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Background: Bleomycin hydrolase (BH), which is expressed in the stratum granulosum and lower stratum corneum (SC), is involved in final filaggrin degradation. Furthermore, BH plays an essential role in producing free amino acids, which constitute the majority of natural moisturizing factors (NMF). However, the effects of BH expression and protease activity on human skin aging remain unclear., Objective: This study was designed to evaluate the activity and expression patterns of BH in SC extracts from healthy young and elderly individuals., Methods: SC samples were collected by tape stripping. BH activity was assessed by measuring the citrulline aminopeptidase activity. BH expression was determined by Western blotting, and NMF was quantified by liquid chromatography/mass spectrometry. Skin barrier function was determined by measuring SC hydration, transepidermal water loss (TEWL), and skin pH., Results: The activity and expression of BH were higher in the elderly skin than in young skin, and BH activity was correlated with BH expression levels. Evaluation of the NMF showed that the levels of total amino acids, such as glycine, serine, aspartic acid, citrulline, pyrrolidone carboxylic acid (a metabolite of glutamic acid), and trans-urocanic acid (a metabolite of histidine), were significantly higher in elderly skin than in young skin. Moreover, SC hydration and TEWL were significantly lower in elderly, indicating dry skin, and pH was significantly higher in elderly, indicating greater skin alkalinization., Conclusion: These results suggest that BH activity and expression, as well as NMF amino acids, increase in elderly people as compensatory mechanisms against dry skin., Competing Interests: Conflict of interest statement None of the authors declare any conflicts of interest., (Copyright © 2023. Published by Elsevier B.V.)

The superficial layer of the skin, the stratum corneum (SC), consists of corneocytes surrounded by lipid regions and acts as a protective barrier for the body against water loss, toxic agents and microorganisms. As most substances permeate the stratum corneum through the lipid regions, lipid organization is considered crucial for the skin barrier function. Here, we investigate the potential of in vivo confocal Raman spectroscopy to describe the composition and organization of the SC. Confocal Raman spectroscopy is finding increasing use in the characterization of skin in biomedical, pharmaceutical and cosmetic applications. In this work, we analyze the spectra using chemometric methods and obtain principal components that correspond to the primary skin constituents: protein (keratin), natural moisturizing factor (NMF), water and lipid contributions in both ordered (orthorhombic) and disordered structural organization. By identifying these important components of the SC, these results highlight the utility of this in vivo, non-invasive, and depth resolved tool at the forefront of skin research., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background: Dry skin in atopic dermatitis (AD) mainly results from barrier impairment due to deficiency of ceramide and natural moisturizing factors including pyrrolidone carboxylic acid (PCA) in stratum corneum (SC). Caspase-14 cleaves filaggrin monomers to free amino acids and their derivatives such as PCA, contributing natural moisturizing factors. Cytokines in the corneocytes represent cutaneous inflammation severity of AD patients., Object: To analyze the correlations of PCA, caspase-14 and cytokines in corneocytes with clinical severity, barrier function and skin inflammation, those were quantitated., Methods: A total of 73 persons were enrolled: 21 patients with mild AD, 21 with moderate-to-severe AD, 13 with X-linked ichthyosis (XLI) as a negative control for filaggrin gene (FLG) mutation, and 18 healthy controls. Skin barrier functions such as basal transepidermal water loss (TEWL), stratum corneum (SC) hydration and skin surface pH were measured. To collect corneocytes, stripping with D-squame discs was done on lesional and non-lesional skin. And then PCA was isolated from D-squame discs and quantitated by LC-MS/MS. Cytokine assays were performed., Results: The quantity of PCA and caspase-14 was decreased in inflammatory lesions compared to non-lesion in AD patients. And the amounts of PCA and caspase-14 in the lesion of AD patients correlated with clinical severity as determined by eczema area and severity index score and the skin barrier functions. Also, the expressions of TNF-α and IL-13 inversely correlated with PCA quantity., Conclusion: The quantity of PCA or caspase-14 in the corneocytes of the lesional skin of AD patients reflects the clinical severity, skin barrier function and the degree of lesional inflammation., (Copyright © 2014 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.)

Background: Although physical properties of neonatal-infantile stratum corneum (SC) change drastically after birth, precise developmental alterations of specific sites have not been fully elucidated., Objective: To determine the longitudinal alterations of neonatal-infantile SC functions and components of upper thighs and diaper-covered buttocks during the first year of life. The data were compared with those of adults., Methods: Nineteen full-term neonates and their mothers were subjected to the measurements. Skin hydration, water sorption/retention capacity, TEWL were measured. Superficial SC analyses for NMF, ester binding sebum, and free fatty acids were performed by ATR-FTIR spectrometer. Total amount of ceramides (CERs) and CER subclasses were analyzed by NPLC-ESI-MS., Results: SC hydration of neonatal thighs was lower than that of their mothers, which rapidly increased during the 1st month. Skin hydration of neonatal buttocks was similar to that of their mothers. This also rapidly increased during the 1st month. The neonatal TEWL was less than those of their mothers indicating more efficient barrier function at both sites, which significantly increased during the 1st year development. This was mostly correlated decreased in the ω-hydroxy fatty acid-esterified CERs. Superficial ester-binding sebum content of neonates was similar to that of their mothers, which significantly decreased during the measurement; the decrease was more marked on buttocks. Neither NMF nor FFA of the superficial SC showed significant alteration during the 1-year development., Conclusion: Our results indicate that physical functions and components of neonatal-infantile SC show considerable alterations between diaper-covered buttocks and upper thighs during the 1st year development., (Copyright © 2013 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.)

Background: Amino acids (AAs) play important roles in maintaining an optimal hydration state of stratum corneum (SC) as a natural moisturizing factor (NMF). Recently, however, we have reported that lactate and potassium significantly affect the hydration state of SC., Objective: To explore the source of lactate and potassium in SC, we compared the concentration of various NMFs such as AAs, pyrrolidone carbonic acid (PCA), lactate, sodium, and potassium in SC between anhidrotic and adjacent hidrotic areas of patients with acquired idiopathic generalized anhidrosis or segmental anhidrosis., Methods: We examined 13 anhidrotic areas and the adjacent hidrotic skin of 10 different patients. We first determined anhidrotic and hidrotic areas of each patient by the iodine starch method and examined the hydration state of SC by measuring the high-frequency conductance. Then we obtained SC by tape stripping and measured the content of AAs, PCA, lactate, urea, sodium, and potassium in SC obtained from the anhidrotic and hidrotic areas. We examined the effect of increased insensible perspiration on the SC hydration and the concentrations of NMFs., Results: The SC of anhidrotic areas showed significantly low hydration. Among NMFs, lactate, urea, sodium, and potassium were significantly decreased in the SC of anhidrotic areas, while AAs and PCA were not significantly different between hidrotic and anhidrotic areas. Increased insensible perspiration increased SC hydration as well as NMFs other than AAs and PCA., Conclusion: Sweat constitutes lactate, urea, sodium, and potassium in NMFs and plays a crucial role in maintaining the physiological hydration state of SC., (Copyright © 2013 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.)