Hyperpolarized 13C MRI uncovers early and progressive metabolic dysfunction in the hAPP-J20 mouse model of Alzheimer's disease.

Impaired brain energy metabolism is an early feature of Alzheimer's disease (AD), but the standard metabolic imaging tool, [ 18 F]FDG-PET, reports only glucose uptake and cannot resolve downstream metabolic flux nor inform on overall metabolic profile of the brain. In this study, we used [ 18 F]FDG-PET, hyperpolarized (HP) [1- 13 C]pyruvate 13 C magnetic resonance spectroscopic imaging (MRSI), and ex vivo ¹H-NMR metabolomics to characterize how amyloid-β (Aβ) associated pathology reshapes brain energy metabolism in the hAPP-J20 mouse model, from glucose uptake to metabolic fluxes and steady-state metabolite concentrations. HP 13 C MRSI was performed in male and female wild-type (WT) and hAPP-J20 mice at 2 and 14 months of age, with FDG-PET and metabolomics acquired at the final timepoint. HP 13 C MRSI revealed a progressive, region-specific increase in glycolytic flux in hAPP-J20 mice, with increased apparent HP [1- 13 C]Lactate/Pyruvate conversion (relative to vascular delivery) localized to the hippocampus in females and to the cortex in males; HP 13 C urea perfusion measures confirmed comparable substrate delivery between genotypes. In contrast, [ 18 F]FDG-PET showed no genotype difference in regional glucose uptake, although the sex- and weight-dependent scaling of FDG uptake observed in the WT controls was lost in hAPP-J20 mice. Ex vivo metabolomics uncovered sex-divergent metabolic rewiring: a succinate-centered strengthening of the TCA cycle and propanoate metabolism in females, versus altered tyrosine and ubiquinone metabolism in males. These data show that HP 13 C MRSI detects an Aβ-associated increase in glycolytic flux before FDG-PET registers a change, and position HP 13 C pyruvate MRS imaging as a sensitive, radiation-free, flux-based biomarker that complements glucose-uptake imaging in AD.