Regular exposure to e-cigarette vapours disrupts the protective layer in the lungs, according to a study using lab mice that comes amid a U.S. investigation into 215 human cases of severe respiratory problems possibly linked to vaping.

Public health authorities say e-cigarettes are likely safer than smoking tobacco but little is known about the long-term risks of vaping.

As more teens and young adults take up vaping, researchers have expressed concerns about potential damage to the lungs and heart, as well as the risk of burns and seizures.

Against that backdrop, Dr. Farrah Kheradmand, a pulmonologist and professor of medicine at Baylor College of Medicine in Houston who has studied the effects of cigarette smoke for years, set out to discover whether vaping causes emphysema in lab mice.

Mice are obviously very different from people, but it's assumed that what happens in their lung cells also occurs in other mammals, including us.

Graduate students in Kheradmand's lab compared the effects of exposing mice to e-cigarette vapours and tobacco smoke for four months. That's the equivalent of starting smoking as a teen and sticking with the habit until about age 49.

The researchers exposed some of the animals to clean air, others to tobacco smoke, a third group to vaping solvents in the same proportions found in e-cigarettes and a fourth group to the solvents as well as nicotine.

They found inhaling vapour impaired important lung defences.

"The mice were suffering from the same problem with or without nicotine, indicating that the solvent is a big problem," Kheradmand said in an interview with CBC News.

"They are causing quite a havoc in the lung, independent of what else is added to them."

Dr. Farrah Kheradmand said she was surprised to find that even without nicotine, e-cigarette vapours damaged the lungs of mice. (Baylor College of Medicine)

As of Aug. 27, more than 200 cases of severe pulmonary disease possibly associated with the use of e-cigarettes had been reported by 25 states, according to the U.S. Centers for Disease Control and Prevention.

Health officials in Oregon and Illinois have each reported cases where a patient died of a respiratory illness they suspect could be linked to vaping. The patient who died in Oregon used an e-cigarette to vape cannabis.

Investigators from the U.S. Food and Drug Administration (FDA) found a chemical in an oil derived from vitamin E in 10 of 18 cannabis products collected from patients across the U.S., the Washington Post reported Thursday. An investigation by New York's Department of Health also found very high levels of vitamin E acetate in nearly all cannabis-containing vaping samples studied in its lab. The vitamin is not an approved vaping additive.

Vitamin E is found in foods, supplements and skin creams. But our lungs simply aren't built to handle it, said David Hammond, a professor in the school of public health at the University of Waterloo.

In many of the cases of pulmonary illnesses under investigation, the CDC said patients experienced a gradual worsening of respiratory symptoms. Some of them also reported mild to moderate gastrointestinal illness including vomiting and diarrhea, or other symptoms such as fevers or fatigue.

Health Canada has issued its own warning about vaping.

"Health Canada wants to advise Canadians who use vaping products to monitor themselves for symptoms of pulmonary illness (e.g., cough, shortness of breath, chest pain) and to seek medical attention promptly if they have concerns about their health, in the wake of the recent cases of acute pulmonary illnesses," spokesperson Maryse Durette said in an email Thursday.

Solvent damage

Kheradmand said she was surprised to find that even without nicotine, e-cigarette vapours made of propylene glycol and vegetable glycerin solvents damaged the lungs of mice.

The FDA and Health Canada both consider propylene glycol and vegetable glycerin to be safe as food additives. In conventional cigarettes, tobacco is burned. In e-cigarettes, the two solvents take the place of tobacco.

Since the cannabis market has shifted from raw herb to highly processed products, unknown contaminants can enter the solutions when purchased from the illicit market, Hammond said.

Instead of seeing signs of inflammation and emphysema caused by vapour without any nicotine, the researchers found an abnormal buildup of fats (lipids) that damaged how the lungs looked and their ability to fight off infection.

Doctors have previously reported cases of lung injury associated with e-cigarette inhalation, including "lipoid pneumonia," which is when fat deposits build up in the lungs. The damage was thought to be from inhaling oil for months.

"Physicians had assumed that these patients were coming in with glycerin deposited in their lungs because of a vape. In fact, there's something else going on in the lungs," said Kheradmand, whose study was published this week in the Journal of Clinical Investigation.

The lungs allow oxygen in the air to be inhaled and carbon dioxide waste to be exhaled. The protective layer of the lungs contains proteins and lipids that are important for exchanging gases. Lungs also contain immune cells to protect the body from invading bacteria, viruses or pollutants.

Vaping and infection

Kheradmand said it's normal for immune cells to collect some fat. But when the mice were exposed to e-cigarette vapour, they accumulated too many big fat globules because the fat wasn't being recycled properly.

The researchers also found chronic inhalation of e-cigarette vapours disrupted the ability of immune cells in the lungs, called macrophages, to successfully fend off influenza infection.

"We wanted to know, if you are a vaper who encounters an infection, what will happen to you? What we found is that in the case of mice exposed to vape, they fare a lot worse."

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Kheradmand and her team also reported that, as they expected, mice that were routinely exposed to cigarette smoke or to e-cigarette vapours containing nicotine had severely damaged lungs and excessive inflammation resembling what's found in human smokers with emphysema.

Kheradmand recalled a graduate student showing her slides of lung cells under a microscope. The shape of the cells looked very different when taken from mice exposed to e-cigarette vapour, with or without nicotine, compared with those exposed to conventional tobacco smoke or to clean air.

The findings could mean that if doctors look only for the kind of emphysema-type damage that they're accustomed to seeing in smokers when assessing patients who vape, they could miss other signs of damage.

Given the large number of teens using e-cigarettes regularly, the study's authors said their findings should "alert officials both at regulatory and epidemiological levels to the potential risk that electronic nicotine delivery system use may pose to this vulnerable population."

Dr. Akshay Bagai, a cardiologist at St. Michael's Hospital in Toronto who was not involved in the study, said we're only beginning to learn about the harmful effects of solvents used for vaping.

It remains to be seen, he said, whether the lung injuries in the more than 200 reported cases in the U.S. are similar to those seen in the lab mice.

No cases have been reported in Canada. Health officials on both sides of the border have warned against buying e-cigarette products, including those with THC or other cannabinoids, off the street, or to modifying vaping products or adding any substances that are not intended by the manufacturer.

"Given what we do know in regards to the addictive nature of nicotine and the mysterious, serious respiratory illnesses associated with vaping, I would advise people to refrain from vaping," Bagai said.