Bubble, Bubble, Toil and DNA Damage


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Prof. Amos Breskin and Dr. Rachel Chechik

When you have an X-ray, what happens to your DNA? When a cancer patient undergoes radiation treatments, how much is too much?

The precise answers to these questions may dwell inside a tiny gas bubble.

Damage to DNA is believed to be the major cause of cell mutation and in some instances, death. A group of physicists whose work overlaps the realm of biology, headed by Professor Amos Breskin of the Particle Physics Department, got to thinking: Just how do you analyze radiation's effects on something as small as DNA if no particle detector has the sensitivity to determine it?

Possible answer: If the DNA were in gaseous form, it would then be considerably expanded in size and thus easier to determine change. And that is how the tiny gas bubble was born. A simulated fragment of DNA in gaseous form, it's only a millimeter in size ­ but one million times the size of our DNA.

Prof. Amos Breskin, together with departmental colleagues Drs. Rachel Chechik and Sergei Shchelmelinin, have succeeded in constructing the first detector that permits measuring the effects of radiation on a DNA-like gas bubble.

Prior to this, scientists throughout the world had constructed gas models of cells and chromosomes. But because cells and chromosomes are much larger than DNA, those models could not predict potential damage to the diminutive DNA. The new particle detector, 100 to 1,000 times more precise than prevailing techniques, could fulfill the task.

How does the detector work? When radiation penetrates the cell, it breaks molecular bonds in the DNA. Each molecule then separates into an electron (negatively charged) and an ion (in this case, positively charged). This means that the more electrons and ions spotted in a cell, the more bonds have been broken.

The question is, have the DNA double strands both broken too? Once you detect a large concentration of particles in the DNA-like gas bubble, and with it proof that many bonds could have been broken at one particular site, you may have found what you were looking for ­ an irreparable break in the DNA double strands.

Causing these electrons or ions to fly out of the bubble, Prof. Breskin can count them using the new detector. The ion rate of release is a telling indicator of the frequency of reactions which went on between the radiation and the gas and their concentration in the vicinity of the DNA strand. The scientists can then use scaling factors to predict the frequency of interactions in the actual smaller, solid volume of DNA.
The same X-ray or particle beam that enters the bubble, exits it and interacts with a sample of living cells. The cells' rate of destruction is compared with the radiation effect on the DNA gas model. The researchers intend to determine the direct correlation between the radiation dose causing potential, permanent damage to DNA, and cell destruction.

Once the researchers have found the details of the correlation between the two experiments, it will pave the way for more accurate predictions of radiation effects on the living cell.
In treating cancer, the object is to destroy the DNA in tumor cells using as little radiation as possible, so as not to damage the surrounding healthy tissue. "Once you know how much radiation breaks DNA strands, you can better determine how much radiation to expose cancer patients to," says Professor Breskin.

Along with its potential impact on cancer screening and treatment, Prof. Breskin's approach may make safer our personal health by allowing scientists to designate more precise limits on the number of X-rays a person may undergo yearly, including those we are exposed to at the dentist's office and during a routine mammography. Better informed standards on radiation exposure in the workplace could be set.

Breskin's group's research may even affect space programs, clarifying radiation's impact on astronauts. It could lead to new approaches on how best to protect advanced electronic equipment in satellites and other space objects from cosmic radiation.

All of this, thanks to Breskin's little gas bubble.