Inflammation–regeneration interplay in the dentine–pulp complex

The effect of chlormadinone acetate on odontogenic differentiation of human dental pulp cells: in vitro study

Background

Chlormadinone acetate (CMA) is a derivative of progesterone and is used as an oral contraceptive. The aim of this study was to investigate the effects of CMA on odontogenic differentiation and mineralization of human dental pulp cells (hDPCs) and related signaling pathways.

Methods

Cell viability was determined by the water-soluble tetrazolium (WST)-1 assay. Odontogenic differentiation of hDPCs was evaluated by real-time polymerase chain reaction using odontogenic marker genes, such as alkaline phosphatase (ALP), osteocalcin (OCN), dentin sialophosphoprotein (DSPP), and dentin matrix protein-1 (DMP-1). Mineralization of hDPCs was evaluated by ALP staining and alizarin red staining. The extracellular signal-regulated kinase (ERK) pathway was examined by Western blot analysis.

Results

There was no statistically significant difference in cell viability between the control and CMA-treated groups. Our analysis of odontogenic marker genes indicated that CMA enhanced the expression of those genes. CMA-treated hDPCs showed increased ALP activity and formation of mineralized nodules, compared with control-treated cells. In addition, CMA stimulation resulted in phosphorylation of ERK and resulted in inhibition of downstream molecules by the ERK inhibitor U0126.

Conclusions

These findings suggest that CMA improves odontogenic differentiation and mineralization of hDPCs through the ERK signaling pathway.

IFN-γ regulates human dental pulp stem cells behavior via NF-κB and MAPK signaling

During caries, dental pulp expresses a range of pro-inflammatory cytokines in response to the infectious challenge. Interferon gamma (IFN-γ) is a dimerized soluble cytokine, which is critical for immune responses. Previous study has demonstrated that IFN-γ at relative high concentration (100 ng/mL) treatment improved the impaired dentinogenic and immunosuppressive regulatory functions of disease-derived dental pulp stem cells (DPSCs). However, little is known about the regulatory effects of IFN-γ at relative low concentration on healthy DPSC behavior (including proliferation, migration, and multiple-potential differentiation). Here we demonstrate that IFN-γ at relatively low concentrations (0.5 ng/mL) promoted the proliferation and migration of DPSCs, but abrogated odonto/osteogenic differentiation. Additionally, we identified that NF-κB and MAPK signaling pathways are both involved in the process of IFN-γ-regulated odonto/osteogenic differentiation of DPSCs. DPSCs treated with IFN-γ and supplemented with pyrrolidine dithiocarbamate (PDTC, an NF-κB inhibitor) or SB203580 (a MAPK inhibitor) showed significantly improved potential for odonto/osteogenic differentiation of DPSCs both in vivo and in vitro. These data provide important insight into the regulatory effects of IFN-γ on the biological behavior of DPSCs and indicate a promising therapeutic strategy for dentin/pulp tissue engineering in future endodontic treatment.

Effect of Low-Intensity Pulsed Ultrasound on a Rat Model of Dentin-Dental Pulp Injury and Repair

This study investigated histopathologic changes in dental pulp after treatment with low-intensity pulsed ultrasound (LIPUS). Fifty rats were randomly divided into an experimental group (n = 25) and a blank control group (n = 25). In the experimental group, a cavity was prepared in the bilateral maxillary first molars. The upper right first molars were stimulated with LIPUS (30 mW/cm², 1.5 MHz) for 20 min/d. The cavities prepared in the left teeth were used as experimental controls (i.e., no LIPUS). Five rats in each group were sacrificed at days 1, 3, 5, 7 and 14. Inflammatory response was visible at different time points after cavity preparation, peaking at day 3, after which it gradually weakened. More reparative dentin was found on the LIPUS treatment side. transforming growth factor-β1 expression increased after treatment, peaking at day 5 and returning to normal at day 14 on both sides, but was stronger with LIPUS treatment. SMAD2 and SMAD3 expressions in the dental pulp gradually increased after cavity preparation, especially in the experimental group. LIPUS promoted the repair of dentin-pulp complex injury, to a certain extent and should be investigated further as a potential therapy.

TNF-alpha stimulation increases dental pulp stem cell migration in vitro through integrin alpha-6 subunit upregulation

OBJECTIVE

The dissemination of stem cells into tissues requiring inflammatory and reparative response is fundamentally dependent upon their chemotactic migration. Expression of TNF-α is up regulated in inflamed pulps. Dental pulp cells are also known to express integrin α6 subunit. Expression of integrin subunit α6 has been linked to the acquisition of migratory potential in a wide variety of cell types in both pathological and physiological capacities. Therefore, in this study we examined the effects of a pleiotropic cytokine TNF-α on the migration of hDPSCs and investigated its relationship with expression of integrin α6 in hDPSCs during chemotactic migration.

DESIGN

hDPSC cultures were established. Protein expression profile of α6 integrin subunit was determined. Effect of exogenous TNF-α (50ng/mL) on hDPSCs' migration potential was evaluated by transwell inserts and in vitro scratch assay. Upregulation/downregulation of TNF-α mediated migration was assayed in presence/absence of integrin α6 respectively. To suppress integrin α6 expression, cells were transfected with integrin α6 siRNA and then cell migration and cytoskeletal changes were evaluated.

RESULTS

Our results showed significant increase of hDPSCs' migration after stimulation with TNF-α. By knockdown of integrin α6, which is upregulated by TNF-α, we observed a decrease in the TNF-α directed chemotaxis of hDPSCs.

CONCLUSION

In this study, we show that activation of integrin α6 brought about by TNF-α led to an increase in migratory activity in DPSCs in vitro thus describing a novel association between a cytokine TNF-α and α6 chain of an adhesion receptor integrin in regulating migration of hDPSCs.

Water-soluble egg membrane enhances the immunoactivating properties of an Aloe vera-based extract of Nerium oleander leaves

Objective

To evaluate a blend of two natural ingredients on immune parameters relevant for their current topical use and potential support of microcirculation in skin tissue.

Materials and methods

A blend (BL) of Aloe vera-based Nerium oleander extract (NAE-8i, oleandrin-free) and hydrolyzed water-soluble egg membrane (WSEM) was applied to human whole-blood cultures for 24 hours, with each separate ingredient serving as a control. Immune-cell subsets were analyzed for expression levels of the activation markers CD69 and CD25. Culture supernatants were analyzed for cytokines, chemokines, and immunoregulating peptides.

Results

BL increased CD69 expression on lymphocytes, monocytes, and CD3^–CD56⁺ natural killer cells, and CD25 expression on natural killer cells. The number of CD69⁺CD25⁺ lymphocytes increased in cultures treated with BL and the separate ingredients. BL triggered production of multiple cytokines and chemokines, where CC chemokines MIP1α and MIP3α, as well as cytokines involved in wound healing – Groα, Groβ, ENA78, and fractalkine – reached levels manyfold above treatment with either NAE-8i or WSEM alone.

Conclusion

Data on BL showed that WSEM strongly enhanced NAE-8i’s effects on immunoactivation in vitro. This has potential relevance for support of immunity in skin tissue, including antibacterial and antiviral defense mechanisms, wrinkle reduction, and wound care.

Dose-response and time-course of α-tocoferol mediating the cytoprotection of dental pulp cells against hydrogen peroxide

This in vitro study evaluated the potential protective effect of vitamin E alpha-tocopherol (α-T) isomer against the toxicity of hydrogen peroxide (HP) applied on dental pulp cells. Odontoblast-like MDPC-23 cells were seeded on 96-well plates for 72 h, treated with different concentrations of α-T (1, 3, 5, and 10 mM) for different times (1, 4, 8, and 24 h) and then exposed or not to a 0.018% HP solution for 30 min. In positive and negative control groups, cells were exposed to HP or culture medium (DMEM containing 5% DMSO), respectively. Cell viability was assessed by the MTT assay and the absorbance numeric data, expressed as percentage values, were subjected to the statistical analysis by Kruskal-Wallis and Mann-Whitney tests (α=5%). Considering the cells in the negative control as having 100% of cell viability, all combinations of α-T concentrations and pretreatment times showed a protective effect against HP cytotoxicity. Significant reduction of cell viability (59%) was observed in the positive control compared with the negative control. The highest values of pulp cell viability were obtained after pretreatment with 1 and 3 mM α-T concentrations for 24 h followed by exposure to HP (126% and 97% of cell viability, respectively). Under the tested conditions, the most effective cell protection against the cytotoxic effects of HP was provided by the lowest concentrations of α-T (1 and 3 mM) applied for 24 h.

Antibacterial activity of a modified unfilled resin containing a novel polymerizable quaternary ammonium salt MAE-HB

Resins with strong and long-lasting antibacterial properties are critical for the prevention of secondary dental caries. In this study, we evaluated the antibacterial effect and the underlying mechanism of action of an unfilled resin incorporating 2-methacryloxylethyl hexadecyl methyl ammonium bromide (MAE-HB) against Streptococcus mutans UA159 (S. mutans UA159). MAE-HB was added into unfilled resin at 10 mass%, and unfilled resin without MAE-HB served as the control. Bacterial growth was inhibited on 10%-MAE-HB unfilled resin compared with the control at 1 d, 7 d, 30 d, or 180 d (P < 0.05). The growth inhibitory effect was independent of the incubation time (P > 0.05). No significant differences in the antibacterial activities of eluents from control versus 10%-MAE-HB unfilled resins were observed at any time point (P > 0.05). The number of bacteria attached to 10%-MAE-HB unfilled resin was considerably lower than that to control. Fe-SEM and CLSM showed that 10%-MAE-HB unfilled resin disturbed the integrity of bacterial cells. Expression of the bacterial glucosyltransferases, gtfB and gtfC, was lower on 10%-MAE-HB unfilled resin compared to that on control (P < 0.05). These data indicate that incorporation of MAE-HB confers unfilled resin with strong and long-lasting antibacterial effects against S. mutans.

Scaffolds to control inflammation and facilitate dental pulp regeneration

In dentistry, the maintenance of a vital dental pulp is of paramount importance because teeth devitalized by root canal treatment may become more brittle and prone to structural failure over time. Advanced carious lesions can irreversibly damage the dental pulp by propagating a sustained inflammatory response throughout the tissue. Although the inflammatory response initially drives tissue repair, sustained inflammation has an enormously destructive effect on the vital pulp, eventually leading to total necrosis of the tissue and necessitating its removal. The implications of tooth devitalization have driven significant interest in the development of bioactive materials that facilitate the regeneration of damaged pulp tissues by harnessing the capacity of the dental pulp for self-repair. In considering the process by which pulpitis drives tissue destruction, it is clear that an important step in supporting the regeneration of pulpal tissues is the attenuation of inflammation. Macrophages, key mediators of the immune response, may play a critical role in the resolution of pulpitis because of their ability to switch to a proresolution phenotype. This process can be driven by the resolvins, a family of molecules derived from fatty acids that show great promise as therapeutic agents. In this review, we outline the importance of preserving the capacity of the dental pulp to self-repair through the rapid attenuation of inflammation. Potential treatment modalities, such as shifting macrophages to a proresolving phenotype with resolvins are described, and a range of materials known to support the regeneration of dental pulp are presented.

DPSCs from Inflamed Pulp Modulate Macrophage Function via the TNF-α/IDO Axis

Human dental pulp stem cells (DPSCs) can be isolated from inflamed pulp derived from carious teeth with symptomatic irreversible pulpitis (I-DPSCs), which possess stemness and multidifferentiation potentials similar to DPSCs from healthy pulp. Since macrophages-essential cell players of the pulpal innate immunity-can regulate pulpal inflammation and repair, the authors investigated the immunomodulatory effects of DPSCs/I-DPSCs on macrophage functions and their underlying mechanisms. Similar to DPSCs, I-DPSCs were capable of colony-forming efficiency and adipogenic and osteo/dentinogenic differentiation under in vitro induction conditions. I-DPSCs also expressed a similar phenotypic profile of mesenchymal stem cell markers, except a relatively higher level of CD146 as compared with DPSCs. Coculture of DPSCs or I-DPSCs with differentiated THP-1 cells, the human monocyte cell line, markedly suppressed tumor necrosis factor α (TNF-α) secretion in response to stimulation with lipopolysaccharides (LPS) and/or nigericin. However, unlike TNF-α, the secreted level of interleukin 1β was not affected by coculture with DPSCs or I-DPSCs. Furthermore, DPSC/I-DPSC-mediated inhibition of TNF-α secretion by macrophages was abolished by pretreatment with 1-methyl-D-tryptophan, a specific inhibitor of indoleamine-pyrrole 2,3-dioxygenase (IDO), but not by NSC-398, a specific inhibitor of COX-2, suggesting IDO as a mediator. Interestingly, IDO expression was significantly augmented in macrophages and mesenchymal stromal cells in inflamed human pulp tissues. Collectively, these findings show that I-DPSCs, similar to DPSCs, possess stem cell properties and suppress macrophage functions via the TNF-α/IDO axis, thereby providing a physiologically relevant context for their innate immunomodulatory activity in the dental pulp and their capability for pulp repair.

Angiogenic mechanisms of human dental pulp and their relationship with substance P expression in response to occlusal trauma

Angiogenesis is the formation of new blood vessels based on a pre-existing vasculature. It comprises two processes, sprouting of endothelial cells and the division of vessels due to abnormal growth of the microvasculature. It has been demonstrated that substance P (SP) can induce angiogenesis either by modulating endothelial cell growth (direct mechanism) or by attracting cells with angiogenic potential to the injury site (indirect mechanism). Therefore, the purpose of this article is to review the angiogenic mechanisms that regulate mineralized tissue formation in human dental pulp tissue and their relationship with SP expression as a defence response to stimuli such as the masticatory function and occlusal trauma. Articles included in this review were searched in PubMed, Scopus and ISI Web of Science databases, combining the following keywords: human dentine pulp, angiogenesis, angiogenic growth factors, neuropeptides, substance P, neurogenic inflammation, dentine matrix, dentinogenesis, occlusal trauma and dental occlusion. It is concluded that human dental pulp tissue responds to occlusal trauma and masticatory function with a neurogenic inflammatory phenomenon in which SP plays an important role in the direct and indirect mechanisms of angiogenesis by the action evoked via NK1 receptors at different cells, such as fibroblasts, endothelial and inflammatory cells, leading to new blood vessel formation which are needed to stimulate mineralized tissue formation as a defence mechanism.

Epigenetic regulation in dental pulp inflammation

Dental caries, trauma, and other possible factors could lead to injury of the dental pulp. Dental infection could result in immune and inflammatory responses mediated by molecular and cellular events and tissue breakdown. The inflammatory response of dental pulp could be regulated by genetic and epigenetic events. Epigenetic modifications play a fundamental role in gene expression. The epigenetic events might play critical roles in the inflammatory process of dental pulp injury. Major epigenetic events include methylation and acetylation of histones and regulatory factors, DNA methylation, and small non-coding RNAs. Infections and other environmental factors have profound effects on epigenetic modifications and trigger diseases. Despite growing evidences of literatures addressing the role of epigenetics in the field of medicine and biology, very little is known about the epigenetic pathways involved in dental pulp inflammation. This review summarized the current knowledge about epigenetic mechanisms during dental pulp inflammation. Progress in studies of epigenetic alterations during inflammatory response would provide opportunities for the development of efficient medications of epigenetic therapy for pulpitis.

Comparative evaluation of platelet-rich fibrin, mineral trioxide aggregate, and calcium hydroxide as pulpotomy agents in permanent molars with irreversible pulpitis: A randomized controlled trial

Background:

Pulpotomy has been proposed as an alternative for the management of irreversible pulpitis in permanent molars with closed apices.

Aim:

To compare the performances of calcium hydroxide (CH), mineral trioxide aggregate (MTA), and platelet-rich fibrin (PRF) as pulpotomy agents in mature permanent molars with irreversible pulpitis.

Materials and Methods:

Fifty-four permanent mandibular molars with carious exposure and symptoms of irreversible pulpitis were randomly allocated to three groups, and full pulpotomy was performed using CH_, MTA, or PRF as pulpotomy agents. Pain intensity was recorded using numeric rating scale score at baseline, 24 h, 7 days, 6 months, and 1 year. Clinical and radiographic assessments were done at 6 months and 1 year.

Statistical Analysis:

Kruskal–Wallis test and Friedman test were used for intergroup and intragroup comparison of pain scores, respectively. The radiographic outcomes between the three study arms were compared using Chi-square test.

Results:

Clinical success rate was 94.4% at 7 days, which dropped to 85.4% at 12 months. All three agents were equally effective in providing pain relief at all the intervals tested, with no significant difference between them (P > 0.05 at all intervals). However, at 6 months and 12 months, 26.2% and 52.4% teeth depicted slight widening of periodontal ligament space. No significant difference was observed between the radiographic success rates observed with the three groups (P = 0.135 at 6 months, 0.717 at 12 months).

Conclusion:

Pulpotomy exhibited a high clinical success rate in mature molars with irreversible pulpitis and selection of biomaterial did not affect its outcome.

Influence of Restoration Type on the Cytotoxicity of a 35% Hydrogen Peroxide Bleaching Gel

OBJECTIVES

The tooth/restoration interface may act as a pathway for hydrogen peroxide (H2O2) diffusion into the pulp chamber. Therefore, the influence of resin-modified glass ionomer cement (RMGIC) and resin composite simulated restorations on the cytotoxicity of an in-office bleaching gel was assessed in vitro.

MATERIALS AND METHODS

Cavities in enamel/dentin discs restored with RMGIC Vitremer (3M ESPE) or Single Bond/Filtek Z350 (3M ESPE) resin composite (RC) were subjected or not subjected to hydrolytic degradation (HD). A 35%-H2O2 bleaching gel was applied to simulated restored and nonrestored enamel surfaces, and culture medium in contact with the dentin substrate (extract) was collected and applied to MDPC-23 cells. Nonrestored discs subjected or not subjected to bleaching were used as positive and negative controls, respectively. Cell viability, oxidative stress, interleukin (IL)-1β expression, alkaline phosphatase (ALP) activity, and mineralized nodule deposition were evaluated. The H2O2 in the extracts was quantified. Data were subjected to statistical analysis.

RESULTS

Higher oxidative stress associated with reduced cell viability, ALP activity, and mineralized nodule deposition was observed for all bleached groups compared with the negative control group. The RMGIC/HD group, which presented the highest H2O2 diffusion, had the lowest values of cell viability, ALP activity, and mineralized nodule deposition, as well as significantly increased IL-1β expression.

CONCLUSIONS

Dental cavities restored with the RMGIC subjected to hydrolytic degradation allowed for more intense diffusion of H2O2 into the pulp chamber, intensifying the toxicity of a 35%-H2O2 bleaching gel to pulp cells.

Dental Pulp Defence and Repair Mechanisms in Dental Caries

Dental caries is a chronic infectious disease resulting from the penetration of oral bacteria into the enamel and dentin. Microorganisms subsequently trigger inflammatory responses in the dental pulp. These events can lead to pulp healing if the infection is not too severe following the removal of diseased enamel and dentin tissues and clinical restoration of the tooth. However, chronic inflammation often persists in the pulp despite treatment, inducing permanent loss of normal tissue and reducing innate repair capacities. For complete tooth healing the formation of a reactionary/reparative dentin barrier to distance and protect the pulp from infectious agents and restorative materials is required. Clinical and in vitro experimental data clearly indicate that dentin barrier formation only occurs when pulp inflammation and infection are minimised, thus enabling reestablishment of tissue homeostasis and health. Therefore, promoting the resolution of pulp inflammation may provide a valuable therapeutic opportunity to ensure the sustainability of dental treatments. This paper focusses on key cellular and molecular mechanisms involved in pulp responses to bacteria and in the pulpal transition between caries-induced inflammation and dentinogenic-based repair. We report, using selected examples, different strategies potentially used by odontoblasts and specialized immune cells to combat dentin-invading bacteria in vivo.

Chemokine expression of oral fibroblasts and epithelial cells in response to artificial saliva

OBJECTIVES

Artificial saliva is widely used to overcome reduced natural salivary flow. Natural saliva provokes the expression of chemokines in oral fibroblasts in vitro. However, if artificial saliva changes the expression of chemokines remains unknown.

MATERIALS AND METHODS

Here, we investigated the ability of Saliva Orthana®, Aldiamed®, Glandosane®, and Saliva Natura® to change the expression of chemokines in human oral fibroblasts and the human oral epithelial cell line HSC-2 by means of reverse transcription polymerase chain reaction and immunoassays. Mucins isolated from bovine submaxillary glands and recombinant human mucin 1 were included in the bioassay. Formazan formation and LIVE/DEAD® staining determined the impact of artificial saliva on cell viability. The involvement of signaling pathways was determined by pharmacologic inhibitors and Western blotting.

RESULTS

In gingival fibroblasts, Saliva Orthana®-containing mucins provoked a significantly increased expression of CXC ligand 8 (CXCL8, or interleukin 8), CXCL1, and CXCL2. Immunoassays for CXCL8 and CXCL1 confirmed the translation at the protein level. The respective dilution of artificial saliva had no impact on formazan formation and LIVE/DEAD® staining. Mucins isolated from bovine submaxillary glands also increased the panel of chemokine expression in gingival fibroblasts. BAY 11-7082, a nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) inhibitor, but also TAK-242, an inhibitor of toll-like receptor 4 signaling, blocked chemokine expression of Saliva Orthana® and bovine mucins. In HSC-2 cells, Glandosane® significantly increased CXCL8 expression.

CONCLUSIONS

Saliva Orthana® stimulated chemokine expression in gingival fibroblasts. Mammalian mucins, but also possible contaminations with endotoxins, might contribute to the respective changes in gene expression. Epithelial cells have a differential response to artificial saliva with Glandosane® changing CXCL8 expression.

CLINICAL RELEVANCE

Artificial saliva can incite a cellular response, if however the changing expression of chemokines by isolated fibroblasts and epithelial cells in vitro translates into a clinical condition, is not clear.

A comparison of the in vitro mineralisation and dentinogenic potential of mesenchymal stem cells derived from adipose tissue, bone marrow and dental pulp

Stem-cell-based therapies provide a biological basis for the regeneration of mineralised tissues. Stem cells isolated from adipose tissue (ADSCs), bone marrow (BMSCs) and dental pulp (DPSCs) have the capacity to form mineralised tissue. However, studies comparing the capacity of ADSCs with BMSCs and DPSCs for mineralised tissue engineering are lacking, and their ability to regenerate dental tissues has not been fully explored. Characterisation of the cells using fluorescence-activated cell sorting and semi-quantitative reverse transcription PCR for MSC markers indicated that they were immunophenotypically similar. Alizarin red (AR) staining and micro-computed tomography (µCT) analyses demonstrated that the osteogenic potential of DPSCs was significantly greater than that of BMSCs and ADSCs. Scanning electron microscopy and AR staining showed that the pattern of mineralisation in DPSC cultures differed from ADSCs and BMSCs, with DPSC cultures lacking defined mineralised nodules and instead forming a diffuse layer of low-density mineral. Dentine matrix components (DMCs) were used to promote dentinogenic differentiation. Their addition to cultures resulted in increased amounts of mineral deposited in all three cultures and significantly increased the density of mineral deposited in BMSC cultures, as determined by µCT analysis. Addition of DMCs also increased the relative gene expression levels of the dentinogenic markers dentine sialophosphoprotein and dentine matrix protein 1 in ADSC and BMSC cultures. In conclusion, DPSCs show the greatest potential to produce a comparatively high volume of mineralised matrix; however, both dentinogenesis and mineral volume was enhanced in ADSC and BMSC cultures by DMCs, suggesting that these cells show promise for regenerative dental therapies.

Interferon Gamma-treated Dental Pulp Stem Cells Promote Human Mesenchymal Stem Cell Migration In Vitro

INTRODUCTION

Chronic inflammation disrupts dental pulp regeneration by disintegrating the recruitment process of progenitors for repair. Bone marrow-derived mesenchymal stem cells (BM-MSCs) share the common features with dental pulp stem cells (DPSCs). The aim of the study was to investigate the migration of BM-MSCs toward DPSCs in response to inflammatory chemoattractants. Additionally, our studies also delineated the signaling mechanisms from BM-MSCs in mediating the proliferation and differentiation of DPSCs in vitro.

METHODS

Human DPSCs and BM-MSCs between passages 2 and 4 were used and were grown in odontogenic differentiation medium. Mineralization was determined by alizarin red staining analysis. Migration was assessed using crystal violet staining in cells grown in Boyden chamber Transwell inserts (Corning Inc Foundation, Tewksbury, MA). The mineralization potential of DPSCs was evaluated using alkaline phosphatase activity assay. Real-time polymerase chain reaction analysis was performed to assess the gene expression profile of chemokine (C-X-C motif) ligand (Cxcl) 3, 5, 6, 10, 11, 12, 14, and 16; stromal cell-derived factor (SDF) α; vascular endothelial growth factor; and fibroblast growth factor.

RESULTS

Interferon gamma (FN-γ) treatment significantly abrogated the differentiation potential of DPSCs as shown by using alizarin red and alkaline phosphatase activity analysis. An increase in the migration of BM-MSCs was documented when cocultured with IFN-γ-treated DPSCs. RNA expression studies showed an increase in the levels of Cxcl6 and Cxcl12 in BM-MSCs when cocultured with IFN-γ-treated DPSCs. Additionally, an up-regulation of proangiogenic factors vascular endothelial growth factor and fibroblast growth factor were observed in DPSCs exposed to IFN-γ.

CONCLUSIONS

Our findings indicate that inflamed IFN-γ-treated DPSCs release factors (presumably Cxcl6 and 12) that contribute to the homing of MSCs. This model might provide a potential research tool for studying MSC-DPSC cross talk and for future studies involving the recruitment and sustainability of progenitor stem cells sustaining the inflammatory cascade to treat pulp inflammation.

Elucidating the cellular actions of demineralised dentine matrix extract on a clonal dental pulp stem cell population in orchestrating dental tissue repair

Bioactive growth factors identified within the extracellular matrix of dentine have been proposed roles in regulating the naturally inherent regenerative dentine formation seen in teeth in response to trauma and infection, which may also be harnessed for novel clinical treatments in augmenting mineralised tissue repair. This study examined the specific biological action of demineralised dentine matrix extract on a clonal population of dental pulp stem cells in stimulating the prerequisite stages of wound healing associated with mineralised tissue repair. A clonal dental pulp stem cell population with sustained proliferative capacity and multi-potentiality towards osteogenic, adipogenic and chondrogenic lineages was isolated from the pulp of human third molars. Dentine was collected from human healthy teeth, powdered and treated with ethylenediaminetetraacetic acid to obtain a solubilised DDM protein extract. The influence of DDM on the DPSC clonal population was assessed in vitro. Exposure of cells to proteolytically degraded DDM or unsupplemented media served as controls. Compared to controls, DDM stimulated cell expansion, reduced apoptotic marker caspase 3, increased cell survival marker Akt1 and enhanced mineralised matrix deposition as determined by mineral deposition and increased expression of bone-related markers, alkaline phosphatase and osteopontin. Dental pulp stem cells successfully migrated into collagen gels supplemented with demineralised dentine matrix, with cells remaining viable and expanding in numbers over a 3-day period. Collectively, the results provide evidence that soluble proteins extracted from dentine matrix are able to exert a direct biological effect on dental pulp stem cells in promoting mineralised tissue repair mechanisms.

Activation of the Nrf2-regulated antioxidant cell response inhibits HEMA-induced oxidative stress and supports cell viability

Oxidative stress due to increased formation of reactive oxygen species (ROS) in target cells of dental resin monomers like 2-hydroxyethyl methacrylate (HEMA) is a major mechanism underlying the disturbance of vital cell functions including mineralization and differentiation, responses of the innate immune system, and the induction of cell death via apoptosis. Although a shift in the equilibrium between cell viability and apoptosis is related to the non-enzymatic antioxidant glutathione (GSH) in HEMA-exposed cells, the major mechanisms of adaptive antioxidant cell responses to maintain cellular redox homeostasis are still unknown. The present study provides insight into the induction of a communicating network of pathways under the control of the redox-sensitive transcription factor Nrf2, a major transcriptional activator of genes coding for enzymatic antioxidants. Here, oxidative stress was indicated by DCF fluorescence in cells after a short exposure (1 h) to HEMA, while DHR123 fluorescence significantly increased about 1.8-fold after a long exposure period (24 h) showing the formation of hydrogen peroxide (H2O2). The corresponding expression of Nrf2 was activated immediately after HEMA exposure (1 h) and remained constant up to 24 h. Nrf2-regulated expression of enzymes of the glutathione metabolism (glutathione peroxidase 1/2, glutathione reductase) decreased in HEMA-exposed cells as a result of GSH depletion, and superoxide dismutase expression was downregulated after H2O2 overproduction. However, the expression of Nrf2-controlled enzymatic antioxidants (catalase, peroxiredoxin, thioredoxin 1, thioredoxin reductase, heme oxygenase-1) and the NADPH-regenerating system (glucose 6-phosphate dehydrogenase, transaldolase) was increased. Phenolic tert-butylhydroquinone (tBHQ), a classic inducer of the Nrf2 pathway, reduced oxidative stress and protected cells from HEMA-induced cell death through a shift in the number of cells in necrosis to apoptosis. The expression of Nrf2 and related enzymatic antioxidants downstream was enhanced by tBHQ in parallel. In conclusion, this investigation expanded the detailed understanding of the underlying mechanisms of HEMA-induced oxidative stress, and highlighted the cross-talk and interdependence between various Nrf2-regulated antioxidant pathways as a major adaptive cell response. The current results demonstrate that modulation of the Nrf2-mediated cellular defense response is an effective means for manipulating the sensitivity of cells to dental resin monomers.

Stage-specific effects of fibroblast growth factor 2 on the differentiation of dental pulp cells

Dentinogenesis is a complex and multistep process, which is regulated by various growth factors, including members of the fibroblast growth factor (FGF) family. Both positive and negative effects of FGFs on dentinogenesis have been reported, but the underlying mechanisms of these conflicting results are still unclear. To gain a better insight into the role of FGF2 in dentinogenesis, we used dental pulp cells from various transgenic mice, in which fluorescent protein expression identifies cells at different stages of odontoblast differentiation. Our results showed that the continuous exposure of pulp cells to FGF2 inhibited mineralization and revealed both the stimulatory and inhibitory effects of FGF2 on the expression of markers of dentinogenesis and various transgenes. During the proliferation phase of in vitro growth, FGF2 increased the expression of markers of dentinogenesis and the percentages of dentin matrix protein 1/green fluorescent protein (DMP1-GFP)-positive functional odontoblasts and dentin sialophosphoprotein (DSPP)-Cerulean-positive odontoblasts. Additional exposure to FGF2 during the differentiation/mineralization phase of in vitro growth decreased the extent of mineralization and the expression of markers of dentinogenesis and of the DMP1-GFP and DSPP-Cerulean transgenes. Recovery experiments showed that the inhibitory effects of FGF2 on dentinogenesis were related to the blocking of the differentiation of cells into mature odontoblasts. These observations together showed the stage-specific effects of FGF2 on dentinogenesis by dental pulp cells, and they provide critical information for the development of improved treatments for vital pulp therapy and dentin regeneration.

Extracellular Signal-regulated Kinase Mitogen-activated Protein Kinase and Phosphatidylinositol 3-Kinase/Akt Signaling Are Required for Lipopolysaccharide-mediated Mineralization in Murine Odontoblast-like Cells

INTRODUCTION

Odontoblasts play an important role in post-developmental control of mineralization in response to external stimuli in the tooth. The present study investigated whether lipopolysaccharide (LPS), a major bacterial cell wall component, influenced mineralization in a murine odontoblast-like cell (OLC) line and the related intracellular signaling pathways involved.

METHODS

Alizarin red S staining was used to assess mineralized nodule formation in OLCs in response to LPS. The effects of LPS on gene expression of odontoblastic markers were investigated by using quantitative real-time reverse-transcriptase polymerase chain reaction. The potential involvement of toll-like receptor 4 (TLR4), nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK), or phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways in the mineralized nodule formation, and mRNA expression of several odontoblastic markers of OLCs induced by LPS was assessed by using alizarin red S staining and quantitative real-time reverse-transcriptase polymerase chain reaction. Moreover, LPS stimulation resulted in phosphorylation of protein that was determined by Western blot analysis.

RESULTS

OLCs showed reduced mineralized nodule formation and several odontoblastic markers expression in response to LPS exposure. Furthermore, inhibition of TLR4, extracellular signal-regulated kinase (ERK), and PI3K/Akt signaling noticeably antagonized LPS-mediated mineralization in OLCs. However, p38 MAPK, c-Jun N-terminal kinase, and NF-κB signaling inhibitors did not affect LPS-mediated mineralization in OLCs. Notably, LPS treatment resulted in a time-dependent phosphorylation of ERK and PI3K/Akt in OLCs, which was abrogated by their specific inhibitors.

CONCLUSIONS

LPS decreased mineralization in OLCs via TLR4, ERK MAPK, and PI3K/Akt signaling pathways, but not p38, c-Jun N-terminal kinase, or NF-κB signaling.

Activation of the NLRP3/caspase-1 inflammasome in human dental pulp tissue and human dental pulp fibroblasts

The NLRP3/caspase-1 inflammasome pathway plays an important role in cellular immune defence against bacterial infection; however, its function in human dental pulp tissue and human dental pulp fibroblasts remains poorly understood. We demonstrate that NLRP3 protein expression occurs to a greater extent in pulp tissue with irreversible pulpitis than in normal pulp tissue and in tissue with reversible pulpitis. Caspase-1 is present in its active (cleaved) form only in pulp tissue with irreversible pulpitis. NLRP3 and caspase-1 are expressed in the odontoblast layers in normal human dental pulp tissue, whereas in inflamed pulp tissue, the odontoblast layers are disrupted and dental pulp cells are positive for NLRP3 and caspase-1. Additionally, we investigate the role of the NLRP3/caspase-1 inflammasome pathway in human dental pulp fibroblasts and show that ATP activates the P2X7 receptor on the cell membrane triggering K(+) efflux and inducing the gradual recruitment of the membrane pore pannexin-1. Extracellular lipopolysaccharide is able to penetrate the cytosol and activate NLRP3. Furthermore, the low intracellular K(+) concentration in the cytosol triggers reactive oxygen species generation, which also induces the NLRP3 inflammasome. Thus, the NLRP3/caspase-1 pathway has a biological role in the innate immune response mounted by human dental pulp fibroblasts.

LPS promote the odontoblastic differentiation of human dental pulp stem cells via MAPK signaling pathway

Human dental pulp stem cells (hDPSCs) show significant potential for exploitation in novel regeneration strategies, although lack of understanding of their responses to bacterial challenge constrains their application. The present study aimed to investigate whether lipopolysaccharide (LPS), the major pathogenic factor of Gram-negative bacteria, regulates the differentiation of hDPSCs and which intracellular signaling pathways may be involved. LPS treatment significantly promoted the differentiation of hDPSCs demonstrable by increased mineralized nodule formation and mRNA expression of several odontoblastic markers in a dose-dependent manner. While inhibition of TLR4, p38, and ERK signaling markedly antagonized LPS-mediated differentiation of hDPSCs. The inhibition of JNK and NF-κB signaling had no detectable effect on LPS activation of hDPSCs. LPS stimulation resulted in phosphorylation of NF-κB p65, IκB-α, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) in DPSCs in a time-dependent manner, which was markedly suppressed by their specific inhibitors, respectively. Data demonstrated that LPS promoted odontoblastic differentiation of hDPSCs via TLR4, ERK, and P38 MAPK signaling pathways, but not NF-κB signaling.

Stimulation of EphB2/ephrin-B1 signalling by tumour necrosis factor alpha in human dental pulp stem cells

OBJECTIVES

The aim of this study was to investigate whether in vitro stimulation of dental pulp stem cells (DPSCs) by tumour necrosis factor alpha (TNF-α) would induce secretion of EphB2/ephrin-B1 signalling.

MATERIALS AND METHODS

Dental pulp stem cells isolated from human dental pulp were treated with TNF-α (5-100 ng/ml) over 2-48 h. EphB2/ephrin-B1 mRNA and protein levels were measured by real-time polymerase chain reaction (RT-PCR) and western blot analysis respectively. Additionally, DPSCs were pre-incubated with TNF-α receptor neutralizing antibodies or infected with nuclear factor-kappa B (NF-ĸB) inhibitor, p38 MAPK inhibitor, Jun N-terminal kinase (JNK) inhibitor and MEK inhibitor before TNF-α treatment. Results were analysed by one-way ANOVA.

RESULTS

Tumour necrosis factor alpha increased EphB2 mRNA expression in DPSCs at concentrations up to 20 ng/ml and ephrin-B1 at concentrations up to 40 ng/ml (P < 0.05). Its mRNA expression reached maximum at 24 h when treated with TNF-α at 20 ng/ml (P < 0.05). EphB2/ephrin-B1 protein expression levels were high at 16 and 24 h as shown by western blotting. Neutralizing antibodies for TNFR1/2 receptors down-regulated EphB2/ephrin-B1 mRNA expression (P < 0.05) and ephrin-B1 protein expression, but not EphB2 protein expression. JNK-inhibitor inhibited EphB2 mRNA expression only (P < 0.05).

CONCLUSIONS

EphB2/ephrin-B1 were invoked in DPSCs with TNF-α treatment via the JNK-dependent pathway, but not NF-ĸB, p38 MAPK or MEK signalling.

Indirect cytocompatibility of a low-concentration hydrogen peroxide bleaching gel to odontoblast-like cells

AIM

To assess the initial cytotoxicity and the late phenotype marker expression of odontoblast-like cells (MDPC-23) subjected to less aggressive in-office bleaching therapies.

METHODOLOGY

A 17.5% hydrogen peroxide (H2O2) gel was applied for 45, 15 or 5 min to enamel/dentine discs adapted to trans-wells positioned over cultured MDPC-23 cells. No treatment was performed on the negative control. Immediately after bleaching, the cell viability, gene expression of inflammatory mediators and quantification of H2O2 diffusion were evaluated. The ALP activity, DSPP and DMP-1 gene expression and mineralized nodule deposition (MND) were assessed at 7, 14 or 21 days post-bleaching and analysed statistically with Mann-Whitney U-tests (α = 5%).

RESULTS

H2O2 diffusion, proportional to treatment time, was observed in all bleached groups. Reductions of approximately 31%, 21% and 13% in cell viability were observed for the 45-, 15- and 5-min groups, respectively. This reduction was significant (P < 0.05) for the 45- and 15-min groups, which also presented significant (P < 0.05) over-expression of inflammatory mediators. The 45-min group was associated with significant (P < 0.05) reductions in DMP-1/DSPP expression at all periods, relative to control. The ALP activity and MND were reduced only in initial periods. The 15-min group had less intense reduction of all markers, with no difference to control at 21 days.

CONCLUSIONS

The 17.5% H2O2 applied to tooth specimens for 5 min caused no alteration in the odontoblast-like cells. When this gel was applied for 45 or 15 min, a slight cytotoxicity, associated with alterations in phenotypic markers, was observed. However, cells were able to recover their functions up to 21 days post-bleaching.

Immunohistochemical study of the inflammatory response of the dental pulp

Defense reactions of the dental pulp involve a variety of biological reactions, in which the immune system plays a very important role. The class II major histocompatibility complex (MHC) molecule expressing cells, termed dendritic cells and lymphocytes in human dental pulp are highly sensitive to exogenous antigenic stimuli. Their drastic changes in number and localization are induced by dental caries. This study investigated the responses of the immune system in two different clinical conditions: shallow and deep cavities. Cells were identified immunohistochemically by using the following monoclonal antibodies: HLA-DR, CD45RO and CD20. Initial pulpal response was characterized by a localized accumulation of HLA-DR antibody-positive cells in the pulp tissue beneath the dentinal tubules communicating with the caries lesion. In the pulp of progressed caries, a large number of HLA-DR-positive cells was observed with a marked increase of other kinds of immunocompetent cells. This might indicate the occurrence of antigen presentation locally in the pulp tissue, which is very important for the immune response. Results obtained in this study demonstrated that dental pulps respond to the progression of the carious lesion and cellular and humoral immune responses occur in the pulp tissue.

Effect of hydrogen-peroxide-mediated oxidative stress on human dental pulp cells

OBJECTIVES

To evaluate the effect of the oxidative stress on human dental pulp cells (HDPCs) promoted by toxic concentrations of hydrogen peroxide (H2O2) on its odontoblastic differentiation capability through time.

METHODS

HDPCs were exposed to two different concentrations of H2O2 (0.1 and 0.3μg/ml) for 30min. Thereafter, cell viability (MTT assay) and oxidative stress generation (H2DCFDA fluorescence assay) were immediately evaluated. Data were compared with those for alkaline phosphatase (ALP) activity (thymolphthalein assay) and mineralized nodule deposition (alizarin red) by HDPCs cultured for 7 days in osteogenic medium.

RESULTS

A significant reduction in cell viability and oxidative stress generation occurred in the H2O2-treated cells when compared with negative controls (no treatment), in a concentration-dependent fashion. Seven days after H2O2 treatment, the cells showed significant reduction in ALP activity compared with negative control and no mineralized nodule deposition.

CONCLUSION

Both concentrations of H2O2 were toxic to the cells, causing intense cellular oxidative stress, which interfered with the odontogenic differentiation capability of the HDPCs.

CLINICAL SIGNIFICANCE

The intense oxidative stress on HDPCs mediated by H2O2 at toxic concentrations promotes intense reduction on odontoblastic differentiation capability in a 7-day evaluation period, which may alter the initial pulp healing capability in the in vivo situation.

EZH2, a potential regulator of dental pulp inflammation and regeneration

INTRODUCTION

Dental pulp has limited capability to regenerate, which happens in the early stage of pulpitis. An ambiguous relationship exists; inflammation may impair or support pulp regeneration. Epigenetics, which is involved in cell proliferation and inflammation, could regulate human dental pulp cell (HDPCs) regeneration. The aim of this study was to determine the role of the epigenetic mark, enhancer of zeste homolog 2 (EZH2), in the inflammation, proliferation, and regeneration of dental pulp. We used trimethylated histone H3 lysine 27(H3K27me3) and its lysine demethylase 6B (KDM6B) to monitor functional effects of altered EZH2 levels.

METHODS

We detected epigenetic marks (EZH2, H3K27me3, and KDM6B) in pulp tissue by immunohistochemistry and immunofluorescence. EZH2 levels in HDPCs in inflammatory responses or differentiation were analyzed by quantitative polymerase chain reaction and Western blot. Quantitative polymerase chain reaction was used to assess the effects of EZH2 inhibition on interleukins in HDPCs upon tumor necrosis factor alpha stimulation. Cell proliferation was tested by cell counting kit-8, cell cycle, and apoptosis analysis. HDPC differentiation was investigated by quantitative polymerase chain reaction, alkaline phosphatase activity, and oil red O staining.

RESULTS

EZH2 and H3K27me3 were decreased, whereas KDM6B was increased in infected pulp tissue and cells, which were similar to HDPC differentiation. EZH2 inhibition suppressed IL-1b, IL-6, and IL-8 messenger RNA (mRNA) in HDPCs upon inflammatory stimuli and impeded HDPC proliferation by decreasing cell number, arresting cell cycle, and increasing apoptosis. Suppressed EZH2 impaired adipogenesis, peroxisome proliferator-activated receptor r (PPAR-r), and CCAAT-enhancer binding protein a (CEBP/a) mRNA in adipogenic induction while enhancing alkaline phosphatase activity, Osx, and bone sialoprotein (BSP) mRNA in mineralization induction of HDPCs.

CONCLUSIONS

EZH2 inhibited HDPC osteogenic differentiation while enhancing inflammatory response and proliferation, suggesting its role in pulp inflammation, proliferation, and regeneration.

Delivery of bioactive lipids from composite microgel-microsphere injectable scaffolds enhances stem cell recruitment and skeletal repair

In this study, a microgel composed of chitosan and inorganic phosphates was used to deliver poly(lactic-co-glycolic acid) (PLAGA) microspheres loaded with sphingolipid growth factor FTY720 to critical size cranial defects in Sprague Dawley rats. We show that sustained release of FTY720 from injected microspheres used alone or in combination with recombinant human bone morphogenic protein-2 (rhBMP2) improves defect vascularization and bone formation in the presence and absence of rhBMP2 as evaluated by quantitative microCT and histological measurements. Moreover, sustained delivery of FTY720 from PLAGA and local targeting of sphingosine 1-phosphate (S1P) receptors reduces CD45+ inflammatory cell infiltration, promotes endogenous recruitment of CD29+CD90+ bone progenitor cells and enhances the efficacy of rhBMP2 from chitosan microgels. Companion in vitro studies suggest that selective activation of sphingosine receptor subtype-3 (S1P3) via FTY720 treatment induces smad-1 phosphorylation in bone-marrow stromal cells. Additionally, FTY720 enhances stromal cell-derived factor-1 (SDF-1) mediated chemotaxis of CD90+CD11B-CD45- bone progenitor cells in vitro after stimulation with rhBMP2. We believe that use of such small molecule delivery formulations to recruit endogenous bone progenitors may be an attractive alternative to exogenous cell-based therapy.