Improved separation and detection of picolinic acid and quinolinic acid by capillary electrophoresis-mass spectrometry: Application to analysis of human cerebrospinal fluid

Abstract

“Quinolinic acid (QA)”, a metabolite of the kynurenine pathway (KP), is implicated as a major neurological biomarker, which causes inflammatory disorders, whereas there is an increase evidence of the role of picolinic acid (PA) in neuroinflammation. Therefore, there is an urgent need to develop new clinical test for early diagnosis of neuroinflammatory disorders. A comparison is made between three different platforms such as high performance liquid chromatography–electrospray mass spectrometry (HPLC–ESI-MS/MS), nano LC–Chip/ESI-MS/MS, as well as the use of cationic (quaternary ammonium) and anionic (sulfonated) coated capillaries in capillary electrophoresis (CE)-ESI-MS/MS. The comparison revealed that CE-ESI-MS/MS method using a quaternary ammonium coated capillary is the best method for analysis of PA and QA. A simple stacking procedure by the inclusion of acetonitrile in the artificial cerebrospinal fluid (CSF) sample was employed to improve the peak shape and sensitivity of KP metabolites in CE-ESI-MS/MS. The developed CE-ESI-MS/MS assay provided high resolution, high specificity and high sensitivity with a total analysis time including sample preparation of nearly 12 min. In addition, excellent intra-day and inter-day repeatability of migration times and peak areas of the metabolites were observed with respective relative standard deviation (RSD) of less than 2.0% and 2.5%. Somewhat broader variations in repeatability for a 3 independently prepared coated capillary (total 35 runs each) with % RSD up to 3.8% and 5.8% was observed for migration time and peak areas, respectively. Artificial CSF was used as a surrogate matrix to simultaneously generate calibration curves over a concentration range of 0.02–10 μM for PA and 0.4–40 μM for QA. The method was then successfully applied to analyze PA and QA in human CSF, demonstrating the potential of this CE-ESI-MS/MS method to accurately quantitate with high specificity and sensitivity.

Kynurenine pathway metabolites and suicidality

“…It has not yet been established whether PIC is able to cross the BBB and enter CNS from the periphery under physiological conditions, but PIC is readily detectable in CSF samples from humans (own unpublished observations) (Coggan et al, 2009; Wang et al, 2013). ACMSD is expressed in the brain, although the expression rate is lower than in kidney and liver (Pucci et al, 2007).…”

Recent advances in combination of capillary electrophoresis with mass spectrometry: Methodology and theory

“…They identified choline, dimethylarginine, arginine, valine, proline, serine, histidine, creatine, carnitine, and suberylglycine as possible disease progression biomarkers. The comparison of various platforms of LC‐ESI‐MS/MS with CE‐ESI‐MS/MS revealed that using a quaternary ammonium‐coated capillary, CE combination is the best method for analysis of quinolinic acid, a metabolite of the kynurenine pathway, and picolinic acid involved in neuroinflammation . Consequently, the method was successfully applied to analyze both acids in cerebrospinal fluid demonstrating the potential of this method to accurately quantitate with high specificity and sensitivity.…”

Contemporary sample stacking in analytical electrophoresis

“…Wang et al. published a method for sensitive determination of the neurological biomarkers quinolinic and picolinic acid in cerebrospinal fluid by CE‐ESI‐MS/MS. They used a (vinylbenzyl)trimethylammonium‐coated capillary and 15 mM (NH 4 ) 2 CO 3 at pH 11.0 as the BGE.…”