Amino Acids as Biomarker Candidates for Suicidality in Male OEF/OIF Veterans: Relevance to NMDA Receptor Modulation and Nitric Oxide Signaling

Veteran populations are exposed to multiple stressful events, and suicidality among veterans is a serious problem. Identifying biomarkers of suicidality may enhance detection, prevention, and treatment. Multiple neurotransmitter systems are implicated in the neurobiology of suicidality, including amino acid neurotransmitter systems. Amino acids as biomarker candidates for suicidality were quantified using mass spectrometry in serum samples from 90 male U.S. Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) veterans. Amino acid levels in veterans reporting suicidal ideation (SI) on the Beck Scale for Suicidal Ideation (BSS) (BSS score > 0, n = 19) were compared with those reporting no SI (BSS score = 0, n = 71). Glycine, an excitatory amino acid and N-methyl-D-aspartate receptor modulator, was significantly elevated in serum samples from veterans reporting SI (p = 0.043). Serine and aspartate/asparagine, also excitatory neurotransmitters, were nonsignificantly increased in veterans reporting SI (p = 0.082 and p = 0.097, respectively). In contrast, arginine (nitric oxide [NO] precursor) and citrulline (by-product of NO formation) were nonsignificantly decreased in veterans reporting SI (p = 0.097 and p = 0.093, respectively). Profiling amino acids as possible biomarker candidates for suicidality in OEF/OIF veterans may have clinical utility for identifying suicidal risk. Glutamatergic neurotransmission and NO signaling may be relevant to the neurobiology of suicidality in OEF/OIF veterans.