PROJECT SUMMARY/ABSTRACT The general population continues to be at risk of exposure to ionizing radiation because of nuclear warfare, terrorism, or radiological accidents. Some countermeasures of the acute radiation syndrome (ARS) have been placed in the national stockpile, increasing the chance of survival in a radiation emergency. However, individuals who survive the ARS may develop delayed effects of acute radiation exposure (DEARE) within months to years after irradiation. Currently, no system is available for the early identification of individuals who are at risk for DEARE and in which particular organ systems late radiation injuries will occur. Therefore, to personalize the clinical management of radiation victims, research is required to develop minimally invasive assays that predict organ-specific DEARE. However, although ~25% of the total population is pediatric, to our knowledge, no research has been performed in predictive biomarker assays of DEARE in victims who have been exposed at a young age. The main goal of the NIAID funded grant U01 AI148308 “Development of a minimally invasive biomarker assay to detect delayed radiation injury” is to develop urine and plasma biomarker assays of radiation injury to major organ systems at risk. In this parent project, the initial identification of urine and plasma biomarkers is performed with untargeted high-resolution mass spectrometry-based metabolomics in adult male and female WAG/RijCmcr rats (11-12 weeks of age) exposed to X-rays (0, 6, 9.5 and 13 Gy) with one hind-leg shielded from radiation to assure long-term survival of the animals. The purpose of this supplement application is to expand the scope of the parent grant by identifying early biomarkers of lung, kidney and heart injury in a juvenile rat model, in which male and female rats are exposed to leg-out X-ray PBI at the age of 41-44 days. We will use the same rat strain and metabolomics/lipidomics approaches as in the parent U01, which will enable us to make comparisons of biomarker panels in juvenile and adult rats.