The effect of ultraviolet-B exposure scheduling on the photodamage of hairless mouse skin

The beneficial role of functional food components in mitigating ultraviolet-induced skin damage

Excessive exposure to ultraviolet (UV) radiation can chemically alter biological molecules and is one of the major environmental health risks with potential to damage the structure and function of the skin. Numerous dietary supplements are known to optimize the skin's defenses against radiation exposure. Several studies in which the beneficial roles of functional food components, that can protect against UV-induced skin damage, have been demonstrated. Supplemental dietary sphingomyelin maintains covalently bound ω-hydroxy ceramides to avert skin barrier defects after UVB irradiation. The oral administration of collagen hydrolysates has been shown to limit decreases in skin elasticity via increases in the dermal hyaluronic acid content. Milk fermented with lactic acid bacteria has been shown to augment DNA repair mechanisms and improve skin immunity in the aftermath of UVB damage. Furthermore, long-term ingestion of fermented milk containing lactic acid bacteria, collagen hydrolysates and sphingomyelin increases the minimal erythema dose (MED) in human subjects with moderate sunburn or redness and tanned skin after exposure to UV solar radiation. Thus, products containing these functional food components are one means by which the adverse effects of UV radiation on the skin can be mitigated.

Saccharomyces cerevisiae strains as bioindicators for titanium dioxide sunscreen photoprotective and photomutagenic assessment

Although several short-term assays are available for cosmetic photosafety assessment, cell models are usually highly sensitive to UV radiation, tending to overestimate both phototoxic and photomutagenic risks. In addition, these assays are performed with UV doses/fluences that do not correspond to actual environmental conditions. In this sense, Saccharomyces cerevisiae has already proved to be an interesting tool to predict photomutagenic potential of several compounds, including sunscreens. Yeast can support environmental UVB doses compatible with human daily sunlight exposure, allowing the use of irradiation sources to faithfully mimic the external conditions of ambient sunlight. Herein, we used a set of S. cerevisiae mutant strains sensitive to UVA, UVB and Solar Simulated Light sources in order to evaluate their potential as bioindicators for sunscreen development. The bioindicator potential of the strains was tested with the widely-used titanium dioxide inorganic sunscreen. The AWP001 (yno1) and LPW002 (ogg1yno1) strains obtained in this study stood out as promising experimental tools for the validation of this assay. Overall, our results evidenced a set of S. cerevisiae strains particularly useful for evaluating both photoprotective (efficacy) and photo/antiphotomutagenic (safety) potential of UV filters, meeting the industries and regulatory agencies demand for robust and efficient in vitro screening tests.

Brazilian Green Propolis Rescues Oxidative Stress-Induced Mislocalization of Claudin-1 in Human Keratinocyte-Derived HaCaT Cells

Claudin-1 (CLDN1) is expressed in the tight junction (TJ) of the skin granular layer and acts as a physiological barrier for the paracellular transport of ions and nonionic molecules. Ultraviolet (UV) and oxidative stress may disrupt the TJ barrier, but the mechanism of and protective agents against this effect have not been clarified. We found that UVB and hydrogen peroxide (H₂O₂) caused the internalization of CLDN1 and increased the paracellular permeability of lucifer yellow, a fluorescent marker, in human keratinocyte-derived HaCaT cells. Therefore, the mechanism of mislocalization of CLDN1 and the protective effect of an ethanol extract of Brazilian green propolis (EBGP) were investigated. The UVB- and H₂O₂-induced decreases in CLDN1 localization were rescued by EBGP. H₂O₂ decreased the phosphorylation level of CLDN1, which was also rescued by EBGP. Wild-type CLDN1 was distributed in the cytosol after treatment with H₂O₂, whereas T191E, its H₂O₂-insensitive phosphorylation-mimicking mutant, was localized at the TJ. Both protein kinase C activator and protein phosphatase 2A inhibitor rescued the H₂O₂-induced decrease in CLDN1 localization. The tight junctional localization of CLDN1 and paracellular permeability showed a negative correlation. Our results indicate that UVB and H₂O₂ could induce the elevation of paracellular permeability mediated by the dephosphorylation and mislocalization of CLDN1 in HaCaT cells, which was rescued by EBGP. EBGP and its components may be useful in preventing the destruction of the TJ barrier through UV and oxidative stress.

Histological observation of hairless mice skin after exposure to Simulated Solar Light: Comparison between the histological findings with different methodologies and 3R principle correlations

BACKGROUND

Albino hairless mouse (AHM) has been used as a biological model in photodermatology. However, the experimental landscape is diverse to follow and need particular attention.

PURPOSE

Irradiation parameters were investigated for the development of a protocol to assess alterations in the AHM skin using Simulated Solar Light (SSL). The present study was compared with published articles (last 15 years) according to irradiation protocols, morphological findings to minimize animal suffering and UV exposure.

MATERIALS AND METHODS

Three groups: Control (G1), experimental - sunburn (G2) and skin photodamage assay (G3). G2 were immobilized and exposed to SSL once for 15, 30 and 45min. G3 were exposed to SSL, without immobilization, for 15min once a day for one week. The dorsal skin was analyzed using hematoxylin and eosin technique.

RESULTS

G2 displayed different sunburn degrees. Based on the profile of the observed morphological alterations, a 15min irradiation was chosen as the exposure time to expose G3, without immobilization, for 5 consecutive days.

CONCLUSION

These conditions produced the same morphological changes in the AHM with a shorter solar exposure time, without immobilizing the animals but using environmental exposure fluences, conforming to 3R (reduction - refinement - replacement) recommendations.

Collagen hydrolysate intake improves the loss of epidermal barrier function and skin elasticity induced by UVB irradiation in hairless mice

BACKGROUND

Ultraviolet B (UVB) irradiation induces serious damage to the skin. Collagen hydrolysate and collagen-derived peptides have effects on skin function in vivo and in vitro. However, few studies have investigated changes in the epidermal barrier or dermal elasticity caused by UVB. Here, we investigated the loss of epidermal barrier function and skin elasticity induced by UVB irradiation in hairless mice fed collagen hydrolysate.

METHODS

Mice were orally administered collagen hydrolysate, in a single dose (20 mJ/cm(2) ) or repeated doses (10-30 mJ/cm(2) , 3 times/week for 6 weeks), and the dorsal skin was exposed to UVB. Skin measurements and histological and analytical studies were performed.

RESULTS

In control mice, a single UVB irradiation induced epidermal barrier dysfunction including an increase in transepidermal water loss (TEWL), epidermal hyperplasia, and a decrease in stratum corneum water content. Administration of collagen hydrolysate significantly decreased TEWL and epidermal thickness and increased stratum corneum water content. Repeated UVB irradiation decreased skin elasticity and dermal hyaluronic acid (HA) content in control mice, whereas collagen hydrolysate significantly suppressed both the increase in TEWL and the decrease in stratum corneum water content and improved skin elasticity and dermal HA content.

CONCLUSIONS

Collagen hydrolysate administration affects epidermal barrier function and dermal skin elasticity.

Effects of a sunscreen formulation on albino hairless mice: a morphological approach

The purpose of the study was to evaluate the effects of a sunscreen formulation on the skin of albino hairless mice subjected to simulated solar light (SSL) in terms of morphological changes. Young adult albino hairless mice HRS/J (n = 36) were used as an experimental model for determining skin photoaging changes. Mice were irradiated with SSL, and the sunscreen (estimated SPF 30, PF-UVA) was obtained from the Pharmacy College/UFRJ, Brazil. The animals were divided into four groups: non-treated (G1), radiation only (G2), sunscreen-treated (G3) and vehicle + radiation (G4). Animals from groups G2, G3 and G4 were irradiated weekly (5 weeks), with no immobilization. One week after the final exposure, the dorsal skin was observed using a dermatoscopic camera. Biopsies were analyzed in order to quantify neovascularization and to evaluate histological aspects of the skin. Neovascularization was also evaluated with immunohistochemical reactions for the Von Willebrand factor. Animals from G2 displayed classical morphological changes denoting skin photoaging: thickening of the epidermis, increased dermal cellularity, follicular keratosis, sebaceous gland hyperplasia, and angiogenesis. Animals from groups G3 and G1 displayed similar morphological profiles, without these changes. Animals from group G4 showed more morphological changes than group G2, emphasizing the relative importance of the putative photosensitizing components present in the vehicle formulation. The extent of the morphological skin changes suggested that the sunscreen formulation was effective against SSL, and showed the importance of assessing the phototoxicity of vehicle formulations.