Center for Drug Discovery, China Pharmaceutical University, Nanjing, PR China.
Biomaterials. 2011 Jul;32(20):4609-20. doi: 10.1016/j.biomaterials.2011.03.005. Epub 2011 Mar 26.
The overall objective of the present investigation was to demonstrate the effect of N-octyl-O-sulfate chitosan (NOSC) micelles on enhancing the oral absorption of paclitaxel (PTX) in vivo and in vitro, and identify the mechanism of this action of NOSC. In vivo, the oral bioavailability of PTX loaded in NOSC micelles (PTX-M) was 6-fold improved in comparison with that of an orally dosed Taxol(®). In the Caco-2 uptake studies, NOSC micelles brought about a significantly higher amount of PTX accumulated in Caco-2 cells via both clathrin- and caveolae-mediated endocytosis, and NOSC had the effect on inhibiting PTX secreted by P-glycoprotein (P-gp), which was also proved by the studies on rhodamine 123 incorporated in NOSC micelles, fluorescence labeled micelles. The mechanism of NOSC on P-gp inhibition was demonstrated in connection with interfering the P-gp ATPase by NOSC rather than reducing the P-gp expression. Moreover, NOSC with the concentration approaching the critical micellar concentration (CMC) had the strongest effect on P-gp inhibition. In the Caco-2 transport studies, the presence of verapamil and NOSC both improved the transport of Taxol(®), which further certified the effect of NOSC on P-gp inhibition, and PTX-M enhanced the permeability of PTX compared with Taxol(®). The apparent permeability coefficient (Papp) of PTX-M decreased significantly at 4 °C in comparison with at 37 °C, which indicated a predominant active endocytic mechanism for the transport of PTX-M, a P-gp-independent way. Furthermore, the transcytosis of PTX-M was via clathrin-mediated rather than caveolae-mediated. In addition, the transepithelial electrical resistance (TEER) of Caco-2 cell monolayers had no significant change during the transport study, which pointed out that NOSC had no effect on opening the intercellular tight junctions. Based on the obtained results, it is suggested that NOSC micelles might be a potentially applicable tool for enhancing the oral absorption of P-gp substrates.
本研究的总体目标是证明 N-辛基-O-硫酸壳聚糖（NOSC）胶束对增强紫杉醇（PTX）体内和体外口服吸收的作用，并确定 NOSC 作用的机制。体内实验表明，与口服紫杉醇（Taxol®）相比，负载 PTX 的 NOSC 胶束（PTX-M）的口服生物利用度提高了 6 倍。在 Caco-2 摄取研究中，NOSC 胶束通过网格蛋白和小窝介导的内吞作用使更多的 PTX 积聚在 Caco-2 细胞中，并且 NOSC 抑制 P-糖蛋白（P-gp）分泌的效果，这也被证明与 Rhodamine 123 结合在 NOSC 胶束中，荧光标记的胶束的研究结果一致。NOSC 对 P-gp 抑制的机制证明与干扰 P-gp 三磷酸腺苷酶有关，而不是降低 P-gp 表达。此外，接近临界胶束浓度（CMC）的 NOSC 浓度对 P-gp 抑制作用最强。在 Caco-2 转运研究中，维拉帕米和 NOSC 的存在均改善了 Taxol®的转运，这进一步证明了 NOSC 对 P-gp 抑制的作用，并且与 Taxol®相比，PTX-M 增强了 PTX 的通透性。与 37°C 相比，PTX-M 的表观渗透系数（Papp）在 4°C 时显著降低，这表明 PTX-M 的转运主要是主动内吞机制，是一种 P-gp 非依赖性途径。此外，PTX-M 的转胞吞作用是通过网格蛋白介导的，而不是小窝介导的。此外，在转运研究过程中，Caco-2 细胞单层的跨上皮电阻（TEER）没有明显变化，这表明 NOSC 对打开细胞间紧密连接没有影响。基于获得的结果，建议 NOSC 胶束可能是增强 P-gp 底物口服吸收的一种潜在应用工具。
