Unit IV a liposomes ndds subject. .pptx

Ndds

1. • • Liposomes are concentric bilayered vesicles in which an aqueous core is entirely enclosed by a membranous lipid bilayer mainly composed of natural or synthetic phospholipids. The size of a liposome ranges from some 20 nm up to several micrometers. Liposomes L i p oso m e 1

2. • The lipid molecules are usually phospholipids- amphipathic moieties with a hydrophilic head group and two hydrophobic tails. • • On addition of excess water, such lipid moieties spontaneously originate to give the most thermodynamically stable conformation. In which polar head groups face outwards into the aqueous medium, and the lipid chains turns inwards to avoid the water phase, giving rise to double layer or bilayer lamellar structures. 2

3. Basic liposome structure 3

4. La m e ll a 4 • A La m ella is a f l a t plate l i ke s t ructure th a t app e a r s during the formation of liposomes. The phospholipids bilayer first exists spheres. • S everal la m e l la of phosp h o lipids bila y e r s as a la m el l a b e f o r e getting converted into are stacked one on top of the other during formation of liposomes to form a multilamellar structure.

5. Multilamellar vesicle 5 Unilamellar vesicle

6. Structural Components of Liposomes 6 The main components of liposomes are :- Phospholipids Cholesterol

7. Phospholipids • Phospholipids are the major structural components of biological membranes such as the cell membrane. Phosphoglycerides Two types of Phospholipids (along with their hydrolysis products) Sphingolipids 7

8. Phosphatidylcholine • Most common phospholipids used is phosphatidylcholine (PC). Phosphatidylcholine is an amphipathic molecule in which exists:- a hydrophilic polar head group, phosphocholine. a glycerol bridge. a pair of hydrophobic acyl hydrocarbon chains. 8

9. Generally phospholipids are represented as follows:- 9

10. Cholesterol 10 Cholesterol by itself does not form bilayer structure. Cholesterol act as fluidity buffer • • • • • After intercalation with phospholipid molecules alter the freedom of motion of carbon molecules in the acyl chain Restricts the transformations of trans to gauche conformations Cholesterol incorporation increases the separation between choline head group & eliminates normal electrostatic & hydrogen bonding interactions

11. Advantages of liposomes 11 • • • • • • • Provides selective passive targeting to tumor tissues. Increased efficacy and therapeutic index. Increased stability of encapsulated drug. Reduction in toxicity of the encapsulated agent. Site avoidance effect (avoids non-target tissues). Improved pharmacokinetic effects (reduced elimination increased circulation life times). Flexibility to couple with site specific ligands to achieve active targetting.

12. Disadvantages 12 • • • • • • • • • • • Physical/ chemical stability Very high production cost Drug leakage/ entrapment/ drug fusion Sterilization Short biological activity / t ½ Oxidation of bilayer phospholipids and low solubility Rate of release and altered bio distribution Low therapeutic index and dose effectiveness Overcoming resistance Extensive clinical and laboratory research to a certain long circulating liposomes Repeated iv administration problems

13. Classification of liposomes MLV M u l t il a m e ll ar Large vesicles (>0.5 um) OLV oligolamellar vesicles (>0.1-1.0 um) UV Unilamellar Vesicles (all size ranges) MVV M u ltivesi c u l a r vesicles (> 1.0 um) MUV Medium Unilamellar Vesicles GUV Giant Unilamellar Vesicles >1um SUV Small Unilamellar Vesicles 20-100nm LUV Large Unilamellar Vesicles >100nm Based on structural parameters 15

14. 16

15. Preparation of liposomes Methods of liposome preparation Passive loading: Involves loading of the entrapped agents before or dur ing the manufacturing procedure. Active or remote loading: Certain types of compounds with ioni s able groups and those with both manufacturing procedure lipid and water solubility can be introduced into the liposomes after the formation of the intact vesicles 17

16. Methods of liposome preparation Solvent dispersion methods  Ethanol injection  Ether injection  Double emulsion vesicles  Stable plurilamellar  Vesicles  Reverse phase evaporation vesicles Detergent removal methods Passive loading techniques  D eterg e nt( C h o l ate, Alkyl glycoside, Triton X-100) removal from mixed micelles by  Dialysis  Column c h ro m atogra p hy  Dilution  Reconstituted sendai virus enveloped vesicles Active loading techniques  Lipid film hydration by hand shaking non-hand shaking and freeze drying  Micro emulsification  Sonication  French pressure cell  Membrane extrusion  Dried reconstituted vesicles  Freeze thawed liposomes Mechanical dispersion methods 18

17. Evaluation of liposomes The liposomes prepared by various techniques are to be evaluated for their physical properties, has these influence the behavior of liposomes in vivo. 18 Physical properties Particle size Both particle size and particle size distribution of liposomes influence their physical stability. These can be determined by the following method. Laser light scattering Transmission electron microscopy

18. 19 2. Surface charge The positive, negative or neutral charge on the surface of the liposomes is due to the composition of the head groups. The surface charge of liposomes governs the kinetic and extent of distribution in vivo, as well as interaction with the target cells. The method involved in the measurement of surface charge is based on free-flow electrophoresis of MLVs .

19. 3. Percent drug encapsulated. 20 • • • • Quantity of drug entrapped in the liposomes helps to estimate the behavior of the drug in biological system Liposomes are mixture of encapsulated and unencapsulated drug fractions The % of drug encapsulation is done by first separating the free drug fraction from encapsulated drug fraction The encapsulated fraction is then made to leak off the liposome into aqueous solution using suitable detergents The methods used to separate the free drug from the sample are: Mini column centrifugation method Protamine aggregated method

20. 4. Phase behavior • At transition temperature liposomes undergo reversible phase transition • • The t ran s i tion te m peratu r e is the indic a t ion of s t a b i lity permeability and also indicates the region of drug entrapment Done by DSC l iposomes undergo a reversible phase transition when heated or cooled, changing from a gel to a liquid phase and vice versa.  5. Drug Release Rate The rate of drug release from the liposomes can be determined by in vivo assays which helps to predict the pharmacokinetics and bioavailability of the drug. 22

21. Applications 22 • • • • • • • • Liposomes as drug or protein delivery vehicles. Liposome in antimicrobial, antifungal(lung therapeutics) and antiviral (anti HIV) therapy. In tumor therapy. In gene therapy. In immunology. Liposomes as artificial blood surrogates. Liposomes as radiopharmaceutical and radio diagnostic carriers. Liposomes in cosmetics and dermatology.

22. 23