Dadsetan, Sherry9; Kukolj, Eva4; Bak, Lasse Kristoffer10; Sørensen, Michael5; Ott, Peter6; Vilstrup, Hendrik7; Schousboe, Arne10; Keiding, Susanne8; Waagepetersen, Helle S10
1 Department of Drug Design and Pharmacology, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet2 Molecular and Cellular Pharmacology, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet3 Drug Research Academy B, Drug Research Academy, Faculty of Pharmaceutical Sciences, Københavns Universitet4 Department of Chromosome Biology, Max F. Perutz Laboratories5 Århus Universitets Hospital6 Department of Medicine V, Aarhus University Hospital7 Institut for Klinisk Medicin - Medicinsk Afd. V, NBG8 PET-Centret, forskningsafdeling9 Drug Research Academy B, Drug Research Academy, Faculty of Pharmaceutical Sciences, Københavns Universitet10 Molecular and Cellular Pharmacology, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet
effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures
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.
Journal of Cerebral Blood Flow and Metabolism, 2013, Vol 33, Issue 8, p. 1235-41