Nose-Only Exposure to Cherry- and Tobacco-Flavored E-Cigarettes Induced Lung Inflammation in Mice in a Sex-Dependent Manner

Chronic exposure to E-cigarette aerosols potentiates atherosclerosis in a sex-dependent manner

Despite being designed for smoking cessation, e-cigarettes and their variety of flavors have become increasingly attractive to teens and young adults. This trend has fueled concerns regarding the potential role of e-cigarettes in advancing chronic diseases, notably those affecting the cardiovascular system. E-cigarettes contain a mixture of metals and chemical compounds, some of which have been implicated in cardiovascular diseases like atherosclerosis. Our laboratory has optimized in vivo exposure regimens to mimic human vaping patterns. Using these established protocols in an inducible (AAV-PCSK9) hyperlipidemic mouse model, this study tests the hypothesis that a chronic exposure to e-cigarette aerosols will increase atherosclerotic plaques. The exposures were conducted using the SCIREQ InExpose™ nose-only inhalation system and STLTH or Vuse products for 16 weeks. We observed that only male mice exposed to STLTH or Vuse aerosols had significantly increased plasma total cholesterol, triglycerides, and LDL cholesterol levels compared to mice exposed to system air. Moreover, these male mice also had a significant increase in aortic and sinus plaque area. Male mice exposed to e-cigarette aerosol had a significant reduction in weight gain over the exposure period. Our data indicate that e-cigarette use in young hyperlipidemic male mice increases atherosclerosis in the absence of significant pulmonary and systemic inflammation. These results underscore the need for extensive research to unravel the long-term health effects of e-cigarettes.

A Review of the Toxicity of Ingredients in e-Cigarettes, Including Those Ingredients Having the FDA's "Generally Recognized as Safe (GRAS)" Regulatory Status for Use in Food

Some firms and marketers of electronic cigarettes (e-cigarettes; a type of electronic nicotine delivery system (ENDS)) and refill liquids (e-liquids) have made claims about the safety of ingredients used in their products based on the term "GRAS or Generally Recognized As Safe" (GRAS). However, GRAS is a provision within the definition of a food additive under section 201(s) (21 U.S.C. 321(s)) of the U.S. Federal Food Drug and Cosmetic Act (FD&C Act). Food additives and GRAS substances are by the FD&C Act definition intended for use in food, thus safety is based on oral consumption; the term GRAS cannot serve as an indicator of the toxicity of e-cigarette ingredients when aerosolized and inhaled (ie, vaped). There is no legal or scientific support for labeling e-cigarette product ingredients as "GRAS." This review discusses our concerns with the GRAS provision being applied to e-cigarette products and provides examples of chemical compounds that have been used as food ingredients but have been shown to lead to adverse health effects when inhaled. The review provides scientific insight into the toxicological evaluation of e-liquid ingredients and their aerosols to help determine the potential respiratory risks associated with their use in e-cigarettes.

Challenges in current inhalable tobacco toxicity assessment models: A narrative review

Emerging tobacco products such as electronic nicotine delivery systems (ENDS) and heated tobacco products (HTPs) have a dynamic landscape and are becoming widely popular as they claim to offer a low-risk alternative to conventional smoking. Most pre-clinical laboratories currently exploit in vitro, ex vivo, and in vivo experimental models to assess toxicological outcomes as well as to develop risk-estimation models. While most laboratories have produced a wide range of cell culture and mouse model data utilizing current smoke/aerosol generators and standardized puffing profiles, much variation still exists between research studies, hindering the generation of usable data appropriate for the standardization of these tobacco products. In this review, we discuss current state-of-the-art in vitro and in vivo models and their challenges, as well as insights into risk estimation of novel products and recommendations for toxicological parameters for reporting, allowing comparability of the research studies between laboratories, resulting in usable data for regulation of these products before approval by regulatory authorities.

The paradox of the safer cigarette: understanding the pulmonary effects of electronic cigarettes

Electronic cigarette (e-cigarette) use continues to rise globally. E-cigarettes have been presented as safer alternatives to combustion cigarettes that can mitigate the harm associated with tobacco products; however, the degree to which e-cigarette use itself can lead to morbidity and mortality is not fully defined. Herein we describe how e-cigarettes function; discuss the current knowledge of the effects of e-cigarette aerosol on lung cell cytotoxicity, inflammation, antipathogen immune response, mucociliary clearance, oxidative stress, DNA damage, carcinogenesis, matrix remodelling and airway hyperresponsiveness; and summarise the impact on lung diseases, including COPD, respiratory infection, lung cancer and asthma. We highlight how the inclusion of nicotine or flavouring compounds in e-liquids can impact lung toxicity. Finally, we consider the paradox of the safer cigarette: the toxicities of e-cigarettes that can mitigate their potential to serve as a harm reduction tool in the fight against traditional cigarettes, and we summarise the research needed in this underinvestigated area.

e-Cigarette Tobacco Flavors, Public Health, and Toxicity: Narrative Review

BACKGROUND

Recently, the US Food and Drug Administration implemented enforcement priorities against all flavored, cartridge-based e-cigarettes other than menthol and tobacco flavors. This ban undermined the products' appeal to vapers, so e-cigarette manufacturers added flavorants of other attractive flavors into tobacco-flavored e-cigarettes and reestablished appeal.

OBJECTIVE

This review aims to analyze the impact of the addition of other flavorants in tobacco-flavored e-cigarettes on both human and public health issues and to propose further research as well as potential interventions.

METHODS

Searches for relevant literature published between 2018 and 2023 were performed. Cited articles about the toxicity of e-cigarette chemicals included those published before 2018, and governmental websites and documents were also included for crucial information.

RESULTS

Both the sales of e-cigarettes and posts on social media suggested that the manufacturers' strategy was successful. The reestablished appeal causes not only a public health issue but also threats to the health of individual vapers. Research has shown an increase in toxicity associated with the flavorants commonly used in flavored e-cigarettes, which are likely added to tobacco-flavored e-cigarettes based on tobacco-derived and synthetic tobacco-free nicotine, and these other flavors are associated with higher clinical symptoms not often induced solely by natural, traditional tobacco flavors.

CONCLUSIONS

The additional health risks posed by the flavorants are pronounced even without considering the toxicological interactions of the different tobacco flavorants, and more research should be done to understand the health risks thoroughly and to take proper actions accordingly for the regulation of these emerging products.

Effects of Short-term Electronic(e)-Cigarette Aerosol Exposure in the Mouse Larynx

OBJECTIVES

The effects of electronic cigarettes (e-cigarettes) on the larynx are relatively unknown. This study examined the short-term effects of e-cigarette inhalation on cellular and inflammatory responses within the mouse laryngeal glottic and subglottic regions after exposure to pod-based devices (JUUL).

METHODS

Male C57BL6/J mice (8-9 weeks) were assigned to control (n = 9), JUUL flavors Mint (JMi; n = 10) or Mango (JMa; n = 10). JUUL mice were exposed to 2 h/day for 1, 5, and 10 days using the inExpose inhalation system. Control mice were in room air. Vocal fold (VF) epithelial thickness, cell proliferation, subglandular area and composition, inflammatory cell infiltration, and surface topography were evaluated in the harvested larynges. Mouse body weight and urinary nicotine biomarkers were also measured. Chemical analysis of JUUL aerosols was conducted using selective ion flow tube mass spectrometry.

RESULTS

JUUL-exposed mice had reduced body weight after day 5. Urinary nicotine biomarker levels indicated successful JUUL exposure and metabolism. Quantitative analysis of JUUL aerosol indicated that chemical constituents differ between JMi and JMa flavors. VF epithelial thickness, cellular proliferation, glandular area, and surface topography remained unchanged after JUUL exposures. Acidic mucus content increased after 1 day of JMi exposure. VF macrophage and T-cell levels slightly increased after 10 days of JMi exposures.

CONCLUSIONS

Short-term e-cigarette exposures cause minimal flavor- and region-specific cellular and inflammatory changes in the mouse larynx. This work provides a foundation for long-term studies to determine if these responses are altered with multiple e-cigarette components and concentrations.

LEVEL OF EVIDENCE

N/A Laryngoscope, 134:1316-1326, 2024.

Tobacco-derived and tobacco-free nicotine cause differential inflammatory cell influx and MMP-9 in mouse lung

BACKGROUND

Electronic nicotine delivery systems (ENDS) or electronic cigarettes (e-cigarettes) aerosolize an e-liquid composed of propylene glycol (PG) and vegetable glycerin (VG) as humectants, flavoring chemicals, and nicotine. Nicotine naturally occurs in two isomers R- and S-nicotine, with tobacco-derived nicotine (TDN) composed of S-nicotine, and tobacco-free/synthetic nicotine (TFN) composed of a racemic mixture of R- and S-nicotine. Currently, there is limited knowledge of the potential differences in the toxicity of TFN versus TDN. We hypothesized that exposure of TFN and TDN salts to C57BL/6J mice would result in a differential response in lung inflammation and protease/ antiprotease imbalance.

METHODS

Five-week-old male and female C57BL/6J mice were exposed to air, PG/VG, PG/VG with TFN salts (TFN), or PG/VG with TDN salts (TDN) by nose-only exposure. Lung inflammatory cell counts, cytokine/chemokine levels, and matrix metalloproteinase (MMP) protein abundance and activity levels were determined by flow cytometry, ELISA, immunoblotting, and gel zymography, respectively.

RESULTS

Exposure to the humectants (PG/VG) alone increased cytokine levels- IL-6, KC, and MCP-1 in the BALF and KC levels in lung homogenate of exposed mice. While no change was observed in the cytokine levels in lung homogenate of TDN aerosol exposed mice, exposure to TFN aerosols resulted in an increase in KC levels in the lungs of these mice compared to air controls. Interestingly, exposure to TDN aerosols increased MMP-9 protein abundance in the lungs of female mice, while exposure to TFN aerosol showed no change. The metabolism of nicotine or the clearance of cotinine for TFN exposure may differ from that for TDN.

CONCLUSION

Exposure to humectants, PG/VG alone, induces an inflammatory response in C57BL/6J mice. TFN and TDN salts show distinct changes in inflammatory responses and lung proteases on acute exposures. These data suggest variable toxicological profiles of the two forms of nicotine in vivo. Future work is thus warranted to delineate the harmful effects of synthetic/natural nicotine with humectants to determine the potential toxicological risks for users.

Tobacco-Derived and Tobacco-Free Nicotine cause differential inflammatory cell influx and MMP9 in mouse lung

Electronic nicotine delivery systems (ENDS) or electronic cigarettes (e-cigarettes) have propylene glycol (PG) and vegetable glycerin (VG) as humectants, flavoring chemicals, and nicotine. Nicotine naturally occurs in two isomers R- and S-nicotine, with both tobacco-derived nicotine (TDN) composed of S-nicotine and synthetic nicotine (TFN) composed of a racemic mixture of R- and S-nicotine. Currently there is limited knowledge of the potential differences in the toxicity of TFN vs TDN. We hypothesized that exposure of TFN salts to C57BL/6J mice will result in a differential response in inflammation and lung protease and antiprotease imbalance compared to TDN salts exposed mice. We studied the toxicological impact of these isomers by exposing mice to air, PG/VG, PG/VG with TFN salts, or PG/VG with TDN salts by nose-only exposure and measured the cytokine levels in BALF and lung homogenate along with MMP protein abundance in the lungs of exposed mice. Exposure to the humectants, PG/VG, used in e-cigarettes alone was able to increase cytokine levels-IL-6, KC, and MCP-1 in BALF and KC levels in lung homogenate. Further, it showed differential responses on exposure to PG/VG with TDN salts and PG/VG with TFN salts since PG/VG with TDN salts did not alter the cytokine levels in lung homogenate while PG/VG with TFN salts resulted in an increase in KC levels. PG/VG with TDN salts increased the levels of MMP9 protein abundance in female exposed mice, while PG/VG with TFN salts did not alter MMP9 levels in female mice. The metabolism of nicotine or the clearance of cotinine from TFN may differ from the metabolism of nicotine or the clearance of cotinine from TDN. Thus exposure of humectants alone to induce an inflammatory response while PG/VG with TFN salts and PG/VG with TDN salts may differentially alter inflammatory responses and lung proteases in acute exposures. These data suggest the harmful effects of synthetic/natural nicotine and PG/VG and potential toxicological risk for users.

Long-term e-cigarette aerosol exposure causes pulmonary emphysema in adult female and male mice

This study aimed to evaluate long-term exposure to conventional cigarette smoke (CC) and electronic cigarette (EC) aerosol in adult male and female C57BL/6 mice. Forty-eight C57BL/6 mice were used, male (n = 24) and female (n = 24), both were divided into three groups: control, CC and EC. The CC and EC groups were exposed to cigarette smoke or electronic cigarette aerosol, respectively, 3 times a day for 60 consecutive days. Afterwards, they were maintained for 60 days without exposure to cigarettes or electronic cigarette aerosol. Both cigarettes promoted an influx of inflammatory cells to the lung in males and females. All animals exposed to CC and EC showed an increase in lipid peroxidation and protein oxidation. There was an increase of IL-6 in males and females exposed to EC. The IL-13 levels were higher in the females exposed to EC and CC. Both sexes exposed to EC and CC presented tissue damage characterized by septal destruction and increased alveolar spaces compared to control. Our results demonstrated that exposure to CC and EC induced pulmonary emphysema in both sexes, and females seem to be more susceptible to EC.

Pulmonary immune response regulation, genotoxicity, and metabolic reprogramming by menthol- and tobacco-flavored e-cigarette exposures in mice

Menthol and tobacco flavors are available for almost all tobacco products, including electronic cigarettes (e-cigs). These flavors are a mixture of chemicals with overlapping constituents. There are no comparative toxicity studies of these flavors produced by different manufacturers. We hypothesized that acute exposure to menthol and tobacco-flavored e-cig aerosols induces inflammatory, genotoxicity, and metabolic responses in mouse lungs. We compared two brands, A and B, of e-cig flavors (PG/VG, menthol, and tobacco) with and without nicotine for their inflammatory response, genotoxic markers, and altered genes and proteins in the context of metabolism by exposing mouse strains, C57BL/6J (Th1-mediated) and BALB/cJ (Th2-mediated). Brand A nicotine-free menthol exposure caused increased neutrophils and differential T-lymphocyte influx in bronchoalveolar lavage fluid and induced significant immunosuppression, while brand A tobacco with nicotine elicited an allergic inflammatory response with increased Eotaxin, IL-6, and RANTES levels. Brand B elicited a similar inflammatory response in menthol flavor exposure. Upon e-cig exposure, genotoxicity markers significantly increased in lung tissue. These inflammatory and genotoxicity responses were associated with altered NLRP3 inflammasome and TRPA1 induction by menthol flavor. Nicotine decreased surfactant protein D and increased PAI-1 by menthol and tobacco flavors, respectively. Integration of inflammatory and metabolic pathway gene expression analysis showed immunometabolic regulation in T cells via PI3K/Akt/p70S6k-mTOR axis associated with suppressed immunity/allergic immune response. Overall, this study showed the comparative toxicity of flavored e-cig aerosols, unraveling potential signaling pathways of nicotine and flavor-mediated pulmonary toxicological responses, and emphasized the need for standardized toxicity testing for appropriate premarket authorization of e-cigarette 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.

Chronic low-level JUUL aerosol exposure causes pulmonary immunologic, transcriptomic, and proteomic changes

E-cigarettes currently divide public opinion, with some considering them a useful tool for smoking cessation and while others are concerned with potentially adverse health consequences. However, it may take decades to fully understand the effects of e-cigarette use in humans given their relative newness on the market. This highlights the need for comprehensive preclinical studies investigating the effects of e-cigarette exposure on health outcomes. Here, we investigated the impact of chronic, low-level JUUL aerosol exposure on multiple lung outcomes. JUUL is a brand of e-cigarettes popular with youth and young adults. To replicate human exposures, 8- to 12-week-old male and female C57BL/6J mice were exposed to commercially available JUUL products (containing 59 mg/ml nicotine). Mice were exposed to room air, PG/VG, or JUUL daily for 4 weeks. After the exposure period, inflammatory markers were assessed via qRT-PCR, multiplex cytokine assays, and differential cell count. Proteomic and transcriptomic analyses were also performed on samples isolated from the lavage of the lungs; this included unbiased analysis of proteins contained within extracellular vesicles (EVs). Mice exposed to JUUL aerosols for 4 weeks had significantly increased neutrophil and lymphocyte populations in the BAL and some changes in cytokine mRNA expression. However, BAL cytokines did not change. Proteomic and transcriptomic analysis revealed significant changes in numerous biological pathways including neutrophil degranulation, PPAR signaling, and xenobiotic metabolism. Thus, e-cigarettes are not inert and can cause significant cellular and molecular changes in the lungs.

Advantages and Disadvantages of Electronic Cigarettes

Despite nearly nine thousand publications on e-cigarettes (EC) in the PubMed database, there is still no consensus in the scientific community and among decision makers regarding the risks and benefits of using these products [...].