Differential expression of RANKL and osteoprotegerin in gingival crevicular fluid of patients with periodontitis

Cytokine production in human periodontal ligament cells stimulated with Porphyromonas gingivalis

BACKGROUND AND OBJECTIVE

Although some functions and characterizations of human periodontal ligament (hPDL) cells have been reported, the role of hPDL cells in periodontal disease is poorly understood. We have previously reported that hPDL cells produce many kinds of inflammatory cytokines by stimulation with Prevotella intermedia. In this study, we examined the production of cytokines in hPDL cells stimulated with Porphyromonas gingivalis as compared with P. intermedia.

MATERIAL AND METHODS

hPDL cells cultured in Dulbecco's modified Eagles's medium (DMEM) containing 10% fetal bovine serum (FBS) and antibiotics. After three to four passages, hPDL cells were stimulated with P. intermedia (ATCC25601) or P. gingivalis (ATCC33277) for 24 h. Total RNA was extracted by ISOGEN and the expression of cytokine mRNA was determined using reverse transcription-polymerase chain reaction. Cytokines in the culture supernatants were assessed by enzyme-linked immunosorbent assay.

RESULTS

The expression of interleukin-1beta, interleukin-6, interleukin-8, tumor necrosis factor-alpha (TNF-alpha), receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) mRNA was detected in hPDL cells after stimulation with P. gingivalis as well as P. intermedia. There were no significant differences in the kind of cytokines expressed in hPDL cells between P. gingivalis and P. intermedia. However, P. gingivalis induced a significantly higher production of cytokines in hPDL cells than P. intermedia (p < 0.05).

CONCLUSION

This study demonstrated that hPDL cells produce many kinds of cytokines as a result of bacterial stimulation, including stimulation with P. gingivalis and P. intermedia. These results suggest that hPDL cells may play a role in cytokine production in periodontal disease.

Effects of aging on RANKL and OPG levels in gingival crevicular fluid during orthodontic tooth movement

OBJECTIVES

To compare the levels of the receptor activator of NFkB ligand (RANKL) and osteoprotegerin (OPG) in the gingival crevicular fluid (GCF) during orthodontic tooth movement in juvenile and adult patients.

DESIGN

Fifteen juveniles and 15 adults served as subjects. GCF was collected from the distal cervical margins of the experimental and control teeth at 0, 1, 24, and 168 h after application of a retracting force. Enzyme-linked immunosorbent assay kits were used to determine RANKL and OPG levels in the GCF samples.

RESULTS

The amount of tooth movement for juveniles was larger than for adults after 168 h. Further, after 24 h RANKL levels were increased and those of OPG decreased in GCF samples from the compression side during orthodontic tooth movement in both juveniles and adults. The RANKL/OPG ratio in GCF from adult patients was lower than that in the juvenile patient samples.

CONCLUSION

Our results suggest that the age-related decrease in amount of tooth movement may be related to a decrease in RANKL/OPG ratio in GCF during the early stages of orthodontic tooth movement.

High Expression Levels of Receptor Activator of Nuclear Factor-Kappa B Ligand Associated With Human Chronic Periodontitis Are Mainly Secreted by CD4+T Lymphocytes

BACKGROUND

Chronic periodontitis is an infectious disease characterized by alveolar bone destruction and teeth loss. Receptor activator of nuclear factor-kappa B ligand (RANKL) is an osteoclastogenic cytokine, a central regulatory factor in the osteoclast's lifespan, and a participant in physiological and pathological bone resorption. Gingival T cells synthesize RANKL, contributing to molecular local imbalance that entails the alveolar bone resorption seen in periodontitis. Our study was aimed at associating the levels of RANKL with the CD4(+) T-cell activity present in gingival tissues of chronic periodontitis patients.

METHODS

Gingival biopsies were obtained from 33 chronic periodontitis patients and 20 healthy controls. Specimens were either formalin fixed and paraffin embedded for real-time reverse transcription-polymerase chain reaction (RT-PCR) and histologic analysis or tissue digestion processed for cell culture and flow-cytometry analysis. RANKL mRNA and protein levels were determined by quantitative RT-PCR and enzyme-linked immunosorbent assay (ELISA) in gingival-cell culture supernatants. Gingival leukocytes were quantified by flow cytometry. RANKL and CD4 immunoreactivity were analyzed by flow cytometry and confocal microscopy.

RESULTS

RANKL mRNA levels were higher in patients with periodontitis than in healthy subjects, and spontaneous and lipopolysaccharide (LPS)- and phytohemagglutinin (PHA)-stimulated RANKL synthesis were higher also in patients than controls. CD4(+) T lymphocytes were the predominant infiltrate cell subset present in gingival tissues of periodontitis patients. Furthermore, an association between RANKL and CD4(+) T cells was determined by double-staining flow cytometry and confocal microscopy.

CONCLUSION

Taken together, these data demonstrate that gingival CD4(+) T cells are the main cells responsible for higher levels of RANKL observed in human chronic periodontitis patients.

Soluble RANKL in Crevicular Fluid of Dental Implants: A Pilot Study

BACKGROUND

Receptor activator of NF-kappaB ligand (RANKL), a member of the tumor necrosis factor superfamily, is a key mediator of osteoclast formation, activation, and survival. Thus, it is reasonable to hypothesize that there might be a functional relationship between RANKL expression and peri-implantitis.

PURPOSE

This pilot study was performed to determine the reference levels for soluble RANKL (sRANKL) in peri-implant crevicular fluid and to correlate them with the clinical parameters associated with inflammatory reactions and bone destruction.

MATERIALS AND METHODS

The clinical parameters probing depth (PD), modified bleeding index (MBI), and modified plaque index (MPI) served as indicators for bone resorption and inflammation. Exclusion criteria for calculations were the detection limit of the immunoassay and the minimum acceptable crevicular volume for measurement. From the 84 collected samples of 16 patients, 30-84 years of age, with a total of 19 implants, 29 met these criteria. The absolute amount of sRANKL within crevicular fluid adsorbed to filter strips was a median of 0.18 femtomol (fmol; range, 0.08-0.53) and 0.26 nM (range, 0.09-1.21) when normalized by volume. PD was 4 mm in median and varied within a range between 2 and 12 mm.

RESULTS

Absolute amounts of sRANKL showed no correlation with the adsorbed volume and the clinical parameters PD, MBI, and MPI. When sRANKL was normalized by volume, no correlation with the clinical parameters PD, MBI, and MPI was observed either. The patients' age was not associated with total sRANKL and the concentration of RANKL within crevicular fluid. Absolute levels of sRANKL and sRANKL concentration did not show any differences based on the sampling sites buccal and lingual, or on the patients' gender. A significant difference in sRANKL concentration was detectable when samples from maxillary implants (0.31 nM median; range, 0.12-1.21) were compared with samples from mandibular implants (0.21 nM median; range, 0.09-0.6) (p=.03). Absolute levels of sRANKL were not different between the maxilla and the mandible.

CONCLUSION

Given the limited sample size, our data provide a basis for future prospective longitudinal studies on the possible relevance of sRANKL as a prognostic marker in peri-implantitis, and for an understanding of the pathophysiologic process of the disease as a prerequisite for the design of treatment strategies.

B and T lymphocytes are the primary sources of RANKL in the bone resorptive lesion of periodontal disease

Receptor activator of nuclear factor-kappaB (RANKL)-mediated osteoclastogenesis plays a pivotal role in inflammatory bone resorption. The aim of this study was to identify the cellular source of RANKL in the bone resorptive lesions of periodontal disease. The concentrations of soluble RANKL, but not its decoy receptor osteoprotegerin, measured in diseased tissue homogenates were significantly higher in diseased gingival tissues than in healthy tissues. Double-color confocal microscopic analyses demonstrated less than 20% of both B cells and T cells expressing RANKL in healthy gingival tissues. By contrast, in the abundant mononuclear cells composed of 45% T cells, 50% B cells, and 5% monocytes in diseased gingival tissues, more than 50 and 90% of T cells and B cells, respectively, expressed RANKL. RANKL production by nonlymphoid cells was not distinctly identified. Lymphocytes isolated from gingival tissues of patients induced differentiation of mature osteoclast cells in a RANKL-dependent manner in vitro. However, similarly isolated peripheral blood B and T cells did not induce osteoclast differentiation, unless they were activated in vitro to express RANKL; emphasizing the osteoclastogenic potential of activated RANKL-expressing lymphocytes in periodontal disease tissue. These results suggest that activated T and B cells can be the cellular source of RANKL for bone resorption in periodontal diseased gingival tissue.

Identification of the osteoprotegerin/receptor activator of nuclear factor-kappa B ligand system in gingival crevicular fluid and tissue of patients with chronic periodontitis

BACKGROUND AND OBJECTIVE

Recent findings have suggested that osteoclastogenesis is directly regulated by receptor activator of nuclear factor-kappa B ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG). However, no studies have described interactions of OPG/RANKL and the gp130 cytokine family in periodontal disease. This study aimed to identify and quantify OPG/RANKL in the gingival crevicular fluid (GCF) and connective tissue of patients with periodontitis, and to clarify possible correlations with disease severity and interleukin-6 (IL-6) cytokines.

MATERIAL AND METHODS

Ninety-five sites in 20 patients with generalized chronic periodontitis were divided into four groups by site based on probing depth (PD) and bleeding on probing (BOP). In periodontitis patients, GCF was obtained using sterile paper strips from clinically healthy sites (PD <or= 3 mm without BOP, n = 12 in periodontitis subjects), mildly diseased sites (PD <or= 3 mm with BOP, n = 23), moderately diseased sites (PD <or= 4-6 mm with BOP, n = 33) and severely diseased sites (PD > 6 mm with BOP, n = 27). Fourteen clinically healthy sites from four periodontally healthy individuals were used as the control group. The levels of OPG, RANKL and two gp130 cytokines - IL-6 and oncostatin M (OSM) - in the GCF were determined by an enzyme-linked immunosorbent assay (ELISA) and are expressed as total amounts (pg/site). Immunohistochemical localization of OPG- and RANKL-positive cells was also performed on gingival connective tissues harvested from patients with periodontitis (inflammatory group, n = 8 biopsies) and from non-diseased individuals (healthy group, n = 8 biopsies).

RESULTS

GCF RANKL, but not OPG, was elevated in diseased sites of patients with periodontitis. However, the expressions of OPG and RANKL showed no correlation with disease severity (r = 0.174 and 0.056, respectively), but the content of RANKL in the GCF was significantly positively correlated with those of IL-6 (r = 0.207) and OSM (r = 0.231) (p < 0.01). Immunohistochemical staining showed that RANKL-positive cells were significantly distributed in the inflammatory connective tissue zone of diseased gingiva, compared with those of samples from non-diseased persons (p < 0.01). However, few OPG-positive cells were found in connective tissue zones of either the diseased gingiva or healthy biopsies.

CONCLUSION

These findings imply that in this cross-sectional study of GCF, RANKL, IL-6 and OSM were all prominent in periodontitis sites, whereas OPG was inconsistently found in a few samples of diseased sites but was undetectable in any of the control sites. The results also imply that the expression of RANKL was positively correlated with IL-6 and OSM in the GCF.

RANKL in human periapical granuloma: possible involvement in periapical bone destruction

OBJECTIVES

The cytokine receptor activator of nuclear factor kappaB-ligand (RANKL) has been involved in both the physiological and pathological regulation of osteoclast life span and bone metabolism. Periapical granuloma is a periradicular lesion characterized by periapical bone destruction. The aims of this study were to associate the RANKL mRNA levels to periapical granulomas using the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) technique and to determine the specific cell involved in RANKL synthesis.

METHODS

In eight periapical granuloma and eight periodontal ligament samples from periodontally healthy volunteers, RANKL mRNA was detected by real-time RT-PCR. Expression of RANKL on infiltrate leukocytes was further investigated by flow cytometry in six periapical granulomas.

RESULTS

Receptor activator of nuclear factor kappaB-ligand mRNA levels were higher in periapical granulomas than in healthy periodontal ligament as its RANKL mRNA cycle threshold (Ct) and DeltaCt were significantly lower than that of controls (33.07 +/- 1.24 vs 36.96 +/- 1.69 and 11.58 +/- 3.02 vs 15.60 +/- 3.31, respectively). A 16.2-fold (2.0-131.6) higher RANKL gene expression was detected in the granulomas compared with the control tissues. We determined by flow cytometry that lymphocytes were the predominant leukocyte cells (53.31%), and monocytes and dendritic cells were the main RANKL synthesizers in granuloma lesions.

CONCLUSIONS

These data indicate that monocytes synthesized RANKL in periapical granulomas and suggest that RANKL is involved in bone loss associated with periapical lesions.

Profiling the Cytokines in Gingival Crevicular Fluid Using a Cytokine Antibody Array

BACKGROUND

Various compounds have been detected in gingival crevicular fluid (GCF) as indicators of periodontal disease activity. Therefore, the analysis of GCF may be especially beneficial for diagnosing current periodontal status and addressing the effects of treatment. Moreover, the identification of new markers in GCF may also contribute to elucidating novel mechanisms involved in periodontal disease. This study sought novel marker proteins specific to chronic periodontitis by profiling cytokines in GCF using a cytokine antibody array system.

METHODS

Human cytokine array V, which detects 79 cytokines on one membrane, was used to determine the profile of cytokines in GCF from seven subjects with chronic periodontitis and seven subjects with healthy periodontia. The profile was exposed to x-ray film and quantified using image analysis software. Healthy and diseased sites were compared statistically.

RESULTS

We detected 10 cytokines in periodontally healthy sites and 36 cytokines in periodontally diseased sites. Interleukin-8 (IL-8) and transforming growth factor-beta 2 (TGF-beta2) were detected at high levels in healthy and diseased subjects. There were significant differences between healthy and diseased subjects in the levels of tissue inhibitor of metalloproteinases-2 (TIMP-2), tumor necrosis factor-beta (TNF-beta), growth-related oncogene (GRO), interferon-inducible protein-10 (IP-10), angiogenin (Ang), vascular endothelial growth factor (VEGF), insulin-like growth factor binding protein-3 (IGFBP-3), osteoprotegerin (OPG), epidermal growth factor (EGF), glial-derived neurotrophic factor (GDNF), pulmonary and activation-regulated chemokine (PARC), oncostatin M (OSM), fibroblast growth factor-4 (FGF-4), IL-16, homologous to lymphotoxins (LIGHT), and placenta growth factor (PlGF). Of these, the newly detected cytokines were GRO, Ang, IGFBP-3, GDNF, PARC, OSM, FGF-4, IL-16, LIGHT, and PlGF.

CONCLUSIONS

In this study, we detected several cytokines in GCF using a cytokine antibody array system, including both inflammatory cytokines and various growth factors. Therefore, periodontal disease may participate in the wound healing process and in tissue destruction via the inflammatory process. Our results suggest that the quantification of these cytokines in GCF provides useful information for the diagnosis of periodontal disease status.

Levels of RANKL and OPG in gingival crevicular fluid during orthodontic tooth movement and effect of compression force on releases from periodontal ligament cells in vitro

OBJECTIVE

To determine the levels of the receptor activator of NFkB ligand (RANKL) and osteoprotegerin (OPG) in the gingival crevicular fluid (GCF) during orthodontic tooth movement. A second objective was to investigate the effect of compression force on RANKL and OPG production from human periodontal ligament (hPDL) cells.

DESIGN

Ten adolescent patients were included. GCF was collected at the distal cervical margins of the experimental and control teeth 0, 1, 24, and 168 h after the retracting force was applied. Thisin vitro study was performed to examine the secretion of RANKL and OPG from hPDL cells following a compression force (0, 0.5, 1.0, 2.0, or 3.0 g/cm(2) for 48 h). Enzyme-linked immunosorbent assay (ELISA) kits were used to determine RANKL and OPG levels in the GCF and the conditioned medium.

RESULTS

GCF levels of RANKL were significantly higher, and the levels of OPG significantly lower, in the experimental canines than in the control teeth at 24 h, but there were no such significant differences at 0, 1, or 168 h. In vitro study indicated that the compression force significantly increased the secretion of RANKL and decreased that of OPG in hPDL cells in a time- and force magnitude-dependent manner. The compression-stimulated secretion of RANKL increased approximately 16.7-fold and that of OPG decreased 2.9-fold, as compared with the control.

CONCLUSIONS

The results obtained suggest that the changes of amount of RANKL and OPG may be involved in bone resorption as a response to compression force.

Cytokine pattern determines the progression of experimental periodontal disease induced by Actinobacillus actinomycetemcomitans through the modulation of MMPs, RANKL, and their physiological inhibitors

OBJECTIVE

Inflammatory and immune reactions raised in response to periodontopathogens are thought to trigger periodontal tissue destruction. We therefore investigated the expression of matrix metalloproteinases (MMPs) and the osteoclastogenic factor RANKL (receptor activator of nuclear factor-kappaB ligand), their respective inhibitors TIMPs (tissue inhibitors of metalloproteinases) and OPG (osteoprotegerin) and their possible correlation with the expression of inflammatory and regulatory cytokines in the course of experimental periodontal disease in mice.

METHODS

We characterized the time course of leukocyte migration and alveolar bone loss in C57BL/6 mice infected with Actinobacillus actinomycetemcomitans. Quantitative polymerase chain reaction (RealTime PCR) and ELISA were performed to determine the expression of MMPs, TIMPs, RANKL, OPG and cathepsin K, interleukin-1beta, tumor necrosis factor-alpha, interferon-gamma, interleukin-12, interleukin-4 and interleukin-10 in periodontal tissue samples harvested throughout the course of experimental disease.

RESULTS

Oral inoculation of A. actinomycetemcomitans results in an intense and widespread migration of leukocytes to the gingival tissues, besides marked alveolar bone resorption. Our data also demonstrate two distinct patterns of MMP/TIMP and RANKL/OPG expression in the course of experimental periodontal disease. The expression of MMPs (MMP-1, 2 and 9) and RANKL was correlated with the expression of interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma, in a time period characterized by the intense increase of inflammatory reaction and alveolar bone loss. On the other hand, interleukin-4 and interleukin-10 were associated with higher expression of TIMPs (TIMP 1, 2 and 3) and OPG, with a lower expression of MMPs and RANKL, and with reduced rates of increase of cellular infiltration in periodontal tissues and alveolar bone loss.

CONCLUSIONS

It is possible that the pattern of cytokines produced in periodontal tissues determines the progression and the severity of experimental periodontal disease, controlling the breakdown of soft and bone tissues through the balance between MMPs/TIMP and RANKL/OPG expression in gingival tissues.

No Association Between Selected Candidate Gene Polymorphisms and Severe Chronic Periodontitis

BACKGROUND

Chronic periodontitis (CP) risk is influenced by environmental and genetic factors. Using a case-control design, we tested for associations between CP and selected DNA sequence variations (single nucleotide polymorphisms [SNPs]) in or near genes coding for proteins that play a role in the pathogenesis of this disease.

METHODS

DNA was analyzed from 219 whites who were examined clinically. Cases (N=137) were >or=35 years of age with eight or more teeth having >or=5 mm of proximal clinical attachment loss. Controls (N=82) were >or=45 years of age with minimal or no proximal attachment loss or pocketing. Nine diallelic polymorphisms (gene and SNP descriptor) were studied in subjects: cytotoxic T-lymphocyte antigen-4 (CTLA-4, 49 A>G), human beta-defensin-1 (DEFB1, 692 G>A), intercellular adhesion molecule-1 (ICAM-1, 1548 A>G), Fas ligand (fasL, -844 C>T), inducible costimulator (ICOS, 3990 G>T), interleukin-6 (IL-6, -174 G>C), cysteine-cysteine chemokine receptor-5 (CCR5, 59653 C>T), osteoprotegerin (OPG, 245 T>G), and osteopontin (OPN, 707 C>T). Genotypes were determined using an automated fluorogenic 5'-nuclease, polymerase chain reaction-based assay. Gender and smoking history (pack-years) were included as covariates in logistic regression analyses.

RESULTS

Heavy smoking (>10 pack-years) and male gender were significantly associated with disease (P<0.001). For all SNPs tested, the allele frequencies and distributions of genotypes did not differ between cases and controls (P>0.05). No unadjusted or adjusted odds ratios (comparing genotypes in cases versus controls) were significantly different than 1.0 (P>0.05) under any additive, dominant, or recessive inheritance model.

CONCLUSIONS

None of the SNPs tested were strongly associated with generalized severe chronic periodontitis in North American whites. A potentially more fruitful approach in future studies will be to test for associations between periodontitis and haplotype blocks constructed from either multiple SNPs in candidate gene regions or from panels of markers that span the entire genome.

Effect of interleukin-10 on gene expression of osteoclastogenic regulatory molecules in the rat dental follicle

The aim of this study was to determine the effect of interleukin-10 (IL-10) on the gene expression of osteoclastogenic regulatory molecules in rat dental follicle cells. Interleukin-10 is an anti-inflammatory cytokine that inhibits alveolar bone resorption, but the molecular basis for this is unknown. Alveolar bone resorption is required for tooth eruption and the dental follicle functions to regulate the osteoclastogenesis needed for eruption. It does this by regulating its expression of receptor activator of nuclear factor-kappa B ligand (RANKL), colony-stimulating factor-1 (CSF-1), and osteoprotegerin (OPG). In this study, dental follicle cells were treated with IL-10, and the effect on gene expression of CSF-1, RANKL, and OPG was measured by reverse transcription-polymerase chain reaction (RT-PCR). Interleukin-10 enhanced the expression of OPG and down-regulated the expression of RANKL and CSF-1. Laser capture microdissection was carried out to detect IL-10 gene expression in the dental follicle. Knockdown of the IL-10 gene expression in the follicle cells was accomplished using a short interfering RNA (siRNA) targeting IL-10 mRNA. In these knockdowns, RANKL expression was increased and OPG expression was decreased. All of these results suggest that IL-10 inhibits bone resorption by up-regulating OPG expression while down-regulating expression of RANKL and CSF-1.

T cells support osteoclastogenesis in an in vitro model derived from human periodontitis patients

BACKGROUND

Periodontitis is characterized by alveolar bone destruction; however, the mechanisms responsible for bone damage are poorly understood. It has been reported that T cells are implicated in the pathogenesis of periodontitis. It has been also demonstrated that activated T lymphocytes secrete receptor activator of nuclear factor-kappa B ligand (RANKL) and can support the differentiation of monocytes into resorbing osteoclasts (OCs). Therefore, the purpose of this study was to examine the OC formation in periodontitis patients (PP) and the role of T cells in osteoclastogenesis.

METHODS

To study OC formation, we used an in vitro model consisting of unstimulated and unfractionated peripheral blood mononuclear cells (PBMCs) from PP and controls. In parallel, T-cell-depleted PBMCs from the same patients were also established. The expression of RANKL and tumor necrosis factor-alpha (TNF-alpha) was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot in fresh T cells isolated from PP and controls. Functional antibodies, anti-RANKL and anti-TNF-alpha, were utilized to study osteoclastogenesis in PBMC cultures from PP.

RESULTS

We showed that, in unfractionated PBMCs from PP, the OCs spontaneously developed in a T-cell-dependent way. The addition of macrophage colony stimulating factor (MCSF) and RANKL was necessary to promote the osteoclastogenesis in T-cell-depleted PBMC cultures from PP and in unfractionated PBMCs from periodontally healthy controls. Moreover, freshly isolated T cells from PBMCs of PP overexpressed RANKL and TNF-alpha. Finally, functional anti-RANKL and anti-TNF-alpha antibodies significantly inhibited osteoclastogenesis.

CONCLUSION

Our data suggest that T cells support spontaneous osteoclastogenesis in PP via RANKL and TNF-alpha overexpression.

Gingival fibroblasts are better at inhibiting osteoclast formation than periodontal ligament fibroblasts

Various studies indicate that periodontal ligament fibroblasts (PLF) have some similarities to osteoblasts, for example they have the capacity to induce the formation of osteoclast-like cells. Here, we investigated whether a second population of tooth-associated fibroblasts, gingival fibroblasts (GF), has similar osteoclastogenesis properties. PLF and GF were co-cultured with peripheral blood mononuclear cells (PBMC) in the presence and absence of dexamethasone and 1alpha,25dihydroxycholecalciferol (dex + vit D(3)) on plastic and on cortical bone slices. Tartrate resistant acid phosphatase (TRACP) positive multinucleated cells (MNCs) were more abundant in co-cultures with PLF than in GF-PBMC co-cultures, more abundant on plastic compared to bone and more abundant in the presence of dex + vit D(3). In line with these findings was an inhibition of MNC formation and not inhibition of existing osteoclasts by medium conditioned by GF. We next investigated whether expression of molecules important for osteoclastogenesis differed between the two types of fibroblasts and whether these molecules were regulated by dex + vit D(3). OPG was detected at high levels in both fibroblast cultures, whereas RANKL could not be detected. Resorption of bone did not occur by the MNCs formed in the presence of either fibroblast subpopulation, suggesting that the fibroblasts secrete inhibitors of bone resorption or that the osteoclast-like cells were not functional. The incapacity of the MNCs to resorb was abolished by culturing the fibroblast-PBMC cultures with M-CSF and RANKL. Our results suggest that tooth-associated fibroblasts may trigger the formation of osteoclast-like cells, but more importantly, they play a role in preventing bone resorption, since additional stimuli are required for the formation of active osteoclasts.

Differential effect of the cytolethal distending toxin of Actinobacillus actinomycetemcomitans on co-cultures of human oral cells

The periodontal pathogen Actinobacillus actinomycetemcomitans expresses a cytolethal distending toxin (CDT) that typically arrests the growth of eukaryotic cells at either the G0/G1 or G2/M phase of the cell cycle. It was previously found that CDT failed to arrest the growth of human periodontal ligament fibroblasts (HPLFs) when grown in pure culture. In contrast, proliferation of an oral epithelial cell line was rapidly inhibited by the toxin. In this study, the feasibility of using mixed-cell cultures and cell-specific markers to evaluate the response of oral cells, when in heterogeneous populations, to CDT was established. Proliferation of epithelial cells was rapidly inhibited and the cells were selectively eliminated in co-culture with HPLFs or cementoblasts by 24-48 h post-intoxication. Epithelial cells and HPLFs were detected and counted in co-cultures following cell-specific immunolabelling with antibodies against simian virus 40 large T antigen and the Ab-1 surface antigen, respectively. These results demonstrated that the activities of potential virulence factors, such as CDT, from periodontal pathogens can be successfully examined in mixed-cell cultures. This approach is especially relevant to infectious diseases that affect tissues with a diverse cellular composition, such as the periodontium.

Future treatment and diagnostic strategies for periodontal diseases

Many new technologies have been developed or are being developed that could enhance the ability to diagnose, predict, and treat periodontitis. Newer treatment strategies may allow clinicians to achieve limited or more robust regeneration of the periodontium. New or refreshed approaches to disease control are being pursued that will benefit those suffering from chronic periodontal disease. In addition to novel therapeutics, there has been increasing focus on the development of more sensitive and specific diagnostic tests for periodontal diseases. Such tests will allow the clinician to determine whether a patient has active disease and what sort of attachment loss might be expected if the patient is not treated. By developing newer diagnostic tests, it also may be possible to detect and monitor active disease during therapy.

Etiology and pathogenesis of periodontal diseases

The two most prevalent and most investigated periodontal diseases are dental plaque-induced gingivitis and chronic periodontitis. The last 10 to 15 years have seen the emergence of several important new findings and concepts regarding the etiopathogenesis of periodontal diseases. These findings include the recognition of dental bacterial plaque as a biofilm, identification and characterization of genetic defects that predispose individuals to periodontitis, host-defense mechanisms implicated in periodontal tissue destruction, and the interaction of risk factors with host defenses and bacterial plaque. This article reviews current aspects of the etiology and pathogenesis of periodontal diseases.

Areca nut extracts modulated expression of alkaline phosphatase and receptor activator of nuclear factor kappaB ligand in osteoblasts

OBJECTIVES

Areca chewers have a higher prevalence of periodontal diseases than non-chewers. This study was to determine the possible effects of ripe areca nut extracts (rANE) on viability and gene expression of alkaline phosphatase (ALP), receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) in human osteoblasts.

METHODS

The effects of rANE on cell viability of osteoblast-like MG63 cells were determined using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) that measures metabolic activity. Gene expression of ALP, RANKL and OPG was examined using reverse transcription-polymerase chain reaction. ALP activity and RANKL protein were further examined using substrate assay and confocal laser scanning microscopy, respectively.

RESULTS

Relative viability was reduced to approximately 50% when 25 microg/ml of rANE was used. The expression of OPG mRNA in MG63 cells was not altered by rANE. However, decreased levels of mRNA and enzyme activity of ALP were observed. Moreover, the expressions of mRNA and protein of RANKL were stimulated by rANE in a dose-dependent manner.

CONCLUSIONS

The rANE affected morphology and viability of osteoblasts. We also present novel evidence demonstrating that areca nut may compromise the periodontal health of areca chewers by suppression of ALP gene expression and elevation of RANKL gene expression in osteoblasts.

The cytolethal distending toxin induces receptor activator of NF-kappaB ligand expression in human gingival fibroblasts and periodontal ligament cells

Actinobacillus actinomycetemcomitans is associated with localized aggressive periodontitis, a disease characterized by rapid loss of the alveolar bone surrounding the teeth. Receptor activator of NF-kappaB Ligand (RANKL) and osteoprotegerin (OPG) are two molecules that regulate osteoclast formation and bone resorption. RANKL induces osteoclast differentiation and activation, whereas OPG blocks this process by acting as a decoy receptor for RANKL. The purpose of this study was to investigate the effect of A. actinomycetemcomitans on the expression of RANKL and OPG in human gingival fibroblasts and periodontal ligament cells. RANKL mRNA expression was induced in both cell types challenged by A. actinomycetemcomitans extract, whereas OPG mRNA expression remained unaffected. Cell surface RANKL protein was also induced by A. actinomycetemcomitans, whereas there was no change in OPG protein secretion. A cytolethal distending toxin (Cdt) gene-knockout strain of A. actinomycetemcomitans did not induce RANKL expression, in contrast to its wild-type strain. Purified Cdt from Haemophilus ducreyi alone, or in combination with extract from the A. actinomycetemcomitans cdt mutant strain, induced RANKL expression. Pretreatment of A. actinomycetemcomitans wild-type extract with Cdt antiserum abolished RANKL expression. In conclusion, A. actinomycetemcomitans induces RANKL expression in periodontal connective tissue cells. Cdt is crucial for this induction and may therefore be involved in the pathological bone resorption during the process of localized aggressive periodontitis.

Levels of Cytokine Receptor Activator of Nuclear Factor κB Ligand in Gingival Crevicular Fluid in Untreated Chronic Periodontitis Patients

BACKGROUND

Receptor activator of nuclear factor kappaB ligand (RANK-L) is a cytokine involved in the regulation of osteoclastogenesis in bone remodeling and inflammatory osteolysis. One of the major causes of tooth loss in humans is bone destruction. The aim of our study was to determine the presence of RANK-L in gingival crevicular fluid (GCF) samples from adult patients with untreated chronic periodontitis and in healthy controls. We also identified the RANK-L present in lesions undergoing episodic attachment loss from GCF.

METHODS

GCF samples were collected from two periodontally affected sites (probing depth > or = 5 mm, attachment loss > or = 3 mm) in 20 patients (N = 40). After monitoring for 4 months, seven patients showed active periodontal disease, and GCF samples were collected from one active and one inactive site (N = 14 samples). The comparison with healthy controls was carried out by collecting GCF samples from 12 healthy volunteers (N = 24 samples). GCF was collected using a paper strip, and enzyme-linked immunosorbent assay (ELISA) was performed to determine the total amount of RANK-L.

RESULTS

RANK-L was found in a higher proportion (85%) of samples from patients than from controls (46%). The total amount of RANK-L was significantly higher in patients (115.53 +/- 78.18 picograms [pg]) than in healthy subjects (63.08 +/- 55.08 pg) (P = 0.003). Active sites, presumably associated with tissue destruction, had significantly higher levels of RANK-L than their inactive counterparts (125.95 pg versus 91.80 pg, P = 0.007).

CONCLUSION

GCF total amount of RANK-L is significantly increased in periodontal disease, supporting its role in the alveolar bone loss developed in this disease.