BackgroundThe metabolic basis of Alzheimer disease (AD) pathology and expression of AD symptoms is poorly understood. Omega-3 and -6 fatty acids have previously been linked to both protective and pathogenic effects in AD. However, to date little is known about how the abundance of these species is affected by differing levels of disease pathology in the brain.Methods and findingsWe performed metabolic profiling on brain tissue samples from 43 individuals ranging in age from 57 to 95 y old who were stratified into three groups: AD (N = 14), controls (N = 14) and “asymptomatic Alzheimer’s disease” (ASYMAD), i.e., individuals with significant AD neuropathology at death but without evidence for cognitive impairment during life (N = 15) from the autopsy sample of the Baltimore Longitudinal Study of Aging (BLSA). We measured 4,897 metabolite features in regions both vulnerable in the middle frontal and inferior temporal gyri (MFG and ITG) and resistant (cerebellum) to classical AD pathology. The levels of six unsaturated fatty acids (UFAs) in whole brain were compared in controls versus AD, and the differences were as follows: linoleic acid (p = 8.8 x 10−8, FC = 0.52, q = 1.03 x 10−6), linolenic acid (p = 2.5 x 10−4, FC = 0.84, q = 4.03 x 10−4), docosahexaenoic acid (p = 1.7 x 10−7, FC = 1.45, q = 1.24 x 10−6), eicosapentaenoic acid (p = 4.4 x 10−4, FC = 0.16, q = 6.48 x 10−4), oleic acid (p = 3.3 x 10−7, FC = 0.34, q = 1.46 x 10−6), and arachidonic acid (p = 2.98 x 10−5, FC = 0.75, q = 7.95 x 10−5). These fatty acids were strongly associated with AD when comparing the groups in the MFG and ITG, respectively: linoleic acid (p < 0.0001, p = 0.0006), linolenic acid (p < 0.0001, p = 0.002), docosahexaenoic acid (p < 0.0001, p = 0.0024), eicosapentaenoic acid (p = 0.0002, p = 0.0008), oleic acid (p < 0.0001, p = 0.0003), and arachidonic acid (p = 0.0001, p = 0.001). Significant associations were also observed between the abundance of these UFAs with neuritic plaque and neurofibrillary tangle burden as well as domain-specific cognitive performance assessed during life. Based on the regional pattern of differences in brain tissue levels of these metabolites, we propose that alterations in UFA metabolism represent both global metabolic perturbations in AD as well as those related to specific features of AD pathology. Within the middle frontal gyrus, decrements in linoleic acid, linolenic acid, and arachidonic acid (control>ASYMAD>AD) and increases in docosahexanoic acid (AD>ASYMAD>control) may represent regionally specific threshold levels of these metabolites beyond which the accumulation of AD pathology triggers the expression of clinical symptoms. The main limitation of this study is the relatively small sample size. There are few cohorts with extensive longitudinal cognitive assessments during life and detailed neuropathological assessments at death, such as the BLSAConclusionsThe findings of this study suggest that unsaturated fatty acid metabolism is significantly dysregulated in the brains of patients with varying degr...

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Unbiased metabolomic analysis of biological samples is a powerful and increasingly commonly utilised tool, especially for the analysis of bio-fluids to identify candidate biomarkers. To date however only a small number of metabolomic studies have been applied to studying the metabolite composition of tissue samples, this is due, in part to a number of technical challenges including scarcity of material and difficulty in extracting metabolites. The aim of this study was to develop a method for maximising the biological information obtained from small tissue samples by optimising sample preparation, LC-MS analysis and metabolite identification. Here we describe an in-vial dual extraction (IVDE) method, with reversed phase and hydrophilic liquid interaction chromatography (HILIC) which reproducibly measured over 4,000 metabolite features from as little as 3mg of brain tissue. The aqueous phase was analysed in positive and negative modes following HILIC separation in which 2,838 metabolite features were consistently measured including amino acids, sugars and purine bases. The non-aqueous phase was also analysed in positive and negative modes following reversed phase separation gradients respectively from which 1,183 metabolite features were consistently measured representing metabolites such as phosphatidylcholines, sphingolipids and triacylglycerides. The described metabolomics method includes a database for 200 metabolites, retention time, mass and relative intensity, and presents the basal metabolite composition for brain tissue in the healthy rat cerebellum.

Background: physiological differences between males and females could contribute to the development of Alzheimer’s Disease (AD). Here, we examined metabolic pathways that may lead to precision medicine initiatives. Methods: We explored whether sex modifies the association of 540 plasma metabolites with AD endophenotypes including diagnosis, cerebrospinal fluid (CSF) biomarkers, brain imaging, and cognition using regression analyses for 695 participants (377 females), followed by sex-specific pathway overrepresentation analyses, APOE ε4 stratification and assessment of metabolites’ discriminatory performance in AD. Results: In females with AD, vanillylmandelate (tyrosine pathway) was increased and tryptophan betaine (tryptophan pathway) was decreased. The inclusion of these two metabolites (area under curve (AUC) = 0.83, standard error (SE) = 0.029) to a baseline model (covariates + CSF biomarkers, AUC = 0.92, SE = 0.019) resulted in a significantly higher AUC of 0.96 (SE = 0.012). Kynurenate was decreased in males with AD (AUC = 0.679, SE = 0.046). Conclusions: metabolic sex-specific differences were reported, covering neurotransmission and inflammation pathways with AD endophenotypes. Two metabolites, in pathways related to dopamine and serotonin, were associated to females, paving the way to personalised treatment.

Three of the four treatments for Alzheimer's disease (Donepezil, Rivastigmine and Galantamine) are cholinesterase inhibitors that target the pathological reduction of acetylcholine levels, while the fourth treatment Memantine is an NMDA antagonist. In this study, six neurotransmitters and nine pathway-associated metabolites were measured in 43 human brain samples from the autopsy cohort of the Baltimore Longitudinal Study of Aging (BLSA). Tissue samples were obtained from three groups of BLSA participants, AD (n=14), controls (n=14) and asymptomatic AD (ASYMAD; n=15) i.e. individuals with significant AD neuropathology at death but with no evidence of cognitive impairment during life. Three brain areas were studied, middle frontal gyrus (MFG), inferior temporal gyrus (ITG) and the cerebellum. When analysing the levels of neurotransmitters and associated metabolites in the brain, 6 of 15 were shown to be significantly associated with disease (p<0.005). Dopamine decreased in the ASYMAD group suggesting a decrease of this neurotransmitter before cognition is impaired (fold change; FC=0.78, p=4.1×10 -3). In the AD brain, changes were mainly seen in the ITG with increases observed in GABA, arginine and ornithine and decreases in aminobutanal, aspartate, glutamate, guanidinobutanoate, glycine and guanosine.Taken together, these results indicate that AD pathology is associated with perturbations in several neurotransmitter systems. These findings may have important implications for drug repurposing and complementary treatment of symptoms.All rights reserved. No reuse allowed without permission.