Targeted and Untargeted Mass Spectrometry Reveals the Impact of High-Fat Diet on Peripheral Amino Acid Regulation in a Mouse Model of Alzheimer's Disease.

Recent research regarding amino acid metabolism has shown that there may be a link between obesity and Alzheimer's disease (AD). This work reports a metabolomics study using targeted and untargeted mass spectrometry-based metabolomic strategies to investigate this link. Targeted hydrophilic interaction liquid chromatography-triple quadrupole mass spectrometry and untargeted reversed-phase liquid chromatography-high resolution tandem mass spectrometry assays were developed to analyze the metabolic changes that occur in AD and obesity. APPSwe/PS1ΔE9 (APP/PSEN1) transgenic mice (to represent familial or early-onset AD) and wild-type littermate controls were fed either a high-fat diet (HFD, 60% kcal from lard) or a low-fat diet (LFD, 10% kcal from lard) from 2 months of age or a reversal diet (HFD, followed by LFD from 9.5 months). For targeted analyses, we applied the guidelines outlined in the Clinical and Laboratory Standards Institute (CLSI) LC-MS C62-A document and the U.S. Food and Drug Administration (FDA) bioanalytical method validation guidance for industry to evaluate the figures of merit of the assays. Our targeted and untargeted metabolomics results suggest that numerous peripheral pathways, specifically amino acid metabolism and fatty acid metabolism, were significantly affected by AD and diet. Multiple amino acids (including alanine, glutamic acid, leucine, isoleucine, and phenylalanine), carnitines, and members of the fatty acid oxidation pathway were significantly increased in APP/PSEN1 mice on HFD compared to those on LFD. More substantial effects and changes were observed in the APP/PSEN1 mice than in the WT mice, suggesting that they were more sensitive to an HFD. These dysregulated peripheral pathways include numerous amino acid pathways and fatty acid beta oxidation and suggest that obesity combined with AD further enhances cognitive impairment, possibly through aggravated mitochondrial dysfunction. Furthermore, partial reversibility of many altered pathways was observed, which highlights that diet change can mitigate the metabolic effects of AD. The same trends in individual amino acids were observed in both strategies, highlighting the biological validity of the results.