Inhibition of glutamine synthesis induces glutamate dehydrogenase-dependent ammonia fixation into alanine in co-cultures of astrocytes and neurons

2011 ◽  
Vol 59 (4) ◽  
pp. 482-488 ◽  
Author(s):  
Sherry Dadsetan ◽  
Lasse K. Bak ◽  
Michael Sørensen ◽  
Susanne Keiding ◽  
Hendrik Vilstrup ◽  
...  
Keyword(s):  
Glutamate Dehydrogenase ◽  
Glutamine Synthesis ◽  
Ammonia Fixation

scholarly journals Glutamate Dehydrogenase Is Important for Ammonia Fixation and Amino Acid Homeostasis in Brain During Hyperammonemia

2021 ◽  
Vol 15 ◽  
Author(s):  
Caroline M. Voss ◽  
Lene Arildsen ◽  
Jakob D. Nissen ◽  
Helle S. Waagepetersen ◽  
Arne Schousboe ◽  
...  
Keyword(s):  
Glutamate Dehydrogenase ◽  
De Novo ◽  
Brain Slices ◽  
Isotopic Labeling ◽  
Impaired Liver Function ◽  
Tissue Extracts ◽  
Impaired Liver ◽  
Glutamine Synthesis ◽  
Ammonia Fixation

Impaired liver function may lead to hyperammonemia and risk for hepatic encephalopathy. In brain, detoxification of ammonia is mediated mainly by glutamine synthetase (GS) in astrocytes. This requires a continuous de novo synthesis of glutamate, likely involving the action of both pyruvate carboxylase (PC) and glutamate dehydrogenase (GDH). An increased PC activity upon ammonia exposure and the importance of PC activity for glutamine synthesis has previously been demonstrated while the importance of GDH for generation of glutamate as precursor for glutamine synthesis has received little attention. We therefore investigated the functional importance of GDH for brain metabolism during hyperammonemia. To this end, brain slices were acutely isolated from transgenic CNS-specific GDH null or litter mate control mice and incubated in aCSF containing [U-13C]glucose in the absence or presence of 1 or 5 mM ammonia. In another set of experiments, brain slices were incubated in aCSF containing 1 or 5 mM 15N-labeled NH4Cl and 5 mM unlabeled glucose. Tissue extracts were analyzed for isotopic labeling in metabolites and for total amounts of amino acids. As a novel finding, we reveal a central importance of GDH function for cerebral ammonia fixation and as a prerequisite for de novo synthesis of glutamate and glutamine during hyperammonemia. Moreover, we demonstrated an important role of the concerted action of GDH and alanine aminotransferase in hyperammonemia; the products alanine and α-ketoglutarate serve as an ammonia sink and as a substrate for ammonia fixation via GDH, respectively. The role of this mechanism in human hyperammonemic states remains to be studied.

scholarly journals Acetate stimulates flux through the tricarboxylic acid cycle in rabbit renal proximal tubules synthesizing glutamine from alanine: a 13C NMR study

1999 ◽  
Vol 342 (3) ◽  
pp. 555-566 ◽  
Author(s):  
Sylvie DUGELAY ◽  
Marie-France CHAUVIN ◽  
Frédérique MEGNIN-CHANET ◽  
Guy MARTIN ◽  
Marie-Catherine LARÉAL ◽  
...  
Keyword(s):  
Glutamate Dehydrogenase ◽  
13C Nmr ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Proximal Tubules ◽  
Experimental Conditions ◽  
Renal Proximal Tubules ◽  
Nmr Study ◽  
Dehydrogenase Reaction ◽  
Glutamine Synthesis

Although glutamine synthesis has a major role in the control of acid-base balance and ammonia detoxification in the kidney of herbivorous species, very little is known about the regulation of this process. We therefore studied the influence of acetate, which is readily metabolized by the kidney and whose metabolism is accompanied by the production of bicarbonate, on glutamine synthesis from variously labelled [13C]alanine and [14C]alanine molecules in isolated rabbit renal proximal tubules. With alanine as sole exogenous substrate, glutamine and, to a smaller extent, glutamate and CO2, were the only significant products of the metabolism of this amino acid, which was removed at high rates. Absolute fluxes through the enzymes involved in alanine conversion into glutamine were assessed by using a novel model describing the corresponding reactions in conjunction with the 13C NMR, and to a smaller extent, the radioactive and enzymic data. The presence of acetate (5 mM) led to a large stimulation of fluxes through citrate synthase and α-oxoglutarate dehydrogenase. These effects were accompanied by increases in the removal of alanine, in the accumulation of glutamate and in flux through the anaplerotic enzyme pyruvate carboxylase. Acetate did not alter fluxes through glutamate dehydrogenase and glutamine synthetase; as a result, acetate did not change the accumulation of ammonia, which was negligible under both experimental conditions. We conclude that acetate, which seems to be an important energy-provider to the rabbit renal proximal tubule, simultaneously traps as glutamate the extra nitrogen removed as alanine, thus preventing the release of additional ammonia by the glutamate dehydrogenase reaction.

scholarly journals Importance of glutamate dehydrogenase stimulation for glucose and glutamine synthesis in rabbit renal tubules incubated with various amino acids.

1998 ◽  
Vol 45 (3) ◽  
pp. 825-831
Author(s):  
K Winiarska ◽  
P Bozko ◽  
T Lietz ◽  
J Bryła
Keyword(s):  
Glutamate Dehydrogenase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Lactate Production ◽  
Renal Tubules ◽  
Glycerol Utilization ◽  
Key Enzyme ◽  
Glutamine Synthesis ◽  
Glutamate Synthesis ◽  
Glucose Formation ◽  
Stimulation Of

The effect of 2-aminobicyclo[2.2.1]heptan-2-carboxylic acid (BCH), an L-leucine nonmetabolizable analogue and an allosteric activator of glutamate dehydrogenase, on glucose and glutamine synthesis was studied in rabbit renal tubules incubated with alanine, aspartate or proline in the presence of glycerol and octanoate, i.e. under conditions of efficient glucose formation. With alanine+glycerol+octanoate the addition of BCH resulted in a stimulation of alanine and glycerol consumption, accompanied by an increased glucose, lactate and glutamine synthesis. In contrast, when alanine was substituted by either aspartate or proline, BCH altered neither glucose formation nor glutamine and glutamate synthesis, while an accelerated glycerol utilization was accompanied by a small increase in lactate production. In view of the BCH-induced changes in intracellular metabolite levels the acceleration of gluconeogenesis by BCH in the presence of alanine+glycerol+octanoate is probably due to (i) increased uptake of alanine via alanine aminotransferase, (ii) stimulation of phosphoenolpyruvate carboxykinase, a key-enzyme of gluconeogenesis, (iii) rise of glucose-6-phosphatase activity, as well as (iv) activation of the malate-aspartate shuttle resulting in an augmented glycerol utilization for lactate and glucose synthesis.

Evaluating the Contribution of Glutamate Dehydrogenase and the Glutamate Synthase Cycle to Ammonia Assimilation by Four Ectomycorrhizal Fungal Isolates

1996 ◽  
Vol 23 (2) ◽  
pp. 151 ◽  
Author(s):  
MH Turnbull ◽  
R Goodall ◽  
GR Stewart
Keyword(s):  
Glutamate Dehydrogenase ◽  
Glutamate Synthase ◽  
Ammonium Assimilation ◽  
Major Product ◽  
Ammonia Assimilation ◽  
Gas Chromatography Mass Spectrometry ◽  
Methionine Sulfoximine ◽  
Fungal Isolates ◽  
Glutamine Synthesis ◽  
Fungal Tissue

Combined gas chromatography-mass spectrometry were used to evaluate the contributions of glutamate dehydrogenase (GDH) and the glutamate synthase cycle in 15N-labelled ammonium assimilation by four ectomycorrhizal fungal isolates. In all four species (Elaphomyces, Amanita, Pisolithus and Gautieria), glutamine was the major product accumulated following transfer of 14-day-old nitrogen-limited cultures to fresh medium. Label was rapidly assimilated into fungal tissue, with rates of 733 nmol g-1 FW h-1 in Pisolithus, 972 nmol g-1 FW h-1 in Amanita, 2760 nmol g-1 FW h-1 in Gautieria and 6756 nmol g-1 FW h-1 in Elaphomyces sp in the first 4 h of incubation. Incorporation of [15N]ammonium was sensitive to the inhibitory effects of both methionine sulfoximine (MSX, an inhibitor of glutamine synthetase (GS)) and albizziin (an inhibitor of glutamate synthase (GOGAT)) in three species (Amanita, Gautieria and Pisolithus) and labelling patterns were consistent with the action of the glutamate synthase cycle in ammonium assimilation. In all three species glutamine synthesis was almost totally blocked by MSX and there was no continued incorporation of 15N into glutamate. Elaphomyces displayed high levels of total incorporation of labelled ammonium in mycelium even in the presence of MSX, although incorporation into glutamine was reduced by 88%. This inhibition of GS by MSX, in addition to its partial inhibition by albizziin suggests strongly the action of glutamate synthase cycle in ammonium assimilation. The reduction in label entering glutamate under the influence of albizziin is direct evidence for the inhibition of GOGAT activity. However, MSX treatment had the effect of increasing significantly the quantity of label recovered in both glutamate and alanine. In the absence of GS inhibition there is clearly competition for ammonium which under normal physiological conditions results in assimilation through the glutamate synthase cycle. However, when GS is blocked by MSX label is able to cycle through the GDH pathway. Extra keywords: ectomycorrhiza, ammonium assimilation, glutamate synthase cycle, glutamate dehydrogenase, amino acid metabolism.

Glutamate and glutamine metabolism in the ovine placenta

1983 ◽  
Vol 101 (2) ◽  
pp. 275-281 ◽  
Author(s):  
Jennifer M. Pell ◽  
Marjorie K. Jeacock ◽  
D. A. L. Shepherd
Keyword(s):  
Glutamine Synthetase ◽  
Glutamate Dehydrogenase ◽  
Placental Transfer ◽  
Umbilical Vein ◽  
Maternal Blood ◽  
Glutamine Metabolism ◽  
Arterial Blood ◽  
Foetal Circulation ◽  
Glutamine Synthesis ◽  
Glutamyl Transferase

SUMMARYThe concentration of glutamate and of glutamine was measured in whole blood obtained from a maternal artery, a uterine vein, a foetal artery and an umbilical vein of chronically catherized ewes and foetuses from 100 to 140 days after conception. The activities of glutamate dehydrogenase, phosphate-dependent glutaminase, phosphateindependent glutaminase, glutamine synthetase, γ-glutamyl transferase and glutamine-oxo-acid aminotransferase were measured in placentomes obtained from ewes during a similar period of gestation.The concentrations of glutamate in blood from maternal vessels remained constant, whereas there was a significant decline (P < 0·001) in the concentration of glutamate in foetal blood. Glutamine concentrations declined significantly (P < 0·05) in maternal blood and in foetal arterial blood (P < 0·001), whereas the concentration of glutamine in umbilical venous blood remained constant.Mean arterio-venous differences for glutamate indicated that there was no net uptake from or release into maternal blood by the uterus. However, there was a significant (P < 0·02) uptake of glutamate by the placenta from the foetal circulation. Glutamine release from the placenta into the foetal circulation increased as the foetus matured.Significant activities of glutamate dehydrogenase, γ-glutamyl transferase, glutamine synthetase and phosphate-dependent glutaminase were found in the placenta but there was no significant relationship between the activities of these enzymes and the gestational age of the foetus. The enzyme profile indicated that the placenta has a substantial potential for net glutamine synthesis.It is concluded that, for a 140-day foetus, the release of glutamine from the placenta accounts for more than half of its nitrogen requirement. Direct placental transfer of glutamine from maternal blood accounts for only one-third of the glutamine released by the placenta into the foetal circulation of a 140-day foetus. Therefore, the remainder of the glutamine is synthesized in the placenta from glutamate. Only one-third of the glutamate required for this placental glutamine synthesis is from the glutamate released by the foetus. The remainder must be derived either from 2-oxoglutarate, as the result of aminotransferase or glutamate dehydrogenase activities, or from glutathione by the action of γ-glutamyl transferase.

scholarly journals Microquantitative analysis of the intra-acinar profiles of glutamate dehydrogenase in rat liver.

1991 ◽  
Vol 39 (8) ◽  
pp. 1121-1124 ◽  
Author(s):  
I P Maly ◽  
D Sasse
Keyword(s):  
Glutamate Dehydrogenase ◽  
Rat Liver ◽  
Adult Male ◽  
Total Activity ◽  
Immunohistochemical Localization ◽  
Female Rat ◽  
Tissue Samples ◽  
Male And Female ◽  
Liver Acinus ◽  
Glutamine Synthesis

In adult male and female rat liver, the activity of NAD(+)-and NADP(+)-dependent glutamate dehydrogenase (GDH) was microquantitatively measured in tissue samples of 50-150 ng, microdissected continuously along the sinusoidal length. Total activity of GDH with NAD+ as co-factor was found to be higher by a ratio of about 1:2.3 than with NADP+. All intra-acinar enzyme profiles, irrespective of sex, showed an increasing gradient of GDH activity from the periportal beginning to the perivenous end. These findings are at variance with the immunohistochemical localization of GDH in rat liver. The microquantitative GDH profiles with higher perivenous values could indicate a more pronounced glutamine synthesis in Zone 3 of the liver acinus.

Sign in / Sign up

Export Citation Format

Share Document