Liposome preparations are simply artificial spherical vesicles consisting principally of cholesterol and phospholipid molecules. These molecules are organised to form bilayers. Vesicles are classified as either being multilamellar or unilamellar. The former is made up of several bilayers while the latter has only one. On average, most of the vesicles have a diameter of less than 400nm.
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.
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.
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.
Apart from drug delivery, lipid vesicles also play a vital role in the administration of nutrients. They are especially useful in supplementing nutrients that are deficient in the diet or those that cannot be easily absorbed orally due to their low bioavailability. Liposome encapsulation is currently one of the most efficient ways of administering vitamin C. The same principle is employed in the delivery of pesticides to plants, delivery of enzymes to their sites of action in the body and in 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.
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.
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.
Apart from drug delivery, lipid vesicles also play a vital role in the administration of nutrients. They are especially useful in supplementing nutrients that are deficient in the diet or those that cannot be easily absorbed orally due to their low bioavailability. Liposome encapsulation is currently one of the most efficient ways of administering vitamin C. The same principle is employed in the delivery of pesticides to plants, delivery of enzymes to their sites of action in the body and in 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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