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International Journal of Universal Pharmacy and Bio Sciences 4(6): November-December 2015
INTERNATIONAL JOURNAL OF UNIVERSAL PHARMACY AND BIO SCIENCES
IMPACT FACTOR 2.093*** ICV 5.13*** Pharmaceutical Sciences REVIEW ARTICLE …………!!!
AN OVERVIEW ON LIPOSOMES: A NOVEL DRUG DELIVERY SYSTEM
Shewale Lankesh1*
.Gondkar S.B1, Saudagar R.B
2.
1*Department of Pharmaceutics, R.G. Sapkal college of pharmacy, Anjaneri, Nashik-422213,
Maharashtra, India. 1*
Department of Pharmaceutics, R.G. Sapkal college of pharmacy, Anjaneri, Nashik-422213,
Maharashtra, India. 2*
Department of Pharmaceutical Chemistry, R.G. Sapkal college of pharmacy, Anjaneri, Nashik-
422213, Maharashtra, India.
KEYWORDS:
Liposomes,
Phospholipids,
Classification,
Limitation,Glycolipids,
Structural Components.
For Correspondence:
Shewale Lankesh*
Address:
Department of
Pharmaceutics, R.G.
Sapkal college of
pharmacy, Anjaneri,
Nashik-422213,
Maharashtra, India.
ABSTRACT
Liposomes represent an important class of carrier vehicles other than the
polymers for drug delivery. This review provides an introduction and
general review of liposomes with emphasis on their classification, their
constituent materials, their preparation and characterization, and their
stability and biodistribution in the body. The main objective of drug
delivery system is to deliver a drug effectively, specifically to site of
action and to achive greater efficacy and to minimize the toxic effect
compared to conventional drug. Among various carrier systems, liposomes
have generated a great interest because of their versatility. Liposomes are
vesicular concentric bilayered structure, which are biocompatible,
biodegradable and nonimmunogenic. They can control the delivery of drug
by targeting the drug to the site of action or by site avoidance drug
delivery or by prolonged circulation of drug. After the formulation, the
evaluation of liposomes are checked by using physical parameters,
chemical parameters, and biologically for the establish the purity and
potency of various lipophilic constituents and establish the safety and
suitability of formulation for therapeutic application.
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INTRODUCTION:
Liposomes were first described by British haematologist Dr Alec D Bhangham in 1961
(published 1964), at Babraham Institute, in Cambridge. They were discovered when
Bangham and R.W. Horne were testing the institute’s new electron microscope by adding
negative stain to dry phospholipids. Liposomes are defined as structure consisting of one or
more concentric spheres of lipid bilayers seprated by water or aqueous buffer compartment or
Liposomes are simple microscopic vesicles in which an aqueous volume is entirely enclosed
by a membrane composed of lipid bilayers. The name liposome is derived from two Greek
words: 'Lipos' meaning fat and 'Soma' meaning body. A liposome can be formed at a variety
of sizes as unillamellar or multi-lamellar construction, and its name relates to its structural
building blocks, phospholipids, and not to its size. A liposome does not necessarily have
lipophobic contents, such as water, although it usually does. Liposomes are artificially
prepared vesicles made of lipid bilayer. Liposomes can be filled with drugs, and used to
deliver drugs for cancer and other diseases. Liposomes can be prepared by disrupting
biological membranes, for example by sonication. Liposomes are micro particulate or
colloidal carriers, usually 0.05- 5.0 μm in diameter which form spontaneously when certain
lipid are hydrated in aqueous media. Liposomes are composed of relatively biocompatible
and biodegradable material, and they consist of an aqueous volume entrapped by one or more
bilayer of natural and/or synthetic lipids. Drug with widely varying lipophilicities can be
encapsulated in liposomes, either in the phospholipids bilayer, in the entrapped aqueous
volume or at the bilayer interface. The delivery of drugs onto the skin is recognized as an
effective means of therapy for local dermatologic diseases. Liposome is acceptable and
superior carrier and has ability to encapsulate hydrophilic and lipophilic drugs and protect
them from degradation. Topical drug administration is a localized drug delivery system any
where in the body through ophthalmic, rectal, vaginal and skin as topical routs. Skin is one of
the most readily accessible organs on human body for topical administration and is main
route of topical drug delivery system. Topical application of liposome vesicles has many
advantages over the conventional dosage forms. However major limitation of using
liposomes topically is the liquid nature of preparation. They can be overcome by their
incorporation in adequate vehicles where original structure of vesicles is preserved. It has
already been shown that liposomes are fairly compatible with gels made from polymers
derived from cross linked polyacrylic acid, such as carbopol resins.
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Fig.1.Structure of liposome
ADVANTAGES OF LIPOSOMES[1,2,7]
1. Provide controlled drug delivery
2. Biodegradable, biocompatible,flexible
3. Non ionic
4. Can carry both water and lipid soluble drugs
5. Drug can be stabilized from oxidation
6. Improve protein stabilization
7. Provide sustain release action
8. Can be administered through various routes
9. Therapeutic index of drug is increased
10. Can act as reservoir of drug
11. Direct interaction of the drug with cell
12. Targeted drug delivery or site specific drug delivery.
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DISADVANTAGES OF LIPOSOMES[1,2,7]
1. Less stability
2. Low solubility
3. Short half life
4. Phospho lipid undergoes oxidation, hydrolysis
5. Leakage and infusion
6. High production cost
7. Allergic reactions may occurs to liposomal constituents
8. Quick uptake by cells of R.E.S
9. Problem to targeting to various tissue due to their large size.
CLASSIFICATION OF LIPOSOMES [1,2,7]
Table no: 1. Based On Structure Parameter
TYPE-1 SPECIFICATION
BASED ON STRUCTURE PARAMETER
MLV
OLV
UV
SUV
MUV
LUV
GUV
MV
Multilamellar large vesicle->0.5μm
Oligolamellar vesicle-0.1-0mm
Unilamellarvesicle (all range size)
Small sized unilamellar vesicle
Medium sized unilamellar vesicle
Large unilamellar vesicle-> 100mm
Giant unilamellar vesicle- >1mm
Multivesicular vesicle >1mm
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Table no:2Based On Liposomes Preparation
TYPE-2 SPECIFICATION
BASED ON LIPOSOMES
PREPARATION
REV
MLV-REV
SPLV
FATMLV
VET
DRV
Single or oligolamellar vesicle made by
reverse phase evaporation method
Multilamellar vesicle made by reverse
phase evaporation method
Stable plurilamellar vesicle
Frozen and thawed MLV
Vesicle prepared by extrutiontechnique
Dehydration rehydration method
Table no:3Based Upon Composition And Application
TYPE-3 SPECIFICATION
BASED UPON COMPOSITION AND
APPLICATION
Conventional liposome
Cationic liposome
Long circulatory liposome
pH sensitive liposome
Immuno liposome
Neutral or negatively charged Phospholipid
Cationic lipid
Neutral high Transition temperature
liposme
Phospholipid like Phosphatidyl
ethanolamine
Long circulatory liposome with attached
monoclonal antibody
STRUCTURAL COMPONENT OF LIOPOSOMES[3,4,5]
A. Phospholipids
Glycerol containing phospholipids are most common used component of liposome
formulation and represent greater than 50% of weight of lipid in biological membranes.
These are derived from Phosphatidic acid. The back bone of the molecule is glycerol moiety.
Examples of phospholipids are
- Phosphatidyl choline (Lecithin) – PC
- Phosphatidyl ethanolamine (cephalic) – PE
B. Sphingolipids
Backbone is sphingosine or a related base. These are important constituents of plant and
animal cells. This contain 3 characteristic building blocks
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- A head group that can vary from simple alcohols such as choline to very complex
carbohydrates.
- Sphingolipids – Sphingomyelin. Glycosphingolipids.
- Gangliosides – found on grey matter, used as amin or component for liposome production.
C. Sterols
Cholesterol & its derivatives are often included in liposomes for
- decreasing the fluidity or micro viscocity of the bilayer
- reducing the permeability of the membrane to water soluble molecules
- Stabilizing the membrane in the presence of biological fluids such as plasma.( This effect
used in formulation of i.v. liposomes)
Liposomes without cholesterol are known to interact rapidly with plasma protein such as
albumin, transferring, and macroglobulin. These proteins tend to extract bulk phospholipids
from liposomes, thereby depleting the outer monolayer of the vesicles leading to physical
instability. Cholesterol appears to substantially reduce this type of interaction. Cholesterol
has been called the mortar of bilayers, because by virtue of its molecular shape and solubility
properties, it fills in empty spaces among the Phospholipids molecules, anchoring them more
strongly into the structure. The OH group at 3rd
position provides small Polar head group and
the hydrocarbon chain at C17 becomes non polar end by these molecules, the cholesterol
intercalates in the bilayers.
D. Synthetic phospholipids
Saturated phospholipids are
1 Dipalmitoylphosphatidyl choline (DPPC)
2 Distearoylphosphatidyl choline (DSPC)
3 Dipalmitoylphosphatidyl ethanolamine (DPPE)
4 Dipalmitoylphosphatidyl serine (DPPS)
5 Dipalmitoylphosphatidicacid (DPPA)
6 Dipalmitoylphosphatidyl glycerol (DPPG
Unsaturated phospholipids
1. Dioleoylphosphatidyl choline (DOPC)
2. Dioleoylphosphatidyl glycerol (DOPG)
E. Polymeric materials
Synthetic phospholipids with diactylenic group in the hydrocarbon chain polymerizes when
exposed to U.V, leading to formation of polymerized liposomes having significantly higher
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permeability barriers to entrapped aqueous drugs. E.g.: for other Polymerisable lipids are –
lipids containing conjugated diene, Methacrylate etc. Also several
Polymerisablesurfactantsare also synthesized.
F. Polymer bearing lipids
Stability of repulsive interactions with macromolecules is governed mostly by repulsive
electrostatic forces. This repulsion can be induced by coating liposome surfaces with charged
polymers. Non ionic and water compatible polymers like polyethylene oxide, polyvinyl
alcohol, and Polyoxazolidines confers higher solubility. But adsorption of such copolymers
containing hydrophilic segments with hydrophobic part leads to liposome leakage, so best
results can be achieved by covalently attaching polymers to phospholipids.
E.g.: DiacylPhosphatidyl ethanolamine with PEGpolymer linked via a carbon at or succinate
bond.
G. Cationic lipids
E.g.: DODAB/C – Dioctadecyl dimethyl ammonium bromide or chloride
DOTAP – Dioleoyl propyl trimethyl ammonium chloride this is an analogue of DOTAP and
various others including various analogues of DOTMA and cationic derivatives of
cholesterol.
METHOD OF PREPARATION OF LIPOSOMES[8,9,10]
The following methods are used for the preparation of liposomes:
· Passive loading techniques
· Active loading technique.
Passive loading techniques include three different methods:
1 Mechanical dispersion method.
2 Solvent dispersion method.
3 Detergent removal method (removal of non encapsulated material).
1. Mechanical dispersion method
The following are types of mechanical dispersion methods:
· Sonication.
· French pressure cell: extrusion.
· Freeze-thawed liposome’s.
· Lipid film hydration by hand shaking, non-handshaking or freeze drying.
· Micro-emulsification.
· Membrane extrusion.
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· Dried reconstituted vesicles.
Sonication
Sonication is perhaps the most extensively used method for the preparation of SUV. Here,
MLVs are sonicated either with a bath type sonicator or a probe sonicator under a passive
atmosphere. The main disadvantages of this method are very low internal
volume/encapsulation efficacy, possible degradation of phospholipids and compounds to be
encapsulated, elimination of large molecules, metal pollution from probe tip, and presence of
MLV along with SUV. There are two sonication techniques:
- Probe sonication. The tip of a sonicator is directly engrossed into the liposome dispersion.
The energy input into lipid dispersion is very high in this method. The coupling of energy at
the tip results in local hotness; therefore, the vessel must be engrossed into a water/ice bath.
Throughout the sonication up to 1 h, more than 5% of the lipids can be de-esterified. Also,
with the probe sonicator, titanium will slough off and pollute the solution.
- Bath sonication. The liposome dispersion in a cylinder is placed into a bath sonicator.
Controlling the temperature of the lipid dispersion is usually easier in this method, in contrast
to sonication by dispersal directly using the tip. The material being sonicated can be protected
in a sterile vessel, dissimilar the probe units, or under an inert atmosphere.
French pressure cell: extrusion
French pressure cell involves the extrusion of MLV through a small orifice. An important
feature of the French press vesicle method is that the proteins do not seem to be significantly
pretentious during the procedure as they are in sonication. An interesting comment is that
French press vesicle appears to recall entrapped solutes significantly longer than SUVs do,
produced by sonication or detergent removal. The method involves gentle handling of
unstable materials. The method has several advantages over sonication method. The resulting
liposomes are rather larger than sonicated SUVs. The drawbacks of the method are that the
high temperature is difficult to attain, and the working volumes are comparatively small
(about 50 mL as the maximum).
Freeze-thawed liposomes
SUVs are rapidly frozen and thawed slowly. The short-lived sonication disperses aggregated
materials to LUV. The creation of unilamellar vesicles is as a result of the fusion of SUV
throughout the processes of freezing and thawing. This type of synthesis is strongly inhibited
by increasing the phospholipid concentration and by increasing the ionic strength of the
medium. The encapsulation efficacies from 20% to 30% were obtained.
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2 Solvent dispersion method
Fig:2 Lipid Film Hydration Method
Ether injection (solvent vaporization)
A solution of lipids dissolved in diethyl ether or ether-methanol mixture is gradually injected
to an aqueous solution of the material to be encapsulated at 55°C to 65°C or under reduced
pressure. The consequent removal of ether under vacuum leads to the creation of liposomes.
The main disadvantages of the technique are that the population is heterogeneous (70 to 200
nm) and the exposure of compounds to be encapsulated to organic solvents at high
temperature.
Ethanol injection
A lipid solution of ethanol is rapidly injected to a huge excess of buffer. The MLVs are at
once formed. The disadvantages of the method are that the population is heterogeneous (30 to
110 nm), liposome’s are very dilute, the removal all ethanol is difficult because it forms into
azeotrope with water, and the probability of the various biologically active macromolecules
to inactivate in the presence of even low amounts of ethanol is high.
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Reverse phase evaporation method
This method provided a progress in liposome technology, since it allowed for the first time
the preparation of liposomes with a high aqueous space-to-lipid ratio and a capability to
entrap a large percentage of the aqueous material presented. Reverse-phase evaporation is
based on the creation of inverted micelles. These inverted micelles are shaped upon
sonication of a mixture of a buffered aqueous phase, which contains the water-soluble
molecules to be encapsulated into the liposomes and an organic phase in which the
amphiphilic molecules are solubilized. The slow elimination of the organic solvent leads to
the conversion of these inverted micelles into viscous state and gel form. At a critical point in
this process, the gel state collapses, and some of the inverted micelles were disturbed. The
excess of phospholipids in the environment donates to the formation of a complete bilayer
around the residual micelles, which results in the creation of liposomes. Liposomes made by
reverse phase evaporation method can be made from numerous lipid formulations and have
aqueous volume-to-lipid ratios that are four times higher than hand-shaken liposomes or
multilamellar liposomes. Briefly, first, the water-in-oil emulsion is shaped by brief sonication
of a two-phase system, containing phospholipids in organic solvent such as isopropyl ether or
diethyl ether or a mixture of isopropyl ether and chloroform with aqueous buffer. The organic
solvents are detached under reduced pressure, resulting in the creation of a viscous gel. The
liposomes are shaped when residual solvent is detached during continued rotary evaporation
under reduced pressure. With this method, high encapsulation efficiency up to 65% can be
obtained in a medium of low ionic strength for example 0.01 M NaCl. The method has been
used to encapsulate small, large, and macromolecules. The main drawback of the technique is
the contact of the materials to be encapsulated to organic solvents and to brief periods of
sonication. These conditions may possibly result in the breakage of DNA strands or the
denaturation of some proteins. Modified reverse phase evaporation method was presented by
Handa et al., and the main benefit of the method is that the liposomes had high encapsulation
efficiency (about 80%).
3 Detergent removal method (removal of nonencapsulated material)
Dialysis
The detergents at their critical micelle concentrations (CMC) have been used to solubilize
lipids. As the detergent is detached, the micelles become increasingly better-off in
phospholipid and lastly combine to form LUVs. The detergents were removed by dialysis. A
commercial device called LipoPrep (Diachema AG, Switzerland), which is a version of
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dialysis system, is obtainable for the elimination of detergents. The dialysis can beperformed
in dialysis bags engrossed in large detergent free buffers (equilibrium dialysis).
Detergent (cholate, alkyl glycoside, Triton X-100) removal of mixed micelles
(absorption)
Detergent absorption is attained by shaking mixed micelle solution with beaded organic
polystyrene adsorbers such as XAD-2 beads (SERVA Electrophoresis GmbH, Heidelberg,
Germany) and Bio-beads SM2 (Bio-Rad Laboratories, Inc., Hercules, USA). The great
benefit of using detergent adsorbers is that they can eliminate detergents with a very low
CMC, which are not entirely depleted.
Dilution
Upon dilution of aqueous mixed micellar solution of detergent and phospholipids with buffer,
the micellar size and the polydispersity increase fundamentally, and as the system is diluted
beyond the mixed micellar phase boundary, a spontaneous transition from polydispersed
micelles to vesicles occurs.
Drug loading in liposomes
Drug loading can be attained either passively (i.e., the drug is encapsulated during liposome
formation) or actively (i.e., after liposome formation). Hydrophobic drugs, for example
amphotericin B taxol or annamycin, can be directly combined into liposomes during vesicle
formation, and the amount of uptake and retention is governed by drug-lipid interactions.
Trapping effectiveness of 100% is often achievable, but this is dependent on the solubility of
the drug in the liposome membrane. Passive encapsulation of water-soluble drugs depends on
the ability of liposomes to trap aqueous buffer containing a dissolved drug during vesicle
formation. Trapping effectiveness (generally <30%) is limited by the trapped volume
delimited in the liposomes and drug solubility. On the other hand, water-soluble drugs that
have protonizable amine functions can be actively entrapped by employing pH gradients,
which can result in trapping effectiveness approaching 100%.
Purification of liposome
Liposomes are generally purified by gel filtration chromatography14, Dialysis and
centrifugation. In chromatographic separation, Sephadex-50 is most widely used. In dialysis
method hollow fibre dialysis cartridge maybe used. In centrifugation method, SUVs in
normal saline may be separated by centrifuging at 200000 g, for 10-20hours. MLVs are
separated by centrifuging at 100000g for less than one hour.
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Mechanism of transportation through liposome[15,16]
The limitations and benefits of liposome drug carriers lie critically on the interaction of
liposomes with cells and their destiny in vivo after administration. In vivo and in vitro studies
of the contacts with cells have shown that the main interaction of liposomes with cells is
either simple adsorption (by specific interactions with cell surface components, electrostatic
forces, or by nonspecific weak hydrophobic) or following endocytosis (by phagocyte cells of
the reticulo endothelial system, for example macrophages and neutrophils). Fusion with the
plasma cell membrane by insertion of the lipid bilayer of the liposome into the plasma
membrane, with simultaneous release of liposomal content into the cytoplasm, is much rare.
The fourth possible interaction is the exchange ofbilayer components, for instance
cholesterol, lipids, and membrane-bound molecules with components of cell membranes.
Targeting of liposomes[12,20]
Two types of targeting.
1) Passive targeting
As a mean of passive targeting, such usually administered liposomes have been shown to be
rapidly cleared from the blood stream and taken up by the RES in liver spleen. Thus capacity
of the macrophages can be exploited when liposomes are to be targeted to the macrophages.
This has been demonstrated by successful delivery of liposomal antimicrobial agents to
macrophages. Liposomes have now been used for targeting of antigens to macrophages as a
first step in the index of immunity. For e.g. in rats the i.v. administration of liposomal antigen
elicited spleen phagocyte mediated antibody response where as the non liposome associated
antigen failed to elicit antibody response.
2) Active targeting
A pre requisite for targeting is the targeting agents be positioned on the liposomal surface
such that the interaction with the target i.e., the receptor is tabulated such as a plug and socket
device. The liposome physically prepared such that the lipophilic part of the connector is
anchored into the membrane during the formation of the membrane. The hydrophilic part on
the surface of the liposome, to which the targeting agent should be held in a stericaly correct
position to bond to the receptor on the cell surface.
Pharmacokinetics of liposomes[13]
- Liposomal drugs can be applied through various routes, but mainly i.v. and topical
administration is preferred. After reaching in the systemic circulation or in the local area, a
liposome can interact with the cell by any of the following methods.
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- Endocytosis by phagocytotic cells of the R.E.S such as macrophages and Neutrophils.
-Adsorption to the cell surface either by non specific weak hydrophobic or electrostatic forces
or by specific interaction with cell surface components.
- Fusion with the plasma cell membrane by insertion of lipid bilayer of liposome into plasma
membrane with simultaneous release of liposomal contents into the cytoplasm.
-Transfer of liposomal lipids to cellular or sub cellular membrane or vice versa without any
association of the liposome contents.
- It is often difficult to determine what mechanism is operative and more than one may
operate at the same time.
Pharmocodynamics of liposomes encapsulated drugs[14]
To continue the action of drugs to a particular site in the body, the general approach is to
deposit drug bearing liposome directly into the site where therapy is desired. Since liposomes
are large and do not easily cross epithelial or connective barriers, they are likely to remain at
the site of local administration. The liposomes would then slowly released into the target site
or perhaps create a local drug level higher than the systemic level. Alternatively the drug
loaded liposomes might interact directly with cells in the target site, without producing
release. The goal of this approach is to maximize the amount of effective drug at the target
site, while minimizing the drug levels at other sites and thus decreasing systemic toxicity. For
e.g. SUV injected into the skin can persist interact at the site for 600 hrs. And release of
entrapped markers from the liposomes occurs only after cellular uptake and intracellular
space remain intact.
Evaluation of liposomes[11]
Liposomal formulation and processing for specified purpose are characterized to ensure their
predictable in-vitro and invivo performance. The characterization parameters for purpose of
evaluation could be classified into 3 broad categories which include physical, chemical, and
biological parameters.
-Physical characterization evaluates various parameters including size, shape, surface
features, lamellarty, phase behaviors and drug release profile.
-Evaluated structural integrity of Liposomal phospholipids membrane by a New technique of
gamma-ray perturb angular correlation (PAC spectroscopy.In this 111 Inlabelln diethyl
enetriaminepenta acetic acid (DTPA) Derivative dipalmitiylphosphatidylethanoamine(DPPE)
lipid were incorporated in the SUVs. This helped in the continuous non-invasive monitoring
of the microenvironment of the lipid bilayer.
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-Chemical Characterization includes those studies which establish the purity and potency of
various lipophilic constituents.
-Biological Characterization parameters are helpful in establishing the safety and suitability
of formulation for therapeutic application.
1 Vesicle shape and Lamellarity
Vesicle shape can be assessed using Electron Microscopic Techniques. Lamellarity of
vesicles i.e. number of bilayer present in liposomes is determined using Freeze- Fracture
Electron Microscopy and P-31 Nuclear Magnetic Resosance Analysis.
2 Vesicle size and size distribution
Various techniques are described in literature for determination of size and size distribution.
These include Light Microscopy, Electron Microscopy (especially Transmission Electron
Microscopy), Laser light scattering Photon correlation Spectroscopy, Field Flow
Fractionation, Gel permeation and Gel Exclusion. The most precise method of determine size
of liposome is Electron Microscopy Since it permit one to view each individual liposome and
obtain exact information about profile of liposome population over the whole range of sizes.
Unfortunately, it is very time consuming and require equipments that may not always be
immediately to hand. In contrast, laser light scattering method is very simple and rapid to
perform but having disadvantage of measuring an average property of bulk of liposomes.
Another more recently developed microscopic technique known as atomic force microscopy
has been utilized to study liposome morphology, size, and stability. Most of methods used in
size, shape and distribution analysis can be grouped into various categories namely
microscopic, diffraction, Scattering, and hydrodynamic techniques.
1 Biological Characterization[17,18,19]
Table no:4
Characterization parameters Instrument for Analysis
Sterility Aerobic/Anaerobic Culture
Pyrogenicity Rabbit Fever Response
Animal toxicity Monitoring Survival Rats.
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2 Physical Characterization
Table no:5
Characterization Parameters Instrument for analysis
Vesicle shape and surface morphology TEM and SEM
Vesicle size and Size distribution Dynamic light scattering TEM
Surface Charge Free flow electrophoresis
Electrical surface potential and surface pH Zeta potential measurement and pH
sensitive probes.
Lamellarity p31 NMR
Phase behavior DSC , freeze fracture electron
microscopy
Percent Capture Mini column centrifugation
Drug release Diffusion cell/ dialysis
3 Chemical Characterization
Table no:6
Characterization
Parameters
Instrument for analysis
Phospholipids concentration HPLC
Cholesterol concentration HPLC/Cholesterol oxide assay
Phospholipids per oxidation U.V observation
pH pH Meter
Osmolarity osmometer
Stabilization of liposomes[17,18,19]
The stability of liposome should meet the same standard as conventional pharmaceutical
formulation. The stability of any pharmaceutical product is the capabilities of the delivery
system in the prescribed formulation to remain within defined or pre-established limits for
predetermined period of time.
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- Chemical Stability involves prevention of both the hydrolysis of ester bonds in the
phospholipids bilayer and the oxidation of unsaturated sites in the lipid chain.
- Chemical instability leads to physical instability or leakage of encapsulated drug from the
bilayers and fusion and finally aggregation of vesicles.
- Introduced the proliposome concept of liposome preparation to avoid physicochemical
instability encountered in liposome suspension such asaggregation, fusion, hydrolysis and / or
oxidation.
- Approaches that can be taken to increase Liposomal stability involve efficient formulation
and lyophilization. Formulation involves the selection of the appropriate lipid composition,
concentration of bilayers, aqueous phase ingredients such as buffers, antioxidant, metal
chelators and cryo protectants. Charge inducing lipids such as phosphotidyl glycerol can
beincorporated into liposome bilayers to decrease permability and leakage of encapsulated
drugs. Buffers at neutral pH can decrease hydrolysis ,addition of antioxidant such as sodium
ascorbate can decrease oxidation.
Marketed Preparation[6]
Table no:7
Name Trade name Company Indication
Liposomal
Amphotericin B
Ablect Enzon Fungal infection
Liposomal
Amphotericin B
Ambisome Gilead Sciences Fungal and
protozoval infection
Liposomal
cytarabine
Depocyt Pacira(Sky pharma) Malignant
lymphomatous
meningitis
Liposomal
daunorubicin
Dauno Sciences Gilead Sciences HIV-related
Kaposi’sarcoma
Application of Liposomes[1,2,7,22]
1. Liposome as drug/protein delivery vehicle:
Controlled and sustained drug release in situ
Enchaned drug solubilization
Altered pharmacokinetic and biodistribution
Enzyme replacement therapy and lysosomal disorders
2. Liposome in antimicrobial, antifungal and antiviral therapy:
Liposomal drugs
Liposomal biological response modifier
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3. Liposomes in tumour therapy:
Crrrier of small cytotoxic molecule
Vehicle for macromolecule as cytokines or genes
4. Liposome in gene therapy:
Gene and antisence therapy
Genetic (DNA) vaccination
5. Liposome in immunology:
Immunoadjuvant
Immunomodulator
Immunodiagnosis
6. Liposome as artificial blood surrogates.
7. Lipososmes as radiopharmaceutical and radiodiagnostic carrier.
8. Liposomes in cosmetics and dermatology.
9. Liposomes in enzyme immobilization and bioreactor technology.
10. Liposomes enhanced the drug uptake via endocytosis.
11. Liposomes can be used as carrier of drug in oral treatment of
a. Arthritis
Treated with steroids using MLVs prepared by DPPC and P.A.
E.g. Drugs are Ibuprofen, cortisol palmitate
b. Diabetes
Alternation in blood glucose level in diabetic animals was obtained by oral administration of
liposome encapsulated insulin.
Limitation in liposome technology:
1) Stability
2) Sterilization
3) Encapsulation efficiency
4) Active targeting
5) Gene therapy
6) Lysosomal degradation
CONCLUSION:
Liposomes have been used in a broad range of pharmaceutical applications. Liposomes are
showing particular promise as intracellular delivery systems for anti-sense molecules,
ribosomes, proteins/peptides, and DNA. Liposomes with enhanced drug delivery to disease
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locations, by ability of long circulation residence times, are now achieving clinical
acceptance. Also, liposomes promote targeting of particular diseased cells within the disease
site. Finally, liposomal drugs exhibit reduced toxicities and retain enhanced efficacy
compared with free complements. However, based on the pharmaceutical applications and
available products, we can say that liposome’s have definitely established their position in
modern delivery systems. The use of liposomes in the delivery of drugs and genes are
promising and is sure to undergo further developments in future.
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