Unlocking the Potential of the 3-Hydroxykynurenine/kynurenic Acid Ratio: a Promising Biomarker in Adolescent Major Depressive Disorder

Metabolites disruptions in tryptophan (TRP) and kynurenine pathway (KP) are believed to disturb neurotransmitter homeostasis and contribute to depressive symptoms. This study aims to investigate serum levels of KP metabolites in adolescent major depressive disorder (AMDD), and examine their relationship with depression severities. Liquid chromatography-tandem mass spectrometry (LC–MS/MS) was used to analyze serum levels of TRP, kynurenic acid (KYNA), kynurenine (KYN), and 3-hydroxy-kynurenine (3-HK) in 143 AMDD participants and 98 healthy controls (HC). Clinical data, including Children’s Depression Inventory (CDI) scores, were collected and analyzed using statistical methods, such as ANOVA, logistic regression, Receiver operating characteristic curve analysis and a significance level of p < 0.05 was used for all analyses. AMDD showed significantly decreased serum levels of KYNA (−25.5 HC healthy controls, AMDD adolescent major depressive disorder, LC-MS/MS Liquid chromatography-tandem mass spectrometry, CDI Children's Depression Inventory, which provides a measure of the severity of depressive symptoms. The CDI scores were categorized into three ranges: mild depression (CDI-I), moderate depression (CDI-II), and severe depression (CDI-III)