Potassium Channel-blockers as Therapeutic Agents to Interfere with Bone Resorption of Periodontal Disease

Porphyromonas gingivalis suppresses adaptive immunity in periodontitis, atherosclerosis, and Alzheimer's disease

Porphyromonas gingivalis, a keystone pathogen in chronic periodontitis, has been found to associate with remote body organ inflammatory pathologies, including atherosclerosis and Alzheimer’s disease (AD). Although P. gingivalis has a plethora of virulence factors, much of its pathogenicity is surprisingly related to the overall immunosuppression of the host. This review focuses on P. gingivalis aiding suppression of the host’s adaptive immune system involving manipulation of cellular immunological responses, specifically T cells and B cells in periodontitis and related conditions. In periodontitis, this bacterium inhibits the synthesis of IL-2 and increases humoral responses. This reduces the inflammatory responses related to T- and B-cell activation, and subsequent IFN-γ secretion by a subset of T cells. The T cells further suppress upregulation of programmed cell death-1 (PD-1)-receptor on CD⁺cells and its ligand PD-L1 on CD11b⁺-subset of T cells. IL-2 downregulates genes regulated by immune response and induces a cytokine pattern in which the Th17 lineage is favored, thereby modulating the Th17/T-regulatory cell (Treg) imbalance. The suppression of IFN-γ-stimulated release of interferon-inducible protein-10 (IP-10) chemokine ligands [ITAC (CXCL11) and Mig (CXCL9)] by P. gingivalis capsular serotypes triggers distinct T cell responses and contributes to local immune evasion by release of its outer membrane vesicles. In atherosclerosis, P. gingivalis reduces Tregs, transforms growth factor beta-1 (TGFβ-1), and causes imbalance in the Th17 lineage of the Treg population. In AD, P. gingivalis may affect the blood–brain barrier permeability and inhibit local IFN-γ response by preventing entry of immune cells into the brain. The scarcity of adaptive immune cells in AD neuropathology implies P. gingivalis infection of the brain likely causing impaired clearance of insoluble amyloid and inducing immunosuppression. By the effective manipulation of the armory of adaptive immune suppression through a plethora of virulence factors, P. gingivalis may act as a keystone organism in periodontitis and in related systemic diseases and other remote body inflammatory pathologies.

KCNK1 inhibits osteoclastogenesis by blocking the Ca2+ oscillation and JNK-NFATc1 signaling axis

KCNK1 (K(+) channel, subfamily K, member 1) is a member of the inwardly rectifying K(+) channel family, which drives the membrane potential towards the K(+) balance potential. Here, we investigated its functional relevance during osteoclast differentiation. KCNK1 was significantly induced during osteoclast differentiation, but its functional overexpression significantly inhibited osteoclast differentiation induced by RANKL (also known as TNFSF11), which was accompanied by the attenuation of the RANKL-induced Ca(2+) oscillation, JNK activation and NFATc1 expression. In contrast, KCNK1 knockdown enhanced the RANKL-induced osteoclast differentiation, JNK activation and NFATc1 expression. In conclusion, we suggest that KCNK1 is a negative regulator of osteoclast differentiation; the increase of K(+) influx by its functional blockade might inhibit osteoclast differentiation by inhibiting Ca(2+) oscillation and the JNK-NFATc1 signaling axis. Together with the increased attention on the pharmacological possibilities of using channel inhibition in the treatment of osteoclast-related disorders, further understanding of the functional roles and mechanisms of K(+) channels underlying osteoclast-related diseases could be helpful in developing relevant therapeutic strategies.

Effects of ibandronate sodium, a nitrogen-containing bisphosphonate, on intermediate-conductance calcium-activated potassium channels in osteoclast precursor cells (RAW 264.7)

Ibanonate sodium (Iban), a nitrogen-containing bisphosphonate, is recognized to reduce skeletal complications through an inhibition of osteoclast-mediated bone resorption. However, how this drug interacts with ion channels in osteoclasts and creates anti-osteoclastic activity remains largely unclear. In this study, we investigated the possible effects of Iban and other related compounds on ionic currents in the osteoclast precursor RAW 264.7 cells. Iban suppressed the amplitude of whole-cell K(+) currents (I K) in a concentration-dependent manner with an IC50 value of 28.9 μM. The I K amplitude was sensitive to block by TRAM-34 and Iban-mediated inhibition of I K was reversed by further addition of DCEBIO, an activator of intermediate-conductance Ca(2+)-activated K(+) (IKCa) channels. Intracellular dialysis with Iban diminished I K amplitude and further addition of ionomycin reversed its inhibition. In 17β-estradiol-treated cells, Iban-mediated inhibition of I K remained effective. In cell-attached current recordings, Iban applied to bath did not modify single-channel conductance of IKCa channels; however, it did reduce channel activity. Iban-induced inhibition of IKCa channels was voltage-dependent. As IKCa-channel activity was suppressed by KN-93, subsequent addition of Iban did not further decrease the channel open probability. Iban could not exert any effect on inwardly rectifying K(+) current in RAW 264.7 cells. Under current-clamp recordings, Iban depolarized the membrane of RAW 264.7 cells and DCEBIO reversed Iban-induced depolarization. Iban also suppressed lipopolysaccharide-stimulated migration of RAW 264.7 cells in a concentration-dependent manner. Therefore, the inhibition by Iban of IKCa channels would be an important mechanism underlying its actions on the functional activity of osteoclasts occurring in vivo.

Kcnn4 is a regulator of macrophage multinucleation in bone homeostasis and inflammatory disease

Macrophages can fuse to form osteoclasts in bone or multinucleate giant cells (MGCs) as part of the immune response. We use a systems genetics approach in rat macrophages to unravel their genetic determinants of multinucleation and investigate their role in both bone homeostasis and inflammatory disease. We identify a trans-regulated gene network associated with macrophage multinucleation and Kcnn4 as being the most significantly trans-regulated gene in the network and induced at the onset of fusion. Kcnn4 is required for osteoclast and MGC formation in rodents and humans. Genetic deletion of Kcnn4 reduces macrophage multinucleation through modulation of Ca²⁺ signaling, increases bone mass, and improves clinical outcome in arthritis. Pharmacological blockade of Kcnn4 reduces experimental glomerulonephritis. Our data implicate Kcnn4 in macrophage multinucleation, identifying it as a potential therapeutic target for inhibition of bone resorption and chronic inflammation.

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We identified a gene network that regulates macrophage multinucleation and includes Kcnn4

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Kcnn4 can be targeted in two inflammatory conditions with macrophage multinucleation

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Kcnn4 regulates bone mass under physiological conditions

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Kcnn4 is a drug target for which inhibitors reached phase III of clinical trials

Receptor activator of NF-kappaB ligand (RANKL) and CD 31 expressions in chronic periodontitis patients before and after surgery

Aim of the study

The present study investigated the hypothesis that upregulation of receptor activator of NF-kappaB ligand (RANKL) expression may be associated with upregulation of endothelial cell activitiy, which is common for periods of periodontal bone loss in chronic periodontitis.

Material and methods

RANKL expression of activated cells in soft tissue biopsies with CD 31 activity and the presence of RANKL and osteoprotegerin (OPG) in gingival crevicular fluid (GCF) were assessed in chronic periodontitis patients. Biopsies from 17 patients and 10 healthy subjects were immunohistochemically analyzed. Clinical measurements [plaque index (PI), the gingival index (GI), probing pocket depth (PPD), clinical attachment level (CAL) and gingival bleeding index (GBI)] and GCF samples were obtained before and after periodontal therapy.

Results

CD31 staining did not support the assumption that endothelium-like cells were predominantly associated with RANKL expression.

Conclusions

RANKL-positive cells were widely distributed in periodontitis patients giving only partial support to the hypothesis that RANKL expression is restricted to T- and B-cell activation.

HIV-1 Tat protein increases microglial outward K(+) current and resultant neurotoxic activity

Microglia plays a crucial role in the pathogenesis of HIV-1-associated neurocognitive disorders. Increasing evidence indicates the voltage-gated potassium (Kv) channels are involved in the regulation of microglia function, prompting us to hypothesize Kv channels may also be involved in microglia-mediated neurotoxic activity in HIV-1-infected brain. To test this hypothesis, we investigated the involvement of Kv channels in the response of microglia to HIV-1 Tat protein. Treatment of rat microglia with HIV-1 Tat protein (200 ng/ml) resulted in pro-inflammatory microglial activation, as indicated by increases in TNF-α, IL-1β, reactive oxygen species, and nitric oxide, which were accompanied by enhanced outward K(+) current and Kv1.3 channel expression. Suppression of microglial Kv1.3 channel activity, either with Kv1.3 channel blockers Margatoxin, 5-(4-Phenoxybutoxy)psoralen, or broad-spectrum K(+) channel blocker 4-Aminopyridine, or by knockdown of Kv1.3 expression via transfection of microglia with Kv1.3 siRNA, was found to abrogate the neurotoxic activity of microglia resulting from HIV-1 Tat exposure. Furthermore, HIV-1 Tat-induced neuronal apoptosis was attenuated with the application of supernatant collected from K(+) channel blocker-treated microglia. Lastly, the intracellular signaling pathways associated with Kv1.3 were investigated and enhancement of microglial Kv1.3 was found to correspond with an increase in Erk1/2 mitogen-activated protein kinase activation. These data suggest targeting microglial Kv1.3 channels may be a potential new avenue of therapy for inflammation-mediated neurological disorders.

Inhibitory effects of blockage of intermediate conductance Ca(2+)-activated K (+) channels on proliferation of hepatocellular carcinoma cells

The roles of intermediate conductance Ca(2+)-activated K(+) channel (IKCa1) in the pathogenesis of hepatocellular carcinoma (HCC) were investigated. Immunohistochemistry and Western blotting were used to detect the expression of IKCa1 protein in 50 HCC and 20 para-carcinoma tissue samples. Real-time PCR was used to detect the transcription level of IKCa1 mRNA in 13 HCC and 11 para-carcinoma tissue samples. The MTT assay was used to measure the function of IKCa1 in human HCC cell line HepG2 in vitro. TRAM-34, a specific blocker of IKCa1, was used to intervene with the function of IKCa1. As compared with para-carcinoma tissue, an over-expression of IKCa1 protein was detected in HCC tissue samples (P<0.05). The mRNA expression level of IKCa1 in HCC tissues was 2.17 times higher than that in para-carcinoma tissues. The proliferation of HepG2 cells was suppressed by TRAM-34 (0.5, 1.0, 2.0 and 4.0 μmol/L) in vitro (P<0.05). Our results suggested that IKCa1 may play a role in the proliferation of human HCC, and IKCa1 blockers may represent a potential therapeutic strategy for HCC.

Immunohistochemical expression of RANKL, RANK and OPG in gingival tissue of patients with periodontitis

OBJECTIVES

To evaluate the expression of the receptor activator of NF-κB (RANK), the receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG), in the gingival tissue of patients with periodontitis.

MATERIALS AND METHODS

Gingival tissue was obtained from 14 systemically healthy subjects with chronic periodontitis during conventional periodontal surgery. Immunohistochemistry was used to detect the expression of RANK, RANKL and OPG in the oral and periodontal pocket epithelium as well as in the connective tissue cells.

RESULTS

RANKL was negatively expressed in both oral and periodontal pocket epithelium. OPG was also negative or weakly positive in the whole epithelium. RANK showed moderate/strong positive staining mainly in the basal and suprabasal layer of oral and periodontal pocket epithelium. In most of the cases, more than 60% of the inflammatory cell infiltrate stained for RANK and RANKL. In these cases the intensity of the stained cells ranged from moderate-to-strong. In less than half of the cases, OPG was positive in more than 60% of the stained cells of the inflammatory cell infiltrate.

CONCLUSION

The RANK, RANKL and OPG proteins are differentially expressed in periodontal tissues and may play a major role in the bone loss occurring in periodontitis.

Evidence for aconitine-induced inhibition of delayed rectifier K(+) current in Jurkat T-lymphocytes

Aconitine (ACO) is a highly toxic diterpenoid alkaloid and known to exert the immunomodulatory action. However, whether it has any effects on ion currents in immune cells remains unknown. The effects of ACO and other related compounds on ion currents in Jurkat T-lymphocytes were investigated in this study. ACO suppressed the amplitude of delayed-rectifier K(+) current (I(K(DR))) in a time- and concentration-dependent manner. Margatoxin (100 nM), a specific blocker of K(V)1.3-encoded current, decreased the I(K(DR)) amplitude in these cells and the ACO-induced inhibition of I(K(DR)) was not reversed by 1-ethyl-2-benzimidazolinone (30 μM) or nicotine (10 μM). The IC(50) value for ACO-mediated inhibition of I(K(DR)) was 5.6 μM. ACO accelerated the inactivation of I(K(DR)) with no change in the activation rate of this current. Increasing the ACO concentration not only reduced the I(K(DR)) amplitude, but also accelerated the inactivation time course of the current. With the aid of minimal binding scheme, the inhibitory action of ACO on I(K(DR)) was estimated with a dissociation constant of 6.8 μM. ACO also shifted the inactivation curve of I(K(DR)) to a hyperpolarized potential with no change in the slope factor. Cumulative inactivation for I(K(DR)) was enhanced in the presence of ACO. In Jurkat cells incubated with amiloride (30 μM), the ACO-induced inhibition of I(K(DR)) remained unaltered. In RAW 264.7 murine macrophages, ACO did not modify the kinetics of I(K(DR)), although it suppressed I(K(DR)) amplitude. Taken together, these effects can significantly contribute to its action on functional activity of immune cells if similar results are found in vivo.

Aggregatibacter actinomycetemcomitans Omp29 is associated with bacterial entry to gingival epithelial cells by F-actin rearrangement

The onset and progressive pathogenesis of periodontal disease is thought to be initiated by the entry of Aggregatibacter actinomycetemcomitans (Aa) into periodontal tissue, especially gingival epithelium. Nonetheless, the mechanism underlying such bacterial entry remains to be clarified. Therefore, this study aimed to investigate the possible role of Aa outer membrane protein 29 kD (Omp29), a homologue of E. coli OmpA, in promoting bacterial entry into gingival epithelial cells. To accomplish this, Omp29 expression vector was incorporated in an OmpA-deficient mutant of E. coli. Omp29⁺/OmpA⁻E. coli demonstrated 22-fold higher entry into human gingival epithelial line cells (OBA9) than Omp29⁻/OmpA⁻E. coli. While the entry of Aa and Omp29⁺/OmpA⁻E. coli into OBA9 cells were inhibited by anti-Omp29 antibody, their adherence to OBA9 cells was not inhibited. Stimulation of OBA9 cells with purified Omp29 increased the phosphorylation of focal adhesion kinase (FAK), a pivotal cell-signaling molecule that can up-regulate actin rearrangement. Furthermore, Omp29 increased the formation of F-actin in OBA9 cells. The internalization of Omp29-coated beads and the entry of Aa into OBA9 were partially inhibited by treatment with PI3-kinase inhibitor (Wortmannin) and Rho GTPases inhibitor (EDIN), both known to convey FAK-signaling to actin-rearrangement. These results suggest that Omp29 is associated with the entry of Aa into gingival epithelial cells by up-regulating F-actin rearrangement via the FAK signaling pathway.

Natural products as a source of Alzheimer's drug leads

This review focuses on recent developments in the use of natural products as therapeutics for Alzheimer's disease. The compounds span a diverse array of structural classes and are organized according to their mechanism of action, with the focus primarily on the major hypotheses. Overall, the review discusses more than 180 compounds and summarizes 400 references.

Role of periodontal pathogenic bacteria in RANKL-mediated bone destruction in periodontal disease

Accumulated lines of evidence suggest that hyperimmune responses to periodontal bacteria result in the destruction of periodontal connective tissue and alveolar bone. The etiological roles of periodontal bacteria in the onset and progression of periodontal disease (PD) are well documented. However, the mechanism underlying the engagement of periodontal bacteria in RANKL-mediated alveolar bone resorption remains unclear. Therefore, this review article addresses three critical subjects. First, we discuss earlier studies of immune intervention, ultimately leading to the identification of bacteria-reactive lymphocytes as the cellular source of osteoclast-induction factor lymphokine (now called RANKL) in the context of periodontal bone resorption. Next, we consider (1) the effects of periodontal bacteria on RANKL production from a variety of adaptive immune effector cells, as well as fibroblasts, in inflamed periodontal tissue and (2) the bifunctional roles (upregulation vs. downregulation) of LPS produced from periodontal bacteria in a RANKL-induced osteoclast-signal pathway. Future studies in these two areas could lead to new therapeutic approaches for the management of PD by down-modulating RANKL production and/or RANKL-mediated osteoclastogenesis in the context of host immune responses against periodontal pathogenic bacteria.

Kv1.3: a potential pharmacological target for diabetes

K(+) channels, which are ubiquitous membrane proteins, play a central role in regulating the resting membrane potential and the shape and duration of the action potential in pancreatic beta-cells. There are at least three types of K(+) channels (K(ATP), K(Ca), and Kv2.1 channels) that are involved in glucose-stimulated insulin secretion in pancreatic beta-cells, and one type (Kv1.3) that is associated with the regulation of insulin sensitivity in peripheral target tissues. This article reviews the function of Kv1.3 channels that contribute to mediating insulin action in insulin-sensitive tissues. Pharmacological strategies for targeting Kv1.3 are then discussed with a focus on a rationale for the potential therapeutic use of Kv1.3 blocker in diabetic treatment.

Kv1.3 potassium channels as a therapeutic target in multiple sclerosis

We discuss the potential use of inhibitors of Kv1.3 potassium channels in T lymphocytes as therapeutics for multiple sclerosis. Current treatment strategies target the immune system in a non-selective manner. The resulting general immunosuppression, toxic side-effects and increased risk of opportunistic infections create the need for more selective therapeutics. Autoreactive effector-memory T (T(EM)) cells, considered to be major mediators of autoimmunity, express large numbers of Kv1.3 channels. Selective blockers of Kv1.3 inhibit calcium signaling, cytokine production and proliferation of T(EM) cells in vitro, and T(EM) cell-motility in vivo. Kv1.3 blockers ameliorate disease in animal models of multiple sclerosis, rheumatoid arthritis, type 1 diabetes mellitus and contact dermatitis without compromising the protective immune response to acute infections. Kv1.3 blockers have a good safety profile in rodents and primates.

The functional network of ion channels in T lymphocytes

For more than 25 years, it has been widely appreciated that Ca2+ influx is essential to trigger T-lymphocyte activation. Patch clamp analysis, molecular identification, and functional studies using blockers and genetic manipulation have shown that a unique contingent of ion channels orchestrates the initiation, intensity, and duration of the Ca2+ signal. Five distinct types of ion channels--Kv1.3, KCa3.1, Orai1+ stromal interacting molecule 1 (STIM1) [Ca2+-release activating Ca2+ (CRAC) channel], TRPM7, and Cl(swell)--comprise a network that performs functions vital for ongoing cellular homeostasis and for T-cell activation, offering potential targets for immunomodulation. Most recently, the roles of STIM1 and Orai1 have been revealed in triggering and forming the CRAC channel following T-cell receptor engagement. Kv1.3, KCa3.1, STIM1, and Orai1 have been found to cluster at the immunological synapse following contact with an antigen-presenting cell; we discuss how channels at the synapse might function to modulate local signaling. Immuno-imaging approaches are beginning to shed light on ion channel function in vivo. Importantly, the expression pattern of Ca2+ and K+ channels and hence the functional network can adapt depending upon the state of differentiation and activation, and this allows for different stages of an immune response to be targeted specifically.

Voltage-gated potassium channel modulation of neurotoxic activity in human immunodeficiency virus type-1(HIV-1)-infected macrophages

Macrophages play an important role in brain immune and inflammatory responses. They are also critical cells in mediating the pathology of neurodegenerative disorders such as HIV-associated dementia. This is largely through their capacity to secrete a variety of bioactive molecules such as cytokines, leading to neuronal dysfunction and/or death. Accumulating evidence indicates that voltage-gated potassium (Kv) channels play a pivotal role in the modulation of macrophage proliferation, activation, and secretion. Blockade of Kv channels by specific antagonists decreases macrophage cytokine production and ameliorates macrophage-associated neuronal injury. These results suggest that Kv channels might become a potential target for the development of new therapeutic strategies for chronic inflammatory diseases.

Cells move when ions and water flow

Cell migration is a process that plays an important role throughout the entire life span. It starts early on during embryogenesis and contributes to shaping our body. Migrating cells are involved in maintaining the integrity of our body, for instance, by defending it against invading pathogens. On the other side, migration of tumor cells may have lethal consequences when tumors spread metastatically. Thus, there is a strong interest in unraveling the cellular mechanisms underlying cell migration. The purpose of this review is to illustrate the functional importance of ion and water channels as part of the cellular migration machinery. Ion and water flow is required for optimal migration, and the inhibition or genetic ablation of channels leads to a marked impairment of migration. We briefly touch cytoskeletal mechanisms of migration as well as cell-matrix interactions. We then present some general principles by which channels can affect cell migration before we discuss each channel group separately.

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.

Immune response: the key to bone resorption in periodontal disease

Periodontal disease infection with oral biofilm microorganisms initiates host immune response and signs of periodontitis, including bone resorption. This review delineates some mechanisms underlying the host immune response in periodontal infection and alveolar bone resorption. Activated T lymphocytes have been historically implicated in experimental periodontal bone resorption. An experimental rat adoptive transfer/gingival challenge periodontal disease model has been demonstrated to require antigen-specific T lymphocytes and gingival instillation of antigen and LPS for bone resorption. Interference with costimulatory interactions between T cells and antigen-presenting cells abrogated bone resorption, further emphasizing the significance of immune response in periodontal disease. Receptor activator of nuclear factor kappaB ligand (RANKL), a critical osteoclast differentiation factor, is expressed on T lymphocytes in human periodontal disease as determined by immunohistochemical and confocal microscopic analyses. Interference with RANKL by systemic administration of osteoprotegerin (OPG), the decoy receptor for (and inhibitor of) RANKL, resulted in abrogation of periodontal bone resorption in the rat model. This finding indicated that T cell-mediated bone resorption is RANKL-dependent. In additional experiments, treatment of T cell-transferred rats with kaliotoxin (a scorpion venom potassium channel inhibitor) resulted in decreases in T-cell RANKL expression, diminished induction of RANKL-dependent osteoclastogenesis, and abrogation of bone resorption, implicating an important role of immune response/RANKL expression in osteoclastogenesis/bone resorption. In other experiments, adoptive transfer of antigen-specific, RANKL-expressing B cells, and infection with the antigen-bearing Actinobaccillus actinomycetemcomitans gave rise to periodontal bone resorption, indicating that B cells also have the capacity to mediate bone resorption, probably via RANKL expression. In humans, prominent T lymphocytes have been identified in periodontal disease, and diseased tissues showed elevated RANKL mRNA expression, as well as decreased OPG mRNA expression. Mononuclear cells from periodontal lesions involving T cells and B cells of patients induced osteoclastogenesis in vitro. In summary, a biofilm interface initiates immune cell infiltration, stimulating osteoclastogenesis/bone resorption in periodontal disease. This resorption can be ameliorated by inhibition of RANKL activity or by diminishing immune cell stimulation. These two procedures, if localized, have the potential to lead to the prevention or therapeutic management of periodontal disease and therefore require further study.