(Reuters Health) - E-cigarette liquids sweetened with flavorings like clove and vanilla may damage cells in the blood vessels and heart even when they don’t contain nicotine, a small experiment suggests.

Researchers examined what happened in lab tests when they exposed endothelial cells, which line arteries and veins as well as the inside of the heart, to a variety of popular e-cigarette flavorings. They tested the effect of different doses and concentrations of nine popular chemical flavorings: banana, butter, cinnamon, clove, eucalyptus, mint, strawberry, vanilla and “burnt” - which is used to impart a popcorn or tobacco-like flavor to foods.

At high concentrations, all nine flavorings damaged cells in lab tests, researchers report in Arteriosclerosis, Thrombosis, and Vascular Biology.

Five flavors - vanilla, mint, cinnamon, clove, and burnt - impaired production of nitric oxide, a molecule that inhibits inflammation and clotting and helps blood vessels widen in response to increased blood flow.

“The loss of nitric oxide is important because it has been associated with heart disease outcomes like heart attacks and strokes,” said lead study author Jessica Fetterman of Boston University School of Medicine.

“It is one of the first changes we observe in the blood vessels in the progression to heart disease and serves as an early indicator of toxicity,” Fetterman said by email. “Our study suggests that the flavoring additives, on their own in the absence of the other combustion products or components, cause cardiovascular injury.”

Big U.S. tobacco companies are all developing e-cigarettes. The battery-powered gadgets feature a glowing tip and a heating element that turns liquid nicotine and flavorings into a cloud of vapor that users inhale.

Even when e-liquids don’t contain nicotine, the lungs are still exposed to flavoring chemicals when the vapors are inhaled. While many of the flavorings are considered safe to eat, some previous research suggests that inhaling vapor from these chemicals may damage the lungs.

In the current study, researchers tested cells from nine nonsmokers and 12 smokers of traditional cigarettes, and they also tested some commercially available endothelial cells from human hearts.

Even before they were exposed to chemical flavorings, tobacco smokers’ cells already had a reduced ability to produce nitric oxide, lab tests showed.

Nonsmokers’ cells had impaired nitric oxide production after they were exposed to chemical flavorings.

Beyond its small size, another limitation of the study is that it wasn’t a controlled experiment designed to prove whether or how chemical flavorings might directly cause damage to blood vessels or lead to heart problems.

It’s also not clear whether exposure to chemical flavorings might be better or worse for human health than nicotine, which also strongly affects blood vessels and the heart.

“We already know that tobacco smoke affects endothelial cells, leading to cardiovascular diseases,” said Irfan Rahman, a researcher at the University of Rochester Medical Center in New York who wasn’t involved in the study.

The current results suggest that vaping isn’t safer than smoking traditional cigarettes, Rahman said by email.

Consumers may also have a hard time determining the amounts of any chemicals in e-cigarettes, making it difficult to avoid higher doses, said Prue Talbot, a molecular biology researcher at the University of California Riverside who wasn’t involved in the study.

“It is currently difficult for the consumer to control exposure to flavor chemicals,” Talbot said by email. “Manufacturers do not list the flavor chemicals and their concentrations on products, so consumers do not have a simple way to identify products they might choose not to use if they had more information on their contents.”

Still, people haven’t been using e-cigarettes long enough yet for scientists to develop a clear picture of any safety issues, especially when it comes to nicotine-free vaping, said Maciej Goniewicz of Roswell Park Comprehensive Cancer Center in Buffalo, New York.

“Combustible tobacco products already release many toxicants that cause cardiovascular diseases, but the situation may be different for e-cigarettes that do not burn tobacco,” Goniewicz said by email. “I think it is important for future studies to compare the cumulative toxicity of the inhaled e-cigarette aerosol with and without flavored chemicals.”

SOURCE: bit.ly/2Jf8iyE Arteriosclerosis, Thrombosis, and Vascular Biology, online June 14, 2018.