Curcumin has been strongly implicated as an anti-inflammatory agent, but the precise mechanisms of its action are largely unknown. In this Study, we show that curcumin contributes to anti-inflammatory activity in the murine asthma model and lung epithelial cell A549 through Suppression of nitric oxide (NO). To address this problem, Curcumin was injected into the peritoneum of ovalbumin (OVA)-sensitized mice before the last allergen challenge. OVA challenge resulted in activation of the production of inducible nitric oxide (iNOS) in lung tissue, inflammatory cytokines, recruitment of eosinophils to lung airways, and airway hyper-responsiveness to inhaled methacholine. These effects of ovalbumin challenge were all inhibited by pretreatment of mice with curcumin. Furthermore, supplementation with curcumin in the A549 human airway epithelial cells decreased iNOS and NO production induced by IFN-gamma. These findings show that curcumin may be useful as an adjuvant therapy for airway inflammation through suppression of iNOS and NO. (c) 2008 Elsevier Inc. All rights reserved.