Effects of Risedronate on Alveolar Bone Loss and Angiogenesis: A Stereologic Study in Rats

Medication-related osteonecrosis of the jaw using periodontitis-induced rat before tooth extraction

OBJECTIVE

This study aimed to investigate the occurrence of medication-related osteonecrosis of the jaw (MRONJ) after tooth extraction due to periodontitis in ovariectomized rats.

METHODS

Twenty-four osteoporosis-induced rats were administered with zoledronic acid (ZA; ZA group) or saline (CONT group). In both groups, tooth extraction was performed after inducing periodontitis, and all animals were sacrificed 8-week after tooth extraction.

RESULTS

Micro-CT of the tibia showed that the bone volume fraction, bone surface density, trabecular number, and bone mineral density were significantly higher in the ZA group than in the CONT group. Histologically, the proliferative zone on the growth plate was thicker in the ZA group than in the CONT group. Micro-CT of the extraction sites revealed that the bone volume fraction was significantly higher in the ZA group than in the CONT group. Radiologically, the ZA group showed partial healing and delayed healing. Histological analysis revealed normal bone healing status with completely healed epithelium in the extraction sites of the CONT group, whereas abnormal empty osteocytes in the necrotic bone and inflammatory infiltration were observed in the ZA group.

CONCLUSION

The incidence of MRONJ increased in the rats administered with ZA.

Can locally applied risedronate be an effective agent when combined with xenografts? An animal study

BACKGROUND

To examine the effects of local risedronate application with xenografts on healing of rabbit skull defects using histological, histomorphometric, immunohistochemical, and three-dimensional radiological methods.

METHODS

Two critical-sized defects with a diameter of 10 mm were created in 16 rabbits and filled with xenogenic bone graft and xenogenic bone graft + 5 mg risedronate in the control I and risedronate (RIS) groups, respectively. Residual graft, new bone, soft tissue areas, and bone volume were evaluated in the 4- and 8-week study groups.

RESULTS

In both the 4- and 8-week samples, the RIS group samples had significantly higher mean new bone area values than the C group (p < 0.05). In both groups, the values for the new bone area were significantly higher in the 8-week-old samples than in the 4-week-old samples (p < 0.05). The h scores obtained for sialoprotein and osteopontin did not differ significantly between the groups at either time point (p > 0.05). The results of radiological evaluation showed that the bone density value was significantly higher in the C group than in the RIS group at either time point (p < 0.05).

CONCLUSIONS

Although this study aimed to demonstrate the effect of risedronate on the osteoconductive properties of xenografts when applied locally, targeted results could not be achieved.

Medication-related osteonecrosis of the jaw: A disease of significant importance for older patients

BACKGROUND

Medication-related osteonecrosis of the jaw (MRONJ) is clinically defined as a non-healing jawbone ulcerative-necrotic lesion appearing after dental therapy or minor trauma in patients treated previously with anti-resorptive, anti-angiogenic or immunomodulators. Older patients with osteoporosis and cancer receive these pharmacological agents regularly. As these patients are long-term survivors, efficient treatment is of paramount importance for their quality of life.

METHODS

Literature searches via PubMed were conducted to identify relevant MRONJ studies. Basic information on MRONJ classification, clinical features, and pathosphysiology is presented herein as well as various clinical studies dealing with MRONJ in patients with osteoporosis and cancer. Lastly, we discuss current managment of patients and new trends in treatment of MRONJ.

RESULTS

Although close follow-up and local hygiene have been advocated by some authors, severe forms of MRONJ are not responsive to conservative therapy. At present, there is no "gold standard" therapy for this condition. However, as the physiopathological basis of MRONJ is represented by the anti-angiogenic action of various pharmacological agents, new methods to increase and promote local angiogenesis and vascularization have recently been successfully tested in vitro, limited preclinical studies, and in a pilot clinical study.

CONCLUSIONS

It appears that the best method implies application on the lesion of endothelial progenitor cells as well as pro-angiogenic factors such as Vascular Endothelial Growth Factor (VEGF) and other related molecules. More recently, scaffolds in which these factors have been incorporated have shown positive results in limited trials. However, these studies must be replicated to include a large number of cases before any official therapeutic protocol is adopted.

Effects of a locally administered risedronate/autogenous bone graft combination on bone healing in a critical-size rabbit defect model

BACKGROUND

Risedronate is a bisphosphonate with poor oral absorption. An extremely hydrophilic molecule that has a high affinity for bone, risedronate also inhibits the farnesyl diphosphate synthase enzyme, inhibiting osteoclastic activity and reducing bone turnover and resorption. Autogenous bone grafts contain osteogenic cells and osteoinductive factors that are essential for bone regeneration and are therefore considered the gold standard. Thus, this study aimed to investigate the impact of local risedronate administered with autogenous bone grafts on the healing of defects in rabbit skulls using histological, histomorphometric, immunohistochemical, and three-dimensional radiological methods.

METHODS

Two 10-mm-diameter critical-size defects were created in 16 rabbits and filled with autogenous bone graft and autogenous bone graft + 5 mg risedronate in the control (C) and risedronate (RIS) groups, respectively. Residual graft, new bone, soft tissue areas, and bone volume were evaluated in the 4- and 8-week study groups.

RESULTS

There were no statistically significant differences in bone graft, new bone, or soft tissue area between the groups at 4 weeks (p > 0.05). At 8 weeks, the new bone area was significantly higher in the RIS group than in the C group (p < 0.05). The h scores obtained from sialoprotein and osteopontin did not differ significantly between the groups (p > 0.05). The radiologically measured total bone volume was significantly higher in the RIS group than in the C group at both time points (p < 0.05).

CONCLUSIONS

In this study, risedronate enhanced the osteoconductive properties of autogenous bone grafts and rapidly created better-quality bone. This could improve future patient outcomes.

THE EFFECT OF BISPHOSPHONATE RISEDRONATE HYDROGEL ON ALKALINE PHOSPHATASE AND OSTEOCLASTS DURING RELAPSE MOVEMENT

Objectives: To analyze the effect of risedronate hydrogel on enzyme alkaline phosphatase (ALP) and osteoclast/osteoblast ratio during tooth relapse movement Materials and methods: The research design is experimental with time series. The lower incisors of 75 guinea pigs are distally moved using open coil spring. The guinea pigs were divided into three groups: without risedronate (group A; n = 25); given 250 µmol/L of risedronate hydrogel (group B; n = 25), and given 500 µmol/L of risedronate hydrogel (group C; n = 25). Risedronate were applied intrasulcularly in the mesial part of the gingival sulcus every 3 days. After 14 days of stabilization, the open coil spring was removed (bisphosphonate administration was continued). The relapsed teeth and ALP levels on days 0, 3, 7, 14, and 21 were measured. The osteoclast/osteoblast ratio was measured by hematoxylin and eosin staining. ANOVA test was used to determine the difference in the three groups and their interactions with concentration and time. Results: There was a significant difference in osteoclast/osteoblast ratio on day 3 (p = 0.019, p

Sustained Release of Risedronate from PLGA Microparticles Embedded in Alginate Hydrogel for Treatment of Bony Lesions

Background:

Inflammatory bone resorption in periodontitis can lead to tooth loss. Systemic administration of bisphosphonates such as risedronate for preventing bone resorption can cause adverse effects. ALG and PLGA microparticles have been studied as drug delivery systems for sustained release of drugs. Therefore, the release pattern of risedronate from PLGA microparticles embedded with ALG was studied as a drug delivery system for sustained release of the drug, which can be used in local administrations.

Methods:

Risedronate-containing PLGA microparticles were fabricated using double emulsion solvent evaporation technique. Ionic cross-linking method was used to fabricate risedronate-loaded ALG. Risedronate-containing PLGA microparticles were then coated with ALG. The calibration curve of risedronate was traced to measure EE and study the release pattern. SEM imaging was carried out, and cell toxicity was examined using MTT assay. Statistical analysis of data was carried out using SPSS ver. 20 software, via one-way ANOVA and Tukey’s tests.

Results:

SEM imaging showed open porosities on ALGs. The mean EE of PLGA microparticles for risedronate was 57.14 ± 3.70%. Risedronate released completely after 72 h from ALG, and the cumulative release was significantly higher (p = 0.000) compared to PLGA microspheres coated with ALG, which demonstrated sustained released of risedronate until day 28. Risedronate-loaded ALG showed a significant decrease in gingival fibroblasts cell viability (p < 0.05).

Conclusion:

Alginate-coated PLGA microspheres could release risedronate in a sustained and controlled way and also did not show cell toxicity. Therefore, they seem to be an appropriate system for risedronate delivery in local applications.

Local delivery of hydrogel encapsulated vascular endothelial growth factor for the prevention of medication-related osteonecrosis of the jaw

The anti-angiogenic effects of bisphosphonates have been hypothesized as one of the major etiologic factors in the development of medication-related osteonecrosis of the jaw (MRONJ), a severe debilitating condition with limited treatment options. This study evaluated the potential of a gelatine-hyaluronic acid hydrogel loaded with the angiogenic growth factor, vascular endothelial growth factor (VEGF), as a local delivery system to aid in maintaining vascularization in a bisphosphonate-treated (Zoledronic Acid) rodent maxillary extraction defect. Healing was assessed four weeks after implantation of the VEGF-hydrogel into extraction sockets. Gross examination and histological assessment showed that total osteonecrosis and inflammatory infiltrate was significantly reduced in the presence of VEGF. Also, total vascularity and specifically neovascularization, was significantly improved in animals that received VEGF hydrogel. Gene expression of vascular, inflammatory and bone specific markers within the defect area were also significantly altered in the presence of VEGF. Furthermore, plasma cytokine levels were assessed to determine the systemic effect of locally delivered VEGF and showed similar outcomes. In conclusion, the use of locally delivered VEGF within healing extraction sockets assists bone healing and prevents MRONJ via a pro-angiogenic and immunomodulatory mechanism.

Preclinical models of medication-related osteonecrosis of the jaw (MRONJ)

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe adverse event affecting patients with cancer and patients with osteoporosis who have been treated with powerful antiresorptives (pARs) or angiogenesis inhibitors (AgIs). pARs, including nitrogen-containing bisphosphonates (N-BPs; e.g., zoledronic acid, alendronate) and anti-RANKL antibodies (e.g., denosumab), are used to manage bone metastases in patients with cancer or to prevent fragility fractures in patients with osteoporosis. Though significant advances have been made in understanding MRONJ, its pathophysiology is still not fully elucidated. Multiple species have been used in preclinical MRONJ research, including the rat, mouse, rice rat, rabbit, dog, sheep, and pig. Animal research has contributed immensely to advancing the MRONJ field, particularly, but not limited to, in developing models and investigating risk factors that were first observed in humans. MRONJ models have been developed using clinically relevant doses of systemic risk factors, like N-BPs, anti-RANKL antibodies, or AgIs. Specific local oral risk factors first noted in humans, including tooth extraction and inflammatory dental disease (e.g., periodontitis, periapical infection, etc.), were then added. Research in rodents, particularly the rat, and, to some extent, the mouse, across multiple laboratories, has contributed to establishing multiple relevant and complementary preclinical models. Models in larger species produced accurate clinical and histopathologic outcomes suggesting a potential role for confirming specific crucial findings from rodent research. We view the current state of animal models for MRONJ as good. The rodent models are now reliable enough to produce large numbers of MRONJ cases that could be applied in experiments testing treatment modalities. The course of MRONJ, including stage 0 MRONJ, is characterized well enough that basic studies of the molecular or enzyme-level findings in different MRONJ stages are possible. This review provides a current overview of the existing models of MRONJ, their more significant features and findings, and important instances of their application in preclinical research.

Allogeneic Bone Marrow Mesenchymal Stem Cell Transplantation in Tooth Extractions Sites Ameliorates the Incidence of Osteonecrotic Jaw-Like Lesions in Zoledronic Acid-Treated Rats

Medication-related osteonecrosis of the jaw (MRONJ) is defined as the exposed necrotic bone involving the maxillofacial structures in bisphosphonate treated patients, and the pathophysiology of this disease remains unclear. The aim of this study was to assess the effects of the allogeneic transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) in a model of Wistar mice with induced MRONJ disease. BM-MSCs from five male Wistar rats were characterized and cultured on β-tricalcium phosphate (β-TCP) granules. Thirty female Wistar rats were injected intraperitoneally with zoledronic acid and afterwards upper jaw molars were extracted. The animals were randomized to receive: Group 1: 1 × 10⁶ BM-MSCs/β-TCP construct in the alveolar socket; and Group 2: Saline solution/β-TCP construct. A clinical and histological analysis was performed. Nested polymerase chain reaction (PCR) was assessed to verify the presence of transplanted male rat cells in the female recipient jaws. Clinical and histological findings evidenced that none of the animals in Group 1 exhibited uncovered sockets or bone exposure associated to MRONJ, whereas we detected 33% of MRONJ cases in Group 2. In addition, male rat cells were detected in the maxillae site four weeks after transplantation in the BM-MSCs-group. Allogeneic BM-MSCs in extractions sites ameliorates MRONJ incidence in zoledronic acid-treated rats compared to non-MSC treatments.

Periodontitis and diabetes interrelationships in rats: biochemical and histopathological variables

Background

A two-way relationship between diabetes and periodontitis is now clinically established. Both conditions share common mechanisms of pathogenesis that are related to altered immune-inflammatory responses at local and/or systemic levels. The aim of this study is to investigate whether periodontitis is associated with the development and progression of diabetes and to evaluate the health impact of coexistence of both diseases.

Material and methods

Male Sprague Dawley rats (10 weeks old) were randomized into seven groups (n = 12): Group 1) Control; Groups 2 and 6) Periodontitis induced at two or six weeks; Groups 3 and 5) Diabetes induced at two or six weeks; Groups 4 and 7) Periodontitis followed by diabetes, and diabetes followed by periodontitis at two or six weeks. For diabetes induction, animals received a one-time intravenous injection of streptozotocin (50 mg/kg). Periodontitis was induced by Lipoppolysaccharide injection (20 μg/rat) through the palatal gingival and by placing a ligature of 0/0 braided silk around the cervix of the upper right second molar. Body weight, glycaemia as well as urine were collected weekly. Rats were sacrificed at the end of week 10, gingival tissue was removed, fixed in formaldehyde and processed for histopathological study.

Results

Body weight was significantly decreased (25%) following diabetes induction (p < 0.01). 40% weight loss was observed when diabetes was induced first compared to 30% when periodontitis was first induced in the animals (p < 0.01). Rats treated with streptozotocin showed a three-fold increase in diabetes compared to the control group (p < 0.01). In rats where periodontitis was induced after diabetes, glucose levels increased significantly (450 mg/dL) compared to glucose levels (410 mg/dL) where periodontitis was induced first (p < 0.01). Histopathological studies showed greater alveolar bone loss when both diabetes and periodontitis were present.

Conclusion

When periodontitis occurs after diabetes it aggravates the symptoms of the two pathologies. When diabetes is induced after periodontitis, no symptoms aggravation is observed for diabetes, although periodontitis gets worse.

The role of HMGB1 in liver inflammation in obese rats

Obesity is a chronic disease that is characterized by increased body fat owing to imbalance between consumed and expended energy. Inflammation generally is accompanied by accumulation of excess lipid in adipose tissue and liver. High mobility group box-1 (HMGB1) participates in the pathogenesis of inflammatory diseases. We investigated the relation of the number of HMGB1 positive cells to body mass index (BMI), liver inflammation and the number of Kupffer cells. We divided 18 female Wistar albino rats into two groups: group 1, untreated control fed normal commercial rat diet and group 2, obese rats fed a special diet containing 40% fat. The plasma concentrations of cholesterol, glucose, superoxide dismutase enzyme (SOD) and catalase activities were measured for all animals. The numbers of hepatocytes, Kupffer cells and HMGB1 positive cells were counted using stereological methods. The mean numbers of Kupffer cells and HMGB1 positive cells were higher for group 2 than for group 1. The concentrations of plasma cholesterol and glucose levels also were higher in group 2. Plasma levels of SOD and catalase were significantly lower in group 2 compared to group 1. The number of HMGB1 cells was related directly to BMI and inflammation. The role of HMGB1 was demonstrated for the liver of the obese group. We demonstrated the relations among HMGB1, BMI, obesity and inflammation.

Pathogenesis of medication-related osteonecrosis of the jaw: a comparative study of in vivo and in vitro trials

Objective This study was performed to determine whether the results of prevailing in vivo and in vitro studies offer a reliable model for investigation of medication-related osteonecrosis of the jaw (MRONJ). Methods Embase, Medline, and the Cochrane Library were searched for articles published from September 2003 to June 2017 involving experimental approaches to the pathogenesis of MRONJ. In vivo and in vitro trials were analyzed with respect to the scientific question, study design, methodology, and results. Results Of 139 studies, 87, 46, and 6 conducted in vivo, in vitro, and both in vivo and in vitro experiments, respectively. Rats, mice, dogs, minipigs, sheep, and rabbits were the preferred animal models used. Osteoblasts, osteoclasts, fibroblasts, keratinocytes, macrophages, and human umbilical vein endothelial cells were the preferred cell types. Zoledronate, alendronate, ibandronate, and risedronate were the most frequent bisphosphonates used. MRONJ was most reliably induced in minipigs because of the close relationship with human bone physiology. In vitro studies showed that reduced viability, growth, and migration of cells in the bone and soft tissues were causative for MRONJ. Other than exposed jawbone after tooth extraction, no reliable cofactors were found. Conclusion The minipig is the most suitable animal model for MRONJ.

Effect of locally administered novel biodegradable chitosan based risedronate/zinc-hydroxyapatite intra-pocket dental film on alveolar bone density in rat model of periodontitis

The aim of this study was to develop a chitosan-based risedronate/zinc-hydroxyapatite intrapocket dental film (CRZHDF) for applications in the treatment of alveolar bone loss in an animal model of periodontitis. The physical characteristics (folding endurance, pH, mucoadhesive strength, risedronate content and release) of CRZHDF, exhibited results within the limit. X-ray diffraction analysis indicates reduced or disappeared crystallinity of risedronate and zinc-hydroxyapatite in presence of chitosan. Further, FTIR studies revealed stability of CRZHDF and compatibility between risedronate, zinc-hydroxyapatite and chitosan. Periodontitis was induced by Porphyromonas gingivalis-lipopolysaccharide injections around the mandibular first molar. We divided rats into 5 groups (12 rats/group): healthy, untreated periodontitis; periodontitis plus CRZHDF-A, periodontitis plus CRZHDF-B, and periodontitis plus chitosan film. After four weeks, blood samples and mandibles were obtained for biochemical, radiographic and histological analysis. Bone specific alkaline phosphatise activity and tartrate resistant acid phosphatase 5b was statistically lower in CRZHDF-A and CRZHDF-B groups as compared to the untreated periodontitis group (p < 0.0001). The expression of osteocalcin was statistically higher in CRZHDF-A and CRZHDF-B groups as compared to the untreated periodontitis group (p < 0.0001). Alveolar bone was intact in the healthy group. Local administration of CRZHDF resulted in significant improvements in the mesial and distal periodontal bone support (MPBS and DPBS, respectively) proportions (%), bone mineral density, and also reversed alveolar bone resorption when compared to the untreated periodontitis group (p < 0.001). The study reported here reveals that novel CRZHDF treatment effectively reduced alveolar bone destruction and contributes to periodontal healing in a rat model of experimental periodontitis.

Treatment of OPG-deficient mice with WP9QY, a RANKL-binding peptide, recovers alveolar bone loss by suppressing osteoclastogenesis and enhancing osteoblastogenesis

Osteoblasts express two key molecules for osteoclast differentiation, receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG), a soluble decoy receptor for RANKL. RANKL induces osteoclastogenesis, while OPG inhibits it by blocking the binding of RANKL to RANK, a cellular receptor of RANKL. OPG-deficient (OPG^–/–) mice exhibit severe alveolar bone loss with enhanced bone resorption. WP9QY (W9) peptide binds to RANKL and blocks RANKL-induced osteoclastogenesis. W9 is also reported to stimulate bone formation in vivo. Here, we show that treatment with W9 restores alveolar bone loss in OPG^–/–mice by suppressing osteoclastogenesis and enhancing osteoblastogenesis. Administration of W9 or risedronate, a bisphosphonate, to OPG^–/–mice significantly decreased the osteoclast number in the alveolar bone. Interestingly, treatment with W9, but not risedronate, enhanced Wnt/β-catenin signaling and induced alveolar bone formation in OPG^–/–mice. Expression of sclerostin, an inhibitor of Wnt/β-catenin signaling, was significantly lower in tibiae of OPG^–/–mice than in wild-type mice. Treatment with risedronate recovered sclerostin expression in OPG^–/–mice, while W9 treatment further suppressed sclerostin expression. Histomorphometric analysis confirmed that bone formation-related parameters in OPG^–/–mice, such as osteoblast number, osteoblast surface and osteoid surface, were increased by W9 administration but not by risedronate administration. These results suggest that treatment of OPG^–/–mice with W9 suppressed osteoclastogenesis by inhibiting RANKL signaling and enhanced osteoblastogenesis by attenuating sclerostin expression in the alveolar bone. Taken together, W9 may be a useful drug to prevent alveolar bone loss in periodontitis.

Is GERD a Factor in Osteonecrosis of the Jaw? Evidence of Pathology Linked to G6PD Deficiency and Sulfomucins

Osteonecrosis of the jaw (ONJ), a rare side effect of bisphosphonate therapy, is a debilitating disorder with a poorly understood etiology. FDA's Adverse Event Reporting System (FAERS) provides the opportunity to investigate this disease. Our goals were to analyze FAERS data to discover possible relationships between ONJ and specific conditions and drugs and then to consult the scientific literature to deduce biological explanations. Our methodology revealed a very strong association between gastroesophageal reflux and bisphosphonate-induced ONJ, suggesting acidosis as a key factor. Overgrowth of acidophilic species, particularly Streptococcus mutans, in the oral microbiome in the context of insufficient acid buffering due to impaired salivary glands maintains the low pH that sustains damage to the mucosa. Significant associations between ONJ and adrenal insufficiency, vitamin C deficiency, and Sjögren's syndrome were found. Glucose 6 phosphate dehydrogenase (G6PD) deficiency can explain much of the pathology. An inability to maintain vitamin C and other antioxidants in the reduced form leads to vascular oxidative damage and impaired adrenal function. Thus, pathogen-induced acidosis, hypoxia, and insufficient antioxidant defenses together induce ONJ. G6PD deficiency and adrenal insufficiency are underlying factors. Impaired supply of adrenal-derived sulfated sterols such as DHEA sulfate may drive the disease process.

Zoledronate induces autophagic cell death in human umbilical vein endothelial cells via Beclin-1 dependent pathway activation

Zoledronate has been reported to exhibit pro-apoptotic and anti-angiogenic effects in endothelial cells, which partially contributes to bisphosphonate-associated osteonecrosis of the jaw (BP-ONJ). Zoledronate can also induce autophagic cell death. The present study hypothesized that Zoledronate may activate autophagy to exert pro-apoptotic effects in endothelial cells and aimed to investigate the effect of Zoledronate on human umbilical vein endothelial cells (HUVECs) and explore the underlying mechanisms. The current study demonstrated that Zoledronate induced autophagy in HUVECs in a dose-dependent manner, as demonstrated by increased levels of microtubule-associated proteins 1A/1B light chain 3B-II (LC3B-II) and Beclin-1, and decreased levels of sequestome 1 (SQSTM1). In addition, treatment with chloroquine further increased LC3B-II and increased SQSTM1 levels, indicating that Zoledronate induces autophagy by increasing autophagic activity. Flow cytometry and Hoechst 33258 staining revealed that inhibition of autophagy with 3-methyladenine markedly attenuated Zoledronate-induced apoptosis. Furthermore, genetic knockdown of Beclin-1 significantly inhibited autophagy and apoptosis induced by Zoledronate. The present study therefore demonstrated that Zoledronate may promote Beclin-1-mediated autophagy to induce endothelial cell apoptosis, and suggests that blocking autophagy may represent a novel approach for the prevention of BP-ONJ in patients receiving Zoledronate.

The effect of an inhibitor of gut serotonin (LP533401) during the induction of periodontal disease

BACKGROUND AND OBJECTIVE

LP533401 is an inhibitor of tryptophan hydroxylase 1, which regulates serotonin production in the gut. Previous work indicates that LP533401 has an anabolic effect in bone. Thus, we hypothesized that inhibition of gut serotonin production may modulate the host response in periodontal disease. In this study, we aimed to analyze the effects of LP533401 in a rat periodontitis model to evaluate the role of gut serotonin in periodontitis pathophysiology.

MATERIAL AND METHODS

Twenty-four rats were divided into three groups: treated group (T: ligature-induced periodontal disease and LP533401, 25 mg/kg/d) by gavage; ligature group (L: ligature-induced periodontal disease only); and control group (C: without ligature-induced periodontal disease). After 28 d, radiographic alveolar bone support was measured on digital radiographs, and alveolar bone volume fraction, tissue mineral density and trabeculae characteristics were quantified by microcomputed tomography in the right hemi-mandible. Left hemi-mandibles were decalcified and alveolar bone loss, attachment loss and area of collagen in the gingiva were histologically analyzed.

RESULTS

Significant difference between the L and C groups was found, confirming that periodontal disease was induced. We observed no difference between the T and L groups regarding alveolar bone destruction and area of collagen.

CONCLUSION

LP533401 (25 mg/kg/d) for 28 d does not prevent bone loss and does not modulate host response in a rat model of induced periodontal disease.

Risk factors for periodontal disease

Risk factors play an important role in an individual's response to periodontal infection. Identification of these risk factors helps to target patients for prevention and treatment, with modification of risk factors critical to the control of periodontal disease. Shifts in our understanding of periodontal disease prevalence, and advances in scientific methodology and statistical analysis in the last few decades, have allowed identification of several major systemic risk factors for periodontal disease. The first change in our thinking was the understanding that periodontal disease is not universal, but that severe forms are found only in a portion of the adult population who show abnormal susceptibility. Analysis of risk factors and the ability to statistically adjust and stratify populations to eliminate the effects of confounding factors have allowed identification of independent risk factors. These independent but modifiable, risk factors for periodontal disease include lifestyle factors, such as smoking and alcohol consumption. They also include diseases and unhealthy conditions such as diabetes mellitus, obesity, metabolic syndrome, osteoporosis, and low dietary calcium and vitamin D. These risk factors are modifiable and their management is a major component of the contemporary care of many periodontal patients. Genetic factors also play a role in periodontal disease and allow one to target individuals for prevention and early detection. The role of genetic factors in aggressive periodontitis is clear. However, although genetic factors (i.e., specific genes) are strongly suspected to have an association with chronic adult periodontitis, there is as yet no clear evidence for this in the general population. It is important to pursue efforts to identify genetic factors associated with chronic periodontitis because such factors have potential in identifying patients who have a high susceptibility for development of this disease. Many of the systemic risk factors for periodontal disease, such as smoking, diabetes and obesity, and osteoporosis in postmenopausal women, are relatively common and can be expected to affect most patients with periodontal disease seen in clinics and dental practices. Hence, risk factor identification and management has become a key component of care for periodontal patients.

Osteoprotegerin-deficient male mice as a model for severe alveolar bone loss: comparison with RANKL-overexpressing transgenic male mice

Periodontitis, an inflammatory disease of periodontal tissues, is characterized by excessive alveolar bone resorption. An increase in the receptor activator of nuclear factor-κB ligand (RANKL) to osteoprotegerin (OPG) ratio is thought to reflect the severity of periodontitis. Here, we examined alveolar bone loss in OPG-deficient (OPG(-/-)) mice and RANKL-overexpressing transgenic (RANKL-Tg) mice. Alveolar bone loss in OPG(-/-) mice at 12 weeks was significantly higher than that in RANKL-Tg mice. OPG(-/-) but not RANKL-Tg mice exhibited severe bone resorption especially in cortical areas of the alveolar bone. An increased number of osteoclasts was observed in the cortical areas in OPG(-/-) but not in RANKL-Tg mice. Immunohistochemical analyses showed many OPG-positive signals in osteocytes but not osteoblasts. OPG-positive osteocytes in the cortical area of alveolar bones and long bones were abundant in both wild-type and RANKL-Tg mice. This suggests the resorption in cortical bone areas to be prevented by OPG produced locally. To test the usefulness of OPG(-/-) mice as an animal model for screening drugs to prevent alveolar bone loss, we administered an antimouse RANKL antibody or risedronate, a bisphosphonate, to OPG(-/-) mice. They suppressed alveolar bone resorption effectively. OPG(-/-) mice are useful for screening therapeutic agents against alveolar bone loss.

Immune modulatory and antioxidant effects of melatonin in experimental periodontitis in rats

Melatonin is an important antioxidant, and through its anti-inflammatory effects it can control immune responses, oxidative stress, and defense cell infiltration. Periodontitis is a disease of the oral cavity and the generation of free radicals is an important consideration in this disease. Therefore, we examined the immune-modulatory and antioxidant roles of melatonin in the treatment of periodontitis. In all, 30 male Wistar rats were randomly divided into three groups: the control group, the periodontitis-induced (PED) group, and the periodontitis+melatonin treatment (MEL+PED) group. The control group received no treatment, whereas periodontitis was induced in both the PED and the MEL+PED groups, with the MEL+PED group being treated with systemic melatonin. For the periodontitis-induced groups, the rats' mandibular first molar teeth were ligatured (3-0 cotton) in a submarginal position for 4 weeks, and then the ligature was removed. After removal of the ligature, melatonin was administered only to the MEL+PED group (an ip dose of 10mg/kg body wt for 15 days at 11:00 PM each day). In the histological examination, the MEL+PED group, which received the melatonin, showed reduced inflammatory cytokines (IL-1β, from 97.47 to 84.24pg/ml; TNF-α, from 0.22530 to 0.22519pg/ml), regulated oxidative stress parameters (MDA, from 41,458 to 30,708nmol/g; GSH, from 18,166 to 25,858nmol/mg), and less periodontal tissue destruction (CEJ-PL, lingual, from 244.54 to 140.57μm; buccal, from 235.6 to 158.93μm; and CEJ-BC, lingual, from 383.65 to 287.76μm; buccal, from 391.92 to 296.12μm). From these findings we conclude that, even when periodontitis was induced, melatonin reduced the oxidative damage in the rats' periodontal tissue by inhibiting the inflammatory effects and by restoring the antioxidants.

Effects of tacrolimus and nifedipine, alone or in combination, on gingival tissues

BACKGROUND

The aim of this study is to compare gingival changes induced by short- and long-term tacrolimus and nifedipine administration, alone or in combination, and evaluate the expression levels of tumor suppressor phosphatase and tensin homolog (PTEN) in drug-induced gingival overgrowth.

METHODS

Eighty rats were equally divided into eight groups: 1) tacrolimus for 8 weeks; 2) nifedipine for 8 weeks; 3) tacrolimus and nifedipine for 8 weeks; 4) 8-week control; 5) tacrolimus for 24 weeks; 6) nifedipine for 24 weeks; 7) tacrolimus and nifedipine for 24 weeks; and 8) 24-week control. Histomorphometric analyses included measurements of epithelial thickness, connective tissue thickness, and height. Stereologic analyses included measurements of volumetric densities of fibroblasts (Vf), collagen fibers (Vcf), and blood vessels (Vbv). In addition, PTEN expression was analyzed using immunohistochemistry.

RESULTS

Epithelial thickness and connective tissue thickness were significantly increased in groups 5, 6, and 7 compared to group 8 (P <0.05), whereas connective tissue height was significantly increased in groups 5 and 7 (P <0.001). Vf and Vcf were significantly increased in group 7 compared to group 8 (P <0.001). PTEN immunoreactivity was significantly decreased in all experimental groups compared to the control groups (P <0.05).

CONCLUSIONS

Results suggest that duration of drug administration is a more important risk factor than drug combination. The results include a potentially new insight about PTEN's role in the etiology of drug-induced gingival overgrowth.

Dose-dependent differential effects of risedronate on gene expression in osteoblasts

Bisphosphonates have multiple effects on bone. Their actions on osteoclasts lead to inhibition of bone resorption, at least partially through apoptosis. Effects on osteoblasts vary, with modifications in the molecule and concentration both resulting in qualitatively different responses. To understand the mechanism of the differential effects of high and low bisphosphonate concentrations on osteoblast activity, we compared the effects of 10⁻⁸ M and 10⁻⁴ M risedronate on gene expression in UMR-106 rat osteoblastic cells. Two targeted arrays, an 84-gene signaling array and an 84-gene osteogeneic array were used. Gene expression was measured at 1 and 24 h. Although some genes were regulated similarly by low and high concentrations of the drug, there was also differential regulation. At 1 h, 11 genes (1 signaling and 10 osteogenesis) were solely regulated by the low concentration, and 7 genes (3 signaling, 4 osteogenesis) were solely regulated by the high concentration. At 24 h, 8 genes (3 signaling, 5 osteogenesis) were solely regulated by the low concentration and 30 genes (16 signaling and 14 osteogenesis) were solely regulated by the high concentration. Interestingly, the low, but not the high concentration of risedronate transiently and selectively upregulated several genes associated with cell differentiation. A number of genes related to apoptosis were regulated, and could be involved in effects of bisphosphonates to promote osteoblast apoptosis. Also, observed gene changes associated with decreased angiogenesis and decreased metastasis could, if they occur in other cell types, provide a basis for the effectiveness of bisphosphonates in the prevention of cancer metastases.

Relationship between periodontal disease and osteoporosis

BACKGROUND

For many years an association between the low bone density of osteoporosis and increased risk of periodontal bone loss has been suspected. In this review the relationship between osteoporosis and periodontal disease is considered.

METHODS

For this narrative review a very broad search strategy of the literature was developed using both PubMed and Scopus databases using the search words "perio" and "osteoporosis". The reference lists from the selected papers were also scanned and this provided an additional source of papers for inclusion. The inclusion/exclusion criteria, were also quite liberal with only those papers dealing with bisphosphonates and osteonecrosis of the jaws, osteoporosis in edentulous individuals, as well as those not written in English being excluded.

RESULTS

The data available suggest that reduced bone mineral density is a shared risk factor for periodontitis rather than a causal factor. However, more prospective studies are required to fully determine what, if any, relationship truly exists between periodontitis and reduced bone mineral density.

CONCLUSIONS

More prospective studies are required to determine what, if any, relationships exist between periodontal disease and reduced bone mineral density.

Effect of alendronate on alveolar bone resorption and angiogenesis in rats with experimental periapical lesions

AIM

To investigate the effects of systemically administered alendronate, one of the most potent bisphosphonates (BPs), on alveolar bone resorption and angiogenesis in rats subjected to experimental periapical lesions over two time periods.

METHODOLOGY

Forty adult Sprague-Dawley (SD) rats were divided equally into control and experimental groups, and the pulp chambers of mandibular first molars of all rats were exposed to the oral environment to induce periapical lesions. The experimental group received daily subcutaneous injections of alendronate at a dose of 0.25 mg kg(-1), whereas the control group received only the saline vehicle. These injections were initiated 1 week before the periapical lesion induction and then continued daily throughout the entire experimental period. After 2 or 4 weeks following pulp exposure, the rats were killed, and the mandibles were examined histologically for periapical bone loss area, number of microvascular vessels (NMV) and tartrate-resistant acid phosphatase (TRAP) activity.

RESULTS

Overall, periapical bone loss area and the number of TRAP-positive cells (osteoclasts) were significantly decreased at 2 and 4 weeks, respectively, after daily subcutaneous injection of alendronate compared with the control group (P < 0.05). There was no significant decrease change in NMV (P > 0.05).

CONCLUSIONS

Administration of alendronate to rats might inhibit alveolar bone resorption associated with periapical disease, which might not lead to impairment of angiogenesis. However, because of the differences between rats and humans, one has to consider the possible consequences of this treatment in the clinic.

Alendronate affects cartilage resorption by regulating vascular endothelial growth factor expression in rats

This study was performed to determine effects of alendronate on the tibial proximal epiphyseal cartilage undergoing endochondral ossification and the expression of vascular endothelial growth factor (VEGF) from the cartilage. Alendronate was injected subcutaneously every other day in postnatal Day 1 Sprague Dawley rats. The rats were sacrificed 3, 5, 7, and 10 days after the first injection. The effect of alendronate treatment for 10 days was demonstrated from the morphological change that the area of the secondary ossification center in the epiphysis was significantly smaller in the alendronate group than that in the control group (P < 0.05). Strong immunoreactivity to VEGF was observed in the hypertrophied chondrocytes and some proliferating chondrocytes in the epiphyseal cartilage at postnatal Day 5 and was decreased after the alendronate treatment for 5 days. Immunoreactivity was observed in not only hypertrophied cells but also the peripheral cartilaginous matrix adjacent to the vascular canals invading into the central portion of the cartilage at postnatal Day 7. This reactivity was also reduced considerably by the alendronate treatment for 7 days. The level of VEGF expression was reduced by the alendronate treatment at both the transcription and translation levels. However, the transcriptional level of the flt-1 and flk-1 receptors was relatively unaltered by the treatment. These results suggest that VEGF expression is required for vascular invasion into the developing cartilage and alendronate can affect its resorption by downregulating VEGF expression.