Experimental Study On Embolic Liquid 2-poly-hydroxyethyl Methacrylate

IntroductionBrain arteriovenous malformations (AVM) are frequent diseases of cerebral vessel, need diagnosing and treating earlier because of leading to cerebral hemorrgage. Surgery, endovascular embolization and radiosurgery are the basic methods for the treatment of AVMs. The endovascular embolization is an important treatment. The embolic material is the most important factor influencing the curative effects besides angioarchitecture of AVM. Embolization materials used to treat AVM ever since include particle polyvinyl alcohol (PVA), liquid n-butyl cyanoacrylate (NBCA), as well as non-adhesive liquid ethylene vinyl alcohol (EVAL). Partical materials are difficult to deliver through microcatheter, and do not penetrate into nidus deeply. Among the liquids, except the persistent embolization effect, NBCA, used widely in clinics, is difficult to handle, sometimes, they cause the catheter to adhere the artery. NBCA precipitates in nidus vessels and form a rigid solid, which impacts upon resection of nidus. Though EVAL, regarded as non-adhesive embolic agent, sometimes make satisfactory embolization, it is based on dimethylsulfoxide (DMSO). DMSO has angionecrotic properties and may cause degeneration of the white matter or damage the tissue surrounding the AVM. Therefore, a search for an embolic material with optimized physical characteristics and better biocompatibility is mandatory. Wuhan institute of technology and us have developed a new liquid embolic material, 2-poly-hydroxyethyl-methacrylate (2-P-HEMA). 2-P-HEMA can be dissolved in ethanol, so can avoid the angiotoxicity as DMSO. The physical property, biocompatibility, and the embolic effects are to be studied, in order to evaluate its embolic property, and to provide evidence for clinical usage.This paper includes four parts. In first part, the physical character of 2-P-HEMA is studied. Secondly, the biocompatibility of 2-P-HEMA is investigated. Then, its embolic effect is evaluated by embolizing renal and other artery of rabbit. Lastly, the different flow AVM animal models are established to test the safety and effect of this material for embolizing AVMs.Part 1. Study on Physical Property of Liquid 2-Poly-Hydroxyethyl MethacrylateObjective: The dissolving property of 2-P-HEMA, a new non-adhensive liquidembolic agent, in ethanol and DMSO, and the precipitation property in water werestudied in this part to test whether 2-P-HEMA is suitable for endovascularembolization.Methods: The highest concentration of 2-P-HEMA in ethanol of differentconcentration was tested respectively. The highest concentration of 2-P-HEMA inother solution such as ethanol/iobitridol mixture, DMSO and DMSO/iobitridol ofdifferent concentration also were tested. The different concentration embolic agents(2%, 3.5%, 5%, 6.5%, 8%, 9.5%) were prepared by mixing 2-P-HEMA with differentsolution (ethanol, ethanol/iobitridol, ethanol/Bi₂O₃, and DMSO/iobitridol). Theseembolic agents were marked as 1A to 6A (ethanol solution), 1B to 6B(ethanol/iobitridol solution), 1C to 6C (ethanol/Bi₂O₃ mixture), and 1D to 6D(DMSO/iobitridol solution). The precipitation time of above agents were tested inimmobile normal sodium (NS) and in floating NS respectively.Results: The solubility of 2-P-HEMA in pure ethanol was low, and solubility became higher in ethanol of 20% to 80% concentration, but also low in less than 20% ethanol. The dissolution degree of 2-P-HEMA in pure DMSO was higher than other concentration, and also higher than all concentration ethanol solution. With the decline of DMSO concentration, the solubility of 2-P-HEMA in DMSO dropped gradually. The solubility of 2-P-HEMA in ethanol or DMSO was not changed when the mixtures were added by opacifiers such as iobitridol, and Bi₂O₃. The mixtures of 2-P-HEMA with ethanol or DMSO were precipitated to formed flocci form solid after injection into water. The precipitation time of embolic mixture as ethanol solvent was longer in low (2%) and high concentration (9.5%) than medial concentration (3.5% to 8.0%), and was longer in high concentration as DMSO solvent than low concentration. The precipitation time was not affected by adding iobitridol or Bi₂O₃ to mixtures with ethanol or DMSO solvent. The mixture of 2-P-HEMA and ethanol or DMSO was precipitated in few seconds time when injected into floating water in tube, and its precipitation time was shorter than in immobile water.Conclusion: 2-P-HEMA could be dissolved in 20%⁸0% ethanol and more than 30% DMSO. The mixture of 2-P-HEMA and ethanol or DMSO can be precipitated when injected into water, and its precipitation time in immobile water is much shorter than in floating water. The solubility and precipitation property of mixtures are not affected by adding opacifiers to mixtures. The physical property of 2-P-HEMA may be suitable for endovascular embolization.Part 2. Study on Biocompatibility of Liquid 2-Poly-Hydroxyethyl MethacrylateObjective: the biocompatibility of 2-P-HEMA in this part was to be studied to evaluate its safety for endovascular embolization and to provide evidence for clinical performance.Methods: In this part, the following items were made to test the biocompatibility of 2-P-HEMA: Ames test, cytotoxicity test in vitro, acute, subacute, andchronic systemic toxicity test, hemolytic test, measurement of bleeding and clotting time, and hemopexis function.Results: In ames test, the MR values of leaching liquors of 2-P-HEMA in different concentration were all less than 2, whereas the MR values in positive control group were both more than 2, which revealed 2-P-HEMA being non-mutagenic. The result of cytotoxicity test in vitro showed that L929 cells growth well without inhibition in all experimental groups, and the cytotoxicity was grade I, which proved no cytotoxicity of this embolic agent. The animals of experimental groups were no change in the acute, subacute, andchronic systemic toxicity test. All specimens of different organs and tissues were not be disclosed the cell degeneration and necrosis, and infiltration of inflammatory cells. The evidences of these systemic toxicity tests indicated that 2-P-HEMA have no systemic toxicity. The fact that the leaching liquors of 2-P-HEMA in all concentration could not result in hemolysis indicated obviously that 2-P-HEMA was no hemolysis. The bleeding and clotting times of rats were all among normal range, provided that 2-P-HEMA could not affect bleeding and clotting time. The last test showed 2-P-HEMA had little impact upon the blood coagulation function because the blood coagulation function in experimental groups was normal.Conclusion: 2-P-HEMA has good biocompatibility with no cytotoxicity, no mutagenic, good hemocompatibility, and not leading to systemic toxicity. 2-P-HEMA can be used as implant for clinical appliance. Part 3. Experimental Study on Endovascular Embolization Effect of Liquid 2-Poly-Hydroxyethyl MethacrylateObjective: The arm of this part is to evaluate the embolism property of 2-P-HEMA by occluding the renal artery, external carotid artery and femoral artery in rabbits.Methods: The short-term and long-term embolism properties of 2-P-HEMA were studied respectively. In short-term study, according to the concentration of 2-P-HEMA, eighteen animals were divided randomly into three groups: low concentration group (2%), medial concentration group (5%), and high concentration group (8%). After general anesthesia achievement, the right femoral artery of rabbit was cannulated surgically by placement of 4F introducer sheath, and the microcatheter was inserted into the renal artery of one side. The embolic agents marked 1B, 1C, 1D, 3B, 3C, 3D, 5B, 5C, 5D were injected into renal arteries of 2 animals in each subgroup respectively. The embolic agent, made radiopacity by Bi₂O₃, was shaked thoroughly before injection to prevent sedimentation of Bi₂O₃. The embolizations of external carotid artery and femoral artery were performed with embolic agent marked 3B. After the complete embolization was achieved in each animal, the animal was executed immediately, and the kidneys of two sides were taken for macroscopic and microscopic exam. In long-term study, the renal arteries of 6 animals were embolized by agent marked 3B. The ultrasonic exam and angiographic follow-up investigation were performed at 7days, 1 month and 3 months respectively after the embolization procedure. The kidneys of animal were inspected macroscopically and microscopically after angiographic follow-up.Results: The 2-P-HEMA of low and medial concentration was easy to inject through microcatheter, and difficult to inject in high concentration. There not existed adhesion of microcatheter to vessels in all procedures. The embolic agents were radiopaque clearly. The renal arteries of animals were occluded completely by 2-P-HEMA of low and medial concentration, and the phenomenon of "remodeling" was observed in some embolizations of kidneys. The renal arteries of animals were not detected and the size of kidneys became shrinking gradually by Doppler ultrasonic examination after embolization for a long time. The recanalization of occluded renal arteries was not visible by angiographic follow-up. The renal arteries were found filled by embolic agents when kidney was cut open. Mild inflammatory reaction surrounding arteries in early stage, and chronic reaction to "foreign body" in later stage were detected microscopically.Conclusion: The embolic agent apparently provides complete occlusion of vessels, is easy to deliver through microcatheter, and unlikely to cause catheter to become adhesive to the vessel. Radiopacity is sufficient, and toxic histopathologic response to the material is mild. The recanalization of occluded vessels is rare and long-term occlusion is achieved. 2-P-HEMA has great potential as an endovascular embolic agent.Part 4. Embolization of Experimental Brain Arteriovenous Malformation with Liquid 2-Poly-Hydroxyethyl Methacrylate in SwineObjective: Three blood flows of brain AVM animal models were to be established. The technique feasibility, embolism effects and safety of 2-P-HEMA as embolic agents were to be explored in this part by occluding these AVM models.Methods: six pigs were randomly divided into three groups: low flow group, medial flow group and high flow group. The normal RMB of pig was used as low flow model. The medial flow model is established by ligation of right common carotid artery, increasing the blood flow through bilateral RMB. The high flow model was built on by surgical anastomosis between right common carotid artery and external jugular vein, which increases greatly the blood flow of RMB because the direct arteriovenous shunt. In medial and high flow models, left and right ascending pharyngeal artery (PA) acted as afferent artery and draining vein respectively, and the bilateral RMB as AVM nidus. All animal models were embolized with 2-P-HEMA by deploying of microcatheter in left PA via transfemoral cannulation. The angiographic follow-up was performed at 1 month and 3 month after embolization procdure in each group. Histopathologic studies of bilateral RMBs were taken to prove occlusion and assess pathologic responses.Results: All procedures were performed successfully, and three flows of AVM models were constructed as expected. The arteriovenous fistula of one animal became narrow detected by Doppler ultrasonic and angiographic exam in high flow group. Each AVM model was embolized repeatedly with only one microcatheter until RMBs became opaque with fluoroscopy. 2-P-HEMA was easily injected through microcatheters without catheter occlusion and adhesion to vessel. The animals in medial and high flow groups were executed shortly after embolization because animals did not eat food. The angiographic follow-up revealed the complete occlusion without recanalization at 1 month and 3 month after embolization. Deep nidus penetration of materials and no marked inflammatory reaction in the vessel wall or perivascular tissue was observed in the embolized RMB.Conclusion: Ligation of common carotid artery of one side can construct medial flow of AVM model, and carotid jugular anastomosis can construct high flow of AVM model. The different flow AVM models embolized with 2-P-HEMA are technically feasible, performed easily and safely in swine. Because of its properties, 2-P-HEMA has great potential as a therapeutic embolic agent.