| The major bioactive components in Rhodiola species is salidroside.Salidroside has been shown to possess the functions such as resisting anoxia,fatigue and radiation.It's reported to be widely used in medicine,food and cosmetic.Unfortunately,functional foods containing salidroside presently developed have some drawbacks,such as low extraction efficiency,low purity and low bioavailability.Separation and purification of salidroside was operated systemically.Salidroside nano-liposomes were prepared by different methods and the physicochenmical properties of salidroside nano-liposomes were investigated.Furthermore,salidroside pro-liposomes were prepared by vacuum freeze-drying and rehydration and stability was investigated.A new mechanistic mathematical model for salidroside release from liposomes was proposed.Radioprotection of salidroside nano-liposomes was studied and in vivo tissue distribution and pharmacokinetic parameters of salidroside extract and salidroside nano-liposomes were investigated after oral administration.Microwave-assisted extraction was employed to separate salidroside from Rhodiola species. Salidroside was obtained in a yield of 80%under the following condition:microwave powder,130 W; ethanol concentration,20%(v/v);solid/liquid ratio,1:29(g/mL),irradiation time,60 s.MAE gives almost 80%extraction efficiency at 1 min,whereas traditional heating extraction method gives about 60% extraction efficiency at 120 min.Ethanol used in conventional reflux is second higher than one used in MAE.Results showed DA201 displayed the optimal adsorption and desorption properties.The static and dynamic adsorption capacities of DA201 were 21.88 and 13.25 mg/mL,respectively.The purity of the partially purified salidroside product was improved from 3.8%to 13.8%by one step separation and purification with 50%ethanol.Further purification by ultra-filtration was used to achieve the optimization: operation pressure was 0.05 MPa,temperature was 40℃and extract was diluted 3 times.Through cut-off MW 10000 and 3000,salidroside purity was 30.65%and 38.72%respectively and salidroside retention ratio was 86.2%and 80.4%,respectively.Salidroside nano-liposomes were prepared by using five different methods:thin film evaporation, sonication,reverse phase evaporation,melting,and freezing-thawing.Results showed the encapsulating efficiency of liposomes was the following:freezing-thawing＞thin film evaporation＞reverse phase evaporation＞melting and sonieation.Loading capacity of salidroside had significant effect on encapsulating efficiency,average diameter and zeta potential of nano-liposomes.Liposomal systems prepared by sonication,melting and reverse phase evaporation displayed better dispersivity.Determination of leakage of salidroside from different liposomal systems revealed that melting method had the lowest leakage of 10%and 15%,at 4 and 30℃after one month of storage,respectively.In all cases,a straight-line leakage behavior of salidroside was found.This revealed that the leakage of salidroside was a diffusion process from the membrane of nano-liposomes.Furthermore,the storage stability of different liposomal systems showed that salidroside liposomes prepared by melting had a better physicochemical stability.Salidroside nano-liposomes showed the slower increase in particle size than liposomes without salidroside.Stability of salidroside nano-liposomes depended on dimensional structure.Salidroside nano-liposomes were prepared by ethanol injection method.Higher encapsulating efficiency of salidroside was obtained with cholesterol to lipid mass ratio of 1:4,Tween 80 and lipid to the molar ratio of 1:2,and ion strength in a range 20-50 mmol/L.The particles of nano-liposomes were below 100 nm and zeta potential was in the range of-10 and -20 mV.The release study of salidroside in vitro from nano-liposomes exhibited a prolonged release profile as studied over a period of 24 h.Based on the above experiments,optimizations were investigated according to encapsulating efficiency and leakage ratio after one month of salidroside.Results showed optimizations were obtained with cholesterol to lipid mass ratio of 1:5,Tween 80 and lipid to the molar ratio of 1:2,and ion strength was 50 mmol/L.And encapsulating efficiency was 45.6%,leakage ratio after one month was 8.5%,particle size was 147.6 nm,zeta potential was -12.5 mV.Particle size of salidroside nano-liposomes was increased 21%and 250%after 180 days at 4℃and 30℃,respectively.AFM scanning image showed particle size of salidroside nano-liposomes increased constantly during the storage.MDA content increased and pH value decreased constantly. Instability was exaggerated with a rise in temperature.Mannitol was used as the optimal cryprotectant to prepare salidroside pro-liposomes.Salidroside pro-liposomes showed full and compact appearance.After rehydration,encapsulating efficiency reached above 40%and retention ratio was above 90%.Compared with salidroside nano-liposomes of 190.1 nm before freezing-drying,particle size was 223.9 nm after rehydration.According to FTIR spectra,mannitol and polar group of lipid interacted and created hydrogen bonds,which could protect the bilayer of liposomes from being destroyed during freezing-drying.There happened almost change in appearance, particle size,encapsulating efficiency,pH value and MDA content of salidroside pro-liposomes in the condition of 20 or 40℃,stored 60 days.Results showed stability of salidroside pro-liposomes was satisfied. Results on moisture absorption experiments illuminated salidroside pro-liposomes must be avoided the higher relatively humidity condition during storage.The mechanistic mathematical model was developed here for quantitative description of the release characteristics.Results showed the model gave excellent correlative accuracy within the release period.The model parameters,diffusion resistant,were theoretical sound and showed good trend,which could be correlated to various factors such as cholesterol content,Tween80 and salidroside loading capacity.The model investigated the effect of various factors on burst release profiles of salidroside based on limited experimental data.The model parameters can be used to describe the underlying mechanisms of the certain salidroside release process as well as for salidroside delivery device design and process optimization.These results suggested the new mechanistic mathematical model was practical for in vitro release of salidroside from liposomes.Experimental results on sub-acute or sub-chronic X-radiation injured mice showed salidroside nano-liposomes had excellent radioprotection effect on sub-acute or sub-chronic X-radiation.In vivo tissue distribution of salidroside was different after oral salidroside nano-liposomes and salidroside extract. Salidroside concentration in liver and brain after oral salidroside nano-liposomes was higher than that of salidroside extract.Pharmacokinetics showed salidroside nano-liposomes had slower release rate,lower clearance rate and was delayed circulation time than salidroside extract.The bioavailability of salidroside was been improved greatly.Nano-liposomes can be used as an excellent carrier for salidroside.
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