An Applied Basic Research Of A New Embolic Agent Of Thermosensitve Nanogel

PART I:An experimental study on the thermosensitive phase transition characteristics and biocompatibility of PIB nanogelPurpose:To study the thermosensitive phase transition characteristics and biocompatibility of poly(N-isopropylacrylamide-co-butyl methylacrylate)(PIB) nanogel.Materials and methods:The thermosensitive sol-gel phase transitions characteristics of PIB nanogel was measured by the inverting-vial method and in vitro injection test. L929cells were in vitro cultured. The Cells were treated with different concentrations of aqueous extract of PIB nanogel for3days. Cell viability was determined by Cell Counting-8assay. The Cells were also treated with different concentrations of PIB nanogel aqueous for2days. Calcein-AM and propidium iodide Double Staining Kit was utilized for simultaneous fluorescence staining of viable and dead cells. Cell survival rate was determined by cell count method, which was observed under laser confocal microscope. PIB nanogel was injected in one side of the back muscle of15rabbits, and normal saline was injected in another side. Pathological examination of the operative muscle was performed at1,2,4,12and26weeks after operation to evaluate the histocompatibility of PIB nanogel.Results:PIB nanogel underwent a sol-gel transition at its lower critical solution temperature of36.5℃. PIB nanogels have good cytocompatibility to L929cells, demonstrating no obvious cytotoxicity of the material. There was no severe inflammatory response and no evidence of abnormal pathological changes was found in muscular tissue. The postoperative histopathologic changes were within the authoritative ranges according to the national standards for local effects after implanation.Conclusions:PIB nanogel has good biocompatibility and showed satisfactory thermosensitive sol-gel phase transitions character. PART II:An experimental study on the embolization of rabbit renal arteries with PIB nanogelPurpose:We have developed a new thermosensitive liquid embolic agent, poly(N-isopropylacrylamide-co-butyl methylacrylate)(PIB) nanogel that can be solidfied by a sol-gel phase transition at body temperature. We thus further investigated the distribution, durability of vascular occlusion, and inflammatory reactions of PIB in embolization of the renal artery of rabbits.Materials and methods:In experiment1,18rabbits were evenly divided into3groups according to the injection rate. The right renal arteries were embolized by PIB with various injection rates. The animals were sacrificed at1hour after embolization. To evaluate the distribution pattern of PIB, the kidneys were examined by contact radiography and tissue section microscopy. In experiment2. we embolized the right renal artery of20rabbits with PIB with the injection rate of0.10ml/s. Angiography was performed before sacrifice1week (n=5),1month (n=5),2months and3months (n=5) after embolization. Pathologic and histologic examination of the kidneys was performed to assess the embolization efficacy and the specific inflammatory response of PIB.Results:The procedure was performed successfully in all rabbits. In experiment1. the higher injection rate, the smaller arteries PIB could reach, and the rate of0.10ml/s produced a homogeneous distribution of PIB from segmental arteries to the precapillary level. In experiment2, no angiographic recanalization appeared during follow-up. We found no disruption of the vessel wall and subintimal bleeding, no extravasation of PIB and no evidence of neocapillarization. Histologically, there was only mild inflammatory response manifested by few lymphocytic and monocellular infiltration, without foreign body granuloma formation.Conclusions:Embolization renal artery with PIB was easy and controllable, which could lead to a homogeneous and persistent occlusion without severe inflammatory changes. PIB might be a suitable material for intravascular embolization. PART Ⅲ:An experimental study on the embolization of rabbit VX2liver tumors with PIB nanogelPurpose:To observe the effect of transcatheter arterial embolization using thermosensitive poly(N-isopropylacrylamide-co-butyl methacrylate)(PIB) nanogel on hepatic function and growth of hepatic tumor of rabbits bearing VX2tumor.Materials and methods:Thirty rabbits implanted liver VX2tumors diagnosed by MR were randomly divided into3groups of10each. A microcatheter was inserted into the hepatic artery and injection was performed via the hepatic artery using physiological saline (group A), lipiodol and gelfoam (group B), and PIB nanogel (group C), respectively. The level of AST and ALT in serum was respectively tested at1day before treatment,3and7days after treatment. All experimental rabbits were sacrificed7days after treatment. Hepatic tumor tissue was obtained for pathological examination to calculate necrotic rate of tumors. The volume and growth rate of tumors were calculated by the examination of MR before sacrifice.Results:There was no significant difference in the volume of tumors at1day before treatment, the level of AST and ALT at1day before treatment and7days after treatment, among3groups (P>0.05). There was significant difference in the level of AST and ALT between each group3days after treatment (P<0.05). The level of AST and ALT in group C was lower than that in group B and higher than that in group A. There was significant difference in the growth rate of tumor between each group7days after treatment (P<0.05). The growth rate of tumor was (392.79±40.39)%in group A,(157.47±26.25)%in group B, and (111.85±20.16)%in group C.Conclusions:Transcatheter arterial embolization using PIB nanogel can inhibit the growth of the implanted VX2tumor, and there is no obvious liver toxicity related it.