Antioxidants modulate acute solar ultraviolet radiation-induced NF-kappa-B activation in a human keratinocyte cell line

Exposure of the human skin to ultraviolet radiation (UVR) leads to depletion of cutaneous antioxidants, regulation of gene expression and ultimately to the development of skin diseases. Although exogenous supplementation of antioxidants prevents UVR-induced photooxidative damage, their effects on components of cell signalling pathways leading to gene expression has not been clearly established. In the present study, the effects of the antioxidants α-lipoic acid, N-acetyl-L-cysteine (NAC) and the flavonoid extract silymarin were investigated for their ability to modulate the activation of the transcription factors nuclear factor kappa B (NF-κB) and activator protein-1 (AP-1) in HaCaT keratinocytes after exposure to a solar UV simulator. The activation of NF-κB and AP-1 showed a similar temporal pattern: activation was detected 2 h after UV exposure and maintained for up to 8 h. To determine the capacity of activated NF-κB to stimulate transcription, NF-κB-dependent gene expression was measured using a reporter gene assay. The effects of the antioxidants on NF-κB and AP-1 activation were evaluated 3 h after exposure. While a high concentration of NAC could achieve a complete inhibition, low concentrations of α-lipoic acid and silymarin were shown to significantly inhibit NF-κB activation. In contrast, AP-1 activation was only partially inhibited by NAC, and not at all by α-lipoic acid or silymarin. These results indicate that antioxidants such as α-lipoic acid and silymarin can efficiently modulate the cellular response to UVR through their selective action on NF-κB activation.