Optimization Of The Preparation Conditions Of Madecassoside Liposomes And Evaluation Of Its Stability

As one of the main components of triterpenoid saponins in centella asiatica,madecassoside (MA) has the effects of scar repair, antioxidation, anti-ulcer, anti-inflammation,anti-depression, immunomodulatory, etc. MA has significant effects on the treatment ofsurgical wounds, burns, infectious hepatitis, epidemic cerebrospinal meningitis, inhibition oftumor cells proliferation and other diseases in clinically. However, MA is a polar moleculewith large molecular weight, and has poor membrane permeability, thus it is difficult to acrossthe skin epidermis. In order to overcome the aforementioned disadvantage, MA was wrappedin a selected carrier named liposome, which could contribute to the improvement of skintransmittance of MA by improving the permeability of cell membranes, due to the structuralsimilarity between phospholipid bilayer membranes of liposomes and phospholipid bilayer ofskin epidermis.This dissertation focused on the stability of MA, and then systematically investigated thepreparation methods and conditions, modification and stability of MA liposomes. The specificresearch ideas were summarized briefly as follows.(1) Experimental parameters such as temperature, light, pH value of the phosphatebuffered solution (PBS) on the stability of MA were discussed in details. These experimentalresults reveal that, MA was a relatively stable material, and the most stable conditions werelow temperature (4℃), photophobic and pH=7.0, in which the retention rate of MA was stillabove96%after48h.(2) MA liposomes were successfully prepared by film dispersion, the free MA wasseparated from MA liposomes by dialysis and further determined by high performance liquidchromatography (HPLC), which was used to calculate the encapsulation efficiency of MAliposomes. The optimum conditions of MA liposomes were optimized by using single factorexperiments and response surface methodology (RSM) in this experiment to achievemaximum drug encapsulation efficiency. The optimum preparation conditions were found tobe0.4424g of MA,8.174ratio of egg yolk lecithin to cholesterol,65s of ultrasonic time,pH=7.0of the PBS. The greatest encapsulation efficiency of MA liposomes was41.41%under the optimum conditions, which was very close to the theoretical value of41.73%, and had a good reproducibility.(3) In order to further improve the stability of MA liposomes, polyethylene glycol (PEG)was used to modify the MA liposomes under the optimum conditions. By evaluating theappearance and encapsulation efficiency of the PEG coated MA liposomes, it is concludedthat, the maximum encapsulation efficiency of46.27%was obtained when the concentrationof PEG-1500was3%, and had a good reproducibility.(4) The morphology, particle size, distribution and Zeta potential of liposomes preparedat the optimum conditions were determined by scanning electron microscope (SEM) and laserparticle-size analyzer. The appearance of liposomes were spherical, and the average particlesize and Zeta potential of MA liposomes were282.7nm and-35.1mV, respectively, whilethose of PEG coated MA liposomes were350.8nm and-44.6mV, respectively, whichindicate that the particle size of MA liposomes increased significantly after PEG coated. Inaddition, the physical and chemical stabilities of MA liposomes were also significantlyinfluenced after PEG coated.