Dysregulation of Trp-Kyn pathway is the most recent hypothesis of mechanisms of schizophrenia. In particular, over-production of kynurenic acid (KYNA), one of the three immediate downstream metabolites of kynurenine (Kyn) along tryptophan (Trp): Kyn pathway, has been considered as a new target for therapeutic intervention in schizophrenia. Up-regulation of KYNA formation was suggested to occur at the expense of down-regulated production of 3-hydroxyKyn (3-HK), the second immediate downstream metabolite of Kyn. We were interested to assess the third immediate downstream Kyn metabolite, anthranilic acid (AA). Serum AA concentrations were evaluated in schizophrenia patients and control subjects by HPLC-mass spectrometry method. We found 2-fold increase of AA and 3-fold decrease of 3-HK concentrations in serum of schizophrenia patients. Up regulated formation of AA might contribute to mechanisms of schizophrenia considering experimental evidences of AA augmentation of autoimmune processes in rat and mice; clinical findings of AA elevation in rheumatoid arthritis and type 1 diabetes, autoimmune diseases diametrical to schizophrenia; and involvement of autoimmunity in development of schizophrenia. Present data warrant further studies of AA as biological marker in, at least, a subgroup (associated with autoimmune mechanisms) of schizophrenia patients and as a new target for therapeutic intervention.
Keywords: Anthranilic acid; Kynurenines; Microbiome; Rheumatoid arthritis; Schizophrenia; Type 1 diabetes.