CYP1A1 and chronic obstructive pulmonary disease: One of PAH-metabolizing cytochrome P450 enzymes, CYP1A1, is a well-known aryl hydrocarbon hydroxylase, widely expressed in tissues including liver, lung, intestine, skin, lymphocytes, and macrophages [12]; many studies had investigated the carcinogenic role of these CYPs in related pulmonary disease including COPD [13–17].