Science1 publisher2 min readPublished
Cells hit by cosmic-ray iron ions push their unhit neighbors toward tumors
Oklahoma State and UT Health researchers report that cells kept near iron-ion-struck cells, though never hit themselves, went on to form tumors in mice. If that holds in people, a Mars crew's risk lies mostly in the 97% of cells iron ions miss.
The Scientist · Science desk
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What happened
- The team fired iron-56 ion beams at human aortic endothelial cells, and the struck cells kept an NF-kB and TNF-alpha inflammatory loop running for up to three days.
- Lung-lining epithelial cells that shared only liquid with the irradiated cells, through a porous mesh, showed free radical spikes and more double-strand DNA breaks.
- In those neighbors, TNF-alpha switched on several anti-death genes and a growth signal, disabling the brake that normally stops a damaged cell from becoming cancerous.
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Why it matters
- exposure Risk models that count only the cells an iron ion strikes would undercount the tissue at risk if struck cells' signals reach the roughly 32 unhit neighbors for each one.
- capability Because the damage passes through a named loop, NF-kB and TNF-alpha, researchers can now test drugs that interrupt it after a cell is struck, a step shielding cannot take.
- constraint Mission planners cannot credit any chain-breaking countermeasure until it works in irradiated animals or people; the evidence so far is dish exposures, implanted cells and one crew's blood.
For every cell an iron ion strikes during a three-year Mars round trip, about 32 escape a direct hit [14]. That ratio comes from an estimate built on radiation data from Curiosity's flight to Mars, which puts the struck share at roughly 3% of an astronaut's cells [5]. Iron nuclei are the most dangerous of the galactic cosmic rays because they leave a dense trail of ionization through DNA [4]. If the harm stayed inside struck cells, that 3% would set the risk [5]. Flight surgeons worry about the radiation-induced bystander effect, in which it spreads [6].
The experiment was built to isolate that spread. Irradiated human endothelial cells sat in a porous mesh above lung-lining epithelial cells, and the two populations shared only liquid medium [9]. Contact is ruled out as the route. Whatever harmed the lower layer had to travel through the fluid [9]. The struck cells released TNF-alpha, some of which bound back to them and kept NF-kB switched on for up to three days [8].
So something in the fluid did the damage. Showing that TNF-alpha is the necessary messenger takes one more step: block it in the shared medium and see whether the DNA breaks and the switched-on survival genes go away [11]. The experiment does not show whether a scattering of struck cells in real tissue can push TNF-alpha to the concentrations a small volume of shared culture medium allows.
The mouse result is narrower than it first sounds. The radiation exposure happened in the dish. The mice received noncancerous epithelial cells that had sat near irradiated cells, and those cells grew substantial tumors once implanted [12].
The astronaut evidence is a correlation. Blood and tissue samples from the Inspiration4 crew in 2021, collected for the Space Omics and Medical Atlas, showed systemic TNF-alpha spikes [1]. A spike on its own cannot say which part of a spaceflight produced it, and it is not a cancer outcome.
According to phys.org, the paper sets out to ask whether crews can be protected by something other than ever more protective layers, and the authors offer some potential solutions [2]. The phys.org account does not describe those solutions, report a test of blocking TNF-alpha, or give effect sizes for the DNA damage. In my view the NF-kB and TNF-alpha loop is where a drug countermeasure would start, because it sits between the hit and the bystander injury [8]. Shielding still matters: in these experiments every bystander injury began with a struck cell, so fewer hits mean fewer sources of the signal [13].
What to watch
- A test that neutralizes TNF-alpha in the shared medium and checks whether the DNA breaks and tumor formation in bystander cells disappear.
- Whole-animal Fe-56 exposures at Brookhaven's NASA Space Radiation Laboratory that track tumors in tissue the beam did not hit.
- Space Omics and Medical Atlas data from longer missions that relate astronauts' TNF-alpha levels to measured radiation dose.