Simple and rapid genotyping of D-amino acid oxidase gene recognizing a crucial variant in the ddY strain using microchip electrophoresis

Enantioselective and simultaneous determination of lactate and 3-hydroxybutyrate in human plasma and urine using a narrow-bore online two-dimensional high-performance liquid chromatography system

For the enantioselective and simultaneous analysis of lactate and 3-hydroxybutyrate, a validated online two-dimensional high-performance liquid chromatography system using 4-nitro-7-piperazino-2,1,3-benzoxadiazole as a fluorescent derivatization reagent has been developed. For the reversed-phase separation in the first dimension, a Capcell Pak C18 ACR column (1.5 × 250 mm, particle size 3 μm) was used, and the target fractions were isolated by their hydrophobicity. In the second dimension, a polysaccharide-coated enantioselective column, Chiralpak AD-H (2.0 × 250 mm, 5 μm), was used. The system was validated by the calibration curve, intraday precision, interday precision, and accuracy using standards and real human samples, and satisfactory results were obtained. The present method was applied to human plasma and urine, and in the plasma, trace amounts of d-lactate (8.4 μM) and l-3-hydroxybutyrate (1.0 μM), besides high levels of l-lactate (860.9 μM) and d-3-hydroxybutyrate (59.4 μM), were successfully determined. In urine, trace levels of d-lactate (3.7 μM), d-3-hydroxybutyrate (2.3 μM), and l-3-hydroxybutyrate (3.3 μM) in addition to a relatively large amount of l-lactate (15.4 μM) were observed. The present online two-dimensional high-performance liquid chromatography system is useful for the simultaneous determination of all the lactate and 3-hydroxybutyrate enantiomers in human physiological fluids, and further clinical applications are ongoing.

Alteration of intrinsic amounts of D-serine in the mice lacking serine racemase and D-amino acid oxidase

For elucidation of the regulation mechanisms of intrinsic amounts of D-serine (D-Ser) which modulates the neuro-transmission of N-methyl-D-aspartate receptors in the brain, mutant animals lacking serine racemase (SRR) and D-amino acid oxidase (DAO) were established, and the amounts of D-Ser in the tissues and physiological fluids were determined. D-Ser amounts in the frontal brain areas were drastically decreased followed by reduced SRR activity. On the other hand, a moderate but significant decrease in D-Ser amounts was observed in the cerebellum and spinal cord of SRR knock-out (SRR(-/-)) mice compared with those of control mice, although the amounts of D-Ser in these tissues were low. The amounts of D-Ser in the brain and serum were not altered with aging. To clarify the uptake of exogenous D-Ser into the brain tissues, we have determined the D-Ser of SRR(-/-) mice after oral administration of D-Ser for the first time, and a drastic increase in D-Ser amounts in all the tested tissues was observed. Because both DAO and SRR are present in some brain areas, we have established the double mutant mice lacking SRR and DAO for the first time, and the contribution of both enzymes to the intrinsic D-Ser amounts was investigated. In the frontal brain, most of the intrinsic D-Ser was biosynthesized by SRR. On the other hand, half of the D-Ser present in the hindbrain was derived from the biosynthesis by SRR. These results indicate that the regulation of intrinsic D-Ser amounts is different depending on the tissues and provide useful information for the development of treatments for neuronal diseases.

Type 1 diabetes mellitus in mice increases hippocampal D-serine in the acute phase after streptozotocin injection

Diabetes mellitus (DM) is known to be a risk factor in the development of deficits in cognition, learning, and memory. In DM animal models, including the streptozotocin (STZ)-induced diabetic rodent model, abnormalities in the regulation of several neurotransmitters have been reported. However, the role in DM of d-serine, an endogenous co-agonist of glutamatergic N-methyl-d-aspartate receptors, remains unknown. Here, we measured the amounts of d-/l-serine and l-glutamate in the hippocampi of STZ-treated mice using a 2D-HPLC system from acute to chronic phases after the induction of DM. STZ treatment significantly increased the d-serine level by 23.7% in the hippocampus compared with vehicle treatment at 1 week after the injection, whereas it did not affect the levels of l-serine. In contrast, l-glutamate levels in the hippocampus were elevated at 3 days after STZ injection and rather decreased at 1 week after that. Such alterations in the amino acids were not evident in the chronic phases. We further tested whether the STZ-induced d-serine increase was caused by DM pathophysiology. In vivo, subcutaneous insulin implants into STZ-treated mice restored the elevated d-serine levels in the hippocampus. An in vitro study using primary cultured hippocampal neurons revealed that treatments of STZ did not directly affect the level of d-serine secreted in the cultured media. These results indicate that DM pathology caused by insulin deficiency triggers transient d-serine increase and l-glutamate alteration in the hippocampus. Such aberrant regulations of excitatory neurotransmitters may be relevant to the formation of DM-related dysfunction of the central nervous system (CNS).

Determination of D-serine and D-alanine in the tissues and physiological fluids of mice with various D-amino-acid oxidase activities using two-dimensional high-performance liquid chromatography with fluorescence detection

Two-dimensional-HPLC procedures have been established for the sensitive and selective determination of D-serine (D-Ser) and D-alanine (D-Ala), and their amounts in the tissues and physiological fluids of mice with various D-amino-acid oxidase (DAO) activities have been demonstrated. These two D-amino acids are modulators of the N-methyl-D-aspartate receptor mediated neurotransmission, and the alterations in their amounts following the changes in the DAO activity are matters of interest. After pre-column derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), the D-amino acids were determined by the 2D-HPLC system with fluorescence detectors. As the first dimension, a microbore-monolithic-ODS column (750 mm x 0.53 mm I.D.) was adopted and a self-packed narrowbore-Pirkle type enantioselective column (Sumichiral OA-2500S, 250 mm x 1.5 mm I.D.) was selected for the second dimension. The lower limits of quantitation of D-Ser and D-Ala were 500 amol, and the within-day and day-to-day precisions were less than 6.8%. Using these methods, the amounts of D-Ser and D-Ala in 6 brain tissues, 4 peripheral tissues, serum and urine of mice having various DAO activities were determined; the amounts of these D-amino acids were drastically increased with a lowering of the DAO activity except for the cases of D-Ser in the frontal brain regions. The present micro-2D-HPLC procedures are powerful tools for the determination of small amounts of D-Ser and D-Ala in mammalian samples, and the obtained results would be useful for developing novel drugs that modulate the DAO activity, such as DAO inhibitors, against neuronal diseases.