Concentration gradients of monoamines, their precursors and metabolites in serial lumbar cerebrospinal fluid of neurologically healthy patients determined with a novel LC-MS/MS technique

Abstract

Background: Potential biomarkers for neuropsychiatric disorders are cerebrospinal fluid (CSF) monoamines and their corresponding precursors and metabolites. During CSF sampling, CSF flows towards the lumbar sampling site from more cranial regions. To compare the results of studies in which different CSF volumes were acquired, it is important to know if ventricular-lumbar concentration gradients exist. This has only been addressed for a few biogenic amines, and almost exclusively in neurologically unwell patients due to the burden of a lumbar puncture (necessary to obtain CSF). The aim of our study was to determine if concentration gradients exist for routinely measured CSF constituents and biogenic amines in neurologically healthy patients. We applied a novel ultrasensitive liquid chromatography mass spectrometry (LC-MS/MS) method for the simultaneous quantification of multiple monoamines, precursors and metabolites in CSF and plasma.

Methods: CSF and blood samples were collected from twenty neurologically healthy patients undergoing spinal anaesthesia. Ten mL of lumbar CSF was collected in five consecutive two mL fractions. We determined leucocyte and erythrocyte counts, glucose, albumin and protein concentrations and quantified monoamines, precursors and metabolites on each of the fractions using LC-MS/MS.

Results: In twenty patients (60% male; median age: 46 years), dopamine, DOPAC, 3-MT, HVA, noradrenaline, normetanephrine and 5-HIAA concentrations increased from the first to the last CSF fraction (all p < 0.001). CSF adrenaline concentrations were below the detection limit, whereas serotonin measurements were regarded as unreliable. Albumin and total protein levels decreased significantly across CSF fractions.

Conclusions: A ventricular-lumbar CSF concentration gradient existed for most of the investigated analytes. This is a novel finding for dopamine, noradrenaline, 3-MT and normetanephrine. These results contribute to the understanding of the neurobiology and underline the importance of standardized procedures for CSF handling to allow comparisons between studies.

Keywords: Biogenic amines; Cerebrospinal fluid (CSF); Concentration gradients; LC–MS/MS.

Fig. 1

Concentrations of monoamines, their precursors and metabolites in five consecutive CSF fractions. Concentrations of A L-DOPA (levodopa), B 3-OMD (3-o-methyldopa), C DA (dopamine), D DOPAC (3,4-Dihydroxyphenylacetic acid), E 3-MT (3-methoxytyramine), F HVA (homovanillic acid), G NA (noradrenalin), H NMN (normetanephrine), I MOPEG (3-Methoxy-4-hydroxyphenylglycol) and J 5-HIAA (5-hydroxyindoleacetic acid) for the five consecutive fractions of CSF: 1: 0–2 mL, 2: 2–4 mL, 3: 4–6 mL, 4: 6–8 mL, 5: 8–10 mL. For all analytes, the bold line shows the median concentration and the grey box the IQR. Concentration gradient for analytes significant at 0.05 level (*), 0.01 level (**) or 0.001 level (***)

Fig. 2

Concentrations of routine laboratory analyses in five consecutive CSF fractions. Concentrations of A albumin, B Qalb, C total protein, D glucose, E erythrocyte count and F leukocyte count for the five consecutive fractions of CSF: 1: 0–2 mL, 2: 2–4 mL, 3: 4–6 mL, 4: 6–8 mL, 5: 8–10 mL. For all analytes, the bold line shows the median concentration and the grey box the IQR. Concentration gradient for analytes significant at 0.05 level (*), 0.01 level (**) or 0.001 level (***). Qalb ratio of CSF to plasma albumin concentration