Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia: effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures

TY - JOUR

T1 - Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia

T2 - effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures

AU - Dadsetan, Sherry

AU - Kukolj, Eva

AU - Bak, Lasse Kristoffer

AU - Sørensen, Michael

AU - Ott, Peter

AU - Vilstrup, Hendrik

AU - Schousboe, Arne

AU - Keiding, Susanne

AU - Waagepetersen, Helle S

PY - 2013/8

Y1 - 2013/8

N2 - 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.

AB - 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.

U2 - 10.1038/jcbfm.2013.73

DO - 10.1038/jcbfm.2013.73

M3 - Journal article

C2 - 23673435

SN - 0271-678X

VL - 33

SP - 1235

EP - 1241

JO - Journal of Cerebral Blood Flow and Metabolism

JF - Journal of Cerebral Blood Flow and Metabolism

IS - 8

ER -