E-cigarette use linked to changes in adrenaline levels in the heart, but not oxidative stress

A new study published in the Journal of the American Heart Association has shown that healthy nonsmokers who used an e-cigarette device with a nicotine-containing liquid experienced increased sympathomimetic effects when compared with those who used a device with a nicotine-free liquid.

Instead of the combustion of tobacco involved in cigarette smoking, e-cigarettes use a flavored liquid containing a mixture of vegetable glycerine, propylene glycol, and artificial flavorings. Some liquids contain nicotine, while others do not.

“While e-cigarettes typically deliver fewer carcinogens than are found in the tar of tobacco cigarette smoke, they also usually deliver nicotine,” said Holly Middlekauff, MD, senior study author and Professor of Medicine (cardiology) and Physiology at the David Geffen School of Medicine at UCLA. “Many believe that the tar—not the nicotine—is what leads to increased cancer and heart attack risks. So we asked the question, are e-cigarettes safe?”

The team of researchers at UCLA had previously reported that chronic e-cigarette users were more likely to have signs of oxidative stress and increased levels of adrenaline in the heart.

The current study was designed to study whether nicotine caused these events.

Dr. Middlekauff and her team relied on measurement of heart rate variability from a prolonged, non-invasive heart rhythm recording. Heart rate variability is calculated from the degree of variability in the time between heartbeats. This variability may be indicative of the amount of adrenaline on the heart.

Prior research has used this technique to link increased adrenaline activity in the heart with increased cardiac risk. People with and without known heart disease who have this pattern of high adrenaline levels in the heart have increased risk of death, Dr. Middlekauff said.

This is the first study to separate the nicotine from the non-nicotine components when examining the cardiac implications of e-cigarette use in humans. Thirty-three healthy adults who were not current e-cigarette or tobacco cigarette users were enrolled.

Each participant used an e-cigarette with nicotine, an e-cigarette without nicotine, or a sham device. Researchers measured cardiac adrenaline activity by assessing heart rate variability and oxidative stress in blood samples by measuring the enzyme plasma paraoxonase.

Results showed that exposure to e-cigarettes with nicotine led to increased adrenaline levels to the heart, but e-cigarettes without nicotine did not.

In addition, measurements of oxidative stress, which increases risks for atherosclerosis and heart attack, did not change after exposure to e-cigarettes with and without nicotine. The number of markers they studied for oxidative stress were minimal, however, and more studies are warranted, Dr. Middlekauff said.

“These findings challenge the concept that inhaled nicotine is benign, or safe,” she explained. “Our study showed that acute electronic cigarette use with nicotine increases cardiac adrenaline levels. And it’s in the same pattern that is associated with increased cardiac risk in patients who have known cardiac disease, and even in patients without known cardiac disease. I think that just seeing this pattern at all is very concerning and it would hopefully discourage nonsmokers from taking up electronic cigarettes.”

Dr. Middlekauff was reassured that non-nicotine components do not have an obvious effect on adrenaline levels in the heart.

Future studies should look more closely at oxidative stress and e-cigarette use, using a broader number of cardiac markers and in a larger population of people, researchers said.

The study was funded by the Tobacco-Related Disease Research Program; American Heart Association, Western States Affiliate; National Institute of Environmental Health Sciences, National Institutes of Health; Irma and Norman Switzer Dean’s Leadership in Health and Science Scholarship; and UCLA Clinical and Translational Science Institute.

To read this study, click here.