Impact of electronic cigarette heating coil resistance on the production of reactive carbonyls, reactive oxygen species and induction of cytotoxicity in human lung cancer cells in vitro

A comparative toxicological evaluation of emerging nicotine analogs 6-methyl nicotine and nicotinamide: a scoping review

Thermal degradation of flavored e-liquids in e-cigarettes (e-cigs) produces oxidants, volatile organic compounds, and heavy metals. Inhalation toxicology studies have revealed exposure to these toxicants may be toxic to humans. These studies informed the FDA's regulation of nicotine-containing E-cigs under the Tobacco Regulation Act (TRA) (2020) and the banning of all flavors in E-cig bars apart from tobacco and menthol. Furthermore, tobacco companies aiming to sell nicotine products on the US market ought to submit a premarket tobacco product application (PMTA) and obtain approval from the FDA before marketing. Nonetheless, because the PMTA process is lengthy/complicated, vape/tobacco companies utilized a loophole in the TRA (2020) and have introduced nicotine analogs in E-cig bars, such as 6-methyl nicotine (6-MN) and nicotinamide, which are not derived from nicotine or tobacco. These companies claim these analogs to be 'safer' alternatives to nicotine while providing similar satisfaction as nicotine. However, the safety profiles of these analogs are entirely unknown. Therefore, in this review, we have extrapolated the current literature on 6-MN and nicotinamide, and speculated their potential mode of toxicity through alterations in intracellular ROS and activation of nicotinic acetylcholine receptors, transient receptor potential ankyrin-1, and NF-κB. These biomolecules are pivotal in the onset and regulation of pulmonary diseases such as COPD, asthma, and lung tumorigenesis/remodeling. Thus, primary research is urgently warranted to inform regulatory agencies of these emerging nicotine analogs' potential adverse health effects. This article provides insightful information on emerging vape products' potential toxicity for environmental toxicology research and regulation.

Heat-not-burn technology affects plasma testosterone levels and markers of inflammation, oxidative stress in the testes of rats

Introduction

Heating tobacco products (HTPs) are advanced electronic cigarette models. Classified by the FDA as a modified-risk tobacco product and can be used as part of efforts to quit smoking. Using heat-not-burn (HnB) technology, these devices heat tobacco avoiding complete combustion. Although the levels of toxicants in the mainstream are significantly lower than those observed in tobacco smoke, some recent studies have raised concerns about potential health risks associated with their use, particularly regarding their effects on male gonadal function, which remain largely unexplored.

Methods

Adult male Sprague-Dawley rats were exposed, whole body, 5 days/week for 4 weeks to HnB mainstream.

Results

The expression of the cell cycle regulators Bax/Bcl-2 ratio is not affected, along with no changes in p-38. On the other hand, an increase in oxidative stress markers, including those associated with DNA damage, was observed in exposed animals, along with the induction of NF-kB dependent pro-inflammatory mediators: TNF-α, IL-1β, IL-6 and COX-2. Furthermore, inactivation of key androgenic enzymes, such as 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase, together with decreased testosterone synthesis suggest a potential impairment of male gonadal function.

Discussion

The results indicate that animals exposed to HnB smoke show higher levels of oxidative stress markers, including those associated with DNA damage, as well as higher levels of pro-inflammatory cytokines. The impairment of some androgenic key enzymes and those related to the activity of seminiferous epithelium, together with the decrease in testosterone levels, suggest an impairment of gonadal function through the alteration of some cellular pathways typically associated with tobacco consumption.

Increasing coil temperature of a third-generation e-cigarette device modulates C57BL/6 mouse lung immune cell composition and cytokine milieu independently of aerosol dose

Higher coil temperature in e-cigarette devices increases the formation of aerosols and toxicants, such as carbonyls. At present, the health implications of vaping at higher temperatures, including exacerbation of pulmonary inflammation, are largely unknown when aerosol dose is considered. To isolate the pulmonary effects of coil temperature, C57BL/6 mice were exposed to e-cigarette aerosols generated at lower (190°C) or higher (250°C) temperature for 3 days, while maintaining a similar chamber aerosol concentration. Increasing coil temperature did not markedly alter aerosol mass-normalized emissions of select carbonyls formed from thermal degradation pathways including formaldehyde, acetaldehyde, propionaldehyde, and acetone under the tested environment. Total bronchoalveolar cells, primarily macrophages, were significantly decreased in mice exposed to aerosols generated with higher coil temperatures compared to lower temperature exposures. The gene expression of IFNβ, IL-1β, TNFα, and IL-10 in mouse lung tissue was significantly reduced following e-cigarette exposure under both conditions, compared to filtered air exposure. Higher temperature exposures further exacerbated downregulation of IFNβ and IL-1β. Data suggest that higher temperature vaping might modulate acute pulmonary immune responses, potentially inducing immune suppression, even when normalized for aerosol dose exposure. Coil temperature thus appears to be an important parameter that needs to be regulated to ensure harm reduction for e-cigarette users.

An electron paramagnetic resonance time-course study of oxidative stress in the plasma of electronic cigarette exposed rats

The long-term consequences of electronic cigarette (Ecig) use in humans are not yet known, but it is known that Ecig aerosols contain many toxic compounds of concern. We have recently shown that Ecig exposure impairs middle cerebral artery (MCA) endothelial function and that it takes 3 days for MCA reactivity to return to normal. However, the sources contributing to impairment of the endothelium were not investigated. We hypothesized that the increased levels of oxidative stress markers in the blood are correlated with impaired MCA reactivity. We used electron paramagnetic resonance (EPR) spectroscopy to examine plasma from 4-month-old male Sprague-Dawley rats that were exposed to either air (n = 5) or 1 h Ecig exposure, after which blood samples were collected at varying times after exposure (i.e., 1-4, 24, 48 and 72 h postexposure, n = 4 or 5 in each time group). The EPR analyses were performed using the redox-sensitive hydroxylamine spin probe 1-hydroxy-3-carboxymethyl-2,2,5,5-tetramethyl-pyrrolidine (CMH) to measure the level of reactive oxidant species in the plasma samples. We found that EPR signal intensity from the CM• radical was significantly increased in plasma at 1-4, 24 and 48 h (P < 0.05, respectively) and returned to control (air) levels by 72 h. When evaluating the EPR results with MCA reactivity, we found a significant negative correlation (Pearson's P = 0.0027). These data indicate that impaired cerebrovascular reactivity resulting from vaping is associated with the oxidative stress level (measured by EPR from plasma) and indicate that a single 1 h vaping session can negatively influence vascular health for up to 3 days after vaping. HIGHLIGHTS: What is the central question of this study? Does the time course of oxidative stress triggered by electronic cigarette exposure follow the cerebral vascular dysfunction? What is the main finding and its importance? Electron paramagnetic resonance analysis shows that the oxidative stress induced after a single 1 h exposure to electronic cigarette aerosol takes ≤72 h to return to normal, which mirrors the time course for vascular dysfunction in the middle cerebral artery that we have reported previously.

In vitro toxicity and chemical analysis of e-cigarette aerosol produced amid dry hitting

Dry hitting, a phenomenon produced by e-cigarettes with refillable cartridges when the liquid in the coil is low, is a common occurrence among regular vapers despite being an unintended consequence of the device. This phenomenon's hazard to public health is still unknown and needs further investigation. Lung cells cultured at the air-liquid interface were exposed to vaped aerosol consisting of 3 % w/v ethyl maltol in propylene glycol for three-second puffs every 30 seconds for 80 total puffs with either dry hit or saturated conditions. Cytotoxicity was measured colorimetrically. The thermal degradation of the heating coils and wicks was visualized using scanning electron microscopy. The chemical byproducts in the aerosol were analyzed using proton nuclear magnetic resonance and inductively coupled plasma mass spectrometry. The results revealed a highly significant increase in cytotoxicity from dry hit treatments. Imaging showed thermal decomposition of the cotton wick after dry hitting, which was confirmed by energy dispersive x-ray spectroscopy with less oxygen in the dry hit cotton. Chemical byproducts were found via unique peaks in the dry hit condensate in the aromatic and alkene regions. Saturated condensate showed higher concentrations of detected metal species than dry-hit condensate. E-cigarette users should avoid dry hitting by refilling tanks or cartridges preemptively or by using disposable coils to avoid increased toxicity during vaping.

Co-existing ambient fine particulate matter exacerbated electronic cigarette toxicity on human respiratory cells

Respiratory co-exposure to ambient PM2.5 and electronic cigarettes (e-cigarettes) frequently occurs in public. However, the combined effects on human respiratory health have not been well documented. To discuss potential co-effects and possible biological mechanisms, A549/THP-1 co-cultures and BEAS-2B cells were exposed to unvapedtobacco or mint-flavored e-liquids (0-7.2% v/v), e-cigarette aerosol extract (ECE, 0-50% v/v), PM2.5 (60 μg/mL), or PM2.5 + ECE for 24 h. Cell viability assessments on e-liquids, ECE, PM2.5 + ECE showed that the mint flavor exhibited higher cytotoxicity compared to the tobacco flavor in both A549/THP-1 and BEAS-2B. However, the influence of flavors on ROS levels and mRNA expression of inflammatory markers (IL-6, TNF-α, IL-8, IL-1β) after ECE exposure demonstrated inconsistency in the two cell models. PM2.5 + ECE treatment notably elevated ROS production and inflammation responses compared to ECE alone exposure. Only co-exposure induced a significant increase in nuclear transcription factor-κB p65 (NF-κB p65) and NOD-like receptor 3 (NLRP3) protein expression regardless of flavors. Our results indicate that PM2.5-treated cells exacerbate the adverse effects induced by ECE in both A549/THP-1 and BEAS-2B cells. Flavors in unvaped e-liquids affect cytotoxicity, oxidative stress and inflammation response, but these effects vary depending on the vaping process and the specific cell line.

Dual Exposure to E-Cigarette Vapour and Cigarette Smoke Results in Poorer Airway Cell, Monocyte, and Macrophage Function Than Single Exposure

E-cigarette users predominantly also continue to smoke cigarettes. These Dual Users either consume e-cigarettes in locations where smoking is not allowed, but vaping is, or to reduce their consumption of cigarettes, believing it will lead to harm reduction. Whilst it is known that e-cigarette vapour is chemically less complex than cigarette smoke, it has a distinct chemical profile, and very little is known about the health impacts of exposure to both chemical profiles vs. either alone. We simultaneously exposed cells in vitro to non-toxic levels of e-cigarette vapour extract (EVE) and cigarette smoke extract (CSE) to determine their effects on 16HBE14o- airway epithelial cell metabolism and inflammatory response, as well as immune cell (THP-1 cells and monocyte-derived macrophages (MDM) from healthy volunteers) migration, phagocytosis, and inflammatory response. We observed increased toxicity, reduced metabolism (a marker of proliferation) in airway epithelial cells, and reduced monocyte migration, macrophage phagocytosis, and altered chemokine production after exposure to either CSE or EVE. These cellular responses were greater after dual exposure to CSE and EVE. The airway epithelial cells from smokers showed reduced metabolism after EVE (the Switcher model) and dual CSE and EVE exposure. When EVE and CSE were allowed to interact, the chemicals were found to be altered, and new chemicals were also found compared to the CSE and EVE profiles. Dual exposure to e-cigarette vapour and cigarette smoke led to worse functional outcomes in cells compared to either single exposure alone, adding to limited data that dual use may be more dangerous than smoking only.

Addressing Cardiovascular Toxicity Risk of Electronic Nicotine Delivery Systems in the Twenty-First Century: "What Are the Tools Needed for the Job?" and "Do We Have Them?"

Cigarette smoking is positively and robustly associated with cardiovascular disease (CVD), including hypertension, atherosclerosis, cardiac arrhythmias, stroke, thromboembolism, myocardial infarctions, and heart failure. However, after more than a decade of ENDS presence in the U.S. marketplace, uncertainty persists regarding the long-term health consequences of ENDS use for CVD. New approach methods (NAMs) in the field of toxicology are being developed to enhance rapid prediction of human health hazards. Recent technical advances can now consider impact of biological factors such as sex and race/ethnicity, permitting application of NAMs findings to health equity and environmental justice issues. This has been the case for hazard assessments of drugs and environmental chemicals in areas such as cardiovascular, respiratory, and developmental toxicity. Despite these advances, a shortage of widely accepted methodologies to predict the impact of ENDS use on human health slows the application of regulatory oversight and the protection of public health. Minimizing the time between the emergence of risk (e.g., ENDS use) and the administration of well-founded regulatory policy requires thoughtful consideration of the currently available sources of data, their applicability to the prediction of health outcomes, and whether these available data streams are enough to support an actionable decision. This challenge forms the basis of this white paper on how best to reveal potential toxicities of ENDS use in the human cardiovascular system-a primary target of conventional tobacco smoking. We identify current approaches used to evaluate the impacts of tobacco on cardiovascular health, in particular emerging techniques that replace, reduce, and refine slower and more costly animal models with NAMs platforms that can be applied to tobacco regulatory science. The limitations of these emerging platforms are addressed, and systems biology approaches to close the knowledge gap between traditional models and NAMs are proposed. It is hoped that these suggestions and their adoption within the greater scientific community will result in fresh data streams that will support and enhance the scientific evaluation and subsequent decision-making of tobacco regulatory agencies worldwide.

Flow Rate and Wall Shear Stress Characterization of a Biomimetic Aerosol Exposure System

Current in vitro emissions and exposure systems lack biomimicry, use unrealistic flow conditions, produce unrealistic dose, and provide inaccurate biomechanical cues to cell cultures, limiting ability to correlate in vitro outcomes with in vivo health effects. A biomimetic in vitro system capable of puffing aerosol and clean air inhalation may empower researchers to investigate complex questions related to lung injury and disease. A biomimetic aerosol exposure system (BAES), including an electronic cigarette adapter, oral cavity module (OCM), and bifurcated exposure chamber (BEC) was designed and manufactured. The fraction of aerosol deposited in transit to a filter pad or lost as volatiles was 0.116±0.021 in a traditional emissions setup versus 0.098 ± 0.015 with the adapter. The observed flowrate was within 5% of programed flowrate for puffing (25 mL/s), puff-associated respiration (450 mL/s), and tidal inhalation (350 mL/s). The maximum flowrate observed in the fabricated BAES was 450 mL/s, exceeding the lower target nominal wall shear stress of 0.025 Pa upstream of the bifurcation and fell below the target of 0.02 Pa downstream. This in vitro system addresses several gaps observed in commercially available systems and may be used to study many inhaled aerosols. The current work illustrates how in silico models may be used to correlate results of an in vitro study to in vivo conditions, rather than attempting to design an in vitro system that performs exactly as the human respiratory tract.

Toxicological Aspects Associated with Consumption from Electronic Nicotine Delivery System (ENDS): Focus on Heavy Metals Exposure and Cancer Risk

Tobacco smoking remains one of the leading causes of premature death worldwide. Electronic Nicotine Delivery Systems (ENDSs) are proposed as a tool for smoking cessation. In the last few years, a growing number of different types of ENDSs were launched onto the market. Despite the manufacturing differences, ENDSs can be classified as "liquid e-cigarettes" (e-cigs) equipped with an atomizer that vaporizes a liquid composed of vegetable glycerin (VG), polypropylene glycol (PG), and nicotine, with the possible addition of flavorings; otherwise, the "heated tobacco products" (HTPs) heat tobacco sticks through contact with an electronic heating metal element. The presence of some metals in the heating systems, as well as in solder joints, involves the possibility that heavy metal ions can move from these components to the liquid, or they can be adsorbed into the tobacco stick from the heating blade in the case of HTPs. Recent evidence has indicated the presence of heavy metals in the refill liquids and in the mainstream such as arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu), and lead (Pb). The present review discusses the toxicological aspects associated with the exposition of heavy metals by consumption from ENDSs, focusing on metal carcinogenesis risk.

Recent advances in the analysis of electronic cigarette liquids and aerosols: Sample preparation and chromatographic characterization

Electronic cigarette (e-cigarette) usage has risen dramatically worldwide in recent years. It has been publicized as a safer alternative to the conventional combustible cigarette. This, however, has not yet been supported by robust toxicological research evidence. Analysis of the chemical compositions of e-liquids and generated aerosols is an important step in evaluating the toxicity effects of e-cigarettes. Currently, a broad spectrum of analytical methods have been employed for qualitative and quantitative analysis of chemical compositions of e-cigarette liquids and aerosols. The aim of this article is to review the advances in the chromatographic characterization of chemical composition of the latter in the recent five years. In addition, sample preparation methods for e-liquids and aerosols are surveyed and discussed. A study of the relevant literature indicates that, expectedly, gas chromatography and liquid chromatography with a variety of detection systems, particularly mass spectrometry, have been the main analytical techniques used in this field. Sample preparation procedures primarily include headspace sampling, dilute-and-shoot approach, liquid-liquid extraction and sorbent-based extraction for e-liquids and for aerosols (the latter usually with laboratory-built collection devices). Some challenges of current e-cigarette analytical research, and an overview on prospective work are also presented.

Clinical impact of vaping on cardiopulmonary function and lung cancer development: an update

The word 'vaping' is used to define the usage of electronic cigarettes or other instruments to inhale a wide variety of heated and aerosolized substances. Although proposed as a less dangerous and oncogenic alternative than standard nicotine products, e-cigarettes and vaping devices are quite far from being considered benign. In fact, although vaping devices do not generate carcinogenic agents as polycyclic aromatic hydrocarbons produced by the combustion of standard cigarettes and their liquids do not present tobacco-related carcinogens like nitrosamines, there is nowadays clear evidence that they produce dangerous products during their use. Several different molecular mechanisms have been proposed for the oncogenic impact of vaping fluids - by means of their direct chemical action or derivative products generated by pyrolysis and combustion ranging from epithelial-mesenchymal transition, redox stress and mitochondrial toxicity to DNA breaks and fragmentation. In this review we focus on vaping devices, their potential impact on lung carcinogenesis, vaping-associated lung injury and other clinical implications on cardiovascular, cerebrovascular and respiratory diseases, as well as on the psychological implication of e-cigarettes both on heavy smokers trying to quit smoking and on younger non-smokers approaching vaping devices because they are considered as a less dangerous alternative to tobacco cigarettes.

Carbonyls and Aerosol Mass Generation from Vaping Nicotine Salt Solutions Using Fourth- and Third-Generation E-Cigarette Devices: Effects of Coil Resistance, Coil Age, and Coil Metal Material

Aerosol formation and production yields from 11 carbonyls (carbonyl concentration per aerosol mass unit) were investigated (1) from a fourth-generation (4th gen) e-cigarette device at different coil resistances and coil age (0-5000 puffs) using unflavored e-liquid with 2% benzoic acid nicotine salt, (2) between a sub-ohm third-generation (3rd gen) tank mod at 0.12 Ω and a 4th gen pod at 1.2 Ω using e-liquid with nicotine salt, together with nicotine yield, and (3) from 3rd gen coils of different metals (stainless steel, kanthal, nichrome) using e-liquid with freebase nicotine. Coil resistance had an inverse relationship with coil temperature, and coil temperature was directly proportional to aerosol mass formation. Trends in carbonyl yields depended on carbonyl formation mechanisms. Carbonyls produced primarily from thermal degradation chemistry (e.g., formaldehyde, acetaldehyde, acrolein, propionaldehyde) increased per aerosol mass with higher coil resistances, despite lower coil temperature. Carbonyls produced primarily from chemistry initiated by reactive oxygen species (ROS) (e.g., hydroxyacetone, dihydroxyacetone, methylglyoxal, glycolaldehyde, lactaldehyde) showed the opposite trend. Coil age did not alter coil temperature nor aerosol mass formation but had a significant effect on carbonyl formation. Thermal carbonyls were formed optimally at 500 puffs in our study and then declined to a baseline, whereas ROS-derived carbonyls showed a slow rise to a maximum trend with coil aging. The 3rd gen versus 4th gen device comparison mirrored the trends in coil resistance. Nicotine yields per aerosol mass were consistent between 3rd and 4th gen devices. Coil material did not significantly alter aerosol formation nor carbonyl yield when adjusted for wattage. This work shows that sub-ohm coils may not necessarily produce higher carbonyl yields even when they produce more aerosol mass. Furthermore, carbonyl formation is dynamic and not generalizable during the coil's lifetime. Finally, studies that compare data across different e-cigarette devices, coil age, and coil anatomy should account for the aerosol chemistry trends that depend on these parameters.

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).

Potential Harm of IQOS Smoke to Rat Liver

The Food and Drug Administration has recently classified the IQOS electronic cigarette as a modified-risk tobacco product. However, IQOS cigarettes still release various harmful constituents typical of conventional cigarettes (CCs), although the concentrations are markedly lower. Here, we investigated the damaging effects of IQOS smoking on the liver. Male Sprague Dawley rats were exposed, whole body, 5 days/week for 4 weeks to IQOS smoke (4 sticks/day), and hepatic xenobiotic metabolism, redox homeostasis and lipidomic profile were investigated. IQOS boosted reactive radicals and generated oxidative stress. Exposure decreased cellular reserves of total glutathione (GSH) but not GSH-dependent antioxidant enzymes. Catalase and xanthine oxidase were greater in the exposed group, as were various hepatic CYP-dependent monooxygenases (CYP2B1/2, CYP1A1, CYP2A1, CYP2E1-linked). Respiratory chain activity was unaltered, while the number of liver mitochondria was increased. IQOS exposure had an impact on the hepatic lipid profile. With regard to the expression of some MAP kinases commonly activated by CC smoking, IQOS increased the p-p38/p38 ratio, while erythroid nuclear transcription factor 2 (Nrf2) was negatively affected. Our data suggest that IQOS significantly impairs liver function, supporting the precautionary stance taken by the WHO toward the use of these devices, especially by young people and pregnant women.

Cytotoxicity and cell injuries of flavored electronic cigarette aerosol and mainstream cigarette smoke: A comprehensive in vitro evaluation

INTRODUCTION

Although electronic cigarettes (e-cigarettes) have attracted much attention due to their claimed harm-reduction effects compared with conventional cigarettes, the adverse effects of e-cigarette aerosol exposure on human health are still unclear. In this work we compared the cytotoxic effects of combustion cigarettes with four commercially available flavored electronic cigarettes and their main components on ten cell lines. Cell injury mechanism of e-cigarette aerosol and combustible cigarette smoke was also explored using cellular models.

METHODS

Eleven kinds of e-cigarettes aerosol condensates (ECSCs) and cigarette smoke constituent's condensates (CSC) were collected by Cambridge filter pad, and the nicotine contents were determined by UPLC to provide an equivalent nicotine dosage. The CCK-8 assay was used to measure the cell viability differences between ECSC and CSC. Based on RNA-seq results, we compared the effects of ECSC and CSC on various cell injury pathways. Oxidative stress and inflammatory responses were further tested by Western Blot, immunofluorescence, and qRT-PCR assays.

RESULTS

CSC was found to be more cytotoxic than flavored ECSC and their main components, and BEAS-2B cell line was the most sensitive cells by comparing the IC50 value. With prolonged exposure duration and higher doses, ECSC began to exhibit cytotoxicity at and above 72 µg/mL. The IC50 values of ECSC were 15-fold higher than that of CSC. Transcriptome analyses indicated that cell injury-related processes were enriched after the treatment of CSC. CSC could significantly induce more oxidative stress and inflammatory signals than ECSC.

CONCLUSION

ECSCs and their components induced significantly less cytotoxicity than CSC under the laboratory exposure conditions, and CSC caused much severe cell injuries. Our study adds to the body of scientific evidence for a more comprehensive safety evaluation of e-cigarette products as compared to cigarettes.

External Factors Modulating Vaping-Induced Thermal Degradation of Vitamin E Acetate

Despite previous studies indicating the thermal stability of vitamin E acetate (VEA) at low temperatures, VEA has been shown to readily decompose into various degradation products such as alkenes, long-chain alcohols, and carbonyls such as duroquinone (DQ) at vaping temperatures of <200 °C. While most models simulate the thermal decomposition of e-liquids under pyrolysis conditions, numerous factors, including vaping behavior, device construction, and the surrounding environment, may impact the thermal degradation process. In this study, we investigated the role of the presence of molecular oxygen (O2) and transition metals in promoting thermal oxidation of e-liquids, resulting in greater degradation than predicted by pure pyrolysis. Thermal degradation of VEA was performed in inert (N2) and oxidizing atmospheres (clean air) in the absence and presence of Ni-Cr and Cu-Ni alloy nanopowders, metals commonly found in the heating coil and body of e-cigarettes. VEA degradation was analyzed using thermogravimetric analysis (TGA) and gas chromatography/mass spectrometry (GC/MS). While the presence of O2 was found to significantly enhance the degradation of VEA at both high (356 °C) and low (176 °C) temperatures, the addition of Cu-Ni to oxidizing atmospheres was found to greatly enhance VEA degradation, resulting in the formation of numerous degradation products previously identified in VEA vaping emissions. O2 and Cu-Ni nanopowder together were also found to significantly increase the production of OH radicals, which has implications for e-liquid degradation pathways as well as the potential risk of oxidative damage to biological systems in real-world vaping scenarios. Ultimately, the results presented in this study highlight the importance of oxidation pathways in VEA thermal degradation and may aid in the prediction of thermal degradation products from e-liquids.

Chemical characterisation of the vapour emitted by an e-cigarette using a ceramic wick-based technology

Fourth-generation 'pod' e-cigarette devices have been driven by technological advances in electronic atomization of the e-liquid. Use of microporous ceramic as a wicking material improves heating efficiency, but how it affects the chemical emissions of these devices is unclear. We assessed the emissions of a pod e-cigarette with innovative ceramic wick-based technology and two flavoured e-liquids containing nicotine lactate and nicotine benzoate (57 and 18 mg mL-1 nicotine, respectively). Among the studied harmful and potentially harmful constituents (HPHCs) listed by the US FDA and/or WHO TobReg, only 5 (acetone, acetaldehyde, formaldehyde, naphthalene and nornicotine) were quantified at levels of 0.14 to 100 ng puff-1. In the combustible cigarette (Kentucky reference 1R6F), levels were from 0.131 to 168 µg puff-1. Nicotine levels ranged 0.10-0.32 mg puff-1 across the 3 study products. From the 19 proposed HPHCs specifically of concern in e-cigarettes, only 3 (glycerol, isoamyl acetate and propylene glycol) were quantified. The low/undetectable levels of HPHCs reflect not only the optimal operating conditions of the e-cigarette, including an efficient supply of e-liquid by the ceramic wick without overheating, but also the potential of the e-cigarettes to be used as an alternative to combustible cigarettes.

On the toxicity of e-cigarettes consumption: Focus on pathological cellular mechanisms

Tobacco smoking remains without a doubt one of the leading causes of premature death worldwide. In combination with conventional protocols for smoking cessation, e-cigarettes have been proposed as a useful tool to quit smoking. Advertised as almost free of toxic effects, e-cigarettes have rapidly increased their popularity, becoming a sought-after device, especially among young people. Recently some health concerns about e-cigarette consumption are being raised. It is well known that they can release several toxic compounds, some of which are carcinogenic to humans, and emerging results are now outlining the risks related to the onset of respiratory and cardiovascular diseases and even cancer. The present review shows the emerging evidence about the role of technical components of the devices, the e-liquid composition as well as customization by consumers. The primary topics we discuss are the main toxicological aspects associated with e-cigarette consumption, focusing on the molecular pathways involved. Here it will be shown how exposure to e-cigarette aerosol induces stress/mitochondrial toxicity, DNA breaks/fragmentation following the same pathological pathways triggered by tobacco smoke, including the deregulation of molecular signalling axis associated with cancer progression and cell migration. Risk to fertility and pregnancy, as well as cardiovascular risk associated with e-cigarette use, have also been reported.

ECAM: A low-cost vaping device for generating and collecting electronic cigarette condensate for in vitro studies

The use of electronic cigarettes (ECs) has become widespread despite many unknowns around their long-term health impact. ECs work by vapourising a liquid, known as an e-liquid, typically consisting of propylene glycol, glycerol, flavourings and nicotine. The chemical constituents and resultant impact on cells and tissue are dependent on several factors, including the flavourings used, the vaping topography/use pattern, and the device used. ECAM (Electronic Cigarette Aerosol Machine) is an open source, portable device for creating EC aerosol - for condensate collection and in vitro studies - using a controlled methodology. ECAM was developed as a low cost, automated, and customisable alternative to commercial devices. ECAM consists of a micro diaphragm gas pump to draw air/EC aerosol through the system. The device is automated using an Arduino and solenoid pinch valves are used to alternate between air and EC vapour. Condensate is collected in a vial within a cold-water bath. Each ECAM unit uses a temperature/humidity sensor to measure ambient air conditions and a differential pressure sensor to determine the pressure within the system. ECAM is programmed to adhere to International Standards Organisation 20768:2018. The design files, source code, and build instructions for this device can be found at https://dx.doi.org/10.17605/OSF.IO/3NGU4.

Electronic cigarettes: Modern instruments for toxic lung delivery and posing risk for the development of chronic disease

Following the emergence of electronic cigarette, or vaping product use associated lung injury (EVALI) in 2019 in the US, regulation of e-cigarettes has become globally tighter and the collective evidence of the detrimental effects of vaping has grown. The danger of cellular distress and altered homeostasis is heavily associated with the modifiable nature of electronic cigarette devices. An array of harmful chemicals and elevated concentrations of metals have been detected in e-cigarette aerosols which have been linked to various pathogeneses. Vaping is linked to increased inflammation, altered lipid homeostasis and mitochondrial dysfunction whilst also increasing microbial susceptibility whilst the long-term damage is yet to be observed. The scientific evidence is mounting and highlighting that, along with traditional tobacco cigarette smoking, electronic cigarette vaping is not a safe practice.

Effects of Manufacturing Variation in Electronic Cigarette Coil Resistance and Initial Pod Mass on Coil Lifetime and Aerosol Generation

This work investigated the effects of manufacturing variations, including coil resistance and initial pod mass, on coil lifetime and aerosol generation of Vuse ALTO pods. Random samples of pods were used until failure (where e-liquid was consumed, and coil resistance increased to high value indicating a coil break). Initial coil resistance, initial pod mass, and e-liquid net mass ranged between 0.89 to 1.14 [Ω], 6.48 to 6.61 [g], and 1.88 to 2.00 [g] respectively. Coil lifetime was µ (mean) = 158, σ (standard deviation) = 21.5 puffs. Total mass of e-liquid consumed until coil failure was µ = 1.93, σ = 0.035 [g]. TPM yield per puff of all test pods for the first session (brand new pods) was µ = 0.0123, σ = 0.0003 [g]. Coil lifetime and TPM yield per puff were not correlated with either variation in initial coil resistance or variation in initial pod mass. The absence of e-liquid in the pod is an important factor in causing coil failure. Small bits of the degraded coil could be potentially introduced to the aerosol. This work suggests that further work is required to investigate the effect of e-liquid composition on coil lifetime and TPM yield per puff.

Lung Damage Caused by Heated Tobacco Products and Electronic Nicotine Delivery Systems: A Systematic Review

The tobacco industry promotes electronic nicotine delivery systems (ENDS) and heated tobacco products (HTP) as a safer alternative to conventional cigarettes with misleading marketing sustained by studies with conflict of interest. As a result, these devices sell without regulations and warnings about their adverse effects on health, with a growing user base targeting young people. This systematic review aimed to describe the adverse effects on the respiratory system in consumers of these devices. We conducted a systematic review and bibliometric analysis of 79 studies without conflict of interest evaluating ENDS and HTP effects in the respiratory system in experimental models, retrieved from the PubMed database. We found that the damage produced by using these devices is involved in pathways related to pulmonary diseases, involving mechanisms previously reported in conventional cigarettes as well as new mechanisms particular to these devices, which challenges that the tobacco industry’s claims. The present study provides significant evidence to suggest that these devices are an emerging public health problem and that they should be regulated or avoided.

Sub-ohm vaping increases the levels of carbonyls, is cytotoxic, and alters gene expression in human bronchial epithelial cells exposed at the air-liquid interface

BACKGROUND

Exposure to electronic-cigarette (e-cig) aerosols induces potentially fatal e-cig or vaping-associated lung injury (EVALI). The cellular and molecular mechanisms underlying these effects, however, are unknown. We used an air-liquid interface (ALI) in vitro model to determine the influence of two design characteristics of third-generation tank-style e-cig devices-resistance and voltage-on (1) e-cig aerosol composition and (2) cellular toxicity.

METHODS

Human bronchial epithelial cells (H292) were exposed to either butter-flavored or cinnamon-flavored e-cig aerosols at the ALI in a Vitrocell exposure system connected to a third-generation e-cig device. Exposures were conducted following a standard vaping topography profile for 2 h per day, for 1 or 3 consecutive days. 24 h after ALI exposures cellular and molecular outcomes were assessed.

RESULTS

We found that butter-flavored e-cig aerosol produced under 'sub-ohm' conditions (< 0.5 Ω) contains high levels of carbonyls (7-15 μg/puff), including formaldehyde, acetaldehyde and acrolein. E-cig aerosol produced under regular vaping conditions (resistance > 1 Ω and voltage > 4.5 V), contains lower carbonyl levels (< 2 μg/puff). We also found that the levels of carbonyls produced in the cinnamon-flavored e-cig aerosols were much lower than that of the butter-flavored aerosols. H292 cells exposed to butter-flavored or cinnamon-flavored e-cig aerosol at the ALI under 'sub-ohm' conditions for 1 or 3 days displayed significant cytotoxicity, decreased tight junction integrity, increased reactive oxygen species production, and dysregulated gene expression related to biotransformation, inflammation and oxidative stress (OS). Additionally, the cinnamon-flavored e-cig aerosol induced pro-oxidant effects as evidenced by increases in 8-hydroxy-2-deoxyguanosine protein levels. Moreover, we confirmed the involvement of OS as a toxicity process for cinnamon-flavored e-cig aerosol by pre-treating the cells with N-acetyl cysteine (NAC), an antioxidant that prevented the cells from the OS-mediated damage induced by the e-cig aerosol.

CONCLUSION

The production of high levels of carbonyls may be flavor specific. Overall, inhaling e-cig aerosols produced under 'sub-ohm' conditions is detrimental to lung epithelial cells, potentially via mechanisms associated with OS. This information could help policymakers take the necessary steps to prevent the manufacturing of sub-ohm atomizers for e-cig devices.

Sub-ohm vaping increases the levels of carbonyls, is cytotoxic, and alters gene expression in human bronchial epithelial cells exposed at the air-liquid interface

Background

Exposure to electronic-cigarette (e-cig) aerosols induces potentially fatal e-cig or vaping-associated lung injury (EVALI). The cellular and molecular mechanisms underlying these effects, however, are unknown. We used an air–liquid interface (ALI) in vitro model to determine the influence of two design characteristics of third-generation tank-style e-cig devices—resistance and voltage—on (1) e-cig aerosol composition and (2) cellular toxicity.

Methods

Human bronchial epithelial cells (H292) were exposed to either butter-flavored or cinnamon-flavored e-cig aerosols at the ALI in a Vitrocell exposure system connected to a third-generation e-cig device. Exposures were conducted following a standard vaping topography profile for 2 h per day, for 1 or 3 consecutive days. 24 h after ALI exposures cellular and molecular outcomes were assessed.

Results

We found that butter-flavored e-cig aerosol produced under ‘sub-ohm’ conditions (< 0.5 Ω) contains high levels of carbonyls (7–15 μg/puff), including formaldehyde, acetaldehyde and acrolein. E-cig aerosol produced under regular vaping conditions (resistance > 1 Ω and voltage > 4.5 V), contains lower carbonyl levels (< 2 μg/puff). We also found that the levels of carbonyls produced in the cinnamon-flavored e-cig aerosols were much lower than that of the butter-flavored aerosols. H292 cells exposed to butter-flavored or cinnamon-flavored e-cig aerosol at the ALI under ‘sub-ohm’ conditions for 1 or 3 days displayed significant cytotoxicity, decreased tight junction integrity, increased reactive oxygen species production, and dysregulated gene expression related to biotransformation, inflammation and oxidative stress (OS). Additionally, the cinnamon-flavored e-cig aerosol induced pro-oxidant effects as evidenced by increases in 8-hydroxy-2-deoxyguanosine protein levels. Moreover, we confirmed the involvement of OS as a toxicity process for cinnamon-flavored e-cig aerosol by pre-treating the cells with N-acetyl cysteine (NAC), an antioxidant that prevented the cells from the OS-mediated damage induced by the e-cig aerosol.

Conclusion

The production of high levels of carbonyls may be flavor specific. Overall, inhaling e-cig aerosols produced under ‘sub-ohm’ conditions is detrimental to lung epithelial cells, potentially via mechanisms associated with OS. This information could help policymakers take the necessary steps to prevent the manufacturing of sub-ohm atomizers for e-cig devices.

Associations between observed formaldehyde concentrations and smoking, environmental tobacco smoke, and self-reported cancers and asthma: data for US children, adolescents, and adults

For the first time, the National Health and Nutrition Examination Survey (NHANES) released data on hemoglobin adducts of formaldehyde (HCHO) in public domain for US children aged 6-11 years, adolescents aged 12-19 years, and adults aged > = 20 years for 2015-2016. This study was undertaken to evaluate the associations between concentrations of HCHO in whole blood and smoking, exposure to environmental tobacco smoke (ETS), and self-reported diagnoses of cancers and asthma. Adult smokers were found to have higher adjusted concentrations of HCHO than nonsmokers (127.7 vs. 125.1 pmol/g Hb, p = 0.02). Exposure to ETS was not found to affect the adjusted concentrations of HCHO. No associations were observed between HCHO concentrations and self-reported diagnosis of "ever" cancer as well as self-reported presence of asthma at the time of participation in NHANES. HCHO concentrations were not found to differ across genders and racial/ethnic groups for children and adolescents. Among adults, non-Hispanic blacks (120.0 pmol/g Hb) had lower adjusted concentrations (p < = 0.01) of HCHO than non-Hispanic whites (128.8 pmol/g Hb), Mexican Americans (129.4 pmol/g Hb), other Hispanics (130.3 pmol/g Hb), and non-Hispanic Asians (127.9 pmol/g Hb). In conclusion, self-reported diagnoses of cancer and asthma were not found to be associated with observed concentrations of HCHO in whole blood.

Method for Quantifying Variation in the Resistance of Electronic Cigarette Coils

In electronic nicotine delivery systems (ENDS), coil resistance is an important factor in the generation of heat energy used to change e-liquid into vapor. An accurate and unbiased method for testing coil resistance is vital for understanding its effect on emissions and reporting results that are comparable across different types and brands of ENDS and measured in different laboratories. This study proposes a robust, accurate and unbiased method for measuring coil resistance. An apparatus is used which mimics the geometric configuration and assembly of ENDS reservoirs, coils and power control units. The method is demonstrated on two commonly used ENDS devices—the ALTO by Vuse and JUUL. Analysis shows that the proposed method is stable and reliable. The two-wire configuration introduced a positive measurement bias of 0.086 (Ω), which is a significant error for sub-ohm coil designs. The four-wire configuration is far less prone to bias error and is recommended for universal adoption. We observed a significant difference in the coil resistance of 0.593 (Ω) (p < 0.001) between the two products tested. The mean resistance and standard deviation of the reservoir/coil assemblies was shown to be 1.031 (0.067) (Ω) for ALTO and 1.624 (0.033) (Ω) for JUUL. The variation in coil resistance between products and within products can have significant impacts on aerosol emissions.

Impact of Atomizer Age and Flavor on In Vitro Toxicity of Aerosols from a Third-Generation Electronic Cigarette against Human Oral Cells

Electronic cigarettes (ECs) are categorized into generations which differ in terms of design, aerosol production, and customizability. Current and former smokers prefer third-generation devices that satisfy tobacco cravings more effectively than older generations. Recent studies indicate that EC aerosols from first- and second-generation devices contain reactive carbonyls and free radicals and can cause in vitro cytotoxicity. Third-generation ECs have not been adequately studied. Further, previous studies have focused on cells from the respiratory tract, whereas those of the oral cavity, which is exposed to high levels of EC aerosols, have been understudied. We quantified the production of reactive carbonyls and free radicals by a third-generation EC and investigated the induction of cytotoxicity and oxidative stress in normal and cancerous human oral cell lines using a panel of eight commercial EC liquids. We found that EC aerosols produced using a new atomizer contained formaldehyde, acetaldehyde, and acrolein, but did not contain detectable levels of free radicals. We found that EC aerosols generated from only one of the eight liquids tested using a new atomizer induced cytotoxicity against two human oral cells in vitro. Treatment of oral cells with the cytotoxic EC aerosol caused a concomitant increase in intracellular oxidative stress. As atomizer age increased with repeated use of the same atomizer, carbonyl production, radical emissions, and cytotoxicity increased. Overall, our results suggest that third-generation ECs may cause adverse effects in the oral cavity and normal EC use, which involves repeated use of the same atomizer to generate aerosol, may enhance the potential toxic effects of third-generation ECs.

Current E-Cigarette Research in the Context of Asthma

PURPOSE OF REVIEW

The purpose of this review is to integrate recent research on the respiratory immune effects of e-cigarettes with the pathogenesis of asthma to better understand how e-cigarettes may affect asthmatics and to note critical knowledge gaps regarding the effects of e-cigarettes on asthmatics.

RECENT FINDINGS

Human, rodent, and cell culture studies show that key cellular functions of epithelial cells, macrophages, and neutrophils are altered by e-cigarette exposure. Because respiratory immunity is already dysregulated in asthma, further alteration of cellular function by e-cigarettes could impact asthma development, severity, and/or exacerbations. Future research is needed to more directly investigate this relationship using controlled human exposure studies and exposure of cell culture or animal models of asthma to e-cigarettes.

An Integrated Approach for Preventing Oral Cavity and Oropharyngeal Cancers: Two Etiologies with Distinct and Shared Mechanisms of Carcinogenesis

Head and neck squamous cell carcinoma (HNSCC) was the 7th most common malignancy worldwide in 2018 and despite therapeutic advances, the overall survival rate for oral squamous cell carcinoma (OSCC; ∼50%) has remained unchanged for decades. The most common types are OSCC and oropharyngeal squamous cell carcinoma (OPSCC, survival rate ∼85%). Tobacco smoking is a major risk factor of HNSCC. In the developed world, the incidence of OSCC is declining as a result of tobacco cessation programs. However, OPSCC, which is also linked to human papillomavirus (HPV) infection, is on the rise and now ranks as the most common HPV-related cancer. The current state of knowledge indicates that HPV-associated disease differs substantially from other types of HNSCC and distinct biological differences between HPV-positive and HPV-negative HNSCC have been identified. Although risk factors have been extensively discussed in the literature, there are multiple clinically relevant questions that remain unanswered and even unexplored. Moreover, existing approaches (e.g., tobacco cessation, vaccination, and chemoprevention) to manage and control this disease remain a challenge. Thus, in this review, we discuss potential future basic research that can assist in a better understanding of disease pathogenesis which may lead to novel and more effective preventive strategies for OSCC and OPSCC.

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.