Transcript
What is a liposome?
– Liposomes are artificially prepared spherical vesicles made of phospholipid bilayer.
Phospholipid Bilayer
Polar Head Groups
Three carbon glycerol
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Liposomes Formation
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TYPE SPECIFICATION
MLV Multilamellar large vesicles->0.5m
OLV Oligolamellar vesicles-0.1-1 m
UV Unilamellar vesicles (all size ranges)
SUV Small Unilamellar Vesicles- 20-100 nm
MUV Medium sized unilamellar vesicles
LUV Large unilamellar vesicles->100nm
GUV Giant unilamellar vesicles->1m
MV Multivesicular vesicles->1m
CLASSIFICATION OF LIPOSOMESBased on Structural Parameters
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REV Single or oligolamellar vesicles made by
reverse- phase evaporation method.
MLV_REV Multilamellar vesicles made by reverse-
phase evaporation method.
SPLV Stable plurilamellar vesicles
FATMLV Frozen and thawed MLV
VET Vesicles prepared by extrusion technique.
DRV Dehydration – rehydration method.
CLASSIFICATION OF LIPOSOMESBased on Method of Liposome Preparation
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Based upon Composition & Applications
CLASSIFICATION OF LIPOSOMES
Conventional liposomes(CL) Neutral or negatively charged
Phospholipids and cholestrol.
Fusogenic liposomes (RSVE) Reconstituted Sendai virus envelopes
pH sensitive liposomes Phospholipid such as PE or DOPE
with either CHEMS or OA
Cationic liposomes Cationic lipids with DOPE
Long circulatory stealth Neutral high Tc, cholestrol and 5- 10%
liposomes (LCL) of PEG - DSPE or GM1
Immuno-liposomes CL or LCL with attached monoclonal
antibody or recognition sequence
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Method of Preparation of Liposomes
Passive loading techniques Active loading techniques
Mechanical dispersion methodsSolvent dispersion methodsDetergent removal methods
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• Mechanical dispersion methods Lipid film hydration by hand shaking,non-hand shaking or freeze drying Microemulsification Sonication French pressure cell Membrane extrusion Dried reconstituted vesicles Freeze-thawed liposomes
• Solvent dispersion methods Ethanol injection Ether injection Double emulsion vesicles Reverse phase evaporation vesicles Stable plurilamellar vesicles
• Detergent removal methods Dialysis Column chromatography Dilution Reconstituted Sendai Virus enveloped vesicles
Method of Preparation of Liposomes
Passive Loading Techniques
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• In order to increase the surface area of dried lipid film and to facilitate instantaneous
hydration, the lipid is dried over a finely divided particulate support, such as powdered
sodium chloride, or sorbitol or other polysacharrides.
• These dried lipid coated particulates are called pro-liposomes.
• Pro-liposomes form dispersion of MLV’s on adding water into them, where support is
rapidly dissolved and lipid film hydrates to form MLV’s.
• This method also overcomes the stability problems of liposomes encountered during
the storage of dispersion, dry or frozen form.
• It is ideally suited for preparations where the material incorporates into lipid membrane.
Pro-Liposomes
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SONICATED UNILAMELLAR VESICLES (SUV’s)
Preparation of SUV’s from Bath/Probe Sonicator from MLV’s
Uses of Liposomes
Chelation therapy for treatment of heavy metal poisoning
Enzyme replacement
Diagnostic imaging of tumors
Study of membranes
Cosmetics
Drug Delivery
Liposome for Drug Delivery
• Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases.
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Drug Targeting
Modes of Liposome/Cell Interaction
Adsorption Endocytosis
Fusion Lipid transfer
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THERAPEUTIC APPLICATION OF LIPOSOMES
LIPOSOMES AS DRUG DELIVERY VEHICLES:
1. Enhanced drug solubilization (amphotericin B, minoxidil, paclitaxel,
cyclosporin),
2. Protection of sensitive drug molecules (cytosine arabinose,
ribozymes)
3. Enhanced intracellular uptake (anticancer, antiviral and antimicrobial
drugs).
4. Altered pharmacokinetics and biodistribution (prolonged or sustained
release of drugs with short circulatory half-lives).
5. Drugs delivered via liposomes may be protected from the actions of
metabolizing enzymes
6. Using liposomes as a drug deliverer allows potentially lower doses of drug to be used, reducing toxicity and side-effects.
Current liposomal drug preparations
Type of Agents ExamplesAnticancer Drugs
Anti bacterial
AntiviralDNA materialEnzymes
RadionuclideFungicidesVaccines
*Currently in Clinical Trials or Approved for Clinical Use
Malaria merozoite, Malaria sporozoiteHepatitis B antigen, Rabies virus glycoprotein
Amphotericin B*In-111*, Tc-99m
Hexosaminidase A Glucocerebrosidase, Peroxidase
Duanorubicin, Doxorubicin*, Epirubicin Methotrexate, Cisplatin*, CytarabinTriclosan, Clindamycin hydrochloride, Ampicillin, peperacillin, rifamicinAZTcDNA - CFTR*
CFTR
Gene TherapyDeliver cDNA of Cystic Fibrosis Transmembrane Conductance
Regulator (CFTR) to epithelial tissue of respiratory system
Fuse to cell membrane and incorporate cDNA into cell
Clinical trials - no significant change in symptoms
Now trying adeno associated virus
Cationic liposome
Doxil
Chemotherapy drug doxorubinAnemia, damage to veins and tissue at injection, decrease
platelet and WBC count.
Treats Kaposi’s sarcoma lesions or cancer tumorsModifications of liposome “stealth”
keeps doxorubin in blood for 50 hours instead of 20 minutes
concentrates at KS lesions and tumors
*Just approved by FDA*
Amphotericin B
Side effects: nephrotoxicity, chills, and fevers
Systemic fungal infections in immune compromised patients
Fungizone - AmB with deoxycholate
AmB - kills ergosterol-containing fungal cells, also kills cholesterol-containing human cells
No decrease in effectiveness of drug against fungi
Liposomal Formulation of AmB
Decrease in toxicity
Exact Mechanism of liposomes not understood
Cholesterol - only few %moles
Phospholipid:AmB ratio
DiffusionLipid transfer
AmB
Lipid
Problems with Liposomal Preparations of Drugs
$$$$
Fungizone $40.58 Amphotec $2334
Doxil $1200 per treatment, twice the cost of normal protocol of chemotherapy and drugs
Lack long term stability (short shelf life)
Freeze dry and pH adjustment
Low “Pay Load” - poor encapsulation
Physical and chemical instability
Polar drugs and drugs without opposite charge
Modifications
Possibility of new side effectsDoxil “hand and foot syndrome”
Problems continued
EfficacyCFTR
Studies with insulin show that liposomes may be an effective way to package proteins and peptides for use
Clinical Trials for several liposomal formulations More studies on the manipulation of liposomes
Future
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Thank You
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