Spending long periods in space not only leads to muscle atrophy and reductions in bone density, it also seems to have lasting effects on the brain. Neuroimaging studies (amongst others from this LMU team of researchers) has hinted at this over the last three years. However, little is known if the observed brain-structural alterations are harmless or clinically relevant. LMU physicians Professor Peter zu Eulenburg and Professor Alexander Choukér together with renowned researchers from the University of Gothenburg (Sweden) and Russian colleagues have assessed the structural integrity of the human brain via blood-based markers in astronauts after return from a long-duration mission. The researchers could demonstrate with their pilot study published in JAMA Neurology that there are strong indications for brain injury and accelerated aging following a long-duration mission.
The scientists examined longitudinal blood samples from five cosmonauts that were on average 169 days aboard the International Space Station (ISS). All spaceflyers had given blood just prior to their missions and immediately after return to Earth. Blood was also taken one and three weeks after landing. ‘This gave us an unprecedented and detailed window to assess brain-structural health via blood-based markers after long-duration spaceflight’, Professor zu Eulenburg points out.
Blood samples show increase in brain-derived proteins
The blood samples showed a substantial increase for several brain-specific proteins in particular during the first week after return compared with the pre-mission baseline values. The detected proteins point towards an injury of the long nerve fibers in the white matter of the human brain and the supporting tissue, the glia. An even larger increase in magnitude was seen in two variants of the amyloid-beta protein. This amyloid elevation lasted for the entire three-week observation period and correlated with the time from mission start. The tau protein as a marker for the grey matter showed a substantial drop-off three weeks after return to Earth compared with preflight blood analyses. The researchers say that the correlated time course for these widely differing proteins argues for a comprehensive brain response and not just one tissue type alone is affected.
‘Taken together, our results point towards a slight but lasting brain injury and potentially accelerated neurodegeneration,’ says zu Eulenburg. ‘All relevant tissue types of the brain seem to be affected,’ he adds. So far the main clinical indication for detrimental neurological effects is a reduction in visual acuity that was demonstrated in several long-term space travelers.
Disturbed venous outflow of the head
The cause for the observed increase in brain-specific proteins may lie in the disturbed venous outflow of the head in microgravity. This mechanism could lead to an increase of the cerebrospinal fluid compartment and pressure on the white and the grey matter over time. There are already some indications of a correlation with time spent in Space for these effects. `Further studies into countermeasures against the effects of microgravity on the human brain are needed to minimize neurological risks for long-duration missions and before we start planning a trip to Mars`, says zu Eulenburg.
JAMA Neurology 2021
Changes in Blood Biomarkers of Brain Injury and Degeneration Following Long-Duration Spaceflight