“Space: the final frontier.”
Anyone who has lived in the United States during the last 60 years can attest to the country’s longstanding obsession with exploring the mysterious void of space, truly the last uncharted region known to man. Beginning in the late 1950s with the Soviet Union’s launch of Sputnik 1—the first artificial satellite to orbit Earth—America fell headfirst into the Space Age, with TV series such as Star Trek and movies like 2001: A Space Odyssey capturing the imagination of the country. Americans brimmed with excitement as the newly formed National Aeronautics and Space Administration (NASA) launched program after program to further the United States’ foothold in space and edge out the USSR in the Space Race; even now, over 40 years after the successful moon landing of Apollo 11 in 1969, outer space still seems to elicit a sort of romantic fascination for many. However, recent research studying the effects of galactic cosmic radiation on neurodegeneration has called our decades-old obsession into question—is space exploration truly worth the physiological price that may be paid by our astronauts?
We have long known that space is filled with radioactive particles of varied compositions and characteristics. Earth’s magnetic field normally provides a layer of protection from this damaging radiation, but once an astronaut leaves the safety of orbit, they are immediately exposed to massive amounts of galactic cosmic radiation (GCR) containing high-energy, high-charged (HZE) particles. One type of HZE particle, 56Fe, is of particular concern; due to their relatively large masses and high travel speeds, these iron-based particles are capable of penetrating solid objects like spacecraft. According to Michael O’Banion, M.D., Ph.D, Professor of Neurobiology at the University of Rochester Medical Center and senior author of the study in question, “[o]ne would have to essentially wrap a spacecraft in a six-foot block of lead or concrete” in order to prevent 56Fe particles from entering. Clearly, this level of protection is not realistic, so scientists must weigh the possible risks of exposure to such radiation with the potential benefits of manned space missions. Previous studies have focused on the link between these particles and cancer and cardiovascular diseases, but O’Banion’s is the first to concentrate on damage to the brain.
At NASA’s Space Radiation Laboratory on Long Island, researchers utilized special particle accelerators to recreate the levels of radioactive 56Fe present in space. After mice were exposed to several different intensities of radiation, they were then tested in two domains—fear conditioning, which focused on the mice’s ability to remember certain locations associated with a painful shock; and object recognition, which tested the mice’s ability to recognize particular objects. Researchers observed that mice exposed to HZE radiation performed markedly worse on these tests than controls, even when the levels of radiation were relatively low. The reason? An increase in the accumulation of amyloid beta (Aβ) plaque in the mice’s brains—a hallmark of Alzheimer’s disease.
In a healthy individual, amyloid beta (a peptide) functions in the brain to regulate cholesterol transport and enzyme activation. The level of Aβ is normally kept steady by the vascular system, but in an Alzheimer’s patient, Aβ begins to accumulate and form harmful deposits of plaque in neural tissue. This buildup initiates a damaging cycle of neuroinflammation and impaired transport of Aβ out of the brain, leading to a decline in cognitive ability. Many factors have been shown to lead to this buildup, but one factor in particular stands out in the context of this study: radiation.
The researchers found evidence implicating the radiation emitted from 56Fe particles and other types of HZE in the deterioration of the blood-brain barrier (BBB), a semi-permeable membranous system that functions as a layer of protection between the brain and substances traveling through the vascular system. Reduce the effectiveness of the BBB, and the nervous system’s delicate chemistry is thrown off balance. Removal of excess amyloid beta may be compromised and result in the aforementioned buildup of plaque and increased neuroinflammation, which prevent the activation of necessary enzymes and glucose uptake by neurons. Cognitive decline ensues. Thus, high levels of amyloid beta are strongly linked with accelerating both the onset and progression of Alzheimer’s.
Currently, NASA is working to send the first manned spaceflight to Mars in 2035, a round-trip mission that could take up to three years. The opportunities for exploration and study afforded by this mission would be unparalleled—but are they truly worth the potential health risks stemming from such an extended period of radiation exposure? Is an increased likelihood of Alzheimer’s for American astronauts simply a price that must be paid for scientific advancement? For the chance to “explore strange new worlds, to seek out new life and new civilizations, [and] to boldly go where no man has gone before”?