Down-regulation of NLRP3 inflammasome in gingival fibroblasts by subgingival biofilms: involvement of Porphyromonas gingivalis

Association of salivary levels of DNA sensing inflammasomes AIM2, IFI16, and cytokine IL18 with periodontitis and diabetes

BACKGROUND

Aberrant deoxyribonucleic acid (DNA) contributes to inflammasome orchestrated progression of chronic inflammatory diseases like diabetes and periodontitis. The purpose of the present study was to estimate salivary levels of DNA sensing inflammasomes, absent in melanoma 2 (AIM2), interferon γ inducible protein (IFI16), and cytokine interleukin 18 (IL18) in individuals with periodontitis, diabetes, and healthy controls and interpret its association with periodontal and diabetic parameters.

METHODS

Salivary levels of AIM2, IFI16, and IL18 were estimated by enzyme linked immunosorbent assay (ELISA) in a total of 120 individuals (n = 30 in each group), namely, healthy (Group 1), periodontitis (Group 2), diabetes (Group 3), and diabetes with periodontitis (Group 4). Correlations of inflammasome levels and periodontal clinical parameters-plaque index (PI), gingival index (GI), bleeding on probing (BOP), probing pocket depth (PPD), clinical attachment level (CAL), and periodontal inflamed surface area (PISA) were performed. Multiple regression was carried out to predict AIM2 and IFI16 with various independent variables.

RESULTS

The mean salivary levels of AIM2, IFI16, and IL18 were highest in diabetes with periodontitis (Group 4) and least in healthy (Group 1) and statistically significant between the groups (p = 0.000). Significant positive correlation between clinical periodontal parameters and AIM2, IFI16, and IL18 was present (p ≤ 0.05). Multiple regression showed glycated hemoglobin (HbA1C) (p = 0.002), GI (p = 0.016), PISA (p = 0.002), and CAL (p = 0.004) were significant predictors of AIM2, while HbA1C (p = 0.012), PISA (p = 0.003), and CAL (p = 0.007) predicted IFI16.

CONCLUSION

The results of the present study showed higher levels of AIM2, IFI16, and IL18 in saliva of individuals with diabetes and periodontitis. HbA1C, PISA, and CAL were significant independent predictors of salivary AIM2 and IFI16 levels.

Correlation between Inflammasomes and Microbiota in Peri-Implantitis

The activation of inflammasomes is thought to induce the inflammatory process around dental implants. No information is available on the correlation between microbiota and inflammasomes in clinical samples from patients suffering peri-implantitis. For this cross-sectional study, 30 biofilm samples were obtained from 19 patients undergoing surgical treatment for peri-implantitis because of the presence of bleeding on probing, probing depth higher than 6 mm, and radiographic bone loss higher than 3 mm. Then, soft tissue samples from around the implant were also collected. The relative abundance of bacteria and alpha-diversity indexes were calculated after analyzing the 16S rRNA gene using next-generation sequencing. The soft-tissue samples were processed for evaluation of the inflammasomes NLRP3 and AIM2 as well as caspase-1 and IL-1β. The relative abundance (mean (SD)) of specific species indicated that the most abundant species were Porphyromonas gingivalis (10.95 (14.17)%), Fusobacterium vincentii (10.93 (13.18)%), Porphyromonas endodontalis (5.89 (7.23)%), Prevotella oris (3.88 (4.94)%), Treponema denticola (2.91 (3.19)%), and Tannerella forsythia (2.84 (4.15)%). Several correlations were found between the species and the immunohistochemical detection of the inflammasomes NLRP3 and AIM2 as well as caspase-1 and IL-1β, both in the epithelium and the lamina propria. A network analysis found an important cluster of variables formed by NLRP3 in the lamina propria and AIM2, caspase-1, and IL-1β in the lamina propria and the epithelium with Prevotella dentalis, Prevotella tannerae, Tannerella forsythia, or Selenomonas timonae. Thus, it could be concluded that inflammasomes NLRP3 and AIM2 and their downstream effectors caspase-1 and interleukin-1β can be significantly associated with specific bacteria.

Salivary levels of NLRP3 protein are significantly raised in chronic periodontitis: A systematic review and meta-analysis of clinical studies

Background

To date, there is no confirmatory diagnostic test that can identify the type of periodontal disease and the disease progress. With the advent of "molecular biomarkers," this systematic review and meta-analysis were designed with the sole purpose of identifying a novel biomarker, namely, nucleotide leucine rich repeat pyrin protein-3 (NLRP3) inflammasome which has already been extensively researched for chronic inflammatory and autoimmune diseases.

Types of Studies Reviewed

Only case observational studies that evaluated the presence of human NLRP3 inflammasome in the saliva of patients with chronic periodontitis with no overlying systemic disease and compared the same to healthy patients to obtain quantitative data that can be statistically analyzed were included. The confirmatory test used in all the studies was the enzyme-linked immunosorbent assay.

Results

The broad-based search led to a total of three articles that fulfilled the inclusion criteria so that a meta-analysis of the results could be carried out. Data reveal that NLRP3 levels are raised in chronic periodontitis cases (P = 0.05; relative risk = 1.05 [0.00-2.09]). The risk of bias assessment was carried out according to the Joanna Briggs Institute Critical Appraisal Checklist where ten-point criteria were outlined indicating a low risk of bias for three studies.

Clinical Implications

NLPR3 inflammasome could be tested as a reliable biomarker in saliva to identify the type and progress of the periodontal disease.

AR-A014418, a glycogen synthase kinase-3β inhibitor, mitigates lipopolysaccharide-induced inflammation in rat dental pulp stem cells via NLR family pyrin domain containing 3 inflammasome impairment

Background/purpose

Cell pyroptosis and gingival inflammation have been implicated in periodontitis progression. Our previous study revealed that AR-A014418, a pharmacological inhibitor of glycogen synthase kinase-3β (GSK-3β), can enhance the migratory and osteogenic differentiation abilities of rat dental pulp stem cells (rDPSCs). The present study aimed to explore the effect of AR on the inflammation of rDPSCs.

Materials and methods

The primary rDPSCs were isolated and identified by flow cytometry, as well as Oil red O and Alizarin Red S staining. The rDPSCs were cultured and exposed to lipopolysaccharide (LPS) before treating them with different concentrations of AR-A014418. The cell viability was detected using the CCK-8 assay. The generation and secretion of pro-inflammatory cytokines (IL-18, TNF-α, L-1β, and IL-6) were examined by qPCR and ELISA, respectively. To investigate the activation of the NLRP3 inflammasome, the expression levels of pro-caspase 1, cleaved caspase 1, as well as NLRP3 were analyzed by western blotting and immunofluorescence, respectively.

Results

In the rDPSCs, LPS prohibited cell viability and enhanced the generation and secretion of pro-inflammatory cytokines. LPS upregulated NLRP3 and cleaved caspase-1 protein levels and promoted ASC speck formation in the rDPSCs. AR-A014418 administration effectively blocked the LPS-induced inflammation of the rDPSCs in a dose-dependent way. Mechanistically, AR-A014418 significantly restrained the up-regulation of NLRP3 and cleaved caspase-1 in LPS-treated rDPSCs.

Conclusion

Collectively, our findings suggest that AR-A014418 significantly mitigates LPS-induced inflammation of rDPSCs by blocking the activation of the NLRP3 inflammasome.

Identification of Key Pyroptosis-Related Genes and Distinct Pyroptosis-Related Clusters in Periodontitis

Aim

This study aims to identify pyroptosis-related genes (PRGs), their functional immune characteristics, and distinct pyroptosis-related clusters in periodontitis.

Methods

Differentially expressed (DE)-PRGs were determined by merging the expression profiles of GSE10334, GSE16134, and PRGs obtained from previous literatures and Molecular Signatures Database (MSigDB). Least absolute shrinkage and selection operator (LASSO) regression was applied to screen the prognostic PRGs and develop a prognostic model. Consensus clustering was applied to determine the pyroptosis-related clusters. Functional analysis and single-sample gene set enrichment analysis (ssGSEA) were performed to explore the biological characteristics and immune activities of the clusters. The hub pyroptosis-related modules were defined using weighted correlation network analysis (WGCNA).

Results

Of the 26 periodontitis-related DE-PRGs, the highest positive relevance was for High-Mobility Group Box 1 (HMGB1) and SR-Related CTD Associated Factor 11 (SCAF11). A 14-PRG-based signature was developed through the LASSO model. In addition, three pyroptosis-related clusters were obtained based on the 14 prognostic PRGs. Caspase 3 (CASP3), Granzyme B (GZMB), Interleukin 1 Alpha (IL1A), IL1Beta (B), IL6, Phospholipase C Gamma 1 (PLCG1) and PYD And CARD Domain Containing (PYCARD) were dysregulated in the three clusters. Distinct biological functions and immune activities, including human leukocyte antigen (HLA) gene expression, immune cell infiltration, and immune pathway activities, were identified in the three pyroptosis-related clusters of periodontitis. Furthermore, the pink module associated with endoplasmic stress-related functions was found to be correlated with cluster 2 and was suggested as the hub pyroptosis-related module.

Conclusion

The study identified 14 key pyroptosis-related genes, three distinct pyroptosis-related clusters, and one pyroptosis-related gene module describing several molecular aspects of pyroptosis in the pathogenesis and immune micro-environment regulation of periodontitis and also highlighted functional heterogeneity in pyroptosis-related mechanisms.

How Pyroptosis Contributes to Inflammation and Fibroblast-Macrophage Cross-Talk in Rheumatoid Arthritis

About thirty years ago, a new form of pro-inflammatory lytic cell death was observed and termed pyroptosis. Only in 2015, gasdermins were defined as molecules that create pores at the plasma membrane and drive pyroptosis. Today, we know that gasdermin-mediated death is an important antimicrobial defence mechanism in bacteria, yeast and mammals as it destroys the intracellular niche for pathogen replication. However, excessive and uncontrolled cell death also contributes to immunopathology in several chronic inflammatory diseases, including arthritis. In this review, we discuss recent findings where pyroptosis contributes to tissue damage and inflammation with a main focus on injury-induced and autoimmune arthritis. We also review novel functions and regulatory mechanisms of the pyroptotic executors gasdermins. Finally, we discuss possible models of how pyroptosis may contribute to the cross-talk between fibroblast and macrophages, and also how this cross-talk may regulate inflammation by modulating inflammasome activation and pyroptosis induction.

Nrf2 in the Field of Dentistry with Special Attention to NLRP3

The aim of this review article was to summarize the functional implications of the nuclear factor E2-related factor or nuclear factor (erythroid-derived 2)-like 2 (Nrf2), with special attention to the NACHT (nucleotide-binding oligomerization), LRR (leucine-rich repeat), and PYD (pyrin domain) domains-containing protein 3 (NLRP3) inflammasome in the field of dentistry. NLRP3 plays a crucial role in the progression of inflammatory and adaptive immune responses throughout the body. It is already known that this inflammasome is a key regulator of several systemic diseases. The initiation and activation of NLRP3 starts with the oral microbiome and its association with the pathogenesis and progression of several oral diseases, including periodontitis, periapical periodontitis, and oral squamous cell carcinoma (OSCC). The possible role of the inflammasome in oral disease conditions may involve the aberrant regulation of various response mechanisms, not only in the mouth but in the whole body. Understanding the cellular and molecular biology of the NLRP3 inflammasome and its relationship to Nrf2 is necessary for the rationale when suggesting it as a potential therapeutic target for treatment and prevention of oral inflammatory and immunological disorders. In this review, we highlighted the current knowledge about NLRP3, its likely role in the pathogenesis of various inflammatory oral processes, and its crosstalk with Nrf2, which might offer future possibilities for disease prevention and targeted therapy in the field of dentistry and oral health.

Periodontitis activates the NLRP3 inflammasome in serum and saliva

BACKGROUND

Nod-like receptor family pyrin domain-containing protein-3 (NLRP3) complex inflammasome has potentially been shown to play an important role in the development of periodontitis and diabetes. The objective of this study was to analyze the association between serum and salivary NLRP3 concentrations in patients with periodontitis and type-II diabetes mellitus (DM) and to evaluate whether this association was influenced by potential confounders.

METHODS

For the present study, a cohort of healthy controls (n = 32), and patients with periodontitis (n = 34), type-II DM (n = 33), and a combination of periodontitis + type-II DM (n = 34) were enrolled. Patients were characterized on the basis of their periodontal status and analyzed for demographic characteristics, serum mediators, and for serum and salivary concentrations of NLRP3. A uni- and multivariate model was established to analyze whether periodontitis, type-II DM, and CRP influenced serum and salivary NLRP3 concentrations.

RESULTS

In comparison to type-II DM patients and healthy controls, patients with periodontitis (serum, P = 0.003; saliva P = 0.012) and periodontitis + type-II DM (serum, P = 0.028; saliva, P = 0.003) had elevated serum and salivary NLRP3 concentrations. The multivariate regression model showed that periodontitis (P = 0.029) and HDL-cholesterol (P = 0.012) were significant predictors of serum NLRP3 concentrations whereas periodontitis (P = 0.036) and CRP (P = 0.012) were significant predictors of salivary NLRP3.

CONCLUSION

The results of the present study showed that periodontitis and periodontitis + type-II DM patients had higher serum and salivary NLRP3 concentrations in comparison to healthy controls and patients with type-II DM. Periodontitis was demonstrated to be a significant predictor of both serum and salivary NLRP3 concentrations.

Pyroptosis-Mediated Periodontal Disease

Pyroptosis is a caspase-dependent process relevant to the understanding of beneficial host responses and medical conditions for which inflammation is central to the pathophysiology of the disease. Pyroptosis has been recently suggested as one of the pathways of exacerbated inflammation of periodontal tissues. Hence, this focused review aims to discuss pyroptosis as a pathological mechanism in the cause of periodontitis. The included articles presented similarities regarding methods, type of cells applied, and cell stimulation, as the outcomes also point to the same direction considering the cellular events. The collected data indicate that virulence factors present in the diseased periodontal tissues initiate the inflammasome route of tissue destruction with caspase activation, cleavage of gasdermin D, and secretion of interleukins IL-1β and IL-18. Consequently, removing periopathogens’ virulence factors that trigger pyroptosis is a potential strategy to combat periodontal disease and regain tissue homeostasis.

NLRP3 Inflammasome Expression in Gingival Crevicular Fluid of Patients with Periodontitis and Chronic Hepatitis C

The study is aimed at assessing the impact that periodontal disease and chronic hepatitis C could have on gingival crevicular fluid levels of the NLRP3 inflammasome, caspase-1 (CASP-1), and interleukin-18 (IL-18) and at evaluating whether the increased local inflammatory reaction with clinical periodontal consequences is correlated to their upregulation. Patients were divided into four groups, according to their periodontal status and previously diagnosed hepatitis C, as follows: (i) CHC group, chronic hepatitis C patients; (ii) P group, periodontal disease patients, systemically healthy; (iii) CHC + P group, patients suffering from both conditions; and (iv) H group, systemically and periodontally healthy controls. Gingival crevicular samples were collected for quantitative analysis of the NLRP3 inflammasome, CASP-1, and IL-18. CHC + P patients expressed the worse periodontal status and the highest NLRP3, CASP-1, and IL-18 levels, the difference being statistically significant (p < 0.05). The P group patients also expressed significantly more elevated NLRP3, CASP-1, and IL-18 levels, as compared to nonperiodontal patients (CHC and H groups). Chronic hepatitis C and periodontal disease could have a significant influence on the upregulation of NLRP3 inflammasome and its components, possibly contributing to an increased local inflammatory reaction and clinical periodontal consequences.

Targeting the Nod-like receptor protein 3 Inflammasome with inhibitor MCC950 rescues lipopolysaccharide-induced inhibition of osteogenesis in Human periodontal ligament cells

OBJECTIVE

We aim to investigate whether lipopolysaccharide-stimulated activition of Nod-like receptor protein 3 (NLRP3) Inflammasome inhibits osteogenesis in Human periodontal ligament cells (HPDLCs). Futhermore, to study whether MCC950 (a inhibitor of NLRP3 Inflammasome) rescues lipopolysaccharide-induced inhibition of osteogenesis in HPDLCs as well as the underlying mechanisms.

METHODS

HPDLCs were isolated from periodontal ligament of healthy orthodontic teeth from teenagers, and cells surface marker protein were detected by flow cytometry. Cells viability were determined by Cell Counting kit 8 assay. Enzyme-linked immunosorbent assay was used to analyze the secretion of proinflammatory factors. Western blot and real-time quantitative polymerase chain reaction (RT-qPCR) were measured assessing the expression of NLRP3 and Caspase-1. RT-qPCR, Alizarin red staining and Alkaline phosphatase staining were tested to determine the osteogenic differentiation capacity of HPDLCs.

RESULTS

It was found that lipopolysaccharide in the range of concentrations from 10 to 100 μg/ml significantly inhibited HPDLCs viability at 24 h and significantly improved proinflammatory cytokine expressions at 8 h and 24 h. MCC950 reversed lipopolysaccharide-stimulated proinflammatory cytokine expressions including interleukin-1β and interleukin-18, but not tumor necrosis factor-α. In addition, MCC950 rescued the lipopolysaccharide-inhibited osteogenic gene (Alkaline phosphatase, Runt-related transcription factor 2, and Osteocalcin). Moreover, MCC950 downregulated lipopolysaccharide-induced relative protein of NLRP3 Inflammasome signaling pathway, such as NLRP3 and Caspase-1.

CONCLUSION

MCC950 rescues lipopolysaccharide-induced inhibition of osteogenesis in HPDLCs via blocking NLRP3 Inflammasome signaling pathway, and it may be used as a promising therapeutic agent for periodontitis or periondontal regenerative related disease.

The Expression of Allele Changes in NLRP3 (rs35829419) and IL-1β (+3954) Gene Polymorphisms in Periodontitis and Coronary Artery Disease

BACKGROUND

Inflammasomes have been shown to play a pivotal role in periodontal disease pathogenesis. However, their role in periodontitis subjects with coronary heart disease remains unclear. This study aimed to obtain the expression of NLRP3 (rs35829419) and IL-1β (+3954) gene polymorphisms in the subgingival plaque and blood samples of generalized periodontitis (GP) subjects with and without coronary heart disease (CHD).

METHODS

A total of 70 subjects were grouped into two; GP and GP with CHD. Demographic variables and periodontal and cardiac parameters were recorded from both the groups. Subgingival plaque and blood samples were obtained from both the groups and were further subjected to the identification of NLRP3 (rs35829419) and IL-1β (+3954) expression and allele change using a conventional polymerase chain reaction (PCR) and gene sequencing (Sanger's method).

RESULTS

Amongst the demographic variables, age and monthly income were statistically significant between the two groups. Plaque index (PI), clinical attachment level (CAL), high-density lipoprotein (HDL), and low density-lipoprotein (LDL) exhibited statistically significant levels between the two groups. The NLRP3 (rs35829419) and IL-1β (+3954) genes showed a statistically significant association with allele change (frequency) among the groups. The general comparison of all the parameters with the allele change of NLRP3 (rs35829419) and IL-1β (+3954) in the subgingival plaque and blood samples showed statistically significant associations among the two groups.

CONCLUSION

The present study highlighted an allele change in IL-1β (+3954) gene polymorphisms which may play an important role in the pathogenesis of periodontitis and coronary heart disease.

Porphyromonas gingivalis survival skills: Immune evasion

Periodontitis is a chronic inflammatory condition that destroys the tooth-supporting tissues and eventually leads to tooth loss. As one of the most prevalent oral conditions, periodontitis endangers the oral health of 70% of people throughout the world. Periodontitis is also related to various systemic diseases, such as diabetes mellitus, atherosclerosis, and rheumatoid arthritis, which not only has a great impact on population health status and the quality of life but also increases the social burden. Porphyromonas gingivalis (P. gingivalis) is a gram-negative oral anaerobic bacterium that plays a key role in the pathogenesis of periodontitis. Porphyromonas gingivalis can express various of virulence factors to overturn innate and adaptive immunities, which makes P. gingivalis survive and propagate in the host, destroy periodontal tissues, and have connection to systemic diseases. Porphyromonas gingivalis can invade into and survive in host tissues by destructing the gingival epithelial barrier, internalizing into the epithelial cells, and enhancing autophagy in epithelial cells. Deregulation of complement system, degradation of antibacterial peptides, and destruction of phagocyte functions facilitate the evasion of P. gingivalis. Porphyromonas gingivalis can also suppress adaptive immunity, which allows P. gingivalis to exist in the host tissues and cause the inflammatory response persistently. Here, we review studies devoted to understanding the strategies utilized by P. gingivalis to escape host immunity. Methods for impairing P. gingivalis immune evasion are also mentioned.

Genetic Polymorphisms of NLRP3 (rs4612666) and CARD8 (rs2043211) in Periodontitis and Cardiovascular Diseases

BACKGROUND

The existing data show that inflammasomes play a role in periodontal disease pathogenesis. However, their role in the pathogenesis of periodontitis and coronary heart disease remains unclear. This study had the objective of assessing NLRP3 (rs4612666) and CARD8 (rs2043211) gene polymorphisms in dental plaque and blood of generalized chronic periodontitis (CP) patients in the presence and absence of coronary heart disease (CHD).

METHODS

A total of 70 subjects were divided into two groups, including CP and CP + CHD subjects. Demographic variables, periodontal, and cardiac parameters were recorded from both groups. Subgingival plaque and blood samples were obtained from both groups and were subjected to further molecular analysis for NLRP3 (rs4612666) and CARD8 (rs2043211) expression and allele change using conventional polymerase chain reaction (PCR) and gene sequencing (Sanger's method).

RESULTS

Amongst the demographic variables, age, and monthly income were statistically significant between the two groups. Plaque index (PI), clinical attachment level (CAL), high-density lipoprotein (HDL), and low density-lipoprotein (LDL) exhibited statistically significant levels between the two groups. NLRP3 (rs4612666) and CARD8 (rs2043211) genes showed a statistically significant association of allele change (frequency) among the groups. In general, when all of the parameters were compared to the allele change of the genes, statistically significant relationships were found between the two groups.

CONCLUSIONS

The present study expressed an allele change of the investigated genes which could profoundly affect the pathobiology of the two diseases under investigation.

Inflammasomes in Alveolar Bone Loss

Bone remodeling is tightly controlled by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Fine tuning of the osteoclast-osteoblast balance results in strict synchronization of bone resorption and formation, which maintains structural integrity and bone tissue homeostasis; in contrast, dysregulated bone remodeling may cause pathological osteolysis, in which inflammation plays a vital role in promoting bone destruction. The alveolar bone presents high turnover rate, complex associations with the tooth and periodontium, and susceptibility to oral pathogenic insults and mechanical stress, which enhance its complexity in host defense and bone remodeling. Alveolar bone loss is also involved in systemic bone destruction and is affected by medication or systemic pathological factors. Therefore, it is essential to investigate the osteoimmunological mechanisms involved in the dysregulation of alveolar bone remodeling. The inflammasome is a supramolecular protein complex assembled in response to pattern recognition receptors and damage-associated molecular patterns, leading to the maturation and secretion of pro-inflammatory cytokines and activation of inflammatory responses. Pyroptosis downstream of inflammasome activation also facilitates the clearance of intracellular pathogens and irritants. However, inadequate or excessive activity of the inflammasome may allow for persistent infection and infection spreading or uncontrolled destruction of the alveolar bone, as commonly observed in periodontitis, periapical periodontitis, peri-implantitis, orthodontic tooth movement, medication-related osteonecrosis of the jaw, nonsterile or sterile osteomyelitis of the jaw, and osteoporosis. In this review, we present a framework for understanding the role and mechanism of canonical and noncanonical inflammasomes in the pathogenesis and development of etiologically diverse diseases associated with alveolar bone loss. Inappropriate inflammasome activation may drive alveolar osteolysis by regulating cellular players, including osteoclasts, osteoblasts, osteocytes, periodontal ligament cells, macrophages, monocytes, neutrophils, and adaptive immune cells, such as T helper 17 cells, causing increased osteoclast activity, decreased osteoblast activity, and enhanced periodontium inflammation by creating a pro-inflammatory milieu in a context- and cell type-dependent manner. We also discuss promising therapeutic strategies targeting inappropriate inflammasome activity in the treatment of alveolar bone loss. Novel strategies for inhibiting inflammasome signaling may facilitate the development of versatile drugs that carefully balance the beneficial contributions of inflammasomes to host defense.

Porphyromonas gingivalis Promotes Colorectal Carcinoma by Activating the Hematopoietic NLRP3 Inflammasome

Porphyromonas gingivalis (P. gingivalis) is a keystone periodontal pathogen associated with various digestive cancers. However, whether P. gingivalis can promote colorectal cancer and the underlying mechanism associated with such promotion remains unclear. In this study, we found that P. gingivalis was enriched in human feces and tissue samples from patients with colorectal cancer compared with those from patients with colorectal adenoma or healthy subjects. Cohort studies demonstrated that P. gingivalis infection was associated with poor prognosis in colorectal cancer. P. gingivalis increased tumor counts and tumor volume in the Apc^Min/+ mouse model and increased tumor growth in orthotopic rectal and subcutaneous carcinoma models. Furthermore, orthotopic tumors from mice exposed to P. gingivalis exhibited tumor-infiltrating myeloid cell recruitment and a proinflammatory signature. P. gingivalis promoted colorectal cancer via NLRP3 inflammasome activation in vitro and in vivo. NLRP3 chimeric mice harboring orthotopic tumors showed that the effect of NLRP3 on P. gingivalis pathogenesis was mediated by hematopoietic sources. Collectively, these data suggest that P. gingivalis contributes to colorectal cancer neoplasia progression by activating the hematopoietic NLRP3 inflammasome. SIGNIFICANCE: This study demonstrates that the periodontal pathogen P. gingivalis can promote colorectal tumorigenesis by recruiting myeloid cells and creating a proinflammatory tumor microenvironment. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/10/2745/F1.large.jpg.

Inflammasome dysregulation in human gingival fibroblasts in response to periodontal pathogens

OBJECTIVE

Uncontrolled production of Interleukin-1β (IL-1β), a major proinflammatory cytokine, is associated with tissue destruction in periodontal disease. IL-1β production is controlled by inflammasomes which are multiprotein regulatory complexes. The current study aimed to elucidate potential regulatory pathways by monitoring the effects of periodontal pathogens Fusobacterium nucleatum (Fn) and Porphyromonas gingivalis (Pg) on inflammasomes and their regulators in human gingival fibroblasts (HGFs) in vitro.

METHODS

HGFs were exposed to Fn and Pg alone or in combination for 24 hr at a multiplicity of infection of 100, ±30 min exposure with 5 mM adenosine triphosphate (ATP) incubation. Gene expression of NLRP3 and AIM2, inflammasome regulatory proteins POP1, CARD16 and TRIM16, and inflammasome components ASC and CASPASE 1, and IL-1β, were evaluated by RT-PCR. Pro- and mature IL-1β levels were monitored intracellularly by immunocytochemistry and extracellularly by ELISA.

RESULTS

Fn + ATP significantly upregulated NLRP3, AIM2, IL-1β, ASC, and CASPASE 1; however, it downregulated POP1 and TRIM16. Pg + ATP downregulated NLRP3, ASC, POP1, but upregulated IL-1β and CARD16. Pg + Fn+ATP significantly upregulated AIM2, IL-1β and CARD16, and downregulated POP1, TRIM16, and CASPASE 1. Pg + ATP exposure significantly increased pro- and mature IL-1β production.

CONCLUSION

Bacterial exposure with ATP may deregulate IL-1β by dysregulating inflammasomes and their regulators in HGFs.

AIM2 Inflammasome's First Decade of Discovery: Focus on Oral Diseases

A common feature of many acute and chronic oral diseases is microbial-induced inflammation. Innate immune responses are the first line of defense against pathogenic microorganisms and are initiated by pattern recognition receptors (PRRs) that specifically recognize pathogen-associated molecular patterns and danger-associated molecular patterns. The activation of certain PRRs can lead to the assembly of macromolecular oligomers termed inflammasomes, which are responsible for pro-inflammatory cytokine maturation and secretion and thus activate host inflammatory responses. About 10 years ago, the absent in melanoma 2 (AIM2) was independently discovered by four research groups, and among the “canonical” inflammasomes [including AIM2, NLR family pyrin domain (NLRP)1, NLRP3, NLR family apoptosis inhibitory protein (NAIP)/NLR family, caspase activation and recruitment domain (CARD) containing (NLRC)4, and pyrin], AIM2 so far is the only one that simultaneously acts as a cytosolic DNA sensor due to its DNA-binding ability. Undoubtedly, such a double-faceted role gives AIM2 greater mission and more potential in the mediation of innate immune responses. Therefore, AIM2 has garnered much attention from the broad scientific community during its first 10 years of discovery (2009–2019). How the AIM2 inflammasome is related to oral diseases has aroused debate over the past few years and is under active investigation. AIM2 inflammasome may potentially be a key link between oral diseases and innate immunity. In this review, we highlight the current knowledge of the AIM2 inflammasome and its critical role in the pathogenesis of various oral diseases, which might offer future possibilities for disease prevention and targeted therapy utilizing this continued understanding.

Relevance of Caspase-1 and Nlrp3 Inflammasome on Inflammatory Bone Resorption in A Murine Model of Periodontitis

This study investigates the role of NLRP3 inflammasome and its main effector Caspase-1 in inflammation and alveolar bone resorption associated with periodontitis. Heat-killed Aggregatibacter actinomycetemcomitans (Aa) was injected 3x/week (4 weeks) into gingival tissues of wild-type (WT), Nlrp3-KO and Caspase1-KO mice. Bone resorption was measured by µCT and osteoclast number was determined by tartrate-resistant acid phosphatase (TRAP) staining. Inflammation was assessed histologically (H/E staining and immunofluorescence of CD45 and Ly6G). In vitro studies determined the influence of Nlrp3 and Caspase-1 in Rankl-induced osteoclast differentiation and activity and on LPS-induced expression of inflammation-associated genes. Bone resorption was significantly reduced in Casp1-KO but not in Nlrp3-KO mice. Casp1-KO mice had increased in osteoclast numbers, whereas the inflammatory infiltrate or on gene expression were similar to those of WT and Nlrp3-KO mice. Strikingly, osteoclasts differentiated from Nlrp3-deficient macrophages had increased resorbing activity in vitro. LPS-induced expression of Il-10, Il-12 and Tnf-α was significantly reduced in Nlrp3- and Casp1-deficient macrophages. As an inceptive study, these results suggest that Nlrp3 inflammasome does not play a significant role in inflammation and bone resorption in vivo and that Caspase-1 has a pro-resorptive role in experimental periodontal disease.

Inflammasomes and their regulation in periodontal disease: A review

Interleukin-1β (IL-1β), which is secreted by host tissues leading to periodontal tissue inflammation, is a major pro-inflammatory cytokine in the pathogenesis of periodontal disease. The conversion of pro-IL-1β into its biologically active form is controlled by multiprotein complexes named as inflammasomes, which are key regulator of host defense mechanisms and inflammasome involved diseases, including the periodontal diseases. Inflammasomes are regulated by different proteins and processes, including pyrin domain (PYD)-only proteins (POPs), CARD-only proteins (COPs), tripartite motif family proteins (TRIMs), autophagy, and interferons. A review of in vitro, in vivo, and clinical data from these publications revealed that several inflammasomes including (NOD)-like receptor (NLR) pyrin domain-containing 3 (NLRP3) and absent in melanoma 2 (AIM2) have been found to be involved in periodontal disease pathogenesis. To the best of our knowledge, the current article provides the first review of the literature focusing on studies that evaluated both inflammasomes and their regulators in periodontal disease. An upregulation for inflammasomes and a downregulation of inflammasome regulator proteins including POPs, COPs, and TRIMs have been reported in periodontal disease. Although interferons (types I and II) and autophagy have been found to be involved in periodontal disease, their possible role in inflammasome activation has not evaluated yet. Modulating the excessive inflammatory response by the use of inflammasome regulators may have potential in the management of periodontal disease.

Interleukin-1β is a potential therapeutic target for periodontitis: a narrative review

Interleukin(IL)-1β, a pro-inflammatory cytokine, was elevated and participates in periodontitis. Not only the link between IL-1β and periodontitis was proved by clinical evidence, but also the increased IL-1β triggers a series of inflammatory reactions and promotes bone resorption. Currently, IL-1β blockage has been therapeutic strategies for autoimmune and autoinflammatory diseases such as rheumatoid arthritis, cryopyrin-associated periodic syndromes, gout and type II diabetes mellitus. It is speculated that IL-1β be a potential therapeutic target for periodontitis. The review focuses on the production, mechanism, present treatments and future potential strategies for IL-1β in periodontitis.

Initial periodontal treatment affects nucleotide-binding domain leucine-rich repeat-containing protein 3 inflammasome priming in peripheral blood mononuclear cells

OBJECTIVE

Accumulating evidence suggests an association between periodontitis and several systemic diseases, such as atherosclerosis. In the lesions of these diseases, nucleotide-binding domain leucine-rich repeat-containing protein 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC) and caspase-1 form inflammasome complex, which leads to the functional maturation of interleukin (IL)-1β via cleavage of caspase-1 in macrophages. IL-1β plays a critical role in the etiology of these diseases; however, inflammasome priming-specifically, IL-1β and NLRP3 upregulation-is necessary for effective IL-1β production. We investigated the effect of initial periodontal treatment on the inflammasome priming of peripheral blood mononuclear cells (PBMCs).

METHODS

Twenty-two patients with chronic periodontitis were enrolled in this study and given initial periodontal treatment. Peripheral blood samples were collected at baseline and re-evaluation (41.1 ± 29.1 d after the treatment), and the relative expression of IL-1β, and three inflammasome components, ASC, NLRP3 and Caspase-1, mRNA was determined using quantitative reverse transcription PCR. PBMCs were stimulated with silica crystals, and the IL-1β secretion was measured via enzyme-linked immunosorbent assay.

RESULTS

Probing pocket depth and bleeding on probing (BOP) were significantly improved after the treatment. Expression of IL-1β and ASC in the PBMCs decreased after the treatment. PBMCs stimulated with silica crystals secreted IL-1β. The treatment attenuated IL-1β secretion by PBMCs in low BOP percentages group whereas IL-1β secretion was increased in high BOP percentages group.

CONCLUSION

Periodontal treatment altered the inflammasome priming status of the PBMCs, however, the effects on systemic diseases need to be further investigated.

Recent progress in experimental and human disease-associated multi-species biofilms

Human bodies are colonized by trillions of microorganisms, which are often referred to as human microbiota and play important roles in human health. Next generation sequencing studies have established links between the genetic content of human microbiota and various human diseases. However, it remains largely unknown about the spatial organizations and interspecies interactions of individual species within the human microbiota. Bacterial cells tend to form surface-attached biofilms in many natural environments, which enable intercellular communications and interactions in a microbial ecosystem. In this review, we summarize the recent progresses on the experimental and human disease-associated multi-species biofilm studies. We hypothesize that engineering biofilm structures and interspecies interactions might provide a tool for manipulating the composition and function of human microbiota.

Differential expression of inflammasome regulatory transcripts in periodontal disease

BACKGROUND

The inflammasome modulates the release of key proinflammatory cytokines associated with periodontal disease pathogenesis. The aim of this study was to evaluate the expression of proteins that regulate the inflammasome, namely pyrin domain-only proteins (POPs), caspase activation recruitment domain (CARD)-only proteins, and tripartite motif-containing (TRIM) proteins, in periodontal diseases.

METHODS

A total of 68 participants (34 males and 34 females) were divided into four groups, including periodontal health (H), gingivitis (G), chronic periodontitis (CP), and aggressive periodontitis (AgP) based on clinical parameters. Gingival tissue samples were obtained from all participants for reverse transcription polymerase chain reaction (RT-PCR)-based gene expression analyses of molecules that regulate the inflammasome, including apoptosis-associated speck-like protein (ASC) containing CARD, caspase-1, interleukin-1β (IL-1β), interleukin-18 (IL-18), nucleotide-binding domain, leucine rich family (NLR) pyrin domain containing 3 (NLRP3), NLR family pyrin domain containing 2 (NLRP2), AIM2 (absent in melanoma 2), POP1, POP2, CARD16, CARD18, TRIM16, and TRIM20 by RT-PCR.

RESULTS

NLRP3 and IL-1β were upregulated in the G, CP, and AgP groups compared with group H (P < 0.05). AIM2 was downregulated in the CP group compared with the H, G, and AgP groups (P < 0.05). TRIM20, TRIM16, and CARD18 were downregulated in the G, CP, and AgP groups compared with the H group (P < 0.05). POP1 and POP2 were downregulated in the CP and AgP, and AgP and G groups, respectively (P < 0.05).

CONCLUSION

Active periodontal disease may result in downregulation of inflammasome regulators that may increase the activity of NLRP3 and IL-1β in periodontal disease.

Doxycycline inhibits NAcht Leucine-rich repeat Protein 3 inflammasome activation and interleukin-1β production induced by Porphyromonas gingivalis-lipopolysaccharide and adenosine triphosphate in human gingival fibroblasts

OBJECTIVE

To investigate the effect of adenosine triphosphate (ATP) on inflammasome activation by Porphyromonas gingivalis-lipopolysaccharide (P. gingivalis-LPS) stimulation and the anti-inflammatory eff ;ect of doxycycline (Dox) in human gingival fibroblasts (HGFs).

DESIGN

The optimal concentration of P. gingivalis-LPS (1.0 μg/mL) for cellular viability was determined by observing cell morphology and measuring the amount of formazan and the expression of pro-caspase-1. The expression of genes and proteins related to the NAcht Leucine-rich repeat Protein 3 (NLRP3) inflammasome, including NLRP3, apoptosis-associated speck-like protein containing CARD (ASC), caspase-1 and its activated forms, and the inflammatory factor interleukin-1β (IL-1β) and its activated forms were measured.

RESULTS

The NLRP3 inflammasome (i.e., NLRP3, ASC, caspase-1) was not affected by stimulation with P. gingivalis-LPS or ATP. However, a combination of P. gingivalis-LPS and ATP significantly enhanced inflammasome activation and IL-1β production at the gene and protein levels as measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot, respectively. Furthermore, doxycycline addition markedly inhibited inflammasome activation and IL-1β production induced by a combination of P. gingivalis-LPS and ATP.

CONCLUSIONS

LPS, ATP, and doxycycline play critical roles in regulating host immune responses. This evidence provides guidance for the application of tetracycline drugs for the clinical treatment of periodontal disease.

Comparative analysis of expression of microbial sensing molecules in mucosal tissues with periodontal disease

Host-derived pattern recognition receptors (PRRs) are necessary for effective innate immune engagement of pathogens that express microbial-associated molecular patterns (MAMP) ligands for these PRRs. This study used a nonhuman primate model to evaluate the expression of these sensing molecules in gingival tissues. Macaca mulatta aged 12-24 with a healthy periodontium (n = 13) or periodontitis (n = 11) provided gingival tissues for assessment of naturally-occurring periodontitis. An additional group of animals (12-23 years; n = 18) was subjected to a 5 month longitudinal study examining the initiation and progression of periodontitis, RNA was isolated and microarray analysis conducted for gene expression of the sensing PRRs. The results demonstrated increased expression of various PRRs in naturally-occurring established periodontitis. Selected PRRs also correlated with both bleeding on probing (BOP) and pocket depth (PD) in the animals. The longitudinal model demonstrated multiple TLRs, as well as selected other PRRs that were significantly increased by 2 weeks during initiation of the lesion. While gene expression levels of various PRRs correlated with BOP and PD at baseline and resolution of disease, few correlated with these clinical parameters during initiation and progression of the lesion. These findings suggest that the levels of various PRRs are affected in established periodontitis lesions, and that PRR expression increased most dramatically during the initiation of the disease process, presumably in response to the juxtaposed microbial challenge to the tissues and goal of reestablishing homeostasis.

Prolyl hydroxylase inhibitor DMOG suppressed inflammatory cytokine production in human gingival fibroblasts stimulated with Fusobacterium nucleatum

OBJECTIVE

Fusobacterium nucleatum (F. nucleatum) is one of the most common bacteria involved in the initiation and progression of periodontal diseases. Pharmacological inhibitor of prolyl hydroxylases (PHDs), dimethyloxallyl glycine (DMOG), has been reported to exert anti-inflammatory effects. The aim of this investigation was to evaluate the role of DMOG in inflammatory cytokine production of human gingival fibroblasts (HGFs) stimulated with F. nucleatum.

MATERIAL AND METHODS

HGFs were pretreated with 10, 50, and 100 μM DMOG for 24 h before infected with F. nucleatum (MOI = 100). Cell morphology and survival after infection with F. nucleatum were determined by crystal violet staining assay. The mRNA levels of interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and IL-1β were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR). The production of IL-6, IL-8, TNF-α, and IL-1β was assessed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

F. nucleatum did not affect the morphology and survival of HGFs by the concentrations of MOI (multiplicity of infection) = 10, 50, and 100. The mRNA levels of IL-6, IL-8, TNF-α, and IL-1β were significantly enhanced with the stimulation of F. nucleatum, and the maximal effect reached at 6 h. The secretion of IL-6, IL-8, and TNF-α was significantly upregulated by the infection of F. nucleatum while the production of IL-1β was nearly unchanged. Above all, DMOG suppressed F. nucleatum-stimulated IL-6, IL-8, TNF-α, and IL-1β expressions.

CONCLUSIONS

These data indicate that prolyl hydroxylase inhibitor DMOG partly downregulates inflammatory cytokine expression in F. nucleatum-infected HGFs.

CLINICAL RELEVANCE

DMOG may provide a novel strategy for the therapy of periodontitis.

Periodontal ligament fibroblasts migration injury via ROS/TXNIP/Nlrp3 inflammasome pathway with Porphyromonas gingivalis lipopolysaccharide

Inflammasomes serve as an intracellular machinery to initiate inflammatory response to various danger signals. However, the chronic periodontitis pathological relevance of this inflammasome activation, particularly in periodontal ligament fibroblasts, remains largely unknown. The present study demonstrated that Nlrp3 inflammasome components abundantly expressed in cultured mouse periodontal ligament fibroblasts (mPDLFs). In addition, our data demonstrated that P.g-LPS (Porphyromonas gingivalis Lipopolysaccharide), a major injurious factor during chronic periodontitis, could induce the mPDLFs migration dysfunction and the inhibition of Nlrp3 inflammasome by Isoliquiritigenin (ISO) markedly recovered the migration dysfunction in mPDLFs. And Nlrp3 inflammasome components could be aggregated to form an inflammasome complex on stimulation of P.g-LPS, as shown by fluorescence confocal microscopy. Correspondingly, P.g-LPS induced Nlrp3 inflammasome activation, caspase-1 activation, IL-1β and HMGB1 release, which were blocked by Nlrp3 inflammasome inhibitor (ISO). Interestingly, reactive oxygen species, TXNIP protein and TXNIP binding to Nlrp3 were markedly increased in mPDLFs with P.g-LPS. Furthermore, ROS generation inhibitor (Apocynin; APO) significantly reduced Nlrp3 inflammasome formation and IL-1β production in mPDLFs with P.g-LPS. And APO attenuated P.g-LPS-induced TXNIP protein expression and mPDLFs injury. In conclusion, our results demonstrate that ROS/TXNIP/Nlrp3 Inflammasome pathway is a key initiating mechanism necessary for P.g-LPS-induced subsequent mPDLFs inflammatory response leading to chronic periodontitis.

Streptococcus oralis maintains homeostasis in oral biofilms by antagonizing the cariogenic pathogen Streptococcus mutans

Bacteria residing in oral biofilms live in a state of dynamic equilibrium with one another. The intricate synergistic or antagonistic interactions between them are crucial for determining this balance. Using the six-species Zürich "supragingival" biofilm model, this study aimed to investigate interactions regarding growth and localization of the constituent species. As control, an inoculum containing all six strains was used, whereas in each of the further five inocula one of the bacterial species was alternately absent, and in the last, both streptococci were absent. Biofilms were grown anaerobically on hydroxyapatite disks, and after 64 h they were harvested and quantified by culture analyses. For visualization, fluorescence in situ hybridization and confocal laser scanning microscopy were used. Compared with the control, no statistically significant difference of total colony-forming units was observed in the absence of any of the biofilm species, except for Fusobacterium nucleatum, whose absence caused a significant decrease in total bacterial numbers. Absence of Streptococcus oralis resulted in a significant decrease in Actinomyces oris, and increase in Streptococcus mutans (P < .001). Absence of A. oris, Veillonella dispar or S. mutans did not cause any changes. The structure of the biofilm with regards to the localization of the species did not result in observable changes. In summary, the most striking observation of the present study was that absence of S. oralis resulted in limited growth of commensal A. oris and overgrowth of S. mutans. These data establish highlight S. oralis as commensal keeper of homeostasis in the biofilm by antagonizing S. mutans, so preventing a caries-favoring dysbiotic state.

Immune response profiling of primary monocytes and oral keratinocytes to different Tannerella forsythia strains and their cell surface mutants

The oral pathogen Tannerella forsythia possesses a unique surface (S-) layer with a complex O-glycan containing a bacterial sialic acid mimic in the form of either pseudaminic acid or legionaminic acid at its terminal position. We hypothesize that different T. forsythia strains employ these stereoisomeric sugar acids for interacting with the immune system and resident host tissues in the periodontium. Here, we show how T. forsythia strains ATCC 43037 and UB4 displaying pseudaminic acid and legionaminic acid, respectively, and selected cell surface mutants of these strains modulate the immune response in monocytes and human oral keratinocytes (HOK) using a multiplex immunoassay. When challenged with T. forsythia, monocytes secrete proinflammatory cytokines, chemokines and vascular endothelial growth factor (VEGF) with the release of interleukin-1β (IL-1β) and IL-7 being differentially regulated by the two T. forsythia wild-type strains. Truncation of the bacteria's O-glycan leads to significant reduction of IL-1β and regulates macrophage inflammatory protein-1. HOK infected with T. forsythia produce IL-1Ra, chemokines and VEGF. Although the two wild-type strains elicit preferential immune responses for IL-8, both truncation of the O-glycan and deletion of the S-layer result in significantly increased release of IL-8, granulocyte-macrophage colony-stimulating factor and monocyte chemoattractant protein-1. Through immunofluorescence and confocal laser scanning microscopy of infected HOK we additionally show that T. forsythia is highly invasive and tends to localize to the perinuclear region. This indicates, that the T. forsythia S-layer and attached sugars, particularly pseudaminic acid in ATCC 43037, contribute to dampening the response of epithelial tissues to initial infection and hence play a pivotal role in orchestrating the bacterium's virulence.

Dysbiotic Biofilms Deregulate the Periodontal Inflammatory Response

Periodontal diseases originate from a dysbiosis within the oral microbiota, which is associated with a deregulation of the host immune response. Although little is known about the initiation of dysbiosis, it has been shown that H₂O₂ production is one of the main mechanisms by which some commensal bacteria suppress the outgrowth of pathobionts. Current models emphasize the critical nature of complex microbial biofilms that form unique microbial ecologies and of their change during transition from health (homeostatic) to disease (dysbiotic). However, very little is known on how this alters their virulence and host responses. The objective of this study was to determine differences in virulence gene expression by pathobionts and the inflammatory host response in homeostatic and dysbiotic biofilms originating from the same ecology. Quantitative polymerase chain reaction was performed to quantify the pathobiont outgrowth. Expression analysis of bacterial virulence and cellular inflammatory genes together with cytokine enzyme-linked immunosorbent assays were used to detect differences in bacterial virulence and to analyze potential differences in inflammatory response. An increase in pathobionts in induced dysbiotic biofilms was observed compared to homeostatic biofilms. The main virulence genes of all pathobionts were upregulated in dysbiotic biofilms. Exposure of these dysbiotic biofilms to epithelial and fibroblast cultures increased the expression of interleukin (IL)-6, IL-1β, tumor necrosis factor-α, and matrix metalloprotease 8, but especially the chemokine CXCL8 (IL-8). Conversely, homeostatic and beneficial biofilms had a minor immune response at the messenger RNA and protein level. Overall, induced dysbiotic biofilms enriched in pathobionts and virulence factors significantly increased the inflammatory response compared to homeostatic and commensal biofilms.

Inflammasome and Oral Diseases

One of the main steps in the development of the life in the earth is multicellularity. It enables cell differentiation and the development of morphological structures within an organism and is an essential factor in how to recognize friendly cells that are part of the multicellular organism and which foreign organisms can be harmful. Recognition includes devices such as the major histocompatibility complex (MHC), and the pattern recognition receptors (PRRs). PRRs are a group of proteins expressed by cells of the innate immune system that identify two classes of products: pathogen-associated molecular patterns (PAMPs), related to microbial pathogens, and damage-associated molecular patterns (DAMPs), associated with cell components that are released during cell damage or death. All these activate the inflammasome, which is a multiprotein oligomer that includes caspase 1, PYCARD, NALP, and caspase 5 (also known as caspase 11 or ICH-3). It is responsible for activation of inflammatory processes and has been shown to induce cell pyroptosis, a programmed cell death distinct from apoptosis, and promotes the maturation of the inflammatory cytokines interleukin 1β (IL-1β) and interleukin 18 (IL-18). We review whether inflammasome is related to diseases that can occur in the oral cavity. The mouth is always a possible environment for the development of pathological conditions because of the wide variety of microorganisms. Small variations in the equilibrium of the oral flora can cause disorders that could affect the organism in a systemic form. We provide data on periodontal disease, candidiasis, herpes virus, oral cancer, caries, and other oral diseases. There are very few papers that study this issue; therefore, we need more investigation and publications about inflammatory molecular processes, and more specifically, related to the inflammasome complex.

Porphyromonas gingivalis-Derived Lipopolysaccharide Combines Hypoxia to Induce Caspase-1 Activation in Periodontitis

Periodontitis is defined as inflammation affecting the supporting tissue of teeth. Periodontal pathogens initiate the disease and induce inflammatory host response. Hypoxia may accelerate the process by producing pro-inflammatory factors. The aim of this study is to investigate the effect of Porphyromonas gingivalis (P. gingivalis) lipopolysaccharides (LPS) and Escherichia coli (E. coli) LPS in inducing caspase-1 activation in normoxic or hypoxic phases. The results showed that healthy gingiva was in a normoxic phase (HIF-1α negative). However, hypoxia appeared in periodontitis, in which NLRP3, cleaved-caspase-1, interleukin 1 beta (IL-1β) and caspase-1-induced cell death was enhanced in periodontitis specimens. The in vitro experiment showed that P. gingivalis LPS slightly decreased the level of NLRP3 and IL-1β in gingival fibroblasts under normoxia. Surprisingly, hypoxia reversed the effects of P. gingivalis LPS, highly promoted caspase-1 activation and IL-1β maturation. E. coli LPS, a kind of pathogen-associated molecular pattern (PAMP) was chosen to simulate the effect of Gram-negative microbiota. Different from P. gingivalis LPS, E. coli LPS enhanced IL-1β maturation both in normoxia and hypoxia. Moreover, E. coli LPS turned normoxia into hypoxia phase in experimental periodontitis model, which may subsequently propel the inflammatory effect of P. gingivalis LPS. It was concluded that E. coli LPS induced a hypoxic phase, which is a combing pathological factor of P. gingivalis LPS in caspase-1 activating and IL-1β maturation in periodontal inflammation.

Involvement of NLRP10 in IL-1α induction of oral epithelial cells by periodontal pathogens

This study investigated the pathogenesis of periodontitis and the role of nucleotide-binding oligomerization domain-like receptor protein 10 (NLRP10). The human oral epithelial cell line HOK-16B was infected with two periodontal pathogens, Tannerella forsythia and Fusobacterium nucleatum, at various MOIs. RT-PCR and immunoblotting demonstrated that infection increased mRNA and protein expression of NLRP10, respectively. The siRNA-mediated NLRP10 knockdown significantly reduced IL-1α expression and secretion. Both bacteria induced phosphorylation of ERK, JNK and p38 MAP kinases in HOK-16B cells. NLRP10 knockdown impaired ERK phosphorylation only. ERK inhibition significantly decreased the expression of T. forsythia- and F. nucleatum-induced IL-1α. Our data suggest that NLRP10 is involved in activating the ERK signalling pathway in HOK-16B cells infected with T. forsythia and F. nucleatum. This pathway likely augments the pro-inflammatory cytokine IL-1α levels, which may play a critical role in periodontitis.

Salivary Levels of NLRP3 Inflammasome-Related Proteins as Potential Biomarkers of Periodontal Clinical Status

BACKGROUND

Emerging evidence suggests that activation of inflammasomes plays a central mechanism in pathogenesis of periodontitis. This study aims to compare salivary levels of nod-like receptor family pyrin domain containing protein (NLRP) 3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), cysteine aspartase (caspase)-1, and interleukin (IL)-1β from individuals with aggressive (AgP) or chronic periodontitis (CP) and healthy controls (HC), as well as elucidate its association with periodontal clinical status.

METHODS

Saliva samples from individuals with CP (n = 75), AgP (n = 20), and HC (n = 69) were collected. Periodontal status was assessed by measurement of probing depth, clinical attachment level, and extent and severity of disease. Salivary levels of analytes were analyzed by enzyme-linked immunosorbent assay. Association between biomarkers with CP or AgP was analyzed using multivariate binary logistic regression models.

RESULTS

Significantly higher levels of NLRP3, ASC, and IL-1β were detected in periodontitis groups in comparison to the periodontally HC group. However, no significant differences were observed for caspase-1 levels between clinical groups, and only NLRP3 salivary concentration was significantly higher in AgP compared with CP patients. Also, positive significant correlations among NLRP3, ASC, and IL-1β salivary concentrations and clinical parameters were observed. Logistic regression analyses revealed a strong/independent association of NLRP3, ASC, and IL-1β salivary levels with CP and AgP.

CONCLUSION

Although the concentration of caspase-1 in saliva samples makes its determination useless for detection of periodontal disease and/or its severity, salivary levels of NLRP3, ASC, and IL-1β may act as strong/independent indicators of amount and extent of periodontal breakdown in both CP and AgP and could potentially be used for prevention and therapy of this group of diseases.

PKR induces the expression of NLRP3 by regulating the NF-κB pathway in Porphyromonas gingivalis-infected osteoblasts

The double-stranded RNA-dependent kinase (PKR), which is activated by double stranded RNA, induces inflammation by regulating NF-κB signaling. The NLR family pyrin domain-containing 3 (NLRP3) inflammasome also modulates inflammation in response to infection. Porphyromonas gingivalis (P.gingivalis) is an oral bacterium which is implicated in the pathogenesis of periodontal diseases. We previously reported that PKR is a key modulator of bone metabolism and inflammation in the periodontal tissue. PKR was also reported to induce inflammation in response to microbes by regulating the NLRP3 inflammasome, suggesting that PKR could affect inflammation along with NLRP3 in periodontal diseases. In this study, we investigated the effects of PKR on NLRP3 expression and NF-κB activity in P. gingivalis infected osteoblasts. We first constructed a SNAP26b-tagged P.gingivalis (SNAP-P. g.) and traced its internalization into the cell. SNAP-P. g. increased the activity of PKR and NF-κB and also induced NLRP3 expression in osteoblasts. Inhibition of NF-κB attenuated SNAP-P. g.-induced NLRP3 expression. The knockdown of PKR using shRNA decreased both the activity of NF-κB and the expression of NLRP3 induced by SNAP-P.g.. We therefore concluded that in osteoblasts, P. gingivalis activated PKR, which in turn increased NLRP3 expression by activating NF-κB. Our results suggest that PKR modulates inflammation by regulating the expression of the NLRP3 inflammasome through the NF-κB pathway in periodontal diseases.

The inflammasome and danger molecule signaling: at the crossroads of inflammation and pathogen persistence in the oral cavity

Inflammasomes are an oligomeric assembly of multiprotein complexes that activate the caspase-1-dependent maturation and the subsequent secretion of inflammatory interleukin-1beta and interleukin-18 cytokines in response to a 'danger signal' in vertebrates. The assessment of their significance continues to grow rapidly as the complex biology of various chronic inflammatory conditions is better dissected. Increasing evidence strongly links inflammasomes and host-derived small 'danger molecule ATP' signaling with the modulation of the host immune response by microbial colonizers as well as with potential altering of the microbiome structure and intermicrobial interactions in the host. All of these factors eventually lead to the destructive chronic inflammatory disease state. In the oral cavity, a highly dynamic and multifaceted interplay takes place between the signaling of endogenous danger molecules and colonizing microbes on the mucosal surfaces. This interaction may redirect the local microenvironment to favor the conversion of the resident microbiome toward pathogenicity. This review outlines the major components of the known inflammasome complexes/mechanisms and highlights their regulation, in particular, by oral microorganisms, in relation to periodontal disease pathology. Better characterization of the cellular and molecular biology of the inflammasome will probably identify important potential therapeutic targets for the treatment and prevention of periodontal disease, as well as for other debilitating chronic diseases.

The expression of gingival epithelial junctions in response to subgingival biofilms

Periodontitis is an infectious inflammatory disease that destroys the tooth-supporting tissues. It is caused by the formation of subgingival biofilms on the surface of the tooth. Characteristic bacteria associated with subgingival biofilms are the Gram-negative anaerobes Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola, collectively known as the “red complex” species. Inter-epithelial junctions ensure the barrier integrity of the gingival epithelium. This may however be disrupted by the biofilm challenge. The aim of this in vitro study was to investigate the effect of subgingival biofilms on the expression of inter-epithelial junctions by gingival epithelia, and evaluate the relative role of the red complex. Multi-layered human gingival epithelial cultures were challenged with a 10-species in vitro subgingival biofilm model, or its variant without the red complex, for 3 h and 24 h. A low-density array microfluidic card platform was then used for analyzing the expression of 62 genes encoding for tight junctions, gap junctions, adherens junctions, and desmosomes. Although there was a limited effect of the biofilms on the expression of tight, adherens and gap junctions, the expression of a number of desmosomal components was affected. In particular, Desmoglein-1 displayed a limited and transient up-regulation in response to the biofilm. In contrast, Desmocollin-2, Desmoplakin and Plakoglobin were down-regulated equally by both biofilm variants, after 24 h. In conclusion, this subgingival biofilm model may down-regulate selected desmosomal junctions in the gingival epithelium, irrespective of the presence of the “red complex.” In turn, this could compromise the structural integrity of the gingival tissue, favoring bacterial invasion and chronic infection.

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.

Titanium ions form particles that activate and execute interleukin-1β release from lipopolysaccharide-primed macrophages

BACKGROUND AND OBJECTIVE

Peri-implantitis is a destructive inflammatory process characterized by destruction of the implant-supporting bone. Inflammasomes are large intracellular multiprotein complexes that play a central role in innate immunity by activating the release of proinflammatory cytokines. Although inflammasome activation has previously been linked to periodontal inflammation, there is still no information on a potential association with peri-implantitis. The aim of this study was to examine cytotoxic and proinflammatory effects, including inflammasome activation, of metals used in dental implants, in an in vitro model, as well as from clinical tissue samples.

MATERIAL AND METHODS

Human macrophages were exposed to different metals [titanium (Ti), cobalt, chromium and molybdenum] in a cell-culture assay. Cytotoxicity was determined using the neutral red uptake assay. Cytokine secretion was quantified using an ELISA, and the expression of genes of various inflammasome components was analysed using quantitative PCR. In addition, the concentrations of interleukin-1β (IL-1β) and Ti in mucosal tissue samples taken in the vicinity of dental implants were determined using ELISA and inductively coupled plasma mass spectrometry, respectively.

RESULTS

Ti ions in physiological solutions stimulated inflammasome activation in human macrophages and consequently IL-1β release. This effect was further enhanced by macrophages that have been exposed to lipopolysaccharides. The proinflammatory activation caused by Ti ions disappeared after filtration (0.22 μm), which indicates an effect of particles. Ti ions alone did not stimulate transcription of the inflammasome components. The Ti levels of tissue samples obtained in the vicinity of Ti implants were sufficiently high (≥ 40 μm) to stimulate secretion of IL-1β from human macrophages in vitro.

CONCLUSION

Ti ions form particles that act as secondary stimuli for a proinflammatory reaction.

Modulation of inflammasome activity by Porphyromonas gingivalis in periodontitis and associated systemic diseases

Inflammasomes are large multiprotein complexes localized in the cytoplasm of the cell. They are responsible for the maturation of pro-inflammatory cytokines such as interleukin-1β (IL-1β) and IL-18 as well as for the activation of inflammatory cell death, the so-called pyroptosis. Inflammasomes assemble in response to cellular infection, cellular stress, or tissue damage; promote inflammatory responses and are of great importance in regulating the innate immune system in chronic inflammatory diseases such as periodontitis and several chronic systemic diseases. In addition to sensing cellular integrity, inflammasomes are involved in the homeostatic mutualism between the indigenous microbiota and the host. There are several types of inflammasomes of which NLRP3 is best characterized in microbial pathogenesis. Many opportunistic bacteria try to evade the innate immune system in order to survive in the host cells. One of these is the periodontopathogen Porphyromonas gingivalis which has been shown to have several mechanisms of modulating innate immunity by limiting the activation of the NLRP3 inflammasome. Among them, ATP-/P2X₇- signaling is recently associated not only with periodontitis but also with development of several systemic diseases. The present paper reviews multiple mechanisms through which P. gingivalis can modify innate immunity by affecting inflammasome activity.

Proteomic profiling of host-biofilm interactions in an oral infection model resembling the periodontal pocket

Periodontal infections cause inflammatory destruction of the tooth supporting tissues. We recently developed a dynamic, in vitro periodontal organotypic tissue model in a perfusion bioreactor system, in co-culture with an 11-species subgingival biofilm, which may recapitulate early events during the establishment of periodontal infections. This study aimed to characterize the global proteome regulations in this host-biofilm interaction model. Semi-quantitative shotgun proteomics were applied for protein identification and quantification in the co-culture supernatants (human and bacterial) and the biofilm lysates (bacterial). A total of 896 and 3363 proteins were identified as secreted in the supernatant and expressed in the biofilm lysate, respectively. Enriched gene ontology analysis revealed that the regulated secreted human tissue proteins were related to processes of cytoskeletal rearrangement, stress responses, apoptosis, and antigen presentation, all of which are commensurate with deregulated host responses. Most secreted bacterial biofilm proteins derived from their cytoplasmic domain. In the presence of the tissue, the levels of Fusobacterium nucleatum, Actinomyces oris and Campylobacter rectus proteins were significantly regulated. The functions of the up-regulated intracellular (biofilm lysate) proteins were associated with cytokinesis. In conclusion, the proteomic overview of regulated pathways in this host-biofilm interaction model provides insights to the early events of periodontal pathogenesis.

The activation of pyrin domain-containing-3 inflammasome depends on lipopolysaccharide from Porphyromonas gingivalis and extracellular adenosine triphosphate in cultured oral epithelial cells

Background

Gingival epithelial cells are the major population of the gingival tissue, acting as the front-line defense against microbial intrusion and regulating the homeostasis of the periodontal tissue in health and disease via NLR family pyrin domain-containing-3 (NLRP3) inflammasome, which recognizes pathogen- and danger-associated molecular patterns (PAMPs and DAMPs). The aim of this study was to determine whether the activation of NLRP3 inflammasome depends on infection with the periodontal pathogen Porphyromonas gingivalis (P. gingivalis), or stimulation with P. gingivalis lipopolysaccharide (LPS), and/or extracellular adenosine triphosphate (ATP).

Methods

An oral epithelial cell line was treated with P. gingivalis, P. gingivalis LPS and ATP. The gene and protein expression of NLRP3 inflammasome components were quantified by real time RT-PCR and immunoblots. Production of IL-1β and IL-18 was measured by ELISA.

Results

There was no increase in NLRP3 inflammasome gene expression after P. gingivalis infection unless pre-stimulated by ATP. Obvious increases of NLRP3 inflammasome gene expression was observed after P. gingivalis LPS stimulation, even pre-stimulated by ATP at 2 h.

Conclusions

The findings indicate that the activation of NLRP3 inflammasome does not rely on P. gingivalis infection, unless stimulated by P. gingivalis LPS and/or extracellular ATP, suggesting diverse signaling pathways are involved in the host immune response.

Incorporation of staphylococci into titanium-grown biofilms: an in vitro "submucosal" biofilm model for peri-implantitis

Objectives

Staphylococcus spp. are postulated to play a role in peri‐implantitis. This study aimed to develop a “submucosal” in vitro biofilm model, by integrating two staphylococci into its composition.

Materials and methods

The standard “subgingival” biofilm contained Actinomyces oris, Fusobacterium nucleatum, Streptococcus oralis, Veillonella dispar, Campylobacter rectus, Prevotella intermedia, Streptococcus anginosus, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola, and was further supplemented with Staphyoccous aureus and/or Staphylococcus epidermidis. Biofilms were grown anaerobically on hydroxyapatite or titanium discs and harvested after 64 h for real‐time polymerase chain reaction, to determine their composition. Confocal laser scanning microscopy and fluorescence in situ hybridization were used for identifying the two staphylococci within the biofilm.

Results

Both staphylococci established within the biofilms when added separately. However, when added together, only S. aureus grew in high numbers, whereas S. epidermidis was reduced almost to the detection limit. Compared to the standard subgingival biofilm, addition of the two staphylococci had no impact on the qualitative or quantitative composition of the biofilm. When grown individually in the biofilm, S. epidermidis and S. aureus formed small distinctive clusters and it was confirmed that S. epidermidis was not able to grow in presence of S. aureus.

Conclusions

Staphyoccous aureus and S. epidermidis can be individually integrated into an oral biofilm grown on titanium, hence establishing a “submucosal” biofilm model for peri‐implantitis. This model also revealed that S. aureus outcompetes S. epidermidis when grown together in the biofilm, which may explain the more frequent association of the former with peri‐implantitis.