ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the changes of plasma levels of the excitatory amino acid neurotransmitter aspartic acid (Asp), inhibitory neurotransmitter glycine (Gly) and asparagine (Asn) in patients with major depressive disorder (MDD).</p><p><b>METHODS</b>Plasma samples were collected from 15 MDD patients (9 males and 6 females, aged 32-64 y) and 14 healthy subjects (7 males and 7 females, aged 30-65 y); and also collected from 7 MDD patients (5 males and 2 females) 2 months after antidepressant treatment. The plasma levels of amino acids were determined by high performance liquid chromatography with fluorescence detection method.</p><p><b>RESULTS</b>Plasma Asp and Gly levels were significantly lower in MDD patients than those in controls (P<0.04). There were positive correlations between plasma levels of Gly and Asp, and between Gly and Asn (P<0.005) in the control group; while in MDD patients, a significant positive correlation was found only between plasma levels of Gly and of Asp (P<0.001). MDD patients did not show significant changes in plasma Asp, Asn and Gly levels after antidepressant treatment compared to those before treatment.</p><p><b>CONCLUSION</b>The reduced plasma Asp and Gly levels may serve as a clinical biomarker for MDD.</p>