Gain of photoprotection afforded by the cyclic merocyanine UVA1 absorber MCE® in sunscreen formulae: A dose effect in vivo clinical trial

To the Editor, Ultraviolet (UV) rays that reach the earth surface is a combination of UVB, UVA2, and UVA1, the latter presenting a relatively constant level and high penetration properties. UVA1 rays have now been shown to contribute to the development of carcinogenesis, immunosuppression, photoaging, and hyperpigmentation.1 To prevent harmful effects of the whole solar UV spectrum, absorption of sunscreen formulae can now be designed to efficiently cover UVB and all the UVA wavelengths up to 400 nm.2 Indeed, addition in state of art sunscreen formulas of the cyclic merocyanine absorber, methoxypropylamino cyclohexenylidene ethoxyethylcyanoacetate (MCE®),3 a new UVA1 filter (λmax 385 nm) recently listed in the Annex VI of EU authorized UV filters,4 enables the coverage of the 360– 400 nm wavelengths range. The maximum concentration of MCE® authorized in sunscreens is 3%. Previous clinical studies have shown that enlarged SPF30 sunscreens with MCE at 1.5% and 2% allow to increase the prevention of hyperpigmentation compared to the sunscreen without MCE.5,6 The objective of this study was to evaluate the efficacy of MCE® at concentrations ranging from 0.5% to 2% using UVinducedpigmentation as a relevant noninvasive end point. The clinical


Gain of photoprotection afforded by the cyclic merocyanine UVA1 absorber MCE® in sunscreen formulae: A dose effect in vivo clinical trial
To the Editor, Ultraviolet (UV) rays that reach the earth surface is a combination of UVB, UVA2, and UVA1, the latter presenting a relatively constant level and high penetration properties. UVA1 rays have now been shown to contribute to the development of carcinogenesis, immunosuppression, photoaging, and hyperpigmentation. 1 To prevent harmful effects of the whole solar UV spectrum, absorption of sunscreen formulae can now be designed to efficiently cover UVB and all the UVA wavelengths up to 400 nm. 2 Indeed, addition in state of art sunscreen formulas of the cyclic merocyanine absorber, methoxypropylamino cyclohexenylidene ethoxyethylcyanoacetate (MCE®), 3  The objective of this study was to evaluate the efficacy of MCE® at concentrations ranging from 0.5% to 2% using UV-induced-  Results show that 50 J/cm 2 UVA1 exposure induced a strong pigmentation on the vehicle-treated zone. For the area treated with the reference sunscreen, the pigmentation level was significantly lower compared to vehicle condition at both time points (p < 0.001). Delta E scores at 2 h and 24 h were, respectively, 6.63 and 5.41 points for vehicle and 3.94 and 3.33 points for reference sunscreen (Delta E = √(ΔL*2 + Δa*2 + Δb*2), where Δ represents the difference between UVA1-exposed and -unexposed areas).
These differences were confirmed by the visual scoring assessment ( Figure 2 Comparing sunscreens + MCE® to each other, no significant difference was found with colorimetric measures at 2 h after exposure. At 24 h, MCE® at 1%, 1.5%, and 2% were not statistically different, but these three concentrations led to significantly lower level of pigmentation compared to 0.5% and 0.75% (p < 0.05). The visual scoring confirmed the results at 24 h and also showed significantly lower scores for 2%, 1.5%, and 1% compared to 0.5% and 0.75% at 2 h.
No adverse effects were observed during this study.
In agreement with previous data, 5,6 this study confirmed that thanks to UVA1 absorption properties, MCE® addition in a reference sunscreen, significantly improves photoprotection's efficacy.
The concentrations 1%, 1.5%, and 2% have a higher photoprotection effect without significant difference between them, indicating that 1% MCE® suffices to reach the highest level of efficacy in our conditions. These data are useful to adapt sunscreen formulations in line with the targeted level of photoprotection.

AUTH O R CO NTR I B UTI O N S
R. de Dormael, C. Tricaud, and F. Bernerd designed the study. A.
Roudot and D. Candau formulated the products. Philippe Bastien performed statistical analysis of the data. All authors contributed to data analysis and writing the article. They have reviewed and approved the final article.

FU N D I N G I N FO R M ATI O N
The work was funded by L'Oréal Research and Innovation, France.

CO N FLI C T O F I NTE R E S T
All authors are employees by L'Oréal, France.

DATA AVA I L A B I L I T Y S TAT E M E N T
The datasets generated during and/or analyzed during this study are available from the corresponding author on reasonable request.

E TH I C S S TATEM ENT
The study was performed in compliance with the ethical principles