脂质纳米载体的跨膜递送机理研究与口服给药系统分子设计

Lipid nanoparticles, which could transport through enterocytes and delivery via lymph system, might be one of the most promising drug delivery system for enhancing oral drug absorption by overcoming the gastrointestinal barriers and improving bioavailability. The present reports on the absorption of lipid nanoparticles in the gut mainly focus on the routes of absorption and the mechanism of internalization. However, the critical steps of transportation in cells of nanoparticles that followed nanoparticle internalization remain to be elaborated systematically, because the transportation of nanoparticles in cells affected the rate and extent of exocytosis directly, and closely related to transmucus transport and absorption ability of drug delivery system. In the present study, different epithelial cell monolayers were employed to systematically clarify the transport mechanisms of lipid nanoparticles across intestinal epithelial cell monolayer. Furthermore, various lipid nanoparticles will be prepared with different properties, e.g. chemical composition, spatial structure under the direction of molecular designing. The transcytosis of lipid nanoparticles in intestinal epithelial cells and its influencing factors will be investigated. The relationship between them will be elucidated and the common regularities will be revealed. Further works will be carried out to design the lipid nanoparticles at the molecular leve with these common regularities, and obtain a kind of oral drug delivery system with high oral efficiency and bio-stability. Therefore, this study will enrich and development the design theory and application foundation of oral drug delivery systems for poorly soluble drugs and biological macromolecules.

脂质纳米粒可通过肠上皮细胞转运并经淋巴循环吸收的特点，使其成为克服消化道吸收屏障、提高药物口服生物利用度的重要技术手段之一。目前脂质纳米给药系统的消化道吸收研究主要涉及吸收途径和肠上皮细胞摄取机理，在纳米粒摄取后的细胞内转运等关键过程尚待系统阐述。纳米粒的细胞内转运过程直接影响到经细胞摄取纳米粒的出胞传递速度和程度，对纳米给药系统的跨肠细胞转运与体内吸收具有密切的相关性。本项目拟通过构建不同的单层细胞膜型来深入阐述脂质纳米载体的跨膜转运机理。进一步通过分子设计手段构建具有不同化学组成、空间结构的脂质纳米载体，考察脂质纳米载体经肠上皮细胞内转运与其影响因素，从而得到脂质纳米载体经肠上皮细胞转运和各种影响因素之间的关系，并得到共性规律。通过这些规律来指导脂质纳米载体的分子设计，从而得到一类转运效率高的口服脂质纳米载体系统，丰富和发展难溶性药物、生物大分子药物的口服给药系统设计理论与应用基础。

本课题以Caco-2单层细胞和MDCK单层细胞为模型，模拟消化道上皮吸收屏障，研究了脂质纳米载体通过单层细胞摄取、胞内转运和出胞等过程，阐明脂质纳米载体的跨膜转运机理。研究结果表明，脂质纳米粒在单层膜中的转运不会影响单层膜的紧密连接，是一种相对安全的口服纳米给药载体。固体脂质纳米粒被细胞摄取是通过脂阀、网格蛋白介导的等途径內吞，是一个时间和能量依赖的过程；内质网、高尔基体以及微管蛋白在固体脂质纳米粒的细胞内转运中发挥着重要的作用。可能存在直接的转运通路将固体脂质纳米粒由顶侧膜转运到基底侧。这条途径是一条非常有效的转运途径，其可不经过内质网和高尔基体，转运的效率显著提高，载体表面亲水性修饰后，经该途径转运的纳米粒增多。进一步的研究发现，脂质材料的碳链长度、油水分配系数和熔点等性质对纳米粒经肠细胞转运效率有较大的影响；大鼠离体肠段渗透试验显示了相似的结果。PEG修饰可以增加固体脂质纳米粒对肠上皮粘液层的粘附以及向亲水性的粘液层内部渗透，增加固体脂质纳米粒的转运吸收。FRET法研究结果显示，脂质纳米粒在经单层细胞转运过程中可能存在一定的结构变化，即部分脂质纳米粒在细胞内发生水解，形成脂肪酸，重新合成甘油三酯，在内质网上重新加工成乳糜微粒并外排，这部分迁移入血液中的粒子与直接跨膜转运入体循环的脂质纳米粒可能具有不同分布与作用特点。