title: Long-term storage of lyophilized liposomal formulations.
abstract: Because aqueous liposomal formulations containing multiply unsaturated lipids are susceptible to chemical degradation, these formulations are often lyophilized. Despite their limited chemical stability, interest in the use of multiply unsaturated lipids to promote intracellular delivery has increased considerably in recent years. The goal of the current study was to examine the long-term storage stability of lyophilized formulations containing lipids with increasing levels of unsaturation, and various strategies that can be employed to improve stability. Aqueous lipid-trehalose formulations containing 1,2-dilinolenoyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLinPC), or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were lyophilized and stored at temperatures ranging from 4°C to 60°C. We observed that the lipid degradation rate increased as the storage temperature and unsaturation level were increased. Even the cleanest sugars, which are available commercially, contain iron contaminants, and it was observed that the chelation of these iron contaminants significantly improved the stability of DLPC during storage. However, the glass transition temperature of the sugar that was included in the formulation, the reduction of the oxygen in the aqueous sample prior to lyophilization, the inclusion of helper lipids (i.e., cholesterol), and the rate of freezing did not significantly improve stability.
authors.affiliation: Department of Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado.
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Payton
authors.affiliation: Department of Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Wempe
authors.affiliation: Center for Pharmaceutical Biotechnology, Department of Biochemistry, University of Colorado, Boulder, Colorado.
authors.forename: Yemin
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado. Electronic address: Tom.anchordoquy@ucdenver.edu.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Anchordoquy
mesh_terms: D002241:Carbohydrates / Q000737:chemistry; D002626:Chemistry, Pharmaceutical / Q000379:methods; D004355:Drug Stability; D004356:Drug Storage / Q000379:methods*; D005612:Freeze Drying / Q000379:methods; D005615:Freezing; D005997:Glycerylphosphorylcholine / Q000031:analogs & derivatives / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry*; D010713:Phosphatidylcholines; D044366:Transition Temperature; D014199:Trehalose / Q000737:chemistry
chemical_list: D002241:Carbohydrates; D008055:Lipids; D008081:Liposomes; D010713:Phosphatidylcholines; D005997:Glycerylphosphorylcholine; D014199:Trehalose; C017251:1,2-oleoylphosphatidylcholine
keywords: DLPC; chemical stability; freeze-drying; liposomes; lyophilization; oxidation; unsaturated lipids