In a groundbreaking new study, researchers from the Karolinska Institute in Sweden have demonstrated that heart cells are able to regenerate themselves, overturning the conventional wisdom that the body cannot replace damaged heart cells.Researchers immediately hailed the study as providing new hope for prevention and treatment of diseased hearts.
"I think this will be one of the most important papers in cardiovascular medicine in years," said Dr. Charles Murry, a heart researcher at the University of Washington in Seattle. "It helps settle a longstanding controversy about whether the human heart has any ability to regenerate itself."
Unlike most cells in the body, heart cells mostly stop reproducing themselves relatively early in life. When injured, the heart tends to simply scar, rather than replacing damaged tissue the way other organs do. For decades, scientists assumed that the heart was simply incapable of natural regeneration.
This idea was challenged in 1987 by Piero Anversa, now a researcher at Harvard Medical School. Anversa believes that the heart regenerates a rate allowing it to replace all of its cells four times in 80 years. Clinical evidence for this idea has been lacking, however.
To determine rates of cell regeneration in animals, scientists typically flood an animal's body with radiation and track the rate at which non-radioactive cells replace the radioactive ones. In one of these so-called pulse labeling experiments in mice, researchers found that mouse heart cells regenerated at a rate of about 1 percent per year -- much lower than the rate hypothesized by Anversa, but still higher than the conventional wisdom.
Although pulse labeling experiments are banned in humans, researcher Jonas Frisen realized that the technique could be replicated by measuring heart cells' levels of the radioactive isotope carbon-14.
Because carbon-14 decays at a fixed rate, researchers can use levels of the isotope to estimate the dates of organic materials that are tens of thousands of years old -- but the isotope decays far too slowly to be used in dating of living cells.
Aboveground nuclear tests in the 1960s, however, injected large quantities of carbon 14 into the air that were then absorbed by life forms around the world. When aboveground testing was banned, atmospheric levels of the isotope began to drop. This means that the amount of carbon-14 contained in a given cell could serve as an indicator of what year that cell was formed.
Examining the heart tissue of 50 people over the course of four years, Frisen and colleagues found that on average, new heart cells appeared to replace old ones at a rate of approximately 1 percent per year in youth and 0.5 percent per year by age 75.
"If you exchange cells at this rate it means that even if you live a very long life you will not have exchanged more than 50 percent of your cells," Frisen said. "So at any given time your heart is a mosaic of cells you carry with you from birth and cells that that have been added later to replace cells that have been lost during life."
Anversa said he was "ecstatic" at the study's findings.
"Now let's discuss the magnitude of the process, and that will let us think about how we can apply this concept to heart failure," he said.
Researchers now hope to find ways to stimulate the regeneration of heart cells, as a way to avoid heart transplants and help people recover from heart attacks. Alternatively, the heart might already be regenerating heart cells after an injury but those cells might simply be dying without getting established. If this is the case, scientists could find a way to help those new cells survive.
Frisen also noted that different regeneration rates might explain why some people are more predisposed to heart disease.
"We are interested in studying whether some heart diseases could potentially be caused by too low an ability to replace heart cells," he said. -naturalnews
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