title: Liposome retention in size exclusion chromatography.
abstract: BACKGROUND
  Size exclusion chromatography is the method of choice for separating free from liposome-encapsulated molecules. However, if the column is not presaturated with lipids this type of chromatography causes a significant loss of lipid material. To date, the mechanism of lipid retention is poorly understood. It has been speculated that lipid binds to the column material or the entire liposome is entrapped inside the void.
  
  
  RESULTS
  Here we show that intact liposomes and their contents are retained in the exclusion gel. Retention depends on the pore size, the smaller the pores, the higher the retention. Retained liposomes are not tightly fixed to the beads and are slowly released from the gels upon direct or inverted eluent flow, long washing steps or column repacking. Further addition of free liposomes leads to the elution of part of the gel-trapped liposomes, showing that the retention is transitory. Trapping reversibility should be related to a mechanism of partitioning of the liposomes between the stationary phase, water-swelled polymeric gel, and the mobile aqueous phase.
  
  
  CONCLUSIONS
  Retention of liposomes by size exclusion gels is a dynamic and reversible process, which should be accounted for to control lipid loss and sample contamination during chromatography.
authors.affiliation: Groupe de biotechnologie des protéines, Institut de Pharmacologie et de Biologie Structurale, F-31077, Toulouse, France. tristan.ruysschaert@ipbs.fr
authors.forename: Tristan
authors.initials: T
authors.lastname: Ruysschaert
authors.forename: Audrey
authors.initials: A
authors.lastname: Marque
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Duteyrat
authors.forename: Sylviane
authors.initials: S
authors.lastname: Lesieur
authors.forename: Mathias
authors.initials: M
authors.lastname: Winterhalter
authors.forename: Didier
authors.initials: D
authors.lastname: Fournier
mesh_terms: D000110:Acetylcholinesterase / Q000737:chemistry; D000818:Animals; D001709:Biotechnology / Q000379:methods*; D002627:Chemistry, Physical / Q000379:methods; D002845:Chromatography / Q000379:methods*; D002850:Chromatography, Gel / Q000379:methods; D004331:Drosophila melanogaster / Q000201:enzymology; D004337:Drug Carriers / Q000737:chemistry; D005452:Fluoresceins / Q000737:chemistry; D005782:Gels / Q000737:chemistry; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry*; D008567:Membranes, Artificial; D008855:Microscopy, Electron, Scanning; D008856:Microscopy, Fluorescence; D010539:Permeability
chemical_list: D004337:Drug Carriers; D005452:Fluoresceins; D005782:Gels; D008055:Lipids; D008081:Liposomes; D008567:Membranes, Artificial; D000110:Acetylcholinesterase; C007740:fluorexon