Long-distance space exploration carries hidden biological costs, as male rats exposed to simulated cosmic radiation accumulated roughly twice as much collagen around small coronary blood vessels at long-term follow-up, according to research published in the journal PLoS One.
Simulated Spaceflight Stresses on Earth
The research program used 72 male WAG/RijCmcr rats, eight to nine months old at the outset. Investigators selected this strain because earlier work showed sensitivity to radiation-related cardiac injury. Investigators analyzing measurements were blinded to the animals’ treatment groups.
Through six beams delivering five ion types, the team conducted work at Brookhaven National Laboratory’s NASA Space Radiation Laboratory. This simplified simulator approximates components of galactic cosmic radiation after spacecraft shielding. It cannot reproduce the entire radiation environment of deep space.
Radiation doses included 0.75 gray and 1.5 gray. A gray measures absorbed radiation energy per unit mass. Instead of setting a single fixed dose for every Mars mission, the researchers viewed 0.75 gray as an approximation of a three-year exploration trip. To model aspects of microgravity, some animals underwent hindlimb unloading for 30 days.
Scar Tissue Measurements Months After Irradiation
Rats given 0.75 gray without hindlimb unloading exhibited roughly twice the level of collagen buildup around their heart vessels 360 days post-exposure. Animals receiving 1.5 gray showed a similar increase at 270 days. The higher-dose experiment also included animals exposed to simulated weightlessness.
This buildup is called perivascular cardiac fibrosis. Only three to six animals per group were used for heart-tissue analyses, representing smaller subsets than the broader experimental group.
What surprised us most was how strongly time influenced what we saw,
said John Baker, the study’s lead researcher and an MCW professor of surgery.
Because earlier studies failed to show a statistically significant impact at the lower dose during shorter observation windows, the extended follow-up period proved critical. However, the new experiment did not establish the exact moment scarring began.
Immune Signaling Responses and Genomic Leads
At 1.5 gray, adding hindlimb unloading did not produce measurably more cardiac fibrosis than radiation alone. Unloading by itself did not significantly increase this cardiac endpoint. Across longitudinal measurements, unloading alone reduced concentrations of 20 of the 27 cytokines examined.
The authors identified six decreased cytokines shared with findings from the NASA Twins Study. The genomic analysis was much smaller. Researchers sequenced blood-cell DNA from three rats exposed to 1.5 gray and three unexposed controls. The team examined variants in 74 genes previously associated with clonal hematopoiesis. Variants appeared in 30 of those genes across the study samples. Seven genes had variants identified only in the irradiated condition.
Future Risk Studies and Limitations
The exposure schedule presents a major limitation. Radiation was delivered within minutes, whereas astronauts would accumulate much of their cosmic-radiation exposure gradually. The interval between particle hits can affect biological repair and signaling.
The study also used only males from one rat strain. Its immune measurements and tissue findings therefore require replication across sexes and models. No countermeasure was tested here. Rather than providing a mathematical prediction of future astronaut health issues, the study provides a foundation for investigating long-term monitoring and possible protective strategies.
