Inflammatory and Oxidative Responses Induced by Exposure to Commonly Used e-Cigarette Flavoring Chemicals and Flavored e-Liquids without Nicotine

Abstract

Background: The respiratory health effects of inhalation exposure to e-cigarette flavoring chemicals are not well understood. We focused our study on the immuno-toxicological and the oxidative stress effects by these e-cigarette flavoring chemicals on two types of human monocytic cell lines, Mono Mac 6 (MM6) and U937. The potential to cause oxidative stress by these flavoring chemicals was assessed by measuring the production of reactive oxygen species (ROS). We hypothesized that the flavoring chemicals used in e-juices/e-liquids induce an inflammatory response, cellular toxicity, and ROS production.Methods: Two monocytic cell types, MM6 and U937 were exposed to commonly used e-cigarette flavoring chemicals; diacetyl, cinnamaldehyde, acetoin, pentanedione, o-vanillin, maltol and coumarin at different doses between 10 and 1,000 μM. Cell viability and the concentrations of the secreted inflammatory cytokine interleukin 8 (IL-8) were measured in the conditioned media. Cell-free ROS produced by these commonly used flavoring chemicals were also measured using a 2′,7′dichlorofluorescein diacetate probe. These DCF fluorescence data were expressed as hydrogen peroxide (H2O2) equivalents. Cytotoxicity due to the exposure to selected e-liquids was assessed by cell viability and the IL-8 inflammatory cytokine response in the conditioned media.Results: Treatment of the cells with flavoring chemicals and flavored e-liquid without nicotine caused cytotoxicity dose-dependently. The exposed monocytic cells secreted interleukin 8 (IL-8) chemokine in a dose-dependent manner compared to the unexposed cell groups depicting a biologically significant inflammatory response. The measurement of cell-free ROS by the flavoring chemicals and e-liquids showed significantly increased levels of H2O2 equivalents in a dose-dependent manner compared to the control reagents. Mixing a variety of flavors resulted in greater cytotoxicity and cell-free ROS levels compared to the treatments with individual flavors, suggesting that mixing of multiple flavors of e-liquids are more harmful to the users.Conclusions: Our data suggest that the flavorings used in e-juices can trigger an inflammatory response in monocytes, mediated by ROS production, providing insights into potential pulmonary toxicity and tissue damage in e-cigarette users.

Nicotine and electronic cigarette (E‐Cig) exposure decreases brain glucose utilization in ischemic stroke

“…A recent study demonstrated inflammatory and oxidative responses in human monocytic cell lines by commonly used e‐Cig flavors and flavored e‐liquids without nicotine (Muthumalage et al . ). The toxic effects of different e‐Cig flavoring agents have been discussed by Kaur et al .…”

Prenatal electronic cigarette exposure decreases brain glucose utilization and worsens outcome in offspring hypoxic–ischemic brain injury

“…Electronic cigarette use is a crucial public health issue because of its perceived safety, widespread popularity, and insufficient data to test health outcomes. There have been reports of adverse health effects of e‐Cig use including enhanced carcinogenic potential (Lee et al, ), oxidative stress and inflammatory activity (Muthumalage et al, ), as well as altered BBB permeability and worsened ischemic brain injury (Kaisar, Villalba, et al, ). We have previously published that e‐Cig exposure can also decrease brain glucose utilization in ischemic stroke (Sifat et al, ).…”

Immunological and pathological effects of electronic cigarettes

“…These three flavourings all contained cinnamaldehyde, which, on its own, showed similar effects, suggesting the potentials of cinnamaldehyde for impairing respiratory immune cell function. Another study also pointed out the deleterious effects of cinnamaldehyde: both flavouring chemicals and flavoured E‐liquid without nicotine‐reduced cell viability and IL‐8 secretion of monocytic cell lines dose‐dependently, with cinnamaldehyde showing the highest cytotoxicity . Flavouring chemicals and seven types of aerosolized E‐liquids including American tobacco, café latte and cinnamon roll induced cell‐free ROS production .…”

“…Another study also pointed out the deleterious effects of cinnamaldehyde: both flavouring chemicals and flavoured E-liquid without nicotine-reduced cell viability and IL-8 secretion of monocytic cell lines dose-dependently, with cinnamaldehyde showing the highest cytotoxicity. 95 Flavouring chemicals and seven types of aerosolized E-liquids including American tobacco, café latte and cinnamon roll induced cell-free ROS production. 95 Interestingly, mixing a variety of flavours induced higher cytotoxicity and cell-free ROS levels compared to individual flavours.…”

“…95 Flavouring chemicals and seven types of aerosolized E-liquids including American tobacco, café latte and cinnamon roll induced cell-free ROS production. 95 Interestingly, mixing a variety of flavours induced higher cytotoxicity and cell-free ROS levels compared to individual flavours. This might give a warning of greater toxic effects to those users who mix E-liquids or those who are exposed to multiple flavourings in public areas.…”