Xie Yunchang, Hu Xiongwei, He Haisheng, Xia Fei, Ma Yuhua, Qi Jianping, Dong Xiaochun, Zhao Weili, Lu Yi, Wu Wei
School of Pharmacy, Fudan University, Key Laboratory of Smart Drug Delivery of MOE and PLA, Shanghai 201203, China.
J Mater Chem B. 2016 May 7;4(17):2864-2873. doi: 10.1039/c5tb02706c. Epub 2016 Mar 15.
Taking advantage of its ability to deal with exogenous pathogens, the M cell passage has proven to be the most reliable pathway for entry of particulates, thus creating opportunities for oral immunization and delivery of biomacromolecules. Albeit a well-known story, the underlying mechanisms of this pathway are not yet well understood, especially concerning direct evidence of translocation of particulates. Herein, model glucan microparticles (GMs) targeting M cells are employed to track translocation through M cell pathways as well as to various organs via the systemic circulation. GMs were first labeled with a novel kind of near-infrared fluorescent water-quenching probe through encapsulation and locking by stearin. In vivo live imaging indicates prolonged residence of GMs in the gastrointestinal tract for as long as 12 h. GMs are found to be gradually absorbed from the ligated ileum segment but little from the jejunum. Histological examination using confocal laser scanning microscopy (CLSM) confirms distribution of GMs to the basolateral side of the ileum through Peyer's patches. However, no detectable fluorescence can be observed in any other organs or tissues until 12 h after administration. After 12 h, GMs can be found in the liver, spleen and lung. At 24 h, GMs accumulate in these organs with approximately 2.3% of the total amount. Repeated administration for three consecutive days augments total accumulation to as high as 4.5%. By tracking GM-bound fluorescence, the particles can be accurately located in these organs. GMs can be transported across Caco-2/Raji and Caco-2/Raji/J774A.1 co-culture monolayers, but not Caco-2 monolayers, in a time-dependent manner. As observed by CLSM, GMs can be voraciously engulfed with as many as 10-15 particles per cell. Evidence of translocation of GMs indicates that GMs can be absorbed through the M cell pathway located at Peyer's patches, especially in the ileum, and translocated to reticulo-endothelial organs.
利用其处理外源病原体的能力，M细胞通道已被证明是颗粒进入的最可靠途径，从而为口服免疫和生物大分子递送创造了机会。尽管这是一个广为人知的情况，但该途径的潜在机制尚未得到充分理解，特别是关于颗粒转位的直接证据。在此，使用靶向M细胞的模型葡聚糖微粒（GMs）来追踪通过M细胞途径以及经由体循环到各个器官的转位情况。GMs首先通过硬脂酸的包封和锁定，用一种新型近红外荧光水淬灭探针进行标记。体内活体成像表明GMs在胃肠道中停留时间长达12小时。发现GMs从结扎的回肠段逐渐吸收，但从空肠吸收很少。使用共聚焦激光扫描显微镜（CLSM）进行的组织学检查证实GMs通过派尔集合淋巴结分布到回肠的基底外侧。然而，在给药后12小时之前，在任何其他器官或组织中均未观察到可检测到的荧光。12小时后，可在肝脏、脾脏和肺中发现GMs。在24小时时，GMs在这些器官中积累，约占总量的2.3%。连续三天重复给药可使总积累量增加至高达4.5%。通过追踪与GM结合的荧光，可将颗粒准确地定位在这些器官中。GMs可以以时间依赖性方式穿过Caco-2/Raji和Caco-2/Raji/J774A.1共培养单层，但不能穿过Caco-2单层。如CLSM所观察到的，GMs可被大量吞噬，每个细胞多达10 - 15个颗粒。GMs转位的证据表明GMs可通过位于派尔集合淋巴结处的M细胞途径吸收，尤其是在回肠中，并转位至网状内皮器官。
