A new hair follicle-derived human epidermal model for the evaluation of sunscreen genoprotection.

Induction of skin cancer is the most deleterious effect of excessive exposure to sunlight. Accurate evaluation of sunscreens to protect the genome is thus of major importance. In particular, the ability of suncare products to prevent the formation of DNA damage should be evaluated more directly since the Sun Protection Factor is only related to erythema induction. For this purpose, we developed an in vitro approach using a recently characterized reconstituted human epidermis (RHE) model engineered from hair follicle. The relevance of this skin substitute in terms of UV-induced genotoxicity was compared to ex vivo explants exposed to solar-simulated radiation (SSR). The yield of bipyrimidine photoproducts, their rate of repair, and the induction of apoptosis were very similar in both types of skin samples. In order to evaluate the protection afforded by sunscreen against DNA damage, bipyrimidine photoproducts were quantified in tissue models following SSR exposure in the presence or absence of a SPF50+ formula. A rather high DNA protection factor of approximately 20 was found in RHE, very similar to that determined for explants. Thus, RHE is a good surrogate to human skin, and also a convenient and useful tool for investigation of the genoprotection of sunscreens.

In vivo persistent pigment darkening method: proposal of a new standard product for UVA protection factor determination.

The European Commission (EC) has recommended assessing the level of ultraviolet A (UVA) protection afforded by sunscreen products using the in vivo persistent pigment darkening (PPD) method or other methods giving equivalent results. In this context, the reproducibility of the in vivo PPD method is of importance. To check the validity of the UVA protection factor (UVAPF) tests, the Japanese Cosmetic Industry Association (JCIA) recommends using a standard product (JCIA standard) with an expected UVAPF 3.75 (SD 1.01). However, considering the increase in UVA efficacy of the new sunscreen products available in the market, with UVAPF up to 30, it seemed useful to develop a new standard product to be used when testing products with expected UVAPF > or =10. The PPD method was used in six centres to determine the UVAPF of the two products. Reproducibility of results was also studied by testing two batches of the new product at two different times. There was no statistical difference between the six centres with regard to the JCIA standard. The ring study showed that the mean value of UVAPF (4.3) was higher than that given by JCIA (3.75). These data enable the proposal of a new acceptance range for the JCIA standard product (3.4-5.2) derived from actual results from European laboratories. Whereas this range is different from that proposed by JCIA (2.74-4.76), there is an overlapping of the values. Data on the new standard product show that reproducibility is not influenced by the batches of this product. The mean UVAPF value obtained is 12.1. An acceptance range (9.6-14.6) is proposed for the new standard. Data presented here demonstrate that if an identical protocol is used, reproducible results can be expected and that the PPD method is reproducible and reliable.

In vitro assessment of water resistance of sun care products: a reproducible and optimized in vitro test method.

The aim of the study was to develop a simple reproducible and reliable in vitro water resistance (WR) method to assess the sun care products. This paper is the result of a scientific collaboration between seven different international industrial laboratories and testing institutes. The same group has already achieved an in vitro protocol for the sun protection factor (SPF) determination [1]. The in vitro WR of sunscreens was tested by applying the same principle as in vivo, which determines the percentage of retention of sunscreen products by assessing the SPF before and after water immersion. Special care was taken to study the parameters influencing the WR and the possibility to follow the kinetics of sunscreen retention during water immersion. The influence of different water qualities has been tested, and osmosed water (1-3 microS cm(-1)) was chosen for the main ring study. Measurement was carried out after 5, 20 and 40 min of immersion. Histograms of selected products demonstrate the percentage of WR at all measuring times and centres, and the regression coefficient to the in vivo determination was shown and statistical calculations clearly demonstrate the reproducibility of the results between the different evaluation centres. The presented method is a practical, convenient and relevant tool for WR screening of sun care and skin care products. It even has the potential to be the starting point for the replacement of the in vivo method in future.