Hydrating skin by stimulating biosynthesis of aquaporins.

Aquaporins (AQPs) are proteins that facilitate the transport of water across cell membranes. AQP3 expression is related to the expressions of other epidermal proteins involved in water maintenance (ie, CD44, claudin-1, and filaggrin). The expressions of AQP3 water channels are strongly affected by age and chronic sun exposure, and a defective osmotic equilibrium could occur in the epidermis, which would account for the skin dryness observed in older people and skin areas most exposed to sunlight. We investigated active ingredients that are able to increase AQP3 levels in order to improve hydration in human skin keratinocytes. We selected an ethanolic/water (70/30 v/v) extract of Ajuga turkestanica, a plant from Central Asia, as the hydrating agent. After 17 days of treatment every 2 days with this extract (2.5 microg/mL) in vitro, AQP3 expression measured at the protein level in human reconstructed epidermis was significantly increased. Water transport through both aquaporins and aquaglyceroporins and glycerol transport through aquaglyceroporins alone are important to skin hydration. The distribution and the variability of aquaporins in human skin cells suggest that these channels may have important roles in skin physiology. AQPs appear to be key protein targets to improve the resistance and quality of the skin surface as well as to improve aging and sun exposure-induced dryness as shown by their roles in 1) hydrating the living layers of the epidermis where the keratinocyte differentiation takes place and 2) barrier formation and recovery.