Quercetin inhibits UV irradiation-induced inflammatory cytokine production in primary human keratinocytes by suppressing NF-κB pathway

BackgroundTopical flavonoids, such as quercetin, have been shown to reduce ultraviolet (UV) irradiation-mediated skin damage. However, the mechanisms and signaling pathways involved in this protective effect are not clear. UV irradiation leads to activation of two major signaling pathways, namely nuclear factor kappa B (NF-κB) and activator protein-1 (AP-1) pathways. Activation of NF-κB pathway by UV irradiation stimulates inflammatory cytokine expression, whereas activation of AP-1 pathway by UV irradiation promotes matrix metalloproteinase (MMP) production. Both pathways contribute to UV irradiation-induced skin damage, such as photoaging and skin tumor formation.ObjectiveTo elucidate the underlying mechanism, we examined the effect of quercetin on UV irradiation induced activation of NF-κB and AP-1 pathways.MethodsPrimary human keratinocytes, the major skin cell type subjected to physiological solar UV irradiation, were used to study the effects of quercetin on UV irradiation-induced signal transduction pathways.ResultsQuercetin decreased UV irradiation-induced NF-κB DNA-binding by 80%. Consequently, quercetin suppressed UV irradiation-induced expression of inflammatory cytokines IL-1β (∼60%), IL-6 (∼80%), IL-8 (∼76%) and TNF-α (∼69%). In contrast, quercetin had no effect on UV irradiation activation of three MAP kinases, ERK, JNK, or p38. Accordingly, induction of AP-1 target genes such as MMP-1 and MMP-3 by UV irradiation was not suppressed by quercetin.ConclusionOur data indicate that the ability of quercetin to block UV irradiation-induced skin inflammation is mediated, at least in part, by its inhibitory effect on NF-κB activation and inflammatory cytokine production.