title: Quantitative In Vitro Assessment of Liposome Stability and Drug Transfer Employing Asymmetrical Flow Field-Flow Fractionation (AF4).
abstract: OBJECTIVE
  In the present study we introduce an efficient approach for a size-based separation of liposomes from plasma proteins employing AF4. We investigated vesicle stability and release behavior of the strongly lipophilic drug temoporfin from liposomes in human plasma for various incubation times at 37°C.
  
  
  METHODS
  We used the radioactive tracer cholesteryl oleyl ether (COE) or dipalmitoyl-phosphocholine (DPPC) as lipid markers and (14)C-labeled temoporfin. First, both lipid labels were examined for their suitability as liposome markers. Furthermore, the influence of plasma origin on liposome stability and drug transfer was investigated. The effect of membrane fluidity and PEGylation on vesicle stability and drug release characteristics was also analyzed.
  
  
  RESULTS
  Surprisingly, we observed an enzymatic transfer of (3)H-COE to lipoproteins due to the cholesterol ester transfer protein (CETP) in human plasma in dependence on membrane rigidity and were able to inhibit this transfer by plasma preincubation with the CETP inhibitor torcetrapib. This effect was not seen when liposomes were incubated in rat plasma. DPPC labels suffered from hydrolysis effects during preparation and/or storage. Fluid liposomes were less stable in human plasma than their PEGylated analogues or a rigid formulation. In contrast, the transfer of the incorporated drug to lipoproteins was higher for the rigid formulations.
  
  
  CONCLUSIONS
  The observed effects render COE-labels questionable for in vivo studies using CEPT-rich species. Here, choline labelled (14)C-DPPC was found to be the most promising alternative. Bilayer composition has a high influence on stability and drug release of a liposomal formulation in human plasma.
authors.affiliation: Department of Pharmaceutical Technology, Friedrich Schiller University Jena, Lessingstraße 8, D-07743, Jena, Germany. Stephan.Holzschuh@uni-jena.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Holzschuh
authors.affiliation: Department of Pharmaceutical Technology, Friedrich Schiller University Jena, Lessingstraße 8, D-07743, Jena, Germany. Kathrin-Ulrike.Kaess@uni-jena.de.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Kaeß
authors.affiliation: Department of Pharmaceutical Technology, Friedrich Schiller University Jena, Lessingstraße 8, D-07743, Jena, Germany. Alfred.fahr@googlemail.com.
authors.forename: Alfred
authors.initials: A
authors.lastname: Fahr
authors.affiliation: Department of Pharmaceutical Technology, Friedrich Schiller University Jena, Lessingstraße 8, D-07743, Jena, Germany. Christiane.Decker@uni-jena.de.
authors.forename: Christiane
authors.identifier: http://orcid.org/0000-0003-2599-7401
authors.initials: C
authors.lastname: Decker
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000097:blood; D001798:Blood Proteins / Q000302:isolation & purification; D002784:Cholesterol / Q000031:analogs & derivatives / Q000737:chemistry; D065546:Drug Liberation; D031521:Fractionation, Field Flow / Q000379:methods*; D006801:Humans; D008081:Liposomes / Q000737:chemistry* / Q000302:isolation & purification; D008297:Male; D008652:Mesoporphyrins / Q000008:administration & dosage* / Q000097:blood; D010743:Phospholipids / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D017208:Rats, Wistar
chemical_list: D000970:Antineoplastic Agents; D001798:Blood Proteins; D008081:Liposomes; D008652:Mesoporphyrins; D010743:Phospholipids; D011092:Polyethylene Glycols; C023511:cholesteryl oleyl ether; D002784:Cholesterol; C072269:temoporfin
keywords: CETP; asymmetrical flow field-flow fractionation; drug transfer; liposomes; plasma proteins