May 15, 1998

Low dose radiation can be good for you

Dr. Chris Le

Researchers in the Faculty of Medicine and Oral Health Sciences have developed an ultrasensitive technique to detect DNA damage so powerful it can find one impaired DNA among a sample of one billion healthy ones. It can detect fewer than 2000 damaged DNA molecules. That's a 10,000 to 100,000-fold increase in sensitivity over the current method available. Dr. X. Chris Le, in environmental health sciences, Dr. Michael Weinfeld, in experimental oncology, and their colleagues have published their findings in the May 15 edition of the journal Science.

"We know human cells are always exposed to DNA damaging agents, even oxygen, from the environment. .If the DNA damage were not repaired, human cells would not function properly, mutations would accumulate, and cancers would develop," said Le. To study the repair of DNA, said Le, scientists need to assess the level of damage. But current DNA repair studies look at high level doses of damaging agents on DNA because of a lack of a more sensitive method. Until now, there was no data available on low level damage, which is similar to the realistic environmental impact to which people are subjected.

A cover story in 1995 on Science's "molecule of the year" piqued Le's interest on DNA research. DNA is the essential code of life for organisms. Damage it and the impact on human health can be deadly: genetic mutations that can lead to cancer.

Le, Weinfeld and Dr. Steven Leadon of the University of North Carolina at Chapel Hill School of Medicine, used a combination of three existing methods: immunochemical recognition (the process by which the body recognizes foreign substances); capillary electrophoresis (an advanced separation technique); and laser-induced fluorescence (a highly sensitive detection technique. A patent is pending on the technique.

What happens is this: primary antibodies that recognize specific forms of genetic damage and attach themselves to the damaged DNA are mixed with secondary antibodies that give off fluorescent light and attach themselves to the damaged DNA. The mixture is then fed through a tiny glass tube to separate various molecular entities. A laser beam is focused on these molecules coming out of the capillary. The DNA that shows up as fluorescent is damaged. Higher light intensity means more damage.

But the researchers didn't stop at the technique. They immediately demonstrated its use in understanding DNA repair and included this experiment in their paper. It found that low dose radiation may not be such a bad thing after all.

"We irradiated the cells with low level gamma radiation," said Le "and we let them adapt, or incubate, for a few hours. Then we gave a higher dose and monitored the speed of repair to compare it to a situation where the cells were not previously exposed but subjected only to high levels and monitored that rate of repair."

The result will probably change what the world thinks about radiation: "It turns out, the cells which were previously exposed repaired the DNA faster," said Le. It "toughens up" the cells and kick starts the repair process.

"This has tremendous implications for environmental and health sciences. It could be a little bit of exposure may not be too bad. It may even be protective," said Le.

This could have an impact on people undergoing cancer radiation therapy.

Questions remain, however. Scientists have to find out how "low" the low-level dose should be. And how long does a potential protective effect last? Furthermore, different agents like radiation, sunlight, tobacco, and other chemicals cause different types of damage. The cells, therefore, use different repair mechanisms.

"It's a start," said Le, "And a new way of thinking about cancer risk from exposure to low levels of environmental contaminants." Needless to say, he's excited about the discoveries and pleased he can bring his analytical chemistry expertise to the Faculty of Medicine and Oral Health Sciences.

"The technique itself I think warrants publication in Science because it's so advanced," said Dr. Steve Hrudey, professor of environmental health sciences. "But how they use the technique, for repair, is remarkable in its own right."

And to think it all got started with the "molecule of the year" story.

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