The current state in liquid chromatography-mass spectrometry methods for quantifying kynurenine pathway metabolites in biological samples: a systematic review.

Kynurenine pathway (KP) metabolites are implicated in various disorders, including Alzheimer's disease, schizophrenia, and adverse pregnancy outcomes. Simultaneous measurement of multiple KP metabolites offers valuable insight into the pathway's role in health and disease, would improve this relatively undeveloped field. This systematic review aim was to summarize the state of the art for measuring the eight key KP metabolites, using liquid chromatography-mass spectrometry (LC-MS), explicitly focusing on whether methods were validated using established guidelines with superior sensitivity and selectivity. We undertook a comprehensive review of the literature using the PRISMA guidelines. Our search uncovered 66 publications, and 39 qualified the defined key criteria. We summarized each publication's method development parameters, analytical design, and method performance specifications. We found notable variability in sample preparation techniques and analytical design across biological matrices, underscoring a lack of universally established and validated methods for KP metabolite quantification. We also identified significant gaps in the basic method evaluation. Our findings highlight that no single method has been evaluated for quantifying the eight key KP metabolites across three or more biological sample types, revealing a critical gap in the field. Our review emphasizes the need for robust analytical methods to quantify KP metabolites across multiple biological matrices, facilitating a better understanding of their roles in health and disease. Given the diversity of disorders involving the KP in the clinical testing lab, developing such methods will reduce diagnostic errors and advance KP metabolite research, supporting more precise, and personalized medical care.