If you’re having a heart attack, your life might someday be saved by pond scum.
That’s because these lowly bacteria are capable of producing something a stricken heart desperately needs: oxygen.
In fact, when Stanford scientists injected massive doses of cyanobacteria into the hearts of rats who suffered the equivalent of a “widow-maker” heart attack, oxygen levels ballooned by a factor of 25.
The results, published Wednesday in the journal Science Advances, suggest a truly original approach to reducing the damage done to heart muscle when it is suddenly deprived of oxygen.
When blood flow to the heart is interrupted by a clot or the narrowing of vessels, the effect can be deadly, either now or later. It’s not uncommon for a heart attack victim to survive his or her immediate ordeal, only to succumb to heart failure — the effects of heart muscle weakened by its brush with oxygen deprivation — months or years after the event.
Physicians have long sought to avert that lingering damage by restoring the flow of oxygenated blood to the heart muscle as quickly as possible. Wielding an arsenal of drugs, stents, grasping devices, saws, scalpels and long, threaded catheters, cardiac surgeons try to isolate, remove or dissolve clots in the arteries feeding the heart before cells start to die off and lasting damage is done. More recently, stem cells have shown great promise in restoring damaged heart muscle.
But this new approach to rescuing living tissue from so-called ischemic damage proceeds from the observation that oxygen abounds in our atmosphere as a result of photosynthesis — the fuel-making industry of green plants all around us.
If a lack of oxygen is the problem when living tissue is deprived of blood flow, perhaps we should invite into our bodies the forest’s genius for manufacturing the gas our cells depend on to survive.
“Every day we walk around and see trees,” said Dr. Joseph Woo, chair of Stanford School of Medicine’s department of cardiothoracic surgery and the paper’s senior author. “We wondered, would there be any possibility of taking plants and putting them next to the heart and getting them to work together?”
Several years ago, researchers in Woo’s Stanford lab started by grinding spinach, and then kale, with mortar and pestle. When they introduced the green slurry to living tissue in Petri dishes and set them in the sun, nothing happened.
But when they tried a more primitive practitioner of photosynthesis — pond scum — the oxygenation effect was clear to see.
The scientists used cyanobacteria, the blue-green algae that often blooms on the surface of still waters, to supply life-giving oxygen to the stricken hearts of rats. After clamping off the largest of three arteries feeding blood to the heart — the left anterior descending coronary artery — the researchers injected those hearts with tens of millions of the single-celled organisms.
For two full hours — one hour while the clamp remained in place and a second hour after it was removed — the animals’ incisions remained open. During that time, the hearts of the treated rats were exposed to strong light, which jump-started the photosynthetic process.
Just as they would on the surface of a pond, the cyanobacteria used the pigment chlorophyll to combine water, carbon dioxide and light to produce glucose. The incidental byproduct of that process — oxygen — kept cells deprived of oxygenated blood from dying off in droves.
A day later, the damage to the hearts of treated rats was less than half as severe as that seen in rats that got an inactive treatment, according to the study.
And four weeks after the ischemic crisis, the hearts of rats that got the photosynthesis treatment performed dramatically better than the hearts of rats that did not.
In humans, an improvement in heart function of the magnitude shown in treated rats “would have profound clinical implications,” the Stanford team wrote. If humans were to reap benefits as great as those seen in the lab rats, they added, such a treatment probably would spell “the difference between a healthy patient and one suffering from heart failure.”
Woo sees the new research as a “proof of principle” that photosynthesis, in some form, might someday be used as a bridge treatment for patients who have had blood flow cut off to any organ. It might be useful in sustaining organs harvested for transplant during their long journey to a new owner, Woo said, and in preventing the death of brain cells during a stroke. It may even one day improve the treatment of malignant tumors that thrive in oxygen-deprived environments, he added.
But in its current form, a photosynthetic bridge treatment is far from ready for use in clinical settings.
“It would be very suboptimal to have to crack someone’s chest open and shine the light on them” to begin the oxygenation process, Woo said. To work around that impracticality, a team at Stanford is already working on “supercharged versions” of the cyanobacteria that rescued rats’ hearts in his team’s new paper.
Researchers may have to engineer ways other than direct exposure to visible light to jump-start the photosynthesis process, he said. Plants or cyanobacteria may be amenable to genetic engineering that would allow them to produce oxygen more copiously, or to initiate photosynthesis in response to energy at wavelengths that can penetrate skin and other tissue.
Remarkably, the direct injection into the heart of millions of cyanobacteria did not cause any infection. Nor did it prompt the rats’ immune systems to mount a defensive response — a reaction that can be just as deadly as infection.
Virtually all of the millions of single-celled organisms injected into the rats’ hearts were gone 24 hours after the experiment. And in a more thorough search four weeks later, the researchers could find no sign of infection or of lingering bacterial cells anywhere near the hearts of rats who got the treatment.
If cyanobacteria were someday to play a key role in the treatment of human disease, it would be a nice footnote to an already striking record of accomplishment. That’s because cyanobacteria — one of the largest, oldest and most important groups of bacteria on Earth — are already pretty much responsible for life as we know it.
In the Archaean and Proterozoic eons 2.5 billion years ago, cyanobacteria flourished by using light and carbon dioxide for nourishment. The oxygen given off by this photosynthesis created Earth’s oxygen-rich atmosphere, making the evolution of ever more complex life forms possible.
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