Effect of liposomes on percutaneous penetration of lipophilic materials

Application of biomacromolecule-based passive penetration enhancement technique in superficial tumor therapy: A review

Transdermal drug delivery (TDD) has shown great promise in superficial tumor therapy due to its noninvasive and avoidance of the first-pass effect. Especially, passive penetration enhancement technique (PPET) provides the technical basis for TDD by temporarily altering the skin surface structure without requiring external energy. Biomacromolecules and their derived nanocarriers offer a wide range of options for PPET development, with outstanding biocompatibility and biodegradability. Furthermore, the abundant functional groups on biomacromolecule surfaces can be modified to yield functional materials capable of targeting specific sites and responding to stimuli. This enables precise drug delivery to the tumor site and controlled drug release, with the potential to replace traditional drug delivery methods and make PPET-related personalized medicine a reality. This review focuses on the mechanism of biomacromolecules and nanocarriers with skin, and the impact of nanocarriers' surface properties of nanocarriers on PPET efficiency. The applications of biomacromolecule-based PPET in superficial tumor therapy are also summarized. In addition, the advantages and limitations are discussed, and their future trends are projected based on the existing work of biomacromolecule-based PPET.

Polysorbate-Based Drug Formulations for Brain-Targeted Drug Delivery and Anticancer Therapy

Polysorbates (PSs) are synthetic nonionic surfactants consisting of polyethoxy sorbitan fatty acid esters. PSs have been widely employed as emulsifiers and stabilizers in various drug formulations and food additives. Recently, various PS-based formulations have been developed for safe and efficient drug delivery. This review introduces the general features of PSs and PS-based drug carriers, summarizes recent progress in the development of PS-based drug formulations, and discusses the physicochemical properties, biological safety, P-glycoprotein inhibitory properties, and therapeutic applications of PS-based drug formulations. Additionally, recent advances in brain-targeted drug delivery using PS-based drug formulations have been highlighted. This review will help researchers understand the potential of PSs as effective drug formulation agents.

LeciPlex, invasomes, and liposomes: A skin penetration study

The present study compares three vesicular systems, cationic LeciPlex, invasomes, and conventional liposomes for their ability to deliver drugs deep into the skin. Skin penetration ability of the three vesicular systems was studied for two drugs namely idebenone (antioxidant/anticancer) and azelaic acid (antiacne). All systems showed sizes in nanometer range with small polydispersity indices. Vesicular systems were characterized by CryoTEM studies to understand the differences in morphology of the vesicular systems. Ex vivo human skin penetration studies suggested a pattern in penetration of drugs in different layers of the skin: LeciPlex showed higher penetration for idebenone whereas invasomes showed higher penetration of azelaic acid. Ex vivo study using a fluorescent dye (DiI) was performed to understand the differences in the penetration behavior of the three vesicular systems on excised human skin. In vitro cytotoxicity studies on B16F10 melanoma cell lines revealed, when loaded with idebenone, LeciPlex formulations had the superior activity followed by invasomes and liposomes. In vitro antimicrobial study of azelaic acid loaded systems on Propionibacterium acne revealed high antimicrobial activity for DDAB leciplex followed by almost equal activity for invasomes and CTAB LeciPlex followed by liposomes. Whereas antiacne efficacy study in rats for azelaic acid loaded systems, invasomes exhibited the best antiacne efficacy followed by liposomes and LeciPlex.

Novel gel formulations with catanionic aggregates enable prolonged drug release and reduced skin permeation

Objectives

The aim of this study was to investigate skin permeation rates of a drug substance when applied in novel gel formulations with catanionic aggregates.

Methods

Reference gel without catanionic aggregates was compared with formulations with catanionic aggregates composed of tetracaine and either sodium dodecyl sulphate (SDS) or capric acid. Carbomer and SoftCAT were used to compare the effect of different gel types to elucidate if physically cross-linked, ‘self-destructing’ systems had benefits compared with classical, covalently cross-linked, gels.

Key findings

The rheological investigation showed that the interactions between the SoftCAT polymer and tetracaine/SDS aggregates were stronger than when the tetracaine/capric acid aggregates were used. The skin permeation was measured ex vivo in horizontal Ussing chambers and the permeation of tetracaine was significantly lower when formulations with tetracaine/SDS aggregates were applied (P < 0.001), but not statistically different from the reference when capric acid was used.

Conclusions

No morphological differences could be distinguished between the skin samples exposed to the different formulations or the reference. Skin permeation was compared with silicone sheet permeation and the results indicated that silicone sheets could be used as a model of skin when using these formulations.

Surface charged temoporfin-loaded flexible vesicles: in vitro skin penetration studies and stability

In order to increase topical delivery of temoporfin (mTHPC), a highly hydrophobic photosensitizer with low percutaneous penetration, neutral, anionic and cationic flexible liposomes (i.e. flexosomes) were prepared and investigated for their penetration enhancing ability. The in vitro skin penetration study was performed using human abdominal skin mounted in Franz diffusion cells. Besides the effect of surface charge of flexosomes on skin penetration of mTHPC, also its effect on physical properties (particle size, polydispersity index, lamellarity) and physicochemical stability of vesicles was investigated. Photon-correlation spectroscopy revealed that vesicles had after preparation a small particle size and low polydispersity index, while cryo-electron microscopy confirmed that these vesicles were mostly unilamellar and of a spherical shape. Regarding stability, contrasting to anionic flexosomes showing lack of long-term stability, neutral and cationic flexosomes were stable during 9 months storage at 4 degrees C. As to the penetration enhancing ability, cationic flexosomes possessed the highest, i.e. they delivered the highest mTHPC-amount to stratum corneum and deeper skin layers compared to conventional liposomes, neutral and anionic flexosomes. In conclusion, mTHPC-loaded cationic flexosomes could be a promising tool for delivering mTHPC to the skin, which would be beneficial for the photodynamic therapy of cutaneous malignant or non-malignant diseases.

Temoporfin-loaded invasomes: development, characterization and in vitro skin penetration studies

Temoporfin (mTHPC) is a highly hydrophobic second generation photosensitizer with low percutaneous penetration. In order to enhance its percutaneous penetration it was necessary to develop a mTHPC-loaded drug carrier system for enhanced skin delivery. mTHPC-loaded invasomes were developed, characterized and investigated for the in vitro percutaneous penetration of mTHPC into abdominal human skin using Franz diffusion cells. mTHPC-loaded invasomes were prepared using non-hydrogenated soybean lecithin (10% w/v), ethanol (3.3% w/v) and a mixture of terpenes (0.5 and 1% w/v). The invasomes obtained were of a sufficiently small particle size (<150 nm) and polydispersity index (<0.3). The particle size of invasomes increased following an increase in the amount of terpenes in the invasomes. All invasomes possessed a negative surface charge. The vesicles appeared to be unilamellar and oligolamellar, spherical and oval in shape. An interesting phenomenon was the finding that with increasing the amount of terpenes, the number of deformed vesicles in the dispersion increased. In vitro skin penetration data revealed that the invasome dispersion with 1% of the mixture of terpenes showed a significantly enhanced deposition (p<0.05) of the drug in the SC compared to liposomes without terpenes and the ethanolic solution.

Human skin penetration and distribution of nimesulide from hydrophilic gels containing nanocarriers

The objective of this work was to study the in vitro skin penetration of a drug model (nimesulide) from semi-solid topical formulations containing nanospheres, nanocapsules or nanoemulsion. Nanoprecipitation, interfacial deposition and spontaneous emulsification methods were used to prepare the nanostructured suspension. The hydrodynamic diameters were 252nm for the nanoemulsion, 277nm for the nanocapsules and 202nm for the nanospheres containing nimesulide. The different nanocarrier systems were incorporated in the hydrophilic gels and their ability of delivering the drug into the human skin were investigated using stripping technique and Franz-type diffusion cells. The amount of nimesulide released into the stratum corneum (SC) from the gel containing nanocapsules (GNM-NC) and the gel containing nanospheres (GNM-NS) was similar. On the other hand, for the gel containing nanoemulsion (GNM-NE), the nimesulide was not quantified in SC, but it has been directly permeated for the dermis. The penetration of the nimesulide using the gel containing nanocapsules (GNM-NC) was larger in the deeper skin than using the gel containing nanospheres (GNM-NS) or the one containing nanoemulsion (GNM-NE). The gels containing nanocarriers (GNM-NC, GNM-NS and GNM-NE) were able to release the drug in the viable layer of the skin, comparing to a non-particulated nimesulide-loaded formulation at the same concentration.

Drug delivery across the skin

Since the introduction of the first through the skin (TTS) therapeutic in 1980, a total of 34 TTS products have been marketed and numerous drugs have been tested by more than 50 commercial organisations for their suitability for TTS delivery. Most of the agents which have been tested have had low molecular weights, due to the impermeability of the skin barrier. This barrier resides in the outermost skin layer, the stratum corneum. It is mechanical, anatomical, as well as chemical in nature; laterally overlapping cell multi-layers are sealed by tightly packed, intercellular, lipid multi-lamellae. Chemical skin permeation enhancers increase the transport across the barrier by partly solubilising or extracting the skin lipids and by creating hydrophobic pores. This is often irritating and not always well-tolerated. The TTS approach allows drugs (< 400 kDa in size) to permeate through the resulting pores in the skin, with a short lag-time and subsequent steady-state period. Drug bioavailability for TTS delivery is typically below 50%, avoiding the first pass effect. Wider, hydrophilic channels can be generated by skin poration, with the aid of a small electrical current (> 0.4 mA/cm2) across the skin (iontophoresis) or therapeutic ultrasound (few W/cm2; sonoporation). High-voltage (> 150 V, electroporation) widens the pores even more and often irreversibly. These standard poration methods require experience and equipment and are therefore, not practical; at best, charged/small molecules (< or = 4000 kDa in size) can be delivered efficiently across the skin. In spite of the potential harm of gadget-driven skin poration, this method is used to deliver molecules which conventional TTS patches are unable to deliver, especially polypeptides. Lipid-based drug carriers (liposomes, niosomes, nanoparticle microemulsions, etc.) were proposed as alternative, low-risk delivery vehicles. Such suspensions provide an improved drug reservoir on the skin, but the aggregates remain confined to the surface. Conventional carrier suspensions increase skin hydration and/or behave as skin permeation enhancers. The recently developed carriers; Transferomes, comprise pharmaceutically-acceptable, established compounds and are thought to penetrate the skin barrier along the naturally occurring transcutaneous moisture gradient. Transfersomes are believed to penetrate the hydrophilic (virtual) channels in the skin and widen the former after non-occlusive administration. Both small and large hydrophobic and hydrophilic molecules are deliverable across the stratum after conjugation with Transfersomes. Drug distribution after transdermal delivery probably proceeds via the lymph. This results in quasi-zero order kinetics with significant systemic drug levels reached after a lag-time of up to a few hours. The relative efficiency of TTS drug delivery with Transfersomes is typically above 50 %; with the added possibility of regional drug targeting.

Hydrocortisone and dexamethasone in very deformable drug carriers have increased biological potency, prolonged effect, and reduced therapeutic dosage

We characterised biological properties of novel formulations of two low-potency glucocorticosteroids, dexamethasone and hydrocortisone, which have an equivalent dose ratio of 1:50 in vasoconstriction tests. The rate of such carrier-mediated, mainly non-diffusive glucocorticosteroids transport with very deformable lipid vesicles (Transfersomes) through the skin, and the corresponding cutaneous drug biodistribution data, were complemented with the drug bio-efficacy studies. The minimum effective drug dose that reduces arachidonic acid-induced murine ear oedema by 50% was used as one bioactivity indicator. The minimum drug amount ensuring such an effect in mouse skin decreases appreciably when a corticosteroid is applied epicutaneously with very deformable vesicles rather than a lotion or a crème. Specifically, the minimum effective dose for hydrocortisone in very deformable carriers is 2-3 microg cm(-2) whereas for the crème- or lotion-like preparations at least 10 microg cm(-2) is required. Such three- to fivefold relative increase of hydrocortisone potency is accompanied by at least 13%, and more often >20%, absolute drug potency enhancement. The delivery of hydrocortisone with very deformable carriers moreover prolongs the suppression of the drug-induced oedema nearly 2-fold (to approximately 24 h per application). The effective dose of dexamethasone delivered with very deformable vesicles into murine skin is reduced >10 times compared with the crème- or lotion-based products. Specifically, less than 0.1 microg cm(-2) dexamethasone in very deformable vesicles suppresses the arachidonic acid-induced murine ear oedema >50%, on the average. Dexamethasone use on the skin in such vesicles extends the duration of drug action fourfold, compared with a commercial crème, i.e. to >48 h per application. Epicutaneous use of glucocorticosteroids in very deformable vesicles also diminishes such drug's abrasion sensitivity and may increase the general robustness of drug effect. Lower frequency of skin treatment, which ensures adequate biological response, is a result of this. Topical corticosteroid delivery with very deformable vesicles, Transfersomes, thus improves the therapeutic risk-benefit ratio, arguably due to better targeting into and longer drug presence in the skin.

Lipid vesicles and other colloids as drug carriers on the skin

Colloids from an aqueous suspension can cross the skin barrier only through hydrophilic pathways. Various colloids have a different ability to do this by penetrating narrow pores of fixed size in the skin, or the relevant nano-pores in barriers modelling the skin. Such ability is governed by colloid adaptability, which must be high enough to allow penetrant deformation to the size of a pore in such barrier: for a 100 nm colloid trespassing the skin this means at least 5-fold deformation/elongation. (Lipid) Bilayer vesicles are normally more adaptable than the comparably large (lipid coated) fluid droplets. One of the reasons for this, and an essential condition for achieving a high bilayer adaptability and pore penetration, is a high bilayer membrane elasticity. The other reason is the relaxation of changing colloid's volume-to-surface constraint during pore penetration; it stands to reason that such relaxation requires a concurrent, but only transient and local, bilayer permeabilisation. Both these phenomena are reflected in bilayer composition sensitivity, which implies non-linear pressure dependency of the apparent barrier penetrability, for example. Amphipats that acceptably weaken a membrane (surfactants, (co)solvents, such as certain alcohols, etc.) consequently facilitate controlled, local bilayer destabilisation and increase lipid bilayer flexibility. When used in the right quantity, such additives thus lower the energetic expense for elastic bilayer deformation, associated with pore penetration. Another prerequisite for aggregate transport through the skin is the colloid-induced opening of the originally very narrow ( approximately 0.4 nm) gaps between cells in the barrier to pores with diameter above 30 nm. Colloids incapable of enforcing such widening-and simultaneously of self-adapting to the size of 20-30 nm without destruction-are confined to the skin surface. All relatively compact colloids seem to fall in this latter category. This includes mixed lipid micelles, solid (nano)particles, nano-droplets, biphasic vesicles, etc. Such colloids, therefore, merely enter the skin through the rare wide gaps between groups of skin cells near the organ surface. Transdermal drug delivery systems based on corresponding drug formulations, therefore, rely on simple drug diffusion through the skin; the colloid then, at best, can modulate drug transport through the barrier. In contrast, the adaptability-and stability-optimised mixed lipid vesicles (Transfersomes, a trademark of IDEA AG) can trespass much narrower pathways between most cells in the skin; such highly adaptable colloids thus mediate drug transport through the skin. Sufficiently stable ultra-adaptable carriers, therefore, can ensure targeted drug delivery deep below the application site. This has already been shown in numerous preclinical tests and several phase I and phase II clinical studies. Drug delivery by means of highly adaptable drug carriers, moreover, allows highly efficient and well-tolerated drug targeting into the skin proper. Sustained drug release through the skin into systemic blood circulation is another field of ultradeformable drug carrier application.

Biological activity and characteristics of triamcinolone-acetonide formulated with the self-regulating drug carriers, Transfersomes

Novel formulations of the halogenated corticosteroid, triamcinolone-acetonide, based on ultradeformable mixed lipid vesicles, Transfersomes, are described. Their performance was tested in vivo using radioactive label measurements, to study the drug biodistribution, and murine ear edema, to determine the drug bioactivity. Sparse use of drug-loaded Transfersomes on the skin ensures an almost exclusive delivery of triamcinolone-acetonide into the organ, thus arguably increasing the treatment safety. Delivery of triamcinolone-acetonide in the skin with ultradeformable vesicles prolongs the anti-inflammatory drug action several times compared to drug usage in a conventional crème or an ointment, the robustness of biological response for the former being at least identical to the latter. The required dose of Transfersome-based triamcinolone-acetonide is also greatly reduced. The drug dose of 0.2 microg cm(-2) suppresses 75% of arachidonic acid-induced murine ear edema for at least 48 h. In contrast, a conventional formulation of triamcinolone-acetonide requires a 10-fold higher drug dosage to achieve a similar effect. In either case, increasing the applied corticosteroid amount delays the onset of anti-edema action.

Liposomes increase skin penetration of entrapped and non-entrapped hydrophilic substances into human skin: a skin penetration and confocal laser scanning microscopy study

Liposomes have been extensively studied and suggested as a vehicle for topical drug delivery systems. However, the mechanism by which liposomes deliver drugs into intact skin is not fully understood. In the present study, we have tried to understand the mechanism of transport of hydrophilic drugs into the skin using liposomes. The effect of separation of the non-entrapped, hydrophilic fluorescent compound, carboxyfluorescein (CF), from liposomally entrapped CF was investigated by measuring the penetration of CF across human skin under non-occlusive conditions in vitro using Franz diffusion cells. The fluorescent dye, CF, was incorporated into the liposomes and applied onto the skin. After a 6 and 12h incubation period, the amount of CF in the epidermal membrane and the full thickness skin was determined by fluorescence spectroscopy or by confocal laser scanning microscopy (CLSM). The liposomal formulation containing CF both inside and outside the vesicles showed statistically enhanced penetration of CF into the human stratum corneum (SC) as compared to the formulations containing CF only outside of the liposomes and CF in Tris buffer. The CLSM results revealed that the formulation in which CF was present outside the liposomes showed bright fluorescence intensity in the SC and very weak fluorescence in the viable epidermis. However, the CF in Tris buffer failed to show any fluorescence in the viable epidermis. The results indicated that phospholipid vesicles not only carry the entrapped hydrophilic substance, but also the non-entrapped hydrophilic substance into the SC and possibly into the deeper layers of the skin.

Skin structure and mode of action of vesicles

The natural function of the skin is to protect the body for unwanted influences from the environment. The main barrier of the skin is located in the outermost layer of the skin, the stratum corneum. Since the lipids regions in the stratum corneum form the only continuous structure, substances applied onto the skin always have to pass these regions. Therefore, in the first part of this paper, the barrier function has been explained, focusing on the lipid composition and organisation. The major obstacle for topical drug delivery is the low diffusion rate of drugs across the stratum corneum. Several methods have been assessed to increase the permeation rate of drugs temporarily. One of the approaches is the application of drugs in formulations containing vesicles. In order to unravel the mechanisms involved in increasing the drug transport across the skin, information on the effect of vesicles on drug permeation rate, the permeation pathway and perturbations of the skin ultrastructure is of importance. In the second part of this paper, the possible interactions between vesicles and skin are described, focusing on differences between the effects of gel-state, liquid-state, and elastic vesicles.

Effect of positively and negatively charged liposomes on skin permeation of drugs

To clarify the effect of the surface charge of liposomes on percutaneous absorption, the permeation of liposomal drugs through rat skin was investigated in vitro and in vivo. Liposomes were prepared using egg yolk lecithin (EPC, phase transition temperature, -15 to -17 degrees C), cholesterol and dicetylphosphate (DP) or stearylamine (SA) (10:1:1, mol/mol). Also examined was the penetration behavior of positively and negatively charged liposomes, using a fluorescent probe (Nile Red). The in vitro penetration rate of melatonin (MT) entrapped in negatively charged liposomes was higher than that of positively charged ones (p<0.05). When the percutaneous absorption of ethosuximide (ES) encapsulated was estimated in vivo, the absorption of ES from negatively charged liposomes was slightly higher than that from positively charged liposomes. Additionally, the absorption of ES from both types of liposomes was superior to that from the lipid mixtures consisting of the same composition as the vesicles. The percutaneous absorption of betahistine (BH) from a gel formulation containing negatively charged liposomes of BH was much more than that from the formulation with positively charged ones, with 2-fold higher AUC (p<0.05). Histological studies revealed that the negatively charged liposomes diffused to the dermis and the lower portion of hair follicles through the stratum corneum and the follicles much faster than the positive vesicles at the initial time stage after application. Thus, the rapid penetration of negatively charged liposomes would contribute to the increased permeation of drugs through the skin.

Non-invasive administration of drugs through the skin: challenges in delivery system design

Vehicles designed to enhance drug delivery through the skin must incorporate specific elements that improve the ability of the delivery system to overcome the barrier posed by the stratum corneum. This review discusses several chemical penetration enhancers that have been investigated as potential tools to increase drug flux. In addition, lipid-based delivery systems offer an attractive alternative to traditional drug vehicles. The relationship between liposome composition and drug permeation is discussed, in addition to the possible mechanism of action of lipid vesicle-mediated drug delivery.

Future drug delivery research in South Korea

According to the Science Citation Index database, over 50 papers related to drug delivery have been published from South Korea during the last 3 years. For the purpose of this presentation, some of the recently carried out research in our department will be introduced and future research directions presented. Proliposomes are free flowing particles which are composed of drugs, phospholipids and a water soluble porous powder, and immediately form a liposomal dispersion upon hydration. The preparation can be stored sterilized in a dried state and, by controlling the size of the porous powder in proliposomes, relatively narrow range of reconstituted liposome size can be obtained. Because of these properties, proliposomes appear to be a potential alternative to liposomes in design and fabrication of liposomal dosage forms. Thus, we tested the feasibility of this preparation as a sustained transdermal dosage form. Proliposomes containing varying amount of nicotine, a model drug, were prepared using sorbitol and lecithin. Microscopic observation revealed that this preparation is converted to liposomes almost completely within minutes following contact with water. The release pattern of the model drug from this preparation was apparently similar to that of the Exodus((R)) patch, a commercially available transdermal nicotine formulation. Compared with nicotine powder, the nicotine flux across rat skin from proliposomes was initially retarded, and appeared to remain constant. This observation indicated that sustained transdermal delivery of nicotine is feasible using proliposomal formulations under occluded condition. In addition to the investigation of the potential application of proliposomes, we were also interested in the role of the stratum corneum (SC) in the enhanced delivery of drugs from liposomes. Thus, liposome-gel formulation containing hydrocortisone (HC), a model hydrophobic drug, was prepared and used in this study. The study was carried out on both normal and stratum corneum removed skins. Percutaneous absorption of HC across SC removed skin was significantly faster than that across normal skin, suggesting that SC behaves as a penetration barrier for the liposome-bound drugs. Interestingly, the liposome-gel in this study reduced the skin absorption of HC, compared with the conventional ointment formulation. The amount of HC absorbed from the liposome-gel after 8 h into the SC-removed skin was less than one third of that from the conventional ointment. Despite the reduced absorption, a higher and sustained skin concentrations of HC were achieved for the liposome-gel. Drug concentration in both viable and deep skin reached a maximum within 0.5 h. However, drug concentrations in these tissues declined as a function of time for conventional ointment, while those from the liposome-gel were greatly sustained, resulting in a 5-fold higher viable skin drug level was obtained at 8 h after the application. In contrast, plasma concentration of HC at 4 h from the liposome-gel was only one-fourth the value from the conventional ointment in the SC-removed skin. Therefore, the higher and sustained drug concentration in the viable skin appeared not to be due to the enhanced percutaneous absorption but due to retarded diffusion of the drug from the skin.

Liposomes as a topical delivery system: the role of size on transport studied by the EPR imaging method

The relative contribution of the liposome size, lamellarity, composition and charge to the transport into the skin of drug, which was applied entrapped in liposomes is a subject of some controversy. In this study the influence of liposome size on the transport of hydrophilic substance was investigated. For this purpose liposomes composed of dipalmitoylphosphatidylcholine (DPPC), or non-hydrogenated soya lecithin (NSL) or hydrogenated soya lecithin (HSL), all in combination with 30% cholesterol, as well as of two types of niosomes: from glyceryl distearate or PEG stearate in combination with 45% of cholesterol and 10% of lipoaminosalt were prepared and their physical characteristics (size, polydispersity index, zeta potential, entrapped volume) were determined. Their size was varied by extrusion and by sonication. The transport of the entrapped spin labeled hydrophilic compounds into the skin was measured by electron paramagnetic resonance imaging methods. No significant transport into the deeper skin layers (more than 100 microm deep) was observed for NSL liposomes, irrespective of vesicle size. For all other vesicular systems some transport into the deeper skin layers was observed, which did not depend on vesicle size, significantly until the vesicle diameter of approximately 200 nm was reached. However, for small vesicles (with diameter less than 200 nm) the transport is significantly decreased. We have proven that small vesicles are not stable and disintegrate immediately in contact with other surfaces. As a consequence, they lose an important influence on the topical delivery of the entrapped hydrophilic substances.

Phospholipids affect stratum corneum lipid bilayer fluidity and drug partitioning into the bilayers

Phospholipids, e.g. fluid-state EPC (l-alpha-phosphatidylcholine from egg yolk), may diffuse into the stratum corneum and enhance dermal and transdermal drug penetration, while many other phospholipids, e.g. gel-state DSPC (distearoylphosphatidyl choline), are not able to do this. These effects are suggested to be due to the interactions between the phospholipids and the skin lipid bilayers, and so an in vitro method was developed to evaluate the influence of phospholipids on the distribution of drugs to stratum corneum lipids. The distribution coefficients of estradiol, progesterone and propranolol between stratum corneum lipid liposomes (SCLLs) without phospholipids or with EPC, DSPC, SPC (l-alpha-phosphatidylcholine from soybean) or DOPE (dioleylphosphatidyl ethanolamine), and pH 7.4 buffer were determined. Fluid-state phospholipids in SCLLs increased the partitioning of drugs into SCLLs, while gel-state lipid, DSPC, did not. The increased distribution of drugs into the SCLLs was at least partially due to the increased fluidity of SCLL bilayers by phospholipids, which was shown using steady-state fluorescence anisotropy. This in vitro method enables screening of the effects of phospholipids and other permeation enhancers on stratum corneum bilayer fluidity and drug partitioning.