Low-dose photons modify liver response to simulated solar particle event protons

Area of Science:

• Space medicine
• Radiation biology
• Molecular toxicology

Background:

• Health risks of space travel radiation exposure remain unclear.
• Understanding radiation effects on vital organs like the liver is crucial for astronaut safety.

Purpose of the Study:

• To investigate the impact of combined low-dose photons and simulated solar particle events (SPEs) on mouse liver gene expression and oxidative burst capacity.
• To determine if prior low-dose radiation exposure modifies the liver's response to subsequent SPE radiation.

Main Methods:

• C57BL/6 mice were exposed to simulated SPE protons (2 Gy/36h) with or without prior low-dose rate photons (0.049 Gy).
• Liver tissues were analyzed on day 0 and day 21 post-irradiation using RT-PCR to assess 84 oxidative stress-related genes.
• Oxygen radical production by liver phagocytes was measured.

Main Results:

• Immediate (day 0) effects showed limited gene expression changes, with some genes upregulated by SPEs and others downregulated by photons or SPEs.
• By day 21, combined exposure (photons + SPE) induced a distinct set of upregulated genes compared to individual exposures.
• Significant downregulation of numerous genes was observed across all irradiated groups by day 21, with minimal overlap.
• Low-dose photons significantly enhanced oxygen radical production by liver phagocytes on day 21.

Conclusions:

• Protracted low-dose photon exposure significantly impacts the liver's response to subsequent simulated solar particle events.
• The timing of exposure and the combination of radiation types critically influence the molecular and cellular responses in the liver.
• These findings underscore the complex risks associated with combined radiation exposures during space missions.