Mechanism of the enhancement effect of n-octyl-beta-D-thioglucoside on the transdermal penetration of fluorescein isothiocyanate-labeled dextrans and the molecular weight dependence of water-soluble penetrants through stripped skin

A Method for Determination and Simulation of Permeability and Diffusion in a 3D Tissue Model in a Membrane Insert System for Multi-well Plates

In vitro cultivated skin models have become increasingly relevant for pharmaceutical and cosmetic applications, and are also used in drug development as well as substance testing. These models are mostly cultivated in membrane-insert systems, their permeability toward different substances being an essential factor. Typically, applied methods for determination of these parameters usually require large sample sizes (e.g., Franz diffusion cell) or laborious equipment (e.g., fluorescence recovery after photobleaching (FRAP)). This study presents a method for determining permeability coefficients directly in membrane-insert systems with diameter sizes of 4.26 mm and 12.2 mm (cultivation area). The method was validated with agarose and collagen gels as well as a collagen cell model representing skin models. The permeation processes of substances with different molecular sizes and permeation through different cell models (consisting of collagen gel, fibroblast, and HaCaT) were accurately described.

Moreover, to support the above experimental method, a simulation was established. The simulation fits the experimental data well for substances with small molecular size, up to 14 x 10^-10 m Stokes radius (4,000 MW), and is therefore a promising tool to describe the system. Furthermore, the simulation can considerably reduce experimental efforts and is robust enough to be extended or adapted to more complex setups.

Flux of ionic dyes across microneedle-treated skin: effect of molecular characteristics

Drug flux across microneedle (MN)-treated skin is influenced by the characteristics of the MN array, formed microconduits and physicochemical properties of the drug molecules in addition to the overall diffusional resistance of microconduits and viable tissue. Relative implication of these factors has not been fully explored. In the present study, the in vitro permeation of a series of six structurally related ionic xanthene dyes with different molecular weights (MW) and chemical substituents, across polymer MN-pretreated porcine skin was investigated in relation of their molecular characteristics. Dyes equilibrium solubility, partition coefficient in both n-octanol or porcine skin/aqueous system, and dissociation constants were determined. Results indicated that for rhodamine dyes, skin permeation of the zwitterionic form which predominates at physiological pH, was significantly reduced by an increase in MW, the skin thickness and by the presence of the chemically reactive isothiocyanate substituent. These factors were generally shown to override the aqueous solubility, an important determinant of drug diffusion in an aqueous milieu. The data obtained provided more insight into the mechanism of drug permeation across MN-treated skin, which is of importance to both the design of MN-based transdermal drug delivery systems and of relevance to skin permeation research.

Absorption of chemicals through compromised skin

Skin is an important route of entry for many chemicals in the work place. To assess systemic uptake of a chemical in contact with the skin, quantitative information on dermal absorption rates of chemicals is needed. Absorption rates are mainly obtained from studies performed with intact, healthy skin. At the work place, however, a compromised skin barrier, although not necessarily visible is common, e.g. due to physical and chemical damage. As reviewed in this article, there are several lines of evidence that reduced integrity of the skin barrier may increase dermal absorption of chemicals in the occupational setting. An impaired skin barrier might lead not only to enhanced absorption of a specific chemical, but also to entrance of larger molecules such as proteins and nanoparticles which normally are not able to penetrate intact skin. In addition to environmental influences, there is increasing evidence that some individuals have an intrinsically affected skin barrier which will facilitate entrance of chemicals into and through the skin making these persons more susceptible for local as well for systemic toxicity. This review addresses mechanisms of barrier alteration caused by the most common skin-damaging factors in the occupational settings and the consequences for dermal absorption of chemicals. Furthermore, this review emphasizes the importance of maintained barrier properties of the skin.

Effect of the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions on barrier properties of mice skin for transdermal permeation of tetracaine hydrochloride: In vitro

Effect of composition of lecithin water-in-oil and oil-in-water microemulsion on in vitro transdermal permeation of tetracaine hydrochloride was studied on mice model. The results were compared with an aqueous solution of tetracaine hydrochloride (2.7 mg/ml). In vitro skin flux and permeability coefficients were obtained using the Franz diffusion cell. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to study the mechanism of action of the microemulsion. Micrographs of TEM and CLSM studies were analyzed by using Image Pro Plus image software. Skin flux of tetracaine hydrochloride was found to be dependent on the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions. At lower Km ratio (i.e. 0.5:1 and 0.8:1) of microemulsion, the rate of permeation of tetracaine hydrochloride was higher when compared to the microemulsion of higher Km ratio (1:1 and 1.5:1). Image analysis of TEM micrograph, 6h after application of lecithin microemulsion, showed 3.5+/-0.75-fold (p<0.001) increase in the intercellular space in the epidermis and 3.8+/-0.4-fold (p<0.001) enhancement in upper dermis. CLMS results show that sweat gland and hair follicles also provided path for permeation of the drug through the skin.

Transdermal permeation of tetracaine hydrochloride by lecithin microemulsion: In vivo

In vivo transdermal permeation of tetracaine hydrochloride encapsulated in lecithin water-in-oil and oil-in-water microemulsion was studied. The effect of the composition of the lecithin microemulsion on analgesic response of tetracaine hydrochloride was evaluated on Wistar rats by tail flick method. To find out the toxicity of lecithin/n-propanol/isopropyl myristate/water/tetracaine hydrochloride microemulsion histopathological and irritation response were measured in Swiss mice. Time course studies were also conducted for the biochemical response of microemulsion by measuring catalase, glutathione and lipid peroxidation levels of the treated mice skin. The analgesic response was found to be dependent on the drug concentration and composition of the systems. The histopathological, irritation and biochemical findings reveal that lecithin/n-propanol/isopropyl myristate/water/tetracaine hydrochloride microemulsion is a safe carrier for transdermal drug delivery systems. Confocal laser scanning microscopy observation indicated that sweat gland and hair follicle also provided the path for transdermal permeation of lecithin/n-propanol/isopropyl myristate/water microemulsion.

Transdermal delivery of macromolecules by erbium:YAG laser

The aim of this study was to assess the effect of molecular weight (MW) on the transdermal delivery of macromolecules by erbium:yttrium-aluminum-garnet (Er:YAG) laser treatment. Fluorescein isothiocyanate (FITC)-labeled dextran (FD) of increasing MWs (4.4, 19.4, 38, and 77 kDa) was used as the model macromolecules to investigate the skin permeation in vitro. Fluorescence microscopy and scanning electron microscopic (SEM) images were utilized to examine the transport mechanisms of the macromolecules via the skin after laser treatment. The results indicate a significant increase in the permeation of FITC and FD across skin treated by the laser. The MWs of macromolecules and laser fluences were found to play important roles in controlling macromolecular absorption. Transdermal delivery of FD with a MW of at least 77 kDa could be achieved with laser treatment. Follicular routes were significant for FITC permeation, whereas intercellular pathways played important roles on the delivery of FD. Ablation of the stratum corneum (SC) layer, photomechanical stress on intercellular regions, and alterations of the morphology and arrangement of corneocytes are possible mechanisms of how the Er:YAG laser promotes macromolecular delivery. No alteration of viable skin morphology was observed after laser treatment and the partly ablation of the SC may be reversible. Hexameric insulin showed higher skin permeation than did FD with similar MWs (38 kDa) with laser enhancement. From the study presented herein, it is concluded that the Er:YAG laser can be effective for transdermal delivery of macromolecules and hydrophilic permeants such as peptides and protein-based drugs.

Effect of lipid bilayer alteration on transdermal delivery of a high-molecular-weight and lipophilic drug: Studies with paclitaxel

Skin forms an excellent barrier against drug permeation, due to the rigid lamellar structure of the stratum corneum (SC) lipids. Poor permeability of drugs can be enhanced through alteration in partition and diffusion coefficients, or concentration gradient of drug with an appropriate choice of solvent system, along with penetration enhancers. The aim of the current investigation was to assess applicability of lipid bilayer alteration by fatty acids and terpenes toward the permeation enhancement of a high-molecular-weight, lipophilic drug, paclitaxel (PCL) through rat skin. From among the fatty acids studied using ethanol/isopropyl myristate (1:1) vehicle, no significant enhancement in flux of PCL was observed (p > 0.05). In the case of cis mono and polyunsaturated fatty acids lag time was found to be similar to control (p > 0.05). This suggests that the permeation of a high-molecular-weight, lipophilic drug may not be enhanced by the alteration of the lipid bilayer, or the main barrier to permeation could lie in lower hydrophilic layers of skin. A significant increase in lag time was observed with trans unsaturated fatty acids unlike the cis isomers, and this was explained on the basis of conformation and preferential partitioning of fatty acids into skin. From among the terpenes, flux of PCL with cineole was significantly different from other studied terpenes and controls, and after treatment with menthol and menthone permeability was found to be reduced. Menthol and menthone cause loosening of the SC lipid bilayer due to breaking of hydrogen bonding between ceramides, resulting in penetration of water into the lipids of the SC lipid bilayer that leads to creation of new aqueous channels and is responsible for increased hydrophilicity of SC. This increased hydrophilicity of the SC bilayer might have resulted in unfavorable conditions for ethanol/isopropyl myristate (1:1) along with PCL to penetrate into skin, therefore permeability was reduced. The findings of this study suggest that the permeation of a high-molecular-weight and lipophilic drug cannot be enhanced through bilayer alteration by penetration enhancers, and alteration in partitioning of drug into skin could be a feasible mode to enhance the permeation of drug.

Novel transdermal drug penetration enhancer: synthesis and enhancing effect of alkyldisiloxane compounds containing glucopyranosyl group

The syntheses of alkyldisiloxanes containing sugar moiety with various alkyl chain length were investigated, in order to develop a silicone-based transdermal penetration enhancer which was expected to show a low irritation to the skin. 1-Alkyl-3-beta-D-glucopyranosyl-1,1,3,3-tetramethyldisiloxanes (Glc-SiCs) were prepared by two-step hydrosilylations of 1-alkene and 1-allyl-beta-D-glucose tetraacetate with 1,1,3,3-tetramethyldisiloxane in the presence of bis(benzonitrile)platinum dichloride as the catalyst, followed by hydrolysis of the acetyl groups with sodium methoxide. The enhancing effect of Glc-SiCs on the percutaneous drug penetration was evaluated by in vitro experiments using a two-chamber diffusion cell. Antipyrine (ANP) and indomethacin (IND) were used as hydrophilic and hydrophobic model drugs, respectively, and the amount of drug permeating through the rat abdominal skin with or without Glc-SiCs was estimated by HPLC. As a result, Glc-SiCs exhibited a enhancing effect on the permeation of both drugs through the skin, which was influenced by the alkyl chain length of Glc-SiCs. In addition, it was suggested that a suitable balance of polarity would be necessary to appear the high enhancing effect, where Glc-SiCs with octyl and decyl groups exhibited the highest enhancing effect. From the determination of kinetic parameters in the drug permeation, it was also found that this enhancing effect was due to the increase of both partition and diffusion coefficients of drug permeation through the skin. By experiments to determine the amount of cholesterol extracted from the skin, the defatting effect would be one of the functions of Glc-SiCs which resulted in the high enhancing activity. Furthermore, according to the Draize test, it was confirmed that Glc-SiCs showed a low irritation to the skin.

Skin as a route of exposure to protein allergens

Protein contact with skin is associated with a number of clinical conditions, including protein contact dermatitis and immunologic contact urticaria. This article reviews the clinical and other selected evidence that proteinaceous materials penetrate skin. It is concluded that whilst penetration of intact proteins through normal skin is extremely low and without consequence, any damage to the skin barrier may allow penetration. As a result, risk assessment for contact of protein with skin must take into account potential barrier impairment and thus the possibility of both the induction and the elicitation of allergic skin reactions.

Polymeric transdermal drug penetration enhancer. The enhancing effect of oligodimethylsiloxane containing a glucopyranosyl end group

Oligodimethylsiloxanes (ODMSs) containing a beta-D-glucopyranosyl group at one chain end (Glc-ODMSs) with various molecular weights were prepared to develop a silicone-based polymeric transdermal penetration enhancer with a non-ionic polar end group. Glc-ODMSs were prepared by hydrosilylation of hydrosilyl-terminated ODMS with 1-allyl-beta-D-glucose tetraacetate in the presence of bis(benzonitrile)platinum dichloride as the catalyst, followed by hydrolysis of the acetyl groups with sodium methoxide. The enhancing effect in the drug penetration was evaluated by in vitro experiments using a two-chamber diffusion cell. Antipyrine was used as a model drug, and the amount of drug permeating through the rat abdominal skin with or without Glc-ODMS was determined by HPLC. These enhancers were effective for the penetration of antipyrine. On the other hand, the enhancing effects were influenced by the concentration of Glc-ODMS coexisted regardless of its ODMS chain length. The enhancing effect was also observed by the pretreatment of the skin with Glc-ODMS before the drug permeation, the results of which suggested that the induction periods to appear the enhancing effects were different between Glc-ODMSs with the short and the long ODMS chain lengths. Furthermore, according to the Draize test, Glc-ODMSs exhibited no irritation to the skin regardless of the ODMS chain length.

Chemical enhancers for transdermal drug transport

In its first part, this review paper discusses skin morphology and barrier function of the stratum corneum for drug permeation after its transdermal administration or topical application. Further, the paper presents the main methods for overcoming the skin permeation barrier, which plays an important role for transdermal drug administration. Focus is on the method of chemical permeation enhancement. The chemical enhancers are categorised by their chemical structure. Examples of the most effective enhancers are given for the chemical groups of alcohols, amines and amides, polyalcohols, terpenes, fatty acids and their esters, macro cyclic compounds, sulfoxides, tensides, and others, as e.g. soft enhancers.

Effects of four detergents on the in-vitro barrier function of human skin

The key to promoting percutaneous penetration is to alter the properties of the dermal barrier function. Mechanisms for changing the barrier function vary. Thus, some enhancers induce reversible conformational changes, whereas others cause prolonged barrier disruption. Discrimination between the influences of detergents on the barrier function may enable the use of those detergents affecting the overall integrity of the skin the least. In an experimental setup using in-vitro static diffusion cells mounted with human skin, the effects of four extensively used detergents on dermal barrier function were evaluated. Three of the detergents (lutensol AP10, nonyl phenyl ethoxylate, ethanol) apparently enhance percutaneous penetration without compromising the overall integrity of the skin barrier. SLS, on the other hand, acts through a time-and-dose-dependent deterioration of the dermal barrier function. The present experimental approach allows discrimination between detergents that act through different mechanisms to enhance percutaneous penetration.

Interaction of octyl-beta-thioglucopyranoside with lipid membranes

Octyl-beta-thioglucopyranoside (octyl thioglucoside, OTG) is a nonionic surfactant used for the purification, reconstitution, and crystallization of membrane proteins. The thermodynamic properties of the OTG-membrane partition equilibrium are not known and have been investigated here with high-sensitivity titration calorimetry. The critical concentration for inducing the bilayer <==> micelle transition was determined as cD* = 7.3 mM by 90 degree light scattering. All thermodynamic studies were performed well below this limit. Sonified, unilamellar lipid vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with and without cholesterol were employed in the titration calorimetry experiments, and the temperature was varied between 28 degrees C and 45 degrees C. Depending on the surfactant concentration in the membrane, the partition enthalpy was found to be exothermic or endothermic, leading to unusual titration patterns. A quantitative interpretation of all titration curves was possible with the following model: 1) The partitioning of OTG into the membrane follows a simple partition law, i.e., Xb = Kc(D,f), where Xb denotes the molar amount of detergent bound per mole of lipid and c(D,f) is the detergent concentration in bulk solution. 2) The partition enthalpy for the transfer of OTG from the aqueous phase to the membrane depends linearly on the mole fraction, R, of detergent in the membrane. All calorimetric OTG titration curves can be characterized quantitatively by using a composition-dependent partition enthalpy of the form deltaHD(R) = -0.08 + 1.7 R (kcal/mol) (at 28 degrees C). At low OTG concentrations (R < or = 0.05) the reaction enthalpy is exothermic; it becomes distinctly endothermic as more and more surfactant is incorporated into the membrane. OTG has a partition constant of 240 M(-1) and is more hydrophobic than its oxygen-containing analog, octyl-beta-D-glucopyranoside (OG). Including a third nonionic amphiphile, octa(ethyleneoxide) dodecylether (C12EO8), an empirical relation can be established between the Gibbs energies of membrane partitioning, deltaGp, and micelle formation, deltaGmic, with deltaGp = 1.398 + 0.647 deltaGmic (kcal/mol). The partition constant of OTG is practically independent of temperature and of the cholesterol content of the membrane. In contrast, the partition enthalpy shows a strong temperature dependence. The molar specific heat capacity of the transfer of OTG from the aqueous phase to the membrane is deltaCp = -98 cal/(mol x K). The OTG partition enthalpy is also dependent on the cholesterol content of the membrane. It increases by approximately 1 kcal/mol at 50 mol% cholesterol. As the partition constant remains unchanged, the increase in enthalpy is compensated for by a corresponding increase in entropy, presumably caused by a restructuring of the membrane hydration layer.