Increased sensitivity of histidinemic mice to UVB radiation suggests a crucial role of endogenous urocanic acid in photoprotection

Sunlight: Time for a Rethink?

UVR is a skin carcinogen, yet no studies link sun exposure to increased all-cause mortality. Epidemiological studies from the United Kingdom and Sweden link sun exposure with reduced all-cause, cardiovascular, and cancer mortality. Vitamin D synthesis is dependent on UVB exposure. Individuals with higher serum levels of vitamin D are healthier in many ways, yet multiple trials of oral vitamin D supplementation show little benefit. Growing evidence shows that sunlight has health benefits through vitamin D-independent pathways, such as photomobilization of nitric oxide from cutaneous stores with reduction in cardiovascular morbidity. Sunlight has important systemic health benefit as well as risks.

Light Sensing beyond Vision: Focusing on a Possible Role for the FICZ/AhR Complex in Skin Optotransduction

Although our skin is not the primary visual organ in humans, it acts as a light sensor, playing a significant role in maintaining our health and overall well-being. Thanks to the presence of a complex and sophisticated optotransduction system, the skin interacts with the visible part of the electromagnetic spectrum and with ultraviolet (UV) radiation. Following a brief overview describing the main photosensitive molecules that detect specific electromagnetic radiation and their associated cell pathways, we analyze their impact on physiological functions such as melanogenesis, immune response, circadian rhythms, and mood regulation. In this paper, we focus on 6-formylindolo[3,2-b]carbazole (FICZ), a photo oxidation derivative of the essential amino acid tryptophan (Trp). This molecule is the best endogenous agonist of the Aryl hydrocarbon Receptor (AhR), an evolutionarily conserved transcription factor, traditionally recognized as a signal transducer of both exogenous and endogenous chemical signals. Increasing evidence indicates that AhR is also involved in light sensing within the skin, primarily due to its ligand FICZ, which acts as both a chromophore and a photosensitizer. The biochemical reactions triggered by their interaction impact diverse functions and convey crucial data to our body, thus adding a piece to the complex puzzle of pathways that allow us to decode and elaborate environmental stimuli.

Prolyl Endopeptidase Is Involved in Filaggrinolysis and Cornification

FLG is a well-known biomarker of atopic dermatitis and skin dryness. Its full proteolysis (or filaggrinolysis) produces the major constituents of the natural moisturizing factor. Some proteases/peptidases remain to be identified in this multistep process. Mining 16 omics analyses, we identified prolyl endopeptidase (PREP) as a candidate peptidase. Indirect immunofluorescence and confocal analysis demonstrated its localization in the granular and deep cornified layers, where it colocalized with FLG. Tandem mass spectroscopy and fluorescent quenching activity assays showed that PREP cleaved several synthetic peptides derived from the FLG sequence, at the carboxyl side of an internal proline. Deimination of these peptides increased PREP enzymatic efficiency. Specific inhibition of PREP in reconstructed human epidermis using benzyloxycarbonyl-pro-prolinal induced the accumulation of FLG monomers. Downregulation of PREP expression in reconstructed human epidermis using RNA interference confirmed the impact of PREP on FLG metabolism and highlighted a more general role of PREP in keratinocyte differentiation. Indeed, quantitative global proteomic, western blotting, and RT-qPCR analyses showed a strong reduction in the expression of bleomycin hydrolase, known to be involved in filaggrinolysis, and of several other actors of cornification such as loricrin. Consequently, at the functional level, the transepidermal electric resistance was drastically reduced.

Melatonin/Sericin Wound Healing Patches: Implications for Melanoma Therapy

Melatonin and sericin exhibit antioxidant properties and may be useful in topical wound healing patches by maintaining redox balance, cell integrity, and regulating the inflammatory response. In human skin, melatonin suppresses damage caused by ultraviolet radiation (UVR) which involves numerous mechanisms associated with reactive oxygen species/reactive nitrogen species (ROS/RNS) generation and enhancing apoptosis. Sericin is a protein mainly composed of glycine, serine, aspartic acid, and threonine amino acids removed from the silkworm cocoon (particularly Bombyx mori and other species). It is of interest because of its biodegradability, anti-oxidative, and anti-bacterial properties. Sericin inhibits tyrosinase activity and promotes cell proliferation that can be supportive and useful in melanoma treatment. In recent years, wound healing patches containing sericin and melatonin individually have attracted significant attention by the scientific community. In this review, we summarize the state of innovation of such patches during 2021-2023. To date, melatonin/sericin-polymer patches for application in post-operational wound healing treatment has been only sparingly investigated and it is an imperative to consider these materials as a promising approach targeting for skin tissue engineering or regenerative dermatology.

Atopic Dermatitis: Disease Background and Risk Factors

Multiple risk factors have been associated with the development of atopic dermatitis (AD). Recent advances in understanding the role of genetics in this disease have been made, with discovery of the filaggrin (FLG) gene as the most notable so far. In addition to FLG gene mutations as a risk factor for AD, a positive family history of atopic or allergic disease in either parent has been shown to confer a greater risk of developing AD. Atopic dermatitis usually presents early in life and is thought to represent the initial step in the "atopic march," which is characterized by the development of other atopic diseases later in life such as asthma, allergic rhinitis, and/or rhinoconjunctivitis, food allergies, and hay fever. Other comorbid diseases that have been associated with AD include increase risk of viral and bacterial skin infections, neuropsychiatric diseases such as attention-deficit hyperactivity disorders (ADHD), and autistic spectrum disorder (ASD). Patients with AD have also been found to have worse sleep quality overall compared to patients without AD. In this chapter, we will discuss the risk factors associated with development of atopic dermatitis as well as the most commonly reported comorbidities in patients with this disease.

Deimination in epidermal barrier and hair formation

Peptidylarginine deiminases (PADs) transform a protein arginine residue into the non-standard amino acid citrulline. This calcium-dependent post-translational modification of proteins is called citrullination or deimination. As described in this special issue, PADs play a role in various physiological processes, and PAD deregulations are involved in many human diseases. Three PADs are expressed in the epidermis, where their roles begin to be deciphered. PAD1 and PAD3 are involved in keratinocyte differentiation, particularly in the epidermal barrier function, keratins, filaggrin and filaggrin-related proteins being the most abundant deiminated epidermal proteins. Reduced amounts of deiminated proteins and PAD1 expression may be involved in the pathogenesis of psoriasis and atopic dermatitis, two very frequent and chronic skin inflammatory diseases. The trichohyalin/PAD3/transglutaminase three pathway is important for hair shaft formation. Mutations of the PADI3 gene, leading to a decreased activity or abnormal localization of the corresponding isotype, are the cause of a rare hair disorder called uncombable hair syndrome, and are associated with the central centrifugal cicatricial alopecia, a frequent alopecia mainly affecting women of African ancestry. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

Cis-urocanic acid improves cell viability and suppresses inflammasome activation in human retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a common eye disease among the elderly, which can result in impaired vision and irreversible loss of vision. The majority of patients suffer from the dry (also known as the atrophic) form of the disease, which is completely lacking an effective treatment. In the present study, we evaluated the potential of cis-urocanic acid (cis-UCA) to protect human ARPE-19 cells from cell damage and inflammasome activation induced by UVB light. Urocanic acid is a molecule normally present in human epidermis. Its cis-form has recently been found to alleviate UVB-induced inflammasome activation in human corneal epithelial cells. Here, we observed that cis-UCA is well-tolerated also by human retinal pigment epithelial (RPE) cells at a concentration of 100 μg/ml. Moreover, cis-UCA was cytoprotective and efficiently diminished the levels of mature IL-1β, IL-18, and cleaved caspase-1 in UVB-irradiated ARPE-19 cells. Interestingly, cis-UCA also reduced DNA damage, whereas its effect against ROS production was negligible. Collectively, cis-UCA protected ARPE-19 cells from UVB-induced phototoxicity and inflammasome activation. This study indicates that due to its beneficial properties of preserving cell viability and preventing inflammation, cis-UCA has potential in drug development of chronic ocular diseases, such as AMD.

The Immune Microenvironment in Basal Cell Carcinoma

The immune system plays a key role in the suppression and progression of basal cell carcinoma (BCC). The primary aetiological factor for BCC development is exposure to ultraviolet radiation (UVR) which, particularly in lighter Fitzpatrick skin types, leads to the accumulation of DNA damage. UVR has roles in the generation of an immunosuppressive environment, facilitating cancer progression. Rates of BCC are elevated in immunosuppressed patients, and BCC may undergo spontaneous immune-mediated regression. Histologic and immunohistochemical profiling of BCCs consistently demonstrates the presence of an immune infiltrate and associated immune proteins. Early studies of immune checkpoint inhibitors reveal promising results in BCC. Therefore, the host immune system and tumor responses to it are important in BCC pathogenesis. Understanding these interactions will be beneficial for disease prognostication and therapeutic decisions.

Skin Barrier Function and Its Relationship With IL-17, IL-33, and Filaggrin in Malar Melasma

BACKGROUND

The pathogenesis of melasma remains unclear. Interleukin (IL)-17, a proinflammatory mediator, disturbs barrier function. Filaggrin (FLG) is a protein involved in epidermal barrier homeostasis and may be affected by IL-17 and IL-33.

OBJECTIVE

To evaluate epidermal barrier function in malar melasma and its association with the expression of FLG, IL-17, and IL-33.

METHODS

Twenty patients with malar melasma were included in this study. Colorimetric and transepidermal water loss (TEWL) was measured in lesional and adjacent unaffected skin at baseline and 30 minutes after barrier disruption using the tape-stripping test. Biopsies from melasma and perilesional skin were performed to evaluate the presence of FLG by immunohistochemistry, and profilaggrin, IL-17, and IL-33 expression were analyzed by reverse transcription-qualitative polymerase chain reaction.

RESULTS

After the stripping test, the erythema and TEWL values were higher in the melasma than in the unaffected skin ( P = 0.01). Thirty minutes later, TEWL diminished, but it remained higher than in the perilesional skin. Profilaggrin increased as TEWL gradually decreased (R = -0.68, P = 0.04). FLG and IL-17 were higher in the melasma than in the perilesional skin ( P = 0.003). IL-17 and profilaggrin expression were positively associated (R = 0.60, P = 0.04). IL-33 expression was higher in the adjacent normal skin than in the melasma ( P = 0.01).

CONCLUSION

This study found subclinical inflammation in the skin adjacent to the melasma, dysfunction of the epidermal barrier in lesions associated with chronic inflammation, and an abnormal differentiation process promoting an increase in FLG. These findings highlight the need to preserve the integrity of the facial stratum corneum in these patients.

The role of single nucleotide variant rs3819817 of the Histidine Ammonia-Lyase gene and 25-Hydroxyvitamin D on bone mineral density, adiposity markers, and skin pigmentation, in Mexican population

PURPOSE

Vitamin D (VD) deficiency and osteoporosis have become a global public health problem. A variant in the Histidine Ammonia-Lyase (HAL) gene has been associated with VD levels and bone mineral density (BMD). However, whether this variant has an influence on VD levels and BMD in Mexican adults remain unclear.

METHODS

This cross-sectional analysis included 1,905 adults participating in the Health Worker Cohort Study and 164 indigenous postmenopausal women from the Metabolic Analysis in an Indigenous Sample (MAIS) cohort. The rs3819817 variant was genotyped by TaqMan probe assay. Total 25 hydroxyvitamin D levels were measured by DiaSorin Liaison. BMD at the different sites was assessed through dual-energy X-ray absorptiometry. Linear and logistic regression models were performed to evaluate the associations of interest.

RESULTS

The prevalence of VD deficiency was 41%, showing differences between sexes. Obesity and skin pigmentation were associated with lower levels of VD in males and females. rs3819817-T allele was associated with low levels of 25-hydroxyvitamin D, VD deficiency, and hip and femoral neck BMD values (g/cm²). We found two interactions with VD levels, one between adiposity and rs3819817-T allele (P = 0.017) and another between skin pigmentation and rs3819817-T allele (P = 0.019). In indigenous postmenopausal women, we observed higher VD levels in the southern region compared to the northern region (P < 0.001); however, we did not observe differences by genotype.

CONCLUSION

Our findings confirm that the genetic variant rs3819817 has an essential function in VD levels and BMD and suggests a role in skin pigmentation in the Mexican population.

Skin Microbiome, Metabolome and Skin Phenome, from the Perspectives of Skin as an Ecosystem

Skin is a complex ecosystem colonized by millions of microorganisms, including bacteria, fungi, and viruses. Skin microbiota is believed to exert critical functions in maintaining host skin health. Profiling the structure of skin microbial community is the first step to overview the ecosystem. However, the community composition is highly individualized and extremely complex. To explore the fundamental factors driving the complexity of the ecosystem, namely the selection pressures, we review the present studies on skin microbiome from the perspectives of ecology. This review summarizes the following: (1) the composition of substances/nutrients in the cutaneous ecological environment that are derived from the host and the environment, highlighting their proposed function on skin microbiota; (2) the features of dominant skin commensals to occupy ecological niches, through self-adaptation and microbe-microbe interactions; (3) how skin microbes, by their structures or bioactive molecules, reshape host skin phenotypes, including skin immunity, maintenance of skin physiology such as pH and hydration, ultraviolet (UV) protection, odor production, and wound healing. This review aims to re-examine the host-microbe interactions from the ecological perspectives and hopefully to give new inspiration to this field.

Human follicular mites: Ectoparasites becoming symbionts

Most humans carry mites in the hair follicles of their skin for their entire lives. Follicular mites are the only metazoans tha continuously live on humans. We propose that Demodex folliculorum (Acari) represents a transitional stage from a host-injuring obligate parasite to an obligate symbiont. Here, we describe the profound impact of this transition on the genome and physiology of the mite. Genome sequencing revealed that the permanent host association of D. folliculorum led to an extensive genome reduction through relaxed selection and genetic drift, resulting in the smallest number of protein-coding genes yet identified among panarthropods. Confocal microscopy revealed that this gene loss coincided with an extreme reduction in the number of cells. Single uninucleate muscle cells are sufficient to operate each of the three segments that form each walking leg. While it has been assumed that the reduction of the cell number in parasites starts early in development, we identified a greater total number of cells in the last developmental stage (nymph) than in the terminal adult stage, suggesting that reduction starts at the adult or ultimate stage of development. This is the first evolutionary step in an arthropod species adopting a reductive, parasitic or endosymbiotic lifestyle. Somatic nuclei show underreplication at the diploid stage. Novel eye structures or photoreceptors as well as a unique human host melatonin-guided day/night rhythm are proposed for the first time. The loss of DNA repair genes coupled with extreme endogamy might have set this mite species on an evolutionary dead-end trajectory.

Revisiting the Roles of Filaggrin in Atopic Dermatitis

The discovery in 2006 that loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and can predispose to atopic dermatitis (AD) galvanized the dermatology research community and shed new light on a skin protein that was first identified in 1981. However, although outstanding work has uncovered several key functions of filaggrin in epidermal homeostasis, a comprehensive understanding of how filaggrin deficiency contributes to AD is still incomplete, including details of the upstream factors that lead to the reduced amounts of filaggrin, regardless of genotype. In this review, we re-evaluate data focusing on the roles of filaggrin in the epidermis, as well as in AD. Filaggrin is important for alignment of keratin intermediate filaments, control of keratinocyte shape, and maintenance of epidermal texture via production of water-retaining molecules. Moreover, filaggrin deficiency leads to cellular abnormalities in keratinocytes and induces subtle epidermal barrier impairment that is sufficient enough to facilitate the ingress of certain exogenous molecules into the epidermis. However, although FLG null mutations regulate skin moisture in non-lesional AD skin, filaggrin deficiency per se does not lead to the neutralization of skin surface pH or to excessive transepidermal water loss in atopic skin. Separating facts from chaff regarding the functions of filaggrin in the epidermis is necessary for the design efficacious therapies to treat dry and atopic skin.

Ichthyosis and hereditary cornification disorders in dogs

The stratum corneum (SC), the outermost layer of the epidermis, serves a crucial role in maintaining body hydration and protection from environmental insults. When the stratum corneum is injured or when the genetic blueprints are flawed, the body is at risk of dehydration, secondary infections and allergen sensitization. Advancements in veterinary dermatology have revealed a wide gamut of disease from relatively benign to lethal that specifically arise from flawed structural proteins, enzymes or lipids needed to create the corneocytes and lipid bilayers of the SC. Some conditions closely mimic their human counterparts while others are unique to the dog. This review will focus on forms of ichthyosis in the dog.

Pellagra a review exploring causes and mechanisms, including isoniazid-induced pellagra

Pellagra is a clinical syndrome caused by a deficiency of niacin (nicotinic acid) and/or its precursor tryptophan. The cardinal manifestations are 4 D's: dermatitis, diarrhoea, dementia and in worst case death. Increased use of isoniazid prophylaxis along with antiretroviral therapy in countries where latent tuberculosis is common has been associated with increased presentations with pellagra.

Skin barrier dysfunction and filaggrin

Skin barrier dysfunction caused by endogenous or exogenous factors can lead to various disorders such as xerosis cutis, ichthyoses, and atopic dermatitis. Filaggrin is a pivotal structural protein of the stratum corneum (SC) and provides natural moisturizing factors that play a role in skin barrier functions. Filaggrin aggregates keratin filaments, resulting in the formation of a keratin network, which binds cornified envelopes and collapse keratinocytes to flattened corneocytes. This complex network contributes to the physical strength of the skin. Filaggrin is degraded by caspase-14, calpain 1, and bleomycin hydrolases into amino acids and amino acid metabolites such as trans-urocanic acid and pyrrolidone carboxylic acid, which are pivotal natural moisturizing factors in the SC. Accordingly, filaggrin is important for the pathophysiology of skin barrier disorders, and its deficiency or dysfunction leads to a variety of skin disorders. Here, the roles and biology of filaggrin, related skin diseases, and a therapeutic strategy targeting filaggrin are reviewed. In addition, several drug candidates of different mode of actions targeting filaggrin, along with their clinical efficacy, are discussed.

Exome sequencing and analysis of 454,787 UK Biobank participants

A major goal in human genetics is to use natural variation to understand the phenotypic consequences of altering each protein-coding gene in the genome. Here we used exome sequencing¹ to explore protein-altering variants and their consequences in 454,787 participants in the UK Biobank study². We identified 12 million coding variants, including around 1 million loss-of-function and around 1.8 million deleterious missense variants. When these were tested for association with 3,994 health-related traits, we found 564 genes with trait associations at P ≤ 2.18 × 10^-11. Rare variant associations were enriched in loci from genome-wide association studies (GWAS), but most (91%) were independent of common variant signals. We discovered several risk-increasing associations with traits related to liver disease, eye disease and cancer, among others, as well as risk-lowering associations for hypertension (SLC9A3R2), diabetes (MAP3K15, FAM234A) and asthma (SLC27A3). Six genes were associated with brain imaging phenotypes, including two involved in neural development (GBE1, PLD1). Of the signals available and powered for replication in an independent cohort, 81% were confirmed; furthermore, association signals were generally consistent across individuals of European, Asian and African ancestry. We illustrate the ability of exome sequencing to identify gene-trait associations, elucidate gene function and pinpoint effector genes that underlie GWAS signals at scale.

miR-155 Contributes to Normal Keratinocyte Differentiation and Is Upregulated in the Epidermis of Psoriatic Skin Lesions

The role of microRNAs (miRNAs) during keratinocyte (KC) differentiation and in skin diseases with epidermal phenotypes has attracted strong interest over the past few years. However, combined mRNA and miRNA expression analyses to elucidate the intricate mRNA–miRNA networks of KCs at different stages of differentiation have not been performed yet. In the present study, we investigated the dynamics of miRNA and mRNA expression during KC differentiation in vitro and in normal and psoriatic epidermis. While we identified comparable numbers of up- and downregulated mRNAs (49% and 51%, respectively), miRNAs were predominantly upregulated (76% vs 24%) during KC differentiation. Further bioinformatics analyses suggested an important inhibitory role for miR-155 in KC differentiation, as it was repressed during KC differentiation in normal skin but strongly upregulated in the epidermis of psoriatic skin lesions. Mimicking the inflammatory milieu of psoriatic skin in vitro, we could show that the pro-inflammatory cytokines IL17, IL1β and INFγ synergistically upregulated miR-155 expression in KCs. Forced over-expression of miR-155 in human in vitro skin models specifically reduced the expression of loricrin (LOR) in KCs, indicating that miR-155 interferes with the establishment of a normal epidermal barrier. Together, our data indicate that downregulation of miR-155 during KC differentiation is a crucial step for epidermal barrier formation. Furthermore, its strong upregulation in psoriatic lesions suggests a contributing role of miR-155 in the altered keratinocyte differentiation observed in psoriasis. Therefore, miR-155 represents as a potential target for treating psoriatic skin lesions.

Dysbiotic Lesional Microbiome With Filaggrin Missense Variants Associate With Atopic Dermatitis in India

Background: Atopic Dermatitis (AD) has been associated with the loss of function (LoF) mutations in Filaggrin (FLG) gene and increase in relative abundance of specific microbes in the lesional skin, predominantly in Caucasians. Our study aims to determine, in Indian AD patients, (a) the prevalence of FLG LoF and missense mutations, and (b) the nature and extent of dysbiosis and altered microbial pathways with and without mutations in FLG. AD patients (n = 34) and healthy controls (n = 54) were recruited from India in this study and shotgun sequencing was carried out in a subset of samples with adequate microbiome DNA concentration. Host DNA from the same subset of samples was subjected to FLG coding region sequencing and host-microbiome association was estimated. Results: The prevalence of FLG LoFs that are associated with AD globally were significantly lesser in our cases and controls (8.6%, 0%) than those reported in Europeans (27%, 2.6%). Staphylococcus aureus was present only on AD skin [abundance in Pediatric AD: 32.86%; Adult AD: 22.17%], but not on healthy skin on which Staphylococcus hominis (Adult controls: 16.43%, Adult AD: 0.20%; p = 0.002), Cutibacterium acnes (Adult controls:10.84%, Adult AD: 0.90%; p = 0.02), and Malassezia globosa (Adult controls: 8.89%, Adult AD: 0.005%; p = 0.001) were significantly more abundant. Microbial pathways mostly associated with skin barrier permeability, ammonia production and inflammation (Arginine and Proline metabolism, Histidine Metabolism and Staphylococcus aureus infection) were significantly enriched on AD skin metagenome. These pathways are also reported to impair antimicrobial peptide activity. Among AD patients with missense single nucleotide polymorphisms harboring "potentially damaging" alleles in FLG gene, damaging allele dosage was significantly (p < 0.02) positively correlated with relative abundance of phylum_Proteobacteria up to order_Pseudomonadales and negatively correlated with phylum_Firmicutes up to species_Staphylococcus aureus. Conclusion: Our study has provided evidence that host DNA profile is significantly associated with microbiome composition in the development of AD. Species and strain level analysis showed that the microbial pathways enriched in AD cases were mostly found in MRSA strains. These evidences can be harnessed to control AD by modulating the microbiome using a personalized strategy. Our findings on the association of FLG genotypes with the microbiome dysbiosis may pave the way for a personalized strategy to provide a more effective control of AD.

Mutations of filament-aggregating protein gene in Romanian children diagnosed with atopic dermatitis

Association of atopic dermatitis (AD) and several mutations of various genes of the immune system, in particular filament-aggregating protein gene (FLG) has been investigated in many studies. The association between defective FLG and AD in the Romanian population has not been assessed or published. The present study focused on the genetic background of AD, aiming to assess the prevalence of FLG mutations in Romanian patients with AD. Genetic background of AD was tested for common FLG-mutations: R501X, 2282del4, S3247X and R2447X. The study involved 48 Romanian Caucasian children aged between two months and six years diagnosed with AD, and 48 healthy volunteers; DNA extraction involved 50% of the patients to give samples by using buccal swabs and 50% by collection of whole blood samples. Genetic predisposition was evaluated based on family history, atopy history and profilaggrin genotyping. DNA extracted from blood samples was adequate to study FLG mutations, although no mutation was identified. Genetic factors do not have a unique critical role in AD; therefore, environmental factors unquestionably play an important role in this disease, but the clear-cut part that these factors trigger toward increasing the risk of AD in childhood is still obscure.

Metabolomics of primary cutaneous melanoma and matched adjacent extratumoral microenvironment

BACKGROUND

Melanoma causes the vast majority of deaths attributable to skin cancer, largely due to its propensity for metastasis. To date, few studies have examined molecular changes between primary cutaneous melanoma and adjacent putatively normal skin. To broaden temporal inferences related to initiation of disease, we performed a metabolomics investigation of primary melanoma and matched extratumoral microenvironment (EM) tissues; and, to make inferences about progressive disease, we also compared unmatched metastatic melanoma tissues to EM tissues.

METHODS

Ultra-high performance liquid chromatography-mass spectrometry-based metabolic profiling was performed on frozen human tissues.

RESULTS

We observed 824 metabolites as differentially abundant among 33 matched tissue samples, and 1,118 metabolites as differentially abundant between metastatic melanoma (n = 46) and EM (n = 34) after false discovery rate (FDR) adjustment (p<0.01). No significant differences in metabolite abundances were noted comparing primary and metastatic melanoma tissues.

CONCLUSIONS

Overall, pathway-based results significantly distinguished melanoma tissues from EM in the metabolism of: ascorbate and aldarate, propanoate, tryptophan, histidine, and pyrimidine. Within pathways, the majority of individual metabolite abundances observed in comparisons of primary melanoma vs. EM and metastatic melanoma vs. EM were directionally consistent. This observed concordance suggests most identified compounds are implicated in the initiation or maintenance of melanoma.

Metabolism and Functions of Amino Acids in the Skin

Amino acids are the building blocks of all proteins, including the most abundant fibrous proteins in the skin, as keratins, collagen and elastin. Sagging and wrinkled skin are features of chronic sun-damaged and aged uncared skin, and they are mainly associated with the deterioration of collagen and elastic fibers. The maintenance of skin structures by self-repair processes is essential to skin health. Thus, amino acids significantly impact the appearance of the skin. Amino acids are important nutrients required for (a) wound healing promotion and repair of the damaged skin; (b) acid-base balance and water retention in cellular layers, such as stratum corneum; (c) protection against sunlight damage; (d) maintenance of an appropriate skin microbiome. This review highlights the contribution of all proteinogenic amino acids and some related metabolites to the skin structures as constituents of the main cutaneous proteins or as signaling molecules for the regulation and determination of skin physiology.

Imaging of metabolic activity adaptations to UV stress, drugs and differentiation at cellular resolution in skin and skin equivalents - Implications for oxidative UV damage

The epidermis is a multi-layered epithelium that consists mainly of keratinocytes which proliferate in its basal layer and then differentiate to form the stratum corneum, the skin's ultimate barrier to the environment. During differentiation keratinocyte function, chemical composition, physical properties, metabolism and secretion are profoundly changed. Extrinsic or intrinsic stressors, like ultraviolet (UV) radiation thus may differently affect the epidermal keratinocytes, depending on differentiation stage. Exposure to UV elicits the DNA damage responses, activation of pathways which detoxify or repair damage or induction of programmed cell death when the damage was irreparable. Recently, rapid diversion of glucose flux into the pentose phosphate pathway (PPP) was discovered as additional mechanism by which cells rapidly generate reduction equivalents and precursors for nucleotides - both being in demand after UV damage. There is however little known about the correlation of such metabolic activity with differentiation state, cell damage and tissue localization of epidermal cells. We developed a method to correlate the activity of G6PD, the first and rate-limiting enzyme of this metabolic UV response, at cellular resolution to cell type, differentiation state, and cell damage in human skin and in organotypic reconstructed epidermis. We thereby could verify rapid activation of G6PD as an immediate UVB response not only in basal but also in differentiating epidermal keratinocytes and found increased activity in cells which initiated DNA damage responses. When keratinocytes had been UVB irradiated before organotypic culture, their distribution within the skin equivalent was abnormal and the G6PD activity was reduced compared to neighboring cells. Finally, we found that the anti-diabetic and potential anti-aging drug metformin strongly induced G6PD activity throughout reconstructed epidermis. Activation of the protective pentose phosphate pathway may be useful to enhance the skin's antioxidant defense systems and DNA damage repair capacity on demand.

Emerging Strategies to Protect the Skin from Ultraviolet Rays Using Plant-Derived Materials

Sunlight contains a significant amount of ultraviolet (UV) ray, which leads to various effects on homeostasis in the body. Defense strategies to protect from UV rays have been extensively studied, as sunburn, photoaging, and photocarcinogenesis are caused by excessive UV exposure. The primary lines of defense against UV damage are melanin and trans-urocanic acid, which are distributed in the stratum corneum. UV rays that pass beyond these lines of defense can lead to oxidative damage. However, cells detect changes due to UV rays as early as possible and initiate cell signaling processes to prevent the occurrence of damage and repair the already occurred damage. Cosmetic and dermatology experts recommend using a sunscreen product to prevent UV-induced damage. A variety of strategies using antioxidants and anti-inflammatory agents have also been developed to complement the skin's defenses against UV rays. Researchers have examined the use of plant-derived materials to alleviate the occurrence of skin aging, diseases, and cancer caused by UV rays. Furthermore, studies are also underway to determine how to promote melanin production to protect from UV-induced skin damage. This review provides discussion of the damage that occurs in the skin due to UV light and describes potential defense strategies using plant-derived materials. This review aims to assist researchers in understanding the current research in this area and to potentially plan future studies.

Seven-day Green Tea Supplementation Revamps Gut Microbiome and Caecum/Skin Metabolome in Mice from Stress

Green tea supplementation has beneficial health effects. However, its underlying mechanisms, such as effects on modulating the intestinal microbiome and endogenous metabolome, particularly following short-term supplementation, are largely unclear. We conducted an integrative metabolomics study to evaluate the effects of short-term (7-day) supplementation of green tea extract (GTE) or its components, epigallocatechin gallate, caffeine, and theanine, on the caecum microbiota and caecum/skin metabolome in mice. Further, we established an integrative metabolome-microbiome model for correlating gut and skin findings. The effects of short-term supplementation with dietary compounds were evaluated with respect to UV stress response, with GTE showing the most remarkable effects. Biplot analysis revealed that Bifidobacteria and Lactobacillus spp. were considerably influenced by short-term GTE supplementation, while Clostridium butyricum was significantly increased by UV stress without supplementation. GTE supplementation helped the skin metabolome defend against UV stress. Interestingly, a significant positive correlation was observed between caecum bacteria (Bifidobacteria, Lactobacillus spp.) and metabolites including skin barrier function-related skin metabolites, caecal fatty acids, and caecal amino acids. Overall, 7-day GTE supplementation was sufficient to alter the gut microbiota and endogenous caecum/skin metabolome, with positive effects on UV stress response, providing insight into the mechanism of the prebiotic effects of GTE supplementation.

The role of filaggrin in atopic dermatitis and allergic disease

OBJECTIVE

To provide an overview of filaggrin biology and the role of filaggrin variants in atopic dermatitis (AD) and allergic disease.

DATA SOURCES

We performed a PubMed literature review consisting mainly of studies relating to filaggrin in the last 5 years.

STUDY SELECTIONS

We selected articles that were found in PubMed using the search terms filaggrin, atopic dermatitis, skin barrier, and atopy.

RESULTS

Filaggrin plays an important role in the development of AD and allergic disease. Novel methods in measuring filaggrin expression and identifying filaggrin mutations aid in stratifying this patient cohort. We review new insights into understanding the role of filaggrin in AD and allergic disease.

CONCLUSION

Filaggrin remains a very important player in the pathogenesis of atopic dermatitis and allergic disease. This review looks at recent studies that aid our understanding of this crucial epidermal protein.

p-Coumaric Acid as An Active Ingredient in Cosmetics: A Review Focusing on its Antimelanogenic Effects

Controlling unwanted hyperpigmentation is a major challenge in dermatology and cosmetology, and safe and efficacious antimelanogenic agents are deemed useful for this purpose. p-Coumaric acid is a natural metabolite contained in many edible plants, and its antioxidant activities in reducing oxidative stress and inflammatory reactions have been demonstrated in various experimental models. p-Coumaric acid has the optimal structure to be a competitive inhibitor of tyrosinase that catalyzes key reactions in the melanin biosynthetic pathway. Experimental evidence supports this notion as it was found to be a more potent inhibitor of tyrosinase, especially toward human enzymes, than other well-known tyrosinase inhibitors such as arbutin and kojic acid. p-Coumaric acid inhibited melanin synthesis in murine melanoma cells, human epidermal melanocytes, and reconstituted three-dimensional human skin models. Ex-vivo skin permeation experiments and in-vivo efficacy tests for p-coumaric acid confirmed its efficient transdermal delivery and functional efficacy in reducing erythema development and skin pigmentation due to ultraviolet radiation exposure. Human studies further supported its effectiveness in hypopigmentation and depigmentation. These findings suggest that p-coumaric acid has good potential to be used as a skin-lightening active ingredient in cosmetics. Future studies are needed to extensively examine its safety and efficacy and to develop an optimized cosmetic formulation for the best performance in skin lightening.

Neuroendocrine Aspects of Skin Aging

Skin aging is accompanied by a gradual loss of function, physiological integrity and the ability to cope with internal and external stressors. This is secondary to a combination of complex biological processes influenced by constitutive and environmental factors or by local and systemic pathologies. Skin aging and its phenotypic presentation are dependent on constitutive (genetic) and systemic factors. It can be accelerated by environmental stressors, such as ultraviolet radiation, pollutants and microbial insults. The skin’s functions and its abilities to cope with external stressors are regulated by the cutaneous neuroendocrine systems encompassing the regulated and coordinated production of neuropeptides, neurohormones, neurotransmitters and hormones, including steroids and secosteroids. These will induce/stimulate downstream signaling through activation of corresponding receptors. These pathways and corresponding coordinated responses to the stressors decay with age or undergo pathological malfunctions. This affects the overall skin phenotype and epidermal, dermal, hypodermal and adnexal functions. We propose that skin aging can be attenuated or its phenotypic presentation reversed by the topical use of selected factors with local neurohormonal activities targeting specific receptors or enzymes. Some of our favorite factors include melatonin and its metabolites, noncalcemic secosteroids and lumisterol derivatives, because of their low toxicity and their desirable local phenotypic effects.

Gene expression imputation identifies candidate genes and susceptibility loci associated with cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is a common skin cancer with genetic susceptibility loci identified in recent genome-wide association studies (GWAS). Transcriptome-wide association studies (TWAS) using imputed gene expression levels can identify additional gene-level associations. Here we impute gene expression levels in 6891 cSCC cases and 54,566 controls in the Kaiser Permanente Genetic Epidemiology Research in Adult Health and Aging (GERA) cohort and 25,558 self-reported cSCC cases and 673,788 controls from 23andMe. In a discovery-validation study, we identify 19 loci containing 33 genes whose imputed expression levels are associated with cSCC at false discovery rate < 10% in the GERA cohort and validate 15 of these candidate genes at Bonferroni significance in the 23andMe dataset, including eight genes in five novel susceptibility loci and seven genes in four previously associated loci. These results suggest genetic mechanisms contributing to cSCC risk and illustrate advantages and disadvantages of TWAS as a supplement to traditional GWAS analyses.

Genetic loci linked to susceptibility for the common skin cancer cutaneous squamous cell carcinoma (cSCC) have been identified by genome wide association studies (GWAS). Here, the authors impute gene expression levels from GWAS data to perform a transcriptome wide association study (TWAS), identifying five novel genetic loci linked to cSCC susceptibility.

Peptidylarginine deiminases and deiminated proteins at the epidermal barrier

Deimination or citrullination is a post-translational modification catalysed by a family of calcium-dependent enzymes called peptidylarginine deiminases (PADs). It corresponds to the transformation of arginine residues within a peptide sequence into citrulline residues. Deimination induces a decreased net charge of targeted proteins; therefore, it alters their folding and changes intra- and intermolecular ionic interactions. Deimination is involved in several physiological processes (inflammation, gene regulation, etc.) and human diseases (rheumatoid arthritis, neurodegenerative diseases, cancer, etc.). Here, we describe the PADs expressed in the epidermis and their known substrates, focusing on their role in the epidermal barrier function.

Moderate UV Exposure Enhances Learning and Memory by Promoting a Novel Glutamate Biosynthetic Pathway in the Brain

Sunlight exposure is known to affect mood, learning, and cognition. However, the molecular and cellular mechanisms remain elusive. Here, we show that moderate UV exposure elevated blood urocanic acid (UCA), which then crossed the blood-brain barrier. Single-cell mass spectrometry and isotopic labeling revealed a novel intra-neuronal metabolic pathway converting UCA to glutamate (GLU) after UV exposure. This UV-triggered GLU synthesis promoted its packaging into synaptic vesicles and its release at glutamatergic terminals in the motor cortex and hippocampus. Related behaviors, like rotarod learning and object recognition memory, were enhanced after UV exposure. All UV-induced metabolic, electrophysiological, and behavioral effects could be reproduced by the intravenous injection of UCA and diminished by the application of inhibitor or short hairpin RNA (shRNA) against urocanase, an enzyme critical for the conversion of UCA to GLU. These findings reveal a new GLU biosynthetic pathway, which could contribute to some of the sunlight-induced neurobehavioral changes.

Atopic Dermatitis: Disease Background and Risk Factors

Multiple risk factors have been associated with the development of atopic dermatitis (AD). Recent advances in understanding the role of genetics in this disease have been made, with discovery of the filaggrin (FLG) gene as the most notable so far. In addition to FLG gene mutations as a risk factor for AD, a positive family history of atopic or allergic disease in either parent, has been shown to confer a greater risk of developing AD. Atopic dermatitis usually presents early in life and is thought to represent the initial-step in the "atopic march" which is characterized by the development of other atopic diseases later in life such as asthma, allergic rhinitis and/or rhinoconjunctivitis, food allergies and hay fever. Other comorbid diseases that have been associated with AD include increase risk of viral and bacterial skin infections, neuropsychiatric diseases such as attention-deficit hyperactivity disorders (ADHD) and autistic spectrum disorder (ASD). Patients with AD, have also been found to have worse sleep quality overall compared to patients without AD. In this chapter, we will discuss the risk factors associated with development of atopic dermatitis as well as the most commonly reported comorbidities in patients with this disease.

Protective effect of neferine against UV-B-mediated oxidative damage in human epidermal keratinocytes

BACKGROUND

Studies have shown that skin exposure to ultraviolet radiation (UVR) results in the formation of reactive oxygen species (ROS), thus altering the cellular function. The human epidermal skin layer is mainly composed of keratinocytes, which is damaged by UV-B radiation-induced intracellular oxidative stress. Neferine is an alkaloid extract from lotus seed embryos and is known to promote antioxidant activity.

OBJECTIVE

In this study for the first time, we investigated the photoprotective action of neferine, against UV-B-produced oxidative damage in human epidermal keratinocytes (HEKs).

METHODS

We established an in Vitro study model using HEKs. Cellular viability was determined by MMT assay kits. The intracellular oxidative stress was measured using ROS and malondialdehyde (MDA) assay kits. Endogenous antioxidants were measured by superoxide dismutase (SOD) and glutathione peroxidase (GPx) assay kits. Photoprotective nature of neferine was further evaluated by analyzing the morphological and ultrastructural alterations in keratinocytes.

RESULTS

Neferine inhibit the UV-B-mediated increase in ROS and MDA levels in pretreated keratinocytes. The antioxidants, SOD and GPx activities were significantly high in neferine pretreated UV-B groups. Mitochondrial and endoplasmic reticulum damage were less evident in neferine-pretreated UV-B groups as compared with the control group, which might be associated with reduced oxidative stress and lipid peroxidation.

CONCLUSION

Taken together, our results suggest that neferine can prevent UV-B-induced oxidative damage and may thus be a potential agent for prevention and treatment of skin damage and photoaging.

Topical cis-urocanic acid prevents ocular surface irritation in both IgE -independent and -mediated rat model

PURPOSE

Our purpose was to investigate the effect of locally administered cis-urocanic (cis-UCA) in two experimental models of allergic conjunctivitis.

METHODS

The compound 48/80 (C48/80)-induced ocular irritation model (IgE-independent) and the ovalbumin (OA)-induced ocular allergy model (IgE-mediated) were used to test and compare the effect of cis-UCA on dexamethasone, ketotifen and olopatadine. In the C48/80 model, clinical severity scoring from photographs, immunohistochemical analysis of nuclear Ki-67 antigen to quantify actively proliferating epithelial cells and of caspase-3 enzyme to identify apoptotic activity in the conjunctival tissue were used. In the OA model, an Evans Blue stain concentration of conjunctival tissue was used to evaluate vascular leakage due to allergic reaction.

RESULTS

The cis-UCA was well tolerated and effective in both the IgE-independent and -mediated rat models. Treatment with C48/80 caused conjunctival hyperaemia, which was significantly inhibited by ketotifen at the 6 h time point (p = 0.014) and by dexamethasone and cis-UCA 0.5% at 12 (p = 0.004) and 24 (p = 0.004) hour time points. In a comparison between the active drug treatments, only ketotifen showed a significant difference (p = 0.023) to cis-UCA treatment at the 1 h time point, otherwise there were no statistically significant differences between the active drugs. Ketotifen, dexamethasone and cis-UCA 0.5% significantly inhibited the C48/80-induced nuclear accumulation of Ki-67, without differences between the active treatment groups. In the OA model, cis-UCA 0.5% did not inhibit the vascular leakage of conjunctiva, whereas cis-UCA 2.5% of was at least equally effective compared to olopatadine, abolishing the allergic vascular leakage response almost completely.

CONCLUSIONS

The present findings in the two AC models suggest that cis-UCA might have anti-allergic potency both in immediate and delayed-type allergic reactions in the eye.

Low-Frequency Synonymous Coding Variation in CYP2R1 Has Large Effects on Vitamin D Levels and Risk of Multiple Sclerosis

Vitamin D insufficiency is common, correctable, and influenced by genetic factors, and it has been associated with risk of several diseases. We sought to identify low-frequency genetic variants that strongly increase the risk of vitamin D insufficiency and tested their effect on risk of multiple sclerosis, a disease influenced by low vitamin D concentrations. We used whole-genome sequencing data from 2,619 individuals through the UK10K program and deep-imputation data from 39,655 individuals genotyped genome-wide. Meta-analysis of the summary statistics from 19 cohorts identified in CYP2R1 the low-frequency (minor allele frequency = 2.5%) synonymous coding variant g.14900931G>A (p.Asp120Asp) (rs117913124[A]), which conferred a large effect on 25-hydroxyvitamin D (25OHD) levels (-0.43 SD of standardized natural log-transformed 25OHD per A allele; p value = 1.5 × 10-88). The effect on 25OHD was four times larger and independent of the effect of a previously described common variant near CYP2R1. By analyzing 8,711 individuals, we showed that heterozygote carriers of this low-frequency variant have an increased risk of vitamin D insufficiency (odds ratio [OR] = 2.2, 95% confidence interval [CI] = 1.78-2.78, p = 1.26 × 10-12). Individuals carrying one copy of this variant also had increased odds of multiple sclerosis (OR = 1.4, 95% CI = 1.19-1.64, p = 2.63 × 10-5) in a sample of 5,927 case and 5,599 control subjects. In conclusion, we describe a low-frequency CYP2R1 coding variant that exerts the largest effect upon 25OHD levels identified to date in the general European population and implicates vitamin D in the etiology of multiple sclerosis.

Lowering relative humidity level increases epidermal protein deimination and drives human filaggrin breakdown

BACKGROUND

Deimination (also known as citrullination), the conversion of arginine in a protein to citrulline, is catalyzed by a family of enzymes called peptidylarginine deiminases (PADs). Three PADs are expressed in the epidermis, one of their targets being filaggrin. Filaggrin plays a central role in atopic dermatitis and is a key protein for the epidermal barrier. It aggregates keratins and is cross-linked to cornified envelopes. Following its deimination, it is totally degraded to release free amino acids, contributing to the natural moisturizing factor (NMF). The mechanisms controlling this multistep catabolism in human are unknown.

OBJECTIVE

To test whether external humidity plays a role, and investigate the molecular mechanisms involved.

METHODS

Specimens of reconstructed human epidermis (RHEs) produced in humid or dry conditions (>95% or 30-50% relative humidity) were compared.

RESULTS

RHEs produced in the dry condition presented structural changes, including a thicker stratum corneum and a larger amount of keratohyalin granules. The transepidermal water loss and the stratum corneum pH were decreased whereas the quantity of NMF was greater. This highly suggested that filaggrin proteolysis was up-regulated. The expression/activity of the proteases involved in filaggrin breakdown did not increase while PAD1 expression and the deimination rate of proteins, including filaggrin, were drastically enhanced. Partial inhibition of PADs with Cl-amidine reversed the effect of dryness on filaggrin breakdown.

CONCLUSION

These results demonstrate the importance of external humidity in the control of human filaggrin metabolism, and suggest that deimination plays a major role in this regulation.

Immunolocalization of a Histidine-Rich Epidermal Differentiation Protein in the Chicken Supports the Hypothesis of an Evolutionary Developmental Link between the Embryonic Subperiderm and Feather Barbs and Barbules

The morphogenesis of feathers is a complex process that depends on a tight spatiotemporal regulation of gene expression and assembly of the protein components of mature feathers. Recent comparative genomics and gene transcription studies have indicated that genes within the epidermal differentiation complex (EDC) encode numerous structural proteins of cornifying skin cells in amniotes including birds. Here, we determined the localization of one of these proteins, termed EDMTFH (Epidermal Differentiation Protein starting with a MTF motif and rich in Histidine), which belongs to a group of EDC-encoded proteins rich in aromatic amino acid residues. We raised an antibody against an EDMTFH-specific epitope and performed immunohistochemical investigations by light microscopy and immunogold labeling by electron microscopy of chicken embryos at days 14-18 of development. EDMTFH was specifically present in the subperiderm, a transient layer of the embryonic epidermis, and in barbs and barbules of feathers. In the latter, it partially localized to bundles of so-called feather beta-keratins (corneous beta-proteins, CBPs). Cells of the embryonic periderm, the epidermis proper, and the feather sheath were immunonegative for EDMTFH. The results of this study indicate that EDMTFH may contribute to the unique mechanical properties of feathers and define EDMTFH as a common marker of the subperiderm and the feather barbules. This expression pattern of EDMTFH resembles that of epidermal differentiation cysteine-rich protein (EDCRP) and feather CBPs and is in accordance with the hypothesis that a major part of the cyclically regenerating feather follicle is topologically, developmentally and evolutionarily related to the embryonic subperiderm.

The Expression of the Endogenous mTORC1 Inhibitor Sestrin 2 Is Induced by UVB and Balanced with the Expression Level of Sestrin 1

Sestrin 2 (SESN2) is an evolutionarily conserved regulator of mechanistic target of rapamycin complex 1 (mTORC1) which controls central cellular processes such as protein translation and autophagy. Previous studies have suggested that SESN2 itself is subjected to regulation at multiple levels. Here, we investigated the expression of SESN2 in the skin and in isolated skin cells. SESN2 was detected by immunofluorescence analysis in fibroblasts and keratinocytes of human skin. Differentiation of epidermal keratinocytes was not associated with altered SESN2 expression and siRNA-mediated knockdown of SESN2 did not impair stratum corneum formation in vitro. However, SESN2 was increased in both cell types when the expression of its paralog SESN1 was blocked by siRNA-mediated knock down, indicating a compensatory mechanism for the control of expression. Irradiation with UVB but not with UVA significantly increased SESN2 expression in both keratinocytes and fibroblasts. Upregulation of SESN2 expression could be completely blocked by suppression of p53. These results suggest that SESN2 is dispensable for normal epidermal keratinization but involved in the UVB stress response of skin cells.

Atopic Dermatitis Susceptibility Variants in Filaggrin Hitchhike Hornerin Selective Sweep

Human skin has evolved rapidly, leaving evolutionary signatures in the genome. The filaggrin (FLG) gene is widely studied for its skin-barrier function in humans. The extensive genetic variation in this gene, especially common loss-of-function (LoF) mutations, has been established as primary risk factors for atopic dermatitis. To investigate the evolution of this gene, we analyzed 2,504 human genomes and genotyped the copy number variation of filaggrin repeats within FLG in 126 individuals from diverse ancestral backgrounds. We were unable to replicate a recent study claiming that LoF of FLG is adaptive in northern latitudes with lower ultraviolet light exposure. Instead, we present multiple lines of evidence suggesting that FLG genetic variation, including LoF variants, have little or no effect on fitness in modern humans. Haplotype-level scrutinization of the locus revealed signatures of a recent selective sweep in Asia, which increased the allele frequency of a haplotype group (Huxian haplogroup) in Asian populations. Functionally, we found that the Huxian haplogroup carries dozens of functional variants in FLG and hornerin (HRNR) genes, including those that are associated with atopic dermatitis susceptibility, HRNR expression levels and microbiome diversity on the skin. Our results suggest that the target of the adaptive sweep is HRNR gene function, and the functional FLG variants that involve susceptibility to atopic dermatitis, seem to hitchhike the selective sweep on HRNR. Our study presents a novel case of a locus that harbors clinically relevant common genetic variation with complex evolutionary trajectories.

Variation in the activities of late stage filaggrin processing enzymes, calpain-1 and bleomycin hydrolase, together with pyrrolidone carboxylic acid levels, corneocyte phenotypes and plasmin activities in non-sun-exposed and sun-exposed facial stratum corneum of different ethnicities

BACKGROUND

Knowledge of the ethnic differences and effects of photodamage on the relative amounts of natural moisturizing factor (NMF) together with filaggrin processing enzymes in facial stratum corneum is limited. Our aim was to characterize the activities of calpain-1 (C-1), bleomycin hydrolase (BH) and the levels of pyrrolidone carboxylic acid (PCA) as a marker for total NMF levels and to relate them to plasmin activities and corneocyte maturation.

METHODS

Enzyme activities, PCA levels and corneocyte maturation were determined from facial tape strippings of photoexposed cheek and photoprotected post-auricular areas (PA) of healthy Caucasian (C), Black African (BA) and albino African (AA) female subjects living in South Africa.

RESULTS

PCA concentration levels were of the order AA > BA > C subjects, and the highest activities of BH were present in the AA subjects. BH activities were greater on the photoexposed sites for the BA and C subjects, but they were only numerically elevated in the AA subjects. Photoprotected sites had an increase in C-1 activity in pigmented groups (C and BA), whereas in the AA subjects, the opposite was measured. Plasmin activities were greater on the cheek compared with the PA site for the AA and C subjects, but the activity was low in the BA subjects. In both test sites, the AA, but not the BA and C subjects, had smaller, parakeratotic and less mature corneocytes.

CONCLUSION

Variation in PCA levels has been found for different ethnic groups in this study (AA > BA > C subjects). The values in the AA subjects are surprising as one might expect that the lack of pigmentation, and thereby increased photodamage, might lead to lower levels. Increased BH, but not C-1 activity, was observed in the AA subjects indicating that BH is associated with PCA production to a greater extent. Surprisingly, corneocyte maturation is still impaired with elevated PCA levels in AA subjects. The higher levels of plasmin and BH activities on the cheeks, especially for AA and C subjects, suggest that they can be used as markers for epidermal photodamage.