Liposomes are small vesicles made up of phospholipids , the very similar constituent of cell membrane, so that the pospholipid vesicles behave more or less as a micro cell inside which drug molecules can be loaded .
The phospholypid molecule is made up of hydrophylic head ( containing choline, phosphate, and glycerol) , to which two long lypopylic chains(essential fatty acid chain) are attached, because of which these molecule aline themselves together in water in a very peculiar manner so as to form a membrane like bilayer.
Formation of phospholypid bilayer.
When phospholypid come in contact with aqueous solution,first they form film like alignment, water soluble head of molecule (hydrophylic ) aline and attache with water molecule, the fat soluble (hydrophobic fatty acid chains ) part of molecule is stay away from water molecules , projecting outwards.
This is a peculiar monolayer formation , up on which anther layer of phospholypid molecule aline themselves , hydrophobic chains attache to hydrophobic chains in first film , now in second layer of phospholypid hydrophobic heads are projecting outwards , this is a peculiar billayer of phospholypid.
All lypopilic heads of pospholipid molecule are aligned inside forming a spherical capsules of varying size, these vesicles may be single layered pospholipid or multi layered pospholipid.They are further categorised in to MLV (multilamellar vesicles) SUV (Small Unilamellar Vesicles) and LUV (Large Unilamellar Vesicles) each one has its unique application, depending up on the requirements of drug delivery and required targeting.
Application of liposome:
1) Drug delivery: Both water soluble and water insoluble, and peptide drug molecules can be delivered with the help of liposome. Liposome’s are used for delivering drug directly in to cells, owning to the property of liposomal membrane which is similar in properties with that of cell wall, liposome’s tend to fuse with the cell wall and can deliver a drug directly inside the cells.
How drug is carried by liposome:
Hydrophilic drug (water soluble) can be encapsulated inside the hydrophilic inner core of liposome, from where it can not come out easily as outer core is hydrophobic , which serves as a protective membrane. A hydrophobic drug can be trapped inside the lipid bi layer of liposome.
Targeted drug delivery system:
Liposome’s can be attached with antibodies against particular cells or tissue, these antibodies along with liposome’s wherein drug is loaded are then attracted by those cells or tissue against which the antibodies work, after attachment of the antibodies with the particular cell, liposome membrane fuses with cell wall and drug molecules entrapped inside the liposome are delivered inside the cell.
Application of liposome’s in anticancer drug delivery system:
Liposome’s of size smaller than 200 nm can enter cancer cells in the tumor and deliver anticancer drug directly in to affected cells, by mechanism explained above.
Liposome’s can be tagged with antibodies against cancerous tissue , and a drug against those cancer cell can be entrapped inside the liposome , these antibody tagged liposome’s get attracted to cancerous cells wall get fused with liposomal wall, and anticancer drug entrapped inside liposome’s is delivered directly inside affected cells.
Application of liposome’s in gene therapy in gene delivery RNA, DNA peptide drug delivery:
Liposomes have great application in gene therapy, as genes can be successfully delivered inside cells for desired incorporation of a gene. Also DNA and RNA and peptide drugs can be delivered directly in to cells for their desired effect on those cells.
Application of liposome’s in protecting drug from external environment:
Drugs which are highly sensitive for external environment, like PH and oxygen, and get degraded easily can be formulated in to liposome’s, for example vitamins can be formulated in liposome’s, which enhances self life of these drugs.
Optimization of cytotoxic drug treatments:
Some drugs are very toxic , for example anticancer drugs like doxorubicin, cisplatin, cytarabine, these drugs when given in conventional dosage form also have cytotoxic side effect on other body tissues and cells, therefore produce more undesired toxic side effects, with liposomal drug delivery systems , the concentration of drug required for desired effect is reduced to very low concentration , which also keeps other body tissue and cells away from such drugs harmful cytotoxic effects.
Long circulation Liposome’s:
Liposome’s can be treated with polyethylene glycol , so that they keep them selves intact for long time in blood circulation with which we can achieve long duration of drug delivery.
Phospholipids used in liposome formulation:
Natural origin: Sphingomyelin , Egg yolk Phospholipids , Soybean Phospholipids
Synthetic origin: Phosphatidylcholine, Lyso-Phosphatidylcholine , Phosphatidylserine ,Phosphatidylethanolamine , Phosphatidic Acid, Phosphatidylglycerol.
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