M.M. MADY

Biophysics Department, Faculty of Science, Cairo University, 12613 Giza, Egypt

There is an efficient, systemic transgene expression in many cell lines (in vitro) by using anionic liposomes, composed of equimolar amounts of 1, 2-dilauroyl-sn-glycero-3-phosphoethanolamine (DLPE), 1, 2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) and cholesterol (CHOL). 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) is added to this liposomal formulation to increase the stability of small unilamellar vesicles in the presence of fetal calf serum (FCS). The liposomal stability was studied by monitoring the retention of a trapped marker, carboxyfluorescien (CF), in the internal liposome compartment. The liposomes containing DOPC had a lower stability in serum compared to the DOPC free liposomes. The extremely low retention in the DOPC liposome was ascribed to a formation of the inverted hexagonal phase of the liposomal membrane. A higher sodium deoxycholate detergent concentration is needed to solubilize DLPE/DOPS/CHOL (1:1:1) liposomes than DLPE/DOPC/DOPS/CHOL (1:1:1:1) liposomes. Phosphorus-31 nuclear magnetic resonance (31P-NMR) is used to investigate the lamellar (Lα) → hexagonal (HII) phase transition of unilamellar lipid vesicles containing DOPC. It was found that unilamellar lipid vesicles containing DOPC are in the bilayer state at pH 4 and undergo a lamellar (Lα) → hexagonal (HII) phase transition at pH 8.

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