Electronic Nicotine Delivery System Aerosol-induced Cell Death and Dysfunction in Macrophages and Lung Epithelial Cells

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.

Smoking on the risk of acute respiratory distress syndrome: a systematic review and meta-analysis

BACKGROUND

The relationship between smoking and the risk of acute respiratory distress syndrome (ARDS) has been recognized, but the conclusions have been inconsistent. This systematic review and meta-analysis investigated the association between smoking and ARDS risk in adults.

METHODS

The PubMed, EMBASE, Cochrane Library, and Web of Science databases were searched for eligible studies published from January 1, 2000, to December 31, 2023. We enrolled adult patients exhibiting clinical risk factors for ARDS and smoking condition. Outcomes were quantified using odds ratios (ORs) for binary variables and mean differences (MDs) for continuous variables, with a standard 95% confidence interval (CI).

RESULTS

A total of 26 observational studies involving 36,995 patients were included. The meta-analysis revealed a significant association between smoking and an increased risk of ARDS (OR 1.67; 95% CI 1.33-2.08; P < 0.001). Further analysis revealed that the associations between patient-reported smoking history and ARDS occurrence were generally similar to the results of all the studies (OR 1.78; 95% CI 1.38-2.28; P < 0.001). In contrast, patients identified through the detection of tobacco metabolites (cotinine, a metabolite of nicotine, and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a metabolite of tobacco products) showed no significant difference in ARDS risk (OR 1.19; 95% CI 0.69-2.05; P = 0.53). The smoking group was younger than the control group (MD - 7.15; 95% CI - 11.58 to - 2.72; P = 0.002). Subgroup analysis revealed that smoking notably elevated the incidence of ARDS with extrapulmonary etiologies (OR 1.85; 95% CI 1.43-2.38; P < 0.001). Publication bias did not affect the integrity of our conclusions. Sensitivity analysis further reinforced the reliability of our aggregated outcomes.

CONCLUSIONS

There is a strong association between smoking and elevated ARDS risk. This emphasizes the need for thorough assessment of patients' smoking status, urging healthcare providers to vigilantly monitor individuals with a history of smoking, especially those with additional extrapulmonary risk factors for ARDS.

Increased oxidative stress responses in murine macrophages exposed at the air-liquid interface to third- and fourth-generation electronic nicotine delivery system (ENDS) aerosols

Background

New fourth generation electronic nicotine delivery system (ENDS) devices contain high levels of nicotine salt (up to 60 mg/mL), whose cellular and molecular effects on immune cells are currently unknown. Here, we used a physiologically-relevant in vitro air-liquid interface (ALI) exposure model to assess the toxicity of distinct ENDS, a 3rd-generation electronic-cigarette (e-cig) and two 4th-generation ENDS devices (JUUL and Posh Plus).

Methods

Murine macrophages (RAW 264.7) were exposed at the ALI to either air, Menthol or Crème Brûlée-flavored ENDS aerosols generated from those devices for 1-hour per day for 1 or 3 consecutive days. Cellular and molecular toxicity was evaluated 24 h post-exposure.

Results

1-day of Menthol-flavored JUUL aerosol exposure significantly decreased cell viability and significantly increased lactate dehydrogenase (LDH) levels compared to air controls. Further, JUUL Menthol elicited significantly increased reactive oxygen species (ROS) and nitric oxide (NO) production compared to air controls. Posh Crème Brûlée-flavored aerosols displayed significant cytotoxicity - decreased cell viability and increased LDH levels -after 1- and 3-day exposures, while the Crème Brûlée-flavored aerosol produced by the 3rd-generation e-cig device only displayed significant cytotoxicity after 3 days compared to air controls. Further, both Posh and third-generation e-cig Crème Brûlée flavored-aerosols elicited significantly increased ROS plus high levels of 8-isoprostane after 1 and 3 days compared to air controls, indicating increased oxidative stress. Posh and third-generation e-cig Crème Brûlée flavored-aerosols elicited reduction in NO levels after one day, but elicited increase in NO after 3 days. Genes in common dysregulated by both devices after 1 day included α7nAChR, Cyp1a1, Ahr, Mmp12, and iNos.

Conclusion

Our results suggest that ENDS Menthol and Crème Brûlée-flavored aerosol exposures from both 3rd- and 4th-generation ENDS devices are cytotoxic to macrophages and cause oxidative stress. This can translate into macrophage dysfunction. Although 4th-generation disposable ENDS devices have no adjustable operational settings and are considered low-powered ENDS devices, their aerosols can induce cellular toxicity compared to air-exposed control cells. This study provides scientific evidence for regulation of nicotine salt-based disposable ENDS products.

Pro-inflammatory effects of aerosols from e-cigarette-derived flavoring chemicals on murine macrophages

Macrophages treated with the flavoring chemicals found in flavored electronic cigarettes have been shown to induce an inflammatory response, however, limited data are available on the effect of aerosol exposure to these chemicals. We hypothesized that aerosol exposure to flavoring chemicals found in commercially available flavored e-liquids would result in an increase in pro-inflammatory cytokines in macrophages. Raw264.7 macrophage cell lines were exposed to a low and high dose of propylene glycol/vegetable glycerin (PG/VG) with almond flavoring benzaldehyde (280 μg/ml and 2.1 mg/ml), PG/VG with spicy/clove flavoring eugenol (3.5 mg/ml and 12 mg/ml), or PG/VG with apple flavoring hexyl acetate (500 μg/ml and 2.5 mg/ml). Exposure to PG/VG with 2.1 mg/ml benzaldehyde resulted in a significant increase in KC levels compared to air and PG/VG exposed cells. Exposure to PG/VG with both doses of hexyl acetate resulted in a significant increase in KC and IL-6 levels compared to air exposed cells. Exposure to PG/VG with both doses of eugenol resulted in a significant increase in KC and IL-6 levels compared to air and PG/VG exposed cells. These data indicate the ability of aerosol exposure to e-cigarette flavoring chemicals to significantly increase pro-inflammatory cytokine release in macrophages.

Aerosolized nicotine from e-cigarettes alters gene expression, increases lung protein permeability, and impairs viral clearance in murine influenza infection

E-cigarette use has rapidly increased as an alternative means of nicotine delivery by heated aerosolization. Recent studies demonstrate nicotine-containing e-cigarette aerosols can have immunosuppressive and pro-inflammatory effects, but it remains unclear how e-cigarettes and the constituents of e-liquids may impact acute lung injury and the development of acute respiratory distress syndrome caused by viral pneumonia. Therefore, in these studies, mice were exposed one hour per day over nine consecutive days to aerosol generated by the clinically-relevant tank-style Aspire Nautilus aerosolizing e-liquid containing a mixture of vegetable glycerin and propylene glycol (VG/PG) with or without nicotine. Exposure to the nicotine-containing aerosol resulted in clinically-relevant levels of plasma cotinine, a nicotine-derived metabolite, and an increase in the pro-inflammatory cytokines IL-17A, CXCL1, and MCP-1 in the distal airspaces. Following the e-cigarette exposure, mice were intranasally inoculated with influenza A virus (H1N1 PR8 strain). Exposure to aerosols generated from VG/PG with and without nicotine caused greater influenza-induced production in the distal airspaces of the pro-inflammatory cytokines IFN-γ, TNFα, IL-1β, IL-6, IL-17A, and MCP-1 at 7 days post inoculation (dpi). Compared to the aerosolized carrier VG/PG, in mice exposed to aerosolized nicotine there was a significantly lower amount of Mucin 5 subtype AC (MUC5AC) in the distal airspaces and significantly higher lung permeability to protein and viral load in lungs at 7 dpi with influenza. Additionally, nicotine caused relative downregulation of genes associated with ciliary function and fluid clearance and an increased expression of pro-inflammatory pathways at 7 dpi. These results show that (1) the e-liquid carrier VG/PG increases the pro-inflammatory immune responses to viral pneumonia and that (2) nicotine in an e-cigarette aerosol alters the transcriptomic response to pathogens, blunts host defense mechanisms, increases lung barrier permeability, and reduces viral clearance during influenza infection. In conclusion, acute exposure to aerosolized nicotine can impair clearance of viral infection and exacerbate lung injury, findings that have implications for the regulation of e-cigarette products.

Electronic Cigarettes: A Pro-Con Review of the Current Literature

Electronic cigarettes (e-cigarettes, e-cigs, or electronic nicotine delivery systems) are battery-operated devices typically containing glycerol and/or propylene glycol-based solutions with varying nicotine content, known as e-liquids. Although e-cigarettes were originally developed as a potentially less harmful alternative to traditional combustible tobacco cigarette smokers, several factors have driven their popularity among smokers and nonsmokers alike, including their sleek product designs, innumerable appealing flavors, lack of combustible smoke and odor, and high potential nicotine concentrations. Furthermore, many advocates have promoted the idea that e-cigarettes are safe to use, or at least safer than conventional tobacco, despite limited longitudinal data to support these claims. Here, we examine what is known about the impacts of e-cigarette use on traditional cigarette smoking cessation, lung health, and youth and young adult tobacco product exposure. Upon review of the currently available literature, the negative effects of e-cigarette use seem to outweigh any potential benefit, because the available evidence does not confirm the use of e-cigarettes as an effective strategy for supporting traditional combustible tobacco cigarette smoking cessation, particularly given the emerging adverse effects on lung health and the potential future public health effects of e-cigarette adoption among a burgeoning new generation of tobacco product users.

A systematic review examining the pulmonary effects of electronic vapor delivery systems

STUDY OBJECTIVE

Despite the popularity of vaping and electronic vapor delivery systems (EVDS), the healthcare community remains largely unfamiliar with their potential to induce harm. The purpose of this systematic review is to identify how EVDS use affects the pulmonary system in order to support future anesthetic guidelines for patients who vape.

DESIGN

Systematic Review. An electronic search of databases CINAHL and PubMed was performed in October 2020.

STUDY ELIGIBILITY CRITERIA

Studies were included if they were deemed original research published in English, if they were performed exclusively in humans or on human tissue, if they examined the effects of EVDS on pulmonary function or tissue, and/or if they produced quantitative data. Studies were excluded if they utilized animal samples, studied subjects under the age of 18, presented expert opinions or reviews, offered qualitative data, reported case studies, or only evaluated EVDS' efficacy as a smoking cessation tool.

MAIN RESULTS

This review identified six EVDS-induced pulmonary implications warranting anesthetic consideration: alterations in pulmonary function tests, disrupted ventilation, impaired mucociliary clearance, tissue destruction, a disrupted immune response, and oxidative stress with DNA fragmentation.

CONCLUSION

A total of 38 studies described the effects of EVDS on pulmonary function, airway epithelial tissue, and inflammatory mechanisms that may lead to chronic pulmonary disease. Anesthesia providers are encouraged to assess patients for EVDS use during the preoperative period and use the information generated by this systematic review to drive subsequent care.

Impact of e-cigarette aerosol on primary human alveolar epithelial type 2 cells

Electronic cigarettes (e-cigarettes) are designed to simulate combustible cigarette smoking and to aid in smoking cessation. Although the number of e-cigarette users has been increasing, the potential health impacts and biological effects of e-cigarettes are still not fully understood. Previous research has focused on the biological effects of e-cigarettes on lung cancer cell lines and distal airway epithelial cells; however, there have been few published studies on the effect of e-cigarettes on primary lung alveolar epithelial cells. The primary purpose of this study was to investigate the direct effect of e-cigarette aerosol on primary human lung alveolar epithelial type 2 (AT2) cells, both alone and in the presence of viral infection. The Melo-3 atomizer caused direct AT2 cell toxicity, whereas the more popular Juul pod's aerosol did not have a detectable cytotoxic effect on AT2 cells. Juul nicotine aerosol also did not increase short-term susceptibility to viral infection. However, 3 days of exposure upregulated genes central to the generation of reactive oxygen species, lipid peroxidation, and carcinogen metabolism and downregulated key innate immune system genes related to cytokine and chemokine signaling. These findings have implications for the potentially injurious impact of long-term use of popular low-power e-cigarette pods on the human alveolar epithelium. Gene expression data might be an important endpoint for evaluating the potential harmful effects of vaping devices that do not cause overt toxicity.

Efferocytosis in lung mucosae: implications for health and disease

Efferocytosis is imperative to maintain lung homeostasis and control inflammation. Populations of lung macrophages are the main efferocytes in this tissue, responsible for controlling immune responses and avoiding unrestrained inflammation and autoimmunity through the expression of a plethora of receptors that recognize multiple 'eat me' signals on apoptotic cells. Efferocytosis is essentially anti-inflammatory and tolerogenic. However, in some situations, apoptotic cells phagocytosis can elicit inflammatory and immunogenic immune responses. Here, we summarized the current knowledge of the mechanisms of efferocytosis, and how any abnormality in this process may have an important contribution to the lung pathophysiology of many chronic inflammatory lung diseases such as asthma, acute lung injury, chronic obstructive pulmonary disease, and cystic fibrosis. Further, we consider the consequences of the dual role of efferocytosis on the susceptibility or resistance to pulmonary microbial infections. Understanding how efferocytosis works in different contexts will be useful to the development of new and more effective strategies to control the diversity of lung diseases.

Aerosolized vitamin E acetate causes oxidative injury in mice and in alveolar macrophages

Although vitamin E acetate (VEA) is suspected to play a causal role in the development of electronic-cigarette, or vaping, product use-associated lung injury (EVALI), the underlying biological mechanisms of pulmonary injury are yet to be determined. In addition, no study has replicated the systemic inflammation observed in humans in a murine EVALI model, nor investigated potential additive toxicity of viral infection in the setting of exposure to vaping products. To identify the mechanisms driving VEA-related lung injury and test the hypothesis that viral infection causes additive lung injury in the presence of aerosolized VEA, we exposed mice to aerosolized VEA for extended times, followed by influenza infection in some experiments. We used mass spectrometry to evaluate the composition of aerosolized VEA condensate and the VEA deposition in murine or human alveolar macrophages. Extended vaping for 28 days versus 15 days did not worsen lung injury but caused systemic inflammation in the murine EVALI model. Vaping plus influenza increased lung water compared with virus alone. Murine alveolar macrophages exposed to vaped VEA hydrolyzed the VEA to vitamin E with evidence of oxidative stress in the alveolar space and systemic circulation. Aerosolized VEA also induced cell death and chemokine release and reduced efferocytotic function in human alveolar macrophages in vitro. These findings provide new insights into the biological mechanisms of VEA toxicity.

E-cigarettes and nicotine abstinence: a meta-analysis of randomised controlled trials

OBJECTIVES

To determine the effects of electronic cigarettes (e-cigarettes) as a therapeutic intervention compared to nicotine replacement therapy (NRT) on nicotine abstinence.

METHODS

Two authors independently searched the PubMed, Embase, PsycInfo and Cochrane Central Register of Controlled Trials databases for articles published up to and including 10 July 2021. We included randomised controlled trials (RCTs) in which nicotine e-cigarettes were compared to NRT among current cigarette users. The primary outcome was abstaining from all nicotine-delivery devices. Secondary outcomes were 1) allocated product use (e-cigarettes or NRT) among successful cigarette quitters and 2) quitting cigarettes at the end of the trial using fixed-effect Mantel-Haenszel models.

RESULTS

We included four RCTs representing 1598 adult participants (51.0% females). The mean age of participants in these studies ranged from 41 to 54 years, while average baseline smoking ranged from 14 to 21 cigarettes per day. Compared to NRT, e-cigarette use was associated with lower nicotine abstinence rates at the longest follow-up (risk ratio 0.50 (95% CI 0.32-0.77)). Among successful cigarette quitters, the risk of allocated product use by the end of the observational time was higher for e-cigarette users compared to NRT (risk ratio 8.94 (95% CI 3.98-20.07)). E-cigarette users had higher cigarette smoking cessation rates compared to NRT users (risk ratio 1.58 (95% CI 1.20-2.08)).

CONCLUSIONS

The use of e-cigarettes as a therapeutic intervention for smoking cessation may lead to permanent nicotine dependence.

Predicting the pulmonary effects of long-term e-cigarette use: are the clouds clearing?

Commercially available since 2007, e-cigarettes are a popular electronic delivery device of ever-growing complexity. Given their increasing use by ex-smokers, smokers and never-smokers, it is important to evaluate evidence of their potential pulmonary effects and predict effects of long-term use, since there has been insufficient time to study a chronic user cohort. It is crucial to evaluate indicators of harm seen in cigarette use, and those potentially unique to e-cigarette exposure. Evaluation must also account for the vast variation in e-cigarette devices (now including at least five generations of devices) and exposure methods used in vivo and in vitroThus far, short-term use cohort studies, combined with in vivo and in vitro models, have been used to probe for the effects of e-cigarette exposure. The effects and mechanisms identified, including dysregulated inflammation and decreased pathogen resistance, show concerning overlaps with the established effects of cigarette smoke exposure. Additionally, research has identified a signature of dysregulated lipid processing, which is unique to e-cigarette exposure.This review will evaluate the evidence of pulmonary effects of, and driving mechanisms behind, e-cigarette exposure, which have been highlighted in emerging literature, and highlight the gaps in current knowledge. Such a summary allows understanding of the ongoing debate into e-cigarette regulation, as well as prediction and potential mitigation of future problems surrounding e-cigarette use.

Vaping and Lung Inflammation and Injury

The use of electronic (e)-cigarettes was initially considered a beneficial solution to conventional cigarette smoking cessation. However, paradoxically, e-cigarette use is rapidly growing among nonsmokers, including youth and young adults. In 2019, this rapid growth resulted in an epidemic of hospitalizations and deaths of e-cigarette users (vapers) due to acute lung injury; this novel disease was termed e-cigarette or vaping use-associated lung injury (EVALI). Pathophysiologic mechanisms of EVALI likely involve cytotoxicity and neutrophilic inflammation caused by inhaled chemicals, but further details remain unknown. The undiscovered mechanisms of EVALI are a barrier to identifying biomarkers and developing therapeutics. Furthermore, adverse effects of e-cigarette use have been linked to chronic lung diseases and systemic effects on multiple organs. In this comprehensive review, we discuss the diverse spectrum of vaping exposures, epidemiological and clinical reports, and experimental findings to provide a better understanding of EVALI and the adverse health effects of chronic e-cigarette exposure.

E-cigarette and vaping product use-associated lung injury in the pediatric population: A critical review of the current literature

Use of electronic nicotine delivery systems (ENDS), also known as e-cigarettes, in the adolescent population has significantly increased over the past several years. This rise led to an outbreak of e-cigarette or vaping product use-associated lung injury (EVALI) in the summer of 2019. Since that time, numerous case reports and case series on vaping and EVALI have been published but the majority of literature highlights the adult population with few articles focusing on pediatric patients. Given the addictive nature of these products and the lack of full understanding of the human health effects, there is concern that use of ENDS may have lasting impacts on users, especially adolescents and young adults. The goal of this review is to critically assess published data on ENDS use in children, report our institutional experience, discuss the reasons why the use of ENDS have increased among young individuals, outline the current understanding of EVALI as it pertains to the pediatric population, and discuss future opportunities for health policy implementation.

Cardiorespiratory and Immunologic Effects of Electronic Cigarettes

PURPOSE OF REVIEW

Although e-cigarettes have become popular, especially among youth, the health effects associated with e-cigarette use remain unclear. This review discusses current evidence relating to the cardiovascular, pulmonary, and immunological effects of e-cigarettes.

RECENT FINDINGS

The use of e-cigarettes by healthy adults has been shown to increase blood pressure, heart rate, and arterial stiffness, as well as resistance to air flow in lungs. Inhalation of e-cigarette aerosol has been shown to elicit immune responses and increase the production of immunomodulatory cytokines in young tobacco-naïve individuals. In animal models, long-term exposure to e-cigarettes leads to marked changes in lung architecture, dysregulation of immune genes, and low-grade inflammation. Exposure to e-cigarette aerosols in mice has been shown to induce DNA damage, inhibit DNA repair, and promote carcinogenesis. Chronic exposure to e-cigarettes has also been reported to result in the accumulation of lipid-laden macrophages in the lung and dysregulation of lipid metabolism and transport in mice. Although, the genotoxic and inflammatory effects of e-cigarettes are milder than those of combustible cigarettes, some of the cardiorespiratory effects of the two insults are comparable. The toxicity of e-cigarettes has been variably linked to nicotine, as well as other e-cigarette constituents, operating conditions, and use patterns.

SUMMARY

The use of e-cigarettes in humans is associated with significant adverse cardiorespiratory and immunological changes. Data from animal models and in vitro studies support the notion that long-term use of e-cigarettes may pose significant health risks.

Electronic Cigarette Aerosol Is Cytotoxic and Increases ACE2 Expression on Human Airway Epithelial Cells: Implications for SARS-CoV-2 (COVID-19)

Tobacco smoking has emerged as a risk factor for increasing the susceptibility to infection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via increased expression of angiotensin-converting enzyme-2 (ACE2) in the lung, linked to coronavirus disease 2019 (COVID-19) development. Given the modifiable nature of electronic cigarettes and the delivery of high concentrations of nicotine, we investigate whether electronic cigarette vaping has the potential to increase susceptibility to SARS-CoV-2 infection. We exposed BEAS-2B cells (bronchial epithelium transformed with Ad12-SV40 2B) and primary small airway epithelial cells (SAECs) to electronic cigarette aerosol condensates produced from propylene glycol/vegetable glycerin or commercially bought e-liquid (±added nicotine) and cigarette smoke extract to investigate if electronic cigarette exposure, like cigarette smoke, increases the expression of ACE2 in lung epithelial cells. In BEAS-2B cells, cytotoxicity (CCK-8), membrane integrity (LDH), and ACE2 protein expression (immunofluorescence) were measured for both 4- and 24 h treatments in BEAS-2B cells and 4 h in SAECs; ACE2 gene expression was measured using quantitative polymerase chain reaction (qPCR) for 4 h treatment in BEAS-2B cells. Nicotine-free condensates and higher concentrations of nicotine-containing condensates were cytotoxic to BEAS-2B cells. Higher LDH release and reduced membrane integrity were seen in BEAS-2B cells treated for 24 h with higher concentrations of nicotine-containing condensates. ACE2 protein expression was observably increased in all treatments compared to cell controls, particularly for 24 h exposures. ACE2 gene expression was significantly increased in cells exposed to the locally bought e-liquid condensate with high nicotine concentration and cigarette smoke extract compared with cell controls. Our study suggests that vaping alone and smoking alone can result in an increase in lung ACE2 expression. Vaping and smoking are avoidable risk factors for COVID-19, which, if avoided, could help reduce the number of COVID-19 cases and the severity of the disease. This is the first study to utilize electronic cigarette aerosol condensates, novel and developed in our laboratory, for investigating ACE2 expression in human airway epithelial cells.

Current Perspectives on Characteristics, Compositions, and Toxicological Effects of E-Cigarettes Containing Tobacco and Menthol/Mint Flavors

Electronic nicotine delivery systems/devices (ENDS) such as electronic cigarettes (e-cigarettes) have been made available globally, with the intent to reduce tobacco smoking. To make these products more appealing to young adults, many brands have added flavoring agents. However, these flavoring agents are shown to progressively result in lung toxicity when inhaled via e-cigarettes. While recent federal regulations have banned the sale of flavored e-cigarettes other than tobacco or menthol flavors, concerns have been raised about the health effects of even these flavors. In this review, we evaluate the current toxicological data with regard to effects upon exposure in animal models and in vitro cell culture for these popular flavorants. We have tabulated the current e-cigarette products containing these most common flavors (menthol, mint, and tobacco) in the market. We have also indicated the prevalence of tobacco and menthol-flavor use among e-cigarette users and highlighted the possible challenges and benefits that will result from new federal regulations.