Vaping Solvents Cause Inflammatory Lung Changes in Healthy Never-Smokers

By Will Boggs MD

November 27, 2019

NEW YORK (Reuters Health) - Two constituents of electronic-cigarette liquids, propylene glycol (PG) and vegetable glycerine (VG), appear to cause inflammatory changes in the lungs of healthy never-smokers, researchers report.

"For those persons who insist on using e-cigs for quitting (versus other known ways), they should realize that while e-cigs may be safer than smoking (which is not tested by this study), safer is not the same as safe, and this study begins to look at how unsafe they may be," Dr. Peter G. Shields of The Ohio State University and James Cancer Hospital, in Columbus, told Reuters Health by email.

PG and VG, solvent carriers for flavors and nicotine in e-cigarette liquids, are generally regarded as safe by the U.S. Food and Drug Administration (FDA) when used in food and cosmetics. What effect they might have when heated and inhaled from e-cigarettes is unknown.

Dr. Shields's team conducted a pilot clinical trial of 30 healthy never-smokers aged 21 to 30 years. Those randomized to e-cigarette use were provided with e-liquids containing 50% PG and 50% VG with no flavor or nicotine and instructed to use the device at least twice daily for four weeks.

At follow-up, there were no significant differences between the e-cigarette and non-use control groups in bronchoalveolar lavage (BAL) cell counts or cytokine levels, the researchers report in Cancer Prevention Research, online October 16.

In the e-cigarette group, however, changes in urinary PG level (a marker of compliance) were positively associated with changes in total BAL cell concentrations and lymphocyte counts and borderline associated with macrophage counts.

Similarly, in this group, changes in urinary PG were significantly correlated with changes in interleukin 8 (IL-8), IL-13 and TNF-alpha.

Gene expression from lung epithelial cells brushings did not change from baseline in either group, and there were no differences between the groups at either point.

"The work provides direct evidence for a role for e-cigs in promoting lung inflammation, which are important pathways for lung cancer and respiratory disease," Dr. Shields said. "However, the lung-injury cases are probably not what is used in conventional e-cig devices. These are separate issues, and we are studying about mechanisms for toxicity from long-term e-cig use."

"This study sets a baseline because use was short and we did not use nicotine or flavors," he said. "So conventional e-cig use may promote much more inflammation."

"Future studies are needed to better understand the clinical significance for the magnitude of the effect by PG and VG, varying ratios of the two and longer duration of use as well as effects of flavors," the researchers note.


Cancer Prev Res 2019.