Modulations of gene expression induced by daily ultraviolet light can be prevented by a broad spectrum sunscreen

Evaluation of human skin response to solar-simulated radiation in an ex vivo model: Effects and photoprotection of L-Carnosine

Sunlight, and more specifically the UV component, induces several skin damages, including sunburns, erythema and photoaging. The purpose of this work is to set up an ex vivo human skin model to assess the capacity of active principles in protecting skin from the deleterious effects of solar radiation. Ex vivo human skin biopsies were cultured in an air-liquid interface and exposed to solar-simulated radiation (SSR, 300-750 nm). L-Carnosine (0.2% and 2%) was applied topically to be tested as photoprotective compound. The effect on oxidative stress induction, photoaging and skin transcriptional profile was assessed by evaluating reactive oxygen species, advanced glycosylation end products formation and gene expression changes. In our model, SSR increases ROS production and AGE accumulation and affects the expression of genes related to oxidative stress, pigmentation, immunity, inflammation and photoaging. Among these pathways, 11 genes were selected as biomarkers to evaluate the skin solar radiation response. Results showed that L-Carnosine provides effective prevention against solar radiation damages reducing ROS, AGEs and mitigating the modulation of the selected biomarker genes. In conclusion, we report that our ex vivo skin model is a valuable system to assess the consequences of solar light exposure and the capacity of topically applied L-Carnosine to counteract them.

Comparison of photodamage in non-pigmented and pigmented human skin equivalents exposed to repeated ultraviolet radiation to investigate the role of melanocytes in skin photoprotection

Introduction

Daily solar ultraviolet (UV) radiation has an important impact on skin health. Understanding the initial events of the UV-induced response is critical to prevent deleterious conditions. However, studies in human volunteers have ethical, technical, and economic implications that make skin equivalents a valuable platform to investigate mechanisms related to UV exposure to the skin. In vitro human skin equivalents can recreate the structure and function of in vivo human skin and represent a valuable tool for academic and industrial applications. Previous studies have utilised non-pigmented full-thickness or pigmented epidermal skin equivalents to investigate skin responses to UV exposure. However, these do not recapitulate the dermal-epidermal crosstalk and the melanocyte role in photoprotection that occurs in vivo. In addition, the UV radiation used in these studies is generally not physiologically representative of real-world UV exposure.

Methods

Well-characterised pigmented and non-pigmented skin equivalents that contain human dermal fibroblasts, endogenous secreted extracellular matrix proteins (ECM) and a well-differentiated and stratified epidermis have been developed. These constructs were exposed to UV radiation for ×5 consecutive days with a physiologically relevant UV dose and subsequently analysed using appropriate end-points to ascertain photodamage to the skin.

Results

We have described that repeated irradiation of full-thickness human skin equivalents in a controlled laboratory environment can recreate UV-associated responses in vitro, mirroring those found in photoexposed native human skin: morphological damage, tanning, alterations in epidermal apoptosis, DNA lesions, proliferation, inflammatory response, and ECM-remodelling.

Discussion

We have found a differential response when using the same UV doses in non-pigmented and pigmented full-thickness skin equivalents, emphasising the role of melanocytes in photoprotection.

Damaging effects of UVA, blue light, and infrared radiation: in vitro assessment on a reconstructed full-thickness human skin

Introduction

Exposure to solar radiation can cause a range of skin damage, including sunburn, erythema, skin carcinogenesis, the release of reactive oxygen species (ROS), inflammation, DNA damage, and photoaging. Other wavelengths beyond UVB, such as UVA, blue light, and infrared radiation, can also contribute to the harmful effects of solar radiation. Reconstructed full-thickness human skin has the potential to serve as effective predictive in vitro tools for evaluating the effects of solar radiation on the skin. The aim of this work was to evaluate the damaging effects of UVA, blue light, and infrared radiation in a full-thickness skin model in terms of viability, inflammation, photoaging, tissue damage, photocarcinogenesis.

Methods

Full thickness skin models were purchased from Henkel (Phenion FT; Düsseldorf, Germany), and irradiated with increasing doses of UVA, blue light, or infrared radiation. Different endpoints were analyzed on the tissues: Hematoxylin-eosin staining, inflammation mediators, photoaging-related dermal markers and oxidative stress marker GPX1, evaluated by real-time quantitative PCR, as well as photocarcinogenesis markers by Western Blot.

Results and Discussion

The results showed differential responses in cytokine release for each light source. In terms of photoaging biomarkers, collagen, metalloproteinases 1 and 9, elastin, and decorin were modulated by UVA and blue light exposure, while not all these markers were affected by infrared radiation. Furthermore, exposure to UVA and blue light induced loss of fibroblasts and modulation of the photocarcinogenesis markers p53 and p21. In conclusion, the presented results suggest that the various wavelengths of solar light have distinct and differential damaging effects on the skin. Understanding the differential effects of UVA, blue light, and infrared radiation can serve as a valuable tool to investigate the efficacy of photoprotective agents in full thickness skin models.

Sunscreen photoprotection and vitamin D status

Background

Global concern about vitamin D deficiency has fuelled debates on photoprotection and the importance of solar exposure to meet vitamin D requirements.

Objectives

To review the published evidence to reach a consensus on the influence of photoprotection by sunscreens on vitamin D status, considering other relevant factors.

Methods

An international panel of 13 experts in endocrinology, dermatology, photobiology, epidemiology and biological anthropology reviewed the literature prior to a 1‐day meeting in June 2017, during which the evidence was discussed. Methods of assessment and determining factors of vitamin D status, and public health perspectives were examined and consequences of sun exposure and the effects of photoprotection were assessed.

Results

A serum level of ≥ 50 nmol L⁻¹ 25(OH)D is a target for all individuals. Broad‐spectrum sunscreens that prevent erythema are unlikely to compromise vitamin D status in healthy populations. Vitamin D screening should be restricted to those at risk of hypovitaminosis, such as patients with photosensitivity disorders, who require rigorous photoprotection. Screening and supplementation are advised for this group.

Conclusions

Sunscreen use for daily and recreational photoprotection does not compromise vitamin D synthesis, even when applied under optimal conditions.

What's already known about this topic?

Knowledge of the relationship between solar exposure behaviour, sunscreen use and vitamin D is important for public health but there is confusion about optimal vitamin D status and the safest way to achieve this.

Practical recommendations on the potential impact of daily and/or recreational sunscreens on vitamin D status are lacking for healthy people.

What does this study add?

Judicious use of daily broad‐spectrum sunscreens with high ultraviolet (UV) A protection will not compromise vitamin D status in healthy people.

However, photoprotection strategies for patients with photosensitivity disorders that include high sun‐protection factor sunscreens with high UVA protection, along with protective clothing and shade‐seeking behaviour are likely to compromise vitamin D status.

Screening for vitamin D status and supplementation are recommended in patients with photosensitivity disorders.

Linked Comment: https://doi.org/10.1111/bjd.18126.

https://doi.org/10.1111/bjd.18494 available online

Validation of a predictive method for sunscreen formula evaluation using gene expression analysis in a Chinese reconstructed full-thickness skin model

OBJECTIVE

This study aimed to establish a predictive in vitro method for assessing the photoprotective properties of sunscreens using a reconstructed full-thickness skin model.

MATERIALS AND METHODS

A full-thickness skin model reconstructed with human fibroblasts and keratinocytes isolated from Chinese skin was exposed to daily UV radiation (DUVR). We examined the transcriptomic response, identifying genes for which expression was modulated by DUVR in a dose-dependent manner. We then validated the methodology for efficacy evaluation of different sunscreens formulas.

RESULTS

The reconstructed skin model was histologically consistent with human skin, and upon DUVR exposure, the constituent fibroblasts and keratinocytes exhibited transcriptomic alterations in pathways associated with oxidative stress, inflammation and extracellular matrix remodelling. When used to evaluate sunscreen protection on the model, the observed level of protection from UV-induced gene expression was consistent with the corresponding protection factors determined clinically and allowed for statistical ranking of sunscreen efficacy.

CONCLUSIONS

Within this study we show that quantification of gene modulation within the reconstructed skin model is a biologically relevant approach with sensitivity and predictability to evaluate photoprotection products.

Transcription factors and stress response gene alterations in human keratinocytes following Solar Simulated Ultra Violet Radiation

Ultraviolet radiation (UVR) from sunlight is the major effector for skin aging and carcinogenesis. However, genes and pathways altered by solar-simulated UVR (ssUVR), a mixture of UVA and UVB, are not well characterized. Here we report global changes in gene expression as well as associated pathways and upstream transcription factors in human keratinocytes exposed to ssUVR. Human HaCaT keratinocytes were exposed to either a single dose or 5 repetitive doses of ssUVR. Comprehensive analyses of gene expression profiles as well as functional annotation were performed at 24 hours post irradiation. Our results revealed that ssUVR modulated genes with diverse cellular functions changed in a dose-dependent manner. Gene expression in cells exposed to a single dose of ssUVR differed significantly from those that underwent repetitive exposures. While single ssUVR caused a significant inhibition in genes involved in cell cycle progression, especially G2/M checkpoint and mitotic regulation, repetitive ssUVR led to extensive changes in genes related to cell signaling and metabolism. We have also identified a panel of ssUVR target genes that exhibited persistent changes in gene expression even at 1 week after irradiation. These results revealed a complex network of transcriptional regulators and pathways that orchestrate the cellular response to ssUVR.

Skin Hyperpigmentation in Indian Population: Insights and Best Practice

Skin pigmentation is one of the most strikingly variable phenotypes in humans, therefore making cutaneous pigmentation disorders frequent symptoms manifesting in a multitude of forms. The most common among them include lentigines, postinflammatory hyperpigmentation, dark eye circles, and melasma. Variability of skin tones throughout the world is well-documented, some skin tones being reported as more susceptible to pigmentation disorders than others, especially in Asia and India. Furthermore, exposure to ultraviolet radiation is known to trigger or exacerbate pigmentation disorders. Preventive strategies for photoprotection and treatment modalities including topical and other medical approaches have been adopted by dermatologists to mitigate these disorders. This review article outlines the current knowledge on pigmentation disorders including pathophysiology, molecular profiling, and therapeutic options with a special focus on the Indian population.

Exposure to non-extreme solar UV daylight: spectral characterization, effects on skin and photoprotection

The link between chronic sun exposure of human skin and harmful clinical consequences such as photo-aging and skin cancers is now indisputable. These effects are mostly due to ultraviolet (UV) rays (UVA, 320–400 nm and UVB, 280–320 nm). The UVA/UVB ratio can vary with latitude, season, hour, meteorology and ozone layer, leading to different exposure conditions. Zenithal sun exposure (for example on a beach around noon under a clear sky) can rapidly induce visible and well-characterized clinical consequences such as sunburn, predominantly induced by UVB. However, a limited part of the global population is exposed daily to such intense irradiance and until recently little attention has been paid to solar exposure that does not induce any short term clinical impact. This paper will review different studies on non-extreme daily UV exposures with: (1) the characterization and the definition of the standard UV daylight and its simulation in the laboratory; (2) description of the biological and clinical effects of such UV exposure in an in vitro reconstructed human skin model and in human skin in vivo, emphasizing the contribution of UVA rays and (3) analysis of photoprotection approaches dedicated to prevent the harmful impact of such UV exposure.

Attenuation of ultraviolet A-induced alterations in NIH3T3 dermal fibroblasts by melatonin

BACKGROUND

Sun exposure is responsible for long-term clinical skin changes such as photoageing, photodamage and photocancers. Ultraviolet (UV)A wavelengths stimulate the production of reactive oxygen species (ROS) that may contribute to photoageing. To protect against oxidative stress, skin cells have developed several defence systems, including ROS and metal ion scavengers and a battery of detoxifying, haem-degrading and repair enzymes. Melatonin's antioxidant activity is the result of three different but complementary actions: (i) a direct action due to its ability to act as a free radical scavenger; (ii) an indirect action that is a consequence of melatonin's ability to reduce free radical generation (radical avoidance); and (iii) its ability to upregulate antioxidant enzymes.

OBJECTIVES

In this study, we focused our attention on the prevention of photodamage, choosing melatonin as an antioxidant agent.

METHODS

In the present study we analysed the effects of pretreatment of murine fibroblasts cells (NIH3T3) with melatonin (1 mmol L(-1) ) followed by UVA irradiation (15 J cm(-2) ). Thereafter, changes in components of the extracellular matrix and in some antioxidant enzymes (inducible and constitutive haem oxygenase) were evaluated.

RESULTS

We observed that UVA radiation caused altered expression of extracellular matrix proteins and induced the expression of inducible haem oxygenase. This increase was not sufficient to protect the cells from damage. Instead, melatonin pretreatment led to increased expression of haem-degrading enzymes and suppression of UVA-induced photodamage.

CONCLUSIONS

These results suggest that melatonin, as a modifier of the dermatoendocrine system, may have utility in reducing the effects of skin ageing.