Accumulated p53 protein and UVA protection level of sunscreens

Nuclear p53 expression is a sensitive parameter for the detection of ultrav iolet (UV)-induced skin damage, and it has been used as an endpoint to eval uate the effectiveness of sunscreens. In this study me compared the protect ion provided by two sunscreens having identical sun protection factors (SPF ) but different UVA protection factors (UVA-PF) measured by the persistent pigment darkening method (PPD). The SPF of the sunscreens was 7 and the UVA -PF mere respectively 7 and 3, Nuclear p53 protein was quantified in human skin biopsies treated with sunscreens and exposed 8 times to 5 MED of solar simulated radiation (SSR), The results showed that both sunscreens offered only partial protection against the increased expression of nuclear p53 pr otein induced by repetitive SSR exposures. However, a significantly lower l evel of p53-positive cells was found in areas protected with the sunscreen having the higher UVA-PF compared to the other sunscreen protected areas. I n order to verify whether the difference in efficacy of these products mas due to the difference in UVA absorption capacity, we quantified epidermal p 53 protein accumulation after 8 exposures to either UVA (320-400 nm) or UVA 1 (340-400 nm), We showed that as with SSR, repetitive exposures to 12.5 an d 25 J/cm(2) of UVA or UVA1 induced a significant increase in p53-positive cells in the human epidermis, These results confirmed that SPF determined o n the basis of an acute erythemal reaction does not predict the level of pr otection against cumulative damage. They also showed that the protection pr ovided by two sunscreens with different UVA protection factors is different (based on nuclear p53 protein accumulation), and that the PPD method can d istinguish varying levels of sunscreen efficacy against UVA-induced cell da mage.