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.
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.
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.
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.
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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