Ultraviolet A not only plays a major part in
photoaging and skin tanning but also induces genetic damage
and mutation in the epidermal basal layer of human skin. The
photoprotective effect of oxyresveratrol and kuwanon O, two
phenolic compounds from the root extract of Morus australis, in
human primary epidermal keratinocytes was investigated in this
study. Both of them were nontoxic to cells at a concentration
less than 10 and 0.5 μM, respectively. After pretreatment at the
concentrations of 5 and 10 μM, oxyresveratrol increased cell
viability, exhibited significant suppressions on UVA- or H2O2-
induced cellular ROS. UVA-enhanced nitrotyrosine was also
reduced by post-treatment with oxyresveratrol at theses
concentrations. Kuwanon O presented similar inhibitions on
cellular ROS and nitrotyrosine with lower concentrations (0.25
and 0.5 μM), but there is no significant protection on cell survival after UVA irradiation. Their photoprotective effects also
involved the enhanced repair of 8-hydroxy-2′-deoxyguanosine (8-OHdG) and cyclobutane pyrimidine dimers (CPDs) as
mediated by the augment of p53 expression after UVA radiation.