Development Of Oleanolic Acid Liposome

As one kind of new drug carrier, liposomes were studied more in recent years, it is one kind of new dosage form belonging to target-oriented drug delivery system, it can entrap both fat-soluble and water-soluble drugs, it can delay in-vivo release. Since liposomes are biomembrane-like vesicles, they were mainly licked up by the reticulo-endothelial system when enter into the human body, thus activate the immunity function, and change the in-vivo distribution of the enveloped drugs, making the drug mainly distributed at the liver, the spleen, the lung and the marrow organizes, thus enhances the treatment index, reduces the therapeutic dosage and the toxicity of the drug. Therefore, liposome acts as a drug delivery system with great potential.Oleanolic acid (OA) belongs to Pentacyclic triterpenoid compounds, as a natural chemical product, it presents extensively in plants, in the form of free or combined glycosides, it has wide range of pharmacological affects, it is mainly used for the treatment of acute jaundice hepatitis and chronic viral hepatitis currently, since it's good efficacy, low toxicity, less side effects, it has very broad prospects of development. We investigated the effect of preparation methods, formulae and so on factors on the encapsulation efficiency of Oleanolic acid liposome, studied its leakage rate, hemolytic and pharmacokinetic characteristics after intravenous injection in rats.Oleanolic acid liposomes were prepared by ethanol injection method, after screened by orthogonal experimental design, the optimized formula was drugs: phospholipids =1:15(weight ration), cholesterol: phospholipids =1: 8 (weight ratio), Tween-80: phospholipids =1:1(weight ratio), the pH is 6.5. To enhance the storage stability of Oleanolic acid liposome, Oleanolic acid liposome freeze-dried powder was produced by freeze-drying method. To prevent the aggregation and fusion of lipid during freeze-drying process, mannitol was used as cryoprotective additives. The content determination was conducted by HPLC. Glucan gel column chromatography was used to determine the encapsulation efficiency of Oleanolic acid liposome. Through the transmission electron microscopy, the form of liposome was observed, with Zetasizer 3000HS laser particle size analytical instrument, the particle size and zeta potential of the particles was measured. Results showed that the liposome was intact spherical or oval-shaped ball vesicle, encapsulation efficiency was over 80%, the mean particle diameter was 431.6nm, and Zeta potential was -21.5mV.After comparing the phenomena of test tubes with negative and positive control, Oleanolic acid liposomes were found not to cause hemolysis in-vitro. Liposomes were preserved at room temperature (29℃to 31℃) and 4℃for seven days respectively ,determine the encapsulation efficiency, leakage rates were 6.5 %,3.1 % separately, the results showed that the better storage for liposomes temperature is 4℃.The pharmacokinetic characteristics of a single dose intravenous injection of oleanolic acid liposomes in rats were investigated compared with that of oleanolic acid solution, and the data were calculated by means of 3p97. According to compartment-model fitting results, oleanolic acid liposomes and oleanolic acid solution were both fitted with two compartment-model with a weight of 1/C. T1/2βof oleanolic acid liposomes and solution was 33.59±12.53min and 15.65±7.91min respectively, and the clearance rate was 2.82±1.57ml·min-1 and 5.94±3.14ml·min-1. As the results calculated according to statistical moment theory; AUC of oleanolic acid liposomes and solution was 3232.60±27.43μg·min·ml-1 and 151.13±10.28μg·min·ml-1 respectively, and MRT was 29.06±1.01min and 18.19±1.02min. Many pharmacokinetic parameters showed significant difference(P<0.05).