Effects Of Hypertension On Rat Aneurysm Model And Therapy By Embolism With New Platinum Coils

Intracranial aneurysm (ICA) is a common neurosurgical disease. It is one of the factors induced subarachnoid hemorrhage, with high morbidity and mortality rates but pathogenesis has unclear yet. Therefore, it is extremely important to study the pathophysiology, histopathology, process and mechanism of intracranial aneurysm for preventing and further treatment. All of these studies are dependent on a stable and reliable model of intracranial aneurysm. In recent years, preclinical and clinical researches based on intracranial aneurysm model have arisen. There were several methods to product aneurysm model including surgical transplantation, arterial structural damage, enzyme destroy the vessel wall, etiology inducement, intravascular interventional technical, and so on. The correlative factors about the formation and rupture of intracranial aneurysm mainly included size, location, morphology, hypertension, sex and age. Some scholars speculated that the hypertension was an important affecting factor on aneurysm, but there was no conclusive evidence until now. This study investigated the relationship between hypertension and the pathophysiological changes on the evolution and rupture mechanism of aneurysms. Recently, the endovascular treatment of intracranial aneurysms with guglielmi detachable coil (GDC) was as the first choice in clinic. Although the role of GDC treatment on the intracranial aneurysms has been confirmed, the material itself showed some of shortcomings especially the lack of the biological activity, which it is difficult to the form the thrombus, scar within the aneurysm, following the GDC administration. And also the endothelial cells can't completely cover the neck of intracranial aneurysms after using GDC. Therefore, there were high recurrence rate and re-bleeding risk, especially for wide-necked, large or giant aneurysms. To redeem the deficiencies of GDC, we tried to use some new techniques such as cellular adhesion, extracellular matrix protein coating, bio-absorbable polymer coating technologies to modify the surface of GDC, in order to promote the aneurysm occlusion. In this experiment, we employed the SD rats as the research object of ICA model and studied the treatment effectiveness of a new platinum micro-coil modified by vascular endothelial cell growth factor (VEGF) on rat intracranial aneurysm model, by embolism rat aneurysm with it.PART 1. Production of rat cerebral aneurysms model and the effect of hypertension on itObjective To establish a rat cerebral aneurysm model, and then to explore the influence of hypertension on it. Methods Total 45 of male Sprague-Dawley rats were randomly divided into 3 groups including Hypertension, Ortho-arteriotony, and Normal Control. The group Hypertension was designed to establish cerebral aneurysm model, and then the stenosis in bilateral renal arteries was performed by the ligated operation. The Group Ortho-arteriotony was only enforced the cerebral aneurysms. At the same time,15 of untreated rats were served as the Normal control. The systolic blood pressures of the rats in 3 of groups were measured respectively before model operation, and also at the 6th week and the 12th week after model operation. All of rats were resected and then fixed by formalin following the record of aneurysms size. Some of histological technologies such as HE, Van-Geson and Verhoeff staining were employed for the pathological examination. At the same time, Immunohistochemistry, western blot, and real-time PCR were used to detect the difference expression of proteins including matrix metalloproteinases 9 (MMP-9) and Type III collagen alphal(Col3a1), and genes (MMP-9 gene, Col3a1 gene) among the 3 of groups, to speculate the affection of hypertension on intracranial aneurysms.Results High blood pressure was found in Group Hypertension, and the aneurysms were enlargement much more distinctively in it than in Groups Ortho-arteriotony and Normal Control(P<0.01). At the same time, pathological examination demonstrated the disappearance of intima and the fracture of elastin layer in Group Hypertension, while the remaining of part elastic fibers in Group Ortho-ateriotony, and no damage in Normal Control. Immunohistochemical staining, real-time quantitative PCR and Western Blot results showed that the expression of two kinds of proteins and genes in Group Hypertension was significantly higher than it in Group Ortho-arteriotony and Normal Control. So we suggested that the hypertension showed a direct impact not only on the structure of blood vessel, but also on the structure and composition of the vascular wall through the over-expression of the related proteins or genes.Conclusion This rat aneurysm model was simple to prepare with the stabilization, which showed the similar structure and pathology to the human cerebral aneurysms. Hypertension played a significant role in the abnormalization of the elastin and collagen, meanwhile, it significantly effected on the structure of artery wall by some proteins such as MMP-9 and Col3a1, which will result in the formation of intracranial aneurysm. Hypertension was one of the important factors for aneurysm enlargement PART 2. Effect of embolism on rat aneurysm model with new platinum coils modified by VEGFObjective To explore the therapeutic effect of embolism on rat intracranial aneurysms with new platinum coils that were coated with [4COOH-P (DLLA-co-TMC)] biodegradable polymer and could release vascular endothelial growth factor (VEGF) in intracranial aneurysms. Methods Total 54 of adult female Sprague-Dawley rats were randomly divided into 3 of groups including Group general platinum coils, Group polymer-coated platinum coils, and Group platinum coils modified with VEGF. The right common carotid artery (CCA) of rat in each group was exposed. The 8mm length of platinum coil segments was inserted into the ligated right common carotid artery of rats. Then, the morphology and VEGF expression of artery in different groups of rats were examined by HE stain, immunohistochemical and western blot separately at the 15th,30th and 90th days following the operation. The distal right common carotid arteries were employed as aneurysm models, and the left common carotid arteries without the coil placement or surgical disruption in Group general platinum coil was as the normal control. Result Cellular proliferation and fibrosis were found in Group platinum coils modified with VEGF, and the grades were higher distinctively in it than in Groups general platinum coils, polymer-coat and normal control(P<0.05). Pathological observations showed that the massive intimal hyperplasia and substantial clot occluded the aneurysm lumen of Group platinum coils modified with VEGF completely. In general, the thrombosis in Group general platinum coils or Group polymer-coat platinum coils was not fully organized and showed a loose hyperplasia structure with a large number of internal spaces. Western Blotting indicated the VEGF level in Group platinum coils modified with VEGF was significantly higher than it in other groups, at the 15th and 30th days after operation. At the 90th day, however, the VEGF level in Group platinum coils modified with VEGF decreased because the lumen completed fibration and degradation of the 4COOH-P (DLLA-co-TMC). Conclusion The VEGF-containing biodegradable polymer that slowly released VEGF to modify the surface of platinum coils could enhance cellular proliferation, thrombosis and formation of dense fibrous tissue in aneurysm lumen. Compared with general platinum coils, this new platinum coils could occlude the rat aneurysm faster and more completely.