Review Article Kynurenines with Neuroactive and Redox Properties: Relevance to Aging and Brain Diseases

License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The kynurenine pathway (KP) is the main route of tryptophan degradation whose final product is NAD+. The metabolism of tryptophan can be altered in ageing andwith neurodegenerative process, leading to decreased biosynthesis of nicotinamide.This fact is very relevant considering that tryptophan is the major source of body stores of the nicotinamide-containing NAD+ coenzymes, which is involved in almost all the bioenergetic and biosynthetic metabolism. Recently, it has been proposed that endogenous tryptophan and its metabolites can interact and/or produce reactive oxygen species in tissues and cells. This subject is of great importance due to the fact that oxidative stress, alterations in KPmetabolites, energetic deficit, cell death, and inflammatory events may converge each other to enter into a feedback cycle where each one depends on the other to exert synergistic actions among them. It is worth mentioning that all these factors have been described in aging and in neurodegenerative processes; however, ha