Predicted Deposition of E-Cigarette Aerosol in the Human Lungs

Use of quantitative in vitro to in vivo extrapolation (QIVIVE) for the assessment of non-combustible next-generation product aerosols

With the use of in vitro new approach methodologies (NAMs) for the assessment of non-combustible next-generation nicotine delivery products, new extrapolation methods will also be required to interpret and contextualize the physiological relevance of these results. Quantitative in vitro to in vivo extrapolation (QIVIVE) can translate in vitro concentrations into in-life exposures with physiologically-based pharmacokinetic (PBPK) modelling and provide estimates of the likelihood of harmful effects from expected exposures. A major challenge for evaluating inhalation toxicology is an accurate assessment of the delivered dose to the surface of the cells and the internalized dose. To estimate this, we ran the multiple-path particle dosimetry (MPPD) model to characterize particle deposition in the respiratory tract and developed a PBPK model for nicotine that was validated with human clinical trial data for cigarettes. Finally, we estimated a Human Equivalent Concentration (HEC) and predicted plasma concentrations based on the minimum effective concentration (MEC) derived after acute exposure of BEAS-2B cells to cigarette smoke (1R6F), or heated tobacco product (HTP) aerosol at the air liquid interface (ALI). The MPPD-PBPK model predicted the in vivo data from clinical studies within a factor of two, indicating good agreement as noted by WHO International Programme on Chemical Safety (2010) guidance. We then used QIVIVE to derive the exposure concentration (HEC) that matched the estimated in vitro deposition point of departure (POD) (MEC cigarette = 0.38 puffs or 11.6 µg nicotine, HTP = 22.9 puffs or 125.6 µg nicotine) and subsequently derived the equivalent human plasma concentrations. Results indicate that for the 1R6F cigarette, inhaling 1/6th of a stick would be required to induce the same effects observed in vitro, in vivo. Whereas, for HTP it would be necessary to consume 3 sticks simultaneously to induce in vivo the effects observed in vitro. This data further demonstrates the reduced physiological potency potential of HTP aerosol compared to cigarette smoke. The QIVIVE approach demonstrates great promise in assisting human health risk assessments, however, further optimization and standardization are required for the substantiation of a meaningful contribution to tobacco harm reduction by alternative nicotine delivery products.

Characterization of mass distribution in a biomimetic aerosol exposure system

OBJECTIVE

Lack of biomimicry in geometry and flow conditions of emissions systems for analytical testing and biological exposure has led to fundamental limitations, including a poor understanding of dose delivered to specific airway locations. This work characterizes mass distribution of a JUUL® brand e-cigarette in a Biomimetic Aerosol Exposure System (BAES).

MATERIALS AND METHODS

A combination of mass balance, direct measurements, and inferences based on direct measurements were used to characterize regional and local dose as a function of system flow path configuration and emissions topography profile.

RESULTS

Doses produced by the emissions topography profile with only puffing were significantly different from profiles with clean air inhalation following puffs. Mass characterization results support that dose can be manipulated using flow path geometry. Local and regional deposition was mapped throughout the system.

DISCUSSION AND CONCLUSIONS

We estimate the fraction of yield to the mouth deposited at several locations throughout the system for a variety of puffing and respiration topographies and show that emissions topography profile and system flow path geometry affect dose. This work provides proof-of-concept for assessing mass distribution as a function of aerosol generator (e-cigarette product), user airway geometry, and inhalation and puffing topography.

Development of a Novel Bronchodilator Vaping Drug Delivery System Based on Thermal Degradation Properties

This work aims to investigate bronchodilator delivery with the use of different vaping drug delivery systems (VDDS) by determining the dose equivalence delivered in relation to different references: a clinical jet nebulizer, a pMDI (pressurized metered dose inhaler) and a DPI (dry powder inhaler). Three different bronchodilators were used (terbutaline, salbutamol hemisulfate, ipratropium bromide). The e-liquids contained the active pharmaceutical ingredient (API) in powder form. Two different VDDS were tested (JUUL and a GS AIR 2 atomizer paired with a variable lithium-ion battery (i-stick TC 40 W), 1.5 ohm resistance, and 15 W power). Samples were collected using a glass twin impinger (GTI). High-performance liquid chromatography (HPLC) was used to quantify the drugs. A next-generation impactor (NGI) was used to measure the particle size distribution. Terbutaline emerged as the optimal API for bronchodilator delivery in both VDDS devices. It achieved the delivery of a respirable dose of 20.05 ± 4.2 µg/puff for GS AIR 2 and 2.98 ± 0.52 µg/puff for JUUL. With these delivered doses, it is possible to achieve a dose equivalence similar to that of a jet nebulizer and DPI, all while maintaining a reasonable duration, particularly with the GS AIR 2. This study is the first to provide evidence that vaping bronchodilators work only with appropriate formulation, vaping technology, and specific drugs, depending on their thermal degradation properties.

Multimodal Diagnostics of Changes in Rat Lungs after Vaping

(1) Background: The use of electronic cigarettes has become widespread in recent years. The use of e-cigarettes leads to milder pathological conditions compared to traditional cigarette smoking. Nevertheless, e-liquid vaping can cause morphological changes in lung tissue, which affects and impairs gas exchange. This work studied the changes in morphological and optical properties of lung tissue under the action of an e-liquid aerosol. To do this, we implemented the "passive smoking" model and created the specified concentration of aerosol of the glycerol/propylene glycol mixture in the chamber with the animal. (2) Methods: In ex vivo studies, the lungs of Wistar rats are placed in the e-liquid for 1 h. For in vivo studies, Wistar rats were exposed to the e-liquid vapor in an aerosol administration chamber. After that, lung tissue samples were examined ex vivo using optical coherence tomography (OCT) and spectrometry with an integrating sphere. Absorption and reduced scattering coefficients were estimated for the control and experimental groups. Histological sections were made according to the standard protocol, followed by hematoxylin and eosin staining. (3) Results: Exposure to e-liquid in ex vivo and aerosol in in vivo studies was found to result in the optical clearing of lung tissue. Histological examination of the lung samples showed areas of emphysematous expansion of the alveoli, thickening of the alveolar septa, and the phenomenon of plasma permeation, which is less pronounced in in vivo studies than for the exposure of e-liquid ex vivo. E-liquid aerosol application allows for an increased resolution and improved imaging of lung tissues using OCT. Spectral studies showed significant differences between the control group and the ex vivo group in the spectral range of water absorption. It can be associated with dehydration of lung tissue owing to the hyperosmotic properties of glycerol and propylene glycol, which are the main components of e-liquids. (4) Conclusions: A decrease in the volume of air in lung tissue and higher packing of its structure under e-liquid vaping causes a better contrast of OCT images compared to intact lung tissue.

Understanding the influence of atomizing power on electronic cigarette aerosol size and inhalation dose estimation

Although many studies have estimated the inhalation dose of aerosols emitted from electronic cigarettes (e-cigs), the association between the atomizing power and inhalation dose of e-cig aerosols has not been fully examined. The aim of this study was to determine the mass and inhalation doses of e-cig aerosols and their association with the atomizing power of vaping devices. Size-segregated aerosol masses were collected using an 11-stage cascade impactor and the deposition dose in the human respiratory tract was estimated using the size-segregated aerosol mass. The results showed that an increase in atomizing power was positively associated with the amount of aerosol mass generated (p-value < 0.001). The mass median aerodynamic diameter and mass mean diameter of aerosol were 0.91 μm and 0.84 μm, respectively. The average deposition fractions of aerosols in the head airway, tracheobronchial region, and alveolar region were 67.2, 6.2, and 26.6%, respectively. In conclusion, vaping with a higher atomizing power increases the e-cig aerosol inhalation dose in the airway.

Menthol flavoring in e-cigarette condensate causes pulmonary dysfunction and cytotoxicity in precision cut lung slices

E-cigarette consumption is under scrutiny by regulatory authorities due to concerns about product toxicity, lack of manufacturing standards, and increasing reports of e-cigarette- or vaping-associated acute lung injury. In vitro studies have demonstrated cytotoxicity, mitochondrial dysfunction, and oxidative stress induced by unflavored e-cigarette aerosols and flavoring additives. However, e-cigarette effects on the complex lung parenchyma remain unclear. Herein, the impact of e-cigarette condensates with or without menthol flavoring on functional, structural, and cellular responses was investigated using mouse precision cut lung slices (PCLS). PCLS were exposed to e-cigarette condensates prepared from aerosolized vehicle, nicotine, nicotine + menthol, and menthol e-fluids at doses from 50 to 500 mM. Doses were normalized to the glycerin content of vehicle. Video-microscopy of PCLS revealed impaired contractile responsiveness of airways to methacholine and dampened ciliary beating following exposure to menthol-containing condensates at concentrations greater than 300 mM. Following 500 mM menthol-containing condensate exposure, epithelial exfoliation in intrabronchial airways was identified in histological sections of PCLS. Measurement of lactate dehydrogenase release, mitochondrial water-soluble-tetrazolium salt-1 conversion, and glutathione content supported earlier findings of nicotine or nicotine + menthol e-cigarette-induced dose-dependent cytotoxicity and oxidative stress responses. Evaluation of PCLS metabolic activity revealed dose-related impairment of mitochondrial oxidative phosphorylation and glycolysis after exposure to menthol-containing condensates. Taken together, these data demonstrate prominent menthol-induced pulmonary toxicity and impairment of essential physiological functions in the lung, which warrants concerns about e-cigarette consumer safety and emphasizes the need for further investigations of molecular mechanisms of toxicity and menthol effects in an experimental model of disease.

Influence of puff topographies on e-liquid heating temperature, emission characteristics and modeled lung deposition of Puff Bar™

Puff Bar™, one of the latest designs of e-cigarettes, heats a mixture of liquid using a battery-powered coil at certain temperatures to emit aerosol. This study presents a mass-based characterization of emissions from seven flavors of Puff Bar™ devices by aerosolizing with three puff topographies [(puff volume: 55 < 65 < 75-mL) within 4-seconds at 30-seconds interval]. We evaluated the effects of puff topographies on heating temperatures; characterized particles using a cascade impactor; and measured volatile carbonyl compounds (VCCs). Modeled dosimetry and calculated mass median aerodynamic diameters (MMADs) were used to estimate regional, total respiratory deposition of the inhaled aerosol and exhaled fractions that could pose secondhand exposure risk. Temperatures of Puff Bar™ e-liquids increased with increasing puff volumes: 55mL (116.6 °C), 65 mL (128.3 °C), and 75mL (168.9 °C). Flavor types significantly influenced MMADs, total mass of particles, and VCCs (μg/puff: 2.15-2.30) in Puff Bar™ emissions (p < 0.05). Increasing puff volume (mL:55 < 65 < 75) significantly increased total mass (mg/puff: 4.6 < 5.6 < 6.2) of particles without substantially changing MMADs (~1μm:1.02~0.99~0.98). Aerosol emissions were estimated to deposit in the pulmonary region of e-cigarette user (41-44%), which could have toxicological importance. More than 2/3 (67-77%) of inhaled particles were estimated to be exhaled by users, which could affect bystanders. The VCCs measured contained carcinogens-formaldehyde (29.6%) and acetaldehyde (16.4%)-as well as respiratory irritants: acetone (23.9%), isovaleraldehyde (14.5%), and acrolein (4.9%). As Puff Bar™ emissions contain respirable particles and harmful chemicals, efforts should be made to minimize exposures, especially in indoor settings where people (including vulnerable populations) spend most of their life-time.

Characterization of aerosols generated by high-power electronic nicotine delivery systems (ENDS): Influence of atomizer, temperature and PG:VG ratios

The aerosol characteristics of electronic nicotine delivery systems (ENDS) are important parameters in predicting health outcomes since parameters such as aerosol particle size correlate strongly to aerosol delivery and deposition efficiency. However, many studies to date do not account for aerosol aging, which may affect the measurement of ultra-fine particles that typically coagulate or agglomerate during puff development. To reduce aerosol aging, we herein present a unique instrumentation method that combines a) positive pressure ENDS activation and sample collection, b) minimization of both sample tubing length and dilution factors, and c) a high-resolution, electrical low-pressure impactor. This novel approach was applied to systematically investigate the effects of coil design, coil temperature, and propylene glycol to vegetable glycerol ratios on aerosol characteristics including aerosol mass generation, aerosol count generation, and the mass and count size distributions for a high-powered ENDS. Aerosol count measurements revealed high concentrations of ultra-fine particles compared to fine and coarse particles at 200°C, while aerosol mass measurements showed an increase in the overall aerosol mass of fine and coarse particles with increases in temperature and decreases in propylene glycol content. These results provide a better understanding on how various ENDS design parameters affect aerosol characteristics and highlight the need for further research to identify the design parameters that most impact ultra-fine particle generation.

Methodological Approaches for Risk Assessment of Tobacco and Related Products

Health risk assessment of tobacco and related products (TRPs) is highly challenging due to the variety in products, even within the product class, the complex mixture of components in the emission and the variety of user behaviour. In this paper, we summarize methods that can be used to assess the health risks associated with the use of TRPs. The choice of methods to be used and the data needed are dependent on the aim. Risk assessment can be used to identify the emission components of highest health concern. Alternatively, risk assessment methods can be used to determine the absolute risk of a TRP, which is the health risk of a product, not related to other products, or to determine the relative risk of a TRP, which is the health risk of a TRP compared to, for example, a cigarette. Generally, health risk assessment can be based on the effects of the complete mixture (whole smoke) or based on the (added) effects of individual components. Data requirements are dependent on the method used, but most methods require substantial data on identity and quantity of components in emissions and on the hazards of these components. Especially for hazards, only limited data are available. Currently, due to a lack of suitable data, quantitative risk assessment methods cannot be used to inform regulation.

Propylene glycol, a component of electronic cigarette liquid, damages epithelial cells in human small airways

Background

Electronic cigarettes (e-cigarettes) are used worldwide as a substitute for conventional cigarettes. Although they are primarily intended to support smoking cessation, e-cigarettes have been identified as a gateway to smoking habits for young people. Multiple recent reports have described the health effects of inhaling e-cigarettes. E-cigarette liquid (e-liquid) is mainly composed of propylene glycol (PG) and glycerol (Gly), and the aerosol generated by these devices primarily contains these two components. Thus, this study aimed to evaluate the effects of PG and Gly on human small airway epithelial cells (SAECs).

Methods

SAECs were exposed to PG or Gly, and cell proliferation, cell viability, lactate dehydrogenase (LDH) release, DNA damage, cell cycle, and apoptosis were evaluated. Additionally, SAECs derived from chronic obstructive pulmonary disease (COPD) patients (COPD-SAECs) were investigated.

Results

Exposure of SAECs to PG significantly inhibited proliferation (1%, PG, p = 0.021; 2–4% PG, p < 0.0001) and decreased cell viability (1–4% PG, p < 0.0001) in a concentration-dependent manner. Gly elicited similar effects but to a reduced degree as compared to the same concentration of PG. PG also increased LDH release in a concentration-dependent manner (3% PG, p = 0.0055; 4% PG, p < 0.0001), whereas Gly did not show a significant effect on LDH release. SAECs exposed to 4% PG contained more cells that were positive for phosphorylated histone H2AX (p < 0.0001), a marker of DNA damage, and an increased proportion of cells in the G1 phase (p < 0.0001) and increased p21 expression (p = 0.0005). Moreover, caspase 3/7-activated cells and cleaved poly (ADP-ribose) polymerase 1 expression were increased in SAECs exposed to 4% PG (p = 0.0054). Furthermore, comparing COPD-SAECs to SAECs without COPD in PG exposure, cell proliferation, cell viability, DNA damage and apoptosis were significantly greater in COPD-SAECs.

Conclusion

PG damaged SAECs more than Gly. In addition, COPD-SAECs were more susceptible to PG than SAECs without COPD. Usage of e-cigarettes may be harmful to the respiratory system, especially in patients with COPD.

Efficacy of Prednisolone/Zn Metal Complex and Artemisinin Either Alone or in Combination on Lung Functions after Excessive Exposure to Electronic Cigarettes Aerosol with Assessment of Antibacterial Activity

The use of transition metal complexes as therapeutic compounds has become more and more pronounced. These complexes offer a great diversity of uses in their medicinal applications. Electronic cigarettes (ECs) are an electronic nicotine delivery system that contain aerosol (ECR). The ligation behavior of prednisolone, which is a synthetic steroid that is used to treat allergic diseases and asthma arthritis, and its Zn (II) metal complex were studied and characterized based on elemental analysis, molar conductance, Fourier-transform infrared (FT-IR) spectra, electronic spectra, XRD, scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and transmission electron microscopy (TEM). The FT-IR spectral data revealed that PRD acts as a mono-dentate ligand via oxygen atoms of the carbonyl group. Electronic and FT-IR data revealed that the PRD/Zn (II) metal complexes have square planner geometry. Artemisinin (ART) is the active main constituent of Artemisia annua extract, and it has been demonstrated to exert an excellent antimalarial effect. The experiment was performed on 40 male mice that were divided into the following 7 groups: Control, EC group, PRD/Zn, ART, EC plus PRD/Zn, EC plus ART, and PRD plus combination of PRD/Zn and ART. Serum CRP, IL-6, and antioxidants biomarkers were determined. Pulmonary tissue histology was evaluated. When in combination with Zn administration, PRD showed potent protective effects against pulmonary biochemical alterations induced by ECR and suppressed severe oxidative stress and pulmonary structure alterations. Additionally, PRD/Zn combined with ART prevented any stress on the pulmonary tissues via antioxidant regulation, reducing inflammatory markers CRP and Il-6 and improving antioxidant enzymatic levels more than either PRD or ART alone. Therefore, PRD/Zn combined with ART produced a synergistic effect against any sort of oxidative stress and also improved the histological structure of the lung tissues. These findings are of great importance for saving pulmonary function, especially during pandemic diseases, such as during the COVID-19 pandemic.

Examining Metal Contents in Primary and Secondhand Aerosols Released by Electronic Cigarettes

The usage of electronic cigarettes (ECs) has surged since their invention two decades ago. However, to date, the health effects of EC aerosol exposure are still not well understood because of insufficient data on the chemical composition of EC aerosols and the corresponding evidence of health risks upon exposure. Herein, we quantified the metals in primary and secondhand aerosols generated by three brands of ECs. By combining aerosol filter sampling and inductively coupled plasma mass spectrometry (ICP-MS), we assessed the mass of metals as a function of EC flavoring, nicotine concentration, device power, puff duration, and aging of the devices. The masses of Cr, Cu, Mn, Ni, Cu, and Zn were consistently high across all brands in the primary and secondhand aerosols, some of which were above the regulated maximum daily intake amount, especially for Cr and Ni with mass (nanograms per 10 puffs) emitted at 117 ± 54 and 50 ± 24 (JUUL), 125 ± 77 and 219 ± 203 (VOOPOO), and 33 ± 10 and 27 ± 2 (Vapor4Life). Our analysis indicates that the metals are predominantly released from the EC liquid, potentially through mechanisms such as bubble bursting or the vaporization of metal-organic compounds. High metal contents were also observed in simulated secondhand aerosols, generally 80-90% of those in primary aerosols. Our findings provide a more detailed understanding of the metal emission characteristics of EC for assessing its health effects and policymaking.

Influence of E-Liquid Humectants, Nicotine, and Flavorings on Aerosol Particle Size Distribution and Implications for Modeling Respiratory Deposition

Electronic cigarette, or vaping, products are used to heat an e-liquid to form an aerosol (liquid droplets suspended in gas) that the user inhales; a portion of this aerosol deposits in their respiratory tract and the remainder is exhaled, thereby potentially creating opportunity for secondhand exposure to bystanders (e.g., in homes, automobiles, and workplaces). Particle size, a critical factor in respiratory deposition (and therefore potential for secondhand exposure), could be influenced by e-liquid composition. Hence, the purposes of this study were to (1) test the influence of laboratory-prepared e-liquid composition [ratio of propylene glycol (PG) to vegetable glycerin (VG) humectants, nicotine, and flavorings] on particle size distribution and (2) model respiratory dosimetry. All e-liquids were aerosolized using a second-generation reference e-cigarette. We measured particle size distribution based on mass using a low-flow cascade impactor (LFCI) and size distribution based on number using real-time mobility sizers. Mass median aerodynamic diameters (MMADs) of aerosol from e-liquids that contained only humectants were significantly larger compared with e-liquids that contained flavorings or nicotine (p = 0.005). Humectant ratio significantly influenced MMADs; all aerosols from e-liquids prepared with 70:30 PG:VG were significantly larger compared with e-liquids prepared with 30:70 PG:VG (p = 0.017). In contrast to the LFCI approach, the high dilution and sampling flow rate of a fast mobility particle sizer strongly influenced particle size measurements (i.e., all calculated MMAD values were &lt; 75 nm). Dosimetry modeling using LFCI data indicated that a portion of inhaled particles will deposit throughout the respiratory tract, though statistical differences in aerosol MMADs among e-liquid formulations did not translate into large differences in deposition estimates. A portion of inhaled aerosol will be exhaled and could be a source for secondhand exposure. Use of laboratory-prepared e-liquids and a reference e-cigarette to standardize aerosol generation and a LFCI to measure particle size distribution without dilution represents an improved method to characterize physical properties of volatile aerosol particles and permitted determination of MMAD values more representative of e-cigarette aerosol in situ, which in turn, can help to improve dose modeling for users and bystanders.

Effect of Puffing Behavior on Particle Size Distributions and Respiratory Depositions From Pod-Style Electronic Cigarette, or Vaping, Products

The current fourth generation ("pod-style") electronic cigarette, or vaping, products (EVPs) heat a liquid ("e-liquid") contained in a reservoir ("pod") using a battery-powered coil to deliver aerosol into the lungs. A portion of inhaled EVP aerosol is estimated as exhaled, which can present a potential secondhand exposure risk to bystanders. The effects of modifiable factors using either a prefilled disposable or refillable pod-style EVPs on aerosol particle size distribution (PSD) and its respiratory deposition are poorly understood. In this study, the influence of up to six puff profiles (55-, 65-, and 75-ml puff volumes per 6.5 and 7.5 W EVP power settings) on PSD was evaluated using a popular pod-style EVP (JUUL® brand) and a cascade impactor. JUUL® brand EVPs were used to aerosolize the manufacturers' e-liquids in their disposable pods and laboratory prepared "reference e-liquid" (without flavorings or nicotine) in refillable pods. The modeled dosimetry and calculated aerosol mass median aerodynamic diameters (MMADs) were used to estimate regional respiratory deposition. From these results, exhaled fraction of EVP aerosols was calculated as a surrogate of the secondhand exposure potential. Overall, MMADs did not differ among puff profiles, except for 55- and 75-ml volumes at 7.5 W (p < 0.05). For the reference e-liquid, MMADs ranged from 1.02 to 1.23 μm and dosimetry calculations predicted that particles would deposit in the head region (36-41%), in the trachea-bronchial (TB) region (19-21%), and in the pulmonary region (40-43%). For commercial JUUL® e-liquids, MMADs ranged from 0.92 to 1.67 μm and modeling predicted that more particles would deposit in the head region (35-52%) and in the pulmonary region (30-42%). Overall, 30-40% of the particles aerosolized by a pod-style EVP were estimated to deposit in the pulmonary region and 50-70% of the inhaled EVP aerosols could be exhaled; the latter could present an inhalational hazard to bystanders in indoor occupational settings. More research is needed to understand the influence of other modifiable factors on PSD and exposure potential.

Modeled Respiratory Tract Deposition of Aerosolized Oil Diluents Used in Δ9-THC-Based Electronic Cigarette Liquid Products

Electronic cigarette, or vaping, products (EVP) heat liquids ("e-liquids") that contain substances (licit or illicit) and deliver aerosolized particles into the lungs. Commercially available oils such as Vitamin-E-acetate (VEA), Vitamin E oil, coconut, and medium chain triglycerides (MCT) were often the constituents of e-liquids associated with an e-cigarette, or vaping, product use-associated lung injury (EVALI). The objective of this study was to evaluate the mass-based physical characteristics of the aerosolized e-liquids prepared using these oil diluents. These characteristics were particle size distributions for modeling regional respiratory deposition and puff-based total aerosol mass for estimating the number of particles delivered to the respiratory tract. Four types of e-liquids were prepared by adding terpenes to oil diluents individually: VEA, Vitamin E oil, coconut oil, and MCT. A smoking machine was used to aerosolize each e-liquid at a predetermined puff topography (volume of 55 ml for 3 s with 30-s intervals between puffs). A cascade impactor was used to collect the size-segregated aerosol for calculating the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD). The respiratory deposition of EVP aerosols on inhalation was estimated using the Multiple-Path Particle Dosimetry model. From these results, the exhaled fraction of EVP aerosols was calculated as a surrogate of secondhand exposure potential. The MMAD of VEA (0.61 μm) was statistically different compared to MCT (0.38 μm) and coconut oil (0.47 μm) but not to Vitamin E oil (0.58 μm); p < 0.05. Wider aerosol size distribution was observed for VEA (GSD 2.35) and MCT (GSD 2.08) compared with coconut oil (GSD 1.53) and Vitamin E oil (GSD 1.55). Irrespective of the statistical differences between MMADs, dosimetry modeling resulted in the similar regional and lobular deposition of particles for all e-liquids in the respiratory tract. The highest (~0.08 or more) fractional deposition was predicted in the pulmonary region, which is consistent as the site of injury among EVALI cases. Secondhand exposure calculations indicated that a substantial amount of EVP aerosols could be exhaled, which has potential implications for bystanders. The number of EVALI cases has declined with the removal of VEA; however, further research is required to investigate the commonly available commercial ingredients used in e-liquid preparations.

Estimation of the dose of electronic cigarette chemicals deposited in human airways through passive vaping

BACKGROUND

Existing studies on the health effects of e-cigarettes focused on e-cigarette users themselves. To study the corresponding effects on passive vapers, it is crucial to quantify e-cigarette chemicals deposited in their airways.

OBJECTIVE

This study proposed an innovative approach to estimate the deposited dose of e-cigarette chemicals in the passive vapers' airways. The effect of the distance between active and passive vapers on the deposited dose was also examined.

METHODS

The chemical constituent analysis was conducted to detect Nicotine and flavoring agents in e-cigarette aerosol. The Mobile Aerosol Lung Deposition Apparatus (MALDA) was employed to conduct aerosol respiratory deposition experiments in real-life settings to generate real-time data.

RESULTS

For e-cigarette aerosol in the ultrafine particle regime, the deposited doses in the alveolar region were on average 3.2 times higher than those in the head-to-TB airways, and the deposited dose in the passive vaper's airways increased when being closer to the active vaper.

SIGNIFICANCE

With prolonged exposure and close proximity to active vapers, passive vapers may be at risk for potential health effects of harmful e-cigarette chemicals. The methodology developed in this study has laid the groundwork for future research on exposure assessment and health risk analysis for passive vaping.

VAPIng into ARDS: Acute Respiratory Distress Syndrome and Cardiopulmonary Failure

"Modern" vaping involving battery-operated electronic devices began approximately one dozen years and has quickly evolved into a multibillion dollar industry providing products to an estimated 50 million users worldwide. Originally developed as an alternative to traditional cigarette smoking, vaping now appeals to a diverse demographic including substantial involvement of young people who often have never used cigarettes. The rapid rise of vaping fueled by multiple factors has understandably outpaced understanding of biological effects, made even more challenging due to wide ranging individual user habits and preferences. Consequently while vaping-related research gathers momentum, vaping-associated pathological injury (VAPI) has been established by clinical case reports with severe cases manifesting as acute respiratory distress syndrome (ARDS) with examples of right ventricular cardiac failure. Therefore, basic scientific studies are desperately needed to understand the impact of vaping upon the lungs as well as cardiopulmonary structure and function. Experimental models that capture fundamental characteristics of vaping-induced ARDS are essential to study pathogenesis and formulate recommendations to mitigate harmful effects attributable to ingredients or equipment. So too, treatment strategies to promote recovery from vaping-associated damage require development and testing at the preclinical level. This review summarizes the back story of vaping leading to present day conundrums with particular emphasis upon VAPI-associated ARDS and prioritization of research goals.

Deposition of Smoke Particles in Human Airways with Realistic Waveform

Exposure to toxic particles from smoke generated either from bush fire, stable burning, or direct smoking is very harmful to our health. The tiny particles easily penetrate deep into the lungs after exposure and damage the airways. Tobacco smoking causes the direct emission of 2.6 million tons of CO2 and 5.2 million tons of methane annually into the atmosphere. Nevertheless, it is one of the significant contributors to various respiratory diseases leading to lung cancer. These particles’ deposition in the human airway is computed in the present article for refining our understanding of the adverse health effects due to smoke particle inhalation, especially cigarette smoke. Until recently, little work has been reported to account for the transient flow pattern of cigarette smoking. Consideration of transient flow may change the deposition pattern of the particle. A high-resolution CT scan image of the respiratory tract model consisting of the oral cavity, throat, trachea, and first to sixth generations of the lungs helps predict cigarette smoke particle (CSP) deposition. With the same scan, a realistic geometric model of the human airways of an adult subject is used to simulate the transport of air and particle. The CSP deposition is determined at different locations from the oral cavity to the sixth generation of the bronchi. In addition, an unsteady breathing curve indicative of realistic smoking behavior is utilized to represent the breathing conditions accurately. The discrete phase model (DPM) technique is used to determine smoke particle deposition in the human airways. It is found that the deposition increases with the size of the smoke particle. Particles tend to deposit in the oral cavity around the bifurcation junction of the airways. The deposition fraction of CSP with the realistic waveform of smoking is found to be smaller compared to that during the stable flow condition. It is also observed that the fine particles (0.1–1.0 micron) escape to lower generations, leading to higher deposition of fine particles in the deeper airways. The outcome of the study is helpful for understanding smoke-related pulmonary complications.

Modeling Aerial Transmission of Pathogens (Including the SARS-CoV-2 Virus) through Aerosol Emissions from E-Cigarettes

We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing through a mouthpiece as convenient proxies to infer the capacity of vaping to transport pathogens in respiratory droplets. Since both exhaled droplets and ECA droplets are within the Stokes regime, the ECA flow acts effectively as a visual tracer of the expiratory flow. To infer quantitatively the direct exposure distance, we consider a model that approximates exhaled ECA flow as an axially symmetric intermittent steady starting jet evolving into an unstable puff, an evolution that we corroborate by comparison with photographs and videos of actual vapers. On the grounds of all this theoretical modeling, we estimate for low-intensity vaping (practiced by 80–90% of vapers) the emission of 6–210 (median 39.9, median deviation 67.3) respiratory submicron droplets per puff and a horizontal distance spread of 1–2 m, with intense vaping possibly emitting up to 1000 droplets per puff in the submicron range with a distance spread over 2 m. The optical visibility of the ECA flow has important safety implications, as bystanders become instinctively aware of the scope and distance of possible direct contagion through the vaping jet.

Differential responses to e-cig generated aerosols from humectants and different forms of nicotine in epithelial cells from nonsmokers and smokers

In the United States, millions of adults use electronic cigarettes (e-cigs), and a majority of these users are former or current cigarette smokers. It is unclear, whether prior smoking status affects biological responses induced by e-cigs. In this study, differentiated human nasal epithelial cells (hNECs) from nonsmokers and smokers at air-liquid interface were acutely exposed to the e-cig generated aerosols of humectants, propylene glycol (PG), and glycerol (GLY). Mucin levels were examined in the apical washes, and cytokine levels were assessed in the basolateral supernatants 24 h postexposure. The aerosol from the GLY exposure increased mucin 5, subtype AC (MUC5AC) levels in the apical wash of hNECs from nonsmokers, but not smokers. However, the aerosol from GLY induced pro-inflammatory responses in hNECs from smokers. We also exposed hNECs from nonsmokers and smokers to e-cig generated aerosol from PG:GLY with freebase nicotine or nicotine salt. The PG:GLY with freebase nicotine exposure increased MUC5AC and mucin 5, subtype B (MUC5B) levels in hNECs from nonsmokers, but the nicotine salt exposure did not. The PG:GLY with nicotine salt exposure increased pro-inflammatory cytokines in hNECs from smokers, which was not seen with the freebase nicotine exposure. Taken together, these data indicate that the e-cig generated aerosols from the humectants, mostly GLY, and the type of nicotine used cause differential effects in airway epithelial cells from nonsmokers and smokers. As e-cig use is increasing, it is important to understand that the biological effects of e-cig use are likely dependent on prior cigarette smoke exposure.

Toxicology of flavoring- and cannabis-containing e-liquids used in electronic delivery systems

Electronic cigarettes (e-cigarettes) were introduced in the United States in 2007 and by 2014 they were the most popular tobacco product amongst youth and had overtaken use of regular tobacco cigarettes. E-cigarettes are used to aerosolize a liquid (e-liquid) that the user inhales. Flavorings in e-liquids is a primary reason for youth to initiate use of e-cigarettes. Evidence is growing in the scientific literature that inhalation of some flavorings is not without risk of harm. In this review, 67 original articles (primarily cellular in vitro) on the toxicity of flavored e-liquids were identified in the PubMed and Scopus databases and evaluated critically. At least 65 individual flavoring ingredients in e-liquids or aerosols from e-cigarettes induced toxicity in the respiratory tract, cardiovascular and circulatory systems, skeletal system, and skin. Cinnamaldehyde was most frequently reported to be cytotoxic, followed by vanillin, menthol, ethyl maltol, ethyl vanillin, benzaldehyde and linalool. Additionally, modern e-cigarettes can be modified to aerosolize cannabis as dried plant material or a concentrated extract. The U.S. experienced an outbreak of lung injuries, termed e-cigarette, or vaping, product use-associated lung injury (EVALI) that began in 2019; among 2,022 hospitalized patients who had data on substance use (as of January 14, 2020), 82% reported using a delta-9-tetrahydrocannabinol (main psychoactive component in cannabis) containing e-cigarette, or vaping, product. Our literature search identified 33 articles related to EVALI. Vitamin E acetate, a diluent and thickening agent in cannabis-based products, was strongly linked to the EVALI outbreak in epidemiologic and laboratory studies; however, e-liquid chemistry is highly complex, and more than one mechanism of lung injury, ingredient, or thermal breakdown product may be responsible for toxicity. More research is needed, particularly with regard to e-cigarettes (generation, power settings, etc.), e-liquids (composition, bulk or vaped form), modeled systems (cell type, culture type, and dosimetry metrics), biological monitoring, secondhand exposures and contact with residues that contain nicotine and flavorings, and causative agents and mechanisms of EVALI toxicity.

Deposition of E-cigarette aerosol in human airways through passive vaping

Secondary exposure to e-cigarette aerosol (passive vaping) will soon become a pressing public health issue in the world. Yet, the current knowledge about respiratory depositions of e-cigarette aerosol through passive vaping in human airways is limited due to critical weaknesses of traditional experimental methods. To fill in this important knowledge gap, this study proposed a special approach involving an upgraded Mobile Aerosol Lung Deposition Apparatus (MALDA) that consists of a set of human airway replicas including a head airway, tracheobronchial airways down to the 11th lung generation, and a representative alveolar section. In addition to the comprehensive coverage of human airways, the MALDA is easily transportable for providing efficient estimations of aerosol respiratory deposition. In this study, the MALDA was first evaluated in the laboratory and then applied to estimate the respiratory deposition associated with passive vaping in an indoor real-life setting. The results showed that the respiratory deposition data aligned closely with the conventional respiratory deposition curves not only in the head-to-TB region but also in the alveolar region. The strengths of MALDA demonstrate great promise for a wide variety of applications in real-life settings that could provide crucial information for future public health and indoor air quality studies.

JUUL e-liquid exposure elicits cytoplasmic Ca2+ responses and leads to cytotoxicity in cultured airway epithelial cells

RATIONALE

The popularity of new and emerging tobacco products such as E-cigarettes (E-cigs) is rapidly expanding worldwide. However, uncertainties surrounding the potential health consequences due to the use of such products exist and warrant further study.

METHODS

Cultured A549 and Calu-3 airway epithelia were exposed to three out of the eight types of JUUL brand e-liquids ("Mint", "Virginia Tobacco" and "Menthol", all containing 3% nicotine at 1% and 3% (vol/vol) dilutions) and assessed for viability using a resazurin-based assay. Intracellular Ca2+ levels were measured using fluorescent indicators and pro-inflammatory cytokine levels were monitored by quantitative PCR (qPCR). Cultures were also analyzed by flow cytometry to evaluate apoptotic markers and cell viability.

RESULTS

Exposing the airway epithelial cells to the flavored JUUL e-liquids led to significant cytotoxicity, with the "Mint" flavor being the overall most cytotoxic. The "Mint" flavored e-liquid also led to significant elevations in intracellular Ca2+ and upregulation of the pro-inflammatory cytokine IL-6 and early apoptotic marker Annexin V.

CONCLUSIONS

JUUL e-liquid challenge resulted in a loss of airway epithelial cell viability, induced pro-inflammatory responses and eventually caused apoptosis.

Aerosol droplet-size distribution and airborne nicotine portioning in particle and gas phases emitted by electronic cigarettes

The reliable characterization of particle size distribution and nicotine delivery emitted by electronic cigarettes (ECs) is a critical issue in their design. Indeed, a better understanding of how nicotine is delivered as an aerosol with an appropriate aerodynamic size is a necessary step toward obtaining a well-designed nicotine transfer from the respiratory tract to the bloodstream to better satisfy craving and improve smoking cessation rates. To study these two factors, recent models of EC devices and a dedicated vaping machine were used to generate aerosols under various experimental conditions, including varying the EC power level using two different types of atomizers. The aerodynamic particle sizing of the resulting aerosol was performed using a cascade impactor. The nicotine concentration in the refill liquid and the aerosol droplet was quantified by liquid chromatography coupled with a photodiode array. The vaporization process and the physical and chemical properties of the EC aerosol were very similar at 15 watts (W) and 25 W using the low-power atomizer but quite distinct at 50 W using the high-power atomizer, as follows: (1) the mass median aerodynamic diameters ranged from 1.06 to 1.19 µm (µm) for low power and from 2.33 to 2.46 µm for high power; (2) the nicotine concentrations of aerosol droplets were approximately 11 mg per milliliter (mg/mL) for low power and 17 mg/mL for high power; and (3) the aerosol droplet particle phase of the total nicotine mass emitted by EC was 60% for low power and 95% for high power. The results indicate that varying the correlated factors (1) the power level and (2) the design of atomizer (including the type of coil and the value of resistance used) affects the particle-size distribution and the airborne nicotine portioning between the particle phase and the gas phase in equilibrium with the airborne droplets.

Whole body electronic cigarette exposure system for efficient evaluation of diverse inhalation conditions and products

Objectives: To develop and test a new system for whole body exposure of small animals to support investigation of the biological effects of aerosol generated by electronic cigarette (e-cig) products under diverse inhalation conditions with improved control and monitoring of the e-cig vape exposure and nicotine delivered to the animal's systemic circulation. Methods: A computer-controlled design, with built-in sensors for real time monitoring of O₂, CO₂, relative humidity, and temperature within the exposure chambers and port for measuring total particulate matter (TPM) was developed, constructed and tested. This design accommodates a variety of commercial vaping devices, offers software flexibility to adjust exposure protocols to mimic different users' puffing patterns, enables variable nicotine delivery to the animal's systemic circulation; minimizes travel time and alterations of aerosol quality or quantity by delivering aerosol directly to the exposure chamber, offers local or remote operation of up to six distinct exposure chambers from a single control unit, and can simultaneously test different exposure conditions or products in diverse animal groups, which reduces inter-run variability, saves time, and increases productivity. Results: The time course pattern of TPM concentration during different phases of the exposure cycle was measured. With increased puffing duration or number of exposure cycles, higher TPM exposure and plasma cotinine levels were observed with plasma cotinine levels in the range reported in light or heavy smokers. Conclusion: Overall, this novel, versatile, and durable exposure system facilitates high-throughput evaluation of the relative safety and potential toxicity of a variety of e-cig devices and liquids.

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.

Effects of Electronic Cigarettes on Indoor Air Quality and Health

With the rapid increase in electronic cigarette (e-cig) users worldwide, secondhand exposure to e-cig aerosols has become a serious public health concern. We summarize the evidence on the effects of e-cigs on indoor air quality, chemical compositions of mainstream and secondhand e-cig aerosols, and associated respiratory and cardiovascular effects. The use of e-cigs in indoor environments leads to high levels of fine and ultrafine particles similar to tobacco cigarettes (t-cigs). Concentrations of chemical compounds in e-cig aerosols are generally lower than those in t-cig smoke, but a substantial amount of vaporized propylene glycol, vegetable glycerin, nicotine, and toxic substances, such as aldehydes and heavy metals, has been reported. Exposures to mainstream e-cig aerosols have biologic effects but only limited evidence shows adverse respiratory and cardiovascular effects in humans. Long-term studies are needed to better understand the dosimetry and health effects of exposures to secondhand e-cig aerosols.

Investigating E-Cigarette Particle Emissions and Human Airway Depositions under Various E-Cigarette-Use Conditions

E-cigarette use is dramatically increasing, particularly with adolescents. While the chemical composition of e-liquids and e-vapor is well characterized, the particle size distribution and the human airways deposition patterns of e-cigarette particles are understudied and poorly understood despite their likely contribution to adverse health effects from e-cigarette usage. In this study, we examined the impacts of e-cigarette device power, e-liquid composition, and vaping topography on e-cigarette particle sizes and their deposition in human airways. In addition, we observed that particle measurement conditions (dilution ratio, temperature, and humidity) significantly affect measured e-cigarette particle sizes. E-cigarette power output significantly increased particle count median diameters (CMD) from 174 ± 13 (particles generated under 6.4 W) to 236 ± 14 nm (particles generated under 31.1 W). E-cigarette particles generated from propylene glycol-based e-liquids (CMD = 145 ± 8 nm and mass median diameter [MMD] = 3.06 ± 0.17 μm) were smaller than those generated from vegetable glycerin-based e-liquids (CMD = 182 ± 9 nm and MMD = 3.37 ± 0.21 μm). Puff volume also impacted vapor particle size: CMD and MMD were 154 ± 11 nm and 3.50 ± 0.27 μm, 163 ± 6 nm and 3.35 ± 0.24 μm, and 146 ± 12 nm and 2.95 ± 0.14 μm, respectively, for 35, 90, and 170 mL puffs. Estimated e-cigarette particle mass deposition fractions in tracheobronchial and bronchoalveolar regions were 0.504-0.541 and 0.073-0.306, respectively. Interestingly, e-cigarette particles are smaller than the particles generated from cigarette smoking but have similar human airway deposition patterns.

State-of-the-art methods and devices for generation, exposure, and collection of aerosols from e-vapor products

E-vapor products (EVP) have become popular alternatives for cigarette smokers who would otherwise continue to smoke. EVP research is challenging and complex, mostly because of the numerous and rapidly evolving technologies and designs as well as the multiplicity of e-liquid flavors and solvents available on the market. There is an urgent need to standardize all stages of EVP assessment, from the production of a reference product to e-vapor generation methods and from physicochemical characterization methods to nonclinical and clinical exposure studies. The objective of this review is to provide a detailed description of selected experimental setups and methods for EVP aerosol generation and collection and exposure systems for their in vitro and in vivo assessment. The focus is on the specificities of the product that constitute challenges and require development of ad hoc assessment frameworks, equipment, and methods. In so doing, this review aims to support further studies, objective evaluation, comparison, and verification of existing evidence, and, ultimately, formulation of standardized methods for testing EVPs.

In Vitro Consequences of Electronic-Cigarette Flavoring Exposure on the Immature Lung

Background: The developing lung is uniquely susceptible and may be at increased risk of injury with exposure to e-cigarette constituents. We hypothesize that cellular toxicity and airway and vascular responses with exposure to flavored refill solutions may be altered in the immature lung. Methods: Fetal, neonatal, and adult ovine pulmonary artery smooth muscle cells (PASMC) were exposed to popular flavored nicotine-free e-cigarette refill solutions (menthol, strawberry, tobacco, and vanilla) and unflavored solvents: propylene glycol (PG) or vegetable glycerin (VG). Viability was assessed by lactate dehydrogenase assay. Brochodilation and vasoreactivity were determined on isolated ovine bronchial rings (BR) and pulmonary arteries (PA). Results: Neither PG or VG impacted viability of immature or adult cells; however, exposure to menthol and strawberry flavored solutions increased cell death. Neonatal cells were uniquely susceptible to menthol flavoring-induced toxicity, and all four flavorings demonstrated lower lethal doses (LD50) in immature PASMC. Exposure to flavored solutions induced bronchodilation of neonatal BR, while only menthol induced airway relaxation in adults. In contrast, PG/VG and flavored solutions did not impact vasoreactivity with the exception of menthol-induced relaxation of adult PAs. Conclusion: The immature lung is uniquely susceptible to cellular toxicity and altered airway responses with exposure to common flavored e-cigarette solutions.

The effect of e-cigarette aerosol emissions on respiratory health: a narrative review

Introduction: Due to the uptake in the use of e-cigarettes (ECs), evidence on their health effects is needed to inform health care and policy. Some regulators and health professionals have raised concerns that the respirable aerosols generated by ECs contain several constituents of potential toxicological and biological relevance to respiratory health. Areas covered: We critically assess published research on the respiratory system investigating the effects of ECs in preclinical models, clinical studies of people who switched to ECs from tobacco cigarettes, and population surveys. We assess the studies for the quality of their methodology and accuracy of their interpretation. To adequately assess the impact of EC use on human health, addressing common mistakes and developing robust and realistic methodological recommendations is an urgent priority. The findings of this review indicate that ECs under normal conditions of use demonstrate far fewer respiratory risks than combustible tobacco cigarettes. EC users and smokers considering ECs have the right to be informed about the relative risks of EC use, and to be made aware that findings of studies published by the media are not always reliable. Expert opinion: Growing evidence supports the relative safety of EC emission aerosols for the respiratory tract compared to tobacco smoke.

Second-hand aerosol from tobacco and electronic cigarettes: Evaluation of the smoker emission rates and doses and lung cancer risk of passive smokers and vapers

Smoking activities still represent the main, and preventable, cause of lung cancer risk worldwide. For this reason, a number of studies were carried out to deepen and better characterize the emission of cigarette-generated mainstream aerosols in order to perform an a-priori evaluation of the particle doses and related lung cancer risks received by active smokers. On the contrary, a gap of knowledge still exists in evaluating the dose and risk received by passive smokers in indoor private micro-environments (e.g. homes). For this purpose, in the present paper, an experimental campaign was performed to evaluate the exposure to second-hand aerosol from conventional and electronic cigarettes and to estimate the consequent dose received by passive smokers/vapers and the related lung cancer risk. Measurements of exposure levels in terms of particle number, PM10 and black carbon concentrations, as well as particle size distributions, were performed in a naturally ventilated indoor environment during smoking activities of tobacco and electronic cigarettes. The particle emission rates of smokers and vapers, for the different aerosol metrics under investigation, were evaluated. Moreover, for a typical exposure scenario, the dose received by the passive smokers/vapers in a naturally ventilated indoor micro-environment was estimated through a Multiple-Path Particle Dosimetry (MPPD) model able to assess the particle dose received in the different tracts of the respiratory systems. Furthermore, on the basis of scientific literature data about mass fraction of carcinogenic compounds contained in cigarette-emitted particles (i.e. Heavy Metals, Benzo-a-pyrene and nitrosamines) and the estimated doses, the excess life cancer risk (ELCR) for passive smokers/vapers was evaluated. Cumulative respiratory doses for passive smokers were up to 15-fold higher than for passive vapers. The ELCR for second-hand smokers was five orders of magnitude larger than for second-hand vapers.

Generation of Electronic Cigarette Aerosol by a Third-Generation Machine-Vaping Device: Application to Toxicological Studies

Electronic-cigarette (e-cig) devices use heat to produce an inhalable aerosol from a liquid (e-liquid) composed mainly of humectants, nicotine, and flavoring chemicals. The aerosol produced includes fine and ultrafine particles, and potentially nicotine and aldehydes, which can be harmful to human health. E-cig users inhale these aerosols and, with the third-generation of e-cig devices, control design features (resistance and voltage) in addition to the choice of e-liquids, and the puffing profile. These are key factors that can significantly impact the toxicity of the inhaled aerosols. E-cig research, however, is challenging and complex mostly due to the absence of standardized assessments and to the numerous varieties of e-cig models and brands, as well as e-liquid flavors and solvents that are available on the market. These considerations highlight the urgent need to harmonize e-cig research protocols, starting with e-cig aerosol generation and characterization techniques. The current study focuses on this challenge by describing a detailed step-by-step e-cig aerosol generation technique with specific experimental parameters that are thought to be realistic and representative of real-life exposure scenarios. The methodology is divided into four sections: preparation, exposure, post-exposure analysis, plus cleaning and maintenance of the device. Representative results from using two types of e-liquid and various voltages are presented in terms of mass concentration, particle size distribution, chemical composition and cotinine levels in mice. These data demonstrate the versatility of the e-cig exposure system used, aside from its value for toxicological studies, as it allows for a broad range of computer-controlled exposure scenarios, including automated representative vaping topography profiles.

Particle Size Dynamics: Toward a Better Understanding of Electronic Cigarette Aerosol Interactions With the Respiratory System

The knowledge of possible acute and long-term health effects of aerosols inhaled from electronic cigarettes (ECs) is still limited partially due to incomplete awareness of physical phenomena related to EC-aerosol dynamics. This short review discusses the basic processes of aerosol transformation (dynamics) upon inhalation, indicating also the need for the accurate determination of the size of droplets in the inhaled EC-mist. The significance of differences in the aerosol particle size distribution for the prediction of regional deposition of inhaled mist in the respiratory system is highlighted as a decisive factor in the interactions of inhaled EC-aerosols with the organism.

Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome

RATIONALE

E-cigarettes vaporize propylene glycol/vegetable glycerin (PG/VG), nicotine, and flavorings. However, the long-term health effects of exposing lungs to vaped e-liquids are unknown.

OBJECTIVES

To determine the effects of chronic vaping on pulmonary epithelia.

METHODS

We performed research bronchoscopies on healthy nonsmokers, cigarette smokers, and e-cigarette users (vapers) and obtained bronchial brush biopsies and lavage samples from these subjects for proteomic investigation. We further employed in vitro and murine exposure models to support our human findings.

MEASUREMENTS AND MAIN RESULTS

Visual inspection by bronchoscopy revealed that vaper airways appeared friable and erythematous. Epithelial cells from biopsy samples revealed approximately 300 proteins that were differentially expressed in smoker and vaper airways, with only 78 proteins being commonly altered in both groups and 113 uniquely altered in vapers. For example, CYP1B1 (cytochrome P450 family 1 subfamily B member 1), MUC5AC (mucin 5 AC), and MUC4 levels were increased in vapers. Aerosolized PG/VG alone significantly increased MUC5AC protein in human airway epithelial cultures and in murine nasal epithelia in vivo. We also found that e-liquids rapidly entered cells and that PG/VG reduced membrane fluidity and impaired protein diffusion.

CONCLUSIONS

We conclude that chronic vaping exerts marked biological effects on the lung and that these effects may in part be mediated by the PG/VG base. These changes are likely not harmless and may have clinical implications for the development of chronic lung disease. Further studies will be required to determine the full extent of vaping on the lung.

Physicochemical studies of direct interactions between lung surfactant and components of electronic cigarettes liquid mixtures

Direct physicochemical interactions between the major components of electronic cigarette liquids (e-liquids): glycerol (VG) and propylene glycol (PG), and lung surfactant (LS) were studied by determining the dynamic surface tension under a simulated breathing cycle using drop shape method. The studies were performed for a wide range of concentrations based on estimated doses of e-liquid aerosols (up to 2500 × the expected nominal concentrations) and for various VG/PG ratios. The results are discussed as relationships among mean surface tension, surface tension amplitude, and surface rheological properties (dilatational elasticity and viscosity) versus concentration and composition of e-liquid. The results showed that high local concentrations (>200 × higher than the estimated average dose after a single puffing session) may induce measurable changes in biophysical activity of LS; however, only ultra-high e-liquid concentrations inactivated the surfactant. Physiochemical characterization of e-liquids provide additional insights for the safety assessment of electronic nicotine delivery systems (ENDS).

Passive exposure to e-cigarette emissions: Immediate respiratory effects

INTRODUCTION

The present work examined the effect of passive exposure to electronic-cigarette (e-cigarette) emissions on respiratory mechanics and exhaled inflammatory biomarkers.

METHODS

A cross-over experimental study was conducted with 40 healthy nonsmokers, 18-35 years old with normal physical examination and spirometry, with body mass index <30 kg/m², who were exposed to e-cigarette emissions produced by a smoker, according to a standardized protocol based on two resistance settings, 0.5 ohm and 1.5 ohm, for e-cigarette use. All participants underwent a 30-minute control (no emissions) and two experimental sessions (0.5 and 1.5 ohm exposure) in a 35 m³ room. The following Impulse Oscillometry (IOS) parameters were measured at pre and post sessions: impedance, resistance, reactance, resonant frequency (fres), frequency dependence of resistance (fdr=R5-R20), reactance area (AX), and fractional exhaled nitric oxide (FeNO). Differences between pre and post measurements were compared using t-tests and Wilcoxon signed rank tests, while analysis of variance (ANOVA) was used for comparisons between experimental sessions (registered under ClinicalTrials.gov ID: NCT03102684).

RESULTS

IOS and FeNO parameters showed no significant changes during the control session. For IOS during the 1.5 ohm exposure session, fres increased significantly from 11.38 Hz at baseline to 12.16 Hz post exposure (p=0.047). FeNO decreased significantly from 24.16 ppb at baseline to 22.35 ppb post exposure in the 0.5 ohm session (p=0.006).

CONCLUSIONS

A 30-minute passive exposure to e-cigarette emissions revealed immediate alterations in respiratory mechanics and exhaled biomarkers, expressed as increased fres and reduced FeNO.

Evaluation of e-liquid toxicity using an open-source high-throughput screening assay

The e-liquids used in electronic cigarettes (E-cigs) consist of propylene glycol (PG), vegetable glycerin (VG), nicotine, and chemical additives for flavoring. There are currently over 7,700 e-liquid flavors available, and while some have been tested for toxicity in the laboratory, most have not. Here, we developed a 3-phase, 384-well, plate-based, high-throughput screening (HTS) assay to rapidly triage and validate the toxicity of multiple e-liquids. Our data demonstrated that the PG/VG vehicle adversely affected cell viability and that a large number of e-liquids were more toxic than PG/VG. We also performed gas chromatography-mass spectrometry (GC-MS) analysis on all tested e-liquids. Subsequent nonmetric multidimensional scaling (NMDS) analysis revealed that e-liquids are an extremely heterogeneous group. Furthermore, these data indicated that (i) the more chemicals contained in an e-liquid, the more toxic it was likely to be and (ii) the presence of vanillin was associated with higher toxicity values. Further analysis of common constituents by electron ionization revealed that the concentration of cinnamaldehyde and vanillin, but not triacetin, correlated with toxicity. We have also developed a publicly available searchable website (www.eliquidinfo.org). Given the large numbers of available e-liquids, this website will serve as a resource to facilitate dissemination of this information. Our data suggest that an HTS approach to evaluate the toxicity of multiple e-liquids is feasible. Such an approach may serve as a roadmap to enable bodies such as the Food and Drug Administration (FDA) to better regulate e-liquid composition.

Health impact of E-cigarettes: a prospective 3.5-year study of regular daily users who have never smoked

Although electronic cigarettes (ECs) are a much less harmful alternative to tobacco cigarettes, there is concern as to whether long-term ECs use may cause risks to human health. We report health outcomes (blood pressure, heart rate, body weight, lung function, respiratory symptoms, exhaled breath nitric oxide [eNO], exhaled carbon monoxide [eCO], and high-resolution computed tomography [HRCT] of the lungs) from a prospective 3.5-year observational study of a cohort of nine daily EC users (mean age 29.7 (±6.1) years) who have never smoked and a reference group of twelve never smokers. No significant changes could be detected over the observation period from baseline in the EC users or between EC users and control subjects in any of the health outcomes investigated. Moreover, no pathological findings could be identified on HRCT of the lungs and no respiratory symptoms were consistently reported in the EC user group. Although it cannot be excluded that some harm may occur at later stages, this study did not demonstrate any health concerns associated with long-term use of EC in relatively young users who did not also smoke tobacco.

E-cigarettes in patients with COPD: current perspectives

Conventional cigarette smoking is known to result in significant COPD morbidity and mortality. Strategies to reduce and/or stop smoking in this highly vulnerable patient group are key public health priorities to reduce COPD morbidity and mortality. Unfortunately, smoking cessation efforts in patients with COPD are poor and there is a compelling need for more efficient approaches to cessation for patients with COPD. Electronic cigarettes (ECs) are devices that use batteries to vaporize nicotine. They may facilitate quit attempts and cessation in many smokers. Although they are not risk free, ECs are much less harmful than tobacco smoking. Hence, the use of ECs in vulnerable groups and in patients with challenges to abstain or multiple relapses to this habit may be promising. To date, little is known about health consequences of EC use among COPD smokers and whether their regular use has any effects on subjective and objective COPD outcomes. In the current review, we discuss the current perspectives and literature on the role of ECs in abstaining from conventional smoking and the effects of ECs on the respiratory tract in patients with COPD.

Electronic cigarettes—A review of the physiological health effects

Electronic cigarettes (ECs) are devices that are used recreationally or as smoking cessation tools, and have become increasingly popular in recent years. We conducted a review of the available literature to determine the health effects caused by the use of these devices. A heating element in the EC aerosolizes a solution of propylene glycol, glycerol, nicotine (optional), and flavouring (optional). These compounds are generally harmless on their own. However, upon heating, they produce various carcinogens and irritants. We found that concentrations of these toxicants vary significantly depending on the type of EC device, the type of EC liquid, and the smoking behaviour of the user. Exposure to these vapours can cause inflammation and oxidative damage to in vitro and in vivo cells. EC aerosol can also potentially affect organ systems and especially cardiovascular and lung function. We concluded that EC use causes acute effects on health but not as severe as those of conventional cigarettes (CCs). These devices could, therefore, be of use for smokers of CCs wishing to quit. However, as EC aerosol introduces new toxicants not found in CCs, long-term studies are needed to investigate possible chronic effects associated with EC use.

Flavored e-cigarette liquids reduce proliferation and viability in the CALU3 airway epithelial cell line

E-cigarettes are generally thought of as a safer smoking alternative to traditional cigarettes. However, little is known about the effects of e-cigarette liquids (e-liquids) on the lung. Since over 7,000 unique flavors have been identified for purchase in the United States, our goal was to conduct a screen that would test whether different flavored e-liquids exhibited different toxicant profiles. We tested the effects of 13 different flavored e-liquids [with nicotine and propylene glycol/vegetable glycerin (PG/VG) serving as controls] on a lung epithelial cell line (CALU3). Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay as an indicator of cell proliferation/viability, we demonstrated a dose-dependent decrease of MTT metabolism by all flavors tested. However, a group of four flavors consistently showed significantly greater toxicity compared with the PG/VG control, indicating the potential for some flavors to elicit more harmful effects than others. We also tested the aerosolized "vapor" from select e-liquids on cells and found similar dose-dependent trends, suggesting that direct e-liquid exposures are a justifiable first-pass screening approach for determining relative e-liquid toxicity. We then identified individual chemical constituents for all 13 flavors using gas chromatography-mass spectrometry. These data revealed that beyond nicotine and PG/VG, the 13 flavored e-liquids have diverse chemical constituents. Since all of the flavors exhibited some degree of toxicity and a diverse array of chemical constituents with little inhalation toxicity available, we conclude that flavored e-liquids should be extensively tested on a case-by-case basis to determine the potential for toxicity in the lung and elsewhere.

Overview of Electronic Nicotine Delivery Systems: A Systematic Review

CONTEXT

Rapid developments in e-cigarettes, or electronic nicotine delivery systems (ENDS), and the evolution of the overall tobacco product marketplace warrant frequent evaluation of the published literature. The purpose of this article is to report updated findings from a comprehensive review of the published scientific literature on ENDS.

EVIDENCE ACQUISITION

The authors conducted a systematic review of published empirical research literature on ENDS through May 31, 2016, using a detailed search strategy in the PubMed electronic database, expert review, and additional targeted searches. Included studies presented empirical findings and were coded to at least one of nine topics: (1) Product Features; (2) Health Effects; (3) Consumer Perceptions; (4) Patterns of Use; (5) Potential to Induce Dependence; (6) Smoking Cessation; (7) Marketing and Communication; (8) Sales; and (9) Policies; reviews and commentaries were excluded. Data from included studies were extracted by multiple coders (October 2015 to August 2016) into a standardized form and synthesized qualitatively by topic.

EVIDENCE SYNTHESIS

There were 687 articles included in this systematic review. The majority of studies assessed patterns of ENDS use and consumer perceptions of ENDS, followed by studies examining health effects of vaping and product features.

CONCLUSIONS

Studies indicate that ENDS are increasing in use, particularly among current smokers, pose substantially less harm to smokers than cigarettes, are being used to reduce/quit smoking, and are widely available. More longitudinal studies and controlled trials are needed to evaluate the impact of ENDS on population-level tobacco use and determine the health effects of longer-term vaping.

Electronic cigarette aerosol induces significantly less cytotoxicity than tobacco smoke

Electronic cigarettes (E-cigarettes) are a potential means of addressing the harm to public health caused by tobacco smoking by offering smokers a less harmful means of receiving nicotine. As e-cigarettes are a relatively new phenomenon, there are limited scientific data on the longer-term health effects of their use. This study describes a robust in vitro method for assessing the cytotoxic response of e-cigarette aerosols that can be effectively compared with conventional cigarette smoke. This was measured using the regulatory accepted Neutral Red Uptake assay modified for air-liquid interface (ALI) exposures. An exposure system, comprising a smoking machine, traditionally used for in vitro tobacco smoke exposure assessments, was adapted for use with e-cigarettes to expose human lung epithelial cells at the ALI. Dosimetric analysis methods using real-time quartz crystal microbalances for mass, and post-exposure chemical analysis for nicotine, were employed to detect/distinguish aerosol dilutions from a reference Kentucky 3R4F cigarette and two commercially available e-cigarettes (Vype eStick and ePen). ePen aerosol induced 97%, 94% and 70% less cytotoxicity than 3R4F cigarette smoke based on matched EC50 values at different dilutions (1:5 vs. 1:153 vol:vol), mass (52.1 vs. 3.1 μg/cm2) and nicotine (0.89 vs. 0.27 μg/cm2), respectively. Test doses where cigarette smoke and e-cigarette aerosol cytotoxicity were observed are comparable with calculated daily doses in consumers. Such experiments could form the basis of a larger package of work including chemical analyses, in vitro toxicology tests and clinical studies, to help assess the safety of current and next generation nicotine and tobacco products.