What e-cigarette factors determine oral epithelial DNA damage in consumers?

Study participants were divided equally into three groups being exclusive vapers (never smokers), current exclusive smokers and non-users. Brush biopsy samples of oral epithelial cells were collected. DNA damage quantification was assessed using LA-QPCR, and analysis interrogated a 12.2 kb region of the DNA polymerase beta gene (POLB). An additional gene, hypoxanthine phosphoribosyltransferase 1 (HPRT), was also interrogated for validity. Enzyme-linked immunosorbent assay (ELISA) was used to measure plasma cotinine levels. Breath monitoring was measured using Bedfont Micro Smokerlyzer in order to quantify exhaled CO and %COHb levels in participants.

72 subjects, consisting of both males and females of diverse ages, races and ethnicities, were recruited. Comprehensive interviews alongside biochemical studies were used to verify smoking and vaping status. Participants classified as vapers reported a minimum use of e-cigarettes three times weekly for 6 months, with no use of cigarettes or tobacco products in their lifetime. Smokers reported cigarette consumption for a minimum of three times weekly for at least 12 months, less than five vaping sessions ever and no use of other tobacco products in the previous 6 months. Participants reporting no or less than five uses of e-cigarettes or tobacco products were classified as non-users. Former smokers, vapers and those who were dual or poly users of e-cigarettes, cigarettes or tobacco products were excluded.

R environment for statistical computing (RStudio), was used for data analysis. The Shapiro-Wilk test was used to evaluate the distribution of data. Student's t test allowed comparison of all variables between two groups (vapers and nonusers, smokers and nonusers, or vapers and smokers), specifically DNA damage levels. A one-way Analysis of Variance (ANOVA) followed by a post hoc Tukey HSD test allowed comparison of damage in three or more groups (heavy vapers, light vapers, and nonusers, as well as heavy smokers, light smokers, and nonusers). DNA damage was also analysed in this manner when assessing e-cigarette device type, liquid type or in non-users. Pearson correlation coefficient analysis allowed examination of relationships between different variables.

Mean levels of DNA damage in the POLB gene was 2.6-fold higher in vapers (p = 0.005) and 2.2-fold higher in smokers (p = 0.020), when compared to non-users. On comparing POLB gene DNA damage in vapers versus smokers, the results were not statistically significant (p = 0.522). Comparing DNA damage in the HPRT gene, levels were much higher in vapers (p = 0.029) and smokers (p = 0.033) versus non-users. Similarly to the POLB gene, DNA damage levels in the HPRT gene in vapers versus smokers were not statistically significant (p = 0.578). When assessing volume of e-cigarette liquid or smoking pack years, levels of DNA damage in increased in the POLB gene in a dose-dependent manner between 'light' and 'heavy' users versus non-users (F = 4.571, p = 0.0156 | Tukey's HSD p = 0.0195 in vapers, F = 4.368, p = 0.0185 | Tukey's HSD p = 0.0135 in smokers). Vaping device type was investigated showing mean level of DNA damage in the oral cells of pod device users was 3.3-fold higher compared to non-users (F = 3.886, p = 0.0152 | Tukey's HSD p = 0.0216). This was followed by a 2.6-fold increase in oral cell DNA damage in Mod device users, and a 1.6-fold increase in multiple device users. Levels of DNA damage was higher in those who consume sweet-flavoured e-liquid (F = 3.238, p = 0.0146 | Tukey's HSD p < 0.05), followed by vapers of multiple flavours, mint or menthol and tobacco, and fruit flavours. No correlation was found between DNA damage of oral cells and cumulative nicotine consumption in vapers (r = 0.3189, p = 0.1288). Plasma cotinine levels, a validated maker of tobacco in cigarettes and e-cigarettes, were not significantly different between vapers and smokers (p = 0.607), but were significantly higher compared to non-users (p < 0.0001). Whist compared to non-users, vapers had similar levels of CO and %COHb, smokers showed significantly increased levels (p = 0.0005 and p = 0.0002, respectively).

Based on the results of this study, there is evidence to support a dose-dependent formation of DNA damage in oral cells in those vapers who have never smoked cigarettes, and in those exclusive cigarette smokers. Additionally, e-cigarette device type and flavour, may also determine levels of DNA damage.