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Gas-filled Liposomes - Essay Example

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Summary
Liposomes have been used for many years as delivery vehicles for pharmaceuticals due to their intrinsic ability to fuse with the cellular membrane to deliver a therapeutic dose directly to the cell. More recently these lipid containing vesicles have demonstrated expanded use as gas-filled membrane-bound vesicles that can act as pressure points for use in magnetic resonance imaging (MRI) studies (Vangala et al, 2007)…
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Gas-filled Liposomes
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Download file to see previous pages In medicine, MRI is an invaluable tool for soft tissue assessment as it analyses the absorption and transmission of high frequency radio waves absorbed by water in high magnetic fields to derive cross-sectional images of soft tissue (Alexander et al, 1996; Maresca et al, 1998). The use of GFLs as components of tracer materials may enhance the use of this technology in medical diagnostics (Klibanov, 1999).
A recently developed method of GFL preparation (Vangala et al, 2007) involves the homogenization of 1,2-dipalmitoyl-sn-glycero3-phosphorocholine (DPPC) or 1,2-distearoyl-sn-glycero-3-phosphorocholine DSPC in aqueous medium below their transition temperatures to effect a stable GFL formation. Biophysical assessment indicated that the initial vesicle size was 10microm, which increased to approximately 12 microm for DPPC and 23 microm for DSPC containing vesicles in 7 days at 25C. The addition of cholesterol 1: 0.5 or 1:1 to the DPPC lipid homogenate produced significant increases in vesicle size as well as enhanced stability compared to DPPC alone (Liu et al, 2000). Surface charge induction was implemented by the addition of stearylamine at a molar ratio of 0.125 or 0.25. The surfactant did not appear to be incorporated into the bilayer. Microscopic analyses demonstrated that spherical structures ranging from 1-8 microm were produced by this method. When used as cardiographic contrast agents in cardiac assessment in experimental animals, GFL performed with greater sensitivity than aqueous liposomes (Mohammed et al, 2004; Unger et al, 1992, 1993).
2-Aim and Objective
The objective of this research is to prepare Gas-filled liposomes (GFL) and to characterize their biophysical properties. The goal is to prepare liposomes that are gas-filled (air) using experimental lipid components and to assess their stability and biophysical properties. This assessment may facilitate the use of GFL for both medicinal purposes in MRI and in environmental studies such as novel methods for oil recovery.
3-Materials
Sigma-Aldrich (Poole, Dorset, UK)
1,2-dimysteroyl-sn-glycero-3-phosphorocholine DMPC(C14)
1,2-dipalmitoyl-sn-glycero-3-phosphorocholone DPPC (C16)
1,2-distearoyl-sn-glycero-3-phosphorylcholine DSPC (C18)
methyl cellulose
cholesterol
stearylamine
phosphate buffered saline tablets
Lipid Products (Nutfield, Surrey, UK)
egg-phosphatidylcholine (PC)
double-distilled water
4-Methods
Gas-filled liposome preparation:
GFL will be prepared using a modified method first developed by Unger (1999). This method involves the following steps:
1. 50 mg of DSPC or other lipid added to 5ml of doubly-distilled water in a 50ml beaker to hydrate the lipid. Cholesterol or stearylamine should be added if these components are to be included in the vesicle preparation.
2. Mixture is homogenized for 4 minutes below the phase transition temperature of the lipid using a high speed homogeniser (Ultra -Turrax T8).
3. A gas (air) filled lipid layer will form above the aqueous layer following homogenization: this constitutes the GFL fraction.
4. Varying GFL concentrations will be prepared by mixing varying volumes ...Download file to see next pagesRead More
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