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.
The phospholipids and the cholesterol are first put into a suspension. They are hydrated to make them swell and separate into various bilayers. They self-close to form large vesicles that have to be modified by some techniques. One of these techniques is known as sonication. Here, an instrument known as a sonicator is used to provide high energy that is used to break down the large vesicles into smaller ones. This is achieved within five to ten 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.
Heterogeneity of particle size is not an uncommon finding. The degree of variation is dependent on a number of factors such as amount of energy used, duration of sonication, composition and proportion of the lipids in the suspension and the level of tuning of the sonicator. The vesicles have been found to closely resemble cell membranes in structure. Both have hydrophilic and hydrophobic ends. The physical characteristics are similar to those of surfactants.
There are numerous uses of lipid vesicles currently. Perhaps the most important of them is the delivery of pharmacological agents to various sites. They are increasingly being preferred over viral vectors due to a number of reasons. One of them is the fact that they are rarely immunogenic and do not lead to allergic reactions unlike the viral vectors. They are also much easier to synthesize than the vectors.
There are a number of lipid vesicle pharmacological preparations being used in routine clinical practice today. These include among others, liposomal amphotericin B (an antifungal agent), liposomal cytarabine (an anticancer agent for treating malignant meningitis), liposomal IRIV vaccine, morphine and doxorubicine (treats metastatic breast cancer). Many more others are undergoing clinical trials.
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.
There are many other uses of liposome preparations. Most of these are still the subject of research that is aimed at increasing their efficiency. The most encouraging news is that, no serious side effects related to the use of these preparations have been reported. There are some concerns, however, that they have a potential to cause cellular toxicity especially when taken in large quantities. The presence of inhibitors in serum may be another downside since these may inhibit the potency of the vesicles.
The phospholipids and the cholesterol are first put into a suspension. They are hydrated to make them swell and separate into various bilayers. They self-close to form large vesicles that have to be modified by some techniques. One of these techniques is known as sonication. Here, an instrument known as a sonicator is used to provide high energy that is used to break down the large vesicles into smaller ones. This is achieved within five to ten 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.
Heterogeneity of particle size is not an uncommon finding. The degree of variation is dependent on a number of factors such as amount of energy used, duration of sonication, composition and proportion of the lipids in the suspension and the level of tuning of the sonicator. The vesicles have been found to closely resemble cell membranes in structure. Both have hydrophilic and hydrophobic ends. The physical characteristics are similar to those of surfactants.
There are numerous uses of lipid vesicles currently. Perhaps the most important of them is the delivery of pharmacological agents to various sites. They are increasingly being preferred over viral vectors due to a number of reasons. One of them is the fact that they are rarely immunogenic and do not lead to allergic reactions unlike the viral vectors. They are also much easier to synthesize than the vectors.
There are a number of lipid vesicle pharmacological preparations being used in routine clinical practice today. These include among others, liposomal amphotericin B (an antifungal agent), liposomal cytarabine (an anticancer agent for treating malignant meningitis), liposomal IRIV vaccine, morphine and doxorubicine (treats metastatic breast cancer). Many more others are undergoing clinical trials.
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.
There are many other uses of liposome preparations. Most of these are still the subject of research that is aimed at increasing their efficiency. The most encouraging news is that, no serious side effects related to the use of these preparations have been reported. There are some concerns, however, that they have a potential to cause cellular toxicity especially when taken in large quantities. The presence of inhibitors in serum may be another downside since these may inhibit the potency of the vesicles.
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