Radiation Study Examines Leukemia Risk From Trip to Mars

Galactic Cosmic Rays—Just Some of the Challenges of the Mars Mission

Sunrise in Mars
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Will Mars Mission astronauts develop leukemia from their journey to the Red Planet? It may sound like a strange question, but NASA-funded studies are looking into all kinds of things in preparation for what may be another giant leap for mankind—a manned trip to the Mars. The journey with a crew of human beings may begin as soon as the 2030s. There are different phases of this momentous project, and the planning and research has already begun.

You can view all of the plans, including the three different phases of exploration, at NASA’s “Journey to Mars Overview” site.

The manned mission to Mars comes with many dangers, some known and some perhaps unknown. One of the concerns for future travelers is the impact of deep-space radiation on human health. In a new NASA-funded study, researchers have found that deep space radiation may heighten the risk of leukemia in astronauts, brought on by changes to vital stem cells in the bone marrow that give rise to all new blood cells in the body.

Radiation From X-rays and CT Scans

Radiation exposure carries with it the potential to do harm. There is ionizing radiation and non-ionizing radiation.

While non-ionizing radiation, like those UV rays from the sun, can be damaging, you can usually shield yourself from this type of radiation pretty easily. Ionizing radiation is harder to avoid. Ionizing radiation can move through substances and change the charge of the atoms in the surrounding material.

The particles associated with ionizing radiation in space come from trapped radiation belt particles (Van Allen Belts), cosmic rays, and solar flare particles.

In the case of radiation used to treat cancer, the benefits of therapeutic ionizing radiation (killing the cancer cells) are weighed against the risks from such exposure, such as short and long-term complications, including the emergence of a new malignancy years later.

Likewise, the exposure to radiation in x-rays and CT scans is not taken lightly, since cumulative and unnecessary exposures to medical and diagnostic radiation can also add to a person’s lifetime risk of malignancy.

Radiation From Galactic Cosmic Rays

Radiation is basically traveling energy, and galactic cosmic rays (GCRs) are one form of radiation that is of great interest as it relates to space travel. GCRs mostly come from outside our solar system, but generally from within our Milky Way galaxy. GCR are essentially heavy, high-energy ions of elements that have had all their electrons taken away while they traversed the galaxy at nearly the speed of light.

The radiation of deep space is different from what we experience on the Earth's surface—or even in low Earth orbit—because there is much more “traffic” of high-energy galactic cosmic rays out there, in addition to radiation from solar events and from the radiation belts that are closer to home. The Earth has radiation belts called Van Allen belts that extend about 1,000 to 60,000 kilometers above the surface.

The Earth’s magnetic field deflects the radiation and protects the Earth's atmosphere from destruction, but a Mars mission requires deep space travel.

What is more, Mars lost it’s magnetic field billions of years ago, so for humans who eventually set foot on the Red Planet, there will be no such protection waiting for them. NASA is well aware of these dangers and is working on possible solutions. NASA scientists have even raised the prospect of creating an artificial magnetic field around Mars to protect future missions.

What Might Galactic Cosmic Rays Do to Humans?

The impact of radiation on humans in space is being examined in a number of different ways, and it is not just leukemia and malignancy that scientists are worried about. NASA is also conducting studies looking into spacewalking astronauts, how such exposures might affect cognition and behavior, and how genes respond to radiation—and specifically, which genes are turned on and which genes are turned off by such exposures.

Life on Mars could bring an increased risk of leukemia, according to data gathered by a research team from Wake Forest Baptist Medical Center. The group investigated the potential impacts of deep space radiation specifically on human hematopoietic stem cells (HSCs). The HSCs are actually the very same stem cells you may have heard about that are used as a cancer treatment in some cases.

When a patient has high doses of chemotherapy planned to kill the cancer cells, the chemo can also take its toll on stem cells. Because of this, bone marrow transplants, or hematopoietic stem cell transplants, may be performed to boost the patient’s ability to get a fresh start with healthy, new blood forming cells. These are the very same blood-forming cells in your bone marrow that produce all of your new blood cells as the old ones wear out. The mature cells in the blood include the red cells that shuttle oxygen from your lungs to the rest of your body, but also the white cells that help to fight infection and malignancy.

The team at Wake Forest took these blood-forming HSCs from healthy donors aged between 30 and 55 and exposed them to simulated radiation and GCRs like the rays expected to bombard astronauts during a Mars mission. They analyzed the cells in the lab afterwards and found that the radiation affected the cells at the stem cell level, causing mutations in genes that affected their ability to develop into mature blood cells. The radiation exposure reduced the stem cells ability to produce almost all types of blood cells, and their capacity to make new cells was often reduced by as much as 60 to 80 percent, according to Christopher Porada, a senior researcher on the project.

What such a reduction in blood cells might mean for astronauts is something many blood cancer patients already know about—the decline in red blood cells can cause anemia, with symptoms such as tiredness, weakness, shortness of breath, and poor exercise tolerance. The reduction of white blood cells can reduce the body’s immune defenses, increasing susceptibility to infection. And the reduction in platelets can make a person more prone to clotting and bleeding problems, with abnormal bruising or bleeding.

Using Mice to Find Out a Bit More

Often in medical research, findings that seem to hold true in the laboratory cannot be reproduced or verified when it matters, in a real, living breathing human being—or a mouse to start with. To try to gain insight into how radiation exposure might look in a living being, the team at Wake Forest transplanted the GCR-irradiated HSCs into mice.

The mice went on to develop T-cell acute lymphoblastic leukemia. The team described this as the first demonstration that deep space radiation may increase the leukemia risk in humans.

T-cell acute lymphoblastic leukemias (T-ALLs) are aggressive blood cancers resulting from the malignant changes in the cells that give rise to T-cells, or the white blood cells known as T-lymphocytes. T-ALL accounts for 10 percent to 15 percent of childhood ALL and 25 percent of adult ALL. Patients with T-ALL often have bone marrow that has become packed with immature T cell lymphoblasts, as well as high white blood cell counts, tumors in the chest area, and frequent involvement of the central nervous system at the time of diagnosis. Cure rates over 75 percent in children and about 50 percent in adults have been seen with this disease.

Bottom Line From Mouse Study

The investigators' findings allowed them to conclude that two different effects of radiation may have been at work in the emergence of the leukemia. First, they found genetic damage to HSCs could directly lead to the development of leukemia. Second, radiation also impaired the ability of HSCs to make new T and B cells, both of which are white blood cells that can be involved in fighting foreign invaders like bacteria, but also tumor cells. So, not only do you have the genetic changes in the stem cells that can lead to leukemia, but you also have an impaired immune system in regard to its ability to eliminate malignant cells that arise from radiation-induced mutations.

Sources

Dachev T, Horneck G, Häder D-P, et al. Time profile of cosmic radiation exposure during the EXPOSE-E Mission: The R3DE Instrument. Astrobiology. 2012;12(5):403-411.

Van Vlierberghe P, Ferrando A. The molecular basis of T cell acute lymphoblastic leukemia. J Clin Invest. 2012;122(10):3398-3406.

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