Encapsulation of Plasmid DNA into Dehydrated-Rehydrated Liposomes and Its Delivery to Cells Omima A. Sammour Department of Pharmaceutics, Faculty of Pharmacy, Zagazig University, Zagazig (Egypt) Present address: Department of Pharmaceutics, Faculty of Pharmacy, King Saud University, Riyadh (Saudi Arabia) The dehydration-rehydration (DR) technique was adopted in order to
improve the encapsulation efficiency of plasmid pBR322 DNA in liposomes. Producing liposomes by the DR technique (DRV) resulted in more than 3 fold increase in liposomal uptake of DNA compared to multilamellar liposomes (MLV) prepared by the mechanical dispersion of lipids and having the same lipid composition. Electron micrograph of negatively stained DRV indicated the formation of heterogeneous population of large aggregates or fused vesicles having diameters up to 250 nm. The biological activity of the liposome-encapsulated plasmid was determined by transformation assays. The incubation of intact liposomes, containing entrapped plasmid DNA, with competent Escherichia coli cells in the standard transformation mixture resulted in the appearance of tetracycline and ampicillin resistant colonies at approximately the same frequency obtained for free plasmid DNA. Importantly, this frequency was unaffected by the addition of deoxyribonuclease I (DNase I) to the incubation mixture, whereas transformation by free plasmid DNA was totally eliminated after treatment with DNase I. Key words Cell transformation · DNA · DNase I · Escherichia coli · Liposomes, dehydration-rehydration · Plasmids |
