Evaluation of the peri-implant repair process in rats treated with oncologic dose or osteoporotic dose of zoledronate

Abstract

Bisphosphonates (BPs) are widely used drugs for the treatment of osteolytic conditions, by acting in the inhibition of bone resorption process. High potency BPs, such as zoledronate, are used to control the progression of bone metastasis in osteotropic malignant neoplasms or for the treatment of severe osteoporosis. However, one of its adverse effects is the occurrence of the medication-related osteonecrosis of the jaws (MRONJ). Among the risk factors for MRONJ are: the chronic use of nitrogen-containing BPs administered intravenously; feminine gender; advanced age; invasive dental procedures, such as dental extractions or surgeries for installation of dental implants. Despite the significant increase in the number of clinical reports of MRONJ after the installation of dental implants in patients treated with BPs, there are few studies that aim to understand the changes that would trigger this condition. So, the objective of this study is to analyze the peri-implant repair process in rats treated with oncologic or osteoporotic doses of zoledronate and to evaluate its correlation with the development of MRONJ. Forty rats (6 months old) will be randomly distributed in 2 experiments: EXPERIMENT I: rats will receive intraperitoneal (IP) injections of 0.45 ml solution of 0.9% NaCl (SAL-ONC group, n = 10) or this same solution plus 100 mg/Kg of zoledronate (ZOL-ONC group, n = 10), every 3 days for 8 weeks. EXPERIMENT II: rats will receive IP injections of 0.45 ml solution of 0.9% NaCl (SAL-OST group, n = 10) or this same solution plus 100 ¼g/Kg of zoledronate (ZOL-OST group, n = 10), every 28 days for 24 weeks. In both experiments, 16 weeks after the beginning of drug treatment, all the animals will be submitted to the installation of a titanium implant in both right and left tibias. The general health status of the animals will be monitored throughout the experimental period and the euthanasia will be performed at 56 postoperative day. After dissection and a thorough clinical examination of the peri-implant region, left tibias will be submitted to the histological processing without demineralization and embedded in resin for histometric analysis of the bone-implant contact. The right tibias will undergo demineralization, conventional histological processing, embedded in paraffin, and the histological sections obtained will be stained by hematoxylin-eosin for histopathological analysis of the peri-implant tissues and histometrical analysis of the newly formed bone tissue, or submitted to the immunohistochemical reaction directed to biomarkers: bone morphogenetic protein 2/4 (BMP2/4); runt-related transcription factor 2 (RUNX-2); osteocalcin (OCN); tartrate-resistant acid phosphatase (TRAP). The results will be analyzed under optical microscopy, submitted to qualitative, quantitative and statistical analyzes at significance level of 5%. As expected results, it is intended to characterize peri-implant changes resulting from the treatment with zoledronate and to elucidate its correlation with MRONJ. (AU)