Relationships between Alzheimer’s disease (AD) pathologies in cognitively unimpaired adults and in vivo neurometabolic properties measured directly from the hippocampus, a vulnerable region early along the AD continuum, are not well-understood in the earliest stages of AD. In a 3T 1H-MRS study, we assessed age and AD-related changes in estimates of absolute concentrations of neurometabolites in the right hippocampus. Participants included older adults (age range: 60–85, n = 19) primarily cognitively unimpaired (CU, n = 16), as well as some with cognitive impairment (n = 3). All participants previously received a lumbar puncture for AD disease staging from cerebrospinal fluid (CSF) AD biomarkers (Aβ42, p-tau181 and t-tau), where all were amyloid positive (A+) and most had subthreshold tau pathology (T-). Hippocampal 1H-MRS metabolites included total N-acetylaspartate (tNAA), myo-inositol (mIns), total creatine (tCr) and total choline (tCho). Regression analyses were performed for assessing relationships among CSF biomarkers, age, and 1H-MRS metabolites measured as tissue-corrected estimates of absolute concentrations (millimoles/kilogram) and as ratios (/tCr and tNAA/mIns). We identified age-related decreases to mIns/tCr, where estimated absolute concentrations revealed that tCr increased while mIns remained stable. Concentrations for tNAA and mIns were positively associated with CSF p-tau181 and t-tau. Levels of tCr and tCho were not associated with any CSF biomarkers. Overall, our results demonstrate that sub-threshold tau pathologies in cognitively unimpaired A+ individuals are associated with hippocampal metabolite changes related to neural metabolism and glial reactivity early in disease progression.
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