Msx-1 is suppressed in bisphosphonate-exposed jaw bone analysis of bone turnover-related cell signalling after bisphosphonate treatment

Thoughts on the Etiology of Cherubism

Cherubism is nowadays classified as an autoimmune disease and was first described in 1933. Although suspected at that time to be the result of defective tooth development, it was primarily classified as a bone disease caused by a mutation in the SH3BP2 gene. Despite a knock-in mouse model, phenotypic signs in the jaw area were not reproducible in this model. The features of classical cherubism can be attributed to a disturbed formation of the dental placode of the second molar. Since 2019, it has become clear that inhibition of the WNT pathway leads to the accumulation of SH3BP2 via tankyrase inhibition. As the dental placode is triggered via WNT (in epithelia) and MSX1 (in mesenchyme), aplasia of the second and third molars occurs due to a block in the WNT pathway. The mesenchymal part, which occurs prior to the body plan regulation of the WNT/MSX1 pathway, remains unaffected and provides the substrate for the giant cell granuloma. Considering macrophage polarization and the role of the extracellular matrix in general, cherubism is situated in the field of tension between autoimmune diseases and cancer. In this sense, we see the cause of cherubism in a WNT-related dysregulation, which can be proven postnatally in the neural crest-related tooth development of the replacement tooth ridge, both genotypically and phenotypically.

Medication-Related Osteonecrosis of the Jaw: A Systematic Review and a Bioinformatic Analysis

The objective was to evaluate the current evidence regarding the etiology of medication-related osteonecrosis of the jaw (MRONJ). This study systematically reviewed the literature by searching PubMed, Web of Science, and ProQuest databases for genes, proteins, and microRNAs associated with MRONJ from the earliest records through April 2023. Conference abstracts, letters, review articles, non-human studies, and non-English publications were excluded. Twelve studies meeting the inclusion criteria involving exposure of human oral mucosa, blood, serum, saliva, or adjacent bone or periodontium to anti-resorptive or anti-angiogenic agents were analyzed. The Cochrane Collaboration risk assessment tool was used to assess the quality of the studies. A total of 824 differentially expressed genes/proteins (DEGs) and 22 microRNAs were extracted for further bioinformatic analysis using Cytoscape, STRING, BiNGO, cytoHubba, MCODE, and ReactomeFI software packages and web-based platforms: DIANA mirPath, OmicsNet, and miRNet tools. The analysis yielded an interactome consisting of 17 hub genes and hsa-mir-16-1, hsa-mir-21, hsa-mir-23a, hsa-mir-145, hsa-mir-186, hsa-mir-221, and hsa-mir-424. A dominance of cytokine pathways was observed in both the cluster of hub DEGs and the interactome of hub genes with dysregulated miRNAs. In conclusion, a panel of genes, miRNAs, and related pathways were found, which is a step toward understanding the complexity of the disease.

Evaluation of trabecular bone changes according to the type of prosthesis in patients using bisphosphonates: a retrospective study

The objective of the study was to retrospectively compare the fractal size values calculated in the trabecular bone according to the type of complete removable denture, removable partial denture, and partial fixed prosthesis between patients using bisphosphonates and healthy patients, retrospectively. Panoramic radiographs of a total of 200 patients, (100 using bisphosphonates,100 control group), were taken from the right and left molar regions before and after treatment with 72 × 72 pixels. The fractal dimension (FD) was computed by using ImageJ Software using the box-counting method on the images obtained. There was an interaction effect between the trabecular bone change-patient group-the type of prosthesis used and the parameters of the area (p < 0.05). In patients using complete removable dentures and removable partial dentures in the maxilla and mandibula in the molar region, a greater decrease in FD values was observed in the control group than in the patient group using bisphosphonates. An increase in FD values over time was observed in the patient group using bisphosphonates with partial fixed maxillary and mandibular prostheses compared to the control group. Partial fixed prostheses should be preferred primarily instead of complete removable or removable partial dentures in patients using bisphosphonates to prevent osteonecrosis due to dental trauma.

Uncovering the unique characteristics of the mandible to improve clinical approaches to mandibular regeneration

The mandible (lower jaw) bone is aesthetically responsible for shaping the lower face, physiologically in charge of the masticatory movements, and phonetically accountable for the articulation of different phonemes. Thus, pathologies that result in great damage to the mandible severely impact the lives of patients. Mandibular reconstruction techniques are mainly based on the use of flaps, most notably free vascularized fibula flaps. However, the mandible is a craniofacial bone with unique characteristics. Its morphogenesis, morphology, physiology, biomechanics, genetic profile, and osteoimmune environment are different from any other non-craniofacial bone. This fact is especially important to consider during mandibular reconstruction, as all these differences result in unique clinical traits of the mandible that can impact the results of jaw reconstructions. Furthermore, overall changes in the mandible and the flap post-reconstruction may be dissimilar, and the replacement process of the bone graft tissue during healing can take years, which in some cases can result in postsurgical complications. Therefore, the present review highlights the uniqueness of the jaw and how this factor can influence the outcome of its reconstruction while using an exemplary clinical case of pseudoarthrosis in a free vascularized fibula flap.

Lineage-associated connexin 43 expression in bisphosphonate-exposed rat bones

Expression of signaling proteins in bone cells depends on their embryological mesoderm-derived (e.g. tibia) or cranial neural crest (CNC)-derived (e.g. jaw) origin. Connexin 43 (Cx43) is a gap junction protein that plays an essential role in the mode of action of bisphosphonates (BP). This study aimed to investigate Cx43 expression and the influence of BP application on mesoderm- and CNC-derived bone. Using a rat model, molar extraction and tibia osteotomy with (Group 4) or without (Group 3) previous BP application was performed. Untreated (Group 1) and animals selectively treated with BPs (Group 2) served as controls. Cx43 expression was immunohistochemically determined 12 and 16 weeks postoperatively via a labeling index. Cx43 expression in CNC-derived bone was significantly higher compared with mesodermal bone. BP application decreased Cx43 expression; however, detected expression levels were still higher in jawbone (Group 2 tibia vs jaw: 5.83 ± 5.06 vs 23.52 ± 6.42; p = 0.007). During bone healing after surgical intervention (Group 3) there were no expression differences between tibia and jawbone. BP treatment prior to surgery resulted in significantly lower Cx43 expression in CNC-derived compared with tibia bone (Group 4 tibia vs jaw: 56.84 ± 15.57 vs 16.40 ± 5.66; p < 0.01). Increased Cx43 expression in jaw compared with tibia bone is in line with their embryological origins. A significant Cx43 suppression in jawbone after BP application and surgery might contribute to the selectively altered osseous turnover and development of MRONJ in CNC-derived bone.

Zoledronate Causes a Systemic Shift of Macrophage Polarization towards M1 In Vivo

BACKGROUND

Immunomodulatory properties of bisphosphonates (BP) are suggested to contribute to the development of medication-associated osteonecrosis of the jaw (MRONJ). Furthermore, bisphosphonate-derived immune modulation might contribute to the anti-metastatic effect observed in breast cancer patients. Macrophages are potential candidates for the mediation of immunomodulatory effects of bisphosphonates. The study aimed to investigate the influence of bisphosphonates alone and in combination with surgical trauma on systemic macrophage polarization (M1 vs. M2) using an in vivo rat model.

METHODS

A total of 120 animals were divided into four groups. Groups 2 and 4 were treated with 8 × 40 μg/kg body weight of the BP Zoledronate i.p. (week 0-7). Groups 3 and 4 were exposed to surgical trauma (week 8, tooth extraction + tibia fracture), whereas in Group 1 neither medication nor surgical trauma was applied. After 8, 10, 12 and 16 weeks, skin, lung and spleen were immunohistochemically examined for macrophage polarization via expression analysis of CD68, CD163 and iNOS using a tissue microarray (TMA).

RESULTS

A significant shift of macrophage polarization towards M1 was observed in skin, spleen and lung tissue of animals, with and without surgical trauma, treated with BP when compared to those without BP application. Surgical trauma did not cause a significant increase towards M1 polarization.

CONCLUSIONS

BP application leads to a systemic pro-inflammatory situation in vivo, independent of surgical trauma, as evidenced by the shift in macrophage polarization towards M1 in various somatic tissues. This provides a possible explanation for the clinically observed anti-tumor effect of bisphosphonates and might also contribute to pathogenesis of MRONJ.

Craniofacial Osteosarcoma-Pilot Study on the Expression of Osteobiologic Characteristics and Hypothesis on Metastasis

Background: Craniofacial osteosarcomas (COS) and extracranial osteosarcomas (EOS) show distinct clinical differences. COS show a remarkably lower incidence of metastases and a better survival. However, in contrast to EOS, they show a poor response to neoadjuvant chemotherapy. Tumor-associated macrophages and their polarization as well as developmental biological signaling pathways are possible candidates for explaining the clinical differences between COS and EOS. The aim of the study was to analyze differential expression of macrophage markers and important regulators of these pathways.

Methods: Twenty osteosarcoma cases (10 COS and 10 EOS) were immunohistochemically stained to assess CD68, CD11c, CD163, MRC1, Gli1, and Gli2 expression. Statistical differences between COS and EOS were tested using the Mann–Whitney U test. Additionally, the paper describes an example of multidisciplinary treatment of a patient suffering from COS and discusses the surgical challenges in treatment and rehabilitation of COS.

Results: COS showed a significantly (p < 0.05) increased infiltration of CD11c-positive M1 macrophages and a shift toward M1 polarization compared to EOS. Additionally, COS revealed a significantly (p < 0.05) lower Gli1 expression than EOS.

Conclusion: The reduced Gli1 expression in COS can be interpreted as reduced activation of the Hedgehog (Hh) signaling pathway. The increased M1 polarization and reduced Hh activation in COS could explain the low incidence of metastases in these osteosarcomas.

MSX1 is differentially expressed in the deepest impacted maxillary third molars

An impacted third molar is one of the most common dental abnormalities. Among the reasons for impaction the most common are: insufficient space, time of eruption, improper position of the tooth bud, and genetic disruptions. To investigate if runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), and msh homeobox 1 (MSX1) are differently expressed depending on the position of the molar, we studied 32 patients who had been referred for surgical removal. An orthopantomogram was used to separate them according to Winter's, and Pell & Gregory's, classifications. Bone samples were harvested during the operation for gene expression assay. The Kruskal-Wallis, Dunn's post hoc, and Spearman's correlation, tests were used to assess the significance of differences. No correlations were found in expression of the genes, and no differences between expression in maxillary and mandibular third molars, nor were they expressed differently according to Winter's or Pell and Gregory's classifications or in relation to impaction of the mandibular ramus. However, MSX1 was expressed differently when account was taken of the depth of impaction in maxillary third molars (p = 0.029), but there was no difference in expression of RUNX2, BMP2, and MSX1 for the Pell and Gregory classification of depth of impaction (p > 0.05). We conclude that MSX1 is expressed differently depending on the depth of maxillary impaction phenotypes.

Saliva diagnostics in patients suffering from bisphosphonate-associated osteonecrosis of the jaw: Results of an observational study

OBJECTIVE

One of the severe side effects of bisphosphonate (BP) therapy is bisphosphonate-associated osteonecrosis of the jaw (BONJ). However, there is no information available about its pathogenesis. Hence, the aim of this observational study was to contribute to discerning this pathogenesis by comparing salivary quantity and quality in patients with BONJ and undergoing BP treatment.

MATERIALS AND METHODS

This study included 60 patients divided into three groups. The first group consisted of 20 patients with established BONJ, the second group had 20 patients undergoing BP treatment, and the third group comprised 20 healthy individuals. These groups were analysed for the flow rate of stimulated saliva, buffer capacity, and salivary pH level.

RESULTS

Reduced salivation was observed in a significantly high number of patients with established BONJ (n = 8) and those undergoing BP treatment (n = 9) in comparison with the healthy control group (n = 4; p = 0.039). Though the distribution of the mean value of stimulated saliva flow rates in patients undergoing BP treatment was lower than in the control group, the difference was not significant. Moreover, there were no significant differences in the salivary pH level and buffer capacity in patients undergoing BP treatment as compared with the healthy control group.

CONCLUSIONS

It is possible that the quantity of human saliva is affected by BP treatment. This reduction in saliva production could have a negative effect on mucosal health and is perhaps a cofactor in the pathogenesis of BONJ.

Experimental periodontitis in Msx2 mutant mice induces alveolar bone necrosis

BACKGROUND

Msx2 homeoprotein is a key transcription factor of dental and periodontal tissue formation and is involved in many molecular pathways controlling mineralized tissue homeostasis such as Wnt/sclerostin pathway. This study evaluated the effect of Msx2-null mutation during experimental periodontitis in mice.

METHODS

Experimental periodontitis was induced for 30 days in wild-type and Msx2 knock-in Swiss mice using Porphyromonas gingivalis infected ligatures. In knock-in mice, Msx2 gene was replaced by n-LacZ gene encoding β-galactosidase. Periodontal tissue response was assessed by histomorphometry, tartrate-resistant acid phosphatase histoenzymology, β-galactosidase, sclerostin immunochemistry, and terminal deoxynucleotidyl transferase-mediated dUTP nickend labeling assay. Expression of Msx2 gene expression was also evaluated in human gingival biopsies using RT-qPCR.

RESULTS

During experimental periodontitis, osteonecrosis area and osteoclast number were significantly elevated in knock-in mice compared with wild-type mice. Epithelial downgrowth and bone loss was similar. Sclerostin expression in osteocytes appeared to be reduced during periodontitis in knock-in mice. Msx2 expression was detected in healthy and inflamed human gingival tissues.

CONCLUSION

These data indicated that Msx2 pathway influenced periodontal tissue response to experimental periodontitis and appeared to be a protective factor against alveolar bone osteonecrosis. As shown in other inflammatory processes such as atherothrombosis, genes initially characterized in early development could also play an important role in human periodontal pathogenesis.

Pharmacogenetics of medication-related osteonecrosis of the jaw: a systematic review and meta-analysis

Medication-related osteonecrosis of the jaw (MRONJ) is a severe complication that can develop in patients treated with anti-resorptive drugs. Although the pathogenesis of MRONJ is still unclear, genetic factors have a demonstrated important role. Thus, the aim of this study was to perform a systematic review on the pharmacogenetics of MRONJ. Studies published until March 2019 were retrieved from eight databases and were selected by two independent reviewers. Evidence on several genetic polymorphisms was summarized and a meta-analysis was conducted when possible. Fourteen studies involving 1515 participants were eligible for systematic review. For CYP2C8 rs1934951, no significant difference was observed between the MRONJ and non-MRONJ groups (odds ratio (OR) 2.04, 95% confidence interval (CI) 0.88-4.73, P=0.09). However, a subgroup analysis based on only multiple myeloma status showed a positive association (OR 3.64, 95% CI 1.29-10.30, P=0.01). PPARG rs1152003 was not differently distributed between groups (OR 0.25, 95% CI 0.01-9.92, P=0.46). Also, VEGF rs3025039 was found to be correlated with the occurrence of MRONJ (OR 0.35, 95% CI 0.15-0.82, P=0.02). CYP2C8 rs1934951 (in multiple myeloma patients) and VEGF rs3025039 are associated with the development of MRONJ in patients treated with bisphosphonates. The results are promising and call for new trials with a larger sample to further explore this growing field.

Impact of bisphosphonate therapy on dental implant outcomes: An overview of systematic review evidence

The purpose of this overview was to assess the methods, quality, and outcomes of systematic reviews conducted to evaluate the impact of bisphosphonates on dental implants and the risk of developing bisphosphonate-related osteonecrosis of the jaw after dental implant surgery. An electronic search without date or language restriction was performed in the PubMed/MEDLINE, Cochrane CENTRAL, Web of Science, and LILACS databases (to January 2018). Eligibility criteria included systematic reviews that evaluated the impact of bisphosphonates on implant outcomes. The quality assessment of the included reviews was done using AMSTAR 2 guidelines. The protocol of this overview was registered in PROSPERO (CRD42018089617). The search and selection process yielded seven reviews, published between 2009 and 2017. None of the systematic reviews included in this study obtained the maximum score in the quality assessment. The scientific evidence available demonstrates that patients with a history of bisphosphonate use do not present a higher risk of dental implant failure or marginal bone loss compared to patients who have not used bisphosphonates. The literature also suggests that patients who undergo surgical trauma during the installation of dental implants may be more susceptible to bisphosphonate-related osteonecrosis of the jaw.

Current Understanding of the Pathophysiology of Osteonecrosis of the Jaw

PURPOSE OF REVIEW

Osteonecrosis of the jaw (ONJ) is a rare and severe necrotic bone disease reflecting a compromise in the body's osseous healing mechanisms and unique to the craniofacial region. Antiresorptive and antiangiogenic medications have been suggested to be associated with the occurrence of ONJ; yet, the pathophysiology of this disease has not been fully elucidated. This article raises the current theories underlying the pathophysiology of ONJ.

RECENT FINDINGS

The proposed mechanisms highlight the unique localization of ONJ. The evidence-based mechanisms of ONJ pathogenesis include disturbed bone remodeling, inflammation or infection, altered immunity, soft tissue toxicity, and angiogenesis inhibition. The role of dental infections and the oral microbiome is central to ONJ, and systemic conditions such as rheumatoid arthritis and diabetes mellitus contribute through their impact on immune resiliency. Current experimental studies on mechanisms of ONJ are summarized. The definitive pathophysiology is as yet unclear. Recent studies are beginning to clarify the relative importance of the proposed mechanisms. A better understanding of osteoimmunology and the relationship of angiogenesis to the development of ONJ is needed along with detailed studies of the impact of drug holidays on the clinical condition of ONJ.

Cathepsin K inhibitor causes changes in crystallinity and crystal structure of newly-formed mandibular bone in rats

Cathepsin K inhibitors are new drugs with the potential for the treatment of osteoporosis because they sustain bony remodelling better than bone resorption inhibitors such as bisphosphonates. The treatment of osteoporosis with inhibitors of bony resorption is associated with osteonecrosis of the jaw, as the deterioration in bony quality that they induce is thought to be one of its causes. The quality of bone is delineated by structural and material characteristics (which include the degree and quality of mineralisation, and depends on the content of proteoglycan and the structural integrity of the bony collagen).^1,2 Animal and clinical studies have shown that cathepsin K inhibitors improve the mineral density and structural characteristics of bone, but their effect on the rest remains unknown. We therefore hypothesised that these inhibitors will affect the material characteristics of newly-formed mandibular bone. To verify our hypothesis, we used Raman microspectroscopy to examine such bone in rats that were given a cathepsin K inhibitor, and found unusual crystallinity and an increased substitution of carbonate (CO₃^2-) in its crystal structure.

Molecular alterations of newly formed mandibular bone caused by zoledronate

Bone quality is defined by structural and material characteristics. Most studies on the mandible have focused on the analysis of structural characteristics, with insufficient investigation of material characteristics. This study tested whether zoledronate affects the material characteristics of newly formed mandibular bone. Thirty-six female Wistar rats were assigned to three groups: sham-ovariectomized rats (SHAM, n=12), ovariectomized rats (OVX, n=12), and ovariectomized rats treated with zoledronate (ZOL, n=12). The left side of the mandibular ramus of all rats was drilled bicortically. Twenty-eight days after surgery, all surviving rats were euthanized and all mandibles were removed. Raman microspectroscopy was performed, and five spectra per specimen of newly formed mandibular bone were analysed. Compared with OVX rats, the mineral/matrix ratio in ZOL rats was significantly increased (5.43±1.88 vs. 7.86±2.05), while crystallinity (0.055±0.002 vs. 0.050±0.002), relative proteoglycan content (0.43±0.10 vs. 0.31±0.05), and collagen structural integrity (1.16±0.21 vs. 0.72±0.06) were significantly decreased. These changes in material characteristics may explain why rats that received zoledronate exhibited peculiar biological phenomena such as bisphosphonate-related osteonecrosis of the jaw.

Paradoxical side effects of bisphosphonates on the skeleton: What do we know and what can we do?

Bisphosphonates are considered the most effective drugs for controlling adult and pediatric osteolytic diseases. Although they have been used successfully for many years, several side effects, such as osteonecrosis of the jaw, delayed dental eruption, atypical femoral fracture, and alterations to the bone growth system, have been described. After an overview of nitrogenous bisphosphonate, the purpose of this article is to describe their mechanisms of action and current applications, review the preclinical and clinical evidence of their side effects in the skeleton ("what we know"), and describe current recommendations for preventing and managing these effects ("what we can do"). Finally, promising future directions on how to limit the occurrence of these side effects will be presented.

Angiogenesis in the Development of Medication-Related Osteonecrosis of the Jaws: An Overview

Medication-related osteonecrosis of the jaws (MR-ONJ) is one of the most relevant side effects of bisphosphonate therapy; it is clinically defined as a non-healing wound in combination with an avascular and necrotic jaw within ongoing bisphosphonate therapy or after completed bisphosphonate therapy. Different theories concerning the development of MR-ONJ have been reported, while the exact pathophysiology is still unknown. Recent studies have increasingly focused on angiogenesis and revascularization concerning MR-ONJ pathophysiology, which seems to be a relevant factor in the development of MR-ONJ and a possible and promising point of action for MR-ONJ prevention and therapy. Therefore, and with respect to the different aspects and specific forms of angiogenesis, the enclosed review summarizes the possible role of angiogenesis and revascularization in the pathophysiology of MR-ONJ. Special focus is given to the strong negative influence of bisphosphonates on progenitor and mature endothelial cells in vitro as well as on microvessel sprouting in vitro and in vivo, which might result in overall reduced wound healing of oral soft and hard tissues, and therefore in an exposed and avascular jaw from a clinical viewpoint. Further, it will be summarized whether and in what way the aspect of angiogenesis might be used for possible MR-ONJ prevention and therapy.

The influence of geranylgeraniol on microvessel sprouting after bisphosphonate substitution in an in vitro 3D-angiogenesis assay

OBJECTIVES

Recent studies focused on angiogenesis in the pathophysiology of bisphosphonate-associated osteonecrosis of the jaws (BP-ONJ) and identified geranylgeraniol (GGOH) as a feasible option for BP-ONJ therapy. This study investigated the influence of GGOH on microvessel sprouting after BP-incubation in vitro.

MATERIALS AND METHODS

Ten experimental set-ups were randomly designed in an in vitro 3D-angiogenesis assay. Two groups included HUVEC cell spheroids with and without (±) GGOH substitution as controls and eight groups pairwise contained either clodronate or the nitrogen-containing bisphosphonates (N-BP) ibandronate, pamidronate, and zoledronate ± GGOH. The size of the cell spheroids including the outbranching sprouts (SpS) as well as the density (SpD) and length of the sprouts (SpL) were analyzed by a grid system after 0, 24, 48, and 72 h.

RESULTS

For controls and NN-BP clodronate, no significant differences at any tested parameter and any point of measurement could be detected within the experimental set-ups ± GGOH (p each ≥0.05). For N-BP ibandronate, the experimental set-ups +GGOH showed a significantly increased SpS, SpD, and SpL after 48 and 72 h (p each ≤0.002) compared to the experimental set-ups -GGOH. For N-BPs pamidronate and zoledronate, the experimental set-ups + GGOH demonstrated a significantly increased SpS, SpD, and SpL after 24, 48, and 72 h (p each ≤0.001) compared to the experimental set-ups -GGOH.

CONCLUSIONS

The strong negative influence of N-BPs on microvessel sprouting could be significantly reversed by GGOH.

CLINICAL RELEVANCE

Since supportive therapeutic options for BP-ONJ are lacking, GGOH might be a promising substitute for BP-ONJ prevention and therapy.

Effects of zoledronic acid and geranylgeraniol on the cellular behaviour and gene expression of primary human alveolar osteoblasts

INTRODUCTION

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a serious complication of bisphosphonate therapy. The mechanism underlying BRONJ pathogenesis is poorly understood.

OBJECTIVES

To determine the effects of zoledronic acid (ZA) and geranylgeraniol (GGOH) on the mevalonate pathway (MVP) in osteoblasts generated from the human mandibular alveolar bone in terms of cell viability/proliferation, migration, apoptosis and gene expression.

MATERIALS AND METHODS

Primary human osteoblasts (HOBs) isolated from the mandibular alveolar bone were phenotyped. HOBs were cultured with or without ZA and GGOH for up to 72 h. Cellular behaviour was examined using a CellTiter-Blue® viability assay, an Ibidi culture-insert migration assay, an Apo-ONE® Homogeneous Caspase-3/7 apoptosis assay and transmission electron microscopy (TEM). Quantitative real-time reverse transcriptase polymerase chain reaction (qRT²-PCR) was used to determine the simultaneous expression of 168 osteogenic and angiogenic genes modulated in the presence of ZA and GGOH.

RESULTS

ZA decreased cell viability and migration and induced apoptosis in HOBs. TEM revealed signs of apoptosis in ZA-treated HOBs. However, the co-addition of GGOH ameliorated the effect of ZA and partially restored the cells to the control state. Twenty-eight genes in the osteogenic array and 27 genes in the angiogenic array were significantly regulated in the presence of ZA compared with those in the controls at one or more time points.

CONCLUSION

The cytotoxic effect of ZA on HOBs and its reversal by the addition of GGOH suggests that the effect of ZA on HOBs is mediated via the MVP.

CLINICAL RELEVANCE

The results suggest that GGOH could be used as a possible therapeutic/preventive strategy for BRONJ.

Surgical treatment of bisphosphonate-associated osteonecrosis: Prognostic score and long-term results

Over a century after the first synthesis of bisphosphonates (1897) and a decade (2003) since the initial report on bisphosphonate-related osteonecrosis of the jaw (ONJ), this osteopathy remains a serious clinical challenge. A single center longitudinal study (2005-2014) was carried out to prospectively characterize inpatients with manifest ONJ and to evaluate their outcomes. The data recorded were: medical history, bisphosphonate treatment, localization, imaging, treatment, histomorphological features, and complications. A prognostic score (modified UCONN-Score) was adopted to predict outcomes. Eighty patients were included (mean age 69.4 years; 40 male, 40 female). Breast cancer (n = 25), multiple myeloma (n = 16), and prostate cancer (n = 15) were the three most common malignancies; and cardiovascular disease (n = 31), diabetes mellitus (16), and renal disorders (6) were the most important comorbidities. The severity of ONJ was stage I in three patients, stage II in 37, and stage III in 40, being predominantly localized in the posterior mandible and needing gradual resection. The average duration of bisphosphonate treatment was 38.3 months. The typical histological aspects of ONJ were predominantly osteonecrosis, bone marrow fibrosis, and bacterial colonization (Actinomyces) with suppurative inflammation. Within the resected jawbone a primary malignancy was diagnosed in two cases. The overall success rate was 83.6% (follow-up 23.5 months), with a UCONN-Score ≥15 predicting unfavorable treatment results (OR = 5.2). The past decade has enhanced experience with ONJ treatment and knowledge about its pathogenesis, which seems to be a multistep process. This study demonstrates the importance of bone and multilayer soft tissue management, preferably as an early intervention. The UCONN-Score might help to assess individual prognosis in ONJ surgery and the potential benefit of an antiresorptive drug holiday. To our knowledge it is the first use of a prognostic score in ONJ surgery.

The influence of geranylgeraniol on human oral keratinocytes after bisphosphonate treatment: An in vitro study

This in vitro study analyzed the influence of geranylgeraniol (GGOH) on human oral keratinocytes (HOK) after exposure to bisphosphonates. HOK were incubated with four different bisphosphonates (clodronate, ibandronate, pamidronate, zoledronate) in two experimental set-ups: with and without GGOH. MTT and PrestoBlue assays were used to analyze HOK cell viability. HOK migration ability was examined with Boyden and Scratch assays, and Tunel and ToxiLight assays were used to detect the HOK apoptosis rate. No significant differences between the experimental set-ups, with and without GGOH, could be found for clodronate (p each >0.3). For the nitrogen-containing bisphosphonates, negative effects could be shown in the experimental set-ups without GGOH in all assays. In the GGOH experimental set-ups, the levels of HOK cell viability were significantly increased (MTT: p each ≤0.001; PrestoBlue: p each ≤0.012). The HOK migration ability was also greater (Boyden: p each <0.001; Scratch: p each ≤0.015). Regarding the apoptosis rate, reduced numbers of apoptotic HOK in the Tunel assay (p each <0.001) and decreased adenylate kinase release in the ToxiLight assay (p each ≤0.002) were observed. GGOH reversed the negative effects of bisphosphonates on HOK. These findings provide evidence that GGOH could be a promising treatment option for BP-ONJ.

BRONJ-related jaw bone is associated with increased Dlx-5 and suppressed osteopontin-implication in the site-specific alteration of angiogenesis and bone turnover by bisphosphonates

OBJECTIVES

Site-specific suppression of bone remodelling has been implicated in bisphosphonate-(BP)-related osteonecrosis of the jaws (BRONJ). Due to the origin of jaw bone from cranial neural crest, osseous differentiation is regulated specifically by the antagonizing BMP-2-downstream-transcription factors Msx-1 and Dlx-5. Osteopontin has been implicated in bone remodelling and angiogenesis. The osteoblast and osteoclast progenitor proliferation mediating Msx-1 has been demonstrated to be suppressed in BRONJ. In vitro BPs were shown to increase Dlx-5 and to suppress osteopontin expression. This study targeted Dlx-5 and osteopontin in BRONJ-related and BP-exposed jaw bone compared with healthy jaw bone samples at protein- and messenger RNA (mRNA) level, since increased Dlx-5 and suppressed osteopontin might account for impaired bone turnover in BRONJ.

MATERIALS AND METHODS

Fifteen BRONJ-exposed, 15 BP-exposed and 20 healthy jaw bone samples were processed for real-time reverse transcription polymerase chain reaction (RT-PCR) and for immunohistochemistry. Targeting Dlx-5, osteopontin and glyceraldehyde 3-phosphate dehydrogenase mRNA was extracted, quantified by the LabChip-method, followed by quantitative RT-PCR. For immunohistochemistry, an autostaining-based alkaline phosphatase antialkaline phosphatase (APAPP) staining kit was used. Semiquantitative assessment was performed measuring the ratio of stained cells/total number of cells (labelling index, Bonferroni adjustment).

RESULTS

The labelling index was significant decreased for osteopontin (p < 0.017) and significantly increased for Dlx-5 (p < 0.021) in BRONJ samples. In BRONJ specimens, a significant fivefold decrease in gene expression for osteopontin (p < 0.015) and a significant eightfold increase in Dlx-5 expression (p < 0.012) were found.

CONCLUSIONS

BRONJ-related suppression of bone turnover is consistent with increased Dlx-5 expression and with suppression of osteopontin. The BP-related impaired BMP-2-Msx-1-Dlx-5 axis might explain the jaw bone specific alteration by BP.

CLINICAL RELEVANCE

The findings of this study help to explain the restriction of RONJ to craniofacial bones. BRONJ might serve as a model of disease elucidating the specific signal transduction of neural crest cell-derived bone structures in health and disease.

Comparison of gene expression between mandibular and iliac bone-derived cells

OBJECTIVES

The purpose of this study is to investigate the differences in gene expression between the human mandibular and iliac bone-derived cells (BCs) for better understanding of the site-specific characteristics of bones.

METHODS

Primary cells were obtained from mandibular and iliac bones from six healthy, elderly donors. To investigate site-specific differences, gene expression profile of mandibular and iliac BC from the same donors were compared via cDNA microarray analysis.

RESULTS

A comparison of the gene expression profiles revealed that 82 genes were significantly upregulated and 66 genes were downregulated with 1.5 fold or greater in mandibular versus iliac BCs. The most significantly differentially regulated genes were associated with skeletal system development or morphogenesis (SIX1, MSX1, MSX2, HAND2, PRRX1, OSR2, HOX gene family, PITX2). Especially, upregulated genes in mandibular BC were related with tooth morphogenesis, originated from the ectomesenchyme. Microarray analysis revealed that Msx1 was 2.03-fold and Msx2 was 1.99-fold upregulated in mandibular versus iliac BCs (both p < 0.01). Furthermore, in mandibular BCs, all members of the HOX gene family that were analyzed were downregulated (p < 0.01) and osteopontin was also downregulated by 2.84-fold (p < 0.01).

CONCLUSIONS

Site-specific differences between jaw and long bones can be explained by the differences in gene expression patterns. Our results suggest that bone cell-derived cells maintain the genetic characteristics of their embryological origin.

CLINICAL RELEVANCE

This study revealed fundamental differences in gene expression between the mandibular and iliac bone in humans. These differences could be important for understanding jaw bone-specific development of bisphosphonate-related osteonecrosis of the jaw.

Mesodermal and neural crest derived ovine tibial and mandibular osteoblasts display distinct molecular differences

Mandibular osteoblasts originate from the neural crest and deposit bone intramembranously, mesoderm derived tibial osteoblasts by endochondral mechanisms. Bone synthesized by both cell types is identical in structure, yet functional differences between the two cell types may exist. Thus, both matched juvenile and adult mandibular and tibial osteoblasts were studied regarding their proliferative capacity, their osteogenic potential and the expression of osteogenic and origin related marker genes. Juvenile tibial cells proliferated at the highest rate while juvenile mandibular cells exhibited higher ALP activity depositing more mineralized matrix. Expression of Hoxa4 in tibial cells verified their mesodermal origin, whereas very low levels in mandibular cells confirmed their ectodermal descent. Distinct differences in the expression pattern of bone development related genes (collagen type I, osteonectin, osteocalcin, Runx2, MSX1/2, TGF-β1, BAMBI, TWIST1, β-catenin) were found between the different cell types. The distinct dissimilarities in proliferation, alkaline phosphatase activity, the expression of characteristic genes, and mineralization may aid to explain the differences in bone healing time observed in mandibular bone when compared to long bones of the extremities.

Osteonecrosis of the Jaw and Nonmalignant Disease: Is There an Association with Rheumatoid Arthritis?

Objective.

To review cases of bisphosphonate-related osteonecrosis of the jaw (BRONJ) occurring in association with benign disease and to describe and compare the clinical course and outcome for patients with BRONJ and rheumatoid arthritis (RA) or osteoporosis.

Methods.

We retrospectively reviewed observations of all patients referred for treatment and followup for BRONJ from January 2007 to December 2011. Only patients with malignant disease were excluded. Demographic data, medical history, maxillofacial findings, BRONJ treatment, and followup were reviewed for each case.

Results.

Over a 5-year period, we diagnosed 112 patients with BRONJ. Among these patients, 15 received bisphosphonate (BP) treatment for nonmalignant disease (mean age 65.7 ± 19.8 yrs, 80% women). Patients received BP for a variety of reasons: 8 (53%) to prevent osteoporosis in association with underlying RA; 6 (40%) to prevent idiopathic osteoporosis; and 1 (7%) to treat ankle algodystrophy. The mean oral BP exposure period was 48.4 months (median 36 mo). In 13 cases (86.6%), BRONJ was diagnosed following dental extraction. Of the 8 patients with RA, 5 (62.5%) were taking prednisone at the time of the discovery of BRONJ. Major surgery, sequestrectomy, or alveolectomy was performed in 9 patients (60%), all of whom healed within 3 to 36 months (mean 11.5 mo). Comparative analysis of all the variables showed no statistically significant differences between patients with RA and others.

Conclusion.

ONJ is a rare adverse effect of BP therapy, especially when administered orally. Within the limits of our study, we were unable to demonstrate a difference in BRONJ disease spectrum, clinical course, or outcome between patients with and those without RA.