Evidence-based Treatment Of Bisphosphonate Related Osteonecrosis And Establishment Of The Animal Models

Background As a new type of bone resorption inhibitor,Bisphosphonates (BPs) were developed in1980s,and have been widely,efficiently used for the treatment of a variety of bone diseases mediated by osteoclast, such as osteoporosis, bone metastasis of solid cancers, multiple myeloma bone diseases,and so on. It can be hailed as a milestone for the treatment of such bone diseases and osteoporosis, however, the adverse events arised after years of clinical application. Since2003there has been an increasing number of publications describe that receiving intravenous or oral BPs is associated with osteonecrosis of the jaw (bisphosphonate-related osteonecrosis of the jaw, BRONJ), which has aroused extensive solicitude. Some experts predicted that it will be a new phossy jaw of the21st century.Through summarizing literature in recent years, The main clinical feature of BONJ include unhealing of dental sockets, loosening of teeth not explained by chronic periodontal disease, periapical/periodontal fistula that is not associated with pulpal necrosis due to caries, exposed and necrotic bone in patients who are asymptomatic and have no evidence of infection,and so on. A small number of patients develop to extraoral fistula and pathologic fracture. All patients had the history of administering BPs. Administrating intravenous and alveolar surgery are the most prevalent risk factors, A few may have no obvious cause.At present, the pathogenesis of BONJ is unclear. Only epidemiological evidence indicated a correlation of time and dosage between BONJ and BPs. Such as BPs treated patients have more osteonecrosis incidence than untreated; osteonecrosis always occurs after giving BPs with positive correlation between time and dosage, biology experiments shows that bone lesions can be induced by BPs,and so on.On account of uncertain pathogenesis, the diagnostic criteria and appropriate approaches for prevention of BONJ have not been established to date. Clinical practice guidelines have successively developed based on literature review and expert opinions in Some developed countries such as England, French, USA, Canada and Japan. That given by the American Association of Oral and Maxillofacial Surgeons (AAOMS) in2007is the most widely used, which consists of three essential elements:1.Current or previous treatment with a bisphosphonate;2.Exposed bone in the maxillofacial region that has persisted for more than 8weeks;3.No history of radiation therapy to the jaws. According to the clinical manifestation, the occurrence stage can be divided into4stages(0～4). For most patients at early lesions, current treatment strategies of BONJ mainly tend to a conservative approach with minimal local intervention, if necessary a local debridement for removal of necrotic tissue at stage1-2, and extensive resection of bone and reconstruction only for patients at stage3. Because BPs has a long half-life and a cumulative effect, there is no evidence that drug discontinuance can alleviate the symptoms. There has been much discussion as to the benefits of stopping the drug for a period, most of recommendations suggest that cessation of BP treatment before alveolar surgery allows for regeneration of osteoclasts and therefore improved bone turnover. The risks and benefits of continuing bisphosphonate therapy should be determined only by the treating oncologist in consultation with the oral and maxillofacial surgeon and the patient.The incidence of BONJ were reported differently in different countries. In Asia,263cases were found through a nationwide survey of2006～2008in Japan. Eight cases were reported in Singapore’s national university hospital from2004～2007. In china, case reports were rare but have increased recently. Twelve cases were reported in Macao Conde hospital, and three patients were diagnosised and give treatment in our hospital. Analysed from reports both at home and abroad, it can be predicted that the domestic incidence is reasonably large. There is just a lack of understanding to this disease.The research of BONJ is becoming a hot topic in recently years, but the mechanisms of them are still not clear enough. The suppression of bone turnover is regarded as leading cause in almost all literature. Other factors which are thought to play a part include tissue toxicity which affect bone metabolism, Inhibition of angiogenesis, infection,acid environment,and so on. The Starting Point for BRONJ:Bone or Soft Tissue? BONJ and Infection:the cause or result? Some diagnostic and treatment methods is effective or not remains unclear.it also lack of high quality Prospective controlled study to clarify.Given the clinical cases having more confounding factors and uncertainty of incidence, it is difficult to make a clinical control test. it is necessary to establish an animal model for further related research. Although several animal experimental model were established in recent years, but the experimental results showed large deviations and deficiency of stability, and the designs are still stayed at simulated stage. so an effective and stable animal model is needed to establish for conduct a further beneficial exploration on etiology, and therapy strategy and provide an experimental basis and theoretical basis for the prevention treatment and cure of BONJ.This study is derived from clinical diagnosis and treatment of3cases, patients suffered BONJ as well as own disease which affect the quality life of seriously, in view of the clinician’s responsibility and the analysis of above research status at home and abroad, on the one hand, based on actual problem domestic, this topic explore the evidence-based treatment combined with clinical cases analysis, and provide a reference for domestic prevention of BONJ; on the other hand, keeping up with international research adcances, we attempt to establish animal experimental model on rabbit, as to provide an experimental basis and valuable reference for further research on BONJ pathogenesis and prevention. The research content is consisted of two main parts:Part one:Evidence-based diagnose and treatment of bisphosphonate related osteonecrosis:report of3casesObjective To explore the diagnostic and treating measures of bisphosphonate-related osteonecrosis of the jaw (BONJ) combined with clinical cases analysis from the view of evidence based medicine and provide a reference for domestic prevention of BONJ; Meterials and Methods:For the symptoms of three patients, including persisting socket, sore gums,fistula and pyorrhea, the clinical questions were raised, the relative evidences were collected and critically assessed. Results:42related references were included. The evidences indicated that①The precise pathogenesis of BONJ remains unknown.The diagnostic criteria that given by the American Association of Oral and Maxillofacial Surgeons is used most widely.②Non-surgical management is recommend at eraly stage when there is exposed or necrotic bone without obvious infection symptoms,including antibiotic therapy and pain control,and so on; Local debridement is adopted when the infection is uncontrolled or recurrent; Resection of bone beyond the alveolus where there is large segment of necrotic bone or pathological fracture.③Diagnostic histopathological characteristics of BONJ have not yet been established; Radiographic images can help diagnosing early and assessing the risk before alveolar surgery.④Discontinuation of BP therapy can not relieve the symptoms but may be good for wound healing after alveolar surgery, which should be done in consultation with the treating physician and patient. Based on the available evidence, individualized treatment plans were developed. After an invalid conservative treatment, local debridement was performed and proved to be effective during follow-up. Conclusion:As a new disease, the exact mechanism of BONJ has not been completely elucidated.There is currently no consensus on the diagnostic criteria and the best way of trerapy. The treatment efficacy has been improved by determining an individulized treatment according to evidence-based approach.Part Two:The establishment of animal experimental model of BONJObjective To establish an animal model of BONJ and provide an experimental foundation for further study on the pathogenic mechanism, prevention and treatment of BONJ.Materials and Methods12adult Japanese big-eared rabbits weighing averagely2.5-3kg Provided by animal experiment center of hubei university of medicine, all animals were randomly divided into experimental group and control group with6cases each. The test group were administered intravenously two weekly dose of a bisphosphonate (zoledonate about0.067mg/kg body weight, approximating the oncologic dose in humans) for five times in succession. After three weeks the animals underwent the extraction of right maxillary and mandibular central incisor (experimental group and control group with3cases each), producing a4mm-diameter bone defects on the contralateral left maxillary and mandibular bacall wall with incision mucous and suture after surgery. Postoperative X films were made every2weeks by the same radiologist at the same condition. The animals were sacrificed at12weeks. The samples of extraction sockets and the defect restoration areas were taken to be observed by Micro-CT scans and evaluated histologically.Results1.clinical observation:All experimental animals kept healthy and no one died. All incisions on the left side of the jaw bone defect were primary healing, but soft tissue coverage around tooth sockets of experimental group were less than the control, there is some bone exposure experimental group. The repairs of the bone defect on left side of jaw bacall wall showed normally in control group, but lack of bone filling in experimental group, with darking osteonecrosis of the surrounding bone. Among them, a left mandible bone defect of one sample emerged an exogenous adenomatous hyperplasia.2. X-ray observation:The socket of both tests and cotrols appeared low density image after extraction, and had increased higher gradually over time but not equal to the density of surrounding bone. There was no obvious difference between two groups.3.Micro-computed tomography microstructure analysis:Observing the repairs of extraction site and bone defect of test sample after8weeks of healing, BV/TV,Conn.D,Tb. N,Tb. Th was significantly lower with higher Tb. Sp and BS/BV than controlled. Representative images showed that the surrounding bone of the right maxillary central incisor socket was relatively dense in the control group with narrow size of trabeculae close to normal level of bone, but appeared loose trabecular structure with wider gap in experimental groups. The repairs of the bone defect on left side of jaw bacall wall was almost healed in control group, while appeared messy trabecular structure, necrosis in experimental group.4histological observation:samples were observed under light microscope (200X) with HE stains. Osteonecrosis can be seen at socket sites in test group with a numbers of empty lacunas but no blue stained nucleus, the trabecular bone is slender with a proliferation of fibrotic tissue. While the trabecular bone arranges orderly with survival of osteocyte in controls. In a similar vein, osteonecrosis can also be observed at the bone defects in tests with a large number of empty lacunas, no nucleus, and disorganized trabecular bone structure. In contrast, the trabecular bone in controls appeared well-organized structures, which was close to normal bone tissue.The results of above observation showed that the healing and repairs of sockets and alveolar bone defects exhibited normally in control group, but had obstacles to restore in experimental group with osteonecrosis.Conclusion:Administered intravenously of BPs simulated dose of human body, symptoms such as delayed healing of tooth socket after extraction, incapable restore of alveolar bone defect and osteonecrosis were observed in BPs treated rabbit but not in controls, which were consistent with the clinical symptoms of BONJ. It is can be concluded that those above symptoms were related to BPs. Therefore a rabbit animal experimental model of BONJ was successfully established, which will provide an experimental basis for study pathogenic mechanism and prevention strategy of BONJ.