Resveratrol induces glutathione synthesis by activation of Nrf2 and protects against cigarette smoke-mediated oxidative stress in human lung epithelial cells: implications in COPD

Nuclear erythroid related factor 2 (Nrf2) is a redox-sensitive transcription factor which is involved in the transcriptional regulation of many antioxidant genes, including glutamatecysteine ligase (GCL). Cigarette smoke is known to cause oxidative stress and deplete glutathione (GSH) levels in alveolar epithelial cells. We hypothesized that resveratrol, a polyphenolic phytoalexin, possesses antioxidant signaling properties by inducing GSH biosynthesis via the activation of Nrf2 and protects lung epithelial cells against cigarette smokemediated oxidative stress. Treatment of human primary small airway epithelial cells (SAEC) and human alveolar epithelial cells (A549) with cigarette smoke extract (CSE) dose-dependently decreased GSH levels and GCL activity, effects that were associated with enhanced production of ROS. Resveratrol restored CSE-depleted GSH levels by upregulation of GCL via activation of Nrf2, and also quenched CSE-induced ROS release. Interestingly, CSE failed to induce nuclear translocation of Nrf2 in both A549 and SAEC. On the contrary, Nrf2 was localized in the cytosol of alveolar and airway epithelial cells due to CSE-mediated post-translational modifications such as aldehyde/carbonyl adduct formation and nitration. On the other hand, resveratrol attenuated CSE-mediated Nrf2 modifications, thereby inducing its nuclear translocation associated with GCL gene transcription as demonstrated by GCL-promoter reporter and Nrf2 siRNA approaches. Thus, resveratrol attenuates CSE-mediated GSH depletion by inducing glutathione synthesis and protects epithelial cells by reversing CSE-induced post-translational modifications of Nrf2. These data may have implications in dietary modulation of antioxidants in treatment of COPD.