Cytokine production in human periodontal ligament cells stimulated with Porphyromonas gingivalis

Red-complex bacteria exhibit distinctly different interactions with human periodontal ligament stromal cells compared to Fusobacterium nucleatum

OBJECTIVE

The red-complex bacteria Porphyromonas gingivalis and Tannerella forsythia together with Fusobacterium nucleatum are essential players in periodontitis. This study investigated the bacterial interplay with human periodontal ligament mesenchymal stromal cells (hPDL-MSCs) which act in the acute phase of periodontal infection.

DESIGN

The capability of the bacteria to induce an inflammatory response as well as their viability, cellular adhesion and invasion were analyzed upon mono- and co-infections of hPDL-MSCs to delineate potential synergistic or antagonistic effects. The expression level and concentration of interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1 were measured using qRT-PCR and ELISA. Viability, invasion, and adhesion were determined quantitatively using agar plate culture and qualitatively by confocal microscopy.

RESULTS

Viability of P. gingivalis and T. forsythia but not F. nucleatum was preserved in the presence of hPDL-MSCs, even in an oxygenated environment. F. nucleatum significantly increased the expression and concentration of IL-6, IL-8 and MCP-1 in hPDL-MSCs, while T. forsythia and P. gingivalis caused only a minimal inflammatory response. Co-infections in different combinations had no effect on the inflammatory response. Moreover, P. gingivalis mitigated the increase in cytokine levels elicited by F. nucleatum. Both red-complex bacteria adhered to and invaded hPDL-MSCs in greater numbers than F. nucleatum, with only a minor effect of co-infections.

CONCLUSIONS

Oral bacteria of different pathogenicity status interact differently with hPDL-MSCs. The data support P. gingivalis' capability to manipulate the inflammatory host response. Further research is necessary to obtain a comprehensive picture of the role of hPDL-MSCs in more complex oral biofilms.

CKIP-1 mediates P. gingivalis-suppressed osteogenic/cementogenic differentiation of periodontal ligament cells partially via p38 signaling pathway

Objectives

Casein kinase 2 interacting protein-1 (CKIP-1) is a versatile player involved in various biological processes. However, whether CKIP-1 mediates the osteogenic/cementogenic differentiation of periodontal ligament cells (PDLCs) under Porphyromonas gingivalis (Pg) stimulation remains unknown.

Material and Methods

The effect of Pg on PDLC differentiation was first verified. CKIP-1 expression in Pg-infected PDLCs or in PDL of apical periodontitis (AP) mice was detected. The changes of CKIP-1 during PDLC differentiation was also determined. PDLC differentiation capacity in CKIP-1 knockout (KO) mice and CKIP-1-silenced PDLCs with or without Pg stimulation were further studied. Inhibitor was finally applied to verify the involvement of p38 signaling pathway in PDLC differentiation.

Results

The suppression effect of Pg on PDLC differentiation was demonstrated. CKIP-1 increased in the PDL of AP mice and Pg-induced PDLCs, and decreased gradually during PDLC differentiation. Increased OSX and RUNX2 expression in PDL were observed in CKIP-1 KO mice. Also, CKIP-1 silencing facilitated and rescued Pg-inhibited PDLC differentiation. Inhibitor for p38 signaling pathway blocked CKIP-1 silencing-facilitated PDLC differentiation.

Conclusions

CKIP-1 mediated the osteogenic/cementogenic differentiation of PDLCs partially through p38 signaling pathway, which may provide evidence for the regeneration of periodontal hard tissues damaged by Pg.

"Efficacy of cytotoxic effect of green tea catechins on the human periodontal fibroblasts and human dental pulp fibroblasts -An in vitro study"

Background

Inflammation of tooth-supporting tissue and the pulp tissue is followed by wound healing and regeneration process that involves the specific type of connective tissue cells, the fibroblasts. During periodontitis and pulpitis, the inflammation of the tissue causes damage to the fibroblasts. These fibroblasts secrete collagen proteins and maintain the structural framework; along with this the inflammatory process moves toward healing where in the specific cells such as the fibroblast cells play important roles. Green tea catechins epigallocatechin-3-gallate (EGCG) being one of the major catechins is known to have multiple beneficial effects on human fibroblasts.

Objective

To assess the in vitro cytotoxicity of green tea catechins on the human periodontal ligament (PDL) fibroblasts and human dental pulp fibroblasts.

Materials and Methods

Human PDL fibroblasts (hPDLFs) and human dental pulp fibroblasts were isolated from the two extracted premolar teeth that were indicated for orthodontic treatment. The fibroblasts were then seeded in 96 well tissue culture plate for cell viability study. EGCG was used at different concentration to treat the cells. After 48 h; (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) (MTT) assay was performed to determine the cell viability.

Results

The vitality of hPDLFs and human dental pulp fibroblasts was found to be inversely proportional to EGCG concentrations.

Conclusions

hPDLFs have shown 37% proliferation at lowest concentration of EGCG used and human dental pulp fibroblasts have shown 99% viability at lowest concentration of EGCG used.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Protective effects of silibinin on LPS-induced inflammation in human periodontal ligament cells

Clinically, periodontitis is a chronic nonspecific inflammation that leads to damaged teeth and their supporting gum tissues. Although many studies on periodontitis have been conducted, therapy with natural products is still rare. Silibinin has been proven to have anti-inflammatory and antioxidant activities. However, the effects of silibinin on lipopolyssacharide (LPS)-induced inflammation in periodontal ligaments (PDLs) have not yet been investigated. In this study, the PDLs were treated with silibinin (10, 20, and 40 μM) in the presence of LPS. The results showed that silibinin treatment reduced the levels of NO, PGE2, IL-6, TNF-α, MMP-1, and MMP-3 and enhanced the activities of superoxide dismutase (SOD) and glutathione (GSH). Moreover, silibinin treatment downregulated RANKL levels and upregulated OPG and ALP levels. In summary, silibinin protected PDLs against LPS-induced inflammation, oxidative stress, and osteogenic differentiation.

Bacterial Microleakage at the Implant-Abutment Interface: An In Vitro Study

The objective of this study is to evaluate, in vitro, the microleakage of bacteria of 3 different implant connections for a period of 14 days. 60 dental implants (AoN) (n = 20) were distinguished into three groups, accordingly to the type of connection: External Hexagon (EH), Internal Hexagon (IH), and Cone Morse (CM) connection. All implants were inserted and fixed on sterile special vinyl support. Ten fixtures for each group were inoculated in the internal platform with 1.0 μL of Streptococcus oralis (SO) and the other ten with the same amount of Pseudomonas aeruginosa (PA). The penetration of bacterial suspension into the surrounding solution was determined by the observation of the turbidity of the broth. Five implants for each sub-group were randomly observed at SEM, to verify the correct fitting of the abutments. Considering the total of the samples analyzed, CM showed significantly lower bacterial contamination, with respect to IH. In particular, bacterial contamination was found in 45%, 55%, and 20% of EH, IH, and CM, respectively. Analyzing results for the type of inoculated bacteria, P. aeruginosa showed a higher ability to contaminate all the connections, with respect to S. oralis.

Daphne jejudoensis Attenuates LPS-Induced Inflammation by Inhibiting TNF-α, IL-1β, IL-6, iNOS, and COX-2 Expression in Periodontal Ligament Cells

Periodontitis is a common disease involving inflammation and tissue destruction in the periodontal region. Although uncontrolled long-term inflammation in the gingiva may lead to loss of the periodontal ligament, treatments or preventive solutions for periodontitis are scarce. The aim of this study is to find anti-inflammatory material from a natural source that can be used to treat or protect against periodontitis. Daphne species (Thymelaeaceae) are important and popular components of traditional Chinese medicine and are used as anti-inflammatory agents. Daphne jejudoensis is an endemic plant that grows on Jeju Island and was identified as a new species in 2013. In this study, for the first time, we investigated the anti-inflammatory effect of D. jejudoensis leaf extract (DJLE) on human periodontal ligament cells. The gene expression levels of pro-inflammatory cytokines (interleukin-1β and 6 and tumor necrosis factor-α) and inflammation-inducible enzymes (inducible nitric oxide synthase and cyclooxygenase-2) were reduced after DJLE treatment with/without lipopolysaccharide stimulation. The findings of this study indicate that D. jejudoensis possesses anti-inflammatory activities, suggesting that DJLE may be a potential preventive and therapeutic agent for periodontitis.

Bacterial-Specific Induction of Inflammatory Cytokines Significantly Decreases upon Dual Species Infections of Implant Materials with Periodontal Pathogens in a Mouse Model

Cytokine profiles are often perturbed after infections of medical implants. With a non-invasive in vivo imaging system, we report in a mouse model that interferon expression after infection of subcutaneous implants with Streptococcus oralis, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Treponema denticola (alone or as a combination) was species-specific, persisted longer in the presence of implants, and notably decreased upon dual species infections. This type I interferon expression disappeared within two weeks; however, histology of implant–tissue interface indicated high recruitment of immune cells even after three weeks. This was suggestive that biomaterial-associated infections could have prolonged effects, including the systemic stimulation of inflammatory cytokines. The present study investigated the systemic impact of this chronic peri-implant inflammation on the systemic expression of inflammatory cytokines (23) using a multiplex assay. Initially, the cytokine measurement in murine fibroblasts exposed to periodontal pathogens remained limited to the expression of five cytokines, namely, IL-6, G-CSF, CXCL-1/KC, MCP-1 (MCAF), and IL-12 (p40). The systemic determination of cytokines in mice increased to 19 cytokines (IL-1α, IL-2, IL-3, IL-5, IL-6, IL-9, IL-12 (p40), IL-12 (p70), IL-13, IL-17A, CCL-11/Eotaxin, G-CSF, IFN-γ, CXCL1/KC, MCP-1 (MCAF), MIP-1α/CCL3, MIP-1β/CCL4, CCL5/RANTES, and TNF-α). Systemic induction of cytokines was species-specific in the mouse model. The cytokine induction from infected implants differed significantly from sole tissue infections and sterile implants. Notably, systemic cytokine induction decreased after infections with dual species compared to single species infections. These findings describe the systemic effect of chronic peri-implant inflammation on the systemic induction of inflammatory cytokines, and this effect was strongly correlated to the type and composition of initial infection. Systemic modulations in cytokine expression upon dual species infections exhibit an exciting pattern that might explain the complications associated with biomaterial-related infection in patients. Moreover, these findings validate the requirement of multispecies infections for pre-clinical studies involving animal models.

Effects of Aging Torque Controllers on Screw Tightening Force and Bacterial Micro-Leakage on the Implant-Abutment Complex

Aim: We assess the accuracy of torque controllers after several aging processes and the bacterial leakage on implant-abutment complexes (IAC). Methods: A total of 12 spring-type and 12 friction-type torque controllers and 48 IAC (24 conical and 24 hexagonal connections) were evaluated. Chemical, mechanical, temperature, and pressure-aging methods were applied individually to replicate clinical use. Torque controller accuracy was analyzed before and after aging using a calibrated gauge. To assess bacterial leakage, the IAC were suspended in a bacterial medium for 24 h. Direct Contact Test (DCT) and Polymerase Chain Reaction Test (RT-PCR) analyzed the infiltration of F. nucleatum and P. gingivalis into the IAC micro-gap. Results: A significant decrease in torque after 10 days of aging was found. The spring-type torque controller was affected the most, regardless of the aging method (P < 0.05). PCR results indicated that all groups exhibited significantly more bacterial leakage, regardless of the method used (P < 0.05). The conical IAC demonstrated more bacterial leakage of P. gingivalis compared with the hexagonal IAC (P = 0.07). DCT found bacterial growth in the IAC only before aging and was not identified after aging. Conclusion: Aging affects torque accuracy. A reduction in force was noticed after 10 days. The conical IAC exhibits more bacterial leakage, although this was not statistically significant.

Activation of GATA-binding protein 4 regulates monocyte chemoattractant protein-1 and chemotaxis in periodontal ligament cells

BACKGROUND AND OBJECTIVES

Periodontitis is a chronic inflammatory disease of periodontal supporting tissues. The persistent inflammatory reaction depends on the release of chemokines to continuously recruit inflammation cells. GATA-binding protein 4 (GATA4) exerts effects on senescence and inflammation, while its role in periodontitis is far from clear. The present study aims to address the effect of GATA4 on regulating chemokines and the chemotaxis in periodontitis.

MATERIAL AND METHODS

Periodontitis rat models were constructed to detect the expression of GATA4 and the chemokine monocyte chemoattractant protein-1 (MCP-1) by immunohistochemistry. Lipopolysaccharide (LPS)-stimulated human periodontal ligament (PDL) cells and GATA4-knockdown by siRNA transient transfection PDL cells were used to explore the correlation between GATA4 and chemokines. Transwell assay was performed to detect the role of GATA4 for the recruitment effect of chemokines on macrophages. Mitogen-activated protein kinase (MAPK) inhibitors were scheduled to intervene in LPS-stimulated PDL cells to examine the association between MAPK signaling pathways and GATA4. The expression of GATA4, chemokines, or MAPK signaling molecules was determined by quantitative real-time polymerase chain reaction, western blotting, or cell immunofluorescence.

RESULTS

The expression of GATA4 and MCP-1 was significantly increased in periodontitis rat models and in LPS-stimulated PDL cells. Knockdown GATA4 inhibited the expression of GATA4 and MCP-1 as well as suppressed the recruitment of macrophage in LPS-stimulated PDL cells. Inhibitors of p38 and ERK1/2 signaling pathways significantly downregulated the increased expression of GATA4 and MCP-1 induced by LPS in PDL cells.

CONCLUSIONS

GATA-binding protein 4 could act as an upstream regulator of MCP-1 and as a downstream regulator of p38 and ERK1/2 signaling pathways to initiate inflammation response and regulate chemotaxis during the progression of periodontitis.

Induction of Apoptotic Cell Death by Oral Streptococci in Human Periodontal Ligament Cells

Initiation and progression of oral infectious diseases are associated with streptococcal species. Bacterial infection induces inflammatory responses together with reactive oxygen species (ROS), often causing cell death and tissue damage in the host. In the present study, we investigated the effects of oral streptococci on cytotoxicity and ROS production in human periodontal ligament (PDL) cells. Streptococcus gordonii showed cell cytotoxicity in a dose- and time-dependent manner. The cytotoxicity might be due to apoptosis since S. gordonii increased annexin V-positive cells, and the cytotoxicity was reduced by an apoptosis inhibitor, Z-VAD-FMK. Other oral streptococci such as Streptococcus mitis, Streptococcus sanguinis, and Streptococcus sobrinus also induced apoptosis, whereas Streptococcus mutans did not. All streptococci tested except S. mutans triggered ROS production in human PDL cells. Interestingly, however, streptococci-induced apoptosis appears to be ROS-independent, as the cell death induced by S. gordonii was not recovered by the ROS inhibitor, resveratrol or n-acetylcysteine. Instead, hydrogen peroxide (H₂O₂) appears to be important for the cytotoxic effects of streptococci since most oral streptococci except S. mutans generated H₂O₂, and the cytotoxicity was dramatically reduced by catalase. Furthermore, streptococcal lipoproteins are involved in cytotoxicity, as we observed that cytotoxicity induced by the lipoprotein-deficient S. gordonii mutant was less potent than that by the wild-type and was attenuated by anti-TLR2-neutralizing antibody. Indeed, lipoproteins purified from S. gordonii alone were sufficient to induce cytotoxicity. Notably, S. gordonii lipoproteins did not induce H₂O₂ or ROS but cooperatively induced cell death when co-treated with H₂O₂. Taken together, these results suggest that most oral streptococci except S. mutans efficiently induce damage to human PDL cells by inducing apoptotic cell death with bacterial H₂O₂ and lipoproteins, which might contribute to the progression of oral infectious diseases such as apical periodontitis.

STAT1/SOCS1/3 Are Involved in the Inflammation-Regulating Effect of GAS6/AXL in Periodontal Ligament Cells Induced by Porphyromonas gingivalis Lipopolysaccharide In Vitro

Periodontitis involves chronic inflammation of the tissues around the teeth caused by plaque and the corresponding immune response. Growth arrest-specific protein 6 (GAS6) and AXL receptor tyrosine kinase (AXL) are known to be involved in inflammatory diseases, while signal transducer and activator of transcription-1 (STAT1) and suppressor of cytokine signaling (SOCS) are related to inflammatory processes. Moreover, miRNA34a directly targets AXL to regulate the AXL expression. However, the specific roles of GAS6 and AXL in periodontitis remain unclear. This study was designed to explore the effect and mechanism of AXL on the expression of inflammatory cytokines induced by Porphyromonas gingivalis lipopolysaccharide (P. gingivalis LPS) in human periodontal ligament cells (hPDLCs). The effects of different concentrations of P. gingivalis LPS on the expression of GAS6/AXL in hPDLCs were observed. Additionally, the effect of LPS on AXL was investigated by transfection of the miRNA34a inhibitor. AXL was knocked down or overexpressed to observe the release of inflammatory cytokines interleukin- (IL-) 8 and IL-6. The results showed that the expression levels of GAS6 and AXL decreased after P. gingivalis LPS infection. Transfection of a miR-34a inhibitor to hPDLCs demonstrated a role of miR-34a in the downregulation of AXL expression induced by LPS. Moreover, AXL knockdown or overexpression influencing the expression of IL-8 and IL-6 was investigated under LPS stimulation. AXL knockdown decreased the expression of STAT1 and SOCS1/3. Overall, these results demonstrate that AXL inhibits the expression of LPS-induced inflammatory cytokines in hPDLCs and that STAT1 and SOCS1/3 are involved in the regulation of inflammation by GAS6/AXL.

Cyclic tensile strain affects the response of human periodontal ligament stromal cells to tumor necrosis factor-α

Objectives

Orthodontic treatment in adult patients predisposed to mild or severe periodontal disease is challenging for orthodontists. Orthodontic malpractice or hyper-occlusal forces may aggravate periodontitis-induced destruction of periodontal tissues, but the specific mechanism remains unknown. In the present study, the combined effect of mechanical stress and tumor necrosis factor (TNF)-α on the inflammatory response in human periodontal ligament stromal cells (hPDLSCs) was investigated.

Materials and methods

hPDLSCs from 5 healthy donors were treated with TNF-α and/or subjected to cyclic tensile strain (CTS) of 6% or 12% elongation with 0.1 Hz for 6- and 24 h. The gene expression of interleukin (IL)-6, IL-8 and cell adhesion molecules VCAM and ICAM was analyzed by qPCR. The protein levels of IL-6 and IL-8 in conditioned media was measured by ELISA. The surface expression of VCAM-1 and ICAM-1 was quantified by immunostaining followed by flow cytometry analysis.

Results

TNF-α-induced IL-6 gene and protein expression was inhibited by CTS, whereas TNF-α-induced IL-8 expression was decreased at mRNA expression level but enhanced at the protein level in a magnitude-dependent manner. CTS downregulated the gene expression of VCAM-1 and ICAM-1 under TNF-α stimulation, but the downregulation of the surface expression analyzed by flow cytometry was observed chiefly for VCAM-1.

Conclusions

Our findings show that mechanical force differentially regulates TNF-α-induced expression of inflammatory mediators and adhesion molecules at the early stage of force application. The effect of cyclic tensile strain is complex and could be either anti-inflammatory or pro-inflammatory depending on the type of pro-inflammatory mediators and force magnitude.

Clinical relevance

Orthodontic forces regulate the inflammatory mediators of periodontitis. The underlying mechanism may have significant implications for future strategies of combined periodontal and orthodontic treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-021-04039-8.

Hyperlipidemic Conditions Impact Force-Induced Inflammatory Response of Human Periodontal Ligament Fibroblasts Concomitantly Challenged with P. gingivalis-LPS

In obese patients, enhanced serum levels of free fatty acids (FFA), such as palmitate (PA) or oleate (OA), are associated with an increase in systemic inflammatory markers. Bacterial infection during periodontal disease also promotes local and systemic low-grade inflammation. How both conditions concomitantly impact tooth movement is largely unknown. Thus, the aim of this study was to address the changes in cytokine expression and the secretion of human periodontal ligament fibroblasts (HPdLF) due to hyperlipidemic conditions, when additionally stressed by bacterial and mechanical stimuli. To investigate the impact of obesity-related hyperlipidemic FFA levels on HPdLF, cells were treated with 200 µM PA or OA prior to the application of 2 g/cm² compressive force. To further determine the additive impact of bacterial infection, HPdLF were stimulated with lipopolysaccharides (LPS) obtained from Porphyromonas gingivalis. In mechanically compressed HPdLF, PA enhanced COX2 expression and PGE2 secretion. When mechanically stressed HPdLF were additionally stimulated with LPS, the PGE2 and IL6 secretion, as well as monocyte adhesion, were further increased in PA-treated cultures. Our data emphasize that a hyperlipidemic condition enhances the susceptibility of HPdLF to an excessive inflammatory response to compressive forces, when cells are concomitantly exposed to bacterial components.

Effect of interleukin-1β on bone morphogenetic protein-9-induced osteoblastic differentiation of human periodontal ligament fibroblasts

Bone morphogenetic protein-9 (BMP-9) has been shown to potently induce osteoblastic differentiation of periodontal ligament fibroblasts (PDLFs) and may be a candidate therapeutic agent for periodontal tissue healing/regeneration, but the effect of the inflammatory environment of periodontitis on such approaches is unclear. We investigated whether interleukin-1β (IL-1β) affected BMP-9-mediated osteoblastic differentiation of human (h) PDLFs. IL-1β suppressed BMP-9-induced osteogenic differentiation of hPDLFs, as evidenced by reduced alkaline phosphatase (ALP) activity and mineralization, and the downregulated expression of BMP-9-mediated bone-related genes, RUNX2, SP7, IBSP, and SPP1. In hPDLFs, with or without BMP-9, IL-1β increased the protein expression of activin A, a BMP-9 antagonist, and decreased follistatin protein, an antagonist of activin A. Similarly, IL-1β upregulated the expression of the activin A gene and downregulated that of the follistatin gene. Notably, follistatin re-established BMP-9-induced ALP activity suppressed by IL-1β. Activin A inhibited the expression of BMP-9-responsive genes and BMP-9-induced ALP activity, while follistatin re-established them. Finally, extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and nuclear factor-kappa B (NF-κB) inhibition significantly blocked IL-1β-induced activin A gene expression. Our data indicate that IL-1β inhibits BMP-9-induced osteoblastic differentiation of hPDLFs, possibly by promoting activin A production via the ERK1/2, p38, and NF-κB pathways.

Effect of Porphyromonas gingivalis lipopolysaccharide on calcification of human umbilical artery smooth muscle cells co-cultured with human periodontal ligament cells

Periodontitis is an independent risk factor for coronary heart disease. Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) was considered to be one of the main virulence factors. In addition, vascular smooth muscle cells transform into osteoblast-like cells in an arterial calcification process under chronic inflammatory conditions. The present study aimed to determine the calcification induced by Pg-LPS in human umbilical artery smooth muscle cells (HUASMCs) co-cultured with human periodontal ligament cells (HPDLCs). An in vitro co-culture system was established using Transwell inserts. HUASMC proliferation and alkaline phosphatase (ALP) activity were measured with a Cell Counting Kit-8 and an ALP kit, respectively. Calcium nodule formation was detected using alizarin red S staining. The effects of Pg-LPS on the mRNA expression of the calcification genes of ALP, core-binding factor α1 (Runx2) and bone sialoprotein (BSP) were assessed using reverse transcription-quantitative PCR. The results indicated that Pg-LPS increased HUASMC proliferation and ALP activity. Furthermore, among all of the groups, calcium nodule formation was most extensive in co-cultured cells in the mineralization-inducing medium containing Pg-LPS. In addition, the expression of specific osteogenic genes (Runx2, ALP and BSP) significantly increased in the presence of Pg-LPS and mineralization-inducing medium, which was further enhanced in co-culture with HPDLCs. In conclusion, co-culture with HPDLCs increased the effect of Pg-LPS to stimulate the calcification of HUASMCs. It was suggested that besides the inflammation, periodontitis may promote the occurrence of vascular calcification. The study indicated that periodontal treatment of subgingival scaling to reduce and/or control Porphyromonas gingivalis may decrease the occurrence or severity of vascular calcification.

Pathophysiological mechanisms of root resorption after dental trauma: a systematic scoping review

Background

The objective of this scoping review was to systematically explore the current knowledge of cellular and molecular processes that drive and control trauma-associated root resorption, to identify research gaps and to provide a basis for improved prevention and therapy.

Methods

Four major bibliographic databases were searched according to the research question up to February 2021 and supplemented manually. Reports on physiologic, histologic, anatomic and clinical aspects of root resorption following dental trauma were included. Duplicates were removed, the collected material was screened by title/abstract and assessed for eligibility based on the full text. Relevant aspects were extracted, organized and summarized.

Results

846 papers were identified as relevant for a qualitative summary. Consideration of pathophysiological mechanisms concerning trauma-related root resorption in the literature is sparse. Whereas some forms of resorption have been explored thoroughly, the etiology of others, particularly invasive cervical resorption, is still under debate, resulting in inadequate diagnostics and heterogeneous clinical recommendations. Effective therapies for progressive replacement resorptions have not been established. Whereas the discovery of the RANKL/RANK/OPG system is essential to our understanding of resorptive processes, many questions regarding the functional regulation of osteo-/odontoclasts remain unanswered.

Conclusions

This scoping review provides an overview of existing evidence, but also identifies knowledge gaps that need to be addressed by continued laboratory and clinical research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01510-6.

Proteomics of extracellular vesicles produced by Granulicatella adiacens, which causes infective endocarditis

When oral bacteria accidentally enter the bloodstream due to transient tissue damage during dental procedures, they have the potential to attach to the endocardium or an equivalent surface of an indwelling prosthesis and cause infection. Many bacterial species produce extracellular vesicles (EVs) as part of normal physiology, but also use it as a virulence strategy. In this study, it was hypothesized that Granulicatella adiacens produce EVs that possibly help it in virulence. Therefore, the objectives were to isolate and characterize EVs produced by G. adiacens and to investigate its immune-stimulatory effects. The reference strain G. adiacens CCUG 27809 was cultured on chocolate blood agar for 2 days. From subsequent broth culture, the EVs were isolated using differential centrifugation and filtration protocol and then observed using scanning electron microscopy. Proteins in the vesicle preparation were identified by nano LC-ESI-MS/MS. The EVs proteome was analyzed and characterized using different bioinformatics tools. The immune-stimulatory effect of the EVs was studied via ELISA quantification of IL-8, IL-1β and CCL5, major proinflammatory cytokines, produced from stimulated human PBMCs. It was revealed that G. adiacens produced EVs, ranging in diameter from 30 to 250 nm. Overall, G. adiacens EVs contained 112 proteins. The proteome consists of several ribosomal proteins, DNA associated proteins, binding proteins, and metabolic enzymes. It was also shown that these EVs carry putative virulence factors including moonlighting proteins. These EVs were able to induce the production of IL-8, IL-1β and CCL5 from human PBMCs. Further functional characterization of the G. adiacens EVs may provide new insights into virulence mechanisms of this important but less studied oral bacterial species.

Ginsenoside Rb3 Inhibits Pro-Inflammatory Cytokines via MAPK/AKT/NF-κB Pathways and Attenuates Rat Alveolar Bone Resorption in Response to Porphyromonas gingivalis LPS

Conventional treatments for chronic periodontitis are less effective in controlling inflammation and often relapse. Therefore, it is necessary to explore an immunomodulatory medication as an adjuvant. Ginsenoside Rb3 (Rb3), one of the most abundant active components of ginseng, has been found to possess anti-inflammatory and immunomodulatory properties. Here, we detected the anti-inflammatory effect of Rb3 on Porphyromonas gingivalis LPS-stimulated human periodontal ligament cells and experimental periodontitis rats for the first time. We found that the expression of pro-inflammatory mediators, including IL-1β, IL-6 and IL-8, upregulated by lipopolysaccharide (LPS) stimulation was remarkably downregulated by Rb3 treatment in a dose-dependent manner at both transcriptional and translational levels. Network pharmacological analysis of Rb3 showed that the mitogen-activated protein kinase (MAPK) signaling pathway had the highest richness and that p38, JNK, and ERK molecules were potential targets of Rb3 in humans. Western blot analysis revealed that Rb3 significantly suppressed the phosphorylation of p38 MAPK and p65 NF-κB, as well as decreased the expression of total AKT. In experimental periodontitis rat models, reductions in alveolar bone resorption and osteoclast generation were observed in the Rb3 treatment group. Thus, we can conclude that Rb3 ameliorated Porphyromonas gingivalis LPS-induced inflammation by inhibiting the MAPK/AKT/NF-κB signaling pathways and attenuated alveolar bone resorption in experimental periodontitis rats.

Effects of mechanical stress on human oral mucosa-derived cells

OBJECTIVES

Placement of a denture results in the application of mechanical stress (MS), such as occlusal force, onto the oral mucosa beneath the denture. To better understand the molecular mechanism underlying MS-induced inflammation in the oral mucosa, we examined the impact of MS on human oral epithelial cells (HO-1-N-1) and human fibroblasts (HGFs) in this study.

MATERIALS AND METHODS

MS was applied on HO-1-N-1 and HGFs using a hydrostatic pressure apparatus. The expression and production of inflammatory cytokines and growth factors were examined by real-time RT-PCR and ELISA. MS-induced intracellular signal transduction via MAP kinase (MAPK) was also examined.

RESULTS

1 MPa MS resulted in a significant increase in inflammatory cytokines, and 3 MPa MS resulted in a significant increase in FGF-2. MS also increased p-38 phosphorylation and the addition of a p-38 inhibitor significantly suppressed the production of inflammatory cytokines.

DISCUSSION

Our study suggested that MS applied through a denture increases the production of inflammatory cytokines from oral mucosal epithelial cells and fibroblasts via the p38 MAPK cascade. These responses to MS likely lead to inflammation of the mucosal tissue beneath dentures. On other hand, up-regulation of growth factors is likely a manifestation of the biological defense mechanism against excessive MS.

Effect of interleukin-22 on osteogenic differentiation and the osteoclastogenic response of human periodontal ligament fibroblasts in vitro

BACKGROUND

Interleukin-22 (IL-22) exerts extensive biological effects, playing both protective and pathological roles in autoimmune and infectious diseases. However, the specific role and mechanism of IL-22 in the pathogenesis of periodontitis have not been clarified. The aim of this study was to analyze the possible roles of IL-22 in the osteoclastogenesis and osteogenesis of periodontitis.

METHODS

Human periodontal ligament fibroblasts (hPDLFs) were treated with IL-22 and/or lipopolysaccharide from Porphyromonas gingivalis (Pg-LPS), and the mRNA and protein expression of RANKL and OPG were measured by qRT-PCR and Western blotting, respectively. Western blotting was also used to examine the phosphorylated and total protein expression of MAPK signaling molecules. The role of the MAPK pathway in osteoclastogenesis marker expression was further confirmed by inhibition assays. For osteogenic assays, the mRNA expression of osteoblastic markers was quantified by qRT-PCR, the alkaline phosphatase (ALP) activity of hPDLFs was measured by an ALP assay, and the mineralized nodules formed by hPDLFs were determined by Alizarin Red S staining.

RESULTS

IL-22 promoted the expression of RANKL in hPDLFs via the MAPK signaling pathway and further upregulated RANKL expression together with Pg-LPS via the p38 MAPK pathway. IL-22 could enhance the ALP activity and mineralized nodule formation of hPDLFs in the early period of osteogenic induction, while exhibiting no profound effect on the expression of osteoblastic markers.

CONCLUSION

IL-22 plays regulatory roles in bone homeostasis, and it is likely to contribute to osteoclastogenesis as a proinflammatory cytokine in the pathogenesis of periodontitis.

Low-intensity pulsed ultrasound activates autophagy in periodontal ligament cells in the presence or absence of lipopolysaccharide

OBJECTIVE

This study aims to determine if low-intensity pulsed ultrasound (LIPUS) activates autophagy in human periodontal ligament cells (PDLCs) irrespective of lipopolysaccharide.

DESIGN

Six groups were designed: control, LIPUS, lipopolysaccharide, LIPUS + lipopolysaccharide, LIPUS+3-Methyladenine, LIPUS + lipopolysaccharide+3-Methyl- adenine. LIPUS pretreated PDLCs for 2 h and lipopolysaccharide treated for different times. Real-time PCR and Western-blot were performed to evaluate mRNA and protein expression levels of autophagic genes Beclin-1 and LC3 respectively. A transmission electronic microscope was used to observe the autophagosome. ELISA was used to test interleukin-6 expression.

RESULTS

Compared with the non-treatment, LIPUS pretreatment increased mRNA expression levels of LC3 (P < 0.05) and Beclin-1 (P < 0.05) at 4 h and 8 h, and enhanced the protein expression levels of LC3-Ⅱ at 8 h (P<0.05) and Beclin-1 at 4 h, 8 h and 16 h(P<0.05). After LIPUS pretreatment and lipopolysaccharide treatment for 8 h, LC3-Ⅱ and Beclin-1 protein expression levels were elevated (P < 0.05) compared with the control. Following further treatment by 3-Methyladenine, Beclin-1 protein expression was decreased (P < 0.05) compared with the LIPUS plus lipopolysaccharide group, but LC3-Ⅱ protein expression was not. Autophagosomes were not found in the LIPUS+3-Methyladenine and LIPUS+lipopolysaccharide+3-Methyladenine groups. After LIPUS pretreatment and lipopolysaccharide treatment for 36 h, intreleukin-6 expression was decreased (P<0.05) compared with the lipopolysaccharide group. However, after addition of 3-Methyladenine, intreleukin-6 expression was elevated (P < 0.05) compared with the LIPUS +lipopolysaccharide group.

CONCLUSIONS

LIPUS can promote autophagy in PDLCs irrespective of lipopolysaccharide. Autophagy might be involved in LIPUS anti-inflammatory mechanism in PDLCS.

Osmunda japonica Extract Suppresses Pro-Inflammatory Cytokines by Downregulating NF-κB Activation in Periodontal Ligament Fibroblasts Infected with Oral Pathogenic Bacteria

Periodontal diseases are caused by bacterial infection and may progress to chronic dental disease; severe inflammation may result in bone loss. Therefore, it is necessary to prevent bacterial infection or control inflammation. Periodontal ligament fibroblasts (PDLFs) are responsible for the maintenance of tissue integrity and immune and inflammatory events in periodontal diseases. The formation of bacterial complexes by Fusobacterium nucleatum and Porphyromonas gingivalis is crucial in the pathogenesis of periodontal disease. F. nucleatum is a facultative anaerobic species, considered to be a key mediator of dental plaque maturation and aggregation of other oral bacteria. P. gingivalis is an obligate anaerobic species that induces gingival inflammation by secreting virulence factors. In this study, we investigated whether Osmunda japonica extract exerted anti-inflammatory effects in primary PDLFs stimulated by oral pathogens. PDLFs were stimulated with F. nucleatum or P. gingivalis. We showed that pro-inflammatory cytokine (IL-6 and IL-8) expression was induced by LPS or bacterial infection but decreased by treatment with O. japonica extract following bacterial infection. We found that the activation of NF-κB, a transcription factor for pro-inflammatory cytokines, was modulated by O. japonica extract. Thus, O. japonica extract has immunomodulatory activity that can be harnessed to control inflammation.

The interaction between serum amyloid A and Toll-like receptor 2 pathway regulates inflammatory cytokine secretion in human gingival fibroblasts

BACKGROUND

Serum amyloid A (SAA) has been identified to trigger inflammation response, and play a crucial role in chronic inflammatory diseases. However, the regulatory mechanism of SAA still remains unclear during the development of periodontitis METHODS: SAA mRNA and protein expression were detected in healthy and inflammatory gingival tissues using real-time polymerase chain reaction (PCR) and immunohistochemistry. Human recombinant SAA (Apo-SAA), Pam3CSK4 (a Toll-like receptor (TLR) 2 ligand), siRNA-SAA, or TLR2 neutralizing antibody was applied to treat human gingival fibroblasts, respectively, or combined. SAA, TLRs, and inflammatory cytokines interleukin (IL)-6 and IL-8 were analyzed by real-time PCR, western blotting, or enzyme-linked immunosorbent assay.

RESULTS

SAA expression increased in human inflammatory gingival tissues from patients with periodontitis (P <0.05). Apo-SAA could increase not only the mRNA expression of TLR2 (P <0.05), but also IL-6 and IL-8 mRNA and protein levels (P <0.05) which was suppressed by TLR2 antibody in human gingival fibroblasts. Pam3CSK4 increased SAA, IL-6, and IL-8 levels (P <0.05). However, the expression of SAA, IL-6, and IL-8 decreased after transfection of siRNA-SAA (P <0.05).

CONCLUSION

SAA not only increases in inflammatory gingiva, but also triggers inflammatory cytokine secretion via interacting with TLR2 pathway in human gingival fibroblasts, which indicates that SAA is involved in periodontal inflammation.

Transplantation of dental pulp-derived cell sheets cultured on human amniotic membrane induced to differentiate into bone

OBJECTIVE

The usefulness of the amniotic membrane as a cell culture substrate has led to its use in the development of dental pulp-derived cell sheets. We induced osteoblastic differentiation of dental pulp-derived cell sheets and conducted histological and immunological examinations in addition to imaging assessments for regeneration of bone defects.

METHODS

Dental pulp cells were obtained by primary culture of the dental pulp tissue harvested from extracted wisdom teeth. These cells were maintained for three to four passages. Subsequently, the dental pulp cells were seeded onto an amniotic membrane to produce dental pulp-derived cell sheets. Following the induction of osteoblastic differentiation, the sheets were grafted into the subcutaneous tissue of the lower back and maxillary bone defect of a nude mouse. Histological and immunological examinations of both grafts were performed.

RESULTS

Dental pulp-derived cell sheets cultured on an osteoblast differentiation-inducing medium demonstrated resemblance to dental pulp tissue and produced calcified tissue. Mineralization was maintained following grafting of the sheets. Regeneration of the maxillary bone defect was observed.

CONCLUSION

Induction of osteoblastic differentiation of the dental pulp-derived cell sheets may be indicated for the regeneration of periodontal tissue.

Assessment of Salivary Levels of RANKL and OPG in Aggressive versus Chronic Periodontitis

RANKL (receptor activator of nuclear factor kappa-β ligand) and OPG (osteoprotegerin) are two proteins involved in bone remodelling. During the active phase of periodontal disease, an imbalance between the ratios of the two elements can be noticed. While the expression of RANKL is elevated compared with that of OPG, the RANKL is available to bond with RANK (receptor activator of nuclear factor kappa-β). This study was conducted on 41 patients: 19 with generalized aggressive periodontitis, 18 with severe chronic periodontitis, and 4 periodontal healthy subjects. For each patient included, we determined the salivary levels of RANKL and OPG with the help of two Human ELISA kits. The results show that the patients affected by periodontitis, either aggressive or chronic, have significant higher values of RANKL and RANKL/OPG ratio. This values correlate with the local inflammation status.

Do electrical current and laser therapies improve bone remodeling during an orthodontic treatment with corticotomy?

OBJECTIVES

Evaluate the bone remodeling during orthodontic movement with corticotomy when submitted to low-intensity electrical stimulation application (microcurrent-MC) and low-level laser therapy (LLLT).

MATERIAL AND METHODS

One hundred and fifty Wistar rats were divided into the following 5 groups: (C) submitted to tooth movement; (Cort) tooth movement/corticotomy; (Cort-L) tooth movement/corticotomy/laser AsGaAl 808 nm (4.96J/50s); (Cort-Mc) tooth movement/corticotomy/microcurrent (10 μA/5 min); (Cort-L-Mc) tooth movement/corticotomy and laser/microcurrent alternated. Inflammation, angiogenesis, and osteogenesis were evaluated in the periodontal ligament (PDL) and alveolar bone on the 7th, 14th, and 21st days of orthodontic movement.

RESULTS

The quantification of inflammatory infiltrate, angiogenesis and expression of TGF-β1, VEGF, and collagen type I were favorably modulated by the application of therapies such as low-level laser therapy (LLLT), MC, or both combined. However, electrical stimulation increased fibroblasts, osteoclasts and RANK numbers, birefringent collagen fiber organization, and BMP-7 and IL-6 expression.

CONCLUSIONS

Low-level laser therapy (LLLT) and MC application both improved the process of bone remodeling during orthodontic treatment with corticotomy. Still, electrical current therapy promoted a more effective tooth displacement but presented expected root resorption similar to all experimental treatments.

CLINICAL RELEVANCE

It is important to know the effects of minimally invasive therapies on cellular and molecular elements involved in the bone remodeling of orthodontic treatment associated with corticotomy surgery, in order to reduce the adverse effects in the use of this technique and to establish a safer clinical routine.

Litsea japonica Leaf Extract Suppresses Proinflammatory Cytokine Production in Periodontal Ligament Fibroblasts Stimulated with Oral Pathogenic Bacteria or Interleukin-1β

Periodontal disease, a chronic disease caused by bacterial infection, eventually progresses to severe inflammation and bone loss. Regulating excessive inflammation of inflamed periodontal tissues is critical in treating periodontal diseases. The periodontal ligament (PDL) is primarily a connective tissue attachment between the root and alveolar bone. PDL fibroblasts (PDLFs) produce pro-inflammatory cytokines in response to bacterial infection, which could further adversely affect the tissue and cause bone loss. In this study, we determined the ability of Litsea japonica leaf extract (LJLE) to inhibit pro-inflammatory cytokine production in PDLFs in response to various stimulants. First, we found that LJLE treatment reduced lipopolysaccharide (LPS)-induced pro-inflammatory cytokine (interleukin-6 and interleukin-8) mRNA and protein expression in PDLFs without cytotoxicity. Next, we observed the anti-inflammatory effect of LJLE in PDLFs after infection with various oral bacteria, including Fusobacterium nucleatum, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia. These anti-inflammatory effects of LJLE were dose-dependent, and the extract was effective following both pretreatment and posttreatment. Moreover, we found that LJLE suppressed the effect of interleukin-1 beta-induced pro-inflammatory cytokine production in PDLFs. Taken together, these results indicate that LJLE has anti-inflammatory activity that could be exploited to prevent and treat human periodontitis by controlling inflammation.

Decreased MORF leads to prolonged endoplasmic reticulum stress in periodontitis-associated chronic inflammation

The association between inflammation and endoplasmic reticulum (ER) stress has been described in many diseases. However, if and how chronic inflammation governs the unfolded protein response (UPR) and promotes ER homeostasis of chronic inflammatory disease remains elusive. In this study, chronic inflammation resulted in ER stress in mesenchymal stem cells in the setting of periodontitis. Long-term proinflammatory cytokines induced prolonged ER stress and decreased the osteogenic differentiation of periodontal ligament stem cells (PDLSCs). Interestingly, we showed that chronic inflammation decreases the expression of lysine acetyltransferase 6B (KAT6B, also called MORF), a histone acetyltransferase, and causes the upregulation of a key UPR sensor, PERK, which lead to the persistent activation of the UPR in PDLSCs. Furthermore, we found that the activation of UPR mediated by MORF in chronic inflammation contributes to the PERK-related deterioration of the osteogenic differentiation of PDLSCs both in vivo and in vitro. Taken together, our results suggest that chronic inflammation compromises UPR function through MORF-mediated-PERK transcription, which is a previously unrecognized mechanism that contributes to impaired ER function, prolonged ER stress and defective osteogenic differentiation of PDLSCs in periodontitis.

Effects of Shock Waves on Expression of IL-6, IL-8, MCP-1, and TNF-α Expression by Human Periodontal Ligament Fibroblasts: An In Vitro Study

Background

Extracorporeal shock wave therapy (ESWT) can modulate cell behavior through mechanical information transduction. Human periodontal ligament fibroblasts (hPDLF) are sensible to mechanical stimulus and can express pro-inflammatory molecules in response. The aim of this study was to evaluate the impacts of shock waves on interleukin-6 (IL-6), interleukin-8 (IL-8), monocyte chemotactic protein 1 (MCP-1), and tumor necrosis factor-alpha (TNF-α) expression by hPDLF.

Material/Methods

After being treated by shock waves with different parameters (100–500 times, 0.05–0.19 mJ/mm²), cell viability was tested using CCK-8. IL-6, IL-8, MCP-1, and TNF-α gene expression was analyzed by quantitative real-time polymerase chain reaction (qRT-PCR) and IL-6 and IL-8 protein was measured by enzyme-linked immunosorbent assay (ELISA) at different time points.

Results

Shock waves with the parameters used in this study had no significant effects on the viability of hPDLF. A statistical inhibition of IL-6, IL-8, MCP-1, and TNF-α expression during the first few hours was observed (P<0.05). Expression of IL-8 was significantly elevated in the group receiving the most pulses of shock wave (500 times) after 4 h (P<0.05). At 8 h and 24 h, all treated groups demonstrated significantly enhanced IL-6 expression (P<0.05). TNF-α expression in the groups receiving more shock pulses (300, 500 times) or the highest energy shock treatment (0.19 mJ/mm²) was statistically decreased (P<0.05) at 24 h.

Conclusions

Under the condition of this study, a shock wave with energy density no higher than 0.19 mJ/mm² and pulses no more than 500 times elicited no negative effects on cell viability of hPDLF. After a uniform initial inhibition impact on expression of inflammatory mediators, a shock wave could cause dose-related up-regulation of IL-6 and IL-8 and down-regulation of TNF-α.

Host response mechanisms in periodontal diseases

Periodontal diseases usually refer to common inflammatory disorders known as gingivitis and periodontitis, which are caused by a pathogenic microbiota in the subgingival biofilm, including Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia and Treponema denticola that trigger innate, inflammatory, and adaptive immune responses. These processes result in the destruction of the tissues surrounding and supporting the teeth, and eventually in tissue, bone and finally, tooth loss. The innate immune response constitutes a homeostatic system, which is the first line of defense, and is able to recognize invading microorganisms as non-self, triggering immune responses to eliminate them. In addition to the innate immunity, adaptive immunity cells and characteristic cytokines have been described as important players in the periodontal disease pathogenesis scenario, with a special attention to CD4⁺ T-cells (T-helper cells). Interestingly, the T cell-mediated adaptive immunity development is highly dependent on innate immunity-associated antigen presenting cells, which after antigen capture undergo into a maturation process and migrate towards the lymph nodes, where they produce distinct patterns of cytokines that will contribute to the subsequent polarization and activation of specific T CD4+ lymphocytes. Skeletal homeostasis depends on a dynamic balance between the activities of the bone-forming osteoblasts (OBLs) and bone-resorbing osteoclasts (OCLs). This balance is tightly controlled by various regulatory systems, such as the endocrine system, and is influenced by the immune system, an osteoimmunological regulation depending on lymphocyte- and macrophage-derived cytokines. All these cytokines and inflammatory mediators are capable of acting alone or in concert, to stimulate periodontal breakdown and collagen destruction via tissue-derived matrix metalloproteinases, a characterization of the progression of periodontitis as a stage that presents a significantly host immune and inflammatory response to the microbial challenge that determine of susceptibility to develop the destructive/progressive periodontitis under the influence of multiple behavioral, environmental and genetic factors.

Exposure of periodontal ligament progenitor cells to lipopolysaccharide from Escherichia coli changes osteoblast differentiation pattern

Periodontal ligament mesenchymal stem cells (PDLMSCs) are an important alternative source of adult stem cells and may be applied for periodontal tissue regeneration, neuroregenerative medicine, and heart valve tissue engineering. However, little is known about the impact of bacterial toxins on the biological properties of PDLSMSCs, including self-renewal, differentiation, and synthesis of extracellular matrix.

Hypoxia augments lipopolysaccharide-induced cytokine expression in periodontal ligament cells

Periodontitis is a chronic inflammatory disease characterized by the destruction of tooth supporting tissues. Hypoxia, the mainly changes of the plateau environment, can induce severe periodontitis by animal experiments. There is, however, very little information on hypoxia and lipopolysaccharide (LPS) induced cytokine expression in periodontal ligament (PDL) cells. In this article, we characterized hypoxia or P. gingivalis lipopolysaccharide (Pg LPS) induced tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 expression by human periodontal ligament (hPDL) cells. We found that hypoxia augmented Pg LPS induced TNF-α, IL-1β, and IL-6 expression in hPDL cells. We also demonstrated that nuclear factor kappa B pathway was involved in hypoxia augmenting Pg LPS induced cytokine expression in hPDL cells. Thus, our results suggest that the hypoxic environment may enhance the immune function of hPDL cells that is induced by Pg LPS.

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.

Biomechanical force induces the growth factor production in human periodontal ligament-derived cells

Although many reports have been published on the functional roles of periodontal ligament (PDL) cells, the mechanisms involved in the maintenance and homeostasis of PDL have not been determined. We investigated the effects of biomechanical force on growth factor production, phosphorylation of MAPKs, and intracellular transduction pathways for growth factor production in human periodontal ligament (hPDL) cells using MAPK inhibitors. hPDL cells were exposed to mechanical force (6 MPa) using a hydrostatic pressure apparatus. The levels of growth factor mRNA and protein were examined by real-time RT-PCR and ELISA. The phosphorylation of MAPKs was measured using BD™ CBA Flex Set. In addition, MAPKs inhibitors were used to identify specific signal transduction pathways. Application of biomechanical force (equivalent to occlusal force) increased the synthesis of VEGF-A, FGF-2, and NGF. The application of biomechanical force increased the expression levels of phosphorylated ERK and p38, but not of JNK. Furthermore, the levels of VEGF-A and NGF expression were suppressed by ERK or p38 inhibitor. The growth factors induced by biomechanical force may play a role in the mechanisms of homeostasis of PDL.

Relationship between gingival inflammation and pregnancy

An increase in the prevalence and severity of gingival inflammation during pregnancy has been reported since the 1960s. Though the etiology is not fully known, it is believed that increasing plasma sex steroid hormone levels during pregnancy have a dramatic effect on the periodontium. Current works of research have shown that estrogen and progesterone increasing during pregnancy are supposed to be responsible for gingivitis progression. This review is focused not only on epidemiological studies, but also on the effects of progesterone and estrogen on the change of subgingival microbiota and immunologic physiological mediators in periodontal tissue (gingiva and periodontal ligament), which provides current information about the effects of pregnancy on gingival inflammation.

Role of periodontal ligament fibroblasts in osteoclastogenesis: a review

During the last decade it has become clear that periodontal ligament fibroblasts may contribute to the in vitro differentiation of osteoclasts. We surveyed the current findings regarding their osteoclastogenesis potential. Periodontal ligament fibroblasts have the capacity to select and attract osteoclast precursors and subsequently to retract and enable migration of osteoclast precursors to the bone surface. There, fusion of precursors takes place, giving rise to osteoclasts. The RANKL-RANK-osteoprotegerin (OPG) axis is considered crucial in this process. Periodontal ligament fibroblasts produce primarily OPG, an osteoclastogenesis-inhibitory molecule. However, they may be influenced in vivo by direct or indirect interactions with bacteria or by mechanical loading. Incubation of periodontal ligament fibroblasts with bacteria or bacterial components causes an increased expression of RANKL and other osteoclastogenesis-stimulating molecules, such as tumor necrosis factor-α and macrophage-colony stimulating factor. Similar results are observed after the application of mechanical loading to these fibroblasts. Periodontal ligament fibroblasts may be considered to play an important role in the remodelling of alveolar bone. In vitro experiments have demonstrated that periodontal ligament fibroblasts adapt to bacterial and mechanical stimuli by synthesizing higher levels of osteoclastogenesis-stimulating molecules. Therefore, they probably contribute to the enhanced osteoclast formation observed during periodontitis and to orthodontic tooth movement.

A challenge with Porphyromonas gingivalis differentially affects the osteoclastogenesis potential of periodontal ligament fibroblasts from periodontitis patients and non-periodontitis donors

AIM

Porphyromonas gingivalis (Pg) may cause an immune-inflammatory response in host cells leading to bone degradation by osteoclasts. We investigated the osteoclast-inducing capacity of periodontal ligament fibroblasts from periodontitis patients and non-periodontitis donors after a challenge with viable Pg.

MATERIALS AND METHODS

PDLFs from periodontitis patients (n = 8) and non-periodontitis donors (n = 7) were incubated for 6 h with or without viable Pg and subsequently co-cultured with osteoclast precursors from peripheral blood mononuclear cells (PBMCs). The number of multinucleated tartrate-resistant acid phosphatase-positive cells was determined at 21 days. Expression of osteoclastogenesis-associated genes was assessed after infection of PDLFs mono-cultures and in PDLFs-PBMCs co-cultures. Resorption activity was analysed on bone slices.

RESULTS

Pg induced the expression of osteoclastogenesis-associated genes by PDLFs. After bacterial challenge the formation of osteoclast-like cell was decreased in co-cultures of PBMCs with non-periodontitis PDLFs, but not with PDLFs from periodontitis patients.

CONCLUSION

PDLFs from sites free of periodontitis respond to an infection with Pg by tempering formation of osteoclast-like cells, probably promoting clearance of the infection. PDLFs from periodontitis sites are desensitized to a Pg challenge in terms of their osteoclast-inducing capacity.

Endothelin-1 stimulates proinflammatory cytokine expression in human periodontal ligament cells via mitogen-activated protein kinase pathway

BACKGROUND

Endothelin-1 (ET-1) is a 21-amino acid peptide with multifunctional regulation. Initial research indicated that ET-1 is related to the inflammatory pathogenesis of periodontitis and involved in the regulation of cytokines, but the mechanisms involved remain unclear. The primary aim of this study is to investigate how ET-1 affects proinflammatory cytokine expression in human periodontal ligament (hPDL) cells.

METHODS

hPDL cells were obtained from both healthy (H)- and periodontitis (P)-affected periodontal tissues. H-hPDL and P-hPDL cells were treated with ET-1 (1, 10, and 100 nM) for 12, 24, and 48 hours. The untreated cells served as a control. To confirm the specificity of the ET-1 effects, 100 nM of the specific endothelin A (ETA) receptor antagonist BQ123 and 100 nM of the specific ETB receptor antagonist BQ788, as negative control, were used. To examine the signaling pathways and molecular mechanisms involved in ET-1-mediated cytokine expression, H-hPDL and P-hPDL cells were pretreated with specific inhibitors for extracellular signal-regulated kinase (ERK1/2) (PD98059), c-Jun N-terminal kinase (SP600125), and p38 kinase (SB203580) for 1 hour before 100 nM ET-1 stimulation. Tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 messenger RNA (mRNA) and protein levels were evaluated by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively.

RESULTS

ET-1 dose- and time-dependently induced the production of proinflammatory cytokines TNF-α, IL-1β, and IL-6 by H-hPDL and P-hPDL cells at both mRNA and protein levels. However, ETA and ETB receptor antagonists inhibited the stimulatory effects of ET-1 on inflammatory cytokine expression in H-hPDL and P-hPDL cells. Furthermore, inhibitors of the mitogen-activated protein kinases (MAPKs) significantly reduced ET-1-stimulated TNF-α, IL-1β, and IL-6 expression in H-hPDL and P-hPDL cells.

CONCLUSION

ET-1 may be involved in the inflammatory process of periodontitis, at least in part, by stimulating proinflammatory cytokine production via the MAPK pathway in hPDL cells.

β-cryptoxanthin regulates bone resorption related-cytokine production in human periodontal ligament cells

OBJECTIVE

β-cryptoxanthin (β-cry) is a type of carotenoid found in certain fruits and vegetables. Although it has been shown that β-cry inhibits alveolar bone resorption, the molecular mechanisms for this have not yet been clarified. In the present study, we investigated the effects of β-cry on bone resorption related-cytokine production in human periodontal ligament (hPDL) cells.

DESIGN

hPDL cells were stimulated with β-cry (1×10(-7)mol/l), mechanical stress (1 or 6MPa), and P. gingivalis. The production of interleukin (IL)-1β, IL-6, IL-8, tumour necrosis factor (TNF)-α, osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL) were analyzed by RT-PCR and ELISA.

RESULTS

The production of IL-1β, IL-6, IL-8, and TNF-α was not induced in hPDL cells after stimulation with β-cry, although these cytokines were produced after stimulation with P. gingivalis. On the other hand, IL-6 and IL-8 were produced after exposure to 6MPa of mechanical stress. The production of IL-6 and IL-8 was significantly decreased by the addition of β-cry. Furthermore, β-cry up-regulated the production of OPG, but not RANKL.

CONCLUSION

β-cry inhibited the production of IL-6 and IL-8 induced by mechanical stress and periodontopathogenic bacteria in hPDL cells. Moreover, β-cry up-regulated OPG production. These results suggest that β-cry may prevent bone resorption in periodontitis.