Metabolomics Analyses of 14 Classical Neurotransmitters by GC-TOF with LC-MS Illustrates Secretion of 9 Cell–Cell Signaling Molecules from Sympathoadrenal Chromaffin Cells in the Presence of Lithium

The classical small molecule neurotransmitters
are essential for
cell–cell signaling in the nervous system for regulation of
behaviors and physiological functions. Metabolomics approaches are
ideal for quantitative analyses of neurotransmitter profiles but have
not yet been achieved for the repertoire of 14 classical neurotransmitters.
Therefore, this study developed targeted metabolomics analyses by
full scan gas chromatography/time-of-flight mass spectrometry (GC-TOF)
and hydrophilic interaction chromatography-QTRAP mass spectrometry
(HILIC-MS/MS) operated in positive ionization mode for identification
and quantitation of 14 neurotransmitters consisting of acetylcholine,
adenosine, anandamide, aspartate, dopamine, epinephrine, GABA, glutamate,
glycine, histamine, melatonin, norepinephrine, serine, and serotonin.
GC-TOF represents a new metabolomics method for neurotransmitter analyses.
Sensitive measurements of 11 neurotransmitters were achieved by GC-TOF,
and three neurotransmitters were analyzed by LC-MS/MS (acetylcholine,
anandamide, and melatonin). The limits of detection (LOD) and limits
of quantitation (LOQ) were assessed for linearity for GC-TOF and LC-MS/MS
protocols. In neurotransmitter-containing dense core secretory vesicles
of adrenal medulla, known as chromaffin granules (CG), metabolomics
measured the concentrations of 9 neurotransmitters consisting of the
catecholamines dopamine, norepinephrine, and epinephrine, combined
with glutamate, serotonin, adenosine, aspartate, glycine, and serine.
The CG neurotransmitters were constitutively secreted from sympathoadrenal
chromaffin cells in culture. Nicotine- and KCl-stimulated release
of the catecholamines and adenosine. Lithium, a drug used for the
treatment of bipolar disorder, decreased the constitutive secretion
of dopamine and norepinephrine and decreased nicotine-stimulated secretion
of epinephrine. Lithium had no effect on other secreted neurotransmitters.
Overall, the newly developed GC-TOF with LC-MS/MS metabolomics methods
for analyses of 14 neurotransmitters will benefit investigations of
neurotransmitter regulation in biological systems and in human disease
conditions related to drug treatments.