Skin barrier modification with organic solvents

Preliminary evaluation of ex vivo and in vivo skin permeability of aromatic amines

A potential link has been reported between skin exposure to aromatic amines, such as ortho-toluidine (OT) and 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), and bladder cancer cases observed in Japanese chemical factories. To evaluate this association, we explored the permeability of OT and MOCA through pig skin and investigated the subsequent changes in plasma and urine concentrations in rats following percutaneous exposure. Employing Yucatan micropig skin, we first executed a permeability test by affixing the skin to a diffusion cell and applying 14C-labeled OT or MOCA. The receptor fluid's radioactivity was quantified at intervals of 1, 3, 6, 8, 24, and 48 h after application using a liquid scintillation counter. Next, we applied lint cloths drenched in OT and MOCA solutions to the backs of 7-week-old male F344 rats and monitored plasma and urine concentrations over time. Additionally, we investigated the pharmacokinetics of 14C-labeled OT or MOCA solutions for 8 h following percutaneous administration. Both OT and MOCA demonstrated high skin penetration; in particular, plasma concentrations significantly rose at 6 h for OT and 8 h for MOCA after exposure. However, OT was rapidly absorbed into the bloodstream and swiftly excreted into the urine, indicating quick absorbability. In contrast, MOCA penetrated the skin quickly but exhibited delayed bloodstream entry and urinary excretion, suggesting slower absorbability. Pharmacokinetic findings revealed the rapid urinary excretion of OT, whereas MOCA was excreted in the urine and potentially in the feces as well via bile. These findings indicate that implementing measures based on chemical absorbability could significantly enhance the management of industrial chemicals where percutaneous absorbability is a concern.

Dermal absorption of cyclic and linear siloxanes: a review

Cyclic and linear siloxanes are compounds synthesized from silicon consisting of alternating atoms of silicone and oxygen [Si-O] units with organic side chains. The most common cyclic siloxanes are octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), while the most common linear siloxanes are high molecular weight polydimethylsiloxanes (PDMS) and low molecular weight volatile linear siloxanes known as hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5). These compounds (1) exhibit low dermal toxicity, (2) are generally inert and non-reactive, and (3) are compatible with a wide range of chemicals offering beneficial chemical properties which include the following: wash-off or transfer resistance from the skin, sun protection factor (SPF) enhancement, emolliency in cleaning products). Because of these properties, these compounds are incorporated into multiple consumer products for use on the skin, such as cosmetics and health-care products, with over 300,000 tons annually sold into the personal care and consumer products sector. Because of their widespread use in consumer products and potential for human dermal exposure, a comprehensive understanding of the dermal absorption and overall fate of siloxanes following dermal exposure is important. This review summarizes available data associated with the dermal absorption/penetration as well as fate of the most commonly used siloxane substances.

Effects of Siegesbeckia herba extract against particulate matter 10 (PM10 ) in skin barrier-disrupted mouse models

OBJECTIVES

Skin barrier disruption is a significant problem of the older population in an aging society. It is characterized by increased transepidermal water loss and decreased skin water content, and particulate matter (PM) is a social issue that can contribute to the exacerbation of skin inflammation. Thus, addressing this problem is urgent.

METHODS

Skin barrier-disrupted mouse models were induced by two methods using acetone application or tape-stripping. This study investigated the antioxidative and anti-inflammatory properties of the Siegesbeckia herba extract (SHE) on PM-induced changes in skin barrier-disrupted mouse models. To examine changes in skin water content, inflammatory cytokines, and keratinocyte differentiation markers, mouse models were treated with vehicle 100 μL, PM10 100 μL (100 μg/mL), SHE 100 μL, or PM10 100 μL (100 μg/mL) plus SHE 100 μL.

RESULTS

SHE preserved skin hydration in the skin barrier-disrupted mouse models regardless of the presence of PM10 . SHE also inhibited the upregulation of inflammatory cytokines such as interleukin (IL)-1β, IL-4, IL-6, IL-8, and tumor necrosis factor-α and normalized the downregulation of keratinocyte differentiation markers against PM10 in skin barrier-disrupted mouse models.

CONCLUSIONS

This study elucidated the therapeutic effects of SHE against PM10 in skin barrier-disrupted mouse models.

Multilayer diffusion modeling and Coherent anti-Stokes Raman scattering microscopy for spatially resolved water diffusion measurements in human skin

In this work using Coherent anti-Stokes Raman Scattering microscopy, it was possible to directly measure the time dependent, spatially resolved change in concentration of water (D₂ O) in intact skin tissue with a spatial resolution of under 1 μm, and combined with a multilayer diffusion model, diffusion coefficients at different depths in the tissue were extracted. The results show that the diffusion varies at different layers throughout the Stratum Corneum (SC), indicating that the SC is not a homogeneous barrier but a complicated heterogeneous structure. Interestingly, averaging over the diffusion at the different depths and samples gave a relatively constant value of 0.047 ± 0.01 μm² /second. Treating the skin with acetone or tape stripping led to an increased diffusion coefficient of 0.064 ± 0.02 μm² /second and 0.079 ± 0.03 μm² /second, respectively. The combined method and model presented here shows potential for wide applications for measuring spatially resolved diffusion of different substances in a variety of different samples.

Occupational exposure assessment with solid substances: choosing a vehicle for in vitro percutaneous absorption experiments

Percutaneous occupational exposure to industrial toxicants can be assessed in vitro on excised human or animal skins. Numerous factors can significantly influence skin permeation of chemicals and the flux determination. Among them, the vehicle used to solubilize the solid substances is a tricky key step. A "realistic surrogate" that closely matches the exposure scenario is recommended in first intention. When direct transposition of occupational exposure conditions to in vitro experiments is impossible, it is recommended that the vehicle used does not affect the skin barrier (in particular in terms of structural integrity, composition, or enzymatic activity). Indeed, any such effect could alter the percutaneous absorption of substances in a number of ways, as we will see. Potential effects are described for five monophasic vehicles, including the three most frequently used: water, ethanol, acetone; and two that are more rarely used, but are realistic: artificial sebum and artificial sweat. Finally, we discuss a number of criteria to be verified and the associated tests that should be performed when choosing the most appropriate vehicle, keeping in mind that, in the context of occupational exposure, the scientific quality of the percutaneous absorption data provided, and how they are interpreted, may have long-range consequences. From the narrative review presented, we also identify and discuss important factors to consider in future updates of the OECD guidelines for in vitro skin absorption experiments.

In Vitro Modeling of Skin Barrier Disruption and its Recovery by Ceramide-Based Formulations

Disrupted skin barrier, one of the severe attributes of inflammatory skin diseases, is caused by lower content and pathological changes of lipids in the uppermost skin layer-stratum corneum (SC). Restoring skin barrier with native skin lipids, especially ceramides (Cers), appears to be a promising therapy with minimum side effects. For testing the efficiency of these formulations, suitable in vitro models of the skin with disrupted barriers are needed. For the similarity with the human tissue, our models were based on the pig ear skin. Three different ways of skin barrier disruption were tested and compared: tape stripping, lipid extraction with organic solvents, and barrier disruption by sodium lauryl sulfate. The level of barrier disruption was investigated by permeation studies, and parameters of each method were modified to reach significant changes between the non-disrupted skin and our model. Fourier transform infrared (FTIR) spectroscopy was employed to elucidate the changes of the skin permeability on the molecular scale. Further, the potential of the developed models to be restored by skin barrier repairing agents was evaluated by the same techniques. We observed a significant decrease in permeation characteristics through our in vitro models treated with the lipid mixtures compared to the untreated damaged skin, which implied that the skin barrier was substantially restored. Taken together, the results suggest that our in vitro models are suitable for the screening of potential barrier repairing agents.

Protocol for the Isolation of Stratum Corneum from Pig Ear Skin: Evaluation of the Trypsin Digestion Conditions

Stratum corneum (SC) represents the outermost layer of the skin, being an effective barrier against the entry of molecules and pathogens. Skin research has given particular focus to SC as it hampers effective drug delivery for cosmetical and therapeutical purposes. Following recommendations to develop alternative models to animals, the SC isolated from skin obtained from medical procedures or from pigs has gained extensive attention. Yet, there is still missing a standard and simple procedure accepted within the scientific community to avoid application of different isolated SC methodologies, a fact that may hamper progress in skin research. Considering this challenge, the present study evaluated different experimental conditions aiming to establish a useful and sustainable solvent-free procedure for the obtention of a realistic SC model. The studied trypsin digestion parameters included concentration, incubation period and temperature. Isolated SC was characterized using histological analysis and calcein’s permeability, after the procedure and during a 6-week storage period. Data recommend trypsin digestion at 4 °C for 20 h as the most effective procedure to isolate SC from pig ear skin. This work contributes to standardize the SC isolation procedure, and to obtain a valuable and reliable SC mimetic model for skin drug development.

Retaining Skin Barrier Function Properties of the Stratum Corneum with Components of the Natural Moisturizing Factor-A Randomized, Placebo-Controlled Double-Blind In Vivo Study

The influence of a topically applied formulation containing components of natural moisturizing factor (NMF) on barrier-related parameters of the stratum corneum (SC) was investigated in vivo using confocal Raman microspectroscopy in a randomized, placebo-controlled double-blind study on 12 volunteers for 14 days. This method allowed for the elucidation of subtle differences between the verum and the placebo even though the components of the verum naturally occur in the SC. This differentiation is not possible non-invasively by conventional methods. In this study, we found that the applied verum and placebo formulations disrupted the equilibrium of water, NMF and lipids in the SC. The adverse effects of the formulation could be mitigated by incorporating it into a simplified supplementation of NMF molecules. As a long-term effect, the amount of strongly bound water increases at 30–40% SC depth (p < 0.05) and the amount of weakly bound water decreases at 30–40% SC depth (p < 0.05) for the verum. This supplement was also unexpectedly able to prevent intercellular lipids (ICL) disorganization in selected depths. In the long term, the verum treatment limited the lateral disorganization of the ICL to the upper 20% SC depth. Further research is required to elucidate the interplay of these factors in the SC, to better understand their contribution to the equilibrium and barrier function of the skin. This understanding of the interaction of these naturally occurring components could help in the future to develop and optimize topical treatments for diseases like psoriasis, atopic dermatitis, ichthyosis where the skin barrier is disrupted.

Human skin permeation rates ex vivo following exposures to mixtures of glycol ethers

Skin exposure to cleaning products in the general and occupational population are a public health concern. Among the most frequently identified amphiphilic organic solvents in cleaning products are propylene glycol monomethyl ether (PGME) and propylene glycol n-butyl ether (PGBE). Internal dose from skin exposure may be efficiently evaluated using in vitro flow-through diffusion cells with excised human skin. Our aim in this study was two-fold; 1) characterize the permeation rates (J), time lag (T_lag), and permeation coefficients (Kp) of PGME and PGBE in human ex-vivo skin permeation assays, and 2) determine a possible mixture effect on skin permeation characteristics when applied together. Our results showed a short T_lag for PGME and was reduced further depending on the amount of PGBE in the mixture (T_lag was reduced from 2 h to 1-1.7 h) for fresh skin. PGBE T_lag slightly increased when mixed with 50 % or more PGME. Permeation rate decreased to half for both PGME and PGBE in mixture at any concentration. This substantial permeation was greater with previously frozen skin. This mixture effect could favor permeation of other compounds through human skin.

Integrated effects of fractional laser microablation and sonophoresis on skin immersion optical clearing in vivo

This study is aimed to find an approach for effective skin optical clearing in vivo using polyethylene glycol 300 (PEG-300) as an optical clearing agent in combination with physical enhancers: fractional laser microablation (FLMA) and/or low-frequency sonophoresis. In this study albino outbred rats were used. Light attenuation coefficient and optical clearing potential (OCP) of these approaches were evaluated in upper (from ~70 to ~200 μm) and middle (from ~200 to ~400 μm) dermis separately using optical coherence tomography. In 30 minutes, OCP of sonophoresis in combination with FLMA and PEG-300 in the upper dermis was the maximal (2.3 ± 0.4) in comparison with other treatments in this time point. The most effective approach for optical clearing of middle dermis was PEG-300 and sonophoresis; but the maximal value of OCP (1.6 ± 0.1) was achieved only in 90 minutes.

Pharmacotherapy: Its impact on morphofunctional characteristics of the epidermal barrier

Various pharmaceuticals used for topical and systemic therapy are capable of exerting significant impact on morphological and physiological characteristics of human epidermis, as well as its barrier properties. This may affect the course of dermatologic diseases and the efficacy of their treatment. In this literature review, the author analyzes the impact of various pharmaceutical classes on the morphofunctional characteristics of the epidermal barrier and formulates recommendations for skin disease treatment.

Action of surfactants on the mammal epidermal skin barrier

BACKGROUND

Daily skin washing routines can promote undesirable effects on skin barrier function. The stratum corneum (SC) lipid matrix is crucial for skin barrier function. Skin cleansing products are mostly composed of surfactants: surface-active molecules that interact with skin lipids in several ways. The main aim of this work was to investigate the effect produced by surfactants on skin barrier permeability. Porcine skin is a well-accepted and readily available model of the human skin barrier. The effect of two cleansing formulations (based on different surfactant mixtures) on the barrier properties of mammalian skin were evaluated.

METHODS

Water sorption/desorption (DVS) experiments were used to measure skin permeability. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and confocal Raman were useful to study SC lipid organization.

RESULTS

The results showed that while anionic surfactants (SLS) had a negative impact on the skin barrier, with a clear increase of alkyl chain disorder; cosurfactants present in the shampoo formulation diminished the detrimental effect of their primary ionic surfactant, inducing less modification on lipid intramolecular chain disorder.

CONCLUSIONS

The obtained results confirmed that the mild cleansing formulations studied had gentle interaction with skin. The capacity to discriminate between detergent systems was clearly established with both DVS and spectroscopy techniques.

Accelerated barrier recovery and enhancement of the barrier integrity and properties by topical application of a pH 4 vs. a pH 5·8 water-in-oil emulsion in aged skin

BACKGROUND

Increased skin-surface pH is an important host-related factor for deteriorated barrier function in aged skin.

OBJECTIVES

We investigated whether restoration of skin pH through topical application of a water-in-oil emulsion with pH 4 improved the barrier homeostasis in aged skin, and compared the effects with an identical galenic formulation with pH 5·8.

METHODS

The effects of the test formulations on barrier recovery were investigated by repeated measurements of transepidermal water loss (TEWL) and skin pH 3 h, 6 h and 24 h after acetone-induced impairment of barrier function in aged skin. The long-term effects of the pH 4 and pH 5·8 emulsions were analysed by investigation of the barrier integrity and cohesion, the skin-surface pH and the skin roughness and scaliness before and after a 4-week, controlled application of the formulations.

RESULTS

The application of the pH 4 emulsion accelerated barrier recovery in aged skin: 3 h and 6 h after acetone-induced barrier disruption the differences in the TEWL recovery between the pH 4 treated and acetone control fields were significant. Furthermore, long-term application of the pH 4 formulation resulted in significantly decreased skin pH, enhanced barrier integrity and reduced skin-surface roughness and scaliness. At the same time points, the pH 5·8 formulation exerted only minor effects on the barrier function parameters.

CONCLUSIONS

Exogenous acidification through topical application of a water-in-oil emulsion with pH 4 leads to improvement of the skin barrier function and maintenance of the barrier homeostasis in aged skin.

Solvent-Extracted Wool Wax: Thermotropic Properties and Skin Efficacy

BACKGROUND/AIMS

Wool wax is a soft, yellow, waxy substance that is secreted by the sebaceous glands of sheep. The purpose of wool wax is to waterproof and protect the wool. Chemically, wool wax is a complex mixture of esters, fatty acids, and alcohols. Wool waxes with different prop-erties can be obtained by following different extraction methodologies.

METHODS

Two differently extracted wool waxes are compared in this study. Their effectiveness in mimicking the properties of skin lipids is evaluated. In addition, the lipid compositions and thermotropic behaviours of the 2 differently extracted wool waxes were evaluated.

RESULTS

The solvent-extracted wool wax was found to have a significantly higher polar lipid content than that of the water-extracted wool wax. This increase in the polar character of the solvent-extracted wool wax was also demonstrated by increased values of transition and degradation temperatures in the differential scanning calorimetry and thermogravimetric analyses, respectively. In addition, solvent-extracted wool wax demonstrated the ability to reinforce stratum corneum lipids, which led to improved skin barrier function.

CONCLUSIONS

The suitability of the solvent-extracted wool wax for application in the preparation of cosmetics and dermatological products was demonstrated.