The Incidence and Severity of Medication Related Osteonecrosis of the Jaws is Similar in Male and Female Mice.

BACKGROUND: Medication related osteonecrosis of the jaws (MRONJ), a rare side-effect of antiresorptive medications, is described as exposed bone in the oral cavity that lasts for at least 8 weeks. Most studies report a female predilection for MRONJ; these findings could be due to the increased use of antiresorptives in females, or due to inherent differences between male versus female patients. PURPOSE: The purpose of this study was to measure and compare the incidence and severity of osteonecrosis of the jaws (ONJ) between male and female mice. STUDY DESIGN, SETTING, SAMPLE: We designed a randomized in-vivo animal study utilizing male and female mice treated with zoledronic acid (ZA). Experimental periodontitis was induced in 24 male and 24 female mice using a silk ligature following administration of saline or a potent bisphosphonate. After 8 weeks, animals were evaluated radiographically and histologically. INDEPENDENT VARIABLE: The independent variables were sex (male vs female) and treatment group (ZA vs saline control). Treatment was randomly assigned with balanced distribution between male and female animals. MAIN OUTCOME VARIABLE: The main outcome variable was ONJ status coded as present or absent. ONJ was defined as present if there was histologic contact between the ligature and the alveolar bone. Secondary outcomes of interest were radiographic and histologic parameters. ANALYSIS: Statistical differences were analyzed using a two-way ANOVA with Tukey's post hoc test using a P value of 0.05 for significance. RESULTS: The final sample was composed of 24 vehicle treated and 24 ZA treated animals. In vehicle treated animals, 8% of female and 8% of male animals developed ONJ. In ZA treated animals, 83% of female and 92% of male animals developed ONJ. Sex was not associated with the risk (measured as incidence of disease) for developing ONJ or in the radiographic or histologic parameters that were assessed (P values >.1). CONCLUSIONS: Sex does not appear to affect the incidence of MRONJ or the severity of the disease as assessed by the radiographic and histologic parameters.

Pathophysiology of Medication-Related Osteonecrosis of the Jaw-A Minireview.

Medication-related osteonecrosis of the jaw (MRONJ) is a rare but serious adverse effect of antiresorptive medications administered for control of osseous malignancy, osteoporosis, or other bone metabolic diseases. Despite being reported in the literature two decades ago, MRONJ etiology, pathophysiology, and progression remain largely unknown, and current nonoperative or operative treatment strategies are mostly empirical. Several hypotheses that attempt to explain the mechanisms of MRONJ pathogenesis have been proposed. However, none of these hypotheses alone is able to capture the complex mechanistic underpinnings of the disease. In this minireview, we aim to highlight key findings from clinical and translational studies and propose a unifying model for the pathogenesis and progression of MRONJ. We also identify aspects of the disease process that require further investigation and suggest areas for future research efforts toward calibrating methodologic approaches and validating experimental findings. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Radiologic findings of osteonecrosis, osteoradionecrosis, osteomyelitis and jaw metastatic disease with cone beam CT.

PURPOSE: The purpose of this study was to assess CBCT scans of patients with medication related osteonecrosis of the jaws (MRONJ), osteoradionecrosis (ORN), osteomyelitis (OM) and jaw metastatic disease (JM), evaluate the presence and extent of radiologic findings, identify radiologic parameters that may distinguish the four entities and last, introduce a new modified radiographic index (CRIm), in order to contribute to the diagnosis of these conditions. METHODS: Τwo major databases were retrospectively searched for fully documented and diagnosed CBCT scans of MRONJ, ORN, OM and JM from 2006 to 2019. 335 CBCT scans met the inclusion criteria and were assessed under standardized viewing conditions blindly by 2 observers. The CRIm index proposed in this study evaluates: lytic changes, sclerosis, periosteal bone formation, sequestration, non-healing extraction sockets and other findings which included: sinus implication, inferior alveolar canal implication and jaw fracture. Lytic changes, sclerosis, periosteal bone formation, sequestration and non-healing extraction sockets were scored as: absent (0), localized/single (1) and extensive/multiple (2). Each one of other findings were scored individually as: absent (0) and present (1). For statistical analysis t-test, Pearson's r correlation coefficient, one-way ANOVA and Bonferonni were performed. RESULTS: Extensive lytic changes were the most common finding, especially for ORN, where it occurred in all CBCT scans (100%). The mean value of the CRIm index differs significantly between CBCT scans with MRONJ and JM, as well as between those with OM and JM (Bonferroni p < 0.001). CONCLUSIONS: The new modified Composite Radiographic Index introduced in this study, appears to have improved an objective approach to the previously used Composite Radiographic Index by means of cumulative radiologic features. Τhe predominance of certain radiologic features in one or more of these entities may lead the diagnostician towards the correct diagnosis.

Inhibition of HMGB1/RAGE Signaling Reduces the Incidence of Medication-Related Osteonecrosis of the Jaw (MRONJ) in Mice.

Medication-related osteonecrosis of the jaw (MRONJ) is a severe complication of antiresorptive or antiangiogenic medications, used in the treatment of bone malignancy or osteoporosis. Bone necrosis, mainly represented by osteocytic death, is always present in MRONJ sites; however, the role of osteocyte death in MRONJ pathogenesis is unknown. High mobility group box 1 (HMGB1) is a non-histone nucleoprotein that in its acetylated form accumulates in the cytoplasm, whereas non-acetylated HMGB1 localizes in the nucleus. SIRT1 deacetylase regulates cellular localization of HMGB1. Interestingly, HMGB1 is released during cell necrosis and promotes inflammation through signaling cascades, including activation of the RAGE receptor. Here, we utilized a well-established mouse MRONJ model that utilizes ligature-induced experimental periodontitis (EP) and treatment with either vehicle or zolendronic acid (ZA). Initially, we evaluated HMGB1-SIRT1 expression in osteocytes at 1, 2, and 4 weeks of treatment. Significantly increased cytoplasmic and perilacunar HMGB1 expression was observed at EP sites of ZA versus vehicle (Veh) animals at all time points. SIRT1 colocalized with cytoplasmic HMGB1 and presented a statistically significant increased expression at the EP sites of ZA animals for all time points. RAGE expression was significantly higher in the submucosal tissues EP sites of ZA animals compared with those in vehicle group. To explore the significance of increased cytoplasmic and extracellular HMGB1 and increased RAGE expression in MRONJ pathogenesis, we used pharmacologic inhibitors of these molecules. Combined HMGB1/RAGE inhibition resulted in lower MRONJ incidence with statistically significant decrease in osteonecrotic areas and bone exposure versus non-inhibitor treated ZA animals. Together, our data point to the role of HMGB1 as a central alarmin, overexpressed at early phase of MRONJ pathogenesis during osteocytic death. Moreover, HMGB1-RAGE pathway may represent a new promising therapeutic target in patients at high risk of MRONJ. © 2022 American Society for Bone and Mineral Research (ASBMR).

Macrophage Involvement in Medication-Related Osteonecrosis of the Jaw (MRONJ): A Comprehensive, Short Review.

Antiresorptive agents such as bisphosphonates (BP) and denosumab are commonly prescribed for the management of primary bone malignancy, bone metastasis, osteoporosis, Paget disease, or other bone disorders. Medication-related osteonecrosis of the Jaws (MRONJ) is a rare but significant complication of antiresorptive medications. Duration, dose, and antiresorptive potency as well as concomitant diseases, additional medications, and local factors affect MRONJ incidence and severity. MRONJ pathophysiology is still poorly understood. Nevertheless, decreased bone resorption due to osteoclastic inhibition along with trauma, infection/inflammation, or blood supply inhibition are considered synergistic factors for disease development. In addition, previous data research examined the effects of antiresorptive medication on immune system components and introduced potential alterations on immune response as novel elements in MRONJ pathogenesis. Considering that macrophages are the first cells in the nonspecific immune response, it is not surprising that these multifaceted players attracted increased attention in MRONJ research recently. This current review attempted to elucidate the effects of antiresorptive medications on several aspects of macrophage activity in relation to the complex inflammatory microenvironment of MRONJ. Collectively, unravelling the mode of action and extent of macrophages' potential contribution in MRONJ occurrence will provide novel insight in disease pathogenesis and potentially identify intrinsic therapeutic targets.

Local RANKL delivery improves socket healing in bisphosphonate treated rats.

Medication related osteonecrosis of the Jaws (MRONJ) is a severe complication of antiresorptive and anti-angiogenic medications. Osteoclast inhibition is central in MRONJ pathogenesis. Here, we investigated if local application of RANKL (a key molecule in osteoclast activation) could enhance osteoclast generation and improve extraction socket healing in the presence of bisphosphonates. Thirty Wistar-Han rats received one saline or 66 µg/kg zoledronate (ZA) i.p. dose before surgery. A week later, mandibular molars were extracted bilaterally. Collagen tapes infused with water or RANKL were placed in the extraction sockets of 60 hemimandibles of veh (veh/RANKL-, veh/RANKL+) or ZA treated rats (ZA/RANKL-, ZA/RANKL+). Rats were euthanized 3 or 12 days after surgery. Animals euthanized at 12 days received two additional veh or ZA injections. Clinical, radiographic and histologic assessments were performed. Visually, at the 3-day timepoint, no sockets demonstrated complete healing. At the 12-day timepoint, sockets of veh/RANKL- and veh/RANKL+ rats showed intact mucosa, while mucosal defects were noted in ZA/RANKL- rats. Importantly, ZA/RANKL+ sockets showed absence of bone exposure. RANKL delivery increased bone healing in the ZA/RANKL+ sites 12 days after extraction compared to the ZA/RANKL- sites. Histologically, at the 3-day timepoint, ZA/RANKL- sockets demonstrated extensive bone exposure and osteonecrosis. In contrast, ZA/RANKL+ rats showed granulation tissue coverage and significantly reduced osteonecrosis, similar to the veh groups. Importantly, in the ZA/RANKL+ group, osteoclasts attached to the bone surface and osteoclast numbers were higher compared to ZA/RANKL- sites. At the 12-day timepoint, persistent osteonecrosis and bone exposure were detected in the sockets of ZA/RANKL- animals. Contrary, ZA/RANKL+ rats demonstrated socket epithelialization and reduced osteonecrosis. Significantly more total and bony attached osteoclasts persisted in the ZA/RANKL+ vs the ZA/RANKL- group. We present a novel approach towards improving socket healing, in the presence of ZA, by enhancing osteoclastic numbers and attachment through local RANKL application. Our approach is clinically applicable and could improve treatment outcomes of patients on high-dose ZA therapy.

The role of M1 and M2 macrophage polarization in progression of medication-related osteonecrosis of the jaw.

OBJECTIVES: The aim of this study was to investigate the relationship between M1 and M2 macrophage polarization and clinical stage in patients with medication-related osteonecrosis of the jaw (MRONJ) who underwent treatment with bisphosphonates or denosumab. MATERIALS AND METHODS: M1 and M2 macrophage density and expression of interleukin (IL)-6 and IL-10 were assessed on biopsies of mucosal tissues surrounding necrotic bone in 30 MRONJ patients with stages 1-3 and controls. For identification of M1 and M2 macrophages, double CD68/iNOS and CD68/CD206 immunofluorescence staining was conducted, respectively. Computer-assisted immunofluorescence quantification of markers was performed. RESULTS: Early stage 1 MRONJ patients showed a switch toward the M2 phenotype, as indicated by the higher density of M2 macrophages, the decreased M1/M2 ratio, and the upregulation of IL-10. MRONJ patients with advanced stages 2 and 3 showed a shift toward M1-polarized macrophages, as suggested by the higher density of M1 macrophages, the increased M1/M2 ratio, and the overexpression of IL-6. The macrophage density of both M1 and M2 subsets was significantly enhanced in patients receiving bisphosphonates compared with those receiving denosumab. CONCLUSIONS: The M1-M2 macrophage polarization status in mucosal tissues bordering necrotic bone correlates with clinical stage of MRONJ. Patients with early-stage MRONJ show a switch toward M2-polarized macrophages, while MRONJ patients with advanced stage demonstrate a shift toward the M1 phenotype. CLINICAL RELEVANCE: Therapeutic molecules targeting the inflammatory microenvironment via the regulation of either M1 or M2 macrophage polarization may represent a novel strategy for treatment of MRONJ.

CCN1/Cyr61 Is Required in Osteoblasts for Responsiveness to the Anabolic Activity of PTH.

CCN1/Cyr61 is a dynamically expressed matricellular protein that serves regulatory functions in multiple tissues. Previous studies from our laboratory demonstrated that CCN1 regulates bone maintenance. Using an osteoblast and osteocyte conditional knockout mouse model (Ccn1OCN ), we found a significant decrease in trabecular and cortical bone mass in vivo, in part through suppression of Wnt signaling since the expression of the Wnt antagonist sclerostin (SOST) is increased in osteoblasts lacking CCN1. It has been established that parathyroid hormone (PTH) signaling also suppresses SOST expression in bone. We therefore investigated the interaction between CCN1 and PTH-mediated responses in this study. We find that loss of Ccn1 in osteoblasts leads to impaired responsiveness to anabolic intermittent PTH treatment in Ccn1OCN mice in vivo and in osteoblasts from these mice in vitro. Analysis of Ccn1OCN mice demonstrated a significant decrease in parathyroid hormone receptor-1 (PTH1R) expression in osteoblasts in vivo and in vitro. We investigated the regulatory role of a non-canonical integrin-binding domain of CCN1 because several studies indicate that specific integrins are critical to mechanotransduction, a PTH-dependent response, in bone. These data suggest that CCN1 regulates the expression of PTH1R through interaction with the αvß3 and/or αvß5 integrin complexes. Osteoblasts that express a mutant form of CCN1 that cannot interact with αvß3/ß5 integrin demonstrate a significant decrease in mRNA and protein expression of both PTH1R and αv integrin. Overall, these data suggest that the αvß3/ß5-binding domain of CCN1 is required to endow PTH signaling with anabolic activity in bone cells. © 2020 American Society for Bone and Mineral Research (ASBMR).

Long-term evaluation of alendronate treatment on the healing of calvaria bone defects in rats. Biochemical, histological and immunohistochemical analyses.

OBJECTIVE: The aim of this study was to investigate the effects of the long-term alendronate administration on bone healing in defects created in rat calvarias. MATERIALS AND METHODS: Female Wistar rats were randomly distributed into 2 groups: Control (CTL): animals received saline solution once a week; and Alendronate (ALD): rats underwent alendronate treatment (1 mg/kg/weekly). After 120 days from the commencement of treatment, a critical size defect was created in all animals, and 10 animals from each group were sacrificed at 5, 10, 15, 20, 25, 30, 45 and 60-days after the defect creation. On the day of sacrifice, urine and blood samples were collected for determination of the serum levels of bone resorption and formation markers by enzyme linked immunosorbent assay, and the urinary concentration of deoxypyridinoline. Bone mineral density (BMD) in the femurs, descriptive histology, tartrate-resistant acid-phosphatase staining and immunohistochemical analyzes were assessed in the calvaria. RESULTS: Alendronate group showed increased BMD compared to the test group. The concentration of C-terminal telopeptide of type I collagen and deoxypyridinoline decreased significantly, and the concentration of aminoterminal propeptide of procollagen type 1 and osteocalcin were significant lower in the alendronate group. Immunohistochemical analysis showed significant downregulation in the inducible nitric oxide synthase, runt-related transcription factor-2, cathepsin-K and receptor activator of nuclear factor kappa-B ligand expression in the alendronate group. Vascular endothelial growth factor and osteopontin were upregulated in the later periods of alendronate group. CONCLUSIONS: Our results suggest that long-term treatment with alendronate did not compromise the repair processing of critical size defects in rat.

Severe magnesium deficiency compromises systemic bone mineral density and aggravates inflammatory bone resorption.

We sought to evaluate the effects of magnesium (Mg) intake deficiency on bone metabolism in rats with induced periodontal disease (PD). Holtzman rats were randomly divided into two groups: Control - animals fed a standard diet and test - animals fed a diet with 90% Mg deficiency. After 60 days on the diets, all animals received ligature on the lower left first molars to induce PD. Animals were euthanized after 30 days following ligature placement. Blood and urine were collected for determination of serum concentrations of Mg, calcium, osteocalcin (OCN), alkaline phosphatase and parathyroid hormone (PTH) by enzyme-linked immunosorbent assay, and the urinary concentration of deoxypyridinoline (DPD). Systemic bone mineral density (BMD), bone volume and architectural bone parameters were evaluated by micro-CT in L4 lumbar vertebrae and mandible. Tartrate-resistant acid phosphatase staining and immunohistochemical (IHC) analysis of inducible nitric oxide synthase (iNOS), Runt-related transcription factor 2 (RUNX2), CD86, CD80, proliferating cell nuclear antigen, vascular endothelial growth factor, OCN and osteopontin were investigated. Reverse-transcription polymerase chain reaction was employed to assess mRNA expression of receptor-activator of nuclear factor-kB ligand, osteoprotegerin (OPG) and interleukin (IL)-6. Mg deficiency was associated with higher concentrations of PTH and DPD, and significant decrease on both systemic and mandibular BMD, as well as greater severity of alveolar and trabecular bone loss. Significant increase in osteoclasts was observed in the test group with PD. IHC analysis showed significant increase in the expression of iNOS and decreased expression of OCN and RUNX2. Increased IL-6 mRNA and decreased OPG mRNA expressions were evidenced in the test group with PD. Mg deficiency caused systemic effects indicative of altered bone metabolism in the vertebrae and affected both immune and stromal cells, aggravating inflammatory bone resorption in the ligature-induced model of periodontitis.

Vasculature submucosal changes at early stages of osteonecrosis of the jaw (ONJ).

Osteonecrosis of the jaw (ONJ), a rare, but potentially severe side effect of anti-resorptive medications, presents as exposed bone in the maxillofacial region lasting for at least 8 weeks. While clinical experience and animal models concur in finding that systemic antiresorptive treatment in conjunction with local risk factors, such as tooth extraction or dental disease may lead to ONJ development, the subclinical molecular changes that precede bone exposure remain poorly understood. The identification of these changes is not only important in understanding disease pathophysiology, but could provide potential for treatment development. Here, we evaluated the early stages of ONJ utilizing a model of experimental periodontitis (EP) in mice treated with two different types of antiresorptives, targeting potential changes in vasculature, hypoxia, oxidative stress, and apoptosis. Antiresorptive treatment in animals with EP increased levels of empty osteocytic lacunae and increased ONJ prevalence compared to Veh animals. The arteriole and venule network seen around EP areas was diminished in animals treated with antiresorptives. Higher levels of vascular endothelial growth factor A (VEGF-A) and vascular cell adhesion protein-1 (VCAM-1) were observed 1-week following EP in treated animals. Finally, levels of hypoxia, oxidative stress, and apoptosis remained high in antiresorptive treated animals with EP through the duration of the experiment. Together, our data point to subclinical vasculature organizational disturbances that subsequently affect levels of hypoxia, oxidative stress, and apoptosis in the area of developing ONJ.

Development of Medication-Related Osteonecrosis of the Jaw After Extraction of Teeth With Experimental Periapical Disease.

PURPOSE: Medication-related osteonecrosis of the jaw (MRONJ) is a rare but severe side effect of antiresorptive medications. Most animal models use tooth extraction as an instigating local factor to induce MRONJ, with varied results. However, these teeth are healthy and absent of dental disease, a rare finding that does not reflect clinical practices. The authors hypothesized that extraction of teeth with periapical inflammation would lead to MRONJ in rats treated with high-dose bisphosphonates. MATERIALS AND METHODS: Rats were pretreated with zoledronic acid (ZA) for 1 week. Pulp exposure (PE) was established by exposing the pulpal chamber of the first and second molars. Experimental periapical disease (EPD) was induced by PE and bacterial inoculation into pulp chambers of the first and second mandibular molars. The mandibular molars were extracted 4 weeks after PE or EPD, and animals were euthanized 4 weeks after tooth extraction. Extraction sockets were assessed clinically, radiographically, and histologically. RESULTS: Clinically, radiographically, and histologically, socket healing was observed in all vehicle-treated animals and in ZA-treated animals after extraction of healthy teeth or teeth with PE. In contrast, bone exposure, lack of socket healing, and osteonecrosis were present in most ZA-treated animals after extraction of teeth with EPD. Bacterial presence was noted in areas of osteonecrotic alveolar bone. CONCLUSION: These data support a synergistic contribution of severe dental disease and tooth extraction to MRONJ pathogenesis. Importantly, this model is amenable to manipulation of methodologic conditions for the dissection of parameters involved in MRONJ pathogenesis.

Evaluation of bone turnover after bisphosphonate withdrawal and its influence on implant osseointegration: an in vivo study in rats.

OBJECTIVES: The aim of this study was to investigate bone turnover alterations after alendronate (ALD) withdrawal and its influence on dental implants osseointegration. MATERIALS AND METHODS: Seventy female Wistar rats were randomly divided in 2 groups that received on day 0 either placebo (control group-CTL; n = 10) or 1 mg/kg sodium alendronate (ALD; n = 60) once a week for 4 months. At day 120, ALD treatment was suspended for 50 animals. Then, a titanium implant was placed in the left tibia of each rat that were randomly allocated in five subgroups of ten animals each, according to the period of evaluation: day 0 (INT-0), day 7 (INT-7), day 14 (INT-14), day 28 (INT-28), and day 45 (INT-45) after ALD withdrawal. CTL group and a group that received ALD until the end of the experimental period (non-interrupted group-non-INT; n = 10) underwent implant placement on day 120. Animals were euthanized 28 days after implant surgery. Bone mineral density (BMD) of femur and lumbar vertebrae were evaluated by DXA, biochemical markers of bone turnover were analyzed by ELISA, and bone histomorphometry was performed to measure bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). RESULTS: All groups receiving ALD showed higher BMD values when compared to CTL group, which were maintained after its withdrawal. Decreased concentrations in all bone turnover markers were observed in the non-INT group, and in the groups in which ALD was discontinued compared to the CTL group. The non-INT group showed lower %BIC and notably changes in bone quality, which was persistent after drug withdrawal. CONCLUSION: Collectively, the findings of this study demonstrated that ALD therapy decreased bone turnover and impaired bone quality and quantity around dental implants, and that its discontinuation did not reverse these findings. CLINICAL RELEVANCE: The severe suppression of bone turnover caused by the prolonged use of ALD may alter the capacity of bone tissue to integrate with the implant threads impairing the osseointegration process.

Medication related osteonecrosis of the jaw in osteoporotic vs oncologic patients-quantifying radiographic appearance and relationship to clinical findings.

OBJECTIVES: To explore whether differences exist in the clinical and radiographic presentation of oncologic vs osteoporotic patients with medication-related osteonecrosis of the jaw (MRONJ). METHODS: We retrospectively assessed panoramic radiographs and CBCT examinations of 70 MRONJ patients receiving antiresorptive medications for the management of either osteoporosis or bone malignancy. Radiographic features of MRONJ were documented and categorized according to severity. A composite radiographic index (CRI) was constructed to account for the heterogeneity in radiographic manifestations of MRONJ and further stratify extent of osseous changes. RESULTS: Patients with osteoporosis were mostly older females and presented more frequently with Stage 2 MRONJ, while patients with malignancy were equally distributed between males and females, and presented mostly with Stage 1 MRONJ. Most MRONJ lesions in oncologic patients occurred in the mandible, whereas the maxilla and mandible were equally affected in osteoporotic patients. Patients with minimal radiographic changes (low CRI score) often presented with MRONJ in dentate areas, while most patients in medium and high CRI groups presented with MRONJ after recent tooth extraction. The low CRI group consisted of primarily oncologic patients, while osteoporotic vs oncologic patients were divided more evenly in the other CRI groups (p = 0.083). While CRI scores increased with clinical staging, a Spearman's rank correlation coefficient of 0.49 suggests that clinical appearance does not reliably predict osseous changes. CONCLUSIONS: Our data identify differences in the MRONJ appearance of patients with osteoporosis vs malignancy and emphasize the significance of detailed radiographic assessment, in addition to the clinical appearance, in characterizing the osseous changes of the disease.

Different duration of parathyroid hormone exposure distinctively regulates primary response genes Nurr1 and RANKL in osteoblasts.

Parathyroid hormone (PTH) exerts dual effects, anabolic or catabolic, on bone when administrated intermittently or continuously, via mechanisms that remain largely unknown. PTH binding to cells induces PTH-responsive genes including primary response genes (PRGs). PRGs are rapidly induced without the need for de novo protein synthesis, thereby playing pivotal roles in directing subsequent molecular responses. In this study, to understand the role of PRGs in mediating osteoblastic cellular responses to PTH, we investigated whether various durations of PTH differentially induce PRGs in primary osteoblasts and MC3T3-E1. Nurr1 and RANKL, PRGs known for their anabolic and catabolic roles in bone metabolism respectively, presented distinctive transient vs. sustained induction kinetics. Corroborating their roles, maximum induction of Nurr1 was sufficiently achieved by brief PTH in as little as 30 minutes and continued beyond that, while maximum induction of RANKL was achieved only by prolonged PTH over 4 hours. Our data suggested distinctive regulatory mechanisms for Nurr1 and RANKL: PKA-mediated chromatin rearrangement for transcriptional regulation of both PRGs and ERK-mediated transcriptional regulation for RANKL but not Nurr1. Lastly, we classified PRGs into two groups based on the induction kinetics: The group that required brief PTH for maximum induction included Nur77, cox-2, and Nurr1, all of which are reported to play roles in bone formation. The other group that required prolonged PTH for maximum induction included IL-6 and RANKL, which play roles in bone resorption. Together, our data suggested the crucial role of PRG groups in mediating differential osteoblastic cellular responses to intermittent vs. continuous PTH. Continued research into the regulatory mechanisms of PKA and ERK for PRGs will help us better understand the molecular mechanisms underlying the dual effects of PTH, thereby optimizing the current therapeutic use of PTH for osteoporosis.

Radiographic predictors of bone exposure in patients with stage 0 medication-related osteonecrosis of the jaws.

OBJECTIVE: The aim of this study was to explore the radiographic appearance of stage 0 medication-related osteonecrosis of the jaws (MRONJ) and examine 5 radiographic parameters (trabecular sclerosis, cortical erosion, periosteal reaction, sequestration, and crater-like defect) as predictors of progression to bone exposure. STUDY DESIGN: Twenty-three patients with a history of antiresorptive therapy, no bone exposure, and nonspecific signs and symptoms were included. Intraoral photographs, panoramic and cone beam computed tomography (CBCT) images at initial visit, and follow-up intraoral photographs were reviewed. Three patients had dental disease (DD), 10 patients with stage 0 MRONJ did not progress to bone exposure (NBE), and 10 patients progressed to bone exposure (BE). Radiographic parameters were scored as absent (0), localized (1), or extensive (2), and their sum formed the composite radiographic index (CRI). RESULTS: DD patients demonstrated minimal radiographic findings, and their CRI was significantly lower than that of NBE and BE patients. Additionally, BE patients demonstrated a higher radiographic index compared with NBE patients. Intriguingly, sequestration was observed in the initial CBCT of 9 (90%) of 10 BE patients, whereas 80% of NBE patients showed absence of sequestration at initial CBCT examination. CONCLUSIONS: CBCT imaging can aid in the differentiation of stage 0 MRONJ from dental disease. Radiographic sequestration at initial presentation can serve as a predictor of future bone exposure in patients with stage 0 MRONJ.

Nonsurgical Management of Medication-Related Osteonecrosis of the Jaws Using Local Wound Care.

PURPOSE: Medication-related osteonecrosis of the jaws (MRONJ) is a known complication of antiresorptive medications with surgical and nonsurgical treatment options. The aim of this study was to evaluate the effectiveness of nonsurgical therapy using local wound care on management of MRONJ lesions. MATERIALS AND METHODS: The authors conducted a retrospective cohort study of patients who presented to the University of California-Los Angeles School of Dentistry Oral and Maxillofacial Surgery Clinic for evaluation and treatment of MRONJ. The primary predictor variable was wound care score; secondary predictors were demographics (age, gender), anatomic location, primary condition, and type and time of antiresorptive treatment. Outcomes assessed were disease resolution and time to disease resolution. Statistical analysis was carried out using the Spearman correlation for continuous and ordinal variables or the χ2 test for categorical variables. Time-to-event statistics and Cox proportional hazards models were calculated; a Kaplan-Meier plot was generated to assess time to healing. RESULTS: One hundred six patients with 117 MRONJ lesions were treated using local wound care; complete disease resolution was observed 71% of lesions, with an additional 22% of lesions undergoing disease improvement. Wound care score was statistically associated with disease resolution and time to resolution, whereas demographics, anatomic site, condition, and type and time of antiresorptive treatment had no effect on resolution. CONCLUSION: Local wound care increased the likelihood of MRONJ resolution and decreased the time to disease resolution. This strategy can be used in patients who cannot undergo surgery and should be implemented in all patients with MRONJ lesions who are managed nonsurgically.

Genomewide Association Study Identifies Cxcl Family Members as Partial Mediators of LPS-Induced Periodontitis.

Periodontitis (PD) is characterized by bacterial infection and inflammation of tooth-supporting structures and can lead to tooth loss. PD affects ∼47% of the US population over age 30 years and has a heritability of about 50%. Although the host immunoinflammatory response and genetic background play a role, little is known of the underlying genetic factors. We examined natural genetic variation in lipopolysaccharide (LPS)-induced PD across a panel of inbred mouse strains, the hybrid mouse diversity panel (HMDP). We observed a strain-dependent sixfold difference in LPS-induced bone loss across the HMDP with a heritability of 53%. We performed a genomewide association study (GWAS) using FAST-LMM, which corrects for population structure, and identified loci significantly associated with PD. We examined candidate genes at a locus on chromosome 5, which suggested a relationship between LPS-induced bone loss and, together with expression data, identified Cxcl family members as associated with PD. We observed an increase in Cxcl10 protein, as well as immune cells and pro-inflammatory cytokines in C57BL/6J (high bone loss strain) but not in A/J (low bone loss strain) after LPS injections. Genetic deletion of CXCR3 (Cxcl9 and10 receptor) demonstrated a ∼50% reduction in bone loss and reduced osteoclasts after LPS injections. Furthermore, WT mice treated with AMG-487 (a CXCR3 antagonist) showed a ∼45% reduction in bone loss and decreased osteoclasts after LPS injections. We conclude that CXCR3 is a strong candidate for modulating the host response in individuals susceptible to PD. © 2018 American Society for Bone and Mineral Research.