Heart attacks occur when oxygen is blocked from getting to crucial heart muscles — but that might be something that can be helped with bacteria. By using bacteria that “eat” light to produce oxygen, researchers were able to provide extra oxygen to rats having heart attacks. The brand-new technique has the potential to one day help humans survive when blood flow to the heart is interrupted.
The bacteria used in the study are powered by light; they convert carbon dioxide into oxygen, just like plants do. They’re called Synechococcus elongatus. In today’s study, published inScience Advances, rats undergoing heart attacks had the bacteria injected into their hearts. When scientists shone lights onto the rats and their new bacterial friends, the bacteria produced oxygen — which was then used by the oxygen-starved heart cells, improving the heart’s overall function.
The technique is still early — of course, rats aren’t humans, and there’s a long way to go before it goes to human tests. But it’s a brand-new approach to the number-one killer in the US, heart disease. Often, heart attacks are caused by blockages in the blood vessels that supply oxygen-rich blood to the heart, which makes the heart muscle die. These blockages affect more than 15 million people in the US.
An MRI of a rat heart after it’s been treated with S. elongatus. | Video by Stanford University School of Medicine, Department of Cardiothoracic Surgery
The only way to treat the problem is to reestablish that blood flow to the heart, Steve Houser, the president of the American Heart Association, tells The Verge. That’s done by taking drugs that dissolve blood clots, or by removing the clot and placing a small mesh tube called a stent in the narrowed artery to prop it open. Sometimes, an open-chest surgery is required.
The researchers in today’s study wanted to find a new way to deliver oxygen to the heart during a heart attack. First, they thought of using plant cells, which naturally consume CO2 to produce oxygen — a process called photosynthesis. “We were grinding up kale and spinach,” says co-author Joseph Woo, chair of the department of cardiothoracic surgery at Stanford University School of Medicine. The researchers extracted the bits inside the plant cells that make photosynthesis possible, called chloroplasts. But the chloroplasts didn’t really work outside plant cells.
So next, Woo and his team decided to use a bacterium that resembles a chloroplast — Synechococcus elongatus. They placed the bacteria next to rat heart cells in a petri dish. The bacteria survived — and when given light, they used CO2 and water to produce oxygen and glucose, compounds heart cells need to function. Then, the researchers tried the bacteria in live animals: they took rats, opened their chests, and caused heart attacks by shutting down one of the arteries carrying blood to the heart. The rats were then injected with the bacteria. When the scientist shined lights onto the bacteria, they began producing oxygen. And the heart cells used that oxygen to survive longer.
Compared to the heart cells that received the S. elongatus therapy in the dark, the heart cells that received the therapy in the light performed better: the hearts contracted better, they were more powerful, and even four weeks after the procedure, the hearts looked more resistant to heart attacks. “A lot of these things are not just subtle differences, they’re pretty significantly different,” Woo tells The Verge. The animals’ immune systems didn’t reject the bacteria. But the bacteria didn’t live long, either — they just died out in the rats’ hearts.
It’s of course possible that the bacteria will react differently in humans. Also, the procedure required an open chest — a dangerous and invasive surgery that most doctors prefer to avoid, Houser says.
“IT COULD BE SOMETHING REALLY GREAT, OR NOT.”
But as the technique is developed, the bacteria may be bound to an antibody that targets heart cells, letting researchers inject the treatment in any vein, rather than directly into the heart, Woo says. That’s one hurdle: another is the light. Right now, the team is trying to figure out a way to shine the light the bacteria needs through the skin and ribs, Woo says. Otherwise, there’s no way around open-heart surgery.
The hope here is that if the research holds up in people, it could represent a new way to treat heart attacks — or at least buy time. It could also be used to keep donated organs healthier by supplying them with oxygen while they’re being transported to the recipient. “That’s a really interesting potential application,” Hauser says. But it’s really too early to tell, he adds. “Like all basic science studies, it could be something really great, or not.”
Next, Woo is working on genetically modifying the bacteria so that they can be even more efficient — producing more oxygen. And the team is moving closer to performing the therapy on larger animals like sheep and pigs. But it’s still impressive, using naturally occurring bacteria in this inventive way.