Alzheimer's disease: amino acid levels and brain metabolic status

Abstract To study brain free amino acids and theirrelation with dementia we measured, by high-performanceliquid chromatography (HPLC), the concentration of eightfree amino acids, amines and related compounds. We usedtemporal cortex (TC) samples obtained from 13 Alzheimer’sdisease (AD) patients and an equal number of agematchedcontrols (AC). The patterns of free amino acids,amines and related compounds showed significant quantitativechanges in AD conditions with respect to healthyones. In Alzheimer patients, lower levels of GABA werefound in the TC (-57 %). Amino acids glutamate (Glu),and aspartate (Asp) concentrations, also appeared significantlyreduced in the TC of AD patients (Glu: -30 %;Asp: -40 %) when compared with controls. The significantgap between methionine (Met: -30 %) and cystathionine(Cysta: ?60 %) levels in TC of AD people tocontrols, might suggest an under/over activity of thetransmethylation and transsulphuration pathways, respectively.Glutamine (Gln) and Urea were an exception to thistrend because their content was higher in AD patients thanin controls. Albeit these compounds may have particularphysiological roles, including the possible mediation ofsynaptic transmission, changes in amino acid levels andrelated compounds (detected in steady state) suggest amodified metabolic status in brains of AD patients thatreveals a reduced function of synaptic transmission.Because several evidences show that patients might displayquite different concentrations of neurotransmitters in brainareas, assessing metabolites in different and well-characterizedAD stages should be investigated further.