DRESDEN, Germany — It turns most healthy people have the liver of a toddler — regardless of how old they really are! A new study has discovered that this unique organ has the ability to regenerate, meaning that it maintains an average age of less than three throughout a person’s lifetime.
An international team says the liver has the ability to regenerate after sustaining damage. Until now, however, scientists didn’t know if this ability deteriorated with age. Researchers used the technique called retrospective radiocarbon birth dating to examine the age of the liver in a group ranging in age from 20 to 84.
Results revealed that no matter how old the person was, the liver maintained an age of roughly three years. Study authors note their findings prove that aging does not apply to the liver and the body’s ability to refresh this vital filter.
What makes the liver so special?
Scientists explain that the liver is so extremely important to human health because it clears out toxins from the body. However, because it is constantly performing this dirty job, the liver has a high risk of suffering damage. To prevent this, the liver constantly regenerates a large portion of its cells.
In previous experiments with animals, scientists were unable to get a clear answer as to whether physical aging weakens this ability in the liver.
“Some studies pointed to the possibility that liver cells are long-lived while others showed a constant turnover. It was clear to us that if we want to know what happens in humans, we need to find a way to directly assess the age of human liver cells,” says Dr. Olaf Bergmann, the research group leader from the Center for Regenerative Therapies Dresden (CRTD) at TU Dresden, in a university release.
To answer this question, a team of biologists, physicists, mathematicians, and clinicians examined the bodies of several human corpses who died between age 20 and 84. While the people died at various stages of life, their livers all showed the same readings.
“No matter if you are 20 or 84, your liver stays on average just under three years old,” explains Dr. Bergmann.
Researchers also note that the size of a person’s liver adjusted to meet the needs of the body over time. This occurred through the constant replacement of liver cells, even during old age.
Some liver cells are a little older
Not every cell in the liver stays in preschool. The team found that a small fraction of these cells can live for nearly a decade before the organ regenerates them. This particular group of cells carries more DNA than the average cell.
“Most of our cells have two sets of chromosomes, but some cells accumulate more DNA as they age. In the end, such cells can carry four, eight, or even more sets of chromosomes,” Dr. Bergmann says.
“When we compared typical liver cells with the cells richer in DNA, we found fundamental differences in their renewal. Typical cells renew approximately once a year, while the cells richer in DNA can reside in the liver for up to a decade,” the researcher continues. “As this fraction gradually increases with age, this could be a protective mechanism that safeguards us from accumulating harmful mutations. We need to find out if there are similar mechanisms in chronic liver disease, which in some cases can turn into cancer.”
Can I see your (liver) ID?
Dr. Bergmann’s team says determining the real biological age of human cells was a massive undertaking — mainly because the methods that work on animal cells doesn’t apply to people. Retrospective radiocarbon birth dating uses a specific variety of carbon which appears naturally in the atmosphere. Plants incorporate this substance through photosynthesis and then pass it on to humans and animals.
Radiocarbon has a weak and unstable radioactive signature. Archeologists use it determine the age of ancient samples.
“Archeologists have used the decay of radiocarbon successfully for many years to assess the age of specimens, one example being dating of the shroud of Turin,” says Dr. Bergmann. “The radioactive decay of radiocarbon is very slow. It provides enough resolution for archeologists but it is not useful for determining the age of human cells. Nevertheless, we can still take advantage of the radiocarbon in our research.”
The team notes that aboveground nuclear tests during the 1950s sent large amounts of radiocarbon into the air, plants, and the rest of the environment. The resulting fallout led to higher amounts of radiocarbon in plant and animal DNA.
These levels dropped off in the 1960s, but the link between atmospheric and cellular radiocarbon levels still have a strong connection.
“Even though these are negligible amounts that are not harmful, we can detect and measure them in tissue samples. By comparing the values to the levels of atmospheric radiocarbon, we can retrospectively establish the age of the cells,” Dr. Bergmann explains.
The study is published in the journal Cell Systems.