In vivo permeation of 2-phenoxyethanol in human skin

A number of baby wipe formulations contain 2-phenoxyethanol (PE) as a preservative and cetylpyridinium chloride (CPC) as a surfactant with antimicrobial activity. Previously, we reported the skin absorption of PE in porcine skin and human skin in vitro. In the present work, the permeation of PE from preparations with CPC and without CPC was investigated in human skin in vivo. The studies were conducted using Confocal Raman Spectroscopy (CRS) and tape stripping (TS) methods. The CRS studies showed that the area under the curve (AUC) of PE for the formulation with and without CPC were not significantly different (p > 0.05). The TS data indicated no significant difference in the amounts of PE recovered from tapes 1-6 for the preparation with and without CPC (p > 0.05). When comparing the in vitro and in vivo data, a correlation was observed between the cumulative amount of PE permeated through human skin in vitro at 24 h and the AUC as measured by CRS (r2 = 0.97). In addition, the cumulative amount of PE permeated through human skin in vitro at 24 h was found to correlate with the amount of PE recovered from tape 1 to 6 in vivo (r2 = 0.95). Both CRS and TS techniques demonstrated limitations in assessing the distribution of PE and CPC in the skin in vivo, primarily attributed to the Raman signal intensities of compounds under investigation and the variability in the amount of SC collected by TS. Despite the limitations of CRS and TS, the results from the present study add further insights to the in vitro permeation data. Additionally, the findings of the present study encourage the further development and application of CRS for non-invasive evaluation of topical skin formulations in vivo.

The Skin Acid Mantle: An Update on Skin pH

The acid mantle concept refers to the buffer system located in the upper stratum corneum of the skin. By sustaining an acidic environment, the acid mantle contributes to the regulation of the microbiome, structural stability, and inflammation. Skin pH is pivotal in maintaining the integrity of the epidermal barrier. Shifts in pH can disrupt barrier properties, and recent studies have emphasized its impact on dermatologic disease processes. This review explores the complex relationship of mechanisms through which skin pH impacts dermatologic pathologies. Furthermore, we highlight the promising potential of pH-targeted therapies for advancing the management of skin conditions.

Wound pH-Modulating Strategies for Diabetic Wound Healing

Significance: Chronic diabetic wounds on the lower extremities (diabetic foot ulcers, DFU) are one of the most prevalent and life-threatening complications of diabetes, responsible for significant loss of quality of life and cost to the health care system. Available pharmacologic treatments fail to achieve complete healing in many patients. Recent studies and investigational treatments have highlighted the potential of modulating wound pH in DFU. Recent Advances: Data from in vitro, preclinical, and clinical studies highlight the role of pH in the pathophysiology of DFU, and topical administration of pH-lowering agents have shown promise as a therapeutic strategy for diabetic wounds. In this critical review, we describe the role of pH in DFU pathophysiology and present selected low-molecular-weight and hydrogel-based pH-modulating systems for wound healing and infection control in diabetic wounds. Critical Issues: The molecular mechanisms leading to pH alterations in diabetic wounds are complex and may differ between in vitro models, animal models of diabetes, and the human pathophysiology. Wound pH-lowering bandages for DFU therapy must be tested in established animal models of diabetic wound healing and patients with diabetes to establish a comprehensive benefit-risk profile. Future Directions: As our understanding of the role of pH in the pathophysiology of diabetic wounds is deepening, new treatments for this therapeutic target are being developed and will be tested in preclinical and clinical studies. These therapeutic systems will establish a target product profile for pH-lowering treatments such as an optimal pH profile for each wound healing stage. Thus, controlling wound bed pH could become a powerful tool to accelerate chronic diabetic wound healing.

Silicone dressing combined with topical oxygen therapy alleviates incontinence-associated dermatitis via NF-κB p65/STAT1 signaling pathway

BACKGROUND

Incontinence-associated dermatitis (IAD) is a tough problem in clinical settings, not only increasing the risk of complications like catheter-related urinary tract infections and pressure ulcers in elderly and critically ill patients, but also prolonging hospital stays, raising hospital costs, and possibly leading to medical disputes. This study is aimed to evaluate the therapeutic effect of silicone dressing combined with topical oxygen therapy on IAD in a rat model.

METHODS

An IAD rat model induced by synthetic urine with trypsin was established. Hematoxylin & eosin staining was carried out to examine skin histology. Using immunofluorescence, the microvessel density in the affected skin tissues was determined. ELISA was performed to measure the concentrations of inflammatory cytokines and angiogenic factors in serum. The mRNA expression of EGF, PDGF, and VEGF was detected via qRT-PCR. Western blotting was employed to determine NF-κB p65/STAT1 pathway-related protein levels.

RESULTS

Compared to single therapy, silicone dressing combined with topical oxygen therapy could significantly reduce the severity of IAD, improve skin histology, inhibit inflammation, and promote angiogenesis in IAD rat models. Additionally, the results showed that relatively speaking, the combined therapy suppressed the NF-κB p65/STAT1 signaling pathway more effectively.

CONCLUSION

These findings indicated that silicone dressing combined with topical oxygen therapy can alleviate IAD through promoting wound healing and inhibiting inflammation via NF-κB p65/STAT1 signaling pathway in a rat model, which provided a theoretical basis for the prevention and treatment of IAD in clinic.

Importance of Stratum Corneum Acidification to Restore Skin Barrier Function in Eczematous Diseases

Skin barrier function relies on three essential components: stratum corneum (SC) lipids, natural moisturizing factors (NMFs), and the acidic pH of the SC surface. Three endogenous pathways contribute to acidity: free fatty acids from phospholipids, trans-urocanic acid from filaggrin (FLG), and the sodium-proton antiporter (NHE1) activity. An acidic SC environment boosts the activity of enzymes to produce ceramides, which are vital for skin health. Conversely, an elevated pH can lead to increased skin infections, reduced lipid-processing enzyme activity, impaired permeability barrier recovery, and compromised integrity and cohesion of the SC due to increased serine protease (SP) activity. Elevated SC pH is observed in neonatal, aged, and inflamed skin. In atopic dermatitis (AD), it results from decreased NMF due to reduced FLG degradation, decreased fatty acids from reduced lamellar body secretion, and reduced lactic acid due to decreased sweating. Moreover, the imbalance between SP and SP inhibitors disrupts barrier homeostasis. However, acidifying the SC can help restore balance and reduce SP activity. Acidic water bathing has been found to be safe and effective for AD. In three different AD murine models, SC acidification prevented the progression of AD to respiratory allergies. In aging skin, a decrease in NHE1 leads to an increased skin pH. Mild acidic skin care products or moisturizers containing NHE1 activators can normalize skin pH and improve barrier function. In conclusion, maintaining the acidity of the SC is crucial for healthy skin barrier function, leading to significant benefits for various skin conditions, such as AD and aging-related skin issues.

The Effects of Incontinence Pad Application on Loaded Skin With Reference to Biophysical and Biochemical Parameters: An Exploratory Cohort Study Using a Repeated-Measures Design

PURPOSE

The purpose of this study was to evaluate temporal changes in skin responses following exposure to moisture alone or moisture in combination with mechanical loading.

DESIGN

Comparison cohort with a repeated-measures design.

SUBJECTS AND SETTINGS

The sample comprised 12 healthy volunteers. Participants were purposely sampled from 2 different age groups; half were 32 to 39 years old and half were 50 to 62 years old. Participants identified as White, Black, or mixed; 83% (n = 10) identified as White; 8 (67%) were female.

METHODS

Four sites at the sacrum were challenged with the application of specimens taken from 2 absorbent products; the pad specimens were applied dry or saturated with synthetic urine (SU; pH = 8); a further site from the sacral skin was also selected and used as a control. Skin assessments were performed at different points in time: (1) 60 minutes after exposure to dry or SU-saturated pad specimens; (2) 60 minutes after exposure to pads and mechanical loading (application of pressure in the form of 45°C high sitting); and (3) 30 minutes after removal of all pads (recovery period). Outcome measures were transepidermal water loss (TEWL), stratum corneum (SC) hydration, erythema, pH, and skin inflammatory biomarkers measured at each of the time points described earlier.

RESULTS

The control site and those exposed to dry pads showed minimal time-dependent changes irrespective of the parameter investigated. In contrast, significant increases in TEWL (P = .0000007) and SC hydration responses (P = .0000007) were detected at the sites under absorbent pad specimens after saturation with SU (exposure to moisture). In some participants, TEWL and SC hydration parameters were significantly higher during pressure application. Skin pH remained in the mildly acidic range throughout the test session, and no consistent trends were observed with erythema. Skin inflammatory biomarkers also exhibited considerable variability across participants; none changed significantly over time. Significant differences (P = .02) were also detected following the exposure of moisture in combination with pressure.

CONCLUSION

We evaluated an array of parameters to identify changes following skin exposure to 2 absorbent pads in the presence and absence of SU and mechanical loading. Analysis revealed changes in skin barrier properties in the presence of moisture and/or pressure. This observation suggests a need for frequent pad changing as well as periods of skin off-loading to protect the skin health of individuals with incontinence.

Carbon dioxide foam bubbles enhance skin penetration through the stratum corneum layer with mechanical mechanism

Topical skin formulations often include penetration enhancers that interact with the outer stratum corneum (SC) layer to chemically enhance diffusion. Alternatively, penetration can be mechanically enhanced with simple rubbing in the presence of solid particles sometimes included to exfoliate the top layers of the SC. Our goal was to evaluate micron-sized carbon dioxide bubbles included in a foamed moisturizing formulation as a mechanical penetration enhancement strategy. We show that moisturizing foam bubbles cause an increase in SC formulation penetration using both mechanical and spectroscopic characterization. Our results suggest viscous liquid film drainage between coalescing gaseous bubbles creates local regions of increased hydrodynamic pressure in the foam liquid layer adjacent to the SC surface that enhances treatment penetration. An SC molecular diffusion model is used to rationalize the observed behavior. The findings indicate marked increased levels of treatment concentration in the SC at 2 h and that persists to 18 h after exposure, far exceeding non-foamed treatments. The study suggests an alternate strategy for increasing formulation penetration with a non-chemical mechanism.

Five dimensions of cleansing: A holistic view on the facets and importance of skin cleansing

Cleansing is an important human ritual practised for hygiene, well-being and relaxation over centuries. As part of body care it is often taken for granted, yet its relevance cannot be underestimated. Although cleansing the skin may seem trivial to some, it is accepted, that this fundamental function of skin cleansing products is highly complex, diverse and crucial for a variety of reasons in the personal, public, healthcare and dermatological settings. Employing a comprehensive and strategic approach in viewing cleansing and its rituals, supports innovation, understanding and development. Apart from being a fundamental function, as far as we know, there is no comprehensive presentation of skin cleansing with all its effects besides 'removing dirt'. To our knowledge, comprehensive analyses on the multi-dimensional facets of skin cleansing are either rare or not published. Against this background, we examine the importance of cleansing in terms of function, relevance and concepts. First, the key functions and efficacies of skin cleansing were investigated by literature research. Based on this survey, the functions were analysed, sorted and merged and a novel approach to skin cleansing 'dimensions' was developed. Herewith, we took into consideration the evolution of skin cleansing in terms of concept evolution, complexity and testing methods for cleansing products and their claims. Several multi-dimensional functions of skin cleansing were identified and then established into five skin cleansing dimensions, namely: hygienic and medical importance; socio-cultural and interpersonal relevance; mood, emotion and well-being; cosmetic and aesthetic function; corneobiological interactions. It became obvious, that these five dimensions with their corresponding 11 sub-dimensions, are influenced by each other throughout history by culture and society, technical progress, scientific knowledge and consumer trends. This article presents the enormous complexity of skin cleansing. Skin cleansing has evolved from basic care up to a highly complex and diverse cosmetic product category in terms of technology, efficacy and usage routine(s). In view of future challenges, such as the effects of climate and associated lifestyle changes, the development of skin cleansing will remain an exciting and important topic and thus will finally, again, further increase the complexity of skin cleansing itself.

Nanostructured Lipid Carriers Enriched Hydrogels for Skin Topical Administration of Quercetin and Omega-3 Fatty Acid

Chronic skin exposure to external hostile agents (e.g., UV radiation, microorganisms, and oxidizing chemicals) may increase oxidative stress, causing skin damage and aging. Because of their well-known skincare and protective benefits, quercetin (Q) and omega-3 fatty acids (ω3) have attracted the attention of the dermocosmetic and pharmaceutical sectors. However, both bioactives have inherent properties that limit their efficient skin delivery. Therefore, nanostructured lipid carriers (NLCs) and enriched PFC® hydrogels (HGs) have been developed as a dual-approach vehicle for Q and/or ω3 skin topical administration to improve bioactives' stability and skin permeation. Two NLC formulations were prepared with the same lipid composition but differing in surfactant composition (NLC1-soy lecithin and poloxamer 407; NLC2-Tween® 80 and dioctyl sodium sulfosuccinate (DOSS)), which have an impact on physicochemical properties and pharmaceutical and therapeutic performance. Despite both NLCs presenting high Q loading capacity, NLC2's physicochemical properties make them more suitable for topical skin administration and ensure longer colloidal stability. Additionally, NLC2 demonstrated a more sustained Q release, indicating higher bioactive storage while improving permeability. The occlusive effect of NLCs-enriched HGs also has a positive impact on skin permeability. Q-loaded NLC2, with or without ω3, -enriched HGs demonstrated efficacy as antioxidant and photoprotective formulations as well as effective reduction in S. aureus growth, indicating that they constitute a promising approach for topical skin administration to prevent skin aging and other damaging cutaneous processes.

Association Between Skin Acid Mantle, Natural Moisturizing Factors, and Antibacterial Activity Against S. aureus in the Stratum Corneum

Purpose

The skin has evolved a system to prevent pathogenic microorganism colonization and infection. This study examined the role of natural moisturizing factors (NMFs) and skin pH on Staphylococcus aureus (S. aureus) growth and colonization on the human stratum corneum (SC).

Study Population and Methods

A survey study with 82 female participants was performed. Participants maintained their daily hygiene routine, except for refraining from using leave-on products on their forearms on the day of the test. Skin sampling was performed using adhesive tapes. An ex vivo method was developed to study the viability and growth of S. aureus on human SC sampled from normal skin. NMFs, including pyrrolidone carboxylic acid (PCA), urocanic acid (UCA), histidine, and proline in SC samples, were measured by liquid chromatography with tandem mass spectrometry. The impact of PCA and UCA on S. aureus growth and metabolic activity was measured by optical density and isothermal microcalorimetry, respectively.

Results

Heterogeneity of S. aureus viability on human SC samples was observed. Skin pH showed a significant negative association (p<0.05) with SC antibacterial activity in the ex vivo assay. One unit of skin pH decrease corresponded to 68.1% of S. aureus cell death. The levels of PCA and histidine were significantly negatively associated (p<0.05) with skin pH. The addition of 5 mM and 10 mM PCA significantly inhibited S. aureus growth by approximately 25% at 20 hours and reduced its metabolic activity in vitro.

Conclusion

The results indicate that PCA, one of the NMFs in human skin, plays an important role in regulating the human skin acid mantle in vivo and contributes to antibacterial activity against S. aureus.

Hydrogel Containing Silibinin-Loaded Pomegranate Oil-Based Nanocapsules for Cutaneous Application: In Vitro Safety Investigation and Human Skin Biometry and Permeation Studies

In previous studies, we developed a hydrogel formulation containing silibinin-loaded pomegranate oil nanocapsules (HG-NCSB) that had improved in vivo anti-inflammatory action in comparison to non-encapsulated silibinin. To determine skin safety and whether the nanoencapsulation influences silibinin skin permeation, NCSB skin cytotoxicity, HG-NCSB permeation in human skin, and a biometric study with healthy volunteers were conducted. The formulation of nanocapsules was prepared by the preformed polymer method while the HG-NCSB was obtained by thickening the suspension of nanocarriers with gellan gum. The cytotoxicity and phototoxicity of nanocapsules were assessed in Keratinocytes (HaCaT) and fibroblast (HFF-1) using the MTT assay. The hydrogels were characterized regarding the rheological, occlusive, and bioadhesive properties, and silibinin permeation profile in human skin. The clinical safety of HG-NCSB was determined by cutaneous biometry in healthy human volunteers. NCSB yielded better cytotoxicity results than the blank nanocapsules (NCPO). NCSB did not cause photocytotoxicity, while NCPO and the non-encapsulated substances (SB and pomegranate oil) were phototoxic. The semisolids presented non-Newtonian pseudoplastic flow, adequate bioadhesiveness, and low occlusive potential. The skin permeation demonstrated that HG-NCSB retained a higher SB amount in the outermost layers than HG-SB. In addition, HG-SB reached the receptor medium and had a superior concentration of SB in the dermis layer. In the biometry assay, there was no significant cutaneous alteration after the administration of any of the HGs. Nanoencapsulation promoted greater SB retention in the skin, averted percutaneous absorption, and made the topical use of SB and pomegranate oil safer.

How do the skin barrier and microbiome adapt to the extra-uterine environment after birth? Implications for the clinical practice

The multiple protective functions of the skin derive from the interactions between epithelial skin and immune cells as well as the commensal microbiota. Developed in the last trimester of intra-uterine life, the skin barrier adapts dynamically after birth. Specific differences in the structure and physiology have been disclosed between infant and adult skin. The stratum corneum of infants is thinner and structured by thicker corneocytes with a more anisotropic surface in comparison to adult skin. Lower levels of the natural moisturizing factor and its constituents, together with the increased protease activity in the epidermis result in dry baby skin and ongoing adaptation of the desquamation to the extra-uterine environment. Infant epidermis is characterized by an accelerated proliferation rate and clinically competent permeability barrier in term neonates, despite the higher baseline values of transepidermal water loss in infants. The skin surface of newborns is less acidic, which could increase susceptibility to diaper and atopic dermatitis. Immediately after birth, skin is colonized by commensal bacteria-a process dependent on the mode of delivery and of major importance for the maturation of the immune system. Skin bacterial diversity and dysbiosis have been related to different pathology such as atopic and seborrheic dermatitis. This paper focuses on the ongoing structural, functional and biochemical adaptation of the human skin barrier after birth. We discuss the interactions on the 'skin barrier/ microbiota/ immune system' axis and their role in the development of competent functional integrity of the epidermal barrier.

In search of the perfect tan: Chemical activity, biological effects, business considerations, and consumer implications of dihydroxyacetone sunless tanning products

As the desire and popularity of a tanned appearance continues, the social effects of UV-free tanning are becoming more important. Dihydroxyacetone (DHA) has seen extensive use as the main tanning agent in sunless tanners. The DHA-induced tan is a result of brown melanoidins formed by a non-enzymatic Maillard reaction between DHA and amino acid species found in the stratum corneum. DHA, thereby, provides a safer route to a tanned appearance compared with exposure to ultraviolet radiation. However, DHA is a highly reactive molecule, posing a multitude of challenges for potential product formulations. With their increased use, the safety considerations of topically applied DHA tanners have been investigated. Many different vehicles have been used for topical delivery of DHA, and they are becoming increasingly multifunctional. This review provides a holistic overview of dihydroxyacetone sunless tanning products.

Natural products in cosmetics

The global cosmetics market reached US$500 billion in 2017 and is expected to exceed US$800 billion by 2023, at around a 7% annual growth rate. The cosmetics industry is emerging as one of the fastest-growing industries of the past decade. Data shows that the Chinese cosmetics market was US$60 billion in 2021. It is expected to be the world's number one consumer cosmetics market by 2050, with a size of approximately US$450 billion. The influence of social media and the internet has raised awareness of the risks associated with the usage of many chemicals in cosmetics and the health benefits of natural products derived from plants and other natural resources. As a result, the cosmetic industry is now paying more attention to natural products. The present review focus on the possible applications of natural products from various biological sources in skin care cosmetics, including topical care products, fragrances, moisturizers, UV protective, and anti-wrinkle products. In addition, the mechanisms of targets for evaluation of active ingredients in cosmetics and the possible benefits of these bioactive compounds in rejuvenation and health, and their potential role in cosmetics are also discussed.

Influence of Acidic pH on Wound Healing In Vivo: A Novel Perspective for Wound Treatment

There has been little understanding of acidification functionality in wound healing, highlighting the need to study the efficacy of wound acidification on wound closure and cellular activity in non-infected wounds. This study is focused on establishing the healing potential of wound acidification in non-infected wounds. Acidic buffers, constituting either phosphoric or citric acid, were employed to modify the physiological pH of non-infected full-thickness excisional murine wounds. Acidification of the wound by acidic buffers was found to be an effective strategy to improve wound healing. A significant improvement in wound healing parameters was observed as early as 2 days post-treatment with acidic buffers compared to controls, with faster rate of epithelialization, wound closure and higher levels of collagen at day 7. pH is shown to play a role in mediating the rate of wound healing, with acidic buffers formulated at pH 4 observed to stimulate faster recovery of wounded tissues than pH 6 buffers. Our study shows the importance of maintaining an acidic wound microenvironment at pH 4, which could be a potential therapeutic strategy for wound management.

Evaluation of Skin Irritation of Acids Commonly Used in Cleaners in 3D-Reconstructed Human Epidermis Model, KeraSkinTM

Cleaners such as dishwashing liquids contain various chemicals that cause skin damage. Alkaline agents used in cleaners alter the lipid composition of the skin and damage the skin barrier. However, little is known about the effects of acids used in cleaners on the skin. Here, we investigated the effects of acidic pH on the skin and evaluated the skin irritation of acids commonly used in cleaners with a 3D-reconstructed human epidermis model, KeraSkin^TM, according to OECD TG439. First, to examine the effects of acidic pH, we evaluated the skin irritation of citrate buffers (0.1 M, McIlvaine buffer) prepared in a wide pH range (pH 1.5-6.0). Surprisingly, cell viability was not significantly affected even at pH 1.5, reflecting that the acidity alone may not be sufficient to induce skin irritation. Even after longer exposure (180 min), the cell viability was not reduced below 50%, a cutoff to determine an irritant. To examine the effect of the anionic part, several organic acids used in cleaners (citric acid, glycolic acid, lactic acid, malic acid, and succinic acid) were examined. These organic acids also failed to reduce viability at 0.1 M. However, at 1 M, most of the acids tested, except lactic acid, were determined to be skin irritants. Histology further supported the skin irritancy of acids at 1 M. Similarly, inorganic acids (hydrogen bromide, hydrogen chloride, nitric acid, and sulfuric acid) were determined to be irritants only at 1 M. In the case of alkaline agents, pH and concentrations were also important factors to determine the skin irritancy, although the epidermal structure and lipids were more damaged than acids. Collectively, we demonstrated that both the pH and concentration are important factors for the skin irritancy of acids, shedding an important insight into the mechanism of skin irritation.

The effect of pH-compatible cleansing cloths on skin pH and the development of pressure ulcers

AIM

Skin care plays an important role in the prevention of the development of pressure ulcers. The aim of this study was to determine the effect of skincare with a body pH-compatible cleansing cloth on the development time of pressure ulcers and on skin pH.

METHODS

This experimental research was conducted with 156 patients hospitalized in intensive care clinics of a state hospital between September 2019 and 2020. The sample was calculated with a power of 80% and a significance level of 0.05 (α error) and as a result, 78 elderly patients formed the intervention group and another 78 elderly patients made up the control group. Data were collected using the Elderly Information Form, Braden Risk Assessment Scale, Pressure Ulcer Staging Tool and Skin pH Measurement Form. The pre- and post-care skin pH of both groups was measured with a skin pH meter. P < 0.05 was considered statistically significant.

RESULTS

The average development time for pressure ulcers was 14.9 days in the control group, 18.9 days in the intervention group and the difference was not statistically significant (p > 0.05). Skin pH decreased in the intervention group after the skin care routine was applied, whereas it increased in the control group.

CONCLUSION

It can be said that care of one's skin with a body pH-compatible cleansing cloth has a positive effect on the development time of pressure ulcers and also positively changes the skin pH to acidic.

Impact of solvent dry down, vehicle pH and slowly reversible keratin binding on skin penetration of cosmetic relevant compounds: I. Liquids

To measure progress and evaluate performance of the newest UB/UC/P&G skin penetration model we simulated an 18-compound subset of finite dose in vitro human skin permeation data taken from a solvent-deposition study of cosmetic-relevant compounds (Hewitt et al., J. Appl. Toxicol. 2019, 1-13). The recent model extension involved slowly reversible binding of solutes to stratum corneum keratins. The selected subset was compounds that are liquid at skin temperature. This set was chosen to distinguish between slow binding and slow dissolution effects that impact solid phase compounds. To adequately simulate the physical experiments there was a need to adjust the evaporation mass transfer coefficient to better represent the diffusion cell system employed in the study. After this adjustment the model successfully predicted both dermal delivery and skin surface distribution of 12 of the 18 compounds. Exceptions involved compounds that were cysteine-reactive, highly water-soluble or highly ionized in the dose solution. Slow binding to keratin, as presently parameterized, was shown to significantly modify the stratum corneum kinetics and diffusion lag times, but not the ultimate disposition, of the more lipophilic compounds in the dataset. Recommendations for further improvement of both modeling methods and experimental design are offered.

A Mechanistic Bayesian Inferential Workflow for Estimation of In Vivo Skin Permeation from In Vitro Measurements

Computational models can play an integral role in the chemical risk assessment of dermatological products. However, a limitation on the ability of mathematical models to extrapolate from in vitro measurements to in human predictions arises from context-dependence: modeling assumptions made in one setting may not carry over to another scenario. Mechanistic models of dermal absorption relate the skin penetration kinetics of permeants to their partitioning and diffusion across elementary sub-compartments of the skin. This endows them with a flexibility through which specific model components can be adjusted to better reflect dermal absorption in contexts that differ from the in vitro setting, while keeping fixed any context-invariant parameters that remain unchanged in the two scenarios. This paper presents a workflow for predicting in vivo dermal absorption by integrating a mechanistic model of skin penetration with in vitro permeation test (IVPT) measurements. A Bayesian approach is adopted to infer a joint posterior distribution of context-invariant model parameters. By populating the model with samples of context-invariant parameters from this distribution and adjusting context-dependent parameters to suit the in vivo setting, simulations of the model yield estimates of the likely range of in vivo dermal absorption given the IVPT data. This workflow is applied to five compounds previously tested in vivo. In each case, the range of in vivo predictions encompassed the range observed experimentally. These studies demonstrate that the proposed workflow enables the derivation of mechanistically derived upper bounds on dermal absorption for the purposes of chemical risk assessment.

Development and Evaluation of an In Silico Dermal Absorption Model Relevant for Children

The higher skin surface area to body weight ratio in children and the prematurity of skin in neonates may lead to higher chemical exposure as compared to adults. The objectives of this study were: (i) to provide a comprehensive review of the age-dependent anatomical and physiological changes in pediatric skin, and (ii) to construct and evaluate an age-dependent pediatric dermal absorption model. A comprehensive review was conducted to gather data quantifying the differences in the anatomy and physiology of child and adult skin. Maturation functions were developed for model parameters that were found to be age-dependent. A pediatric dermal absorption model was constructed by updating a MoBi implementation of the Dancik et al. 2013 skin permeation model with these maturation functions. Using a workflow for adult-to-child model extrapolation, the predictive performance of the model was evaluated by comparing its predicted rates of flux of diamorphine, phenobarbital and buprenorphine against experimental observations using neonatal skin. For diamorphine and phenobarbital, the model provided reasonable predictions. The ratios of predicted:observed flux in neonates for diamorphine ranged from 0.55 to 1.40. For phenobarbital, the ratios ranged from 0.93 to 1.26. For buprenorphine, the model showed acceptable predictive performance. Overall, the physiologically based pediatric dermal absorption model demonstrated satisfactory prediction accuracy. The prediction of dermal absorption in neonates using a model-based approach will be useful for both drug development and human health risk assessment.

Oxygen, pH, Lactate, and Metabolism-How Old Knowledge and New Insights Might Be Combined for New Wound Treatment

Over time, we have come to recognize a very complex network of physiological changes enabling wound healing. An immunological process enables the body to distinguish damaged cells and begin a cleaning mechanism by separating damaged proteins and cells with matrix metalloproteinases, a complement reaction, and free radicals. A wide variety of cell functions help to rebuild new tissue, dependent on energy provision and oxygen supply. Like in an optimized “bio-reactor,” disturbance can lead to prolonged healing. One of the earliest investigated local factors is the pH of wounds, studied in close relation to the local perfusion, oxygen tension, and lactate concentration. Granulation tissue with the wrong pH can hinder fibroblast and keratinocyte division and proliferation, as well as skin graft takes. Methods for influencing the pH have been tested, such as occlusion and acidification by the topical application of acidic media. In most trials, this has not changed the wound’s pH to an acidic one, but it has reduced the strong alkalinity of deeper or chronic wounds. Energy provision is essential for all repair processes. New insights into the metabolism of cells have changed the definition of lactate from a waste product to an indispensable energy provider in normoxic and hypoxic conditions. Neovascularization depends on oxygen provision and lactate, signaling hypoxic conditions even under normoxic conditions. An appropriate pH is necessary for successful skin grafting; hypoxia can change the pH of wounds. This review describes the close interconnections between the local lactate levels, metabolism, healing mechanisms, and pH. Furthermore, it analyzes and evaluates the different possible ways to support metabolism, such as lactate enhancement and pH adjustment. The aim of wound treatment must be the optimization of all these components. Therefore, the role of lactate and its influence on wound healing in acute and chronic wounds will be assessed.

Influence of age, sex, body condition score, rectal temperature, anatomical location and hair on skin pH in dogs

BACKGROUND

Physiological skin pH levels are well-documented in human medicine, and assessment of variations may be important in assessing the efficacy of wound healing. By contrast, physiological skin pH levels in dogs are sparsely described.

HYPOTHESIS/OBJECTIVES

To determine the pH of intact skin in healthy dogs and to study the influence of different physiological factors on the pH level of canine skin.

ANIMALS

Seventy-seven client-owned dogs of various breeds, age and sex.

METHODS AND MATERIALS

A prospective study was designed and the pH of intact skin was measured at the concave surface of both pinnae, and in both axillary and inguinal regions. For each location, the colour and density of the hairs also was recorded. Each dog's rectal body temperature and body condition scores also were determined.

RESULTS

The skin pH in dogs <12 weeks of age was significantly lower (3.97-5.70) than in older dogs (4.40-8.18) (P < 0.001). In dogs >12 weeks of age, skin pH was significantly lower in the inguinal regions compared to the pinnae (P = 0.008), and female dogs had a significantly lower skin pH in the inguinal regions than male dogs (P = 0.043). Pinnae covered with light-coloured hair had a lower skin pH than those with dark-coloured hair (P = 0.04). No significant differences were found between dogs with different body condition scores, body temperatures or differences in hair density.

CONCLUSIONS AND CLINICAL RELEVANCE

The pH of intact healthy skin is lower in puppies of <12 weeks of age. Regional differences of body location also were seen which were variably affected by hair colour and sex. A baseline assessment of skin pH in healthy dogs is important for future studies of disease and wound healing.

Omega-3- and Resveratrol-Loaded Lipid Nanosystems for Potential Use as Topical Formulations in Autoimmune, Inflammatory, and Cancerous Skin Diseases

Resveratrol (RSV) and omega 3 (ω₃), because of their biological favorable properties, have become subjects of interest for researchers in dermocosmetic and pharmaceutical industries; however, these bioactives present technological limitations that hinder their effective delivery to the target skin layer. To overcome the stability and skin permeation limitations of free bioactives, this work proposes a combined strategy involving two different lipid nanosystems (liposomes and lipid nanoparticles) that include ω₃ in their lipid matrix. Additionaly, RSV is only encapsulated in liposomes that provid an adequate amphiphilic environment. Each formulation is thoroughly characterized regarding their physical–chemical properties. Subsequently, the therapeutic performance of the lipid nanosystems is evaluated based on their protective roles against lipid peroxidation, as well as inhibition of cicloxygenase (COX) and nitric oxid (NO) production in the RWA264.7 cell line. Finally, the lipid nanosystems are incorporated in hydrogel to allow their topical administration, then rheology, occlusion, and RSV release–diffusion assays are performed. Lipid nanoparticles provide occlusive effects at the skin surface. Liposomes provide sustained RSV release and their flexibility conferred by edge activator components enhances RSV diffusion, which is required to reach NO production cells and COX cell membrane enzymes. Overall, the inclusion of both lipid nanosystems in the same semisolid base constitutes a promising strategy for autoimmune, inflammatory, and cancerous skin diseases.

Towards Optimal pH of the Skin and Topical Formulations: From the Current State of the Art to Tailored Products

Acidic pH of the skin surface has been recognized as a regulating factor for the maintenance of the stratum corneum homeostasis and barrier permeability. The most important functions of acidic pH seem to be related to the keratinocyte differentiation process, the formation and function of epidermal lipids and the corneocyte lipid envelope, the maintenance of the skin microbiome and, consequently, skin disturbances and diseases. As acknowledged extrinsic factors that affect skin pH, topically applied products could contribute to skin health maintenance via skin pH value control. The obtained knowledge on skins’ pH could be used in the formulation of more effective topical products, which would add to the development of the so-called products ‘for skin health maintenance’. There is a high level of agreement that topical products should be acidified and possess pH in the range of 4 to 6. However, formulators, dermatologists and consumers would benefit from some more precise guidance concerning favorable products pH values and the selection of cosmetic ingredients which could be responsible for acidification, together with a more extensive understanding of the mechanisms underlaying the process of skin acidification by topical products.

How to control interactions of cellulose-based biomaterials with skin: the role of acidity in the contact area

Being able to control the interactions of biomaterials with living tissues and skin is highly desirable for many biomedical applications. This is particularly the case for cellulose-based materials which provide one of the most versatile platforms for tissue engineering due to their strength, biocompatibility and abundance. Achieving such control, however, requires detailed molecular-level knowledge of the dominant interaction mechanisms. Here, we employed both biased and unbiased atomic-scale molecular dynamics simulations to explore how cellulose crystals interact with model stratum corneum bilayers, ternary mixtures of ceramides, cholesterol, and free fatty acids. Our findings show that acidity in the contact area directly affects binding between cellulose and the stratum corneum bilayer: Protonation of free fatty acids in the bilayer promotes attractive cellulose-bilayer interactions. We identified two major factors that control the cellulose-skin interactions: (i) the electrostatic repulsion between a cellulose crystal and the charged (anionic due to deprotonated fatty acids) surface of a stratum corneum bilayer and (ii) the cellulose-stratum corneum hydrogen bonding. When less than half of the fatty acids in the bilayer are protonated, the first factor dominates and there is no binding to skin. At a larger degree of fatty acid protonation the cellulose-stratum corneum hydrogen bonding prevails yielding a tight binding. Remarkably, we found that ceramide molecules are the key component in hydrogen bonding with cellulose. Overall, our findings highlight the critical role of fatty acid protonation in biomaterial-stratum corneum interactions and can be used for optimizing the surface properties of cellulose-based materials aimed at biomedical applications such as wound dressings.

Design, fabrication, and characterisation of a silicon microneedle array for transdermal therapeutic delivery using a single step wet etch process

The fabrication of silicon in-plane microneedle arrays from a simple single wet etch step is presented. The characteristic 54.7° sidewall etch angle obtained via KOH etching of (100) orientation silicon wafers has been used to create a novel microneedle design. The KOH simultaneously etches both the front and back sides of the wafer to produce V shaped grooves, that intersect to form a sharp pyramidal six-sided microneedle tip. This method allows fabrication of solid microneedles with different geometries to determine the optimal microneedle length and width for effective penetration and minimally invasive drug delivery. A modified grooved microneedle design can also be used to create a hollow microneedle, via bonding of two grooved microneedles together, creating an enclosed hollow channel. The microneedle arrays developed, effectively penetrate the skin without significant indentation, thereby enabling effective delivery of active ingredients via either a poke and patch application using solid microneedles or direct injection using hollow microneedles. This simple, scalable and cost effective method utilises KOH to etch the silicon wafer in-plane, allowing microneedles with variable length of several mm to be fabricated, as opposed to out-of-plane MNs, which are geometrically restricted to dimensions less than the thickness of the wafer. These microneedle arrays have been used to demonstrate effective delivery of insulin and hyaluronic acid into the skin.

An Extract from Ficus carica Cell Cultures Works as an Anti-Stress Ingredient for the Skin

Psychological stress activates catecholamine production, determines oxidation processes, and alters the lipid barrier functions in the skin. Scientific evidence associated with the detoxifying effect of fruits and vegetables, the growing awareness of the long-term issues related to the use of chemical-filled cosmetics, the aging of the population, and the increase in living standards are the factors responsible for the growth of food-derived ingredients in the cosmetics market. A Ficus carica cell suspension culture extract (FcHEx) was tested in vitro (on keratinocytes cells) and in vivo to evaluate its ability to manage the stress-hormone-induced damage in skin. The FcHEx reduced the epinephrine (-43% and -24% at the concentrations of 0.002% and 0.006%, respectively), interleukin 6 (-38% and -36% at the concentrations of 0.002% and 0.006%, respectively), lipid peroxide (-25%), and protein carbonylation (-50%) productions; FcHEx also induced ceramide synthesis (+150%) and ameliorated the lipid barrier performance. The in vivo experiments confirmed the in vitro test results. Transepidermal water loss (TEWL; -12.2%), sebum flow (-46.6% after two weeks and -73.8% after four weeks; on the forehead -56.4% after two weeks and -80.1% after four weeks), and skin lightness (+1.9% after two weeks and +2.7% after four weeks) defined the extract's effects on the skin barrier. The extract of the Ficus carica cell suspension cultures reduced the transepidermal water loss, the sebum production, the desquamation, and facial skin turning to a pale color from acute stress, suggesting its role as an ingredient to fight the signs of psychological stress in the skin.

Acidic pH Is Required for the Multilamellar Assembly of Skin Barrier Lipids In Vitro

Lipid membrane remodeling belongs to the most fundamental processes in the body. The skin barrier lipids, which are ceramide dominant and highly rigid, must attain an unusual multilamellar nanostructure with long periodicity to restrict water loss and prevent the entry of potentially harmful environmental factors. Our data suggest that the skin acid mantle, apart from regulating enzyme activities and keeping away pathogens, may also be a prerequisite for the multilamellar assembly of the skin barrier lipids. Atomic force microscopy on monolayers composed of synthetic or human stratum corneum lipids showed multilayer formation (approximately 10-nm step height) in an acidic but not in a neutral environment. X-ray diffraction, Fourier transform infrared spectroscopy, and permeability studies showed markedly altered lipid nanostructure and increased water loss at neutral pH compared with that at acidic pH. These findings are consistent with the data on the altered organization of skin lipids and increased transepidermal water loss under conditions such as inadequate skin acidification, for example, in neonates, the elderly, and patients with atopic dermatitis.

Pruritus in psoriasis and atopic dermatitis: current treatments and new perspectives

Psoriasis and atopic dermatitis (AD) are two common chronic inflammatory skin diseases. Although showing different etiology and clinical manifestations, patients with either disease suffer from low health-related quality of life due to pruritus (dermal itch). Recent studies have revealed that more than 85% of psoriasis patients suffer from pruritus, and it is also the dominating symptom of AD. However, as this is a non-life treating symptom, it was partly neglected for years. In this review, we focus on current findings as well as the impact and potential treatments of pruritus in these two skin diseases. We first distinguish the type of itch based on involved mediators and modulators. This clear delineation between the types of pruritus based on involved receptors and pathways allows for precise treatment. In addition, insights into recent clinical trials aimed to alleviate pruritus by targeting these receptors are presented. We also report about novel advances in combinatorial treatments, dedicated to the type of pruritus linked to a causal disease. Altogether, we suggest that only a focused treatment tailored to the primary disease and the underlying molecular signals will provide fast and sustained relief of pruritus associated with psoriasis or AD.

A review of clothing microbiology: the history of clothing and the role of microbes in textiles

Humans have worn clothing for thousands of years, and since its invention, clothing has evolved from its simple utilitarian function for survival to become an integral part of society. While much consideration has been given to the broad environmental impacts of the textile and laundering industries, little is known about the impact wearing clothing has had on the human microbiome, particularly that of the skin, despite our long history with clothing. This review discusses the history of clothing and the evolution of textiles, what is and is not known about microbial persistence on and degradation of various fibres, and what opportunities for the industrial and environmental application of clothing microbiology exist for the future.

A Novel Method for the Evaluation of the Long-Term Stability of Cream Formulations Containing Natural Oils

This aim of this study is to prepare four novel oil-in-water creams from 100% naturally sourced oil ingredients such as jojoba, baobab and coconut oil, and compare the effect of the oils on the physico-chemical properties of the creams and their short- and long-term stability. Four 100 g each oil-in-water active containing creams and their controls (without the active ingredient) were formulated and stored in eight separate glass jars. The short-term stability of the creams was assessed via phase separation resistance, pH, microscopic size analysis, globule size, zeta potential, conductivity and microbial challenge evaluation after 8, 14 and 28 days, under three different storage temperature conditions (4 °C, 25 °C and 40 °C) and at ambient relative humidity. Model creams IA, IB, IIA, and IIB containing 1:1 of jojoba and baobab oil mix, all had good shelf-life or stability at the end of the 28 days after storage at 4 °C, 25 °C and 40 °C, compared to models IIIA, IVA and pairs. The long-term stability of creams stored at 25 °C for 28 days, was subsequently assessed using the Dynamic Vapor Sorption system. Model creams IB, IIB, IA and IIA showed the lowest percentage moisture loss or change in mass during a period of desorption steps. Therefore, the creams containing a mixture of jojoba and baobab oils are capable of retaining moisture easily for an extended period of time when compared to the creams containing jojoba and coconut oil or baobab and coconut oil combinations, thus they were proven to be the best products in terms of stability and quality. The stability ranking of the creams using the novel DVS method was in congruence with the results from the short-term stability experiments. This novel DVS method can, therefore, be generically applied in the cosmetic, food and pharmaceutical industries for the evaluation of the long-term stability of semisolids.

Non-ionic surfactant vesicles as a carrier system for dermal delivery of (+)-Catechin and their antioxidant effects

Numerous skin disorders and diseases are related to oxidative stress. The application of an antioxidant, serving as a strong defense agent against oxidation, is of great interest in dermatology yet remains challenging for delivery. This paper aimed to develop a niosome carrier system to deliver the antioxidant (+) Catechin into the skin. (+) Catechin-loaded niosomes were prepared using film hydration technique and the physicochemical properties of drug-loaded niosomes were characterised and investigated by a series of in vitro and ex vivo studies. The optimised formulation displayed an acceptable size in nanoscale (204 nm), high drug entrapment efficiency (49%) and amorphous state of drug in niosomes. It was found that (+) Catechin-loaded niosomes could effectively prolong the drug release. Drug deposition in the viable layers of human skin was significantly enhanced when niosomal carriers were applied (p < 0.05). Compared to the pure drug, the niosomal formulation had a greater protective effect on the human skin fibroblasts (Fbs). This is consistent with the observation of internalisation of niosomes by Fbs which was concentration-, time- and temperature-dependent, via an energy-dependent process of endocytosis. The research highlighted that niosomes are potential topical carriers for dermal delivery of antioxidants in skin-care and pharmaceutical products.

Determination of the pH Gradient in Hair Follicles of Human Volunteers Using pH-Sensitive Melamine Formaldehyde-Pyranine Nile Blue Microparticles

Nanoparticles can be applied to the hair follicles, which can serve as reservoirs for triggered drug release. A valid measurement method for the determination of the pH within the hair follicle in vivo has not been shown yet. Here, melamine formaldehyde particles up to 9 µm in size were applied on 40 freshly plucked scalp hairs of eight individuals to determine the pH along the hair shaft down to the root area of the hair. For fluorescent pH indicators, pyranine and Nile blue were incorporated into the particles. Measurements were conducted using confocal laser scanning microscopy. A pH decay gradient could be found from the hair sheath towards the external hair shaft (p = 0.012) with pH values at the hair sheath of 6.63 ± 0.09, at the hair sheath end at 6.33 ± 0.11, and at the external hair shaft at 6.17 ± 0.09 (mean ± SE). The pH difference between the hair sheath end and the external hair shaft was found to be significant (p = 0.036). The results might be comparable with the pH within the hair follicle in vivo indicating a pH increase towards the hair root.

Nanomedicines to Treat Skin Pathologies with Natural Molecules

The skin and mucous membranes are subjected to many disorders and pathological conditions. Nature offers a wide range of molecules with antioxidant activity able to neutralize, at least in part, the formation of free radicals and therefore to counteract the phenomena of cellular aging. Since synthetic drugs for the treatment of skin diseases can induce resistance, it is particularly interesting to use compounds of plant origin, transporting them in pharmaceutical forms capable of controlling their release and absorption. This review provides an overview of new findings about the use of lipid-based nanosystems for the delivery of natural molecules useful on the topical treatment of skin disorders. Several natural molecules encapsulated in lipid nanosystems have been considered in the treatment of some skin pathologies or diseases. Particularly, the use of rosemary and eucalyptus essential oil, saffron derivatives, curcumin, eugenol, capsaicin, thymol and lycopene has been reported. The molecules have been alternatively encapsulated in viscous systems, such as the organogels, or in liquid systems, such as ethosomes, transferosomes, solid lipid nanoparticles and monoolein based dispersions thickened by inclusion in carbomer gels. The nanostructured forms have been in vitro and in vivo investigated for the treatment of skin disorders due to dehydration, inflammation, melanoma, wound healing, fungal infections or psoriasis. The data reported in the different studies have suggested that the cutaneous application of lipid nanosystems allows a deep interaction between lipid matrix and skin strata, promoting a prolonged release and efficacy of the loaded natural molecules. This review suggests that the application of natural molecules onto the skin by lipid-based nanosystems can provide numerous clinician benefits in dermatology and cosmetics.

Glucocerebrosidase: Functions in and Beyond the Lysosome

Glucocerebrosidase (GCase) is a retaining β-glucosidase with acid pH optimum metabolizing the glycosphingolipid glucosylceramide (GlcCer) to ceramide and glucose. Inherited deficiency of GCase causes the lysosomal storage disorder named Gaucher disease (GD). In GCase-deficient GD patients the accumulation of GlcCer in lysosomes of tissue macrophages is prominent. Based on the above, the key function of GCase as lysosomal hydrolase is well recognized, however it has become apparent that GCase fulfills in the human body at least one other key function beyond lysosomes. Crucially, GCase generates ceramides from GlcCer molecules in the outer part of the skin, a process essential for optimal skin barrier property and survival. This review covers the functions of GCase in and beyond lysosomes and also pays attention to the increasing insight in hitherto unexpected catalytic versatility of the enzyme.

Role of pH Value in Clinically Relevant Diagnosis

As a highly influential physiological factor, pH may be leveraged as a tool to diagnose physiological state. It may be especially suitable for diagnosing and assessing skin structure and wound status. Multiple innovative and elegant smart wound dressings combined with either pH sensors or drug control-released carriers have been extensively studied. Increasing our understanding of the role of pH value in clinically relevant diagnostics should assist clinicians and improve personal health management in the home. In this review, we summarized a number of articles and discussed the role of pH on the skin surface as well as the factors that influence skin pH and pH-relevant skin diseases, but also the relationship of skin pH to the wound healing process, including its influence on the activity of proteases, bacterial enterotoxin, and some antibacterial agents. A great number of papers discussing physiological pH value have been published in recent decades, far too many to be included in this review. Here, we have focused on the impact of pH on wounds and skin with an emphasis on clinically relevant diagnosis toward effective treatment. We have also summarized the differences in skin structure and wound care between adults and infants, noting that infants have fragile skin and poor skin barriers, which makes them more vulnerable to skin damage and compels particular care, especially for wounds.

The role of bacterial skin infections in atopic dermatitis: expert statement and review from the International Eczema Council Skin Infection Group

Patients with atopic dermatitis (AD) have an increased risk of bacterial skin infections, which cause significant morbidity and, if untreated, may become systemic. Staphylococcus aureus colonizes the skin of most patients with AD and is the most common organism to cause infections. Overt bacterial infection is easily recognized by the appearance of weeping lesions, honey‐coloured crusts and pustules. However, the wide variability in clinical presentation of bacterial infection in AD and the inherent features of AD – cutaneous erythema and warmth, oozing associated with oedema, and regional lymphadenopathy – overlap with those of infection, making clinical diagnosis challenging. Furthermore, some features may be masked because of anatomical site‐ and skin‐type‐specific features, and the high frequency of S. aureus colonization in AD makes positive skin swab culture of suspected infection unreliable as a diagnostic tool. The host mechanisms and microbial virulence factors that underlie S. aureus colonization and infection in AD are incompletely understood. The aim of this article is to present the latest evidence from animal and human studies, including recent microbiome research, to define the clinical features of bacterial infections in AD, and to summarize our current understanding of the host and bacterial factors that influence microbial colonization and virulence.

Polymeric Electrospun Fibrous Dressings for Topical Co-delivery of Acyclovir and Omega-3 Fatty Acids

Herpetic infections caused by Herpes simplex virus (HSV) are among the most common human infections, affecting more than two quarters of the world's population. The standard treatment for orofacial herpes is the administration of antiviral drugs, mainly acyclovir (ACV). However, current products are mostly based on semisolid formulations that have limited ability to promote drug skin penetration and tend to leak from the application site, thus showing reduced ability to sustain local drug residence. This work reports on the production of poly (ε-caprolactone) (PCL) fibrous matrices with ACV and omega-3 fatty acids (ω3) for application as dressings to the topical treatment of orofacial herpes. PCL fibrous matrices with the co-incorporated bioactive compounds were obtained by electrospinning and characterized regarding their morphology, chemical, physical, and mechanical properties. The potential use of the developed polymeric fibrous matrices for topical applications was evaluated by: (i) the release kinetics of the bioactive compounds; (ii) the occlusive factor of the fibrous mat; (iii) ACV skin permeation capacity; and (iv) the cytotoxicity in a keratinocyte cell line. PCL fibrous matrices loaded with the bioactive compounds presented a smooth morphology and a good balance between flexibility and hardness essential to be durable for handling, while having a desirable texture to be used comfortably. The fibrous mat also provided a sustained release of ACV during 96 h and improved the skin permeability of this drug (Kp = 0.00928 ± 0.000867 cm/h) presenting also high porosity (74%) and a water vapor transmission rate (WVTR) of 881 ± 91 g/m²day, essential to maintain moist and oxygen for faster healing of herpes lesions. Furthermore, cytotoxicity studies suggest that the fibrous mat are safe for topical application. Overall, the PCL based electrospun fibrous matrices with ACV and ω3 hereby described have the potential to be used as therapeutic bandage systems for the treatment of orofacial herpes.

Challenges and opportunities of pH in chronic wounds

Regarded as a silent epidemic, chronic wounds are a global public health issue. Wound healing is a complex, synchronized cascade of physiological processes restoring the anatomic and functional integrity of the skin; however, chronic wounds fail to proceed through the wound healing cascade. Wound pH oscillates during wound healing, usually traversing from a neutral pH to an acidic pH, while chronic wounds perpetuate in an elevated alkaline milieu. Although a neglected clinical parameter, pH has implications for relatively all pathologies of wound healing affecting oxygen release, angiogenesis, protease activity, bacterial toxicity and antimicrobial activity. Despite the array of wound healing products currently marketed, understanding the implications of pH on arresting wound healing can stimulate innovation within this vast market.

Pathophysiology of Atopic Dermatitis and Psoriasis: Implications for Management in Children

Atopic dermatitis (AD) and psoriasis are chronic inflammatory skin diseases associated with a significant cutaneous and systemic burden of disease as well as a poor health-related quality of life. Here, we review the complex pathophysiology of both AD and psoriasis and discuss the implications for treatment with current state-of-the-art and emerging topical and systemic therapies. Both AD and psoriasis are caused by a complex combination of immune dysregulation, skin-barrier disruption, genetic factors, and environmental influences. Previous treatments for both diseases were limited to anti-inflammatory agents that broadly suppress inflammation. Emerging insights into relevant pathways, including recognition of the role of T-helper type 2 driven inflammation in AD and T-helper 1 and 17 driven inflammation in psoriasis, have led to a therapeutic revolution. There are a number of novel treatment options available for AD and psoriasis with many more currently under investigation.

Unravelling effects of relative humidity on lipid barrier formation in human skin equivalents

Relative humidity (RH) levels vary continuously in vivo, although during in vitro generation of three-dimensional human skin equivalents (HSEs) these remain high (90-95%) to prevent evaporation of the cell-culture medium. However, skin functionality is directly influenced by environmental RH. As the barrier formation in HSEs is different, there is a need to better understand the role of cell-culture conditions during the generation of HSEs. In this study, we aim to investigate the effects of RH on epidermal morphogenesis and lipid barrier formation in HSEs. Therefore, two types of HSEs were developed at 90% or at 60% RH. Assessments were performed to determine epidermal morphogenesis by immunohistochemical analyses, ceramide composition by lipidomic analysis, and lipid organization by Fourier transform infrared spectroscopy and small-angle X-ray diffraction. We show that reduction of RH mainly affected the uppermost viable epidermal layers in the HSEs, including an enlargement of the granular cells and induction of epidermal cell activation. Neither the composition nor the organization of the lipids in the intercorneocyte space were substantially altered at reduced RH. In addition, lipid processing from glucosylceramides to ceramides was not affected by reduced RH in HSEs as shown by enzyme expression, enzyme activity, and substrate-to-product ratio. Our results demonstrate that RH directly influences epidermal morphogenesis, albeit the in vitro lipid barrier formation is comparable at 90% and 60% RH.

Non-Invasive Extraction of Gabapentin for Therapeutic Drug Monitoring by Reverse Iontophoresis: Effect of pH, Ionic Strength, and Polyethylene Glycol 400 in the Receiving Medium

Background:

Monitoring of plasma concentrations is a necessity for narrow therapeutic index potent drugs. Development of non-invasive methods can save the patients from the trauma of needles and hence is considered as a research priority.

Introduction:

Gabapentin, an anti-epileptic drug requires therapeutic monitoring because of its narrow therapeutic index. The objective of the study was to develop a suitable method for the non-invasive extraction of gabapentin for the same.

Methods:

Transdermal reverse iontophoresis was performed using pig ear skin as a barrier membrane. Three compartment iontophoretic cells were used for the extraction study. Extractions were carried out under low intensity electric field (current intensity- 0.5 mA/cm2, electrical field approximately 5 V). The donor compartment was charged with aqueous gabapentin (10 µg/ml in phosphate buffer of pH 7.4). For studying the effect of receiving vehicle (pH, ionic strength, and enhancer) on the extraction efficiency of gabapentin, the two receiver chambers were charged with media having varying concentration of these factors. Drug content was determined by HPLC.

Results:

Compared to other pHs, cumulative extraction of gabapentin at pH 5 was significantly higher at both anode and cathode (p<0.001). At low ionic strength, extraction of gabapentin increased linearly with the increase in concentration of ions up to a certain value but at very high ionic strength the pattern reversed. Similar results were obtained with enhancer (polyethylene glycol 400). Extraction increased with increase in polyethylene glycol 400 up to 3% and then decreased.

Conclusion:

Extraction flux can be optimized by manipulation of the receiver media.

Prediction of the skin permeability of topical drugs using in silico and in vitro models

The main challenge of topically applied drugs is to overcome the skin barrier to reach the site of action at the concentration needed for efficacy. In the research of new topical drugs, design of molecules with optimized properties for skin penetration is a key factor and assays for its characterization are needed. A group of 20 representative topical molecules of clinical use were studied in two in silico models (Potts & Guy and Barratt), and an in vitro assay with artificial membrane (Skin-PAMPA). A subset of 9 drugs were also evaluated in the Franz cells assay, formulated in a solvent and in a marketed formulation. Each assay allowed us to grade compounds according to their permeability value. Globally good alignments were found for the studied compounds when comparing models, although discrepancies for some compounds such as tazarotene, tacrolimus, ketoconazole and metronidazole were observed. Overall, the studied in silico and the in vitro models are useful tools to support selection and characterization of research compounds in terms of skin permeability.

Aging of the skin barrier

The skin barrier is mainly present in the stratum corneum (SC), composed of corneocytes surrounded by intercellular lipid lamellae, and attached by corneodesmosome. The tight junction attached to the lateral walls of keratinocytes in the upper part of the stratum granulosum is also included in the skin barrier. During aging, the following structures and functions of the skin barrier are changed or disturbed: (1) skin barrier structure, (2) permeability barrier function, (3) epidermal calcium gradient, (4) epidermal lipid synthesis and SC lipid processing, (5) cytokine production and response after insults, (6) SC acidity, (7) SC hydration, and (8) antimicrobial barrier. Patients with diabetes also show changes in the skin barrier similar to those in aged skin, and the characteristics of the skin barrier are very similar. Understanding the pathogenic mechanisms of the skin barrier in aging will permit us to develop therapeutic strategies for aged or diabetic skin.

Extraction of levetiracetam for therapeutic drug monitoring by transdermal reverse iontophoresis

Recently, transdermal reverse iontophoresis across the skin has been investigated as a novel technology for the purpose of diagnosis as well as therapeutic drug monitoring. Accordingly, the objective of this study was to investigate ex vivo and in vivo transdermal extraction of levetiracetam, an antiepileptic drug, across the pig ear skin by reverse iontophoresis. Reverse iontophoresis experiments were performed using three chambered diffusion cells. Extractions profiles were generated in phosphate buffers at different current intensities, pH and ionic strength as well donor drug concentrations. This was followed by ex vivo extraction in gels and in vivo extractions using New Zealand rabbits. Results indicate that levetiracetam was extracted at both anode and cathode. Flux values were unaffected by increase in current intensities (0.5 mA and 0.6 mA) but affected by pH and ionic strength. Neither in cathodal nor in anodal extraction, flux values did show a proportional relationship with the donor drug concentration. At low and medium concentration levels, flux values did not show any major change but the extraction flux at high donor concentration was much higher. In contrast, in vivo experiment with rabbits resulted in wide variation of fluxes with very high fluxes recorded at the cathodal end. Reasons attributed to this difference may include lower current intensity, and species variation. The most significant finding of this study is that measurable amounts of the levetiracetam were extracted at both the ends indicating its feasibility for non-invasive drug monitoring.