The flavonoid quercetin inhibits proinflammatory cytokine (tumor necrosis factor alpha) gene expression in normal peripheral blood mononuclear cells via modulation of the NF-kappa beta system.

The flavonoids comprise a large class of low-molecular-weight plant metabolites ubiquitously distributed in food plants. These dietary antioxidants exert significant antitumor, antiallergic, and anti-inflammatory effects. The molecular mechanisms of their biological effects remain to be clearly understood. We investigated the anti-inflammatory potentials of a safe, common dietary flavonoid component, quercetin, for its ability to modulate the production and gene expression of the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) by human peripheral blood mononuclear cells (PBMC). Our results showed that quercetin significantly inhibited TNF-alpha production and gene expression in a dose-dependent manner. Our results provide direct evidence of the anti-inflammatory effects of quercetin by PBMC, which are mediated by the inhibition of the proinflammatory cytokine TNF-alpha via modulation of NF-kappabeta1 and Ikappabeta.