Plasma amino acid concentrations in patients with amnestic mild cognitive impairment or Alzheimer disease

Background: Plasma concentrations of several amino acids may affect the availability of important neurotransmitter precursors in the brain. Abnormalities in the plasma amino acid profile have been reported in elderly persons with cognitive impairment, but no data exist for the prodromal phase of Alzheimer disease (AD), which is characterized by amnestic mild cognitive impairment (aMCI). Objective: The objective was to investigate whether the plasma amino acid profiles of elderly patients with aMCI or AD are abnormal. Design: The plasma amino acid profile was assessed in 29 cognitively normal control subjects (age: 86.7 +/- 5.9 y), 21 patients with aMCI (age: 84.9 +/- 7.0 y), and 51 patients with AD (age: 86.7 +/- 5.4 y). The participants were from the University of Bologna Research Center for Physiopathology of Aging, Italy. Results: Higher plasma concentrations of the aromatic amino acid phenylalanine were found in the aMCI (68 mumol/L; 95% CI: 63, 73) and AD (62 mumol.L; 95% CI: 59, 65) patients than in the control subjects(54 mumol/L; 95% CI: 48,61; P < 0.05). The ratio of arginine to other basic amino acids was also higher in the aMCI (0.31 +/- 0.04) and AD (0.27 +/- 0.08) patients than in the control subjects (0.21 +/- 0.05: P < 0.05). Adjustment for differences in body composition, serum vitamin B-12 concentrations, and serum folate concentrations did not significantly affect the results. Conclusions: The plasma amino acid profiles of elderly patients with aMCI or AD show abnormalities in aromatic and basic amino acids that potentially affect neurotransmitter biosynthesis.