title: Protein antigen adsorption to the DDA/TDB liposomal adjuvant: effect on protein structure, stability, and liposome physicochemical characteristics.
abstract: OBJECTIVE
  Understanding the nature of adjuvant-antigen interactions is important for the future design of efficient and safe subunit vaccines, but remains an analytical challenge. We studied the interactions between three model protein antigens and the clinically tested cationic liposomal adjuvant composed of dimethyldioctadecylammonium (DDA) and trehalose 6,6'-dibehenate (TDB).
  
  
  METHODS
  The effect of surface adsorption to DDA/TDB liposomes on colloidal stability and protein physical stability/secondary structure was investigated by dynamic light scattering, circular dichroism, Fourier transform infrared spectroscopy and differential scanning calorimetry.
  
  
  RESULTS
  Bovine serum albumin and ovalbumin showed strong liposome adsorption, whereas lysozyme did not adsorb. Upon adsorption, bovine serum albumin and ovalbumin reduced the phase transition temperature and narrowed the gel-to-liquid phase transition of the liposomes implying interactions with the lipid bilayer. The protein-to-lipid ratio influenced the liposome colloidal stability to a great extent, resulting in liposome aggregation at intermediate ratios. However, no structural alterations of the model proteins were detected.
  
  
  CONCLUSIONS
  The antigen-to-lipid ratio is highly decisive for the aggregation behavior of DDA/TDB liposomes and should be taken into account, since it may have an impact on general vaccine stability and influence the choice of analytical approach for studying this system, also/especially at clinically relevant protein-to-lipid ratios.
authors.affiliation: Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen Ø, Denmark. mette.hamborg@sund.ku.dk
authors.forename: Mette
authors.initials: M
authors.lastname: Hamborg
authors.forename: Lene
authors.initials: L
authors.lastname: Jorgensen
authors.forename: Anders Riber
authors.initials: AR
authors.lastname: Bojsen
authors.forename: Dennis
authors.initials: D
authors.lastname: Christensen
authors.forename: Camilla
authors.initials: C
authors.lastname: Foged
mesh_terms: D000276:Adjuvants, Immunologic / Q000737:chemistry*; D000327:Adsorption; D000818:Animals; D002417:Cattle; D003102:Colloids / Q000737:chemistry; D006017:Glycolipids / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D009113:Muramidase / Q000737:chemistry*; D010047:Ovalbumin / Q000737:chemistry*; D044367:Phase Transition; D055550:Protein Stability; D017433:Protein Structure, Secondary; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012710:Serum Albumin, Bovine / Q000737:chemistry*
chemical_list: D000276:Adjuvants, Immunologic; D003102:Colloids; D006017:Glycolipids; D008081:Liposomes; D000644:Quaternary Ammonium Compounds; C507803:trehalose 6,6'-dibehenate; C015831:dimethyldioctadecylammonium; D012710:Serum Albumin, Bovine; D010047:Ovalbumin; D009113:Muramidase