纳米银是一种应用广泛的纳米生物材料，已有多种含纳米银的医疗产品进入了临床应用。本研究的目的是比较纳米银颗粒和微米银颗粒生物学特性的区别，考察纳米银颗粒是否具有在体内迁移的生物特性，是否具有能够进入细胞内的生物效应，如果它具有这些特性，是否会造成一些负效应。 通过系统的研究，结果发现虽然纳米银颗粒和微米银颗粒在体内均基本不会溶解为Ag⁺，而是大部分(超过99.9%)都形成为覆盖蛋白质膜的银颗粒，但是由于尺寸的差异，两者在体内的分布具有明显的差异，纳米银颗粒具有在体内迁移的生物特性，而微米银颗粒却不具备这一特性。在本研究中，皮下注射后，最高曾经有约0.15%的单分散的纳米银颗粒以覆蛋白颗粒的形式通过血液循环系统分布于动物体内各脏器，并蓄积在肾、肝、脾、脑、肺等部位。而微米银颗粒或是注入体内后纳米银颗粒形成的团聚体则不能在体内迁移。迁移到脏器中的分散的纳米银颗粒，还可以通过肾小管上皮细胞、肝细胞、脾脏淋巴细胞、脑神经元、肺泡细胞的细胞膜进入这些细胞内。另外，还发现纳米银颗粒可以使星形细胞脚板肿胀，破坏血脑屏障，进入脑部的纳米银颗粒能够引起神经元变性。这说明纳米银颗粒所具有的在体内迁移的生物特性，在某些条件下会带来生物负效应，应该对其进行系统的生物安全性研究。 因为体内试验证明了纳米银颗粒可进入细胞内，在某些情况下还能使细胞变性，所以通过体外细胞试验考察了不同剂量纳米银颗粒的细胞毒性，结果显示分散的纳米银颗粒能够通过细胞吞噬的方式进入细胞内，当纳米银颗粒剂量达到50μg/ml之后，可以对线粒体等细胞器产生影响，使细胞坏死，从而使细胞增殖能力下降，对细胞产生明显的毒性效应。而相同条件下微米银颗粒不会进入细胞内，因此没有产生细胞毒性。这说明纳米银颗粒和微米银颗粒产生细胞毒性的机理是不同的，其中最关键的区别就是分散的纳米银颗粒具有能够进入细胞内的生物效应，而微米银颗粒不能进入细胞内。 由于体内细胞试验发现纳米银颗粒能够破坏血脑屏障，因此采用建立体外细胞模型的方法对纳米银穿过血脑屏障的机理进行研究。在研究中，通过脑微血管内皮细胞/星形胶质细胞(脑毛细血管内皮细胞/星形胶质细胞)共培养的方法，建立了 BBB体外试验模型。再利用此模型研究纳米银颗粒对血脑屏障的作用，结果发现，有部分纳米银颗粒可以通过血脑屏障，而微米银颗粒不能通过血脑屏障。而超微结构照片显示有纳米银颗粒可进入血管内皮细胞，而微米银只能在细胞间质中有分布，而无法进入细胞内；因此推测纳米银颗粒通过血脑屏障的机理主要是通过脑毛细血管内皮细胞的胞吞转运而通过血脑屏障的。 通过以上的研究，第一，首次证明了纳米银颗粒在体内不会完全溶解为Ag⁺，而是基本上都形成为覆盖蛋白质的纳米银银颗粒。第二，首次证明了分散的纳米银颗粒具有在体内迁移的生物特性，比较系统的研究了纳米银颗粒在生物体内分布、排泄和蓄积的规律，找到了纳米银颗粒蓄积的器官。第三，证明了纳米银颗粒具有能够进入细胞内的生物效应，并首次证明这一生物效应是纳米银颗粒产生细胞毒性的根本原因。第四，首次发现纳米银颗粒可以破坏并通过血脑屏障，纳米银颗粒主要是通过脑毛细血管内皮细胞的胞吞转运而通过血脑屏障的。 通过以上试验，可以基本了解皮下注射纳米银后，其在体内的分布、排泄、蓄积规率，其与细胞的相互作用，并且了解了纳米银颗粒通过血脑屏障的机理。希望在进一步的试验中能够观察测试纳米银颗粒进入细胞后引起的生物化学反应，以从分子水平进一步阐明纳米银对细胞作用的机理。 关键词：纳米银颗粒，体内分布，细胞吞噬，血脑屏障

 Silver nanoparticles (SNPs) are widely used in the field of biomedicine. Some medical devices which contain these two nanoparticles have been used in clinic. The purpose of the study is to compare the difference in biological characteristic between SNPs and silver microparticles (SMPs), to investigate that if SNPs could translocate all over the body and show a systemic distribution, if SNPs could enter into cells, and what negative health effects may cause by SNPs. The results showed that only a small quantity of SNPs and SMPs (＜0.01 %) would dissolve to Ag⁺ in simulated body fluids (SBFs), most SNPs and SMPs (＞99.9%) keep in the form of particle with a proteinic membrane was formed outside the particle's surface. Owing to the difference in diameter between SNPs and SMPs, these two particles show a significantly different distribution in vivo. SNPs could translocate all over the body and show a systemic distribution whereas SMPs could not. After subcutaneous injection in rats, monodisperse SNPs has at most 0.15% that translocated into blood circulation and distributed throughout the body, and accumulated in kidney, liver, spleen, brain, and lung in the form of particle. But SMPs and aggregates made up of SNPs could not translocate into blood circulation. After translocation to the different organs, monodisperse SNPs could enter into some kinds of cells such as renal tubular epithelial cell, hepatocyte, neuron, and disperse in the cytoplasm. In addition, SNPs could cause manifestation of astrocyte swelling out of the BBB and neuronal pyknosis and apoptosis. That means SNPs may induce the BBB abnormal, cross the BBB and induce brain toxicity. Therefore, more cautions are needed in biomedical applications of SNPs, in particular, the long term uses. It is proved that SNPs could enter into cells in experiment in vivo. The cytoxicity of SNPs was investigated in vitro. The results showed that monodisperse SNPs could enter into L929 cell by cell phagocytosis. Moreover, when the dose is higher than 50μg/ml, SNPs possess cytoxicity; they would influence the function of some organelles, such as Mitochondria, and cause the cell necrosis. But SMPs could not enter into cells, so they did not show cytoxicity under the same condition. The results demonstrste that it is different in cytoxicity mechanism of SNPs with SMPs. The key factors of these differences is SNPs could enter into cells but SMPs could not. Because we found that SNPs could cause the BBB abnormal and cross the BBB in the experiment in vivo. To elucidate the mechanisms by which SNPs cross the BBB we utilized an in vitro model. First, a coculture model of brain microvessel vescular endothelial cell (BMVEC) and Astrocyte cell (AC) of rats were used to establish an in vitro BBB model. Second, BBB model were in direct contact to SNPs and SMPs for 4h. Then the silver contents of permeating through BBB were determined by ICP-MS. In the end, ultrastructures of BBB were investigated by transmission electron microscopy (TEM). The results showed that only SNPs could cross the BBB, but SMPs could not. In ultrastructural analysis, only SNPs, in the form of particle, appeared inside the endothelial cells when the BBB model was exposed to SNPs or SMPs. SMPs were only distributed in the intercellular matrix and could not enter inside the endothelial cells. Hence, we suggested that brain microvessel vascular endothelial cells's transcytosis was the primary mechanism by which SNPs may cross the BBB. According to the study, first, it is the first time to prove that only a small quantity of SNPs (＜0.01%) would dissolve to Ag⁺ in simulated body fluids (SBFs), most SNPs (＞99.9%) keep in the form of particle with a proteinic membrane was formed outside the particle's surface. Second, it is first time to found that monodisperse SNPs could translocate throughout the body and show a systemic distribution. Kidney, liver, spleen, brain and lung may be the targeted organs of SNPs. Third, we prove that only SNPs could enter into cell, and found that this ability is the key factor that SNPs induce cytoxicity for the first time. In the end, it is the first time to found that silver nanoparticles could cross blood-brain barrier in the form of particles. In the further study, biochemical reaction between SNPs and various organelles, cytokines, proteins would be investigated. Then the mechanisms of SNPs with cell would be illustrated at molecular level. Key Words: silver nanoparticle, distribution in body, cell phagocytisis, blood-brain barrier