Complementary photoprotective antioxidant effect of sun filters and a combination of active molecules in a model of irridiated human keratinocytes

Skin photoprotection has become a real public health issue in view of the consequences of the sun on unprotected skin such as erythema, immunosuppression, skin cancer. The major role of UVA rays has long been neglected, even though their harmful effect over the long term, by notably generating oxidative stress. To prevent it, it has become important to provide biological protection in addition to sun filters. The aim of this study was to demonstrate the in vitro complementary efficacy of an active complex with sun filters on intracellular oxidative stress in normal human epidermal keratinocytes (NHEK) irradiated with the full solar spectrum (FSS).

NHEK were pre-incubated for 24 hours with the combination of ectoine and mannitol at 2 doses (n=3). Then, the formula containing sun filters (SPF30) was applied (1 mg/cm2) on a quartz plate placed above the culture plates. Cells were then irradiated with the FSS (calibrated on UVB 100mJ/cm2 + UVA 0,7 J/cm2) with a SOL 500 Sun Simulator equipped with H2 filter. The intracellular reactive oxygen species (ROS) production was then evaluated 30 minutes post-irradiation with the fluorescent probe H2DCF-DA. Control conditions without cream were performed in parallel. Fluorescence levels quantified with a spectrophotometer (λex= 485 nm, λem= 538 nm) are proportional to the quantity of intracellular ROS. A control of cell viability was performed on cell layers using a MTT reduction protocol.

The intracellular oxidative stress induced by FSS (2.5-fold change) was significantly reduced by the sun filters alone by 51%. The active complex increased the antioxidant protection provided by filters, by 31% for the 0.003% ectoine and 0.003% mannitol condition and by 35% for the 0.01% ectoine and 0.01% mannitol condition. The combination of sun filters with this active complex attributes to the finished product until 86% antioxidant protection.