The Effect of Vaped Electronic Cigarettes on Oral Cells

Objectives: Nicotine delivery by cigarettes has been linked to an increased risk of periodontal disease. As an alternative to traditional cigarettes, electronic cigarettes administer nicotine by vaporizing a liquid component (e-juice). Experiments concerning the flavoring agent propose that the flavor is responsible for the toxic effects of electronic cigarette usage on oral cells. This set of experiments explores two varieties of e-juice in its liquid and vaporized forms to assess the effects of e-juice on the toxicity and cellular activity of three cell lines.
Methods: Gingival and periodontal ligament (PDL) fibroblasts as well as osteoblast-like UMR-106 cells were treated for 24 hours with various concentrations (2.8mM to 14.2mM) of e-Juice originally containing 24mg/ml nicotine in unflavored and menthol varieties in unvaporized and vaporized states. Cell survival was assessed fluorometrically using Calcein-AM. Alkaline Phosphatase (AP) activity of UMR cells was assessed colormetrically using p-nitrophenylphosphate and cell number was assessed fluorometrically using CyQuant.
Results: Concentrations of unflavored e-juice containing up to 14mM nicotine did not significantly reduce gingival or PDL cell survival. Above 8.5mM nicotine cell survival decreased selectively in the Menthol flavored samples. No significant difference was noted between unvaporized and vaporized trials. Interestingly, UMR cells were more sensitive to all solutions tested, with reduced cell survival beginning at 5.7mM for menthol flavored e-juice. In contrast, cigarette smoke extracts were toxic at nicotine concentrations as low as 4uM. In addition AP activity was reduced by both vaped and unvaped e-juices, with vaped menthol e-juice significantly reducing AP activity at 2.8mM nicotine concentrations.
Conclusions: Menthol flavoring selectively decreases cell survival more severely than other flavors. Vaporizing e-juice does not increase its cytotoxicity. AP activity was decreased in the presence of e-juice. This study supports the likelihood that electronic cigarettes would be safer than conventional cigarettes for nicotine delivery, but may have detrimental effects on bone remodeling.