Reduction-responsive release property of egg phosphatidylcholine liposomes incorporating benzyl disulfide

Abstract

Reduction-responsive liposome was prepared by incorporating benzyl disulfide in egg phosphatidylcholine (egg PC) liposomal bilayer. The fluorescence quenching degree of calcein enveloped in egg PC liposome bearing benzyl disulfide decreased from 62.7% to 49.2% and the mean hydrodynamic diameter of the liposome decreased from 276nm to 206nm when the egg PC to benzyl disulfide weight ratio increased from 20:0 to 20:10. The liposomes bearing benzyl disulfide were multi-lamellar vesicles on TEM photos. It was confirmed by Raman spectroscopy that benzyl disulfide was loaded in the liposomal bilayer. The release degree of calcein enveloped in liposome incorporating benzyl disulfide was investigated for 24h at 25°C, 37°C, and 45°C, when the concentration of dl-dithiothreitol (DTT) was 0mM, 5mM, 10mM and 30mM. At all the DTT concentrations tested, the release degree was more extensive as the temperature was higher. At all the temperatures tested, the release degree became more extensive as the DTT concentration increased. For example, the maximum release degree at 37°C of calcein loaded in liposome of which egg PC to benzyl disulfide weight ratio was 20:5 increased from 2.9% to 14.8% when DTT concentration increased from 0mM to 10mM. DTT could reduce benzyl disulfide to benzyl thiols and the fragments of benzyl disulfide would re-orient due to its polarity change in the liposomal membrane, resulting in the membrane fluctuation and the promoted release. At all the temperatures and all the DTT concentrations tested, the release was more sensitive to the DTT concentration as the benzyl disulfide content in liposome was higher, indicating that the reduction of the disulfide compound was responsible for the promoted release.