Flavored e-cigarette liquids and cinnamaldehyde impair respiratory innate immune cell function

Abstract

Innate immune cells of the respiratory tract are the first line of defense against pathogenic and environmental insults. Failure of these cells to perform their immune functions leaves the host susceptible to infection and may contribute to impaired resolution of inflammation. While combustible tobacco cigarettes have been shown to suppress respiratory immune cell function, the effects of flavored electronic cigarette liquids (e-liquids) and individual flavoring agents on respiratory immune cell responses are unknown. We investigated the effects of seven flavored nicotine-free e-liquids on primary human alveolar macrophages, neutrophils, and natural killer (NK) cells. Cells were challenged with a range of e-liquid dilutions and assayed for their functional responses to pathogenic stimuli. End points included phagocytic capacity (neutrophils and macrophages), neutrophil extracellular trap formation, proinflammatory cytokine production, and cell-mediated cytotoxic response (NK cells). E-liquids were then analyzed via mass spectrometry to identify individual flavoring components. Three cinnamaldehyde-containing e-liquids exhibited dose-dependent broadly immunosuppressive effects. Quantitative mass spectrometry was used to determine concentrations of cinnamaldehyde in each of the three e-liquids, and cells were subsequently challenged with a range of cinnamaldehyde concentrations. Cinnamaldehyde alone recapitulated the impaired function observed with e-liquid exposures, and cinnamaldehyde-induced suppression of macrophage phagocytosis was reversed by addition of the small-molecule reducing agent 1,4-dithiothreitol. We conclude that cinnamaldehyde has the potential to impair respiratory immune cell function, illustrating an immediate need for further toxicological evaluation of chemical flavoring agents to inform regulation governing their use in e-liquid formulations.

Electronic Cigarettes: Their Constituents and Potential Links to Asthma

“…However, the broad and unregulated use of flavoring agents may also present more immediate health concerns. Toxicological data on inhalational exposures of flavoring chemicals is extremely limited and recent studies have noted high concentrations of flavoring chemicals in e-liquids and e-cig aerosols [68, 69]. Furthermore, there is precedent for food-safe flavoring chemicals causing irreversible lung disease.…”

A Comparison of Flavorless Electronic Cigarette-Generated Aerosol and Conventional Cigarette Smoke on the Planktonic Growth of Common Oral Commensal Streptococci

“…While usage of ECIGs do not necessarily eliminate dependence of nicotine, it does eliminate the intake of many hazardous constituents inherent in cigarette smoke [38,39]. In contrast, E-liquids are comprised of only a few ingredients (i.e., propylene glycol (PG) or vegetable glycerin (VG) ± nicotine and flavorings), of which the myriad of available flavors [40] appear to provide most of the detriment to the ECIG user [41][42][43][44][45] when inhaled. Regardless of the apparent "harm reduction" provided by ECIGs, more research is needed to determine additional health related risks [34], especially since it is known that vaporization of E-liquid can induce chemical alterations yielding substances (such as carbonyl emissions) that could potentially cause lung injury [46,47].…”

Immunological and pathological effects of electronic cigarettes

“…Aerosolized E‐liquids had similar toxicity profiles to neat E‐liquids. Sini‐cide and kola‐flavoured E‐liquid altered phagocytic ability and cytokine production in alveolar macrophages . Moreover, hot cinnamon candies, banana pudding, menthol tobacco and sini‐cide affected phagocytosis of human airway neutrophils in comparison with PG/VG mixture.…”

“…Sini-cide and kola-flavoured E-liquid altered phagocytic ability and cytokine production in alveolar macrophages. 94 Moreover, hot cinnamon candies, banana pudding, menthol tobacco and sini-cide affected phagocytosis of human airway neutrophils in comparison with PG/VG mixture. Kola and sini-cide also altered formation of neutrophil extracellular traps (NETs), which contain chromatin filaments and granule protein to expel extracellular pathogens, and killing reduced the efficiency of NK cells.…”