Hanjiang Zhu

Proposed human stratum corneum water domain in chemical absorption.

Compounds with varying physical and chemical properties may have different affinities to the stratum corneum (SC) and/or its intercellular lipids, keratin protein, and possible water domains. To better understand the mechanism of percutaneous absorption, we utilized 21 carbon‐14 labeled chemicals, with wide hydrophilicity (log P = −0.05 to 6.17), and quantified their absorption/adsorption properties for a short incubation time (15 min) with regards to intact SC membrane, delipidized SC membrane and SC lipid. A facile method was developed for SC/lipid absorption, providing a more equivalent procedure and comparable data. SC lipid absorption of chemical solutes positively correlated with the octanol/water partition coefficient (log P). Differences between the percent dose of chemical absorption to intact SC and the total percent dose contributed by the protein and lipid domains suggest the possibility and significance of a water domain. Absorption rate experiments showed a longer lag time for intact SC than for delipidized SC or SC lipid, suggesting that the water domain may delay chemical binding to protein and lipid domains, and may be a factor in the resistance of many chemicals to current decontamination methods. Copyright

Effects of soap–water wash on human epidermal penetration

Skin decontamination is a primary interventional method used to decrease dermal absorption of hazardous contaminants, including chemical warfare agents, pesticides and industrial pollutants. Soap and water wash, the most common and readily available decontamination system, may enhance percutaneous absorption through the “wash‐in effect.” To understand better the effect of soap–water wash on percutaneous penetration, and provide insight to improving skin decontamination methods, in vitro human epidermal penetration rates of four C14‐labeled model chemicals (hydroquinone, clonidine, benzoic acid and paraoxon) were assayed using flow‐through diffusion cells. Stratum corneum (SC) absorption rates of these chemicals at various hydration levels (0–295% of the dry SC weights) were determined and compared with the results of the epidermal penetration study to clarify the effect of SC hydration on skin permeability. Results showed accelerated penetration curves of benzoic acid and paraoxon after surface wash at 30 min postdosing. Thirty minutes after washing (60 min postdosing), penetration rates of hydroquinone and benzoic acid decreased due to reduced amounts of chemical on the skin surface and in the SC. At the end of the experiment (90 min postdosing), a soap–water wash resulted in lower hydroquinone penetration, greater paraoxon penetration and similar levels of benzoic acid and clonidine penetration compared to penetration levels in the non‐wash groups. The observed wash‐in effect agrees with the enhancement effect of SC hydration on the SC chemical absorption rate. These results suggest SC hydration derived from surface wash to be one cause of the wash‐in effect. Further, the occurrence of a wash‐in effect is dependent on chemical identity and elapsed time between exposure and onset of decontamination. By reducing chemical residue quantity on skin surface and in the SC reservoir, the soap–water wash may decrease the total quantity of chemical absorbed in the long term; however, the more immediate accelerated absorption of chemical toxins, particularly chemical warfare agents, may be lethal. Copyright

Antifungal ME1111 in vitro human onychopharmacokinetics

Abstract This study determined ME1111 onychopharmacokinetics and possible topical antifungals’ clinical efficacy in human great toenails using an in vitro finite dose model. ME1111 topical formulations in 1, 5, 10 or 15% for 3 days observation and 1, 5 or 10% for 14 days observation, respectively, were used to determine ME1111 penetration rate and transungual kinetics. ME1111 concentrations in the deeper nail (ventral/intermediate layers) and a cotton pad/nail bed, were several orders of magnitude greater than MIC90 and MFC90 for three major dermatophytes. ME1111 concentrations 3 days after a single and 14 days after multiple dosing of 10% formulation were 253 and 7991 μg/g nail, respectively, and superior to those of 8% ciclopirox control. ME1111 concentration (μg equivalent/cm3) in the cotton pad following 10% ME1111 multiple applications increased linearly throughout the 336 h experiment and was significantly greater than that of 8% ciclopirox. Flux rate of ME1111 averaged as 50.9 μg/cm3/day, which was ca. two orders of magnitude greater than the MIC90 values. The novel antifungal ME1111 penetrated well into human nail plate and its concentrations in the deeper nail and cotton pad after application of 10% formulation were significantly greater than those of ciclopirox.

Stratum corneum reservoir as a predictive method for in vitro percutaneous absorption.

Interaction between drug and proteins and lipids in stratum corneum (SC) is an important pharmacokinetic parameter in early steps of absorption. Previous in vivo studies showed that the total amount of compound, regardless of properties, penetrating over a 96 h period could be predicted by the amount present in SC 30 min after application by a linear relationship. Validating this linear relationship through in vitro study would facilitate testing of transdermal drug delivery platforms. We aimed to determine in vitro penetration behavior across SC of humans by determining the relationship between quantity present in SC reservoir 30 min after application with 24 h skin absorption and penetration. In this study, use of the SC reservoir effect to predict absorption and penetration of topical compounds is reaffirmed with in vitro models involving human skin. These results indicate the amount in short‐term (30 min) SC reservoir predict long‐term (24 h) skin absorption and penetration, as characterized by statistically significant linear relationships determined via regression. This may be explained by the fact that SC is a rate‐limiting barrier to percutaneous drug transport. After molecules diffuse through SC barrier, passage into deeper dermal layers and systemic uptake occur relatively quickly. These results enable one to measure quantity in SC reservoir shortly after topical application as a proxy for absorption and penetration over longer periods. With respect to drug development and risk assessment of toxic substances, this may simplify assays attempting to quantitate penetration capacity. Further investigation with a larger range of compounds is needed to clarify the observations recorded here. Copyright

Biology of Stratum Corneum: Tape Stripping and Protein Quantification

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Abstract Stratum corneum (SC) adhesive tape stripping has been utilized in the measurement of stratum corneum mass, barrier function, drug reservoir, and percutaneous penetration of topical substances. The process involves a methodical, relatively noninvasive layer-by-layer removal of the SC, which comprises the outermost epidermal cell layers. Complete SC removal may require over 70 tape strips (Lademann et al., J Biomed Opt 11(5):054026, 2006; Weigmann et al., Skin Pharmacol Appl Skin Physiol 12 (1–2):34–45, 1999). The quantity of SC harvested diminishes with each sequential strip, possibly due to increased SC cohesiveness in deeper layers. Thus, the mass of any single strip depends on the mass removed by the prior strip (Bashir et al., Skin Res Technol 7 (1):40–48, 2001). SC removal may rely on the interaction between the adhesive stripping force and the cohesive intercellular force (Bashir et al., Skin Res Technol 7 (1):40–48, 2001).

Depth-dependent stratum corneum permeability in human skin in vitro.

The stratum corneum (SC), a permeable membrane, limits percutaneous penetration. As SC chemical and structural properties responsible for skin barrier function appear depth‐related, we conducted an in vitro dermatopharmacokinetic study on intact and adhesive tape‐stripped skin samples to clarify whether SC is a homogeneous barrier for chemical transport. SC concentration–thickness profiles were determined for four C‐14 labeled model chemicals, panthenol, benzoic acid, paraoxon and butenafine, using the tape‐stripping approach. Data analysis with the unsteady‐state diffusion equation of Ficks second law permitted a chemical diffusion coefficient in SC. To evaluate the consistency of SC permeability from its surface to lower levels, the skin was tape‐stripped five to 10 times to remove the upper cell layers before chemical application, such that diffusion coefficients could be determined from three SC depth levels (0, 5 and 10 tape strips). Results suggested the depth‐dependency of SC permeability to panthenol, benzoic acid and butenafine; the diffusion coefficient of panthenol decreased significantly after the first five tape strips and subsequently remained consistent. A progressive increase in diffusion coefficients of benzoic acid and butenafine was observed as tape‐stripping levels increased. The removal of superficial SC did not result in a significant difference in the paraoxon diffusion coefficient. For individual chemicals, a variation in the diffusion coefficient from SC surface to deeper layers agreed with the change of the diffusion coefficient over time in intact skin. Characterization of the SC properties contributing to the depth‐dependent SC permeability will hopefully provide further insight to skin penetration/decontamination. Copyright

Binding affinity and decontamination of dermal decontamination gel to model chemical warfare agent simulants: Skin decontamination

Six chemical warfare agent simulants (trimethyl phosphate, dimethyl adipate, 2‐chloroethyl methyl sulfide, diethyl adipate, chloroethyl phenyl sulfide and diethyl sebacate) were studied in in vitro human skin to explore relationship between dermal penetration/absorption and the mechanisms of simulant partitioning between stratum corneum (SC) and water as well as between dermal decontamination gel (DDGel) and water. Both binding affinity to and decontamination of simulants using DDGel were studied. Partition coefficients of six simulants between SC and water (Log PSC/w) and between DDGel and water (Log PDDGel/w) were determined. Results showed that DDGel has a similar or higher binding affinity to each simulant compared to SC. The relationship between Log P octanol/water and Log PSC/w as well as between Log P octanol/water and Log PDDGel/w demonstrated that partition coefficient of simulants correlated to their lipophilicity or hydrophilicity. Decontamination efficiency results with DDGel for these simulants were consistent with binding affinity results. Amounts of percentage dose of chemicals in DDGel of trimethyl phosphate, dimethyl adipate, 2‐chloroethyl methyl sulfide, diethyl adipate, chloroethyl phenyl sulfide and diethyl sebacate were determined to be 61.15, 85.67, 75.91, 53.53, 89.89 and 76.58, with corresponding amounts absorbed in skin of 0.96, 0.65, 1.68, 0.72, 0.57 and 1.38, respectively. In vitro skin decontamination experiments coupled with a dermal absorption study demonstrated that DDGel can efficiently remove chemicals from skin surface, back‐extract from the SC, and significantly reduced chemical penetration into skin or systemic absorption for all six simulants tested. Therefore, DDGel offers a great potential as a NextGen skin Decon platform technology for both military and civilian use.

Effect of ultrasound and heat on percutaneous absorption of l-ascorbic acid: human in vitro studies on Franz cell and Petri dish systems

Percutaneous absorption of l‐ascorbic acid (LAA) is limited due to its high hydrophilicity and low stability. Here, we investigated the effect of post‐dosing sonophoresis (329 kHz, 20 mW cm−2) and heat (36°C) on transdermal delivery of LAA.

Confocal laser scanning microscopy to estimate nanoparticles’ human skin penetration in vitro

Objective With rapid development of nanotechnology, there is increasing interest in nanoparticle (NP) application and its safety and efficacy on human skin. In this study, we utilized confocal laser scanning microscopy to estimate NP skin penetration. Methods Three different-sized polystyrene NPs marked with red fluorescence were applied to human skin, and Calcium Green 5N was used as a counterstain. Dimethyl sulfoxide (DMSO) and ethanol were used as alternative vehicles for NPs. Tape stripping was utilized as a barrier-damaged skin model. Skin biopsies dosed with NPs were incubated at 4°C or 37°C for 24 hours and imaged using confocal laser scanning microscopy. Results NPs were localized in the stratum corneum (SC) and hair follicles without penetrating the epidermis/dermis. Barrier alteration with tape stripping and change in incubation temperature did not induce deeper penetration. DMSO enhanced NP SC penetration but ethanol did not. Conclusion Except with DMSO vehicle, these hydrolyzed polystyrene NPs did not penetrate intact or barrier-damaged human “viable” epidermis. For further clinical relevance, in vivo human skin studies and more sensitive analytic chemical methodology are suggested.

In vitro human skin permeation and decontamination of 2-chloroethyl ethyl sulfide (CEES) using Dermal Decontamination Gel (DDGel) and Reactive Skin Decontamination Lotion (RSDL)

This study compared the efficiency for in vitro human skin decontamination using DDGel and RSDL. Experiments were performed using in vitro human skin models, in which skin was mounted onto Flow-Through diffusion cells. The mass of 14-C CEES removed from skin surface after decontamination was quantitated by measuring radioactivity with a liquid scintillation spectrometer. Both decontaminants removed more than 82% of CEES from skin. DDGel skin decontamination significantly reduced toxicant amount when compared to RSDL. Mean CEES remaining in stratum corneum (SC), viable epidermis, dermis, and systemic absorption of DDGel and RSDL were, 0.12 and 0.55% (P < 0.01), 0.31 and 0.95% (p < 0.01), 1.08 and 2.92% (p < 0.05), 3.13 and 6.34% (p < 0.05), respectively. DDGel showed higher decontamination efficiency (twice decontamination efficacy factor, DEF) than RSDL and efficiently removed chemicals from the skin surface, importantly back-extracted from the SC, and significantly reduced both chemical penetration into skin and systemic absorption. Thus, DDGel can offer a potential as a next generation skin decontamination platform technology for military and civilian applications.