title: Effects of lipid segregation and lysolipid dissociation on drug release from thermosensitive liposomes.
abstract: Lysolipid-containing thermosensitive liposomes (LTSL) release their contents instantly when heated to temperatures close to their gel to liquid-crystalline phase transition temperature (TC). We have recently shown that during the melting transition these liposomes undergo major morphology changes, including the formation of open liposomes, bilayer discs, and pore-like defects. The hyperthermia-induced release of liposomal contents appears to depend on the presence and accumulation of membrane additives in grain boundaries, which enhance packing defects and, in the case of micelle-forming membrane additives, stabilize the bilayer rim of open liposome structures and transient membrane pores. In the present study, we used the fluorescent label 1-pyrenehexadecanoicacid (PHDA) and a radiolabelled lysolipid as markers for lysolipid membrane distribution and retention, respectively. PHDA dimer formation indicated local PHDA accumulation in cholesterol-free liposomes but not in cholesterol-containing liposomes. When LTSL were incubated at a temperature of 37 degrees C together with egg-phosphatidylcholine (EPC) multilamellar vesicles (MLVs) approximately 50% of the lysolipids transferred rapidly from LTSL to EPC MLVs. This transfer led to a significant reduction in the amount of carboxyfluorescein released from LTSL upon heating. Our results imply that poor retention of lysolipids in the LTSL membrane could also affect drug release characteristics of LTSL in vivo.
authors: Department of Physical Chemistry, Uppsala University, Box 579, 75123 Uppsala, Sweden.
authors: Maria C
authors: MC
authors: Sandström
authors: Ludger M
authors: LM
authors: Ickenstein
authors: Lawrence D
authors: LD
authors: Mayer
authors: Katarina
authors: K
authors: Edwards
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D002250:Carbon Radioisotopes; D020285:Cryoelectron Microscopy; D004337:Drug Carriers / Q000737:chemistry / Q000378:metabolism*; D005452:Fluoresceins / Q000032:analysis / Q000378:metabolism; D006358:Hot Temperature; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism*; D008246:Lysophospholipids / Q000737:chemistry / Q000378:metabolism*; D004364:Pharmaceutical Preparations / Q000737:chemistry / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000737:chemistry; D013997:Time Factors
chemical_list: D015415:Biomarkers; D002250:Carbon Radioisotopes; D004337:Drug Carriers; D005452:Fluoresceins; D008051:Lipid Bilayers; D008081:Liposomes; D008246:Lysophospholipids; D004364:Pharmaceutical Preparations; D010713:Phosphatidylcholines; C024098:6-carboxyfluorescein