The nutrients a heart uses to help it pump vary depending on how healthy the heart is, according to a new study published in Science—and the findings could have implications for future treatments, researchers say.
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The new study, the first of its kind, maps out how the heart intakes and releases 277 metabolites.
For the study, researchers from the Perelman School of Medicine tested the blood circulation in 110 patients who were preparing to undergo a procedure to treat atrial fibrillation, a condition that causes the heart to beat irregularly. Of the 110 patients, 87 had no history of heart failure and 23 had cardiomyopathy—a disease that weakens the heart's muscles, making it more difficult to pump blood. All of the patients had fasted overnight, which is a common practice for patients undergoing surgeries that require anesthesia.
The researchers then tested the levels of 600 metabolites in the patients' blood, and they found 277 metabolites that were reliably present in each participant's blood. However, the researchers noted that the levels of 65 of the metabolites entering the heart varied significantly compared with the amount excreted from the heart, which suggested that the nutrients were consumed or broken down during circulation through the blood vessels.
In general, the researchers found that healthy hearts relied on fats, proteins, and ketones—a fuel produced by the body when it runs out of sugar. According to Zoltan Arany, a co-author of the study and a professor of cardiovascular medicine at the University of Pennsylvania, hearts typically heavily rely on fats. "It'll use every fat that it can use," he said. "That's really its main source of energy."
But in comparison, failing hearts relied more heavily on just proteins and ketones, the researchers found.
The researchers also discovered that both healthy and unhealthy hearts seemed to extract ketones efficiently, and that failing hearts consumed ketones more than healthy ones.
"My sense is that a failing heart is energetically not happy and it's reaching for what it can get," Arany said. "That makes sense, especially if you haven't eaten."
Further, the researchers found that while both healthy and failing hearts break down entering proteins to continue help them keep beating, failing hearts broke down more protein molecules than healthy hearts.
"That's not trivial," Arany said, explaining, "It places a burden on the machinery of the heart." He added, "We think that there are things that are wrong in the way the heart uses fuel in heart failure."
Findings could have implications for future treatments
To this point, researchers typically have relied on the cardiovascular systems of rats and mice to get a sense of how hearts use energy during blood circulation. "Nobody has really clearly laid out what the human heart is doing," Arany said. "That's because it's not so easy to do given that you can't exactly take a person's heart out and study it."
However, the researchers' findings provide a detailed look at "how the heart handles fuel and nutrients" which "should inform the development of future treatments for heart failure and related conditions," Arany said. He added, "Now that we have a clear picture of how the heart fuels itself, we can set our sights on devising ways to improve heart metabolism in heart failure."
According to CDC, there are more than six million adults in the United States who are living with heart failure.
Gregory Aubert, a cardiologist at Loyola University's Stritch School of Medicine, said he found the study interesting, mostly because it utilizes human subjects, but he wondered whether nutrient processing might be different in a person who was well-fed.
For example, if someone had eaten recently (in comparison to the patients in the study, who had fasted overnight) their heart might use more glucose for fuel—or it may attempt to replenish the proteins it lost, Aubert said.
Arany also said that further study is needed, and he noted that his team intends to study fuel use in people who don't have an empty stomach (Runwal, "In The Lab," STAT+, 10/15 [subscription required]; Medical Xpress, 10/15).