Periodontal bone level and gingival proteinase activity in gnotobiotic rats immunized with Bacteroides gingivalis

Advances and challenges in the development of periodontitis vaccines: A comprehensive review

Periodontitis is a prevalent polymicrobial disease. It damages soft tissues and alveolar bone, and causes a significant public-health burden. Development of an advanced therapeutic approach and exploration of vaccines against periodontitis hold promise as potential treatment avenues. Clinical trials for a periodontitis vaccine are lacking. Therefore, it is crucial to address the urgent need for developing strategies to implement vaccines at the primary level of prevention in public health. A deep understanding of the principles and mechanisms of action of vaccines plays a crucial role in the successful development of vaccines and their clinical translation. This review aims to provide a comprehensive summary of potential directions for the development of highly efficacious periodontitis vaccines. In addition, we address the limitations of these endeavors and explore future possibilities for the development of an efficacious vaccine against periodontitis.

Temporal changes of periodontal tissue pathology in a periodontitis animal model

PURPOSE

This study aimed to characterize the early stages of periodontal disease and determine the optimal period for its evaluation in a mouse model. The association between the duration of ligation and its effect on the dentogingival area in mice was evaluated using micro-computed tomography (CT) and histological analysis.

METHODS

Ninety mice were allocated to an untreated control group or a ligation group in which periodontitis was induced by a 6-0 silk ligation around the left second maxillary molar. Mice were sacrificed at 1, 2, 3, 4, 5, 8, 11, and 14 days after ligature placement. Alveolar bone destruction was evaluated using micro-CT. Histological analysis was performed to assess the immune-inflammatory processes in the periodontal tissue.

RESULTS

No significant difference in alveolar bone loss was found compared to the control group until day 3 after ligature placement, and a gradual increase in alveolar bone loss was observed from 4 to 8 days following ligature placement. No significant between-group differences were observed after 8 days. The histological analysis demonstrated that the inflammatory response was evident from day 4.

CONCLUSIONS

Our findings in a mouse model provide experimental evidence that ligature-induced periodontitis models offer a consistent progression of disease with marginal attachment down-growth, inflammatory infiltration, and alveolar bone loss.

Future Drug Targets in Periodontal Personalised Medicine-A Narrative Review

Periodontal disease is an infection-driven inflammatory disease characterized by the destruction of tooth-supporting tissues. The establishment of chronic inflammation will result in progressive destruction of bone and soft tissue changes. Severe periodontitis can lead to tooth loss. The disease has complex pathogenesis with an interplay between genetic, environmental, and host factors and pathogens. Effective management consists of plaque control and non-surgical interventions, along with adjuvant strategies to control inflammation and disrupt the pathogenic subgingival biofilms. Recent studies have examined novel approaches for managing periodontal diseases such as modulating microbial signaling mechanisms, tissue engineering, and molecular targeting of host inflammatory substances. Mounting evidence suggests the need to integrate omics-based approaches with traditional therapy to address the disease. This article discusses the various evolving and future drug targets, including proteomics, gene therapeutics, vaccines, and nanotechnology in personalized periodontal medicine for the effective management of periodontal diseases.

Targeting a cysteine protease from a pathobiont alleviates experimental arthritis

Background

Several lines of evidence suggest that the pathobiont Porphyromonas gingivalis is involved in the development and/or progression of auto-inflammatory diseases. This bacterium produces cysteine proteases, such as gingipain RgpA, endowed with the potential to induce significant bone loss in model systems and in patients.

Objective

We sought to gain further insight into the role of this pathobiont in rheumatoid arthritis (RA) and to identify novel therapeutic targets for auto-inflammatory diseases.

Methods

We profiled the antibody response to RgPA-specific domains in patient sera. We also tested the potential protective effects of RgpA domains in an experimental arthritis model.

Results

Pre-immunization of rats with purified recombinant RgpA domains alleviated arthritis in the joints of the rodents and reduced bone erosion. Using a functional genomics approach at both the mRNA and protein levels, we report that the pre-immunizations reduced arthritis severity by impacting a matrix metalloprotease characteristic of articular injury, a chemokine known to be involved in recruiting inflammatory cells, and three inflammatory cytokines. Finally, we identified an amino acid motif in the RgpA catalytic domain of P. gingivalis that shares sequence homology with type II collagen.

Conclusion

We conclude that pre-immunization against gingipain domains can reduce the severity of experimentally induced arthritis. We suggest that targeting gingipain domains by pre-immunization, or, possibly, by small-molecule inhibitors, could reduce the potential of P. gingivalis to translocate to remote tissues and instigate and/or exacerbate pathology in RA, but also in other chronic inflammatory diseases.

Porphyromonas gingivalis: Immune subversion activities and role in periodontal dysbiosis

Purpose of review

This review summarizes mechanisms by which Porphyromonas gingivalis interacts with community members and the host so that it can persist in the periodontium under inflammatory conditions that drive periodontal disease.

Recent findings

Recent advances indicate that, in great part, the pathogenicity of P. gingivalis is dependent upon its ability to establish residence in the subgingival environment and to subvert innate immunity in a manner that uncouples the nutritionally favorable (for the bacteria) inflammatory response from antimicrobial pathways. While the initial establishment of P. gingivalis is dependent upon interactions with early colonizing bacteria, the immune subversion strategies of P. gingivalis in turn benefit co-habiting species.

Summary

Specific interspecies interactions and subversion of the host response contribute to the emergence and persistence of dysbiotic communities and are thus targets of therapeutic approaches for the treatment of periodontitis.

Restriction Fragment Length Polymorphism Analysis of the Fimbrillin Locus, fimA, of Porphyromonas gingivalis

With hybridization probes derived from the fimbrial locus of Porphyromonas gingivalis strain 381, fimA381' restriction fragment length polymorphisms (RFLPs) were examined at the fimbrillin locus in 39 human and animal strains of this species. The 39 strains were subdivided into nine RFLP groups (I-IX) after genomic digests were probed with the internal coding sequence of the fimA381 gene. Thirty-three strains showed one or more AluI fragments of moderate-to-high homology (≥77%) with the internal coding sequence of fimA381. These strains were distributed into the first seven RFLP groups, based solely on the size of the major hybridizing AluI fragment. Five human strains (RFLP Group VIII) had only one Alu I fragment that hybridized very poorly with this probe. One animal strain did not have homology at all (RFLP Group IX). When all AluI fragments that hybridized with fimA381 were analyzed, RFLP groups I-VIII were further differentiated into 25 distinct RFLP patterns. Hybridizations were also performed with the internal coding sequence of fimA381 to probe PstI genomic digests of selected strains that appeared to have lesser homology with fimA381. These hybridizations were performed to determine the level and location of the region of poor homology within the fimA genes of these strains. The results suggested that fimbrial coding sequences are more commonly conserved between these strains in the 5'-region of the fimA locus (≥92% sequence homology). However, the five human strains of RFLP Group VIII had only one PstI fragment that hybridized very poorly with a probe derived from fimA381 coding sequence, and this sequence homology (only > 66%) was located in the central or 3'-end of the fimA gene. The 5'-region of the fimA allele in Group VIII strains did not have any detectable sequence homology. In contrast, the Group VIII strains were highly homologous with the sequences flanking the fimA381 gene. This indicates that these strains do possess a fimA allele at the same chromosomal location as fimA381.

Vaccination with recombinant RgpA peptide protects against Porphyromonas gingivalis-induced bone loss

OBJECTIVE

Following Porphyromonas gingivalis infection in mice, the efficacy of vaccination by recombinant and native RgpA in modulating the early local anti-inflammatory and immune responses and periodontal bone loss were examined.

MATERIAL AND METHODS

Using the subcutaneous chamber model, exudates were analyzed for cytokines after treatment with native RgpA and adjuvant (test), or adjuvant and saline alone (controls). Mice were also immunized with recombinant RgpA after being orally infected with P. gingivalis. After 6 wk, serum was examined for anti-P. gingivalis IgG1 and IgG2a titers and for alveolar bone resorption.

RESULTS

Immunization with native RgpA shifted the immune response toward an anti-inflammatory response as demonstrated by decreased proinflammatory cytokine IL-1β production and greater anti-inflammatory cytokine IL-4 in chamber exudates. Systemically, immunization with recombinant RgpA peptide prevented alveolar bone loss by 50%, similar to immunization with heat-killed whole bacteria. Furthermore, recombinant RgpA shifted the humoral response toward high IgG1 and low IgG2a titers, representing an in vivo anti-inflammatory response.

CONCLUSIONS

The present study demonstrates the potential of RgpA to shift the early local immune response toward an anti-inflammatory response while vaccination with recRgpA protected against P. gingivalis-induced periodontitis.

The enduring importance of animal models in understanding periodontal disease

Whereas no single animal model can reproduce the complexity of periodontitis, different aspects of the disease can be addressed by distinct models. Despite their limitations, animal models are essential for testing the biological significance of in vitro findings and for establishing cause-and-effect relationships relevant to clinical observations, which are typically correlative. We provide evidence that animal-based studies have generated a durable framework for dissecting the mechanistic basis of periodontitis. These studies have solidified the etiologic role of bacteria in initiating the inflammatory response that leads to periodontal bone loss and have identified key mediators (IL-1, TNF, prostaglandins, complement, RANKL) that induce inflammatory breakdown. Moreover, animal studies suggest that dysbiosis, rather than individual bacterial species, are important in initiating periodontal bone loss and have introduced the concept that organisms previously considered commensals can play important roles as accessory pathogens or pathobionts. These studies have also provided insight as to how systemic conditions, such as diabetes or leukocyte adhesion deficiency, contribute to tissue destruction. In addition, animal studies have identified and been useful in testing therapeutic targets.

Synergistic virulence of Porphyromonas gingivalis and Treponema denticola in a murine periodontitis model

Chronic periodontitis is characterized by the destruction of the tissues supporting the teeth and has been associated with the presence of a subgingival polymicrobial biofilm containing Porphyromonas gingivalis and Treponema denticola. We have investigated the potential synergistic virulence of P. gingivalis and T. denticola using a murine experimental model of periodontitis. An inoculation regime of four intra-oral doses of 1 × 10(10) P. gingivalis cells induced significant periodontal bone loss compared with loss in sham-inoculated mice, whereas doses of 1 × 10(9) cells or lower did not induce bone loss. Inoculation with T. denticola with up to eight doses of 1 × 10(10) cells failed to induce bone loss in this model. However, four doses of a co-inoculum of a 1 : 1 ratio of P. gingivalis and T. denticola at 5 × 10(8) or 1 × 10(9) total bacterial cells induced the same level of bone loss as four doses of 1 × 10(10) P. gingivalis cells. Co-inoculation induced strong P. gingivalis-specific T-cell proliferative and interferon-γ-dominant cytokine responses, and induced a strong T. denticola-specific interferon-γ dominant cytokine response. Only at the higher co-inoculum dose of 1 × 10(10) total cells was a T. denticola-specific T-cell proliferative response observed. These data show that P. gingivalis and T. denticola act synergistically to stimulate the host immune response and to induce alveolar bone loss in a murine experimental periodontitis model.

Sterodin, a novel immunostimulating drug: some toxicological and pharmacological evaluations in vivo, and drug-lipid interaction studies in vitro

Sterodin is a novel non-specific immunostimulating drug produced by a combination of bile lipids and bacterial metabolites. In the present study, we investigated some of its (i) toxicological and (ii) pharmacological properties in vivo, and (iii) drug-lipid interaction (lipid peroxidation) in vitro. We also evaluated the possible (iv) Sterodin-induced lipid peroxidation as well as the effect of ascorbic acid on this peroxidation. We found LD50 of Sterodin to be 31.50 mL kg-1 body mass. In male albino mice, Sterodin increased the total white blood cells and neutrophils count by 59 and 26%, respectively, on the 6th day, compared to day 0 after injection and stimulated phagocytic activity in vivo. We used goat liver as lipid source in drug-lipid interaction studies in vitro. Our experiments show that Sterodin induces lipid peroxidation, which was prevented by ascorbic acid.

An improved cost-effective, reproducible method for evaluation of bone loss in a rodent model

AIM

This study was designed to investigate the utility of two "new" definitions for assessment of bone loss in a rodent model of periodontitis.

MATERIAL AND METHODS

Eighteen rats were divided into three groups. Group 1 was infected by Aggregatibacter actinomycetemcomitans (Aa), group 2 was infected with an Aa leukotoxin knock-out, and group 3 received no Aa (controls). Microbial sampling and antibody titres were determined. Initially, two examiners measured the distance from the cemento-enamel-junction to alveolar bone crest using the three following methods; (1) total area of bone loss by radiograph, (2) linear bone loss by radiograph, (3) a direct visual measurement (DVM) of horizontal bone loss. Two "new" definitions were adopted; (1) any site in infected animals showing bone loss >2 standard deviations above the mean seen at that site in control animals was recorded as bone loss, (2) any animal with two or more sites in any quadrant affected by bone loss was considered as diseased.

RESULTS

Using the "new" definitions both evaluators independently found that infected animals had significantly more disease than controls (DVM system; p<0.05).

CONCLUSIONS

The DVM method provides a simple, cost effective, and reproducible method for studying periodontal disease in rodents.

Toll gates to periodontal host modulation and vaccine therapy

Toll-like receptors (TLRs) are central mediators of innate antimicrobial and inflammatory responses and play instructive roles in the development of the adaptive immune response. Thus when stimulated by certain agonists, TLRs serve as adjuvant receptors that link innate and adaptive immunity. However, when excessively activated or inadequately controlled during an infection, TLRs may contribute to immunopathology associated with inflammatory diseases, such as periodontitis. Moreover, certain microbial pathogens appear to exploit aspects of TLR signalling in ways that enhance their adaptive fitness. The diverse and important roles played by TLRs suggest that therapeutic manipulation of TLR signalling may have implications in the control of infection, attenuation of inflammation, and the development of vaccine adjuvants for the treatment of periodontitis. Successful application of TLR-based therapeutic modalities in periodontitis would require highly selective and precisely targeted intervention. This would in turn necessitate precise characterization of TLR signalling pathways in response to periodontal pathogens, as well as development of effective and specific agonists or antagonists of TLR function and signalling. This review summarizes the current status of TLR biology as it relates to periodontitis, and evaluates the potential of TLR-based approaches for host-modulation therapy in this oral disease.

The use of rodent models to investigate host-bacteria interactions related to periodontal diseases

Even though animal models have limitations, they are often superior to in vitro or clinical studies in addressing mechanistic questions and serve as an essential link between hypotheses and human patients. Periodontal disease can be viewed as a process that involves four major stages: bacterial colonization, invasion, induction of a destructive host response in connective tissue and a repair process that reduces the extent of tissue breakdown. Animal studies should be evaluated in terms of their capacity to test specific hypotheses rather than their fidelity to all aspects of periodontal disease initiation and progression. Thus, each of the models described below can be adapted to test discrete components of these four major steps, but not all of them. This review describes five different animal models that are appropriate for examining components of host-bacteria interactions that can lead to breakdown of hard and soft connective tissue or conditions that limit its repair as follows: the mouse calvarial model, murine oral gavage models with or without adoptive transfer of human lymphocytes, rat ligature model and rat Aggregatibacter actinomycetemcomitans feeding model.

Rat model of polymicrobial infection, immunity, and alveolar bone resorption in periodontal disease

One of the predominant polymicrobial infections of humans is expressed clinically as periodontal disease. Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia have been strongly implicated as members of a pathogenic consortium in the etiology of adult periodontitis. In this study we hypothesized that P. gingivalis, T. denticola, and T. forsythia are synergistic in terms of virulence potential and induce chronic periodontal inflammation that leads to alveolar bone resorption in a polymicrobial infection in rats. Groups of rats were infected with either P. gingivalis, T. denticola, or T. forsythia in monomicrobial infections or with all three species in polymicrobial oral infections with or without Fusobacterium nucleatum. PCR analyses of oral microbial samples demonstrated that rats infected with one bacterium were orally colonized by each of the bacteria during the study interval, and increased serum immunoglobulin G (IgG) antibody levels substantiated the interaction of the host with the infecting bacteria. PCR analyses of the rats with polymicrobial infections demonstrated that most rats were infected with P. gingivalis, T. denticola, and T. forsythia as a consortium. Furthermore, all rats exhibited a significant increase in the level of IgG antibody to the polymicrobial consortium. Radiographic measurement of alveolar bone resorption showed that rats infected with the polymicrobial consortium with or without F. nucleatum exhibited significantly increased alveolar bone resorption compared to the resorption in uninfected control rats, as well as the resorption in rats infected with one of the microbes. These results documented that P. gingivalis, T. denticola, and T. forsythia not only exist as a consortium that is associated with chronic periodontitis but also exhibit synergistic virulence resulting in the immunoinflammatory bone resorption characteristic of periodontitis.

Porphyromonas gingivalis heat shock protein vaccine reduces the alveolar bone loss induced by multiple periodontopathogenic bacteria

OBJECTIVES

Heat shock protein (HSP) can be utilized as a vaccine to cross-protect against multiple pathogenic species. The present study was performed to evaluate Porphyromonas gingivalis heat shock protein 60 (HSP60) as a vaccine candidate to inhibit multiple bacteria-induced alveolar bone loss.

MATERIAL AND METHODS

Recombinant P. gingivalis HSP60 was produced and purified from P. gingivalis GroEL gene. Rats were immunized with P. gingivalis HSP60, and experimental alveolar bone loss was induced by infection with multiple periodontopathogenic bacteria.

RESULTS

There was a very strong inverse relationship between postimmune anti-P. gingivalis HSP immunoglobulin G (IgG) levels and the amount of alveolar bone loss induced by either P. gingivalis or multiple bacterial infection (p=0.007). Polymerase chain reaction data indicated that the vaccine successfully eradicated the multiple pathogenic species.

CONCLUSIONS

We concluded that P. gingivalis HSP60 could potentially be developed as a vaccine to inhibit periodontal disease induced by multiple pathogenic bacteria.

Recognition and phagocytosis of multiple periodontopathogenic bacteria by anti-Porphyromonas gingivalis heat-shock protein 60 antisera

The present study has been performed to evaluate Porphyromonas gingivalis heat shock protein (HSP) 60 as a candidate vaccine to protect against multiple putative periodontopathic bacteria. Mouse anti-P. gingivalis HSP antisera demonstrated the elevated IgG antibody titers against the multiple bacteria tested and cross-reacted with heat-induced bacterial proteins of the target bacteria. The antisera also demonstrated a significantly higher opsonophagocytosis function against all the target bacteria than the control sera (P<0.01). We concluded that P. gingivalis HSP 60 could potentially be developed as a vaccine against multiple periodontopathic bacteria.

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

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

Characterization and expression of a novel Porphyromonas gingivalis outer membrane protein, Omp28

We report the characterization of a Porphyromonas gingivalis gene, designated omp28, encoding a protein that we have previously purified and characterized as a 28-kDa outer membrane protein. The deduced amino acid sequence of the omp28 open reading frame displayed an outer membrane leader sequence and lipoprotein attachment site but did not exhibit any significant overall sequence identity with protein sequences in the databases. A small stretch of amino acids (19 residues) exhibits 50% sequence identity with a segment of a fimbrial protein from Dichelobacter nodosus involved in adhesion, suggesting that Omp28 may be a surface adhesin/receptor of P. gingivalis. Using the pET-24 vector we expressed recombinant Omp28 (rOmp28) in Escherichia coli. Western blot analyses of purified rOmp28 with rabbit antisera to a P. gingivalis outer membrane preparation, protective rat anti-whole P. gingivalis antisera and pooled human sera from chronic periodontitis patients showed that the recombinant was recognized by all antisera. Further, anti-rOmp28 antisera exhibited strong reactivity with a panel of four laboratory strains and 10 clinical isolates of P. gingivalis from the United States, Sudan, Romania and Norway. These results suggest that Omp28 is expressed by a wide distribution of P. gingivalis strains.

Immunization with the RgpA-Kgp proteinase-adhesin complexes of Porphyromonas gingivalis protects against periodontal bone loss in the rat periodontitis model

A major virulence factor of Porphyromonas gingivalis is the extracellular noncovalently associated complexes of Arg-X- and Lys-X-specific cysteine proteinases and adhesins designated the RgpA-Kgp complexes. In this study we investigated the ability of RgpA-Kgp as an immunogen to protect against P. gingivalis-induced periodontal bone loss in the rat. Specific-pathogen-free Sprague-Dawley rats were immunized with either formalin-killed whole P. gingivalis ATCC 33277 cells with incomplete Freund's adjuvant, RgpA-Kgp with incomplete Freund's adjuvant, or incomplete Freund's adjuvant alone. The animals were then challenged by oral inoculation with live P. gingivalis ATCC 33277 cells. Marked periodontal bone loss was observed in animals immunized with incomplete Freund's adjuvant alone; this bone loss was significantly (P < 0.05) greater than that detected in animals immunized with formalin-killed whole cells or RgpA-Kgp or in unchallenged animals. There was no significant difference in periodontal bone loss between animals immunized with formalin-killed whole cells and those immunized with RgpA-Kgp. The bone loss in these animals was also not significantly different from that in unchallenged animals. DNA probe analysis of subgingival plaque samples showed that 100% of the animals immunized with incomplete Freund's adjuvant alone and challenged with P. gingivalis ATCC 33277 were positive for the bacterium. However, P. gingivalis ATCC 33277 could not be detected in subgingival plaque samples from animals immunized with formalin-killed whole cells or with RgpA-Kgp. Immunization with formalin-killed whole cells or RgpA-Kgp induced a high-titer serum immunoglobulin G2a response. Western blot analysis of RgpA-Kgp using pooled protective antisera taken from rats immunized with RgpA-Kgp revealed immunodominant bands at 44, 39, and 27 kDa. In conclusion, immunization with RgpA-Kgp restricted colonization by P. gingivalis and periodontal bone loss in the rat.

Modulation of the host response in periodontal therapy

This paper was prepared by the Research, Science, and Therapy Committee of the American Academy of Periodontology to provide the dental profession an overview of current and potential methods to modulate the host response in the treatment of periodontal diseases. Specifically, it discusses components of periodontal disease pathogenesis (i.e., immune and inflammatory responses, excessive production of matrix metalloproteinases and arachidonic acid metabolites, and regulation of bone metabolism) and their modulation.

Prevention of Porphyromonas gingivalis-induced oral bone loss following immunization with gingipain R1

The arginine gingipains RgpA and RgpB of Porphyromonas gingivalis are well-documented virulence factors of this organism. Structurally, RgpA and RgpB have nearly identical catalytic domains, while RgpA possesses an additional hemagglutinin domain. In this study, we examined the abilities of these proteins to elicit protection against P. gingivalis-mediated oral bone loss in a murine oral challenge model. Mice immunized subcutaneously with heat-killed P. gingivalis or purified RgpA or RgpB possessed elevated levels of P. gingivalis-specific immunoglobulin G; however, only the animals immunized with P. gingivalis whole cells or RgpA were protected from maxillary bone loss. These data suggest that immunization with RgpA stimulates the production of hemagglutinin domain-specific antibodies, which contribute to the prevention of P. gingivalis-mediated periodontal disease.

Identification of vaccine candidate antigens from a genomic analysis of Porphyromonas gingivalis

Porphyromonas gingivalis is a key periodontal pathogen which has been implicated in the etiology of chronic adult periodontitis. Our aim was to develop a protein based vaccine for the prevention and or treatment of this disease. We used a whole genome sequencing approach to identify potential vaccine candidates. From a genomic sequence, we selected 120 genes using a series of bioinformatics methods. The selected genes were cloned for expression in Escherichia coli and screened with P. gingivalis antisera before purification and testing in an animal model. Two of these recombinant proteins (PG32 and PG33) demonstrated significant protection in the animal model, while a number were reactive with various antisera. This process allows the rapid identification of vaccine candidates from genomic data.

Suppression of gingival inflammation induced by Porphyromonas gingivalis in rats by leupeptin

In this study, we developed a procedure to produce gingivitis in rats by inoculation of Porphyromonas gingivalis and studied the contribution of the bacterial cysteine proteinases, Arg-gingipain (Rgp) and Lys-gingipain (Kgp), to the pathology in the gingiva. To adhere the bacterium to periodontal tissues, a cotton thread was inserted between the first and second molar of right maxillary sites of rats. Rats in group A were administered with vehicle alone after bacterial (strain W83) inoculation. In group B, the bacteria were inoculated in combination with leupeptin, a potent inhibitor of Rgp and Kgp, and then leupeptin alone was administered the week after. Rats in group C were administered leupeptin for 6 weeks after bacteria inoculation. All left maxillary gingiva in three groups showed no inflammatory changes. Right maxillary gingiva of group A showed most of the clinical landmarks of gingivitis. Leupeptin exhibited only a little inhibitory effect on this gingivitis in group B, whereas it had a strong inhibitory effect on the inflammation in group C. These results suggest that P. gingivalis-induced gingivitis is attributable to Rgp and Kgp and that leupeptin is more effective in the late phase than the early stage of gingivitis.

Immunostimulating and protective effects of an oral polybacterial immunomodulator 'Dentavax' in a rabbit experimental model

The immunostimulating and protective effects of an oral polybacterial immunomodulator, Dentavax (D), composed of killed cells from Klebsiella pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Candida albicans and Lactobacillus acidophilus and their lysates, have been investigated on an experimental rabbit model. In this model, mixed suspensions of the above bacterial wild strains have been injected in six sides of oral mucosa. A long-lasting inflammation with the development of infiltrates and confluating abscesses has been observed. The influence of orally given Dentavax on the course of the model infection as well as on the dynamics of the immune response has been studied. A two-fold decrease in the duration and severity of inflammatory reaction, confirmed by the histological findings, has been registered. In immunised animals, an activation of polymorphonuclear phagocytosis, together with stimulation of humoral systemic and mucosal immunity with synthesis of specific serum (predominantly, IgG) and coproantibodies (predominantly, S-IgA) determined by ELISA, has been found. The results obtained proved the strong immunostimulating and protective effects of the preparation D, which is meant for the prophylaxis and treatment of inflammatory periodontal diseases.

Genetic diversity of Porphyromonas gingivalis and its possible importance to pathogenicity

During recent years much effort has been put into understanding the genetic composition of the oral populations of black-pigmented anaerobic bacteria. One of them, Porphyromonas gingivalis, is a putative periodontopathogenic organism considered to be particularly relevant in the etiology of adult periodontitis. It has been shown in studies using molecular typing methods that most bacterial populations consist of numerous genetic clones, and that only a small proportion of these clones cause disease. Elucidation of a possible association of genotypic profiles with either disease or clinical healthy condition is important for understanding the pathogenic characteristics of bacteria. Studies addressing this issue as it relates to P. gingivalis are reviewed in the present article. Genotypic characterization of P. gingivalis strains has revealed extensive heterogeneity in natural populations of this bacterium. Some of the potential virulence factors of P. gingivalis have been purified and cloned and methods have been established to identify their genes. Although no studies have clearly defined the relationship between a specific genotype of P. gingivalis and periodontal status of the host, it seems that molecular typing tools, which are undergoing rapid improvements, will allow us to distinguish between virulent and avirulent strains of the same species in the near future.

Prevaccination with SRL172 (heat-killed Mycobacterium vaccae) inhibits experimental periodontal disease in Wistar rats

Periodontal disease is a bacterial dental plaque-induced destructive inflammatory condition of the tooth-supporting tissues, which is thought to be mediated by T lymphocytes secreting T helper 2 (Th2) cytokines, resulting in recruitment of high numbers of antibody-producing B lymphocytes/plasma cells as well as polymorphonuclear leucocytes (PMN) secreting tissue-destructive components, such at matrix metalloproteinases and reactive oxygen metabolites into the gingival connective tissues. One treatment strategy may be to down-regulate the Th2 response to those dental plaque microorganisms which induce the destructive inflammatory response. In this study we have examined the effects of a potent down-regulator of Th2 responses on ligature-induced periodontal disease in an experimental rat model. A single s.c. injection into Wistar rats of 0.1 or 1 mg of SRL172, a preparation of heat-killed Mycobacterium vaccae (NCTC 11659), 13 days before application of the ligature, significantly reduced the subsequent destruction of the tooth-supporting tissues, as measured by loss of periodontal attachment fibres (P < 0.001) and bone (P < 0.002). This protective effect occurred not only on the experimental (ligatured) side but also on the control unligatured side. SRL172 has undergone extensive toxicological studies and safety assessments in humans, and it is suggested that it may provide a safe and novel therapeutic approach to periodontal disease.

A 55-kilodalton immunodominant antigen of Porphyromonas gingivalis W50 has arisen via horizontal gene transfer

A 55-kDa outer membrane protein of Porphyromonas gingivalis W50 is a significant target of the serum immunoglobulin G antibody response of periodontal disease patients and hence may play an important role in host-bacterium interactions in periodontal disease. The gene encoding the 55-kDa antigen (ragB, for receptor antigen B) was isolated on a 9.5-kb partial Sau3AI fragment of P. gingivalis W50 chromosomal DNA in pUC18 by immunoscreening with a monoclonal antibody to this antigen. The 1.6-kb open reading frame (ORF) encoding RagB was located via subcloning and nested-deletion analysis. Sequence analysis demonstrated the presence of an upstream 3.1-kb ORF (ragA) which is cotranscribed with ragB. A number of genetic characteristics suggest that the ragAB locus was acquired by a horizontal gene transfer event. These include a significantly reduced G+C content relative to that of the P. gingivalis chromosome (42 versus 48%) and the presence of mobility elements flanking this locus in P. gingivalis W50. Furthermore, Southern blotting and PCR analyses showed a restricted distribution of this locus in laboratory and clinical isolates of this bacterium. The association of ragAB+ P. gingivalis with clinical status was examined by PCR analysis of subgingival samples. ragAB+ was not detected in P. gingivalis-positive shallow pockets from periodontal disease patients but was present in 36% of the P. gingivalis-positive samples from deep pockets. These data suggest that the ragAB locus was acquired by certain P. gingivalis strains via horizontal gene transfer and that the acquisition of this locus may facilitate the survival of these strains at sites of periodontal destruction.

Oral immunization with recombinant Salmonella typhimurium expressing a cloned Porphyromonas gingivalis hemagglutinin: effect of boosting on mucosal, systemic and immunoglobulin G subclass response

Live avirulent Salmonella typhimurium are convenient vaccine vectors for the delivery of recombinant antigens for the induction of mucosal and systemic immunity. The hagB gene encodes a hemagglutinin of Porphyromonas gingivalis, a suspected causal agent in human adult periodontal disease. In previous studies, we have shown that hagB can be expressed in avirulent S. typhimurium and is immunogenic when given orally to mice. In this study, we evaluated recall responses in both serum and mucosal secretions after boosting. In addition, we have examined the immunoglobulin G (IgG) subclass response in serum to both HagB and the Salmonella carrier. Mice were orally immunized with S. typhimurium expressing the hagB gene and then boosted 14 weeks later. Responses were measured through 27 weeks. Both primary and recall IgG and IgA responses were seen in serum to the purified HagB as well as to the Salmonella carrier. Likewise, mucosal primary and recall responses were seen in saliva, fecal extracts and vaginal washes although the kinetics of the responses differed. The anti-HagB response in serum was dominated by IgG2a during the peak of primary response, prior to boosting and during the peak of the recall response. The anti-S. typhimurium response shifted from predominantly IgG3 following primary immunization to IgG2a after boosting. The IgG1 response was minimal against each antigen. This pattern of IgG subclass distribution is consistent with a Th1-type response. These data indicate that avirulent S. typhimurium is capable of delivering a putative virulence factor from P. gingivalis and inducing a primary and recall response in both serum and secretions and provides a means of studying P. gingivalis virulence factors and for the development of a potential vaccine.

Diabetes prevents periodontitis-induced increases in gingival platelet derived growth factor-B and interleukin 1-beta in a rat model

Periodontitis is a chronic inflammatory disease characterized by a progression that is very much dependent on host response. The gingiva can be considered to be in a constant state of wounding (pathologic wounding by bacterial plaque) and a constant state of maintenance/repair. In this context, any metabolic disturbance in the host which compromises tissue repair/wound healing will exacerbate the progression of periodontitis. Diabetes presents an interesting example because two major complications of diabetes are delayed wound healing and periodontitis. Our previous studies indicate that delayed wound healing and periodontitis may be manifestations of a general systemic deficit in diabetes involving alteration of macrophage cytokine gene expression. The present study was designed to determine whether: 1) diabetes-induced metabolic alterations affect gingival cytokine levels; and 2) diabetes-induced metabolic alterations modify the gingival cytokine profile in periodontitis. Sprague-Dawley rats (N=12/group) were injected with streptozotocin (65 mg/kg) into the tail vein to induce diabetes (defined by blood glucose levels > 250 mg/dl) or received the injection vehicle or no treatment as controls. Periodontitis was induced in additional groups of diabetic and control rats by gavage with Porphyromonas gingivalis A7436. After 90 days, serum glucose was analyzed to document diabetes; alveolar bone level was measured to document severity of periodontitis; gingiva was harvested circumferentially from the first and second molars; and cytokines in gingival homogenates were assayed by ELISA using commercial kits. Cytokine levels were expressed as mean+/-SEM pg/microg protein. Diabetes alone did not alter the gingival cytokine profile for platelet-derived growth factor B (PDGF-B), interleukin 1-beta (IL-1beta), transforming growth factor-beta (TGF-beta), and tumor necrosis factor-alpha (TNF-alpha). Periodontitis alone demonstrated a significant increase (P < 0.05) in levels of PDGF-B and IL-1beta. Diabetes superimposed on periodontitis prevented these increases. Thus, diabetes-induced metabolic alterations do not affect gingival cytokine levels per se; however, they do alter the normal host response to periodontitis through blockage of periodontitis-induced increases in PDGF-B and IL-1beta.

Increased susceptibility of RAG-2 SCID mice to dissemination of endodontic infections

Specific immunity has been implicated in the pathogenesis of periapical lesions, although the extent to which these mechanisms are actually involved in either protection or destruction of the pulp-periapex complex is yet to be established. To investigate this question we compared periapical-lesion pathogenesis in RAG-2 severe combined immunodeficient (SCID) mice with immunocompetent control mice following surgical pulp exposure. In order to equalize the bacterial challenge, an infection protocol using Prevotella intermedia, Fusobacterium nucleatum, Peptostreptococcus micros, and Streptococcus intermedius was devised. The results demonstrated that after infection, the proportion of the root canal flora represented by the four pathogens was almost identical in both groups (39.9 and 42.2% for RAG-2 and immunocompetent control mice, respectively). The effects of abrogation of T- and B-cell mechanisms on periapical pathogenesis were then assessed. Approximately one-third of the RAG-2 mice developed endodontic abscesses, while no immunocompetent controls had abscesses, results which indicated regional dissemination of the infection. A similar incidence of abscesses was found in two additional experiments. Abscessed RAG-2 teeth had significantly larger periapical lesions than did nonabscessed RAG-2 teeth (P < or = 0.05) and exposed immunocompetent controls (P < or = 0.01), whereas nonabscessed RAG-2 teeth were not significantly different from those of exposed immunocompetent controls in periapical-lesion size. We conclude that B- and T-cell-mediated immunity protects the host from the dissemination of endodontic infections and that RAG-2 mice are more susceptible to infection-induced pulp-periapex destruction.

Endotoxin induces increased intracellular cathepsin B activity in THP-1 cells

Macrophage cathepsin B (CB) is implicated in tissue injury in inflammatory diseases. Lipopolysaccharide (LPS) is an activator of macrophages whose effect on CB is unknown. This study was undertaken to investigate the potential of macrophages as a source of increased CB and to determine if exposure to LPS might stimulate CB levels. As a model we chose the macrophage-like tumor line, THP-1. Incubation with LPS led to a time and dose-dependent increase in CB activity. LPS potentiated interferon-gamma (IFN-gamma)-induced elevations of CB and led to an additive increase in CB activity. Pretreatment of the cells with LPS not only caused a marked stimulation of CB activity over that seen with IFN-gamma alone, but also decreased the concentration and exposure time to the cytokine necessary to achieve maximum induction of the enzyme. The LPS and IFN-gamma induced CB increases were abolished by cycloheximide or actinomycin D in the cultures, indicating that the increases in CB required increased RNA transcription and de novo protein synthesis. Direct measurement of CB mRNA showed increases. These data indicate that although LPS alone appears to induce the production of CB in THP-1 cells, it augments IFN-gamma induced increases, suggesting that two signals are necessary for maximum CB induction in this system.

Stimulating effect of an oral polybacterial immunomodulator on the proliferative activity of guinea pig lymphocytes

A preparation for the prophylaxis and treatment of inflammations of oral mucosa and parodont Dentavax (D) was investigated in guinea pigs. Animals were given orally D for 5 consecutive days and a month later the procedure was repeated. On day 3, 10, 21, and 28 after immunization and reimmunization lymphoproliferative responses to PHA, rIL-2, LPS and D were measured by the radiometric blast transformation assay in peripheral blood, spleen, mesenteric lymph nodes (MLN) and Peyer's patches (PP). The percentage of cells entering S and G2/M-phases of cell cycle was assessed by the flow cytometric DNA analysis. A correlation in proliferative activity of cells after in vitro stimulation with PHA and LPS has been established by both methods. Peak values of lymphocyte stimulation were found on day 10, especially after the second administration of D in all organs tested, mainly in MLNs and spleen. Electron-microscopic studies demonstrated an extensive development of the endoplasmatic reticulum in plasmatic cells from spleen, PPs, mesenteric, bronchial and inguinal lymph nodes. The results obtained may be considered a proof of the immunostimulating effect of Dentavax.

Alveolar bone loss in rats infected with a strain of Prevotella intermedia and Fusobacterium nucleatum isolated from a child with prepubertal periodontitis

Prevotella intermedia and fusobacterium nucleatum are associated with various forms of periodontal disease. The purpose of the present study was to infect the clinical isolates of these periodontopathic bacteria and to induce a significant loss of alveolar bone in specific pathogen-free (SPF) rats in the absence of ligatures. P. intermedia YKD8 and F. nucleatum YKZ5 were isolated from a prepubertal periodontitis patient, while P. gingivalis MWB13 was from a patient with juvenile periodontitis. At first, SPF Sprague-Dawley rats (70 days of age, male) were infected with A. viscosus Ny1R and subsequently superinfected with P. gingivalis MWB13, P. intermedia YKD8, or F. nucleatum YKZ5, respectively. The control group was infected with A. viscosus Ny1R alone. All rats were killed and periodontal bone levels were assessed morphometrically 135 days after the first infection with A. viscosus. P. intermedia YKD8 was recovered frequently from rats, with serum antibody levels remaining highly elevated throughout the experiment. Significant loss of alveolar bone was found in rats infected with P. intermedia YKD8, the virulence of which was equivalent to that of P. gingivalis MWB13. F. nucleatum YKZ5 also induced alveolar bone loss, but not significantly when compared with rats infected with A. viscosus Ny1R alone.

Effect of host responses on the pathogenicity of strains of Porphyromonas gingivalis

Porphyromonas gingivalis is implicated in the etiology of periodontitis. Strains of P. gingivalis have been classified as invasive or noninvasive based on their ability to form abscesses in a mouse model. The purpose of this study was to investigate the ability of P. gingivalis strains to cause abscesses and periodontal bone loss in an experimental rat model and the effect of serum and salivary responses on the pathogenicity of these strains. Subcutaneous injection of animals with P. gingivalis 33277, A7A1-28, W50 or 381 resulted in abscesses in a higher percentage of mice than rats. P. gingivalis 33277 caused lesions at the site of injection, whereas strains A7A1-28 and W50 induced abscesses at distant sites in both mice and rats. Local lesions were seen in rats injected with strain 381, whereas lesions formed distant from the site of injection in mice. When periodontal bone loss was assessed in the experimental rat model, animals challenged with 33277 had the highest amount of horizontal and vertical bone loss. Rats challenged with strain A7A1-28, W50 or 381 had some or no periodontal bone loss compared with controls. Assessment of antibody responses to P. gingivalis in these animals revealed that rats challenged with 33277 had lower levels of serum immunoglobulin G-(IgG) and especially salivary IgA antibody activity than A7A1-28-challenged rats. Serum IgG and in particular salivary IgA anti-P. gingivalis responses were seen in W50- and 381-challenged rats. These results indicate that the ability of P. gingivalis strains to cause abscesses does not relate directly to their periodontal pathogenicity as assessed by periodontal bone loss in the same animal model. The results further suggest the importance of salivary IgA antibody responses in protection against experimental periodontal bone loss after challenge with P. gingivalis.

Antibody responses to suspected periodontal pathogens in elderly subjects with periodontal disease

Little is known about the relationship of aging to periodontal disease. The immune response undergoes aging-related changes resulting in loss of functional capacity. The aim of this study was to investigate the relationship between levels of serum IgG antibodies against suspected periodontal pathogenic microorganisms to the presence or absence of periodontal disease in an elderly (65-75 yrs) population. From this study, we obtained information concerning: (1) the ability to differentiate elderly individuals without disease from those with disease by their levels of antibodies against periodontal pathogens and (2) which periodontal pathogen(s) triggered those responses. IgG anti- Porphyromonas gingivalis (strains W83 and 381) levels in the serum of elderly patients with severe periodontal disease were the only antibody responses measured which were elevated compared to the elderly control group of subjects with no periodontal disease. Anti- Prevotella intermedia IgG levels in both elderly patient groups were depressed compared to anti- P. intermedia levels in the young normal control subjects. Serum IgG antibody levels to six other plaque microorganisms did not differentiate between diseased and normal, elderly or young subjects. This data suggested that P. gingivalis was associated with periodontal disease in this elderly group of individuals and that those elderly individuals were able to respond with a normal IgG immune response.

Purification and characterization of Porphyromonas gingivalis outer membrane antigens

Porphyromonas gingivalis is strongly associated with periodontal disease. Significant titres of specific IgG antibodies to P. gingivalis can be found in healthy individuals and those with periodontitis. In this study, 22 outer membrane antigens ranging from 15.5 to 107.6 kDa were recognized by sera from persons with periodontitis and controls. Serum from individuals with periodontitis showed a significantly higher IgG response to a 31.4-kDa antigen (p < 0.05); serum from those with gingivitis demonstrated a significantly higher response to a 15.5-kDa antigen (p < 0.05). The response to the 15.5-kDa antigen might represent a protective immune response while that to the 31.4-kDa could serve as a marker for disease susceptibility. These two antigens were purified to homogeneity and their N-terminal amino acid sequences determined. The sequences did not correspond to any previously described P. gingivalis antigens. The role of these two antigens in the pathogenesis of periodontal disease remains to be determined.

Tetracyclines inhibit Porphyromonas gingivalis-induced alveolar bone loss in rats by a non-antimicrobial mechanism

Tetracyclines have been widely used as adjuncts in periodontal therapy due to the antimicrobial efficacy of these drugs. Recently, their ability to inhibit host-derived matrix metalloproteinases (collagenase and gelatinase) and bone resorption in organ culture has also been invoked as a therapeutic rationale. The current study was undertaken to determine whether tetracyclines can inhibit alveolar bone loss in vivo due to a non-antimicrobial action of these drugs. Experimental periodontitis was induced by inoculating adult, male Sprague-Dawley rats with P. gingivalis (strain 381) following kanamycin/ampicillin pretreatment. Doxycycline, non-antimicrobial chemically-modified tetracycline (CMT-1) and vehicle alone were administered daily to 3 infected groups of rats (n = 6 rats per group; each group housed in a sterilized inflatable isolator) beginning 10 days after P. gingivalis inoculation. The control group (n = 6; non-infected rats) received only vehicle. After 5 weeks of daily drug administration by gastric intubation, the experiment was terminated and blood samples were taken from each animal to determine antibody levels against P. gingivalis. Plaque samples were collected from each group of animals before and after P. gingivalis inoculation and at the end of the experiment for microbiological examination. The jaws were removed from each rat, defleshed and then analyzed morphometrically and radiographically to assess bone loss. Serum antibody levels against P. gingivalis were significantly elevated in the 3 infected groups compared to the non-infected controls. This, together with the microbiologic findings, indicated that these groups of rats were infected with P. gingivalis.(ABSTRACT TRUNCATED AT 250 WORDS)