Liposome preparations consist of artificial spherical vesicles whose main chemical components are phospholipids and cholesterol organised in two layers. The process of forming this bilayer is known as sonication. Based on the structure, the vesicles may be classified as either multilammellar or unilamellar. The former have several bilayers while the latter has just a single bilayer. Most vesicles measure less than 400nm in diameter.
During preparation, lipid films are hydrated and they become swollen. The films detach and self-close to form a lipid suspension of large vesicles that have to be broken down into smaller particles. One of the methods used to break them down is sonication. Here, instruments known as sonicators are used to deliver high energy to the suspension for 5 to 10 minutes. Residual large particles are removed through centrifugation.
Another popularly used technique is known as extrusion. In this technique, the suspension is subjected to a cyclical process of freezing and thawing that eventually results in the breakdown of the large vesicles. Homogenous of size is achieved after a few cycles. Another variant of the same is the passage of the vesicles through progressively decreasing pores until very fine particles are obtained.
The sizes of the vesicles will slightly depending on among other factors, duration of the process, energy used, the composition of the suspension used and the tuning of the sonicator. Regardless of the size, the vesicles have been found to bear very close resemblance to the cell membranes in structure. Both cell membranes and lipid vesicles have phospholipid heads that are hydrophilic and fatty acid tails that are hydrophobic. Their physical properties are like those of surfactants.
Lipid vesicles have gained wide clinical usage in recent times. They now play a very important role in drug delivery systems and are rapidly replacing viral vectors. This is due to the various advantages that they have over the viral systems. One of these advantages is that they are rarely immunogenic and hence are unlikely to cause immunological reactions which are fairly common with viral vectors. Another major advantage is the fact that they can be synthesized more easily than the vectors.
Many drugs that utilize lipid vesicles are in use today. These include, among others, liposomal amphotericin B, a potent antifungal agent, liposomal cytarabine (a drug used for treatment of malignant meningitis and other cancers), liposomal IRIV vaccine (used for hepatitis A and influenza), doxorubicin and morphine. There are many more others that are the subject of research.
Another common application of the vesicles is in the delivery of various nutrients. Many of these nutrients are either deficient in the diet or are difficult to absorb because of a low bioavailability. Vitamin C is frequently administered through lipid encapsulation. Pesticides are applied to plants using the same principle. Other areas of liposome encapsulation application include delivery of enzymes and the fixing of dyes to textiles.
The vesicles have many other uses most of which are yet to be approved for routine use. A major advantage of liposome preparations is that there are very few serious side effects that have been identified. One of them is the fact that there is a potential to cause cellular toxicity especially when taken in very large quantities or for a prolonged period of time. There are also some concerns regarding the presence various lipid inhibitors in serum.
During preparation, lipid films are hydrated and they become swollen. The films detach and self-close to form a lipid suspension of large vesicles that have to be broken down into smaller particles. One of the methods used to break them down is sonication. Here, instruments known as sonicators are used to deliver high energy to the suspension for 5 to 10 minutes. Residual large particles are removed through centrifugation.
Another popularly used technique is known as extrusion. In this technique, the suspension is subjected to a cyclical process of freezing and thawing that eventually results in the breakdown of the large vesicles. Homogenous of size is achieved after a few cycles. Another variant of the same is the passage of the vesicles through progressively decreasing pores until very fine particles are obtained.
The sizes of the vesicles will slightly depending on among other factors, duration of the process, energy used, the composition of the suspension used and the tuning of the sonicator. Regardless of the size, the vesicles have been found to bear very close resemblance to the cell membranes in structure. Both cell membranes and lipid vesicles have phospholipid heads that are hydrophilic and fatty acid tails that are hydrophobic. Their physical properties are like those of surfactants.
Lipid vesicles have gained wide clinical usage in recent times. They now play a very important role in drug delivery systems and are rapidly replacing viral vectors. This is due to the various advantages that they have over the viral systems. One of these advantages is that they are rarely immunogenic and hence are unlikely to cause immunological reactions which are fairly common with viral vectors. Another major advantage is the fact that they can be synthesized more easily than the vectors.
Many drugs that utilize lipid vesicles are in use today. These include, among others, liposomal amphotericin B, a potent antifungal agent, liposomal cytarabine (a drug used for treatment of malignant meningitis and other cancers), liposomal IRIV vaccine (used for hepatitis A and influenza), doxorubicin and morphine. There are many more others that are the subject of research.
Another common application of the vesicles is in the delivery of various nutrients. Many of these nutrients are either deficient in the diet or are difficult to absorb because of a low bioavailability. Vitamin C is frequently administered through lipid encapsulation. Pesticides are applied to plants using the same principle. Other areas of liposome encapsulation application include delivery of enzymes and the fixing of dyes to textiles.
The vesicles have many other uses most of which are yet to be approved for routine use. A major advantage of liposome preparations is that there are very few serious side effects that have been identified. One of them is the fact that there is a potential to cause cellular toxicity especially when taken in very large quantities or for a prolonged period of time. There are also some concerns regarding the presence various lipid inhibitors in serum.
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