Effect of preparation method and cholesterol on drug encapsulation studies by phospholipid liposomes

Abstract

Unilamellar liposomes, prepared from synthetic lipid mixture of DMPC and DMPG either by sonication or extrusion, were used to entrap water soluble and water insoluble molecules to investigate the efficacy of encapsulation by different liposome preparation methods. In the case of entrapment of hydrophilic protein cytochrome-C, the solutions were subjected to a series of ultrafiltration steps to eliminate any free protein outside the vesicles. It was observed that the protein could be encapsulated by the vesicles only if cholesterol was present in the bilayer. The release of cytochrome-C was observed spectrophotometrically upon vesicle-breakdown. The amount of protein encapsulated depended on the method of preparation and was found to be 10 times greater in extruded liposomes compared to those produced by sonication. Hydrophobic Vitamin E, on the other hand, could be encapsulated in the liposome bilayer, independently of the presence of cholesterol and the method of preparation. These fundamental results can be used to develop more efficient drug encapsulations and to have better understanding about their release.

Keywords::

• Sonication
• extrusion
• DMPC/DMPG liposomes
• cytochrome-C
• Vitamin E

Acknowledgements

The authors thank Prof. T. Varnali for her valuable contribution in PM3 calculations.

Declaration of interest

The authors thank Bogazici University Research Fund (Project Numbers 06HB501 and 09B509P) for financial support. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.