Metabolic profiling of Alzheimer's disease brains

Abstract

Alzheimer's disease (AD) is an irreversible, progressive brain disease and can be definitively diagnosed after death through an examination of senile plaques and neurofibrillary tangles in several brain regions. It is to be expected that changes in the concentration and/or localization of low-molecular-weight molecules are linked to the pathological changes that occur in AD, and determining their identity would provide valuable information regarding AD processes. Here, we propose definitive brain metabolic profiling using ultra-performance liquid chromatography coupled with electrospray time-of-flight mass spectrometry analysis. The acquired data were subjected to principal components analysis to differentiate the frontal and parietal lobes of the AD/Control groups. Significant differences in the levels of spermine and spermidine were identified using S-plot, mass spectra, databases and standards. Based on the investigation of the polyamine metabolite pathway, these data establish that the downstream metabolites of ornithine are increased, potentially implicating ornithine decarboxylase activity in AD pathology.

Figure 1. The plaque/tangle pattern of Gallyas-Braak (GB) and Aβ/Tau staining from representative AD/Control brain tissues.

(a), Frontal lobe region from Control patient. (b), Parietal lobe region from Control patient. (c), Occipital lobe region from Control patient. (d), Frontal lobe region from AD patient. (e), Parietal lobe region from AD patient. (f), Occipital lobe region from AD patient. (g), Aβ staining from frontal lobe region (a). (h), Tau staining from frontal lobe region (a). For routine immunohistochemistry, an anti-human β amyloid antibody (Dako, mouse monoclonal, 1:30), an anti-human pTau antibody (INNOGENETICS, clone AT8 1:1000) were used for detection of plaque/tangle.

Figure 2. PCA score-plots and S-plots between AD and Control groups in each brain region (n = 10 for each sample).

(a), PCA score-plot of frontal lobe region (explained variance (R2): component 1, 0.32 and component 2, 0.49, and predictive ability (Q2): component 1, 0.22 and component 0.21). (b), PCA score-plot of parietal lobe region (R2: component 1, 0.3 and component 2, 0.45, and Q2: component 1, 0.21 and component 2, 0.17). (c), PCA score-plot of occipital lobe region (R2: component 1, 0.18 and component 2, 0.28, and Q2: component 1, 0.08 and component 2, 0.03). (d), S-plot of frontal lobe region. (e), S-plot of parietal lobe region. (f), S-plot of occipital lobe region.

Figure 3. UPLC-ESI/MS/MS with derivatization for the analysis of biogenic polyamine in the brain.

(a), SRM chromatograms of polyamine in AD frontal lobe (No. 11). (b), Concentration levels of polyamine in frontal lobe (n = 10 for each sample). (c), Concentration levels of polyamine in occipital lobe (n = 10 for each sample). * P < 0.05, ** P < 0.01, *** P < 0.005.

Figure 4. Metabolic pathway of polyamine.

Our results indicate increased SPD, SPM, PUT, Ac-SPD and Ac-SPM without a change of ORN in AD pathology. One theory suggests that the NMDA receptor excitotoxicity is caused by an excess of SPD and SPM due to ODC activity induced by plaque and/or tangle deposition in specific brain regions.