Chiral Amino Acid Analysis in the Plasma of B6DAO<sup>-/-</sup> Mice Lacking D-Amino Acid Oxidase Activity

Abstract

A B6DAO-/- mouse strain lacking D-amino acid oxidase (DAO) activity with the genetic background of C57BL strain, frequently used to produce disease model mice in the current medical/life science areas, was newly developed. In the plasma of the control C57BL/6J and mutant B6DAO-/- mice, five D-amino acids widely found in mammals were determined using a highly-selective two-dimensional LC-MS/MS system. As the targets, D-alanine (Ala), D-aspartic acid (Asp), D-leucine (Leu), D-proline (Pro) and D-serine (Ser) were selected. All five chiral amino acids were clearly observed, and the D-enantiomers of the neutral amino acids (Ala, Leu, Pro and Ser) significantly increased in the mutant B6DAO-/- mice (3.69-36.91 nmol/mL) compared to those in the control C57BL/6J mice (0.24-2.03 nmol/mL), whereas the amounts of D-Asp were almost equal between the two strains. The obtained values are consistent with those in previous reports using ddY/DAO-/- mice having spontaneous DAO deficiency and the control ddY/DAO+/+ mice. These results indicated that the newly-developed B6DAO-/- strain is practically useful to clarify the controlling mechanism of intrinsic D-amino acids that are expected as new bio-functional molecules and/or biomarkers in mammals.