Liposomes and their Advantages in Drug Delivery

Liposomes are spherical, self-closed vesicles formed by one or several concentric lipid bilayers with an aqueous phase inside and between the lipid bilayers (Fig. 3a). Therefore, liposomes usually have hydrophilic outer surfaces, hydrophilic inner cores, and hydrophobic matrices in between. Figure 3b gives an example of a transmission electron microscope (TEM) image of liposomes (adapted with permission from reference (Ran et al. 2002)).

There are several advantages of using liposomes for drug delivery in cancer treatment. First, liposomes are highly biocompatible, biodegradable, and nonimmuno-genic. These properties are attributed to their composition from naturally occurring lipids. Second, the size, charge, and surface properties of liposomes can be easily changed by adding new ingredients to the lipid mixture before their preparation and/ or by varying the preparation methods. For example, small unilamellar liposomes formed by a single bilayer can be around 100 nm in size, larger unilamellar vesicles have sizes ranging from 200 to 800 nm, and multilamellar vesicles can be as large as 5,000 nm and consist of several concentric bilayers (Torchilin 2005).

Fig. 3 Schematic structure of a liposome with both water-soluble and water-insoluble encapsulation (a) and TEM image of liposome (b) (adapted with permission from reference (Ran et al. 2003))

Maybe the biggest advantage of using liposomes for drug delivery is their amphiphilicity (i.e., having both hydrophilic and hydrophobic domains) that allows them to be conjugated with both hydrophilic and hydrophobic therapeutic agents. Water-soluble (hydrophilic) pharmaceutical agents can be entrapped in internal aqueous compartments of liposomes and water-insoluble (hydrophobic) drugs can be placed into the membrane of liposomes (Torchilin 2005; Tiwari and Amiji 2006). Liposomes can also fuse with cell membranes and transfer drugs in the liposome to the inside of the cells. There are two main mechanisms of liposomes releasing encapsulated drugs. One mechanism is based on the development of an affinity reaction. In the other mechanism, the triggered-release mechanism, some elements are incorporated into the liposome and this induces structural changes in the bilayer membrane under an external stimulus, e.g., pH (Hafez et al. 2000; Mizoue et al. 2002; Reddy and Low 2000; Yamada et al. 2005), temperature variation (Anyarambhatla and Needham 1999; Liu and Huang 1994), light irradiation (Benkoski et al. 2006), or ultrasound (Huang and MacDonald 2004). Membrane integrity of liposomes is lost under effects of the external stimulus leading to the release of entrapped compounds (Jesorka and Orwar 2008).

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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