Silk nanoparticles are viewed as promising vectors for intracellular drug delivery as they can be taken up into cells by endocytosis and trafficked to lysosomes, where lysosomal enzymes and the low pH trigger payload release. However, the subsequent degradation of the silk nanoparticles themselves still requires study. Here, we report the responsiveness of native and PEGylated silk nanoparticles to degradation following exposure to proteolytic enzymes (protease XIV and α-chymotrypsin) and papain, a cysteine protease. Both native and PEGylated silk nanoparticles showed similar degradation behavior over a 20 day exposure period (degradation rate: protease XIV > papain ≫ α-chymotrypsin). Within 1 day, the silk nanoparticles were rapidly degraded by protease XIV, resulting in a ∼50% mass loss, an increase in particle size, and a reduction in the amorphous content of the silk secondary structure. By contrast, 10 days of papain treatment was necessary to observe any significant change in nanoparticle properties, and α-chymotrypsin treatment had no effect on silk nanoparticle characteristics over the 20-day study period. Silk nanoparticles were also exposed ex vivo to mammalian lysosomal enzyme preparations to mimic the complex lysosomal microenvironment. Preliminary results indicated a 45% reduction in the silk nanoparticle size over a 5-day exposure. Overall, the results demonstrate that silk nanoparticles undergo enzymatic degradation, but the extent and kinetics are enzyme-specific.

中文翻译：

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纳米丝的降解行为—酶响应

蚕丝纳米颗粒被视为细胞内药物递送的有前途的载体，因为它们可以通过内吞作用吸收到细胞中并运输到溶酶体中，在溶酶体中溶酶体酶和低pH值会触发有效载荷的释放。但是，丝纳米颗粒本身的后续降解仍需要研究。在这里，我们报告天然和聚乙二醇化的丝绸纳米粒子降解后暴露于蛋白水解酶（蛋白酶XIV和α-胰凝乳蛋白酶）和木瓜蛋白酶（一种半胱氨酸蛋白酶）对降解的反应性。天然和聚乙二醇化的丝绸纳米粒子在20天的暴露时间内均表现出相似的降解行为（降解速率：蛋白酶XIV>木瓜蛋白酶≫α-胰凝乳蛋白酶）。在1天之内，蚕丝纳米粒子被蛋白酶XIV迅速降解，导致〜50％的质量损失，粒径增加，并降低了丝二级结构的无定形含量。相比之下，木瓜蛋白酶处理需要10天才能观察到纳米粒子性能的任何显着变化，而α-胰凝乳蛋白酶处理在20天的研究期内对丝纳米粒子的特性没有影响。丝纳米颗粒还离体暴露于哺乳动物的溶酶体酶制剂中，以模拟复杂的溶酶体微环境。初步结果表明，经过5天的暴露，丝纳米颗粒尺寸减少了45％。总体而言，结果表明，丝绸纳米颗粒会发生酶促降解，但是其程度和动力学是酶特异性的。在20天的研究期内，α-胰凝乳蛋白酶对丝纳米颗粒的特性没有影响。丝纳米颗粒还离体暴露于哺乳动物的溶酶体酶制剂中，以模拟复杂的溶酶体微环境。初步结果表明，经过5天的暴露，丝纳米颗粒尺寸减少了45％。总体而言，结果表明，丝绸纳米颗粒会发生酶促降解，但是其程度和动力学是酶特异性的。在20天的研究期内，α-胰凝乳蛋白酶对丝纳米颗粒的特性没有影响。丝纳米颗粒还离体暴露于哺乳动物的溶酶体酶制剂中，以模拟复杂的溶酶体微环境。初步结果表明，经过5天的暴露，丝纳米颗粒尺寸减少了45％。总体而言，结果表明，丝绸纳米颗粒会发生酶促降解，但是其程度和动力学是酶特异性的。