Selective modification of skin barrier lipids

Guarding skin under PPE: Mechanistic insights and technological innovations

In the presence of diseases transmitted through respiratory droplets and direct contact, healthcare workers (HCWs) necessitate the use of personal protective equipment (PPE). For optimal safety, PPE should securely conform to the skin during extended wear. However, conventional PPE often lacks adequate air permeability and hygroscopicity, trapping heat and moisture emitted by the body within the enclosure. Such a hot and humid internal environment can induce skin damage, such as erythema, rash, pruritus, and itching among others, leading to microbial growth on the skin surface, the production of inflammatory mediators at the wound site and an increased risk of infection. This review strives to comprehensively elucidate the fundamental mechanisms triggering adverse skin reactions and their resultant manifestations. Furthermore, we explore recent advancements aimed at inhibiting these mechanisms to effectively mitigate the occurrence of skin lesions.

Systematic investigation of factors, such as the impact of emulsifiers, which influence the measurement of skin barrier integrity by in-vitro trans-epidermal water loss (TEWL)

Trans-epidermal water loss (TEWL) has been the most widely used method to assess the integrity of the skin barrier and evaluate the irritation potential or the protective properties of topical products for many years. It detects the amount of water that diffuses across the stratum corneum (SC) to the external environment. As one of the most important functions of the skin is to keep water inside the body, an increase in TEWL is used to indicate the skin's impaired barrier function. So far, a variety of commercial instruments are available to measure the TEWL. Their applications mainly focus on the in-vivo TEWL measurements for dermatological examinations or formulation development. Recently, an in-vitro TEWL probe has also been commercially released enabling preliminary tests with excised skin samples. In our study, we first aimed to optimize the experimental procedures for detecting the in-vitro TEWL of porcine skin. Secondly, different kinds of emulsifiers were applied to the skin, including polyethylene glycol-containing emulsifiers (PEG-ylated emulsifiers), sorbitan esters, cholesterol, and lecithin. Sodium lauryl sulfate (SLS) was used as a positive control, and water as a negative control. Based on the findings, we established a protocol for accurately measuring the in-vitro TEWL values, emphasizing that the temperature of the skin sample should be constantly maintained at 32℃. Subsequently, the influences of emulsifiers on the in-vitro TEWL were analyzed. They indicated a significant skin barrier impairment of PEG-20 cetyl ether, PEG-20 stearyl ether, and SLS on in-vitro skin. Furthermore, we interestingly found that there consistently was an alteration of the TEWL values, even after the application of water to the skin. Our findings are of special interest, as the European Medicines Agency (EMA) recommends the use of in-vitro TEWL to determine skin barrier intactness during Franz cell experiments. Thus, this study provides a validated protocol for measuring the in-vitro TEWL and elucidates the impact of emulsifiers on the skin barrier. It also improves the understanding of tolerable variations of in-vitro TEWL and offers recommendations for its use in research.

Evaluating the Skin Interactions and Permeation of Alginate/Fucoidan Hydrogels Per Se and Associated with Different Essential Oils

Marine polysaccharides are recognized for their biological properties and their application in the drug delivery field, favoring hydrogel-forming capacities for cutaneous application towards several dermatological conditions. Essential oils have been widely used in skin, not only for their remarkable biological properties, but also for their capacity to enhance permeation through the skin layers and to confer a pleasant scent to the formulation. In this study, menthol, L-linalool, bergamot oil, and β-pinene were incorporated in alginate/fucoidan hydrogels to evaluate their skin permeation enhancement profile and assess their influence on the skin organization. The combinations of different essential oils with the marine-based fucoidan/alginate hydrogel matrix were characterized, resulting in formulations with pseudoplastic rheological properties favorable for a uniform application in the skin. The ex vivo Franz diffusion permeation assays revealed that calcein loaded in bergamot-alginate/fucoidan hydrogel permeated more than 15 mg out of the initial 75 mg than when in linalool-alginate/fucoidan, alginate/fucoidan or hydrogel without any incorporated oil. Skin calcein retention for menthol- and pinene-alginate/fucoidan hydrogels was 15% higher than in the other conditions. Infrared micro-spectroscopic analysis through synchrotron-based Fourier Transform Infrared Microspectroscopy evidenced a symmetric shift in CH₃ groups towards higher wavenumber, indicating lipids' fluidization and less lateral packing, characterized by a band at 1468 cm^-1, with the bergamot-alginate/fucoidan, which contributes to enhancing skin permeation. The study highlights the effect of the composition in the design of formulations for topical or transdermal delivery systems.

Synchrotron-based infrared microspectroscopy of polymeric nanoparticles and skin: Unveiling molecular interactions to enhance permeation

The application of nanoparticles as permeation enhancers in skin drug delivery is a growing research field. However, the mechanisms of nanoparticles' interaction with the skin structure are still unknown. Fucoidan/chitosan nanoparticles have demonstrated several physicochemical and biological advantages, among which is the enhancement of skin permeation. This study aims to elucidate permeation enhancement mechanisms using synchrotron-based Fourier Transform Infrared Microspectroscopy (SR-FTIRM) combined with multivariate analysis and in vitro skin permeation assay. Given the molecular weight influence on chitosan's properties, the nanoparticles-skin interactions were evaluated with nanoparticles produced using low- and medium-molecular-weight chitosan. Chemical maps and spectral analysis revealed that fucoidan/chitosan nanoparticles induced changes in the lipids and protein regions. Inter-sample spectral differences were identified using principal component analysis. Low molecular weight fucoidan/ chitosan nanoparticles caused changes in the skin lipids' lateral packing and structure at the stratum corneum layer towards a less ordered state and higher fluidity, and no evidence was found on proteins structure. The opposite was revealed for medium molecular weight fucoidan/chitosan nanoparticles, which induced changes in the secondary structure of keratin and altered lipid structure to an ordered and dense conformation. In vitro permeation assays with Franz diffusion cells correlate with the observed changes in the skin lipid and protein structure with enhanced skin permeation of a hydrophilic molecule incorporated within the fucoidan/chitosan nanoparticles. The findings of this study unveil molecular changes in the skin structure induced by the nanoparticles only possible with the application of the powerful and precise SR-FTIRM technique. This knowledge allows the design of nanoparticles towards an internalization pathway determining their fate within the skin structure.

Application of in vitro methods to evaluate the safety of baby care products

Draize rabbit eye irritation and skin irritation tests are widely used in the chemical industry as traditional methods to evaluate the safety of cosmetics. However, great differences among laboratories have caused great doubt in the industry. In addition, with vigorous development of the global animal protection movement, developed countries have launched the "3R" campaign, and various kinds of in vitro alternative methods have emerged. Hen's egg test on the chorioallantoic membrane (HET-CAM), which is similar to the structure of the human cornea and has a clear and complete vascular system, is based on the characteristics of the chorioallantoic membrane (CAM) in mid-term SPF egg embryos. The reconstructed human epidermis (EpiSkin®) is composed of normal human keratinocytes that are histologically similar to human epidermises seen in vivo, and it is cultured on a collagen matrix. Similar to EpiSkin®, Human Corneal Epithelium (SkinEthic™) is another reconstructed 3D human-corneal structure that is an alternative to the traditional eye irritation test. Three in vitro methods were conducted to evaluate the safety of 12 baby care products, which included the most common types. In addition, a consumer research study was also carried out for two weeks to evaluate the safety. The results of the reconstructed human epidermis model, human corneal epithelium model and consumer research showed that no irritation was found in any test products; however, HET-CAM tests showed positive results.

Lipidomic analysis of facial skin surface lipid reveals the causes of pregnancy-related skin barrier weakness

Self-reported skin discomfort is a common problem during pregnancy, but it is not clear whether skin barrier function is altered in the process. Few studies have described the skin barrier function during pregnancy. In this work, we used highly sensitive and high-resolution ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) to distinguish skin surface lipid (SSL) combined with multivariate analysis of lipids and metabolic changes to determine the relationship between SSL changes and skin physiology during pregnancy in order to better understand the skin condition of pregnant women. The results showed a significant reduction in the total lipid content in pregnant women. A total of 2270 lipids were detected, and the relative abundances of fatty acyls and glycerolipids were significantly reduced, while glycerophospholipids (GPs), sphingolipids, and saccharolipids was significantly increased in the pregnancy group. Multivariate data analysis indicated that 23 entities constituted the most important individual species responsible for the discrimination and phosphatidylcholine was the most abundant lipid in pregnancy group. In addition, compared to SSL profile of control group, it was observed that the average chain length of ceramides and fatty acids both decreased in SSL profile of pregnancy group. The main and most commonly affected pathway was that of GP pathways. These findings indicate that skin lipids are significantly altered in mid-pregnancy compared to the control group. Changes in ostrogen during pregnancy also make the skin more susceptible to inflammatory factors and lead to more fragile and susceptible skin, weakening the skin barrier along with the lipid alterations.

Development of a reversed-phase high-performance liquid chromatographic method for the determination of propranolol in different skin layers

The aim of this work was to develop and validate an analytical method using HPLC for the determination of propranolol in the different layers of the skin to be used in kinetic studies of skin permeation. The development of the method was based on the suitability of the chromatogram, and the validation followed the international health regulation for bioanalytical methods. In addition, the method was tested in an in vitro permeation assay using porcine skin. The drug was determined using an RP-C18 column at 30°C, a mobile phase comprising acidic aqueous phase:acetonitrile (75:25 v/v), at a flow rate of 1.0 mL min^-1 , and UV detection at 290 nm. The method was demonstrated to be selective against skin contaminants, linear in a wide range of concentrations (3-20 μg mL^-1 ), sensitive enough to quantify less than 0.1% of the drug dosage in skin matrices, and precise regardless of analysis variations such as day of analysis, analyst, or equipment. In addition, the method presented a high drug extraction capacity greater than 90% for all skin layers (stratum corneum, hair follicle, and remaining skin). Finally, the method was successfully tested in skin permeation assays, proving its value in the development of topical formulations containing propranolol.

Food-derived bioactive compounds with anti-aging potential for nutricosmetic and cosmeceutical products

Besides providing essential nutrients for humans, food contains bioactive compounds that exert diverse biological activities such as anti-microbial, anti-cancerogenic, anti-viral, anti-inflammatory and antioxidant. The cosmetic industry is interested in natural bioactive compounds for their use in nutricosmetic and cosmeceutical products. These products aimed to reduce skin aging, inflammation or provide photoprotection against UV radiation. As a result, nutricosmetics and cosmeceuticals are becoming innovative self-care products in the beauty market. These products contain phytochemicals as active compounds obtained from fruits, vegetables, legumes, medicinal herbs and plants with anti-aging potential. This review summarizes the information within the last 5 years related to bioactive compounds present in fruits, vegetables, herbs and spices commonly used for human consumption. Their antioxidant and biological potential for modulating molecular markers involved in the aging process, as well as their mechanism of action. Diverse natural foods and their byproducts could be used as a source of bioactive compounds for developing cosmeceutical and nutricosmetic products.

In vitro and in vivo trans-epidermal water loss evaluation following topical drug delivery systems application for pharmaceutical analysis

The measurement of Trans-Epidermal Water Loss (TEWL) allows to evaluate the integrity of Stratum Corneum Epidermis (SCE) barrier after topical application of colloidal nanocarriers by using a non-invasive method. The temporarily modifications of SCE lipids are important for the passage of colloidal nanocarriers across the skin; this passage causes a modification of TEWL values. Niosomes, ethosomes®, and transfersomes® are used as topical drug delivery systems due to their biopharmaceutical properties, and capability to permeate intact through the SCE. In vitro and in vivo evaluation of TEWL values was studied for niosomes, ethosomes® and transfersomes® in occlusive and non-occlusive conditions. TEWL values in vivo, using healthy human volunteers, are ∼12 g/m²∙× h for all nanoformulations after 72 h, due to the rearrangement of lipids forming the SCE membranes. Conversely, TEWL values of healthy human volunteers, that are topically treated with niosomes, ethosomes® and transfersomes®, in non-occlusive conditions, are ∼20 g/m²∙× h. This data was lower than those obtained in occlusive conditions (∼35 g/m²∙× h). In vitro studies agreed results which are obtained in occlusive conditions using healthy human volunteers. SCE lipids of the skin restore their native structure after 72 h of nanocarrier application. In vitro and in vivo results showed that niosomes, ethosomes®, and transfersomes® interact with the skin in a temporary and reversible mode, and they can be used as suitable colloidal nanocarriers to increase the percutaneous permeation of drugs after topical application without damaging the native structure of the skin.

Effect of Surfactant-Keratin Hydrolysate Interactions on the Hydration Properties of a Stratum Corneum Substitute

A novel stratum corneum substitute (SCS) has been developed, and the fundamental mechanism of the dehydration process has been studied using the SCS. After washing with cleansers which contain surfactants, our skin "feels" dehydrated (or hydrated). Although many studies have focused on the effect of surfactants on the regulation of the water loss by the lipid bilayers in the stratum corneum (SC) for a long timescale or at equilibrium, only few studies have focused on the acute effect of the surfactant interaction on dehydration. In addition, the interaction between the surfactant and keratin has been often underappreciated compared to lipid bilayers although keratin is the major nonaqueous component of the SC. Here, we have developed novel SCS models, nonkeratinized (lipid only) and keratinized, to study the effect of keratin hydrolysates on the dehydration rate. We have confirmed that the lipid organizational structure of the SCS was similar to that of the human SC using X-ray scattering. We have revealed that keratin hydrolysates play a significant role in the dehydration rate, accelerating the rate for the short term. We have also demonstrated that the effect of surfactants on dehydration is more pronounced for keratinized samples than that for the nonkeratinized sample. However, the dehydration rate for the nonkeratinized SCS with the surfactant became faster than the that for the keratinized SCS after the 20 min evaporation process, suggesting that the water binding sites of keratin hydrolysates slowed down evaporation, while the surfactant interacting with the lipids accelerated the water loss. Lastly, the study demonstrated that the SCS model can be a great platform to test macroscopic properties and analyze the underlying mechanism at the molecular level for various chemicals.

Development and In Vivo Evaluation of Multidrug Ultradeformable Vesicles for the Treatment of Skin Inflammation

The aim of this work was to evaluate the effect of two chemically different edge activators, i.e., Tween^® 80 and sodium deoxycholate, on (i) the physical, mechanical, and biological properties of ultradeformable vesicles, and (ii) the administration of naproxen sodium-loaded multidrug ultradeformable vesicles for the transdermal route in order to obtain therapeutically meaningful drug concentrations in the target tissues and to potentiate its anti-inflammatory effect by association with the antioxidant drug idebenone. The results obtained in this investigation highlighted a synergistic action between naproxen and idebenone in the treatment of inflammatory disease with a more pronounced anti-inflammatory effect in multidrug ultradeformable vesicles compared to the commercial formulation of Naprosyn^® gel. Systems made up of Tween^® 80 appeared to be the most suitable in terms of percutaneous permeation and anti-inflammatory activity due to the greater deformability of these vesicles compared to multidrug ultradeformable vesicles with sodium deoxycholate. Our findings are very encouraging and suggest the use of these carriers in the topical treatment of inflammatory diseases.