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Liposome preparations are artificially made lipid vesicles consisting primarily of phospholipids and cholesterol. They are organised as bilayers with some consisting of a single bilayer and others, several. They may therefore be classified as unilamellar or multilamellar based on the number of bilayers. They measure on average about 400 nm in diameter.
One of the methods used in forming the vesicles is known as sonication. Here, the lipid suspension containing cholesterol and phospholipids is hydrated and made to swell so as to separate the various bilayers. As the bilayers separate, they form large lipid vesicles. These are later broken down into smaller units by use of an instrument known as a sonicator. The sonicator delivers high levels of energy to the large molecules and breaks them down within 5 to 10 minutes.
Another technique that may be used is known as extrusion. In this technique, the suspension is first subjected to cyclical freezing and thawing. The aim of this is to improve the homogeneity in the size of the final vesicles obtained. The other alternative is to pass the vesicles through a series of progressively decreasing pores. The large particles are gradually decreased in size and they become smaller and finer.
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 major area of application is in the administration of nutrients. These may either be deficient in the diet or there may be difficulties in their absorption particularly due to a low bioavailability. One of the commonest nutrients that are delivered in this manner is vitamin C. Other uses of liposome encapsulation include the use in the delivery of pesticides, enzymes and in the fixation of dyes to textiles.
If the successes being seen in research involving liposome preparations is anything to go by, then the future is very bright as regards the use of these vesicles. The lack of serious side effects associated with their use is a very encouraging fact. There have been a few reports suggesting that there may be cellular toxicity particularly in prolonged or heavy uses but these are just isolated cases. Another cause for concern is the presence of inhibitors in serum which could potentially reduce the effectiveness.
One of the methods used in forming the vesicles is known as sonication. Here, the lipid suspension containing cholesterol and phospholipids is hydrated and made to swell so as to separate the various bilayers. As the bilayers separate, they form large lipid vesicles. These are later broken down into smaller units by use of an instrument known as a sonicator. The sonicator delivers high levels of energy to the large molecules and breaks them down within 5 to 10 minutes.
Another technique that may be used is known as extrusion. In this technique, the suspension is first subjected to cyclical freezing and thawing. The aim of this is to improve the homogeneity in the size of the final vesicles obtained. The other alternative is to pass the vesicles through a series of progressively decreasing pores. The large particles are gradually decreased in size and they become smaller and finer.
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 major area of application is in the administration of nutrients. These may either be deficient in the diet or there may be difficulties in their absorption particularly due to a low bioavailability. One of the commonest nutrients that are delivered in this manner is vitamin C. Other uses of liposome encapsulation include the use in the delivery of pesticides, enzymes and in the fixation of dyes to textiles.
If the successes being seen in research involving liposome preparations is anything to go by, then the future is very bright as regards the use of these vesicles. The lack of serious side effects associated with their use is a very encouraging fact. There have been a few reports suggesting that there may be cellular toxicity particularly in prolonged or heavy uses but these are just isolated cases. Another cause for concern is the presence of inhibitors in serum which could potentially reduce the effectiveness.
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