HMOX1 and chronic obstructive pulmonary disease: In a study of ex-smokers with and without COPD, the expression of HMOX1 (p < 0.001) was significantly upregulated in PBMCs from individuals suffering from COPD, thus emphasizing the role of the NRF2 pathway as a systemic response aiming to reduce the burden of the disease-induced oxidative stress [34].