By David Warmflash
Star Trek medicine includes a fictional drug called hyronalin, administered to offset the effects of acute radiation exposure. First airing in the 1960s, the original Star Trek series imagined humanity with a positive social future, enhanced with scientific advances projected three centuries into the future. At the time, virtually all Star Trek technologies seemed to lie far ahead, but the next decades brought cell phones resembling Star Trek communicators, two-way video communication, and a plethora of other technologies. Today, there is a medical tricorder under development and physicists are attempting to measure mini–warp fields from certain technology with actual NASA funding.
Starfleet doctors used hyronalin, and NASA wants something like it, because ionizing radiation is plentiful in space, especially outside the geomagnetosphere. Also known as the Van Allen belts, the geomagnetosphere is generated by the movement of liquid metals deep in the planet. The belts trap charged particle radiation—both low linear energy transfer (low LET) from solar particle events (SPEs) and high LET from interstellar sources (galactic cosmic radiation [GCR], consisting of high-energy protons, high charge [Z] particles, and high energy [HZE] nuclei)—preventing it from reaching the Earth’s surface. SPE radiation and GCR can cause damage to cell membranes, genetic mutations, cataracts, and cancer, plus acute radiation sickness. Potentially fatal within just hours of radiation exposure, the latter condition develops after very high dose exposures, those on the order of several grays (Gy), or more. Astronauts could be exposed to such levels if an SPE were to occur while they were walking on the surface of the moon or an asteroid (although they could avoid it by entering a shelter.)
Since acute doses in excess of 10 Gy are typical on earth in the setting of radiation therapy (RT) for cancer, real-life scientists have been developing pharmacological agents to enhance cellular radiation resistance, akin to Star Trek’s hyronalin. The idea is to reduce damage to normal tissue without compromising the detrimental effects of radiation on malignant cells.
Antiradiation drugs can be grouped into two categories: radioprotectors (or cytoprotectors) that are given prior to RT to reduce long-term radiation sequelae, and radiomitigators that are given after radiation exposure to lesson radiation effects. Thus far, two radioprotectors, amifostine and palifermin, are FDA approved for use with RT.
The International Space Station (ISS) orbits at low altitudes, far below the geomagnetosphere. So astronauts are fairly well protected from charged particle radiation when ISS is over equatorial and temperate latitudes. But the geomagnetosphere is bell-shaped and the ISS orbit is fairly inclined (meaning it also crosses high latitudes); so astronauts receive higher doses than they would in more equatorial low orbits. The high inclination of the ISS orbit notwithstanding, radiation exposure is not high enough to support the use of radioprotectors or radiomitigators, because the drug toxicity outweighs the risk of long-term radiation sequelae. This is based on a radiation dose limit that NASA sets based on a 3 percent risk of fatal malignancy.
Beyond low Earth orbit, however, things will be different. For the kind of 3-year Mars mission that is on the drawing boards, with several months of time in interplanetary space, estimates of cancer mortality exceed 5 percent, plus there is a high risk of central nervous system (CNS) damage. If more advanced propulsion systems are used when the first human crews actually travel to Mars, the risk will come down significantly, but researchers are considering a variety
of such drugs for use in the event of an SPE occurring while astronauts are in unprotected environments. One group of space researchers, for instance, suggests amifostine 30 minutes before radiation exposure at 910 mg/m-2. In such a scenario, astronauts would treat themselves with the drug having been notified that SPE radiation is on its way to them.
Researchers are also testing more than a dozen radioprotectant and radiomitigating agents, and conceivably a cocktail of multiple agents could be developed to enhance the efficacy while minimizing toxicity. Essentially, it can be concluded that real-life hyronalin is in the works, a development that may aid not just space travel but medical scenarios on earth such as RT protection and nuclear accidents.