Background: The use of electronic cigarettes (ECs) and vaping products has been a significant concern in recent years, due to increased usage of these products amongst the general population as well as juveniles. With the innovation of nicotine salts in newer generations EC such as the JUUL, nicotine delivery has become easier and much higher. There is limited research on the effects of nicotine on oral health and specifically dental pulp stem cells (DPCS), the cells that provide protection and reparation to the teeth.
Objectives: This study aimed to evaluate the effects of protonated nicotine on apoptosis, necrosis, viability, and gene expression of stem cells from human exfoliated deciduous teeth (SHEDs) over time.
Methods: Characterized SHEDs were used in this study. The cells were seeded in 12-well cell culture plates at a concentration of 3.5 x 104 cells/well. Negative (non-treated) control cells, positive apoptosis control cells (100 nM Staurosporine 2 hours before collection) and positive necrosis control cells (0.2% Tritonax 10 minutes before collection) were compared with cells treated with 15 ng/mL, 30 ng/mL, and 300 ng/mL nicotine in media. Triplicates were performed for each experiment for all SHEDs isolates. SHEDs were dosed daily with the appropriate concentrations of nicotine in media and collected after 3, 7, and 10 day intervals. After each time points, cells were evaluated for immunofluorescence for caspase-3; % of apoptotic, necrotic, and viable cells; and RNA isolation and RT-qPCR gene expression of BAX, BCL2, DMP-1, RUNX2, and ALP.
Results: Mean percentage for apoptosis, necrosis, and viability of SHEDs were not significantly affected at nicotine concentrations of 0 ng/mL, 15 ng/mL, 30 ng/mL and 300 ng/mL after 3, 7, and 10 days of exposure. This was further supported by the results of immunofluorescence experiments, which showed that different concentrations of nicotine over time appear to have little effect on the cleavage of caspase-3. Furthermore, trends in RT-PCR suggested that gene expression for Bcl-2 and BAX in nicotine treated cells were not affected by exposure to different concentrations of nicotine at any time point. Finally, RT-PCR also showed no effect in gene expression for dentin matrix acidic phosphoprotein 1 (DMP-1), Runt-related transcription factor 2 (RUNX2), and Alkaline phosphatase (ALP).
Conclusions: This study has demonstrated that apoptosis, necrosis, viability, and gene expression of SHEDs were not significantly affected at nicotine concentration found in the blood after 3, 7, and 10 days. However, it is unclear how long-term exposure to nicotine might affect SHEDs and oral health. The results of this current study may suggest that short term use of EC and nicotine exposure does not affect SHEDs significantly. More research is needed to understand the effects and mechanism of nicotine on DPSCs
