We have previously found expression of the genes ABCB1 encoding P-gp, SLC47A1 encoding MATE1, SLC22A1 encoding OCT1, SLC22A4 encoding OCTN1, and SLC22A5 encoding OCTN2 in both the central and peripheral regions of the lung of ex-smokers with severe stage of COPD and healthy controls [7]. Here, SLC22A4 is linked to chronic obstructive pulmonary disease.