Study On Long-circulation Effects And ABC Phenomena Of Emodin Liposomes Mixed With Different Forms Of PEG

ObjectiveDrug would be quickly taken up by the Reticuloendothelial system(RES)in vivo when the drug was delivered by ordinary liposomes.The liposomes were eliminated as exogenous substances,making it difficult to achieve effective therapeutic concentrations at the target sites.In this study,we used emodin as a model drug and made polyethylene glycol and its derivatives(m PEG 2000,DSPE-PEG 2000,Chol-PEG 2000)mixing with ordinary liposomes.The PEG could form hydrated membranes on their surfaces,cover the opsonin binding sites and increase the steric hindrance.So the liposomes could prolong the circulation time of liposomes in vivo,avoiding identified and taken up by RES.However,the accelerated blood clearance(ABC)phenomenon was caused when the PEGylated liposomes were administered repeatedly,which lead to reduce the circulation time of drug.In this study,we performed a pharmacokinetic experiment and detected the levels of anti-PEG Ig M in rats.The weak ABC phenomenon liposome has been selected which can provide a reference of PEGylated liposomes for further study.MethodsThe central composite design and response surface method were adopted to optimize the preparation of emodin liposomes,taking drug encapsulation efficiency as the evaluation index and ratio of drug-lipid,cholesterol-lipid andPEGylated molecules-lipid as the investigation factors.Emo-Lip,m PEG-EmoLip,DSPE-Emo-Lip and Chol-Emo-Lip were prepared by film-ultrasonic dispersion.The particle sizes were measured with dynamic laser scattering method,and the morphologies were observed by transmission election microscopy(TEM).Meanwhile,their entrapped efficiency(EE%),drug loading capacity(LC)and leakage(LK%)were studied with mini-column centrifugation method.Besides,the release properties of liposomes were inspected in p H7.4,p H5.8 and 5%FBS PBS by dynamic dialysis method.The emodin liposomes were injected to rats through caudal vein respectively.An HPLC method was established to determine concentrations of emodin in plasma samples and the kinetics equations were fit according to compare the 3 emodin liposomes.In the end,the ABC phenomena of 3 emodin liposomes mixed with different forms of PEG were studied by the pharmacokinetic experiment and anti-PEG Ig M level ELISA detection.ResultsThe prepared prescription of emodin long-circulating liposomes were determined as 1:20 of drug-lipid,1:5 of cholesterol-lipid,1:20 of PEGylated molecules-lipid.The particle sizes of Emo-Lip and 3 emodin liposomes were between 123~143 nm and the distributions were more homogeneous in which Emo-Lip and m PEG-Emo-Lip were larger.The EE% of Emo-Lip and 3 emodin liposomes was all above 88.25%,the LC was between 32.21~35.75 mg/g and the leakage was low.The release rate in p H7.4,p H5.8 and 5%FBS PBS was Emo-Lip>DSPE-Emo-Lip>m PEG-Emo-Lip>Chol-Emo-Lip with the same tendency.In the study of pharmacokinetic,compared to Emo-Lip,mean residence time(MRT)of m PEG-Emo-Lip,DSPE-Emo-Lip and Chol-Emo-Lip was increased 1.72,3.52,2.42 folds.Areas under the concentration-time curve(AUC)was increased 2.23,5.30,3.83 folds.Clearances(CL)in plasmas was decreased 0.44,0.19,0.26 folds.In the study of ABC phenomenon,comparedto the corresponding pharmacokinetic parameters in the first administration,MRT of m PEG-Emo-Lip,DSPE-Emo-Lip and Chol-Emo-Lip in the third administration was decreased 0.87,0.69,0.91 folds,AUC was decreased 0.69,0.53,0.82 folds and CL in plasmas was increased 1.45,1.82,1.20 folds.Anti-PEG Ig M was produced on the third day after the first administration in rats.The number of antibody decreased dramaticly in vivo after the second administration.A small amount of anti-PEG Ig M was produced on the third day after the second administration.Antibody was consumed to the level of ordinary liposome group after the third dose,and not increased any more.ConclusionsThe central composite design and response surface method could be used to choose the best prescription of emodin liposomes,with high precision and good reproducibility.The film-ultrasonic dispersion could be used to prepare Emo-Lip and 3 emodin liposomes with good preparation properties.Chol-EmoLip had a best sustained-release character.Pharmacokinetic experiment had illustrated that m PEG-Emo-Lip,DSPE-Emo-Lip and Chol-Emo-Lip could prolong MRT,which demonstrated long-circulation effects.The DSPE-Emo-Lip showed obvious long-circulation effect.Pharmacokinetic experiment and ELISA detection had illustrated that m PEG-Emo-Lip,DSPE-Emo-Lip and Chol-Emo-Lip could decrease MRT and AUC,and increased CL and anti-PEG Ig M level after repeated injections.The results proved ABC phenomena of PEGylated liposomes,and ABC phenomenon of Chol-Emo-Lip showed less.