Enhanced Nrf2 up-regulation by extracellular basic pH in a human skin equivalent system.

Extracellular basic pH regulates cellular processes in wounds, and consequently influenced wound healing. Oxidative defence system modulation in the skin helps heal wounds, inhibits skin ageing and improves the skin condition. Moreover, the role of keratinocyte growth factor (KGF) and nuclear factor erythroid 2-related factor 2 (Nrf2) in antioxidant systems has been reported in various skin models. However, the effects of extracellular basic pH on wound- or skin ageing-related skin damage have not been examined. Thus, we investigated the antioxidant systems affected by extracellular basic pH in a 3D human skin equivalent system (3HSE). Extracellular basic pH decreased KGF expression and enhanced the oxidative defence system, and thus activated Nrf2 in the 3HSE. Additionally, extracellular basic pH and KGF treatment up-regulated Nrf2 activation and its regulation of the oxidative defence system in the 3HSE. This indicates that Nrf2 up-regulation is enhanced by reactive oxygen species production, rather than KGF, and by extracellular basic pH of the skin. The inhibition of skin damage through pH imbalance and KGF regulation suggests that the development of pH-regulating or pH-maintaining materials may provide effective therapeutic strategies for maintaining a healthy skin.