title: Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia: effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures.
abstract: Hyperammonemia is a major etiological toxic factor in the development of hepatic encephalopathy. Brain ammonia detoxification occurs primarily in astrocytes by glutamine synthetase (GS), and it has been proposed that elevated glutamine levels during hyperammonemia lead to astrocyte swelling and cerebral edema. However, ammonia may also be detoxified by the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT) leading to trapping of ammonia in alanine, which in vivo likely leaves the brain. Our aim was to investigate whether the GS inhibitor methionine sulfoximine (MSO) enhances incorporation of (15)NH4(+) in alanine during acute hyperammonemia. We observed a fourfold increased amount of (15)NH4 incorporation in brain alanine in rats treated with MSO. Furthermore, co-cultures of neurons and astrocytes exposed to (15)NH4Cl in the absence or presence of MSO demonstrated a dose-dependent incorporation of (15)NH4 into alanine together with increased (15)N incorporation in glutamate. These findings provide evidence that ammonia is detoxified by the concerted action of GDH and ALAT both in vivo and in vitro, a mechanism that is accelerated in the presence of MSO thereby reducing the glutamine level in brain. Thus, GS could be a potential drug target in the treatment of hyperammonemia in patients with hepatic encephalopathy.
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Sherry
authors.initials: S
authors.lastname: Dadsetan
authors.forename: Eva
authors.initials: E
authors.lastname: Kukolj
authors.forename: Lasse K
authors.initials: LK
authors.lastname: Bak
authors.forename: Michael
authors.initials: M
authors.lastname: Sørensen
authors.forename: Peter
authors.initials: P
authors.lastname: Ott
authors.forename: Hendrik
authors.initials: H
authors.lastname: Vilstrup
authors.forename: Arne
authors.initials: A
authors.lastname: Schousboe
authors.forename: Susanne
authors.initials: S
authors.lastname: Keiding
authors.forename: Helle S
authors.initials: HS
authors.lastname: Waagepetersen
mesh_terms: D000409:Alanine / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000187:drug effects*; D001923:Brain Chemistry / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D018920:Coculture Techniques; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors*; D022124:Hyperammonemia / Q000378:metabolism*; D008717:Methionine Sulfoximine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D000596:Amino Acids; D004791:Enzyme Inhibitors; D008717:Methionine Sulfoximine; D005680:gamma-Aminobutyric Acid; D000641:Ammonia; D005974:Glutamate-Ammonia Ligase; D000409:Alanine