Chapter 17: Role of the kynurenine pathway in stroke

Abstract

Stroke is the second and fi fth leading cause of death for people aged >60 and 15–59 years, respectively. Many stroke survivors suffer from chronic health problems that necessitate a long-term process of recovery and rehabilitation. There is increasing evidence that infl ammation plays an important role in acute ischemic stroke (AIS), indicating the presence of important interactions between the nervous and immune systems. Furthermore, there are currently strong indications for a close relationship between the immune system and indoleamine-2,3-dioxygenase (IDO)- induced tryptophan catabolism [the kynurenine (KYN) pathway]. Although KYN pathway metabolites can produce excitatory and oxidative neurotoxicity, they can also protect neurons from infl ammatory damage and attenuate excitatory neurotoxicity via N -methyl- D -aspartate receptor antagonism. Thus, activation of IDO in the central nervous system might be a double-edged sword. Recent studies indicate that the KYN pathway is activated immediately after a stroke, that this is related to the strokeinduced infl ammatory response, and also that this IDO-induced tryptophan catabolism is correlated with a worse outcome. Since activation of the KYN pathway may disturb brain serotonin (5-hydroxytryptamine) and glutamate neurotransmission, it is reasonable to assume that infl ammation-induced IDO activity in AIS is involved in several sequelae following stroke, such as cognitive impairment, depression, and fatigue. Many AIS survivors suffer from post-stroke fatigue and post-stroke depression, indicating the importance of increasing the base of knowledge about the mechanisms underlying these sequelae. In this chapter, we present and discuss fi ndings that support the notion that the AIS-induced immune response and IDO activation are related to post-stroke fatigue but not to post-stroke depression.