One-two particle punch poses greater risk for astronauts

It doesn't just matter how much radiation an astronaut is exposed to, time and the order in which charged particles strike human cells are important factors as well. That's the main finding of a study simulating radiation exposure conducted at the U.S.

Department of Energy's Brookhaven National Laboratory and published in the September 2006 edition of Radiation Research. In the study, human cells were three times more likely to develop properties similar to those in the initial stages of cancer when they were exposed to two types of high-energy particles in a short period of time.

The radiation field in space contains high levels of high-energy protons and much lower levels of high atomic number, high-energy (HZE) particles such as iron and titanium.

"Most people studying the effects of space radiation have looked at the effects of just one type of particle, either the protons or the HZE particles," said Brookhaven biologist Betsy Sutherland, the paper's lead author. "This is one of the first studies to try to imitate real space radiation conditions closely, where, on average, a cell will be hit by a proton first and then by an HZE particle. We decided to examine what this does to human cells."

To test the effect of dual-particle irradiation, Sutherland's team at the NASA Space Radiation Laboratory, a facility built at Brookhaven Lab specifically for space radiation studies, first exposed normal human cells to a beam of protons. Then, anywhere from 2.5 minutes to 48 hours later, they exposed the cells to iron or titanium particles. After

allowing the cells to grow, the researchers counted the number of cells that survived to form colonies and those that acquired the ability to grow without being affixed to a solid surface. This characteristic, known as anchorage-independent growth, is an early indicator that these cells might be on the pathway to cancer.

"There are a lot of animal-based systems for measuring the induction of cancer, but you can't just take human cells and treat them with radiation or chemicals and immediately get cancer cells," Sutherland said. "You have to do several treatments in order to get a real cancer cell. Some people study the end stages of this process, but we look at the very first step."

The research team found that the probability that cells undergo this initial transformation depends on the time interval between the cell's exposure to protons and HZE particles. When the cells received both irradiations within 2.5 minutes to one hour, they produced about three times more anchorage-independent colonies per survivor than expected from the sum of the effects of the two radiation exposures.

"If you hit cells in less than an hour with a little tickle of protons and, on average, one iron ion per cell, that's when you get the big increase in transformation," Sutherland said. "If this were to happen in space, a certain fraction of the astronaut's cells would have a higher risk of going along this initial path to cancer development."

The good news, Sutherland said, is that in real space, most of the charged particle hits do not occur that close together in time. Therefore, only a small part of the astronaut's cells would have an increased risk of becoming cancerous.

The reason for the observed increase in anchorage independence in response to the one-two particle punch is not yet clear. The obvious effects – those related to survival or the cell cycle – tuned out not to be the cause of increased transformation, Sutherland said. The team observed a further complication when the order of particle exposure was reversed; there was no increase in anchorage independence when the cells were hit with either an iron or titanium particle first, followed by protons.

"Now our challenge is to figure out exactly what is happening," Sutherland said, adding that the results of this study and projects like it help NASA assess the hazards of space travel. "If we're going to send people into space, it's our responsibility to tell them what their risks are and investigate ways to mitigate the danger."

Source: Brookhaven National Laboratory

Related stories:

Scientists demonstrate the sharpest measurement of ice crystals in clouds
Scientists have created an instrument designed to help determine the shapes and sizes of tiny ice crystals typical of those found in high-altitude clouds, down to the micron level (comparable to the tiniest cells in the human body), according to a new study in Optics Letters, a journal published by the Optical Society. The data produced using this instrument likely will help improve computer models used to predict climate change.
Visualizing atomic-scale acoustic wavesin nanostructures
Acoustic waves play many everyday roles - from communication between people to ultrasound imaging. Now the highest frequency acoustic waves in materials, with nearly atomic-scale wavelengths, promise to be useful probes of nanostructures such as LED lights. However, detecting them isn't so easy.
Testing, Radiation Testing: Northwestern Transistors On Space Station
Transistors based on a new kind of material created by Northwestern University researchers have been lifted into outer space on the space shuttle Endeavour and attached to the outside of the International Space Station for radiation testing.
Space radiation may cause prolonged cellular damage to astronauts
With major implications for long-duration space travel, a study from the Lombardi Comprehensive Cancer Center at Georgetown University Medical Center demonstrates that the high-energy radiation found in space may lead to premature aging and prolonged oxidative stress in cells. The findings suggest that astronauts may be at increased risk of colon cancer due to exposure to the high linear energy transfer (LET) radiation found in space.
Missions to Mars: GSI will investigate radiation risks for astronauts
The European Space Agency (ESA) has chosen the GSI accelerator facility to assess radiation risks that astronauts will be exposed to on a Mars mission. GSI was selected because its accelerator is the only one in Europe able to create ion beams similar to those found in space. To determine possible health risks of manned space flights, scientists from all over Europe have been asked to investigate the effects of ion beams in human cells and organs. The first experiments will be launched this year and subsequently continued at GSI’s planned FAIR accelerator system.
New Method Offers Insight into Radiation Damage to DNA
A new technique for assessing the damage radiation causes to DNA indicates that the spatial arrangement of damaged sites, or lesions, is more important than the number of lesions in determining the severity of the damage. The technique, developed by scientists at the U.S. Department of Energy (DOE)'s Brookhaven National Laboratory, helps reveal why high-energy charged particles such as the heavy ions in outer space are more potentially harmful than lower-energy forms of radiation such as x-rays and gamma rays.
Vanguard I celebrates 50 years in space
The Vanguard I satellite celebrates its 50th birthday this year. Its launch on March 17, 1958 from Cape Canaveral, Florida, culminated the efforts of America’s first official space satellite program begun in September 1955. The first solar-powered satellite, Vanguard I has the distinction of being the oldest artificial satellite orbiting the earth. Its predecessors, Sputniks I and II and Explorer I, have since fallen out of orbit.
Brain stem cells sensitive to space radiation
Cold Spring Harbor Laboratory (CSHL) scientists recently led a team of researchers to study potential effects of space radiation on astronauts. The results of their study are revealing and will provide the foundation for ensuring the safety of crew members participating in long distance space travel. Measures to protect astronauts from health risks caused by space radiation will be important during extended missions to the moon or Mars, say researchers in a paper currently online in Experimental Neurology.

News discussion:

Space & Earth science news