The study compared the effect on heart cells of tobacco cigarette smoke and e-cigarette aerosol.
In a paper published in the journal Drug and Alcohol Dependence, researchers from the University of Bristol in the United Kingdom explain how they ran tests on the vapor and smoke using heart cells grown in the lab from donated human coronary artery endothelial cells.
The past few years have seen a rapid rise in the use of e-cigarettes (electronic cigarettes) - products that deliver nicotine via aerosol or vapor that is inhaled by the user.
Many people believe e-cigarettes are less harmful to health than conventional cigarettes, but there is not a lot of scientific evidence to back this up, say the researchers.
The researchers are not saying that the evidence to date does not support this view, only that the body of evidence itself is small, likely because it is still early days. "Absence of evidence does not equal evidence of absence," as the adage goes.
In their paper, they mention a need for robust laboratory models that can reliably quantify the biological effects of e-cigarettes, compared with tobacco products.
For example, there is some evidence that chemicals present in e-cigarette vapor can be harmful, but this depends on many variables, including the solution that is used and the battery output voltage.
Also, much of the research published to date on e-cigarette toxicity has used diluted refill solutions (e-liquid), say the authors, noting that even if the levels in the e-liquid are found to be toxic, it does not necessarily mean that the levels delivered via aerosol will be.
Findings are preliminary, need to be confirmed
The researchers, therefore, decided that a "valuable approach might be to examine the biological response of human primary cells to e-cigarette aerosol."
Marcus Munafò, joint senior author and professor of biological psychology, says "research into these biological effects is critical. Our study looked at the stress response in heart cells in response to cigarette smoke and e-cigarette aerosol."
For their study, the researchers analyzed changes in gene expression in the heart cells as a result of having smoke extract from a conventional cigarette or extract from e-cigarette aerosol passed through them.
Prof. Munafò says they "found the cells showed a stress response from the cigarette smoke extract, but not from the electronic cigarette aerosol extract."
"This result suggests tobacco smokers may be able to reduce immediate tobacco-related harm by switching from conventional cigarettes to e-cigarettes."
Prof. Marcus Munafò
The researchers caution, however, that due to some of the study's limitations, their findings should be regarded as preliminary and need to be confirmed by future models.
Among the limitations, they list the fact that they only investigated a single e-cigarette product, a single cell line, and only a limited number of outcomes.
Another limitation was their "puffing protocols were not designed to directly mimic real-world smoking or vaping, but to standardize nicotine exposure," and also that using constant flows may not have captured the effects of "spikes" in puffing.
The authors also note that they investigated e-cigarettes and tobacco cigarettes separately, whereas in reality many smokers use both, so future studies should also look at their combined effects.