Electronic Cigarettes: Their Constituents and Potential Links to Asthma

Abstract

Purpose of Review Vaping is gaining popularity in the USA, particularly among teens and young adults. While e-cigs are commonly represented as safer alternatives to tobacco cigarettes, little is known regarding the health effects of their short- or long-term use, especially in individuals with pre-existing respiratory diseases such as asthma. Flavored e-cig liquids (e-liquids) and e-cig aerosols contain airway irritants and toxicants that have been implicated in the pathogenesis and worsening of lung diseases. In this review, we will summarize existing data on potential health effects of components present in e-cig aerosols, such as propylene glycol, vegetable glycerin, nicotine, and flavorings, and discuss their relevance in the context of asthma. Recent Findings Recent survey data indicate that adolescents with asthma had a higher prevalence of current e-cig use (12.4%) compared to their non-asthmatics peers (10.2%) and conveyed positive beliefs about tobacco products, especially e-cigs. Similarly, a study conducted among high school students from Ontario, Canada, indicated a greater likelihood of e-cig use in asthmatics as compared to their non-asthmatic peers. Availability of different flavorings is often cited as the main reason among youth/adolescents for trying e-cigs or switching from cigarettes to e-cigs. Occupational inhalation of some common food-safe flavoring agents is reported to cause occupational asthma and worsen asthmatic symptoms. Moreover, workplace inhalation exposures to the flavoring agent diacetyl have caused irreversible obstructive airway disease in healthy workers. Additionally, recent studies report that thermal decomposition of propylene glycol (PG) and vegetable glycerin (VG), the base constituents of e-liquids, produces reactive carbonyls, including acrolein, formaldehyde, and acetaldehyde, which have known respiratory toxicities. Furthermore, recent nicotine studies in rodents reveal that prenatal nicotine exposures lead to epigenetic reprogramming in the offspring, abnormal lung development, and multigenerational transmission of asthmatic-like symptoms. Summary Comparisons of the toxicity and health effects of e-cigs and conventional cigarettes often focus on toxicants known to be present in cigarette smoke (CS) (i.e., formaldehyde, nitrosamines, etc.), as well as smoking-associated clinical endpoints, such as cancer, bronchitis, and chronic obstructive pulmonary disease (COPD). However, this approach disregards potential toxicity of components unique to flavored e-cigs, such as PG, VG, and the many different flavoring chemicals, which likely induce respiratory effects not usually observed in cigarette smokers.

Environmental exposures and mechanisms in allergy and asthma development

“…Evidence indicates that e-cigarette vapor can produce oxidative stress and inflammation in airways and may exacerbate or induce rhinitis, asthma, eczema, and allergic symptoms (173). Epidemiologic investigations found increased e-cigarette use among asthmatics (174,175) and associations between e-cigarette use and increased asthma (176) and asthma attack (175) prevalence. Exposure to nicotine-containing e-liquid in "asthmatic" mice increased airway eosinophils, Th2 cytokines, and AHR (172,177).…”

“…Exposure to nicotine-containing e-liquid in "asthmatic" mice increased airway eosinophils, Th2 cytokines, and AHR (172,177). The toxicity of components unique to e-cigarettes likely induces unique respiratory and possibly allergic effects and warrants further investigation (172,174).…”

Pulmonary toxicity and inflammatory response of e-cigarettes containing medium-chain triglyceride oil and vitamin E acetate: Implications in the pathogenesis of EVALI but independent of SARS-COV-2 COVID-19 related proteins

“…These animal studies suggest that in our murine model, exposure to VEA and cartridges has promoted allergic asthmarelated in ammation-causing lung injury, especially in VEA exposed mice. However, it may be possible that these lower LTC4 levels seen in the cartridge exposed group may be confounded by the presence of nicotine as nicotine has LTC4 suppressive effects [53,54].…”

Electronic Cigarettes and Cardiovascular Risk: Caution Waiting for Evidence

“…[49][50][51] This association was documented in two independent surveys carried out among teenage electronic cigarette users with a risk of bronchitis symptoms directly related to the frequency of electronic cigarette usage. 46,52,53 Detrimental acute effects of electronic cigarettes inhalation were demonstrated in a study conducted by Antoniewicz et al among 17 healthy individuals, which showed that inhaled electronic cigarette aerosol with nicotine caused a significant increase in heart rate and arterial stiffness, and a sharp increase in flow resistance in the conducting airways. 54 Similarly, acute vaping of propylene glycol/ glycerol aerosol at high wattage with or without nicotine induced significant injury to airway epithelium and impaired pulmonary gas exchange.…”