Brain Research 981 (2003) 193–200 www.elsevier.com / locate / brainres Research report Sources of oxygen radicals in brain in acute ammonia intoxication in vivo a a a b Elena Kosenko , Natalia Venediktova , Yury Kaminsky , Carmina Montoliu , b, * Vicente Felipo a Institute of Theoretical and Experimental Biophysics RAS, Pushchino, 142290 Russia b ´ Laboratory of Neurobiology, Instituto de Investigaciones Citologicas, Fundacion Valenciana de Investigaciones Biomedicas, Amadeo de Saboya 4, 46010 Valencia, Spain Accepted 13 May 2003 Abstract The effects of acute ammonia intoxication on reactive oxygen species production by different sources in rat brain were studied. Ammonia intoxication in vivo leads to reduced activity of superoxide dismutase (SOD), catalase and glutathione peroxidase in brain 2 nonsynaptic mitochondria and increased formation of O by submitochondrial particles. It also results in increased xanthine oxidase (XO) 2 activity and decreased xanthine dehydrogenase (XDH) / XO activity ratio indicating conversion of XDH to XO and also increases monoamine oxidase A (MAO-A) activity but not of MAO-B. Blocking NMDA receptors with MK-801 prevents ammonia-induced oxidative stress, XDH to XO conversion and MAO-A activation. Ammonia intoxication did not lead to H O formation by mitochondria, 2 2 2 in spite of increased O generation. The main source of H O in the mitochondrial matrix was Mn-SOD. Ammonia intoxication in vivo 2 2 2 leads to increased superoxide and decreased hydrogen peroxide in nonsynaptic brain mitochondria. Increased superoxide is due to increased formation by the respiratory chain and by xanthine and aldehyde oxidases and decreased elimination by antioxidant enzymes. The reduced formation of hydrogen peroxide is due to the reduced activity of Mn-SOD. Prevention of ammonia-induced production of reactive oxygen species by MK-801 supports the idea that it is mediated by activation of NMDA receptors.  2003 Elsevier B.V. All rights reserved. Theme: Disorders of the nervous system Topic: Neurotoxicity Keywords: Hyperammonemia; Ammonia toxicity; NMDA receptor; Glutamate receptor; Free radical; Brain mitochondria 1. Introduction receptors (mainly of NMDA receptors) is neurotoxic, leading to neuronal degeneration and death. Excessive Glutamate is the main excitatory neurotransmitter in activation of NMDA receptors is involved in the neuronal mammals. However, excessive activation of glutamate damage found in brain ischemia and in the origin of some neurodegenerative diseases [2]. The mechanisms by which excessive activation of NMDA receptors leads to neuronal 21 Abbreviations: DCPIP, 2,6-dichlorophenol indophenol; DTT, dithio- degeneration and death involve the increase in Ca threitol; HRP, horseradish peroxidase; MK-801, [5R,10S]-(1)-5-methyl- 21 concentration in the postsynaptic neuron [8,29]. Ca 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate; MAO, binds to calmodulin and activates nitric oxide synthase, monoamine oxidase; Mops, 3-(N-morpholino)propane-sulfonate; NMDA, N-methyl-D-aspartate; NO, nitric oxide; NTB, nitrotetrazolium blue; increasing the formation of nitric oxide (NO), that contri- PMSF, phenylmethylsulfonyl fluoride; ROS, reactive oxygen species; butes to the neurotoxic process. This is supported by SMP, submitochondrial particles; SOD, superoxide dismutase; XDH, experiments showing that glutamate and NMDA neuro- xanthine dehydrogenase; XO, xanthine oxidase. toxicity are prevented by inhibitors of nitric oxide synthase *Corresponding author. Tel.: 134-96-3391-250; fax: 134-96-3601- such as nitroarginine [16,11,25,36,30]. Activation of 453. E-mail address: vfelipo@ochoa.fib.es (V. Felipo). NMDA receptors also leads to increased production of 0006-8993 / 03 / $ – see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0006-8993(03)03035-X