Research Of HydroCoil Embolization In Experimental Rat Aneurysms

Part IIn vivo study of hydrocoil embolization in experimental rat aneurysmsBACKGROUND/OBJECTIVE:The HELPS clinical trial comparing HydroCoil vs. platinum coils reports an8.6%reduction in significant recurrence following coil embolization of cerebral aneurysms. Our objective was to better understand the mechanism of aneurismal healing following HydroCoil implantation using rat ECA blind pouch aneurysm model.METHODS:Our rat model was created by ligating the proximal ECA to create a blind pouch. HydroCoil or bare platinum coil segments measuring5mm were inserted into aneurysms. Sham operated control rats underwent the identical procedure but without coil insertion. Fourteen days after coil embolization, animals were sacrificed and the entire CCA/ICA/ECA complex was removed. Sac and surrounding vasculature underwent microscopic and histopathologic evaluation. Cellular and fibrotic components within the sac were defined as the organized area. Percentage of organized area and residual length of internal elastic lamina were calculated.RESULTS:The organized tissue area in the ECA sac2weeks following coil embolization was significantly greater in HydroCoil group than in bare coil (60.42±22.58%vs.15.62±19.24%; P=.01) and sham (60.42±22.58%vs.4.61±3.86%, P=.002) groups. Elastic lamina was significantly reduced in HydroCoil group than in sham and bare coil groups (21.67±16.50%vs.100%and96.06±8.78%, both P<.001). No significant difference was found between bare coil and sham groups for organized tissue formation or reduction in elastic lamina.CONCLUSIONS:In a rat ECA blind pouch aneurysm model, hydrogel-coated coils are capable of causing more tissue reaction and organization compared to bare platinum coils. This could be attributed to the observed elastic lamina damage and vascular smooth muscle cell proliferation. Part IIGrowth of vascular endothelial cells on HydroCoilBACKGROUND/OBJECTIVE:In the first part of experiment, through rat ECA blind pouch aneurysm model, we found that HydroCoil could cause damage of vascular endothelial and elastic lamina of aneurysmal wall and proliferation of vascular smooth muscle cells. In this experiment we seed vascular endothelial cells on coils for culture and compare the difference of vascular endothelial cell proliferation on the two kinds of coil, to analysis the possible mechanism of different tissue reaction caused by the two kinds of coil in rat aneurysm model.METHODS:bEnd3, cerebrovascular endothelial cell line of mice, was cultured and seeded on the5mm fragment of HydroCoil and bare platinum coil. The cells were washed out of coils for count using trypsin at various time points (D0, D1, D3, D7, D14and D21). Gowth curve of cells on bare platinum coils and HydroCoils was described and statistically analyzed. Live/Dead cell fluorescent staining and PECAM-1(Platelet endothelial cell adhesion molecule-1, CD-31) fluorescent staining was also performed.RESULTS:From Growth curve of cells, we found that growth of bEnd3cells on HydroCoil peaked on the3rd day after seeding, and then the cell apoptosis accelerated. But the growth of bEnd3cells on bare platinum coil peaked on the14th day after seeding and the peak cell number is less than HydroCoil. Live/Dead cell staining revealed adhesion of dead bEnd3cells on bare platinum coil and no adhesion on HYdroCoil. The PECAM-1expression of vascular endothelial cells on HydroCoil was significantly weaker than those on bare platinum coil.CONCLUSIONS:Vascular endothelial cell proliferation on HydroCoil is quicker and greater than those on bare platinum coil and the cell apoptosis on HydroCoil starts earlier. The adhesive capacity of vascular endothelial cell on HydroCoil is poorer than on bare platinum coil. Part ⅢAnti-platelet drugs and aneurysmal thrombosis after coil embolization in experimental rat aneurysmsOBJECTIVE:To study the effect of common anti-platelet drugs on aneurysmal thrombosis after coil embolization in experimental rat aneurysms.METHODS:30rats were randomly divided into6groups,5rats/each group.3groups for bare platinum coil implantation with anti-platelet:aspirin group, clopidogrel group and combination group (aspirin and clopidogrel).3groups for HydroCoil implantation with anti-platelet:aspirin group, clopidogrel group and combination group (anspirin and clopidogrel). The data in the first part of this research was used as each control group for bare platinum coil and HydroCoil implantation. Aspirin dose was200mg/Kg, clopidogrel dose was75mg/Kg, and combination was200mg/Kg aspirin+75mg/Kg clopidogrel given at the same time. Drug administration time was1hour before surgery and once every day after surgery until sacrifice. Drug delivery approach was gavage with1-2ml suspension liquid mixed with drinking water and crushed anti-platelet drug according body weight of rat. ECA blind pouch aneurysm model of rats was used.14days after coil embolization, animals were sacrificed and the entire CCA/ICA/ECA complex was removed. Sac and surrounding vasculature underwent microscopic and histopathologic evaluation. Cellular and fibrotic components within the sac were defined as the organized area. Percentage of organized area was calculated and statistically analyzed.RESULTS:There was no significant difference between control group, aspirin group, clopidogrel group and combination group in the organized tissue area in the ECA sac2weeks following bare platinum coil embolization (15.62±19.24%vs.13.62±5.22%vs.8.20±9.23%vs.24.46±23.90%). There was no significant difference as well between control group, aspirin group, clopidogrel group and combination group in the organized tissue area in the ECA sac2weeks following Hydrocoil embolization.CONCLUSIONS:The commonly used anti-platelet drug at present, aspirin and clopidogrel, either single drug or combination, does not significantly affect aneurysmal thrombosis and tissue organization after coil embolization in experimental rat aneurysms in the short term Part IVThrombus Formation in a Coil Embolized Rat Carotid Artery Side-Wall Aneurysm Model:A7Tesla Cross-Sectional MRI Correlation with HistologyBackground/Objective:There are various types of animal models that have been used to study consequences of iatrogenically created aneurysms treated by coil implantation. Traditionally, in the small animal models, this has been done upon sacrifice of the animal followed by histological examination. We aim to assess correlation of aneurysm healing in a rat carotid artery side wall aneurysm on histology with standard cross-sectional7Tesla MR imaging.Materials and Methods:Male Sprague Drawley rats were utilized to create a small sidewall carotid artery blind pouch aneurysm. A5mm segment of hydrocoil or bare platinum coils was inserted into the ligated external carotid artery (ECA) representing the aneurysmal sac. Sham-operated control rats underwent an identical procedure except that no coil was inserted into the ECA lumen. The entire common carotid artery (CCA), internal carotid artery (ICA), and ECA complex was removed on postop day14with the aneurysmal sac and surrounding vasculature. The entire block of tissue was then evaluated with microscopy, histopathology, immunohistochemistry, and electron microscopy. Prior to sacrifice the animal was imaged under inhalational anesthesia in a small bore7Tesla MRI. Statistical analysis was then performed to assess the correlation of signal abnormality within the aneurysm with extent of intra-aneurysmal thrombus formation on histology.Results:Ten rats were utilized for the experiment. Five had implantation of5mm of hydrocoil and the rest of the rat aneurysms were implanted with bare platinum coils. On the14day mark there was a statistically significant linear correlation between the extent of intra-aneurysmal thrombus formation on histology and the MR signal on imaging. There was no such correlation demonstrated in the hydrocoil implanted group of rats. No thrombus formation and no abnormal signal were demonstrated in the sham operated group of rats.Conclusion:A reliable correlation of extent of thrombus formation in aneurysms treated with bare platinum coils may be demonstrated on cross-sectional7tesla MR imaging. Potentially non-invasive MR imaging with a high strength magnet may have a wider application in larger animal aneurysm models and possibly in the human population to assess aneurysmal healing. Studies need to be performed to validate the above results in larger animal models to begin with.