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LIPOSOMES

LIPOSOMES (2)

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Page 1: LIPOSOMES (2)

LIPOSOMES

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DEFINITIONThe name liposome is derived from two

Greek words:Lipo: meaning FatSoma: meaning body

“Liposomes are simple microscopic vesicles in which an aqueous volume is entirely enclosed by a membrane composed of a lipid molecule”

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History

Liposomes were first described by British haematologist Dr Alec D Bangham and colleagues in 1961 (published 1964).

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Structure

Structurally liposomes are concentric bilayered vesicles in which an aqueous volume is entirely enclosed by a membranous lipid bilayer mainly composed of natural or synthetic phospholipids

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COMPONENTS

Phospholipidsmajor structural

components of biological membranes.

In the membrane cholesterol increases separation

between choline head groups which reduces the normal hydrogen bonding

and electrostatic interaction

Drug is encapsulated ini. Phospholipid bilayer

ii. In the entrapped aqueous

iii. At bilayer interface.

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Activity

Head……. Hydrophillic Tail………. Hydrophobic) Hydrophobic portion is repelled by water Hydrophilic portion is attracted by water Activity of liposomes is enhancesd by modifying

the surface of liposomes with different molecules such as glycolipids.

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ACTIVITY

Hydrophilic drug is entrapped in

hydrophilic portion of liposomes.

Hydrophobic drug is entrapped in lipophillic portion.

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Modes of Liposome/Cell Interaction

Adsorption Endocytosis

Fusion Lipid transfer

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Mechanism of Drug Release

Liposome attaches to plasma membrane and appears to fuse with them, releasing their content into cell.

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• Improved solubility of lipophilic and amphiphilic drugs .• Liposomes have both a lipophilic and aqueous environment

making it useful for delivering hydrophobic, amphipathic, and hydrophilic medicines

• It shows drug effect at its specific targeted site • Shows sustained release action.• Liposomes improved penetration of various drugs into tissues • Liposomes increases efficacy and therapeutic index.• Liposomes protect the drug from environment and the

sensitive areas from drug.

Need For Liposomes

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Disadvantages

High production

cost

Liposome phospholipi

d may undergo

oxidation & hydrolysis

Shorter Half life

May have leakage of encapsulat

ed drug

Liposomes are quickly taken up by

the reticular

endothelial cells

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CLASSIFICATION OF LIPOSOMES

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According to SizeName Diameter No. of lamella

Small unilamellar vesicles 20-100nm Single

Large unilamellar vesicles 100 nm - 400 nm Single

Intermediate-sized unilamellar vesicles

100-200 nm Single

Giant Unilamellar Vesicles 1 µm & larger Single

Multivesicular Vesicles 200 nm - ~3 µm Multiple

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Names Diameter Number of lamella

Unilamellar vesicles All sizes Single

Multilamellar vesicles 200 nm - ~3 µm Multiple(5 & 20)

Multivesicular liposomes

- -

ACCORDING TO MORPHOLOGY

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According To Composition

ImmunoliposomesLiposomes using immunological

molecules particularly, immunoglobulins for targeting

purposes may be attached to liposomes surface by covalent linkage through

membrane possessing functional group

s

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According to FunctionStealth Tranfersomes

•Long circulatory liposome

•Any liposome that avoids uptake by the RES as a result of coating the surface of the liposomes with hydroxylated polymers

•Particular composition that are capable of transferring equeous content across the skin

•There membrane contains a certain proportion of the bile salt distributed among the phospholipid, which confers the increased flexibility on membrane

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Methods Of Preparation

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METHODS OF PREPARATIONAll the methods of preparing the liposomes involve four

basic stages:

The difference between these methods is the steps by which lipids are drying down from organic solvents and then redispersed in aqueous media.

1. Drying down lipids from organic solvent

2. Dispersing the lipid in aqueous media

3. Purifying the resultant liposome

4. Analyzing the final product

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SELECTION CRITERIA

Choice of method for liposomes production:

Physicochemical characteristics of drug to be loaded and ingredients.

Nature of dispersion medium in which liposomes are dispersed.

Effective concentration and toxicity of entrapped substance. Size, dispersity and shelf life of vesicles for intended

application. Batch to batch reproducibility. Large-scale production of safe and efficient liposomal products.

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Mechanical Dispersion Method

1. Lipid Hydration Method2. Lyophillization3. Proliposomes

To Reduce Liposome Size

•Sonication•French Pressure Cell•Microemulsification•Membrane Extrusion

To Increase Liposome Size

•Freeze thawing•Direct reconstituted vesicles

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1. Mechanical Dispersion MethodLipid dissolve in organic solvent/co-solvent

Remove organic solvent under vacuum

Film deposition

Solid lipid mixture is hydrated by using aqueous buffer

Lipid spontaneously swell and hydrate

Liposome

Post hydration vortexing, sonication, freeze thawing and high pressure extrusion

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i. Lipid Hydration MethodHand shaken vesicles

most widely used for the preparation of MLV

Drying of lipid solution forms a thin film at bottom

Hydrating this film by adding aqueous buffer

Vortexing it for some time

MLVs prepared

Lipids +Solvent

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Non-shaking vesicles

Solution of Lipids +

solvent

MLV are floating on

surface remaining

fluid produces

LUV

Nitrogen gas is

passed

Hydration

Until the opacitiy of the dried lipid film disappears.

Flask is slowly returned to

upright position.Take care not to disturb the flask

in any way.

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ii. Lyophilization • Freeze-drying involves the removal of water

from products in the frozen state at extremely low pressures.

• The process is generally used for dry products.

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iii. PROLIPOSOMES

Lipid is dried over the finely divided particulate support i.e.- NaCl, Sorbitol, or other polysaccharides.

These dried lipid coated particulates are called as proliposomes.

Drying

lipid

on finely divided support (NaCl

)

Surface

area

increases and continuous

hydration

hydration

swelling

MLVs

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To Reduce Liposome Size•Sonication•French Pressure Cell•Micro emulsification•Membrane Extrusion

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Sonication

• most extensively used for the preparation of small unilamellar vesicle (SUV). Sonication is the act of applying sound energy to agitate particles in a sample to reduce the size.

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French pressure cell: extrusion

MLV dispersion are placed in the French Pressure Cell and extruded at about 20,000psi at 45C

95% of MLVs get converted to SUVs which can be determined by size extrusion chromatoraphy

Dispersion of MLVs can be converted to SUVs by passage through a small orifice under high pressure.

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MICRO EMULSIFICATION LIPOSOMES

The lipids can be introduced into fluidizers, either as a dispersion of large mlvs or as a slurry of unhydrated lipids in organic medium.

Microfluidizer pumps the fluid at very high pressure through a 5um orifice.

Forced along defined micro channels,

Two streams of fluid to collide together at right angles at a very high velocity.

The fluid collected of can be recycled through the pump and interaction chamber until vesicles of the spherical dimension are obtained.

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Membrane extrusion

Size of liposomes is reduced by gently passing them through polycarbonate membrane filter of defined pore size (100nm) at much lower pressure (<100psi)

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To Increase Liposome Size•Freeze thawing•Direct reconstituted vesicles

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Freeze-thawing

This method is based upon freezing of SUV then

thawing by standing at room temperature for

15mins.

Finally subjecting to a brief

sonication cycle.

It results in a high proportion of large unilamellar vesicles

formation.

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Freeze SUVsThaw at

room temp. for 15 min

Sonicate SUVs rupture LUVs

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Dried Reconstituted Vesicles

Empty SUVs

Hydrate with entrapping material

Freeze drying

Rehydrate with material to be encapsulated

Uni or oligolamellar vesicles

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2. Solvent Dispersion Method:Lipid dissolve in organic solvent

Excess addition of aqueous phase

Lipids align at interface of aqueous and organic layer

Formation of monolayer and bilayer of phospholipids

Liposome

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Solvent Dispersion

Method

solvent injection (ether

and ethanol)

Double emulsificati

on

Reverse phase

evaporation

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i. SOLVENT (Ether or Ethanol) INJECTION TECHNIQUE

Ethanol injection

• Lipid +ethanol• Rapid injection• Saline buffer + material to be

entrapped• SUVs

Ether injection

• Lipid + ether• Slow injection• In aqueous phase (heat in

water bath 60°C)• SUVs• Disadvantage:• Longer time• low efficiency

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ii. Double Emulsification

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iv. Reverse phase evaporation method

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Drawback: These conditions may possibly result in the breakage of DNA strands or the denaturation of some proteins.

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3.Detergent Solubilization

The detergents at their critical micelles concentrations have been used to solubilize lipids.

Phospholipid brought into intimate contact with aqueous phase

By addition optimized concentration of detergent

Formation of micelles (liposome)

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Detergent is removed by following methods:i. dialysisii. column chromatographyii. use of biobeads

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ACTIVE LOADING TECHNIQUE This technique employs the principle that certain type of

compounds with ionizable groups and those with both lipid and water solubility can be introduced into the liposomes after the formation of intact vesicle.

Loads drug molecules into preformed liposomes using pH gradients and potential difference across cell membranes.

The transmembrane pH gradient can be developed using various methods depending on nature of the drug to be encapsulated.

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• 2 step process generates the pH imbalance and remote loading:

The vesicles are prepared in low pH solution

It is followed by addition of base to the extraliposomal medium

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ADVANTAGES OVER THE PASSIVE LOADING METHODS

A high encapsulation efficiency and capacity.

A reduced leakage of the encapsulated compounds.

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REFERENCES• Drug Delivery Systems By Vasant V. Ranade, John B. Cannon. Third Edition. Page no. 1 and 2

@ 2011 by Taylor and Francis Group, LLC.• (http://www.news-medical.net/health/What-is-a-Liposome.aspx) visited on 1st April,

2014 at 8:16pm. This article is licensed under the Creative Commons Attribution-ShareAlike License.

• (http://www.avantilipids.com/index.php?option=com_content&view=article&id=1384&Itemid=372) visited on 1st April, 2014 at 8:50pm. © Avanti Polar Lipids, Inc. All rights reserved. Terms and Conditions Privacy Policy Comments.

• By Jean R. Philippot, F. S. (1994). Liposomes as tools in basic research and industry . The liposomes . Florida: CRC Press.

• J.S. Dua1, P. A. (2012, april-june). International Journal of Pharmaceutical Studies and Research. LIPOSOME: METHODS OF PREPARATION AND APPLICATIONS . Jodhpur, Rajasthan,Nawanshahr, Panjab, India: IJPSR.

• Liposome Drug Delivery: A Review By Chauhan Tikshdeep*, Arora Sonia, Parashar Bharat and Chandel Abhishek. INTERNATIONAL JOURNAL OF PHARMACEUTICAL AND CHEMICAL SCIENCES ISSN: 2277-5005

• Liposome: classification, preparation, and applications. BY Abolfazl Akbarzadeh, Rogaie Rezaei-Sadabady Soodabeh Davaran,Sang Woo Joo, Nosratollah Zarghami,Younes Hanifehpour, Mohammad Samiei, Mohammad Kouhi and Kazem Nejati-Koshki. Nanoscale Research Letters © 2013 Akbarzadeh et al.; licensee Springer