Dissecting the Epigenomic Differences between Smoking and Nicotine Dependence in a Veteran Cohort

Background: Smoking is a serious public health issue linked to more than 8 million deaths per year worldwide. It also may lead to nicotine dependence (ND). Smoking can induce long-lasting epigenetic changes. Although epigenetic alterations related to tobacco smoke have been largely studied, few works have investigated ND and its interaction with smoking status (SS). Objective: We investigated the peripheral epigenomic profile of SS and ND in a U.S. male veteran cohort. Methods: DNA from saliva was collected from 1,135 European American (EA) male U.S. military veterans. DNAm was assessed using the Illumina Infinium Human MethylationEPIC BeadChip array. SS was evaluated as: current smokers (n=137; 12.1%) and non-current smokers (never and former smokers; n=998; 87.9%). ND was assessed using the Fagerstrom Test for Nicotine Dependence (FTND). EWAS and co-methylation analyses were conducted for SS and ND. Results: A total of 450 and 22 genome-wide significant differentially methylated sites (DMS) were associated with SS and ND, respectively (fifteen overlapped sites). We identified 97 DMS (43 genes) in SS-EWAS previously reported in the literature, including AHRR, and F2RL3 genes (p-value range: 1.95x10-83 to 4.5x10-33). ND novel DMS mapped to NEUROG1, ANPEP, and SLC29A1. Co-methylation analysis identified 386 modules (11 SS-related and 19 ND-related). SS-related modules showed enrichment for alcoholism, chemokine signaling pathway, and neurogenesis; while ND-related modules were enriched for cellular adhesion, and nicotine addiction. Conclusions: This study confirms previous findings and identifies novel and -potentially specific - epigenetic signatures for SS and ND in a sample of EA male veterans.