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

Alendronate sodium induces G1 phase arrest and apoptosis in human umbilical vein endothelial cells by inhibiting ROS-mediated ERK1/2 signaling

Bisphosphonates are potent bone resorption inhibitors, among which alendronate sodium (ALN) is commonly prescribed for most osteoporosis patients, but long-term application of ALN can cause bisphosphonate-related osteonecrosis of jaw (BRONJ), the pathogenesis of which remains unclear. Previous studies have suggested that bisphosphonates cause jaw ischemia by affecting the biological behavior of vascular endothelial cells, leading to BRONJ. However, the impacts of ALN on vascular endothelial cells and its mechanism remain unclear. The purpose of this work is to assess the influence of ALN on human umbilical vein endothelial cells (HUVECs) and clarify the molecular pathways involved. We found that high concentration of ALN induced G1 phase arrest in HUVECs, demonstrated by downregulation of Cyclin D1 and Cyclin D3. Moreover, high concentration of ALN treatment showed pro-apoptotic effect on HUVECs, demonstrated by increased levels of the cleaved caspase-3, the cleaved PARP and Bax, along with decreased levels of anti-apoptotic protein Bcl-2. Further experiments showed that ERK1/2 phosphorylation was decreased. Additionally, ALN provoked the build-up of reactive oxygen species (ROS) in HUVECs, leading to ERK1/2 pathway suppression. N-acetyl-L-cysteine (NAC), a ROS scavenger, efficiently promoted the ERK1/2 phosphorylation and mitigated the G1 phase arrest and apoptosis triggered by ALN in HUVECs. PD0325901, an inhibitor of ERK1/2 that diminishes the ERK1/2 phosphorylation enhanced the ALN-induced G1 phase arrest and apoptosis in HUVECs. These findings show that ALN induces G1 phase arrest and apoptosis through ROS-mediated ERK1/2 pathway inhibition in HUVECs, providing novel insights into the pathogenic process, prevention and treatment of BRONJ in individuals receiving extended use of ALN.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Micro-angiogenic patterns around orthodontic implants migrating in bone: A micro-CT study in the rat tail model

AIM

Recent studies revealed that implants can migrate in bone when subjected to continuous loading. Since this process is suspected to be accompanied by bone remodelling, which requires blood vessel formation, the present work aimed at assessing the micro-angiogenic patterns around migrating implants.

MATERIALS AND METHODS

In 16 rats, two customized implants were placed in a single tail vertebra and connected with contraction springs (forces: 0 N, 0.5 N, 1.0 N, 1.5 N). After 2 or 8 weeks of loading, the animals were scanned by micro-CT before and after vasculature perfusion with a silicone rubber. Vessels were segmented by subtraction of the two micro-CT scans. Vessel thickness (V.Th), vessel volume per total volume (VV/TV), and vascular spacing (V.Sp) were assessed in a peri-implant volume of interest (VOI) around each implant.

RESULTS

At 2 weeks of loading, force magnitude was significantly associated with VV/TV and V.Th values (χ²  = 10.942, p < .001 and χ²  = 6.028, p = .010, respectively). No significant differences were observed after 8 weeks of loading.

CONCLUSIONS

Within the limitations of an animal study, peri-implant vessel thickness and density were associated with force magnitude in the early loading phase, whereas effects diminished after 8 weeks of loading.

Alendronate-induced Perturbation of the Bone Proteome and Microenvironmental Pathophysiology

Objectives: Bisphosphonates (BPs) are powerful inhibitors of osteoclastogenesis and are used to prevent osteoporotic bone loss and reduce the risk of osteoporotic fracture in patients suffering from postmenopausal osteoporosis. Patients with breast cancer or gynecological malignancies being treated with BPs or those receiving bone-targeted therapy for metastatic prostate cancer are at increased risk of bisphosphonate-related osteonecrosis of the jaw (BRONJ). Although BPs markedly ameliorate osteoporosis, their adverse effects largely limit the clinical application of these drugs. This study focused on providing a deeper understanding of one of the most popular BPs, the alendronate (ALN)-induced perturbation of the bone proteome and microenvironmental pathophysiology. Methods: To understand the molecular mechanisms underlying ALN-induced side-effects, an unbiased and global proteomics approach combined with big data bioinformatics was applied. This was followed by biochemical and functional analyses to determine the clinicopathological mechanisms affected by ALN. Results: The findings from this proteomics study suggest that the RIPK3/Wnt/GSK3/β-catenin signaling pathway is significantly perturbed upon ALN treatment, resulting in abnormal angiogenesis, inflammation, anabolism, remodeling, and mineralization in bone cells in an in vitro cell culture system. Conclusion: Our investigation into potential key signaling mechanisms in response to ALN provides a rational basis for suppressing BP-induced adverse effect and presents various therapeutic strategies.

Mechanism, prevention, and treatment for medication-related osteonecrosis of the jaws

The morbidity rate of medication-related osteonecrosis of the jaws (MRONJ) increased rapidly in recent years. Thusfar, the mechanism of MRONJ has no consensus. The possible mechanisms may include bone remodeling inhibition theory, angiogenesis inhibition theory, oral microorganism infection theory, immunosuppression theory, cytotoxicity-targeted oral epithelial cells, microcrack formation of maxillary or mandibular bone, and single nucleotide polymorphism. However, the efficacy of prevention and treatment based on a single mechanism is not ideal. Routine oral examination before MRONJ-related drug treatment, treatment of related dental diseases, and regular oral follow-up during drug treatment are of great significance for the prevention of MRONJ. During the treatment of MRONJ, the stage of MRONJ must be determined accurately, treatment must be standardized in accordance with the guidelines, and personalized adjustments must be made considering the specific conditions of patients. This review aimed to combine the latest research and guidelines for MRONJ and the experiences on the treatment of MRONJ in the Maxillofacial Surgery Department of West China Hospital of Stomatology, Sichuan University, and discuss the strategies to improve the clinical process.

Comparison of Vascular Morphometry in Jawbones and Long Bones: Micro-CT Study in a Rat Model Treated with Zoledronic Acid

The study was aimed at investigating the effect of zoledronic acid on vascular morphometry in jawbones and long bones on a rat model. Twenty-four skeletal mature Sprague-Dawley female rats were administered oncologic dose of zoledronic acid (ZA) or normal saline for 4 weeks and then subjected to tooth extraction on the mandible and maxilla and a bone defect creation on the femur. After the surgical procedures, ZA or saline treatment was continued until sacrifice at week 2, week 4, and week 8 postoperatively. Vascular perfusion with MICROFIL was performed on all the animals. Micro-CT analysis demonstrated a tendency of decreased vessel density and vessel number in ZA-treated groups but no statistical difference. In conclusion, the neovessel formation is suppressed but not significantly by ZA treatment, indicating that angiogenesis inhibition may contribute to the development of MRONJ but does not play a key role.

Treatment of Stage 2 Medication-Induced Osteonecrosis of the Jaw: A Case Series

Medication-induced jaw osteonecrosis (MRONJ) is a rare and serious disease with a negative impact on patients’ quality of life, whose exact cause remains unclear and which may have a multifactorial origin. Although there are different therapeutic protocols, there is still no consensus. This case series evaluated three patients diagnosed with staged 2 MRONJ treated at the University of Murcia dental clinic according to the protocols described by the Spanish Society of Oral and Maxillofacial Surgery and the American Association of Oral and Maxillofacial Surgeons. Within 12 months of the application of therapeutic protocols, the lesions were completely healed in all cases. Radiography showed slow but progressive healing with normal bone structure. Conservative treatment with antibiotics, chlorhexidine rinses and minimally invasive surgical intervention with necrotic bone resection is effective in treating stage 2 of MRONJ. In cases of refractory osteonecrosis, the application of platelet and leukocyte-rich fibrin (PRF-L) in the surgical approach improves the outcome in soft tissue healing and bone regeneration but further research is needed to confirm its effectiveness.

Compressive force strengthened the pro-inflammatory effect of zoledronic acid on il-1ß stimulated human periodontal fibroblasts

OBJECTIVES

The number of patients in dentistry taking bisphosphonates (BP) increases every year. There are only little data about the influence of biomechanical stress due to orthodontic treatment and periodontal inflammation in BP patients. This study focused on the effects of the induced inflammation by IL-1ß in compressed human periodontal ligament fibroblasts (HPdLF) exposed to the nitrogen-containing BP zoledronate in vitro.

MATERIALS AND METHODS

HPdLF were incubated with 5 μmol/l zoledronate and 10 ng/ml IL-1ß for 48 h. In the last 3 h, cells were exposed to a compressive, centrifugal force of 34.9 g/cm². Cell viability was analyzed directly after the compressive force by MTT assay. Gene expression of COX-2 and IL-6 was investigated using quantitative qRT-PCR. PGE-2 and IL-6 protein secretion were measured via ELISA.

RESULTS

The cell viability of HPdLF was not affected. Without inflammatory pre-stimulation, COX-2 expression was increased by compression and zoledronate. IL-6 expression was increased under compression. On secretion level, the combination of compression and zoledronate induced a slightly increase of IL-6 secretion. In contrast, inflammatory pre-stimulation strengthened the compressive upregulation of COX-2, as well as induced a higher PGE-2 secretion. Further addition of zoledronate to pre-stimulated cells additionally strengthened the compression-induced upregulation of COX-2 and IL-6 expression as well as protein secretion compared to all other groups.

CONCLUSIONS

Biomechanical stress might trigger a pro-inflammatory potential of BP further enhanced in the presence of an inflammatory pre-stimulation.

CLINICAL RELEVANCE

To prevent excessive host inflammatory responses, occlusal overloading and mechanical stress due to orthodontic treatment should be avoided in BP patients with untreated periodontitis.