NF-κB-dependent induction of osteoprotegerin by Porphyromonas gingivalis in endothelial cells

Osteoprotegerin modulates platelet adhesion to von Willebrand factor during release from endothelial cells

BACKGROUND

Platelet-binding Von Willebrand Factor (VWF) strings assemble upon stimulated secretion from endothelial cells.

OBJECTIVES

To investigate the efficiency of platelet binding to multi-molecular VWF bundles secreted from endothelial cells and to investigate the role of osteoprotegerin, a protein located in Weibel-Palade bodies that interacts with the VWF platelet binding domain.

METHODS

The nanobody VWF/AU-a11 that specifically binds to VWF in its active platelet-binding conformation was used to investigate the conformation of VWF.

RESULTS

Upon stimulated secretion from endothelial cells, VWF strings were only partially covered with platelets, while a VWD-type 2B mutation or ristocetin enhanced platelet binding by 2-3-fold. Osteoprotegrin, reduces platelet adhesion to VWF by 40% ± 18% in perfusion assays. siRNA-mediated down-regulation of endothelial osteoprotegerin expression resulted in a 1.8-fold increase in platelet adhesion to VWF strings. Upon viral infection, there is a concordant rise in VWF and osteoprotegerin plasma levels. Unexpectedly, no such increase was observed in plasma of desmopressin-treated hemophilia A-patients. In a mouse model, osteoprotegerin expression was low in liver endothelial cells of vehicle-treated mice, and concanavalin A-treatment increased VWF and osteoprotegerin expression 4- and 40-fold, respectively. This increase was translated in a 30-fold increased osteoprotegerin/VWF ratio in plasma.

CONCLUSIONS

Release of VWF from endothelial cells opens the platelet-binding site, irrespective of the presence of flow. However, not all available platelet-binding sites are being occupied, suggesting some extent of regulation. Part of this regulation involves endothelial proteins that are co-secreted with VWF, like osteoprotegerin. This regulatory mechanism may be of more relevance under inflammatory conditions.

Assessment of the Healing of Dental Implant Surgical Site Following Low-Level Laser Therapy Using Bioclinical Parameters: An Exploratory Study

The purpose of this study was to evaluate whether low-level laser therapy improves healing of the implant surgical site with clinical and biochemical parameters. Thirty patients with an edentulous space spanning a single tooth were selected. The patients were randomly allocated to 1 of 2 groups: control group and test group. The test group received laser energy at a power of 2 J/cm2 with a total of 4-6 J energy over each implant. Clinical parameters (implant stability quotient, probing index, modified sulcus bleeding index) and osteoprotegerin were assessed at baseline and follow-up intervals (2 weeks, 6 weeks, and 3 months). The test group showed significantly higher implant stability quotient than the control group at 2 weeks (57.93 ± 3.95 vs 35.67 ± 3.08; P < . 01) and 3 months (58.86 ± 3.75 vs 67.06 ± 3.78; P < . 01). A significant rise in osteoprotegerin levels of the test group (686.30 ± 125.36 pg/mL at baseline and 784.25 ± 108.30 pg/mL at 3 months; P < . 01) was seen contrary to significant decline in the control group (839.50 ± 249.08 pg/mL at baseline vs 415.30 ± 78.39 pg/mL at 3 months; P < . 01). Within the limitations of the study, the findings suggest that the healing of peri-implant hard and soft tissues may be enhanced with the use of low-level laser therapy as an explicit modality during the postoperative period.

Role of Osteoprotegerin as Novel Marker in Urinary Stone Formers: A Pilot Study

Background: Urinary tract calculus formation can be prevented by identifying molecules and metabolic disturbances that affect this process. Osteoprotegerin (OPG), a cytokine of the TNF receptor superfamily, has been demonstrated to mediate vascular calcification and intimal calcification. Endothelial injury and oxidative stress are known to play a role in urolithiasis in the form of Randall’s plaques. Objectives: The present study aimed to compare 24-h urinary and serum OPG levels of patients with and without urolithiasis. Methods: In this case-control study, 24-h urinary levels of OPG (pg/mL), serum levels of OPG (pg/mL), and creatinine (mg/dL) were measured in both groups. Urinary and serum levels of OPG were determined by enzyme-linked immunosorbent assay (ELISA) using human OPG kits. Results: Mean serum creatinine was 0.86 ± 0.21 mg/dL in the case group and 0.77± 0.16 mg/dL in controls. The difference in the mean serum OPG levels between the cases (227.13 ± 98.02 pg/mL) and controls (47.28 ± 29.61 pg/mL) was highly significant (P value < 0.0001). The difference in the mean 24-h urinary OPG levels between the cases (156.12 ± 174.31 pg/mL) and controls (9.32 ± 23.72 pg/mL) was highly significant (P value < 0.001). Conclusions: There were significantly higher levels of OPG in serum and 24-h urine samples of cases than in controls. Hence, it requires further large studies to make OPG a diagnostic and prognostic marker.

RANK-RANKL signaling upregulates Il-10 mRNA expression in mucosal Candida infection in vivo

Osteoprotegerin (OPG) prevents binding of receptor activator of nuclear factor-kappa B ligand (RANKL) to RANK. Recent studies have reported that immune cell RANK-RANKL interactions are critical to the infection process. Candida albicans is an opportunistic pathogenic fungus and a common cause of candidiasis. This study utilized an orally inoculated mouse model of C. albicans infection to determine whether superficial or systemic candidiasis was associated with alterations in RANK/RANKL/OPG expression. Invasive systemic C. albicans infection increased serum OPG levels in mice. In addition, tongue Opg, Rankl, and Rank mRNA expression were upregulated in mice with superficial oral cavity C. albicans infection. Moreover, administration of exogenous soluble RANKL upregulated Rank and interleukin-10 (Il-10) mRNA in superficially infected tissue, suggesting suppression of localized inflammation. Taken together, these findings suggested that RANK/RANKL/OPG signaling contributes to the pathogenesis of candidiasis. This is the first in vivo study to identify a relationship between this opportunistic infection and the RANK/RANKL/OPG axis.

The Role of Osteoprotegerin in Vascular Calcification and Bone Metabolism: The Basis for Developing New Therapeutics

Osteoporosis (OP) and cardiovascular diseases (CVD) are both important causes of mortality and morbidity in aging patients. There are common mechanisms underlying the regulation of bone remodeling and the development of smooth muscle calcification; a temporal relationship exists between osteoporosis and the imbalance of mineral metabolism in the vessels. Vascular calcification appears regulated by mechanisms that include both inductive and inhibitory processes. Multiple factors are implicated in both bone and vascular metabolism. Among these factors, the superfamily of tumor necrosis factor (TNF) receptors including osteoprotegerin (OPG) and its ligands has been established. OPG is a soluble decoy receptor for receptor activator of nuclear factor-kB ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL). OPG binds to RANKL and TRAIL, and inhibits the association with their receptors, which have been labeled as the receptor activator of NF-kB (RANK). Sustained release of OPG from vascular endothelial cells (ECs) has been demonstrated in response to inflammatory proteins and cytokines, suggesting that OPG/RANKL/RANK system plays a modulatory role in vascular injury and inflammation. For the development of potential therapeutic strategies targeting vascular calcification, critical consideration of the implications for bone metabolism must be taken into account to prevent potentially detrimental effects to bone metabolism.

The Role of Osteoprotegerin and Its Ligands in Vascular Function

The superfamily of tumor necrosis factor (TNF) receptors includes osteoprotegerin (OPG) and its ligands, which are receptor activators of nuclear factor kappa-B ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL). The OPG/RANKL/RANK system plays an active role in pathological angiogenesis and inflammation as well as cell survival. It has been demonstrated that there is crosstalk between endothelial cells and osteoblasts during osteogenesis, thus establishing a connection between angiogenesis and osteogenesis. This OPG/RANKL/RANK/TRAIL system acts on specific cell surface receptors, which are then able to transmit their signals to other intracellular components and modify gene expression. Cytokine production and activation of their receptors induce mechanisms to recruit monocytes and neutrophils as well as endothelial cells. Data support the role of an increased OPG/RANKL ratio as a possible marker of progression of endothelial dysfunction in metabolic disorders in relationship with inflammatory marker levels. We review the role of the OPG/RANKL/RANK triad in vascular function as well as molecular mechanisms related to the etiology of vascular diseases. The potential therapeutic strategies may be very promising in the future.

Oral Mucosal Lamina Propria-Progenitor Cells Exert Antibacterial Properties via the Secretion of Osteoprotegerin and Haptoglobin

The oral cavity possesses a diverse microflora, yet recurrent infections within healthy individuals are rare. Wound healing within the buccal mucosa is preferential, potentially because of the presence of oral mucosal lamina propria-progenitor cells (OMLP-PCs). In addition to their multipotency, OMLP-PCs demonstrate potent immunosuppressive properties. The present study investigated whether OMLP-PCs possess antibacterial properties, directly interacting with microorganisms and contributing to the maintenance of a balanced oral microflora. Gram-positive and -negative bacteria were cocultured with OMLP-PCs, buccal mucosal fibroblasts, or their respective conditioned media (CM). Bacterial growth was significantly inhibited when cocultured with OMLP-PCs or their CM. No antibacterial activity was apparent within the fibroblasts. Analysis of the OMLP-PC CM indicated constitutive secretion of osteoprotegerin (OPG) and haptoglobin (Hp). Exposure of the bacteria to OPG or Hp demonstrated their differential antibacterial properties, with neutralization/blocking studies confirming that the growth of Gram-positive bacteria was partially restored by neutralizing OPG within OMLP-PC CM; blocking Hp restored the growth of Gram-negative bacteria. The present study demonstrates, for the first time, the broad-spectrum antibacterial properties of OMLP-PCs. We report the direct and constitutive antibacterial nature of OMLP-PCs, with retention of this effect within the CM suggesting a role for soluble factors such as OPG and Hp. Knowledge of the immunomodulatory and antibacterial properties of these cells could potentially be exploited in the development of novel cell- or soluble factor-based therapeutics for the treatment of infectious diseases such as pneumonia or ailments such as chronic nonhealing wounds.

SIGNIFICANCE

Oral mucosal lamina propria-progenitor cells (OMLP-PCs) are a cell source with known immunomodulatory properties. The present report demonstrates the novel finding that OMLP-PCs possess potent antibacterial properties, halting the growth of Gram-positive and -negative bacteria through the secretion of soluble factors. OMLP-PCs constitutively secrete osteoprotegerin (OPG) and haptoglobin (Hp) at levels high enough to exert antibacterial action. OPG, a glycoprotein not previously known to be antibacterial, can suppress Gram-positive bacterial growth. Hp is only active against Gram-negative microorganisms. These findings indicate that OMLP-PCs could offer great potential in the development of novel cell- or soluble factor-based therapies for the treatment of infectious illness, such as bacterial pneumonia, through systemic infusion and of chronic wounds through local administration.

Effect of periodontal surgery on osteoprotegerin levels in gingival crevicular fluid, saliva, and gingival tissues of chronic periodontitis patients

Objectives. This study was undertaken to investigate the OPG profiles in gingival crevicular fluid (GCF), saliva, and gingival tissues of chronic periodontitis (CP) patients in response to open flap debridement (OFD). Subjects and Methods. The study included 30 subjects divided into 2 groups: 20 CP patients and 10 periodontally healthy subjects. Plaque index, gingival index, pocket depth, and clinical attachment level measurements were recorded for all subjects. GCF, salivary, and gingival samples were collected from all 30 subjects at baseline and 3 and 6 month after OFD from the 20 CP patients. GCF and salivary OPG levels were assessed by ELISA assay, while OPG expression in gingival tissues was examined by immunohistochemistry. Results. GCF, salivary and gingival OPG profiles were significantly higher in control subjects compared to CP patients at baseline (P < 0.001). Within CP group, OPG levels in GCF, saliva, and gingival samples showed a significant increase at 3 and 6 months after OFD (P < 0.001) compared to baseline. Although OPG values increased significantly in gingival samples and insignificantly in saliva after 3 months compared to 6 months, yet GCF levels were significantly decreased. Conclusions. OPG might be considered as a diagnostic and prognostic biomarker of periodontal bone destruction. This trial is registered with NCT02160613.

Transglutaminase-2 Is Involved in Expression of Osteoprotegerin in MG-63 Osteosarcoma Cells

Osteoprotegerin (OPG) is a secreted glycoprotein and a member of the tumor necrosis factor receptor superfamily. It usually functions in bone remodeling, by inhibiting osteoclastogenesis through interaction with a receptor activator of the nuclear factor κB (RANKL). Transglutaminases-2 (Tgase-2) is a group of multifunctional enzymes that plays a role in cancer cell metastasis and bone formation. However, relationship between OPG and Tgase-2 is not studied. Therefore, we investigated the involvement of 12-O-Tetradecanoylphorbol 13-acetate in the expression of OPG in MG-63 osteosarcoma cells. Interleukin-1β time-dependently induced OPG and Tgase-2 expression in cell lysates and media of the MG-63 cells by a Western blot. Additional 110 kda band was found in the media of MG-63 cells. 12-O-Tetradecanoylphorbol 13-acetate also induced OPG and Tgase-2 expression. However, an 110 kda band was not found in TPA-treated media of MG-63 cells. Cystamine, a Tgase-2 inhibitor, dose-dependently suppressed the expression of OPG in MG-63 cells. Gene silencing of Tgase-2 also signifi cantly suppressed the expression of OPG in MG-63 cells. Next, we examined whether a band of 110 kda of OPG contains an isopeptide bond, an indication of Tgase-2 action, by monoclonal antibody specifi c for the isopeptide bond. However, we could not fi nd the isopeptide bond at 110 kda but 77 kda, which is believed to be the band position of Tgase-2. This suggested that 110 kda is not the direct product of Tgase-2’s action. All together, OPG and Tgase-2 is induced by IL-1β or TPA in MG-63 cells and Tgase-2 is involved in OPG expression in MG-63 cells.

MicroRNA-181b regulates NF-κB-mediated vascular inflammation

EC activation and dysfunction have been linked to a variety of vascular inflammatory disease states. The function of microRNAs (miRNAs) in vascular EC activation and inflammation remains poorly understood. Herein, we report that microRNA-181b (miR-181b) serves as a potent regulator of downstream NF-κB signaling in the vascular endothelium by targeting importin-α3, a protein that is required for nuclear translocation of NF-κB. Overexpression of miR-181b inhibited importin-α3 expression and an enriched set of NF-κB-responsive genes such as adhesion molecules VCAM-1 and E-selectin in ECs in vitro and in vivo. In addition, treatment of mice with proinflammatory stimuli reduced miR-181b expression. Rescue of miR-181b levels by systemic administration of miR-181b "mimics" reduced downstream NF-κB signaling and leukocyte influx in the vascular endothelium and decreased lung injury and mortality in endotoxemic mice. In contrast, miR-181b inhibition exacerbated endotoxin-induced NF-κB activity, leukocyte influx, and lung injury. Finally, we observed that critically ill patients with sepsis had reduced levels of miR-181b compared with control intensive care unit (ICU) subjects. Collectively, these findings demonstrate that miR-181b regulates NF-κB-mediated EC activation and vascular inflammation in response to proinflammatory stimuli and that rescue of miR-181b expression could provide a new target for antiinflammatory therapy and critical illness.

Extraskeletal benefits and risks of calcium, vitamin D and anti-osteoporosis medications

Drugs used for the prevention and the treatment of osteoporosis exert various favourable and unfavourable extra-skeletal effects whose importance is increasingly recognized notably for treatment selection.

INTRODUCTION

The therapeutic armamentarium for the prevention and the treatment of osteoporosis is increasingly large, and possible extra-skeletal effects of available drugs could influence the choice of a particular compound.

METHODS

The present document is the result of a national consensus, based on a systematic and critical review of the literature.

RESULTS

Observational research has suggested an inverse relationship between calcium intake and cardiovascular diseases, notably through an effect on blood pressure, but recent data suggest a possible deleterious effect of calcium supplements on cardiovascular risk. Many diverse studies have implicated vitamin D in the pathogenesis of clinically important non-skeletal functions or diseases, especially muscle function, cardiovascular disease, autoimmune diseases and common cancers. The possible effects of oral or intravenous bisphosphonates are well-known. They have been associated with an increased risk of oesophageal cancer or atrial fibrillation, but large-scale studies have not found any association with bisphosphonate use. Selective oestrogen receptor modulators have demonstrated favourable or unfavourable extra-skeletal effects that vary between compounds. Strontium ranelate has a limited number of non-skeletal effects. A reported increase in the risk of venous thromboembolism is not found in observational studies, and very rare cases of cutaneous hypersensitivity reactions have been reported. Denosumab has been introduced recently, and its extra-skeletal effects still have to be assessed.

CONCLUSION

Several non-skeletal effects of bone drugs are well demonstrated and influence treatment choices.

The RANKL-OPG system in clinical periodontology

BACKGROUND AND OBJECTIVES

The receptor activator of NF-κB ligand-osteoprotegerin (RANKL-OPG) bi-molecular system is the "bottle-neck" regulator of osteoclastogenesis and bone resorption, both in physiological and pathological conditions. This review aims to elaborate the current knowledge on RANKL and OPG in periodontal disease, and to evaluate their diagnostic and prognostic potential as biomarkers of the disease.

MATERIALS AND METHODS

To pursue this aim, electronic and manual searches were performed for identifying clinical and in vivo studies on RANKL and OPG in gingival tissue, gingival crevicular fluid, saliva and blood. Smoking and diabetes mellitus were also considered for their potential effects.

RESULTS

Papers fulfilling the inclusion criteria demonstrate that RANKL is up-regulated, whereas OPG is down-regulated in periodontitis, compared to periodontal health, resulting in an increased RANKL/OPG ratio. This ratio is further up-regulated in smokers and diabetics, and is not affected by conventional periodontal treatment.

CONCLUSIONS

The increased RANKL/OPG ratio may serve as a biomarker that denotes the occurrence of periodontitis, but may not necessarily predict on-going disease activity. Its steadily elevated levels post treatment may indicate that the molecular mechanisms of bone resorption are still active, holding an imminent risk for relapse of the disease. Additional adjunct treatment modalities that would "switch-off" the RANKL/OPG ratio may therefore be required.

Osteoprotegerin induces cytoskeletal reorganization and activates FAK, Src, and ERK signaling in endothelial cells

Osteoprotegerin (OPG) is a soluble tumor necrosis factor receptor family member that is expressed by a range of cell types in bone as well as in the vasculature. However, the specific role of OPG in the vascular system is unclear. We recently reported that OPG treatment protects endothelial cells from detachment and apoptotic cell death induced by cysteine proteases of Porphyromonas gingivalis, an important pathogen of adult periodontitis. We also found that OPG activates the extracellular signal-regulated kinase (ERK) 1/2, which has been linked to cell survival and angiogenesis. In this study, we demonstrate that exposure to OPG induces a substantial morphological change in human dermal microvascular endothelial cells. Our results show that OPG induced a dose-dependent increase in the length of microtubules, which coincided with the transition of the cells from a polygonal to an elongated shape. Furthermore, we demonstrated that OPG activates signaling pathways that lead to the activation of Src, focal adhesion kinase, and ERK1/2. These findings suggest that OPG regulates at least two distinct pathways: one that induces cell proliferation via ERK signaling and another that induces angiogenesis via Src signaling. The findings of this study suggest that OPG may function as a regulator of angiogenesis.

Breast cancer cells stimulate osteoprotegerin (OPG) production by endothelial cells through direct cell contact

Background

Angiogenesis, the sprouting of capillaries from existing blood vessels, is central to tumour growth and progression, however the molecular regulation of this process remains to be fully elucidated. The secreted glycoprotein osteoprotegerin (OPG) is one potential pro-angiogenic factor, and clinical studies have demonstrated endothelial cells within a number of tumour types to express high levels of OPG compared to those in normal tissue. Additionally, OPG can increase endothelial cell survival, proliferation and migration, as well as induce endothelial cell tube formation in vitro. This study aims to elucidate the processes involved in the pro-angiogenic effects of OPG in vitro, and also how OPG levels may be regulated within the tumour microenvironment.

Results

It has previously been demonstrated that OPG can induce tube formation on growth factor reduced matrigel. In this study, we demonstrate that OPG enhances the pro-angiogenic effects of VEGF and that OPG does not stimulate endothelial cell tube formation through activation of the VEGFR2 receptor. We also show that cell contact between HuDMECs and the T47D breast cancer cell line increases endothelial cell OPG mRNA and protein secretion levels in in vitro co-cultures. These increases in endothelial cell OPG secretion were dependent on α_νβ₃ ligation and NFκB activation. In contrast, the pro-angiogenic factors VEGF, bFGF and TGFβ had no effect on HuDMEC OPG levels.

Conclusion

These findings suggest that the VEGF signalling pathway is not involved in mediating the pro-angiogenic effects of OPG on endothelial cells in vitro. Additionally, we show that breast cancer cells cause increased levels of OPG expression by endothelial cells, and that direct contact between endothelial cells and tumour cells is required in order to increase endothelial OPG expression and secretion. Stimulation of OPG secretion was shown to involve α_νβ₃ ligation and NFκB activation.

Pathophysiological roles of osteoprotegerin (OPG)

Osteoprotegerin (OPG) is a secreted glycoprotein central to bone turnover via its role as a decoy receptor for the receptor activator of nuclear factor kappaB ligand (RANKL) and has traditionally been linked to a number of bone-related diseases. However, there is additional evidence that OPG can promote cell survival by inhibiting TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. As a result, a number of in vitro, in vivo and clinical studies have been performed assessing the role of OPG in tumourigenesis. Similar studies have been performed regarding vascular pathologies, resulting from observations of expression and regulation of OPG in the vasculature. This review aims to provide an update on this area and assess the potential protective or detrimental role of OPG in both vascular pathologies and tumourigenesis.

Analysis of the association of polymorphism in the osteoprotegerin gene with susceptibility to chronic kidney disease and periodontitis

BACKGROUND AND OBJECTIVE

Chronic kidney disease (CKD) is a complex disorder, which results in several complications involving disturbance of mineral metabolism. Periodontal disease is an infectious disease that appears to be an important cause of systemic inflammation in CKD patients. Periodontal disease is characterized by clinical attachment loss (CAL) caused by alveolar bone resorption around teeth, which may lead to tooth loss. Osteoprotegerin (OPG) is a key regulator of osteoclastogenesis. Polymorphisms are the main source of genetic variation, and single nucleotide polymorphisms (SNPs) have been reported as major modulators of disease susceptibility. The aim of this study was to investigate the association of a polymorphism located at position -223 in the untranslated region of the OPG gene, previously known as -950, with susceptibility to CKD and periodontal disease.

MATERIAL AND METHODS

A sample of 224 subjects without and with CKD (in hemodialysis) was divided into groups with and without periodontal disease. The OPG polymorphism was analyzed by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

No association was found between the studied OPG polymorphism and susceptibility to CKD or periodontal disease.

CONCLUSION

It was concluded that polymorphism OPG-223 (C/T) was not associated with CKD and periodontal disease in a Brazilian population. Studies on other polymorphisms in this and other genes of the host response could help to clarify the involvement of bone metabolism mediators in the susceptibility to CKD and periodontal disease.

Role of alphav integrin in osteoprotegerin-induced endothelial cell migration and proliferation

Osteoprotegerin (OPG) is a decoy receptor for the receptor activator of nuclear factor kappaB ligand (RANKL). However, the role of OPG in the endothelium remains unknown. In this study, we demonstrate that OPG stimulates the proliferation and migration of human microvascular endothelial cells (HMVECs). In addition, we show that treatment with integrin alpha(v)beta(3) or integrin alpha(v)beta(5) blocking antibody inhibits endothelial cell migration. In contrast, treatment with anti-alpha(v)beta(3) antibody or anti-alpha(v)beta(5) antibody alone did not inhibit OPG-induced proliferation. However, OPG-induced proliferation was inhibited when these antibodies were applied simultaneously. Furthermore, OPG evoked activation of extracellular signal-regulated kinase (ERK) 1/2, which has been linked to integrin alpha(v) activity. Taken together, these results suggest that integrins alpha(v)beta(3) and/or alpha(v)beta(5) contribute to endothelial cell proliferation and migration induced by OPG.

Expression of receptor activator of nuclear factor kappa B ligand relates to inflammatory bone resorption, with or without occlusal trauma, in rats

BACKGROUND AND OBJECTIVE

Receptor activator of nuclear factor kappa B ligand (RANKL) is an important factor in osteoclast differentiation, activation and survival; however, its involvement in inflammatory bone resorption, with or without occlusal trauma, is unclear. The purpose of the present study was to investigate the distribution of RANKL-expressing cells in rat periodontium during lipopolysaccharide-induced inflammation with or without occlusal trauma.

MATERIAL AND METHODS

Lipopolysaccharide was injected into rat gingiva of the lower left first molar to induce inflammation. In addition, the occlusal surface of the upper left first molar of rat was raised by placing a gold inlay to induce occlusal trauma in the lower left first molars. The distribution of RANKL-expressing cells was immunohistochemically observed.

RESULTS

In the inflammatory model, many osteoclasts were observed at the apical inter-radicular septum on day 5 and they were reduced by day 10. On the other hand, in the inflammatory model with occlusal trauma, many osteoclasts were still observed on day 10. RANKL expression was similar to the changes in osteoclast number. The expression of RANKL increased in endothelial cells, inflammatory cells and periodontal ligament cells.

CONCLUSION

These findings clearly demonstrated that RANKL expression on endothelial cells, inflammatory cells and periodontal ligament cells is involved in inflammatory bone resorption and the expression is enhanced by traumatic occlusion. These results suggest that RANKL expression on these cells is closely involved in the increase of osteoclasts induced by occlusal trauma.

RANKL Upregulation Associated With Periodontitis andPorphyromonas gingivalis

BACKGROUND

Receptor activator of nuclear factor-kappa B (NF-kappaB) ligand (RANKL) and osteoprotegerin (OPG) are critical for homeostatic control of osteoclast activity, suggesting their vital roles in the progression of bone loss in periodontitis. In this study, the expression of RANKL and OPG mRNA and the relationship between these factors and periodontopathic bacteria in periodontal tissue were studied.

METHODS

Gingival tissue and subgingival plaque samples were collected from 15 patients with chronic periodontitis and 15 periodontally healthy subjects. RNA was extracted from the tissue and subjected to reverse transcription-polymerase chain reaction (RT-PCR) using primers specific for RANKL or OPG. Beta-actin was amplified as a control to ensure equal loading. The intensity of RT-PCR products was analyzed by a densitometer in proportion to the intensity of beta-actin. The numbers of Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans were determined by quantitative real-time PCR.

RESULTS

Our results showed increased levels of RANKL mRNA in chronic periodontitis tissues. The RANKL/OPG expression ratio was significantly higher in the periodontitis group compared to the healthy control group (P = 0.001). Interestingly, the expression of RANKL (r = 0.64; P <0.001), but not OPG (r = -0.24; P = 0.20), was significantly correlated with increased numbers of P. gingivalis. A. actinomycetemcomitans was detected in only 6.7% of all sites.

CONCLUSIONS

Chronic periodontitis was associated with RANKL mRNA upregulation and increased RANKL/OPG mRNA expression ratio. In addition, our data showed for the first time to our knowledge an association between upregulated RANKL levels and the number of P. gingivalis in clinically obtained periodontal tissues.

Pyrrolidine dithiocarbamate reduced experimental periodontitis

Nuclear factor-kappaB (NF-kappaB) is a transcription factor which plays a pivotal role in the induction of genes involved in physiological processes as well as in the response to injury and inflammation. Dithiocarbamates are antioxidants which are potent inhibitors of NF-kappaB. We postulated that pyrrolidine dithiocarbamate (PDTC) would attenuate inflammation. In the present study, we have investigated the effects of PDTC, in a rat model of periodontitis. Periodontitis was induced in rats by placing around the lower left first molar a 2/0 braided silk. At day eight the gingivomucosal tissue encircling the mandibular first molar was removed for biochemical and histological analysis. At day eight ligations significantly induced an increase neutrophil infiltration as well as the gingivomucosal tissue expression of TNF-alpha and iNOS as well as nitrotyrosine formation and poly (ADP-ribose) polymerase activation. Ligation significantly increased Evans blue extravasation in gingivomucosal tissue and alveolar bone destruction. Intraperitonial injection of PDTC (10 mg/kg daily for eight days) significantly reduced all of the parameters of inflammation as described above. These data demonstrate that PDTC exerts an anti-inflammatory role during experimental periodontitis and is able to ameliorate the tissue damage associated with ligature-induced periodontitis.

Mechanisms ofPorphyromonas gingivalis-induced monocyte chemoattractant protein-1 expression in endothelial cells

Monocyte chemoattractant protein-1 (MCP-1) is expressed in vascular endothelial cells of inflamed gingival tissues and plays an important role in periodontal pathogenesis. Endothelial cells produce high levels of MCP-1 in response to Porphyromonas gingivalis, an important periodontal pathogen. The present study investigated the mechanisms involved in MCP-1 production by human umbilical vein endothelial cells (HUVEC) following infection with P. gingivalis. In contrast to P. gingivalis, Bacteroides forsythus only weakly stimulated MCP-1 production while Treponema denticola could not induce MCP-1 in HUVEC. The MCP-1 production was independent of endogenous interleukin (IL)-1alpha as IL-1 receptor antagonist treatment did not reduce MCP-1 production by P. gingivalis. Meanwhile, antioxidant treatment and inhibition of NAD(P)H oxidase significantly reduced MCP-1 production. Pharmacological inhibition of p38 mitogen-associated protein (MAP) kinase, c-Jun N-terminal kinase (JNK), nuclear factor-kappaB (NF-kappaB) or activator protein-1 (AP-1) also substantially attenuated P. gingivalis-induced MCP-1 expression by HUVEC. Indeed, activation of NF-kappaB and AP-1 was observed in P. gingivalis-infected HUVEC. These results suggest that MCP-1 expression is upregulated in P. gingivalis-infected endothelial cells via reactive oxygen species, p38 MAP kinase, JNK, NF-kappaB, and AP-1.