Astaxanthin attenuates the UVB-induced secretion of prostaglandin E2 and interleukin-8 in human keratinocytes by interrupting MSK1 phosphorylation in a ROS depletion-independent manner

To elucidate the effects of redox balance regulation on cutaneous inflammation, we used the potent antioxidant astaxanthin (AX) to assess its effect on the UVB-induced secretion of PGE2 and IL-8 in human keratinocytes and analysed its biological mechanism of action. The addition of AX (at 8 mu m) to human keratinocytes even after UVB irradiation significantly down-regulated the increased secretion of PGE2 or IL-8. Those suppressive effects were accompanied by significantly decreased expression of genes encoding COX-2 or IL-8 as well as COX-2 protein. Analysis using a specific NF-kappa B tanslocation inhibitor demonstrated that the UVB-stimulated secretion of PGE2 and IL-8 was significantly abolished by its treatment prior to UVB irradiation. Western blotting of phosphorylated signalling molecules revealed that UVB irradiation (80 mJ/cm2) significantly stimulated the phosphorylation of p38, ERK and JNK, which was not suppressed by treatment with AX after irradiation. In contrast, AX significantly inhibited the UVB-increased phosphorylation of mitogen- and stress-activated protein kinase (MSK)-1, NF-kBp65 or CREB even when treated postirradiation. Further, the MSK1 inhibitor H89 significantly down-regulated the increased secretion of PGE2 and IL-8 in UVB-exposed human keratinocytes, following post-irradiation treatment. These findings suggests that AX attenuates the auto-phosphorylation of MSK1 required for its activation, which results in the decreased phosphorylation of NF-kBp65, which in turn probably leads to a deficiency of NF-kB DNA binding activity. This may be associated with the significant suppression of PGE2/IL-8 secretion via the down-regulated expression of COX-2 and IL-8 at the gene and/or protein levels.