Liposomes and Liposome Research Tools
Liposomes are spherical artificial vesicles consisting of one or more lipid bilayers. Liposomes are utilized to increase stability, solubility, bioaccessibility, and bioavailability of bioactive compounds, and to provide targeted delivery and controlled release in food, pharmaceutical, and cosmetic industries, due to their structural versatility, biocompatibility, biodegradability, non-toxic, and non-immunogenicity nature.
The main component of liposomes are glycerophospholipids, which are amphiphilic lipids composed of a glycerol molecule bound to a phosphate group and to two fatty acid chains that may be saturated or unsaturated. The phosphate group can be also bonded to another organic molecule. According to this organic group, natural phospholipids are classified as phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylserine (PS). Glycerophospholipids that are responsible to form liposomes can be divided in two different forms: natural and synthetic. The most natural phospholipids used to produce liposomes are PC and PE, that are abundant phosphatides in plants and animals.
Synthetic phospholipids are produced from natural lipids. Modification in head groups, aliphatic chains and alcohols of natural phospholipids creates a variety of synthetic phospholipids, that have proved to be more stable, such as 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-Distearoyl-sn-glycero3-phosphoethanolamine (DSPE). DPPC can be used to prepare temperature-sensitive liposomes as the primary lipid. Because DPPC membranes undergo the phase transition at 41℃, DPPC based liposomes release encapsulated molecules at this clinically attainable temperature.
In addition, the stability difficulties of liposomes can be solved by surface modification of the liposomes with amphipathic polyethylene glycol (PEG), coating liposomes with chitin derivatives, freeze drying, polymerization, etc.
Product Range
Amerigo Scientific offers a wide range of liposomes of different components, modified liposomes, and other liposome research tools to meet the needs of drug delivery and other scientific research applications:
- Empty liposomes ready for loading various drugs with amine groups
- Liposome-encapsulated drugs
- Liposome-encapsulated ions or biomolecules
- Liposome-encapsulated fluorescence dyes or biomarkers
- Liposomes for reconstitution of membrane proteins
- Liposome purification, drug encapsulation, drug dissolution, stability
Liposome-encapsulated Ions or Biomolecules
Amerigo Scientific offers liposome products that encapsulate ions or biomolecules for delivery of the ion or biomolecule across the cell membranes.
Empty liposomes Ready for Loading Drugs with Amine Groups
Liposomal drug formulations provide great opportunities of improving the drug efficacy and toxicity profiles. Doxorubicin and ciprofloxacin with amine groups can be loaded by ammonium-based pH gradient.
Liposomal Fluorescence Dyes
Fluorescence dyes encapsulated in liposomes are used to track liposome distributions in biological systems. The pH-sensitive fluorescence dyes such as Rhodamine delivered by liposomes into cells may be used to monitor pH changes in the cells. The liposomal fluorescence dyes contain 0.1 mM fluorescence dyes encapsulated in PEGylated or non-PEGylated liposomes. The total lipid concentration is 10 mg/ml. The PEGylated liposomes are composed of hydrogenated soy phosphocholine (HSPC), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG2000) and cholesterol in a mass ratio of HSPC:DSPE-PEG2000:Cholesterol = 3:1:1. The non-PEGylated liposomes are composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol in a mass ratio of 1.9:1. The fluorescence dye encapsulation percentage is more than 99%. The average size of liposomes is about 80 nm with a poly dispersity index (dpi) of 0.1.
Liposome Purification, Drug Encapsulation, Drug Dissolution, Stability
- Liposome Plasma Stability Test
The Liposome Plasma Stability Test Kit (Catalog number SPS20) is designed for study stability of liposomal drugs in human or animal plasma or serum. Ready-to-use spin columns are employed for separation of liposomal drugs from non-encapsulated drugs and drugs that binds plasma proteins. After a quick spin-column process, more than 95% of plasma proteins together with the or free drugs stay on the column. The intact liposomal drugs are in the elute. For example, the recovery yield of the intact liposomal doxorubicin was 96% after incubation of the liposomal drug with human plasma at 37°C for 2 hours.
- Lipid Bilayer Permeability Disruption Assay
Disruption of cell membranes that are composed of lipid bilayers leads to dramatic biological effects. For example, pore-forming cytotoxins disrupt the cell membrane permeability causing the release of inflammatory cytokines and tissue damage. The Lipid Bilayer Permeability Disruption Assay employs a liposome-encapsulated dye to monitor the release of the dye due to damage of the integrity of the lipid bilayer. Since liposomes have the bilayer structure similar to cell membranes, this dye-releasing assay may be used to test compounds that disrupt the permeability and damage cell membranes. The released dye is monitored by fluorescence at 580 nm (excitation at 540 nm). It is a high throughput assay using 96-well plates and is suitable for screening of compound collections.
The liposome bilayer is composed of lipids HSPC: cholesterol: DSPE-PEG2000 (3:1:1 mass ratio) which is the same as the lipids for an existing liposomal drug in clinic. The dye is rhodamine conjugated with diethylenetriamine and its fluorescence is quenched inside of the liposome. When the bilayer permeability is disrupted, the encapsulated dye is released and the fluorescence is generated in the presence of the color development agent outside of the liposome.
- Liposome Drug Dissolution Assay
Liposome drug dissolution is release of the encapsulated drug into the medium of the liposome. The in vitro liposomal drug dissolution test is performed under certain chemical and physical pressure to simulate the release of the encapsulated drug. For liposomes with encapsulated drugs by pH gradient remote loading, ammonium salt is added in the medium to accelerate the drug release. The Liposome Drug Dissolution Assay kit (Catalog number LDD05) is designed to analyze liposome drug dissolution under optimized conditions. The released drug is removed by spin-column and the intact liposome is quantified.
- Liposome Drug Encapsulation Assay
Liposome-formulated drug samples may contain free (non-encapsulated) drug molecules that are not encapsulated within the liposomes. Encapsulated drugs may leak out of liposomes during storage or due to exposure of the liposomes to organic solvent, ultrasound vibration or freezing or elevated temperatures. During production of liposomal drugs, drug loading may not be complete leaving certain percentage of the drug non-encapsulated. The Liposome Drug Encapsulation Assay kit (Catalog number LDE10) is designed to analyze the percentage of drug encapsulation in liposomes.
The kit is based on spin-column separation of the liposomes from the non-encapsulated drug molecules. It recovers 100% ±2% liposomes and removes > 98% non-encapsulated drugs. The complete separation between the liposomes and the non-encapsulated drug is based on a combination effect of absorbance and size between liposomes and non-encapsulated drug molecules.
- Spin-columns for Liposome Purification
The Spin-columns for Liposome Purification (Catalog number SLP20) is designed for quick removal of free or non-encapsulated drugs. It removes > 99% of the non-encapsulated drugs in a few minutes. Removal of the non-encapsulated drugs is based on a combination effect of absorbance and size exclusion. When a purified 2 mg/ml liposomal doxorubicin is loaded, 99.3% liposomal doxorubicin is recovered. When a 2 mg/ml free doxorubicin is loaded, 0.2 % free doxorubicin is recovered.
The columns are pre-packed in water and specifically designed for removal of free drugs in a liposome sample. Removal of the free drug is nearly complete. A minimal number of liposomes may also bind to the column. For liposomal drug encapsulation and liposomal drug dissolution tests, please use assay kits specifically designed for drug encapsulation assays (Catalog number LDE10) or drug dissolution assays (Catalog number LDD10).
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