Mustard gas, single ventricle heart disease and COVID-19
Funded via CounterACT, a National Institutes of Health-sponsored counter-terrorism program, Drs. White and Veress specialize in studying the effects of inhaled chemical weapons and toxic industrial agents.
“We use our clinical knowledge to understand the injury patterns, and then we come back to the lab and study animal models,” says Dr. Veress. “Then we start testing therapies based on what’s already on the shelf and FDA-approved.”
Plastic bronchitis in single ventricle heart disease
Some years ago, studying mustard gas inhalation, Drs. White and Veress noted the persistent presence of a white clot-like substance in the airways. It looked a lot like plastic bronchitis, rubbery white strands patients would sometimes cough up after the Fontan operation, a surgery that reroutes circulation to descend through the lungs before returning to the heart in patients with single-ventricle heart disease.
“We remembered having these kids in the PICU and having no way to treat them,” says Dr. Veress. “We’d go in with a bronchoscope to pull these plugs out of the airways so patients could breathe, but they’d just come right back. Our animal model looked exactly like that. So we wondered, what’s in these plugs? And it turns out they’re mainly made up of fibrin, which is exactly what a clot is made up of.”
“It was all clot with no red cells,” Dr. White adds. “Pure fibrin.”
Nebulizing a plasminogen activator
It stood to reason that a clot-busting drug might be effective. After some experimentation, they settled on a plasminogen activator, plasmin being an important factor in the breakdown of fibrin. They’re typically administered intravenously. Dr. Veress had the idea to administer it directly to the lungs. (For severe cases, they use a bronchoscope to deliver it.)
The results were striking. After dosing an animal model with mustard gas, the mortality rate for those who didn’t get the treatment was 100%. Of those that got it, 100% survived.
“It absolutely reversed the acute injury,” says Dr. Veress.
Plastic bronchitis and severe respiratory distress
It didn’t take long before the therapy was being tested on plastic bronchitis after the Fontan operation, with positive results. And it turns out that clotting and fibrin buildup in the lungs is a complication of many forms of respiratory distress — including COVID-19.
In fact, preliminary studies have shown that, in patients with acute COVID-19, aerosolized plasminogen activators were an effective method of reducing mortality. Dr. Veress helped publish a case report on that in the Journal of Thrombosis and Haemostasis in July.
The SARS-CoV-2 virus infects the human body by binding to a protein called angiotensin-converting enzyme 2, or ACE2, which regulates inflammation and vasoconstriction in the lungs and other tissues. There’s increasing evidence that cigarette smoking increases the gene expression of ACE2, which may in turn increase viral load. To date, however, it’s not known whether vaping might produce a similar effect. Equipped with a newly acquired robot, one of the nation’s preeminent chemical weapons preparedness labs is collaborating with a top virology lab to investigate.
The chemical composition of an e-cigarette
In liquid form, the basic ingredients of a run-of-the-mill vape pen are pretty innocuous. Two of them are common food additives: propylene glycol, an emulsifier and anti-caking agent and glycerine, a moisture-retaining compound also found in cosmetics and wound salves. The third is nicotine.
“So that’s what’s going into the vape,” says pediatric pulmonologist Carl White, MD. “But when it comes out, it’s in small hot particles, so small they can penetrate very deep into the lungs. The chemical composition of what’s being delivered in the aerosol is quite different.”
That composition includes formaldehyde; acetaldehyde, a chemical formed in the liver when it’s breaking down alcohol; and acrolein, an aldehyde that occurs in closed fires, especially where plastic is burning — like a car fire. And the effects on the body of that chemical mix, short- or long-term, still aren’t well understood.
Chemical inhalants from a translational perspective
Dr. White is looking to understand them better, and he comes from a unique vantage. Along with his mentee and partner Livia Veress, MD, another pediatric pulmonologist at Children’s Hospital Colorado, he heads up one of the nation’s preeminent labs for the translational study of chemical inhalants. Much of their work, in fact, is funded through a national counter-terrorism program that supports the development of treatments for chemical weapons attacks.
“In a lot of chemical labs there’s no link to the human world,” says Dr. Veress. “The models we create are very human disease relevant.”
Their latest model: a robot that vapes.
Designed by research partners in Canada and manufactured in China, the robot, the first of its kind, was originally commissioned to study EVALI, the outbreak of acute lung injuries associated with vaping. That disease turned out to be the result of an additive in some marijuana vaping devices sold on the street.
But just as soon as the mystery of EVALI resolved, another new and dangerous potentially complicating factor of vaping came up: COVID-19.
The role of the ACE2 receptor in COVID-19
Every virus comes with a key, an appendage of protein that unlocks some structure within the cell. For SARS-CoV-2, that structure is ACE2, a receptor protein on the surface of epithelial cells. It’s the door that lets the virus inside.
Generally speaking, the cellular function of ACE2 is to break up a large protein called angiotensin II, or ANG II, which is generated by another protein called ACE. ANG II promotes vasoconstriction and inflammation of the epithelia, which line mucous membranes like those in the nose, mouth and lungs — including the alveoli, the air sacs that facilitate gas exchange and oxygenate the blood. ACE2 breaks it into smaller proteins that counteract those effects.
“Basically, ACE and ACE2 have a yin-yang kind of relationship,” Dr. White observes.
A possible mechanism for severe COVID-19 infection
One prominent hypothesis for the pathology of COVID-19 is that the SARS-CoV-2 virus throws ACE and ACE2 out of balance. The mechanism carries increased risk for cigarette smokers, because smoking seems to increase the gene expression of ACE2. In fact, smokers produce 30 to 55% more ACE2 than nonsmokers.
“ACE2 is the receptor, so it’s possible that making more targets for the virus, you could get a more severe infection and a bigger viral load,” says Dr. White. “You look at the population that goes into intensive care or has respiratory distress to the extent they need a ventilator, if you’re a smoker your odds are at least 2 to 1.”
And new research out this summer shows that adolescents who vape are five times as likely to be diagnosed with COVID-19 — close to seven times as likely if they’ve reported vaping within 30 days. But the mechanism remains to be studied.
An animal model to study vaping and COVID-19
Sixty miles north of Drs. White and Veress’s lab, in Ft. Collins, Colorado, the Infectious Disease Research Center at Colorado State University is chasing down one of the world’s most promising leads for a COVID-19 vaccine. The technology, called SolaVAX, inactivates viruses using a combination of riboflavin and UV light. It’s already been validated on other coronaviruses. They’re making fast progress on SARS-CoV-2.
“Their team has some highly reputed virologists who have been studying SARS and MERS and all these precursors of COVID-19 for years,” says Dr. White. “They know how to handle them. And they have a lot of experience with animal models.”
That’s key, because in certain small animal models, ACE and ACE2 operate in much the same way as they do in humans.
A robot that vapes
An animal model that tests the effects of a virus coupled with the effects of a behavior is complicated: You have to find a way to replicate the behavior first. That’s where the robot comes in.
“It’s programmed for pull times, dwell times, volume of air,” says Dr. White. “All this is based on published studies developing inhalation patterns that mimic how humans vape.” Dr. White and Veress’ study calls for two variations: chronic vaping, where the models will get “vaped” multiple times a day for three weeks, and acute, which is based on patient reports of vaping behavior. A teen might not vape every day, but they might go to a party and vape all night — and might contract COVID-19 at that same party.
After the model is vaped, it goes to Ft. Collins, where it’s inoculated with SARS-CoV-2 virus by CSU’s Angela Bosco-Lauth, DVM, PhD, and her virology team. Pathology tends to be at its worst around day six or seven, so they’ll monitor for a week.
The study stands to answer some crucial questions regarding the relationship between smoking, vaping and COVID-19, and perhaps even the mechanism of COVID-19 itself. Does vaping increase the expression of ACE2, as it does in smoking? Does increased ACE2 expression in fact lead to a higher viral load? And is there a through-line from increased ACE2 to worse pathology? If so, the study could offer insight on potential treatment options, such as angiotensin receptor blockers, which inhibit the action of ANG II.
“Ultimately,” says Dr. White. “This could answer those kinds of questions.” And in the midst of the pandemic, the answers are more crucial than ever.