Vol 3 Suppl 3, August 2014 www.mintagejournals.com 1
VESICULAR DRUG DELIVERY SYSTEM: A NOVEL APPROACH
KALPESH CHHOTALAL ASHARA
*1, JALPA S. PAUN
1, M.M SONIWALA
1, J.R.CHAVDA
1, S. V. NATHAWANI
1,
NITIN M. MORI
2,3AND VISHAL P. MENDAPARA
21Department of Pharmaceutics, B. K. Mody Govt. Pharmacy College Rajkot-360003, Gujarat, India, 2 Department of Pharmaceutical Sciences, Saurashtra University, Rajkot-360005, Gujarat, India, 3 Torrel (Hospital Division) a member of Torrent group, Ahmedabad, Gujarat, India, E [email protected]
Received 19-06-14; Reviewed and accepted 03-07-14
ABSTRACT
A novel drug delivery system is that delivers drug at predetermined rate decided as per the requirement, pharmacological aspects, drug profile, physiological conditions of body etc. In current conditions not a single novel drug delivery system behaves ideally those high goals with fewer side effects. A Vesicular drug delivery system (VDDS) is the system in which encapsulation of active moieties in vesicular structure, which bridges gap between ideal and available of novel drug delivery system.Varrious types of vesicular drug delivery system like liposome, niosome, archeosome, transferosome etc. were developed. Advances have since been made in vesicular drug delivery system. Focus of this review is to bring about a brief of vesicular drug delivery system as novel approach.
Keywords: Vesicular Drug Delivery System, VDDS, Liposome, Niosome.
INTRODUCTION
Discussion never ends that from very ancient era discussion is already going on newer & better alternatives & in case of drugs it will continue till we got a drug with maximum efficacy & no side effects. Many drugs have narrow therapeutic window so their clinical uses are limited. Thus therapeutic effectiveness of existing drugs is improved by formulating them in advantageous ways.[1]In previous years, noticable work had been done to develop Novel Drug Delivery System (NDDS), fulfills desirable characteristics that it should deliver drug at a rate directed by need of body, over period of treatment & should channel active entity at site of action.Convetional dosage forms including prolonged released dosage forms unable to fulfilled none of these desired characteristics. At present, no available drug delivery systems behave ideally but attempts have been made to bridge gap between ideal & available.[2]
Definition
“Vesicles have become the vehicle of choice in drug delivery
system called Vesicular Drug Delivery System.”, e.g. liposomes,
Niosomes, Pharmacosomes etc.[1]
Advantages
Vesicular drug delivery systems have several advantages over the conventional dosages forms as well as prolonged released dosage forms as[1, 3]:
Effective permeation of drugs into cells
Prolongation of existence of drugs in systemic circulation. As selective uptake is taken place so reduces toxicity. Reduces the cost of therapy.
Improves bioavailability.
Hydrophilic-Lipophilic drugs can be incorporated. Sustained-release system function.
Delayed elimination of rapidly metabolized drugs.
Overcomes the problems of the drug insolubility, instability, and rapid degradations.
Why VDDS
Conventional chemotherapy for treatment of intracellular infections is not effective due to limited permeation of drugs into cells. To improve bioavailability at the site of diseases, reduces harmful side effects of conventional & controlled release drug delivery systems, overcome problem of degradation of drug &/or drug lose.[4]
Disadvantages
Along with numbers of advantages VDDS has some serious disadvantages which restrict their use. Drugs passively , which may lead to low drug loading efficiency and drug leakage in preparation, preservation and transport in vivo. Need of intensive sonication, lead to leakages of drug during storage. Thus the major problem of their stability acts as a barrier and thus limiting their use.[5, 6]
TYPES OF VDDS
There are various types of VDDS as
LIPOSOMES
Name Liposome is derived from Greek words:’Lipos’ meaning fat
& “soma’ meaning body. 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. Amongst various carriers, few drug carriers reached stages of clinical trials where phospholipid vesicles (liposome) show strong potential for effective drug delivery to site of action. Liposomes can be composed of naturally-derived phospholipids with mixed lipid chains or other surfactants. Liposome has covered predominantly medical, albeit some non-medical areas like bioreactor, catalysts, cosmetics and ecology. However, their predominance in drug delivery and targeting has enabled them to be used as therapeutics tool in fields like tumor targeting, gene and antisense therapy etc.
Liposomes were first described by British hematologist Dr Alec D Bangham in 1961(Published 1964), at Babraham Institute, in Cambridge. They were discovered when Bangham and R. W. Horne were testing institute's new electron microscope by adding negative stain to dry phospholipids[2, 7]
“Liposome is simple microscopic vesicles in which an aqueous
volume is entirely enclosed by a membrane composed of lipid
molecule.” Various amphipathic molecules have been used to
form liposome; drug molecules can either be encapsulated in aqueous space or intercalated into lipid bilayer.
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 2 Fig.1: Liposome
Fig.2: Ambiosome
Advantages
It provides selective passive targeting to tumor tissue (liposomal doxorubicin), increased efficacy and therapeutic index of drug (Actinomycin-D) and stability via encapsulation, biocompatible, completely biodegradable, non-toxic, flexible and no immunogenic for systemic and non-systemic administrations, reduce toxicity of the encapsulated agent (Amphotericin B, Taxol) and exposure of sensitive tissues to toxic drugs, site avoidance effect, Flexibility to couple with site-specific ligands to achieve active targeting.
Disadvantages
High production cost, leakage and fusion of encapsulated drug / molecules; phospholipid undergoes oxidation and hydrolysis like reaction, Short half-life, and Low solubility.
CLASSIFICATION
Liposome may be produced by variety of methods. Their nomenclature also depends upon the method of preparation, structural parameters or special functions assigned to them (table 1)1.Classification according to size:
Table 1: Classification of Liposomes according to size
Type Specifications
MLV Multilamellar large vesicles- >0.ημm OLV Oligolamellar vesicles- 0.1-1μm UV Unilamellar vesicles (all size range) SUV Small Unilamellar vesicles- 20-100nm MUV Medium sized Unilamellar vesicles LUV Large Unilamellar vesicles- >100 GUV Giant Unilamellar vesicles- >1μm MV Multivesicular vesicles- 1μm
Classifications according to method of preparations
I) Extraction method: VET (Vesicles prepared by Extraction Technique)
II) French Pressure Cell method
III) Fusion method
IV) Reverse Phase Evaporation method: SUVs, MLVs & OLVs are made by reverse phase evaporation (REV) Method
V) Frozen & Thawed Multilayered Vesicles:
VI) Dehydration & Rehydration method: DRV
VII) Stable Plurilamella air Vesicles Method: SPLV
Based on In-Vivo applications
I. Conventional Liposomes
These can be defined as liposomes that are typically composed of only phospholipids (neutral and/or negatively charged) and/or cholesterol. Most early work on liposomes as a drug-carrier system employed this type of liposomes. Conventional liposomes are a family of vesicular structures based on lipid bilayers surrounding aqueous compartments. Conventional liposomes are characterized by a relatively short blood circulation time due to rapid uptake by MPS system. They are useful for macrophage targeting, as local depot and for vaccination purpose. The fast and efficient elimination from the circulation by liver and spleen macrophages has seriously compromised application for the treatment of the wide range of diseases involving other tissues.
II. Long circulatory Liposomes
The advent of new formulations of liposomes that can persist for prolonged periods of time in the bloodstream led to a revival of interest in liposomal delivery systems at the end of the 1980s. In fact, the long-circulating liposomes opened a realm of new therapeutic opportunities that were up to then unrealistic because of efficient MPS uptake of conventional liposomes. Perhaps the most important key feature of long circulating liposomes is that they are able to extravagate at body sites where the permeability of the vascular wall is increased.
Fortunately, regions of increased capillary permeability include pathological areas such as solid tumors and sites of infection and inflammation. It is illustrative for the importance of the long-circulation concept that the only two liposomal anticancer products that are approved for human use are based on the use of long-circulating liposomes for tumor-selective delivery of antitumor drugs (Doxil, DaunoXome). At present the most popular way to produce long-circulating liposomes is to attach hydrophilic polymer polyethylene glycol (PEG) covalently to the outer surface.
III. Immunoliposomes
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 3 A. Temperature-sensitive Immunoliposomes
The heat induced drug release concept is based on the large increase in the permeability of liposomal bilayers around their phase transition temperature. Local heating of tumor tissue up to this phase transition temperature will enhance drug release from liposomes present in the heated area. Both the degree of extravasation and the rate of drug release increases in this case. Example of polymer that is used for preparation of temperature sensitive immunoliposomes is N-isopropyl acrylamide.
B. pH-Sensitive Immunoliposomes
pH sensitive ImmunoLiposomes targeted to internalizing receptors will end up in endosomes, where acidification will trigger liposome destabilization and possible fusion with endosomal membrane. They have been successfully applied in vitro for the delivery of antitumor drugs into cytoplasm of tumor cells. Example of polymer that is used for preparation of temperature sensitive immunoliposomes is propylacrylic acid.
IV. Cationic Liposomes
These delivery systems are under development for improving the delivery of genetic material. Their cationic lipid components interact with, and neutralize, the negatively-charged DNA, thereby condensing the DNA into a more compact structure. The resulting lipid–DNA complexes, rather than DNA encapsulated within liposomes, provide protection and promote cellular internalization and expression of the condensed Plasmid.
V. Fusogenic Liposomes
Here reconstituted Sandal Virus is enveloped.
General steps involved in the preparations of Liposomes various general steps that are evolved in the preparations of liposomes are:
1. Preparation of Lipids for Hydration
2. Hydration of lipid film/cake
3. Sizing of lipid suspension
i. Sonication
ii. Extraction
Methods of Liposomes Preparations[9]
All the method of preparing liposomes involves four basic stages:
1. Drying down lipids from organic solvent.
2. Dispersion of lipid in aqueous media.
3. Purification of resultant liposome.
4. Analysis of final product.
PASSIVE LOADING TECHNIQUE
Loading of entrapped agents before or during the manufacturing process. Used for drugs which are aqueous soluble but lipid insoluble. It is further divided into
1. Mechanical dispersion Method
Lipid hydration Method
Fig.3: Multilamelar Vesicles (MLVs) formed either Hand shaking technique or Rotatory flash Evaporator
In this method, lipid mixtures are dissolved in solvent mixture of chloroform: methanol (2:1) in rotary evaporator flask and dried thin film of lipid is made using rotary evaporator under reduced pressure (60 rpm, 30ºC, and about 15 min). Flask is flushed with nitrogen and Hydration of lipid is done by adding 5ml of saline phosphate buffer containing drug/solute to be encapsulated and again use of rotary evaporator for making homogeneous milky white suspension. It is allowed to stand for 2 hr at RT/above Tc for complete swelling process. This will give MLVs.
Sonication
At high energy level, preformed MLVs are sonicated using either probe or bath ultrasonic disintegrator.
Fig.4: Preparations of Small Unilemilar Vesicles (SUVs) by Bath/Probe Sonication Process from MLVs
Using Probe: Used for suspensions which require high energy in a small volume. And contamination of preparation with metal can lead to degradation of lipid.
Using Bath: Used for large volume of dilute lipids where may not necessary to reach the vesicle size limit. Finally, they are purified into the SUVs by ultracentrifugation and collected from supernant of centrifuge tube. Size of liposome is influenced by temperature, composition, and concentration, sonication time & power, volume of product.
Microfludization/Micro-emulsification Method
In this method, Micro fluidizer pumps the fluid at very high
pressure through a ημm screen. Then, it is forced along defined
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 4 recycled through the pump and interaction chamber until vesicles
of the spherical dimension are obtained.
Fig.5: Representation of use of micro-fluidizer to prepare Small Unilamellar Vesicles (SUVs) from MLVs
Advantages
Excellent size reduction up to 0.2mm, High rate of production, for encapsulation of water soluble materials due to high proportion of lipid.
French Pressure Cell
In this method, liquid sample of preformed MLVs are introduced into the sample cavity, then the position of piston and pressure is set up to fill sample up to the outlet hole. Then power is switched on. At high pressure (2000 psi) and at 40ºC, MLVs are extruded through small orifice, which is collected in suitable container. This technique yields uni- or oligo lamellar liposome of intermediate size. More stable than they obtained by sonication method and also leakage of the content from the liposomes are lesser.
Fig. 6: French pressure cell & parts used for pre-parations of Uni or oligo Lamellar Vesicles
Drawback
High cost of the pressure cell.
Membrane Extraction Method
Size of prepared liposomes is reduced by gently passing them
Fig.7: Liposomes Preparations using extractions techniques based on polycarbonate filters
Through membrane filter of defined pore size and this can be achieved at much lower pressure.
In this process, the vesicles content are extruded with the dispersion medium during breaking and resealing of phospholipids as they pass through the polycarbonate membrane in order to achieve high entrapment. The liposomes produced by this method have been termed as LUVETs and 30% encapsulation can be obtained using high lipid concentration.
Dried Reconstituted Vesicles
Fig.8: Preparations of Dried-Reconstituted Vesicles (DRVs) membrane r restructures enclosing a proportion of solutes, which was originally present in Extra-Liposomal Medium
It starts with freeze drying of a dispersion of empty SUVs and rehydrating it with the aqueous fluid containing the materials to be entrapped. This leads to dispersion of solid lipids in finely subdivided form. Freeze drying is used to freeze and lyophilize the preformed SUVs dispersion rather than to dry the lipids from an organic solution. This leads to organized membrane structure which on addition of water can rehydrate, fuse and reseal to form vesicle with high capture capacity. It is used for manufacturing of uni - or olio lamellar of the order of 1.0μm or less in diameter.
Advantages
High entrapment of water soluble content and use of mild condition for preparation & loading of bioactive.
Freeze Thawed Sonication
This method is based on freezing of unilamellar dispersion and thawing (melting) by standing at RT for 15 min. and finally subjected to a sonication cycle. This process ruptures and refuses SUVs during which the solute equilibrates between inside and outside, and liposomes themselves fuse and markedly increase in size. The second step of the sonication considerably reduces the permeability of the liposome membrane, by accelerating the rate at which the packing defects are eliminated. For producing giant vesicles of diameter having 10 –η0 μm, the sonication step is replaced by the dialysis against hypo-osmolar buffer. In this case, SUVs are mixed with salt solution followed by freeze thawing. During this dialysis, the large vesicles formed by freeze thawing swell and rupture as a result of the osmotic lysis, where the fuse and prepare as giant vesicles.
Disadvantage
- Lesser encapsulation efficiency,
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 5 Advantage
- Simple, rapid, result in proportion of large unilamellar vesicles formation.
2. Solvent Dispersion Method
Ethanol Injection method
Ethanol is used to dissolve the lipids and solution is rapidly injected through a fine needle into an excess of buffer solution. SUVs form spontaneously. Method is restricted to the production of relatively dilute SUVs suspension. Removal of residual ethanol is also present a problem. This can be done by ultrafiltration or vacuum distillation
Ether Injection Method
In this method, solution of lipids in diethyl ether or ether: methanol mixture is slowly injected to aqueous solution of materials to be encapsulated at 55 - 65ºC. Subsequent removal of ether under vacuum leads to the formation of liposomes.
Drawbacks
Heterogeneous size (70 - 190μm), exposure of compounds to organic solvents or high temperature.
Fig.9: Principles of Vesicles formations by solvent dispersion methods in which two phases (Aqueous & organic) are miscible with each other & forms different types of vesicles
Double Emulsion Vesicles
When organic solution which already contain water droplet, is introduced into excess aqueous phase followed by mechanical dispersion, multi compartment vesicles are obtained. The ordered dispersion so obtained is desirable as a w/o/w system. The vesicles with aqueous core are suspended in aqueous medium. So two aqueous compartments being separated from each other by pair of phospholipids monolayer whose hydrophobic surface face each other across a thin film of organic solvent. Removal of this solvent clearly results in intermediate sized unilamellar vesicle. The theoretical entrapment may reach up to 90%.
Reversed- phase Evaporation of Vesicles
The essential feature of this method is the removal of solvent from emulsion by evaporation. In this method, lipids dissolved in organic solvents are sonicated by bath sonication which forms emulsion (w/o) and then emulsion is dried down to a semi solid gel using rotary evaporator under reduced pressure. The next step is to Bing about the collapse of a certain proportion of water droplets by vigorous mechanical shaking with a vortex mixer. This will give LUVs. Encapsulation percentage: up to 50%.
Stable plurilamellar vesicles
In this method, w/o dispersion is prepared as described in REV
Method with excess lipid, but drying process is accompanied by continued bath sonication with a stream of nitrogen. The redistribution and equilibration of aqueous solvent and solute occur during this time in between the various bilayers in each plurilamellar vesicle. Entrapment percentage: 30%.
Fig.10:Formation of different liposomes using reverse-phase Evaporation method.MLVs are formed in presence of excess of phospholipids whereas LUV-REVs are formed in absence
of extra lipids.
3. Detergent Removal Method
In this method, the phospholipids are brought into intimate contact with the aqueous phase via the intermediary of detergents, which associate with phospholipid molecules and serve to screen the hydrophobic portions of the molecule from water. Detergent depletion is achieved by four following approaches:
Dialysis
The dialysis can be performed in dialysis bags immersed in large detergent free buffers (equilibrium dialysis) or by using continuous flow cells, diafiltration and cross filtration.
Gel filtration
In this method the detergent is depleted by size exclusive chromatography. Sephadex G-50, Sephadex G-100, Sepharose 2B-6B and Sephacryl S200-S1000 can be used for gel filtration. The liposomes do not penetrate into the pores of the beads packed in a column.
Adsorption using bio beads
Detergent adsorption is achieved by shaking of mixed micelle solution with beaded organic polystyrene absorbers such as XAD-2 beads and Bio-beads SMXAD-2. The great advantage of the using detergent absorbers is that they can remove detergents with a very low critical micelle concentration (CMC) which are not completely depleted by dialysis or gel filtration methods.
Dilution
Upon dilution of aqueous mixed micellar solution of detergent and phospholipids with buffer the micellar size and the polydispersity increases dramatically, and, as the system is diluted beyond the mixed micellar phase boundary, a spontaneous transition from polydisperse micelles to monodisperse vesicles occurs.
ACTIVE (REMOTE) LOADING TECHNIQUE
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 6 Approach for remote loading
Vesicles are prepared in low pH solution, thus generating low pH within liposome interior followed by addition of the base to external medium of liposomes. Basic compounds with amino group are relatively lipophilic at high pH and hydrophilic at low pH. Unprotonated form of basic drug can diffuse through the bilayer. At the low pH side, the molecules are predominantly protonated, which lower the concentration of the drug in the unprotonated form.
Structural components of Liposomes
Various lipids and amphiphiles are available as liposome raw materials or additives that are required for the formation of lipid bilayers. Phospholipids, Synthetic Phospholipids, Glycerolipids, Sphingolipids, Glycosphingolipids, Steroids, Polymeric material, Charge-inducing lipids
Phospholipids
Natural Phospholipids
Phosphotidylcholine,
Phosphotidylserine,
Phosphotidylethanolamine
Phosphatidylinositol
Synthetic Phospholipids
1, Dilauroyl-sn-Glycero-3-Phosphocholine (DLPC), 1, 2-Dioleoyl-Sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt) (DOPS), Dipalmitoylphosphotidylcholine (DPPC), Distearoylphosphotidylcholine (DSPC), Dipalmitoylphosphotidylserine (DPPS), Dipalmitoylphosphotidylglycerol (DPPG), 1, 2-Dilauroyl-sn-Glycero-3-Phosphocholine (DLPC)
Unsaturated
1-Stearoyl-2-Linoleoyl-Sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt),
Dioleaylphosphotidylcholine (DOPC), Dioleayphosphotidylglycerol (DOPG),
Dioleayphosphotidyl ethanolamine (DOPE)
Sphingolipids: Sphingomyelin, Glycosphingolipids: Gangliosides, Steroids: Cholesterol, Polymeric material: Lipids conjugated to dine, methacrylate, & thiol group, Charge-inducing lipids: Dioctadecyldimethyl ammonium bromide/chloride (DODAB/C), Dioleoyl trimethylammonium propane (DOTAP), Other Substances: Stearylamine & Dicetylphosphates, Polyglycerol & polyethoxylated mono & dialkyl amphiphiles.
Issues to Consider while Selecting Lipids
Phase transition temperature
The phase transition temperature is defined as the temperature required to induce a change in the lipid physical state from the ordered gel phase, where the hydrocarbon chains are fully extended and closely packed, to the disordered liquid crystalline phase, where the hydrocarbon chains are randomly oriented and
fluid. There are several factors which directly affect the phase transition temperature including hydrocarbon length, unsaturation, charge, and head group species. When developing a new product, procedure, or method, controlling the transition temperature of the lipid could be useful. Using a high transition lipid when filtration is necessary could present some technical problems.
Stability
The long term stability or shelf-life of a drug product containing lipids can be dramatically affected by the lipid species used in the formulation. Generally, the more unsaturated a compound, the easier the product is oxidized, and thus the shorter the shelf life of the product. Lipids from biological sources (e.g., egg, bovine, or soybean) typically contain significant levels of polyunsaturated fatty acids and therefore are inherently less stable than their synthetic counterparts. While saturated lipids offer the greatest stability in terms of oxidation; they also have much higher transition temperatures and thus present other difficulties in formulation.
Charge
The charge is generally imparted by the presence of anionic phospholipid species in the membrane. The major naturally occurring anionic phospholipids are phosphatidylserine, phosphatidylinositol, phosphatidic acid, and cardiolipin. The charge may provide a special function for the membrane. Several steps of the blood coagulation cascade require a lipid membrane. The assembling of protein aggregates on the surface of platelets requires a negatively charged surface.
Lipid mixtures
In many cases, a single lipid species does not yield the exact physical properties needed for a particular system, or does not adequately mimic the natural system for which it is intended to replace or reproduce. For these issues, consider a complex lipid mixture composed of two or more individual lipid species, the composition designed to create or reproduce a particular charge ratio, unsaturation ratio, phase transition temperature, or biological function.
Cholesterol
Cholesterol is a membrane constituent widely found in biological systems which serves a unique purpose of modulating membrane fluidity, elasticity, and permeability. It literally fills in the gaps created by imperfect packing of other lipid species when proteins are embedded in the membrane. Unfortunately, cholesterol presents certain problems when used in human pharmaceuticals. Purity sources and Stability problem for lipid based drug products
Source
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 7 Egg sources are not currently restricted; however, additional
testing for viral contamination may be required for pharmaceutical products.
CHARACTERIZATION OF LIPOSOMES
PHYSICAL CHARACTERIZATION
Size & size distribution
Most precise method to determine size of the liposome is electron microscopy, since it allows to view each individual liposome and to obtain exact information about the profile of liposome population over the whole range of sizes.Unfortunately it is very time consuming and requires equipments that may not always be immediately available to hand. In contrast, laser light scattering (quasi elastic laser light scattering) method is very simple and rapid to perform. Above methods require very costly equipments.If only approximate idea of size range is required then gel exclusion chromatographic techniques are recommended, since only expense incurred is that of buffers and gel materials.
Surface Charge
Vesicle surface charge can be estimated by measurement of particle electrophoretic mobility & is expressed as the zeta potential which can be calculated using the Henry equation:
= µEζπ / Σ
Where, = zeta potential, µE = electrophoretic mobility, = viscosity of the medium, Σ = dielectric constant.
Lameliarity
The average number of bilayers present in a liposome can be found by freeze electron microscopy and by NMR.
In the latter technique, the signals are recorded before and after the addition of broadening agent such as manganese ions which interact with the outer leaflet of the outermost bilayers. Thus, a 50% reduction in NMR signal means that the liposome preparation is unilamellar and a 25% reduction in the intensity of the original NMR signal means that there are 2 bilayers in the liposome.
Nowadays, freeze fracturing electron microscopy has become a very popular method to study structural details of aqueous lipid dispersions.
Encapsulation Capacity
Amount of Encapsulated drug X 100/Total amount of drug
Encapsulation/Entrapped drug capacity is measured by two methods:
-Mini column centrifugation
-Protamine aggregation
Mini column centrifugation: This method serves for both- isolation of liposomes and analysis of entrapped material.
A sephadex or sepharose column is used which is prostrated with dispersion medium.
Sample is applied to the column and column is centrifuged at 2000 rpm for 3 min.
Concentration of free or entrapped material is then found out.
Entrapped material can be assayed after disrupting the liposomes by ethanol(2ml ethanol for 10 µl of liposomes)
Protamine aggregation method
Concentration of free or entrapped material is then found out. Entrapped material can be assayed after disrupting the liposomes by ethanol (2ml ethanol for 10 µl of liposomes).
Entrapped or internal Volume
“To describe entrapment of water soluble drugs in the aqueous
compartments of Liposomes.”
The best way to measure internal volume is to measure the quantity of water directly, and this may be done very conveniently by replacing the external medium with a spectroscopically inert fluid, (e.g. D2O) and then
Measuring the water signal by NMR
Trapped volumes are also determined by dispersing lipid in an aqueous medium containing non-permeable radioactive solute such as [22
Na] and [14
C]. The proportion of solute is determined by removing external radioactivity by centrifugation or dialysis.
Drug release
The mechanism of drug release from the liposomes can be assessed by the use of a well calibrated in vitro diffusion cell.
The liposome based formulations can be assisted by employing in vitro assays to predict pharmacokinetics and bioavailability of the drug before employing costly and
Time consuming in vivo studies
Another assay which determined intracellular drug release induced by liposomes degradation in the presence of mouse liver lysosome lysate was used to assess the bioavailability of the drug.
CHEMICAL PROPERTIES
Determination of Phospholipids
The phospholipids are measured by
Bartlett assay
The problem is that the test is easily upset by trace contamination with inorganic phosphate. Therefore, precaution is to be taken
– Using a set of borosilicate glass tubes which are washed well and not used for any other purpose.
– Use of double distilled water for making up solutions.
The sensitivity of the Bartlett assay to inorganic phosphate creates problem with measurement of phospholipid liposomes suspended in physiological buffers, which usually contain phosphate ions. This can be overcome by employing a more specific method which is unaffected by inorganic phosphate.
Stewart assay
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 8 Phospholipid Hydrolysis
The major product of lecithin hydrolysis is lysolecithin where one fatty acid chain is lost by de esterification. Ideally, estimation of phospholipid hydrolysis by quantitation of lysolecithin could be carried out by HPLC
Phospholipid Oxidation
Oxidation products of phospholipids (such a phospholipids hydroperoxides) are analyzed using HPLC or GLC.
Cholesterol analysis
Cholesterol is qualitatively analyzed using Chromatography.Whereas it is quantitatively estimated by measuring the absorbance of purple complex produced with iron upon reaction with a combined reagent containing ferric perchlorate, ethyl acetate and sulphuric acid at 610nm.
BIOLOGICAL CHARACTERIZATION
Liposomes for parenteral use should be sterile and pyrogen free.
APPLICATION OF LIPOSOMES
Twenty five year of research into the use of liposome in drug delivery. Liposomes are one of the unique drug delivery system, which can be of potential use in controlling and targeting drug delivery. Liposomes are administrated orally, parenteral and topically as well as used in cosmetic and hair technologies, sustained release formulations, diagnostic purpose and as good carriers in gene delivery various drugs with liposomal delivery systems have been approved. Nowadays liposomes are used as versatile carriers for targeted delivery of drug.
Liposomes also have applications in other disciplines like mathematics, physics, biophysics, chemistry, biochemistry, etc.
As of 2008, 11 drugs with liposomal delivery systems have been approved and six additional liposomal drugs were in clinical trials. List of clinically-approved liposomal drugs (Table 2).
Therapeutic Application of Liposome [10]
1. Liposome as drug/protein delivery vehicles, Controlled and sustained drug release, Enhanced drug solubilization, altered pharmacokinetics and biodistribution, Enzyme replacement therapy and biodistribution, Enzyme replacement therapy and lysosomal storage disorders
2. Liposome in antimicrobial, antifungal and antiviral therapy, Liposomal drugs, Liposomal biological response modifiers
3. Liposome in tumor therapy: Carrier of small cytotoxic molecules Vehicle for macromolecules as cytokines or genes
4. Liposome in gene delivery: Gene and antisense therapy, Genetic (DNA) vaccination
5. Liposome in immunology: Immunoadjuvant Immunomodulation, Immunodiagnostics
6. Liposome as artificial blood surrogates
7. Liposome as radiopharmaceutical and radio diagnostic carriers
8. Liposome in cosmetics and dermatology
9. Liposome in enzyme immobilization and bioreactor technology.
NIOSOMES
Controlled release formulations are often prepared to permit the establishment and maintenance of any concentration at target site for longer period of time. One such technique of drug targeting is niosomes. Niosomes are microscopic lamellar structures formed on admixture of a nonionic surfactant, cholesterol and diethyl ether with subsequent hydration in aqueous media. Non-ionic surfactant vesicles (or niosomes) are now widely studied as alternates to liposomes.[11] Structure of Niosomes: Nonionic surfactant vesicles (NSVs or niosomes) result from the self assembly of hydrated surfactant monomers. They are similar in physical structure and form to the more widely studied phospholipid vesicles (liposomes) [12], consisting of single or multiple surfactant bilayers (lamellae) enclosing an aqueous core. A schematic diagram of a non-ionic surfactant vesicle is shown in Fig. 4 Preliminary X-ray scattering data on unilamellar sorbitan monostearate (C18- sorbitan monoester)-cholesterol niosomes suggest a bilayer spacing of 15 nm and a bilayer thickness of 3.3-3.4 nm [13], the latter similar to the figure obtained for the bilayer thickness of phospholipid vesicles (3.4-3.9 nm) [14]. Although terminology suggests that distinctions exist between liposomes and niosomes, of which the basic unit of assembly is the amphiphile, their properties are largely similar and the differences between liposomes (phospholipid vesicles) and non-ionic surfactant vesicles are sometimes blurred as liposomes are often prepared incorporating a non-ionic surfactant component [15, 16], while non-ionic surfactant vesicles may also be formulated with various ionic amphiphiles such as stearylamine and dicetylphosphate to achieve greater protection against flocculation in vesicle suspensions. The association of nonionic surfactant monomers into vesicles on hydration is a result of the fact that there exists a high interfacial tension between water and the hydrocarbon portion (or any other hydrophobic group) of the amphiphile which causes these groups to associate. Simultaneously, the steric, hydrophilic and/or ionic repulsion between the head groups ensures that these groups are in contact with water. These two opposing forces result in a supramolecular assembly.
Fig.11: A Schematic diagramme of Non-Ionic Surfactant
Method of preparation of niosomes
Various methods are reported for the preparation of niosomes such as
1. Ether injection method
2. Hand shaking method (Thin film hydration technique)
3. Sonication method
4. Reverse phase evaporation technique (REV)
5. Micro fluidization
6. Multiple membrane extrusion method
Table 2: List of Clinically-Approved Liposomal Drugs
Name Trade Name Company Indication
Liposomal Amphotericin B Abelcet Enzon
Fungal & Protozoal Infections Ambisome Gilead Sciences
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 9 7. Trans membrane pH gradient (inside acidic) drug uptake
process (remote loading)
8. Bubble method
9. Formation of niosomes from proniosomes
Ether injection method
This method provides a means of making niosomes by slowly introducing a solution of surfactant dissolved in diethyl ether (volatile organic solvent) into warm water maintained at 60°C. The surfactant mixture in ether is injected through 14- gauge needle into an aqueous solution of material. Vaporization of ether (volatile organic solvent) leads to formation of single layered vesicles. Depending upon the conditions used the diameter of the vesicle range from 50 to 1000 nm[17, 18].
Hand shaking method (Thin film hydration technique)
The mixture of vesicles forming ingredients like surfactant and cholesterol are dissolved in a volatile organic solvent (diethyl ether, chloroform or methanol) in a round bottom flask. The organic solvent is removed at room temperature (20°C) using rotary evaporator leaving a thin layer of solid mixture deposited on the wall of the flask. The dried surfactant film can be rehydrated with aqueous phase at 0-60°C with gentle agitation. This process forms typical multilamellar niosomes[18].
Sonication
In this method an aliquot of drug solution in buffer is added to the surfactant/cholesterol mixture in a 10-ml glass vial. The mixture is probe sonicated at 60°C for 3 minutes using a sonicator with a titanium probe to yield niosomes.[18]
Reverse phase evaporation technique (REV)
Cholesterol and surfactant (1:1) are dissolved in a mixture of ether and chloroform. An aqueous phase containing drug is added to this and the resulting two phases are sonicated at 4- 5°C. The clear gel formed is further sonicated after the addition of a small amount of phosphate buffered saline (PBS). The organic phase is removed at 40°C under low pressure. The resulting viscous niosome suspension is diluted with PBS and heated on a water bath at 60°C for 10 min to yield niosomes [19].
Micro fluidization
It is a recent technique used to prepare unilamellar vesicles of defined size distribution. This method is based on submerged jet principle in which two fluidized streams Interact at ultra high velocities, in precisely defined micro channels within the interaction chamber. The impingement of thin liquid sheet along a common front is arranged such that the energy supplied to the system remains within the area of niosomes formation [20]. The result is a smaller size, greater uniformity and better reproducibility of niosomes formed.
Multiple membrane extrusion method
Mixture of surfactant, cholesterol and dicetyl phosphate in chloroform is made into thin film by evaporation. The film is
hydrated with aqueous drug polycarbonate membranes
and the resultant suspension extruded through which are placed in series for up to 8 passages. Multiple membrane extrusion method is better for the controlling of niosome size [20].
Trans membrane pH gradient (inside acidic) drug uptake process (remote loading)
Surfactant and cholesterol are dissolved in chloroform. The solvent is then evaporated under reduced pressure to get a thin film on the wall of the round bottom flask. The film is hydrated with 300 mm citric acid (pH 4.0) by vortex mixing. The multilamellar vesicles are frozen and thawed 3 times and later sonicated. To this niosomal suspension, aqueous solution containing 10 mg/ml of drug is added and vortexes. The pH of the sample is then raised to 7.0-7.2 with 1M disodium phosphate. This mixture is later heated at 60°C for 10 minutes to give niosomes [21].
Bubble method
It is novel technique for the one step preparation of liposomes and niosomes without the use of organic solvents. The bubbling unit consists of round-bottomed flask with three necks positioned in water bath to control the temperature. Water-cooled reflux and thermometer is positioned in the first and second neck and nitrogen supply through the third neck .Cholesterol and surfactant are dispersed together in this buffer (pH 7.4) at 70°C, the dispersion mixed for 15 seconds with high shear homogenizer and
immediately afterwards “bubbled” at 70°C using nitrogen gas. Formation of niosomes from proniosomes
Another method of producing niosomes is to coat a water-soluble carrier such as sorbitol with surfactant. The result of the coating process is a dry formulation [22]. In which each water-soluble particle is covered with a thin film of dry surfactant. This
preparation is termed “Proniosomes”.
4. RECENT ADVANCES IN VDDS:
Fig. 12: Different Pharmaceutical Carriers[23]
Difference between Liposomes & Niosomes:
Characteristics Liposomes Niosomes
Availability Phospholipids are comparatively hard in availability Synthetic non-ionic surfactants are readily available
Cost Expensive Cheaper
Storage Required special handling & storage conditions Don’t Required special handling & storage conditions
Stability Instability problem Chemically stable
Chemical composition Not Précised Précised
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 10 Different types of pharmaceutical carriers are present. (Fig
No.:4)They are particulate, polymeric, macromolecular, & cellular carrier. Particulate carrier also knows as colloidal carrier system includes lipid particles (Low & High density lipoprotein).The vesicular systems have been advanced as[8]:
Ethosome
Ethosomes has initiated a new area in vesicular research for transdermal drug delivery which can provide better skin permeation and stability than liposomes. Application of ethosomes provides the advantages such as improved entrapment and physical stability.
Ethosomes are lipid based elastic vesicles. Phospholipids, alcohol (In high concentration) & water. Size: Nanometers-Microns. High concentration ethanol (20-50%).Lipid membrane packed less tightly than conventional vesicles hence improved drug distribution through stratum corneum. Increase fluidity of cell membrane, increases cell permeability, Ulters solubility properties of stratum corneum & Increase solubility of drugs, e.g. Levonorgesterol, hydrocortisone, 5-flurouracil(TDDS).
Ethosomes are lipid “Soft malleablevesicles”embodying a
permeation enhancer & composed of phospholipid, ethanol and water. Ethosomes are used mainly as Targeted delivery to deep skin layer. [24]
Transferosomes
Transferosomes was introduced for the effective transdermal delivery of number of low and high molecular weight drugs. Transfersomes can penetrate the intact stratum corneum spontaneously along two routes in the intracellular lipid that differ in their bilayers properties [25]. It consist of both hydrophilic and hydrophobic properties, high deformability gives better penetration of intact vesicles [26].These vesicular transfersomes are several orders of magnitudes more elastic than the standard liposomes and thus well suited for the skin penetration. Transfersomes overcome the skin penetration difficulty by squeezing themselves along the intracellular sealing lipid of the stratum corneum. There is provision for this, because of the high vesicle deformability, which permits the entry due to the mechanical stress of surrounding, in a self-adapting manner. Flexibility of transfersomes membrane is achieved by mixing suitable surface-active components in the proper ratios. Transferosome based formulations of local anesthetics- lidocaine and tetracaine showed permeation equivalent to subcutaneous injections. Anti cancer drugs like methotrexate were tried for transdermal delivery using transferosome technology. This provided a new approach for treatment especially of skin cancer.[4]
Advantage
Transferosomes possess an infrastructure consisting of hydrophobic and hydrophilic moieties together and as a result can accommodate drug molecules with wide range of solubility.
Transferosomes can deform and pass through narrow constriction (from 5 to 10 times less
Than their own diameter) without measurable loss.
Poses high entrapment efficiency, in case of lipophilic drug near to 90%.
Used for both systemic as well as topical delivery of drug.
Limitation
Transferosomes are chemically unstable because of their predisposition to oxidative degradation.
Purity of natural phospholipids is another criteria militating against adoption of transfersomes as drug delivery vehicles.
Transferosomes formulations are expensive.[27]
Table 3: Therapeutic Application of Drugs after incorporation with Transferosomes
Drug
Effects after incorporation of drugs in transferosomes
Applications
Insulin Transferulin[28]
Delivery of insulin by Dermal Route
Zudovudin Increases the level of IgA
Higher AUC Transdermal
Immunization [29, 30] NSAIDS
Ketoprofen Transferosomes
Increases Bioavailability
Pharmacosomes
Pharmacosomes are amphiphilic lipid vesicular system possessing phospholipid complexes of drugs. Pharmacon means drugs & Soma means Carrier thus Pharmacosomes means drug carriers. System formed by linking drugs’ o the carrier. Colloidal dispersion of drugs co-valant bond to lipids. Composed of amphiphilic prodrugs, so high drug loading amount & very low drug leakages can be achieved easily. Increases interfacial tensions so increases contact area & finely increases bioavailability.
Advantages
Drug targeting, Controlled released, High entrapment efficacy, No need of removal of entrapment drugs from formulations as required in Liposomes, Improves bioavailability of purely soluble drugs, Reduces cost of therapy[31]
Disadvantages
Co-valent bond is required to protect leakages of drugs, Amphiphilic nature is responsible for the synthesis of the compounds, On storages undergoes fusion, aggression & Chemical hydrolysis.[32]
Preparation Methods
Generally pharmacosomes can be prepared by two methods which are as follows[33]:
Hand shaking method
In this method a mixture of drug and lipid are dissolved in a volatile organic solvent such as dichloromethane in a round bottom flask. The organic solvent is removed at room temperature using a rotary evaporator, which leaves a thin film of solid mixture deposited on the walls of flask. The dried film can then be hydrated with aqueous medium and readily gives a vesicular suspension.
Ether injection method
In this method organic solution of drug-lipid complex is injected slowly into the hot aqueous medium wherein the vesicles are formed readily.
APPLICATIONS OF PHARMACOSOMES
As Novel Drug Delivery System
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 11 Was 91.88% (w/w) for aceclofenac phospholipid complex (1:1)
and 89.03% (w/w) for aceclofenac phospholipid complex (2:1)? Solubility of aceclofenac pharmacosome was found to be higher than the aceclofenac. In this study the free aceclofenac showed a total of only 68.69% drug release at the end of 4hr dissolution study while aceclofenac pharmacosome (1:1) showed 79.78% and aceclofenac pharmacosome (2:1) showed 76.17% at the end of 4hr dissolution study. A. Semalty et al. studied development of diclofenac pharmacosome and physicochemical evaluation for drug solubility, in vitro dissolution study, drug content, surface morphology, crystallinity and phase transition behavior. Water
solubility of diclofenac pharmacosome was found to be 22.1μg/ml as compared to 10.η μg/ml of diclofenac. Drug release of
diclofenac pharmacosome was 87.8% as compared to 60.4% of diclofenac at the end of 10hr dissolution study and the drug content of diclofenac pharmacosome was found to be 96.2+/-1.1 %. In SEM, pharmacosomes of diclofenac were found to be disc shaped. XRPD analysis and DSC thermo grams proved the formation of phospholipid complex. M. Han et al. optimized preparation and evaluation of 20(S) protopanaxadiol pharmacosome and showed that the encapsulation efficiency of protopanaxadiol pharmacosome was (80.84+/-0.53) with the diameter of 100.1 nm and (72.76+/-0.63) with the diameter of 117.3 nm. Thus the selected formulation and technology are simple and preparation properties are more stable. AI PING ET al.prepared didanosine pharmacosomes by using tetra hydro furan injection method and investigate the in vivo behavior of pharmacosomes in rats by determining the drug in plasma and tissues with HPLC. From the result it can be concluded that pharmacosomes elicit liver targeting and sustained release effect in target tissues. Z R Zhang, J X Wang successfully optimized the preparation of 3',5'-dioctanoyl-5-fluoro-2'-deoxyuridine pharmacosomes [35] by using central composite design and concluded that 3',5'- dioctanoyl-5-fluoro-2'-deoxyuridine pharmacosomes showed a good targeting efficiency in vivo and can improve the ability of drug to cross the blood brain barrier. JIN Yi-Guang et al. prepared acyclovir pharmacosomes by tetrahydro furan injection and investigate the following properties) the negatively charged pharmacosome were nanometer vesicles based on analysis of trans-mission electron scanning calorimetry.
ii) The effects of centrifugation and heating on stability of pharmacosomes were weak.
iii) Freezing and lyophilisation disrupted pharmacosomal structure.
iv) The amphiphilic pharmacosomes would insert into rabbit erythrocyte membranes and led to hemolysis. Plasma proteins in blood absorbed pharmacosomes or interfered the interaction with erythrocytes to reduce hemolytic reaction. A. Semalty et al. investigate development and characterization of aspirin – phospholipid complex (in 1:1 molar ratio) for improved drug delivery and found that the drug content was 95.6% for aspirin-phospholipid complex. The free aspirin showed a total of only 69.42% drug release at the end of 10 hr dissolution study while aspirin pharmacosome showed a total of only 90.93% drug release at the end of 10 hr dissolution study in pH 1.2 acid buffers. Thus it can be concluded that aspirin pharmacosomes enhance the bioavailability of aspirin. The GI toxicity is also reduced in case of aspirin-phospholipid complex. Peng-Fei Yue et al. prepared and investigate the characteristics of geniposide pharmacosome and optimize the process by response surface design. The phospholipid to drug ratio, reaction temperature and drug concentration were determined as 3, 50⁰C, 5.5mg/ml respectively. Thus pharmacosomes can improve absorption and permeation of biologically active constituents. V.E.Ivan et al. studied the effect of temperature on cascade system of pharmacosome fusion and demonstrated that a combination of cell-specific drug vehicles (pharmacosomes) containing cascade fusion system, at appropriate temp will have a prominent effect on drug delivery to appropriate sites within an organism by using both heating and cooling of tissues.
COLLOIDOSOME
Hollow shell microcapsules consits of coagulated or fused
Particles at interphase of emulsion droplets. Control of size allows flexibility in applications. Colloidosome membrane offers great potential in controlling the permeability of entrapped spices. Allows selective & timed release.
Colloidosomes are the hollow shell microcapsules consisting of coagulated or fused particles at interface of emulsion droplets. Colloidosomes have exciting potential applications in controlled release of drugs, proteins, vitamins as well as in cosmetics and food supplements.
Colloidosomes have a great encapsulation efficacy with a wide control over size, permeability, mechanical strength and compatibility. Colloidosomes is a novel class of microcapsules whose shell consists of coagulated or fused colloid particles at interface of emulsion droplets. The particles self assemble on the surface of droplets in order to minimize the total interfacial energy forming colloidosomes. Such structures were produced for first time by templating latex particles adsorbed on the surface of octanolin- water emulsion drops and subsequent removal of oil after fusing the particles monolayers. Similar structures have also been obtained by templating water-in-oil emulsions and template solid nanoparticles on the surface of solid sacrificial micro particles based on electrostatic attraction and layer by layer assembly of multilayer shells consisting of alternating positively and negatively charged nanoparticles or polyelectrolytes. The final hollow shells are obtained by removal of central, sacrificial colloidal particles. Colloidosomes assemble polymer latex colloidal particles into shells around water-in-oil emulsion drops followed by partial fusion of shell and centrifugal transfer into water to yield stable capsules in which the shell permeability can be controlled by adjustment of partial fusion conditions. Hairy colloidosomes, whose shell consists of micro rod particles, are designed and fabricated novel colloidosome capsules that consist of aqueous gel core and shells of polymeric micro rods. This has been achieved by templating water-in-oil emulsions stabilized by rod like particles followed by gelling of the aqueous phase, dissolution of oil phase in ethanol and redispersion of obtained colloidosome microcapsules in water.
Advantages: Control of the size allows flexibility in applications and choice of encapsulated materials, Colloidosome membrane offer great potential in controlling the permeability of the entrapped species and allow the selective and time release, Control of the mechanical strength allows the yield stress to be adjusted to withstand, varying of mechanical loads and to enable release by defined shear rates[5].
HERBOSOMES
The term "herbo" means plant, while "some" means cell like. Over the past century, phytochemical and phyto‐ pharmacological sciences established the compositions, biological activities and health promoting benefits of numerous botanical products. Most of the biologically active constituents of plants are polar or water soluble molecules. However, water soluble phytoconstituents (like flavonoids, tannins, glycosidic aglycones etc) are poorly absorbed either due to their large molecular size which cannot absorbed by passive diffusion, or due to their poor lipid solubility, severely limiting their ability to pass across the lipid rich biological membranes, resulting poor bioavailability. Phytomedicines, complex chemical mixtures prepared from plants, have been used for health maintenance since ancient times. But many phytomedicines are limited in their effectiveness because they are poorly absorbed when taken by mouth. Herbosomes are also often known as phytosomes. Herbosomes exhibit better pharmacokinetic and pharmacodynamics profile than conventional herbal extracts. Molecular layer consisting of PC and other phospholipids provides a continuous matrix into which the proteins insert.
Advantages
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 12 dose requirement is also reduced, Phosphatidylcholine used in
preparation of herbosomes, besides acting as a carrier also acts as a hepatoprotective, hence giving the synergistic effect when hepatoprotective substances are employed, Herbosome permeates the non-lipophilic botanical extract to be better absorbed in intestinal lumen, Unlike liposome, chemical bonds is formed between phosphatidylcholine molecule and phytoconstituent, so the Herbosomes show better stability profile.
SPHINOSOMES
Liposome stability problems are of course much more severe so it is very important task to improve the liposomal stability. Liposomal phospholipid can undergo chemical degradation such as oxidation and hydrolysis either as a result of these changes or otherwise liposome maintained in aqueous suspension may aggregate, fuse, or leak their content. Hydrolysis of ester linkage will slow at pH value close to neutral. The hydrolysis may be avoided altogether by use of lipid which contains ether or amide linkage instead of ester linkage (such are found in sphingolipid) or phospholipid derivatives with the 2- ester linkage replaced by carbomoyloxy function. Thus sphingolipid are been nowadays used for the preparation of stable liposomes known as sphingosomes. Sphingosome may be defined as “concentric, bilayer vesicle in which an aqueous volume is entirely enclosed by a membranous lipid bilayer mainly composed of natural or synthetic sphingolipid.
Sphingosomes are administered in many ways these include parenteral route of administration such as intravenous, intramuscular, subcutaneous, and intra-arterial. Generally it will be administered intravenous or some cases by inhalation. Often it will be administered into a large central vein, such as the superior vena cava and inferior vena cava to allow highly concentrated solution to be administered into large volume and flow vessels. Sphingosomes may be administered orally or transdermal. In simple way we can say sphingosome is liposome which is composed of sphingolipid.
Advantages
Provide selective passive targeting to tumor tissue, Increase efficacy and therapeutic index, Increase stability via encapsulation., Reduction in toxicity of the encapsulated agent, Improve pharmacokinetic effect (increase circulation time), Flexibility to couple with site specific ligands to achieve active targeting.[5]
LAYEROSOMES
Layerosomes are conventional liposomes coated with one or more multiple layers of biocompatible polyelectrolytes in order to stabilize their structures. The layer-by-layer coating concept is one of the strategies used for the preparation or the stabilization of nanosystems[36]. The layersomes are conventional liposomes coated with one or multiple layers of biocompatible polyelectrolytes in order to stabilize their structure. The formulation strategy is based on an alternative coating procedure of positive poly (lysine) (pLL) and negative poly (glutamic acid) (PGA) polypeptides on initially charged small unilamellar liposomes. The major drawback of liposomes is their instability during storage or in biological media which is related to surface properties. This surface modification stabilized the structure of the liposomes and led to stable drug delivery systems. Oral administration or their incorporation in biomaterials are among potential fields of application[37]. Thus the concept of layerosomes has brought forward the stable nanosystem.
UFOSOMES
The formations of fatty acid vesicles are named "ufasomes," ufosomes are unsaturated fatty acid liposomes. Fatty acid vesicles are colloidal suspensions of closed lipid bilayers that are composed of fatty acids and their ionized species (soap). They are observed in a small region within the fatty acid-soap-water ternary phase diagram above the chain melting temperature (Tm) of the corresponding fatty acid-soap mixture[38]. Fatty acid vesicles always contain two types of amphiphiles, the nonionized neutral form and the ionized form (the negatively charged soap).
The ratio of nonionized neutral form and the ionized form is critical for the vesicle stability. Fatty acid vesicles are actually mixed "fatty acid/soap vesicles". Ufasome membranes are much more stabilized in comparison to liposomes[39].
STRATEGIES TO IMPROVE VDDS
To improve VDDS mainly two strategies are
Pro-Vesicular Drug Delivery:
Pro vesicular drug delivery developed to overcome the stability problems associated with vesicular drug delivery systems composed of dry products or liquid crystalline gel that can be hydrated immediately before use, e.g. Proliposomes, Proniosomes.[40]
Characterization
Morphology, Angle of Repose, Rate of hydration, Entrapment efficiency, Degree of deformity & permeability measurements, Size & Size distribution etc.
Types of pro vesicular drug delivery systems Proliposomes
Proniosomes
Proliposomes
In proliposomes, lipid and drug are coated onto a soluble carrier to form free-flowing granular material which on hydration forms an isotonic liposomal suspension. The proliposome approach may provide an opportunity for cost-effective large scale manufacture of liposomes containing particularly lipophilic drugs. Proliposomes: Comparatively high stability, less required storage & handling conditions. High encapsulation & drug release profile than Liposomes. Types: Dry granular Proliposomes and Mixed mecellar Proliposomes.
Comparison between liposomes and proliposomes
Liposomes-unilamellar or multilamellar spheroid structures composed of lipid molecules, often phospholipids. They show controlled release and increased solubility. But have tendency to aggregate or fuse, susceptible to hydrolysis or oxidation. Proliposomes-an alternative forms to conventional liposomal formulation Composed of water soluble porous powder as a carrier, phospholipids and drugs dissolved in organic solvent. Lipid and drug are coated on to a soluble carrier to form free-flowing granular material. Show controlled release, better stability, ease of handling and increased solubility.
Proniosomes
Versatile Drug Delivery System, Ease of transfer, Feasibility, distribution, storage, and high drug loading capacity, less side effects, high efficacy, Type & concentration of surfactant affect encapsulation efficiency & drug release rate from Proniosomes.
Method of Preparation of Proniosome: To create proniosomes, a water soluble carrier such as sorbitol is first coated with the surfactant.
Vol 3 Suppl 3, August 2014 www.mintagejournals.com 13
The evaporation of the organic solvent yields a thin coat on the sorbitol particles. The resulting coating is a dry formulation in which a water soluble particle is coated with a thin film of dry surfactant. This preparation is termed Proniosome. Other methods of preparations are:
Slurry method
Co-acervation phase separation
Slow spray-coating method
Higher the Lipophilicity grater will be the encapsulation efficiency.e.g. Proniosomal TDS of Losartan potassium, Alprenolol HCl, Valsartan proniosome.
Comparison between niosomes and Proniosomes: Niosomes-are non-ionic surfactant based multilamellar or unilamellar vesicles, aqueous solution of solute is entirely enclosed by a membrane of surfactant macro-molecules as bilayers. They are cheap and
chemically stable but posses’ problems related to physical stability
such as fusion, aggregation, sedimentation and leakage on storage.
Proniosomes-approach minimizes the problems associated with niosomes as it is a dry and free flowing product which is more stable during sterilization and storage. Ease of transfer, distribution, measuring and storage make it a versatile delivery system. Proniosomes are water-soluble carrier particles that are coated with surfactant.
Improve permeability:
Physical means
Iontophoresis
Effective method of drug transport in deeper layer of the bladder, e.g. Mitomycin C, Bethanecol.Electroporation (high voltage than Ionotophoresis).Increases permeability of tissues electric field. Helpful for delivery of drug in Bladder carcinoma treatment.Electroporation-Sonophoresis (Low density ultrasound waves), decreases tissue damage.
Chemical means
Perior instillation of DMSO enhances absorption of chemotherapeutic drugs, e.g. Paclitaxal, Pirarubicin.Intravesicle instillation of Saponin before administration of anticancer drugs, e.g. 4-0-Tetrahydropyranaldoxorubicin (THP).Increases concentrations of THP in bladder tissues. Topical administration of chitosan & cyclodextrin-disturbs intracellular tight junction. Increases paracellular transport.
FUTURE PROSPECTIVES IN VDDS
Aquasomes
Three layered self assembly compositions with ceramics carbon nanocrystalline particulate core coated with, glassy cellobiose specific targeting and molecular shielding[41]
Cryptosmes
Lipid vesicles with a surface coat composed of pc and of suitable polyoxoyethylene derivative of phosphotidyl ethanolamine. Capable of Ligand mediated drug targeting.
Discomes: Niosomes solubilized with non ionic surfactant solutions (polyoxyethylene cetyl ether class). Show ligand mediated drug targeting.
Emulsomes: Nanosize Lipid particles (bioadhesives nanoemulsion) consisted of microscopic lipid assembly with apolar core used parenteral delivery of poor water soluble drugs.
Enzymosomes: Liposomal constructs engineered to provide a mini bioenvironmental in which enzymes are covalently immobilized or coupled to the surface of liposomes. Targeted delivery to tumor cell.
Genosomes: Artificial macromolecular complexes for functional gene transfer .Cationic lipids are most suitable because they possess high biodegradability and stability in the blood stream. Cell specific gene transfer.
Photosomes: Photolysase encapsulated in liposomes, which release the content photo triggered charges in membrane permeability characteristics.
Virosomes: Liposomes spiked with virus glycoprotein, incorporated into the liposomal bilayers based on retro viruses’ derived lipids.
Vesosomes: Nested bilayer compartment in vitro via the inter digested bilayer phase formed by adding ethanol to a variety of saturated phospholipids. Multiple compartments of the vesosomes give better protection to the interior contents in serum.
Proteosomes: High molecular weight multi-submit enzyme complexes with catalytic activity, which is specifically due to the assembly pattern of enzymes. Better catalytic activity turnover than non associated enzymes.
Emulsomes: Hb containing liposome engineered by immobilizing Hb with polymerisable phospholipids.
Erythrosomes: Liposomal system in which chemically cross linked human erythrocytes used as support to which lipid bilayer is coated.
Enzymosomes: Enzymes are co-valently immobilized or coupled to the surface of liposomes.
Archaeosome: made from natural archaeal membrane lipids and/or synthetic lipid analogues have been extensively studied for potential applications in drug and vaccine delivery over the past decade only. Archaeal-type lipids consist of archaeol (diether) and/or caldarchaeol (tetraether) core structures wherein regularly branched and usually fully saturated phytanyl chains (20-40 carbons in lengths), are attached via ether bonds to the sn-2, 3 carbons of the glycerol backbone. Archaeosomes constitute a novel generation of liposomes that exhibit high stabilities to low or high temperatures, acidic or alkaline pH, oxidative conditions, high pressure, action of phospholipases, bile salts and serum proteins. These properties associated with a good safety profile are beneficial for nanotechnological applications in drug and gene delivery. Additionally, archaeosome formulations could be used as efficient carriers of antigens and/or adjuvants promoting antigen- specific, humoral and cell-mediated immune responses, in addition to antigen-specific mucosal immune responses in the vaccinated hosts. The immune responses are well sustained over time, and are subject to strong memory responses. Nanodelivery- based vaccinations using archaeosomes could then represent a promising approach for treating and preventing infections, allergies, and neoplastic or cancer diseases. In this review, the
Table 4:Non-ionic surfactants and coating carriers used for the preparation of proniosomes
Non-ionic Surfactants
Coating materials Investigated
Non-ionic surfactants
Coating materials Investigated
Non-ionic surfactants
Coating materials Investigated
Non-ionic Surfactants
Coating materials Investigated
Span20 Sucrose stearate Tween60 Lactose monohydrate Span80 Maltodextrin M700 Span60 Maltodextrin M500
