Simultaneous determination of free DL-amino acids in human hair with a novel DBD-M-Pro derivatization by UHPLC-HRMS: An application in diabetes patients

Human hair is a non-invasive biological sample that is easy to collect and store and can reflect long-term body health. However, the correlation between DL-amino acids and metabolic diseases in hair samples has not been studied. Therefore, we propose a novel UHPLC-HRMS method for analyzing seven free chiral amino acids (DL-Thr, DL-Glu, DL-Ala, DL-Val, DL-Pro, DL-Leu, and DL-Phe) simultaneously in hair samples by derivatization of chiral probe 4-(N,N-dmethylaminosulfonyl)-2,1,3-benzoxadiazole-trans-2-methyl-L-proline (DBD-M-Pro) labeled with targeted amino functional groups. Gradient elution was carried out using an ACQUITYTM BEH C18 (100x2.1 mm,1.7 mu m) column with a mobile phase of 0.15 % formic acid (FA) in 10 mM ammonium acetate (CH3-COONH4) and 0.2 % FA in acetonitrile. The labelled DL-amino acid diastereoisomers could be completely separated, with a resolution (Rs) of 1.59-11.44. These amino acids show a strong linear correlation within the range of 3.1-99.2 pmol (R-2 >= 0.9990). Intraday and interday precision was 1.87 %-14.87 %. The average recovery was 96.12 %-105.33 %. The limit of detection (LOD) ranged from 0.29 to 2.11 pmol. We then employed the method to determine the concentration of free chiral amino acids in hair samples from 30 healthy volunteers (HVs) and 30 diabetes patients (DPs). Male diabetes patients had significantly higher levels of L-Thr, L-Val, L-Leu (p < 0.05), and D-Ala (p < 0.01) in their hair samples than male healthy volunteers and female diabetes patients had significantly higher levels of D-Ala (p < 0.05) in their hair samples than female healthy volunteers. This is the first study to confirm the feasibility of using free DL-amino acids in human hair as potential biomarkers for diabetes.