Defense mechanism of heme oxygenase-1 against cytotoxic and receptor activator of nuclear factor-kappaB ligand inducing effects of hydrogen peroxide in human periodontal ligament cells

Comparative study of hyperpure chlorine dioxide with two other irrigants regarding the viability of periodontal ligament stem cells

Objectives

Periodontal ligament stem cells (PDLSCs) have an underlined significance as their high proliferative capacity and multipotent differentiation provide an important therapeutic potential. The integrity of these cells is frequently disturbed by the routinely used irrigative compounds applied as periodontal or endodontic disinfectants (e.g., hydrogen peroxide (H₂O₂) and chlorhexidine (CHX)). Our objectives were (i) to monitor the cytotoxic effect of a novel dental irrigative compound, chlorine dioxide (ClO₂), compared to two traditional agents (H₂O₂, CHX) on PDLSCs and (ii) to test whether the aging factor of PDLSC cultures determines cellular responsiveness to the chemicals tested.

Methods

Impedimetry (concentration-response study), WST-1 assays (WST = water soluble tetrazolium salt), and morphology analysis were performed to measure changes in cell viability induced by the 3 disinfectants; immunocytochemistry of stem cell markers (STRO-1, CD90, and CD105) measured the induced mesenchymal characteristics.

Results

Cell viability experiments demonstrated that the application of ClO₂ does not lead to a significant decrease in viability of PLDSCs in concentrations used to kill microbes. On the contrary, traditional irrigants, H₂O₂, and CHX are highly toxic on PDLSCs. Aging of PLDSC cultures (passages 3 vs. 7) has characteristic effects on their responsiveness to these agents as the increased expression of mesenchymal stem cell markers turns to decreased.

Conclusions and clinical relevance

While the active ingredients of mouthwash (H₂O₂, CHX) applied in endodontic or periodontitis management have a serious toxic effect on PDLSCs, the novel hyperpure ClO₂ is less toxic providing an environment favoring dental structure regenerations during disinfectant interventions.

Electronic supplementary material

The online version of this article (10.1007/s00784-020-03618-5) contains supplementary material, which is available to authorized users.

Differential gene expression profiles of human periodontal ligament cells preserved in Hank's balanced salt solution and milk

BACKGROUND/AIM

Various types of storage media have been investigated to preserve avulsed teeth. However, the efficacies of storage media mainly focus on the aspect of cell viability. The aim of this study was to evaluate and compare the gene expression profiles of human periodontal ligament cells preserved in Hank's balanced salt solution (HBSS) and milk over different storage durations.

MATERIAL AND METHODS

Human periodontal ligament cells were cultured and preserved in HBSS and milk for 3 and 6 hours. Next, total RNA was isolated. QuantSeq 3' mRNA-Sequencing was used to examine differences in gene expression in HBSS- and milk-grown periodontal ligament cells. Bioinformatics analysis was also performed to predict the function of the differentially expressed genes.

RESULTS

The number of differentially expressed genes shared among all groups was 101. In gene set enrichment analysis, the shared differentially expressed genes in HBSS and milk were associated with the TNF-α signaling pathway (P = 1.07E^-7 ). Seven hallmark gene sets were also identified in HBSS. Moreover, hallmark gene sets associated with hypoxia (P = 7.26E^-5 ) and apoptosis (P = 4.06E^-4 ) were identified in HBSS. In milk, 10 hallmark gene sets along with gene sets for inflammatory response (P = 6.87E^-3 ) were identified.

CONCLUSIONS

Compared to those in milk, genes in HBSS were differentially expressed with increasing storage duration, suggesting that diverse and different gene expression may be involved in HBSS and milk. However, a more detailed functional analysis of these differentially expressed genes in storage solutions should be performed in the future.

Involvement of Nrf2-mediated upregulation of heme oxygenase-1 in mollugin-induced growth inhibition and apoptosis in human oral cancer cells

Although previous studies have shown that mollugin, a bioactive phytochemical isolated from Rubia cordifolia L. (Rubiaceae), exhibits antitumor effects, its biological activity in oral cancer has not been reported. We thus investigated the effects and putative mechanism of apoptosis induced by mollugin in human oral squamous cell carcinoma cells (OSCCs). Results show that mollugin induces cell death in a dose-dependent manner in primary and metastatic OSCCs. Mollugin-induced cell death involved apoptosis, characterized by the appearance of nuclear shrinkage, flow cytometric analysis of sub-G₁ phase arrest, and annexin V-FITC and propidium iodide staining. Western blot analysis and RT-PCR revealed that mollugin suppressed activation of NF-κB and NF-κB-dependent gene products involved in antiapoptosis (Bcl-2 and Bcl-xl), invasion (MMP-9 and ICAM-1), and angiogenesis (FGF-2 and VEGF). Furthermore, mollugin induced the activation of p38, ERK, and JNK and the expression of heme oxygenase-1 (HO-1) and nuclear factor E2–related factor 2 (Nrf2). Mollugin-induced growth inhibition and apoptosis of HO-1 were reversed by an HO-1 inhibitor and Nrf2 siRNA. Collectively, this is the first report to demonstrate the effectiveness of mollugin as a candidate for a chemotherapeutic agent in OSCCs via the upregulation of the HO-1 and Nrf2 pathways and the downregulation of NF-κB.

Anti-inflammatory effects of lindenenyl acetate via heme oxygenase-1 and AMPK in human periodontal ligament cells

The molecular basis for the anti-inflammatory effects of lindenenyl acetate (LA) was investigated in the lipopolysaccharide (LPS)-stimulated human periodontal ligament (HPDL) cell model. LA concentration-dependently inhibited LPS-induced inducible nitric oxide synthase (iNOS) derived nitric oxide (NO) and cyclooxygenase-2 (COX-2) derived prostaglandin E2 (PGE(2)) production in HPDL cells. LA also attenuated the production of LPS-induced tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-12. LA stimulated heme oxygenase-1 (HO-1) protein expression and enzyme activity of HPDL cells in a dose-dependent manner. Pretreatment with the HO-1 inhibitor, tin protoporphyrin (SnPP), attenuated the inhibitory activities of LA on LPS-induced inflammatory NO, PGE(2), IL-1β, TNF-α, IL-6 and IL-12 production. LA induced translocation of Nrf-2. Furthermore, an inhibitor of JNK MAPK abolished LA-induced HO-1 expression. LA exposure up-regulated the levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its upstream kinase activators, including LKB1 and Ca2+/calmodulin-dependent protein kinase kinase-II. Furthermore, compound C, a specific AMPK inhibitor, partially blocked the LA-induced anti-inflammatory effect. Taken together, these results indicate that LA has anti-inflammatory activity in HPDL cells that might be mediated by the HO-1, AMPK, JNK MAPK, and Nrf-2 pathways. Thus, LA may serve as a potential therapeutic agent in periodontal disease.

SIRT1 modulates high-mobility group box 1-induced osteoclastogenic cytokines in human periodontal ligament cells

Bone resorptive cytokines contribute to bone loss in periodontal disease. However, the involvement of SIRT1 in high-mobility group box 1 (HMGB1)-induced osteoclastic cytokine production remains unknown. The aim of this study was to investigate the role of SIRT1 in the responses of human periodontal ligament cells to HMGB1 and to identify the underlying mechanisms. The effect of HMGB1 on osteoclastic cytokine expression and secretion, and the regulatory mechanisms involved were studied by ELISA, reverse transcription-polymerase chain reaction, and Western blot analysis. HMGB1 upregulated the mRNA expression levels of the osteoclastic cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-11, and IL-17. In addition, HMGB1 upregulated RANKL mRNA expression, and SIRT1 mRNA and protein expression. The upregulation of these cytokines by HMGB1 was attenuated by pretreatment with inhibitors of p38 mitogen-activated protein kinase and NF-κB, as well as neutralizing antibodies against Toll-like receptors 2 and 4. Inhibition of SIRT1 by sirtinol or SIRT1 siRNA blocked the HMGB1-stimulated expression of RANKL and cytokines. These results suggest that the inhibition of SIRT1 may attenuate HMGB1-mediated periodontal bone resorption through the modulation of osteoclastogenic cytokine levels in human periodontal ligament cells.

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.

Heme oxygenase-1 protects human periodontal ligament cells against substance P-induced RANKL expression

BACKGROUND AND OBJECTIVE

Although substance P (SP) stimulates bone resorption activity and this is reported to be correlated with the degree of periodontal inflammation, it is unclear how human periodontal ligament cells regulate neuropeptide-induced osteoclastogenesis or the possible involvement of heme oxygenase-1 (HO-1) might be. This study examines how SP affects osteoprotegerin (OPG) and RANKL expression via HO-1.

MATERIAL AND METHODS

Using immortalized human periodontal ligament cells, the effects of SP on the expression of HO-1, RANKL and OPG mRNA and proteins were determined by RT-PCR and western blotting, respectively. Various concentrations of SP (10(-7), 10(-8), 10(-9) and 10(-10) m) were added to the medium, and the cells were treated for 0, 0.25, 0.5, 1, 2 and 3 d.

RESULTS

Substance P upregulated RANKL and HO-1 and downregulated OPG mRNA and protein expression in periodontal ligament cells, in a concentration- and time-dependent manner. A HO-1 inducer inhibited both the upregulation of RANKL expression and downregulation of OPG expression by SP in periodontal ligament cells. By contrast, treatment with a HO-1 inhibitor or HO-1 small interferring RNA (siRNA) enhanced SP-stimulated RANKL expression. Inhibitors of ERK and p38 MAP kinases, phosphoinositide 3-kinase and nuclear factor-kappaB blocked the effects of SP on RANKL expression in periodontal ligament cells.

CONCLUSION

These results suggest that SP stimulates osteoclastic differentiation by increasing the expression of RANKL vs. OPG via the HO-1 pathway in periodontal ligament cells. The HO-1 pathway may be an effective therapeutic target for inhibiting chronic periodontitis involving alveolar bone resorption.

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.

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.

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

This study was conducted to investigate the effects of mechanical stress, particularly cyclic strain, on proinflammatory cytokines as well as antioxidant properties and their interactions with cellular defense systems in human dental pulp (HDP) cells. Exposure of HDP cells to mechanical strain induced inflammatory cytokines such as interleukin-1 beta, tumor necrosis factor-alpha, and interleukin-6, as well as antioxidant genes such as heme oxygenase-1, superoxide dismutases, reduced nicotinamide adenine dinucleotide phosphate quinone oxidoreductase-1, and glutathione peroxidases. In addition, treatment with N-acetylcysteine, indomethacin, and heme oxygenase-1 inhibitors blocked reactive oxygen species production, antioxidant response element (ARE) gene expression, and Nrf2 accumulation that occurred in response to mechanical stress. These data demonstrate that mechanical strain activates inflammatory cytokines and oxidative stress, which then act in concert to induce the Nrf2-/ARE-mediated antioxidant enzymes. Therefore, we suggest that the activation of a compensatory adaptation or defense antioxidant system might represent a novel mechanism for protecting HDP cells against mechanical stress.

Differential induction of heme oxygenase-1 against nicotine-induced cytotoxicity via the PI3K, MAPK, and NF-kappa B pathways in immortalized and malignant human oral keratinocytes

BACKGROUND

Heme oxygenase-1 (HO-1) exhibits cytoprotective effects in many different cell types and is induced by nicotine exposure in human gingival fibroblasts. However, the role of HO-1 in cancer cells exposed to nicotine has not previously been described.

METHODS

We investigated the effects of nicotine on HO-1 protein expression and cell viability in immortalized (IHOK) and malignant (HN12) human oral keratinocyte cells using the 3,4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide assay and Western blotting. We also examined the involvement of the phosphoinositide-3-kinase (PI3K), mitogen-activated protein kinase (MAPK), and nuclear factor-kappaB (NF-kappaB) signaling pathways in nicotine-induced cytotoxicity and HO-1 levels in IHOK and HN12 cells.

RESULTS

Nicotine-induced HO-1 production and had cytotoxic effects on cells in both a concentration- and time-dependent manner. Nicotine-induced cytotoxicity and accumulation of HO-1 were greater in IHOK cells than in HN12 cells. Molecular inhibitors of the ERK, p38 MAP kinase, PI3 K, and NF-kappaB signaling pathways blocked the cytotoxic effects and induction of HO-1 expression by nicotine. Treatment with antioxidants (bilirubin, N-acetylcysteine) protected cells against nicotine-induced cytotoxicity and blocked the upregulation of HO-1, the effects of which were more pronounced in IHOK cells than in HN12 cells.

CONCLUSIONS

Collectively, these results suggest that HO-1 plays a principal role in the protective response to nicotine in oral cancer and immortalized keratinocytes. Moreover, the addition of exogenous antioxidants may help to protect oral epithelial cells as chemopreventive agents against nicotine-induced oxidative stress.

Substance P regulates macrophage inflammatory protein 3alpha/chemokine C-C ligand 20 (CCL20) with heme oxygenase-1 in human periodontal ligament cells

Although substance P (SP), a potent proinflammatory peptide, is involved in inflammation and immune responses, the effect of SP on the expression of macrophage inflammatory protein 3alpha[MIP-3alpha, chemokine C-C ligand 20 (CCL20)] in periodontal ligament (PDL) cells is unknown. Equally enigmatic is the link between SP, the stress protein heme oxygenase-1 (HO-1), and CCL20 production. We investigated whether SP induces the release of chemokine CCL20 from immortalized PDL (IPDL) cells, and further clarify SP-mediated pathways. We also examined the relationship between HO-1 and CCL20 by treating PDL cells with SP. Incubating IPDL cells with SP increased expression of CCL20 mRNA and CCL20 protein in a dose-time-dependent manner. Highly selective p38 and extracellular-regulated kinase 1/2 (ERK1/2) inhibitors abrogated SP-induced expression of CCL20 in IPDL cells. SP is also responsible for initiating phosphorylation of IkappaB, degradation of IkappaB and activation of nuclear factor (NF)-kappaB. SP induced expression of HO-1 in both a concentration- and time-dependent manner, and CCL20 reflected similar patterns. The inductive effects of SP on HO-1 and CCL20 were enhanced by HO-1 inducer hemin and the membrane-permeable guanosine 3',5'-monophosphate (cGMP) analogue 8-bromo-cGMP. Conversely, this pathway was inhibited by the HO-1 inhibitor zinc protoporphyrin IX (ZnPP IX) and the selective inhibitor of guanylate cyclase, 1H-(1,2,4)oxadiazole(4,3-a)quinoxalin-1-one (ODQ). We report herein the pathway that connects SP along with other modulators of neuroimmunoregulation to the induction of HO-1 and the inflammatory mediator macrophage inflammatory protein (MIP)-3alpha/CCL20 in IPDL cells, which play an important role in the development of periodontitis or inflammation during orthodontic tooth movement.