Mechanical stress activates proinflammatory cytokines and antioxidant defense enzymes in human dental pulp cells

Evaluation of oxidative stress cycle in healthy and inflamed dental pulp tissue: a laboratory investigation

OBJECTIVES

The purpose of this study was to investigate the oxidative stress cycle consisting of reactive oxygen molecules (ROS), glutathione (GSH) and glutathione S-transferase (GST) in caries-related pulp inflammation.

METHODOLOGY

Fifty-four pulp tissue samples were collected from healthy donors with the diagnosis of reversible pulpitis, symptomatic irreversible pulpitis, and healthy pulp. Twelve pulp samples from each group were homogenized and total protein, ROS, GSH, and GST were measured by spectrophotometer. The remaining 6 samples from each group were prepared for paraffin block and used for the histopathologic and immunohistochemical evaluation of oxidative stress parameters and TUNEL labeling. Data were analyzed statistically.

RESULTS

The results revealed that total protein levels significantly decreased; however, ROS levels increased in both reversible and irreversible pulpitis compared to the healthy pulp (p < 0.01). Also, as inflammation increases, GST enzyme levels decrease while GSH levels increase significantly (p < 0.05). It was found that the number of TUNEL (+) cells was increased in irreversible pulpitis samples compared to healthy and reversible pulpitis groups (p < 0.05). GSTP1 and GSH immunoreactivity were also observed in irreversible pulpitis samples.

CONCLUSIONS

It has been revealed that caries-related inflammation alters the oxidative stress cycle in dental pulp tissue. The increase in GSH levels in the inflamed dental pulp due to the increase in ROS levels may improve the defensive ability of the dental pulp.

CLINICAL RELEVANCE

There is a relationship between oxidative stress and inflammation. Control of excessive oxidative stress in pulpitis can stimulate reparative and regenerative processes. The present findings may provide an overview of the management of oxidative stress in cases with pulpitis during regenerative treatments.

Bioprinting-associated pulsatile hydrostatic pressure elicits a mild proinflammatory response in epi- and endothelial cells

During nozzle-based bioprinting, like inkjet and microextrusion, cells are subjected to hydrostatic pressure for up to several minutes. The modality of the bioprinting-related hydrostatic pressure is either constant or pulsatile depending on the technique. We hypothesized that the difference in the modality of hydrostatic pressure affects the biological response of the processed cells differently. To test this, we used a custom-made setup to apply either controlled constant or pulsatile hydrostatic pressure on endothelial and epithelial cells. Neither bioprinting procedure visibly altered the distribution of selected cytoskeletal filaments, cell-substrate adhesions, and cell-cell contacts in either cell type. In addition, pulsatile hydrostatic pressure led to an immediate increase of intracellular ATP in both cell types. However, the bioprinting-associated hydrostatic pressure triggered a pro-inflammatory response in only the endothelial cells, with an increase of interleukin 8 (IL-8) and a decrease of thrombomodulin (THBD) transcripts. These findings demonstrate that the settings adopted during nozzle-based bioprinting cause hydrostatic pressure that can trigger a pro-inflammatory response in different barrier-forming cell types. This response is cell-type and pressure-modality dependent. The immediate interaction of the printed cells with native tissue and the immune system in vivo might potentially trigger a cascade of events. Our findings, therefore, are of major relevance in particular for novel intra-operative, multicellular bioprinting approaches.

Effects of aging and inflammation on catalase activity in human dental pulp

OBJECTIVES

In this study, it was aimed to examine the catalase activity in clinically healthy and caries-related inflamed symptomatic human dental pulps of young and old individuals.

DESIGN

Sixty pulp samples from young and old healthy donors, were collected depending on pulpal status. 48 samples were used for spectrophotometric analysis and 12 samples for immunohistochemistry. Healthy pulps were maintained from non-carries, extracted third molars. Reversible and irreversible pulpitis samples were obtained by pulp extirpation during endodontic treatment. Following homogenization catalase enzyme activity was determined by spectrophotometry. Additionally, two pulp tissue samples from each group were fixed and evaluated for catalase immunoreactivity.

RESULTS

Catalase enzyme activity in old healthy pulp samples were significantly higher than healthy young samples (p ≤ 0.05). Reversible and irreversible pulpitis samples indicated significantly decreased activity compared to healthy samples in elderly group (p ≤ 0.05). Young reversible pulpitis samples showed significantly increased catalase activity when compared to irreversible pulpitis and the reversible pulpitis samples in elderly group (p ≤ 0.05). Immunohistochemical evaluation indicated that there was intense catalase immunoreactivity in young patients with reversible pulpitis compared with reversible pulpitis in elderly group. However, weak immunoreactivity was observed in young irreversible pulpitis and elderly reversible pulpitis samples.

CONCLUSIONS

The pulp tissues presented different levels of catalase activities against pulpitis and aging.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells (MSCs) have attracted intense interest in the field of dental tissue regeneration. Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures. MSCs possess distinct inherent properties of self-renewal, immunomodulation, proangiogenic potential, and multilineage potency, as well as being readily available and easy to culture. However, major issues, including poor engraftment and low survival rates in vivo, remain to be resolved before large-scale application is feasible in clinical treatments. Thus, some recent investigations have sought ways to optimize MSC functions in vitro and in vivo. Currently, priming culture conditions, pretreatment with mechanical and physical stimuli, preconditioning with cytokines and growth factors, and genetic modification of MSCs are considered to be the main strategies; all of which could contribute to improving MSC efficacy in dental regenerative medicine. Research in this field has made tremendous progress and continues to gather interest and stimulate innovation. In this review, we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration, antiapoptotic effect, proangiogenic potential, and regenerative properties. Challenges in current approaches associated with MSC modification and possible future solutions are also indicated. We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

Effect of 1-MHz ultrasound on the proinflammatory interleukin-6 secretion in human keratinocytes

Keratinocytes, the main cell type of the skin, are one of the most exposed cells to environmental factors, providing a first defence barrier for the host and actively participating in immune response. In fact, keratinocytes express pattern recognition receptors that interact with pathogen associated molecular patterns and damage associated molecular patterns, leading to the production of cytokines and chemokines, including interleukin (IL)-6. Herein, we investigated whether mechanical energy transported by low intensity ultrasound (US) could generate a mechanical stress able to induce the release of inflammatory cytokine such IL-6 in the human keratinocyte cell line, HaCaT. The extensive clinical application of US in both diagnosis and therapy suggests the need to better understand the related biological effects. Our results point out that US promotes the overexpression and secretion of IL-6, associated with the activation of nuclear factor-κB (NF-κB). Furthermore, we observed a reduced cell viability dependent on exposure parameters together with alterations in membrane permeability, paving the way for further investigating the molecular mechanisms related to US exposure.

The Role of Adipose Stem Cells in Bone Regeneration and Bone Tissue Engineering

Bone regeneration is a complex process that is influenced by tissue interactions, inflammatory responses, and progenitor cells. Diseases, lifestyle, or multiple trauma can disturb fracture healing, which might result in prolonged healing duration or even failure. The current gold standard therapy in these cases are bone grafts. However, they are associated with several disadvantages, e.g., donor site morbidity and availability of appropriate material. Bone tissue engineering has been proposed as a promising alternative. The success of bone-tissue engineering depends on the administered cells, osteogenic differentiation, and secretome. Different stem cell types offer advantages and drawbacks in this field, while adipose-derived stem or stromal cells (ASCs) are in particular promising. They show high osteogenic potential, osteoinductive ability, and immunomodulation properties. Furthermore, they can be harvested through a noninvasive process in high numbers. ASCs can be induced into osteogenic lineage through bioactive molecules, i.e., growth factors and cytokines. Moreover, their secretome, in particular extracellular vesicles, has been linked to fracture healing. The aim of this review is a comprehensive overview of ASCs for bone regeneration and bone tissue engineering.

Probing Osteocyte Functions in Gelatin Hydrogels with Tunable Viscoelasticity

Bone is an attractive site for metastatic cancer cells and has been considered as "soil" for promoting tumor growth. However, accumulating evidence suggests that some bone cells (e.g., osteocytes) can actually suppress cancer cell migration and invasion via direct cell-cell contact and/or through cytokine secretion. Toward designing a biomimetic niche for supporting 3D osteocyte culture, we present here a gelatin-based hydrogel system with independently tunable matrix stiffness and viscoelasticity. In particular, we synthesized a bifunctional macromer, gelatin-norbornene-boronic acid (i.e., GelNB-BA), for covalent cross-linking with multifunctional thiol linkers [e.g., four-arm poly(ethylene glycol)-thiol or PEG4SH] to form thiol-NB hydrogels. The immobilized BA moieties in the hydrogel readily formed reversible boronate ester bonds with 1,3-diols on physically entrapped poly(vinyl alcohol) (PVA). Adjusting the compositions of GelNB-BA, PEG4SH, and PVA afforded hydrogels with independently tunable elasticity and viscoelasticity. With this new dynamic hydrogel platform, we investigated matrix mechanics-induced growth and cytokine secretion of encapsulated MLO-A5 pre-osteocytes. We discovered that more compliant or viscoelastic gels promoted A5 cell growth. On the other hand, cells encapsulated in stiffer gels secreted higher amounts of pro-inflammatory cytokines and chemokines. Finally, conditioned media (CM) collected from the encapsulated MLO-A5 cells (i.e., A5-CM) strongly inhibited breast cancer cell proliferation, invasion, and expression of tumor-activating genes. This new biomimetic hydrogel platform not only serves as a versatile matrix for investigating mechano-sensing in osteocytes but also provides a means to produce powerful anti-tumor CM.

Tumor-initiating cells establish an IL-33-TGF-β niche signaling loop to promote cancer progression

Targeting the cross-talk between tumor-initiating cells (TICs) and the niche microenvironment is an attractive avenue for cancer therapy. We show here, using a mouse model of squamous cell carcinoma, that TICs play a crucial role in creating a niche microenvironment that is required for tumor progression and drug resistance. Antioxidant activity in TICs, mediated by the transcription factor NRF2, facilitates the release of a nuclear cytokine, interleukin-33 (IL-33). This cytokine promotes differentiation of macrophages that express the high-affinity immunoglobulin E receptor FcεRIα and are in close proximity to TICs. In turn, these IL-33-responding FcεRIα+ macrophages send paracrine transforming growth factor β (TGF-β) signals to TICs, inducing invasive and drug-resistant properties and further upregulating IL-33 expression. This TIC-driven, IL-33-TGF-β feedforward loop could potentially be exploited for cancer treatment.

Mechanical stress induced S100A7 expression in human dental pulp cells to augment osteoclast differentiation

OBJECTIVES

Mechanical injury of dental pulp leads to root resorption by osteoclasts/odontoclasts. S100 proteins have been demonstrated to be involved in inflammatory processes and bone remodeling. This study aimed to investigate the effect of mechanical stress on S100A7 expression by human dental pulp cells (HDPCs) and the effect of S100A7 proteins on osteoclast differentiation.

MATERIALS AND METHODS

Isolated HDPCs were stimulated with compressive loading (2 and 6 hr), or shear loading (2, 6, and 16 hr). S100 mRNA expression and S100A7 protein levels were determined by real-time PCR and ELISA, respectively. Osteoclast differentiation was analyzed using primary human monocytes. The differentiation and activity of osteoclasts were examined by TRAcP staining and dentine resorption. In addition, the expression of S100A7 was analyzed in pulp tissues obtained from orthodontically treated teeth.

RESULTS

Compressive and shear mechanical stress significantly upregulated both mRNA and protein level of S100A7. Dental pulp tissues from orthodontically treated teeth exhibited higher S100A7mRNA levels compared to non-treated control teeth. S100A7 promoted osteoclast differentiation by primary human monocytes. Moreover, S100A7 significantly enhanced dentine resorption by these cells.

CONCLUSIONS

Mechanical stress induced expression of S100A7 by human dental pulp cells and this may promote root resorption by inducing osteoclast differentiation and activity.

Dental Pulp Stem Cell Mechanoresponsiveness: Effects of Mechanical Stimuli on Dental Pulp Stem Cell Behavior

Dental pulp is known to be an accessible and important source of multipotent mesenchymal progenitor cells termed dental pulp stem cells (DPSCs). DPSCs can differentiate into odontoblast-like cells and maintain pulp homeostasis by the formation of new dentin which protects the underlying pulp. DPSCs similar to other mesenchymal stem cells (MSCs) reside in a niche, a complex microenvironment consisting of an extracellular matrix, other local cell types and biochemical stimuli that influence the decision between stem cell (SC) self-renewal and differentiation. In addition to biochemical factors, mechanical factors are increasingly recognized as key regulators in DPSC behavior and function. Thus, microenvironments can significantly influence the role and differentiation of DPSCs through a combination of factors which are biochemical, biomechanical and biophysical in nature. Under in vitro conditions, it has been shown that DPSCs are sensitive to different types of force, such as uniaxial mechanical stretch, cyclic tensile strain, pulsating fluid flow, low-intensity pulsed ultrasound as well as being responsive to biomechanical cues presented in the form of micro- and nano-scale surface topographies. To understand how DPSCs sense and respond to the mechanics of their microenvironments, it is essential to determine how these cells convert mechanical and physical stimuli into function, including lineage specification. This review therefore covers some aspects of DPSC mechanoresponsivity with an emphasis on the factors that influence their behavior. An in-depth understanding of the physical environment that influence DPSC fate is necessary to improve the outcome of their therapeutic application for tissue regeneration.

Mechanical stretch induces antioxidant responses and osteogenic differentiation in human mesenchymal stem cells through activation of the AMPK-SIRT1 signaling pathway

Mesenchymal stem cells (MSCs) are promising cell sources for regenerative medicine. Growing evidence has indicated that mechanical stimuli are crucial for their lineage-specific differentiation. However, the effect of mechanical loading on redox balance and the intracellular antioxidant system in MSCs was unknown. In this study, human bone marrow-derived MSCs (BM-MSCs) were subjected to cyclic stretch at the magnitude of 2.5%, 5%, and 10%. Cell proliferation, intracellular reactive oxygen species (ROS), expression of antioxidant enzymes, and osteogenic differentiation were evaluated. RNA was extracted and subjected to DNA microarray analysis. Sirtinol and compound C were used to investigate the underlying mechanisms involved silent information regulator type 1 (SIRT1) and AMP-activated protein kinase (AMPK). Our results showed that mechanical stretch at appropriate magnitudes increased cell proliferation, up-regulated extracellular matrix organization, and down-regulated matrix disassembly. After 3 days of stretch, intracellular ROS in BM-MSCs were decreased but the levels of antioxidant enzymes, especially superoxide dismutase 1 (SOD1), were up-regulated. Osteogenesis was improved by 5% stretch rather than 10% stretch, as evidenced by increased matrix mineralization and osteogenic marker gene expression. The expression of SIRT1 and phosphorylation of AMPK were enhanced by mechanical stretch; however, inhibition of SIRT1 or AMPK abrogated the stretch-induced antioxidant effect on BM-MSCs and inhibited the stretch-mediated osteogenic differentiation. Our findings reveal that mechanical stretch induced antioxidant responses, attenuated intracellular ROS, and improved osteogenesis of BM-MSCs. The stretch-induced antioxidant effect was through activation of the AMPK-SIRT1 signaling pathway. Our findings demonstrated that appropriate mechanical stimulation can improve MSC antioxidant functions and benefit bone regeneration.

Biological Activities and Potential Oral Applications of N-Acetylcysteine: Progress and Prospects

N-Acetylcysteine (NAC), a cysteine prodrug and glutathione (GSH) precursor, has been used for several decades in clinical therapeutic practices as a mucolytic agent and for the treatment of disorders associated with GSH deficiency. Other therapeutic activities of NAC include inhibition of inflammation/NF-κB signaling and expression of proinflammatory cytokines. N-Acetylcysteine is also a nonantibiotic compound possessing antimicrobial property and exerts anticarcinogenic and antimutagenic effects against certain types of cancer. Recently, studies describing potentially important biological and pharmacological activities of NAC have stimulated interests in using NAC-based therapeutics for oral health care. The present review focused on the biological activities of NAC and its potential oral applications. The potential side effects of NAC and formulations for drug delivery were also discussed, with the intent of advancing NAC-associated treatment modalities in oral medicine.

Antimicrobial effect and physicochemical properties of an adhesive system containing nanocapsules

OBJECTIVE

To incorporate indomethacin and triclosan-loaded nanocapsules into primer and adhesive, and evaluate its properties.

METHODS

Indomethacin and triclosan were encapsulated by deposition of preformed polymer and subsequently characterized regarding morphology, particle size, drug content and cytotoxicity. Nanocapsules (NCs) were incorporated into primer at 2% and into adhesive at 1, 2, 5, and 10% concentrations. Degree of conversion (DC) and softening in ethanol of the adhesive were evaluated. Drug release and drug diffusion through dentin was quantified by high performance liquid chromatography. Antimicrobial test was performed until 96h.

RESULTS

Spherical and biocompatible NCs presented mean size of 159nm. Drugs content was 3mg indomethacin/g powder and 2mg triclosan/g powder. Incorporating NCs in adhesive showed no influence in DC (p=0.335). The addition of 2% of NCs showed no influence in softening in ethanol (p>0.05). After 120h, 93% of indomethacin and 80% of triclosan were released from primer, 20% of indomethacin and 17% of triclosan were released from adhesive with 10% of NCs. Indomethacin showed diffusion through dentin. In 24h, adhesive containing 2 and 5% of NCs using primer with NCs showed antimicrobial effect. In 96h, adhesives containing different concentration of NCs promoted antimicrobial effect.

CONCLUSIONS

Indomethacin and triclosan-loaded nanocapsules were successfully incorporated into primer and adhesive, promoting controlled drugs release, indomethacin diffusion through dentin and antimicrobial effect without compromising its physicochemical properties.

SIGNIFICANCE

Indomethacin and triclosan-loaded nanocapsules have potential to prevent recurrent caries and to be used in deep cavities controlling pulpar inflammatory process.

Caspase-8 and Caspase-9 Functioned Differently at Different Stages of the Cyclic Stretch-Induced Apoptosis in Human Periodontal Ligament Cells

Background

Human periodontal ligament (PDL) cells underwent apoptosis after mechanical stretch loading. However, the exact signalling pathway remains unknown. This study aimed to elucidate how the apoptotic caspases functioned in the cyclic stretch-induced apoptosis in human PDL cells.

Materials and Methods

In the present study, 20% cyclic stretch was selected to load the cells for 6 or 24 h. The following parameters were analyzed: apoptotic rates, the protein levels of caspase-3, -7, -8 and -9 and the activities of caspase-8 and -9. Subsequently, the influences of caspase-8 and caspase-9 inhibitors on the apoptotic rate and the protein level of the activated caspase-3 were assessed as well.

Results

The apoptotic rates increased in response to cyclic stretch, but the cells entered different apoptotic stages after 6 and 24 h stretches. Caspase-3, -7, -8 and -9 were all activated after stretch loading. The stretch-induced apoptosis and the protein level of the activated caspase-3 were inhibited after inhibiting both caspase-8 and caspase-9 in both 6 and 24 h stretched cells and after inhibiting caspase-9 in 24 h stretched cells.

Conclusion

Caspase-8 and -9 functioned differently at different apoptotic stages in human PDL cells after cyclic stretch.

Co-Cr dental alloys induces cytotoxicity and inflammatory responses via activation of Nrf2/antioxidant signaling pathways in human gingival fibroblasts and osteoblasts

OBJECTIVE

Although cobalt-chromium (Co-Cr) dental alloys are routinely used in prosthodontics, the biocompatibility of Co-Cr alloys is controversial. The aims of the present study were to investigate the effects of Co-Cr alloys on human gingival fibroblasts (HGF) and osteoblasts in an in vitro model as well as their potential molecular mechanisms, focusing on NF-E2-related factor 2 (Nrf2) pathways.

METHODS

Cells were directly seeded on prepared Co-Cr alloy discs (15.0mm diameter, 1.0mm thickness) or indirectly treated with Co-Cr alloy located at the bottom of an insert well and incubated for 3 days. Cytotoxicity and reactive oxygen species (ROS) production was evaluated by MTS assay and flow cytometry, respectively. Protein and mRNA levels were determined by Western blotting and RT-PCR analysis, respectively.

RESULTS

Cell viability and flow cytometric assay demonstrated that the Co-Cr alloy was cytotoxic to HGFs and osteoblasts, and significantly increased ROS production. In addition, the Co-Cr alloys upregulated pro-inflamamtory cytokines (TNF-α, IL-1β, IL-6, and IL-8) and increased levels of various inflammatory mediators (iNOS derived nitrite oxide, and COX-2-derived PGE2) in both cells. A mechanistic study showed that Co-Cr alloys activates the NRF2 pathway and up-regulate antioxidant enzymes including heme oxygenase-1 (HO-1). Co-Cr alloys activated JAK2/STAT3, p38/ERK/JNK MAPKs and NF-κB signaling pathways. Furthermore, antioxidants (resveratrol and NAC) and HO-1 inhibitor (SnPP) significantly inhibited the production of ROS and inflammatory mediators, as well as the activation of NF-κB signaling in Co-Cr alloy stimulated HGFs and osteoblasts.

SIGNIFICANCE

This study is the first to show that Co-Cr alloys exert cytotoxic and inflammatory effects via activation of Nrf2/ARE signaling and up-regulation of downstream HO-1, which could represent candidate targets for the regulation of inflammatory responses to Co-Cr alloys.

Effect of indomethacin-loaded nanocapsules incorporation in a dentin adhesive resin

OBJECTIVES

The aim of this study was to produce indomethacin-loaded nanocapsules (IndOH-NCs) and evaluate the influence of their incorporation into an adhesive resin.

MATERIALS AND METHODS

Indomethacin was encapsulated by the deposition of preformed polymer. IndOH-NCs were characterized by laser diffractometry, Fourier transformed infrared spectrometry, transmission electron microscopy (TEM), scanning electron microscopy, high-performance liquid chromatography (HPLC), and MTT assay. Nanocapsules (NCs) were incorporated into an adhesive in concentrations of 1, 2, 5, and 10 %. The addition was visualized by TEM and drug release was evaluated by HPLC until 120 h of immersion in simulated body fluid (SBF). Drug diffusion through dentin was tested using a Franz diffusion cell apparatus and quantified by HPLC. The degree of conversion (DC), softening in ethanol, and microtensile bond strength (μTBS) were evaluated to determine whether the nanocapsules influenced the adhesive. Data were analyzed using one-way ANOVA and Tukey's post hoc test for DC, softening in ethanol, μTBS, and cytotoxicity, and paired t test for comparison between the initial and final Knoop microhardness.

RESULTS

IndOH-NCs, with a spherical shape and a mean diameter of 165 nm, were incorporated into an adhesive. Indomethacin content was 7 mg drug/g powder. IndOH-NCs maintained high cell viability. At 120 h, an amount of 13.83 % of indomethacin was released, and after 7 days, 7.07 % of this drug was diffused through dentin for an adhesive containing 10 % of nanocapsules. No alteration in the DC, softening in ethanol, and μTBS resulted from NC addition.

CONCLUSIONS

IndOH-NCs may be incorporated into adhesive systems, without compromising properties, to add an anti-inflammatory drug controlled release for restorative procedures in deep cavities.

CLINICAL SIGNIFICANCE

Here is the first step toward the goal of providing agents to act at an inflammatory process of pulp tissue through dental adhesives via encapsulation of drug.

P2X7 receptor-Pannexin1 interaction mediates stress-induced interleukin-1 beta expression in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Pannexin 1 (Panx1) has been found to form nonjunctional hemichannels. It is also proposed to combine with the P2X7 receptor, forming a complex involved in adenosine triphosphate (ATP)-induced interleukin-1beta (IL-1β) release in macrophages. Previously, we reported that mechanical stress induced IL-1β expression via the ATP/P2X7 receptor-dependent pathway in human periodontal ligament (HPDL) cells and that ATP was released through the connexin 43 (Cx43) hemichannel. In the present work, we examined the role of Panx1 in stress-induced IL-1β induction in HPDL cells.

MATERIAL AND METHODS

Cultured HPDL cells were treated with compressive loading or ATP to stimulate IL-1β expression. Inhibitors, antagonists and the small interfering RNA technique were used to investigate the involvement of Panx1 in IL-1β induction. Co-immunoprecipitation (Co-IP) and immunostaining were used to determine the association of Panx1 with the P2X7 receptor. The IL-1β release mechanism was analyzed using inhibitors.

RESULTS

Blocking Panx1 significantly decreased ATP release, as well as IL-1β up-regulation, upon stimulation with stress or ATP. Co-IP revealed the association of Panx1 and the P2X7 receptor in HPDL cells, which was increased in response to mechanical loading. Pretreatment with vesicular trafficking inhibitors significantly reduced the amount of IL-1β released from stimulated cells, suggesting that IL-1β might be released through vesicles.

CONCLUSION

We clearly illustrated the contribution of Panx1 in ATP release, as well as in IL-1β induction in HPDL cells. The association of Panx1 and the P2X7 receptor might be required for IL-1β induction, and their possible novel role in IL-1β vesicular release was indicated.

Mechanical stress-induced interleukin-1beta expression through adenosine triphosphate/P2X7 receptor activation in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Mechanical stress is an important factor in maintaining homeostasis of the periodontium. Interleukin-1beta (IL-1β) and adenosine triphosphate (ATP) are considered potent inflammatory mediators. In macrophages, ATP-activated P2X7 receptor is involved in IL-1β processing and release. Our previous works demonstrated mechanical stress-induced expression of osteopontin and RANKL through the ATP/P2Y1 receptor in human periodontal ligament (HPDL) cells. This study was designed to examine the effect of mechanical stress on IL-1β expression in HPDL cells, as well as the mechanism and involvement of ATP and the P2 purinergic receptor.

MATERIAL AND METHODS

Cultured HPDL cells were treated with continuous compressive loading. IL-1β expression was analyzed at both mRNA and protein levels, using RT-PCR and ELISA, respectively. Cell viability was examined using the MTT assay. ATP was also used to stimulate HPDL cells. Inhibitors, antagonists and the small interfering RNA (siRNA) technique were used to investigate the role of ATP and the specific P2 subtypes responsible for IL-1β induction along with the intracellular mechanism.

RESULTS

Mechanical stress could up-regulate IL-1β expression through the release of ATP in HPDL cells. ATP alone was also capable of increasing IL-1β expression. The induction of IL-1β was markedly inhibited by inhibitors and by siRNA targeting the P2X7 receptor. ATP-stimulated IL-1β expression was also diminished by intracellular calcium inhibitors.

CONCLUSION

Our work clearly indicates the capability of HPDL cells to respond directly to mechanical stimulation. The results signified the important roles of ATP/P2 purinergic receptors, as well as intracellular calcium signaling, in mechanical stress-induced inflammation via up-regulation of the proinflammatory cytokine, IL-1β, in HPDL cells.

Mechanical stress-activated immune response genes via Sirtuin 1 expression in human periodontal ligament cells

Recently, Sirtuin 1 (SIRT1) has been implicated in the molecular control of ageing and immune response. Although the remodelling of periodontal ligament (PDL) in response to mechanical stress (MS) is mediated by several host factors, including cytokines and chemokines, the transmission of mechanical stimuli into specific cellular activity is still not understood fully. This study aimed to investigate the effects of MS, particularly cyclic strain, on immune response genes, as well as SIRT1 and its signal transduction pathways, in human PDL cells. MS up-regulated the expression of SIRT1 and immune response genes encoding cytokines [tumour necrosis factor (TNF)-α, interleukin (IL)-1β], chemokines [IL-8, monocyte cheoattractant protein (CCL)-20], defensins [human β-defensin (hBD)-2, hBD-3] and Toll-like receptors (TLR-2 and TLR-4) in a force- and time-dependent manner. The SIRT1 inducers resveratrol and isonicotinamide attenuated MS-induced cytokine and chemokine expression, but enhanced the expression of defensins and TLRs. Blockade of SIRT1 activity by the SIRT1 inhibitors sirtinol and nicotinamide and down-regulation of SIRT1 expression by SIRT1 siRNA reduced the stimulatory effects of MS on defensins and TLRs, but increased its effects on cytokines and chemokines. MS induced activation of protein kinase B (Akt), protein kinase C (PKC), nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Treatment with the anti-oxidants N-acetylcysteine and glutathione inhibited MS-induced reactive oxygen species production and expression of cytokines, chemokines, defensins and TLRs. These results suggest that MS activates human PDL cells to express immune/defence genes encoding cytokines, chemokines, defensins and TLRs via a SIRT1 pathway.

Regulation of vascular cell adhesion molecule-1 in dental pulp cells by interleukin-1β: the role of prostanoids

INTRODUCTION

Vascular cell adhesion molecule (VCAM-1) plays a critical role in the inflammatory processes by stimulating the recruitment, extravasation, and migration of leukocytes. Its expression and regulation in the dental pulp is not well elucidated.

METHODS

Primary dental pulp cells were exposed to prostaglandin E(2) (PGE(2)), prostaglandin F(2α) (PGF(2α)), or interleukin 1β (IL-1β) with/without aspirin. VCAM-1 messenger RNA expression was analyzed by reverse transcriptase-polymerase chain reaction. Soluble VCAM-1 (sVCAM-1) in the culture medium was determined by enzyme-linked immunosorbent assay, and the number of viable cells was estimated by (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

IL-1β induced VCAM-1 gene expression of pulp cells. IL-1β also stimulated sVCAM-1 production. The IL-1β-induced sVCAM-1 production was not inhibited but rather enhanced by aspirin, a cyclooxygenase (COX) inhibitor. PGE(2) and PGF(2α) decreased the VCAM-1 expression and sVCAM-1 production of pulp cells. U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene), a mitogen-activated protein kinase kinase (MEK) inhibitor, attenuated IL-1β-induced sVCAM-1 production. However, no marked cytotoxicity was noted in these experimental conditions as analyzed by MTT assay.

CONCLUSIONS

IL-1β may be involved in the pulpal inflammatory processes via stimulation of VCAM-1 expression and sVCAM-1 production. This event is not mediated by COX activation and prostanoid production but is associated with MEK signaling. PGE(2) and PGF(2α) may potentially regulate inflammatory processes by the inhibition of VCAM-1.

In vivo astaxanthin treatment partially prevents antioxidant alterations in dental pulp from alloxan-induced diabetic rats

AIM

To evaluate the effect of astaxanthin on antioxidant parameters of dental pulp from diabetic rats. The hypothesis tested was that supplementation of diabetic rats with astaxanthin might eliminate, or at least attenuate, the defect in their antioxidative status.

METHODOLOGY

Wistar rats (n=32) were divided into four groups: untreated control, treated control, untreated diabetic and treated diabetic rats. A prophylactic dose of astaxanthin (20 mg kg(-1) body weight) was administered daily by gavage for 30 days. On day 23, diabetes was induced by injection of alloxan (60 mg kg(-1) body weight). After 7 days of diabetes induction, the rats were killed, and pulp tissue from incisor teeth removed. Superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and reductase activities were determined. Data were compared by anova and the Newman-Keuls test (P<0.05).

RESULTS

Diabetes caused a reduction in SOD, GPx and reductase activity in dental pulp tissue. Astaxanthin had no effect on SOD and catalase activities; however, it stimulated GPx in control and diabetic rats.

CONCLUSIONS

Diabetes altered the antioxidant system in dental pulp tissue; astaxanthin partially improved the diabetic complications.

Heme oxygenase-1 mediates nicotine- and lipopolysaccharide-induced expression of cyclooxygenase-2 and inducible nitric oxide synthase in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Although heme oxygenase-1 (HO-1) plays a key role in inflammation, its anti-inflammatory effects and mechanism of action in periodontitis are still unknown. This study aimed to identify the effects of HO-1 on the proinflammatory mediators activated by nicotine and lipopolysaccharide (LPS) stimulation in human periodontal ligament (PDL) cells.

MATERIAL AND METHODS

The production of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) was evaluated using Griess reagent and an enzyme immunoassay, respectively. The expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and HO-1 proteins was evaluated by Western blot analysis.

RESULTS

Lipopolysaccharide and nicotine synergistically induced the production of NO and PGE(2) and increased the protein expression of iNOS, COX-2 and HO-1. Treatment with an HO-1 inhibitor and HO-1 small interfering RNAs blocked the LPS- and nicotine-stimulated NO and PGE(2) release as well as the expression of iNOS and COX-2.

CONCLUSION

Our data suggest that the nicotine- and LPS-induced inflammatory effects on PDL cells may act through a novel mechanism involving the action of HO-1. Thus, HO-1 may provide a potential therapeutic target for the treatment of periodontal disease associated with smoking and dental plaque.

Human dental pulp cells exhibit bone cell-like responsiveness to fluid shear stress

BACKGROUND AIMS

For engineering bone tissue to restore, for example, maxillofacial defects, mechanosensitive cells are needed that are able to conduct bone cell-specific functions, such as bone remodelling. Mechanical loading affects local bone mass and architecture in vivo by initiating a cellular response via loading-induced flow of interstitial fluid. After surgical removal of ectopically impacted third molars, human dental pulp tissue is an easily accessible and interesting source of cells for mineralized tissue engineering. The aim of this study was to determine whether human dental pulp-derived cells (DPC) are responsive to mechanical loading by pulsating fluid flow (PFF) upon stimulation of mineralization in vitro.

METHODS

Human DPC were incubated with or without mineralization medium containing differentiation factors for 3 weeks. Cells were subjected to 1-h PFF (0.7 ± 0.3 Pa, 5 Hz) and the response was quantified by measuring nitric oxide (NO) and prostaglandin E₂ (PGE₂) production, and gene expression of cyclooxygenase (COX)-1 and COX-2.

RESULTS

We found that DPC are intrinsically mechanosensitive and, like osteogenic cells, respond to PFF-induced fluid shear stress. PFF stimulated NO and PGE₂ production, and up-regulated COX-2 but not COX-1 gene expression. In DPC cultured under mineralizing conditions, the PFF-induced NO, but not PGE₂, production was significantly enhanced.

CONCLUSIONS

These data suggest that human DPC, like osteogenic cells, acquire responsiveness to pulsating fluid shear stress in mineralizing conditions. Thus DPC might be able to perform bone-like functions during mineralized tissue remodeling in vivo, and therefore provide a promising new tool for mineralized tissue engineering to restore, for example, maxillofacial defects.

Mechanosensitivity of dental pulp stem cells is related to their osteogenic maturity

For engineering bone tissue, mechanosensitive cells are needed for bone (re)modelling. Local bone mass and architecture are affected by mechanical loading, which provokes a cellular response via loading-induced interstitial fluid flow. We studied whether human dental pulp-derived mesenchymal stem cells (PDSCs) portraying mature (PDSC-mature) or immature (PDSC-immature) bone cell characteristics are responsive to pulsating fluid flow (PFF) in vitro. We also assessed bone formation by PDSCs on hydroxyapatite-tricalcium phosphate granules after subcutaneous implantation in mice. Cultured PDSC-mature exhibited higher osteocalcin and alkaline phosphatase gene expression and activity than PDSC-immature. Pulsating fluid flow (PFF) stimulated nitric oxide production within 5 min by PDSC-mature but not by PDSC-immature. In PDSC-mature, PFF induced prostaglandin E(2) production, and cyclooxygenase 2 gene expression was higher than in PDSC-immature. Implantation of PDSC-mature resulted in more osteoid deposition and lamellar bone formation than PDSC-immature. We conclude that PDSCs with a mature osteogenic phenotype are more responsive to pulsating fluid shear stress than osteogenically immature PDSCs and produce more bone in vivo. These data suggest that PDSCs with a mature osteogenic phenotype might be preferable for bone tissue engineering to restore, for example, maxillofacial defects, because they might be able to perform mature bone cell-specific functions during bone adaptation to mechanical loading in vivo.

The anti-inflammatory role of heme oxygenase-1 in lipopolysaccharide and cytokine-stimulated inducible nitric oxide synthase and nitric oxide production in human periodontal ligament cells

BACKGROUND

Although heme oxygenase-1 (HO-1) is involved in anti-inflammation, the mechanisms of its activity in regulating periodontal inflammation are largely unclear. Therefore, the aim of this study is to investigate the anti-inflammatory properties of HO-1 in lipopolysaccharide (LPS)- and proinflammatory cytokine-stimulated inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in human periodontal ligament (PDL) cells.

METHODS

PDL cells were treated with LPS plus a combination of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta in serum-free media for 1 day. The production of NO was evaluated using a Griess reagent kit. The expression of iNOS and HO-1 proteins and mRNAs was evaluated using Western blotting and reverse transcriptase-polymerase chain reaction, respectively.

RESULTS

Proinflammatory cytokines and LPS triggered iNOS and HO-1 expression and NO production in PDL cells. HO-1 inhibitor and HO-1 small interfering RNA (siRNA) attenuated the LPS- and cytokine-stimulated NO release and iNOS and HO-1 expression. Specific inhibitors of p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases phosphatidylinositol 3-kinase (PI3K), nuclear factor-kappa B (NF-kappaB), and protein kinase C delta (PKC-delta) greatly reduced the levels of iNOS and HO-1 expression induced by LPS plus cytokines.

CONCLUSIONS

Collectively, these data suggested that HO-1 inhibition blocked LPS- and proinflammatory cytokine-stimulated iNOS expression and NO production in PDL cells via a mechanism that involves p38, ERK, PI3K, NF-kappaB, and PKC-delta. Thus, the regulation of HO-1 activity may be a therapeutic strategy for periodontal disease.

Mechanical stress promotes odontoblastic differentiation via the heme oxygenase-1 pathway in human dental pulp cell line

AIMS

Although heme oxygenase-1 (HO-1) is involved in osteoblastic differentiation, the HO-1- and odontoblastic differentiation-inducing effects of mechanical stress (MS) have not been clarified in human dental pulp cells (HDPCs). In this study, we examined the effects of MS on the odontoblastic differentiation of immortalized HDPCs and on the primary intracellular signaling pathways, including the HO-1 pathway, implicated in this differentiation.

MAIN METHODS

A Flexercell strain unit was used to generate cyclic tensile strain in HDPCs. Expressions of mRNAs encoding HO-1 and HDPC differentiation markers, such as osteopontin (OPN), bone sialoprotein (BSP), dentin sialophosphoprotein (DSPP), and dentin matrix-protein-1 (DMP-1), were evaluated using the reverse transcription-polymerase chain reaction. Expression of the NF-E2-related transcription factor 2 (Nrf2) protein was analyzed by Western blotting.

KEY FINDINGS

MS significantly increased the expression of HO-1, OPN, BSP, DSPP, and DMP-1 mRNAs in HDPCs. HO-1 silencing and inhibitors of HO-1, p38 MAPK, ERK, phosphoinositide 3-kinase, and nuclear factor-kappaB (NF-kappaB) all attenuated MS-stimulated differentiation. The MS-induced nuclear translocation of Nrf2 was suppressed by inhibitors of PI3K and NF-kappaB.

SIGNIFICANCE

Collectively, these results provide the first evidence that MS stimulates odontoblastic differentiation of HDPCs via modulation of the Nrf2-mediated HO-1 pathway.

Heat stress activates interleukin-8 and the antioxidant system via Nrf2 pathways in human dental pulp cells

INTRODUCTION

This study tested whether heat stress (42 degrees C for 30 minutes) induces reactive oxygen species (ROS), proinflammatory cytokines, Nrf2 activation, and Nrf2 target genes such as antioxidant enzymes in human dental pulp (HDP) cells.

METHODS

ROS was evaluated by using flow cytometry. Proteins and messenger RNA levels for cytokines and antioxidant genes were determined by using Western blotting and reverse transcription-polymerase chain reaction (RT-PCR) analysis, respectively.

RESULTS

Heat stress induced the production of ROS and the increased expression of the interleukin (IL)-8 and IL-8 receptor genes. Exposure of cells to heat stress resulted in the nuclear translocation of Nrf2 and increased expression of Nrf2 target genes including heme oxygenase-1. Pretreatment with an exogenous antioxidant inhibited the heat-induced expression of IL-8 and Nrf2 target genes and Nrf2 translocation.

CONCLUSION

Collectively, these results show that heat-induced Nrf2 activation is the major regulatory pathway of cytoprotective gene expression against oxidative stress in HDP cells.

Anti-inflammatory effects of apigenin on nicotine- and lipopolysaccharide-stimulated human periodontal ligament cells via heme oxygenase-1

BACKGROUND AND OBJECTIVES

Although apigenin exhibits various biological effects, its anti-inflammatory role in the periodontal field remains unknown. We examined the anti-inflammatory effects of apigenin and the underlying mechanism in nicotine- and lipopolysaccharide (LPS)-stimulated human periodontal ligament (hPDL) cells.

MATERIALS AND METHODS

Western blotting was used to examine the effect of apigenin (10-40 microM) on the LPS- and nicotine-induced expression of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and heme oxygenase-1 (HO-1), as well as the phosphorylation of mitogen-activated protein kinases (MAPKs), in hPDL cells. Pro-inflammatory mediators, including nitric oxide (NO), prostaglandin E2 (PGE2), interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-6, and IL-12 were monitored using Griess reagents and ELISA.

RESULTS

Incubation of hPDL cells with apigenin decreased LPS- and nicotine-induced HO-1 protein expression and activity. Apigenin significantly inhibited the nicotine- and LPS-induced production of NO, PGE2, IL-1beta, TNF-alpha, IL-6, and IL-12, and the upregulation of iNOS and COX-2 in hPDL cells. Hemin, a selective HO-1 inducer, reversed the apigenin-mediated suppression of nicotine- and LPS-induced NO, PGE2 and cytokine production. Treatment with inhibitors of the phosphoinositide 3-kinase, MAPKs, p38, and JNK, as well as a protein kinase C inhibitor, blocked the anti-inflammatory effects of apigenin in nicotine- and LPS-treated cells.

CONCLUSIONS

Apigenin possesses anti-inflammatory activity in hPDL cells and works through a novel mechanism involving the action of HO-1. Thus, apigenin may have potential benefits as a host modulatory agent in the prevention and treatment of periodontal disease associated with smoking and dental plaque.