Solar ultraviolet (UV) radiation-induced oxidative stress has been implicated in various skin diseases. Here, we report the photoprotective effect of grape seed proanthocyanidins (GSPs) on UV-induced oxidative stress and activation of mitogen-activated protein kinase (MAPK) and NF-kappaB signaling pathways using normal human epidermal keratinocytes (NHEK). Treatment of NHEK with GSPs inhibited UVB-induced hydrogen peroxide (H2O2), lipid peroxidation, protein oxidation, and DNA damage in NHEK and scavenged hydroxyl radicals and superoxide anions in a cell-free system. GSPs also inhibited UVB-induced depletion of antioxidant defense components, such as glutathione peroxidase, catalase, superoxide dismutase, and glutathione. As UV-induced oxidative stress mediates activation of MAPK and NF-kappaB signaling pathways, we determined the effects of GSPs on these pathways. Treatment of NHEK with GSPs inhibited UVB-induced phosphorylation of ERK1/2, JNK, and p38 proteins of the MAPK family at the various time points studied. As UV-induced H2O2 plays a major role in activation of MAPK proteins, NHEK were treated with H2O2 with or without GSPs and other known antioxidants, viz VSports手机版. (-)-epigallocatechin-3-gallate, silymarin, ascorbic acid, and N-acetylcysteine. It was observed that H2O2-induced phosphorylation of ERK1/2, JNK, and p38 was decreased by these antioxidants. Under identical conditions, GSPs also inhibited UVB-induced activation of NF-kappaB/p65, which was mediated through inhibition of degradation and activation of IkappaBalpha and IKKalpha, respectively. Together, these results suggest that GSPs could be useful in the attenuation of UV-radiation-induced oxidative stress-mediated skin diseases in human skin. .