Introduction to Liposomes.

 

Introduction.

  • Liposome was first discovered in the early 1965 by Alec D. Bangham.

  • Liposome word is derived from two Greek words,

    • Lipo: Fatty. + Soma: Body= Hence literally it means a lipid body. 

  • They are relatively small in size and it ranges from 50 nm to several micrometers in diameter. 

  • They are spherical vesicles in which an aqueous core is entirely enclosed by one or more phospholipid bilayers. 

  • It has the unique ability to entrap both lipophilic and hydrophilic compounds. 

  • The hydrophobic or lipophilic molecules are inserted into the bilayer membrane, whereas hydrophilic molecules can be entrapped in the aqueous center. 

  • Because of their biocompatibility, biodegradability, low toxicity, and aptitude to trap both hydrophilic and lipophilic drugs they simplify site-specific drug delivery to tumor tissues, being so versatile they have emerged as a prominent Targeted drug delivery system.

ADVANTAGES OF LIPOSOMES.

  • Hydrophobic (e.g., amphotericin B), hydrophilic (e.g., cytarabine), and amphipathic agents can be delivered. 

  • Liposomes improve drug efficacy and therapeutic index (actinomycin-D). 

  • Liposomes improve stability through encapsulation of the drugs. 

  • Appropriate for targeted drug delivery. 

  • Suitable for providing localized action in a specific tissue 

  • Suitable for administration via a variety of routes 

  • Liposomes aid in reducing toxic drug exposure to sensitive tissue. 

DISADVANTAGES OF LIPOSOMES.

  1. Liposomes cannot be removed once they have been administered. 

  2. Dumping is a possibility as a result of poor administration. 

  3. Encapsulated drug leakage during storage 

  4. Solubility is low. 

  5. The cost of production is high.

CLASSIFICATION OF THE LIPOSOMES:

  • Depending on various criteria they are classified as follows,

    • Based on structural parameters.

    • Based on method of preparation: 

    • Based on composition and application.

  1. Based on structural parameters:

    1. MLV: 

      • multilamellar large vesicles .0.5 µm. 

      • They have several bilayer 

    2. OLV: 

      • oligo lamellar vesicles 0.1-1µm. 

      • Made up of 2-10 bilayer of lipids surrounding a large internal volume. 

    3. UV: 

      • unilamellar vesicles (all size range) 

    4. SUV: 

      • Small unilamellar vesicle composed of single lipid bilayer with diameter ranging from 30-70 nm.

    5. MUV: 

      • Medium unilamellar vesicle

  2. Based on composition and application:

    1. Conventional Liposomes (CL): 

      • Neutral or negatively charged phospholipid and cholesterol 

    2. Fusogenic Liposomes (RSVE): 

      • Reconstituted Sendai virus envelopes 

    3. pH sensitive Liposomes: 

      • Phospholipid such as PE or DOPE with either CHEMS or OA 

    4. Cationic Liposomes: Cationic lipids with DOPE 

    5. Long Circulatory (Stealth) Liposomes (LCL): 

      • Liposome that persist for prolong period of time in the bloodstream 

    6. Immuno-Liposomes: 

      • Immune liposomes have specific antibodies on their surface to enhance target site binding.

  3. Based on method of preparation:

    1. REV: single or oligo lamellar vesicles made by reverse phase evaporation method 

    2. MLV-REV: multilamellar vesicle made by reverse phase evaporation method 

    3. SPLV: stable pluri lamellar vesicle 

    4. FATMLV: Frozen and thawed MLV 

    5. VET: vesicle prepared by extraction method 

    6. DRV: dehydration-rehydration method

PREPARATION OF LIPOSOMES:

  • There are many ways of preparing liposomes. Some of the important methods are as follows,

  1. Hydration of lipids in presence of solvent 

  2. Ultrasonication 

  3. French Pressure cell 

  4. Solvent injection method

    1. Ether injection method 

    2. Ethanol injection

  5. Detergent removal Detergent can be removed by 

    1. Dialysis 

    2. Column chromatography 

    3. Bio-beads

  6. Reverse phase evaporation technique 

  7. High pressure extrusion 

  8. Miscellaneous methods 

    1. Removal of Chaotropic ion 

    2. Freeze-Thawing.

Characterization OF liposomes:

  • It can be done by following three ways,

  1. Physical characterisation: evaluates parameters including size, Shape, surface features, lamellarity, phase behavior and drug release profile. 

  2. Chemical characterisation: includes those studies which establish the purity, potency of various lipophilic constituents. 

  3. Biological characterisation: establishes the safety and suitability of formulation for therapeutic application. 

Applications of Liposomes:

  1. Cancer chemotherapy: 

    • Liposomes have been used successfully to entrap anticancer drugs. 

    • This prolongs circulation lifetime and protects against metabolic degradation. 

  2. Liposome as carrier of drug in oral treatment: 

    • Steroids used to treat arthritis can be incorporated into large MLVs. 

    • Oral administration of liposome-encapsulated insulin altered blood glucose levels in diabetic animals. 

  3. Liposome for topical application: 

    • Triamcinolone, methotrexate, benzocaine, corticosteroids, and other drugs can be successfully incorporated as a topical liposome. 

  4. Liposome for pulmonary delivery: 

    • Inhalation devices like nebulizers are used to produce an aerosol of droplets containing liposomes.

Commonly asked Question.

  1. Write in detail about Liposomes.

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