Effects of Low Dose Space Radiation Exposures on the Splenic Metabolome.

Future space missions will include a return to the Moon and long duration deep space roundtrip missions to Mars. Leaving the protection that Low Earth Orbit provides will unavoidably expose astronauts to higher cumulative doses of space radiation, in addition to other stressors, e.g., microgravity. Immune regulation is known to be impacted by both radiation and spaceflight and it remains to be seen whether prolonged effects that will be encountered in deep space can have an adverse impact on health. In this study, we investigated the effects in the overall metabolism of three different low dose radiation exposures (γ-rays, 16O, and 56Fe) in spleens from male C57BL/6 mice at 1, 2, and 4 months after exposure. Forty metabolites were identified with significant enrichment in purine metabolism, tricarboxylic acid cycle, fatty acids, acylcarnitines, and amino acids. Early perturbations were more prominent in the γ irradiated samples, while later responses shifted towards more prominent responses in groups with high energy particle irradiations. Regression analysis showed a positive correlation of the abundance of identified fatty acids with time and a negative association with γ-rays, while the degradation pathway of purines was positively associated with time. Taken together, there is a strong suggestion of mitochondrial implication and the possibility of long-term effects on DNA repair and nucleotide pools following radiation exposure.

Effect of 3,3'-Diindolylmethane on Pulmonary Injury Following Thoracic Irradiation in CBA Mice.

The molecule 3,3'-diindolylmethane (DIM) is small, a major bioactive metabolite of indole-3 carbinol (13C), and a phytochemical compound from cruciferous vegetables released upon exposure to the gut acid environment. DIM is a proposed anti-cancer agent and was previously demonstrated to prevent radiation damage in the bone marrow and the gastrointestinal tract. Here we investigated the effect of DIM on radiation-induced injury to the lung in a murine model through untargeted metabolomics and gene expression studies of select genes. CBA mice were exposed to thoracic irradiation (17.5 Gy). Mice were treated with vehicle or DIM (250 mg kg, subcutaneous injection) on days -1 pre-irradiation through +14 post-irradiation. DIM induced a significant improvement in survival by day 150 post-irradiation. Fibrosis-related gene expression and metabolomics were examined using lung tissue from days 15, 45, 60, 90, and 120 post-irradiation. Our qRT-PCR experiments showed that DIM treatment reduced radiation-induced late expression of collagen Iα and the cell cycle checkpoint proteins p21/waf1 (CDKN1A) and p16ink (CDKN2A). Metabolomic studies of lung tissue demonstrated a significant dampening of radiation-induced changes following DIM treatment. Metabolites associated with pro-inflammatory responses and increased oxidative stress, such as fatty acids, were suppressed by DIM treatment compared to irradiated samples. Together these data suggest that DIM reduces radiation-induced sequelae in the lung.