Sunscreens with the New MCE Filter Cover the Whole UV Spectrum: Improved UVA1 Photoprotection In Vitro and in a Randomized Controlled Trial

Abstract

Background: UVA1 rays (340-400 nm) contribute to carcinogenesis, immunosuppression, hyperpigmentation, and aging. Current sunscreen formulas lack sufficient absorption in the 370-400 nm wavelengths range. Recently, a new UVA1 filter, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate (MCE) exhibiting a peak of absorption at 385 nm, was approved by the Scientific Committee on Consumer Safety for use in sunscreen products. These studies evaluated, in a three-dimensional skin model and in vivo, the protection afforded by state-of-the-art sunscreen formulations enriched with MCE.

Trial design: This study is a monocentric, double-blinded, randomized, and comparative trial. This study is registered at ClinicalTrials.gov with the identification number NCT04865094.

Methods: The efficacy of sunscreens with MCE was compared with that of reference formulas. In a three-dimensional skin model, histology, protein, and gene expression were analyzed. In the clinical trial, pigmentation was analyzed in 19 volunteers using colorimetric measurements and visual scoring.

Results: MCE addition in reference formulas enlarged the profile of absorption up to 400 nm; reduced UVA1-induced dermal and epidermal alterations at cellular, biochemical, and molecular levels; and decreased UVA1-induced pigmentation.

Conclusions: Addition of MCE absorber in sunscreen formulations leads to full coverage of UV spectrum and improved UVA1 photoprotection. The data support benefits in the long term on sun-induced consequences, especially those related to public health care issues.

Keywords: FC, fold change; ITA°, individual typology angle; KC, keratinocyte; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; MMP, matrix metalloproteinase; SPF, sun-protection factor.

© 2021 The Authors.

Figures

Figure 1

Characteristics of the MCE filter. (a, b) Structural and (c) absorption characteristics. MCE has a 322.41 g/mol molecular weight. (a) Molecular structure of the MCE filter in 2D with a Z configuration. (b) Molecular geometry in 3D of the MCE filter issued from the crystal structure (CCDC references JOKPOQ 973065) and visualized with Accelerys Discovery Studio 4.1. (c) Absorption spectrum of the MCE filter measured using a spectrophotometer by a 1-cm path length cuvette at 10 mg/l solution or by a 1-mm cuvette at 100 mg/l (measured absorbance every 5 nm). 2D, two-dimensional; 3D, three-dimensional; CCDC, Cambridge Crystallographic Data Center; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate.

Figure 2

Composition, protection factors and absorption spectrum of the sunscreen formulas. Composition and protection factors were given for (a) in vitro and (c) in vivo studies. The formula absorption spectra were obtained using transmission measurement carried out spectroradiometrically (290‒450 nm) through formulas dissolved in ethanol 0.1 g/l. (b) The absorption spectra of Reference vitro, Formula vitro 0.7% MCE, and Formula vitro 1.5% MCE were practically superimposed from 290 nm to 350 nm, leading to the close SPF values (between 17 and 20) of the three tested formulations. (d) The same results are observed for Reference vivo and Formula vivo 1.5% MCE (SPFs 27 and 32, respectively). Formulas vitro and vivo containing the UVA1 absorbing MCE filter exhibited broader absorption profiles in the UVA1 wavelength range than their respective reference. Fla, formula; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; PPD, persistent pigment darkening; Ref, reference; SPF, sun-protection factor.

Figure 3

Evaluation of sunscreen formulations on the morphology and number of fibroblasts of reconstructed skins exposed to UVA1. At 48 hours after UVA1 exposure, sections of reconstructed skins were realized to perform (a) histology, (b) vimentin immunostaining, and (c) fibroblasts counting. Four independent experiments were performed. In panel a, circles and arrows indicate epidermal alterations and depth of fibroblasts disappearance, respectively. In panel b, vimentin staining appears green and is located in fibroblasts’ cytoplasm. Cell nuclei counterstained using propidium iodide appear in red. In panel c, each point shows the mean value of fibroblasts number per field ± SEM. Asterisk (∗) indicates a significant difference from the Reference vitro; degree symbol (°) indicates significant difference from Formula vitro 0.7% MCE (Student’s t-test, P < 0.05). Fla, formula; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; Ref, reference.

Figure 4

Evaluation of sunscreen formulations on overall gene expression modulations in reconstructed skins exposed to UVA1. Six hours after exposure to 40 J/cm2 UVA1, the level of 27 and 24 transcripts were measured by qPCR in (a) fibroblasts and (b) keratinocytes of reconstructed skins, respectively, protected or not by a sunscreen formula. Three independent experiments were performed. Transcripts levels of UVA1-exposed samples were compared with those of nonexposed samples using a Student’s t-test. A transcript level was considered modulated if the ratio of transcripts level R in UVA1-exposed sample to transcript level in the nonexposed sample was >2 or <0.5 and if the P-value was <0.05. Color code gives the intensity of modulation of transcripts level by UVA1. ECM, extracellular matrix; Fla, formula; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; Ref, reference.

Figure 5

Levels of expression of 27 genes in fibroblasts of reconstructed skins protected or not by a formula and exposed to UVA1. Six hours after exposure to 40 J/cm2 UVA1, level of transcripts was quantified in a relative manner using qPCR in fibroblasts of the reconstructed skins. Three independent experiments were performed. The studied genes were distributed in the following functional families: (a) apoptosis/cancer/growth/development, (b) inflammation, (c) antiviral recognition/defense, (d) response to oxidative stress, (e) response to stress, and (f) extracellular matrix. White bars indicate nonprotected samples, pale gray bars indicate Reference vitro‒protected samples, and dark gray bars indicate Formula vitro 1.5% MCE‒protected samples. Each bar shows the mean value ± SEM. Differentially expressed genes are shown in bold versus those of the nonexposed sample. The significant differences between the ratio of Reference vitro‒protected and Formula vitro 1.5% MCE‒protected samples are indicated by superscript symbols, ∗P < 0.05; §0.05 ≤ P < 0.1 (Student's t-test). AU, arbitrary unit; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate.

Figure 6

Levels of expression of 24 genes in keratinocytes of reconstructed skins protected or not by a formula and exposed to UVA1. Six hours after exposure to 40 J/cm2 UVA1, levels of transcripts were quantified in a relative manner using qPCR in keratinocytes of reconstructed skins. Three independent experiments were performed. The studied genes were distributed in the following functional families: (a) apoptosis/cancer/growth/DNA repair/development, (b) inflammation, (c) extracellular matrix, (d) antiviral recognition/defense, and (e) response to stress/oxidative stress. White bars indicate nonprotected samples, pale gray bars indicate Reference vitro‒protected samples, and dark gray bars indicate Formula vitro 1.5% MCE‒protected samples. Each bar shows the mean value ± SEM. The differentially expressed genes are shown in bold versus those of the nonexposed sample. The significant differences between the ratio of reference vitro‒ and formula vitro 1.5% MCE‒protected samples are indicated by superscript symbols, ∗P < 0.05; §0.05 ≤ P < 0.1 (Student's t-test). AU, arbitrary unit; Fla, formula; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; Ref, reference.

Figure 7

Graphical representation and statistical analysis of the overall gene expression modulation. For (a) fibroblasts and (b) keratinocytes, the graphic (biplot) displays the first factorial plan of a PCA on the basis of the FC values (R > 1, FC = R; R < 1, FC = 1/R) induced by UVA1 exposure. It shows the similarities and dissimilarities between conditions (UVA1 in green, Reference vitro + UVA1 in blue, and Formula vitro 1.5% MCE + UVA1 in red) and allows for us to interpret these conditions in terms of modulated genes that are also plotted. Upregulated and downregulated genes by UVA1 exposure appear in gray and in yellow, respectively. The results of the associated nonparametric Jonckheere‒Terpstra trend test are detailed in the tables. They showed a significant evolution of the scores by conditions (P = 0.0009). FC, fold change; Fla, formula; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; PCA, principal component analysis; Ref, reference.

Figure 8

In vivo evaluation of sunscreen formulations on UVA1-induced pigmentation. A total of 2 mg/cm2 of products were applied per zone onto the back skin of 19 volunteers before UVA1 exposure (50 J/cm2). Colorimetric parameters (L∗, a∗, b∗) were measured before and 2 h and 24 h after UVA1 exposure. (a) Skin luminance (ΔL∗), skin pigmentation (ΔE), and ΔITA° between UVA1-exposed and -unexposed zones were calculated for each formula-treated zone. In parallel, a visual pigmentation scoring was performed using a 13-point scale grading from absence (0) to pronounced brown pigmentation (13). The (b) percentages of volunteers per score and (c) mean scores of pigmentation were plotted. (d) A representative photograph 24 h after UVA1 exposure is shown. Values are expressed as means ± 95% CI. Orange and blue asterisks indicate the differences from vehicle and from Reference vivo, respectively (P < 0.05). CI, confidence interval; Fla, formula; h, hour; ITA°, individual typology angle; MCE, Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate; Ref, reference.

Figure 9

UVA1 emission spectra. In the (a) in vitro and (b) in vivo studies, UVA1 rays were delivered using an Oriel solar simulator (1,000 W and 1,600 W, respectively) equipped with a dichroic mirror and a WG360 2 mm thick filter. Emission spectra were recorded using a calibrated Macam spectroradiometer. To deliver all of the UVA1 wavelengths (up to 400 nm), a part of the visible light spectrum (400–450 nm) could not be separated from applied UVA spectra of wavelengths.

Figure 10

CONSORT flow diagram of the clinical trial. A total of 22 volunteers were included in the study. Two of them were excluded for noneligibility and consent withdrawal reasons. A total of 20 randomized volunteers finalized the study, and one of them was excluded from the statistical analysis owing to an issue related to the application quantity of the product. Therefore, the data analysis was performed on 19 volunteers. CONSORT, Consolidated Standards of Reporting Trials; ISO, International Organization for Standardization; SPF, sun-protection factor.