Gastrointestinal Transport Investigation Of Stearic Acid-grafted Chitosan Oligosaccharide Micelles

In the past decades polymeric micelles have received great attention as a new drug delivery vehicle for its unique properties such as wide drug loading spectrum, a stable spatial structure, excellent tissue penetration and prolonged drug retention. Their application in oral administration which based on their ability to improve the bioavailability of the drug has also been extensively investigated recently. The purpose of this study is to utilize chitosan as the main material, the conjugated stearic acid-grafted chitosan was synthesized and its in vitro cell transport properties were investigated to obtain some knowledge about the vehicle as the oral drug delivery system.The stearic acid-grafted chitosan oligosaccharide (Mw:5 kDa, CSO) with different amino-substitution degree (SD) were synthesized by using 1-ethyl-3-(3-dimethyl-aminoproyl) carbodiimide (EDC). The chemical structure of CSO-SA was confirmed by 1HNMR; The amino substitution degrees of the CSO-SA micelles were measured as 4.47%,24.36%,40.36%, respectively; The diameter and zeta potential of the micelles with the concentration of 1 mg/mL were measured by Zeta-sizer, which was in the range of 33.4-130.9 nm and 22.9-48.4 mV; The critical micelles concentration (CMC) of CSO-SA micelles was determined as 161.85,218.42,246.9μg/mL, respectively.Caco-2, a well recognized in vitro model for permeability estimation of intestinal absorbed drugs were used to explore the permeability of the CSO-SA micelles and related transport pathway. The Papp value of the micelles was more than 10'6 cm/s, and the transport was energy and concentration dependent. Besides, the transport was absorption site dependent which was enhanced with the pH lowering of the medium. The micelles could stay stable in SIF with different pH condition. The permeability was enhanced with the increasing SD of the CSO-SA. Selective inhibitors assay implied that the micelles mainly transported through macro-pinocytosis and paracellular pathway.Doxorubicin (DOX) loaded CSO-SA micelles was prepared by dialysis method. Compared with blank micelles, the size of the DOX-loaded micelles was decreased while the zeta potential was increased. The drug loading ability (DL) of CSO-SA micelles with different SD had no significant difference. The highest DL was about 12.69%, and correspond drug encapsulating efficiency was about 76.15%. The release profile of different CSO-SA/DOX micelles showed no significant difference, and 70-86%drug was released after 72 h. Both the permeability and the bioavailabity of the drug were significantly improved after the drug encapsulated into the micelles, while the drug pumped by P-gp was decreased. The Papp ratio of the drug transport from apical to basolateral side was improved by 20-40 folds and the absolute bioavailability was improved by about 2.25 folds. Besides, the drug blood retention time was prolonged by using micelles which not only enhanced the intestinal absorption of the drug but also facilitated the efficiency performs of the drug.