AHR and chronic obstructive pulmonary disease: The analyses demonstrated that within the top 10 canonical pathways impacted by differentially methylated genes in the SAE of waterpipe smokers vs nonsmokers, there was significant enrichment of pathways previously associated with cigarette smoking and chronic obstructive pulmonary disease (COPD) including aryl hydrocarbon receptor signaling (15 genes), G-protein coupled receptor signaling (20 genes) and xenobiotic metabolism signaling (20 genes) further suggesting that both waterpipe and cigarette smoking have overlapping effects on the SAE epigenome (Table 3) [24, 25].