Dual E-Cigarette Users Show Nicotine Addiction Risk Alleles and Nuclear Abnormalities in Oral Epithelial Cells

Background: This study was conducted to identify genetic risk variants associated with nicotine addiction in the CHRNA5, HTR2A, DRD4, and CYP2A6 genes among electronic cigarette users who also smoke combustible cigarettes (dual users), and to assess potential genotoxic and cytotoxic damage in the oral mucosal cells of the study population. Methods: We included dual e-cig users (ECIG, n = 70), combustible cigarette smokers (CCU, n = 24), and non-smokers and non-e-cig users (NS, n = 110). Genetic variants in CHRNA5, HTR2A, DRD4, and CYP2A6 were genotyped. Micronucleus analysis was performed on oral mucosal cells to detect cellular abnormalities. Results: The ECIG group demonstrated greater nicotine addiction on the Fagerström Test for Nicotine Dependence (FTND, 5.5 vs. 1, p = 0.023). Salivary cotinine levels were significantly higher in the ECIG group compared to the CCU group (39 vs. 12 ng/mL, p < 0.001). The carriers of the A allele (rs16969968/CHRNA5) had higher FTND scores, carriers of the C allele (rs1800955/DRD4) used electronic cigarettes more frequently each day, and carriers of the T allele (rs4105144/CYP2A6) started using nicotine products at a younger age. The number of micronuclei and cellular abnormalities in the oral mucosa was higher in the ECIG and CCU groups compared to the NS group. Conclusions: Salivary cotinine levels and FTND are higher in dual e-cigarette users than in combustible cigarette users. Dual users exhibit risk alleles in the CHRNA5, DRD4, and CYP2A6 genes, which are associated with traits linked to increased nicotine addiction. Dual e-cigarette use poses comparable genotoxic risks to combustible smoking.