Tissue From Chernobyl Yields Clue To Preventing Radiation Damage

UC and German researchers studying thyroid tumors from victims of the1986 Chernobyl nuclear reactor accident have identified a new type of genetic damage that appears to be a specific characteristic of radiation exposure.

The finding contradicts standard textbook assertions that radiation damage has no characteristic “signature.” It’s important, the researchers believe, because it could provide a clue to developing a treatment that protects specifically against radiation exposure.

Understanding the actual mechanism of radiation damage, says UC’s Yuri Nikiforov, MD, PhD, will help scientists develop some form of protection against radiation exposure -- be it from a nuclear industry accident, the side effects of medical radiation, or even a terrorist attack with a “dirty bomb.”

The study was collaboration between UC’s pathology and internal medicine departments

and the Institute of Pathology at the University of Munich. The research team’s findings appear in the January edition of the Journal of Clinical Investigation.

It was already known that two types of genetic damage appear in thyroid cancer cells -- "point mutation,” which affects just one small sub-unit of the gene, and chromosomal “inversion,” or rearrangement, in which a piece of genetic material breaks off the chromosome and reattaches itself in the wrong place.

What the Cincinnati and Munich scientists now report is a type of chromosomal inversion involving the BRAF gene that is characteristic of radiation-induced thyroid cancer. By contrast, nonradiation, or “sporadic,” thyroid cancers are only associated with point mutations on that gene.

“This is a novel type of fusion in thyroid cancer, and it’s is the first time that the BRAF gene has been found to participate in chromosomal rearrangement,” says Dr. Nikiforov, who led the project.

“As a result of this finding,” he says, “we conclude that radiation in most cases is associated with specific genetic damage -- a chromosomal inversion.

“Finding that radiation exposure has its own mechanism is important,” he says, “because it argues against the dogma. If we accept that radiation exposure causes a specific type of DNA damage in the cells, we might be able in the future to develop a pill or some other prophylaxis to prevent this damage. That’s our long-term goal.”

Located in the throat below the larynx, the thyroid gland secretes hormones vital to metabolism and growth. One of few cancers that are increasing in recent years, although relatively easily treated, thyroid cancer will be diagnosed in about 23,600 Americans in 2004, the American Cancer Society predicts.

Besides such factors as family history, gender (women have a higher incidence) and age (the majority of cases occur in people over 40), radiation exposure is one of the major causes of thyroid cancer. The atomic bombs dropped on Hiroshima and Nagasaki during World War II, and the melt-down at the Chernobyl nuclear power plant in Ukraine, caused thousands of cases.

And before strict controls were imposed in the 1960s on high-dose therapeutic radiation, then used routinely to treat tonsils in children and thymus problems, medical exposure was also a significant cause.

Currently the only protection for people who risk potential radiation exposure, besides shielding from the source, is prior doses of potassium iodide.