| Glycyrrhetinic acid(GA)is a pentacyclic triterpenoid extracted from licorice.Owing to its antioxidant activities as well as the abilities of scavenging free radicals and protecting cells from oxidative damage,GA has important application in cosmetics.However,the poor water solubility of GA(only 6.32 mg/L)greatly limits its application.As a new type of nano liposomes,glycethosomes can improve the solubility,stability and transdermal effects of drugs.In this study,GA loaded glycethosomes were prepared with soybean lecithin(PC60),and the stability and transdermal effects of GA glycethosome vesicles were investigated.The stabilization and transdermal mechanisms of the vesicles were explored.On this basis,the vesicles were further modified.Poloxamer 407(P407)was added as a modifier to improve the stability of the vesicles.Eventually,the antioxidant effects of GA glycethosomes were evaluated.Firstly,the particle size,PDI,entrapment efficiency and storage stability were selected as indexes to screen out the best formulation and preparation process of GA glycethosomes.The particle size of GA glycethosomes was the smallest and the stability was the best under the following conditions: the mass ratio of PC60 to cholesterol was 6:1,the drug loading was 2.5mg/m L,the volume fraction of glycerol was 50%,the volume fraction of ethanol was 25%,the hydration temperature was 45 ℃,the hydration time was 100 min and the ultrasonic time was150 s.The particle size was(94.50±3.45)nm,the PDI was 0.216±0.006,and the entrapment efficiency was(99.80±0.35)%.The prepared GA glycethosome vesicles showed multilamellar spherical structure.Different contents of glycerol and ethanol had significant effects on the microviscosity and viscosity of lipid vesicles.When the glycerol volume fraction was 50% and the ethanol volume fraction was 25%,the microviscosity in the hydrophilic and hydrophobic regions of the vesicles were both large,which indicated that the fluidity of the vesicle membranes decreased.Meanwhile,the viscosity of GA glycethosome vesicles was very large,which was conducive to reduce the fluidity of the vesicles,to prevent aggregation and fusion between the vesicles,as well as to improve the stability of the vesicles.The effect of GA glycethosomes on the transdermal absorption of GA and the transdermal mechanisms were investigated through Franz diffusion cells method.Compared with the control group,glycethosomes significantly improved the transdermal effect of GA,and the total skin permeation percentage was(20.67±0.91)%.The attenuated total reflection-Fourier transform infrared spectroscopy results showed that GA glycethosomes could enhance the hydration and change secondary structures of keratins.Consequently,it could enhance the fluidity of lipids in the stratum corneum,so as to improve the transdermal effect of GA.In addition,the prepared GA glycethosomes had good storage stability at 4 ℃.After stored at 25 ℃ for 90 days,the particle size of GA glycethosomes increased to(186.40±2.44)nm.After stored at 42 ℃ for 30 days,the particle size of GA glycethosomes increased to(664.75±11.01)nm.GA glycethosomes had good dilution stability,but poor ionic stability.Secondly,in order to further improve the stability of GA glycethosomes,P407 was used as a modifier to modify the vesicles,and the stability of the vesicles was improved by the effect of steric stabilization.When the mass ratio of PC60 to P407 was 5:1,the storage stability of the vesicles was the best.Under such condition,the particle size of P407-GA glycethosomes was(129.20±3.19)nm,the PDI was 0.227±0.010,and the encapsulation efficiency was(99.36±0.28)%.It was observed by TEM that the vesicles were still multilayer spherical structure.The results of permeation experiments showed that the addition of P407 would not affect the transdermal effect of GA glycethosomes,and the total skin permeation percentage of GA was(22.52±0.95)%.P407-GA glycethosomes had excellent storage stability at 4 ℃ and25 ℃.After stored at 42 ℃ for 30 days,the particle size of P407-GA glycethosomes increased to(299.70±10.41)nm.Compared with the vesicles before modification,the high temperature storage stability of P407-GA glycethosomes was improved significantly owing to the effect of steric stabilization.P407-GA glycethosomes still had good dilution stability,and the ionic stability was improved.Finally,the antioxidant properties of P407-GA glycethosomes were explored by chemical methods and cell experiments.The results showed that the antioxidant abilities of GA was poor due to its low water solubility.P407-GA glycethosomes significantly improved the antioxidant abilities of GA due to the improvement of the water solubility of GA.When the concentration of GA was 1000 μg/m L,the scavenging rate of hydroxyl radicals increased from(3.35±0.67)%to(33.07±1.01)%.When the concentration of GA was 250 μg/m L,the scavenging rate of superoxide anion radicals increased from(5.36±1.55)% to(61.52±3.22)%.The cell experiment results showed that GA and P407-GA glycethosomes had a protective effect on the oxidative damage caused by UVB.When GA concentration was 1.25 μg/m L,the viability of the cells treated with P407-GA glycethosomes increased from(81.31±1.68)% to(93.23±3.50)%,and the CAA value increased significantly,compared with the cells treated with GA.When GA concentration was 1.25 μg/m L,the activity of SOD increased from(4.71±0.29)U/mg to(6.36±0.33)U/mg,and the activity of GSH-Px increased from(80.86±3.26)U/mg to(94.30±4.39)U/mg.The level of IL-1β decreased from(16.43±2.39)pg/m L to(12.58±0.89)pg/mL. |
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