An Unrecognized Hazard in E-Cigarette Vapor: Preliminary Quantification of Methylglyoxal Formation from Propylene Glycol in E-Cigarettes

Abstract

Up to 95% of the liquid volume in an e-cigarette consists of propylene glycol. Previous research has shown that propylene glycol can generate diacetyl and formaldehyde when heated. New research shows that propylene glycol can also generate methylglyoxal, an alpha di-carbonyl compound recently shown to cause epithelial necrosis at even lower concentrations than diacetyl, the flavoring chemical associated with bronchiolitis obliterans (“Popcorn Lung”). We analyzed chemical emissions from 13 JUUL pod flavors. Diacetyl and methylglyoxal was detected in 100% of samples with median concentration (range) of 20 µg/m3 (less than limit of quantification: 54 µg/m3) and 4219 µg/m3 (677–15,342 µg/m3), respectively. We also detected acetaldehyde (median concentration: 341 µg/m3) and propionaldehyde (median concentration: 87 µg/m3) in all samples. The recent evidence that methylglyoxal is more cytotoxic to airway epithelial cells than diacetyl makes this an urgent public health concern. Current smokers considering e-cigarettes as a smoking cessation tool, and never users, who may be under the impression that e-cigarettes are harmless, need information on emissions and potential risks to make informed decisions.

Methylglyoxal-Dependent Glycative Stress Is Prevented by the Natural Antioxidant Oleuropein in Human Dental Pulp Stem Cells through Nrf2/Glo1 Pathway

“…Additionally, mounting in vitro evidence, using cell models from gingival connective tissue, suggests that MG and MG-derived AGEs participate to the pathogenesis of some oral diseases, such as gingivitis and periodontitis [ 18 , 19 ], and some in vivo studies report the accumulation of MG in some biological fluids from gingival crevicular fluid of chronic periodontitis patients [ 20 ], where they can be conveyed by bacterial infections [ 20 , 21 ]. Moreover, MG is an endogenous metabolite but also a compound that can be introduced from some foodstuffs (e.g., milk, coffee, bread, fruit juices), food cooking, cigarette smoke or aerosols from nicotine delivery systems (NDS) [ 22 , 23 , 24 ]. Given that the oral cave is the gateway for these substances into our body, knowledge of the effects generated by agents favoring glycative stress is important in order to prevent oral tissues damage.…”

“…Mounting in vitro evidence, using mainly cell models from gingival connective tissue, suggests that MG and MG-derived AGEs are also involved in the pathogenesis of some oral diseases, such as gingivitis and periodontitis [ 18 , 19 ]. Moreover, some in vivo observations have pointed out the accumulation of MG in some biological fluids from the gingival crevicular fluid of chronic periodontitis patients [ 20 ] that can also be conveyed by bacterial infections [ 21 ], dietary compounds [ 22 ], and cigarette smoke or aerosols from nicotine delivery systems (NDS) (Electronic Cigarette and Heat-not-burn tobacco product IQOS) [ 23 , 24 ]. Notably, numerous clinical and experimental studies have highlighted the presence of a strong association between periodontitis, which represents the most common pathology of the oral cave in the adult population, and some systemic diseases, in particular, diabetes and obesity [ 25 , 26 ], which, as mentioned before, are characterized by increased levels of MG and MG-derived “glycative stress” onset.…”

Early Diagnosis of Oral Mucosal Alterations in Smokers and E-Cigarette Users Based on Micronuclei Count: A Cross-Sectional Study among Dental Students

“…E-cigarettes have become more popular in the last years as an alternative to conventional cigarettes and data show that the decrease of conventional smokers or dual users is accompanied by an increase in exclusive e-cigarette users. Although considered safer in comparison to conventional cigarettes, e-cigarettes have been associated with health risks, including cardiac and pulmonary diseases, but also with nicotine addiction leading to a tendency of experiencing other forms of tobacco [46,47]. While conventional smoking is recognized as an important risk factor affecting the oral health, there is still a debate in the scientific literature regarding the possible risks of e-cigarette use.…”

“…Several studies reported milder oral symptomatology in e-cigarette compared to conventional cigarette users [48], but others found more frequent oral lesions, burns or inflammation compared to former or nonsmokers [20]. Therefore, recent data support the need for correct information about health-related risks before the decision of using these products, which are highly prevalent in the young population [47].…”

Predicting molecular mechanisms, pathways, and health outcomes induced by Juul e-cigarette aerosol chemicals using the Comparative Toxicogenomics Database

“…Chemicals detected by these two methods include nicotine, acetaldehyde, formaldehyde, free radicals, crotonaldehyde, acetone, pyruvaldehyde, and particulate matter. Additional evidence for the presence of nicotine, acetaldehyde, formaldehyde, reactive oxygen species, acetone, pyruvaldehyde and particulate matter have also recently been described in Juul aerosols ( Muthumalage et al, 2019 , Mallock et al, 2020 , Azimi et al, 2021 ). Concentrations of these chemicals in Juul emissions are listed in Table 1 .…”