Physiology of the kynurenine pathway and its implications in CNS disorders

The kynurenine pathway (KP), a crucial route of tryptophan (TRP) catabolism, has emerged as a focal point of investigation because of its complex involvement in regulating central nervous system (CNS) function. This metabolic pathway, which operates in various cell types within the CNS, closely links immune responses, neurotransmission, and neuroinflammation. This review provides an in-depth exploration of the KP, delineating its enzymatic constituents, metabolite profiles, and multifarious roles in sustaining CNS homeostasis, with potential implications for neuropathological conditions including Alzheimer's disease (AD), Parkinson's disease (PD), major depressive disorder (MDD), and schizophrenia (SCZ). In addition to the roles of the KP in the pathogenesis of the abovementioned diseases, the related advancements in treatment are discussed.