Irsogladine maleate regulates epithelial barrier function in tumor necrosis factor-α-stimulated human gingival epithelial cells

Expression of tight junction proteins in smokers and non-smokers with generalized Stage III periodontitis

OBJECTIVE

This study aims to evaluate the gingival crevicular fluid (GCF) levels of tumor necrosis factor-α (TNF-α), zonula occludens-1 (ZO-1), occludin (Occ), and tricellulin (Tric) in periodontitis, as well as their alterations due to smoking.

BACKGROUND

Tight junctions (TJ), which consist of transmembrane and cytoplasmic scaffolding proteins, connect the epithelial cells of the periodontium. Occ, claudins, junctional adhesion molecules, and Tric are transmembrane TJ proteins found at the cell membrane. The transmembrane TJ proteins and the intracellular cytoskeleton are directly linked by cytoplasmic scaffolding proteins such as ZO-1. Although the functions and locations of these molecules have been defined, their behavior in periodontal inflammation is unknown.

METHODS

The study included four groups: individuals with periodontal health without smoking (C; n = 31), individuals with generalized Stage III periodontitis without smoking (P; n = 28), individuals with periodontal health while smoking (CS; n = 22), and individuals with generalized Stage III periodontitis while smoking (PS; n = 18). Clinical periodontal parameters were recorded, and enzyme-linked immunosorbent assay (ELISA) was used to examine ZO-1, Occ, Tric, and TNF-α levels in GCF.

RESULTS

In the periodontitis groups, clinical parameters were significantly higher (p < .001). The site-specific levels of TNF-α, ZO-1, Tric, and Occ in the P group were statistically higher than those in the other groups (p < .05). TNF-α, probing pocket depth (PPD), and bleeding on probing (BOP) exhibited positive correlations with all TJ proteins (p < .005).

CONCLUSIONS

Smoking could potentially affect the levels of epithelial TJ proteins in the GCF, thereby potentially playing a significant role in the pathogenesis of the periodontal disease.

P38α contributes to TNF-α-induced IL-8 production in human gingival cells

Tumor necrosis factor-alpha (TNF-α) is a major inflammatory cytokine that induces interleukin (IL)-8 production. Although some studies have reported the involvement of the p38 MAPK signaling pathway in TNF-α-induced IL-8 production, its specific regulatory mechanisms in gingival epithelial cells (GECs) are still poorly understood. In the present study, Ca9-22 cells were used as representative GECs to investigate the effect of p38 signaling on TNF-α-induced IL-8 production. We found that TNF-α enhanced IL-8 production in Ca9-22 cells by activating the p38 signaling pathway, and one of its isoforms, p38α, played a key role. P38α deletion markedly inhibited TNF-α-induced IL-8 expression in Ca9-22 cells, while p38α gene rescue could reverse this effect. Further studies revealed that TNF-α-induced IL-8 production was markedly reduced when the threonine 180 and tyrosine 182 p38α phosphorylation sites were targeted for mutagenesis to alanine and phenylalanine, respectively, suggesting their critical role in the process. In conclusion, p38α plays an important role in TNF-α-induced IL-8 production, providing a potential therapeutic target to prevent and treat periodontal disease.

The burden of diabetes on the soft tissue seal surrounding the dental implants

Soft tissue seal around implant prostheses is considered the primary barrier against adverse external stimuli and is a critical factor in maintaining dental implants' stability. Soft tissue seal is formed mainly by the adhesion of epithelial tissue and fibrous connective tissue to the transmembrane portion of the implant. Type 2 diabetes mellitus (T2DM) is one of the risk factors for peri-implant inflammation, and peri-implant disease may be triggered by dysfunction of the soft tissue barrier around dental implants. This is increasingly considered a promising target for disease treatment and management. However, many studies have demonstrated that pathogenic bacterial infestation, gingival immune inflammation, overactive matrix metalloproteinases (MMPs), impaired wound healing processes and excessive oxidative stress may trigger poor peri-implant soft tissue sealing, which may be more severe in the T2DM state. This article reviews the structure of peri-implant soft tissue seal, peri-implant disease and treatment, and moderating mechanisms of impaired soft tissue seal around implants due to T2DM to inform the development of treatment strategies for dental implants in patients with dental defects.

Porphyromonas gingivalis survival skills: Immune evasion

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

A Dual Zinc plus Arginine formulation protects against tumor necrosis factor-alpha-induced barrier dysfunction and enhances cell proliferation and migration in an in vitro gingival keratinocyte model

OBJECTIVE

To investigate the effects of Dual Zinc plus Arginine formulations (aqueous solution and dentifrice) on tumor necrosis factor-alpha (TNF-α)-induced barrier dysfunction as well as on cell proliferation and migration in an in vitro gingival keratinocyte model.

DESIGN

Gingival keratinocytes were seeded onto the membrane of a double-chamber system in the absence and presence of recombinant TNF-α and the formulations under investigation. The barrier function was assessed by determination of transepithelial electrical resistance (TER) and paracellular transport of fluorescein isothiocyanate (FITC)-dextran. The distribution of zonula occludens-1 (ZO-1) and occludin was visualized by immunofluorescence microscopy. The effects of the formulations on keratinocyte cell proliferation were determined using a fluorescent cell tracker dye, while a migration assay kit was used to investigate their effects on cell migration.

RESULTS

Under conditions where TNF-α induces loss of keratinocyte barrier integrity, the Dual Zinc plus Arginine formulations (aqueous solution and dentifrice) protected the keratinocyte tight junction against the damages since they prevented the TNF-α-induced drop in TER and increase in FITC-dextran paracellular flux in the in vitro model. The treatment of keratinocytes with the formulations markedly mitigated the altered distribution of ZO-1 and occludin. Both formulations increased the proliferation of keratinocytes and alleviated the negative impact caused by TNF-α. Lastly, the formulations increased the migration capacity of keratinocytes.

CONCLUSIONS

The ability of the Dual Zinc plus Arginine formulations to protect the barrier integrity of gingival keratinocytes from TNF-α-induced damage and to promote their proliferation and migration suggests that they may offer benefits for oral health.

Effects of oxidative stress-induced increases in Zn2+ concentrations in human gingival epithelial cells

BACKGROUND AND OBJECTIVE

Previous studies have reported that oxidative stress increases intracellular Zn²⁺ concentrations and induces cytotoxicity. However, no studies have investigated whether oxidative stress induces such changes in periodontal tissue cells. In the present study, we investigated the effect of oxidative stress on intracellular Zn²⁺ concentration in periodontium constituent cells and its potential relationship with periodontal disease.

METHODS

We analyzed changes in intracellular Zn²⁺ concentrations in human gingival epithelial (epi4) cells treated with hydrogen peroxide (H₂ O₂ ). The fluorescent probes FluoZin-3 AM and CellTracker Green CMFDA were used to detect intracellular Zn²⁺ and thiol groups, respectively. Western blot analyses, luciferase reporter assays, and real-time polymerase chain reaction (PCR) analyses were performed to examine the effect of intracellular Zn²⁺ on epi4 cells.

RESULTS

H₂ O₂ treatment increased intracellular concentrations of Zn²⁺ in epi4 cells by facilitating the movement of Zn²⁺ from cellular nonprotein thiols to the cytoplasm and promoting cell membrane permeability to Zn²⁺ . Furthermore, H₂ O₂ -induced increases in intracellular Zn²⁺ activated the p38 cAMP response element-binding protein/mitogen-activated protein kinase (p38 CREB/MAPK) cascade, upregulated nuclear factor kappa B (NF-κB) DNA binding, and increased the expression of inflammatory cytokines and matrix metallopeptidase-9 (MMP-9).

CONCLUSION

Increases in intracellular Zn²⁺ induced by oxidative stress activate signaling pathways involved in inflammation, potentially contributing to the progression of periodontal disease.

Reduction of inflammation in a chronic periodontitis model in rats by TNF-α gene silencing with a topically applied siRNA-loaded calcium phosphate paste

We developed a calcium phosphate-based paste containing siRNA against TNF-α and investigated its anti-inflammatory and bone-healing effects in vitro and in vivo in a rat periodontitis model. The bioactive spherical CaP/PEI/siRNA/SiO₂ nanoparticles had a core diameter of 40-90 nm and a positive charge (+23 mV) that facilitated cellular uptake. The TNF- α gene silencing efficiency of the nanoparticles in J774.2 monocytes, gingival-derived cells, and bone marrow-derived cells was 12 ± 2%, 36 ± 8%, and 35 ± 22%, respectively. CaP/PEI/siRNA/SiO₂ nanoparticles cancelled the suppression of alkaline phosphatase (ALP) activity in LPS-stimulated bone marrow-derived cells. In vivo, ALP mRNA was up-regulated, TNF-α mRNA was down-regulated, and the amount of released TNF-α was significantly reduced after topical application of the calcium phosphate-based paste containing siRNA-loaded nanoparticles. The number of TNF-α-positive cells in response to CaP/PEI/siRNA/SiO₂ nanoparticle application was lower than that observed in the absence of siRNA. Elevated ALP activity and numerous TRAP-positive cells (osteoclasts) were observed in response to the application of all calcium phosphate pastes. These results demonstrate that local application of a paste consisting of siRNA-loaded calcium phosphate nanoparticles successfully induces TNF-α silencing in vitro and in vivo and removes the suppression of ALP activity stimulated by inflammation. STATEMENT OF SIGNIFICANCE: We developed a calcium phosphate-based paste containing nanoparticles loaded with siRNA against TNF-α. The nanoparticles had a core diameter of 40-90 nm and positive charge (+23 mV). The anti-inflammatory and osteoinductive effects of the paste were investigated in vitro and in vivo in a rat periodontitis model. In vitro, the TNF-α gene silencing efficiency of the nanoparticles in J774.2 monocytes, gingival-derived cells, and bone marrow-derived cells was 12 ± 2%, 36 ± 8%, and 35 ± 22%, respectively. The ALP activity of bone marrow-derived cells was recovered. In vivo, TNF-α mRNA was down-regulated and the amount of released TNF-α was significantly reduced, whereas the ALP mRNA was up-regulated. Elevated ALP activity and TRAP-positive cells were observed by immunohistochemistry.

Vitamin D maintains E-cadherin intercellular junctions by downregulating MMP-9 production in human gingival keratinocytes treated by TNF-α

Purpose

Despite the well-known anti-inflammatory effects of vitamin D in periodontal health, its mechanism has not been fully elucidated. In the present study, the effect of vitamin D on strengthening E-cadherin junctions (ECJs) was explored in human gingival keratinocytes (HGKs). ECJs are the major type of intercellular junction within the junctional epithelium, where loose intercellular junctions develop and microbial invasion primarily occurs.

Methods

HOK-16B cells, an immortalized normal human gingival cell line, were used for the study. To mimic the inflammatory environment, cells were treated with tumor necrosis factor-alpha (TNF-α). Matrix metalloproteinases (MMPs) in the culture medium were assessed by an MMP antibody microarray and gelatin zymography. The expression of various molecules was investigated using western blotting. The extent of ECJ development was evaluated by comparing the average relative extent of the ECJs around the periphery of each cell after immunocytochemical E-cadherin staining. Vitamin D receptor (VDR) expression was examined via immunohistochemical analysis.

Results

TNF-α downregulated the development of the ECJs of the HGKs. Dissociation of the ECJs by TNF-α was accompanied by the upregulation of MMP-9 production and suppressed by a specific MMP-9 inhibitor, Bay 11-7082. Exogenous MMP-9 decreased the development of ECJs. Vitamin D reduced the production of MMP-9 and attenuated the breakdown of ECJs in the HGKs treated with TNF-α. In addition, vitamin D downregulated TNF-α-induced nuclear factor kappa B (NF-κB) signaling in the HGKs. VDR was expressed in the gingival epithelium, including the junctional epithelium.

Conclusions

These results suggest that vitamin D may avert TNF-α-induced downregulation of the development of ECJs in HGKs by decreasing the production of MMP-9, which was upregulated by TNF-α. Vitamin D may reinforce ECJs by downregulating NF-κB signaling, which is upregulated by TNF-α. Strengthening the epithelial barrier may be a way for vitamin D to protect the periodontium from bacterial invasion.

Estrogen reinforces barrier formation and protects against tumor necrosis factor alpha-induced barrier dysfunction in oral epithelial cells

Purpose

Epithelial barrier dysfunction is involved in the pathophysiology of periodontitis and oral lichen planus. Estrogens have been shown to enhance the physical barrier function of intestinal and esophageal epithelia, and we aimed to investigate the effect of estradiol (E2) on the regulation of physical barrier and tight junction (TJ) proteins in human oral epithelial cell monolayers.

Methods

HOK-16B cell monolayers cultured on transwells were treated with E2, an estrogen receptor (ER) antagonist (ICI 182,780), tumor necrosis factor alpha (TNFα), or dexamethasone (Dexa), and the transepithelial electrical resistance (TER) was then measured. Cell proliferation was measured by the cell counting kit (CCK)-8 assay. The levels of TJ proteins and nuclear translocation of nuclear factor (NF)-κB were examined by confocal microscopy.

Results

E2 treatment increased the TER and the levels of junctional adhesion molecule (JAM)-A and zonula occludens (ZO)-1 in a dose-dependent manner, without affecting cell proliferation during barrier formation. Treatment of the tight-junctioned cell monolayers with TNFα induced decreases in the TER and the levels of ZO-1 and nuclear translocation of NF-κB. These TNFα-induced changes were inhibited by E2, and this effect was completely reversed by co-treatment with ICI 182,780. Furthermore, E2 and Dexa presented an additive effect on the epithelial barrier function.

Conclusions

E2 reinforces the physical barrier of oral epithelial cells through the nuclear ER-dependent upregulation of TJ proteins. The protective effect of E2 on the TNFα-induced impairment of the epithelial barrier and its additive effect with Dexa suggest its potential use to treat oral inflammatory diseases involving epithelial barrier dysfunction.

Regulation of defensive function on gingival epithelial cells can prevent periodontal disease

Periodontal disease is a bacterial biofilm-associated inflammatory disease that has been implicated in many systemic diseases. A new preventive method for periodontal disease needs to be developed in order to promote the health of the elderly in a super-aged society. The gingival epithelium plays an important role as a mechanical barrier against bacterial invasion and a part of the innate immune response to infectious inflammation in periodontal tissue. The disorganization of cell–cell interactions and subsequent inflammation contribute to the initiation of periodontal disease. These make us consider that regulation of host defensive functions, epithelial barrier and neutrophil activity, may become novel preventive methods for periodontal inflammation. Based on this concept, we have found that several agents regulate the barrier function of gingival epithelial cells and suppress the accumulation of neutrophils in the gingival epithelium. We herein introduce the actions of irsogladine maleate, azithromycin, amphotericin B, and Houttuynia cordata (dokudami in Japanese), which is commonly used in traditional medicine, on the epithelial barrier and neutrophil migration in gingival epithelial cells in vivo and in vitro, in order to provide support for the clinical application of these agents to the prevention of periodontal inflammation.

Lactoferrin: A Natural Glycoprotein Involved in Iron and Inflammatory Homeostasis

Human lactoferrin (hLf), an iron-binding multifunctional cationic glycoprotein secreted by exocrine glands and by neutrophils, is a key element of host defenses. HLf and bovine Lf (bLf), possessing high sequence homology and identical functions, inhibit bacterial growth and biofilm dependently from iron binding ability while, independently, bacterial adhesion to and the entry into cells. In infected/inflamed host cells, bLf exerts an anti-inflammatory activity against interleukin-6 (IL-6), thus up-regulating ferroportin (Fpn) and transferrin receptor 1 (TfR1) and down-regulating ferritin (Ftn), pivotal actors of iron and inflammatory homeostasis (IIH). Consequently, bLf inhibits intracellular iron overload, an unsafe condition enhancing in vivo susceptibility to infections, as well as anemia of inflammation (AI), re-establishing IIH. In pregnant women, affected by AI, bLf oral administration decreases IL-6 and increases hematological parameters. This surprising effect is unrelated to iron supplementation by bLf (80 μg instead of 1-2 mg/day), but to its role on IIH. AI is unrelated to the lack of iron, but to iron delocalization: cellular/tissue overload and blood deficiency. BLf cures AI by restoring iron from cells to blood through Fpn up-expression. Indeed, anti-inflammatory activity of oral and intravaginal bLf prevents preterm delivery. Promising bLf treatments can prevent/cure transitory inflammation/anemia/oral pathologies in athletes.

Lactoferrin: A Natural Glycoprotein Involved in Iron and Inflammatory Homeostasis

Human lactoferrin (hLf), an iron-binding multifunctional cationic glycoprotein secreted by exocrine glands and by neutrophils, is a key element of host defenses. HLf and bovine Lf (bLf), possessing high sequence homology and identical functions, inhibit bacterial growth and biofilm dependently from iron binding ability while, independently, bacterial adhesion to and the entry into cells. In infected/inflamed host cells, bLf exerts an anti-inflammatory activity against interleukin-6 (IL-6), thus up-regulating ferroportin (Fpn) and transferrin receptor 1 (TfR1) and down-regulating ferritin (Ftn), pivotal actors of iron and inflammatory homeostasis (IIH). Consequently, bLf inhibits intracellular iron overload, an unsafe condition enhancing in vivo susceptibility to infections, as well as anemia of inflammation (AI), re-establishing IIH. In pregnant women, affected by AI, bLf oral administration decreases IL-6 and increases hematological parameters. This surprising effect is unrelated to iron supplementation by bLf (80 μg instead of 1-2 mg/day), but to its role on IIH. AI is unrelated to the lack of iron, but to iron delocalization: cellular/tissue overload and blood deficiency. BLf cures AI by restoring iron from cells to blood through Fpn up-expression. Indeed, anti-inflammatory activity of oral and intravaginal bLf prevents preterm delivery. Promising bLf treatments can prevent/cure transitory inflammation/anemia/oral pathologies in athletes.

Aggregatibacter actinomycetemcomitans regulates the expression of integrins and reduces cell adhesion via integrin α5 in human gingival epithelial cells

Gingival epithelial cells form a physiological barrier against bacterial invasion. Excessive bacterial invasion destroys the attachment between the tooth surface and the epithelium, resulting in periodontitis. Integrins play a significant role in cell attachment; therefore, we hypothesized that bacterial infection might decrease the expressions of these integrins in gingival epithelial cells, resulting in reduced cell adhesion. Immortalized human gingival epithelial cells were co-cultured with Aggregatibacter actinomycetemcomitans Y4 (Aa Y4), and the gene expression levels of IL-8, proliferating cell nuclear antigen (PCNA), and integrins (α2, α3, α5, β4, and β6) were measured using quantitative reverse transcription polymerase chain reaction. Expression of PCNA and integrins, except integrin α5, was significantly downregulated, while expression of IL-8 and integrin α5 was significantly upregulated in the cells co-cultured with Aa Y4. The number of adherent cells significantly decreased when co-cultured with Aa Y4, as determined using cell adhesion assays. In the cells co-cultured with Aa Y4 and an integrin α5 neutralizing antibody, there was no effect on the expression of IL-8 and PCNA, while the expressions of integrins α2, α3, β4, and β6, and the number of adherent cells did not decrease. The number of invading bacteria in the cells was reduced in the presence of the antibody and increased in the presence of TLR2/4 inhibitor. Therefore, integrin α5 might be involved in Aa Y4 invasion into gingival epithelial cells, and the resulting signal transduction cascade reduces cell adhesion by decreasing the expression of integrins, while the TLR2/4 signaling cascade regulates IL-8 expression.

Establishment of Epithelial Attachment on Titanium Surface Coated with Platelet Activating Peptide

The aim of this study was to produce epithelial attachment on a typical implant abutment surface of smooth titanium. A challenging complication that hinders the success of dental implants is peri-implantitis. A common cause of peri-implantitis may results from the lack of epithelial sealing at the peri-implant collar. Histologically, epithelial sealing is recognized as the attachment of the basement membrane (BM). BM-attachment is promoted by activated platelet aggregates at surgical wound sites. On the other hand, platelets did not aggregate on smooth titanium, the surface typical of the implant abutment. We then hypothesized that epithelial BM-attachment was produced when titanium surface was modified to allow platelet aggregation. Titanium surfaces were coated with a protease activated receptor 4-activating peptide (PAR4-AP). PAR4-AP coating yielded rapid aggregation of platelets on the titanium surface. Platelet aggregates released robust amount of epithelial chemoattractants (IGF-I, TGF-β) and growth factors (EGF, VEGF) on the titanium surface. Human gingival epithelial cells, when they were co-cultured on the platelet aggregates, successfully attached to the PAR4-AP coated titanium surface with spread laminin5 positive BM and consecutive staining of the epithelial tight junction component ZO1, indicating the formation of complete epithelial sheet. These in-vitro results indicate the establishment of epithelial BM-attachment to the titanium surface.

Decreased expression of E-cadherin by Porphyromonas gingivalis-lipopolysaccharide attenuates epithelial barrier function

BACKGROUND AND OBJECTIVE

The gingival epithelium is a first line of defense against bacterial challenge. E-cadherin (E-cad) plays an important role in cell-cell adhesion as a barrier in the epithelium. Recently, a decrease in the expression of E-cad has been observed in inflamed gingival tissue. The aims of this study were to clarify the changes in E-cad expression and barrier function in human gingival epithelial cells stimulated with Porphyromonas gingivalis-lipopolysaccharide (P. gingivalis-LPS) and to evaluate the influence of these changes on the inflammatory reaction. Furthermore, to clarify the mechanism of the E-cad changes induced by P. gingivalis-LPS, we focused on reactive oxygen species (ROS) that are reported to induce a decrease in E-cad expression.

MATERIAL AND METHODS

Human gingival epithelial cells were incubated in Humedia-KG2 in the presence or absence of P. gingivalis-LPS and antioxidants to analyze ROS involvement in P. gingivalis-LPS-induced E-cad changes. E-cad protein expression was analyzed by immunofluorescence staining. To investigate barrier function and inflammatory changes, we performed transport and cytokine assays using gingival epithelial cells and macrophages co-culture model in transwell plates. Medium containing 10 μg/mL P. gingivalis-LPS (transport substance) was added to the upper compartment, which harvested gingival epithelial cells, and medium without P. gingivalis-LPS was added to the lower compartment, which harvested macrophages. In the transport assay, P. gingivalis-LPS penetration was analyzed using the Limulus amebocyte lysate test. In the cytokine assay, we examined the change in tumor necrosis factor-α (TNF-α) production from the macrophages in the lower compartment using enzyme-linked immunosorbent assay.

RESULTS

Expression of E-cad in human gingival epithelial cells was decreased by P. gingivalis-LPS, and the decrease in E-cad accelerated the penetration of P. gingivalis-LPS through the monolayer. In addition, the concentration of TNF-α was higher under the E-cad reduced monolayer. Antioxidants, particularly vitamin E and l-ascorbic acid 2-phosphate magnesium salt, inhibited the decrease in E-cad expression, penetration of P. gingivalis-LPS and increase in TNF-α.

CONCLUSION

These results suggest that the decrease in E-cad caused by P. gingivalis-LPS leads to destruction of the epithelial barrier function in human gingival epithelial cells, and finally accelerates the inflammatory reaction under the barrier. Antioxidants, particularly vitamin E and l-ascorbic acid 2-phosphate magnesium salt, may restore the impaired function by scavenging ROS, which are related to the decrease in E-cad expression by P. gingivalis-LPS.

Azithromycin recovers reductions in barrier function in human gingival epithelial cells stimulated with tumor necrosis factor-α

OBJECTIVE

The gingival epithelium plays an important role in protecting against the invasion of periodontal pathogens, and the permeability of gingival epithelial cells has been implicated in the initiation of periodontitis. Azithromycin (AZM) has been used in the treatment of chronic inflammatory airway diseases because it regulates cell-cell contact in airway epithelial cells. Therefore, AZM may also regulate barrier function in gingival epithelial cells. In the present study, we examined the effects of AZM on the permeability of human gingival epithelial cells (HGEC) under inflammatory conditions in vitro.

MATERIALS AND METHODS

HGEC were stimulated by tumor necrosis factor-α (TNF-α) in the presence of AZM or p38 MAP kinase and ERK inhibitors. Permeability was assessed based on transepithelial electrical resistance (TER). The expression of E-cadherin, phosphorylated p38 MAP kinase, and ERK was analyzed by Western blotting.

RESULTS

TNF-α decreased TER in HGEC, and AZM and the p38 MAP kinase and ERK inhibitors recovered this decrease. AZM inhibited the phosphorylation of ERK and p38 MAP kinase in TNF-α-stimulated HGEC. Furthermore, AZM recovered the decrease in E-cadherin expression in HGEC stimulated with TNF-α.

CONCLUSIONS

These results suggested that AZM regulated gingival epithelial permeability through p38 MAP kinase and ERK signaling, and may contribute to suppress the inflammation in gingival tissue.

Necrosis-induced TLR3 Activation Promotes TLR2 Expression in Gingival Cells

Damage-associated molecular patterns (DAMPs), endogenous molecules released from injured or dying cells, evoke sterile inflammation that is not induced by microbial pathogens. Periodontal diseases are infectious diseases caused by oral microorganisms; however, in some circumstances, DAMPs might initiate inflammatory responses before host cells recognize pathogen-associated molecular patterns. Here, we showed that the necrotic cell supernatant (NCS) functioned as an endogenous danger signal when released from necrotic epithelial cells exposed to repeat freeze thawing. The NCS contained RNA and stimulated the production of inflammatory cytokines interleukin 6 (IL-6) and IL-8 from gingival epithelial cells and gingival fibroblasts. Targeted knockdown of Toll-like receptor 3 (TLR3) in these cells significantly suppressed the ability of the NCS to induce IL-6 and IL-8 production. Epithelial cells and fibroblasts recognized the NCS from heterologous cells. Interestingly, the activation of TLR3, rather than other TLRs, induced TLR2 mRNA expression and proteins in gingival epithelial cells, and pretreatment with the NCS or polyinosinic:polycytidylic acid (Poly(I:C)), a strong TLR3 activator, enhanced inflammatory cytokine production induced by subsequent stimulation with Porphyromonas gingivalis (P. gingivalis) lipopolysaccharide, a TLR2 agonist. Moreover, the NCS reduced the expression of epithelial tight junction molecules zona occludens 1 and occludin and increased the permeability of epithelial tight junctions. These findings suggest that endogenous danger signal molecules such as self-RNA released from necrotic cells are recognized by TLR3 and that a subsequent increase of TLR2 expression in periodontal compartments such as gingival epithelial cells and gingival fibroblasts may enhance the inflammatory response to periodontopathic microbes recognized by TLR2 such as P. gingivalis, which also disrupts epithelial barrier functions. Thus, DAMPs may be involved in the development and prolongation of periodontal disease.

Irsogladine maleate regulates gap junctional intercellular communication-dependent epithelial barrier in human nasal epithelial cells

The airway epithelium of the human nasal mucosa acts as the first physical barrier that protects against inhaled substances and pathogens. Irsogladine maleate (IM) is an enhancer of gastric mucosal protective factors via upregulation of gap junctional intercellular communication (GJIC). GJIC is thought to participate in the formation of functional tight junctions. However, the effects of IM on GJIC and the epithelial barrier in human nasal epithelial cells (HNECs) remain unknown. To investigate the effects of IM on GJIC and the tight junctional barrier in HNECs, primary cultures of HNECs transfected with human telomerase reverse transcriptase (hTERT-HNECs) were treated with IM and the GJIC inhibitors oleamide and 18β-GA. Some cells were pretreated with IM before treatment with TLR3 ligand poly(I:C) to examine whether IM prevented the changes via TLR3-mediated signal pathways. In hTERT-HNECs, GJIC blockers reduced the expression of tight junction molecules claudin-1, -4, -7, occludin, tricellulin, and JAM-A. IM induced GJIC activity and enhanced the expression of claudin-1, -4, and JAM-A at the protein and mRNA levels with an increase of barrier function. GJIC blockers prevented the increase of the tight junction proteins induced by IM. Furthermore, IM prevented the reduction of JAM-A but not induction of IL-8 and TNF-α induced by poly(I:C). In conclusion, IM can maintain the GJIC-dependent tight junctional barrier via regulation of GJIC in upper airway nasal epithelium. Therefore, it is possible that IM may be useful as a nasal spray to prevent the disruption of the epithelial barrier by viral infections and exposure to allergens in human nasal mucosa.

Interleukin-8 induces DNA synthesis, migration and down-regulation of cleaved caspase-3 in cultured human gingival epithelial cells

BACKGROUND AND OBJECTIVE

Migration of the junctional epithelium occurs in association with the formation of a periodontal pocket. Although the migration of junctional epithelium is known to be related to the proliferation and migration of gingival junctional epithelial cells, the mechanism has not been clarified. In patients with periodontitis, the levels of interleukin-8 (IL-8) in both gingival tissue and gingival crevicular fluid are dramatically increased. IL-8 has broad bioactive functions. In this study, we examined the role of IL-8 in DNA synthesis, migration and protection against apoptosis in cultured human gingival epithelial cells (HGEC).

MATERIAL AND METHODS

DNA synthesis was estimated by measuring the incorporation of bromodeoxyuridine. The migration of gingival epithelial cells was assessed in a wound-healing assay. The expression of integrin beta-1 was analyzed using immunofluorescence confocal microscopy and western blotting. Cleaved caspase-3 was detected using western blotting and a Caspase-Glo assay kit.

RESULTS

IL-8 increased the synthesis of DNA in HGEC, and the maximal effect was seen at 25 or 50 ng/mL of IL-8. In addition, 50 ng/mL of IL-8 induced cell migration, and a neutralizing antibody of integrin beta-1 inhibited the migration. IL-8 also activated expression of integrin beta-1. Furthermore, IL-8 reduced the Aggregatibacter actinomycetemcomitans-induced increase in caspase-3 expression in HGEC.

CONCLUSION

IL-8 may facilitate the migration of gingival junctional epithelium by enhancing DNA synthesis, migration and preventing apoptosis of gingival epithelial cells.

Irsogladine maleate inhibits Porphyromonas gingivalis-mediated expression of toll-like receptor 2 and interleukin-8 in human gingival epithelial cells

BACKGROUND AND OBJECTIVE

Periodontitis is an infectious disease caused by an interaction between the host and periodontopathogenic bacteria. Regulating the immune response in human gingival epithelial cells (HGEC) may contribute to the prevention of periodontitis. Irsogladine maleate (IM) has previously been shown to regulate inflammation and the cell-cell junctional barrier in HGEC. In addition to these functions, control of bacterial recognition is important for preventing inflammation in periodontal tissue. Innate immunity in gingival epithelium is the first line of defense and plays a crucial role against bacterial challenge. Therefore, the effect of IM on regulating toll-like receptor 2 (TLR2), which is part of the innate immunity, was determined in this study.

MATERIAL AND METHODS

OBA-9, an immortalized human gingival epithelial cell line, and primary cultured HGEC were used in this study. Real-time PCR and western blotting were performed in OBA-9 or HGEC stimulated with whole cells of Porphyromonas gingivalis or with lipopolysaccharide (LPS) derived from P. gingivalis (PgLPS) in the presence or absence of IM to determine expression of TLR2 mRNA and production of TLR2 protein. Small interfering RNA (siRNA) against TLR2 was transfected into OBA-9 to clarify the association between the induction of TLR2 and interleukin-8 (IL-8) production.

RESULTS

The addition of IM into P. gingivalis or PgLPS-induced OBA-9 suppressed IL-8 production (p < 0.01). The addition of IM also abolished the induction of TLR2 by P. gingivalis or PgLPS in OBA-9 and primary cultured HGEC (p < 0.01). The suppressive effect of IM on the induction of TLR2 was also confirmed by immunohistostaining. Stimulation with peptidoglycan, a specific ligand for TLR2, suppressed the expression of toll-like receptor 4 (TLR4) mRNA in the presence of IM (p < 0.01). However, LPS derived from Escherichia coli, a ligand for TLR4, did not induce the expression of TLR2 mRNA. The PgLPS-induced expression of TLR4 mRNA was abolished by IM. Knockdown of TLR2 by siRNA transfection resulted in a weaker response of induction of IL8 mRNA in P. gingivalis or PgLPS-stimulated OBA-9.

CONCLUSION

These results suggest that IM suppresses the induction of IL-8 production by regulating increased levels of TLR2.

miR-584 expressed in human gingival epithelial cells is induced by Porphyromonas gingivalis stimulation and regulates interleukin-8 production via lactoferrin receptor

BACKGROUND

MicroRNAs (miRNAs) are short, non-coding RNAs that are involved in post-transcriptional regulation of gene expression. Differential miRNA expression in innate and acquired immunity has been shown to regulate immune cell development and function. miRNA expression has been demonstrated to affect pathophysiology of inflammatory diseases, such as rheumatoid arthritis and lupus. As such, this study explores the role of miRNA in the context of pathophysiology of destructive periodontitis. Specifically, this investigation profiles the differentially expressed miRNA of Porphyromonas gingivalis (Pg)-stimulated human gingival epithelial cells (HGECs).

METHODS

The specific miRNAs differentially expressed in Pg-stimulated OBA-9, immortalized HGECs, were analyzed using microarray. Real-time polymerase chain reaction (PCR) and Western blotting were performed to confirm the level of miRNA expression and determine target production of miRNA in OBA-9. The production of interleukin (IL)-8 was measured to determine the bioactivity of target protein regulated by miRNA.

RESULTS

miR-584, which targets lactoferrin receptor (LfR), was 3.39-fold upregulated by Pg stimulation. This upregulation of miR-584 was confirmed by real-time PCR. Pg stimulation resulted in the suppression of LfR at mRNA and protein levels. The transfection of the miR inhibitor for miR-584 in OBA-9 recovered Pg-induced suppression of LfR. The addition of human lactoferrin (hLf) had a suppressive effect on IL-8 production in Pg-stimulated OBA-9. However, hLf also decreased IL-8 production strongly in Pg-stimulated OBA-9 in the presence of the miR inhibitor for miR-584.

CONCLUSION

These findings suggest that the upregulation of miR-584 by Pg in OBA-9 inhibits the anti-inflammatory effects of hLf via the suppression of LfR.

Irsogladine maleate regulates the inflammatory related genes in human gingival epithelial cells stimulated by Aggregatibacter actinomycetemcomitans

Periodontitis is an infectious inflammatory disease. Our previous studies have revealed that irsogladine maleate (IM) regulates intercellular junctional function and chemokine secretion in gingival epithelium, resulting in the suppression of the onset of periodontal disease in a rat model. Therefore, it is plausible that IM is a promising preventive remedy for periodontal disease. In this study, to gain a better understanding of IM in gingival epithelial cells, we employed a DNA microarray analysis. More specifically, human gingival epithelial cells (HGEC) were exposed to Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) in the presence or absence of IM. Then, a human genome focus array was used. A. actinomycetemcomitans facilitated the expression of several inflammatory-related genes, including these for matrix metalloproteinase (MMP)-3, interleukin (IL)-6, and intercellular adhesion molecule-1 (ICAM-1) in HGEC, while these mRNA levels were attenuated by IM treatment. Importantly, consistent with mRNA levels, immunoblotting, immunofluorescence staining and ELISA analysis indicated that IM also abrogated the A. actinomycetemcomitans-induced increase in MMP-3, IL-6, and ICAM-1 at the protein level. In addition, inhibition of the ERK or p38 MAP kinase signaling cascade, previously reported to be disturbed by IM treatment in HGEC, clearly blocked A. actinomycetemcomitans-induced MMP-3, IL-6, or ICAM-1 protein expression. Moreover, animal study revealed that IM-pretreatment inhibited the A. actinomycetemcomitans-induced increase of ICAM-1 in gingival junctional epithelium. Taken together, these results suggested that IM can regulate inflammatory responses in HGEC by inhibiting the ERK or p38 MAP kinase signaling cascade, which may result in suppression of inflammation in gingival tissue, thereby contributing to the prevention of periodontitis.