Study On Amphiphilic Chitosan Copolymer Self-assembled Micelles

The chitosan was hydrophobically modified with deoxycholic acid or cholesterol by the reaction with primary amino groups in chitosan. This reaction was activated by 1-ethyl-3-（3-dimethyl-aminopropyl）-carbodiimide hydrochloride to obtain the ultimate product deoxycholic acid hydrophobic-modified chitosan（CS-DA）, deoxycholic acid hydrophobic- modified chitosan oligosaccharides（COS-DA）, cholesterol hydrophobic,modified chitosan（CS-Chol）. The structure of products was confirmed by FT-IR spectra. Various amphiphilic chitosan copolymers with different substitute degree were obtained by controlling the feed ratio of deoxycholic acid or cholesterol to chitosan. （The substitute degree, defined as the number of deoxycholic acid or cholesterol per 100 sugar residues of chitosan）Solubility of Amphiphilic chitosan copolymers was determined and the conclusion as the substitute degree and the mean molecular weight of chitosan are the key factors to determine solubility. It suggested that the lipophilicity of chitosan was greatly increased after derivation. The critical micelle concentration of amphiphilic chitosan copolymer was about 10^-2mg·mL^-1 which was got by fluorometer in the presence of pyrene as a fluorescent probe and surface tension technique. Its value is lower than the critical micelle concentration of various low molecular weight surfactant, i.e., 0.65 mg·mL^-1 for alkyl benzenesulfonate(C_10-13 alkyl group)in water and 0.3 mg·mL^-1 for C_15-18α-olefinsulfonate in water. It indicates that self- assembled micelles are stable in aqueous solution.In the study, physical and chemical properties of vinpocetine（VIN）such as equilibrium solubility, stability in various solutions was investigated, and developed an analytical HPLC method for the determination of vinpocetine concentration in vitro. Vinpocetine is a hydrophobic base type drug, which shows a pH-dependent solubility profile. The solubility of Vinpocetine is much higher at low pH values or with existence of the surfactant.Solvent evaporation technique was applied to prepare the vinpocetine loaded self-assembled micelle system. The drug loaded micelles with lower size and narrow size distribution and higher encapsulation efficiency can be obtained. Moreover the stability in room temperature condition of vinpocetine-loaded amphiphilic chitosan copolymer self-assembled micelles was investigated. The result suggested that deoxycholic acid hydrophobic-modified chitosan maintained its self-aggregate structure in room temperature condition for 60 days, while deoxycholic acid hydrophobic-modified chitosan oligosac- charides（COS-DA） and cholesterol hydrophobic modified chitosan（CS-Chol）aggregated and precipitated within 10 days.Drug release from amphiphilic chitosan copolymer self-assembled micelles in pH 7.4 phosphate buffer（0.5％SDS）was studied using a dialysis bag method. From the experimental data, amphiphilic chitosan copolymer self-assembled micelles released VIN slower than VIN solution. Albumen made an important contribution to a high release velocity of VIN in micelles.After single bolus iv administration to rats, vinpocetine injection was eliminated from blood circulation rapidly with t_1/2 only 1.48h, while the t_1/2 of amphiphilic chitosan copolymer self-assembled micelles was about 9h.The biodistribution of the VIN-CS-DA-100ku and VIN-CS-DA-50ku showed a similar behavior: compared to vinpocetine injection, a less amount of vinpocetine was found in all tissues, and the concentration of vinpocetine in tissue remained a lower level for relatively longer time. The ability of amphiphilic chitosan copolymer self-assembled micelles to accumulate selectively in tissue was not confirmed without further experiment.