Central and Peripheral Characterization of Key Kynurenine Pathway Metabolites in Mexican Patients with Multiple Sclerosis: An Exploratory Study

<b>Background/Objectives</b>: Multiple Sclerosis (MS) is a chronic immune-mediated disorder characterized by neuroinflammation and neurodegeneration. Increasing evidence implies the kynurenine pathway (KP) in the MS pathophysiology; however, data from Mexican populations are lacking. This exploratory study aimed to characterize central and circulating KP metabolites in Mexican patients with MS and to investigate potential genetic variants in KP-related genes. <b>Methods</b>: Serum concentrations of kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK), as well as cerebrospinal fluid (CSF) levels of KYNA, quinolinic acid (QUIN), interleukin-4 (IL-4), and interleukin-6 (IL-6), were determined in treatment-naïve relapsing-remitting MS (RRMS), primary progressive MS (PPMS), and treated PMS patients. Serum levels were compared with those of healthy controls, and CSF findings contrasted with those of non-MS neurological patients and individuals with neurocysticercosis (NCC). Public whole-exome datasets were analyzed for variants in KP-related genes, and target exome sequencing was performed in three Mexican patients with MS. <b>Results</b>: Serum concentrations of KYNA and 3-HK were decreased in MS patients compared with healthy controls. CSF KYNA and QUIN levels did not differ significantly among MS subtypes or the non-MS neurological group, but they were lower than those observed in NCC. IL-4 and IL-6 were detectable in MS CSF samples, supporting the presence of intrathecal inflammation. Genetic and bioinformatic analyses identified variants in genes encoding KP enzymes in both public MS datasets and in Mexican patients with MS. <b>Conclusions</b>: These findings indicate an altered KP metabolism in Mexican MS patients, particularly during the relapse phase, and suggest a possible contribution of genetic variability. Further large-scale studies are needed to confirm these observations and to determine the functional implications of KP-related genetic variants in MS.