A novel liquid chromatography/tandem mass spectrometry method for the quantification of glycine as biomarker in brain microdialysis and cerebrospinal fluid samples within 5 min

Glycine is an important amino acid neurotransmitter in the central nervous system (CNS) and a useful biomarker to indicate biological activity of drugs such as glycine reuptake inhibitors (GRI) in the brain. Here, we report how a liquid chromatography/tandem mass spectrometry (LC–MS/MS) method for the fast and reliable analysis of glycine in brain microdialysates and cerebrospinal fluid (CSF) samples has been established. Additionally, we compare this method with the conventional approach of high performance liquid chromatography (HPLC) coupled to fluorescence detection (FD). The present LC–MS/MS method did not require any derivatisation step. Fifteen microliters of sample were injected for analysis. Glycine was detected by a triple quadrupole mass spectrometer in the positive electrospray ionisation (ESI) mode. The total running time was 5 min. The limit of quantitation (LOQ) was determined as 100 nM, while linearity was given in the range from 100 nM to 100 μM. In order to demonstrate the feasibility of the LC–MS/MS method, we measured glycine levels in striatal in vivo microdialysates and CSF of rats after administration of the commercially available glycine transporter 1 (GlyT1) inhibitor LY 2365109 (10 mg/kg, p.o.). LY 2365109 produced 2-fold and 3-fold elevated glycine concentrations from 1.52 μM to 3.6 μM in striatal microdialysates and from 10.38 μM to 36 μM in CSF, respectively. In conclusion, we established a fast and reliable LC–MS/MS method, which can be used for the quantification of glycine in brain microdialysis and CSF samples in biomarker studies.