ARTICLE: Alteration to the Skin Barrier Integrity Following Broad-Spectrum UV Exposure in an Ex Vivo Tissue Model

April 2021 | Volume 20 | Issue 4 | Supplement Individual Articles | 23s | Copyright © April 2021


Published online April 6, 2021

Rebecca Barresi , Emily Chen , I-Chien Liao PhD, Xue Liu PhD, Nada Baalbaki PhD, Stephen Lynch PhD, Patricia Brieva PhD, Miao Wang , Qian Zheng MD PhD, Charbel Bouez PhD

L’Oréal Research and Innovation, Clark, NJ

Abstract
Dynamic changes to the skin barrier’s molecular structure and ceramide profile are well-documented in skin conditions such as atopic dermatitis and psoriasis. Pathological and environmental factors have been shown to impair barrier integrity and demonstrate shifts in ceramide composition in the skin. However, the relationship between acute and prolonged sun exposure and its effects on skin barrier homeostasis is insufficiently investigated. This study aims to uncover new scientific evidence to elucidate the relationship of UV irradiation with the skin barrier using an ex vivo tissue model following simulated UVA/UVB exposure. 

Fresh ex vivo human skin pretreated either with or without a broad-spectrum sunscreen was exposed to either a physiological or elevated UV condition. Following eight days in culture, structural and molecular changes were evaluated. UV irradiated skin displayed epidermal cell death and altered expression of key barrier proteins. TEM analysis demonstrated disruption to adherens junctions and dissociation between tissue layers following both physiological and extensive UV exposures. An effective broad-spectrum sunscreen containing essential skin ceramides completely protected the skin from such changes. This is one of the first works demonstrating a clear correlation of altered skin barrier integrity using a physiologically relevant dose in an ex vivo tissue model. Our findings also further support the additional importance and benefits of sun protection among the consumers. 

J Drugs Dermatol. 20(4 Suppl):s23-28. doi:10.36849/JDD.S589D

INTRODUCTION

The human skin barrier is a complex structure comprising of physical, chemical, immunological, and microbial components that maintain skin homeostasis whilst protecting the body from external irritants.1 The outermost layer of the skin, or the stratum corneum (SC), is the skin’s first line of defence against external irritants and comprises of corneocytes embedded in a lipid matrix composed of an equimolar ratio of cholesterol (CHOL), free fatty acids (FFAs), ceramides (CERs), and sterol/wax esters.2 Pathological conditions, such as atopic dermatitis (AD) or psoriasis, are known to trigger barrier disturbance through disruption of the natural ceramide profile, adherens junctions, and key barrier proteins.3–6 Furthermore, a direct correlation was observed in AD patients, where decreased FFA and CER chain lengths in AD skin caused less dense lipid organization increased transepidermal water loss (TEWL).7

The health concerns of prolonged UV exposure are welldocumented; it is shown to induce premature photoaging, altered pigmentation, inflammation, and carcinoma.8–10 In addition, there are several articles investigating the effects of ultraviolet (UV) radiation on skin barrier function.11–13 UV exposure was reported to induce epidermal barrier damage by altering the tight junction protein expression, disruption to the basement membrane junctions, decrease in the level of covalently bound ceramides, increase stratum corneum (SC) thickness & increase stratum corneum (SC) thickness and TEWL, and induce degradation to the structural and mechanical integrity of the skin.11,13–22 While each of the studies has furthered the understanding on UV on barrier function, the connection between a physiologically relevant UV dose with the molecular changes to the barrier of the skin remains unclear. This study is the first of two parts that utilized a physiologically relevant, fresh ex vivo skin model to understand how broad-spectrum UV affects the composition of epidermal barrier and illustrate how the application of sunscreen can provide barrier protection. This study also investigated the effects of a physiologically relevant dose, which mimics a chronic exposure to the maximum level of daily UV condition, and an elevated non-physiological exposure dose to serve as a contrast group.

Experimental Design
Ex Vivo Tissue Culture
Fresh ex vivo human skin was acquired from BioIVT LLC (Westbury, NY) one day post-abdominoplasty. A total of seven lots of fresh ex vivo skin was utilized in this study, (Caucasian (n=6), Hispanic (n=1), Male (n=1), Female (n=6), 29–51 years old). Tissue was defatted, cleaned of blood residue, and 1.2mm skin biopsy punches were created. Broad-spectrum CeraVe Hydrating Sunscreen SPF 50 Face Lotion, which contains Ceramides 1, 3, 6, in addition to other essential skin lipids, was applied (4.42 μL/cm2) to the respective biopsy punches fifteen minutes prior to irradiation. At this time, the study solely studied ceramide-incorporated formulas. These biopsy punches were then exposed to one-time exposure of 20J/cm2, a five-time exposure of 20J/cm2 over 1 week or one-time exposure of 100J/