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

Oral microbiome, periodontal disease and systemic bone-related diseases in the era of homeostatic medicine

BACKGROUND

Homeostasis is a state of self-regulation and dynamic equilibrium, maintaining the good physiological functions of each system in living organisms. In the oral cavity, the interaction between the host and the oral microbiome forms oral microbial homeostasis. Physiological bone remodeling and renewal can occur under the maintenance of oral microbial homeostasis. The imbalance of bone homeostasis is a key mechanism leading to the occurrence of systemic bone-related diseases. Considering the importance of oral microbial homeostasis in the maintenance of bone homeostasis, it still lacks a complete understanding of the relationship between oral microbiome, periodontal disease and systemic bone-related diseases.

AIM OF REVIEW

This review focuses on the homeostatic changes, pathogenic routes and potential mechanisms in the oral microbiome in periodontal disease and systemic bone-related diseases such as rheumatoid arthritis, osteoarthritis, osteoporosis and osteomyelitis. Additionally, this review discusses oral microbiome-based diagnostic approaches and explores probiotics, mesenchymal stem cells, and oral microbiome transplantation as promising treatment strategies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review highlights the association between oral microbial homeostasis imbalance and systemic bone-related diseases, and highlights the possibility of remodeling oral microbial homeostasis for the prevention and treatment of systemic bone-related diseases.

Platr3/NUDT21/NF-κB Axis Mediates P. gingivalis-Suppressed Cementoblast Mineralization

Porphyromonas gingivalis (P. gingivalis) is one of the major pathogens causing periodontitis and apical periodontitis (AP). Long noncoding RNA (lncRNA) can regulate cellular mineralization and inflammatory diseases. The aim of this study was to investigate the role and mechanism of lncRNA in P. gingivalis-stimulated cementoblast mineralization. In vivo, C57BL/6 mice were divided into the healthy, the AP, and AP + P. gingivalis groups (n = six mice per group). Micro computed tomography, immunohistochemistry staining, and fluorescence in situ hybridization were used to observe periapical tissue. In vitro, cementoblasts were treated with osteogenic medium or P. gingivalis. Pluripotency associated transcript 3 (Platr3), interleukin 1 beta (IL1B), and osteogenic markers were analyzed by quantitative real-time polymerase chain reaction and western blot. RNA pull-down and RNA immunoprecipitation assays were used to detect proteins that bind to Platr3. RNA sequencing was performed in Platr3-silenced cementoblasts. In vivo, P. gingivalis promoted periapical tissue destruction and IL1B expression, but inhibited Platr3 expression. In vitro, P. gingivalis facilitated IL1B expression (P < 0.001), whereas suppressed the expression of Platr3 (P < 0.001) and osteogenic markers (P < 0.01 or 0.001). In contrast, Platr3 overexpression alleviated the repressive effect of P. gingivalis on cementoblast mineralization (P < 0.01 or 0.001). Furthermore, Platr3 bound to nudix hydrolase 21 (NUDT21) and regulated the nuclear factor-κB (NF-κB) signaling pathway. Knocking down NUDT21 suppressed osteogenic marker expression and activated the above signaling pathway. Collectively, the results elucidated that Platr3 mediated P. gingivalis-suppressed cementoblast mineralization through the NF-κB signaling pathway by binding to NUDT21.

Preventive effect of Lacticaseibacillus paracasei LMT18-32 on Porphyromonas gingivalis induced periodontitis

Periodontitis is a severe gum infection leading to chronic inflammation in the gums, damage of tissues around teeth, and destruction of alveolar bones. Porphyromonas gingivalis is the major causative pathogen that induces periodontitis. Numerous probiotic bacteria are reported to produce antibacterial substances against pathogens especially oral pathogens, and these are proposed as preventive measures for periodontitis. In this study, Lacticaseibacillus paracasei LMT18-32 was evaluated and its antibacterial activity against P. gingivalis, and antioxidant activity in vitro were established. In addition, when L. paracasei LMT18-32 was administered to periodontitis induced mice, it successfully alleviated the alveolar bone loss and suppressed induced expression of proinflammatory and tissue destruction related genes in the gingival tissue. In conclusion, L. paracasei LMT18-32 is proposed as a potential probiotics to prevent periodontitis.

Imbalanced EphB4/EphrinB2 Signaling Modulates Bone Resorption in Periodontitis Induced by Porphyromonas gingivalis

Periodontitis, a chronic infectious disease in periodontal tissues, is characterized by an imbalance of alveolar bone resorption and remodeling, which eventually results in tooth loosening and even tooth loss. The etiology of periodontitis is polymicrobial synergy and dysbiosis, in which Porphyromonas gingivalis (P. gingivalis) is one of the primary pathogens responsible for periodontitis progression. The interplay of EphrinB2/EphB4 is crucial for osteoblast-osteoclast communication during bone remodeling and healing. This study investigates the mechanism of EphB4/EphrinB2 transduction modulating osteogenesis inhibition and bone resorption in periodontitis induced by P. gingivalis. An in vivo model of chronic periodontitis provoked by P. gingivalis was constructed, the inflammation and bone resorption were evaluated. The expression of EphB4 and EphrinB2 proteins in periodontal tissues was detected, which was also evaluated, respectively, in osteoblasts and osteoclasts infected with P. gingivalis in vitro. Then, a simulated coculture model of osteoblasts and osteoclasts was established to activate the forward and reverse pathways of EphB4/EphrinB2 with P. gingivalis infection. This study showed that P. gingivalis infection promoted alveolar bone resorption in rats and enhanced EphB4 and EphrinB2 expression in periodontal tissues. EphB4 and molecules associated with osteogenesis in osteoblasts infected with P. gingivalis were inhibited, while EphrinB2 and osteoclast differentiation-related markers in osteoclasts were activated. In conclusion, this study suggested that EphB4/EphrinB2 proteins were involved in alveolar bone remodeling in the process of periodontitis induced by P. gingivalis infection. Moreover, attenuated EphB4/EphrinB2 with P. gingivalis infection weakened osteoblast activity and enhanced osteoclast activity.

The IL-33/ST2 axis is protective against acute inflammation during the course of periodontitis

Periodontitis, which is induced by repeated bacterial invasion and the ensuing immune reactions that follow, is the leading cause of tooth loss. Periodontal tissue is comprised of four different components, each with potential role in pathogenesis, however, most studies on immune responses focus on gingival tissue. Here, we present a modified ligature-induced periodontitis model in male mice to analyze the pathogenesis, which captures the complexity of periodontal tissue. We find that the inflammatory response in the peri-root tissues and the expression of IL-6 and RANKL by Thy-1.2- fibroblasts/stromal cells are prominent throughout the bone destruction phase, and present already at an early stage. The initiation phase is characterized by high levels of ST2 (encoded by Il1rl1) expression in the peri-root tissue, suggesting that the IL-33/ST2 axis is involved in the pathogenesis. Both Il1rl1- and Il33-deficient mice exhibit exacerbated bone loss in the acute phase of periodontitis, along with macrophage polarization towards a classically activated phenotype and increased neutrophil infiltration, indicating a protective role of the IL-33/ST2 axis in acute inflammation. Thus, our findings highlight the hidden role of the peri-root tissue and simultaneously advance our understanding of the etiology of periodontitis via implicating the IL-33/ST2 axis.

CXXC5 mitigates P. gingivalis-inhibited cementogenesis by influencing mitochondrial biogenesis

BACKGROUND

Cementoblasts on the tooth-root surface are responsible for cementum formation (cementogenesis) and sensitive to Porphyromonas gingivalis stimulation. We have previously proved transcription factor CXXC-type zinc finger protein 5 (CXXC5) participates in cementogenesis. Here, we aimed to elucidate the mechanism in which CXXC5 regulates P. gingivalis-inhibited cementogenesis from the perspective of mitochondrial biogenesis.

METHODS

In vivo, periapical lesions were induced in mouse mandibular first molars by pulp exposure, and P. gingivalis was applied into the root canals. In vitro, a cementoblast cell line (OCCM-30) was induced cementogenesis and submitted for RNA sequencing. These cells were co-cultured with P. gingivalis and examined for osteogenic ability and mitochondrial biogenesis. Cells with stable CXXC5 overexpression were constructed by lentivirus transduction, and PGC-1α (central inducer of mitochondrial biogenesis) was down-regulated by siRNA transfection.

RESULTS

Periapical lesions were enlarged, and PGC-1α expression was reduced by P. gingivalis treatment. Upon apical inflammation, Cxxc5 expression decreased with Il-6 upregulation. RNA sequencing showed enhanced expression of osteogenic markers, Cxxc5, and mitochondrial biogenesis markers during cementogenesis. P. gingivalis suppressed osteogenic capacities, mitochondrial biogenesis markers, mitochondrial (mt)DNA copy number, and cellular ATP content of cementoblasts, whereas CXXC5 overexpression rescued these effects. PGC-1α knockdown dramatically impaired cementoblast differentiation, confirming the role of mitochondrial biogenesis on cementogenesis.

CONCLUSIONS

CXXC5 is a P. gingivalis-sensitive transcription factor that positively regulates cementogenesis by influencing PGC-1α-dependent mitochondrial biogenesis. Video Abstract.

Effective Modalities of Periodontitis Induction in Rat Model

Induction of periodontal disease using the rat model is the preferred model for human periodontal disease studies that are related to gene expression, mechanisms of inflammatory regulation, microbial and host responses, resolution, and the healing process. There are 3 methods that are frequently used to induce periodontal disease, which are: ligature application, oral bacterial inoculation, and the lipopolysaccharide injection technique. In the ligature model, sterile non-absorbable sutures or orthodontic wires are widely used to induce local irritation and bacterial plaque accumulation. Secondly, mono and mixed cultures of periodontal bacteria are inoculated orally by gavage or topical application. Lastly, lipopolysaccharide extracted from pathogenic bacteria can be directly injected into the gingival sulcus to induce inflammation and stimulate osteoclastogenesis and alveolar bone loss. Among these methods, ligature application induces inflammation and alveolar bone resorption more promptly compared to other methods. This review will provide an overview of the main induction methods in experimental periodontal disease, with their advantages and disadvantages.

Ageing and Inflammation: What Happens in Periodontium?

Periodontitis is a chronic inflammatory disease with a high incidence and severity in the elderly population, making it a significant public health concern. Ageing is a primary risk factor for the development of periodontitis, exacerbating alveolar bone loss and leading to tooth loss in the geriatric population. Despite extensive research, the precise molecular mechanisms underlying the relationship between ageing and periodontitis remain elusive. Understanding the intricate mechanisms that connect ageing and inflammation may help reveal new therapeutic targets and provide valuable options to tackle the challenges encountered by the rapidly expanding global ageing population. In this review, we highlight the latest scientific breakthroughs in the pathways by which inflammaging mediates the decline in periodontal function and triggers the onset of periodontitis. We also provide a comprehensive overview of the latest findings and discuss potential avenues for future research in this critical area of investigation.

The Presence of Periodontitis Exacerbates Non-Alcoholic Fatty Liver Disease via Sphingolipid Metabolism-Associated Insulin Resistance and Hepatic Inflammation in Mice with Metabolic Syndrome

Clinical studies have shown that periodontitis is associated with non-alcoholic fatty liver disease (NAFLD). However, it remains unclear if periodontitis contributes to the progression of NAFLD. In this study, we generated a mouse model with high-fat diet (HFD)-induced metabolic syndrome (MetS) and NAFLD and oral P. gingivalis inoculation-induced periodontitis. Results showed that the presence of periodontitis increased insulin resistance and hepatic inflammation and exacerbated the progression of NAFLD. To determine the role of sphingolipid metabolism in the association between NAFLD and periodontitis, we also treated mice with imipramine, an inhibitor of acid sphingomyelinase (ASMase), and demonstrated that imipramine treatment significantly alleviated insulin resistance and hepatic inflammation, and improved NAFLD. Studies performed in vitro showed that lipopolysaccharide (LPS) and palmitic acid (PA), a major saturated fatty acid associated with MetS and NAFLD, synergistically increased the production of ceramide, a bioactive sphingolipid involved in NAFLD progression in macrophages but imipramine effectively reversed the ceramide production stimulated by LPS and PA. Taken together, this study showed for the first time that the presence of periodontitis contributed to the progression of NAFLD, likely due to alterations in sphingolipid metabolism that led to exacerbated insulin resistance and hepatic inflammation. This study also showed that targeting ASMase with imipramine improves NAFLD by reducing insulin resistance and hepatic inflammation.

Molecular Basis beyond Interrelated Bone Resorption/Regeneration in Periodontal Diseases: A Concise Review

Periodontitis is the sixth most common chronic inflammatory disease, destroying the tissues supporting the teeth. There are three distinct stages in periodontitis: infection, inflammation, and tissue destruction, where each stage has its own characteristics and hence its line of treatment. Illuminating the underlying mechanisms of alveolar bone loss is vital in the treatment of periodontitis to allow for subsequent reconstruction of the periodontium. Bone cells, including osteoclasts, osteoblasts, and bone marrow stromal cells, classically were thought to control bone destruction in periodontitis. Lately, osteocytes were found to assist in inflammation-related bone remodeling besides being able to initiate physiological bone remodeling. Furthermore, mesenchymal stem cells (MSCs) either transplanted or homed exhibit highly immunosuppressive properties, such as preventing monocytes/hematopoietic precursor differentiation and downregulating excessive release of inflammatory cytokines. In the early stages of bone regeneration, an acute inflammatory response is critical for the recruitment of MSCs, controlling their migration, and their differentiation. Later during bone remodeling, the interaction and balance between proinflammatory and anti-inflammatory cytokines could regulate MSC properties, resulting in either bone formation or bone resorption. This narrative review elaborates on the important interactions between inflammatory stimuli during periodontal diseases, bone cells, MSCs, and subsequent bone regeneration or bone resorption. Understanding these concepts will open up new possibilities for promoting bone regeneration and hindering bone loss caused by periodontal diseases.

Human periodontitis-associated salivary microbiome affects the immune response of diabetic mice

Background

The bidirectional association between periodontitis and diabetes mellitus has been well accepted; however, pathways connecting them remain unclear. Some oral bacteria are able to induce immunologic changes favoring insulin resistance individually. However, it is unclear if and how the systemic immune system responds to a disturbed oral microbial community in diabetic sufferers.

Aim

This study aimed to investigate the impact of the human periodontitis-associated salivary microbiome on the splenic immune responses of diabetic mice.

Methods

An in vivo diabetic animal model was established by feeding high fat food. After microbial depletion with quadruple antibiotic treatment, human saliva from healthy and periodontitis volunteers was transplanted into the mouth of these diabetic mice (N = 3), respectively.

Results

Osteoclasts and expression levels of TNF-α and IL-1β were significantly increased in periodontal tissues of mice receiving periodontitis patients donated microbiome compared to these transplanted with healthy subjects donated microbiome. The proportion of monocyte (an innate immunocyte) decreased in mice receiving periodontitis patients donated microbiome. However, the abundance of an adaptive immunocyte Th17 was up-regulated. The IL17 production of ILC3 cells in human periodontitis-associated salivary microbiome recipient mice was significantly impaired.

Conclusions

A disturbed oral microbiome imposes a stress on the splenic immune responses of diabetic mice.

Osteocytes directly regulate osteolysis via MYD88 signaling in bacterial bone infection

The impact of bone cell activation on bacterially-induced osteolysis remains elusive. Here, we show that matrix-embedded osteocytes stimulated with bacterial pathogen-associated molecular patterns (PAMPs) directly drive bone resorption through an MYD88-regulated signaling pathway. Mice lacking MYD88, primarily in osteocytes, protect against osteolysis caused by calvarial injections of bacterial PAMPs and resist alveolar bone resorption induced by oral Porphyromonas gingivalis (Pg) infection. In contrast, mice with targeted MYD88 restoration in osteocytes exhibit osteolysis with inflammatory cell infiltration. In vitro, bacterial PAMPs induce significantly higher expression of the cytokine RANKL in osteocytes than osteoblasts. Mechanistically, activation of the osteocyte MYD88 pathway up-regulates RANKL by increasing binding of the transcription factors CREB and STAT3 to Rankl enhancers and by suppressing K48-ubiquitination of CREB/CREB binding protein and STAT3. Systemic administration of an MYD88 inhibitor prevents jawbone loss in Pg-driven periodontitis. These findings reveal that osteocytes directly regulate inflammatory osteolysis in bone infection, suggesting that MYD88 and downstream RANKL regulators in osteocytes are therapeutic targets for osteolysis in periodontitis and osteomyelitis.

N-Terminal Lysozyme Conjugation to a Cationic Polymer Enhances Antimicrobial Activity and Overcomes Antimicrobial Resistance

Microbial resistance to antibiotics is one of the greatest global healthcare challenges. There is an urgent need to develop effective strategies to overcome antimicrobial resistance. We, herein, report photoinduced in situ growth of a cationic polymer from the N-terminus of lysozyme. The attachment of the cationic polymer improves the proteolytic and thermal stability of lysozyme. Notably, the conjugate can efficiently overcome lysozyme resistance in Gram-positive bacteria and antibiotics-resistance in Gram-negative bacteria, which may be ascribed to the synergistic interactions of lysozyme and the cationic polymer with the bacteria to disrupt their cell membranes. In a rat periodontitis model, the lysozyme-polymer conjugate not only greatly outperforms lysozyme in therapeutic efficacy but also is superior to minocycline hydrochloride, which is the gold standard for periodontitis therapy. These findings may provide an efficient strategy to dramatically enhance the antimicrobial activities of lysozyme and pave a way to overcome antimicrobial resistance.

Açaí (Euterpe oleracea Mart.) Attenuates Oxidative Stress and Alveolar Bone Damage in Experimental Periodontitis in Rats

Açaí (Euterpe oleracea Mart.) juice is rich in phenolic compounds with high antioxidant capacity. It has been observed that the use of antioxidants may be an additional strategy to nonsurgical periodontal therapy as well as to prevent alveolar bone loss. Thus, the objective of this study was to investigate the effects of açaí supplementation on experimental periodontitis in rats. Twenty male Rattus norvegicus (Wistar) rats were assigned into control, açaí, experimental periodontitis, and experimental periodontitis with açaí supplementation groups. Periodontitis was induced by placing ligatures around the lower first molars. Animals in the açaí groups received 0.01 mL/g of clarified açaí juice for 14 days by intragastric gavage. At the end of the experimental period, blood was collected to assess the reduced glutathione (GSH), Trolox equivalent antioxidant capacity (TEAC), and lipid peroxidation (TBARS) levels. Moreover, hemimandibles were analyzed by micro-computed tomography (micro-CT) for alveolar bone loss and bone quality. Açaí supplementation increased blood total antioxidant capacity and decreased lipid peroxidation. It also reduced alveolar bone loss when compared to the experimental periodontitis group. Moreover, clarified açaí per se modulated the oxidative biochemistry and bone microstructure. Thus, açaí may be considered a viable alternative for managing periodontal oxidative stress and preventing alveolar bone loss.

Roles of osteoclasts in alveolar bone remodeling

Osteoclasts are large multinucleated cells from hematopoietic origin and are responsible for bone resorption. A balance between osteoclastic bone resorption and osteoblastic bone formation is critical to maintain bone homeostasis. The alveolar bone, also called the alveolar process, is the part of the jawbone that holds the teeth and supports oral functions. It differs from other skeletal bones in several aspects: its embryonic cellular origin, the form of ossification, and the presence of teeth and periodontal tissues; hence, understanding the unique characteristic of the alveolar bone remodeling is important to maintain oral homeostasis. Excessive osteoclastic bone resorption is one of the prominent features of bone diseases in the jaw such as periodontitis. Therefore, inhibiting osteoclast formation and bone resorptive process has been the target of therapeutic intervention. Understanding the mechanisms of osteoclastic bone resorption is critical for the effective treatment of bone diseases in the jaw. In this review, we discuss basic principles of alveolar bone remodeling with a specific focus on the osteoclastic bone resorptive process and its unique functions in the alveolar bone. Lastly, we provide perspectives on osteoclast-targeted therapies and regenerative approaches associated with bone diseases in the jaw.

Host and bacterial factors linking periodontitis and rheumatoid arthritis

Observations from numerous clinical, epidemiological and serological studies link periodontitis with severity and progression of rheumatoid arthritis. The strong association is observed despite totally different aetiology of these two diseases, periodontitis being driven by dysbiotic microbial flora on the tooth surface below the gum line, while rheumatoid arthritis being the autoimmune disease powered by anti-citrullinated protein antibodies (ACPAs). Here we discuss genetic and environmental risk factors underlying development of both diseases with special emphasis on bacteria implicated in pathogenicity of periodontitis. Individual periodontal pathogens and their virulence factors are argued as potentially contributing to putative causative link between periodontal infection and initiation of a chain of events leading to breakdown of immunotolerance and development of ACPAs. In this respect peptidylarginine deiminase, an enzyme unique among prokaryotes for Porphyromonas gingivalis, is elaborated as a potential mechanistic link between this major periodontal pathogen and initiation of rheumatoid arthritis development.

M101, a therapeutic oxygen carrier derived from Arenicola marina, decreased Porphyromonas gingivalis induced hypoxia and improved periodontal healing

BACKGROUND

P. gingivalis exacerbates tissue hypoxia and worsens periodontal inflammation. This study investigated the effect of a therapeutic oxygen carrier (M101), derived from Arenicola marina, on hypoxia and associated inflammation in the context of periodontitis.

METHODS

The effect of M101 on GLUT-1, GLUT-3, HIF-1α and MMP-9 expression, hypoxia and antioxidant status in oral epithelial cells (EC) exposed to CoCl₂ (1000μM), P. gingivalis (MOI 100) and CoCl₂ + P. gingivalis was evaluated through hypoxia detection fluorescence assay, antioxidant concentration colorimetric assay and RTqPCR. Evaluation of M101 on EC proliferation was evaluated in an in vitro wound assay. In experimental periodontitis, periodontal wound healing and osteoclastic activity were compared among natural wound healing, placebo and gels containing M101 (1 g/L and 2 g/L) groups through histomorphometry and TRAP assay respectively. The expression of HIF-1α, MMP-9 and NFκB in periodontal tissues was also evaluated through immunofluorescence studies.

RESULTS

M101 downregulated GLUT-1, GLUT-3, HIF-1α and MMP-9 levels in EC exposed to CoCl₂ , P. gingivalis and CoCl₂ + P. gingivalis (p < 0.05). Fluorescence and colorimetric analyses confirmed hypoxia reduction and antioxidant capacity improvement in such EC upon M101 treatment. Moreover, M101 improved significantly the in vitro wound closure. In vivo, the attachment level was significantly improved, and osteoclastic activity was reduced in mice treated with M101 gels compared to placebo and natural wound healing groups (p < 0.05). HIF-1α, MMP-9 and NFκB expression in periodontal tissues was reduced in M101 gels treated mice compared to the controls.

CONCLUSION

M101 showed promise in resolving hypoxia and associated inflammation mediated tissue degradation. Its potential in the clinical management of periodontitis must be further investigated. This article is protected by copyright. All rights reserved.

Application of Ginsenoside Rd in Periodontitis With Inhibitory Effects on Pathogenicity, Inflammation, and Bone Resorption

Periodontitis is a worldwide oral disease induced by the interaction of subgingival bacteria and host response and is characterized by local inflammation, bone resorption, and tooth loss. Ginsenoside Rd (Rd) is a biologically active component derived from Panax ginseng and has been demonstrated to exert antibacterial and anti-inflammatory activities. This study aims to investigate the inhibitory efficiency of Rd towards Porphyromonas gingivalis (P. gingivalis), periodontal inflammatory response, and osteoclastogenesis in vitro and to further validate the results in a mouse periodontitis model, thus, evaluate the potential effects of Rd on the control and prevention of periodontitis. According to the results, Rd exerted excellent antibacterial activities against planktonic P. gingivalis, along with attenuating P. gingivalis virulence and inhibiting its biofilms. Meanwhile, the inflammatory cytokine production and osteoclastogenesis were remarkably inhibited by Rd both in vitro and in vivo. Furthermore, Rd efficiently ameliorated the subgingival P. gingivalis abundance and suppressed the alveolar bone resorption in vivo as well. In conclusion, Rd has the potential to be developed as a promising medication in the control and prevention of periodontitis.

The expression of interleukin-1β and nuclear factor erythroid-2 in the periodontitis after treatment of liquid smoke rice hull

Nonsurgical treatment such as scaling and root planing has been the main therapy of periodontal management. However, some individuals are nonresponsive with only mechanical therapy. Rice hull liquid smoke (RH-LS) with higher of phenolic compound supposed to interfere with inflammation process. Thus, the purpose of this study is to investigate the anti-inflammation properties of RH-LS for chronic periodontitis adjunct therapy by observing the expression of nuclear factor erythroid-2 (Nrf-2) and interleukin-1β (IL-1β). Two groups of Wistar rats were used. Control group was induced by 1 × 10⁹ colony-forming unit (CFU)/ml Porphyromonas gingivalis (PG) and treated with aquadest for 2 and 7 days. Meanwhile, the other group was induced by 1 × 10⁹ CFU/ml PG and treated with RH-LS for 2 and 7 days. Two central incisive/mandibulae were dissected and stained with immunohistochemistry for analyzed the expression of Nrf-2 and IL-1β. Data were then analyzed statistically using independent t-test (P = 0.05). Treatment with RH-LS for 7 days showed lower expression of IL-1β (4.00 ± 1.58) than control group (13.60 ± 2.70) and showed higher expression of Nrf-2 (11.60 ± 1.95) than control group (4.20 ± 1.64) (P = 0.000) (P < 0.05). Treatment of RH-LS for 2 days showed higher expression of Nrf-2 (2.20 ± 1.31) than control group (6.80 ± 1.92) (P = 0.003) (P < 0.05). RH-LS showed anti-inflammation properties by elevating the expression of Nrf-2 and depressing expression of IL-1β in periodontitis induced by PG.

Oral Microbiome Using Colocasia antiquorum var. esculenta Extract Varnish in a Mouse Model with Oral Gavage of P. gingivalis ATCC 53978

Background and Objective: There is increasing interest in preventing periodontitis using natural products. The purpose of this study was to investigate the effect of Colocasia antiquorum var. esculenta (CA) varnish on the oral microbiome and alveolar bone loss in a mouse periodontitis model. Materials and Methods: Antibacterial activity against Porphyromonas gingivalis (P. gingivalis) ATCC 53978 and cell cytotoxicity using CCK-8 on L929 cells were measured. Balb/c mice were assigned into five groups (negative control, positive control, CA in drinking water, varnish, and CA varnish). P. gingivalis was administered to the mice by oral gavage three times. After sacrifice, the oral microbiome and the levels of the inflammatory cytokine IL-1β and matrix metalloproteinase-9 were analyzed. Alveolar bone loss was measured using micro-computed tomography. Results: CA extract showed an antibacterial effect against P. gingivalis (p < 0.05) and showed no cytotoxicity at that concentration (p > 0.05). Although alpha diversity of the oral microbiome did not statistically differ between the groups (p > 0.05), the relative abundance of dominant bacteria tended to be different between the groups. The inflammatory cytokine IL-1β was reduced in the CA varnish group (p < 0.05), and no difference was observed in MMP-9 expression and alveolar bone loss (p > 0.05). Conclusions: CA varnish did not affect the overall microflora and exhibited an anti-inflammatory effect, suggesting that it is possibility a suitable candidate for improving periodontitis.

Experimental Periodontitis Deteriorated Atherosclerosis Associated With Trimethylamine N-Oxide Metabolism in Mice

Background

Periodontitis is considered a risk factor for atherosclerosis, but the mechanism is not clear. It was reported that oral administration of Porphyromonas gingivalis altered the gut microbiota in mice. Gut dysbiosis and the intestinal metabolite trimethylamine N-oxide (TMAO) were verified to be associated with atherosclerosis. Therefore, the possible TMAO-related mechanism between periodontitis and atherosclerosis needs to be explored.

Methods

Experimental periodontitis was established by oral administration of P. gingivalis for 2 months in ApoE^−/− mice. Mouse hemi-mandibles were scanned using Micro-CT. Quantification of TMAO was performed using liquid chromatography–tandem mass spectrometry. Mouse feces were collected and the bacterial DNA was extracted, then the gut microbiota was analyzed using 16S rRNA genes. Atherosclerotic lesion areas were quantified. Livers, small intestines, and large intestines were analyzed for gene expression.

Results

Aggravated atherosclerosis plaques were found in experimental periodontitis mice. Plasma TMAO, a pathogenic factor of atherosclerosis, was initially found to be increased in periodontitis mice. Changes in the composition and abundance of the intestinal microflora of periodontitis mice were found. Flavin monooxygenase 3 (FMO3), the catalyzing enzyme of TMAO in the liver, was significantly increased, accompanied by an increase of IL-6 in liver, the abnormal intestinal integrity and enhanced plasma LPS. The IL-6 and LPS were verified to be able to increase FMO3 in HepG2 cells.

Conclusion

Our research discovered that experimental periodontitis in ApoE^−/− mice induced gut dysbiosis and an increase in TMAO. These results suggest a possible mechanism by which periodontitis may accelerate atherosclerosis by influencing the intestinal microbes and the metabolism, which were triggered by inflammation of the liver and intestine.

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.

Tetracycline, an Appropriate Reagent for Measuring Bone-Formation Activity in the Murine Model of the Streptococcus mutans-Induced Bone Loss

Tetracycline is used as a fluorescent reagent to measure bone formation activity in bone histomorphometric analyses. However, there is a possibility to lead a different conclusion when it is used in a bacteria-infected murine model since the tetracycline is considered to work as an antibiotic reagent. There are non-antibiotic fluorescent reagents such as alizarin and calcein for measuring bone formation activity. The purpose of this study was to clarify whether tetracycline could be an appropriate reagent to measure bone formation activity in a murine bacterial model in the same way as a non-antibiotic fluorescent reagent. We used Streptococcus mutans (S. mutans), a normal inhabitant in the oral cavity and tetracycline-sensitive bacteria, for inducing the bacterial model. The murine bacterial model was generated by intravenously inoculating S. mutans to the tail vein, followed immediately by the injection of the first fluorescent reagent, and the second one was injected 2 days prior to euthanization. After one day of inoculation with S. mutans, the subcutaneously injected alizarin had a similar colony count derived from the liver and the bone marrow tissue compared to the phosphate buffered saline (PBS)-injected control group. On the other hand, subcutaneous injection of tetracycline led to a significantly lower colony count from the liver compared to alizarin- or calcein-injected group. However, on day seven, after S. mutans intravenous injections, bone mineral density of distal femurs was significantly reduced by the bacteria inoculation regardless of which fluorescent reagents were injected subcutaneously. Finally, S. mutans inoculation reduced bone-formation-activity indices in both the tetracycline-alizarin double-injected mice and the calcein-alizarin double-injected mice. These results suggested that a one-time injection of tetracycline did not affect bone formation indices in the S. mutans-induced bone loss model. Tetracycline could be used for measuring bone formation activity in the same way as non-antibiotic fluorescent reagent such as calcein and alizarin, even in a tetracycline-sensitive bacterium-infected model.

Working goal of Brazilein sappan wood as a candidate for SARS-coV-2 antivirus drug against spike (S) glycoprotein, papain-like proteinase, and main protease: In silico study

Brazilein sappan wood, played by Spike (S) glycoprotein, Papain-Like proteinase (PLpro), and Main protease (Mpro), is expected to be a candidate for the antiviral drug SARS-CoV-2, which can inhibit viral attachment to the human body, replication, and transcription processes. The aim of this study was to predict in silico, using the comparative drug hydroxychloroquine, the working goal of brazilein sappan wood as a candidate for the antiviral drug SARS-CoV-2 against protein S, PLpro, and Mpro. The approach used is the in silico docking test using the computer program Molegro Virtual Docker. Receptor used by protein S, Protein Data Bank (PDB) code: 6M0J, NAG_601[E] ligand; PLpro, PDB code: 7JIT, Y95_501[A] ligand; and Mpro, PDB code: 1WOF, I12_1145[A] ligand. Data analysis was carried out by comparing the docking bond energies between the ligands at the target receptor. Silico test results for protein S: ligand bond energy NAG_601 [E] = -59.4555, brazilein = -71.5537, hydroxychloroquine = -79.3704; PLpro protein: Ligand bond energy Y95_501 [A] = -129.561, brazilein = -94.9761, hydroxychloroquine = -100.984; Mpro protein: Ligand bond energy I12 1145 [A] = -141.135, brazilein = -96.6169, hydroxychloroquine = -104.88. The above test results indicate that brazilein sappan wood has potential as a SARS-CoV-2 drug candidate, has a stable bond, and that the biological activity of the compound is stronger against S protein than the proteins of PLpro and Mpro.

Modulation of proinflammatory mediators by viruses-bacteria synergism in human osteoblasts-an in vitro study

BACKGROUND/PURPOSE

Viruses-bacteria synergistic interaction is associated with destructive periodontal diseases. However, the underlying mechanism for tissue destruction is not fully elucidated. In this study, lipopolysaccharide from Porphyromonas gingivalis (Pg-LPS) and polyinosinic-polycytidylic acid (poly I:C) were used to simulate bacteria and viruses, respectively. The possible combined effects of both molecular patterns on secretion of interleukin (IL)-6 and prostaglandin E₂ (PGE₂) from osteoblasts were determined. The effects of povidone-iodine (PVP-I) on the secretion of IL-6 and PGE₂ were also examined.

METHODS

Viability of treated osteoblastic cells (MG63) was examined by detection the mitochondrial dehydrogenase activity. Secretion of IL-6 and PGE₂ was detected using the enzyme-linked immunosorbent assay (ELISA). Mitogen-activated protein kinases (MAPKs) and cyclooxygenase-2 (COX-2) were determined using the Western blotting analysis.

RESULTS

Pg-LPS or poly I:C significantly enhanced the production of IL-6 and PGE₂ in MG63 cells. The additive/synergistic effects of Pg-LPS/poly I:C on production of IL-6 and PGE₂ were evident. The levels of phosphorylation of p38 MAPK and c-Jun N-terminal kinase (JNK) and expression of COX-2 protein were enhanced by Pg-LPS and/or poly I:C. On the other hand, the level of phosphorylation of extracellular signal-regulated kinase (ERK) was reduced by Pg-LPS and/or poly I:C. The stimulatory secretion of PGE₂ by poly I:C was significantly reduced by PVP-I.

CONCLUSION

Concomitant infection of viruses and bacteria may be potentially harmful to the tooth supporting tissues by production of proinflammatory mediators. The results suggest the potential anti-inflammatory effect of PVP-I on bacterial or viral infection.

The Pathogenic Effects of Fusobacterium nucleatum on the Proliferation, Osteogenic Differentiation, and Transcriptome of Osteoblasts

As one of the most common oral diseases, periodontitis is closely correlated with tooth loss in middle-aged and elderly people. Fusobacterium nucleatum (F. nucleatum) contributes to periodontitis, but the evidence in alveolar bone loss is still unclear. In this study, cytological experiments and transcriptome analyses were performed to characterize the biological process abnormalities and the molecular changes of F. nucleatum-stimulated osteoblasts. F. nucleatum could inhibit cell proliferation, promote cell apoptosis, and elevate pro-inflammatory cytokine production of osteoblasts, and it also inhibited osteoblast differentiation and mineralized nodule formation and decreased the expression of osteogenetic genes and proteins. Whole-transcriptome analyses identified a total of 235 transcripts that were differentially expressed in all six time points, most of which were inflammation-related genes. The genes, Ccl2, Ccl20, Csf1, Cx3cl1, Cxcl1, Cxcl3, Il6, Birc3, Map3k8, Nos2, Nfkb2, Tnfrsf1b, and Vcam1, played core roles in a PPI network, and interacted closely with other ones in the infection. In addition, 133 osteogenesis-related differential expression genes (DEGs) were time-serially dynamically changed in a short time-series expression miner (STEM) analysis, which were enriched in multiple cancer-related pathways. The core dynamic DEGs (Mnda, Cyp1b1, Comp, Phex, Mmp3, Tnfrsf1b, Fbln5, and Nfkb2) had been reported to be closely related to the development and metastasis in tumor and cancer progress. This study is the first to evaluate the long-term interaction of F. nucleatum on osteoblasts, which might increase the risk of cell carcinogenesis of normal osteoblasts, and provides new insight into the pathogenesis of bacterial-induced bone destruction.

Knockout of NRAGE promotes autophagy-related gene expression and the periodontitis process in mice

BACKGROUND AND OBJECTIVE

Neurotrophin receptor-interacting MAGE homologue (NRAGE) plays a crucial role in the regulation of bone metabolism. The present study investigated the regulation role of NRAGE on autophagy activation and periodontitis process during experimental periodontitis.

MATERIALS AND METHODS

Six-week-old wild-type (WT) and NRAGE-/- mice were randomly divided into three time points in the periodontitis groups (0, 2, and 4 weeks). Histopathological changes were determined using the tooth mobility, hematoxylin and eosin (H&E) staining, and micro-computed tomography (micro-CT). Osteoclasts activation and number were investigated using tartrate-resistant acid phosphatase (TRAP) staining, immunohistochemistry, and real-time quantitative PCR (RT-PCR). The level of autophagy-related gene expression was measured using immunohistochemistry, immunofluorescence, and RT-PCR.

RESULTS

H&E staining and Micro-CT showed that the destruction of the alveolar bone was considerably more severe in the NRAGE-/- group than the WT group after ligation. Tooth mobility in the NRAGE-/- group was obviously higher than that in the WT group. The activation and number of osteoclasts and the level of autophagy-related gene expression in NRAGE-/- group were significantly higher than that in WT group.

CONCLUSIONS

The present study showed that knockout of NRAGE induced autophagy-related gene expression and accelerated the process of periodontitis disease via increasing the activity and differentiation of osteoclast.

Invasion of Human Retinal Pigment Epithelial Cells by Porphyromonas gingivalis leading to Vacuolar/Cytosolic localization and Autophagy dysfunction In-Vitro

Recent epidemiological  studies link Periodontal disease(PD) to age-related macular degeneration (AMD). We documented earlier that Porphyromonas gingivalis(Pg), keystone oral-pathobiont, causative of PD, efficiently invades human gingival epithelial and blood-dendritic cells. Here, we investigated the ability of dysbiotic Pg-strains to invade human-retinal pigment epithelial cells(ARPE-19), their survival, intracellular localization, and the pathological effects, as dysfunction of RPEs leads to AMD. We show that live, but not heat-killed Pg-strains adhere to and invade ARPEs. This involves early adhesion to ARPE cell membrane, internalization and localization of Pg within single-membrane vacuoles or cytosol, with some nuclear localization apparent. No degradation of Pg or localization inside double-membrane autophagosomes was evident, with dividing Pg suggesting a metabolically active state during invasion. We found significant downregulation of autophagy-related genes particularly, autophagosome complex. Antibiotic protection-based recovery assay further confirmed distinct processes of adhesion, invasion and amplification of Pg within ARPE cells. This is the first study to demonstrate invasion of human-RPEs, begin to characterize intracellular localization and survival of Pg within these cells. Collectively, invasion of RPE by Pg and its prolonged survival by autophagy evasion within these cells suggest a strong rationale for studying the link between oral infection and AMD pathogenesis in individuals with periodontitis.

Axin 1 knockdown inhibits osteoblastic apoptosis induced by Porphyromonas gingivalis lipopolysaccharide

BACKGROUND

Porphyromonas gingivalis (Pg) is one of the pathogenic bacteria that cause periodontal diseases, lipopolysaccharide (LPS) is the key factor that triggers alveolar bone absorption. This study explored the action of Axin 1 on Pg-LPS-induced osteoblasts injury, so as to search a possible treatment for periodontal diseases.

METHODS

Rat osteoblasts were dealt with Pg-LPS and Axin 1 knockdown alone or in combination. The effect of Pg-LPS and Axin 1 on osteoblast viability and apoptosis were detected by Cell Counting Kit-8 and flow cytometry. The expressions of alkaline phosphatase (ALP) and Axin 1 in processed osteoblasts were measured by western blot (WB) and quantitative real-time polymerase chain reaction (qRT-PCR) assays. Furthermore, the role of Axin 1 knockdown in the levels of inflammatory cytokines and apoptosis-related proteins were also determined.

RESULTS

Pg-LPS inhibited the viability of osteoblasts and promote apoptosis with concentration and time dependence. ALP expression in Pg-LPS-treated osteoblasts was reduced, while Axin 1 expression was increased. On the one hand, Axin 1 knockdown reversed the Pg-LPS-induced reduction of cell activity and pro-apoptosis effect. On the other hand, Axin 1 knockdown not only improved the ALP activity of Pg-LPS-treated cells, but also reduced the elevation of inflammatory cytokines (TNF-α, IL-1β and IL-6) caused by Pg-LPS. Moreover, Pg-LPS increased the expressions of cleaved Caspase-3 and Bax, and inhibited Bcl-2 expressed, which was rescued by Axin 1 knockdown.

CONCLUSION

Axin 1 knockdown inhibited Pg-LPS-induced osteoblastic apoptosis by regulating the levels of inflammatory cytokines, which may be helpful for the treatment of periodontal diseases.

CXXC5 Mediates P. gingivalis-suppressed Cementoblast Functions Partially via MAPK Signaling Network

Porphyromonas (P.) gingivalis associates tightly with periodontal diseases and it is also a dominant pathogen of periapical periodontitis. However, the influence of P. gingivalis on cementoblasts, root surface cells pivotal in the apical areas, and the possible involvement of other molecules remain largely elusive. CXXC5 is a nuclear protein that regulates gene expression as well as cell growth, differentiation, and apoptosis. In this study, P. gingivalis repressed the mineralization capacity of cementoblasts by inducing inflammatory reactions and inhibiting cell differentiation. Intriguingly, the expression of CXXC5 decreased in P. gingivalis-treated OCCM-30 cells and apical periodontitis models but gradually increased during mineralization. Furthermore, RNA interference of CXXC5 significantly inhibited cementoblast differentiation, represented by decline of bone-associated markers Osterix, osteocalcin (OCN), and alkaline phosphatase (ALP). CXXC5 overexpression facilitated differentiation, and therefore attenuated the P. gingivalis-repressed effects on OCCM-30 cells. In addition, Erk1/2, p38, and PI3K-Akt were inactivated by silencing CXXC5 and activated upon its overexpression, whereas Wnt/β-catenin exhibited an opposite trend. The employment of specific inhibitors revealed that the CXXC5-dependent promotions of cementoblast differentiation were partially abrogated by p38 and PI3K-Akt inhibitors but were exacerbated by inhibiting Erk1/2. Overall, our experiment demonstrated a novel function of CXXC5 in the regeneration of impaired cementum caused by P. gingivalis invasion and suggested that MAPK signaling network balances the facilitation effects of CXXC5 in cementoblast differentiation.

Bee venom attenuates Porphyromonas gingivalis and RANKL-induced bone resorption with osteoclastogenic differentiation

Porphyromonas gingivalis (P. gingivalis) is one of the major periodontal pathogens leading to inflammation and alveolar bone resorption. Bone resorption is induced by osteoclasts, which are multinucleated giant cells. Osteoclastic bone resorption is mediated by enhanced receptor activator of nuclear factor-kappa B ligand (RANKL) signaling. Therefore, the down-regulation of RANKL downstream signals is regarded as an effective therapeutic target in the treatment of bone loss-associated disorders. The aim of this study was to evaluate whether purified bee venom (BV) could attenuate P. gingivalis-induced inflammatory periodontitis and RANKL-induced osteoclast differentiation. Inflammatory periodontitis induced by P. gingivalis increased alveolar bone resorption and increased expression of TNF-α and IL-1β, while BV treatment resulted in decreased bone loss and pro-inflammatory cytokines. Similarly, RANKL-induced multinucleated osteoclast differentiation and osteoclast-specific gene expression, such as nuclear factor of activated T cells 1 (NFATc1), cathepsin K, tartrate-resistant acid phosphatase (TRAP), and integrin αvβ3 were significantly suppressed by treatment with BV. We show that BV reduces P. gingivalis-induced inflammatory bone loss-related periodontitis in vivo and RANKL-induced osteoclast differentiation, activation, and function in vitro. These results suggest that BV exerts positive effects on inflammatory periodontitis associated osteoclastogenesis.

Ligature-induced periodontitis induces systemic inflammation but does not alter acute outcome after stroke in mice

Background

Stroke is a major cause of disability and mortality. Poorer outcome after stroke is associated with concomitant inflammatory and infectious disease. Periodontitis is a chronic inflammatory disease of the dental supporting structures and is a prominent risk factor for many systemic disorders, including cardiovascular disease and stroke. While epidemiological studies suggest that periodontitis increases the likelihood of stroke, its impact on stroke severity is poorly understood. Here, we sought to determine the contribution of periodontitis to acute stroke pathology.

Methods

We characterized a murine ligature model of periodontitis for inflammatory responses that could potentially impact stroke outcome. We applied this model and then subjected mice to either transient or permanent middle cerebral artery occlusion. We also enhanced the periodontitis model with repeated intravenous administration of a periodontal-specific lipopolysaccharide to better mimic the clinical condition.

Results

Ligature-induced periodontitis caused bone loss, bacterial growth, and increased local inflammatory cell trafficking. Systemically, periodontitis increased circulating levels of pro-inflammatory cytokines, and primed bone marrow monocytes to produce elevated tumour necrosis factor-alpha (TNFα). Despite these changes, periodontitis alone or in tandem with repeated lipopolysaccharide challenge did not alter infarct volume, blood–brain barrier breakdown, or systemic inflammation after experimental stroke.

Conclusions

Our data show that despite elevated systemic inflammation in periodontitis, oral inflammatory disease does not impact acute stroke pathology in terms of severity, determined primarily by infarct volume. This indicates that, at least in this experimental paradigm, periodontitis alone does not alter acute outcome after cerebral ischemia.

Streptococcus gordonii induces bone resorption by increasing osteoclast differentiation and reducing osteoblast differentiation

Streptococcus gordonii is commonly found in the periapical endodontic lesions of patients with apical periodontitis, a condition characterized by inflammation and periapical bone loss. Since bone metabolism is controlled by osteoclastic bone resorption and osteoblastic bone formation, we investigated the effects of S. gordonii on the differentiation and function of osteoclasts and osteoblasts. For the determination of bone resorption activity in vivo, collagen sheets soaked with heat-killed S. gordonii were implanted on mouse calvaria, and the calvarial bones were scanned by micro-computed tomography. Mouse bone marrow-derived macrophages (BMMs) were stimulated with M-CSF and RANKL for 2 days and then differentiated into osteoclasts in the presence or absence of heat-killed S. gordonii. Tartrate-resistant acid phosphatase staining was performed to determine osteoclast differentiation. Primary osteoblast precursors were differentiated into osteoblasts with ascorbic acid and β-glycerophosphate in the presence or absence of heat-killed S. gordonii. Alkaline phosphatase staining and alizarin red S staining were conducted to determine osteoblast differentiation. Western blotting was performed to examine the expression of transcription factors including c-Fos, NFATc1, and Runx2. Heat-killed S. gordonii induced bone destruction in a mouse calvarial implantation model. The differentiation of RANKL-primed BMMs into osteoclasts was enhanced in the presence of heat-killed S. gordonii. Heat-killed S. gordonii increased the expression of c-Fos and NFATc1, which are essential transcription factors for osteoclast differentiation. On the other hand, heat-killed S. gordonii inhibited osteoblast differentiation and reduced the expression of Runx2, an essential transcription factor for osteoblast differentiation. S. gordonii exerts bone resorptive activity by increasing osteoclast differentiation and reducing osteoblast differentiation, which may be involved in periapical bone resorption.

Oral Biofilms from Symbiotic to Pathogenic Interactions and Associated Disease -Connection of Periodontitis and Rheumatic Arthritis by Peptidylarginine Deiminase

A wide range of bacterial species are harbored in the oral cavity, with the resulting complex network of interactions between the microbiome and host contributing to physiological as well as pathological conditions at both local and systemic levels. Bacterial communities inhabit the oral cavity as primary niches in a symbiotic manner and form dental biofilm in a stepwise process. However, excessive formation of biofilm in combination with a corresponding deregulated immune response leads to intra-oral diseases, such as dental caries, gingivitis, and periodontitis. Moreover, oral commensal bacteria, which are classified as so-called “pathobionts” according to a now widely accepted terminology, were recently shown to be present in extra-oral lesions with distinct bacterial species found to be involved in the onset of various pathophysiological conditions, including cancer, atherosclerosis, chronic infective endocarditis, and rheumatoid arthritis. The present review focuses on oral pathobionts as commensal and healthy members of oral biofilms that can turn into initiators of disease. We will shed light on the processes involved in dental biofilm formation and also provide an overview of the interactions of P. gingivalis, as one of the most prominent oral pathobionts, with host cells, including epithelial cells, phagocytes, and dental stem cells present in dental tissues. Notably, a previously unknown interaction of P. gingivalis bacteria with human stem cells that has impact on human immune response is discussed. In addition to this very specific interaction, the present review summarizes current knowledge regarding the immunomodulatory effect of P. gingivalis and other oral pathobionts, members of the oral microbiome, that pave the way for systemic and chronic diseases, thereby showing a link between periodontitis and rheumatoid arthritis.

Agreement, correlation, and kinetics of the alveolar bone-loss measurement methodologies in a ligature-induced periodontitis animal model

Periodontal research involves the use of animal models to better understand the biological processes of periodontal diseases and the potential of new or existing therapies. Currently, ligature-induced periodontitis in rats is the main model used in periodontal research, in this model, alveolar bone loss (ABL) is the main parameter evaluated by radiographic, morphometric, and histological techniques. Interestingly, although these methodologies are widely used, it is not totally clarified neither the kinetics of ABL over the induction time nor the agreement degree (repeatability and reproducibility) of these techniques. Objective: To characterize ABL kinetics at 0, 3, 7, 15, 30, and 60 days after ABL induction by ligature and to evaluate the intra- (repeatability) and inter-examiner (reproducibility) agreement and the correlation among the radiographic, morphometric, and histological methodologies. Material and Methods: 60 male Wistar rats with induced ABL were randomly divided into 6 experimental groups (n = 10 animals/group). After 0, 3, 7, 15, 30, and 60 days, the animals were euthanized and their hemimandibles were removed for ABL determination using radiographic, morphometric and histological techniques. Results: Radiographic and morphometric/linear techniques allowed the detection of statistically significant ABL on the third day, while histological and morphometric/area techniques could only detect ABL after the seventh day (ANOVA/Tukey, p<0.05). After the fifteenth day, except for histological analysis, the ABL was stabilized. Concerning the agreement of the methodologies, Bland Altman's test (intra and inter-examiner evaluations) showed no difference among the measurements (p>0.05). In addition, high correlations (Pearson's test, r2>0.9, p<0.05) were observed. Conclusion: The results indicated that the minimum time for ABL induction could vary from 3 to 7 days, according to the chosen analysis methodology. Agreement and correlation data support the comparison of results between studies with same induction time.

Periodontitis induced by bacterial infection exacerbates features of Alzheimer's disease in transgenic mice

Periodontitis is a localized infectious disease caused by periodontopathic bacteria, such as Porphyromonas gingivalis. Recently, it has been suggested that bacterial infections may contribute to the onset and the progression of Alzheimer’s disease (AD). However, we do not have any evidence about a causative relationship between periodontitis and AD. In this study, we investigated by using a transgenic mouse model of AD whether periodontitis evoked by P. gingivalis modulates the pathological features of AD. Cognitive function was significantly impaired in periodontitis-induced APP-Tg mice, compared to that in control APP-Tg mice. Levels of Amiloid β (Aβ) deposition, Aβ40, and Aβ42 in both the hippocampus and cortex were higher in inoculated APP-Tg mice than in control APP-Tg mice. Furthermore, levels of IL-1β and TNF-α in the brain were higher in inoculated mice than in control mice. The levels of LPS were increased in the serum and brain of P. gingivalis-inoculated mice. P. gingivalis LPS-induced production of Aβ40 and Aβ42 in neural cell cultures and strongly enhanced TNF-α and IL-1β production in a culture of microglial cells primed with Aβ. Periodontitis evoked by P. gingivalis may exacerbate brain Aβ deposition, leading to enhanced cognitive impairments, by a mechanism that involves triggering brain inflammation.

Alzheimer’s disease is a scourge of longevity that will drain enormous resources from health budgets in the future. Unfortunately, the pathogenesis of the disease remains an enigma and there is no adequate treatment or prophylaxis for the disease. One key priority is to examine the modifiable risk factors that influence the development of dementia. A risk factor relationship between periodontal pathogens/periodontal disease and AD exists. In Alzheimer’s model mice infected with Porphromonas gingivalis, a type of periodontopathic bacterium, cognitive function was reduced and deposition of amyloid β peptide was increased. Moreover, inflammatory cytokines and bacterial endotoxin were increased in the serum and brain. Neuroinflammation may be caused by an increase in these inflammatory mediators, and the pathology of Alzheimer’s disease may be exacerbated. Since periodontal infections are treatable, treatment of periodontal diseases during this period may be effective for delaying the onset or progression of AD.

Development and evaluation of novel biodegradable chitosan based metformin intrapocket dental film for the management of periodontitis and alveolar bone loss in a rat model

OBJECTIVE

The aim of this study was to develop a chitosan-metformin based intrapocket dental film (CMIDF) for applications in the treatment of periodontitis and alveolar bone loss in an rat model of periodontitis.

DESIGN

CMIDF inserts were fabricated by the solvent casting technique. The fabricated inserts were evaluated for physical characteristics such as folding endurance, surface pH, mucoadhesive strength, metformin content uniformity, and release. X-ray diffraction analysis indicates no crystallinity of metformin in presence of chitosan which confirmed successful entrapment of metformin into the CMIDF. Fourier-transform infrared spectroscopy revealed stability of CMIDF and compatibility between metformin and chitosan. Periodontitis was induced by a combination of Porphyromonas gingivalis- lipopolysaccharide injections in combinations with ligatures around the mandibular first molar. We divided rats into 5 groups (8 rats/group): healthy, untreated periodontitis; periodontitis plus CMIDF-A (1.99±0.09mg metformin; total mass-4.01±0.05mg), periodontitis plus CMIDF-B (2.07±0.06mg metformin; total mass-7.56±0.09mg), and periodontitis plus chitosan film (7.61±0.08mg). After four weeks, mandibles were extracted to evaluate alveolar bone loss by micro-computerized tomography and histological techniques.

RESULTS

Alveolar bone was intact in the healthy group. Local administration of CMIDF resulted in significant improvements in the alveolar bone properties when compared to the untreated periodontitis group. The study reported here demonstrates that novel CMIDF showed good antibacterial activity and effectively reduced alveolar bone destruction in a rat model of experimental periodontitis.

CONCLUSIONS

Novel CMIDF showed good antibacterial activity and improved alveolar bone properties in a rat model.

Bone regeneration: Biomaterials as local delivery systems with improved osteoinductive properties

Bone is a mineralized conjunctive tissue, with a unique trauma healing capability. However, the replacement or regeneration of lost bone is not always successful and becomes more difficult the wider the bone defect. A significant growth in the demand for orthopedic and maxillofacial surgical procedures as a result of population aging and increase in chronic diseases as diabetes is a fact and successful approaches for bone regeneration are still needed. Until today, autogenous bone graft continues to be the best solution even with important limitations, as quantity and the requirement of a donator area. Alternatively, local delivery systems combining an osteoconductive biomaterial with osteoinductive compounds as hormones, growth factors or drugs is a popular approach aiming to replace the need for autogenous bone grafts. Nevertheless, in spite of the intense research in the area, presently there is no system that can mimic all the biological functions of the autogenous bone grafts. In this context, the present work provides an overview of the most recent advances in the field of synthetic bone grafts. The opportunities and limitations are detailed along with the remaining gaps in the research that are still preventing the successful translation of more products into the market able to be a valuable option in comparison to the autogenous bone grafts.

[Effects of paeonol on the function of bone marrow-derived macrophage from Porphyromonas gingivalis-induced mice]

OBJECTIVE

This work aims to examine the effects of paeonol treatment on the ability of bone marrow-derived macrophage (BMM) to excrete inflammatory factors and to differentiate into osteoclasts upon induction with Porphyromonas gingivalis (P. gingivalis). This work also aims to investigate the underlying mechanisms of these abilities.

METHODS

BMM culture was treated with different paeonol concentrations at for 1 h and then stimulated with P. gingivalis for 24 h before programmed death-ligand 1 (PD-L1) was quantified with flow cytometry. Tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 were detected by enzyme-linked immunosorbent assay (ELISA). The BMM culture was treated with the receptor activator for nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF), and then with paeonol for 1 h prior to induction with P. gingivalis. Then, osteoclast formation was assessed using tartrate resistant acid phosphatase (TRAP) staining. The osteoclast-related proteins TRAP and receptor activator of nuclear factor-κB (RANK) were quantified by Western blotting.

RESULTS

Paeonol was nontoxic to BMM within a range of 10-50 μmol·L⁻¹. Flow cytometry showed that paeonol inhibited PD-L1 expression in P. gingivalis-induced BMM in a dose-dependent manner. ELISA indicated that paeonol dose-dependently inhibited the excretion of TNF-α, IL-1β, and IL-6 by P. gingivalis-induced BMM (P<0.01). TRAP staining revealed that paenol treatment inhibited the differentiation of P. gingivalis-induced BMM into osteoclasts. Western blot results suggested that paeonol decreased the expression of TRAP and RANK in BMM.

CONCLUSIONS

Paeonol dose-dependently inhibited the excretion of the inflammatory factors TNF-α, IL-1β, and IL-6 by P. gingivalis-induced BMM in a dose-dependent manner. Moreover, paenol treatment prevented the differentiation of P. gingivalis-induced BMM differentiation into osteoclasts.
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A Modified Glycosaminoglycan, GM-0111, Inhibits Molecular Signaling Involved in Periodontitis

Background

Periodontitis is characterized by microbial infection, inflammation, tissue breakdown, and accelerated loss of alveolar bone matrix. Treatment targeting these multiple stages of the disease provides ways to treat or prevent periodontitis. Certain glycosaminoglycans (GAGs) block multiple inflammatory mediators as well as suppress bacterial growth, suggesting that these GAGs may be exploited as a therapeutic for periodontitis.

Methods

We investigated the effects of a synthetic GAG, GM-0111, on various molecular events associated with periodontitis: growth of Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) pathogenic bacteria associated with periodontitis; activation of pro-inflammatory signaling through TLR2 and TLR4 in mouse macrophage RAW 264.7 cells and heterologously expressed HEK 293 cells; osteoclast formation and bone matrix resorption in cultured mouse pre-osteoclasts.

Results

(1) GM-0111 suppressed the growth of P. gingivalis and A. actinomycetemcomitans even at 1% (w/v) solution. The antibacterial effects of GM-0111 were stronger than hyaluronic acid (HA) or xylitol in P. gingivalis at all concentrations and comparable to xylitol in A. actinomycetemcomitans at ≥2% (w/v) solution. We also observed that GM-0111 suppressed biofilm formation of P. gingivalis and these effects were much stronger than HA. (2) GM-0111 inhibited TLR-mediated pro-inflammatory cellular signaling both in macrophage and HEK 293 cells with higher selectivity for TLR2 than TLR4 (IC₅₀ of 1–10 ng/mL vs. > 100 μg/mL, respectively). (3) GM-0111 blocked RANKL-induced osteoclast formation (as low as 300 ng/mL) and bone matrix resorption. While GM-0111 showed high affinity binding to RANKL, it did not interfere with RANKL/RANK/NF-κB signaling, suggesting that GM-0111 inhibits osteoclast formation by a RANKL-RANK-independent mechanism.

Conclusions

We report that GM-0111 inhibits multiple molecular events involved in periodontitis, spanning from the early pro-inflammatory TLR signaling, to pathways activated at the later stage component of bone loss.

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.

SOCS-3 Regulates Alveolar Bone Loss in Experimental Periodontitis

The host immune response plays a key role in bacteria-induced alveolar bone resorption. Endogenous control of the magnitude and duration of inflammatory signaling is considered an important determinant of the extent of periodontal pathology. Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine signaling pathways and may play a role in restraining periodontal inflammation. We hypothesized that SOCS-3 regulates alveolar bone loss in experimental periodontitis. Periodontal bone loss was induced in 16-wk-old myeloid-specific SOCS-3-knockout and wild-type (WT) C57Bl6-B.129 mice by oral inoculation 9 times with 10(9) colony-forming units of Porphyromonas gingivalis A7436 through an oral gavage model for periodontitis. Sham controls for both types of mice received vehicle without bacteria. The mice were euthanized 6 wk after the last oral inoculation. Increased bone loss was demonstrated in P. gingivalis-infected SOCS-3-knockout mice as compared with P. gingivalis-infected WT mice by direct morphologic measurements, micro-computed tomography analyses, and quantitative histology. Loss of SOCS-3 function resulted in an increased number of alveolar bone osteoclasts and increased RANKL expression after P. gingivalis infection. SOCS-3 deficiency in myeloid cells also promotes a higher P. gingivalis lipopolysaccharide-induced inflammatory response with higher secretion of IL-1β, IL-6, and KC (IL-8) by peritoneal macrophages as compared with WT controls. Our data implicate SOCS-3 as a critical negative regulator of alveolar bone loss in periodontitis.

[Effect of specific sequence oligodeoxynucleotide MT01 on the proliferation, apoptosis, and cell cycle of osteoblasts invaded by Porphyromonas gingivalis]

OBJECTIVE

This aimed to investigate the effect of specific sequence oligodeoxynucleotide MT01 on the biological properties of osteoblasts invaded by Porphyromonas gingivalis (P. gingivalis ) by evaluating proliferation, cell cycle, and apoptosis.

METHODS

MG63 osteoblasts were recovered and incubated with MT01, CpG ODN, metronidazole (MNZ), and gentamicin (GEN) for 3 h. P. gingivalis (the multiplicity of infection was 100:1) was added subsequently and cocultured for another 24 and 48 h. Cells with PBS comprised the blank group, whereas cells with P. gingivalis comprised the negative controls. Six experimental groups were established: PBS group, P. gingivalis group, MT01+P. gingivalis group, CpG ODN+ P. gingivalis group, MNZ+P. gingivalis group, and GEN+P. gingivalis group. The proliferative ability was measured by methyl thiazolyl tetrazolium assay, and the percentages of apoptosis and cell cycle were examined by flow cytometry.

RESULTS

Compared with the blank group, proliferation increased significantly in the MT01+P. gingivalis group (P < 0.05). The ratio of cells was lower at the G₁ phase and higher at the S phase in the MT01+P. gingivalis group compared with the results in the P. gingivalis group (P < 0.05). Early cell apoptosis in the MT01+P. gingivalis group was significantly lower than that in the P. gingivalis group (P < 0.05).

CONCLUSION

MT01 can promote the proliferation, reduce the ratio of the G₁phase, increase the ratio of the S phase, and inhibit the early apoptosis of osteoblasts invaded by P. gingivalis.

Porphyromonas gingivalis promotes the cell cycle and inflammatory cytokine production in periodontal ligament fibroblasts

OBJECTIVE

The infection of Porphyromonas gingivalis (P. gingivalis) modulates host immune-inflammatory responses and destructs homeostasis of normal cell cycle, thereby leading to periodontal tissue destruction. Human periodontal ligament fibroblasts (PDLFs) are key players in the host immune responses and periodontal tissue regeneration. The aim of the present study was to discover the effects of P. gingivalis infection on the cell cycle and inflammatory cytokine production in PDLFs.

DESIGN

P. gingivalis infection model into PDLFs was established. The effect of P. gingivalis on the cell proliferation and cell cycle were detected by MTT and flow cytometry. The p21, cyclin D1 and cyclin E mRNA expression, p21 protein expression, as well as IL-6 and IL-8 protein levels were analyzed by RT-qPCR, Western blot and ELISA, respectively.

RESULTS

P. gingivalis promoted proliferation and G1 phase of PDLFs. G1 phase promotion was associated with the decreased level of p21 and the up-regulation of cyclin D1 at 6h, and with the increased level of cyclin E at 12h. Simultaneously, the immune-inflammatory response of PDLFs was initiated by P. gingivalis during the initial stage of infection, including the increased expressions of IL-6 and IL-8.

CONCLUSION

We confirmed that the infection of P. gingivalis could modulate the expression of PDLF genes, which control cell cycle and inflammatory cytokine production. Thus, P. gingivalis may contribute to the proliferation and inflammation of periodontal tissue.