[The kynurenic acid hypothesis - a new look at etiopathogenesis and treatment of schizophrenia].

Abstract

Kynurenic acid (KYNA) is a neuroactive metabolite of tryptophan formed in the brain and in the periphery, known to block ionotropic glutamate receptors and α7 nicotinic receptors, and to act as a ligand of G protein-coupled GPR35 receptors and human aryl hydrocarbon (AHR) receptors. KYNA seems to modulate a number of mechanisms involved in the pathogenesis of schizophrenia including dopaminergic transmission in mesolimbic and mesocortical areas or glutamatemediated neurotransmission. The kynurenine hypothesis of schizophrenia links the occurrence of positive and negative symptoms of schizophrenia and cognitive impairments characteristic for the disease with the disturbances of kynurenine pathway function. Available data suggest that antipsychotic drugs may restore balance among kynurenine pathway metabolites, and that co-administration of glycine with antipsychotics may reduce extrapyramidal symptoms in patients suffering from schizophrenia. Central level of KYNA may increase in the course of inflammation, which is consistent with the inflammatory hypothesis of schizophrenia. Alterations of immune response and disturbed functioning of kynurenine pathway may lead to disproportion between neuroprotective and neurotoxic mechanisms in the brain. Currently, intense research efforts are focused on the role of kynurenine pathway metabolites in pathogenesis of schizophrenia, their association with the response to antipsychotic treatment, and search for novel medications modulating the function of kynurenine pathway.