Imagine a suitcase-sized device containing a radioactive powder exploding in a crowded concert hall, movie theater or on a busy street. Now imagine the radionuclides are inhaled, swallowed or absorbed. The possibility of these and similar scenarios actually occurring led Pacific Northwest National Laboratory scientist Tatiana Levitskaia and a team of researchers from the lab and Washington State University Tri-Cities to investigate a unique treatment based on chitosan, a material found in the shells of lobsters and other aquatic inhabitants. “This work addresses a national need to treat accidental and terrorist-type exposures to radionuclides,” said PNNL Fellow Larry Greenwood.
“It could also open doors to a whole new way of protecting industrial and nuclear workers.”
Few treatments are available for people exposed to radionuclides. The most common treatment is DTPA, which stands for diethylenetriaminepentaacetate. This material chelates or binds plutonium, americium and curium. Once bound, the radionuclide is eliminated from the body. Chelation treatment reduces the time it takes to eliminate the radioactive material from the body, which decreases the amount of time that radiation can damage kidneys, liver, spleen and other organs.
DTPA treatments present several challenges. Administered via an intravenous or IV drip, DTPA is effective in the blood stream, but it does not reduce the level of materials that have already moved inside the cells. Nor can DTPA treatments be used on pregnant women, children and people suffering from certain kidney, liver or intestinal diseases.
Currently, no single drug or therapy can be used to increase chelation, and thus removal, for the wide variety of radionuclides possible in the explosion of a radiological dispersion device or dirty bomb. Further, many of the radio-
nuclides that could be present or which are found in certain industrial
settings, such as cobalt-60, radium-226 and strontium-90, lack an effective treatment regimen.
At the start of a three-year effort, the research team began studying how chitosan, which has been reported on in the scientific literature for years, chelates with radioactive materials. While DTPA and other treatments address only a few radionuclides, chitosan appears to bind multiple metal ions and radionuclides, including strontium and cobalt. Chitosan is obtained from chitin in the shells of many invertebrates, including lobsters, crabs and shrimp. It is one of the most abundant and renewable natural biopolymers.
Because of its chemical structure, chitosan can move across cell membranes, accessing radioactive molecules that have already lodged inside the tissues of the liver, kidneys and other organs. This ability to move between tissues and through blood stream means that chitosan might be administered via a simple pill or two.
“Chitosan and its derivatives are non-toxic and exhibit versatile functional properties that are potentially beneficial for human health, such as antioxidant, immuno-enhancing, antibacterial, antitumor, liver protecting and other biological activities,” said Levitskaia.
Preliminary in vivo results support the team’s hypothesis that chitosan may suppress deposition in the bone structure and in critical organs like the liver and kidneys, and accelerate decorporation or removal from the body. The team has tested 15 commercially available chitosan materials along with glucosamine, which is often taken to lubricate stiff joints and main ingredient of chitosan.
Using both in vivo and in vitro experiments, the team discovered that chitosan reduced neodymium levels in liver, spleen and bone by 20 to 43 percent.
Because chitosan is easy to chemically modify, alternative structures could be developed to enhance its affinity for a particular radionuclide or chemical. It could also be designed to control or enhance specific properties related to how it behaves inside the body. In the autumn of 2006, Levitskaia’s team received a $725,000 BioShield grant to rapidly develop chitosan as a chelation therapy for those that inhale, swallow or absorb radionuclides. This grant is from the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. When completed, people exposed to the radioactive materials from a terrorist’s weapon could be easily treated.
Kristine Manke is an information specialist at Pacific Northwest National Laboratory.
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