Electrolytic-reduction ion water protects keratinocytes from hydrogen peroxide through radical scavenging activity and induction of AQP3 expression

Skin exposed to ultraviolet light produces hydrogen peroxide (H₂O₂) and reactive oxygen species (ROS) that cause protein denaturation and other disorders. We investigated whether electrolytic-reduction ion water (ERI), which has reducing properties and has been reported to protect skin, exhibits antioxidant activity in skin keratinocytes. The antioxidant activity of ERI was first examined using DPPH assay and Electron Spin Resonance to test for radicals, and using the Amplex Red method to test for H₂O₂. Concentration-dependent scavenging of hydroxyl radical but no H₂O₂ depletion were detected. An investigation of the expression of heme oxygenase-1, which is upregulated by oxidative response in cells, showed an increase through H₂O₂ oxidation, which was inhibited by ERI in a concentration-dependent manner. This suggests that ERI directly removes ROS. Quantitative real-time polymerase chain reaction analysis was performed to determine whether ERI regulates the expression of aquaporin 3 (AQP3), a known H₂O₂ transporter. This analysis revealed that ERI enhances AQP3 expression in a concentration-dependent manner and is involved in the transport of intracellular H₂O₂ to the extracellular space. In addition, ERI inhibited H₂O₂-induced cytotoxicity in a concentration-dependent manner. These results suggest that ERI protects keratinocytes from ROS by directly scavenging them and indirectly by eliminating them through the promotion of the efflux of intracellular H₂O₂.