- Scientists studied combined impact space radiation and microgravity on bone and muscle.
- They found that radiation would worsen the muscle and bone loss due to microgravity.
- Also, Mineral density and trabecular thickness reduced in hind limb suspension.
A new research at VCU School of Engineering suggests that extended periods of space radiation and mechanical unloading in outer space may cause astronauts to lose bone and muscle from their legs, lower backs and hips. The space radiation includes radiation from solar particle events and galactic cosmic radiation.
The study also raised interesting questions about the relationship between human muscle and bone, especially for those who are dealing with age related muscle and bone loss. As space agencies prepare for deep space travels, astronauts will face increased, prolonged exposure to space radiation.
Outside the Earth’s atmosphere and protective magnetic field, there is a complex radiation field of protons and all elements on the periodic table are coming in at energies reaching the speed of light. Exposure to radiation on Earth is much different than the exposure to radiation in space.
While previous researches have examined the effects of protons or high atomic number and energy on muscle or bone with unloading, the new study examines the effects of proton and high atomic number and energy on muscle and bone, during unloading – very much similar to what would be experienced in deep space.
Scientists investigate the combined impact space radiation and microgravity on muscle and bone, hypothesizing that radiation would worsen the muscle and bone loss due to microgravity. They studied this by exposing mice to a similar environment – mice’s movements were restricted and exposed to simulated space radiation.
All mice were about 16 weeks old and skeletally mature at initial day of the experiment. They were kept in standard polycarbonate enclosures at 25 °C for 12 hour light/dark cycle. Mice were randomly assigned to 6 different experimental groups.
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What they found in the experiment was while microgravity alone led to both muscle and bone loss, radiation alone didn’t. The absolute trabecular and cortical bone volume fraction was reduced 24 and 6 percent, respectively hind limb suspension (HLS) -no radiation versus the normally loaded no-radiation group.
Mineral density and trabecular thickness also reduced in HLS. In some cases, like tissue mineral density and trabecular number, additional bone loss was recorded in HZE (high atomic number and energy) radiation group, compared to HLS alone.
While HLS alone reduced protein synthesis, muscle mass (35% quadriceps, 19% gastrocnemius) and elevated proteasome activity, radiation’ didn’t worsen these catabolic outcomes. Overall, the study suggests that combining HLS and simulated space radiation results in additional bone loss that may not be experienced by muscle.
Reference: journals.plos.org | 10.1371/journal.pone.0182403
NASA Space Radiation Laboratory (NSRL) has already demonstrated bone loss with low dose HZE radiation (50 cGy), but they didn’t examine muscle. Moreover, several interventions have been examined to attenuate either muscle losses or catabolic bone, but not both.
Previous studies have shown that the quadriceps appear to be less sensitive as compared to gastrocnemius muscle to unloading-induced atrophy. However, this research shows a greater loss in the quadriceps than gastrocnemius weight in mice that were exposed to HLS.
Other than this, space radiations can also alter the cardiovascular system, impairing the heart, narrow or harden arteries, and damage cells in linings of the blood vessels, leading to cardiovascular disease. Exposure to radiation can also affect the process of generating new cells, called neurogenesis. In central nervous system, this can even lead to memory deficits and cognitive impairment.
Scientists want to discover how to maintain muscle and bone health during space mission and learn what preventive exercises could be helpful for astronauts. The upcoming stage of the project will be bioinformatics research to scrutinize genetic variability induced by radiation or microgravity in bone and muscle.