Effect of glycation focusing on the process of epidermal lipid synthesis in a reconstructed skin model and membrane fluidity of stratum corneum lipids

Bioactive lipids in the skin barrier mediate its functionality in health and disease

Our skin protects us from external threats including ultraviolet radiation, pathogens and chemicals, and prevents excessive trans-epidermal water loss. These varied activities are reliant on a vast array of lipids, many of which are unique to skin, and that support physical, microbiological and immunological barriers. The cutaneous physical barrier is dependent on a specific lipid matrix that surrounds terminally-differentiated keratinocytes in the stratum corneum. Sebum- and keratinocyte-derived lipids cover the skin's surface and support and regulate the skin microbiota. Meanwhile, lipids signal between resident and infiltrating cutaneous immune cells, driving inflammation and its resolution in response to pathogens and other threats. Lipids of particular importance include ceramides, which are crucial for stratum corneum lipid matrix formation and therefore physical barrier functionality, fatty acids, which contribute to the acidic pH of the skin surface and regulate the microbiota, as well as the stratum corneum lipid matrix, and bioactive metabolites of these fatty acids, involved in cell signalling, inflammation, and numerous other cutaneous processes. These diverse and complex lipids maintain homeostasis in healthy skin, and are implicated in many cutaneous diseases, as well as unrelated systemic conditions with skin manifestations, and processes such as ageing. Lipids also contribute to the gut-skin axis, signalling between the two barrier sites. Therefore, skin lipids provide a valuable resource for exploration of healthy cutaneous processes, local and systemic disease development and progression, and accessible biomarker discovery for systemic disease, as well as an opportunity to fully understand the relationship between the host and the skin microbiota. Investigation of skin lipids could provide diagnostic and prognostic biomarkers, and help identify new targets for interventions. Development and improvement of existing in vitro and in silico approaches to explore the cutaneous lipidome, as well as advances in skin lipidomics technologies, will facilitate ongoing progress in skin lipid research.

The Association between the Level of Advanced Glycation End Products and Objective Skin Quality Parameters

Advanced glycation end products (AGEs) represent an endogenously produced or exogenously derived group of compounds derived from nonenzymatic glycation. Recent experimental studies are suggesting that AGEs could play an important role in the skin's quality and its aging process. Hence, the aim of this study was to clinically evaluate the AGEs and skin quality parameters across different age groups in the general population. The study included 237 participants. Melanin, erythema, hydration, friction and transepidermal water loss (TEWL) were evaluated using noninvasive probes, while AGEs were evaluated using a skin autofluorescence reader. There was a significant positive correlation between AGEs and the amount of melanin (p < 0.001), erythema (p < 0.001) and TEWL (p < 0.001), while there was a significant negative correlation between AGEs and hydration (p < 0.001) and friction (p < 0.001). After dividing the sample into three groups depending on their age, in all three groups, there was a significant positive correlation between AGEs and the melanin count (p < 0.001) and TEWL (p < 0.001), while there was a significant negative correlation between AGEs and skin hydration (p < 0.001). Multiple linear regression analysis showed that the level of AGEs as a dependent variable retained a significant association with age (p < 0.001), melanin (p < 0.001), erythema (p = 0.005) and TEWL (p < 0.001) as positive predictors. Moreover, AGEs retained a significant association with skin hydration (p < 0.001) and friction (p = 0.017) as negative predictors. These outcomes imply that AGEs could be linked with the complex physiology of the skin and its aging process.

Advanced Glycation End Products in the Skin: Molecular Mechanisms, Methods of Measurement, and Inhibitory Pathways

Advanced glycation end products (AGEs) are a series of stable compounds produced under non-enzymatic conditions by the amino groups of biomacromolecules and the free carbonyl groups of glucose or other reducing sugars commonly produced by thermally processed foods. AGEs can cause various diseases, such as diabetes, atherosclerosis, neurodegeneration, and chronic kidney disease, by triggering the receptors of AGE (RAGEs) in the human body. There is evidence that AGEs can also affect the different structures and physiological functions of the skin. However, the mechanism is complicated and cumbersome and causes various harms to the skin. This article aims to identify and summarise the formation and characteristics of AGEs, focussing on the molecular mechanisms by which AGEs affect the composition and structure of normal skin substances at different skin layers and induce skin issues. We also discuss prevention and inhibition pathways, provide a systematic and comprehensive method for measuring the content of AGEs in human skin, and summarise and analyse their advantages and disadvantages. This work can help researchers acquire a deeper understanding of the relationship between AGEs and the skin and provides a basis for the development of effective ingredients that inhibit glycation.

Development of Evaluation Methods for Anti-Glycation Activity and Functional Ingredients Contained in Coriander and Fennel Seeds

Spices are known to have various physiological functions. We focused on the anti-glycation effects of spices, researched anti-glycation active ingredients in coriander (Coriandrum sativum L.) and fennel (Foeniculum vulgare) seeds, and conducted experiments using human skin-derived fibroblast TIG-110 cells as a model of glycation. We isolated 11 compounds from two spice seeds and found several substances that showed anti-glycation activity. A new compound (5,5′-diallyl-2,2′-diglucopyranosyl-3,3′-dimethoxy diphenyl ether) was isolated from fennel seeds and showed high anti-glycation activity with an IC50 value of 0.08 mM, thereby indicating a high anti-glycosylation activity. In this study, we established a glyoxal (GO)-induced glycation test method for human skin cells, confirmed the anti-glycation effect of spice seeds using this glycation induction model, and found that the exposure of TIG-110 human skin-derived fibroblast cells to GO reduced cell viability. The most stable conditions for cell viability were found to be a GO concentration of 1.25 mM and a culture time of 48 h. We evaluated extracts and isolates of spice seeds using this model as a model test for glycation induction. We conducted qualitative and quantitative analyses of carboxymethyl lysine (CML), a type of AGE, to determine the relationship between cell viability and AGEs. The relationship between cell viability and the amount of CML was correlated. Establishing a glycation induction model test using skin cells makes it possible to quickly screen extracts of natural ingredients in the future. Moreover, the results of this model showed that extracts of two spice seeds and their isolates have high anti-glycation activity, and they are expected to be used as cosmetics, health foods, and pharmaceutical ingredients.

Human skin equivalents: Impaired barrier function in relation to the lipid and protein properties of the stratum corneum

To advance drug development representative reliable skin models are indispensable. Animal skin as test model for human skin delivery is restricted as their properties greatly differ from human skin. In vitro 3D-human skin equivalents (HSEs) are valuable tools as they recapitulate important aspects of the human skin. However, HSEs still lack the full barrier functionality as observed in native human skin, resulting in suboptimal screening outcome. In this review we provide an overview of established in-house and commercially available HSEs and discuss in more detail to what extent their skin barrier biology is mimicked in vitro focusing on the lipid properties and cornified envelope. Further, we will illustrate how underlying factors, such as culture medium improvements and environmental factors affect the barrier lipids. Lastly, potential improvements in skin barrier function will be proposed aiming at a new generation of HSEs that may replace animal skin delivery studies fully.

Effect of Lactic Fermentation Products on Human Epidermal Cell Differentiation, Ceramide Content, and Amino Acid Production

INTRODUCTION

Lactic fermentation products (LFPs) are thought to affect "good" bacteria in the gut. We previously reported that oral administration of LFPs has beneficial therapeutic effects in a mouse model of atopic dermatitis. However, it is unclear how LFPs affect human epidermal cell differentiation, ceramide (Cer), and amino acid production.

OBJECTIVE

The aim of this study was to determine the effects of LFPs on epidermal cell differentiation, by assessing amino acid and Cer production.

METHODS

A 3-dimensional cultured human epidermis model and normal human epidermal keratinocytes were used. Cytotoxicity tests were performed using alamar Blue. Transepidermal water loss (TEWL) was used as an index to assess barrier function. Keratin 1 (K1), keratin 5 (K5), keratin 10 (K10), involucrin (INV), calpain 1, and transglutaminase (TGase) (markers of differentiation) and profilaggrin (proFLG) and bleomycin hydrolase (amino acid synthesis-related genes) expression levels were quantified by RT-PCR. In addition, TGase protein levels were measured by Western blotting. The intercellular lipid content of the stratum corneum was measured by high-performance thin-layer chromatography. Amino acids were quantified using an amino acid analyzer. Finally, bound water content in the stratum corneum was measured by differential scanning calorimetry.

RESULTS

Cell viability did not change, but TEWL was significantly decreased in the cells treated with LFPs compared with the control cells. Treatment with LFPs significantly increased expression of the late-differentiation markers INV and TGase at the RNA level. Furthermore, TGase protein expression was significantly increased by treatment with LFPs. Treating a 3-dimensional cultured epidermis model with LFPs significantly increased the intercellular lipid content of the stratum corneum and production of the amino acid arginine (Arg). The amount of bound water in the stratum corneum was increased significantly in the LFP application group.

CONCLUSION

Treatment with LFPs promotes human epidermal cell differentiation and increases the intercellular content of the free fatty acid, Chol, Cer [NS], Cer [AS], and Cer [AP]. This may result in improved skin barrier function. The increased amount of Arg observed in keratinocytes may help improve water retention.

Human Induced Pluripotent Stem Cell-Based Skin for Assessing Transdermal Drug Permeability and Irritancy

To establish a system for assessing drug permeation and irritation of the skin, the permeation of benzoic acid and isosorbide dinitrate, which are listed in the Pharmacopoeia, and the chemical irritation were evaluated using skin generated from human induced pluripotent stem cells (iPSCs). Multilayer structures and cellular markers (keratin 14 and 10, which are in basal and suprabasal epidermal layers) were clearly detected in our iPSC-based skin. Transepidermal water loss (TEWL) decreased after iPSC-derived keratinocytes were cultured on collagen gels from human primary fibroblasts. These results indicate that the barrier function was partly increased by formation of the living epidermis. The cumulative amount of benzoic acid and isosorbide dinitrate across human iPSC-based skin gradually increased after an initial lag time. Moreover, the irritancy of various chemicals (non-irritants: ultrapure water, allyl phenoxy-acetate, isopropanol, and hexyl salicylate and irritants: 5% sodium dodecyl sulfate (SDS), heptanal, potassium hydroxide (5% aq.) and cyclamen aldehyde) to iPSC-based skin was almost met the irritation criteria of the Organisation for Economic Co-operation and Development (OECD) guideline. The results of our iPSC-based skin evaluation provide useful basic information for developing an assessment system to predict the permeation and safety of new transdermal drugs in human skin.

Antiglycation and Antioxidant Activity from Methanol Extract and Fraction of Xylocarpus granatum Stem

The objective of this research was to determine the antioxidant and antiglycation activity of methanol crude extract of Xylocarpus granatum stem and its fraction. The methanol crude extract was fractioned by liquid-liquid extraction to obtain three fractions, which were n-hexane fraction, ethyl acetate fraction, and methanol fraction. Antioxidant activity was performed using scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH). The antiaging activity was identified based on the ability to inhibit the formation of advanced glycation end products (AGEs). The results of the study showed that methanol crude extract and all fractions had an antioxidant and antiglycation activity that significantly different from each other (P<0.05). The results show that the most active antiglycation and antioxidant activity was the methanol fraction with IC50 were 71.55 ppm and 8.52 ppm, respectively. The methanol fraction contained an alkaloid, flavonoid, phenolic, and triterpenoid compounds. Subsequent fractionation of the methanol fraction guided by bioassay showed that sub-fraction 1 had the best antiglycation and antioxidant activity. Based on the color of the chromatogram obtained at UV 366 nm, the chemical component contained in the most active fraction was the flavonoid group.