Structural lipidomics identifies murine plasma C=C location isomers for radiation dose stratification

Abstract Background Rapid and early radiation biodosimetry is essential for post-exposure medical triage and timely intervention. Owing to their high radiosensitivity, lipids are promising biodosimetry biomarkers. However, radiation-induced structural alterations, particularly changes in carbon–carbon double bond (C=C) location isomers, remain poorly characterized. Here, the Paternò-Büchi reaction coupled with liquid chromatography-tandem mass spectrometry (LC-PB-MS/MS) was employed to quantify unsaturated C=C location isomers with minimal interindividual variation. These isomers served as the basis for developing biodosimetry. Methods Plasma structural lipidomic profiling was performed in C57BL/6 mice at 4 h and 24 h following irradiation at doses of 0, 2, and 6 Gy using LC-PB-MS/MS. Least absolute shrinkage and selection operator (LASSO) regression was applied to filter dose-dependent lipids for constructing multivariate regression models, validated by receiver operating characteristic analysis curves and bootstrap optimism correction. Mechanistic investigations were conducted using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, quantitative real-time polymerase chain reaction, Western blotting, and publicly available transcriptomic databases. Results Eighty-three species-level lipids and 311 C=C location isomers in phosphatidylcholine and phosphatidylethanolamine were identified in plasma samples. LASSO regression selected 11 isomers at 4 h and 8 lipids at 24 h. Optimized three-feature biodosimetry models demonstrated good performance across both sexes (R 2 > 0.8; optimism-corrected area under the curve = 0.8224‒1.0000). Profiling of Δ9 monounsaturated isomer together with KEGG analysis suggested dysregulation of fatty acid desaturation, accompanied by reduced expression of stearoyl-CoA desaturase 1 in AHH-1 cells and murine models. Conclusions C=C location isomers exhibited favorable dose classification performance in murine plasma. These promising biomarkers provide a foundation for developing translational approaches for acute radiation biodosimetry. Graphical Abstract Integrating structural lipidomics with acute radiation dose assessment for the first time; Developing a promising, C=C-based dose classification model; Linking SCD1 reduction in murine blood and bone marrow to Δ9 isomer depletion.