Long-Term Cuprizone Administration Resulted in Cognitive Decline and Kynurenine Metabolic Disturbance

The cuprizone (CPZ) toxin-induce animal model is suitable for studying the neurodegenerative processes of multiple sclerosis (MS) and the underlying molecular mechanisms. Cognitive de-cline is widespread in MS and has a marked impact on the quality of life of patients. Further-more, alterations in the kynurenine pathway (KP) of tryptophan degradation are remarkably evident not only in MS but also in its CPZ model too. Our aim was to investigate the KP in de-tail while simultaneously analyzing cognitive abilities during long-term CPZ exposure at dif-ferent time points during intoxication and recovery period. In our study, mice were fed with 0.2% CPZ toxin for 12 weeks followed by a 4-week recovery phase after toxin withdrawal. In the fourth, eighth and twelfth weeks of the demyelination period and at the end of the fourth week of the remyelination phase, we analyzed the cognitive ability of the animals with the Y-Maze test and we examined the distribution of all metabolites involved in the KP of TRP breakdown in plasma and five brain regions using ultra-high-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) technique. During bioanalytical analyses, we ob-served discrepancies in the levels of all neuroactive metabolites of KP, including anthranilic acid (AA), xanthurenic acid (XA), kynurenic acid (KYNA), quinaldic acid (QAA), 3-hydoxykynurenine (3-HK), 3-hydroxyanthranilic acid (3-HANA), picolinic acid (PA) and quinolinic acid (QUIN), in response to toxin treatment both in the periphery and in the CNS. As the treatment progressed, the concentration of metabolites XA, KYNA, QAA, 3-HK, 3-HANA moved at drastically lower values, while QUIN or PA showed dynamic changes. Nevertheless, we noticed normalization of the metabolite levels upon remyelination. In parallel, we determined a notable cognitive de-cline in the CPZ-treated group. Overall, we identified the profile of neuroactive metabolites of the KP in periphery and CNS, as well as cognitive impairment during chronic treatment. Con-sequently, our studies were the first to confirm the link between the kynurenine metabolite ab-normalities seen in the CPZ model and MS, thereby emphasizing the relevance of the kynurenine metabolite profile, opening further opportunities to identify and investigate the mechanisms of neurodegenerative processes.