The fact that many e-cigarette users are former or current cigarette smokers (dual users) complicates understanding the health effects of e-cigarette use. Stella Tommasi, Ahmad Besaratinia and their colleagues at USC have used sophisticated genomic analysis of white blood cells (leukocytes) collected from people to pry these effects apart.
In their paper, “A novel role for vaping in mitochondrial gene dysregulation and inflammation fundamental to disease development,” they report adverse effects of e-cigarette use on genes that control mitochondria – the cell’s energy factory – as well as those related to inflammation independent of the effects of prior cigarette smoking .
Specifically, they investigated, at the molecular and subcellular level, the effects of vaping in people who were regular users of e-cigs. In addition, they studied the impact of past smoking in vapers because the vast majority of current vapers either have smoked in the past, or vaped and smoke simultaneously (i.e., dual users).
To investigate the biological effects of vaping in adult e-cig users, while simultaneously accounting for their ‘past’ smoking exposure they recruited healthy adult volunteers and divided them into three groups:
- Current vapers, with and without a prior history of smoking
- Exclusive cigarette smokers
- A control group of never-smokers and never-vapers.
They interviewed each participant individually to get a comprehensive and detailed record of their vaping/smoking history (how long they’ve smoked/vaped, how many cigarettes or e-cigs they’ve smoked/vaped), then verified the participants vaping/smoking histories by performing biochemical analyses on their blood plasma to measure the concentration of cotinine, a breakdown product of nicotine.
Then, they used next generation sequencing and bioinformatic data analysis to search for changes in gene regulation in the blood cells of each of the participants.
They found more adverse effects on genes due to smoking cigarettes with some overlap with the effects of vaping, but many of the vaping effects were not observed among smokers (see graph above, from Figure 1C of the paper). This is an important finding because it adds to the case that e-cigarettes do not simply have a subset of the effects smoking, but also pose different and unique risks.
The finding that cigarette smokers had more adverse changes than e-cigarette users needs to be interpreted cautiously. Among the people in the study, smokers had smoked cigarettes for an average of 21 years, whereas vapers had only used e-cigs for 3 years (Table 2 of the paper). So, it’s not surprising to see more pronounced adverse effects in smokers than vapers (simply based on dose [duration & intensity] of smoking/vaping). The fact that the smokers were exposing themselves for much longer than the vapers likely contribute to some of the differences in the number of affected genes. Indeed, the study replicates the real-life situation in which vapers, using a relatively newer tobacco product, and smokers, who have used combustible cigarettes (a product that has been in the market for years), both show adverse biological effects.
A normal and balanced regulation of genes is required for health state, whereas dysregulated genes, depending on their functions, can cause different diseases.
That is why we need to stop just thinking about the diseases that cigarettes cause when assessing e-cigarettes.
Here is the USC press release on the study:
Vaping – not prior smoking – is associated with changes in gene regulation linked to disease
November 23, 2021
The latest vaping study from Keck School of Medicine of USC shows that, like smoking, use of e-cigarettes is linked to dysregulation of mitochondrial genes and immune response genes.
Since they hit the market, e-cigarettes have been touted as a safe alternative to tobacco cigarettes for adult smokers. When research began to suggest otherwise, many questioned whether smoking was still to blame for adverse effects, since most vapers are either “dual users” who also smoke cigarettes or have a prior history of smoking.
Now, a team of researchers at the Keck School of Medicine of USC has demonstrated that – independent of the effects of prior smoking – using e-cigarettes is linked to adverse biological changes that can cause disease. The study, published in Scientific Reports, revealed that vapers experience a similar pattern of changes to gene regulation as smokers do, although the changes are more extensive in people who smoke.
“Our study, for the first time, investigates the biological effects of vaping in adult e-cigarette users, while simultaneously accounting for their past smoking exposure,” said Ahmad Besaratinia, PhD, corresponding author and professor of research population and public health sciences at the Keck School of Medicine. “Our data indicate that vaping, much like smoking, is associated with dysregulation of mitochondrial genes and disruption of molecular pathways involved in immunity and the inflammatory response, which govern health versus disease state.”
Isolating the effects of vaping from smoking
The researchers recruited a diverse group of 82 healthy adults and separated them into three categories: current vapers, with and without a prior history of smoking; people who exclusively smoke cigarettes; and a control group of never-smokers and never-vapers. They conducted comprehensive in-person interviews to get a detailed vaping and smoking history from each participant. The team verified the histories by performing biochemical analyses on the participants’ blood to measure the concentration of cotinine, a breakdown product of nicotine.
Using next generation sequencing and bioinformatic data analysis, researchers then conducted a genome-wide search for changes in gene regulation in the blood cells of each of the participants. When the normal regulation of genes is disrupted and genes become dysregulated, that dysregulation can interfere with gene function, leading to disease.
For current vapers, they further performed computational modeling to determine whether the detected gene dysregulation was associated with the intensity and duration of their current vaping or the intensity and duration of their past smoking.
“We found that more than 80% of gene dysregulation in vapers correlated with the intensity and duration of current vaping,” said Besaratinia. “Whereas none of the detected gene dysregulation in vapers correlated to their prior smoking intensity or duration.”
Effects of vaping mirror those of smoking
In previous research, Besaratinia and his team have shown that e-cigarette users develop some of the same cancer-related molecular changes in oral tissue as cigarette smokers. They also discovered vapers had the same kind of cancer-linked chemical changes to their genome as smokers.
In this study, they found that, in both vapers and smokers, mitochondrial genes are preferential targets of gene dysregulation. They also found that vapers and smokers had significant dysregulation of immune response genes.
Besaratinia says the findings are not only novel and significant, but they are also interrelated, since growing evidence shows that mitochondria play a critical role in immunity and inflammation.
“When mitochondria become dysfunctional, they release key molecules,” said Besaratinia. “The released molecules can function as signals for the immune system, triggering an immune response that leads to inflammation, which is not only important for maintaining health but also plays a critical role in the development of various diseases, such as cardiovascular and respiratory diseases, metabolic diseases, and cancer.”
Adults aren’t the only ones vaping. The Centers for Disease Control estimates that more than 2 million middle and high school students in the U.S. report using e-cigarettes. Besaratinia says that this is one of the main reasons why the team’s research is so critical to informing policy around vaping.
“Given the popularity of e-cigarettes among young never-smokers, our findings will be of importance to the regulatory agencies,” said Besaratinia. “To protect public health, these agencies are in urgent need of scientific evidence to inform the regulation of the manufacture, distribution, and marketing of e-cigarettes.”
Next, the team plans to identify and investigate chemicals common to both e-cigarette vapor and cigarette smoke to find out which ones might be causing similar adverse effects in vapers and smokers.
About this study
In addition to Besaratinia, the study’s other authors are Stella Tommasi, Niccolo Pabustan and Kimberly D. Siegmund, of the Keck School of Medicine of USC and Meng Li and Yibu Chen of USC Libraries Bioinformatics Service.
This work was supported by grants from the National Cancer Institute of the National Institutes of Health (1R21CA268197) and the University of California Tobacco-Related Disease Research Program (28IR-0060 and T31IR1839). The bioinformatics software and computing resources used in the analysis are funded by the USC Office of Research and the Norris Medical Library.
Here is the abstract from the paper:
We constructed and analyzed the whole transcriptome in leukocytes of healthy adult vapers (with/without a history of smoking), ‘exclusive’ cigarette smokers, and controls (non-users of any tobacco products). Furthermore, we performed single-gene validation of expression data, and biochemical validation of vaping/smoking status by plasma cotinine measurement. Computational modeling, combining primary analysis (age- and sex-adjusted limmaVoom) and sensitivity analysis (cumulative e-liquid- and pack-year modeling), revealed that ‘current’ vaping, but not ‘past’ smoking, is significantly associated with gene dysregulation in vapers. Comparative analysis of the gene networks and canonical pathways dysregulated in vapers and smokers showed strikingly similar patterns in the two groups, although the extent of transcriptomic changes was more pronounced in smokers than vapers. Of significance is the preferential targeting of mitochondrial genes in both vapers and smokers, concurrent with impaired functional networks, which drive mitochondrial DNA-related disorders. Equally significant is the dysregulation of immune response genes in vapers and smokers, modulated by upstream cytokines, including members of the interleukin and interferon family, which play a crucial role in inflammation. Our findings accord with the growing evidence on the central role of mitochondria as signaling organelles involved in immunity and inflammatory response, which are fundamental to disease development.
The full citation is Tommasi, S., Pabustan, N., Li, M. et al. A novel role for vaping in mitochondrial gene dysregulation and inflammation fundamental to disease development. Sci Rep 11, 22773 (2021). https://doi.org/10.1038/s41598-021-01965-1. It is available for free here.