It seemed similarly paradoxical in 1986 when researchers at Duke University announced that depriving oxygen to the heart briefly by stopping its blood flow—as happens during heart attack—appeared to "precondition" the heart to resist subsequent heart attack.

And yet, this too, appears to work.

At the Baylor College of Medicine in Houston, cardiology researcher Roberto Bolli had already been exploring the same line of inquiry. He, too, had simulated the damaging effects of heart attack on tissue by inducing ischemia—oxygen deprivation in heart tissue—in animal models.

In 1994, Bolli was invited to bring his research to newly renovated, state-of-the-art cardiology labs at the U of L School of Medicine. As the head of U of L’s cardiology division, Bolli said his goal would be to "develop a first-class cardiac department both in the experimental and clinical areas," and added, "I want this division (of cardiology) to be among the top 10 divisions in the country in 10 years. I am confident we can get there."

Indications are that Bolli is close to making good on his promise, making U of L the home to several new discoveries and "firsts" in the field of heart preconditioning research.

In the last 16 months, his research team has published six papers of original findings in the field’s top journal, Circulation Research—a publication rate he says is unmatched by any other lab in the world. "We’ve been moving at a prodigiously fast pace in the last year," Bolli says. "We had nine peer-reviewed papers published in the top journals of cardiology" during that short time.

Bolli’s discovery, published in 1995, of a post-heart-attack phenomenon called "late phase preconditioning" has led his research team to a series of new findings on how the heart reacts to the trauma of heart attack. The findings may lead not only to treatments for heart attack but, more importantly, to therapies that may prevent them.

For his work, Bolli was named U of L’s first Distinguished University Scholar in 1995. University Scholars receive substantial income supplements and administrative support in publishing findings and seeking grant support. The designation is valid for five years.

University Scholars are expected to publish their findings frequently, as Bolli has done. He presents regularly at national meetings and his research is published in peer-reviewed journals such as Circulation Research, Circulation, The Journal of Clinical Investigation, and the proceedings of the National Academy of Sciences of the USA. He also serves on the editorial board of many major peer-reviewed journals. His credentials include training at the National Heart, Lung and Blood Institute, more than a decade on the faculty at the Baylor College of Medicine, and ongoing grant support from the National Institutes of Health.

The "Preconditioning" Paradox

The studies at Duke that interested Bolli had shown that stopping blood flow to the heart for five minutes and then restoring it preconditions the heart to resist heart attacks. Researchers had found that, during a heart attack, if the blood flow is stopped for 90 minutes, 50 percent to 75 percent of the heart tissue will be damaged. However, if the heart has been preconditioned, there will be 80 to 90 percent less damage to the heart tissue.

"Of course, I was very interested in that observation," Bolli says. "It seemed paradoxical at that time. When you stress the heart with ischemia (before heart attack) you end up having less damage than if you don’t stress the heart with ischemia before (heart attack). One would have expected the opposite."

The major drawback of this treatment was that the protective effects of the preconditioning lasted only about one hour. This short-lived, immediate response to induced preconditioning came to be known as "early phase preconditioning."

Bolli wanted to find out if the heart protection following preconditioning could be made to last longer. While investigating this possibility, he discovered what is now called "late phase preconditioning." The findings, published in 1995 in The Journal of Clinical Investigation after four years of study, revealed that a long-lasting state of heart protection occurs 24 hours after the initial stress of preconditioning and can last between three and seven days.

The finding was consistent with his initial hypothesis. "It just seems to me, intuitively," he says, "that if the heart is offended by some kind of stress or insult that the heart will respond not just for one hour, but for a more sustained period of time, and that it may require several hours for the mechanism to develop."

The preconditioning phenomenon suggests that the best medicine for preventing heart attacks already exists within the patients. "Mother nature usually has its own remedies that are far more effective than anything we can manufacture," Bolli says.

Still, the body will need a kick from science to actually unlock the therapeutic possibilities of preconditioning. That means understanding preconditioning at the molecular and genetic levels.

The complexity of the research requires a multidisciplinary research team. Bolli’s includes Xian-Liang Tang, a physiologist and pharmacologist; Yumin Qui, a cardiac physiologist; John Auchampach, a pharmacologist; W. Keith Jones, a molecular biologist; Peipei Ping, a cellular biologist; and Yu-Ting Xuan, a physiologist and pharmacologist.

New Findings

Scientists have been searching for a decade to find exactly what is responsible for starting the preconditioning phenomenon (what Bolli calls the "trigger") and for causing the heart protection later ("the mediator").

In 1997, Bolli’s team found answers. When the heart undergoes ischemic stress, the body produces the molecule nitric oxide. Nitric oxide is produced by enzymes in the body to play key roles in controlling many body processes and in fighting disease.

"We were the first lab in the world to demonstrate that nitric oxide can act as a signal that induces changes in what we call the phenotype of the heart," Bolli says. "The phenotype means the way that the heart is made up, the expression of proteins in the heart cells... and (nitric oxide) induces this delayed adaptation that we call late preconditioning."

Bolli’s team found that when the production of nitric oxide was blocked, preconditioning, and the later heart protection associated with it, did not occur.

"We’ve published that nitric oxide is the trigger or initiator of preconditioning at the time of the first ischemic stress and is also the mediator of the protection 24 hours later at the time of the second ischemic stress," Bolli says.

The clinical implications of these discoveries could be dramatic. Nitrates, drugs that can deliver nitric oxide to the heart, are just as effective as ischemia at inducing the preconditioning heart protection—and less dangerous. One nitric oxide-delivering drug, nitroglycerin, has been in use to treat post heart-attack patients for years. The same principal might be applicable in making hearts resistant to heart attacks. Studies will be needed, Bolli says, to find the proper dosage of nitrates that will be safe and effective.

At some point, Bolli hopes to recruit a faculty researcher to experiment with myoblasts, immature skeletal muscle cells that show promise in regenerating lost heart muscle after heart attack.

Meanwhile, Bolli’s team continues to find out, at the basic studies level, what happens in the heart in the 24 hours from the time of the first ischemic stress to the second one. They’ve found that several molecules, protein kinases, tyrosine kinases, and a gene transcription factor called NF-KB, play roles in the preconditioning process. Bolli’s current studies also suggest that different forms of nitric oxide, or nitric oxide sythases, play different roles in controlling different parts of the preconditioning
response.

Even with all these brand new findings, Bolli says only a fraction of the preconditioning process is known.

"Nature is always incredibly complicated," he says. "I personally know that the more I do research the more I am bewildered by the complexity of nature. Life is an incredible miracle. It’s mind-boggling how complex and incredibly intricate the biology of living organisms is. So, preconditioning, like everything else, is incredibly complex, and for us to really fully understand it it’s going to require an extensive and presumably long-lasting endeavor that is going to span over several years, easily."

Cardiology researcher Roberto Bolli

CVD: A Heartless Killer

—American Heart Association