Metabolomics of the Kynurenine Pathway by Laser Desorption Ionization Mass Spectrometry (LDI-MS)

The kynurenine (KYN) pathway is a branch of tryptophan metabolic cascade. The KYN pathway is unique since it generates multiple neuroactive metabolites, including 3-hydroxykynurenine (3-HK), kynurenic acid (KYNA), quinolinic acid (QUIN), and picolinic acid (PIC). Whereas KYNA and PIC are neuroprotective, 3-HK and QUIN are potently neurotoxic and attribute to major neurodegenerative diseases like schizophrenia, Alzheimer's disease, Huntington's disease, bipolar disorder, and depression. It is increasingly evident that the ratio(s) between the neurotoxic versus neuroprotective metabolites may help predict the manifestations of disease versus health. Therefore, high-throughput platforms for determining the relative levels of these kynurenine metabolites in biofluids offer considerable potential. Current analytical tools for studying the KYN pathway include assays of branching enzymes, PCR, immunoanalysis, and liquid chromatography-mass spectrometry. Neither of these offers high-throughput, cost-effective analyses suited for clinical or drug-screening applications. In this report, a Laser Desorption Ionization Mass Spectrometry (LDI-MS) method is described using SBA-15 mesoporous silica. The system allows fast, high-resolution relative quantitation of neurotoxic kynurenines using targeted metabolomics on conventional Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (mass spectrometry) (MALDI-TOF) platforms.