Measurement of glutamate, aspartate and glycine and its potential precursors in human brain using high-performance liquid chromatography by pre-column derivatization with diethylaminoazobenzene sulphonyl chloride

High-performance liquid chromatographic analysis of physiological amino acids in human brain tumors by pre-column derivatization with phenylisothiocyanate

A reversed-phase high-performance liquid chromatographic technique for the determination of free amino acids in five biopsies of human brain tumors (two meningiomas, one glioblastoma and two oligodendrogliomas) is described. The frozen tissues were homogenized, deproteinized with perchloric acid and neutralized with potassium hydroxide. Aliquots of the supernatant containing the physiological amino acids are used for pre-column derivatization with phenylisothiocyanate. The derivatized PTC-amino acids (phenylthiocarbamyl derivatives) are stable for a five day period if stored as a powder at -20 degrees C in an inert atmosphere and they can be analyzed on a reversed-phase column (PicoTag) using a gradient of two eluents with absorption detection at a wavelength of 254 nm. Good resolution of several amino acids (>30) is achieved within ca. 60 min. For most amino acids this method is suitable for an accurate measurement over a wide range of physiological concentrations (50-400 pmol) starting from a very small amount of sample.

A postmortem study of glycine and its potential precursors in chronic schizophrenics

We have measured the concentrations of glycine and its potential precursors, serine and threonine, in 20 areas of the postmortem brains of chronic schizophrenics and controls using high-performance liquid chromatography by pre-column derivatization with dimethyl-amino-azobenzene sulphonyl chloride. The regional distribution pattern of glycine in the postmortem brains with and without the disease was more similar to that of serine (r = 0.874, P < 0.0001) than to that of threonine (r = 0.476, P < 0.01). A multiple regression analysis with regressor variables including diagnosis, age at death and interval between death and freezing revealed that there is a significant difference between schizophrenics and controls in the contents of these amino acids in a number of brain areas. The level of glycine in the orbitofrontal cortex of schizophrenics was found to be significantly increased in schizophrenics, with a tendency to an increase in that of serine. The increase in glycine was also significantly high in the off-drug group of schizophrenics who had not taken antipsychotics more than 40 days before death. Prominent decreases in both glycine and serine were observed in the somesthetic cortex of the on-drug schizophrenics. Serine was found to be significantly decreased in the putamen of the off-drug schizophrenics. A marked decrease in threonine was also observed in the supramarginal cortex and posterior portion of the lateral occipitotemporal cortex of the off-drug group of schizophrenics and in the putamen of all schizophrenics. The highly similar distribution pattern of glycine and serine in the postmortem brains supports the close coupling of synthesis and metabolism between these chemicals in human brains. The increased content of glycine in the orbitofrontal cortex, the reduced level of serine in the putamen and the decrease in threonine in the cerebral cortices, which were prominent in the off-drug schizophrenics, may be involved in the pathophysiology of schizophrenia.

Free D-serine in post-mortem brains and spinal cords of individuals with and without neuropsychiatric diseases

We have measured the concentrations of free D-serine post-mortem in the prefrontal cortex, parietal cortex, cerebellum and spinal cord from individuals with and without (controls) neuropsychiatric diseases using high-performance liquid chromatography with fluorometric detection. The levels of D-serine were found to be high in the prefrontal and parietal cortex (around 100 nmol/g wet weight) and very low in the cerebellum and spinal cord (below 10 nmol/g wet weight). The uneven distribution of the D-amino acid in the human central nervous system (CNS) resembles that observed in rodents, suggesting that, as shown in the rat CNS, the regional variation of D-serine content in the human brain might also be closely correlated with those of the N-methyl-D-aspartate (NMDA) type excitatory amino acid receptor. In the prefrontal cortex, the gray and white matter had a similar concentration of D-serine. These findings, together with the selective action of D-serine at the NMDA-related glycine site and the non-neurogenic nature of extracellular D-serine release, add further support to the view that D-serine could be an intrinsic modulator of the NMDA receptor liberated from certain glial cells in the mammalian brain. Despite the anti-psychotogen activity of D-serine in the rat, there were no statistically significant differences between the D-serine contents in the prefrontal or parietal cortex of controls and those of patients with schizophrenia or dementia of the Alzheimer type.

General strategies and selection of derivatization reactions for liquid chromatography and capillary electrophoresis

The general strategies, reasons and the different possibilities for the derivatization of biomedically important compounds are reviewed. Different approaches apply for small versus large analyte molecules, different advantages and disadvantages are visualized with pre- and post-column arrangements. Particular interest is focused upon solid-phase derivatization reagents.

Presence of the N-methyl-D-aspartate-associated glycine receptor agonist, D-serine, in human temporal cortex: comparison of normal, Parkinson, and Alzheimer tissues

The amino acid D-serine (D-Ser), previously recognized as a pharmacological tool for potentiating neuronal activity mediated by the N-methyl-D-aspartate (NMDA) receptor complex, in vitro and in vivo, has been observed in several brain regions of the rat and mouse, most prominently in cortex. In addition to reconfirming the presence and distribution of D-Ser in rat brain, we have observed, for the first time, endogenous, free D-Ser in temporal cortex of normal human brains at a level of 2.18 +/- 0.12 nmol/mg of protein, representing 15 +/- 2% of the free L-Ser pool. The D- and L-Ser specific content and the D/L-Ser ratio obtained from temporal cortex of Parkinson and Alzheimer brains did not differ significantly from those of controls. However, at the levels observed here, and considering its specificity and affinity for the NMDA-associated glycine receptor, endogenous D-Ser is a plausible NMDA receptor glycine site agonist.