In vivo effects of geranylgeraniol on the development of bisphosphonate-related osteonecrosis of the jaws

Geranylgeraniol (GGOH), incorporated into a bone cement pellet promotes osteoclast function and healing in a model of medication-related osteonecrosis of the jaw

Introduction

There is no cause -based treatment for Medication-Related Osteonecrosis of the Jaw (MRONJ). MRONJ is a morbid condition including exposed, infected bone and mandibular fractures in osteoporotic individuals and metastatic cancers patients treated with nitrogen containing bisphosphonates (NBP). NBPs inhibit farnesyl diphosphate synthase (FDPS) in the mevalonate pathway, depriving osteoclasts and other bone cells of small GTPases necessary for their function and survival. We test the hypothesis that geranylgeraniol (GGOH),a metabolite downstream of FDPS, when incorporated into a bone cement pellet, enhances osteoclast function and promotes local bone healing in in vitro and in a proven animal model of MRONJ.

Methods

3H labelled GGOH (2 mM) was incorporated into a Hydroset bone cement pellet and release from the cement was assessed over time. To assess the effect on bone cell function, the GGOH-loaded cement was placed in a porous filter above cultured osteoclasts treated with bisphosphonate and the effect on osteoclast survival and function were measured. In a pilot study the effect of GGOH on osteotomy microstructure was measured in a rat model of MRONJ using a split mouth design.

Results

The release of GGOH from bone cement increased osteoclast survival/metabolic activity, and promoted resorption of the calcified substrate. In vivo released GGOH limited the effects of the bisphosphonate and promoted healing. In an animal pilot study, GGOH from the infused cement carrier stabilizes bone structure and restores the ability of osteoclasts to remodel.

Conclusion

These initial findings point to GGOH in a bone cement carrier as a useful therapeutic approach to prevent or mitigate the pathogenesis of MRONJ.

Recent Insights in Pyrin Inflammasome Activation: Identifying Potential Novel Therapeutic Approaches in Pyrin-Associated Autoinflammatory Syndromes

Pyrin is a cytosolic protein encoded by the MEFV gene, predominantly expressed in innate immune cells. Upon activation, it forms an inflammasome, a multimolecular complex that enables the activation and secretion of IL-1β and IL-18. In addition, the Pyrin inflammasome activates Gasdermin D leading to pyroptosis, a highly pro-inflammatory cell death. Four autoinflammatory syndromes are associated with Pyrin inflammasome dysregulation: familial Mediterranean fever, hyper IgD syndrome/mevalonate kinase deficiency, pyrin-associated autoinflammation with neutrophilic dermatosis, and pyogenic arthritis, pyoderma gangrenosum, and acne syndrome. In this review, we discuss recent advances in understanding the molecular mechanisms regulating the two-step model of Pyrin inflammasome activation. Based on these insights, we discuss current pharmacological options and identify a series of existing molecules with therapeutic potential for the treatment of pyrin-associated autoinflammatory syndromes.

The Capacity of Magnesium to Induce Osteoclast Differentiation Is Greatly Enhanced by the Presence of Zoledronate

Bisphosphonates (BPs) are successfully used to cure a number of diseases characterized by a metabolic reduction in bone density, such as Osteoporosis, or a neoplastic destruction of bone tissue, such as multiple myeloma and bone metastases. These drugs exert their therapeutic effect by causing a systemic osteoclast depletion that, in turn, is responsible for reduced bone resorption. Unfortunately, in addition to their beneficial activity, BPs can also determine a frightening side effect known as osteonecrosis of the jaw (ONJ). It is generally believed that the inability of osteoclasts to dispose of inflamed/necrotic bone represents the main physiopathological aspect of ONJ. In principle, a therapeutic strategy able to elicit a local re-activation of osteoclast production could counteract ONJ and promote the healing of its lesions. Using an experimental model of Vitamin D3-dependent osteoclastogenesis, we have previously demonstrated that Magnesium is a powerful inducer of osteoclast differentiation. Here we show that, surprisingly, this effect is greatly enhanced by the presence of Zoledronate, chosen for our study because it is the most effective and dangerous of the BPs. This finding allows us to hypothesize that Magnesium might play an important role in the topical therapy of ONJ.

In Vitro Cytotoxicity of Antiresorptive and Antiangiogenic Compounds on Oral Tissues Contributing to MRONJ: Systematic Review

BACKGROUND

Invasive dental treatment in patients exposed to antiresorptive and antiangiogenic drugs can cause medication-related osteonecrosis of the jaw (MRONJ). Currently, the exact pathogenesis of this disease is unclear.

METHODS

In March 2022, Medline (Ovid), Embase (Ovid), Scopus, and Web of Science were screened to identify eligible in vitro studies investigating the effects of antiresorptive and antiangiogenic compounds on orally derived cells.

RESULTS

Fifty-nine articles met the inclusion criteria. Bisphosphonates were used in 57 studies, denosumab in two, and sunitinib and bevacizumab in one. Zoledronate was the most commonly used nitrogen-containing bisphosphonate. The only non-nitrogen-containing bisphosphonate studied was clodronate. The most frequently tested tissues were gingival fibroblasts, oral keratinocytes, and alveolar osteoblasts. These drugs caused a decrease in cell proliferation, viability, and migration.

CONCLUSIONS

Antiresorptive and antiangiogenic drugs displayed cytotoxic effects in a dose and time-dependent manner. Additional research is required to further elucidate the pathways of MRONJ.

Geranylgeraniol Application in Human Osteoblasts and Osteoclasts for Reversal of the Effect of Bisphosphonates

Nitrogen-containing bisphosphonates lead to the depletion of geranylgeranyl pyrophosphate involved in the mevalonate pathway. The effect of geranylgeraniol (GGOH) on human osteoblast and osteoclast activities suppressed by zoledronate was investigated in this study. The effect of GGOH on human osteoblasts and osteoclasts subjected to treatment with zoledronate was analyzed by assessing cell viability, osteoclast differentiation, resorption ability, gene expression, and protein synthesis. Cell viability suppressed by bisphosphonates in osteoblasts and osteoprogenitor cells was restored with GGOH. Osteoclast differentiation was analyzed by vitronectin receptor immunofluorescence staining, and the addition of GGOH to zoledronate significantly increased osteoclast differentiation compared with zoledronate alone. A trend of reversal of osteoclast resorption by GGOH was observed; however, it was not significant in all groups. The expression of ALP, type 1 collagen, and RUNX2 in osteoblasts was recovered by the addition of GGOH. Only CALCR expression in osteoclasts was significantly recovered by GGOH addition in the zoledronate group. Although the activities of osteoblasts and osteoclasts were not entirely restored, the possibility that the topical application of GGOH in MRONJ patients or patients with dental problems and bisphosphonates might lessen the risk of development and recurrence of MRONJ is shown.

Alterations in macrophage polarization in the craniofacial and extracranial skeleton after zoledronate application and surgical interventions - an in vivo experiment

Purpose

Medication-related osteonecrosis occurs exclusively in the jaw bones. However, the exact pathogenesis of medication-related osteonecrosis of the jaw (MRONJ) and the unique predisposition of the jaw bones have not been elucidated, making its treatment a challenge. Recent evidence indicates that macrophages might play a pivotal role in MRONJ pathogenesis. The aim of the present study was to compare the macrophage populations between the craniofacial and extracranial skeleton and to investigate the changes induced by zoledronate (Zol) application and surgical interventions.

Materials and methods

An in vivo experiment was performed. 120 wistar rats were randomized to 4 groups (G1, G2, G3, G4). G1 served as an untreated control group. G2 and G4 received Zol injections for 8 weeks. Afterwards, the right lower molar of the animals from G3 and G4 was extracted and the right tibia osteotomized followed by osteosynthesis. Tissue samples were taken from the extraction socket and the tibia fracture at fixed time points. Immunohistochemistry was conducted to determine the labeling indexes of CD68+ and CD163+ macrophages.

Results

Comparing the mandible and the tibia, we observed a significantly higher number of macrophages and a heightened pro-inflammatory environment in the mandible compared to the tibia. Tooth extraction caused an increase of the overall number of macrophages and a shift toward a more pro-inflammatory microenvironment in the mandible. Zol application amplified this effect.

Conclusion

Our results indicate fundamental immunological differences between the jaw bone and the tibia, which might be a reason for the unique predisposition for MRONJ in the jaw bones. The more pro-inflammatory environment after Zol application and tooth extraction might contribute to the pathogenesis of MRONJ. Targeting macrophages might represent an attractive strategy to prevent MRONJ and improve therapy. In addition, our results support the hypothesis of an anti-tumoral and anti-metastatic effect induced by BPs. However, further studies are needed to delineate the mechanisms and specify the contributions of the various macrophage phenotypes.

The Biomedical Importance of the Missing Pathway for Farnesol and Geranylgeraniol Salvage

Isoprenoids are the output of the polymerization of five-carbon, branched isoprenic chains derived from isopentenyl pyrophosphate (IPP) and its isomer, dimethylallyl pyrophosphate (DMAPP). Isoprene units are consecutively condensed to form longer structures such as farnesyl and geranylgeranyl pyrophosphate (FPP and GGPP, respectively), necessary for the biosynthesis of several metabolites. Polyprenyl transferases and synthases use polyprenyl pyrophosphates as their natural substrates; however, it is known that free polyprenols, such as farnesol (FOH), and geranylgeraniol (GGOH) can be incorporated into prenylated proteins, ubiquinone, cholesterol, and dolichols. Furthermore, FOH and GGOH have been shown to block the effects of isoprenoid biosynthesis inhibitors such as fosmidomycin, bisphosphonates, or statins in several organisms. This phenomenon is the consequence of a short pathway, which was observed for the first time more than 25 years ago: the polyprenol salvage pathway, which works via the phosphorylation of FOH and GGOH. Biochemical studies in bacteria, animals, and plants suggest that this pathway can be carried out by two enzymes: a polyprenol kinase and a polyprenyl-phosphate kinase. However, to date, only a few genes have been unequivocally identified to encode these enzymes in photosynthetic organisms. Nevertheless, pieces of evidence for the importance of this pathway abound in studies related to infectious diseases, cancer, dyslipidemias, and nutrition, and to the mitigation of the secondary effects of several drugs. Furthermore, nowadays it is known that both FOH and GGOH can be incorporated via dietary sources that produce various biological effects. This review presents, in a simplified but comprehensive manner, the most important data on the FOH and GGOH salvage pathway, stressing its biomedical importance The main objective of this review is to bring to light the need to discover and characterize the kinases associated with the isoprenoid salvage pathway in animals and pathogens.

Cytoprotective effect of Fridericia chica (Bonpl.) L.G. Lohmann extract associated with geranylgeraniol enriched-fraction from Bixa orellana L. on epithelial cells treated with bisphosphonate

Bisphosphonates are drugs used to treat bone disorders. The chronic use of bisphosphonates is associated with the occurrence of medication-related osteonecrosis of the jaw (MRONJ). Previous data reported the positive effects of Geranylgeraniol on different cell types treated with Bisphosphonates. Foregoing work done by our research group demonstrated the wound healing capacity of Fridericia chica (Bonpl.) L.G.Lohmann standardized ethanol extract. Herein in vitro cytoprotective synergistic effect of the association of F. chica extract associated with an enriched geranylgeraniol fraction on keratinocytes exposed to zoledronic acid is reported. An association of F. chica at 1 and 5 µg/mL with geranylgeraniol at 15 µg/mL, increased cell viability by 73.5% and 71.1%, respectively. This treatment did not increase tumor cells viability; whereas the clonogenic potential assessment showed that, the association with F. chica (5 µg/mL) reversed the effects of zoledronic acid on the cells. This study provides data for a potential treatment for MRONJ.

In vitro Effect of Geranylgeraniol (GGOH) on Bisphosphonate-Induced Cytotoxicity of Oral Mucosa Cells

Medication-related osteonecrosis of the jaw (MRONJ) is an often-severe complication found in patients receiving bisphosphonates in the management of Paget's, osteoporosis and metastatic bone cancer. Mucosal breakdown with bone exposure is a primary clinical presentation of MRONJ linked to the inhibitory effect of nitrogen-containing bisphosphonates (N-BP) on the mevalonate pathway. Geranylgeraniol (GGOH) has demonstrated a rescue effect on N-BP-treated osteoclasts but the biological effects on oral soft tissues and cells remain unclear. This study aimed to determine whether GGOH could prevent bisphosphonate induced toxicity to oral mucosa cells in vitro. Primary oral fibroblasts and keratinocytes were exposed to different GGOH concentrations or GGOH in combination with two nitrogen-containing bisphosphonates, zoledronic acid (ZA) or pamidronic acid (PA), for 72 h. The metabolic activity of each cell type was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. GGOH without bisphosphonates significantly reduced the metabolic activity of oral mucosa cells. Fibroblasts treated with GGOH and ZA in combination showed a slight increase in metabolic status compared to fibroblasts treated with ZA alone, however this positive effect was not observed in keratinocytes. In the presence of PA, GGOH was unable to increase the metabolic activity of either cell type. These findings demonstrate that GGOH is toxic to oral mucosa cells and that GGOH was not able to prevent bisphosphonate induced toxicity. These data show that GGOH does not have therapeutic potential for bisphosphonate-induced soft tissue toxicity in MRONJ and the use of GGOH as an MRONJ treatment should be strongly reconsidered.

The Role of Geranylgeraniol in Managing Bisphosphonate-Related Osteonecrosis of the Jaw

Medication-related osteonecrosis of the jaw (ONJ) is a rare but significant adverse side effect of antiresorptive drugs. Bisphosphonate-related ONJ (BRONJ) is the most prevalent condition due to the extensive use of the drug in cancer and osteoporosis treatment. Nitrogen-containing bisphosphonates suppress osteoclastic resorption by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway, leading to deficiency of the substrate for GTPase prenylation. The bone remodelling process is uncoupled, subsequently impairing bone healing and causing ONJ. Targeted administration of geranylgeraniol (GGOH) represents a promising approach to mitigate BRONJ because GGOH is a substrate for GTPase prenylation. In the current review, the in vitro effects of GGOH on osteoclasts, osteoblasts and other related cells of the jaw are summarised. We also present and appraise the current in vivo evidence of GGOH in managing BRONJ in animal models. Lastly, several considerations of using GGOH in the clinical management of BRONJ are highlighted. As a conclusion, GGOH is a promising topical agent to manage BRONJ, pending more research on an effective delivery system and validation from a clinical trial.

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.

Geranylgeraniol Restores Zoledronic Acid-Induced Efferocytosis Inhibition in Bisphosphonate-Related Osteonecrosis of the Jaw

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a severe side effect of long-term administration of bisphosphonates such as zoledronic acid (ZA), but its pathogenesis remains unclear. Impairment of the clearance of apoptotic cells (termed “efferocytosis”) by ZA may be associated with the pathogenesis of BRONJ. The aim of this study was to investigate whether ZA might inhibit macrophage efferocytosis and promote osteocytic apoptosis, and the underlying mechanisms responsible for the disturbing balance between clean and generation of osteocytic apoptosis. We found that ZA significantly promoted the apoptosis of osteocyte and pre-osteoblast via BRONJ mouse models and in vitro MC3T3-E1 but also inhibited the efferocytosis of macrophage on apoptotic cells. Moreover, supplement with geranylgeraniol (GGOH), a substrate analog for geranylgeranylation of Rac1, could restore Rac1 homeostasis and rescue macrophage efferocytosis. GGOH partially inhibits MC3T3-E1 apoptosis induced by ZA via downregulation of Rac1/JNK pathway. We also examined the Rac1 distribution and activation conditions in bone marrow-derived macrophages (BMDMs) and MC3T3-E1 under ZA treatment, and we found that ZA impaired Rac1 migration to BMDM membrane, leading to round appearance with less pseudopodia and efferocytosis inhibition. Moreover, ZA simultaneously activated Rac1, causing overexpression of P-JNK and cleaved caspase 3 in MC3T3-E1. Finally, the systemic administration of GGOH decreased the osteocytic apoptosis and improved the bone healing of the extraction sockets in BRONJ mouse models. Taken together, our findings provided a new insight and experimental basis for the application of GGOH in the treatment of BRONJ.

Beneficial effect of dietary geranylgeraniol on glucose homeostasis and bone microstructure in obese mice is associated with suppression of proinflammation and modification of gut microbiome

Geranylgeraniol (GGOH) is found in edible oils such as olive, linseed, and sunflower oils, which have favorable metabolic effects. However, it is unknown whether these physiological benefits are mediated through the gut microbiome. Thus, the purpose of this study was to test the hypothesis that GGOH supplementation would improve glucose homeostasis and benefit the bone microstructure in obese mice through suppression of inflammation and modification of gut microbiota composition. Thirty-six male C57BL/6J mice were divided into 3 groups: a low-fat diet, a high-fat diet (HFD), and an HFD supplemented with 800 mg GGOH/kg diet (GG) for 14 weeks. Glucose and insulin tolerance tests were measured at baseline and end of study. The concentrations of adipokine cytokines (resistin, leptin, monocyte chemoattractant protein-1, interleukin-6) were measured via ELISA. Bone microarchitecture and quality were measured by micro-CT. Microbiome analysis was performed using 16S rRNA amplicon sequencing on cecal content. Relative to the HFD group, the GG group: (1) improved glucose tolerance and insulin sensitivity; (2) reduced production of pro-inflammatory adipokines, (3) increased serum procollagen I intact N-terminal propeptide (bone formation marker) concentrations, while decreasing serum collagen type 1 cross-linked C-telopeptide (bone resorption marker) levels, and (4) increased stiffness at both femur and LV-4 and cortical thickness at femoral midshaft. Compared to the HFD group, the GG group had an increased abundance of Butyricicoccus pullicaecorum and decreased Dorea longicatena in the cecal microbiome. Collectively, GGOH improves glucose homeostasis and bone microstructure in obese mice, probably via suppression of pro-inflammation and modification of microbiome composition.

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.

Adjuvant therapies for MRONJ: A systematic review

OBJECTIVE

Medication-related osteonecrosis of the jaw (MRONJ) is a severe adverse reaction caused by the use of antiresorptive antiangiogenic medication. Treating MRONJ is difficult and besides standard treatments, which are conservative medical and surgical approaches, there are some adjuvant therapies that might further stimulate healing. The aim of this systematic review is to compare outcome and effectiveness of currently available adjuvant therapies for MRONJ.

METHODS

This systematic review was conducted following the PRISMA guidelines. Articles focusing on mucosal healing in patients treated with an adjuvant therapy for MRONJ were selected and analysed. Inclusion was not limited to randomized controlled trials to present a complete review of the current literature.

RESULTS

A search was performed in Pubmed, Embase, Web of Science and Cochrane Central Register of Controlled Trials. Thirty articles out of 3297 were included. Laser ablation had a success of 60-95% for complete healing. The controlled trials of leukocyte- and platelet-rich-fibrine (LPRF) showed 60-100% success for the same outcome. Fluorescence guided surgery had a complete healing percentage of 85-90%.

CONCLUSIONS

The results suggest that laser ablation, LPRF and fluorescence guided surgery might have a potential in improving the healing process. Interpreting the results should however be done with great care and a critical point of view, as most articles had a medium to high risk of bias. More randomized controlled trials are necessary to define the most beneficial therapy protocols.

CLINICAL RELEVANCE

It seems that adjuvant surgical therapies for treating MRONJ are beneficial for mucosal healing, but there is only low scientific evidence.

Bisphosphonate-related osteonecrosis induced change in alveolar bone architecture in rats with participation of Wnt signaling

OBJECTIVE

This work aimed to study the role of inflammation in medication-related osteonecrosis of the jaw (MRONJ) in rats with focus on Wnt signaling.

METHODS

A total of 36 female Wistar rats (12 weeks ± 200 g) were divided into 2 groups (n = 6) in 3 experiments: saline (SAL) and zoledronic acid (ZOL). For MRONJ induction, rats received 0.1 mg/kg of ZOL (ip) 3×/week for 9 weeks. Animals from the SAL group received 0.1 mg/kg of 0.9% SAL, ip 3×/week for 9 weeks. On the 8th week, 3 left upper molars were extracted, and on the 11th week, they were euthanized. Maxillae were evaluated by macroscopic and histopathological analyses; scanning electron microscopy (SEM); immunohistochemistry for DKK-1, Wnt 10b, and caspase-3; and Raman spectrometry. Gingiva was also collected for TNF-α e IL-1β quantification.

RESULTS

Bone necrosis was confirmed by healing impairment, reduced number of viable osteocytes, increased caspase-3 immunoexpression, and increased number of empty lacunae (p < 0.05). ZOL enhanced inflammation and increased gingival levels of IL-1β and TNF-α (p < 0.05). Irregular indentations were seen on bone after ZOL administration. Bone necrosis was marked by reduced amount of total and type I collagen. ZOL reduced the mineral/matrix ratio and increased carbonate/phosphate ratio. It was observed a significant reduction on Wnt10b and beta-catenin immunolabeling in the bone tissue of ZOL group.

CONCLUSION

In summary, MRONJ model caused bone necrosis due to intense inflammation. Wnt signaling seems to play an important role in this process.

CLINICAL RELEVANCE

New therapeutic strategies focusing on Wnt pathway can provide an interesting approach for future treatments.

The effect of melatonin on prevention of bisphosphonate-related osteonecrosis of the jaw: an animal study in rats

Objectives

Melatonin induces human stem cells, converts pre-osteoblasts to mature osteoblasts, and reduces the duration of this transition. However, melatonin itself prevents activation of osteoclasts. Here, we evaluate the role of melatonin in prevention of bisphosphonate-related osteonecrosis of the jaw.

Materials and Methods

In this experimental-interventional study, 30 rats were evaluated in 3 groups. The first and second groups received saline and zoledronic acid, respectively, for 4 weeks and the third group received 4 weeks of zoledronic acid and 3 weeks of melatonin simultaneously. First-right-maxillary-molar extraction was performed for all animals, which were sacrificed after 4 weeks of recovery. The extraction sockets were examined histologically for the presence of osteonecrosis, number of osteoclasts and fibroblasts, severity of inflammation, and vascularization. Data were analyzed by chi-square, one-way ANOVA, Tukey, Kruskal–Wallis and Fisher’s exact statistical tests (α=0.05).

Results

Osteonecrosis was observed in 20%, 90%, and 70% of the first, second and third groups, respectively (P=0.008). The lowest number of osteoclasts and fibroblasts was seen in the third group.

Conclusion

Melatonin may effectively prevent some undesirable side effects of bisphosphonates. However, further studies are required to confirm the results of this study.

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.

Geranylgeraniol (GGOH) as a Mevalonate Pathway Activator in the Rescue of Bone Cells Treated with Zoledronic Acid: An In Vitro Study

Bisphosphonates (BPs) are the keystone to treat bone disorders. Despite the great benefits of BPs, medication-related osteonecrosis of the jaw (MRONJ) arouse as a potential side effect. Nitrogen-containing BPs (N-BPs) as zoledronate (ZA) act by the inhibition of specific enzymes of the mevalonate pathway resulting in altering protein prenylation which is required for the posttranslational maturation of the small GTP-binding proteins. Geranylgeraniol (GGOH) is an intermediate product in the mevalonate pathway having positive effects on different cell types treated with BPs by salvaging protein prenylation improving cell viability and proliferation in tissue regeneration, thus overcoming N-BP-induced apoptosis. Here, the effect of different concentrations of zoledronate (ZA) on the bone cells has been investigated by cell viability assay, live/dead staining, and western blot to understand if GGOH was able to rescue bone cells and levels of statistical significance were indicated at ^∗P < 0.05, ^∗∗P < 0.01, ^∗∗∗P < 0.001, and ^∗∗∗∗P < 0.0001. Although the high concentration of ZA had significantly decreased the cell viability in the bone cells, GGOH reversed the action of ZA on the cells while at very high concentration; it caused severe reduction in the cell viability. Rap1A, a member of the GTPases family, was expressed in the negative controls but was absent in cells treated with high concentrations of ZA. The addition of GGOH had increased the expression of Rap1A up to a certain limit. The experiments proved that ZA acts directly on the mevalonate pathway and protein prenylation and that GGOH could be applied as a future local therapy to MRONJ.

Cordycepin Accelerates Osteoblast Mineralization and Attenuates Osteoclast Differentiation In Vitro

Bone homeostasis destruction is triggered by the uncontrolled activity of osteoblasts and osteoclasts. Targeting both the regulation of bone formation and resorption is a promising strategy for treating bone disorders. Cordycepin is a major component of Chinese caterpillar fungus Cordyceps militaris. It exerts a variety of biological actions in various cells and animal models. However, its function on bone metabolism remains unclear. In the present study, we discovered a dual-action function of cordycepin in murine MC3T3-E1 and RAW264.7 cells. MC3T3-E1 cells were cultured in an osteogenic medium in the presence of 1 μM cordycepin for up two weeks. Cordycepin was used for effects of osteoblast and osteoclast differentiation. Cell viability was measured using the MTT assay. Osteoblast differentiation was confirmed by alizarin red staining, ALP activity, western blot, and real-time PCR. Osteoclast differentiation and autophagic activity were confirmed via TRAP staining, pit formation assay, confocal microscopy, western blot, and real-time PCR. Cordycepin promoted osteoblast differentiation, matrix mineralization, and induction of osteoblast markers via BMP2/Runx2/Osterix pathway. On the other hand, RAW264.7 cells were differentiated into osteoclast by RANKL treatment for 72 h. 1 μM cordycepin significantly inhibited RANKL-induced osteoclast formation and resorption activity through disturbing the actin ring-formatted sealing zone and activating cathepsin K and MMP9. These findings indicate that cordycepin might be an innovative dual-action therapeutic agent for bone disease caused by an imbalance of osteoblasts and osteoclasts.