Alternative kynurenic acid synthesis routes studied in the rat cerebellum

作者：Blanco Ayala Tonali; Lugo Huitron Rafael; Carmona Aparicio Liliana; Ramirez Ortega Daniela; Gonzalez Esquivel Dinora; Pedraza Chaverri Jose; Perez de la Cruz Gonzalo; Rios Camilo; Schwarcz Robert; Perez de la Cruz Veronica

来源：Frontiers in Cellular Neuroscience, 2015, 9: 178.

DOI：10.3389/fncl.2015.00178

• D-amino acid oxidase
• kynurenine
• microdialysis
• oxidative stress
• reactive oxygen species

Kynurenic acid (KYNA), an astrocyte-derived, endogenous antagonist of alpha 7 nicotinic acetylcholine and excitatory amino acid receptors, regulates glutamatergic, GABAergic, cholinergic and dopaminergic neurotransmission in several regions of the rodent brain. Synthesis of KYNA in the brain and elsewhere is generally attributed to the enzymatic conversion of L-kynurenine (L-KYN) by kynurenine aminotransferases (KATs). However, alternative routes, including KYNA formation from D-kynurenine (D-KYN) by D-amino acid oxidase (DAAO) and the direct transformation of kynurenine to KYNA by reactive oxygen species (ROS), have been demonstrated in the rat brain. Using the rat cerebellum, a region of low KAT activity and high DAAO activity, the present experiments were designed to examine KYNA production from L-KYN or D-KYN by KAT and DAAO, respectively, and to investigate the effect of ROS on KYNA synthesis. In chemical combinatorial systems, both L-KYN and D-KYN interacted directly with peroxynitrite (ONOO-) and hydroxyl radicals (OH center dot), resulting in the formation of KYNA. In tissue homogenates, the non-specific KAT inhibitor aminooxyacetic acid (AOAA; 1 mM) reduced KYNA production from L-KYN and D-KYN by 85.1 +/- 1.7% and 27.1 +/- 4.5%, respectively. Addition of DAAO inhibitors (benzoic acid, kojic acid or 3-methylpyrazole5-carboxylic acid; 5 mu M each) attenuated KYNA formation from L-KYN and D-KYN by similar to 35% and similar to 66%, respectively. ONOO- (25 mu M) potentiated KYNA production from both L-KYN and D-KYN, and these effects were reduced by DAAO inhibition. AOAA attenuated KYNA production from L-KYN + ONOO- but not from D-KYN + ONOO-. In vivo, extracellular KYNA levels increased rapidly after perfusion of ONOO- and, more prominently, after subsequent perfusion with L-KYN or D-KYN (100 mu M). Taken together, these results suggest that different mechanisms are involved in KYNA production in the rat cerebellum, and that, specifically, DAAO and ROS can function as alternative routes for KYNA production.

• 出版日期2015-5-18