Perfusion-Independent Tissue Hypoxia in Cardiac Hypertrophy in Mice Measured by 64Cu-CTS PET Imaging

Background Hypoxia is central to many cardiac pathologies, but clinically its presence can only be inferred by indirect biomarkers including hypoperfusion and energetic compromise. Imaging hypoxia directly could offer new opportunities for the diagnosis and sub-stratification of cardiovascular diseases. Objectives To determine whether [64Cu]CuCTS Positron Emission Tomography (PET) can identify hypoxia in a murine model of cardiac hypertrophy. Methods Male C57BL/6 mice underwent abdominal aortic constriction (AAC) to induce cardiac hypertrophy, quantified by echocardiography over 4 weeks. Hypoxia and perfusion were quantified in vivo using [64Cu]CuCTS and [64Cu]CuGTSM PET, respectively, and radiotracer biodistribution was quantified post-mortem. Cardiac radiotracer retention was correlated with contractile function (measured by echocardiography), cardiac hypertrophy (measured by histology), HIF-1α stabilization and NMR-based metabolomics. The effect of anesthesia on [64Cu]CuCTS uptake was additionally investigated in a parallel cohort of mice injected with radiotracer while conscious. Results Hearts showed increased LV wall thickness, reduced ejection fraction and fractional shortening following AAC. [64Cu]CuCTS retention was 317% higher in hypertrophic myocardium (p<0.001), despite there being no difference in perfusion measured by 64CuGTSM. Radiotracer retention correlated on an animal-by-animal basis with severity of hypertrophy, contractile dysfunction, HIF1α stabilization and metabolic signatures of hypoxia. [64Cu]CuCTS uptake in hypertrophic hearts was significantly higher when administered to conscious animals. Conclusions [64Cu]CuCTS PET can quantify cardiac hypoxia in hypertrophic myocardium, independent of perfusion, suggesting the hypoxia is caused by increased oxygen diffusion distances at the subcellular level. Alleviation of cardiac workload by anesthesia in preclinical models partially alleviates this effect. ### Competing Interest Statement The authors have declared no competing interest. * AAC : abdominal aortic constriction BTSC : bisthiosemicarbazone EF : ejection fraction FAC : fractional area change FS : fractional shortening HIF : hypoxia inducible factor IVS : intraventricular septum LVID : left ventricular internal diameter LVAW : left ventricular anterior wall LVPW : left ventricular posterior wall PET : positron emission tomography