A recent study in mice might shed some light on why electronic cigarettes (e-cigarettes) are harmful, even when there is no nicotine present in the vapors themselves.
A study out of the Baylor College of Medicine in Houston, TX, found that chronic exposure to e-cigarette vapors, even without nicotine, could negatively impact normal lung function.
This exposure could also have ramifications for how the body responds to infections, as it can make immune cells in the lungs less able to respond to viruses.
The findings appear in The Journal of Clinical Investigation.
As the authors of the new paper explain, some studies have suggested that the chemicals in e-cigarettes are harmful to the health of those who inhale them. Others, however, have noted that in comparison with regular tobacco cigarettes, these products are safer.
"These opposing views on the safety of e-cigarettes prompted one of my graduate students, Matthew Madison, to investigate the effects of chronic exposure to e-cigarette vapors and to conventional tobacco smoke on murine lung function," says corresponding author Dr. Farrah Kheradmand, a pulmonologist and professor of medicine at the Baylor College of Medicine.
"We also looked at the effect of vapors or smoke on the function of immune cells called macrophages residing within the lung. These cells represent a first line of defense against viral infections such as those caused by influenza virus."
Vaping solvents, nicotine, and lung health
The study comprised four groups of mice. The researchers exposed one group to e-cigarette type vapors that contained nicotine and other vaping solvents, such as propylene glycol and vegetable glycerin.
They exposed another group to the same solvents but without the nicotine. They explosed a third group to tobacco smoke. The fourth group had access to clean air.
To mimic the amount of time a person would inhale these substances for, the researchers exposed the mice to them for 4 months. This roughly corresponds to a person smoking from their teenage years through their fifth decade of life.
There were no surprises when the researchers examined the mice they exposed to cigarette smoke: They experienced severe lung damage and inflammation comparable with emphysema. This is similar to what happens in humans when they smoke tobacco for a long period of time.
However, the researchers were surprised to learn that the mice exposed to the vaping solvents that lacked nicotine also had damage to their lungs.
Although it was not the same type of damage they observed in the tobacco smoke-exposed mice, it was still a significant finding. Although there was no emphysema-like illness present, the researchers discovered an abnormal buildup of lipids in the lungs.
This fatty buildup was not exactly from the vaping solvents themselves or any oils present in the fluids. Instead, what occurred was an "abnormal turnover of the protective fluid layer in the lungs."
The researchers found an excessive accumulation of lipids in resident macrophages, which are cells that work to detect and destroy harmful organisms.
This accumulation prevented the macrophages from responding as they normally would to infections. The implication for humans is that an illness would be more likely to have a negative impact than if the person had a healthy population of macrophages.
"In summary, our experimental findings reveal that, independent of nicotine, chronic inhalation e-cigarette vapors disrupts normal murine lung function and reduces the ability of resident immune cells to respond to infection, increasing the susceptibility to diseases such as influenza."
Dr. Farrah Kheradmand
"Our experimental findings share similarities with previous multiple case reports describing the presence of lipid-laden macrophages in pulmonary fluid from people with e-cigarette associated pneumonia."
The researchers feel that their findings should prompt further investigation into how e-cigarette vapors affect health, even when people do not use nicotine products.