Reprogramming of Lipid Metabolism by FLASH Radiotherapy Selectively Protects Radiosensitive Normal Tissues

FLASH radiotherapy, delivered at ultra-high dose rates exceeding 100 Gy/s, spares normal tissues while maintaining tumor control, yet the molecular mechanisms underlying this differential response remain poorly understood. Here we employed spatial and bulk multi-omics to investigate lipid and protein remodeling in tongue tissue and Mouse oral carcinoma 2 (MOC2) tumors at two weeks post-irradiation with FLASH or conventional dose-rate (CONV) proton radiotherapy. Bulk lipidomics revealed that CONV irradiation induced marked triglyceride (TG) depletion in tongue tissue, whereas FLASH attenuated this depletion. Spatial lipidomics using MALDI-MSI demonstrated that this TG loss was spatially restricted to minor salivary glands, identifying these radiosensitive structures as focal points of radiation-induced lipid damage. Additionally, FLASH irradiation uniquely promoted increases in membrane phospholipids and their lysophospholipid intermediates, consistent with active phospholipid turnover rather than passive damage avoidance. Proteomics revealed divergent metabolic programs: CONV activated a destructive cascade characterized by Ces1d depletion, Acox1-mediated peroxisomal {beta}-oxidation, and Acot7-driven fatty acid overflow, collectively defining a lipid droplet collapse; whereas FLASH engaged a protective program featuring Mgll suppression, Apoe-mediated triglyceride redistribution, and Lypla2-mediated lysophospholipid clearance. We propose a lipid metabolic reprogramming hypothesis in which FLASH not only minimizes acute oxidative damage but actively reprograms lipid metabolism to preserve lipid droplet stores and promote membrane remodeling. These findings provide a putative molecular foundation for the FLASH effect and support published data on the protection of normal tissues.