Tilmicosin (TMS) is widely used to treat bacterial infections in veterinary medicine, but the clinical effect is limited by its poor solubility, bitterness, gastric instability, and intestinal efflux transport. Nanostructured lipid carriers (NLCs) are nowadays considered to be a promising vector of therapeutic drugs for oral administration. In this study, an orthogonal experimental design was applied for optimizing TMS-loaded NLCs (TMS-NLCs). The ratios of emulsifier to mixed lipids, stearic acid to oleic acid, drugs to mixed lipids, and cold water to hot emulsion were selected as the independent variables, while the hydrodynamic diameter (HD), drug loading (DL), and entrapment efficiency (EE) were the chosen responses. The optimized TMS-NLCs had a small HD, high DL, and EE of 276.85 ± 2.62 nm, 9.14 ± 0.04%, and 92.92 ± 0.42%, respectively. In addition, a low polydispersity index (0.231 ± 0.001) and high negative zeta potential (−31.10 ± 0.00 mV) indicated the excellent stability, which was further demonstrated by uniformly dispersed spherical nanoparticles under transmission electron microscopy. TMS-NLCs exhibited a slow and sustained release behavior in both simulated gastric juice and intestinal fluid. Furthermore, MDCK-chAbcg2/Abcb1 cell monolayers were successfully established to evaluate their absorption efficiency and potential mechanism. The results of biodirectional transport showed that TMS-NLCs could enhance the cellular uptake and inhibit the efflux function of drug transporters against TMS in MDCK-chAbcg2/Abcb1 cells. Moreover, the data revealed that TMS-NLCs could enter the cells mainly via the caveolae/lipid raft-mediated endocytosis and partially via macropinocytosis. Furthermore, TMS-NLCs showed the same antibacterial activity as free TMS. Taken together, the optimized NLCs were the promising oral delivery carrier for overcoming oral administration obstacle of TMS.

中文翻译：

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正交设计优化替米考星负载纳米结构脂质载体克服口服给药的障碍

替米考星（TMS）被广泛用于兽医学中的细菌感染，但其溶解性，苦味，胃不稳定性和肠外排转运性差，限制了其临床效果。如今，纳米结构脂质载体（NLC）被认为是用于口服给药的治疗药物的有前途的载体。在这项研究中，正交实验设计用于优化TMS加载的NLC（TMS-NLC）。选择乳化剂与混合脂质的比例，硬脂酸与油酸的比例，药物与混合脂质的比例以及冷水与热乳液的比例作为自变量，而流体动力学直径（HD），载药量（DL）和包封率（ EE）是选择的答案。优化的TMS-NLC的HD小，高DL和EE分别为276.85±2.62 nm，9.14±0.04％和92.92±0.42％。另外，低的多分散指数（0.231±0.001）和高的负ζ电势（-31.10±0.00 mV）表示优异的稳定性，这在透射电子显微镜下通过均匀分散的球形纳米颗粒得到了进一步证明。TMS-NLC在模拟胃液和肠液中均表现出缓慢且持续的释放行为。此外，成功建立了MDCK-chAbcg2 / Abcb1细胞单层膜，以评估其吸收效率和潜在机制。生物定向转运的结果表明，TMS-NLCs可以增强细胞吸收，并抑制MDCK-chAbcg2 / Abcb1细胞中转运蛋白对TMS的外排功能。此外，数据显示TMS-NLCs可以主要通过小窝/脂质筏介导的内吞作用进入细胞，部分通过巨胞饮作用进入细胞。此外，TMS-NLCs具有与游离TMS相同的抗菌活性。综上所述，优化的NLC是克服TMS口服给药障碍的有希望的口服载体。