Liposomes Defined

Liposomes Defined

Liposomes are bilayer vesicles routinely used in the pharmaceutical industry as a drug delivery system for transport of chemotherapeutic drugs to the tumor area. They are composed of phospholipids that have a polar end attached to a non-polar chain that self assemble into bilayer vesicles with the polar ends facing the aqueous medium and non-polar ends forming a bilayer. In pharmaceutical applications the active pharmaceutical ingredient (API) is usually incorporated into the liposome either into the hydrophilic pocket or sandwiched between the bilayers depending on the hydrophilicity of the API.

Liposomes play pivotal roles in the parameters of the drug.

The size of the liposomes and the amount of drug loaded into the liposomes play pivotal roles in the pharmacokinetic and pharmacodynamic parameters of the drug. Hence accurate and rapid measurement of the size of liposomes is essential for novel and effective drug delivery systems. Most liposomes are below 1 µm and the most common particle size technique used is dynamic light scattering (DLS). The Nicomp DLS system is used around the world for accurate size analysis of liposomes. For larger liposomes (> 1 µm) the AccuSizer single particle optical sizing (SPOS) system can be used. Liposomes can be categorized by either by structure/size (Table 1) or by the manufacturing process used.

Small unilamellar vesicles (SUV) Large unilamellar vesicles (LUV)
Multilamellar vesicles (MLV) Multivesicular vesicles (MVV)
Oligolamellar vesicles (OLV) Medium sized unilamellar vesicles (MUV)
Giant unilamellar vesicles (GUV) Giant multilamellar vesicles (GMV)

Table 1: Categories of Liposomes

A recent report from Japan1 documents how the Nicomp and AccuSizer systems are used to determine a broad range of liposome sizes. DOPC (dioleoylphosphatidylcholine) and DOPG (dioleoylphosphatidylglycerol) were used as phospholipids to create the liposomes. MLV, SUV and SMV, LUV and LMV, and GUV and GMV were prepared by Bangham, ultrasonication, improved reverse-phase evaporation, and sugar-doped lipid-film hydration methods, respectively. Size distributions of liposomes with diameters < 1 µm were measured using Nicomp DLS system and the AccuSizer780AD was used for liposomes > 1µm.

Example results: SUV

Liposomes

Electron microscopy image of SUV Nicomp DLS SUV result, one extrusion through 0.1 µm filter

Example Results: GMV

Phase-contrast GMV image AccuSizer SPOS GMV result, one extrusion through 10 µm filter

Click here to download the entire report.

Click here to download the liposome application note.

1. Yoshimura, T., Hashimoto, M., & Hara, M., Size Distribution of Various Types of Liposomes Analyzed by Nicomp380 and AccuSizer780AD