Immunological and pathological effects of electronic cigarettes

Chronic airway inflammatory diseases and e-cigarette use: a review of health risks and mechanisms

Chronic airway inflammatory diseases, which primarily include chronic obstructive pulmonary disease (COPD), asthma, allergic rhinitis, and chronic sinusitis, continue to have a high global prevalence, highlighting their significant public health impact. Concurrently, the use of e-cigarettes (tobacco e-cigarettes) has been rising worldwide, with many users perceiving them as a safer alternative to traditional cigarettes. However, accumulating evidence from international studies suggests that e-cigarettes pose substantial health risks. This review aims to explore recent research on the relationship between e-cigarette use and chronic airway inflammatory diseases. The findings indicate that e-cigarette usage increases the risk of developing these conditions. Specifically, studies have shown that e-cigarettes exacerbate airway inflammatory responses, elevate levels of type 2 inflammatory cytokines such as IL-4, IL-5, and IL-13, increase cellular oxidative stress, and impair lung function. These mechanisms may collectively contribute to an increased risk of chronic airway inflammatory diseases potentially associated with e-cigarette use.

The impact of electronic cigarette use on chronic obstructive pulmonary disease: A systematic review and meta-analysis

OBJECTIVES

Electronic cigarette (or e-cigarette) use is increasing globally. To date, there are limited pooled estimates regarding the impact of e-cigarette use on chronic obstructive pulmonary disease (COPD). The present meta-analysis of large-scale population-based observational studies evaluates the impact of e-cigarette use on COPD.

METHODS

A systematic search of observational studies published between 1/2020-1/2024 was conducted in MEDLINE and Scopus based on PRISMA Guidelines.

RESULTS

Of 3670 originally retrieved papers, 7 observational studies (including 4 cross-sectional studies and 3 prospective cohort studies) fulfilled all search criteria and were used for the present meta-analysis which encompassed in total, 3,552,424 participants, including 138,698 cases with COPD. The findings from the random-effects meta-analysis (I2 = 22 %, Cochran Q (6) = 7.19, p = 0.307) suggested that use of e-cigarette among non-cigarette users was associated with (pooled Relative Risk, pRR) 1.50-times higher likelihood of COPD (95 % Confidence Interval (CI): 1.27, 1.73). Sensitivity analysis by leave-one-out analysis confirmed the aforementioned results (range of pRR values: 1.46 to 1.61, all p < 0.001). Stratified pooled effect estimates of cross-sectional studies only (pOR = 1.55, 95 % CI: 1.26, 1.84) and of prospective cohort studies only (pRR = 1.52, 95 % CI: 0.98-2.06), revealed that the e-cigarette users exhibit between 52 % and 55 % significantly higher likelihood of COPD.

CONCLUSIONS

The current meta-analysis highlights that e-cigarette users face an increased risk of developing COPD. Therefore, public health interventions aimed at diminishing e-cigarette are necessary for preventing COPD.

Electronic cigarette vapor exposure exaggerates the pro-inflammatory response during influenza A viral infection in human distal airway epithelium

Electronic cigarettes or vaping products have been marketed as a safer alternative to smoking, but very little is known about the health effects in the human lung, particularly in the distal airways, a key site of airway obstruction and destruction in chronic obstructive pulmonary disease that is often exacerbated by viral infections. The aim of this study was to investigate the effects of electronic cigarette vapor (e-vapor) on human distal airway epithelial responses to influenza A virus (IAV) infection. We isolated primary small airway epithelial cells (SAECs) from donor lungs free of lung disease, and cultured them at air-liquid interface (ALI). To measure markers of epithelial injury such as integrity of epithelial barrier structure and function, we selected a regimen of non-toxic, barrier preserving e-vapor exposure of cultured cells to 15 puffs of e-vapor from a commercially available e-cigarette once per day for 3 days, prior to IAV infection. After 72 h of infection, media and cell lysates were collected to measure cytokines involved in inflammatory and antiviral responses. Pre-exposure to e-vapor with IAV infection, compared to IAV infection alone, significantly increased inflammatory and antiviral mediators including IL-8, CXCL10, IFN-beta, and MX1. Our results suggest that e-vapor exposure amplifies human distal airway pro-inflammatory response to IAV infection, independently of the severity of cell injury during viral infection.

Cell invasion, RAGE expression, and inflammation in oral squamous cell carcinoma (OSCC) cells exposed to e-cigarette flavoring

Objective

Electronic cigarettes have given rise to a new, largely unregulated market within the smoking industry. While generally supposed to be less harmful than traditional tobacco smoke, awareness of the biological effects of electronic cigarette liquid is still scarce. Our objective was to determine the impact of electronic cigarette flavoring and nicotine on gingival squamous cell carcinoma invasion, RAGE expression, and the elaboration of pro‐inflammatory molecules.

Methods and Materials

Gingival and tongue squamous cell carcinoma cells were exposed to Red Hot or Green Apple flavored electronic cigarette flavoring with or without nicotine. Immunofluorescence determined RAGE expression. Real‐time cellular invasion was assessed using a RTCA DP instrument. Culture medium was assayed for cytokine secretion.

Results

Compared to controls we observed: increased cell invasion in gingival cells with Red Hot electronic cigarette flavoring and decreased cell invasion with Green Apple; decreased cell invasion in tongue cells treated with Red Hot electronic cigarette flavoring and no differences in invasion with Green Apple; flavor and nicotine dependent increases in RAGE expression; and differential expression of IL‐1α, IL‐8, and MMP‐13.

Conclusion

We conclude that electronic cigarette flavoring and nicotine orchestrate differential regulation of oral squamous cell carcinoma (OSCC) cell invasion and inflammatory effects. This study provides an important initial step in dissecting RAGE‐mediated mechanisms of cancerous invasion and molecular avenues employed by OSCC.

Effect of sub-chronic exposure to cigarette smoke, electronic cigarette and waterpipe on human lung epithelial barrier function

BACKGROUND

Taking into consideration a recent surge of a lung injury condition associated with electronic cigarette use, we devised an in vitro model of sub-chronic exposure of human bronchial epithelial cells (HBECs) in air-liquid interface, to determine deterioration of epithelial cell barrier from sub-chronic exposure to cigarette smoke (CS), e-cigarette aerosol (EC), and tobacco waterpipe exposures (TW).

METHODS

Products analyzed include commercially available e-liquid, with 0% or 1.2% concentration of nicotine, tobacco blend (shisha), and reference-grade cigarette (3R4F). In one set of experiments, HBECs were exposed to EC (0 and 1.2%), CS or control air for 10 days using 1 cigarette/day. In the second set of experiments, exposure of pseudostratified primary epithelial tissue to TW or control air exposure was performed 1-h/day, every other day, until 3 exposures were performed. After 16-18 h of last exposure, we investigated barrier function/structural integrity of the epithelial monolayer with fluorescein isothiocyanate-dextran flux assay (FITC-Dextran), measurements of trans-electrical epithelial resistance (TEER), assessment of the percentage of moving cilia, cilia beat frequency (CBF), cell motion, and quantification of E-cadherin gene expression by reverse-transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

When compared to air control, CS increased fluorescence (FITC-Dextran assay) by 5.6 times, whereby CS and EC (1.2%) reduced TEER to 49 and 60% respectively. CS and EC (1.2%) exposure reduced CBF to 62 and 59%, and cilia moving to 47 and 52%, respectively, when compared to control air. CS and EC (1.2%) increased cell velocity compared to air control by 2.5 and 2.6 times, respectively. The expression of E-cadherin reduced to 39% of control air levels by CS exposure shows an insight into a plausible molecular mechanism. Altogether, EC (0%) and TW exposures resulted in more moderate decreases in epithelial integrity, while EC (1.2%) substantially decreased airway epithelial barrier function comparable with CS exposure.

CONCLUSIONS

The results support a toxic effect of sub-chronic exposure to EC (1.2%) as evident by disruption of the bronchial epithelial cell barrier integrity, whereas further research is needed to address the molecular mechanism of this observation as well as TW and EC (0%) toxicity in chronic exposures.

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

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

Electronic cigarette vapour moderately stimulates pro-inflammatory signalling pathways and interleukin-6 production by human monocyte-derived dendritic cells

Dendritic cells (DCs) are professional antigen presenting cells that play a critical role in bridging innate and adaptive immunity. Numerous studies have shown that tobacco constituents present in conventional cigarettes affect the phenotype and function of DCs; however, no studies have examined the effects of vapour from E-cigarettes on human DCs. Here, the effects of E-cigarette vapour extract (ECVE) on the phenotype and function of DCs were investigated by creating an in vitro cell culture model using human monocyte-derived DCs (MoDCs). Immature DCs were generated from peripheral blood monocytes and mature DCs were then produced by treatment with LPS or Poly I:C for 24 h. For LPS-matured DCs, 3% ECVE treatment slightly suppressed HLA-DR and CD86 expression, whereas 1% ECVE treatment enhanced IL-6 production. The overall expression of 29 signalling molecules and other cytoplasmic proteins (mainly associated with DC activation) was significantly upregulated in immature DCs by 1% ECVE, and in LPS-treated DCs by 3% ECVE. In particular, the condition that induced IL-6 production also upregulated MAPK pathway activation. These findings indicate that E-cigarette vapour moderately affects human DCs, but the effects are less pronounced than those reported for tobacco smoke.