title: Protein encapsulation in unilamellar liposomes: high encapsulation efficiency and a novel technique to assess lipid-protein interaction.
abstract: OBJECTIVE
  To encapsulate a large amount of protein (superoxide dismutase, SOD) into unilamellar liposomes using a simple process and to investigate the lipid-protein interaction.
  
  
  METHODS
  To achieve protein encapsulation, preformed unilamellar empty liposomes were mixed with SOD and subjected to freeze-thaw cycling. To investigate the lipid-protein interaction, a novel light scattering technique was used.
  
  
  RESULTS
  Up to 50% protein encapsulation was achieved at ∼150 nm. There was no significant change in particle size following the freeze-thaw cycling. SOD had a strong interaction with DPPC liposomes containing high concentration of cholesterol. Light scattering data revealed that in some cases the SOD molecules were present inside the lipid bilayer.
  
  
  CONCLUSIONS
  The method reported here allows great flexibility in the manufacturing process as the liposome preparation and protein-loading operations can be separated. Accordingly, empty liposomes can be prepared without concern about protein stability, making the manufacturing process more flexible and easy to control and ultimately leading to improved product quality. To explain the SOD-lipid interaction, a "pocket-embedding" theory was proposed. The encapsulation method reported here can be applied to hydrophilic small molecules as well as most hydrophilic proteins to achieve high encapsulation efficiency.
authors.affiliation: Department of Pharmaceutical Sciences, University of Connecticut, 69 N Eagleville Rd U3092, Storrs, Connecticut 06269, USA.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Xu
authors.forename: Antonio
authors.initials: A
authors.lastname: Costa
authors.forename: Diane J
authors.initials: DJ
authors.lastname: Burgess
mesh_terms: D000818:Animals; D002417:Cattle; D002784:Cholesterol / Q000378:metabolism; D005615:Freezing; D008027:Light; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D010316:Particle Size; D012542:Scattering, Radiation; D013482:Superoxide Dismutase / Q000008:administration & dosage* / Q000378:metabolism*; D053835:Unilamellar Liposomes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D008055:Lipids; D053835:Unilamellar Liposomes; D002784:Cholesterol; D013482:Superoxide Dismutase