How stress causes heart attacks?

New research suggests films of bacteria are keeping heart attack-causing plaque out of the blood stream, but stress hormones are setting them free.

Image: Bernard B. Lanter/Binghamton University

Scientists have long thought that stress triggers heart attacks, but they’ve never been able to work out how. Now new research has identified the bacteria that may be involved.

It's long been suspected that bacteria attaches to and infects plaque - a substance that builds up in arteries when cholesterol combines with fat and calcium, and can harden over time to cause heart attack or stroke. Researchers from Binghamton University in New York set out to study which bacteria were involved, and whether the process was being affected by stress.

Using fluorescent tags, they discovered more than 10 species of bacteria clustered tightly around plaque, including Pseudomonas aeruginosa - a bacteria known for growing in clumps called biofilms (red in the microscope image above, the artery is green).

According to lead researcher David Davies, these biofilms can affect the risk of cardiovascular disease by binding tightly to plaque and stopping them from entering the bloodstream. And he suspected that stress hormones were breaking them down.

His team tested this theory by growing P. aeruginosa biofilms in artificial arteries in the lab. As Sara Reardon reports for Nature, they then flooded the system with stress hormone noradrenaline to see what happened.

What they found was that noradrenaline triggers the body’s cells to release iron, which in turn breaks down the bonds that hold P. aeruginosa biolfilms together.

And as collateral damage, the plaque is also set free, their research suggests. The results are published in mBio.

More work needs to be done to determine whether this same mechanism is happening in humans and animals, but if it pans out, it “introduces a completely unexpected potential culprit” for heart attacks, Davies told Nature.

One criticism so far is that the amount of noradrenaline released in the experiment is much higher than would be present in the human body, but it’s possible that lower levels could have a similar affect - we’ll just have to wait and see.

In the meantime, let’s all try to stress less…

Source: Nature