Selective lipid Metabolic remodelling in radiosensitive normal tissues after FLASH radiotherapy.

BACKGROUND AND PURPOSE: FLASH radiotherapy, delivered at ultra-high dose rates, spares normal tissues while maintaining tumor control, but the molecular basis of this differential response remains poorly defined, particularly at timepoints relevant to tissue repair. We investigated whether lipid metabolism contributes to the FLASH effect in head and neck cancer.

MATERIALS AND

METHODS

MOC2 tumor-bearing mice received a single 10 Gy fraction of conventional (CONV) or ultra-high dose-rate FLASH protons, with non-irradiated controls (CTRL). Tongue and contralateral tumors were collected two weeks later and analyzed by bulk lipidomics, spatial lipidomics and proteomics. After biochemical filtering, 1,547 lipid species across 37 classes were quantified.

RESULTS

At two weeks, CONV irradiation was associated with a triglyceride-catabolic, oxidative-stress signature in tongue tissue, marked by loss of the lipid-droplet hydrolase Ces1d alongside induction of the peroxisomal β-oxidation enzyme Acox1. FLASH irradiation was instead associated with a distinct lipid-remodelling signature: suppression of Mgll, induction of Apoe, membrane phospholipid remodelling (increased phosphatidylcholine and phosphatidylethanolamine), and Lypla2 upregulation. Spatial lipidomics provided illustrative spatial context consistent with concentration of these changes in minor salivary gland acini. Tumor tissue showed no comparable modality-specific divergence.

CONCLUSIONS

These correlative multi-omics data indicate that FLASH is associated with remodelling of lipid metabolism in radiosensitive normal tissue, beyond a simple reduction of acute oxidative damage. We propose a Lipid Metabolic Remodelling Hypothesis for testing: the remodelling of lipid metabolism observed after FLASH may contribute to normal-tissue sparing rather than representing solely a downstream consequence of reduced acute oxidative damage. This model complements existing physicochemical models and offers a basis for radioprotection strategies in head and neck radiotherapy.