Ischemic acute kidney injury perturbs homeostasis of serine enantiomers in the body fluid in mice: early detection of renal dysfunction using the ratio of serine enantiomers.
The imbalance of blood and urine amino acids in renal failure has been studied mostly without chiral separation. Although a few reports have shown the presence of D-serine, an enantiomer of L-serine, in the serum of patients with severe renal failure, it has remained uncertain how serine enantiomers are deranged in the development of renal failure. In the present study, we have monitored serine enantiomers using a two-dimensional HPLC system in the serum and urine of mice after renal ischemia-reperfusion injury (IRI), known as a mouse model of acute kidney injury. In the serum, the level of D-serine gradually increased after renal IRI in parallel with that of creatinine, whereas the L-serine level decreased sharply in the early phase after IRI. The increase of D-serine was suppressed in part by genetic inactivation of a D-serine-degrading enzyme, D-amino acid oxidase (DAO), but not by disruption of its synthetic enzyme, serine racemase, in mice. Renal DAO activity was detected exclusively in proximal tubules, and IRI reduced the number of DAO-positive tubules. On the other hand, in the urine, D-serine was excreted at a rate nearly triple that of L-serine in mice with sham operations, indicating that little D-serine was reabsorbed while most L-serine was reabsorbed in physiological conditions. IRI significantly reduced the ratio of urinary D-/L-serine from 2.82 ± 0.18 to 1.10 ± 0.26 in the early phase and kept the ratio lower than 0.5 thereafter. The urinary D-/L-serine ratio can detect renal ischemia earlier than kidney injury molecule-1 (KIM-1) or neutrophil gelatinase-associated lipocalin (NGAL) in the urine, and more sensitively than creatinine, cystatin C, or the ratio of D-/L-serine in the serum. Our findings provide a novel understanding of the imbalance of amino acids in renal failure and offer a potential new biomarker for an early detection of acute kidney injury.
Department of Anatomy, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan.
Jumpei
J
Sasabe
Department of Anatomy, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan.
Masataka
M
Suzuki
Graduate School of Pharmaceutical Sciences, Kyushu University, Maidashi, Higashi-ku, Fukuoka, Japan.
Yurika
Y
Miyoshi
Innovative Science Research and Development Center, Shiseido Co., Ltd., Fukuura, Kanazawa-ku, Yokohama, Japan.
Yosuke
Y
Tojo
Innovative Science Research and Development Center, Shiseido Co., Ltd., Fukuura, Kanazawa-ku, Yokohama, Japan.
Chieko
C
Okamura
Department of Anatomy, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan.
Sonomi
S
Ito
Department of Pharmacological Sciences, International University of Health and Welfare, Kitakanemaru, Ohtawara, Tochigi, Japan.
Ryuichi
R
Konno
Innovative Science Research and Development Center, Shiseido Co., Ltd., Fukuura, Kanazawa-ku, Yokohama, Japan.
Masashi
M
Mita
Graduate School of Pharmaceutical Sciences, Kyushu University, Maidashi, Higashi-ku, Fukuoka, Japan.
Kenji
K
Hamase
Department of Anatomy, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan.
Sadakazu
S
Aiso
D058186:Acute Kidney Injury / Q000097:blood* / Q000473:pathology / Q000652:urine*; D000209:Acute-Phase Proteins / Q000652:urine; D000818:Animals; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000097:blood; D003605:D-Amino-Acid Oxidase / Q000652:urine; D006801:Humans; D007677:Kidney Function Tests; D000071068:Lipocalin-2; D054834:Lipocalins / Q000652:urine; D008297:Male; D051379:Mice; D015513:Oncogene Proteins / Q000652:urine; D015427:Reperfusion Injury / Q000097:blood* / Q000473:pathology / Q000652:urine*; D012694:Serine / Q000097:blood / Q000652:urine; D013237:Stereoisomerism
D000209:Acute-Phase Proteins; D055316:Cystatin C; D000071068:Lipocalin-2; D054834:Lipocalins; D015513:Oncogene Proteins; C071332:Lcn2 protein, mouse; D012694:Serine; D003404:Creatinine; D003605:D-Amino-Acid Oxidase