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.
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 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.
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 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.
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 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.
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 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.
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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