响应面法优化西罗莫司胶束及其促小肠吸收作用

Optimization of Sirolimus Micelles by Response Surface Methodology and Its Effect on Small Intestinal Absorption

关键词:  西罗莫司  壳聚糖  聚合物胶束  星点设计-效应面法  在体单向肠灌流

Key words:  sirolimus  chitosan  micelle  central composite design-response surface method  in situ single pass perfusion model

摘要:

目的 制备和优化西罗莫司（sirolimus，SRL）聚合物胶束，考察其对大鼠在体肠吸收动力学的影响。方法 以去氧胆酸修饰的壳聚糖（deoxycholic acid grafted chitosan，CS-DCA）为载体，采用溶剂蒸发法制备SRL CS-DCA胶束。以包封率、载药量、粒径和电位作为考察指标，结合星点设计-效应面法优化处方。建立大鼠在体单向肠灌流模型，并通过肠腔有效吸收系数（P_eff）、吸收速率常数（K_a）和药物吸收剂量分数（f_a）研究不同浓度SRL CS-DCA的肠吸收特性。结果 SRL CS-DCA最优处方：载体浓度（CS-DCA）为10 mg·mL^-1，药物与载体质量比为20%，该条件下制备得到的SRL CS-DCA带正电荷（37.0±2.7）mV，粒径（182.2±5.7）nm，包封率>90%，载药量（15.8±0.5）%。SRL CS-DCA经大鼠全肠后，反映药物肠吸收程度的评价指标P_eff、K_a和f_a均较SRL有显著提高（P<0.05）；不同浓度的SRL CS-DCA在大鼠全肠段的P_eff、K_a、f_a值无显著性差异，提示胶束在10~100 μg·mL^-1吸收无浓度抑制，吸收特征为被动转运的线性动力学过程，推测其可能的吸收机制为被动扩散。结论 SRL制备成聚合物胶束后，对其在大鼠小肠的吸收具有明显的促进作用，从侧面证明SRL CS-DCA能有效改善SRL口服生物利用度。

Abstract:

OBJECTIVE To prepare sirolimus(SRL) polymer micelles and investigate its effects on the absorption kinetics of rat intestine. METHODS The SRL CS-DCA micelles were prepared by solvent evaporation using deoxycholic acid grafted chitosan(CS-DCA) as carrier. The encapsulation efficiency, drug loading, particle size and potential were taken as the evaluation indexes, and the formulation was optimized by the central composite design-response surface optimization method. In situ single pass perfusion model of rat was set up to investigate intestinal absorption characteristics of SRL CS-DCA micelles with different concentrations. Meanwhile, the intestinal absorption coefficient(P_eff), absorption rate constant(K_a) and the dose fraction(f_a) were used to evaluate drug absorption. RESULTS The optimum formulation of SRL CS-DCA micelles was as follows:the concentration of CS-DCA was 10 mg·mL^-1, and the mass ratio of drug to carrier was 20%. Under this condition, the system had the positive charge of (37.0±2.7)mV, particle size of (182.2±5.7)nm, the encapsulation efficiency greater than 90%, and the drug loading of (15.80±0.5)%. After the SRL CS-DCA micelles passed through the rat intestine, the P_eff, K_a and f_a were significantly higher than those of SRL(P<0.05). There was no significant difference in the P_eff, K_a and f_a values of SRL CS-DCA micelles with different concentration in the whole intestine of rats, suggesting that the micelles had no concentration inhibition at 10-100 μg·mL^-1, and the absorption characteristics were linear dynamics of passive transport. It was speculated that its possible absorption mechanism was passive diffusion. CONCLUSION The SRL CS-DCA micelles can enhance effect on intestine absorption of SRL monomer, which proves that SRL CS-DCA can effectively improve the oral bioavailability of sirolimus.