Synergistic enhancement of skin permeability by N-lauroylsarcosine and ethanol

To develop formulations for transdermal drug delivery, this study tested the hypothesis that the anionic surfactant, N-lauroylsarcosine (NLS), and ethanol synergistically increase skin permeability by increasing the fluidity of stratum corneum lipid structure. Skin permeability experiments showed that transdermal delivery of fluorescein across human cadaver epidermis was increased by up to 47-fold using formulations containing NLS in aqueous ethanol solutions. Skin permeability was increased by increasing NLS concentration in combination with 25-50% ethanol solutions. Skin permeability was shown to correlate with skin electrical conductivity measurements, changes in differential scanning calorimetry lipid transition peak temperature, and Fourier transform infrared spectroscopy CH stretching peak shifts indicative of stratum corneum lipid fluidization and changes in protein conformation. Evidence for lipid extraction was also evident, but did not appear to be responsible for the observed increases in skin permeability. We conclude that NLS in aqueous ethanol formulations can dramatically increase skin permeability by a mechanism involving synergistic lipid-fluidization activity in the stratum corneum.     

Use of electroporation to accelerate the skin permeability enhancing action of oleic acid

Rat skin permeability after treatment by electroporation (newly developed frog type electrode, 100V, 10 pulses), oleic acid/propylene glycol (PG) and a combination of both were investigated using Fourier transformed infrared attenuated total reflectance (FT-IR/ATR) analysis. Electroporation immediately disordered the stratum corneum lipid structure up to a certain threshold level. This action lasted throughout the experiment. This may be attributed to the formation of long lifetime of metastable lipid structures, which may allow molecules to pass to the inside of the stratum corneum due to the electroporation-induced fluidized lipid membranes. Electroporation also altered the protein structure of the stratum corneum. When electroporation was combined with 0.05 M oleic acid/PG, uptake of oleic acid and PG into the stratum corneum was remarkably accelerated compared to the application of only 0.05 M oleic acid/PG to the skin. This indicates that electroporation enables oleic acid and PG to penetrate the stratum corneum easily by disrupting the structure of the latter. PG transfer into the dermis from the epidermis was accelerated, not because of the direct action of electroporation on the dermis, but because electroporation induced the rapidly disordering action of oleic acid on the stratum corneum. Lipid-soluble indomethacin permeated the skin more rapidly when the skin was treated with electroporation plus oleic acid/PG than with 0.05 M oleic acid/PG in vitro.     

Assessment of the potential irritancy of oleic acid on human skin: Evaluation in vitro and in vivo

As skin barrier modulating compounds, fatty acids are frequently used in formulations for transdermal or topical delivery. In this study the effects of oleic acid on keratinocytes in vitro was compared with its in vivo skin irritancy in humans. Dose- and time-dependent effects of oleic acid were examined in submerged human keratinocyte cultures, in reconstructed human epidermis (RE-DED), and in excised human skin, using alterations in morphology and changes in interleukin-1 mRNA levels as endpoints. In vitro results were compared with responses of living human skin after topical application of oleic acid, using non-invasive bioengineering methods. Direct interaction of oleic acid and submerged keratinocyte cultures resulted in cell toxicity at very low concentrations of the fatty acid. By contrast, when oleic acid was applied topically on RE-DED or on excised skin, no alterations in morphology were observed. Modulation of stratum corneum thickness indicated a key role of the stratum corneum barrier in the control of oleic acid-induced toxicity. In agreement with these findings, no epidermal tissue damage was seen in vivo, whereas oleic acid induced a mild but clearly visible skin irritation and inflammatory cells were present in the upper dermal blood vessels. Small amounts of oleic acid induced IL-1 mRNA expression in submerged keratinocyte cultures, whereas in RE-DED and in excised skin, IL-1 mRNA levels were increased only when the concentration applied topically was at least two orders of magnitude higher. It is concluded that minute amounts of oleic acid are sufficient to cause local (i.e. inside the viable epidermis) modulation of cytokine production. These concentrations do not affect morphology but induce skin irritation in vivo. To achieve comparable effects in the skin, much higher topical doses are needed than expected according to the locally required levels, owing to the rate-limiting transport of the fatty acid across the stratum corneum barrier.     

Role of stratum corneum lipid fluidity in transdermal drug flux

Fatty acids are effective penetration enhancers for the transdermal delivery of certain co-applied drugs. In order to assess the mechanism of enhancement, spectrometric, calorimetric, and flux techniques were used to study porcine stratum corneum following treatment with a series of cis- and trans-positional isomers of octadecenoic acid. Results obtained from spectrometric and calorimetric measurements show increased lipid fluidity following treatment of the stratum corneum with the cis monoenoic acids which have the site of unsaturation centrally located. Under similar conditions, these same cis monounsaturated acids resulted in enhancement of salicyclic acid flux through porcine skin. The striking parallelism between flux and fluidity measurements suggests that transdermal drug flux may be ultimately related to stratum corneum lipid structure.     

Optimization of microdermabrasion for controlled removal of stratum corneum

Microdermabrasion has been shown to increase skin permeability for transdermal drug delivery by damaging or removing skin's outer layer, stratum corneum. However, relationships between microdermabrasion parameters and effects on the stratum corneum barrier have not been developed. In this study, we determined the effect of microdermabrasion crystal flow rate, time, and suction pressure applied in both static and dynamic modes on the extent of stratum corneum removal from excised porcine skin. In addition to controlling the depth of tissue removal by microdermabrasion parameters, we also controlled the area of tissue removal by applying a metal mask patterned with 125- or 250-μm holes to selectively expose small spots of tissue to microdermabrasion. We found that the extent of stratum corneum removal depended strongly on the crystal flow rate and exposure time and only weakly on pressure or static/dynamic mode operation. Masking the skin was effective to localize stratum corneum removal to exposed sites. Overall, this study demonstrates that optimized microdermabrasion in combination with a mask can be used to selectively remove stratum corneum with three-dimensional control, which is important to translating this technique into a novel method of transdermal drug delivery.     

Enhanced transdermal delivery of triprolidine from the ethylene-vinyl acetate matrix.

Triprolidine-containing matrix was fabricated with ethylene-vinyl acetate (EVA) copolymer to control the release of the drug. The permeation rate of triprolidine in the stripped skin was greatly larger than that in the whole skin. Thus it showed that the stratum corneum acts as a barrier of skin permeation. The effect of penetration enhancer and stripping of skin on the permeation of triprolidine through the excised mouse skin was studied. Penetrating enhancers showed increased flux probably due to the enhancing effect on the skin barrier, the stratum corneum. Among enhancers used such as glycols, fatty acids and non-ionic surfactants, polyoxyethylene-2-oleyl ether showed the best enhancement. The permeability of triprolidine was markedly increased with stripping of the mouse skin to remove the stratum corneum that acts as a barrier of skin permeation. For the controlling transdermal delivery of triprolidine, the application of EVA membrane containing permeation enhancer could be useful in the development of transdermal drug delivery system.     

The regulation of epidermal lipid synthesis by permeability barrier requirements

A major function of the skin is to prevent the loss of fluids. The barrier to fluid loss resides in the intercellular lipids (primarily sterols, fatty acids, and sphingolipids) of the stratum corneum. The epidermis is a very active site of lipid synthesis and when the permeability barrier is disrupted by topical solvents or detergents a marked stimulation of sterol, fatty acid, and sphingolipid synthesis occurs. Essential fatty acid deficient mice, with a chronic disturbance in barrier function, also have an increase in epidermal lipid synthesis. When the defect in barrier function is artificially corrected by occlusion with a water vapor impermeable membrane the increase in epidermal lipid synthesis is prevented, suggesting that water flux may be a regulatory factor. The activity of the key rate limiting enzyme in cholesterol synthesis, HMG CoA reductase is increased following barrier disruption due to both an increased quantity of enzyme and an increase in activation state. Similarly, the activity of serine palmitoyl transferase, the rate limiting enzyme in sphingolipid synthesis is also increased following barrier disruption. Occlusion prevents the increase in HMG CoA reductase and serine palmitoyl transferase activity. When the increase in epidermal lipid synthesis is inhibited by occlusion the characteristic rapid return of stratum corneum lipids and recovery of barrier function is prevented. Moreover, when epidermal cholesterol synthesis is inhibited by lovastatin, an inhibitor of HMG CoA reductase, the rate of recovery of barrier structure and function is delayed. Similarly, B chloroalanine, an inhibitor of serine palmitoyl transferase and sphingolipid synthesis, also impairs barrier recovery. Thus, disruption of the barrier stimulates epidermal lipid synthesis which provides the lipids necessary for the repair of the barrier. The signals that initiate and coordinate this response are yet to be defined, but the understanding of this process may allow for pharmacological interventions that will specifically disrupt the barrier and allow for the transcutaneous delivery of drugs.     

Epidermal cell culture model with tight stratum corneum as a tool for dermal gene delivery studies

The purpose of this study was to evaluate the feasibility of organotypic cultures of rat epidermal cells as a tool to study non-invasive dermal gene delivery. Also, a novel transfection method employing liposomal pre-treatment of stratum corneum (SC) was evaluated. Rat epidermal cells were cultured on Transwell tissue culture inserts and formation of stratum corneum barrier was evaluated in permeability studies with two model compounds. Transfections were performed with naked pCMV-SEAP2 plasmid and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/dioleyl-phosphatidylethanolamine (DOPE)/DNA lipoplexes. Naked DNA was administered on the stratum corneum of the cell culture model with or without prior treatment of the stratum corneum with DOTAP/DOPE liposomes. Transfection was evaluated non-invasively by monitoring concentrations of secreted alkaline phosphatase (SEAP) in the culture medium of the basolateral compartment at 24-h intervals. Transfection with lipoplexes produced significant gene expression in rat epidermal keratinocyte (REK) epidermal culture model. Likewise, delivery of naked DNA on stratum corneum after DOTAP/DOPE liposome pre-treatment produced gene expression. Naked DNA alone did not result in detectable gene expression. In dermal gene delivery studies REK epidermal culture model is a suitable tool that includes tight stratum corneum and allows transgene expression in viable epidermis and non-invasive sampling of secreted gene product in the basolateral compartment. Liposomal pre-treatment of the stratum corneum augments transfection of viable epidermis.     

焦谷氨酸油醇酯作为经皮渗透促进剂及其促渗机理焦谷氨酸油醇酯作为经皮渗透促进剂及其促渗机理

目的研究焦谷氨酸油醇酯作为经皮渗透促进剂,试验其促渗活性和促渗机理。方法考察焦谷氨酸油醇酯、油醇和油酸对咖啡因、替硝唑和醋酸可的松经皮渗透促渗效果;通过衰减全反射-傅立叶变换红外光谱(ATR-FTIR)法分析焦谷氨酸油醇酯的促渗机理。结果焦谷氨酸油醇酯使3种不同类型药物经皮渗透的累积渗透量有明显提高,增渗倍数分别为7.9, 41.8和2.8。 作用后的人体皮肤ATR-FTIR谱图上2 800～2 950 cm^-1和酰胺I吸收峰随角质层的逐步剥离出现不同的位移变化。结论焦谷氨酸油醇酯对药物有较好的促渗效果,其促渗机理除了使角质层中的脂质变得无序外可能还使角质蛋白的二级结构发生改变。     

Effect of oleic acid/ethanol and oleic acid/propylene glycol on the in vitro percutaneous absorption of 5-fluorouracil and tamoxifen and the macroscopic barrier property of porcine epidermis

Transdermal delivery of most drugs is precluded due to the impervious nature of the stratum corneum. Chemical penetration enhancers offer an approach to enhance the transdermal transport of drugs by partitioning into and interacting with skin constituents, inducing a temporary reversible increase in skin permeability. The effect of penetration enhancers (e.g. oleic acid/ethanol and oleic acid/propylene glycol) was investigated on the in vitro percutaneous absorption of a hydrophilic (5-fluorouracil) and a lipophilic (tamoxifen) anticancer drug through porcine epidermis. In vitro transepidermal water loss (TEWL) studies were undertaken to investigate the effect of the above enhancers on the macroscopic barrier properties of the epidermis. Oleic acid/ethanol and oleic acid/propylene glycol significantly enhanced (P<0.05) the permeability coefficient of 5-fluorouracil (5-FU) and tamoxifen in comparison to their controls. In vitro TEWL was significantly greater (P<0.01) through epidermis treated with the above enhancers in comparison with control (epidermis that was not treated). However, neither oleic acid/ethanol nor oleic acid/propylene glycol enhanced (P>0.05) TEWL in comparison with ethanol and propylene glycol alone. Thus, changes in the permeability of 5-FU and tamoxifen caused by oleic acid/ethanol or oleic acid/propylene glycol could not be correlated with the in vitro TEWL.     

Biochemical enhancement of transdermal delivery with magainin peptide: modification of electrostatic interactions by changing pH

Magainin is a naturally occurring, pore-forming peptide that has recently been shown to increase skin permeability. This study tested the hypothesis that electrostatic forces between magainin peptides and drugs mediate drug transport across the skin. Electrostatic interaction between positively charged magainin and a negatively charged model drug, fluorescein, was attractive at pH 7.4 and resulted in a 35-fold increase in delivery across human epidermis in vitro when formulated with 2% N-lauroylsarcosine in 50% ethanol. Increasing to pH 10 or 11 largely neutralized magainin's charge, which eliminated enhancement due to magainin. Shielding electrostatic interactions with 1-2M NaCl solution similarly eliminated enhancement. Showing the opposite dependence on pH, electrostatic interaction between magainin and a positively charged anti-nausea drug, granisetron, was largely neutralized at pH 10 and resulted in a 92-fold increase in transdermal delivery. Decreasing to pH 5 increased magainin's positive charge, which repelled granisetron and progressively decreased transdermal flux. Circular dichroism analysis, multi-photon microscopy, and FTIR spectroscopy showed no significant pH effect on magainin secondary structure, magainin deposition in stratum corneum, or stratum corneum lipid order, respectively. We conclude that magainin increases transdermal delivery by a mechanism involving electrostatic interaction between magainin peptides and drugs.     

Mechanistic studies of molecular transdermal transport due to skin electroporation

The application of electrical high voltage pulses has been shown to greatly enhance the transdermal transport of water-soluble compounds. The resistance of the skins most important barrier, the stratum corneum, drops within less than 1 μs by orders of magnitude. This effect is attributed to electroporation, a nonthermic phenomena known to occur in phospholipid double layers. The striking difference between the stratum corneum lipid layers and the usually investigated phospholipid systems is the phase transition temperature. While lipid layers used for electroporation experiments are in liquid crystal phase above the phase transition temperature, the stratum corneum lipids (phase transition at approximately 70 degrees C) form a rigid quasi-crystalline membrane at room temperature.After the electrical stimulus a recovery of the passive flux was found making high voltage pulsing a suitable tool for controlling transdermal drug delivery. By ordinary light microscopy no dramatic changes in skin structure were found supporting the thesis of electroporation. However the microstructure shows clearly persistent structural changes. Recently the involvement of Joule heating due to the electric stimulus was shown as an important factor for skin permeabilization and molecular transport.     

Liposomes and niosomes as topical drug delivery systems

The skin acts as a major target as well as a principle barrier for topical/transdermal (TT) drug delivery. The stratum corneum plays a crucial role in barrier function for TT drug delivery. Despite major research and development efforts in TT systems and the advantages of these routes, low stratum corneum permeability limits the usefulness of topical drug delivery. To overcome this, methods have been assessed to increase permeation. One controversial method is the use of vesicular systems, such as liposomes and niosomes, whose effectiveness depends on their physicochemical properties. This review focuses on the effect of liposomes and niosomes on enhancing drug penetration, and defines the effect of composition, size and type of the vesicular system on TT delivery.     

Investigating the barrier function of skin lipid models with varying compositions

The lipids in the uppermost layer of the skin, the stratum corneum (SC), play an important role in the barrier function. The main lipid classes in stratum corneum are ceramides, cholesterol, and free fatty acids. In previous publications, a lipid model was presented, referred to as the stratum corneum substitute (SCS), that closely mimics the SC lipid organization and SC barrier function. In the present study, we use the SCS to study the effect of changes in lipid organization on the lipid barrier function using benzoic acid as permeation compound. First, in the SCS, we increased the level of one of the three major lipid classes keeping the ratio between the other lipid classes constant. An increased cholesterol level resulted in an increase in phase-separated cholesterol and a reduction in the permeability. An increase in ceramide or free fatty acid level resulted in the formation of additional phases, but had no significant influence on the permeability. We also examined models that mimic selected changes in lipid composition reported for dry or diseased skin. The SCS that mimics the composition in recessive X-linked ichthyosis skin displayed a twofold increase in permeability. This increase is possibly related to the formation of an additional, less ordered phase in this model.     

Biomaterials as novel penetration enhancers for transdermal and dermal drug delivery systems

Abstract

The highly organized structure of the stratum corneum provides an effective barrier to the drug delivery into or across the skin. To overcome this barrier function, penetration enhancers are always used in the transdermal and dermal drug delivery systems. However, the conventional chemical enhancers are often limited by their inability to delivery large and hydrophilic molecules, and few to date have been routinely incorporated into the transdermal formulations due to their incompatibility and local irritation issues. Therefore, there has been a search for the compounds that exhibit broad enhancing activity for more drugs without producing much irritation. More recently, the use of biomaterials has emerged as a novel method to increase the skin permeability. In this paper, we present an overview of the investigations on the feasibility and application of biomaterials as penetration enhancers for transdermal or dermal drug delivery systems.     

Novel approach to improve permeation of ondansetron across shed snake skin as a model membrane.

The purpose of this study was to investigate the feasibility of transdermal drug delivery of ondansetron, an antagonist of the 5-HT3 receptor, used for the treatment of chemotherapy-induced emesis. The permeability of ondansetron from an aqueous suspension through shed snake skin as a model membrane was very low and in order to improve it, several enhancers were tested. Ethanol increased the flux at a concentration of 40% or more. The solubility of ondansetron also increased as the ethanol concentration increased. The permeability coefficient increased after pretreatment of the shed snake skin with Azone, oleic acid or lauryl alcohol. Further improvement of the permeability was observed when ethanol was combined with other enhancers and was maximum for the combination of ethanol and oleic acid. Oleic acid dramatically increased the partition of ondansetron to n-hexane and shed snake skin. Oleic acid may enhance the permeation of ondansetron in two ways: by a direct effect on the stratum corneum or via counterion formation of an ion-pair. The maximum flux obtained from the combination of ethanol and other enhancers seems to be high enough to obtain a therapeutic effect.     

Strategies for overcoming the stratum corneum

Transdermal drug delivery has many advantages over the oral administration of drugs. This is the reason why many researchers have extensively investigated the transdermal absorption of drugs. However, a much smaller number of drugs are marketed using this route of delivery, compared to oral dosage forms, because drug absorption across the skin is very low due to the stratum corneum (the main barrier for drug absorption across the skin). Overcoming the penetration barrier would significantly improve the development of an efficient transdermal drug delivery system. Several techniques have been developed, or are under development, to bypass the stratum corneum. Approaches that have been made to overcome the stratum corneum fit into five different categories: (i) device and formulation; (ii) modification of stratum corneum by chemical enhancers; (iii) ablation; (iv) bypassing the stratum corneum via appendages; and (v) electrically assisted methods such as iontophoresis and electroporation. Furthermore, possible combinatorial uses of several approaches have been studied. Although the safety issues of these synergistic approaches still require clarification, several combinations could be promising. Finally, there is a necessity to regulate the intradermal disposition of drugs to develop a more efficient transdermal drug delivery system after overcoming the skin barrier.     

Dose-Dependent Enhancement Effects of Azone on Skin Permeability

In vitro permeability experiments have been combined with differential scanning calorimetry (DSC) studies in an attempt to address the dose-dependent influence of Azone on the permeability coefficients of solutes for hairless mouse stratum corneum. A spray technique was developed to deliver uniformly and quantitatively small amounts of Azone to the stratum corneum. Permeability data obtained for several model solutes of varying lipophilicity suggest lipid fluidization and polar route enhancement as the mechanisms of action for Azone. Alkanols and steroids, both of which are enhanced primarily by lipid fluidization, had different degrees of relative enhancement. This provides evidence that the stratum corneum barrier is heterogeneous, rather than a homogeneous slab barrier. Two effects of Azone on the stratum corneum were detected by DSC. A decrease in the area and a shift to lower temperatures were noted for the lipid endotherms with increasing doses of Azone. A lipid fluidizing effect would qualitatively account for the increases in the permeability coefficients noted for more lipophilic solutes. The stratum corneum keratin endotherm also appears to be altered in the presence of Azone. It is possible that alteration of the keratin structure could lead to the development of polar routes in the stratum corneum.     

弹性脂质囊泡在经皮给药系统的研究进展

目的 对近年来弹性脂质囊泡在经皮给药系统的研究与应用进行文献整理和归纳,为以后该领域的研究提供借鉴。方法 查阅近5年弹性脂质囊泡在经皮给药系统的相关文献,总结弹性脂质囊泡的分类、制备方法、促透机制、应用的研究进展,提出其今后研究的重点方向。结果 弹性脂质囊泡具有较好的变形性、皮肤渗透性,可以通过角质层,更利于药物到达毛细血管被吸收,提高生物利用度,更有利于皮肤用药。结论 弹性脂质囊泡经皮给药系统是一种安全、有效的给药途径,其顺应性更好,在经皮给药方面有很好的应用前景。     

Skin permeation of physostigmine from fatty acids-based formulations: evaluating the choice of solvent

This study was conducted to gain an understanding of the enhancement mechanism of fatty acids in skin permeation of physostigmine (PHY) by using a series of fatty acids and two solvents of opposing lipophilicity (propylene glycol (PG) and mineral oil (MO)). Interaction between fatty acid and drug was proven using NMR and conductivity measurements that showed a dependence on type of solvent used. Permeation flux of physostigmine from mineral oil-based formulations to skin was increased as solubility of physostigmine in mineral oil was enhanced in the presence of fatty acids having a longer chain. Thus, the dominant role of fatty acids in mineral oil was to increase solubility of physostigmine in the formulations that increased the driving force for physostigmine permeation through skin. As for propylene glycol, enhancement caused by fatty acids was attributed to their ability to increase the lipophilicity of formulation and to disrupt the lipid bilayers within the stratum corneum (SC). In conclusion, fatty acids enhancement for drug permeation across the skin was found to be dependent on the solvent used. Among various formulations here, oleic acid in mineral oil yielded fast permeation of PHY with a short lag time, which may be a good vehicle for transdermal delivery of PHY.