LIPOSOMES
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”
History
Liposomes were first described by British haematologist Dr Alec D Bangham and colleagues in 1961 (published 1964).
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
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.
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.
ACTIVITY
Hydrophilic drug is entrapped in
hydrophilic portion of liposomes.
Hydrophobic drug is entrapped in lipophillic portion.
Modes of Liposome/Cell Interaction
Adsorption Endocytosis
Fusion Lipid transfer
Mechanism of Drug Release
Liposome attaches to plasma membrane and appears to fuse with them, releasing their content into cell.
• 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
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
CLASSIFICATION OF LIPOSOMES
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
Names Diameter Number of lamella
Unilamellar vesicles All sizes Single
Multilamellar vesicles 200 nm - ~3 µm Multiple(5 & 20)
Multivesicular liposomes
- -
ACCORDING TO MORPHOLOGY
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
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
Methods Of Preparation
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
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.
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
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
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
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.
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.
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
To Reduce Liposome Size•Sonication•French Pressure Cell•Micro emulsification•Membrane Extrusion
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.
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.
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.
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)
To Increase Liposome Size•Freeze thawing•Direct reconstituted vesicles
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.
Freeze SUVsThaw at
room temp. for 15 min
Sonicate SUVs rupture LUVs
Dried Reconstituted Vesicles
Empty SUVs
Hydrate with entrapping material
Freeze drying
Rehydrate with material to be encapsulated
Uni or oligolamellar vesicles
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
Solvent Dispersion
Method
solvent injection (ether
and ethanol)
Double emulsificati
on
Reverse phase
evaporation
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
ii. Double Emulsification
iv. Reverse phase evaporation method
Drawback: These conditions may possibly result in the breakage of DNA strands or the denaturation of some proteins.
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)
Detergent is removed by following methods:i. dialysisii. column chromatographyii. use of biobeads
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.
• 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
ADVANTAGES OVER THE PASSIVE LOADING METHODS
A high encapsulation efficiency and capacity.
A reduced leakage of the encapsulated compounds.
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
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