Chiral amino acid metabolomics for novel biomarker screening in the prognosis of chronic kidney disease

Abstract

D-Amino acids, the enantiomers of L-amino acids, are increasingly recognized as novel biomarkers. Although the amounts of D-amino acids are usually very trace in human, some of them have sporadically been detected in blood from patients with kidney diseases. This study examined whether multiple chiral amino acids would be associated with kidney functions, comorbidities, and prognosis of chronic kidney disease (CKD) by enantioselective analyses of all chiral amino acids with a micro-two-dimensional high-performance liquid chromatograph (2D-HPLC)-based analytical platform. 16 out of 21 D-amino acids were detected in plasma from 108 CKD patients in a longitudinal cohort. The levels of D-Ser, D-Pro, and D-Asn were strongly associated with kidney function (estimated glomerular filtration ratio), the levels of D-Ala and D-Pro were associated with age, and the level of D-Asp and D-Pro were associated with the presence of diabetes mellitus. D-Ser and D-Asn were significantly associated with the progression of CKD in mutually-adjusted Cox regression analyses; the risk of composite end point (developing to ESKD or death before ESKD) was elevated from 2.7- to 3.8-fold in those with higher levels of plasma D-Ser and D-Asn. These findings identified chiral amino acids as potential biomarkers in kidney diseases.

Figure 1. Detection of 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD)-labeled amino acid enantiomers in the plasma of patients with chronic kidney disease using a 2D-HPLC-MS/MS system.

The detailed MS/MS conditions were described in the Method section.

Figure 2. Kaplan-Meier curves of D/L-amino acids for the prognosis of kidney disease.

Patients with first (thick line), second (dotted line), and third (thin gray line) tertile of levels of amino acids were subjected to these analyses.