Quantitative analysis of neurochemical panel in rat brain and plasma by liquid chromatography-tandem mass spectrometry.

The dopamine, serotonin, and kynurenine metabolic pathways play pivotal roles on brain function, and their disturbances are closely related to various neurological diseases. Comprehensive measurements of these metabolites is thus essential for monitoring the global neurochemical responses to pathological challenges or drug intervention. However, simultaneous measurement of various neurochemcial metabolites represents a great challenge. We developed herein an original and feasible method using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). A chemical derivatization approach using benzoyl chloride (benzoylation) was developed to achieve better chromatographic behavior and mass-detecting sensitivity. The developed method enables a rapid quantification of 11 metabolites spanning dopamine, serotonin, and kynurenine metabolic pathways within 10.5 min. With this method, we were able to simultaneously monitor inflammation induced alternations of all these metabolites in a rat brain and in particular their dynamics in plasma matrix. The balance between the serotonin and kynurenine branches of tryptophan metabolism was disrupted by lipopolysaccharide (LPS)-induced inflammation, characterized with the overproduction of neurotoxic metabolite 3-hydroxykynurenine and decreased levels of serotonin. The measured levels of this panel of neurotransimtters ranged from 4.3 ng to 10.6 μg per gram of brain tissue. All these results suggest that the presently developed method is sufficiently sensitive and robust to simultaneously monitor a large panel of metabolites with diverse properties and a large range of concentration differences. Therefore, this method will be expected to be highly useful for comprehensive studies of the pathophysiological roles and mechanisms of these critical neurotransmitters.