Preparation of freeze-dried long-circulation oridonin liposomes and their pharmacokinetics in rats

Abstract

To prepare freeze-dried long-circulation oridonin liposomes with optimized parameters. Ethanol injection method followed by freeze-drying was used to prepare the liposomes. Sephadex column was used to purify liposomes. Effects of formulation factors on entrapment efficiency of long-circulation oridonin liposomes were studied. The particle size, distribution and in vitro release were determined. Pharmacokinetics of oridonin liposomes in rats was determined by HPLC and the pharmacokinetic parameters calculated by Kinetica(TM) software were compared with conventional oridonin liposomes and solution. The optimized lipid formulation for long-circulation liposomes was composed of soy lecithin, cholesterol and DSPE-PEG 2000 with a ratio of 1:0.5:1.8(w/w). The ratio of drug to lipid was 1:6. Freeze-drying protectant was a mixture of glucose and mannitol (3:1). The entrapment efficiency (EE) of long-circulation oridonin liposomes was about 65%. The particle size of liposomes after hydrolyzation was 164 nm with good DPI. The liposomes showed a sustained drug release in vitro. Intravenous injected oridonin fitted with two-compartment pharmacokinetic model. The MRT of long-circulation liposomes was 2 times and 6 times and AUC was about 2 times and 3 times of conventional liposomes and oridonin solution, respectively. Freeze-dried liposomes with high EE have been obtained by the proposed approach. This long-circulation liposomes extend oridonin half time and significantly increase AUC in rats.