Formaldehyde from e-cigarettes--it's not as simple as some suggest

The relationship between the use of electronic nicotine delivery systems (ENDS) and effects on pulmonary immune responses-a literature review

INTRODUCTION

The use of electronic nicotine delivery systems (ENDS), or vaping, is a relatively recent phenomenon, and there are various gaps in our current knowledge regarding the specific effects of e-cigarettes, such as their immunological effects. The importance of this question became even more relevant in light of the COVID-19 pandemic.

OBJECTIVE

This literature review examines the relationship between the use of electronic nicotine delivery systems (ENDS) and immunological effects to examine available information and identify gaps in the current knowledge. Our search strategy included studies focusing on the effects of ENDS on the immune response during infectious respiratory diseases such as COVID-19 and pneumonia.

METHODS

Peer-reviewed studies presenting quantitative data published from 2007, the year that e-cigarettes were introduced to the US market until 2022 have been included. All studies were indexed in PubMed. We excluded papers on THC and EVALI (E-cigarette, or Vaping Product, Use Associated Lung Injury) as we wanted to focus on the effects of nicotine devices.

RESULTS

Among the 21 articles that assessed the relationship between ENDS and immunological health effects, we found eight studies based on cell models, two articles based on both cell and mouse models, five articles based on mouse models, and six studies of human populations. Most of the articles identified in our review demonstrated a potential association between vaping and adverse immunological health effects.

DISCUSSION

Overall, the evidence from the cell and animal studies indicates that there is a positive, statistically significant association between vaping and adverse immune response during infectious respiratory diseases. The evidence from human studies is not conclusive.

Critical Review of the Recent Literature on Organic Byproducts in E-Cigarette Aerosol Emissions

We review the literature on laboratory studies quantifying the production of potentially toxic organic byproducts (carbonyls, carbon monoxide, free radicals and some nontargeted compounds) in e-cigarette (EC) aerosol emissions, focusing on the consistency between their experimental design and a realistic usage of the devices, as determined by the power ranges of an optimal regime fulfilling a thermodynamically efficient process of aerosol generation that avoids overheating and "dry puffs". The majority of the reviewed studies failed in various degrees to comply with this consistency criterion or supplied insufficient information to verify it. Consequently, most of the experimental outcomes and risk assessments are either partially or totally unreliable and/or of various degrees of questionable relevance to end users. Studies testing the devices under reasonable approximation to realistic conditions detected levels of all organic byproducts that are either negligible or orders of magnitude lower than in tobacco smoke. Our review reinforces the pressing need to update and improve current laboratory standards by an appropriate selection of testing parameters and the logistical incorporation of end users in the experimental design.

Daily exposure to formaldehyde and acetaldehyde and potential health risk associated with use of high and low nicotine e-liquid concentrations

Recent evidence suggests that e-cigarette users tend to change their puffing behaviors when using e-liquids with reduced nicotine concentrations by taking longer and more frequent puffs. Using puffing regimens modelled on puffing topography data from 19 experienced e-cigarette users who switched between 18 and 6 mg/mL e-liquids with and without power adjustments, differences in daily exposure to carbonyl compounds and estimated changes in cancer risk were assessed by production of aerosols generated using a smoking machine and analyzed using gas and liquid chromatography. Significant differences across conditions were found for formaldehyde and acetaldehyde (p < 0.01). Switching from a higher to a lower nicotine concentration was associated with greater exposure regardless of whether power settings were fixed or adjustable which is likely due to increased liquid consumption under lower nicotine concentration settings. Daily exposure for formaldehyde and acetaldehyde was higher for 17/19 participants when using low (6 mg/mL) compared with high (18 mg/mL) nicotine e-liquid concentration when power was fixed. When power adjustments were permitted, formaldehyde and acetaldehyde levels were higher respectively for 16/19 and 14/19 participants with the use of 6 compared with 18 mg/mL nicotine e-liquid.

E-cigarette Aerosol Condensate Enhances Metabolism of Benzo(a)pyrene to Genotoxic Products, and Induces CYP1A1 and CYP1B1, Likely by Activation of the Aryl Hydrocarbon Receptor

E-cigarette aerosol contains lower levels of most known carcinogens than tobacco smoke, but many users of e-cigarettes are also smokers, and these individuals may be vulnerable to possible promoting and/or cocarcinogenic effects of e-cigarettes. We investigated the possibility that a condensate of e-cigarette aerosol (EAC) enhances the metabolism of the tobacco carcinogen, benzo(a)pyrene (BaP), to genotoxic products in a human oral keratinocyte cell line. Cells were pretreated with EAC from two popular e-cigs and then with BaP. Metabolism to its ultimate carcinogenic metabolite, anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydro B[a]P (BPDE), was assayed by measuring isomers of its spontaneous hydrolysis products, BaP tetrols. The pretreatment of cells with EAC enhanced the rate of BaP tetrol formation several fold. Pretreatment with the e-liquid resulted in a smaller enhancement. The treatment of cells with EAC induced CYP1A1/1B1 mRNA and protein. The enhancement of BaP tetrol formation was inhibited by the aryl hydrocarbon receptor (AhR) inhibitor, α-napthoflavone, indicating EAC likely induces CYP1A1/1B1 and enhances BaP metabolism by activating the AhR. To our knowledge, this is first report demonstrating that e-cigarettes can potentiate the genotoxic effects of a tobacco smoke carcinogen.

E-cigarettes emit very high formaldehyde levels only in conditions that are aversive to users: A replication study under verified realistic use conditions

PURPOSE

In 2015, a study identified 5-15-fold higher levels of formaldehyde emissions from an old-generation e-cigarette tested at 5.0 V compared to tobacco cigarettes. We set to replicate this study using the same e-cigarette equipment and e-liquid, while checking for the generation of dry puffs.

DESIGN

Experienced e-cigarette users (n = 26) took 4 s puffs at different voltage settings and were asked to report the generation of dry puffs. Formaldehyde emissions were measured at both realistic and dry puff conditions.

RESULTS

Dry puffs were detected at ≤4.2 V by 88% of participants; thus, 4.0 V was defined as the upper limit of realistic use. Levels ranged from 3.4 (SE = 2.2) μg/10 puffs at 3.3 V to 718.2 (SE = 58.2) μg/10 puffs at 5.0 V. The levels detected at 4.0 V were 19.8 (SE = 5.6) μg/10 puffs. At 4.0 V, the daily exposure to formaldehyde from consuming 3 g of liquid with the device tested would be 32% lower compared to smoking 20 tobacco cigarettes.

CONCLUSIONS

The high levels of formaldehyde emissions that were reported in a previous study were caused by unrealistic use conditions that create the unpleasant taste of dry puffs to e-cigarette users and are thus avoided.

The Use of E-Cigarettes

BACKGROUND

Electronic cigarettes (e-cigarettes) are a consumer product whose benefits and risks are currently debated. Advocates of the "tobacco harm reduction" strategy emphasize their potential as an aid to smoking cessation, while advocates of the precautionary principle emphasize their risks instead. There have been only a few studies to date on the prevalence of e-cigarette use in Germany.

METHODS

In May 2016, in collaboration with Forsa, an opinion research firm, we carried out a survey among 4002 randomly chosen persons aged 14 and older, asking them about their consumption of e-cigarettes with and without nicotine, reasons for using e-cigarettes, plans for future use, estimation of danger compared to that of tobacco products, smoking behavior, and sociodemographic features.

RESULTS

1.4% of the respondents used e-cigarettes regularly, and a further 2.2% had used them regularly in the past. 11.8% had at least tried them, including 32.7% of smokers and 2.3% of persons who had never smoked. 24.5% of ex-smokers who had quit smoking after 2010 had used e-cigarettes at least once. 20.7% of the respondents considered electronic cigarettes less dangerous than conventional cigarettes, 46.3% equally dangerous, and 16.1% more dangerous. An extrapolation of these data to the general population suggests that about one million persons in Germany use e-cigarettes regularly and another 1.55 million have done so in the past.

CONCLUSION

The consumption of electronic cigarettes in Germany is not very widespread, but it is not negligible either. Nearly 1 in 8 Germans has tried e-cigarettes at least once. Regular consumers of e-cigarettes are almost exclusively smokers and ex-smokers.