The Protective Effect Of Edaravone On Radiation Injury In Primary Cultured Rat Hippocampal Neuron

【Background】The incidence and mortality rate of malignant tumor roar up globally these years with Lifestyle change and environmental pollution. Now it has become 'the first killer' which damages people's health seriously as all know and increases medical expenditure.Recently, treatments of malignant tumor include surgery, chemotherapy, radiotherapy, biological therapy and chinese medicine treatment etc.Radiotherapy is one of the three major therapeutic tools for malignant tumor and the radical cure tool for partial of them such as nasopharyngeal carcinoma. According to WHO statistics in 1998, malignant tumor control rate of all over the body is 45%, while operation occupies 22%, chemotherapy occupies 5% and radiotherapy 18%. Over 70% malignant tumor patients had radiotherapeutic experience. However, X-ray can result in normal tissue injury at the same time of killing tumor cells. Radiation brain injury is a radioactive syndrome caused by various kinds of reasons and one of the most serious long-term complications after radiotherapy for intracranial and pate malignant tumors and cerebrovascular malformation. Following oncotherapy level improvement, life span unceasing prolongation and development of imaging Diagnostic technology, the incidence and diagnosis of radiation brain injury go up year by year. It impacts living quality, life span and prognosis of patients seriously or even Causes of death of patients. The mechanism of radiation brain injury is not clear, so the effective treatment is still lack up to now. Therefore, it is very important to study the radiation brain injury and explore new therapeutic targets.The pathogenesis of radiation brain injury is not very clear recently. Several factors may be associated with the following:①Direct radiation damage to cells②schemic change is caused by vascular injury. radiation makes vascular endothelial cell oedematous and necrotic, thickens vascular wall, stenoses or occludes vascular cavity and causes thrombosis, then neurocyte becomes ischemic,anoxic and necrotic.③immunologic injury mechanism:when radiation is applied to nervous tissue, it makes protein and lipoid antigenic.Then autoimmune response such as edema, necrosis and demyelination arises. oxygen free radical plays an important role in all of aspects above-mentioned. Physiologically, the generation and removal of oxygen free radical keep homeostatic. On Radiation brain injury state, a lot of free radical will be produced which can destroy the brain tissue. There is a large amount of unsaturated fatty acid in the central nervous system, which is prone to lipid peroxidation then generates a large number of lipid peroxide. MDA is stable metabolite of lipid peroxidation, which could reflect the content of free radical and lipid peroxidation level. SOD is a very important antioxidant enzyme in the body which can eliminate the superoxide anion and plays an important role in the body's balance between oxidation and anti-oxidation. A large number of oxygen free radical which results from radiation injury consumes SOD and lowers its activity. Lack of SOD activity could decrease the body's ability to eliminate free radical and Oxygen free radical damage arises.The chemical name of edaravone is 3-Methyl-1-phenyl-2-pyrazolin-5-one, which is a synthetic free radical scavenger. Edaravone could suppress the oxidative damage of Brain cell, vascular endothelial cell and nerve cell from Scavenging free radical and inhibiting lipid peroxidation which is applied to improvement of neurological symptom, activities of daily living and disfunction caused by acute cerebral infarction. Since edaravone is a free radical scavengerand free radical damage plays a important role in the mechanism of radiation brain injury, whether edaravone could protect patients from radiation brain injury or not? it is a riddle worth exploring.On this ground, we exposed the hippocampal neurons at 12days to single x-ray doses of 30Gy and used apoptosis measuring technology to investigate whether the protective effect of edaravone on radiation injury in hippocampal neuron results from free radical Scavenging or not.【Objective】To study the protective effect of edaravone on radiation injury in rat hippocampal neuron and provide new means for prevention and treatment of radiation encephalopathy.【Methods】(1) The cultured rat hippocampal neurons at 12days were exposed to single x-irradiation with doses of 30Gy.(2) To observe the effect of edaravone treatment on neuronal apoptosis induced by x-irradiation, the cells were stained with 4',6-diamidino-2-phenylindole (DAPI) at 24 h after irradiation, the apoptotic changes were measured quantitatively by nuclear pyknosis, special kit was used to detect MDA content and SOD activity.(3) All values were expressed as mean±SD. Statistical significance was defined as P≤0.05.【Results】(1) Apoptosis experiment showed that administration edaravone (100μmol/L) at 15 minutes before x-irradiation can protect the hippocampal neuronal death induced by irradiation (F (2,22.848)=245.759, P<0.001, N=15).The percentage of nuclear pyknosis in the group of 30Gy (25.3%±4.20%) was significantly increased over that in the group of OGy at 24 h after irradiation (1.96%±0.94%, P<0.001), while the percentage of nuclear pyknosis in the group of 30Gy & edaravone (7.44%±1.90%)was significantly different from that in the group of 30Gy at 24 h after irradiation (P<0.001). There was significant difference between the group of 30Gy & edaravone and the group of OGy (P<0.001).(2) MDA content and SOD activity in biocytoculture fluid detected by special kit showed that:administration edaravone (100μmol/L) at 15 minutes before x-irradiation can change the MDA content and SOD activity in biocytoculture fluid of edaravone group significantly. (MDA:F (2,25.934)=147.781, P<0.001, N= 15; SOD:F (2,24.231)=341.178, P<0.001, N=15); The content of MDA occurred in (1.74±0.23) nmol/L of the neurons 24 h after 30 Gy X-ray exposure, a rate significantly higher than that in the nonexposed cells [(0.58±0.11) nmol/L P<0.001], while activity of SOD occurred in (31.29±3.20) U/mL of the neurons 24 h after 30 Gy X-ray exposure, a rate significantly lower than that in the nonexposed cells [(80.44±7.22) U/mL P<0.001]. The content of MDA occurred in (0.83±0.16) nmol/L of the neurons 24 h after 30 Gy X-ray exposure with pretreated edaravone, a rate significantly different from that in the nonexposed cells (P<0.001) and the neurons 24 h after 30 Gy X-ray exposure (P<0.001), while activity of SOD occurred in (60.26±6.79) U/mL of the neurons 24 h after 30 Gy X-ray exposure with pretreated edaravone, a rate significantly different from that in the nonexposed cells (P<0.001) and the neurons 24 h after 30 Gy X-ray exposure (P<0.001)【Conclusion】Edaravone can significantly protect the neurons from apoptosis by reducing production of free radicals.