Fluidity enhancement: a critical factor for performance ...

http://informahealthcare.com/lpr ISSN: 0898-2104 (print), 1532-2394 (electronic) J Liposome Res, Early Online: 1–7 ! 2013 Informa Healthcare USA, Inc. DOI: 10.3109/08982104.2013.847956

REVIEW ARTICLE

Fluidity enhancement: a critical factor for performance of liposomal transdermal drug delivery system Vipin Kumar Sharma1, Khomendra Kumar Sarwa2, and Bhaskar Mazumder2 1

Department of Pharmaceutical Sciences, Faculty of Ayurved & Medical Sciences, Gurukul Kangri University, Haridwar, Uttarakhand, India and Department of Pharmaceutical Sciences, Dibrugarh University, Dibrugarh, Assam, India

Journal of Liposome Research Downloaded from informahealthcare.com by 14.139.239.114 on 10/25/13 For personal use only.

2

Abstract

Keywords

Liposomes are well known lipid carriers for drug delivery of bioactive molecules encapsulated inside their membrane. Liposomes as skin drug delivery systems were initially promoted primarily for localized effects with minimal systemic delivery. Subsequently, a novel vesicular system, transferosomes was reported for transdermal delivery with efficiency similar to subcutaneous injection. The multiple bilayered organizations of lipids applied in these vesicles structure are somewhat similar to complex nature of stratum corneal intercellular lipids domains. The incorporation of novel agents into these lipid vesicles results in the loss of entrapped markers but it is similar to fluidization of stratum corneum lipids on treatment with a penetration enhancer. This approach generated the utility of penetration enhancers/fluidizing agents in lipids vesicular systems for skin delivery. For the transdermal and topical applications of liposomes, fluidity of bilayer lipid membrane is rate limiting which governs the permeation. This article critically reviews the relevance of using different types of vesicles as a model for skin in permeation enhancement studies. This study has also been designed to encompass all enhancement measurements and analytical tools for characterization of permeability in liposomal vesicular system.

Flexibility, fluidizing agents, lipid bilayer, lipid vesicles

Introduction Liposomes are just hollow spheres of lipids, i.e. some lipids form membranes that close on themselves forming liposomes. The main component of liposome membranes is dipalmitoyl phosphatidylcholine (DPPC), phosphatidylcholine (PC) or egg-phosphatidylcholine (EPC). The water soluble compounds/drugs are present in aqueous compartments while lipid soluble compounds/drugs and amphiphilic compounds/ drugs insert themselves in phospholipid bilayers. Molecules from low molecular weight (glucose) to high molecular weight (peptides and proteins) have been incorporated in liposomes (Riaz, 1996). Regarding stability of these systems, some other compounds are added in order to improve stability or other structural properties, e.g. dipalmitoyl phosphatidyl glycerol (DPPG or PG), cholesterol, etc. Apparently, cholesterol has the effect of making the membrane less permeable by filling up holes or disruptions. The membrane consists of two different phases. One, at low temperatures (between 0 C and the transition temperature) is kind of a rigid gel phase. Above the transition temperature, the membrane is in fluidized phase. The difference between these two phases seems to be the way in which liposomes are arranged in the Address for correspondence: Vipin K. Sharma, Department of Pharmaceutical Sciences, Faculty of Ayurved and Medical Sciences, Gurukul Kangri University, Haridwar 249404, Uttarakhand, India. Tel: +91 01334 212144. E-mail: [email protected]

History Received 23 June 2013 Revised 24 August 2013 Accepted 19 September 2013 Published online 25 October 2013

membrane. Since the latter phase is somewhat more malleable, redispersion in buffer and extrusion are both made above the transition temperature. The liposomes containing drugs can be administrated by many routes (intravenous, oral inhalation, local application, ocular, etc.) and these can be used for the treatment of various diseases (Weinatein & Lenetman, 1984). From ancient time, liposomes have created the research interest and a number of studies have been performed about liposomes in general (Riaz et al., 1989) and about various aspects of liposomes: mechanism of liposomes fusion (Rand & Parsegiam, 1986), as drug carriers (Stuhne-Sekalec & Slanacev, 1991), temperature sensitive liposomes (Ozer et al., 1993), liposomes as topical drug carriers (Schreier & Bouwstra, 1994), target sensitive liposomes (Huang, 1994), pH sensitive liposomes (Szoka & Tang, 1993), and the stability and uses of liposomes (Riaz, 1995). Number of processes has been applied for the development of stable liposomes and the feasibility of methods depends upon their structure and integrity (Hauser & Gains, 1982). Multilamellar liposomes (MLVs) usually range from 500 to 10 000nm. Unilamellar liposomes can be called as small (SUV) and as large (LUV); SUVs are usually smaller than 50 nm and LUVs are usually large than 50 nm. The liposomes of very large size are called giant liposomes (10 000–1 00 000 nm). They can be either unilamellar or multilamellar. The liposomes containing encapsulated vesicles are called multi-vesicular and their size range is from


2

V. K. Sharma et al.

2000 to 40 000nm. LUVs having asymmetric distribution of phospholipids in the bilayers are called asymmetric liposomes. For MLVs preparation, lipid hydration method (Bangham et al., 1974; Gruner et al., 1985) and solvent spherule method (Kim et al., 1985) have been reported. Sanitation method (Oezden & Hasirci, 1991), French pressure cell method (Hamilton & Guo, 1984; Lasic et al., 1995) has been reported for SULs preparation. The LUVs having high internal volume/encapsulation efficiency are generally prepared by solvent injection method (Batzri & Korn, 1973; Deamer & Bangham, 1976; Schieren et al., 1978), detergent removal method (Philippot et al., 1985), reserve phase evaporation method (Riaz & Weiner, 1994), calcium-induced fusion method (Papahadjopoulos & Vail, 1978), microfluidization method (Lasic, 1988) and freeze-thaw method (Liu & Yonetaini, 1994; Ohsawa et al., 1985; Pick, 1981). Giant liposomes, multivesicular liposomes and asymmetric liposomes are also the area of research interest for the development of novel drug delivery devices and are fabricated by different methods (Cullis et al., 1987; Kim et al., 1983; Oku & MacDonald, 1983). Among several preparation methods described in the literature, only a few have potential for large scale manufacture of liposomes. The main issues faced to formulator are presence of organic solvent residues, physical and chemical stability, pyrogen control, sterility, size and size distribution, and batch to batch reproducibility. The integrity and the flexibility of the liposomal membrane are the critical factors that govern the retention, stability, and release of entrapped drug. Moreover, these factors are generally considered the limiting factors in liposomal drug delivery systems for skin.

Liposomes versus skin drug delivery Several advantages of liposomal carriers have been accepted in skin delivery including avoidance of first-pass metabolism, lower fluctuations in plasma drug levels, targeting of the active ingredient for a local effect and good patient compliance (Williams, 2003), but barrier nature of skin makes it difficult for most drugs to penetrate into and permeate through it (El Maghraby et al., 2001). During the past decades, there has been wide interest in exploring new techniques to increase drug absorption through skin (Barry, 2001; Honeywell-Nguyen & Bouwstra, 2005; Williams, 2003). Topical delivery of drugs by lipid vesicles has also evoked a considerable interest. Mezei & Gulasekharam (1980, 1982) reported that liposomal encapsulation of triamcinolone acetonide increased drug disposition in the epidermis and dermis. Several other studies suggested a slower skin transport of highly polar compounds in vesicle formulations than in buffer solutions (Barry, 2001). The transport rate of lipophilic compounds through liposomes is generally very high to that of free drug solutions.

Need of fluidizing agent With the success, various drawbacks have also been encountered during research trail on liposomes, mainly instability, low permeation profile. Previous studies concluded that the conventional vesicles disintegrate at the skin surface and their molecularly dispersed components penetrate into the

J Liposome Res, Early Online: 1–7

intercellular lipid matrix and then mix with the skin lipids (Hofland et al., 1995; Kirjavainen et al., 1996; Zellmer et al., 1995). Hence for better results in terms of therapeutic efficacy, new class of liposomes prepared by conformational changes in bilayer for better permeation power is to be required (Coderch et al., 2000). Classical liposomes are of little value as carriers for transdermal drug delivery because they do not deeply penetrate into the skin. Only specially designed vesicles are shown to be able to allow transdermal delivery. Cevc and coworkers introduced the first elastic liposomes with high deformability referred as transfersomes, consisting of phosphatidylcholine (PC) with sodium cholate or sodium deoxycholate (Cevc & Blume, 1992; Cevc et al., 1997). El Maghraby developed the so-called ultradeformable liposomes, which are considered to be elastic enough to permeate into the skin (El Maghraby et al., 2000). Ethosomes developed by Touitou’s group are vesicles composed of PC and a high proportion of ethanol generally, 430% with higher permeability (Touitou et al., 2000a). Regarding drug penetration, conventional liquid state vesicles have proven to be superior to gel-state vesicles (El Maghraby et al., 2001; van Kuijk-Meuwissen et al., 1998), whereas elastic vesicles have shown to be superior to conventional gel-state and even liquid-state vesicles in terms of interactions with human skin (van den Bergh et al., 1999a) and enhanced drug penetration (El Maghraby et al., 2001). Therefore, a series of liquid-state vesicles with elastic membranes have been developed by addition of chemical compound which enhanced the fluidity of bilayer membrane and produced liquid-state vesicles. These may be broadly classified in some groups include vesicles containing PC and edge activators (sodium cholate, polysorbate 80 or polysorbate 20), i.e. the so called TransfersomesÕ (Cevc & Blume, 2003; Cevc et al., 2002), vesicles composed of the bilayerforming surfactant L-595 (sucrose laurate ester) and the micelle-forming surfactant PEG-8-L (octaoxyethylene laurate ester) (van den Bergh et al., 1999b), ethosomes containing phospholipids and high amounts of ethanol (Touitou et al., 2000b) and invasomes composed of PC, ethanol and a mixture of terpenes as penetration enhancers (DragicevicCuric et al., 2008, 2009).

Fluidizing agents The physico-chemical properties of liposomes have significant effect on drug permeation (Cevc et al., 2002; Knepp et al., 1990). These properties can be easily modulated by fluidizing agent which provides elasticity to the vesicles. Elasticity developed on the vesicle membrane by changes in the phases of the amphiphiles formed in the membranes of the vesicles (a liquid or a gel phase) is an important feature, which plays a vital role in liposomes effectiveness as a dermal delivery vehicle. Permeation studies (in vitro) have revealed that liquid-state vesicles are more effective than gel-state vesicles in enhancing drug transport (Ogiso et al., 1996). These special class of liposomes are known as various names like flexible (Ogunsola et al., 2012), elastic (Benson, 2010) and most accepted as deformable liposomes (Oh et al., 2006). Deformable liposomes accepted as transfersomes are the first generation of elastic


DOI: 10.3109/08982104.2013.847956

vesicles introduced by Cevc & Blume (1992). This class of vesicles is well known by various names depending upon additives used. However, there are several new vesicle types, e.g. transfersomes, flexosomes, ethosomes, niosomes, vesosomes, invasomes and polymerosomes. The meta-stable lipid matrices of flexible liposomes, consisting of mixtures of conventional phospholipids both from animal source and plant source, e.g. egg and soya phospholipid, respectively, and additional compound often called edge activator such as surfactants (bile salts) or co-solvents (ethanol), are capable of experiencing strong spontaneous fluctuation at room temperature (Cevc, 1995). The edge activator is often a single chain surfactant, having a high radius of curvature that destabilizes lipid bilayers of the vesicles and increases the potential for deformability of the bilayers (Cevc, 1996; Honeywell-Nguyen & Bouwstra, 2005). Sodium cholate, sodium deoxycholate, Span 60, Span 65, Span 80, Tween 20, Tween 60, Tween 80 and dipotassium glycyrrhizinate have been employed as edge activators (El Maghraby et al., 2000; Garg et al., 2006; Oh et al., 2006; Trotta et al., 2004). Deformability is well depended upon the type of edge activator and the structural difference may be responsible for response difference. Tween 80 has been reported to produce higher deformable liposomes than sodium deoxycholate and sodium cholate. The effect was considered due to the highly flexible and non bulky hydrocarbon chains of Tween 80 in comparison to steroid-like structures which are bulkier than the hydrocarbon chains of Tween (El Maghraby et al., 2000). On the other hand, in case of spans, the hydrophobicity of these surfactants reduced the formation of transient hydrophilic holes through minimizing the amphiphilic property of the bilayers responsible for membrane fluidity. Furthermore, span 85 being a sorbitan triester in comparison span 80 (a sorbitan monoester), offered less flexible membranes due to bulkiness and resulted less deformablility than Span80 (El Zaafarany et al., 2010). Yet now, there is no standard composition of flexible agents and the various chemicals have been tested for enhancement of vesicles flexibility. This class of vesicles are known by various names like transfersomes, edge activator (Trotta et al., 2002, 2004), ethosomes (Verma et al., 2003), invasomes (El Zaafarany et al., 2010), etc. Invasomes are also used and composed of PC, ethanol and a mixture of terpenes to enhance the permeability of lipid vesicles. The natural terpenes, e.g. cineole, citral and D-limonene have been applied for permeability enhancement (Dragicevic-Curic et al., 2008). Ethosomes with ethanol as penetration enhancer has been applied for drug delivery systems with their proposed mechanism. Ethanol in these preparations is one of the most commonly used chemical permeation enhancer which reduces the barrier resistance of the stratum corneum (SC). Numbers of mechanisms have been proposed for permeation enhancing action of ethanol. As a solvent, ethanol can be included in the formulation to enhance the solubility of the drug. This is particularly important for poorly soluble permeants, as they are prone to depletion in the donor vehicle (Lodzki et al., 2003). It is a relatively volatile solvent and rapidly evaporates at skin temperature. Ethanol loss from a formulation may lead

Fluidity enhancement

3

to the drug becoming supersaturated, which will influence drug flux across the membrane. But there is no specific proposed mechanism for how ethanol provides the flexibility to the lipid bilayer. Some available interaction concluded that the ethanol induced non-lamellar phases may be responsible for better penetration (Lodzki et al., 2003). The interactions of elastic and rigid vesicles affected the hairless mouse skin in in vivo study and it has also been observed that only the elastic liquid state vesicles induce changes in the ultra-structure of the viable tissue while classical liposomes remain ineffective for making the significant changes (van den Bergh et al., 1999a). Due to the elasticity, these vesicular bodies squeeze themselves between the cells in the SC and consequently results in greater efficacy (van den Bergh, 1999).

Mechanism of penetration of fluidized liposomes There is no specific known mechanism depicting the flexibility enhancement process induced by chemicals on lipid bilayer. Flexible agents are classified as chemical penetration enhancer and create general effects on enhancement of drug, formulation into the skin. These enhancers may (Lodzki et al., 2003) Increase the diffusivity of the drug in the skin; Cause SC lipid-fluidization which leads to decreased barrier function (a reversible action); Increase and optimize the thermodynamic activity of the drug in the vehicle and the skin; Results in a reservoir of drug within the skin; Affect the partition coefficient of the drug, increasing its release from the formulation into the upper layers of the skin; One proposed mechanism of the penetration enhancement of elastic vesicles is that vesicles or vesicle materials disorganize and disrupt intercellular lipid lamellae thereafter form channel-like penetration pathways through which drug molecules penetrate (van den Bergh, 1999). The second possibility is that intact vesicles penetrate into SC through pre-existing channels with low penetration resistance (Cevc et al., 2002; Schatzlein & Cevc, 1998). Flexible liposomes are having an elastic energy () in the order of ambient thermal energy (kT), which is nearly 20-fold lower than that of conventional liposomes. Remarkably, flexible liposomes make use of the transepithelial water gradient as driving force to penetrate across the skin. The resultant force (F ¼ rv2 105 Pa), where rv is the vesicle ratio in order of 1011 to 1012 N and it is sufficient to impulse the locomotion of the flexible liposomes across the nanochannels of the SC without collapse/or coalesce (Barry, 2001; Cevc & Blume, 2003; Verma et al., 2003). Two penetration mechanisms for transfersomes permeability have been proposed (Honeywell-Nguyen & Bouwstra, 2005). In first mechanism, vesicles act as drug carrier systems, whereby intact vesicles enter the SC carrying vesicle-bound drug molecules into the skin. In another mechanism, vesicles acts as penetration enhancers, whereby vesicle bilayers enter the SC and subsequently modify the intercellular lipid lamellae and it facilitates penetration of free drug molecules into and across the SC.


4

V. K. Sharma et al.

Enhanced permeation by ethosomes has been suggested by a synergistic mechanism between ethanol, vesicles and skin lipids (Touitou et al., 2001) but this mechanism does not reveal about happening in bilayer by addition of ethanol. It has been analyzed that the first part of the mechanism is due to the ethanol effect, where ethanol interacts with the lipid molecules in the polar head group region resulting in a reduction in the transition temperature of the lipids in the SC, increasing their fluidity and decreasing the density of the lipid multilayer. This is followed by the ‘‘ethosome effect,’’ which includes lipid penetration and permeation by opening of new pathways, due to the malleability and fusion of ethosomes with skin lipids, resulting in the release of the drug into the deep layers of the skin. Ethanol may also provide vesicles with soft flexible characteristics, which allow them to penetrate more easily into the deeper layers of the skin. The release of the drug in the deep layers of the skin and its transdermal absorption then results due to fusion of ethosomes with skin lipids and drug release at various points along the penetration pathway (Elsayed et al., 2006).

Analysis of flexibility/deformability of liposomes Extrusion method Comparative measurement of elasticity of the bilayer flexible liposomes is carried out by extrusion measurement through a locally fabricated stainless steel pressure filter holder. The vesicles are extruded through polycarbonate filter with a pore size of 50–200 nm at a constant pressure. The elasticity is measured as a function of time (i.e. the time taken for the extrusion of 10 mL or specified quantity of formulation). Generally distilled water is applied as a vehicle for flexibility analysis of these vesosomes (Kim et al., 2004). Commercially available extruders are also used and two stacked sandwich of polycarbonate membrane filter of 50– 200 nm size depending upon desired size and nature, are applied in the measurement of flexibility. These are mostly driven by an external pressure 0.3–1.2 MPa for a specified period (Cevc, 1995; Mahor et al., 2007). In some studies, liposomes dispersions are diluted with suitable vehicle. Thereafter, a quantified volume of the diluted vehicle is extruded through a sandwich of three sheets of 50 nm polycarbonate membrane under constant pressure, 300 kPa. The extruded volume is measured using a syringe and the volumes are compared before and after extrusion (Dubey et al., 2006; Song & Kim, 2006). In some another studies, three polycarbonate membranes with decreasing size (200, 100, 50 nm) have been used for same purpose (Montanari et al., 2007). Deformability index The elasticity of vesicle is expressed in terms of deformability index which is proportional to j(rv/rp)2 where, j is the weight of suspension, which is extruded in specified time (mostly take 10 min) through a polycarbonate filter of 50 nm pore (in case of single membrane or average pore size in case of two or more membrane) size, rv is the size of vesicle and rp is the pore size of membrane (Hiruta et al., 2006; Gupta et al., 2005; Mahor et al., 2007; Mishra et al., 2006; Trotta et al., 2004).


Retention degree In another studies, the retention degree (RD) of flexible liposomal inner aqueous phase is determined after passage through the nanoporous barrier. The fluorophore/quencher pair [fluorophore: 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS)] and the quencher p-xylene-bis-pyridinium bromide (DPX) is incorporated into flexible liposomes and after extrusion, non incorporated HPTS and DPX are eliminated by gel permeation in Sephadex G-50. Fluorescence emission intensity of HPTS (exc, 465 nm; em, 516 nm) is monitored in a multi-frequency phase fluorometer, before and after passage through the 50 nm barrier, driven by 0.8 MPa for UDL and 2.5 MPa for conventional liposomes. RD is calculated by the expression such as: 100[(I50Io)/IT] 100, where I50 was the fluorescence intensity after passage through 50 nm, Io the fluorescence intensity before passage and IT was the total intensity obtained after addition of Triton X-100 at 0.1% (v/v) (Montanari et al., 2007). Electron spin resonance Penetration enhancing ability of vesicles depends on the fluidity, elasticity of their bilayers, and the interaction of membrane-softening components such as terpenes, mixtures of terpenes and ethanol with phospholipid membranes. The measurement of fluidity of liposomal vesicles by electron spin resonance (ESR) is assessed by the order parameter S that is a measure of the average angular deviation of the fatty acid ‘‘acyl’’ chain of the spin label at the nitroxide group from the average orientation of the fatty acids in the membrane (Hubbel & McConnel, 1971; Seelig, 1970). An S value of 1.0 is characteristic for rigid lipid membranes, while a reduction in this value indicates an increase in the fluidity of the membranes. The order parameter S is calculated from the ESR spectra (Gaffney, 1975). Regarding 5-doxyl stearic acid liposomes without mTHPC [7,8-dihydro5,10,15,20-tetrakis-(3-hydroxyphenyl) porphyrin], a low S value (in the range 0.38–0.43) has been observed suggesting a high bilayer fluidity in the region of the phospholipid acyl chains close to the polar head groups of the phospholipids. The highest S value has been detected for the liposomes without ethanol (conventional liposomes). Another decrease of the S value has achieved by the addition of 1% terpenes/terpene mixtures. The lowest value for S has been obtained for invasomes with 1% citral (Dragicevic-Curic et al., 2011). More detailed information should be obtained from the rotational correlation time c analyzed by ESR study. Since in the rapid motion regime, the calculation of S is less reliable and molecular freedom of motion is related quantitatively to the rotational correlation time c of the nitroxide spin-labeled molecule. This parameter can be used to measure the motion of the phospholipid acyl chains near their hydrophobic end (Keith et al., 1970). A low value of c has been observed for all samples of 5-doxyl stearic acid and 16-doxyl stearic acid spin label liposomes (in the range 0.45–1.02), suggesting an increased molecular dynamics of the phospholipid acyl chains near to their hydrophobic end. The highest value for c has been detected for liposomes without ethanol, which was in accordance with the S


DOI: 10.3109/08982104.2013.847956

value obtained for the same formulation (Dragicevic-Curic et al., 2011).


Differential scanning calorimetry Thermal analysis (differential scanning calorimetry, DSC) has been successfully used to probe the mechanisms of action of skin penetration enhancers. The originators used human stratum corneum (SC)) and tested a variety of penetration enhancers with different lipophilicities (Barry, 1987; Goodman & Barry, 1983, 1985, 1986, 1988). Based on the DSC results as well as permeation and partitioning data, Barry (1987) proposed four possible mechanisms of action of skin penetration enhancers: (1) Disruption of the organization of the intercellular lipids of the SC increasing the fluidity and thus permitting easier drug permeation through the less rigid environment. Lipophilic enhancers may act primarily via this mechanism. (2) Many accelerants also interact with intracellular protein. The exceptions were azone and oleic acid; however, these were most effective as enhancers when dissolved in a polar co-solvent such as propylene glycol (PG), which itself interacts with protein. Although drug flux can increase via lipid interaction alone, once the lipid barrier weakens, the protein-filled cells may still provide a significant diffusional resistance. Thus an enhancer that affects both lipid and protein domains could be more potent. Intracellular drug transport could be increased by a solvating action of enhancers on the protein helices. This mechanism encompasses the displacement of bound protein–water, the expansion of protein structure and the competition with permeants for hydrogen-bonding sites. (3) The diffusional resistance of the intracellular contents alters markedly with skin hydration—water itself is quite a potent penetration enhancer. The reason for this is that in the fully hydrated skin, the intracellular regions will be more fluid and water will compete for drug-binding sites, lowering the diffusional barrier. (4) Small polar enhancers such as dimethylsulphoxide (DMSO) and its analogues, the pyrrolidones and PG may accumulate in both intercellular and protein regions of the tissue. The presence of these powerful solvents may then increase drug partitioning into the skin, yielding increased fluxes. The action of a penetration enhancer has been related to its partition coefficient. Small polar enhancers may partition preferentially at low concentrations into the protein region of the SC. At high concentrations they could also interact with SC lipids, increasing fluidity. Non-polar materials appear to enter the lipid regions only, where they disrupt the lipid bilayers while enhancers of intermediate polarity interact with both protein and lipid (El Maghraby et al., 2008). Lipid vesicles undergo distinct structural changes at the phase transition temperature (Tm). Below the pre-transition temperature, the bilayer lipids are in highly ordered gel state, in the tilted one-dimensional arrangement. At the pretransition temperature, lipids change from tilted one-dimensional arrangements to two-dimensional arrangements with

5

periodic undulations. Above Tm, rotational isomerization occurs which decreases the thickness of the bilayer and the system reverts to one-dimensional arrangements, thus, the lipids become more fluid (El Maghraby et al., 2000). The transition change of sol–gel in lipids in presence of fluidizing agents can be studied by differential scanning electron microscopy. In edge activator transferosomes containing tween and spans, it has been observed that Tm was decreased on adding stearylamine and it has been considered due to interaction of stearylamine with the lipid vesicles, by fitting its lipophilic portions between the hydrocarbon chains of the lipid bilayers, thus perturbing the packing characteristics and fluidizing the lipid bilayers (El Zaafarany et al., 2010). In another study, the effect of fluidizing agent has also been observed as in hydrogenated phosphatidyl choline liposomes, the transition temperature was decreased on addition of dipotassium glycyrrhizinate. The decrease in Tm value indicated that the surfactant perturbs the packing characteristics and, thus, fluidizes the lipid bilayer (Trotta et al., 2004).

Conclusion The precise reach, as well as the kinetics of elastic liposome penetration through the skin depends on the carrier type, total mass applied, and the detailed application conditions. In order to achieve an optimum carrier efficacy of these systems and the best possible therapeutic results, a number of the carrier system properties must, therefore, be simultaneously considered and perfected. Such multiple inter dependencies bring many formulation difficulties but also offer the means for achieving special, and frequently quite desirable drug distribution. Various drawback has been encountered mainly instability, low permeation profile, but if these systems are tailored suitably in terms of their permeation enhancement, the liposomal drug delivery may be the benchmark for topical systems.

Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

References Bangham AD, Hill MW, Miller NGA. (1974). Preparation and use of liposomes as models of biological membranes. In: Korn ND, ed. Methods in Membrane Biology. Vol. 1. New York: Plenum, 1–68. Barry BW. (2001). Novel mechanisms and devices to enable successful transdermal drug delivery. Eur J Pharm Sci 14:101–14. Barry BW. (1987). Mode of action of penetration enhancers in human skin. J Control Release 6:85–97. Batzri S, Korn ED. (1973). Single bilayer liposomes prepared without sonication. Biochim Biophys Acta 298:1015–19. Benson HA. (2010). Elastic liposomes for topical and transdermal drug delivery. Methods Mol Biol 605:77–86. Cevc G, Scha¨tzlein A, Richardsen H. (2002). Ultra deformable lipid vesicles can penetrate the skin and other semi-permeable barriers unfragmented. Evidence from double label CLSM experiments and direct size measurements. Biochim Biophys Acta 1564:21–30. Cevc G. (1995). Material transport across permeability barriers by means of lipid vesicles. In: Lipowsky RSE, ed. Handbook of Biological Physics. Amsterdam: Elsevier, 465–90. Cevc G. (1996). Transfersomes, liposomes and other lipid suspensions on the skin: permeation enhancement, vesicle penetration, and


6

V. K. Sharma et al.

transdermal drug delivery. Crit Rev Ther Drug Carrier Syst 13: 257–388. Cevc G, Blume G. (1992). Lipid vesicles penetrate into intact skin owing to the transdermal osmotic gradients and hydration force. Biochim Biophys Acta 1104:226–32. Cevc G, Blume G. (2003). Biological activity and characteristics of triamcinolone-acetonide formulated with the self-regulating drug carriers, transfersomes. Biochim Biophys Acta 1614:156–64. Cevc G, Blume G, Schatzlein A. (1997). Transfersomes-mediated transepidermal delivery improves the regio-specificity and biological activity of corticosteroids in vivo. J Control Release 45:211–26. Coderch L, Fonollosa J, De Pera M, et al. (2000). Influence of cholesterol on liposome fluidity by EPR—relationship with percutaneous absorption. J Control Release 68:85–95. Cullis PR, Hope MJ, Bally MB, et al. (1987). Liposomes as pharmaceuticals. In: Ostro MJ, ed. Liposomes from Biophysics to Therapeutics. New York: Marcel Dekker, Chapter 2, 39–72. Deamer D, Bangham AD. (1976). Large volume liposomes by an ether vaporization method. Biochim Biophys Acta 443:629–34. Dragicevic-Curic N, Scheglmann D, Albrecht V, Fahr A. (2008). Temoporfin-loaded invasomes: development, characterization and in vitro skin penetration studies. J Control Release 127:59–69. Dragicevic-Curic N, Scheglmann D, Albrecht V, Fahr A. (2009). Development of different temoporfin-loaded invasomes-novel nanocarriers of temoporfin: characterization, stability and in vitro skin penetration studies. Colloids Surf B Biointerfaces 70:198–206. Dragicevic-Curic N, Friedrich M, Petersen S, et al. (2011). Assessment of fluidity of different invasomes by electron spin resonance and differential scanning calorimetry. Int J Pharm 412:85–94. Dubey V, Mishra D, Asthana A, Jain NK. (2006). Transdermal delivery of a pineal hormone: melatonin via elastic liposomes. Biomaterials 27: 3491–6. El Maghraby GM, Barry BW, Williams AC. (2008). Liposomes and skin: from drug delivery to model membranes. Eur J Pharm Sci 34:203–22. El Maghraby GM, Williams AC, Barry BW. (2001). Skin hydration and possible shunt route penetration in controlled estradiol delivery from ultradeformable and standard liposomes. J Pharm Pharmacol 53: 1311–22. El Maghraby GMM, Williams AC, Barry BW. (2000). Oestradiol skin delivery from ultradeformable liposomes: refinement of surfactant concentration. Int J Pharm 196:63–74. Elsayed MMA, Abdallah OY, Naggar VF, Khalafallah NM. (2006). Deformable liposomes and ethosomes: mechanism of enhanced skin delivery. Int J Pharm 322:60–6. El Zaafarany GM, Awad GA, Holayel SM, Mortada ND. (2010). Role of edge activators and surface charge in developing ultradeformable vesicles with enhanced skin delivery. Int J Pharm 397:164–72. Gaffney BJ. (1975). Fatty acid chain flexibility in the membranes of normal and transformed fibroblasts. Proc Natl Acad Sci USA 72: 664–8. Garg M, Mishra D, Agashe H, Jain NK. (2006). Ethinylestradiol loaded ultraflexible liposomes: pharmacokinetics and pharmacodynamics. J Pharm Pharmacol 58:459–68. Goodman M, Barry BW. (1983). Differential scanning calorimetry of human stratum corneum: effect of penetration enhancers azone and DMSO. Anal Proc 26:397–8. Goodman M, Barry BW. (1985). Differential scanning calorimetry (DSC) of human stratum corneum: effect of azone. J Pharm Pharmacol 37:80P. Goodman M, Barry BW. (1986). Action of skin permeation enhancers azone, oleic acid and decylmethyl sulphoxide: permeation and DSC studies. J Pharm Pharmacol 38:71P. Goodman M, Barry BW. (1988). Action of penetration enhancers on human skin as assessed by permeation of model drugs 5-fluorouracil and estradiol. I. Infinite dose technique. J Invest Dermatol 91:323–7. Gruner SM, Leak RP, Janoff S, Ostro MJ. (1985). Novel multilayered lipid vesicles: comparison of physical characteristics of multilamellar liposomes and stable plurilamellar vesicles. Biochemistry 24: 2833–42. Gupta PN, Mishra V, Rawat A, et al. (2005). Non-invasive vaccine delivery in transfersomes, niosomes and liposomes: a comparative study. Int J Pharm 293:73–82. Hamilton RL, Guo LSS. (1984). French pressure cell liposomes: preparation, properties, and potential. In: Gregoriades G, ed. Liposome Technology. Vol. 1. Florida: CRC Press, Chapter 4, 37–49.


Hauser H, Gains N. (1982). Spontaneous vesiculation of phospholipids: a simple and quick method of forming unilamellar vesicles. Proc Natl Acad Sci USA 79:1683–7. Hiruta Y, Hattori Y, Kawano K, et al. (2006). Novel ultra-deformable vesicles entrapped with bleomycin and enhanced to penetrate rat skin. J Control Release 113:146–54. Hofland HE, Bouwstra JA, Bodde HE, et al. (1995). Interactions between liposomes and human stratum corneum in vitro: freeze fracture electron microscopical visualization and small angle X-ray scattering studies. Br J Dermatol 132:853–66. Honeywell-Nguyen PL, Bouwstra J. (2005). Vesicles as a tool for transdermal and dermal delivery. Drug Discov Today Technol 2: 67–74. Huang L. (1994). Forum in ‘‘Liposomes in Controlled Release’’. J Liposome Res 4:327–30. Hubbel WL, McConnel HM. (1971). Molecular motion in spin-labeled phospholipids and membranes. J Am Chem Soc 93:314–26. Keith AD, Bulfield G, Snipes W. (1970). Spin-labeled Neurospora mitochondria. Biophys J 10:618–26. Kim A, Lee EH, Choi SH, Kim CK. (2004). In vitro and in vivo transfection efficiency of a novel ultradeformable cationic liposome. Biomaterials 25:305–13. Kim S, Jacobs RE, White SH. (1985). Preparation of multilamellar vesicles of defined size-distribution by solvent-spherule evaporation. Biochim Biophys Acta 812:793–801. Kim S, Turker MS, Chi EY, et al. (1983). Preparation of multivesicular liposomes. Biochim Biophys Acta 728:339–48. Kirjavainen M, Urtti A, Jaaskelainen I, et al. (1996). Interaction of liposomes with human skin in vitro—the influence of lipid composition and structure. Biochim Biophys Acta 1304:179–89. Knepp VM, Szoka FC, Guy RH. (1990). Controlled drug release from a novel liposomal delivery system. II. Transdermal delivery characteristics. J Control Release 12:25–30. Lasic DD. (1988). The mechanism of vesicle formation. Biochem J 256: 1–11. Lasic DD, Ceh B, Stuart MC, et al. (1995). Transmembrane gradient driven phase transitions within vesicles: lessons for drug delivery. Biochim Biophys Acta 1239:145–56. Liu L, Yonetaini T. (1994). Preparation and characterization of liposome-encapsulated haemoglobin by a freeze-thaw method. J Microencapsulation 11:409–21. Lodzki M, Godin B, Rakou L, et al. (2003). Cannabidiol—transdermal delivery and anti-inflammatory effect in a murine model. J Control Release 93:377–87. Mahor S, Rawat A, Dubey PK, et al. (2007). Cationic transfersomes based topical genetic vaccine against hepatitis B. Int J Pharm 340: 13–19. Mezei M, Gulasekharam V. (1980). Liposomes – a selective drug delivery system for the topical route of administration: lotion dosage form. Life Sci 26:1473–7. Mezei M, Gulasekharam V. (1982). Liposomes – a selective drug delivery system for the topical route of administration: gel dosage form. J Pharm Pharmacol 34:473–4. Mishra D, Dubey V, Asthana A, et al. (2006). Elastic liposomes mediated transcutaneous immunization against Hepatitis B. Vaccine 24: 4847–55. Montanari J, Perez AP, Di Salvo F, et al. (2007). Photodynamic ultradeformable liposomes: design and characterization. Int J Pharm 330:183–94. Oezden MY, Hasirci VN. (1991). Preparation and characterization of polymer coated small unilamellar vesicles. Biochim Biophys Acta 1075:102–8. Ogiso T, Niinaka N, Iwaki M. (1996). Mechanism for enhancement effect of lipid disperse system on percutaneous absorption. J Pharm Sci 85: 57–64. Ogunsola OA, Margaret E, Kraeling B, et al. (2012). Structural analysis of ‘‘flexible’’ liposome formulations: new insights into the skinpenetrating ability of soft nanostructures. Soft Mater 8:10226–32. Oh YK, Kim MY, Shin JY, et al. (2006). Skin permeation of retinol in Tween 20-based deformable liposomes: in-vitro evaluation in human skin and keratinocyte models. J Pharm Pharmacol 58:161–6. Ohsawa T, Miura H, Harada K. (1985). Studies on the effect of watersoluble additives and on the encapsulation mechanism in liposome preparation by the freeze-thawing method. Chem Pharm Bull 33: 5474–83.


DOI: 10.3109/08982104.2013.847956

Oku N, MacDonald RC. (1983). Solubilization of phospholipids by chaotropic ion solutions. J Biol Chem 258:8733–8. Ozer A, Yekta A, Farivar MM, Hincal AA. (1993). Temperature and pH-sensitive liposomes. Eur J Pharm Biopharm 39:97–101. Papahadjopoulos D, Vail WJ. (1978). Incorporation of macromolecules within large unilamellar vesicles (LUV). Ann N Y Acad Sci 308: 259–67. Philippot JR, Mutafschicv S, Liautard JP. (1985). Extemporaneous preparation of large unilamellar liposomes. Biochim Biophys Acta 821:79–84. Pick U. (1981). Liposomes with a large trapping capacity prepared by freezing and thawing of sonicated phospholipid mixtures. Arch Biochem Biophys 212:186–94. Rand RP, Parsegiam VA. (1986). Mimicry and mechanism in phospholipid models of membrane fusion. Ann Rev Physiol 48:201–12. Riaz M. (1996). Liposomes preparation methods. Pak J Pharm Sci 19: 65–77. Riaz M. (1995). Stability and uses of liposomes. Pak J Pharm Sci 8: 69–79. Riaz M, Weiner N. (1994). Stability of phosphoinosityles containing liposomes: effects of triton x-100, temperature and 68 rpm. Pak J Pharm Sci 7:61–8. Riaz M, Weiner N, Martin F. (1989). Liposomes. In: Lieberman HA, Reiger MM, Banker GS, eds. Pharmaceutical Dosage Forms: Disperse Systems. NY: Marcel Dekker, Chapter 16, p. 567. Schatzlein A, Cevc G. (1998). Non-uniform cellular packing of the stratum corneum and permeability barrier function of intact skin: a high resolution confocal laser scanning microscopy study using highly deformable vesicles (transfersomes). Br J Dermatol 138:583–92. Schieren H, Rudolph S, Findelstein M, et al. (1978). Comparison of large unilamellar vesicles prepared by a petroleum ether vaporization method with multilamellar vesicles: ESR, diffusion and entrapment analyses. Biochim Biophys Acta 542:137–53. Schreier H, Bouwstra J. (1994). Liposomes and niosomes as topical drug carriers – dermal and transdermal drug-delivery. J Control Release 30: 1–15. Seelig J. (1970). Spin label studies for oriented smectic crystals: a model system for bilayer membranes. J Am Chem Soc 92:3881–7. Song YK, Kim CK. (2006). Topical delivery of low-molecular-weight heparin with surface-charged flexible liposomes. Biomaterials 27: 271–80.


7

Stuhne-Sekalec L, Slanacev NZ. (1991). Liposomes as carriers of cyclosporin A. J Microencapsulation 8:441–6. Szoka FC, Tang M. (1993). Amphotericin B formulated in liposomes and lipid based systems: a review. J Liposome Res 3:363–75. Touitou E, Dayan N, Bergelson L, et al. (2000a). Ethosomes—novel vesicular carriers for enhanced delivery: characterization and skin penetration properties. J Control Release 65:403–18. Touitou E, Godin B, Dayan N. (2001). Intracellular delivery mediated by ethosomal carrier. Biomaterials 22:3055–9. Touitou E, Godin B, Weiss C. (2000b). Enhanced delivery of drugs into and across the skin by ethosomal carriers. Drug Dev Res 50:406–15. Trotta M, Peira E, Debernardi F, Gallarate M. (2002). Elastic liposomes for skin delivery of dipotassium glycyrrhizinate. Int J Pharm 241: 319–27. Trotta M, Peira E, Carlotti ME, Gallarate M. (2004). Deformable liposomes for dermal administration of methotrexate. Int J Pharm 270: 119–25. van den Bergh BA. (1999). Elastic liquid state vesicles as a tool for topical drug delivery [PhD thesis]. The Netherlands: Leiden University. van den Bergh BA, Bouwstra JA, Junginger HE, Wertz PW. (1999a). Elasticity of vesicles affects hairless mouse skin structure and permeability. J Control Release 62:367–79. van den Bergh BA, Vroom J, Gerritsen H, et al. (1999b). Interactions of elastic and rigid vesicles with human skin in vitro: electron microscopy and two-photon excitation microscopy. Biochim Biophys Acta 1461:155–73. van Kuijk-Meuwissen ME, Junginger HE, Bouwstra JA. (1998). Interactions between liposomes and human skin in vitro, a confocal laser scanning microscopy study. Biochim Biophys Acta 1371:31–9. Verma DD, Verma S, Blume G, Fahr A. (2003). Liposomes increase skin penetration of entrapped and non-entrapped hydrophilic substances into human skin: a skin penetration and confocal laser scanning microscopy study. Eur J Pharm Biopharm 55:271–7. Weinatein JN, Lenetman LD. (1984). Liposomes as drug carriers in cancer chemotherapy. Pharmacol Ther 24:207–33. Williams A. (2003). Transdermal and Topical Drug Delivery. 1st ed. London: Pharmaceutical Press. Zellmer S, Pfeil W, Lasch J. (1995). Interaction of phosphatidylcholine liposomes with the human stratum corneum. Biochim Biophys Acta 1237:176–82.