Induction of experimental periodontitis in mice with Porphyromonas gingivalis-adhered ligatures

TRPV1 Regulates Proinflammatory Properties of M1 Macrophages in Periodontitis Via NRF2

Periodontitis, characterized by progressive alveolar bone destruction, leads to the loss of attachment and stability of the affected teeth. Macrophages, especially the proinflammatory M1 subtype, are key in periodontitis pathogenesis, driving the disease's inflammatory and destructive processes. Despite existing insight into their involvement, comprehensive understanding of the underlying molecular mechanisms remains limited. TRPV1 is a non-selective cation channel protein and is known to regulate cellular function and homeostasis in macrophages. Our research objective was to investigate the impact of TRPV1 on the proinflammatory attributes of M1 macrophages in periodontal tissues, exploring potential mechanistic pathways. A mouse model of periodontitis was established using Porphyromonas gingivalis inoculation and ligature application around the maxillary second molar. Immunohistological analysis showed a significant reduction in macrophage TRPV1 expression in periodontitis-induced mice. Treatment with capsaicin, a TRPV1 agonist, was observed to effectively elevate TRPV1 expression in these macrophages. Furthermore, micro-computed tomography analysis revealed a marked decrease in alveolar bone resorption in the capsaicin -treated group, compared with vehicle and healthy control groups. Our in vitro findings show that capsaicin treatment successfully attenuated LPS-induced TNF-α and IL-6 production in macrophages, mediated through NRF2 activation, consequently reducing intracellular ROS levels. These findings suggest that TRPV1 agonists, through modulating M1 macrophage activity and up-regulating TRPV1, could be a novel therapeutic approach in periodontal disease management.

The antimicrobial peptide Microcin C7 inhibits the growth of Porphyromonas gingivalis and improves the perodontal status in a rat model

AIMS

This study aimed to investigate the antibacterial and anti-inflammatory effects of the antimicrobial peptide Microcin C7 for Porphyromonas gingivalis-associated diseases.

METHODS AND RESULTS

Reverse-phase high-performance liquid chromatography revealed that Microcin C7 could remain 25.5% at 12 h in saliva. At a concentration of <10 mg ml-1, Microcin C7 showed better cytocompatibility, as revealed by a hemolysis test and a subchronic systemic toxicity test. Moreover, the minimum inhibitory concentration and minimum bactericidal concentration of Microcin C7 were analyzed using a broth microdilution method, bacterial growth curve, scanning electron microscopy, and confocal laser microscopy and determined to be 0.16 and 5 mg ml-1, respectively. Finally, in a rat model, 5 mg ml-1 Microcin C7 showed better performance in decreasing the expression of inflammatory factors (IL-1β, IL-6, IL-8, and TNF-α) and alveolar bone resorption than other concentrations.

CONCLUSIONS

Microcin C7 demonstrated favorable biocompatibility, antibacterial activity, and anti-inflammatory effect, and could decrease the alveolar bone resorption in a rat model, indicating the promising potential for clinical translation and application on P. gingivalis-associated diseases.

D-mannose alleviates chronic periodontitis in rats by regulating the functions of neutrophils

BACKGROUND

Periodontitis is a chronic inflammatory disease characterized by the destruction of the components of the periodontium. It significantly impacts oral health and has been linked to systemic conditions like cardiovascular disease and diabetes. The critical role of neutrophils in the occurrence and development of chronic periodontitis has been paid increasing attention. The study aimed to explore the protective effects of D-mannose on chronic periodontitis and determine whether its underlying mechanisms is related to neutrophils.

METHODS

To explore the protective effects of D-mannose on chronic periodontitis, the eight-week-old Sprague Dawley rat model of lipopolysaccharide (LPS)-induced periodontitis was established, followed by D-mannose treatment by oral gavage. To evaluate the protective effects of D-mannose against periodontal bone loss, methylene blue staining, hematoxylin and eosin (H&E) staining, and micro-CT scanning were utilized. Then, immunofluorescence (IF), Western Blot, and RT-PCR were applied to assess the expression levels of pro-inflammatory cytokines (IL-1β, IL-6, and IL-17), anti-inflammatory cytokine (IL-10), tumor necrosis factor-alpha (TNF-α), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), ten-eleven translocation 2 (TET2), and key glycolytic enzymes (HK1, HK2, PFKFB3), and to examine D-mannose's impact on the recruitment and activation of neutrophils in the gingiva. Additionally, neutrophils isolated from the peripheral blood of healthy rats were treated with LPS and D-mannose, and changes in the expression levels of myeloperoxidase (MPO), IL-1β, IL-6, IL-17, IL-10, and TET2 were observed via IF.

RESULTS

In vivo, D-mannose inhibited LPS-induced alveolar bone resorption in rats. After D-mannose treatment, the expression levels of IL-17 (p<0.01) and TET2 (p<0.01) were suppressed by IF, and the expression levels of IL-1β (p<0.05), IL-17 (p<0.05) and TET2 (p<0.01) were downregulated by WB. The results of qPCR showed that D-mannose reduced the expression levels of IL-1β (p<0.05), IL-6 (p<0.01), IL-17 (p<0.01), TNF-α (p<0.01), G-CSF (p<0.01), GM-CSF (p<0.01), TET2 (p<0.01), HK1 (p<0.01), HK2 (p<0.01), and PFKFB3 (p<0.01). D-mannose also inhibited the recruitment and activation of neutrophils in LPS-treated rat gingival tissues. In vitro, the results of IF showed that D-mannose inhibited the activation of neutrophils stimulated by LPS, downregulated the expression of IL-1β (p < 0.05), IL-6, IL-17 (p < 0.01), and TET2 (p < 0.01), and upregulated the expression of IL-10 (p < 0.01).

CONCLUSIONS

D-mannose can alleviate chronic periodontitis in rats by regulating the functions of neutrophils, potentially associated with the expression of TET2 and glycolysis, providing new insights into the potential application of D-mannose to chronic periodontitis.

Oral Lactobacillus zeae exacerbates the pathological manifestation of periodontitis in a mouse model

INTRODUCTION

The worldwide prevalence of periodontitis is considerably high, and its pathogenic mechanisms must be investigated and understood in order to improve clinical treatment outcomes and reduce the disease prevalence and burden. The exacerbation of the host immune system induced by oral microbial dysbiosis and the subsequent tissue destruction are the hallmarks of the periodontitis. However, the oral bacteria involved in periodontitis are not fully understood. We used the Oxford Nanopore Technologies (ONT) sequencing system to analyze metagenomic information in subgingival dental plaque from periodontitis and non-periodontitis patients. The number of Lactobacillus zeae (L. zeae) in the periodontitis patients was 17.55-fold higher than in the non-periodontitis patients, suggesting that L. zeae is a novel periodontitis-associated pathogen. Although several Lactobacillus species are used in vivo as probiotics to treat periodontitis and compete with Porphyromonas gingivalis (P. gingivalis), the roles of L. zeae in periodontitis progression, and the relationship between L. zeae and P. gingivalis needs to be investigated.

METHODS

Both L. zeae and P. gingivalis were inoculated in the ligature-implant site of periodontitis mice. We collected mouse gingival crevicular fluid to analyze inflammatory cytokine secretion using a multiplex assay. Intact or sliced mouse maxilla tissue was used for micro-computed tomography analysis or hematoxylin and eosin staining, immunohistochemistry, and tartrate-resistant acid phosphatase staining to evaluate alveolar bone loss, neutrophil infiltration, and osteoclast activation, respectively.

RESULTS

We observed that L. zeae competed with P. gingivalis, and it increased inflammatory cytokine secretion at the ligature-implant site. Similar to P. gingivalis, L. zeae promoted ligature-induced neutrophile infiltration, osteoclast activation, and alveolar bone loss.

DISCUSSION

We, therefore, concluded that L. zeae accelerated the progression of periodontitis in the ligature-induced periodontitis mouse model.

CXCR4-mediated neutrophil dynamics in periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is a common oral disease closely related to immune response and this study is aimed to identify the key immune-related pathogenic genes and analyze the infiltration and function of immune cells in the disease using bioinformatics methods.

METHODS

Transcriptome datasets and single-cell RNA sequencing (scRNA-seq) datasets were downloaded from the GEO database. We utilized weighted correlation network analysis and least absolute selection and shrinkage operator, protein-protein interaction network construction to screen out key pathogenic genes as well as conducted the cell-type identification by estimating relative subsets of RNA transcripts algorithm to analyze and characterize immune cell types in periodontal tissues. In addition to bioinformatics validations, clinical and cell samples were collected and mouse periodontitis models were constructed to validate the important role of key genes in periodontitis.

RESULTS

Bioinformatics analysis pointed out the positive correlation between CXCR4 expression and periodontitis, and revealed the increased infiltration of neutrophils in periodontal inflammatory. Similar results were obtained from clinical samples and animal models. In addition, the clustering and functional enrichment results based on CXCR4 expression levels included activation of immune response and cell migration, implying the possible function of CXCR4 on regulating neutrophil dynamics, which might contribute to periodontitis. Subsequent validation experiments confirmed that the increased expression of CXCR4 in neutrophils under periodontitis, where cell migration-related pathways also were activated.

CONCLUSION

CXCR4 could be the key pathogenic gene of periodontitis and CXCR4/CXCL12 signal axial might contribute to the development of periodontitis by mediating neutrophil dynamics, suggesting that CXCR4 could be a potential target to help identify novel strategies for the clinical diagnosis and treatment of periodontitis.

hTERT Peptide Fragment GV1001 Prevents the Development of Porphyromonas gingivalis-Induced Periodontal Disease and Systemic Disorders in ApoE-Deficient Mice

GV1001, an anticancer vaccine, exhibits other biological functions, including anti-inflammatory and antioxidant activity. It also suppresses the development of ligature-induced periodontitis in mice. Porphyromonas gingivalis (Pg), a major human oral bacterium implicated in the development of periodontitis, is associated with various systemic disorders, such as atherosclerosis and Alzheimer's disease (AD). This study aimed to explore the protective effects of GV1001 against Pg-induced periodontal disease, atherosclerosis, and AD-like conditions in Apolipoprotein (ApoE)-deficient mice. GV1001 effectively mitigated the development of Pg-induced periodontal disease, atherosclerosis, and AD-like conditions by counteracting Pg-induced local and systemic inflammation, partly by inhibiting the accumulation of Pg DNA aggregates, Pg lipopolysaccharides (LPS), and gingipains in the gingival tissue, arterial wall, and brain. GV1001 attenuated the development of atherosclerosis by inhibiting vascular inflammation, lipid deposition in the arterial wall, endothelial to mesenchymal cell transition (EndMT), the expression of Cluster of Differentiation 47 (CD47) from arterial smooth muscle cells, and the formation of foam cells in mice with Pg-induced periodontal disease. GV1001 also suppressed the accumulation of AD biomarkers in the brains of mice with periodontal disease. Overall, these findings suggest that GV1001 holds promise as a preventive agent in the development of atherosclerosis and AD-like conditions associated with periodontal disease.

Intestinal Translocation of Live Porphyromonas gingivalis Drives Insulin Resistance

Periodontitis has been emphasized as a risk factor of insulin resistance-related systemic diseases. Accumulating evidence has suggested a possible "oral-gut axis" linking oral infection and extraoral diseases, but it remains unclear whether periodontal pathogens can survive the barriers of the digestive tract and how they play their pathogenic roles. The present study established a periodontitis mouse model through oral ligature plus Porphyromonas gingivalis inoculation and demonstrated that periodontitis aggravated diet-induced obesity and insulin resistance, while also causing P. gingivalis enrichment in the intestine. Metabolic labeling strategy validated that P. gingivalis could translocate to the gastrointestinal tract in a viable state. Oral administration of living P. gingivalis elicited insulin resistance, while administration of pasteurized P. gingivalis had no such effect. Combination analysis of metagenome sequencing and nontargeted metabolomics suggested that the tryptophan metabolism pathway, specifically indole and its derivatives, was involved in the pathogenesis of insulin resistance caused by oral administration of living P. gingivalis. Moreover, liquid chromatography-high-resolution mass spectrometry analysis confirmed that the aryl hydrocarbon receptor (AhR) ligands, mainly indole acetic acid, tryptamine, and indole-3-aldehyde, were reduced in diet-induced obese mice with periodontitis, leading to inactivation of AhR signaling. Supplementation with Ficz (6-formylindolo (3,2-b) carbazole), an AhR agonist, alleviated periodontitis-associated insulin resistance, in which the restoration of gut barrier function might play an important role. Collectively, these findings reveal that the oral-gut translocation of viable P. gingivalis works as a fuel linking periodontitis and insulin resistance, in which reduction of AhR ligands and inactivation of AhR signaling are involved. This study provides novel insight into the role of the oral-gut axis in the pathogenesis of periodontitis-associated comorbidities.

Evaluation of morphological, histological, and immune-related cellular changes in ligature-induced experimental periodontitis in mice

Background/purpose

The ligature-induced periodontitis model is an effective approach to induce inflammation and bone loss similar to that of human periodontitis. Previous clinical and in vitro studies have shown the involvement of lymphocytes in periodontitis, while, the local and systemic profile of immune cells associated with periodontitis in the ligature-induced periodontitis model in mice remains unclear.

Materials and methods

Experimental periodontitis was constructed in mice by ligating around the maxillary second molars for 14 and 28 days, respectively. Alveolar bone loss was assessed by micro-computed tomography (micro-CT). Hematoxylin and eosin (H&E) and tartrate-resistant acid phosphatase (TRAP) staining were used to evaluate the histological changes in the periodontal tissues. B and T cells in the cervical lymph nodes, spleen, and peripheral blood were analyzed by flow cytometry.

Results

The 14-day ligation effectively induced significant periodontal inflammation and alveolar bone loss in C57BL/6J mice, which were progressive and maintained for a relatively long-term period until day 28. In addition, CD3+ T cells and CD19+ B cells were the dominant population in both health and disease, and the B cell population within the cervical lymph nodes (LN) increased significantly under periodontitis condition, while, no significant differences of the T and B cell population among the spleen and peripheral blood were observed.

Conclusion

The ligature-induced periodontitis mice model was established to perform a longitudinal assessment of changes in periodontal tissues morphologically and histologically, meanwhile, explore the local and systemic changes of the predominant immune-associated cells.

Stevioside reduces inflammation in periodontitis by changing the oral bacterial composition and inhibiting P. gingivalis in mice

BACKGROUND

Excessive sugar intake has become a major challenge in modern societies. Stevioside is a promising non-calorie sweetener with anti-inflammatory effects; however, its effects on the oral environment and periodontitis remain unclear. Therefore, this study explores the effect of stevioside on periodontitis in mice.

METHODS

Mice were divided into four groups, namely, control, treated with water, and periodontitis models, established using 5 - 0 silk sutures ligation around the second molar then infected the oral cavity with Porphyromonas gingivalis (P. gingivalis) viscous suspension, divided into three groups treated with 0.1% stevioside (P + S), 10% glucose (P + G), or water (P). Micro-CT scanning was used to assess alveolar bone resorption, while RT-PCR was used to evaluate the inflammatory factors expression and P. gingivalis invasion in the gingiva. The composition of the oral bacteria was analysed using 16 S rRNA sequence in the saliva. In addition, P. gingivalis was co-cultured with stevioside at different concentrations in vitro, and bacterial activity was detected via optical density values and live/dead staining. The virulence was detected using RT-PCR, while biofilm formation was detected using scanning electron microscopy.

RESULTS

Compared with 10% glucose, treatment with 0.1% stevioside reduced alveolar bone absorption and osteoclasts while decreasing IL-6, TNF-α, IL-1β, and P. gingivalis in the gingiva of periodontitis mice. The CEJ-ABC distance in the P + S group was significantly lower than that in the P and P + G groups (P < 0.05). Moreover, the composition of the oral bacteria in the P + S group was similar to that of the control. In vitro stevioside treatment also reduced the bacterial activity and toxicity of P. gingivalis in a dose-dependent manner and affected its biofilm composition.

CONCLUSION

Our results indicate that, compared with 10% glucose, 0.1% stevioside intake can reduce alveolar bone resorption and inflammation in periodontal tissues in mice; the bacterial composition following 0.1% stevioside intake was similar to that of a healthy environment. In vitro, high concentrations of stevioside reduced P. gingivalis activity, biofilm formation, and virulence expression. Therefore, stevioside is a potential alternative to glucose for patients with periodontitis.

Porphyromonas gingivalis induces an inflammatory response via the cGAS-STING signaling pathway in a periodontitis mouse model

Periodontitis is an inflammatory disease initiated by periodontopathogenic bacteria in the dental plaque biofilms. Understanding the role of Porphyromonas gingivalis (P. gingivalis), a keystone pathogen associated with chronic periodontitis, in the inflammatory response is crucial. Herein, we investigated whether P. gingivalis infection triggers the expression of the type I IFN gene and various cytokines and leads to activation of the cGAMP synthase-stimulator of IFN genes (cGAS-STING) pathway both in vitro and in a mouse model. Additionally, in an experimental model of periodontitis using P. gingivalis, Sting^Gt mice showed lower levels of inflammatory cytokines and bone resorption than wild-type mice. Furthermore, we report that a STING inhibitor (SN-011) significantly decreased inflammatory cytokine production and osteoclast formation in a periodontitis mouse model with P. gingivalis. In addition, STING agonist (SR-717) -treated periodontitis mice displayed enhanced macrophage infiltration and M1 macrophage polarization in periodontal lesions compared with that in vehicle-treated periodontitis mice. In conclusion, our results demonstrate that the cGAS-STING signaling pathway may be one of the key mechanisms crucial for the P. gingivalis-induced inflammatory response that leads to chronic periodontitis.

Contribution of -Omics Technologies in the Study of Porphyromonas gingivalis during Periodontitis Pathogenesis: A Minireview

Periodontitis is a non-communicable chronic inflammatory disease characterized by the progressive and irreversible breakdown of the soft periodontal tissues and resorption of teeth-supporting alveolar bone. The etiology of periodontitis involves dysbiotic shifts in the diversity of microbial communities inhabiting the subgingival crevice, which is dominated by anaerobic Gram-negative bacteria, including Porphyromonas gingivalis. Indeed, P. gingivalis is a keystone pathogen with a repertoire of attributes that allow it to colonize periodontal tissues and influence the metabolism, growth rate, and virulence of other periodontal bacteria. The pathogenic potential of P. gingivalis has been traditionally analyzed using classical biochemical and molecular approaches. However, the arrival of new techniques, such as whole-genome sequencing, metagenomics, metatranscriptomics, proteomics, and metabolomics, allowed the generation of high-throughput data, offering a suitable option for bacterial analysis, allowing a deeper understanding of the pathogenic properties of P. gingivalis and its interaction with the host. In the present review, we revise the use of the different -omics technologies and techniques used to analyze bacteria and discuss their potential in studying the pathogenic potential of P. gingivalis.

Aberrant pulmonary immune response of obese mice to periodontal infection

Obesity and periodontitis constitute mutual risk factors in respiratory disorders; this study aimed to explore the pulmonary immune response to periodontal infection using combined animal models with diet-induced obesity (DIO). Thirty-two C57 BL/6J mice were randomly divided into low-fat (LF) or high-fat (HF) diet groups and fed an LF diet as a control or an HF diet to induce obesity. The 30-week mice in the diet group were divided into periodontal ligation group (10 days using Porphyromonas gingivalis ATCC 33277) or sham-ligation group. The expressions of the macrophage-specific maker (F4/80), macrophage chemotactic protein1 (MCP1), and inflammatory cytokines in lung tissues were analyzed. The mRNA and protein levels of F4/80, MCP1, interleukin (IL)-1β, and IL-6 expressions were significantly upregulated by obesity in lung tissues. However, the mRNA and protein levels of F4/80, MCP1, and IL-6 were downregulated by periodontitis in DIO mice relative to that of the HF control group. Periodontitis increased tumor necrosis factor-α level of lung tissues under LF, while IL-10 was not affected by obesity regardless of periodontitis. Periodontitis may aggravate pulmonary immune response in obese rodents. This may relate to the imbalance of the pro- and anti-inflammatory cytokine status of lung lesions, which tends to attenuate the infiltration of alveolar macrophages.

Topical application of Porphyromonas gingivalis into the gingival pocket in mice leads to chronic‑active infection, periodontitis and systemic inflammation

Porphyromonas gingivalis (Pg), one of the 'red-complex' perio-pathogens known to play a critical role in the development of periodontitis, has been used in various animal models to mimic human bacteria-induced periodontitis. In order to achieve a more realistic animal model of human Pg infection, the present study investigated whether repeated small-volume topical applications of Pg directly into the gingival pocket can induce local infection, including periodontitis and systemic vascular inflammation in wild-type mice. Freshly cultured Pg was topically applied directly into the gingival pocket of the second molars for 5 weeks (3 times/week). After the final application, the mice were left in cages for 4 or 8 weeks and sacrificed. The status of Pg colony formation in the pocket, gingival inflammation, alveolar bone loss, the expression levels of pro-inflammatory cytokines in the serum and aorta, the presence of anti-Pg lipopolysaccharide (LPS) and gingipain (Kpg and RgpB) antibodies in the serum, as well as the accumulation of Pg LPS and gingipain aggregates in the gingiva and arterial wall were evaluated. The topical application of Pg into the gingival pocket induced the following local and systemic pathohistological changes in mice when examined at 4 or 8 weeks after the final topical Pg application: Pg colonization in the majority of gingival pockets; increased gingival pocket depths; gingival inflammation indicated by the increased expression of TNF-α, IL-6 and IL-1β; significant loss of alveolar bone at the sites of topical Pg application; and increased levels of pro-inflammatory cytokines, such as TNF-α, IL-1β, IL-17, IL-13, KC and IFN-γ in the serum in comparison to those from mice receiving PBS. In addition, the Pg application/colonization model induced anti-Pg LPS and gingipain antibodies in serum, as well as the accumulation of Pg LPS and gingipain aggregates in the gingivae and arterial walls. To the best of our knowledge, this mouse model represents the first example of creating a more sustained local infection in the gingival tissues of wild-type mice and may prove to be useful for the investigation of the more natural and complete pathogenesis of the bacteria in the development of local oral and systemic diseases, such as atherosclerosis. It may also be useful for the determination of a treatment/prevention/efficacy model associated with Pg-induced colonization periodontitis in mice.

NLRP3 Is Involved in Neutrophil Mobilization in Experimental Periodontitis

The NLRP3 inflammasome is overexpressed in gingiva of periodontitis patients but its role remains unclear. In our study, we use a periodontitis mouse model of ligature, impregnated or not with Porphyromonas gingivalis, in WT or NLRP3 KO mice. After 28 days of induction, ligature alone provoked exacerbated periodontal destruction in KO mice, compared to WT mice, with an increase in activated osteoclasts. No difference was observed at 14 days, suggesting that NLRP3 is involved in regulatory pathways that limit periodontitis. In contrast, in the presence of P. gingivalis, this protective effect of NLRP3 was not observed. Overexpression of NLRP3 in connective tissue of WT mice increased the local production of mature IL-1β, together with a dramatic mobilization of neutrophils, bipartitely distributed between the site of periodontitis induction and the alveolar bone crest. P. gingivalis enhanced the targeting of NLRP3-positive neutrophils to the alveolar bone crest, suggesting a role for this subpopulation in bone loss. Conversely, in NLRP3 KO mice, mature IL-1β expression was lower and almost no neutrophils were mobilized. Our study sheds new light on the role of NLRP3 in periodontitis by highlighting the ambiguous role of neutrophils, and P. gingivalis which affects NLRP3 functions.

Mechanism of alveolar bone destruction in periodontitis - Periodontal bacteria and inflammation

Periodontal disease is an inflammatory disease caused by periodontopathogenic bacteria, which eventually leads to bone tissue (alveolar bone) destruction as inflammation persists. Periodontal tissues have an immune system against the invasion of these bacteria, however, due to the persistent infection by periodontopathogenic bacteria, the host innate and acquired immunity is impaired, and tissue destruction, including bone tissue destruction, occurs. Osteoclasts are essential for bone destruction. Osteoclast progenitor cells derived from hematopoietic stem cells differentiate into osteoclasts. In addition, bone loss occurs when bone resorption by osteoclasts exceeds bone formation by osteoblasts. In inflammatory bone disease, inflammatory cytokines act on osteoblasts and receptor activator of nuclear factor-κB ligand (RANKL)-producing cells, resulting in osteoclast differentiation and activation. In addition to this mechanism, pathogenic factors of periodontal bacteria and mechanical stress activate osteoclasts and destruct alveolar bone in periodontitis. In this review, we focused on the mechanism of osteoclast activation in periodontitis and provide an overview based on the latest findings.

Application of Ligature-Induced Periodontitis in Mice to Explore the Molecular Mechanism of Periodontal Disease

Periodontitis is an inflammatory disease characterized by the destruction of the periodontium. In the last decade, a new murine model of periodontitis has been widely used to simulate alveolar bone resorption and periodontal soft tissue destruction by ligation. Typically, 3-0 to 9-0 silks are selected for ligation around the molars in mice, and significant bone loss and inflammatory infiltration are observed within a week. The ligature-maintained period can vary according to specific aims. We reviewed the findings on the interaction of systemic diseases with periodontitis, periodontal tissue destruction, the immunological and bacteriological responses, and new treatments. In these studies, the activation of osteoclasts, upregulation of pro-inflammatory factors, and excessive immune response have been considered as major factors in periodontal disruption. Multiple genes identified in periodontal tissues partly reflect the complexity of the pathogenesis of periodontitis. The effects of novel treatment methods on periodontitis have also been evaluated in a ligature-induced periodontitis model in mice. This model cannot completely represent all aspects of periodontitis in humans but is considered an effective method for the exploration of its mechanisms. Through this review, we aimed to provide evidence and enlightenment for future studies planning to use this model.

TLR-4 targeting contributes to the recovery of osteoimmunology in periodontitis

OBJECTIVE

The aim of this study was to determine the potential role of TLR-4 in the osteoimmunological imbalance of periodontitis.

BACKGROUND

Although current evidence supports that TLR-4 plays an important role in the inflammatory response of periodontal tissues triggered by microorganisms, little information is available regarding the function of TLR-4 in the osteoimmune regulation of homeostasis in periodontitis.

METHODS

Human gingival epithelial cells (HGEC) were isolated from the gingival tissues of 3 healthy volunteers and the expression of osteoclastogenic cytokines was evaluated by ELISA and real time RT-PCR. In addition, 30 C57BL/6 mice were used and randomly divided into three groups: control group, periodontitis group (CP) and periodontitis+TAK-242 (a specific inhibitor of TLR-4) group (TAK-242) and the expression of osteoclastogenic cytokines and the osteoclast density in the periodontal tissue were evaluated by immunohistochemical staining and tartrate resistant acid phosphatase staining. Moreover, micro-computed tomography (Micro-CT) was used to assess bone resorption.

RESULTS

The in vitro results showed that TAK-242 blocked the overproduction of IL-1, IL-6, TNF-α and RANKL in HGEC treated with LPS. The in vivo results revealed that TAK-242 also effectively decreased these osteoclastogenic cytokines in periodontal tissue of mice with periodontitis. More importantly, Micro-CT analysis showed a significant reduction of the alveolar bone loss in the TAK-242 group compared with the CP group. Furthermore, the TRAP staining showed a significant lower density of osteoclasts in the alveolar bone area of the TAK-242 group.

CONCLUSION

TLR-4 inhibition decreased the differentiation of osteoclast through the inhibition of the overproduction of osteoclastogenic cytokines and the prevention of the alveolar bone absorption in mouse periodontitis models. Therefore, the use of TAK-242 might contribute to the recovery of the osteoimmunological homeostasis and might provide a potential strategy to treat periodontal diseases.

Exacerbation of AMD Phenotype in Lasered CNV Murine Model by Dysbiotic Oral Pathogens

Emerging evidence underscores an association between age-related macular degeneration (AMD) and periodontal disease (PD), yet the biological basis of this linkage and the specific role of oral dysbiosis caused by PD in AMD pathophysiology remains unclear. Furthermore, a simple reproducible model that emulates characteristics of both AMD and PD has been lacking. Hence, we established a novel AMD+PD murine model to decipher the potential role of oral infection (ligature-enhanced) with the keystone periodontal pathogen Porphyromonas gingivalis, in the progression of neovasculogenesis in a laser-induced choroidal-neovascularization (Li-CNV) mouse retina. By a combination of fundus photography, optical coherence tomography, and fluorescein angiography, we documented inflammatory drusen-like lesions, reduced retinal thickness, and increased vascular leakage in AMD+PD mice retinae. H&E further confirmed a significant reduction of retinal thickness and subretinal drusen-like deposits. Immunofluorescence microscopy revealed significant induction of choroidal/retinal vasculogenesis in AMD+PD mice. qPCR identified increased expression of oxidative-stress, angiogenesis, pro-inflammatory mediators, whereas antioxidants and anti-inflammatory genes in AMD+PD mice retinae were notably decreased. Through qPCR, we detected Pg and its fimbrial 16s-RrNA gene expression in the AMD+PD mice retinae. To sum-up, this is the first in vivo study signifying a role of periodontal infection in augmentation of AMD phenotype, with the aid of a pioneering AMD+PD murine model established in our laboratory.

Eye on the Enigmatic Link: Dysbiotic Oral Pathogens in Ocular Diseases; The Flip Side

Mouth and associated structures were regarded as separate entities from the rest of the body. However, there is a paradigm shift in this conception and oral health is now considered as a fundamental part of overall well-being. In recent years, the subject of oral-foci of infection has attained a resurgence in terms of systemic morbidities while limited observations denote the implication of chronic oral inflammation in the pathogenesis of eye diseases. Hitherto, there is a paucity for mechanistic insights underlying the reported link between periodontal disease (PD) and ocular comorbidities. In light of prevailing scientific evidence, this review article will focus on the understudied theme, that is, the impact of oral dysbiosis in the induction and/or progression of inflammatory eye diseases like diabetic retinopathy, scleritis, uveitis, glaucoma, age-related macular degeneration (AMD). Furthermore, the plausible mechanisms by which periodontal microbiota may trigger immune dysfunction in the Oro-optic-network and promote the development of PD-associated AMD have been discussed.

DiTaxa: nucleotide-pair encoding of 16S rRNA for host phenotype and biomarker detection

SUMMARY

Identifying distinctive taxa for micro-biome-related diseases is considered key to the establishment of diagnosis and therapy options in precision medicine and imposes high demands on the accuracy of micro-biome analysis techniques. We propose an alignment- and reference- free subsequence based 16S rRNA data analysis, as a new paradigm for micro-biome phenotype and biomarker detection. Our method, called DiTaxa, substitutes standard operational taxonomic unit (OTU)-clustering by segmenting 16S rRNA reads into the most frequent variable-length subsequences. We compared the performance of DiTaxa to the state-of-the-art methods in phenotype and biomarker detection, using human-associated 16S rRNA samples for periodontal disease, rheumatoid arthritis and inflammatory bowel diseases, as well as a synthetic benchmark dataset. DiTaxa performed competitively to the k-mer based state-of-the-art approach in phenotype prediction while outperforming the OTU-based state-of-the-art approach in finding biomarkers in both resolution and coverage evaluated over known links from literature and synthetic benchmark datasets.

AVAILABILITY AND IMPLEMENTATION

DiTaxa is available under the Apache 2 license at http://llp.berkeley.edu/ditaxa.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Periodontal Disease Impairs Muscle Recovery by Modulating the Recruitment of Leukocytes

The purpose of this study is to analyze the impact of periodontal disease (PD) associated with physical exercise on inflammatory mediators and muscle repair. Twenty-four Wistar rats were divided into four groups: control (SH), healthy trained (TH), sedentary with PD (SP), and trained with PD (TP). PD was induced in groups SP and TP while the trained groups performed treadmill exercises for 8 weeks. For the analysis of IL-6, IL-10, TNF-α, and leukocyte count, we collected blood samples. Cryolesions were induced in the tibialis anterior and gastrocnemius, which were analyzed for morphological changes. The presence of PD modified leukocyte counts, while exercise showed an additive role. PD increased levels of IL-6, IL-10, and TNF-α, and physical exercise changed only values of IL-10. The association between physical exercise and PD was responsible for an increased concentration of leukocytes in the region of the inflammation. Serum levels of inflammatory markers were modified by PD and, when combined with exercise, may negatively modulate inflammation. The association between PD and physical exercise showed the most significant changes in the number of inflammatory cells and may negatively influence the process of muscle repair.

Aberrant Periodontal and Systemic Immune Response of Overweight Rodents to Periodontal Infection

This study aimed to explore periodontal and systemic immune response of overweight hosts to periodontitis. Forty C57 BL/6J male mice were divided into high (HF) or low fat (LF) diet groups and fed with the two diets, respectively, for 8 weeks. Each diet group was then divided into periodontitis (P) or control (C) groups (n = 10 per group) for 10-day ligation or sham-ligation. Overweight-related parameters including body weight were measured. Alveolar bone loss (ABL) was morphometrically analyzed and periodontal osteoclasts were stained. Periodontal immune response including leukocyte and macrophage number and inflammatory cytokines were analyzed by histology and quantitative PCR. Serum cytokine and lipid levels were quantified using electrochemiluminescence immunoassays, enzyme-linked immunosorbent assays, and biochemistry. It was found that HF group had 14.4% body weight gain compared with LF group (P < 0.01). ABL and periodontal osteoclast, leukocyte, and macrophage number were higher in P group than C group regardless of diet (P < 0.05). ABL and periodontal osteoclast number were not affected by diet regardless of ligation or sham-ligation. Leukocyte and macrophage number and protein level of tumor necrosis factor α (TNF-α) in periodontium and serum interleukin-6 level were downregulated by HF diet in periodontitis mice (P < 0.05). Periodontal protein level of TNF-α was highly correlated with serum interleukin-6 and low-density lipoprotein cholesterol levels (P < 0.01). These findings indicated that impaired immune response occurs both periodontally and systemically in preobesity overweight individuals. Given a well-reported exacerbating effect of obesity on periodontitis, overweight, if let uncontrolled, might place the individuals at potential risk for future periodontal tissue damage.

Functional assessment of peptide-modified PLGA nanoparticles against oral biofilms in a murine model of periodontitis

The interaction of the periodontal pathogen Porphyromonas gingivalis (Pg) with commensal streptococci promotes Pg colonization of the oral cavity. Previously, we demonstrated that a peptide (BAR) derived from Streptococcus gordonii (Sg) potently inhibited adherence of Pg to streptococci and reduced Pg virulence in a mouse model of periodontitis. Thus, BAR may represent a novel therapeutic to control periodontitis by preventing Pg colonization of the oral cavity. However, while BAR inhibited the initial formation of Pg/Sg biofilms, much higher concentrations of peptide were required to disrupt an established Pg/Sg biofilm. To improve the activity of the peptide, poly(lactic-co-glycolic acid) (PLGA) nanoparticles were surface-modified with BAR and shown to more potently disrupt Pg/Sg biofilms relative to an equimolar amount of free peptide. The goal of this work was to determine the in vivo efficacy of BAR-modified NPs (BNPs) and to assess the toxicity of BNPs against human gingival epithelial cells. In vivo efficacy of BNPs was assessed using a murine model of periodontitis by measuring alveolar bone resorption and gingival IL-17 expression as outcomes of Pg-induced inflammation. Infection of mice with Pg and Sg resulted in a significant increase in alveolar bone loss and gingival IL-17 expression over sham-infected animals. Treatment of Pg/Sg infected mice with BNPs reduced bone loss and IL-17 expression almost to the levels of sham-infected mice and to a greater extent than treatment with an equimolar amount of free BAR. The cytotoxicity of the maximum concentration of BNPs and free BAR used in in vitro and in vivo studies (1.3 and 3.4 μM), was evaluated in telomerase immortalized gingival keratinocytes (TIGKs) by measuring cell viability, cell lysis and apoptosis. BNPs were also tested for hemolytic activity against sheep erythrocytes. TIGKs treated with BNPs or free BAR demonstrated >90% viability and no significant lysis or apoptosis relative to untreated cells. In addition, neither BNPs nor free BAR exhibited hemolytic activity. In summary, BNPs were non-toxic within the evaluated concentration range of 1.3-3.4 μM and provided more efficacious protection against Pg-induced inflammation in vivo, highlighting the potential of BNPs as a biocompatible platform for translatable oral biofilm applications.

Synthesis of a Novel Electrospun Polycaprolactone Scaffold Functionalized with Ibuprofen for Periodontal Regeneration: An In Vitro andIn Vivo Study

Ibuprofen (IBU) has been shown to improve periodontal treatment outcomes. The aim of this study was to develop a new anti-inflammatory scaffold by functionalizing an electrospun nanofibrous poly-ε-caprolactone membrane with IBU (IBU-PCL) and to evaluate its impact on periodontal inflammation, wound healing and regeneration in vitro and in vivo. IBU-PCL was synthesized through electrospinning. The effects of IBU-PCL on the proliferation and migration of epithelial cells (EC) and fibroblasts (FB) exposed to Porphyromonas gingivlais lipopolysaccharide (Pg-LPS) were evaluated through the AlamarBlue test and scratch assay, respectively. Anti-inflammatory and remodeling properties were investigated through Real time qPCR. Finally, the in vivo efficacy of the IBU-PCL membrane was assessed in an experimental periodontitis mouse model through histomorphometric analysis. The results showed that the anti-inflammatory effects of IBU on gingival cells were effectively amplified using the functionalized membrane. IBU-PCL reduced the proliferation and migration of cells challenged by Pg-LPS, as well as the expression of fibronectin-1, collagen-IV, integrin α3β1 and laminin-5. In vivo, the membranes significantly improved the clinical attachment and IBU-PCL also reduced inflammation-induced bone destruction. These data showed that the IBU-PCL membrane could efficiently and differentially control inflammatory and migratory gingival cell responses and potentially promote periodontal regeneration.

[Periodontal inflammation affects the mechanical and immune barrier functions of mice gut]

OBJECTIVE

To explore the effects of periodontal inflammation on the functions of gut barrier (ecological barrier, mechanical barrier, and immune barrier) in mice.

METHODS

Twenty male C57BL/6J mice were randomly divided into perio-dontitis (P) or control (C) groups. The P group was subjected under a 10-day ligation with Porphyromonas gingivalis to induce periodontitis, whereas the C group was ligated with sham. Maxillae were obtained to assess alveolar bone loss. The phylogenetic structure and diversity of microbial communities in the gut were analyzed by 16s rRNA pyrosequencing. Immunohisto-chemical analysis was performed to determine the expressions of occludin, claudin2, and NOD2 in the ileum.

RESULTS

Com-pared with the C group, the P group displayed significant alveolar bone loss (P<0.001). In addition, no significant influence on the main phyla and genus Parabacteroides of the two groups was observed (P>0.05). However, the ileum of the P group showed significantly upregulated occludin, claudin2, and NOD2 (P=0.039, P=0.011, and P=0.039, respectively).

CONCLUSIONS

Periodontal inflammation influences to some extent the mechanical and immune barrier functions of the mice gut. 
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Macrophages Play a Key Role in the Obesity-Induced Periodontal Innate Immune Dysfunction via Nucleotide-Binding Oligomerization Domain-Like Receptor Protein 3 Pathway

BACKGROUND

Obesity is associated with infiltration of macrophages into adipose tissue. However, effects of obesity on macrophage infiltration and activation in periodontal tissues with periodontitis are still to be elucidated.

METHODS

A diet-induced obesity 16-week mouse model was constructed, and periodontitis was induced by periodontal ligation for 10 days. The model consisted of periodontitis (P) and control (C) groups, with high fat (HF) and normal (N) diet conditions. Bone loss (BL) was analyzed by microcomputed tomography. In periodontal tissues, immunohistochemical staining and quantitative polymerase chain reaction (qPCR) detected expressions of: 1) nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) pathway; 2) macrophage-specific marker (F4/80); and 3) macrophage chemotactic protein 1 (MCP1). Bone marrow-derived macrophages (BMDMs) from the mouse model were stimulated by Porphyromonas gingivalis lipopolysaccharide (LPS) in vitro (NC/NC + LPS: BMDMs from NC group without/with LPS stimulation; HFC/HFC + LPS: BMDMs from HFC group without/with LPS stimulation). Expressions of NLRP3 pathway in BMDMs were detected by immunocytochemical staining and qPCR.

RESULTS

BL increased significantly with periodontitis (NC versus NP; HFC versus HFP) and obesity (NP versus HFP). Expressions of NLRP3 pathway were significantly elevated in gingival tissues with periodontitis (NC versus NP; HFC versus HFP), but not with obesity (NC versus HFC; NP versus HFP). F4/80 and MCP1 expressions were significantly upregulated in gingival tissues with periodontitis (NC versus NP; HFC versus HFP) but significantly downregulated in the context of obesity (NP versus HFP). In vitro, NLRP3 pathway expressions were significantly upregulated in BMDMs after LPS stimulation (NC + LPS versus NC; HFC + LPS versus HFC), but significantly downregulated in HFC groups (HFC versus NC; HFC + LPS versus NC + LPS).

CONCLUSION

Obesity may paralyze innate immune response of periodontium via attenuating infiltration and activation of macrophages and further aggravate periodontal disease.

Enhanced Activity of the Macrophage M1/M2 Phenotypes and Phenotypic Switch to M1 in Periodontal Infection

BACKGROUND

Macrophages are central players in the pathogenesis of periodontitis. However, the phenotypic switch of macrophage M1/M2 remains uncertain.

METHODS

Adult male mice were divided into periodontitis (P) or control (C) groups. Bone marrow-derived macrophages (BMMs) were stimulated with Porphyromonas gingivalis lipopolysaccharide (LPS). In both the periodontium and serum, macrophage M1 and M2 phenotypes were detected in vivo and in vitro via the following: 1) immunofluorescence; 2) immunohistochemistry; 3) electrochemiluminescence immunoassays; 4) quantitative polymerase chain reaction assays; and 5) enzyme-linked immunosorbent assays. The M1-type markers used included the following: 1) nitric oxide synthase (NOS)-2; 2) tumor necrosis factor-alpha; 3) interleukin (IL)-1β; 4) IL-6; and 5) C-reactive protein. The M2-type markers were as follows: 1) arginase-1; 2) cluster of differentiation (CD) 206; and 3) IL-10.

RESULTS

Compared with the C group, the P group had a 14-fold increase in F4/80(+) NOS2(+) cells and four-fold more F4/80(+) CD206(+) cells with an enhanced NOS2/CD206 ratio in the periodontium (P <0.01). NOS2(-) CD206(+) and dual NOS2(+) CD206(+) macrophages dominated in the C and P groups, respectively. The P group had significantly increased M1- and M2-type cytokines in both the periodontium and serum and also had an enhanced IL-6/IL-10 ratio in the serum (P <0.05). M1-type markers were significantly upregulated at the mRNA level, whereas M2-type markers were downregulated at both the mRNA and protein levels in BMMs after LPS stimulation (P <0.01).

CONCLUSION

Periodontal inflammation is associated with an enhancement of both the M1 and M2 phenotypes of macrophages, in which a phenotypic switch of M2 to M1 might be a critical mechanism in mediating periodontal tissue damage, including alveolar bone loss.

Periodontitis aggravated pancreatic β-cell dysfunction in diabetic mice through interleukin-12 regulation on Klotho

Aims/Introduction

Recent studies have shown that periodontitis can contribute to adipose tissue inflammation and subsequent systemic insulin resistance in the obese rat model. However, the related inflammatory mechanism is not yet clear. The present study aims to investigate the effects of periodontitis on the function of pancreatic β‐cells with pro‐inflammatory cytokines‐related immune mechanism in a mouse model.

Materials and Methods

C57BL/6‐db/db and inbred C57BL/6 mice were chosen here to establish a mouse model with periodontitis, which was induced by ligatures for 8 weeks. Glucose‐stimulated insulin secretion was introduced to evaluate the function of pancreatic islets and β‐cells. Serum levels of pro‐inflammatory cytokines and Klotho were also measured, and the correlation between immunostimulation and Klotho level was deeply investigated in vitro.

Results

Pancreatic β‐cell failure, with insulin resistance, was observed in db/db mice, while periodontitis could aggravate β‐cell dysfunction‐related features. Serum levels of interleukin (IL)‐12 and Klotho showed a negatively synergistic change, whereas the expression of Klotho was also inhibited under IL‐12 treatment in MIN6 β‐cells or isolated islets. Furthermore, IL‐12‐induced immune stimulation and also decreased insulin secretion were proven to be reversed by Klotho overexpression.

Conclusions

Periodontitis aggravated pancreatic β‐cell failure in diabetic mice. Further in vitro studies showed IL‐12 regulation on Klotho, while Klotho also acted as an inhibitor on IL‐12, indicating the potential of Klotho for preserving pancreatic β‐cell function in diabetes.

Long-term evaluation of oral gavage with periodontopathogens or ligature induction of experimental periodontal disease in mice

OBJECTIVE

To evaluate in long-term periods the destruction of periodontal tissues and bacterial colonization induced by oral gavage with periodontopathogens or ligature experimental periodontal disease models.

MATERIAL AND METHODS

Forty-eight C57BL/6 J mice were divided into four groups: group C: negative control; group L: ligature; group G-Pg: oral gavage with Porphyromonas gingivalis; and group G-PgFn: oral gavage with Porphyromonas gingivalis associated with Fusobacterium nucleatum. Mice were infected by oral gavage five times in 2-day intervals. After 45 and 60 days, animals were sacrificed and the immune-inflammatory response in the periodontal tissue was assessed by stereometric analysis. The alveolar bone loss was evaluated by live microcomputed tomography and histometric analysis. qPCR was used to confirm the bacterial colonization in all the groups. Data were analyzed using the Kruskal-Wallis, Wilcoxon, and ANOVA tests, at 5 % of significance level.

RESULTS

Ligature model induced inflammation and bone resorption characterized by increased number of inflammatory cells and decreased number of fibroblasts, followed by advanced alveolar bone loss at 45 and 60 days (p < 0.05). Bacterial colonization in groups G-Pg and G-PgFn was confirmed by qPCR but inflammation and bone resorption were not observed (p < 0.05).

CONCLUSIONS

The ligature model but not the oral gavage models were effective to induce inflammation and bone loss in long-term periods. Pg colonization was observed in all models of experimental periodontal disease induction, independent of tissue alterations. These mice models of periodontitis validates, compliments, and enhances published PD models that utilize ligature or oral gavage and supports the importance of a successful colonization of a susceptible host, a bacterial invasion into vulnerable tissue, and host-bacterial interactions that lead to tissue destruction.

CLINICAL RELEVANCE

The ligature model was an effective approach to induce inflammation and bone loss similar to human periodontitis, but the oral gavage models were not efficient in inducing periodontal inflammation and tissue destruction in the conditions studied. Ligature models can provide a basis for future interventional studies that contribute to the understanding of the disease pathogenesis and the complex host response to microbial challenge.

Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells

Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

Porphyromonas gingivalis infection increases osteoclastic bone resorption and osteoblastic bone formation in a periodontitis mouse model

Background

Porphyromonas gingivalis has been shown to invade osteoblasts and inhibit their differentiation and mineralization in vitro. However, it is unclear if P. gingivalis can invade osteoblasts in vivo and how this would affect alveolar osteoblast/osteoclast dynamics. This study aims to answer these questions using a periodontitis mouse model under repetitive P. gingivalis inoculations.

Methods

For 3-month-old BALB/cByJ female mice, 10⁹ CFU of P. gingivalis were inoculated onto the gingival margin of maxillary molars 4 times at 2-day intervals. After 2 weeks, another 4 inoculations at 2-day intervals were applied. Calcein was injected 7 and 2 days before sacrificing animals to label the newly formed bone. Four weeks after final inoculation, mice were sacrificed and maxilla collected. Immunohistochemistry, micro-CT, and bone histomorphometry were performed on the specimens. Sham infection with only vehicle was the control.

Results

P. gingivalis was found to invade gingival epithelia, periodontal ligament fibroblasts, and alveolar osteoblasts. Micro-CT showed alveolar bone resorption and significant reduction of bone mineral density and content in the infected mice compared to the controls. Bone histomorphometry showed a decrease in osteoblasts, an increase in osteoclasts and bone resorption, and a surprisingly increased osteoblastic bone formation in the infected mice compared to the controls.

Conclusions

P. gingivalis invades alveolar osteoblasts in the periodontitis mouse model and cause alveolar bone loss. Although P. gingivalis appears to suppress osteoblast pool and enhance osteoclastic bone resorption, the bone formation capacity is temporarily elevated in the infected mice, possibly via some anti-microbial compensational mechanisms.

The adaptive nature of the bone-periodontal ligament-cementum complex in a ligature-induced periodontitis rat model

The novel aspect of this study involves illustrating significant adaptation of a functionally loaded bone-PDL-cementum complex in a ligature-induced periodontitis rat model. Following 4, 8, and 15 days of ligation, proinflammatory cytokines (TNF-α and RANKL), a mineral resorption indicator (TRAP), and a cell migration and adhesion molecule for tissue regeneration (fibronectin) within the complex were localized and correlated with changes in PDL-space (functional space). At 4 days of ligation, the functional space of the distal complex was widened compared to controls and was positively correlated with an increased expression of TNF-α. At 8 and 15 days, the number of RANKL(+) cells decreased near the mesial alveolar bone crest (ABC) but increased at the distal ABC. TRAP(+) cells on both sides of the complex significantly increased at 8 days. A gradual change in fibronectin expression from the distal PDL-secondary cementum interfaces through precementum layers was observed when compared to increased and abrupt changes at the mesial PDL-cementum and PDL-bone interfaces in ligated and control groups. Based on our results, we hypothesize that compromised strain fields can be created in a diseased periodontium, which in response to prolonged function can significantly alter the original bone and apical cementum formations.

Periodontal and systemic responses in various mice models of experimental periodontitis: respective roles of inflammation duration and Porphyromonas gingivalis infection

BACKGROUND

The great variability of periodontal and systemic responses to experimental periodontitis reflects the inherent pathogenic complexity of mice models and could limit the resulting interpretations and their extension to human diseases. This study compared the effect of Porphyromonas gingivalis (Pg) infection and experimental periodontitis duration at local and systemic levels in various models.

METHODS

Periodontitis was induced in C57BL/6J mice by ligatures previously incubated with Pg (LIGPG group) or not (LIG group) or by oral gavage (GAV) with Pg ATCC 33277. Blood samples were taken, and mice were euthanized at different times. Periodontal tissue destruction, osteoclast number, and inflammation were assessed by histomorphometry, tartrate-resistant acid phosphatase histoenzymology, and cathepsin B (CATB) and matrix metalloproteinase 9 (MMP9) immunochemistry. Serum levels of interleukin-6 (IL-6) and IL-1β were measured using enzyme-linked immunosorbent assay bioplex methods.

RESULTS

Periodontal tissue destruction and osteoclast numbers were significantly elevated in LIGPG models compared to LIG and GAV models. They increased with time with the exception of osteoclast numbers in the LIG model. CATB and MMP9 expression was related to bone destruction processes and Pg infection. The highest serum levels of IL-6 and IL-1β were observed in the LIGPG group. A decrease of IL-6 and an increase of IL-1β serum level were observed with time in LIGPG group contrary to LIG group.

CONCLUSIONS

These data indicate that Pg infection worsened periodontal tissue destruction through specific pathogenic pathways and modified systemic response to periodontal inflammation. Furthermore, the blood cytokine response to ligature models showed their relevance for evaluating the systemic impact of periodontal disease.

Impact of Porphyromonas gingivalis inoculation on ligature-induced alveolar bone loss. A pilot study in rats

BACKGROUND AND OBJECTIVE

Periodontitis is a polymicrobial infection characterized by the loss of connective tissue attachment, periodontal ligament and alveolar bone. The aim of this study was to evaluate the impact of Porphyromonas gingivalis inoculation on the ligature-induced alveolar bone loss (ABL) model in rats.

MATERIAL AND METHODS

Forty male Wistar rats were randomly assigned to the following groups: G1, control (n = 10); G2, ligature-induced ABL (n = 15); and G3, ligature-induced ABL + P. gingivalis inoculation (n = 15). Rats in G2 and G3 were killed 15, 21 and 30 d after ligature placement, and the following parameters were assessed: microbiological load; ABL; and interleukin (IL)-1β (Il1beta)/Il1ra, Il6/Il10 and Rankl/osteoprotegerin (Opg) mRNA ratios in the gingival tissues, as determined by quantitative PCR.

RESULTS

Microbiological analyses demonstrated that rats in G1, G2 and G3 were positive for the presence of bacteria (determined using PCR amplification of the 16S gene), but that only the treatment sites of rats in G3 were positive for P. gingivalis at all time-points investigated. Histometrically, significant bone loss (p<0.001) was observed for both ligated groups (G2 and G3) compared with the nonligated group (G1), with higher ABL observed for G2 at all the experimental time-points. Furthermore, gene-expression analysis demonstrated that the presence of P. gingivalis in the dentogingival area significantly decreased the Il1β/Il1ra, Il6/Il10 and Rankl/Opg mRNA ratios compared with ligature alone.

CONCLUSION

Within the limits of this pilot study, it was concluded that inoculation of P. gingivalis affected the ligature-induced ABL model by the induction of an anti-inflammatory and antiresorptive host response.

Involvement of toll-like receptor 4 in alveolar bone loss and glucose homeostasis in experimental periodontitis

BACKGROUND AND OBJECTIVE

There is general agreement that certain fatty acids and lipopolysaccharides (LPS) promote inflammation through toll-like receptor 4 (TLR4), and that inflammation promotes insulin resistance. We therefore hypothesized that mice with periodontitis and a TLR4 loss-of-function (LOF) mutation fed a high-fat (HF) diet would develop improved glucose homeostasis compared with wild-type (WT) animals with periodontitis fed a HF diet.

MATERIAL AND METHODS

Wild-type and TLR4 mutant mice fed a HF diet were divided into four groups (n = 6/group): WT; WT with periodontitis (WT/P); mutant (Mut); and mutant with periodontitis (Mut/P). Periodontitis was induced by placing LPS soaked ligatures around maxillary second molars. Fasting insulin and glucose levels were measured weekly for 10 wk. Glucose tolerance was evaluated at baseline (week 1) and at 9 wk. Insulin signaling (phosphorylation of Akt) and tumor necrosis factor-α (TNF-α) mRNA levels in liver were determined when the mice were killed at week 10.

RESULTS

Mut/P mice developed less alveolar bone loss compared with WT/P mice (p < 0.05). Fasting glucose levels were improved after 8 wk of feeding a HF diet (weeks 9 and 10) in Mut/P mice compared with Mut, WT and WT/P mice (p < 0.05). Glucose tolerance was impaired in all groups compared with baseline (p < 0.05), except for the Mut/P group. Insulin signaling was improved (p < 0.05), and expression of TNF-α was decreased (p < 0.05) in the liver of Mut/P mice compared with the liver of WT/P mice.

CONCLUSION

The TLR4 LOF mutation partially protects against alveolar bone loss and improves glucose homeostasis in mice with periodontitis fed a HF diet.

Inhibition of SFRP1 reduces severity of periodontitis

Porphyromonas gingivalis (P. gingivalis) is implicated as a major pathogen in periodontitis, a common infectious disease characterized by the inflammation and destruction of periodontal tissues. Secreted frizzled-related protein 1 (SFRP1) modulates apoptosis in different cell types. To characterize the roles of SFRP1 in periodontitis, we used a P. gingivalis-induced murine periodontitis model. Inflammatory responses were measured by morphometric and histomorphometric analysis, apoptosis assay, and immunohistochemistry. We found that P. gingivalis-infected mouse periodontal tissues expressed significantly more SFRP1 compared with those of control mice. Also, in P. gingivalis-infected animals, more apoptosis of inflammatory cells, fibroblasts, and bone-lining cells was observed compared with controls. Antibody experiments aimed at inhibiting SFRP1 expression in periodontitis resulted in a reduction of periodontal breakdown, inflammatory cell infiltrate, osteoclastogenesis, and apoptosis of inflammatory cells and fibroblasts. The results of our studies suggest that SFRP1 may be involved in the development of periodontitis, since inhibiting SFRP1 resulted in reduced periodontal breakdown.

Morphometric, histomorphometric, and microcomputed tomographic analysis of periodontal inflammatory lesions in a murine model

BACKGROUND

Porphyromonas gingivalis is recognized as one of the major periodontal pathogens in chronic periodontitis, a common infectious disease characterized by inflammation and destruction of periodontal tissues. Several animal models with P. gingivalis have been used in periodontitis studies. Additionally, multiple approaches have also been applied to measuring alveolar bone loss in periodontitis models, including histomorphometry, morphometry, and radiography. The aims of this study were to assess periodontal inflammatory lesions after P. gingivalis-induced periodontitis and use this model to compare three approaches for assessing alveolar bone loss.

METHODS

Twelve-week-old male C57BL/6 mice were divided into two groups: 48 P. gingivalis-infected and 52 untreated control mice. Periodontitis was induced by wrapping P. gingivalis-soaked ligatures around the left maxillary second molar and changing the ligatures every other day. Mice were euthanized on days 0, 3, 7, and 10 after ligature placement, for a total of 12 experimental and 13 control mice per time point. Epithelial downgrowth, inflammation, and osteoclast activity were evaluated; alveolar bone loss was determined by histomorphometry, morphometry, and microcomputed tomography.

RESULTS

The P. gingivalis-infected group showed significantly increased epithelial downgrowth (P <0.05), inflammation (P <0.05), alveolar bone loss (P <0.05), and osteoclast activity (P <0.05) throughout the experimental period compared to the controls. All three methods yielded efficient evaluation of alveolar bone loss.

CONCLUSIONS

Our results show evidence that the P. gingivalis-soaked ligature-induced murine model mounts an adequate inflammatory response and exhibits periodontal tissue breakdown compatible with other models of periodontal disease. In addition, alveolar bone loss can accurately be quantified using any of the three alveolar bone analyses presented in this article.

Relationship Between Transmission ofPorphyromonas gingivalisandfimAType in Spouses

BACKGROUND

Porphyromonas gingivalis is one of the major microbial pathogens associated with chronic periodontitis. To eradicate such pathogens by periodontal therapy, it is essential to clarify the source of infection. Recent findings suggest that the genotype of the fimbriae is one of the important factors in infection by P. gingivalis. The objectives of the present study were to investigate the transmission of P. gingivalis between spouses and to determine the relationship between P. gingivalis fimA type and colonization.

METHODS

A total of 14 couples were selected to investigate the transmission of P. gingivalis and its association with the fimA types. To examine the distribution of fimA type in the general population, 32 subgingival plaque samples from 47 patients with periodontitis were also tested. The transmission of P. gingivalis strains was determined by using pulsed field gel electrophoresis (PFGE). P. gingivalis strains isolated from the couples and subgingival dental plaque samples were studied for fimA classification.

RESULTS

The PFGE patterns of P. gingivalis strains from matched husbands and wives were identical for six of the 14 couples. In five of these six couples (83.3%), P. gingivalis strains harboring the type II fimA gene were present. The proportion of type II fimA in the strains isolated from couples with probable intrafamilial transmission was significantly higher than that in patients with periodontitis or in the group of samples isolated from one member of a couple.

CONCLUSION

This study suggests that fimA type II, even though widely distributed in patients with periodontitis, may be an important factor in the transmission of P. gingivalis between spouses.