Dual use of e-cigarettes and combustible cigarettes elevates salivary DKK1 levels similar to exclusive smoking.

BACKGROUND

Animal models and in vitro studies have demonstrated that the use of electronic cigarettes causes inflammation, oxidative stress, and cell death. This study aimed to quantify molecules associated with cell death in the saliva of dual electronic cigarette users and to compare these levels with those observed in users of combustible cigarettes.

METHODOLOGY: We included three groups: (1) e-cigarette users who additionally smoke combustible cigarettes, "dual users" (DU users, n = 56), combustible cigarette smokers (CCS, n = 23), and non-smokers (NS, n = 40). We evaluated 10 molecules using a multiplex assay.

RESULTS

Dual users of e-cigarettes showed elevated cotinine levels and higher scores on the Fagerström Test for Nicotine Dependence (FTND), indicating greater nicotine dependence compared to combustible cigarette smokers. The dual-user group had significantly higher levels of Dickkopf-1 (DKK1) than the non-smoker group (220.6 pg./mL vs. 0, p = 0.030). Positive correlations were identified between DKK1 and 70-kilodalton heat shock protein (HSP70) (rho = 0.298, p = 0.042). A negative correlation was also found between HSP70 and the age of vaping initiation (rho = -0.289, p = 0.043), and a positive correlation with the duration of vaping sessions (rho = 0.292, p = 0.042), indicating that starting vaping at a young age and prolonging sessions may increase the expression of this protein.

CONCLUSION

Dual users of electronic cigarettes exhibit elevated salivary DKK1 levels and significant correlations with HSP70; these results suggest that chronic use may alter the inflammatory process. The pattern of e-cigarette consumption and the age of initiation modify salivary HSP70 levels. These proteins are involved in cellular stress and inflammatory mechanisms.