Abstract
Quercetin (3,3',4',5,7-pentahydroxyflavone), a dietary flavonoid, is an inhibitor of phosphatidylinositol (PI) 3-kinase and potent antioxidant. We hypothesized that quercetin blocks airway epithelial cell chemokine expression via PI 3-kinase-dependent mechanisms. Pretreatment with quercetin and the PI 3-kinase inhibitor LY294002 each reduced TNF-alpha-induced IL-8 and monocyte chemoattractant protein (MCP)-1 (also called CCL2) expression in cultured human airway epithelial cells. Quercetin also inhibited TNF-alpha-induced PI 3-kinase activity, Akt phosphorylation, intracellular H(2)O(2) production, NF-kappaB transactivation, IL-8 promoter activity, and steady-state mRNA levels, consistent with the notion that quercetin inhibits chemokine expression by attenuating NF-kappaB transactivation via a PI 3-kinase/Akt-dependent pathway. Quercetin also reduced TNF-alpha-induced chemokine secretion in the presence of the transcriptional inhibitor actinomycin D, while inducing phosphorylation of eukaryotic translation initiation factor (eIF)-2alpha, suggesting that quercetin attenuates chemokine expression by post-transcriptional as well as transcriptional mechanisms. Finally, we tested the effects of quercetin in cockroach antigen-sensitized and -challenged mice. These mice show MCP-1-dependent airways hyperresponsiveness and inflammation. Quercetin significantly reduced lung MCP-1 and methacholine responsiveness. We conclude that quercetin blocks airway cell chemokine expression via transcriptional and post-transcriptional pathways.