Nicotine emissions from electronic cigarettes: Individual and interactive effects of propylene glycol to vegetable glycerin composition and device power output

E-Cigarettes and Associated Health Risks: An Update on Cancer Potential

The potential cancer risk associated with electronic-cigarette (e-cigarette) use is ongoing and remains a subject of debate. E-Cigarettes work by heating a liquid that usually contains nicotine, flavorings, and other chemicals. When the liquid is heated, users inhale an aerosol into their lungs. While e-cigarettes are generally considered less harmful than traditional tobacco products, they still contain potentially harmful chemicals, which can damage DNA and lead to cancer. Several studies have investigated the potential cancer risk associated with e-cigarette use, while other studies have suggested that e-cigarette aerosol may contain carcinogenic chemicals that could increase the risk of lung and bladder cancer in humans. However, these studies are limited in their scope and do not provide conclusive evidence. Overall, the long-term cancer risk associated with e-cigarette use remains uncertain, more research is needed to fully understand the potential risks and benefits of e-cigarettes. However, this review will allow the investigator to get more recent updates about e-cigarettes.

Examination of the impact of myblu electronic nicotine delivery system e-liquid nicotine strength on self-reported measures of dependence

BACKGROUND

Greater nicotine delivery is associated with higher nicotine concentrations in electronic nicotine delivery system (ENDS) liquids. However, there is a current debate as to whether this leads to increased dependence and mitigates ENDS public health potential.

METHODS

Self-reported dependence among users of myblu ENDS containing different nicotine concentrations was examined with data from a multiwave cross-sectional survey of US young adults and adults. Questions examined responses related to dependence measures and participants' most often used myblu ENDS nicotine concentration (low: 0%, 1% and 1.2%; medium: 2%, 2.4% and 2.5%; or high: 3.6% and 4%).

RESULTS

A global general linear model using nicotine concentration, age and days myblu that was used in the past 30 revealed a significant difference in PROMIS scores among nicotine concentration groups (F = 4.07, p = 0.02). However, pairwise comparisons to examine which specific groups differed significantly from others showed no significant differences. Logistic regression demonstrated that strong past 30-day cravings to use myblu among participants using high or medium nicotine concentrations were not significantly different from those using a low concentration (ORs 0.66 [0.42, 1.03], p = 0.07 and 0.95 [0.49, 1.82], p = 0.98, respectively). Time to daily first use for high or medium nicotine concentration users was not significantly different from those using a low concentration (ORs 0.89 [0.70, 1.14], p = 0.35 and 0.84 [0.57, 1.25], p = 0.40, respectively).

CONCLUSIONS

Use of myblu ENDS with different nicotine concentrations is not associated with differing levels of dependence. Our findings contradict the notion that high ENDS e-liquid nicotine levels generate increased dependence.

Device and liquid characteristics used with sweet, menthol/mint, and tobacco ENDS liquid flavors: The population-based VAPER study

INTRODUCTION

Electronic nicotine delivery system (ENDS) device and liquid characteristics (e.g., wattage, nicotine concentration) are diverse and important in determining product appeal, aerosol volume/nicotine levels, and toxicity. Little is known about how device and liquid characteristics vary by flavor; we address this gap to identify potential regulatory implications.

METHODS

Data are from a longitudinal cohort study (Waves 2 and 3; December 2020-December 2021) of adult (≥21 years) U.S. ENDS users (≥5 days of use/week). Participants (n = 1809) reported on and submitted photos of their most used device and liquid. Participants were categorized into flavor groups of high prevalence in our sample and in prior literature: sweet, menthol/mint, or tobacco. Participants using liquids without nicotine or flavors other than sweet, menthol/mint, or tobacco were excluded (n = 320). Data were analyzed cross-sectionally. Chi-square and linear regression (n = 1489) were used to examine device and liquid characteristics by flavor.

RESULTS

Sweet flavors were most common (n = 1135; 76.2%), followed by menthol/mint (n = 214, 14.4%) and tobacco (n = 140, 9.4%). Sweet flavors were less common among participants using reusable devices with disposable pods/cartridges (nicotine salt) than those using other device-liquid groupings (5.2% vs 86.5-93.9%; p < 0.001). Sweet flavors were less common among those using ENDS for non-flavor reasons vs the flavor (73.5% vs 90.4%; p < 0.001). Sweet flavors correlated with lower nicotine concentrations, higher wattages, and lower ages of ENDS first use (p < 0.001).

CONCLUSIONS

Regulatory agencies must consider how regulations on device and liquid characteristics may affect ENDS users' behaviors (e.g., limiting availability of sweet flavors may encourage use of non-sweet flavors and lower wattages).

Effects of Device Settings and E-Liquid Characteristics on Mouth-Throat Losses of Nicotine Delivered with Electronic Nicotine Delivery Systems (ENDS)

Currently it is not fully understood how the device settings and electronic liquid (e-liquid) composition, including their form of nicotine content, impact mouth and throat losses, and potentially lead to the variations in total nicotine delivery to the human lungs. An in situ size assessment method was developed for real-time measurements at the mouthpiece and outlet of a biorelevant mouth-throat to account for the dynamic nature of the aerosol. The aerosol size, temperature, and delivery through the mouth-throat replica and the exhaled aerosol between the puff intervals were measured at different wattages using various e-liquid compositions. The effects of body temperature and humidity on aerosol size and nicotine delivery were also explored to evaluate the importance of considering realistic in vivo conditions in in vitro measurements. Notably, in vitro tests with body temperature and humidity in mouth-throat model vs room conditions, resulted in larger aerosol size at the end of the throat (Dv₅₀=5.83±0.33 μm vs 3.05±0.15 μm), significantly higher thoracic nicotine delivery (>90% vs 50-85%) potentially due to the lower exhaled amount (<10% vs 15-50%). Besides, higher VG/PG ratios resulted in significantly lower exhaled amount and higher mouth-throat nicotine deposition. One of the main outcomes of the study was finding significantly lower exhaled amount and higher thoracic nicotine delivery with nicotine salt form vs free-base. Considering body temperature and humidity also showed significant enhancement in nicotine delivery, so it is essential to account for biorelevant experimental conditions in benchtop testing.

Non-Targeted Chemical Characterization of JUUL-Menthol-Flavored Aerosols Using Liquid and Gas Chromatography

The aerosol constituents generated from JUUL Menthol pods with 3.0% and 5.0% nicotine by weight (Me3 and Me5) are characterized by a non-targeted approach, which was developed to detect aerosol constituents that are not known to be present beforehand or that may be measured with targeted methods. Three replicates from three production batches (n = 9) were aerosolized using two puffing regimens (intense and non-intense). Each of the 18 samples were analyzed by gas chromatography electron ionization mass spectrometry and by liquid chromatography electrospray ionization high-resolving power mass spectrometry. All chemical constituents determined to differ from control were identified and semi-quantified. To have a complete understanding of the aerosol constituents and chemistry, each chemical constituent was categorized into one of five groups: (1) flavorants, (2) harmful and potentially harmful constituents, (3) leachables, (4) reaction products, and (5) chemical constituents that were unable to be identified or rationalized (e.g., chemical constituents that could not be categorized in groups (1–4). Under intense puffing, 74 chemical constituents were identified in Me3 aerosols and 68 under non-intense puffing, with 53 chemical constituents common between both regimens. Eighty-three chemical constituents were identified in Me5 aerosol using an intense puffing regimen and seventy-five with a non-intense puffing regimen, with sixty-two chemical constituents in common. Excluding primary constituents, reaction products accounted for the greatest number of chemical constituents (approximately 60% in all cases, ranging from about 0.05% to 0.1% by mass), and flavorants—excluding menthol—comprised the second largest number of chemical constituents (approximately 25%, ranging consistently around 0.01% by mass). The chemical constituents detected in JUUL aerosols were then compared to known constituents from cigarette smoke to determine the relative chemical complexities and commonalities/differences between the two. This revealed (1) a substantial decrease in the chemical complexity of JUUL aerosols vs. cigarette smoke and (2) that there are between 55 (Me3) and 61 (Me5) unique chemical constituents in JUUL aerosols not reported in cigarette smoke. Understanding the chemical complexity of JUUL aerosols is important because the health effects of combustible cigarette smoke are related to the combined effect of these chemical constituents through multiple mechanisms, not just the effects of any single smoke constituent.

e-Cigarette Vapour Condensate Reduces Viability and Impairs Function of Human Osteoblasts, in Part, via a Nicotine Dependent Mechanism

Cigarette consumption negatively impacts bone quality and is a risk-factor for the development of multiple bone associated disorders, due to the highly vascularised structure of bone being exposed to systemic factors. However, the impact on bone to electronic cigarette (e-cigarette) use, which contains high doses of nicotine and other compounds including flavouring chemicals, metal particulates and carbonyls, is poorly understood. Here, we present the first evidence demonstrating the impact of e-cigarette vapour condensate (replicating changes in e-cigarette liquid chemical structure that occur upon device usage), on human primary osteoblast viability and function. 24 h exposure of osteoblasts to e-cigarette vapour condensate, generated from either second or third generation devices, significantly reduced osteoblast viability in a dose dependent manner, with condensate generated from the more powerful third generation device having greater toxicity. This effect was mediated in-part by nicotine, since exposure to nicotine-free condensate of an equal concentration had a less toxic effect. The detrimental effect of e-cigarette vapour condensate on osteoblast viability was rescued by co-treatment with the antioxidant N-Acetyl-L-cysteine (NAC), indicating toxicity may also be driven by reactive species generated upon device usage. Finally, non-toxic doses of either second or third generation condensate significantly blunted osteoblast osteoprotegerin secretion after 24 h, which was sustained for up to 7 days. In summary we demonstrate that e-cigarette vapour condensate, generated from commonly used second and third generation devices, can significantly reduce osteoblast viability and impair osteoblast function, at physiologically relevant doses. These data highlight the need for further investigation to inform users of the potential risks of e-cigarette use on bone health, including, accelerating bone associated disease progression, impacting skeletal development in younger users and to advise patients following orthopaedic surgery, dental surgery, or injury to maximise bone healing.

Reinforcing effects of fentanyl and sufentanil aerosol puffs in rats

RATIONALE

Rapidly evolving e-cigarette technology developed for self-administering nicotine aerosol has the potential to be utilized to self-administer other aerosolized drugs of abuse. Rodent models which mirror characteristics of human e-cigarette use are necessary to explore the degree to which this may be a public health concern.

OBJECTIVES

Our goal was to develop a highly translational model of discrete nose-only aerosol puff drug delivery to explore the reinforcing effects of fentanyl and sufentanil aerosols in rats.

METHODS

Male and female Sprague-Dawley rats were trained to perform a multiple schedule FR1 lever-press, 4-s (second) nose hold operant during which the subject's orofacial areas were exposed to drug-free glycerol/propylene glycol aerosol produced by a commercial e-cigarette at a power setting of 18 watts. Each completed 4-s drug-free vehicle aerosol exposure resulted in a 3-s presentation of a 0.1-ml dipper of sweetened milk solution. After training, rats were then allowed to self-administer 4-s nose-only puffs of fentanyl (100-6000 µg/ml) or sufentanil (30-500 µg/ml) aerosol in the absence of paired milk dipper reinforcers.

RESULTS

All 31 rats learned the lever-press/nose-poke multiple schedule for milk dippers alone and 25 accepted exposure to 4 s of 18 watts of drug-free vehicle aerosol when paired with milk dipper presentations. In the absence of paired milk dipper presentations, fentanyl aerosol puffs at concentrations of 1000 and 3000 µg/ml as well as 100 µg/ml puffs of sufentanil served as reinforcers compared to both air puffs and drug-free vehicle aerosol puffs. There were no significant differences between males and females in number of fentanyl or sufentanil puffs self-administered.

CONCLUSIONS

Discrete nose-only puffs of two potent opioids under exposure conditions comparable to puff durations in human e-cigarette users serve as reinforcers in rats. This outcome suggests that under appropriate conditions e-cigarettes might be a potential alternative delivery mechanism for illicit opioids.

Emission and Gas/Particle Partitioning Characteristics of Nicotine in Aerosols for Electronic Cigarettes

Nicotine is a dependence-producing component in electronic cigarettes. The nicotine release characteristics of electronic cigarettes are closely connected with human exposure and respiratory health. In this paper, a theoretical model was established to study the effects of the compositions of e-liquids and the heating powers of device on the emission and gas/particle partitioning characteristics of nicotine in aerosols at equilibrium. The simulation results of nicotine emissions were compared with the experimental data. The errors between them were within a reasonable range. At a larger heating power level, a higher nicotine yield and a larger vaporization amount of e-liquids could be observed. Under the same heating power condition, a higher vegetable glycerin content in e-liquids could result in a lower nicotine emission. When the heating powers supplied by the device increased, a larger mass fraction of particle-phase nicotine in aerosols at equilibrium would appear. As more propylene glycol was added into e-liquids, a lower mass fraction of gas-phase nicotine would exist in aerosols at equilibrium. The results may provide more information for the industry to set technical standards for electronic cigarettes and for the government department to make regulatory policies.

Effect of Heating on Physicochemical Property of Aerosols during Vaping

Many electronic cigarette manufacturers have offered different types of “high-end mods” that allow for controlled heating of the e-liquid. However, the controlled heating condition can drastically alter the inhaled aerosols’ physical properties and chemical substances, causing potential health risks. To investigate the contribution of heating on aerosol properties, we used four common power settings in the mods to conduct a physicochemical analysis. Our data showed that the aerosol mass and nicotine content in the aerosols increased at high power. Additionally, high power led to aerosolization of a viscous component in the e-liquid, increasing the viscosity of aerosol. However, the pH of the aerosol was constant regardless of the applied power. In addition, high-power operation made nicotine prone to oxidation, resulting in the color of the aerosol turning yellow. Lastly, we demonstrated that e-cigarette aerosol could contain various metals, including aluminum, arsenic, cadmium, chromium, copper, iron, magnesium, nickel, lead, and zinc. Even though these metal contents proportionally increased with the power setting, they remained far below the recommended exposure limits. Our finding demonstrates that the heating conditions of the e-cigarette change the physicochemical properties of the aerosols and their metal contents, thereby possibly affecting users’ oral and respiratory systems.

Pharmacokinetic and subjective assessment of prototype JUUL2 electronic nicotine delivery system in two nicotine concentrations, JUUL system, IQOS, and combustible cigarette

RATIONALE

Electronic nicotine delivery systems and heated tobacco products are noncombustible alternatives for adult smokers. Evidence suggests sufficient nicotine delivery and satisfying effects are necessary to facilitate switching away from smoking; nicotine delivery varies across electronic nicotine delivery systems within limited nicotine concentrations.

OBJECTIVES

To assess the nicotine delivery and subjective effects of prototype JUUL2 System in two nicotine concentrations, currently-marketed US JUUL System ("JUUL"), IQOS-brand heated tobacco product, and combustible cigarettes.

METHODS

Adult smokers (N = 40) completed a 5-arm cross-over product-use laboratory confinement study. Nicotine pharmacokinetics and subjective effects were assessed following use of: (1) JUUL2 prototype 18 mg/mL nicotine; (2) JUUL2 prototype 40 mg/mL; (3) JUUL 59 mg/mL; (4) IQOS 18 mg/g; and (5) usual brand combustible cigarette, each evaluated during ad libitum (10 min) and controlled (5 min, 10 standardized puffs) use.

RESULTS

Nicotine delivery was greatest for combustible cigarettes, followed by JUUL2 prototype 40 mg/mL, IQOS, JUUL2 prototype 18 mg/mL, and JUUL 59 mg/mL. Nicotine delivery from JUUL2 prototype 18 mg/mL was significantly greater than JUUL 59 mg/mL after ad libitum use. JUUL products were significantly more satisfying and effective at reducing craving than IQOS. JUUL2 prototype 40 mg/mL was significantly more aversive than other JUUL products.

CONCLUSIONS

Prototype JUUL2 and JUUL 59 mg/mL products were rated higher than IQOS on subjective measures associated with switching away from smoking. The JUUL2 prototype 40 mg/mL produced aversive responses and would require modifications to be a viable product for adult smokers. Nicotine delivery and subjective responses to JUUL2 prototype 18 mg/mL suggest a product based on this prototype may facilitate increased switching among adult smokers.

Non-Targeted Chemical Characterization of JUUL Virginia Tobacco Flavored Aerosols Using Liquid and Gas Chromatography

The chemical constituents of JUUL Virginia Tobacco pods with 3.0% and 5.0% nicotine by weight (VT3 and VT5) were characterized by non-targeted analyses, an approach to detect chemicals that are not otherwise measured with dedicated methods or that are not known beforehand. Aerosols were generated using intense and non-intense puffing regimens and analyzed by gas chromatography electron ionization mass spectrometry and liquid chromatography electrospray ionization high resolving power mass spectrometry. All compounds above 0.7 µg/g for GC–MS analysis or above 0.5 µg/g for LC–HRMS analysis and differing from blank measurements were identified and semi-quantified. All identifications were evaluated and categorized into five groups: flavorants, harmful and potentially harmful constituents, extractables and/or leachables, reaction products, and compounds that could not be identified/rationalized. For VT3, 79 compounds were identified using an intense puffing regimen and 69 using a non-intense puffing regimen. There were 60 compounds common between both regimens. For VT5, 85 compounds were identified with an intense puffing regimen and 73 with a non-intense puffing regimen; 67 compounds were in common. For all nicotine concentrations, formulations and puffing regimens, reaction products accounted for the greatest number of compounds (ranging from 70% to 75%; 0.08% to 0.1% by mass), and flavorants comprised the second largest number of compounds (ranging from for 15% to 16%; 0.1 to 0.2% by mass). A global comparison of the compounds detected in JUUL aerosol to those catalogued in cigarette smoke indicated an approximate 50-fold decrease in chemical complexity. Both VT3 and VT5 aerosols contained 59 unique compounds not identified in cigarette smoke.

Review of data on chemical content in an aerosol resulting from heating a tobacco or a solution used in e-cigarettes and in the smoke generated from the reference cigarettes

BACKGROUND

The article presents a review of the literature on the chemical composition of smoke generated from a standard cigarette and the aerosol generated after heating tobacco and chemical compounds formed in the aerosol of electronic cigarettes.

METHODS

The literature review was carried out on the PubMed online bibliographic database, Google search engine, Google Scholar based on science articles published in recent 20 years.

RESULTS

The bibliographic analysis shows that: replacing smoking in the traditional way by heating tobacco modifies significantly the content of chemical substances found in aerosol, the substances found in aerosols generated by e-cigarettes have proven toxic effects, e.g. pro-inflammatory effect on lung epithelial cells (e.g. crotonaldehyde) or a mutagenic effect (e.g. NNK), using e-cigarette aerosol does not rule out a health risk for people, which is not fully recognized at present.

CONCLUSIONS

Replacing smoking in the traditional way by heating tobacco modifies significantly the content of chemical substances found in aerosol. Using e-cigarette aerosol does not rule out a health risk for people, because the substances found in aerosols generated by e-cigarettes have proven toxic effects.

Potential factors affecting free base nicotine yield in electronic cigarette aerosols

BACKGROUND

The free base and protonated nicotine forms in e-cigarette aerosol have shown different absorption profiles in users. Therefore, it is also important to identify the factors which can affect the ratio of these nicotine forms in the aerosol. Such factors may include nicotine concentrations, flavors, PG:VG ratios, types of nicotine chemical compounds and e-cigarette battery power outputs. The current study attempts to identify such factors using a controlled experiment.

RESEARCH DESIGNS AND METHODS

The aerosol was generated using validated aerosol generating model. Various factors were tested for their effect on nicotine forms. Additionally, a degradation study of one of the nicotine compounds, nicotine salicylate, was also carried out using mass spectrometry.

RESULTS

The free base nicotine in the aerosol was found to be affected by flavors, battery power output, nicotine compound type and PG:VG ratios. Based on the preliminary mass spectrometry data, degradation of nicotine salicylate was found to be one of the significant factors affecting free base nicotine in aerosol.

CONCLUSIONS

Potential factors affecting free base nicotine in e-cigarette aerosol have been identified in this study. These findings would help in understanding the nicotine delivery better and assist for better regulations.

Indoor Air Quality and Passive E-cigarette Aerosol Exposures in Vape-Shops

INTRODUCTION

Direct emissions of nicotine and harmful chemicals from electronic cigarettes (e-cigarettes) have been intensively studied, but secondhand and thirdhand e-cigarette aerosol (THA) exposures in indoor environments are understudied.

AIMS AND METHODS

Indoor CO2, NO2, particulate matter (PM2.5), aldehydes, and airborne nicotine were measured in five vape-shops to assess secondhand exposures. Nicotine and tobacco-specific nitrosamines were measured on vape-shop surfaces and materials (glass, paper, clothing, rubber, and fur ball) placed in the vape-shops (14 days) to study thirdhand exposures.

RESULTS

Airborne PM2.5, formaldehyde, acetaldehyde, and nicotine concentrations during shop opening hours were 21, 3.3, 4.0, and 3.8 times higher than the levels during shop closing hours, respectively. PM2.5 concentrations were correlated with the number of e-cigarette users present in vape-shops (ρ = 0.366-0.761, p < .001). Surface nicotine, 4-(N-methyl-N-nitrosamino)-4-(3-pyridyl)butanal (NNA), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were also detected at levels of 223.6 ± 313.2 µg/m2, 4.78 ± 11.8 ng/m2, and 44.8 ± 102.3 ng/m2, respectively. Substantial amounts of nicotine (up to 2073 µg/m2) deposited on the materials placed within the vape-shops, and NNA (up to 474.4 ng/m2) and NNK (up to 184.0 ng/m2) were also formed on these materials. The deposited nicotine concentrations were strongly correlated with the median number of active vapers present in a vape-shop per hour (ρ = 0.894-0.949, p = .04-.051). NNK levels on the material surfaces were significantly associated with surface nicotine levels (ρ=0.645, p = .037).

CONCLUSIONS

Indoor vaping leads to secondhand and THA exposures. Thirdhand exposures induced by e-cigarette vaping are comparable or higher than that induced by cigarette smoking. Long-term studies in various microenvironments are needed to improve our understanding of secondhand and THA exposures.

IMPLICATIONS

This study adds new convincing evidence that e-cigarette vaping can cause secondhand and THA exposures. Our findings can inform Occupational Safety and Health Administration, state authorities, and other government agencies regarding indoor air policies related to e-cigarette use, particularly in vape-shops. There is an urgent need to ensure that vape-shops maintain suitable ventilation systems and cleaning practices to protect customers, employees, and bystanders. Our study also demonstrates that nicotine can deposit or be adsorbed on baby's clothes and toys, and that tobacco-specific nitrosamines can form and retain on baby's clothes, highlighting children's exposure to environmental e-cigarette aerosol and THA at home is of a particular concern.

What factors reliably predict electronic cigarette nicotine delivery?

BACKGROUND

The ability of an electronic cigarette (e-cigarette) to deliver nicotine effectively may be dependent on features of the device, the liquid and the user. Some of these features have been examined in previous work (eg, liquid nicotine concentration and puff topography), while others have not (eg, nicotine dependence and demographic characteristics). The purpose of this secondary analysis is to examine such features as predictors of e-cigarette nicotine delivery using a relatively large sample.

METHODS

Four studies were combined in which e-cigarette-experienced users (n=63; 89% men; 75% white) and e-cigarette-naïve cigarette smokers (n=67; 66% men; 54% white) took 10 puffs from an eGo-style e-cigarette (~7.3 watts) filled with liquid that had a nicotine concentration of 18, 25 or 36 mg/mL. Thus, held constant across all studies were device features of battery/cartomiser style and power level and the topography parameters of puff number and interpuff interval. Blood was sampled before and after use, and puff topography was measured. Three general linear models were conducted to predict plasma nicotine concentrations (pre-post increase) for: (1) e-cigarette users only, (2) smokers only and (3) both groups combined. Predictor variables included puff duration, puff volume, liquid nicotine concentration, presession plasma nicotine concentration, nicotine dependence score (smokers only), gender and race.

RESULTS

In all models tested, longer puff durations and higher liquid nicotine concentrations were associated significantly with increased nicotine delivery (ps<0.05). For e-cigarette users only, higher presession nicotine concentration was associated significantly with increased nicotine delivery (p<0.05).

CONCLUSIONS

Puff duration and liquid nicotine concentration may be among the more important factors to consider as regulators attempt to balance e-cigarette safety with efficacy. These findings should be interpreted in the context of devices with relatively low power output, a variable not studied here but likely also directly relevant to product regulation.

Effect of free-base and protonated nicotine on nicotine yield from electronic cigarettes with varying power and liquid vehicle

Nicotine in electronic cigarette (ECIG) liquids can exist in a free-base or protonated (or "salt") form. Protonated nicotine is less aversive upon inhalation than free-base nicotine, and many ECIG manufacturers have begun marketing protonated nicotine products, often with high nicotine concentrations. Regulations intended to control ECIG nicotine delivery limit nicotine concentration but do not consider nicotine form. In this study, we systematically examined the effect of nicotine form on nicotine yield for varying powers and liquid vehicles. A Kanger Subox Mini-C tank ECIG (0.5 Ω) was used to generate aerosols at varying powers (5-45 W) from liquid solutions that contained either free-base or protonated nicotine at 15 mg/g concentration, with a liquid vehicle consisting of either propylene glycol (PG) or vegetable glycerin (VG), resulting in four different solutions (free-base/PG, free-base/VG, protonated/PG, and protonated/VG). Nicotine yield was quantified using gas chromatography-mass spectrometry. Nicotine yields were not influenced by nicotine form under any condition investigated. At each power level, PG-based liquids resulted in approximately double the nicotine yield of VG-based liquids. Nicotine concentrations in the aerosols matched those of the parent liquids for both the PG and VG conditions. Increasing power led to greater nicotine yield across all conditions. The amount of nicotine emitted by an ECIG is independent of whether the nicotine is free-base or protonated, however the liquid vehicle has a strong effect on yield. Regulations intended to limit nicotine emissions must consider not only nicotine concentration, but also liquid vehicle and device power.

Nicotine forms: why and how do they matter in nicotine delivery from electronic cigarettes?

INTRODUCTION

Unregulated e-cigarette devices and their nicotine content have amplified the potential of e-cigarettes as addictive agents. Several e-cigarette-related parameters have been identified altering nicotine's absorption profile, so their potential effects on addiction should be considered. Of these factors, nicotine forms (protonated and free base) play a significant role in the addiction potential yet their impact on nicotine's absorption has been studied with limited research.

AREAS COVERED

Current review aims to emphasize on the possible mechanism behind different absorption profiles of nicotine forms considering their physical states (droplet and vapor phase) and the aerosol particle size, their analysis in e-cigarette research and the regulatory attention warranted by them to combat nicotine addiction in the population due to e-cigarettes.

EXPERT OPINION

The protonated form of nicotine is being correlated with the smooth sensory effects and high nicotine absorption as compared to free base nicotine. With the introduction of nicotine salts, which yield mostly the protonated form, the youth popularity of e-cigarettes has spiked exponentially. While it is important to control nicotine levels in e-cigarette products, attention should also be given to the nicotine forms present in these products in order to address nicotine addiction in the population.

A review of toxic effects of electronic cigarettes/vaping in adolescents and young adults

In this review, we examine the known and suspected toxicity of electronic cigarettes (e-cigarettes) in adolescents and young adults, to improve awareness of risks and identification of complications of their use. The use of e-cigarettes, or "vaping," is exploding among the pediatric population. E-cigarettes heat a solution containing a psychoactive compound, most commonly nicotine or tetrahydrocannabinol (THC), along with flavorings and other additives to a vapor, which users inhale. Since their introduction in the early 2000s, e-cigarette use is now prolific among youth, per the Monitoring the Future survey, with over 40% of high school seniors reporting use within the past year. Adolescents are vulnerable to the risks of e-cigarettes, as they are targeted as new consumers with advertisements and flavoring compounds, and are not utilizing them as a means to smoking cessation. The pulmonary risks of vaping are rapidly emerging, with the most immediately alarming being the condition electronic-cigarette/vaping associated lung injury (EVALI). Additionally, there have been more recent studies showing extrapulmonary effects including cardiovascular, immunologic and neuro-developmental effects. Many of these effects are likely dose-dependent. Public health efforts are urgently needed to decrease or eliminate new e-cigarette initiation, and support should be established to assist current e-cigarette users with cessation. We strongly advocate for the elimination of e-cigarette flavorings and advertising directed at adolescents, and call for physicians to be cognizant of this expanding epidemic.

Method Validation Approaches for Analysis of Constituents in ENDS

OBJECTIVE

We assessed how many peer-reviewed publications reporting chemical quantities and/or yields from electronic nicotine delivery systems (ENDS) have included adequate method validation characteristics in the publication for appropriate interpretation of data quality for informing tobacco regulatory science.

METHODS

We searched 5 databases (Web of Knowledge, PubMed, SciFinder, Embase, EBSCOhost) for ENDS publications between January 2007 and September 2018. Of the 283 publications screened, 173 publications were relevant for analysis. We identified the publications that report a certain degree of control in data quality, ie, the publications that report marginally validated methods (MVMs). MVMs refer to the methods that: (1) report 3 or more International Conference on Harmonisation (ICH) method validation characteristics, (2) state the method was validated, (3) cite their own previous publication(s) that report MVMs, or (4) use a method within the accreditation scope of an accredited laboratory.

RESULTS

Overall, 97 publications (56%) report MVMs in their studies. This percentage also reflects the publication distribution for the majority of the 28 chemicals measured by MVMs.

CONCLUSIONS

This study highlights the need for reporting sufficient validation characteristics following appropriate guidance to ensure the accuracy and reliability of the published analytical data for proper data interpretations that may support policy.

Twenty-four-hour subjective and pharmacological effects of ad-libitum electronic and combustible cigarette use among dual users

BACKGROUND AND AIMS

Relative pharmacological effects of e-cigarettes and cigarettes during 24 hours of ad-libitum use have not been described. In this study, 24-hour blood plasma nicotine concentrations and 48-hour subjective effects with use of cigarettes and e-cigarettes were measured among dual users.

DESIGN

Two-arm within-subject cross-over design with preferred e-cigarette or cigarette ad-libitum use over 48 hours.

SETTING

Hospital research ward in San Francisco, California, USA.

PARTICIPANTS

Thirty-six healthy dual users of e-cigarettes and cigarettes (n = 8, 25% females).

MEASUREMENTS

Twenty-four-hour blood plasma nicotine and cotinine concentrations and 48-hour self-reported nicotine withdrawal symptoms and rewarding effects.

FINDINGS

Analyses used analysis of variance (ANOVA)-based mixed models with order of product (e-cigarette or cigarette) and product type (combustible cigarette or type of e-cigarette) as fixed effects, and subject as a repeated effect. During a 24-hour period, e-cigarettes produced lower nicotine exposure than cigarettes for the majority of users, although 25% received more nicotine from e-cigarettes, which was predicted by more frequent e-cigarette use or greater dependence. Compared to cigarette smoking, nicotine exposure for variable-power tank users was similar, while cig-a-like (t₍₃₀₎  = 2.71, P = 0.011, d = 0.745) and fixed-power tank users (t₍₃₀₎  = 3.37, P = 0.002, d = 0.993) were exposed to less nicotine. Cigarettes were rated higher than e-cigarettes on some desirable subjective effects (e.g. psychological reward, t₍₃₂₂₎  = 7.24 P < 0.001, d = 0.432), but withdrawal symptom reduction was comparable. No differences were found between e-cigarette types, but Bayes factors indicate that these measures were insensitive.

CONCLUSIONS

During a 24-hour period in a hospital setting in the United States, nicotine exposure for dual users of e-cigarettes and cigarettes was similar when using cigarettes or variable-power tank devices only but was lower for those using cig-a-like or fixed-power devices only. Despite lower nicotine levels, all types of e-cigarette were effective in preventing withdrawal symptoms. E-cigarettes were rated less rewarding than cigarettes.

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.

Selected Harmful and Potentially Harmful Constituents Levels in Commercial e-Cigarettes

A broad range of commercially available electronic cigarette (e-cigarette) systems were tested for levels of emissions of harmful and potentially harmful constituents (HPHC), with a particular focus on the carbonyls: acetaldehyde, acrolein, and formaldehyde. The tobacco-specific nitrosamines N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-bipyridyl)-1-butanone; the elements arsenic, cadmium, chromium, lead, and nickel; benzene; 1,3-butadiene; and benzo(a)pyrene were also quantified. The results show that except for the levels of carbonyls, all types of e-cigarettes performed in a similar manner, and emission levels for HPHCs were generally not quantifiable. However, levels of carbonyls, especially formaldehyde, were highly variable. Overall, the lowest levels of formaldehyde were observed in cartridge systems, which generally achieved substantial reductions in yields in comparison with cigarette smoke. Formaldehyde levels in open tank systems were variable; however, the median formaldehyde levels across different brands were substantially lower than the formaldehyde levels in cigarette smoke. The results for variable-power devices operated at the highest voltage confirmed existing literature data regardless of orientation and differences in puffing regimes. Furthermore, our results show that many products deliver consistent HPHC yields over a broad range of testing conditions (with minimal variability from one device to another, under a range of puffing conditions). However, some products exhibit high variability in emissions of HPHCs. The use of air blanks is further highlighted to assess nonproduct-related contributions to HPHC levels to avoid misrepresentation of the data. Overall, our results highlight that some but not all electronic cigarettes deliver low levels of carbonyls consistently across the full e-liquid depletion cycle under different test conditions. The need for further research and standardization work on assessment of variable-voltage electronic cigarettes is emphasized.

Impact of Vaping Regimens on Electronic Cigarette Efficiency

Most recent studies on electronic cigarettes (e-cigs) have been carried out using vaping regimens consistent with mouth-to-lung inhalation (MTL) and not with direct-to-lung (DTL) inhalation. This paper aimed to characterizing the influence of inhalation properties (puff duration, puff volume, airflow rate) on the mass of vaporized e-liquid (MVE). Because the literature on DTL is non-existent, an intense vaping regimen consistent with DTL inhalation (i.e., puff volume = 500 mL) was defined. The use of a low or standard (ISO/DIS 20768) regimen and the proposed intense vaping regimen were first compared using the Cubis 1 Ω atomizer on a large power range, and then by using two atomizers below 1 Ω and two others above 1 Ω on their respective power ranges. An analysis of the e-cig efficiency on the e-liquid vaporization was proposed and calculated for each MVE. The intense vaping regimen allowed a broader power range in optimal heating conditions. MVE linearly increased with the supplied power, up to over-heating conditions at higher powers. Moreover, the e-cigs' efficiencies were higher when low-resistance atomizers were tested at high powers. All these results highlighted that the generated vapor might be better evacuated when an intense vaping regimen is used, and illustrate the obvious need to define a suitable standardized vaping regimen consistent with DTL inhalation.

Assessing the hazard of E-Cigarette flavor mixtures using zebrafish

Since 2007, electronic cigarette (e-cigarette) sales in the U.S. have surpassed those of tobacco cigarettes. This is due, in part, to manufacturer's claims that they are a safer alternative to tobacco cigarettes. However, formaldehyde, acrolein, and diacetyl have been detected in e-cigarettes and public knowledge of e-cigarette composition and ingredient bioactivity is conspicuously lacking. We evaluated the toxicity of nine e-cigarette flavor mixtures and their constituents in the developmental zebrafish, an excellent whole animal biosensor of chemical hazard. Seven of the nine flavors (78%) elicited adverse developmental responses at 1% by volume. The number of toxic endpoints varied greatly between flavors. Two flavors, Grape and Bubble Gum, had similar chemical compositions, but different toxicity profiles. We hypothesized that the toxicity was driven by a constituent present only in the Bubble Gum flavor, cinnamaldehyde. To replicate this toxicity, we built our own defined mixture. The addition of varying concentrations of cinnamaldehyde suggested that it drove the toxicity of these mixtures and that e-cigarette hazard can be flavor dependent.

Metal concentrations in electronic cigarette aerosol: Effect of open-system and closed-system devices and power settings

BACKGROUND

Electronic cigarettes (E-cigarettes) generate aerosol containing metal contaminants. Our goals were to quantify aerosol metal concentrations and to compare the effects of power setting and device type (closed-system vs. open-system) on metal release.

METHODS

Aerosol samples were collected from two closed-system devices (a cigalike and pod) and two open-system devices (mods). Each open-system device was operated at three different power settings to examine the effect of device power on metal release. Concentrations of 14 metals in e-cigarette aerosol collected via droplet deposition were measured using inductively coupled plasma mass spectroscopy. Aerosol metal concentrations were reported as mass fractions (μg/kg) in the e-liquid.

RESULTS

For open-system device 1 (OD1), median arsenic (As), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), antimony (Sb), tin (Sn), and zinc (Zn) concentrations increased 14, 54, 17, 30, 41, 96, 14, 81, 631, and 7-fold when the device power was increased from low (20 W) to intermediate (40 W) setting. When the power was further increased from intermediate (40 W) to high (80 W) setting, concentrations of As, Cr, Cu, Mn, Ni, and Sb did not change significantly. For open-system device 2 (OD2), Cr and Mn concentrations increased significantly when device power was increased from low (40 W) to intermediate (120 W) setting, and then decreased significantly when power was further increased from intermediate (120 W) to high (200 W) setting. Among the four devices, aerosol metal concentrations were higher for the open-system than the closed-system devices, except for aluminum (Al) and uranium (U). For Cr, median (interquartile range) concentrations (μg/kg) from the open-system devices were 2.51 (1.55, 4.23) and 15.6 (7.88, 54.5) vs. 0.39 (0.05, 0.72) and 0.41 (0.34, 0.57) for the closed-system devices. For Ni, concentrations (μg/kg) from the open-system devices were 793 (508, 1169) and 2148 (851, 3397) vs. 1.32 (0.39, 3.35) and 11.9 (10.7, 22.7) from the closed-system devices. Inhalation of 0% and 100% of samples from OD1, 7.4% and 88.9% from OD2 by typical e-cigarette users would exceed chronic minimum risk levels (MRL) of Mn and Ni, respectively. No MRL exceedance was predicted for the closed-system devices. A large fraction of users of OD1 (100%) and OD2 (77.8%) would be exposed to Ni levels higher than those from reference tobacco cigarette 3R4F.

CONCLUSIONS

Our findings suggest that power setting and device type affect metal release from devices to aerosol which would subsequently be inhaled by users. Metal concentrations from open-system devices first increased with device power, and then leveled off for most metals. Open-system devices generate aerosol with higher metal concentrations than closed-system devices. These findings inform tobacco regulatory science, policy makers and health professionals on potential metal health risks associated with e-cigarette use, design and manufacturing.

Experimental Method of Emission Generation Calibration Based on Reference Liquids Characterization

This work focuses on an experimental study of the influence of e-liquid composition on the mass of vaporized e-liquid after standardized emission generation using a U-SAV (Universal System for Analysis of Vaping) vaping machine. All the experiments were based on the use of a Cubis 1Ω clearomiser and on the standard protocol for electronic cigarettes emission generation. Currently, there is no standardized method available to calibrate the emission generations of electronic cigarettes. Since the e-liquid compositions are not always known, we propose a simple, practical, effective, and fast method of emission generation calibration. Therefore, this paper examines a major issue in this new and constantly evolving field, allowing the validation of the emission generation results. To our knowledge, this method is a novelty in our discipline and could be easily developed in laboratories. Pure propylene-glycol, glycerol, ethanol, and water and their mixtures (20 e-liquids) were tested as reference materials, allowing an e-liquids benchmarking and the characterization of 800 commercial e-liquids (with known and unknown compositions) at a fixed power and for one inhalation profile (3 s puff duration and 55 mL of puff volume). The influence of ethanol and/or water addition in the e-liquid was characterized.

E-Cigarette Chemistry and Analytical Detection

The study of e-cigarette aerosol properties can inform public health while longer-term epidemiological investigations are ongoing. The determination of aerosol levels of known toxins, as well as of molecules with unknown inhalation toxicity profiles, affords specific information for estimating the risks of e-cigarettes and for uncovering areas that should be prioritized for further investigation.

Nicotine absorption from e-cigarettes over 12 months

BACKGROUND

Research indicates that, over time, exclusive e-cigarette users (vapers) gradually reduce the nicotine concentration in their e-liquid and transition to more sophisticated devices. Alongside this, consumption of e-liquid increases and constant cotinine levels are maintained.

AIMS

We aimed to confirm these observations in 27 experienced vapers tested at baseline and 12 months later, by measuring nicotine absorption (via salivary levels of the nicotine metabolite cotinine; ng/mL), nicotine concentrations in e-liquid (mg/mL), volume of e-liquid consumed (mL per day), device types and flavours used, both at baseline and 12 months.

RESULTS

Vapers reduced both their nicotine concentrations in e-liquid over 12 months (from 13.83 mg/mL at baseline to 9.91 at follow up) but significantly increased their e-liquid consumption (from 4.44 to 6.84 mL). No significant changes in salivary cotinine concentrations (370.88 ng/mL at baseline and 415.78 ng/mL at follow up) were observed. There was an increase in sub-ohming (using an atomiser coil with resistance of <1 Ω with increased power) at 12 months, and in the use of fruit flavoured e-liquids.

CONCLUSIONS

Our sample of experienced vapers reduced the concentration of nicotine in their e-liquid over time, but maintained their nicotine intake possibly through self-titration via more intensive puffing. Findings suggest there may be little benefit in reducing nicotine e-liquid concentration since this appears to result in higher e-liquid consumption which may incur both a financial and health cost. Gaining an understanding of underlying reasons for lowering e-liquid concentration would be a useful line of empirical enquiry.

Influence of Coil Power Ranges on the E-Liquid Consumption in Vaping Devices

As electronic cigarettes (e-cigarettes) represent a new constantly evolving product category, the systematic analysis of the developed devices and the e-liquid vaporization is challenging. Indeed, understanding how e-cigarettes work and the role of key parameters in the process are major issues. This work focuses on an experimental study of how the power supplied by the battery to the atomizer coil influences e-liquid consumption. The reproducibility and the repeatability of e-liquid consumption were investigated over 20 series of 20 puffs for one of the tested atomizers. Then, the reproducibility and the repeatability of the e-liquid consumption was investigated over five series of 20 puffs for each tested atomizer. The wire behavior according to the supplied power could be separated into three regimes: under-heating (insufficient power to generate an aerosol), optimal vaporization characterized by a linear trend (vaporization of the e-liquid proportional to the supplied energy) and over-heating (dry-burn occurs). Using a controllable and repeatable energy supply, the reproducibility of the quantity of vaporized e-liquid was verified for each of the five series of 20 puffs programed for all the atomizers except one. Finally, the influence of the supplied power on the vaporization and the consumption of the e-liquid as well as the optimal power ranges were investigated and discussed. The results showed that atomizers with resistance ranging from 1 Ω to 1.8 Ω are efficient using all the energy supplied by the battery to vaporize the e-liquid and reducing the energy lost in the cotton or in the metal part of atomizer coil.

Evaluation of E-Vapor Nicotine and Nicotyrine Concentrations under Various E-Liquid Compositions, Device Settings, and Vaping Topographies

Nicotine is one of the major components of electronic cigarette (e-cigarette) emissions. Nicotyrine is a product of nicotine dehydrogenation in e-vapor and is a known inhibitor of human cytochrome P450 enzyme, which mediates nicotine metabolism. However, the emission of nicotine and especially nicotyrine from e-cigarettes has not been studied under real-world vaping patterns. This study examined the impact of e-liquid composition, e-cigarette device power output, and vaping topography on nicotine and nicotyrine concentrations under real-world vaping patterns. The amount of nicotine emitted from e-cigarettes vaped at high e-liquid nicotine levels, high device power, and large puff volumes ranged from 0.365 μg/puff to 236 μg/puff and was comparable to the amount of nicotine emitted from regular cigarettes. E-cigarette coil temperatures (200-300 °C) favored the formation of nicotyrine: E-cigarette vaping generated 2- to 63-fold more nicotyrine per unit nicotine emission than conventional cigarette smoking. High nicotyrine emission from e-cigarettes indicates that nicotine metabolism could be potentially interrupted, which could lead to reduced e-cigarette usage, and result in lower exposures to toxic chemicals (e.g., formaldehyde and acetaldehyde). However, higher serum nicotine levels might increase cancer risks by stimulating nicotinic acetylcholine receptors (nAchRs).