The radiation astronauts encounter
in deep space could put vital blood-making cells in jeopardy.
Writer's Note: Stem cells
discussed in this story are adult stem cells, not to be confused
with controversial embryonic stem cells. All adults have stem cells; they're crucial to everyday health.
NASA is working to learn how space radiation might affect
the blood-making stem cells of astronauts en route to the Moon or
by Patrick L Barry and Dr Tony
In the time it takes
you to read this sentence, more than 10 million red blood cells
in your body will die. Don't be alarmed; it's natural, and stem
cells in your bone marrow are constantly making enough new cells
to replace the dying ones.
But what if those blood-making
cells stopped working? Without a fresh supply of red and white blood
cells, you would quickly become anemic, your immune system would
collapse, and without medical attention, you would die.
This could be a concern
for astronauts taking long trips beyond Earth orbit. It's well known
that space radiation can damage cells in astronauts' bodies. Less
well understood is the specific threat to the key blood-making cells.
threat, and developing remedies, is the job of Alan Gewirtz, a medical
doctor at the University of Pennsylvania (Division of Hematology
and Oncology). He's bombarding stem cells with simulated space radiation
to see how the cells are affected. By exploring the molecular damage,
and testing candidate drug-remedies, "this research could benefit
not only astronauts, but also people here on Earth who suffer from
blood disorders such as leukemia and aplastic anemia," says Gewirtz.
Image courtesy Andrew Leonard, Stanford Magazine. More
A false-color micrograph of a bone marrow stem cell, shown
The work is being done
at the NASA Space Radiation Laboratory ("NSRL" for short) in New
York. NSRL draws high-speed particles from one of the atom smashers
at Brookhaven National Laboratory in Long Island and channels them
to a special facility for biological research. The radiation consists
of protons and heavy ions moving at almost light speed--much like
the cosmic rays astronauts encounter in deep space.
Apollo astronauts absorbed
some cosmic rays on their way to the moon, but they didn't suffer
much from it because those trips were short, a matter of days. Astronauts
traveling to Mars, on the other hand, will be "out there" for at
least six months. Accumulated cosmic ray damage could become important.
To see how cosmic rays
affect an astronaut's internal blood supply, Gewirtz irradiates
Petri dishes containing samples of blood-making stem cells. Each
sample contains about a million cells collected from the bloodstream
of paid, healthy volunteers. Once the cells have been exposed, the
team looks closely for damage. Are the cells' DNA strands (the "memory
chips" for making new cells) affected? If so, how, and how badly?
Are other parts of the cells' internal machinery damaged? In what
These stem cells should
not be confused with controversial embryonic stem cells: Gewirtz
is working with adult stem cells.
Adult stem cells live
in several places within every person's body, such as the bone marrow,
the brain, the skin, and the gut. Unlike most of the body's cells,
stem cells aren't pigeonholed into being only one kind of cell,
such as a heart or a kidney cell; instead, they retain the ability
to become any type of cell--a trait called "pluripotency" or "multipotency."
Bone marrow stem cells,
called "hematopoietic progenitor" cells, generate a continuous supply
of cells that can become any of the following: platelets, lymphocytes
and granulocytes (white blood cells), erythrocytes (red blood cells),
and others. In this way, stem cells are a source of fresh replacement
cells to fill in as older cells wear out.
Beyond assessing radiation
damage to hematopoietic progenitor cells, Gewirtz's group also plans
to test some drug-like "countermeasures" that could help astronauts
better endure low levels of radiation exposure.
courtesy Stem Cell World
cells in the bone marrow can spawn any of a wide range
of blood cell types.
One idea is to give
the cells antioxidants. Much of the damage to DNA isn't caused by
the radiation itself, but by chemically reactive "free radicals"
created when the radiation strikes some other molecule. These roving
free radicals then go on to "oxidize", and thus damage, the DNA.
Mopping up free radicals with antioxidants, in the form of pills,
perhaps, could slow or halt the damage.
Another approach they're
considering is to amplify a natural system in people's cells for
repairing DNA. Normally, cells contain dozens of specialized repair
enzymes that constantly run up and down the long, stringy DNA molecules,
checking for damage and making repairs. "We hope to find ways to
stimulate the natural repair mechanisms," Gewirtz says. "It's hard
to beat millions of years of evolution for picking out what works,
and works well."
Will these countermeasures
help protect the cultured cell samples? Gewirtz says his team ought
to have some results by the end of the year. If they're successful,
astronauts on their way to Mars may not have to worry about their
own internal wellsprings of new blood cells running dry.