Dadsetan, Sherry3; Kukolj, Eva4; Bak, Lasse Kristoffer5; Sørensen, Michael8; Ott, Peter9; Vilstrup, Hendrik9; Schousboe, Arne6; Keiding, Susanne8; Waagepetersen, Helle S.7
1 Department of Clinical Medicine - Positron Emission Tomography Center, Department of Clinical Medicine, Health, Aarhus University2 Department of Clinical Medicine - The Department of Hepatology and Gastroenterology V, Department of Clinical Medicine, Health, Aarhus University3 2012 Forskeruddannelse B4 unknown5 Molecular and Cellular Pharmacology6 2012 Institut for Farmakologi og Farmakoterapi7 Kommunikation8 Department of Clinical Medicine - Positron Emission Tomography Center, Department of Clinical Medicine, Health, Aarhus University9 Department of Clinical Medicine - The Department of Hepatology and Gastroenterology V, Department of Clinical Medicine, Health, Aarhus University
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