Targeted serum metabolomics reveals novel metabolic associations between fatty acid and kynurenine metabolism in nonalcoholic fatty liver.

Nonalcoholic fatty liver disease (NAFLD) is fundamentally characterized by dysregulated hepatic lipid metabolism. Recent evidence suggests that peripheral neurotransmitter metabolism may be involved in NAFLD pathogenesis, yet the relationship between neurotransmitter and lipid metabolism remains incompletely understood. This study employed targeted serum metabolomics to simultaneously investigate alterations in the kynurenine (KYN) pathway and lipid metabolism. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified a concurrent reduction in serum levels of KYN pathway metabolites, including KYN, xanthurenic acid (XA), and its precursor tryptophan (TRP), in NAFLD patients. These changes were significantly accompanied by dysregulated levels of palmitic acid (PA), arachidonic acid (AA), and eicosapentaenoic acid (EPA). Method validation confirmed analytical reliability, with limit of detection (LOD) of 0.2-5 ng/mL and limit of quantification (LOQ) of 0.5-10 ng/mL for both KYN metabolites and fatty acids. Calibration curves displayed excellent linearity (R2 > 0.995), and both intra-day and inter-day precision was satisfactory, with recovery rates meeting validation criteria. To validate these associations, an HFD-induced NAFLD mouse model was used. Parallel reductions in KYN pathway metabolites and dysregulated fatty acid metabolism were observed in the liver. Logistic regression with false discovery rate (FDR) correction revealed that most KYN metabolite levels varied concordantly with fatty acid levels in mice. In summary, this study provides the first systematic demonstration of concurrent dysregulation of the KYN pathway and lipid metabolism in NAFLD, supported by robust chromatographic-mass spectrometric validation. The observed parallel metabolic disturbances offer new perspectives for therapeutic strategies targeting NAFLD.