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.
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.
The uses of lipid vesicles continue to increase by the day. Clinically, they play a central role in the delivery of drugs to various targets. They are now widely preferred over viral vectors for a number of reasons. One of the greatest advantages that they have is the fact that they are not immunogenic and rarely cause allergic reactions. This has been a big problem with the viral vectors. Another significant strength is that they are easier to synthesise and put to use.
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.
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.
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.
The uses of lipid vesicles continue to increase by the day. Clinically, they play a central role in the delivery of drugs to various targets. They are now widely preferred over viral vectors for a number of reasons. One of the greatest advantages that they have is the fact that they are not immunogenic and rarely cause allergic reactions. This has been a big problem with the viral vectors. Another significant strength is that they are easier to synthesise and put to use.
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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