For the faint of heart, a microbial flash mob might just do the trick.

A direct injection of photosynthetic bacteria—plus a little light—provided cellular life-support to the weak, blood-starved hearts of rats suffering simulated heart attacks. The bacterial jolt supplied much-needed oxygen to the gasping tissue and prevented long-term damage, Stanford researchers report this week in Science Advances. In fact, after a short recovery period the treated rodents had a 30-percent boost in heart function compared with control animals.

“In humans, an increase of this magnitude would have profound clinical implications, likely representing the difference between a healthy patient and one suffering from heart failure,” the authors conclude. They’re hopeful that one day the microbial menders could be used to help human heart attack patients and those undergoing heart surgery or heart transplants. There are some tall hurdles to get to those goals, the authors admit, but the results so far show promise.

Bright friendship

For the study, the researchers first made sure that the bacteria were benign and happy cohabitants with mammalian cells. In well-lit experiments, the researchers, led by cardiovascular surgeon Joseph Woo, grew rat cells alongside Synechococcus elongates. These photosynthetic bacteria convert carbon dioxide and light across a broad wavelength spectrum into oxygen and energy. In petri dishes, the two types of cells seemed chummy. S. elongates even shared their home-made oxygen with their heart cell neighbors—exactly what the researchers hoped to see.

Stanford University School of Medicine

Stanford University School of Medicine

Stanford University School of Medicine

Cohen et al.

This is because during a heart attack, open heart surgery, or a heart transplant, a living heart gets cut off from full blood flow. And that blood delivers critical oxygen and nutrients to the cells that make up the hard-working organ, plus it sweeps away waste products, such as carbon dioxide. Without blood flow, the cells become stressed, damaged, and can eventually die off—for a patient, that means heart failure and possibly death. But if well-lit S. elongates were around, they could provide microbial life-support for the heart cells, the researchers hypothesized.

Light-hearted

In rats, the bacteria seemed to do just that. Woo and colleagues cut off blood flow to the hearts of rats and then injected bacteria—either in the light and dark—or saline. After ten minutes and twenty minutes, rats that got the dark bacteria treatment had oxygen levels in their heart tissue boosted, at most, three-fold compared with those that got the saline control. At both time points, the rats with lit bacteria showed an average oxygen level boost of a more-impressive 25-fold.

After 45 minutes, the bacteria treatment with light improved heart function by 30 percent compared with the dark therapy. There was an average of 60-percent improvement compared with the saline control rats, but there was a lot more variation on this figure.

In another experiment, Woo and colleagues blocked the blood flow to rats’ hearts for 60 minutes while injecting either saline or S. elongates. Then the researchers left the heart exposed under light for another 60 minutes. Twenty-four hours and four weeks later, the S. elongates-treated rats had less heart damage and improved function over the saline controls.

The researchers also noted that the bacteria didn’t seem to produce any immune response in the rats and cleared from the heart quietly within a day.

Though the results are promising, there is still a lot of work to be done to figure out if it will work in humans. For one thing, researchers will need far more data to prove that S. elongates won’t cause any complications or infections in humans. Also, most heart-attack victims don’t have invasive surgery, so getting a light source directly into the heart to power the bacterial life-line will be tricky. The researchers are already brewing up ideas, including engineering the bacteria to produce their own light.

“Because S. elongatus is amenable to genetic engineering, there are countless possibilities regarding the augmentation of energy production, in vivo tracking, and growth control,” the researchers conclude optimistically. Despite the obstacles in the therapy’s infancy, “the data suggest a very real benefit from the use of photosynthesis to treat [blood-starved heart] disease.”

Science Advances, 2017. DOI:10.1126/sciadv.1603078 (About DOIs).