Multimodal investigation of neuropathology and neurometabolites in mild cognitive impairment and late-life depression with ¹¹C-PiB beta-amyloid PET and 7T magnetic resonance spectroscopy

Positron emission tomography (PET) and magnetic resonance spectroscopy (¹H-MRS) are complementary techniques that can be applied to study how proteinopathy and neurometabolism relate to cognitive deficits in preclinical stages of Alzheimer's disease (AD)—mild cognitive impairment (MCI) and late-life depression (LLD). We acquired beta-amyloid (Aβ) PET and 7 T ¹H-MRS measures of GABA, glutamate, glutathione, N-acetylaspartate, N-acetylaspartylglutamate, myo-inositol, choline, and lactate in the anterior and posterior cingulate cortices (ACC, PCC) in 13 MCI and 9 LLD patients, and 13 controls. We used linear regression to examine associations between metabolites, Aβ, and cognitive scores, and whether metabolites and Aβ explained cognitive scores better than Aβ alone. In the ACC, higher Aβ was associated with lower GABA in controls but not MCI or LLD patients, but results depended upon MRS data quality control criteria. Greater variance in California Verbal Learning Test scores was better explained by a model that combined ACC glutamate and Aβ deposition than by models that only included one of these variables. These findings identify preliminary associations between Aβ, neurometabolites, and cognition.