Which ones are more harmful?
Cigarette smoke turned out to be more harmful than the aerosol of electronic cigarettes for human lung cells
Vyacheslav Gomenyuk, N+1
An aerosol of electronic cigarettes has less harmful effects on the culture of human lung cells than an equivalent dose of cigarette smoke. In the experiment, cigarette smoke increased the frequency of beating cilia and led to the release of pro-inflammatory cytokines, whereas no such changes were observed when exposed to a vaping aerosol.
The study is published in the journal Toxicology Research and Application (Phillips et al., Acute electronic vapour product whole aerosol exposure of 3D human bronchial tissue results in minimal cellular and transcriptomic responses when compared to cigarette smoke).
In 2017, there were about one billion cigarette smokers worldwide. Since it is difficult for many people to quit smoking immediately due to habit and addiction, many medical communities believe that the transition of such people to electronic cigarettes is the best option in the phased therapy of nicotine addiction (however, this strategy does not work without medical support). The World Health Organization, however, states that these devices are harmful to health and unsafe, while noting that "it is still too early to give a clear answer about their long-term effects."
Various studies speak of both positive and negative effects of e-cigarettes compared to conventional cigarettes. Thus, the Royal College of Physicians states that "the health hazard arising from prolonged inhalation of vapors is unlikely to exceed 5 percent of the harm from tobacco smoking." At the same time, there is evidence that glycerin from e-cigarettes provokes the growth of biofilms in the mouth and thus contributes to inflammation, and this is just one of the many negative effects reported by doctors and scientists.
The Imperial Brands PLC research group, led by Gary Phillips, in collaboration with Khalid Amin from the University of Minnesota Medical Center, decided to find out what effects e-cigarette vapor and tobacco smoke have on a three-dimensional culture of lung tissue obtained from a healthy non-smoking European. The MyBlue vaporizer with the following liquid composition was used as a reference for an electronic cigarette: 2.78 percent blueberry flavor; 2.42 percent nicotine, 55.82 percent propylene glycol, 38.98 percent glycerin.
To study the effects of tobacco smoke, reference cigarettes 3R4F with an acetate cellulose filter and a resin yield of 9.4 milligrams were used. A smoking machine was used to inject smoke and aerosol into the system, in which they could be diluted with air. In total, 24 lung tissue samples were used in the experiment, eight in each group – air, an evaporator and a cigarette. The measured values were evaluated four and 48 hours after exposure.
A non-toxic water-soluble tetrazolium salt (WST-8) was used to measure cell viability. When it interacts with enzymes of the respiratory chain of mitochondria of cells, the dye is restored with the formation of formazams (derivatives of formic acid) having an orange color. Cytotoxicity (the degree of harm done to the cell) was determined by measuring adenylate kinase, an enzyme involved in energy metabolism that is released by cells when they are damaged.
The barrier integrity of each tissue was assessed using transepithelial electrical resistance, and the frequency of cilia beats was studied to assess the functional activity of the tissue. In addition, cytokine levels and histological changes were studied.
There was a sigmoidal dose-response relationship between exposure to cigarette smoke and cytotoxicity. There was also a significant (p<0.0001) linear dose-response relationship between cigarette smoke and cell viability.
Adenylate kinase concentration and cell viability depending on the concentration of cigarette smoke. Figures from the article by Phillips et al.
At equivalent deposition levels, there was significantly more nicotine in the cells after 100 puffs of cigarette smoke (p<0.05) than after the same number of puffs of an electronic cigarette. (69.5±4.5 micrograms per milliliter versus 28.9±4.3 micrograms per milliliter).
The barrier integrity of tissues after four and 48 hours from exposure to cigarette smoke was significantly lower than in the air and e-cigarette groups. However, four hours after exposure to e-cigarette aerosol, the values of transepithelial electrical resistance were significantly higher (p<0.005) than in the air group.
After exposure to cigarette smoke, the frequency of beating of the cilia increased significantly after four hours and remained high after 48 hours (p<0.005) compared to the equivalent time of exposure to air and aerosol of electronic cigarettes. There was no significant difference between the aerosol and air groups. Histological examination failed to find any differences between all three groups, that is, no organic disorders were observed in any group.
Histological structure of lung tissue after exposure to air (left), e-cigarette aerosol (center) and cigarette smoke (right) after four and 48 hours.
No significant effect on any of the measured cytokines was observed in any group. However, compared with time-equivalent air controls, exposure to cigarette smoke led to an increase in the concentration of six of the nine cytokines after four hours, and by 48 hours, the levels of all cytokines were higher than the control values. At the same time, there was no significant effect of the e-cigarette aerosol on the concentration of inflammatory cytokines for four hours compared to the equivalent time comparable to air control.
In addition, cigarette smoke activated many pathophysiological processes, including oxidative stress and inflammation, whereas e-cigarette aerosol did not. In general, changes in the gene expression profile of lung cells after exposure to aerosol were insignificant, and after 48 hours they disappeared altogether.
Thus, this study complements the knowledge about the effects of tobacco smoke and e-cigarette aerosol. Of the significant limitations of the study, it should be noted that the experimental lung tissue culture was obtained from one healthy adult European and additional studies are needed with tissue cultures of people from different parts of the world, of different ages and genders.
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