Sex Differences in Urinary Metabolite Profiles between Survivors and Non-Survivors of Radiation-induced Lung Injury in the C57L/J Murine Model

Novel biodosimetry assays are needed to categorize both acute ionizing radiation injury and delayed effects of radiation exposure, such as radiation-induced lung injury (RILI) -associated mortality. In this study, we utilized the C57L/J mouse model, a well-established system for replicating the clinical pathology of RILI. Lung injury was induced using a combination of neutron total-body irradiation (TBI) (30% of total dose +7% of total dose concomitant gamma rays) and whole-thoracic X-irradiation (WTI) boost for the balance of the required dose at total doses of 9, 9.5, 10 and 10.5 Gy. The animals were monitored for a period of 180 days postirradiation to evaluate the progression of injury. Both male and female mice were included in the study, with cohorts exposed to either sham dose (0 Gy) or 100% X-ray WTI at 11.35 Gy (LD50/180 dose) to serve as controls. Tissue injury was characterized using whole-body plethysmography, histopathology, and targeted lipidomics. Urinary metabolites were detected using untargeted metabolomic profiling to determine if they could serve as early predictors of RILI survival. A survival rate of 40-45% was observed at 180 days postirradiation consistent with the established LD50/180 value for WTI (11.35 Gy), except at 10.5 Gy, where survival dropped to 20%. Irradiated mice exhibited increased pulmonary immune infiltration and collagen deposition, reduced alveolar spaces, thickened bronchiolar walls, and dose-independent alterations in lipid profiles that were not sex-specific. We developed a multiplex urinary metabolite panel that was associated with RILI and radiation exposure. Some compounds were statistically different between sham-irradiated male and female mice, with sex specific differences at 120 days were observed for homocitrulline, xanthosine, acetyl-arginine, methylhistidine, niacinamide, xanthurenic acid, cyclic adenosine monophosphate, taurine, and prolyl-proline urinary metabolite levels. Baseline differences in sham-irradiated C57L/J mice show sex needs to be considered as a variable when developing biomarker panels for long-term RILI effects. However, urinary metabolite panels can provide excellent to very good sensitivity and specificity at predicting survival from RILI.