of purified RgpA(cat) from W50 and D7 strains gave identical peptide mass fingerprints, suggesting that they have identical polypeptide chains. However, RgpA(cat) from D7 strain had a higher isoelectric point and a dramatic decrease in thermostability and did not cross-react with a monoclonal antibody which recognizes a glycan epitope on the parent strain enzyme. Although it had the same total sugar content as the parent strain enzyme, there were significant differences in the monosaccharide composition and linking sugars. These data suggest that RgpB is required for the normal posttranslational glycosylation of Arg-gingipains derived from rgpA and that this process is required for enzyme stabilization.

Periodontal infection and dyslipidemia in type 2 diabetics: association with increased HMG-CoA reductase expression

Recent studies have suggested that the periodontal disease, chronic sub-clinical inflammation, is associated with atherosclerosis, although "cause or effect" relationship is still unclear. The aim of this study was to assess the association between the degree of periodontal infection and lipid profiles in diabetic subjects. Additionally, the association of such sub-clinical inflammation with HMG-CoA reductase gene expression was evaluated. One hundred and thirty-one non-obese relatively well-controlled Japanese type 2 diabetic patients were enrolled for the study. Although no significant association was observed between serum triglycerides, HLD-cholesterol and antibody titer to Porphyromonas gingivalis (Pg), the most predominant periodontal pathogen in adults, LDL-cholesterol was significantly associated with antibody titer to Pg. Concomitantly, the same works out to be true for total cholesterol. To understand the possible mechanisms underlying this association, we evaluated 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase gene expression in cultured HepG2 cells stimulated by either bacterial lipopolysaccharide (LPS) or inflammatory cytokines. Although Pg and E. coli LPS had no effect on HMG-CoA reductase gene expression, both tumor necrosis factor-alpha and interleukin-6 (IL-6), especially IL-6 at low concentration, markedly up-regulated HMG-CoA reductase gene expression. It can be concluded that Pg infection is associated with increased LDL-cholesterol in diabetic subjects, which may be accompanied by increased cholesterol synthesis by inflammatory cytokines.

The association of two recombinant proteinases of a feline strain of Porphyromonas gingivalis with periodontal disease in cats

Serum from 40 domestic cats with various grades of periodontal disease was used to probe two recombinant functional proteinases from feline strain VPB 3457 of Porphyromonas gingivalis expressed in E. coli. One recombinant proteinase (VPB 2856) was constructed using polymerase chain reaction and had 91% DNA identity with the prtC collagenase gene of the human type strain of P. gingivalis, while the other proteinase (VPB 2814) was isolated from a size selected genomic library and had an amino-terminal sequence with no significant identity with deposited sequences. Thirteen of 40 cats showed a serum antibody response to VPB 2856 using Western immunoblot detection. All the 13 cats had an overall periodontal grade of 3 or greater and greater than 1.68x10(5) cfu P. gingivalis at the canine and premolar periodontium sample sites. Fourteen of 40 cats showed a serum antibody response to VPB 2814. Thirteen of these 14 cats had an overall periodontal grade of 3 or greater. Regression analysis of overall periodontal grade against the serum antibody response showed significant positive relationships for both VPB 2856 (r2 = 0.351; p<0.001) and VPB 2814 (r2 = 0.247; p<0.001). Regression analysis of the total colony forming units of feline strain P. gingivalis against the grade of serum antibody response showed a positive relationship for both VPB 2856 (r2 = 0.662; p<0.001) and VPB 2814 (r2 = 0.531; p<0.001). These data provide strong evidence that the recombinant proteinases of feline P. gingivalis expressed in E. coli clones VPB 2856 and VPB 2814 are associated with periodontal disease in cats.

Identification of Small-Molecule Inhibitors against Meso-2, 6-Diaminopimelate Dehydrogenase from Porphyromonas gingivalis

Species-specific antimicrobial therapy has the potential to combat the increasing threat of antibiotic resistance and alteration of the human microbiome. We therefore set out to demonstrate the beginning of a pathogen-selective drug discovery method using the periodontal pathogen Porphyromonas gingivalis as a model. Through our knowledge of metabolic networks and essential genes we identified a “druggable” essential target, meso-diaminopimelate dehydrogenase, which is found in a limited number of species. We adopted a high-throughput virtual screen method on the ZINC chemical library to select a group of potential small-molecule inhibitors. Meso-diaminopimelate dehydrogenase from P. gingivalis was first expressed and purified in Escherichia coli then characterized for enzymatic inhibitor screening studies. Several inhibitors with similar structural scaffolds containing a sulfonamide core and aromatic substituents showed dose-dependent inhibition. These compounds were further assayed showing reasonable whole-cell activity and the inhibition mechanism was determined. We conclude that the establishment of this target and screening strategy provides a model for the future development of new antimicrobials.

Extracellular Release of a Disintegrin and Metalloproteinase Correlates With Periodontal Disease Severity

AIM

Periodontal disease is driven by oral pathogens, including Porphyromonas gingivalis, and the release of inflammatory cytokines. These cytokines (e.g., TNF) or their receptors (e.g., IL-1R) are substrates of a disintegrin and metalloproteinases (ADAMs). In this study, we aimed to determine the effects of ADAMs on periodontal disease phenotypes.

MATERIALS AND METHODS

Western blot and FRET-based activity measurements of the gingival crevicular fluid (GCF) of patients were compared with those of infected (P. gingivalis) or cytokine-stimulated oral keratinocytes and primary human neutrophils, respectively. This was accompanied by an analysis of the released extracellular vesicles and MMP9 activity.

RESULTS

In the GCF of patients, ADAM8 protein expression and activity were correlated with disease stage, whereas ADAM10 protein expression was inversely correlated with disease stage. Infection and the resulting cytokine release orchestrated the release of soluble ADAM8 by oral keratinocytes and primary neutrophils as soluble ectodomain and on exosomes, respectively. Furthermore, ADAM8 regulated the release of ADAM10 and MMP9.

CONCLUSION

Dysregulation of cell-associated and extracellular ADAM proteolytic activity may be an essential regulatory element in the progression of periodontal disease driven by ADAM8. The influence of ADAM8 on disease onset and the evaluation of targeting ADAM8 as a potential and novel local treatment option should be addressed in future translational in vivo studies.