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Sørensen M, Walls AB, Dam G, Bak LK, Andersen JV, Ott P, Vilstrup H, Schousboe A. Low cerebral energy metabolism in hepatic encephalopathy reflects low neuronal energy demand. Role of ammonia-induced increased GABAergic tone. Anal Biochem 2022; 654:114766. [PMID: 35654134 DOI: 10.1016/j.ab.2022.114766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 05/11/2022] [Accepted: 05/26/2022] [Indexed: 11/01/2022]
Abstract
Hepatic encephalopathy (HE) is a frequent and devastating but generally reversible neuropsychiatric complication secondary to chronic and acute liver failure. During HE, brain energy metabolism is markedly reduced and it remains unclear whether this is due to external or internal energy supply limitations, or secondary to depressed neuronal cellular functions - and if so, which mechanisms that are in play. The extent of deteriorated cerebral function correlates to blood ammonia levels but the metabolic link to ammonia is not clear. Early studies suggested that high levels of ammonia inhibited key tricarboxylic acid (TCA) cycle enzymes thus limiting mitochondrial energy production and oxygen consumption; however, later studies by us and others showed that this is not the case in vivo. Here, based on a series of translational studies from our group, we advocate the view that the low cerebral energy metabolism of HE is likely to be caused by neuronal metabolic depression due to an elevated GABAergic tone rather than by restricted energy availability. The increased GABAergic tone seems to be secondary to synthesis of large amounts of glutamine in astrocytes for detoxification of ammonia with the glutamine acting as a precursor for elevated neuronal synthesis of vesicular GABA.
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Affiliation(s)
- Michael Sørensen
- Department of Hepatology & Gastroenterology, Aarhus University Hospital, Denmark; Department of Internal Medicine, Viborg Regional Hospital, Denmark.
| | - Anne Byriel Walls
- Department of Drug Design & Pharmacology, University of Copenhagen, Denmark
| | - Gitte Dam
- Department of Hepatology & Gastroenterology, Aarhus University Hospital, Denmark
| | - Lasse Kristoffer Bak
- Department of Drug Design & Pharmacology, University of Copenhagen, Denmark; Department of Clinical Biochemistry, Copenhagen University Hospital, Rigshospitalet, Denmark
| | | | - Peter Ott
- Department of Hepatology & Gastroenterology, Aarhus University Hospital, Denmark
| | - Hendrik Vilstrup
- Department of Hepatology & Gastroenterology, Aarhus University Hospital, Denmark
| | - Arne Schousboe
- Department of Drug Design & Pharmacology, University of Copenhagen, Denmark
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2
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Voss CM, Arildsen L, Nissen JD, Waagepetersen HS, Schousboe A, Maechler P, Ott P, Vilstrup H, Walls AB. Glutamate Dehydrogenase Is Important for Ammonia Fixation and Amino Acid Homeostasis in Brain During Hyperammonemia. Front Neurosci 2021; 15:646291. [PMID: 34220417 PMCID: PMC8244593 DOI: 10.3389/fnins.2021.646291] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Accepted: 04/19/2021] [Indexed: 01/06/2023] Open
Abstract
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.
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Affiliation(s)
- Caroline M Voss
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lene Arildsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jakob D Nissen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Medical Centre, Geneva, Switzerland
| | - Peter Ott
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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3
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Astrocytic pyruvate carboxylation: Status after 35 years. J Neurosci Res 2019; 97:890-896. [DOI: 10.1002/jnr.24402] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/11/2019] [Accepted: 02/05/2019] [Indexed: 12/24/2022]
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Mani R, Natesan V, Arumugam R. Neuroprotective effect of chrysin on hyperammonemia mediated neuroinflammatory responses and altered expression of astrocytic protein in the hippocampus. Biomed Pharmacother 2017; 88:762-769. [DOI: 10.1016/j.biopha.2017.01.081] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 01/12/2017] [Accepted: 01/12/2017] [Indexed: 01/19/2023] Open
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Multifactorial Effects on Different Types of Brain Cells Contribute to Ammonia Toxicity. Neurochem Res 2016; 42:721-736. [PMID: 27286679 DOI: 10.1007/s11064-016-1966-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2016] [Revised: 05/20/2016] [Accepted: 05/24/2016] [Indexed: 12/12/2022]
Abstract
Effects of ammonia on astrocytes play a major role in hepatic encephalopathy, acute liver failure and other diseases caused by increased arterial ammonia concentrations (e.g., inborn errors of metabolism, drug or mushroom poisoning). There is a direct correlation between arterial ammonia concentration, brain ammonia level and disease severity. However, the pathophysiology of hyperammonemic diseases is disputed. One long recognized factor is that increased brain ammonia triggers its own detoxification by glutamine formation from glutamate. This is an astrocytic process due to the selective expression of the glutamine synthetase in astrocytes. A possible deleterious effect of the resulting increase in glutamine concentration has repeatedly been discussed and is supported by improvement of some pathologic effects by GS inhibition. However, this procedure also inhibits a large part of astrocytic energy metabolism and may prevent astrocytes from responding to pathogenic factors. A decrease of the already low glutamate concentration in astrocytes due to increased synthesis of glutamine inhibits the malate-aspartate shuttle and energy metabolism. A more recently described pathogenic factor is the resemblance between NH4+ and K+ in their effects on the Na+,K+-ATPase and the Na+,K+, 2 Cl- and water transporter NKCC1. Stimulation of the Na+,K+-ATPase driven NKCC1 in both astrocytes and endothelial cells is essential for the development of brain edema. Na+,K+-ATPase stimulation also activates production of endogenous ouabains. This leads to oxidative and nitrosative damage and sensitizes NKCC1. Administration of ouabain antagonists may accordingly have therapeutic potential in hyperammonemic diseases.
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Hertz L. The Glutamate-Glutamine (GABA) Cycle: Importance of Late Postnatal Development and Potential Reciprocal Interactions between Biosynthesis and Degradation. Front Endocrinol (Lausanne) 2013; 4:59. [PMID: 23750153 PMCID: PMC3664331 DOI: 10.3389/fendo.2013.00059] [Citation(s) in RCA: 160] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 05/02/2013] [Indexed: 01/28/2023] Open
Abstract
The gold standard for studies of glutamate-glutamine (GABA) cycling and its connections to brain biosynthesis from glucose of glutamate and GABA and their subsequent metabolism are the elegant in vivo studies by (13)C magnetic resonance spectroscopy (NMR), showing the large fluxes in the cycle. However, simpler experiments in intact brain tissue (e.g., immunohistochemistry), brain slices, cultured brain cells, and mitochondria have also made important contributions to the understanding of details, mechanisms, and functional consequences of glutamate/GABA biosynthesis and degradation. The purpose of this review is to attempt to integrate evidence from different sources regarding (i) the enzyme(s) responsible for the initial conversion of α-ketoglutarate to glutamate; (ii) the possibility that especially glutamate oxidation is essentially confined to astrocytes; and (iii) the ontogenetically very late onset and maturation of glutamine-glutamate (GABA) cycle function. Pathway models based on the functional importance of aspartate for glutamate synthesis suggest the possibility of interacting pathways for biosynthesis and degradation of glutamate and GABA and the use of transamination as the default mechanism for initiation of glutamate oxidation. The late development and maturation are related to the late cortical gliogenesis and convert brain cortical function from being purely neuronal to becoming neuronal-astrocytic. This conversion is associated with huge increases in energy demand and production, and the character of potentially incurred gains of function are discussed. These may include alterations in learning mechanisms, in mice indicated by lack of pairing of odor learning with aversive stimuli in newborn animals but the development of such an association 10-12 days later. The possibility is suggested that analogous maturational changes may contribute to differences in the way learning is accomplished in the newborn human brain and during later development.
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Affiliation(s)
- Leif Hertz
- Clinical Pharmacology, Medical University of ChinaShenyang, China
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The role of glutamine synthetase and glutamate dehydrogenase in cerebral ammonia homeostasis. Neurochem Res 2012; 37:2439-55. [PMID: 22618691 DOI: 10.1007/s11064-012-0803-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 04/24/2012] [Accepted: 05/07/2012] [Indexed: 02/07/2023]
Abstract
In the brain, glutamine synthetase (GS), which is located predominantly in astrocytes, is largely responsible for the removal of both blood-derived and metabolically generated ammonia. Thus, studies with [(13)N]ammonia have shown that about 25 % of blood-derived ammonia is removed in a single pass through the rat brain and that this ammonia is incorporated primarily into glutamine (amide) in astrocytes. Major pathways for cerebral ammonia generation include the glutaminase reaction and the glutamate dehydrogenase (GDH) reaction. The equilibrium position of the GDH-catalyzed reaction in vitro favors reductive amination of α-ketoglutarate at pH 7.4. Nevertheless, only a small amount of label derived from [(13)N]ammonia in rat brain is incorporated into glutamate and the α-amine of glutamine in vivo. Most likely the cerebral GDH reaction is drawn normally in the direction of glutamate oxidation (ammonia production) by rapid removal of ammonia as glutamine. Linkage of glutamate/α-ketoglutarate-utilizing aminotransferases with the GDH reaction channels excess amino acid nitrogen toward ammonia for glutamine synthesis. At high ammonia levels and/or when GS is inhibited the GDH reaction coupled with glutamate/α-ketoglutarate-linked aminotransferases may, however, promote the flow of ammonia nitrogen toward synthesis of amino acids. Preliminary evidence suggests an important role for the purine nucleotide cycle (PNC) as an additional source of ammonia in neurons (Net reaction: L-Aspartate + GTP + H(2)O → Fumarate + GDP + P(i) + NH(3)) and in the beat cycle of ependyma cilia. The link of the PNC to aminotransferases and GDH/GS and its role in cerebral nitrogen metabolism under both normal and pathological (e.g. hyperammonemic encephalopathy) conditions should be a productive area for future research.
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Inhibition of glutamine synthesis induces glutamate dehydrogenase-dependent ammonia fixation into alanine in co-cultures of astrocytes and neurons. Neurochem Int 2011; 59:482-8. [PMID: 21397649 DOI: 10.1016/j.neuint.2011.03.008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 02/24/2011] [Accepted: 03/06/2011] [Indexed: 01/29/2023]
Abstract
It has been previously demonstrated that ammonia exposure of neurons and astrocytes in co-culture leads to net synthesis not only of glutamine but also of alanine. The latter process involves the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT). In the present study it was investigated if the glutamine synthetase (GS) inhibitor methionine sulfoximine (MSO) would enhance alanine synthesis by blocking the GS-dependent ammonia scavenging process. Hence, co-cultures of neurons and astrocytes were incubated for 2.5h with [U-(13)C]glucose to monitor de novo synthesis of alanine and glutamine in the absence and presence of 5.0 mM NH(4)Cl and 10 mM MSO. Ammonia exposure led to increased incorporation of label but not to a significant increase in the amount of these amino acids. However, in the presence of MSO, glutamine synthesis was blocked and synthesis of alanine increased leading to an elevated content intra- as well as extracellularly of this amino acid. Treatment with MSO led to a dramatic decrease in glutamine content and increased the intracellular contents of glutamate and aspartate. The large increase in alanine during exposure to MSO underlines the importance of the GDH and ALAT biosynthetic pathway for ammonia fixation, and it points to the use of a GS inhibitor to ameliorate the brain toxicity and edema induced by hyperammonemia, events likely related to glutamine synthesis.
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Leke R, Bak LK, Anker M, Melø TM, Sørensen M, Keiding S, Vilstrup H, Ott P, Portela LV, Sonnewald U, Schousboe A, Waagepetersen HS. Detoxification of ammonia in mouse cortical GABAergic cell cultures increases neuronal oxidative metabolism and reveals an emerging role for release of glucose-derived alanine. Neurotox Res 2010; 19:496-510. [PMID: 20480276 DOI: 10.1007/s12640-010-9198-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 03/22/2010] [Accepted: 05/03/2010] [Indexed: 12/24/2022]
Abstract
Cerebral hyperammonemia is believed to play a pivotal role in the development of hepatic encephalopathy (HE), a debilitating condition arising due to acute or chronic liver disease. In the brain, ammonia is thought to be detoxified via the activity of glutamine synthetase, an astrocytic enzyme. Moreover, it has been suggested that cerebral tricarboxylic acid (TCA) cycle metabolism is inhibited and glycolysis enhanced during hyperammonemia. The aim of this study was to characterize the ammonia-detoxifying mechanisms as well as the effects of ammonia on energy-generating metabolic pathways in a mouse neuronal-astrocytic co-culture model of the GABAergic system. We found that 5 mM ammonium chloride affected energy metabolism by increasing the neuronal TCA cycle activity and switching the astrocytic TCA cycle toward synthesis of substrate for glutamine synthesis. Furthermore, ammonia exposure enhanced the synthesis and release of alanine. Collectively, our results demonstrate that (1) formation of glutamine is seminal for detoxification of ammonia; (2) neuronal oxidative metabolism is increased in the presence of ammonia; and (3) synthesis and release of alanine is likely to be important for ammonia detoxification as a supplement to formation of glutamine.
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Affiliation(s)
- Renata Leke
- Department of Biochemistry, ICBS, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
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10
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Gottschalk S, Zwingmann C. Altered fatty acid metabolism and composition in cultured astrocytes under hyperammonemic conditions. J Neurochem 2009; 109 Suppl 1:258-64. [PMID: 19393036 DOI: 10.1111/j.1471-4159.2009.05985.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In vitro 1H- and 13C-NMR spectroscopy was used to investigate the effect of ammonia on fatty acid synthesis and composition in cultured astrocytes. Cells were incubated 3 and 24 h with 5 mM ammonia in the presence or absence of the glutamine synthetase inhibitor methionine sulfoximine. An increase of de novo synthesized fatty acids and the glycerol subunit of lipids was observed after 3 h treatment with ammonia (35% and 40% over control, respectively), the initial time point examined. Both parameters further increased significantly to 85% and 60% over control after 24 h ammonia treatment. Three hours incubation with ammonia increased the synthesis of diacylglycerides, while formation of triacylglycerides was decreased (40% over and 15% under control, respectively). The degradation of fatty acids was not affected by ammonia treatment. Furthermore, ammonia caused alterations in the composition of fatty acids, e.g. increased mono- and decreased polyunsaturated fatty acids (85% over and 15% under control concentrations, respectively). The decrease of polyunsaturated fatty acids was even more pronounced in isolated astrocytic mitochondria (39% lower than controls). Our results suggest ammonia-induced abnormalities in astrocytic membranes, which may be related to astrocytic mitochondrial dysfunction in hyperammonemic states. Most of the observed effects of ammonia on fatty acid synthesis and composition were ameliorated when glutamine synthetase was inhibited by methionine sulfoximine, supporting a pathological role of glutamine in ammonia toxicity. This study further emphasizes the importance of investigating the relative contribution of exogenous ammonia, effects of glutamine and of glutamine-derived ammonia on astrocytes and astrocytic mitochondria.
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Affiliation(s)
- Sven Gottschalk
- Centre de recherche du Centre Hospitalier de l'Université de Montréal, Hôpital Saint-Luc, Montréal, Québec, Canada
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11
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Abstract
Metabolic alterations in the brain underly many of the mechanisms leading to acute and chronic Hepatic Encephalopathy (HE). Controversy exists about the role of glutamine accumulation as a causal factor in HE. Glutamine formation contributes to detoxify ammonia, whereby anaplerotic mechanisms in the astrocytes have to be sufficient to replenish Krebs cycle intermediates. The application of ex vivo high-resolution nuclear magnetic resonance (NMR) spectroscopy permits direct measurements of metabolites and different metabolic pathways. Ex vivo (13)C-NMR studies in experimental animal models of acute and chronic HE have provided new insights. In an experimental rat model of ALF, (13)C isotopomer analysis of glucose metabolism showed that alterations of glucose flux through astrocytic pyruvate carboxylase might be linked to the pathogenesis of ALF as a limited anaplerotic flux in the brain, but not in the muscle, correlates with the development of brain edema. Moreover, (13)C-NMR data from a rat model of mild HE demonstrated relative differences in the pathway of glucose through pyruvate carboxylase in thalamus compared to frontal cortex, which might explain the vulnerability of this brain region compared to thalamus. These findings further support that glutamine accumulation might be not the primary cause of neurological symptoms in HE, and show that anaplerotic mechanisms could be essential for ammonia detoxification in HE.
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Affiliation(s)
- Claudia Zwingmann
- Neuroscience Research Unit, CHUM Hôpital Saint-Luc, Montreal, Quebec, Canada.
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12
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Abstract
Both neurons and astrocytes have high rates of glucose utilization and oxidative metabolism. Fully 20% of glucose consumption is used for astrocytic production of glutamate and glutamine, which during intense glutamatergic activity leads to an increase in glutamate content, but at steady state is compensated for by an equally intense oxidation of glutamate. The amounts of ammonia used for glutamine synthesis and liberated during glutamine hydrolysis are large, compared to the additional demand for glutamine synthesis in hyperammonemic animals and patients with hepatic encephalopathy. Nevertheless, elevated ammonia concentrations lead to an increased astrocytic glutamine production and an elevated content of glutamine combined with a decrease in glutamate content, probably mainly in a cytosolic pool needed for normal activity of the malate-asparate shuttle (MAS); another compartment generated by glutamine hydrolysis is increased. As a result of reduced MAS activity the pyruvate/lactate ratio is decreased in astrocytes but not in neurons and decarboxylation of pyruvate to form acetyl coenzyme A is reduced. Elevated ammonia concentrations also inhibit decarboxylation of alpha-ketoglutarate in the TCA cycle. This effect occurs in both neurons and astrocytes, is unrelated to MAS activity and seen after chronic treatment with ammonia even in the absence of elevated ammonia concentrations.
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Affiliation(s)
- Leif Hertz
- Department of Clinical Pharmacology, China Medical University, Shenyang, PR China.
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13
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Mommsen TP, Busby ER, von Schalburg KR, Evans JC, Osachoff HL, Elliott ME. Glutamine synthetase in tilapia gastrointestinal tract: zonation, cDNA and induction by cortisol. J Comp Physiol B 2003; 173:419-27. [PMID: 12783264 DOI: 10.1007/s00360-003-0350-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/01/2003] [Indexed: 10/26/2022]
Abstract
Glutamine synthetase, an enzyme generally associated with ammonia detoxication in the vertebrate brain and with hepatic nitrogen turnover in mammals, shows substantial activities in the gastrointestinal tract of teleostean fishes. Enzyme activity is highest in the central area of the stomach and reveals a distinct distribution pattern in stomach and along the intestine of tilapia (Oreochromis niloticus), rainbow trout (Oncorhynchus mykiss) and copper rockfish (Sebastes caurinus). In all three species, intestinal activity peaks in the distal region of the intestine. The brain contains the highest titre of the enzyme (46 U g(-1) in tilapia brain versus 15 U g(-1) in tilapia stomach), but because of the relative mass of the stomach, the largest glutamine synthetase pool in tilapia body appears to be localized in the stomach. Activities in white and red muscle are very modest at 0.1% of the brain. Independent of distribution, peak activities of glutamine synthetase in selected areas of tilapia stomach and intestine are significantly (two- to fourfold) increased after a 5-day treatment with an intraperitoneal cortisol deposit. Cortisol also increases glutamine synthetase activity in tilapia liver, white and red muscle, while activities in brain remain unaffected. We cloned and sequenced the predominant transcript of tilapia stomach glutamine synthetase (about 1.9 kb), encoding a 371-amino acid peptide. The open reading frame shows considerable identity with glutamine synthetase in toadfish (92% at peptide level, 87% at nucleotide level), but possesses a longer 3'-untranslated region than the toadfish. The tilapia glutamine synthetase mRNA contains a remnant of a putative mitochondrial leader sequence, but without a conserved second site for initiation of translation. We also find evidence for additional transcripts of glutamine synthetase in tilapia, suggesting multiple genes. Finally, we present evidence for similar abundance of glutamine synthetase transcripts in all regions of rockfish intestine. The physiological significance of the presence of glutamine synthetase in teleostean intestine is discussed.
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Affiliation(s)
- T P Mommsen
- Department of Biochemistry and Microbiology, University of Victoria, P.O. Box 3055, Victoria, B.C., V8W 3P6, Canada.
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Zwingmann C, Chatauret N, Leibfritz D, Butterworth RF. Selective increase of brain lactate synthesis in experimental acute liver failure: results of a [H-C] nuclear magnetic resonance study. Hepatology 2003; 37:420-8. [PMID: 12540793 DOI: 10.1053/jhep.2003.50052] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Acute liver failure (ALF) results in alterations of energy metabolites and of glucose-derived amino acid neurotransmitters in brain. However, the dynamics of changes in glucose metabolism remain unclear. The present study was undertaken using (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy to determine the rates of incorporation of glucose into amino acids and lactate via cell-specific pathways in relation to the severity of encephalopathy and brain edema in rats with ALF because of hepatic devascularization. Early (precoma) stages of encephalopathy were accompanied by significant 2- to 4.5-fold (P <.001) increases of total brain glutamine and lactate concentrations. More severe (coma) stages of encephalopathy and brain edema led to a further significant increase in brain lactate but no such increase in glutamine. Furthermore, (13)C isotopomer analysis showed a selective increase of de novo synthesis of lactate from [1-(13)C]glucose resulting in 2.5-fold increased fractional (13)C enrichments in lactate at coma stages. [2-(13)C]glutamine, synthesized through the astrocytic enzyme pyruvate carboxylase, increased 10-fold at precoma stages but showed no further increase at coma stages of encephalopathy. (13)C-label incorporation into [4-(13)C]glutamate, synthesized mainly through neuronal pyruvate dehydrogenase, was selectively reduced at coma stages, whereas brain GABA synthesis was unchanged at all time points. In conclusion, increased brain lactate synthesis and impaired glucose oxidative pathways rather than intracellular glutamine accumulation are the major cause of brain edema in ALF. Future NMR spectroscopic studies using stable isotopes and real-time measurements of metabolic rates could be valuable in the elucidation of the cerebral metabolic consequences of ALF in humans.
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Affiliation(s)
- Claudia Zwingmann
- Neuroscience Research Unit, CHUM Hôpital Saint-Luc, Montreal, Quebec, Canada
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15
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Warskulat U, Görg B, Bidmon HJ, Müller HW, Schliess F, Häussinger D. Ammonia-induced heme oxygenase-1 expression in cultured rat astrocytes and rat brain in vivo. Glia 2002; 40:324-36. [PMID: 12420312 DOI: 10.1002/glia.10128] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Ammonia is a key factor in the pathogenesis of hepatic encephalopathy (HE), which is a major complication in acute and chronic liver failure and other hyperammonemic states. The molecular mechanisms underlying ammonia neurotoxicity and the functional consequences of ammonia on gene expression in astrocytes are incompletely understood. Using cDNA array hybridization technique we identified ammonia as a trigger of heme oxygenase-1 (HO-1) mRNA levels in cultured rat astrocytes. As shown by Northern and Western blot analysis, HO-1 mRNA levels were upregulated by ammonia (0.1-5 mmol/L) after 24 h and protein expression after 72 h in astrocytes. These ammonia effects on HO-1 are probably triggered to a minor extent by ammonia-induced glutamine synthesis or by astrocyte swelling, because HO-1 expression was not inhibited by the glutamine synthetase inhibitor methionine sulfoximine (which abrogated ammonia-induced cell swelling in cultured astrocytes), and ammonia-induced HO-1 expression could only partly be mimicked by hypoosmotic astrocyte swelling. Hypoosmotic (205 mOsm/L) exposure of astrocytes led even to a decrease in HO-1 mRNA levels within 4 h, whereas hyperosmotic (405 mOsm/L) exposure increased HO-1 mRNA expression. After 24 h, hypoosmolarity slightly raised HO-1 mRNA expression. Taurine and melatonin diminished ammonia-induced HO-1 mRNA or protein expression, whereas other antioxidants (dimethylthiourea, butylated hydroxytoluene, N-acetylcysteine, and reduced glutathione) increased HO-1 mRNA levels under ammonia-free conditions. An in vivo relevance is suggested by the finding that increased HO-1 expression occurs in the brain cortex from acutely ammonia-intoxicated rats. It is concluded that ammonia-induced HO-1 expression may contribute to cerebral hyperemia in hyperammonic states.
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Affiliation(s)
- Ulrich Warskulat
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich Heine University, Düsseldorf, Germany.
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Merle M, Bouzier-Sore AK, Canioni P. Time-dependence of the contribution of pyruvate carboxylase versus pyruvate dehydrogenase to rat brain glutamine labelling from [1-(13) C]glucose metabolism. J Neurochem 2002; 82:47-57. [PMID: 12091464 DOI: 10.1046/j.1471-4159.2002.00924.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
[1-(13) C]glucose metabolism in the rat brain was investigated after intravenous infusion of the labelled substrate. Incorporation of the label into metabolites was analysed by NMR spectroscopy as a function of the infusion time: 10, 20, 30 or 60 min. Specific enrichments in purified mono- and dicarboxylic amino acids were determined from (1) H-observed/(13) C-edited and (13) C-NMR spectroscopy. The relative contribution of pyruvate carboxylase versus pyruvate dehydrogenase (PC/PDH) to amino acid labelling was evaluated from the enrichment difference between either C2 and C3 for Glu and Gln, or C4 and C3 for GABA, respectively. No contribution of pyruvate carboxylase to aspartate, glutamate or GABA labelling was evidenced. The pyruvate carboxylase contribution to glutamine labelling varied with time. PC/PDH decreased from around 80% after 10 min to less than 30% between 20 and 60 min. This was interpreted as reflecting different labelling kinetics of the two glutamine precursor glutamate pools: the astrocytic glutamate and the neuronal glutamate taken up by astrocytes through the glutamate-glutamine cycle. The results are discussed in the light of the possible occurrence of neuronal pyruvate carboxylation. The methods previously used to determine PC/PDH in brain were re-evaluated as regards their capacity to discriminate between astrocytic (via pyruvate carboxylase) and neuronal (via malic enzyme) pyruvate carboxylation.
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Affiliation(s)
- Michel Merle
- Unité de Résonance Magnétique des Systèmes Biologiques, UMR 5536, Centre National de la Recherche Scientifique-Université Victor Segalen, 146 rue Léo-Saignat, 33076 Bordeaux, France.
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17
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Affiliation(s)
- Saul W Brusilow
- Department of Pediatrics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
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18
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Affiliation(s)
- S vom Dahl
- Division of Gastroenterology, Hepatology and Infectious Diseases, Heinrich Heine University, Moorenstr 5, D-40225 D sseldorf, Germany.
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Engelmann J, Leyhausen G, Leibfritz D, Geurtsen W. Metabolic effects of dental resin components in vitro detected by NMR spectroscopy. J Dent Res 2001; 80:869-75. [PMID: 11379887 DOI: 10.1177/00220345010800030501] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Earlier studies have shown that the comonomer triethyleneglycol-dimethacrylate (TEGDMA) and the photostabilizer 2-hydroxy-4-methoxybenzophenone (HMBP) are cytotoxic and inhibit cell growth. It was the aim of this study to elucidate the underlying metabolic effects of TEGDMA and HMBP on immortal contact-inhibited Swiss albino mouse embryo cells (3T3 fibroblasts) by nuclear magnetic resonance (NMR) spectroscopy. Cell extracts and culture media were analyzed by NMR spectroscopy for metabolic changes after incubation for 24 hours with ED20-concentrations of TEGDMA and HMBP. TEGDMA could be detected in all fractions (cytosol, lipid fractions, and culture media) of 3T3 cells, while HMBP was found only in the lipid fraction accumulated at a maximum rate (51 nmol/mg DNA) compared with TEGDMA (27 nmol/mg DNA). TEGDMA increased the concentration of phosphomonoesters to 180+/-36% and decreased the phosphodiesters to 65+/-5% of controls (control = 100%). Thus, the turnover of phospholipids was enhanced, whereas content and composition of phospholipids of membranes did not alter markedly. Additionally, TEGDMA changed the metabolic state of cells, indicated by slight decreases of nucleoside triphosphates and an increase in the ratio of nucleoside diphosphates to nucleoside triphosphates, while HMBP had no effect. The most remarkable effect of TEGDMA was a nearly complete decline of the intracellular glutathione levels. Analysis of our data shows that NMR spectroscopy of cell-material interactions may reveal metabolic effects of organic test substances which are not detectable by standard in vitro assays. The comonomer TEGDMA affected the metabolism of the cells on different levels, while HMBP accumulated in the lipid fraction and induced significantly fewer effects on cell metabolism.
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Affiliation(s)
- J Engelmann
- Department of Organic Chemistry, University of Bremen, Germany
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Leibfritz D, Pfeuffer J, Flögel U, Meier C, Bröer S. Cell volume and water exchange in neural cells monitored by diffusion weighted 1H NMR spectroscopy. PROGRESS IN BRAIN RESEARCH 2001; 125:255-63. [PMID: 11098662 DOI: 10.1016/s0079-6123(00)25015-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
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Abstract
The pathogenesis of hepatic encephalopathy (HE) is unknown. Many theories have been proposed. Most established therapies are based on such theories but since no theory has have ever been proved, therapies have to be considered empiric. The spectrum of HE ranges from minimal cerebral functional deficits, which can only be found by sensitive psychometric tests, to coma with signs of decerebration. HE has arbitrarily been divided into stages. A number of precipitating factors are known and the first line of therapy should always be the elimination of these factors. The differential diagnosis includes all states of impaired consciousness and deficits in cerebral function in patients with chronic liver disease, and clinical and biochemical tests to differentiate are indicated. The therapeutic options for HE include: protein restriction only for a limited time in comatous patients; nonabsorbable antibiotics (aminoglycosides), which because of adverse effects are also limited to higher grades of HE: intestinal cleansing which is applicable in all degrees of HE; lactulose, branched chain aminoacids and ornithin aspartate which have been proven to be effective and can be applied long term in patients with lower grades of HE.
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Affiliation(s)
- T Gerber
- Medical Clinic II, Diakoniekrankenhaus, Rotenburg, Germany
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22
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Häussinger D, Kircheis G, Fischer R, Schliess F, vom Dahl S. Hepatic encephalopathy in chronic liver disease: a clinical manifestation of astrocyte swelling and low-grade cerebral edema? J Hepatol 2000; 32:1035-8. [PMID: 10898326 DOI: 10.1016/s0168-8278(00)80110-5] [Citation(s) in RCA: 340] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- D Häussinger
- Department of Gastroenterology, Heinrich-Heine-University-Düsseldorf, Germany
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