Contact:
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
Single Radiation Dose Causes 30% Loss Of
Spongy Bone In Mice
Study has implications for radiation
therapy, deep space travel
BETHESDA, MD. (July 12, 2006) – Mice receiving just one
therapeutic dose of radiation lost up to 39% of the spongy portion of their
inner bone, reducing the inner bone’s weight bearing connections by up to
64%, researchers reported. The study, which appears in the online edition of
the Journal of Applied Physiology, has implications for patients
receiving radiation therapy and astronauts traveling on long space flights.
“We were really surprised at the extent of bone loss,”
said lead researcher Ted A. Bateman of Clemson University. “We’re seeing
bone loss at much lower doses of radiation than we expected.” The mice
suffered the loss of trabecular bone, the spongy area of bone inside the
dense outer area known as the cortical bone.
“It’s interesting that the trabecular bone, not the
cortical bone, suffered the damage,” said Bateman, a bioengineer who studies
bone biomechanics. The remaining spongy bone must redistribute the load to
bear the weight, but this makes the bone support structure less efficient
and leaves the bone more vulnerable to fracture.
“A murine model for bone loss from therapeutic and
space-relevant sources of radiation,” by Sarah A. Hamilton, Neil D. Travis,
Jeffrey S. Willey, Eric R. Bandstra and Ted A. Bateman, Clemson University;
and Michael J. Pecaut, Daila S. Gridley and Gregory A. Nelson, Loma Linda
University and Medical Center, appears in the online edition of the
Journal of Applied Physiology, published by The American
Physiological Society.
Mouse model applies to
humans
The results of a mouse study cannot be directly applied
to humans. However, both mice and humans lose bone after radiation exposure,
so the results raise a red flag. Bateman noted that a recent clinical study
of 6,000 cancer patients reported in the Journal of the American Medical
Association found that post-menopausal women who received pelvic
radiation for cervical and colorectal cancer increased their bone fracture
risk by 60%. Radiation following anal cancer increased the risk of fracture
by 200%, he said.
Astronauts lose 2% of bone mass for each month they are
exposed to the effects of microgravity. So far, astronauts have not been
exposed to the increased radiation of outer space, but that will change when
they undertake a proposed 30-month trip to Mars, Bateman said. NASA has
focused on radiation’s cancer-causing properties and its ability to
compromise the central nervous and immune systems. But the effect on bone
health is an unexamined concern.
The murine (mouse) model such as the one in this study
provides a way to study the physiological effects of radiation using
controlled experiments. Clinical studies of people who undergo radiation to
treat cancer are limited because of the complicating factors of the illness
itself and the chemotherapy which often accompanies it. “You can’t study
this in people, so having a well-defined animal model is important,” Bateman
said.
Study focuses on four types
of radiation
In the current study, the mice received a single 2 Gray
(Gy) dose, which is comparable to the single dose of 1-2 Gy that human
cancer patients receive. However, cancer patients receive a series of doses
over the course of therapy, totaling 10-70 Gy. (The amount of radiation in a
Gy varies, because it is calculated based on the recipient’s weight.)
The mice were divided into five groups. The control
group received no radiation. Each of the remaining four groups received a
different type of radiation: gamma, proton, ion or carbon. Those exposed to
the carbon radiation suffered 39% spongy bone loss; proton, 35%; ion, 34%;
and gamma, 29%. The loss of spongy connections in the four groups ranged
from 46-64%, he said.
Cancer patients typically receive either gamma or, less
commonly, proton radiation. Astronauts on a Mars mission are expected to
receive extended periods of low-dose radiation of multiple types, including
protons and heavy ions, Bateman said.
Source
“A murine model for bone loss from therapeutic and
space-relevant sources of radiation,” by S.A. Hamilton, N.D. Travis, J.S.
Willey and T.A. Bateman, Department of Bioengineering, Clemson University,
Clemson, South Carolina; M.J. Pecaut, D.S. Gridley and G.A. Nelson,
department of Radiation Medicine, Loma Linda University and Medical Center,
Loma Linda, California, appears in the online edition of the Journal of
Applied Physiology published by The American Physiological
Society.
Bateman’s team received the mouse bones from the Loma
Linda group, which had used the mice to examine the effects of radiation on
the immune system.
Funding
Procter and Gamble Pharmaceuticals, the
National Space Biomedical Research Institute and NASA provided
grants to fund this research.
Editor’s notes: Bateman will be at the Kennedy
Space Center and available for interviews July 13-17 to give a presentation
to university undergraduate students spending the summer at the Spaceflight
and Lunar Sciences Technology Program.
The media may obtain a copy of
Hamilton et al. by contacting Christine Guilfoy, American
Physiological Society, (301) 634-7253 or
cguilfoy@the-aps.org.
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