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.
Apart from sonication, the other method that can be used for formation of lipid vesicles is known as extrusion. In this method, phospholipid and cholesterol suspensions undergo a continuous process of freezing and thawing so as to improve the homogeneity of size of final vesicles. Alternatively, the suspension may be passed through a filter of large pore sizes before subsequently being passed through one with smaller pores so as to yield finer particles.
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.
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.
The available drug formulations are used in the treatment of a wide variety of disease processes. The drugs include cytarabine (an anticancer agent), liposomal amphotericin B, a highly potent antifungal agent, liposomal IRIV vaccine, morphine and doxorubicin among others. Many other drug formulations are in different phases of 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.
Apart from sonication, the other method that can be used for formation of lipid vesicles is known as extrusion. In this method, phospholipid and cholesterol suspensions undergo a continuous process of freezing and thawing so as to improve the homogeneity of size of final vesicles. Alternatively, the suspension may be passed through a filter of large pore sizes before subsequently being passed through one with smaller pores so as to yield finer particles.
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.
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.
The available drug formulations are used in the treatment of a wide variety of disease processes. The drugs include cytarabine (an anticancer agent), liposomal amphotericin B, a highly potent antifungal agent, liposomal IRIV vaccine, morphine and doxorubicin among others. Many other drug formulations are in different phases of 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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