Demonstration of kynurenine aminotransferases I and II and characterization of kynurenic acid synthesis in cultured cerebral cortical neurons

✍ Scribed by Wojciech Rzeski; Tomasz Kocki; Anna Dybel; Katarzyna Wejksza; Barbara Zdzisińska; Martyna Kandefer-Szerszeń; Waldemar A. Turski; Etsuo Okuno; Jan Albrecht

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 273 KB
• Volume: 80
• Category: Article
• ISSN: 0360-4012
• DOI: 10.1002/jnr.20505

✦ Synopsis

Abstract

The present study characterizes the synthesis of kynurenic acid (KYNA) from exogenously added kynurenine and its regulation by extrinsic factors, in cultured cerebral cortical neurons and, for comparison, in astrocytes incubated under identical conditions. The neuronal culture showed positive immunostaining for both kynurenic acid aminotransferase (KAT) isoforms I and II. Neurons synthesized KYNA at a rate about 2.3 times higher than astrocytes. Neuronal, but not astrocytic, KYNA synthesis was lowered ∼30% by ionotropic glutamate receptor agonists [(R,S)‐3‐hydroxy‐5‐methoxyloxasole‐4‐propionic acid (AMPA; 100 μM) and N‐methyl‐D‐aspartic acid (NMDA; 100 μM)] and depolarizing agents [KCl (50 mM) and 4‐aminopyridine (4‐AP; 10 μM)]. Neuronal and astrocytic synthesis alike were vulnerable to inhibition exerted by the aminotransferase inhibitor aminooxyacetic acid (AOAA), glutamate (IC~50~: 31 and 85 μM, respectively), substrates of the L‐amino transport system [leucine (Leu); IC~50~: 19 and 42 μM, respectively] and 2‐aminobicyclo[2,2,1]heptane‐2‐carboxylic acid (BCH; IC~50~: 19 and 28 μM, respectively). Glutamine (Gln), which is a metabolic precursor of glutamate in astrocytes and L‐system substrate in both cell types, inhibited KYNA synthesis both in neurons and in astrocytes (IC~50~: 268 and 318 μM, respectively). α‐Ketoisocaproic acid (KIC), a Leu transamination product that is produced mainly in astrocytes and shuttled to neurons to modulate intraneuronal concentration of glutamate, stimulated KYNA synthesis in neurons but did not affect the synthesis in astrocytes. In conclusion, this study is the first to demonstrate active, regulation‐prone KYNA synthesis in neurons. © 2005 Wiley‐Liss, Inc.