Metabolic Profiling of Neocortical Tissue Discriminates Alzheimer’s Disease from Mild Cognitive Impairment, High Pathology Controls, and Normal Controls

Abstract

BackgroundAlzheimer's disease (AD) is the most common cause of dementia, accounting for an estimated 60 to 80% of cases, and is the sixth-leading cause of death in the United States. While considerable advancements have been made in the clinical care of AD, it remains a complicated disorder that can be di cult to identify de nitively in its earliest stages. Recently, mass spectrometry (MS)-based metabolomics has shown signi cant potential for elucidation of disease mechanisms and identi cation of therapeutic targets as well diagnostic and prognostic markers that may be useful in resolving some of the di culties affecting clinical AD studies, such as effective strati cation. MethodsIn this study, complementary gas chromatography-and liquid chromatography-MS platforms were used to detect and monitor 2,080 metabolites and features in 48 post-mortem tissue samples harvested from the superior frontal gyrus of male and female subjects. Samples were taken from four groups: 12 normal control (NC) patients, 12 cognitively normal subjects characterized as high pathology controls (HPC), 12 subjects with non-speci c mild cognitive impairment (MCI), and 12 subjects with AD. ResultsMultivariate statistics informed the construction and cross-validation (p < 0.01) of partial least squaresdiscriminant analysis (PLS-DA) models de ned by a 9-metabolite panel of disease markers (lauric acid, stearic acid, myristic acid, palmitic acid, palmitoleic acid, and four unidenti ed mass spectral features). Receiver operating characteristic analysis showed high predictive accuracy of the resulting PLS-DA models for discrimination of NC (97%), HPC (92%), MCI (~ 96%), and AD (~ 96%) groups. Pathway analysis revealed signi cant disturbances in lysine degradation, fatty acid metabolism, and the degradation of branched-chain amino acids. Network analysis showed signi cant enrichment of 11 enzymes, predominantly within the mitochondria. ConclusionsThe results expand basic knowledge of the metabolome related to AD and reveal pathways that can be targeted therapeutically. This study also provides a promising basis for the development of larger multisite projects to validate these candidate markers in readily available biospecimens such as blood to enable the effective screening, rapid diagnosis, accurate surveillance, and therapeutic monitoring of AD. BackgroundImportantly, this study provides clinically relevant candidate biomarkers capable of accurate post-mortem classi cation which may, eventually, prove useful to in vivo diagnosis and disease monitoring. Methods ReagentsAcetonitrile (ACN), methanol (MeOH), ammonium acetate (NH 4 OAc), acetic acid (AcOH), and isopropanol (IPA), all LC-MS grade, were purchased from Fisher Scienti c (Pittsburgh, PA). Ammonium hydroxide (NH 4 OH), methyl tert-butyl ether (MTBE), O-methylhydroxylamine hydrochloride (MeOX), and N-Methyl-N-(tert-butyldimethylsilyl) tri uoroacetamide (MTBSTFA) were bought from Sigma-Aldrich (Saint Louis, MO). High performance LC grade chloroform (CHCl 3 ) was obtained from VWR (Radnor, P...

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