Researchers have found that using e-cigarettes with the e-liquid refills containing propylene glycol (PG) and vegetable glycerine (VG) may lead to inflammation of the lungs over a period of time. The results of the study titled, “Effects of Electronic Cigarette Constituents on the Human Lung: A Pilot Clinical Trial,” was published in the latest issue of the journal Cancer Prevention Research this week.
E-cigarette use may lead to lung inflammation finds study - Image Credit: DedMityay / Shutterstock
The team of researchers, in the pilot clinical trial have found that those who smoked e-cigarettes twice a day for just a month had higher levels of chemicals such as propylene glycol in their blood. This was associated with inflammatory changes in their lungs. The count of the inflammatory cells in their lungs rises over time, speculate the researchers. However, they agree that this was a small study of a short duration and the magnitude of the changes noted in the lungs were small.
This study is a follow up on a recent report of cases of lung injuries associated with vaping across United States. There has been speculation about the amount of damage being caused by vaping. The researchers planned on quantifying the changes in the lungs after use of e-cigarettes, they explained.
The US Centers for Disease Control and Prevention (CDC) states that among those who have experienced lung injuries with vaping, “most patients report a history of using tetrahydrocannabinol (THC)-containing products.” The CDC adds, “Exclusive use of nicotine containing products has been reported by some patients with lung injury cases, and many patients with lung injury report combined use of THC- and nicotine-containing products.”
This was the first “experimental design” study that showed the damage caused by e-cigarettes say the researchers. Lead author Dr. Peter Shields, a medical oncologist at the Ohio State University Comprehensive Cancer Center in Columbus said, “Obviously inhaling stuff is going to have some impact on the lungs. This is another piece of information.” He added, “I would not make the conclusion that this shows that e-cigs are harmful to your health, but one piece of evidence for that. I would say that we have choices in the world and it makes sense that if you're not a smoker, you shouldn't start using e-cigs.”
Min-Ae Song, first author of the manuscript and environmental health researcher at the Ohio State College of Public Health, said in a statement, “Human clinical trials can provide valuable information regarding actual toxicant exposure and risk for disease. Through the randomized clinical trial of healthy never-smokers over a month, we found that an increase in urinary propylene glycol, a marker of inhalation-e-cig intake, was significantly correlated with increased inflammatory response in the lung.”
Shields said, “But it is still unknown what role, if any, nicotine containing e-cigs are involved in the patients with severe respiratory illness. In that context, a lot of us are really looking hard for what might be unique to e-cigs that we wouldn't see in traditional smokers.” For this study the team looked at two constituents of the e-cigarettes refills - propylene glycol and vegetable glycerine. These are used as vehicles to carry nicotine and the flavours of the e-fluids.
For this study the team included 30 youths aged between 21 and 30 years between 2015 and 2017. They did not have a history of traditional smoking or e-cigarettes. The participants were divided into two groups – one of the groups was a control group while the other was asked to use e-cigarettes at least twice a day taking 20 puffs during an hour at one time. To measure the puff count, the refills given to the users had LED screens with a puff counter. The e-cigarette refills used contained 50% propylene glycol (PG) and 50% vegetable glycerine (VG) and no nicotine or flavours. The study duration was for one month.
For all the participants, a bronchoscopy was performed at the start of the study and again five weeks after. The lung tissues, bronchi and the lung health were recorded at these sessions. The team wrote, “Inflammatory cell counts and cytokines were determined in bronchoalveolar lavage (BAL) fluids. Genome-wide expression, microRNA, and mRNA were determined from bronchial epithelial cells.”
Results revealed that there was no significant difference in levels of inflammatory cells among the e-cigarette users and the control group. The levels of inflammatory cells and proteins in the adult lungs were slightly raised however among those who used higher amounts of propylene glycol. The levels of propylene glycol could be measured from the urine samples of the participants. This helped the team analyze the extent of use of this chemical. Shields explained, “So people with higher changes in levels actually inhaled more, and when you look at that, you see an increase in inflammation.”
Shields said that the question now was how much inflammation was too much. He said, “Given that these people were no different than the control group, what it says is that we measured an increase but they were still within the normal range.”
The team of researchers agree that this was a small study with few participants and for only a month. Thus no strong associations could be made between e-cigarette use and lung inflammation. They also write that since nicotine or flavours were absent from the refills, the damage caused by these components is also not assessed in this study. Shields said that, “we have direct evidence for inflammation from an important part of e-liquids,” and this means that if they could look at longer use with e-cigarettes containing nicotine and flavours, they could come up with more concrete results. Song added, “Future studies could be of longer duration, include an assessment of flavors, the effect by varying ratios of propylene glycol and vegetable glycerine, and examine randomization of smokers to e-cigs.”
Authors wrote in conclusion, “The data from this study provide direct safety information regarding the e-cig solvent carriers, PG and VG... 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.”
Effects of Electronic Cigarette Constituents on the Human Lung: A Pilot Clinical Trial Min-Ae Song, Sarah A. Reisinger, Jo L. Freudenheim, Theodore M. Brasky, Ewy A. Mathé, Joseph P McElroy, Quentin A Nickerson, Daniel Y Weng, Mark D. Wewers and Peter G. Shields, Cancer Prev Res, DOI: 10.1158/1940-6207.CAPR-19-0400, https://cancerpreventionresearch.aacrjournals.org/content/early/2019/10/11/1940-6207.CAPR-19-0400