Deletion of Keap1 in the Lung Attenuates Acute Cigarette Smoke–Induced Oxidative Stress and Inflammation

Exposure to cigarette smoke (CS) is the primary factor associated with the development of chronic obstructive pulmonary disease (COPD). CS increases the level of oxidants in the lungs, resulting in a depletion of antioxidants, which promotes oxidative stress and the destruction of alveolar tissue. In response to CS, pulmonary epithelial cells counteract increased levels of oxidants by activating Nrf2-dependent pathways to augment the expression of detoxification and antioxidant enzymes, thereby protecting the lung from injury. We hypothesize that increasing the pathways activated by Nrf2 will afford protection against CS-induced lung damage. To this end we have developed a novel mouse model in which the cytosolic inhibitor of Nrf2, Keap1, is genetically deleted in Clara cells, which predominate in the upper airways in mice. Deletion of Keap1 in Clara cells resulted in increased expression of Nrf2-dependent genes, such as Nqo1 and Gclm, as determined by microarray analysis and quantitative PCR. Deletion of Keap1 in airway epithelium decreased Keap1 protein levels and significantly increased the total level of glutathione in the lungs. Increased Nrf2 activation protected Clara cells against oxidative stress ex vivo and attenuated oxidative stress and CS-induced inflammation in vivo. Expression of KEAP1 was also decreased in human epithelial cells through siRNA transfection, which increased the expression of Nrf2-dependent genes and attenuated oxidative stress. In conclusion, activating Nrf2 pathways in tissue-specific Keap1 knockout mice represents an important genetic approach against oxidant-induced lung damage

Denitrosylation of HDAC2 by targeting Nrf2 restores glucocorticosteroid sensitivity in macrophages from COPD patients

Chronic obstructive pulmonary disease (COPD), which is caused primarily by cigarette smoking, is a major health problem worldwide. The progressive decline in lung function that occurs in COPD is a result of persistent inflammation of the airways and destruction of the lung parenchyma. Despite the key role of inflammation in the pathogenesis of COPD, treatment with corticosteroids — normally highly effective antiinflammatory drugs — has little therapeutic benefit. This corticosteroid resistance is largely caused by inactivation of histone deacetylase 2 (HDAC2), which is critical for the transrepressive activity of the glucocorticoid receptor (GR) that mediates the antiinflammatory effect of corticosteroids. Here, we show that in alveolar macrophages from patients with COPD, S-nitrosylation of HDAC2 is increased and that this abolishes its GR-transrepression activity and promotes corticosteroid insensitivity. Cys-262 and Cys-274 of HDAC2 were found to be the targets of S-nitrosylation, and exogenous glutathione treatment of macrophages from individuals with COPD restored HDAC2 activity. Treatment with sulforaphane, a small-molecule activator of the transcription factor nuclear factor erythroid 2–related factor 2 (NRF2), was also able to denitrosylate HDAC2, restoring dexamethasone sensitivity in alveolar macrophages from patients with COPD. These effects of sulforaphane were glutathione dependent. We conclude that NRF2 is a novel drug target for reversing corticosteroid resistance in COPD and other corticosteroid-resistant inflammatory diseases

Targeting Nrf2 with the triterpenoid CDDO- imidazolide attenuates cigarette smoke-induced emphysema and cardiac dysfunction in mice

Chronic obstructive pulmonary disease (COPD), which comprises emphysema and chronic bronchitis resulting from prolonged exposure to cigarette smoke (CS), is a major public health burden with no effective treatment. Emphysema is also associated with pulmonary hypertension, which can progress to right ventricular failure, an important cause of morbidity and mortality among patients with COPD. Nuclear erythroid 2 p45 related factor-2 (Nrf2) is a redox-sensitive transcription factor that up-regulates a battery of antioxidative genes and cytoprotective enzymes that constitute the defense against oxidative stress. Recently, it has been shown that patients with advanced COPD have a decline in expression of the Nrf2 pathway in lungs, suggesting that loss of this antioxidative protective response is a key factor in the pathophysiological progression of emphysema. Furthermore, genetic disruption of Nrf2 in mice causes early-onset and severe emphysema. The present study evaluated whether the strategy of activation of Nrf2 and its downstream network of cytoprotective genes with a small molecule would attenuate CS-induced oxidative stress and emphysema. Nrf2+/+ and Nrf2−/− mice were fed a diet containing the potent Nrf2 activator, 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im), while being exposed to CS for 6 months. CDDO-Im significantly reduced lung oxidative stress, alveolar cell apoptosis, alveolar destruction, and pulmonary hypertension in Nrf2+/+ mice caused by chronic exposure to CS. This protection from CS-induced emphysema depended on Nrf2, as Nrf2−/− mice failed to show significant reduction in alveolar cell apoptosis and alveolar destruction after treatment with CDDO-Im. These results suggest that targeting the Nrf2 pathway during the etiopathogenesis of emphysema may represent an important approach for prophylaxis against COPD