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.
During preparation, lipid films are hydrated and they become swollen. The films detach and self-close to form a lipid suspension of large vesicles that have to be broken down into smaller particles. One of the methods used to break them down is sonication. Here, instruments known as sonicators are used to deliver high energy to the suspension for 5 to 10 minutes. Residual large particles are removed through centrifugation.
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.
A number of factors are known to cause a variation in the size of vesicles. These include among others, the duration for which the vesicles are processed, the amount of energy applied, composition and proportion of the lipids and the the tuning of the sonicator. The vesicles have a lot of similarities with cell membranes due to the presence of phospholipids and cholesterol. Both have a hydrophobic and hydrophilic ends.
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.
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.
The vesicles have many other uses most of which are yet to be approved for routine use. A major advantage of liposome preparations is that there are very few serious side effects that have been identified. One of them is the fact that there is a potential to cause cellular toxicity especially when taken in very large quantities or for a prolonged period of time. There are also some concerns regarding the presence various lipid inhibitors in serum.
During preparation, lipid films are hydrated and they become swollen. The films detach and self-close to form a lipid suspension of large vesicles that have to be broken down into smaller particles. One of the methods used to break them down is sonication. Here, instruments known as sonicators are used to deliver high energy to the suspension for 5 to 10 minutes. Residual large particles are removed through centrifugation.
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.
A number of factors are known to cause a variation in the size of vesicles. These include among others, the duration for which the vesicles are processed, the amount of energy applied, composition and proportion of the lipids and the the tuning of the sonicator. The vesicles have a lot of similarities with cell membranes due to the presence of phospholipids and cholesterol. Both have a hydrophobic and hydrophilic ends.
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.
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.
The vesicles have many other uses most of which are yet to be approved for routine use. A major advantage of liposome preparations is that there are very few serious side effects that have been identified. One of them is the fact that there is a potential to cause cellular toxicity especially when taken in very large quantities or for a prolonged period of time. There are also some concerns regarding the presence various lipid inhibitors in serum.
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