title: High sensitivity differential scanning calorimetry study of DNA-cationic liposome complexes.
abstract: OBJECTIVE
  To investigate plasmid DNA interactions with liposomes prepared from dimyristoylglyceroethylphosphocholine (EDMPC) and DOPE using high sensitivity differential scanning calorimetry (HSDSC).
  
  
  METHODS
  Large unilamellar liposomes of EDMPC with DOPE (mol ratio 0-50%) were prepared. Plasmid DNA was added to give a final DNA/lipid (-/+) charge ratio of 0.5. Samples were placed into an HSDSC and cooled to 3 degrees C, held isothermally for 30 min and then the temperature was ramped to 120 degrees C at a rate of 1 degree C/min.
  
  
  RESULTS
  On heating EDMPC liposomes, the main phase transition occurred at 21.2 degrees C, with a low temperature shoulder on the endothermic peak. At low DOPE concentrations the main phase transition temperatures and enthalpies of transition were lower than for pure EDMPC, with a peak corresponding to a pure EDMPC phase occurring at DOPE concentrations of 12-17 mol%. At 50 mol%, no main transition endotherm was observed. DNA solution produced two endothermic peaks with numerous 'satellite' peaks indicating thermal denaturation. DNA binding to EDMPC changed the shape of the thermogram, indicating alteration in lipid packing within the bilayer. DNA induced demixing in the bilayers of DOPE-containing liposomes.
  
  
  CONCLUSIONS
  HSDSC provided information for characterizing liposome formulations and DNA interactions with such vesicles.
authors.affiliation: School of Pharmacy, University of London, 29-39 Brunswick Square, London, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Saunders
authors.forename: Kevin M G
authors.initials: KM
authors.lastname: Taylor
authors.forename: Duncan Q M
authors.initials: DQ
authors.lastname: Craig
authors.forename: Karen
authors.initials: K
authors.lastname: Palin
authors.forename: Hazel
authors.initials: H
authors.lastname: Robson
mesh_terms: D002152:Calorimetry, Differential Scanning; D002412:Cations; D004247:DNA / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000031:analogs & derivatives* / Q000737:chemistry; D009690:Nucleic Acid Conformation; D044367:Phase Transition; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D015203:Reproducibility of Results; D013696:Temperature; D053835:Unilamellar Liposomes
chemical_list: C108836:1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine; D002412:Cations; D010714:Phosphatidylethanolamines; D053835:Unilamellar Liposomes; C020888:1,2-dielaidoylphosphatidylethanolamine; D004247:DNA; D004134:Dimyristoylphosphatidylcholine