Nrf-2/HO-1/NQO1 signaling activation led to attenuation in oxidative stress via downregulating ROS and NO production, thereby suppressing lung inflammation in the cigarette smoke extract-stimulated COPD and PPE-induced emphysema models (Cui et al., 2017; Yomoto et al., 2020). Here, NQO1 is linked to pulmonary emphysema.