Researchers at the University of Rochester Medical Center, New York, have shown that long-term exposure to certain electronic nicotine delivery systems (ENDS) may cause lung toxicity and injury among vapers.
Thivanka Muthumalage and colleagues found that exposure to substances found in e-cigarette cartridges increased cytotoxicity and inflammation, both in vitro and in mice.
The team says it might be exposure to these same compounds that cause a condition called e-cigarette, or vaping, associated lung injury (EVALI) among people.
A pre-print version of the paper can be accessed in the server bioRxiv*, while the article undergoes peer review.
About ENDS and EVALI
The ENDS contains a tank, pod, or cartridge filled with an e-liquid that contains various substances, including a carrier oil (humectant) such as propylene glycol or vegetable glycerin, nicotine, and flavor enhancers. Upon heating, the humectant emits volatile organic compounds (VOCs), which can generate toxic compounds that lead to lung damage.
More recently, products containing tetrahydrocannabinol (THC) have arrived on the market, and these tend to use a humectant made of mineral oil and medium-chain triglycerides (MCT), rather than propylene glycol or vegetable glycerin.
The use of these ENDS has caused acute lung injury among vapers, and in August 2019, affected patients were classified as having EVALI.
According to the Centers for Disease Control and Prevention, as of February this year, there have been more than 2,800 cases of hospitalization or death associated with EVALI, which causes cough, chest pain, difficulty breathing, and in severe cases, respiratory failure.
All these patients reported using e-cigarettes, and most of them report using THC-containing products.
Suspected culprits in e-liquid
No single substance has yet been identified as responsible for EVALI, but vitamin E acetate (VEA) has been identified in bronchoalveolar lavage fluid (BALF) samples taken from patients. Many studies have subsequently focused on VEA, but research investigating any causative role in EVALI is urgently needed.
Muthumalage and colleagues say that currently, there is little information reporting on the physiological and biological effects of exposure to VEA and MCT.
“We hypothesized that these e-cig cartridges and their constituents (VEA and MCT) induce pulmonary toxicity, mediated by oxidative damage and inflammatory responses, leading to acute lung injury,” writes the team.
What did the study involve?
The researchers assessed the total VOCs present in VEA and MCT, cartridges aerosols, mineral oil, and air. Compared with air, vape cartridges released the most VOCs, followed by MCT, mineral oil, and VEA.
To investigate the potential mechanisms underlying any inflammatory response, the team assessed the production of reactive oxygen species (ROS) by e-cigarette cartridges, MCT and VEA, and the in vitro and in vivo effects on the epithelium and immune cells.
To assess in vitro exposure, cell cultures were exposed to two 70 mL puffs of the aerosols and incubated in the vapor for ten minutes. In vivo exposures were assessed using wild-type mice exposed to two 70 mL puffs per minute for one hour.
What did the researchers find?
Cells exposed to the aerosols generated ROS and showed severe toxicity, as well as significantly increased levels of the inflammatory marker interleukin 6 (IL-6), which is a biomarker for lung injury.
“This indicates that in less than 24 hours, the immune system can be primed towards a pro-inflammatory response,” writes the team.
Two puffs of the aerosols also significantly altered the function of the epithelial barrier.
“Toxicants emitted in these aerosols damage tight junctions between the epithelial cells disrupting the epithelial barrier,” writes the team. “This alteration of the epithelial permeability drives pathogenesis by promoting inflammatory signaling pathways.”
In the mouse model, exposure to the aerosols resulted in the infiltration of neutrophils and CD4 lymphocytes, along with significant increases in IL-6 and granulocyte colony-stimulating factor in BALF.
Exposure to ENDS may cause significant lung damage and EVALI
“This study demonstrates acute exposure to specific e-cig cartridges induce in vitro cytotoxicity, barrier dysfunction, and inflammation and in vivo mouse exposure induces acute inflammation with elevated pro-inflammatory markers,” writes the team. “Overall, this study suggests that prolonged exposure to these ENDS may cause significant lung damage, which is involved in the pathogenesis of EVALI.”
Given the interest currently surrounding coronavirus disease 2019 (COVID-19) and its causative agent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the team also assessed the impact of exposure to these substances on SARS-CoV-2-related proteins. However, no effect on these proteins was observed.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Muthumalage T, et al. 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, bioRxiv 2020.06.14.151381; doi: doi: https://doi.org/10.1101/2020.06.14.151381