Molecular and microscopic analysis of the effect of zoledronic acid on bone healing of dental socket and bone defects created in femurs of Wistar rats

Abstract

Bisphosphonates comprehend a class of stable synthetic compounds that have a potent inhibition of bone resorption and have a high affinity for bone tissue hydroxyapatite. These are considered the drugs of choice for the treatment of osteolytic disorders such as multiple myeloma and bone metastases of breast and prostate cancer. However prolonged use of these drugs may induce the onset of osteonecrosis of the jaws, which is defined as an exposure of bone persisting for more than 8 weeks in patients who has taken or currently are taking a bisphosphonate and who has no history of radiation therapy to the jaws. Because it is a recently described disease in the medical literature, little is known about its actual pathogenesis. Concerning these facts the aim of this study is to assess the cellular and molecular mechanisms involved in the development of osteonecrosis of the jaws induced by bisphosphonate. For this purpose, a qualitative and quantitative analysis (histomorphometry) of the bone healing process will be done through optical microscopy analysis of sections stained with HE, immunohistochemistry for TRAP (Tartrate-Resistant Acid Phosphatase) and TUNEL test (terminal-deoxynucleotidyl transferase-mediated dUTP nick end labeling). Will be also carried out a quantitative analysis of mRNA expression of proteins involved in the process of bone repair correlated with osteoclasts (RANK, RANKL, OPG and TNF-±), osteoblasts (OCN, ALP), osteocytes (PHEX and DMP-1) and angiogenesis (VEGF), by the method of polymerase chain reaction in real time (RealTimePCR). These tests will be used to evaluate the possible cellular and molecular alterations in the process of bone repair of post-extraction sockets and bone defects created in the epiphyses of rat's femurs (Rattus norvegicus, Albinus, Wistar) in therapy with 0.6 mg/kg zoledronic acid, as described by Maahs et al. (2011) in their animal model. Through these tests we will be able to evaluate the influence of zoledronic acid on the molecular and cellular mechanisms of bone repair, helping to better understand the development of the osteonecrosis induced by bisphosphonates. Will be also be explored why these bone lesions affect almost that exclusively the jaws. A better understanding of the mechanism of development of this disease through the findings of this study will aid in the management of patients on bisphosphonate therapy. As also guide the choice and / or development of treatments for these types of injuries, since it has been proved that these are refractory to the treatments performed today, demanding for an effective therapy against this condition. (AU)