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The Effect of TGF-β1 Reduced Functionality on the Expression of Selected Synaptic Proteins and Electrophysiological Parameters: Implications of Changes Observed in Acute Hepatic Encephalopathy. Int J Mol Sci 2022; 23:ijms23031081. [PMID: 35163004 PMCID: PMC8835518 DOI: 10.3390/ijms23031081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 01/11/2022] [Accepted: 01/14/2022] [Indexed: 12/10/2022] Open
Abstract
Decreased platelet count represents a feature of acute liver failure (ALF) pathogenesis. Platelets are the reservoir of transforming growth factor 1 (TGF-β1), a multipotent cytokine involved in the maintenance of, i.a., central nervous system homeostasis. Here, we analyzed the effect of a decrease in TGF-β1 active form on synaptic proteins levels, and brain electrophysiology, in mice after intraperitoneal (ip) administration of TGF-β1 antibody (anti-TGF-β1; 1 mg/mL). Next, we correlated it with a thrombocytopenia-induced TGF-β1 decrease, documented in an azoxymethane-induced (AOM; 100 mM ip) model of ALF, and clarified the impact of TGF-β1 decrease on blood–brain barrier functionality. The increase of both synaptophysin and synaptotagmin in the cytosolic fraction, and its reduction in a membrane fraction, were confirmed in the AOM mice brains. Both proteins’ decrease in analyzed fractions occurred in anti-TGF-β1 mice. In turn, an increase in postsynaptic (NR1 subunit of N-methyl-D-aspartate receptor, postsynaptic density protein 95, gephyrin) proteins in the AOM brain cortex, but a selective compensatory increase of NR1 subunit in anti-TGF-β mice, was observed. The alterations of synaptic proteins levels were not translated on electrophysiological parameters in the anti-TGF-β1 model. The results suggest the impairment of synaptic vesicles docking to the postsynaptic membrane in the AOM model. Nevertheless, changes in synaptic protein level in the anti-TGF-β1 mice do not affect neurotransmission and may not contribute to neurologic deficits in AOM mice.
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Ochoa-Sanchez R, Rose CF. Pathogenesis of Hepatic Encephalopathy in Chronic Liver Disease. J Clin Exp Hepatol 2018; 8:262-271. [PMID: 30302043 PMCID: PMC6175755 DOI: 10.1016/j.jceh.2018.08.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Accepted: 08/09/2018] [Indexed: 12/12/2022] Open
Abstract
Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome that occurs during chronic liver disease (CLD). While ammonia and other precipitating factors in liver disease including inflammation, bile acids, oxidative stress, and lactate play a role in the pathogenesis of HE, the exact mechanism that leads to HE is not fully understood. Notably, accumulating evidence points toward a synergic effect rather than independent actions among precipitating factors that contributes to the development and severity of HE in CLD. Hence, this review is aimed to briefly discuss the single and synergic interplay of pathological factors in the progression and severity of HE.
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Key Words
- AQP4, Aquaporin 4
- BAs, Bile Acids
- BBB, Blood-Brain Barrier
- BDL, Bile Duct Ligation
- CLD, Chronic Liver Disease
- CSF, Cerebrospinal Fluid
- GABA, Gamma-Aminobutyric Acid
- GAMSAs, GABAA Receptor Modulating Steroid Antagonists
- GFAP, Glial Fibrillary Acid Protein
- GLAST, Glial Glutamate-Aspartate Transporter
- GPR81, G-Protein-Coupled Receptor 81
- GS, Glutamine Synthetase
- HE, Hepatic Encephalopathy
- ICP, Intracranial Pressure
- ILs, Interleukins
- MRI, Magnetic Resonance Imaging
- NF-?B, Nuclear Factor Kappa B
- NMDA, N-Methyl-d-Aspartate Glutamate Receptor
- NO, Nitric Oxide
- PCA, Portacaval Anastomosis
- ROS, Reactive Oxygen Species
- TJ, Tight Junction
- TNF-a, Tumor Necrosis Alpha
- ammonia
- astrocyte swelling
- bile acids
- brain edema
- cGMP, Cyclic Guanosine Monophosphate
- cirrhosis
- hepatic encephalopathy
- inflammation
- lactate
- mGluR, Metabotropic Glutamate Receptor
- neurotransmission
- oxidative stress
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Affiliation(s)
| | - Christopher F. Rose
- Address for correspondence. Christopher F. Rose Professor, Dept. Medicine, Université de Montréal, CRCHUM, 900 Saint-Denis Street, Montréal, Québec, H2X 0A9, Canada.
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Fried DE, Watson RE, Robson SC, Gulbransen BD. Ammonia modifies enteric neuromuscular transmission through glial γ-aminobutyric acid signaling. Am J Physiol Gastrointest Liver Physiol 2017; 313:G570-G580. [PMID: 28838986 PMCID: PMC5814673 DOI: 10.1152/ajpgi.00154.2017] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 08/17/2017] [Accepted: 08/17/2017] [Indexed: 01/31/2023]
Abstract
Impaired gut motility may contribute, at least in part, to the development of systemic hyperammonemia and systemic neurological disorders in inherited metabolic disorders, or in severe liver and renal disease. It is not known whether enteric neurotransmission regulates intestinal luminal and hence systemic ammonia levels by induced changes in motility. Here, we propose and test the hypothesis that ammonia acts through specific enteric circuits to influence gut motility. We tested our hypothesis by recording the effects of ammonia on neuromuscular transmission in tissue samples from mice, pigs, and humans and investigated specific mechanisms using novel mutant mice, selective drugs, cellular imaging, and enzyme-linked immunosorbent assays. Exogenous ammonia increased neurogenic contractions and decreased neurogenic relaxations in segments of mouse, pig, and human intestine. Enteric glial cells responded to ammonia with intracellular Ca2+ responses. Inhibition of glutamine synthetase and the deletion of glial connexin-43 channels in hGFAP::CreERT2+/-/connexin43f/f mice potentiated the effects of ammonia on neuromuscular transmission. The effects of ammonia on neuromuscular transmission were blocked by GABAA receptor antagonists, and ammonia drove substantive GABA release as did the selective pharmacological activation of enteric glia in GFAP::hM3Dq transgenic mice. We propose a novel mechanism whereby local ammonia is operational through GABAergic glial signaling to influence enteric neuromuscular circuits that regulate intestinal motility. Therapeutic manipulation of these mechanisms may benefit a number of neurological, hepatic, and renal disorders manifesting hyperammonemia.NEW & NOTEWORTHY We propose that local circuits in the enteric nervous system sense and regulate intestinal ammonia. We show that ammonia modifies enteric neuromuscular transmission to increase motility in human, pig, and mouse intestine model systems. The mechanisms underlying the effects of ammonia on enteric neurotransmission include GABAergic pathways that are regulated by enteric glial cells. Our new data suggest that myenteric glial cells sense local ammonia and directly modify neurotransmission by releasing GABA.
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Affiliation(s)
- David E. Fried
- 1Neuroscience Program and Department of Physiology,
Michigan State University, East Lansing,
Michigan;
| | - Ralph E. Watson
- 2Department of Medicine, Michigan State
University, East Lansing, Michigan; and
| | - Simon C. Robson
- 3Divisions of Gastroenterology and Transplantation, Department
of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical
School, Boston, Massachusetts
| | - Brian D. Gulbransen
- 1Neuroscience Program and Department of Physiology,
Michigan State University, East Lansing,
Michigan;
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4
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Jayakumar AR, Norenberg MD. Glutamine Synthetase: Role in Neurological Disorders. ADVANCES IN NEUROBIOLOGY 2016; 13:327-350. [PMID: 27885636 DOI: 10.1007/978-3-319-45096-4_13] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Glutamine synthetase (GS) is an ATP-dependent enzyme found in most species that synthesizes glutamine from glutamate and ammonia. In brain, GS is exclusively located in astrocytes where it serves to maintain the glutamate-glutamine cycle, as well as nitrogen metabolism. Changes in the activity of GS, as well as its gene expression, along with excitotoxicity, have been identified in a number of neurological conditions. The literature describing alterations in the activation and gene expression of GS, as well as its involvement in different neurological disorders, however, is incomplete. This review summarizes changes in GS gene expression/activity and its potential contribution to the pathogenesis of several neurological disorders, including hepatic encephalopathy, ischemia, epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, traumatic brain injury, Parkinson's disease, and astroglial neoplasms. This review also explores the possibility of targeting GS in the therapy of these conditions.
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Affiliation(s)
| | - Michael D Norenberg
- Laboratory of Neuropathology, Veterans Affairs Medical Center, Miami, FL, USA.
- Departments of Pathology, University of Miami School of Medicine, 016960, Miami, FL, 33101, USA.
- Departments of Biochemistry & Molecular Biology, University of Miami School of Medicine, Miami, FL, USA.
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Abstract
The earliest hypothesis of the pathogenesis of HE implicated ammonia, although effects of appreciable concentrations of this neurotoxin did not resemble HE. Altered eurotransmission in the brain was suggested by similarities between increased GABA-mediated inhibitory neurotransmission and HE, specifically decreased consciousness and impaired motor function. Evidence of increased GABAergic tone in models of HE has accumulated; potential mechanisms include increased synaptic availability of GABA and accumulation of natural benzodiazepine receptor ligands with agonist properties. Pathophysiological concentrations of ammonia associated with HE, have the potential of enhancing GABAergic tone by mechanisms that involve its interactions with the GABAa receptor complex.
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Affiliation(s)
- E Anthony Jones
- Division of Gastroenterology, MetroHealth Medical Center, Case Western Reserve University, 2500 MetroHealth Drive, Cleveland, OH 44109, USA
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Sanders RD. Hypothesis for the pathophysiology of delirium: Role of baseline brain network connectivity and changes in inhibitory tone. Med Hypotheses 2011; 77:140-3. [DOI: 10.1016/j.mehy.2011.03.048] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Accepted: 03/23/2011] [Indexed: 01/06/2023]
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Toris GT, Bikis CN, Tsourouflis GS, Theocharis SE. Hepatic encephalopathy: an updated approach from pathogenesis to treatment. Med Sci Monit 2011; 17:RA53-63. [PMID: 21278704 PMCID: PMC3524698 DOI: 10.12659/msm.881387] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
One of the most serious complications of chronic or fulminant liver failure is hepatic encephalopathy (HE), associated most commonly with cirrhosis. In the presence of chronic liver disease, HE is a sign of decompensation, while in fulminant liver failure its development represents a worrying sign and usually indicates that transplantation will be required. Despite the significance of HE in the course of liver disease, the progress in development of new therapeutic options has been unremarkable over the last 20 years. An up-to-date review regarding HE, including both research and review articles. HE is a serious and progressive, but potentially reversible, disorder with a wide spectrum of neuropsychiatric abnormalities and motor disturbances that ranges from mild alteration of cognitive and motor function to coma and death. Although a clear pathogenesis is yet to be determined, elevated ammonia in serum and the central nervous system is the mainstay for pathogenesis and treatment of HE. Management includes early diagnosis and prompt treatment of precipitating factors. Clinical trials and extensive clinical experience have established the efficacy of diverse substances in HE treatment. Novel therapies with clinical promise include: L-ornithine L-aspartate, sodium benzoate, phenylacetate, AST-120, and the molecular adsorbent recirculating system. Eventually, liver transplantation is often the most successful long-term therapy for HE.
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Affiliation(s)
- Giannakis T Toris
- Department of Forensic Medicine and Toxicology, Medical School, National and Kapodistrian University of Athens, Athens, Greece
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Leke R, Bak LK, Iversen P, Sørensen M, Keiding S, Vilstrup H, Ott P, Portela LV, Schousboe A, Waagepetersen HS. Synthesis of neurotransmitter GABA via the neuronal tricarboxylic acid cycle is elevated in rats with liver cirrhosis consistent with a high GABAergic tone in chronic hepatic encephalopathy. J Neurochem 2011; 117:824-32. [PMID: 21395584 DOI: 10.1111/j.1471-4159.2011.07244.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Hepatic encephalopathy (HE) is a neuropsychiatric complication to liver disease. It is known that ammonia plays a role in the pathogenesis of HE and disturbances in the GABAergic system have been related to HE. Synthesis of GABA occurs by decarboxylation of glutamate formed by deamidation of astrocyte-derived glutamine. It is known that a fraction of glutamate is decarboxylated directly to GABA (referred to as the direct pathway) and that a fraction undergoes transamination with formation of alpha-ketoglutarate. The latter fraction is cycled through the neuronal tricarboxylic acid cycle, an energy-generating pathway, prior to being employed for GABA synthesis (the indirect pathway). We have previously shown that ammonia induces an elevation of the neuronal tricarboxylic acid cycle activity. Thus, the aims of the present study were to determine if increased levels of ammonia increase GABA synthesis via the indirect pathway in a rat model of HE induced by bile-duct ligation and in co-cultures of neurons and astrocytes exposed to ammonia. Employing (13) C-labeled precursors and subsequent analysis by mass spectrometry, we demonstrated that more GABA was synthesized via the indirect pathway in bile duct-ligated rats and in co-cultures subjected to elevated ammonia levels. Since the indirect pathway is associated with synthesis of vesicular GABA, this might explain the increased GABAergic tone in HE.
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Affiliation(s)
- Renata Leke
- PET Centre, Department of Medicine V, Aarhus University Hospital, Aarhus, Denmark
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9
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Angel MJ, Chen R, Bryan Young G. Metabolic encephalopathies. HANDBOOK OF CLINICAL NEUROLOGY 2010; 90:115-66. [PMID: 18631820 DOI: 10.1016/s0072-9752(07)01707-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Michael J Angel
- University of Toronto, Division of Neurology, Toronto Western Hospital, Toronto, Ontario, Canada.
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10
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Hunter GRW, Young GB. Recovery of Awareness after Hyperacute Hepatic Encephalopathy with “Flat” EEG, Severe Brain Edema and Deep Coma. Neurocrit Care 2010; 13:247-51. [DOI: 10.1007/s12028-010-9391-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Harris MK, Elliott D, Schwendimann RN, Minagar A, Jaffe SL. Neurologic Presentations of Hepatic Disease. Neurol Clin 2010; 28:89-105. [DOI: 10.1016/j.ncl.2009.09.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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12
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Cauli O, Mansouri MT, Agusti A, Felipo V. Hyperammonemia increases GABAergic tone in the cerebellum but decreases it in the rat cortex. Gastroenterology 2009; 136:1359-67, e1-2. [PMID: 19245864 DOI: 10.1053/j.gastro.2008.12.057] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 12/05/2008] [Accepted: 12/29/2008] [Indexed: 01/08/2023]
Abstract
BACKGROUND & AIMS GABAA receptors modulate the function of the glutamate-nitric oxide-guanosine 3',5'-cyclic monophosphate (cGMP) pathway, which is reduced in cerebellum in hyperammonemic rats. It has been proposed that hyperammonemia-induced increases in gamma-aminobutyric acid "(GABAergic) tone" contribute to the pathogenesis of hepatic encephalopathy (HE), although this has not been assessed in vivo in animal models. We studied whether chronic hyperammonemia in rats increases GABAergic tone in the cerebellum and/or cerebral cortex and whether this increase contributes to cognitive impairment. METHODS We blocked GABAA receptors of rats with bicuculline and analyzed the function of this pathway in cerebellum and effects on learning ability. RESULTS Hyperammonemia increased GABAergic tone in cerebellum but decreased it in the cerebral cortex of rats. Increased GABAergic tone in the cerebellum of rats with hyperammonemia could have been caused by increases in extracellular GABA; tetrahydrodeoxy-corticosterone (a neurosteroid that enhances GABAA receptor activation); or amounts of the alpha1, alpha6, and gamma2 subunits of GABAA receptors. The decrease in GABAergic tone observed in the cortex could have resulted from the reduced amount of GABAA receptors delta and gamma2 subunits or increased levels of pregnanolone (5-fold), which selectively reduces activation of GABAA receptors that contain alpha4 subunits (widely expressed in cortex but not in cerebellum). Treatment with bicuculline normalized GABAergic tone and restored the increase in cGMP that was induced by activation of N-methyl-D-aspartate receptors and learning ability in hyperammonemic rats. CONCLUSIONS Increased GABAergic tone in the cerebellum contributes to cognitive impairment in hyperammonemic rats.
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Affiliation(s)
- Omar Cauli
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Valencia, Spain
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13
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Cauli O, Rodrigo R, Llansola M, Montoliu C, Monfort P, Piedrafita B, El Mlili N, Boix J, Agustí A, Felipo V. Glutamatergic and gabaergic neurotransmission and neuronal circuits in hepatic encephalopathy. Metab Brain Dis 2009; 24:69-80. [PMID: 19085094 DOI: 10.1007/s11011-008-9115-4] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Accepted: 10/28/2008] [Indexed: 01/16/2023]
Abstract
Patients with hepatic encephalopathy (HE) may present different neurological alterations including impaired cognitive function and altered motor activity and coordination. HE may lead to coma and death. Many of these neurological alterations are the consequence of altered neurotransmission. Hyperammonemia is a main contributor to the alterations in neurotransmission and in neurological functions in HE. Both glutamatergic and GABAergic neurotransmission are altered in animal models of HE. We review some of these alterations, especially those alterations in glutamatergic neurotransmission responsible for some specific neurological alterations in hyperammonemia and HE: the role 1) of excessive NMDA receptors activation in death induced by acute hyperammonemia; 2) of impaired function of the glutamate-nitric oxide-cGMP pathway, associated to NMDA receptors, in cognitive impairment in chronic HE; 3) of increased extracellular glutamate and activation of metabotropic glutamate receptors in substantia nigra in hypokinesia in chronic HE. The therapeutic implications are discussed. We also review the alterations in the function of the neuronal circuits between basal ganglia-thalamus-cortex modulating motor activity and the role of sequential alterations in glutamatergic and GABAergic neurotransmission in these alterations. HE would be a consequence of altered neuronal communication due to alterations in general neurotransmission involving different neurotransmitter systems in different neurons.
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Affiliation(s)
- Omar Cauli
- Laboratory of Neurobiology, Centro de Investigacion Principe Felipe, Avdas Autopista del Saler, 16, 46013 Valencia, Spain
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Glutamine synthetase protects the spinal cord against hypoxia-induced and GABA(A) receptor-activated axonal depressions. ACTA ACUST UNITED AC 2008; 70:122-8; discussion 128. [PMID: 18262603 DOI: 10.1016/j.surneu.2007.07.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 07/03/2007] [Indexed: 01/19/2023]
Abstract
BACKGROUND We investigated the effects of exogenous GS on hypoxia- and GABA(A) receptor-induced axonal depression in neonatal rats. METHODS To assess the effects of GS on spinal cord axons, CAPs were recorded. Hemicords were exposed to hypoxia by 30-minute superfusion with Ringer's solution saturated with 95% N(2) and 5% CO(2) followed by 60-minute exposure to 95% N(2) and 5% CO(2) gassing (N(2) gassing phase) and then 90 minutes of resuperfusion with oxygenated Ringer's solution (resuperfusion phase). Exogenous high GS (15 U) or low GS (1.5 U) was delivered during the N(2) gassing phase. The effects of GS on GABA(A) receptor-induced axonal depression were analyzed with oxygenated isolated dorsal columns. RESULTS The high GS significantly reduced the decline in the CAP amplitudes during the N(2) gassing and resuperfusion phases (P = .0185) compared to the hypoxia control. The low GS treatment showed a trend toward recovery during the N(2) gassing and resuperfusion phases, but the effect was not significant (P = .3953). In isolated dorsal columns, GS significantly reduced the CAP amplitude depression induced by GABA(A) receptor agonist. CONCLUSIONS Our findings suggest that GS had dose-dependent protective effects on the spinal cord against hypoxia-induced axonal depression. It may inhibit the depression of CAP amplitudes by blocking GABA(A) receptors.
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Brosnan RJ, Yang L, Milutinovic PS, Zhao J, Laster MJ, Eger EI, Sonner JM. Ammonia has anesthetic properties. Anesth Analg 2007; 104:1430-3, table of contents. [PMID: 17513636 DOI: 10.1213/01.ane.0000264072.97705.0f] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
BACKGROUND A recent theory of anesthesia predicts that some endogenous compounds should have anesthetic properties. This theory raises the possibility that metabolites that are profoundly elevated in disease may also exert anesthetic effects. Because in pathophysiologic concentrations, ammonia reversibly impairs memory, consciousness, and responsiveness to noxious stimuli in a manner similar to anesthetics, we investigated whether ammonia had anesthetic properties. METHODS The effect of ammonia was studied on alpha1beta2 and alpha1beta2gamma2s gamma-amino butyric acid type A, alpha1 glycine, and NR1/NR2A N-methyl-D-aspartate receptors, and the two-pore domain potassium channel TRESK. Channels were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping. The immobilizing effect of ammonia in rats was evaluated by determining the reduction in isoflurane minimum alveolar concentration produced by IV infusion of ammonium chloride. The olive oil-water partition coefficient was measured to determine whether free ammonia (NH3) followed the Meyer-Overton relation. RESULTS Ammonia positively modulated TRESK channels and glycine receptors. No effect was seen on alpha1beta2 and alpha1beta2gamma2s gamma-amino butyric acid type A receptors or NR1/NR2A N-methyl-d-aspartate receptors. Ammonia reversibly decreased the requirement for isoflurane, with a calculated immobilizing EC50 of 1.6 +/- 0.1 mM NH4Cl. The Ostwald olive oil-water partition coefficient for NH3 was 0.018. At a pH of 7.4, and at the anesthetic EC50, the NH3 concentration in bulk olive oil is 0.42 muM, approximately five orders of magnitude less than observed by anesthetics that follow the Meyer-Overton relation. CONCLUSIONS These findings support the hypothesis that ammonia has anesthetic properties. Bulk oil concentration did not predict the potency of ammonia.
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Affiliation(s)
- Robert J Brosnan
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, Calif 94143-0464, USA
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Anderzhanova E, Saransaari P, Oja SS. Neuroprotective mechanisms of taurine in vivo. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 583:377-87. [PMID: 17153623 DOI: 10.1007/978-0-387-33504-9_42] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
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17
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Chepkova AN, Sergeeva OA, Haas HL. Taurine rescues hippocampal long-term potentiation from ammonia-induced impairment. Neurobiol Dis 2006; 23:512-21. [PMID: 16766203 DOI: 10.1016/j.nbd.2006.04.006] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Revised: 04/11/2006] [Accepted: 04/12/2006] [Indexed: 11/19/2022] Open
Abstract
Hyperammonemia, a major pathophysiological factor in hepatic encephalopathy, impairs long-term potentiation (LTP) of synaptic transmission, a cellular model of learning and memory, in the hippocampus. We have now studied the protective action of taurine on this paradigm by analyzing LTP characteristics in mouse hippocampal slices treated with ammonium chloride (1 mM) in the presence of taurine (1 mM), an ubiquitous osmolyte, antioxidant, and neuromodulator, as well as other substances with such properties. Ammonia-treated slices displayed a significant impairment of LTP maintenance. Taurine and the mitochondrial enhancer l-carnitine, but not the antioxidants (ascorbate, carnosine, and the novel compound GVS-111) or the osmolyte betaine prevented this impairment. The protective effect of taurine was preserved under the blockade of inhibitory GABA(A) and glycine receptors. It is suggested that taurine may rescue the mechanisms of hippocampal synaptic plasticity by improving mitochondrial function under hyperammonemic conditions.
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Affiliation(s)
- Aisa N Chepkova
- Department of Neurophysiology, Heinrich-Heine University, POB 101007, D-40001 Düsseldorf, Germany
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18
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Influence of external and intracellular pH on propofol-induced responses in rat locus coeruleus neurons. Eur J Pharmacol 2006. [DOI: 10.1016/j.ejphar.2006.07.042] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Titz S, Hormuzdi S, Lewen A, Monyer H, Misgeld U. Intracellular acidification in neurons induced by ammonium depends on KCC2 function. Eur J Neurosci 2006; 23:454-64. [PMID: 16420452 DOI: 10.1111/j.1460-9568.2005.04583.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The Cl(-)-extruding neuron-specific K(+)-Cl(-) cotransporter KCC2, which establishes hyperpolarizing inhibition, can transport NH(4) (+) instead of K(+). It is, however, not clear whether KCC2 provides the only pathway for neuronal NH(4) (+) uptake. We therefore investigated NH(4) (+) uptake in cultured rat brain neurons. In neurons cultured for > 4 weeks, the response to NH(4)Cl applications (5 mM) consisted of an alkaline shift which reversed to an acid shift within seconds. Rebound acid shifts which followed brief applications of NH(4)Cl were blocked by furosemide (100 microM). They were rather insensitive to bumetanide (1 and 100 microM), in contrast to those induced in cultured glial cells. Rebound acid shifts persisted in the presence of 1 mM Ba(2+) and in Na(+)-free solution but were inhibited by extracellular K(+). In neurons with depolarizing GABA responses, indicating the absence of functional KCC2, applications of NH(4)Cl barely induced an acidosis. However, large rebound acid shifts occurred in neurons that had changed their GABA response from Ca(2+) increases to Ca(2+) decreases. Rebound acid shifts continued to increase even after the change in the GABA response had occurred and could be induced earlier in neurons transfected with KCC2 cDNA. We conclude that KCC2 provides the main pathway for fast neuronal NH(4) (+) uptake. Therefore, NH(4)Cl-induced rebound acid shifts can be used to indicate the development of KCC2 function. Further, the well known up-regulation of KCC2 function during development has the inevitable consequence of opening a major pathway for NH(4) (+) influx, which can be relevant under pathophysiological conditions.
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Affiliation(s)
- Stefan Titz
- Institut für Physiologie und Pathophysiologie und Interdisziplinäres Zentrum für Neurowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 326, 69120 Heidelberg, Germany
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Jones EA. Potential mechanisms of enhanced GABA-mediated inhibitory neurotransmission in liver failure. Neurochem Int 2003; 43:509-16. [PMID: 12742098 DOI: 10.1016/s0197-0186(03)00041-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- E Anthony Jones
- Department of Gastrointestinal and Liver Diseases, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam-ZO, The Netherlands.
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Albrecht J, Zielińska M. The role of inhibitory amino acidergic neurotransmission in hepatic encephalopathy: a critical overview. Metab Brain Dis 2002; 17:283-94. [PMID: 12602505 DOI: 10.1023/a:1021901700493] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Gamma-Aminobutyric acid (GABA) is the main inhibitory amino acid in the central nervous system (CNS). Experiments with animal models of HE, and with brain slices or cultured CNS cells treated with ammonia, have documented changes in GABA distribution and transport, and modulation of the responses of both the GABA(A)-benzodiazepine receptor complex and GABA(B) receptors. Although many of the data point to an enhancement of GABAergic transmission probably contributing to HE, the evidence is not unequivocal. The major weaknesses of the GABA theory are (1) in a vast majority of HE models, there were no alterations of GABA content in the brain tissue and/or extracellular space, indicating that exposure of neurons to GABA may not have been altered, (2) changes in the affinity and capacity of GABA receptor binding were either absent or qualitatively different in HE models of comparable severity and duration, and (3) no sound changes in the GABAergic system parameters were noted in clinical cases of HE. Taurine (Tau) is an amino acid that is thought to mimic GABA function because of its agonistic properties towards GABA(A) receptors, and to contribute to neuroprotection and osmoregulation. These effects require Tau redistribution between the different cell compartments and the extracellular space. Acute treatment with ammonia evokes massive release of radiolabeled or endogenous Tau from CNS tissues in vivo and in vitro, and the underlying mechanism of Tau release differs from the release evoked by depolarizing conditions or hypoosmotic treatment. Subacute or chronic HE, and also long-term treatment of cultured CNS cells in vitro with ammonia, increase spontaneous Tau "leakage" from the tissue. This is accompanied by a decreased potassium- or hypoosmolarity-induced release of Tau and often by cell swelling, indicating impaired osmoregulation. In in vivo models of HE, Tau leakage is manifested by its increased accumulation in the extrasynaptic space, which may promote inhibitory neurotransmission and/or cell membrane protection. In chronic HE in humans, decreased Tau content in CNS is thought to be one of the causes of cerebral edema. However, understanding of the impact of the changes in Tau content and transport on the pathogenic mechanisms of HE is hampered by the lack of clear-cut evidence regarding the various roles of Tau in the normal CNS.
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Affiliation(s)
- Jan Albrecht
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland.
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Abstract
There appears to be a consensus that hepatic encephalopathy (HE) is a metabolic encephalopathy with a multifactorial pathogenesis. One of the factors considered to be important in the pathogenesis of HE is ammonia. However, the mechanisms by which ammonia contributes to the manifestations of HE remain poorly defined. Ammonia could be more definitively implicated in the pathogenesis of HE if its effects can be shown to lead to an enhancement of inhibitory neurotransmission. In this context the effects of ammonia on the GABA (gamma-aminobutyric acid) neurotransmitter system may be relevant. Ammonia, at the modestly increased concentrations that commonly occur in precoma HE (0.15 mM-0.75 mM), has been shown to increase GABA-induced chloride current in cultured neurons, probably by modifying the affinity of the GABA(A) receptor for GABA. Comparable ammonia concentrations also enhanced synergistically the binding of a GABA agonist and a benzodiazepine (BZ) agonist to the GABA(A) receptor complex, phenomena which would enhance the neuroinhibitory effects of these ligands. Also, GABA increased the potency of ammonia-induced enhancement of the binding of a BZ agonist to the GABA(A) receptor complex, and brain levels of BZ agonists are elevated in liver failure. In addition, ammonia has been shown to inhibit astrocytic uptake of GABA by 30%-50%, an effect which would increase the synaptic availability of GABA at GABA(A) receptors. Furthermore, increased ammonia concentrations upregulate the peripheral-type benzodiazepine receptor in the outer membrane of astroglial mitochondria, thereby enhancing astrocytic mitochondrial synthesis and release of neurosteroids. Some neurosteroids, for example tetrahydroprogesterone (THP) and tetrahydrodeoxycorticosterone (THDOC), are potent agonists of the GABA(A) receptor complex, on which there are specific binding sites for neurosteroids, that are distinct from those for BZs and barbiturates. Tetrahydroprogesterone and tetrahydrodeoxycorticosterone levels were found to be increased in a mouse model of acute liver failure, and, when THP or THDOC was injected into normal mice, sedation and Alzheimer type II astrocytic changes in the cortex, striatum, and hypothalmus were induced. Each of these direct or indirect effects of ammonia on the GABA neurotransmitter system has the potential of increasing inhibitory neurotransmission, and, hence, contributing to the manifestations of HE.
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Affiliation(s)
- E Anthony Jones
- Department of Gastrointestinal and Liver Diseases, Academic Medical Center, Amsterdam, The Netherlands
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Basile AS. Direct and indirect enhancement of GABAergic neurotransmission by ammonia: implications for the pathogenesis of hyperammonemic syndromes. Neurochem Int 2002; 41:115-22. [PMID: 12020612 DOI: 10.1016/s0197-0186(02)00032-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Experimental evidence indicates that ammonia causes neuroexcitation and seizures. This contrasts with the lethargy, confusion and other manifestations of global CNS depression commonly considered to be major components of hyperammonemic encephalopathies. Substantial data now indicates that ammonia can modulate GABAergic neurotransmission through direct and indirect mechanisms. This modulation consists of an enhancement of GABAergic neurotransmission at concentrations commonly encountered in hyperammonemic states and precedes the suppression of inhibitory neuronal function observed at higher (>1mM) ammonia concentrations. Not only is this increase in GABAergic neurotransmission consistent with the clinical picture of lethargy, ataxia and cognitive deficits associated with liver failure and congenital hyperammonemia, but it also provides a mechanism for testing new therapeutic modalities for the treatment of hyperammonemic encephalopathy.
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Affiliation(s)
- Anthony S Basile
- Laboratory of Bioorganic Chemistry, National Institutes of Health, Building 8, Room 121, MSC 0826, NIDDK, NIH, Bethesda, MD 20892, USA.
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Abstract
Hepatic encephalopathy is considered to be a reversible metabolic encephalopathy, which occurs as a complication of hepatocellular failure and is associated with increased portal-systemic shunting of gut-derived nitrogenous compounds. Its manifestations are most consistent with a global depression of CNS function, which could arise as a consequence of a net increase in inhibitory neurotransmission, due to an imbalance between the functional status of inhibitory (e.g., GABA) and excitatory (e.g., glutamate) neurotransmitter systems. In liver failure, factors that contribute to increased GABAergic tone include increased synaptic levels of GABA and increased brain levels of natural central benzodiazepine (BZ) receptor agonists. Ammonia, present in modestly elevated levels, may also augment GABAergic tone by direct interaction with the GABAA receptor, synergistic interactions with natural central BZ receptor agonists, and stimulation of astrocytic synthesis and release of neurosteroid agonists of the GABAA receptor. Thus, there is a rationale for therapies of HE that lower ammonia levels and incrementally reduce increased GABAergic tone towards the physiologic norm.
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Affiliation(s)
- E A Jones
- Department of Gastrointestinal and Liver Diseases, Academic Medical Center, Amsterdam, The Netherlands.
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Abstract
While the pathogenesis of hepatic encephalopathy (HE) is unclear, there is evidence of enhanced GABAergic neurotransmission in this condition. Ammonia is believed to play a major pathogenetic role in HE. To determine whether ammonia might contribute to abnormalities in GABAergic neurotransmission, its effects on GABA uptake and release were studied in cultured astrocytes, cells that appear to be targets of ammonia neurotoxicity. Acutely, ammonium chloride (5 mM) inhibited GABA uptake by 30%, and by 50-60% after 4-day treatment. GABA uptake inhibition was associated with a predominant decrease in Vmax; the Km was also decreased. Ammonia also enhanced GABA release after 4-day treatment, although such release was initially inhibited. These effects of ammonia (inhibition of GABA uptake and enhanced GABA release) may elevate extracellular levels of GABA and contribute to a dysfunction of GABAergic neurotransmission in HE and other hyperammonemic states.
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Affiliation(s)
- A S Bender
- Veterans Administration Medical Center and Department of Pathology, University of Miami School of Medicine, FL 33101, USA
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Abstract
Hepatic encephalopathy (HE) and portal-systemic encephalopathy (PSE) are the terms used interchangeably to describe a complex neuropsychiatric syndrome associated with acute or chronic hepatocellular failure, increased portal systemic shunting of blood, or both. Hepatic encephalopathy complicating acute liver failure is referred to as fulminant hepatic failure (FHF). The clinical manifestations of HE or PSE range from minimal changes in personality and motor activity, to overt deterioration of intellectual function, decreased consciousness and coma, and appear to reflect primarily a variable imbalance between excitatory and inhibitory neurotransmission. Pathogenic mechanisms that may be responsible for HE have been extensively investigated using animal models of HE, or cultures of CNS cells treated with neuroactive substances that have been implicated in HE. Of the many compounds that accumulate in the circulation as a consequence of impaired liver function, ammonia is considered to play an important role in the onset of HE. Acute ammonia neurotoxicity, which may be a cause of seizures in FHF, is excitotoxic in nature, being associated with increased synaptic release of glutamate (Glu), the major excitatory neurotransmitter of the brain, and subsequent overactivation of the ionotropic Glu receptors, mainly the N-methyl-D-aspartate (NMDA) receptors. Hepatic encephalopathy complicating chronic liver failure appears to be associated with a shift in the balance between inhibitory and excitatory neurotransmission towards a net increase of inhibitory neurotransmission, as a consequence of at least two factors. The first is down-regulation of Glu receptors resulting in decreased glutamatergic tone. The down-regulation follows excessive extrasynaptic accumulation of Glu resulting from its impaired re-uptake into nerve endings and astrocytes. Liver failure inactivates the Glu transporter GLT-1 in astrocytes. The second factor is an increase in inhibitory neurotransmission by gamma-aminobutyric acid (GABA) due to (a) increased brain levels of natural benzodiazepines; (b) increased availability of GABA at GABA-A receptors, due to enhanced synaptic release of the amino acid; (c) direct interaction of modestly increased levels of ammonia with the GABA-A-benzodiazepine receptor complex; and (d) ammonia-induced up-regulation of astrocytic peripheral benzodiazepine receptors (PBZR). Brain ammonia is metabolised in astrocytes to glutamine (Gln), an osmolyte, and increased Gln accumulation in these cells may contribute to cytotoxic brain edema, which often complicates FHF. Glutamine efflux from the brain is an event that facilitates plasma-to-brain transport of aromatic amino acids. Tryptophan and tyrosine are direct precursors of the aminergic inhibitory neurotransmitters, serotonin and dopamine, respectively. Changes in serotonin and dopamine and their receptors may contribute to some of the motor manifestations of HE. Finally, oxindole, a recently discovered tryptophan metabolite with strong sedative and hypotensive properties, has been shown to accumulate in cirrhotic patients and animal models of HE.
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Affiliation(s)
- J Albrecht
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Warsaw.
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Abstract
The ammonia and GABAergic neurotransmission hypotheses of the pathogenesis of hepatic encephalopathy (HE) have appeared to be unrelated and perhaps mutually exclusive. Observations in animal models of fulminant hepatic failure, that are consistent with increased GABAergic inhibitory neurotransmission contributing to the manifestations of HE, include: (i) abnormal visual evoked potential waveforms that resemble those induced by GABA(A)/benzodiazepine (BZ) receptor complex agonists; (ii) GABA(A)/BZ receptor complex antagonist-induced ameliorations of encephalopathy; (iii) increased resistance to drugs which decrease GABAergic tone; and (iv) hypersensitivity of CNS neurons to depression by GABA(A)/BZ receptor complex agonists. Mechanisms of increased GABAergic tone in HE may include the following: (i) increased brain concentrations of natural BZs; and (ii) increased GABA concentrations in synaptic clefts, possibly due to increased blood-brain-barrier permeability to GABA and a decrease in GABA(B) receptor density. Both neuroelectrophysiological and behavioral data indicate that ammonia concentrations in the range 0.75-2 mM induce increased excitatory neurotransmission. In contrast, recently, ammonia concentrations in the range 0.15-0.75 mM, i.e. concentrations that commonly occur in plasma in precoma HE, have been shown: (i) to increase GABA-induced chloride current in cultured neurons; and (ii) to enhance synergistically the binding of GABA(A)/BZ receptor agonists. In addition, increased ammonia concentrations enhance synthesis of neurosteroids in astrocytes, and some neurosteroids potently augment GABAergic neurotransmission. Thus, the modestly elevated concentrations of ammonia, that commonly occur in liver failure, may contribute to the manifestations of HE by enhancing GABAergic inhibitory neurotransmission. This concept appears to unify the ammonia and GABAergic neurotransmission hypotheses.
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Affiliation(s)
- E A Jones
- Department of Gastrointestinal and Liver Diseases, Academic Medical Center, Amsterdam, The Netherlands
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Irie T, Hara M, Yasukura T, Minamino M, Omori K, Matsuda H, Inoue K, Inagaki C. Chloride concentration in cultured hippocampal neurons increases during long-term exposure to ammonia through enhanced expression of an anion exchanger. Brain Res 1998; 806:246-56. [PMID: 9739146 DOI: 10.1016/s0006-8993(98)00700-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The effects of long-term exposure to ammonia on [Cl-]i in cultured hippocampal neurons were examined. Ammonia increased the [Cl-]i time- (>/=24 h) and concentration- (>/=2 mM) dependently, resulting in a depolarizing shift of the equilibrium potential of the GABAA receptor-Cl- channel opening (EGABA). Such an effect of ammonia was diminished by the inhibitors of Cl-/HCO3- exchangers, 0.1 mM 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) and 0.1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and a carbonic anhydrase inhibitor, 2 mM acetazolamide, but not by a Na+/K+/2Cl-cotransport inhibitor, 50 microM bumetanide, suggesting an enhanced Cl-/HCO3- exchange activity by ammonia. The ammonia-induced increase in [Cl-]i was also abolished by the inhibitors of protein kinase C (PKC), 0.1 microM calphostin C and 10 microM 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine dihydrochloride (H-7), and of transcription and de novo protein synthesis, 1 microM actinomycin D and 0.5 microg/ml cycloheximide, while a PKC activator, 0.1 h microM phorbor 12-myristate 13-acetate (PMA), increased the [Cl-]i. The mRNA level of the AE3 Cl-/HCO3- exchanger was increased by ammonia in a calphostin C- and H-7-sensitive manner. The AE3-like immunoreactivity was also increased by ammonia. These findings suggest that long-term exposure to ammonia increases the expression of AE3 through the activation of PKC, resulting in an increase in [Cl-]i in neurons and a reduction of inhibitory postsynaptic potentials.
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Affiliation(s)
- T Irie
- Department of Pharmacology, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi, Osaka, 570-8506, Japan
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Lees G, Edwards MD, Hassoni AA, Ganellin CR, Galanakis D. Modulation of GABA(A) receptors and inhibitory synaptic currents by the endogenous CNS sleep regulator cis-9,10-octadecenoamide (cOA). Br J Pharmacol 1998; 124:873-82. [PMID: 9692771 PMCID: PMC1565467 DOI: 10.1038/sj.bjp.0701918] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
1. Cis-9,10-octadecenoamide (cOA) accumulates in the CSF of sleep-deprived cats and may represent a novel signalling molecule. Synthetic cOA has been shown to induce physiological sleep when injected into laboratory rats. Here we assess the cellular mode of action of cOA in vitro. 2. In all rat cultured cortical neurones (pyramidal cells) examined, the synthetic brain lipid (3.2-64 microM) enhanced the responses to subsaturating GABA concentrations (up to circa 2x) in a concentration-dependent manner (EC50, circa 15 microM). 3. (20 microM) cOA significantly enhanced the affinity of exogenous GABA for its receptor without changing the Hill slope or the maximal response. These effects were not voltage-dependent or secondary to shifts in E(Cl). 4. In the absence of GABA, cOA directly evoked small inhibitory currents in a subpopulation (<7%) of sensitive cells. 5. 20 microM cOA reversibly enhanced the duration of spontaneous inhibitory post synaptic currents (circa 2 fold) without significantly altering their amplitude. 6. At 32-64 microM, cOA reversibly reduced the incidence and amplitude of both inhibitory post synaptic currents (i.p.s.cs) and excitatory post synaptic currents (e.p.s.cs) in the cultured neuronal circuits in common with other depressant drugs acting at the GABA(A) receptor. 7. 32 microM Oleic acid did not modulate exogenous GABA currents or synaptic activity suggesting that cOAs actions are mediated through a specific receptor. 8. A specific, protein-dependent interaction with GABA(A) receptors was confirmed in Xenopus oocytes. Recombinant human receptors were modulated by 10 microM cOA (and diazepam) only when a gamma2 subunit was co-expressed with alpha1beta2: the cOA response was not sensitive to the specific benzodiazepine antagonist flumazenil (1 microM). 9. cOA may represent an endogenous ligand for allosteric modulatory sites on isoforms of GABA(A) receptors which are crucial for the regulation of arousal and have recently been implicated in the circadian control of physiological sleep.
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Affiliation(s)
- G Lees
- School of Health Sciences, University of Sunderland
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30
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Stauch S, Kircheis G, Adler G, Beckh K, Ditschuneit H, Görtelmeyer R, Hendricks R, Heuser A, Karoff C, Malfertheiner P, Mayer D, Rösch W, Steffens J. Oral L-ornithine-L-aspartate therapy of chronic hepatic encephalopathy: results of a placebo-controlled double-blind study. J Hepatol 1998; 28:856-64. [PMID: 9625322 DOI: 10.1016/s0168-8278(98)80237-7] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND/AIMS In the current state of knowledge of the pathophysiology of hepatic encephalopathy, a reduction in hyperammonemia is the most important evidence of effective treatment. Therefore, the therapeutic efficacy of oral L-ornithine-L-aspartate, which improves impaired ammonia detoxification, was investigated in patients with cirrhosis, hyperammonemia and stable, overt, chronic hepatic encephalopathy, and in subclinical hepatic encephalopathy in a randomized, double-blind, placebo-controlled clinical trial. METHODS Oral L-ornithine-L-aspartate was administered three times daily at fixed times for 14 consecutive days in a total dose of 18 g per day. The design was chosen to prevent an increase in ammonia induced by a protein meal of 0.25 g/kg body weight, given at the start of the daily treatment period. Efficacy variables were: fasting and postprandial ammonia concentration, Number-Connection-Test time, mental state grades, and a Portosystemic Encephalopathy Index. Analyses were based on the total study sample of 32 placebo- and 34 L-ornithine-L-aspartate-treated patients as well as on the subgroup samples in the overt (20 placebo- and 23 L-ornithine-L-aspartate-treated) and subclinical hepatic encephalopathy (12 placebo- and 11 L-ornithine-L-aspartate-treated) patients. RESULTS Number Connection Test performance times (p<0.01) as well as fasting (p<0.01) and postprandial (p<0.05) venous blood ammonia concentrations in the L-ornithine-L-aspartate-treated group showed improvement in comparison to placebo. Also, the mental state grade (p<0.05) and the Portosystemic Encephalopathy Index (p<0.01), improved to a much greater degree in the L-ornithine-L-aspartate group than in the placebo group. Adverse events were observed in neither the placebo nor the L-ornithine-L-aspartate-treated patients. CONCLUSION Oral L-ornithine-L-aspartate is a safe, well-tolerated treatment with a good compliance rate and a beneficial therapeutic effect in patients with cirrhosis and stable, overt, chronic hepatic encephalopathy.
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Affiliation(s)
- S Stauch
- Hospital Nordwest, Dept. of Internal Medicine, Frankfurt/Main, Germany
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Ha JH, Knauer S, Moody E, Jones EA, Basile AS. Direct enhancement of GABA-ergic neurotransmission by ammonia. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1997; 420:85-94. [PMID: 9286428 DOI: 10.1007/978-1-4615-5945-0_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- J H Ha
- Laboratory of Neuroscience, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
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Jones EA, Basile AS. The involvement of ammonia with the mechanisms that enhance GABA-ergic neurotransmission in hepatic failure. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1997; 420:75-83. [PMID: 9286427 DOI: 10.1007/978-1-4615-5945-0_5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- E A Jones
- Department of Gastrointestinal and Liver Diseases, Academic Medical Center, Amsterdam, The Netherlands
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Ha JH, Basile AS. Modulation of ligand binding to components of the GABAA receptor complex by ammonia: implications for the pathogenesis of hyperammonemic syndromes. Brain Res 1996; 720:35-44. [PMID: 8782894 DOI: 10.1016/0006-8993(96)00104-7] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effects of 5-2500 microM concentrations of neutral ammonium salts on the binding of ligands to components of the GABAA receptor complex were investigated. [3H]Flunitrazepam binding to the benzodiazepine receptor was enhanced by ammonium (10-500 microM), but not sodium tartrate with EC50 = 98 microM and Emax = 31%. Further increasing ammonium tartrate concentrations (500-2500 microM) decreased [3H]flunitrazepam binding to control levels. The ammonium tartrate-induced increase in [3H]flunitrazepam binding was manifested as a 50% decrease in Kd. Furthermore, GABA increased the potency of ammonium tartrate in enhancing [3H]flunitrazepam binding by 63%. [3H]Ro 15-1788 and [3H]Ro 15-4513 binding to the benzodiazepine receptor was not significantly enhanced by ammonium tartrate (Emax approximately 13%). Ammonium tartrate also increased, then decreased the binding of 500 nM [3H]muscimol to the GABAA receptor (EC50 = 52 microM, Emax = 30%) in a concentration-dependent manner, but had no effect on [3H]SR 95-531 binding (Emax < 16%). The ammonium tartrate-induced alterations in [3H]muscimol binding were demonstrated in saturation assays as the loss of the high affinity binding site and a 27% increase in the Bmax of the low affinity binding site. These results indicate that ammonia biphasically enhances, then returns ligand binding to both the GABA and benzodiazepine receptor components of the GABAA receptor complex to control levels in a barbiturate-like fashion. This suggests that ammonia may enhance GABAergic neurotransmission at concentrations commonly encountered in hepatic failure, an event preceding the suppression of inhibitory neuronal function observed at higher (> 1 mM) ammonia concentrations. This increase in GABAergic neurotransmission is consistent with the clinical picture of lethargy, ataxia and cognitive deficits associated with liver failure and congenital hyperammonemia.
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Affiliation(s)
- J H Ha
- Laboratory of Neuroscience, NIDDKD, National Institutes of Health, Bethesda, MD 20892, USA
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Abstract
gamma-Aminobutyric acid (GABA)A receptors for the inhibitory neurotransmitter GABA are likely to be found on most, if not all, neurons in the brain and spinal cord. They appear to be the most complicated of the superfamily of ligand-gated ion channels in terms of the large number of receptor subtypes and also the variety of ligands that interact with specific sites on the receptors. There appear to be at least 11 distinct sites on GABAA receptors for these ligands.
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Affiliation(s)
- G A Johnston
- Adrien Albert Laboratory of Medicinal Chemistry, Department of Pharmacology, University of Sydney, NSW, Australia
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35
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Yurdaydin C, Walsh TJ, Engler HD, Ha JH, Li Y, Jones EA, Basile AS. Gut bacteria provide precursors of benzodiazepine receptor ligands in a rat model of hepatic encephalopathy. Brain Res 1995; 679:42-8. [PMID: 7648264 DOI: 10.1016/0006-8993(95)00241-h] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Benzodiazepine receptor (BZR) ligands are elevated in animals and humans with fulminant hepatic failure (FHF) and contribute to the pathogenesis of the associated hepatic encephalopathy (HE). As gut factors are proposed to play a role in the pathogenesis of HE, we investigated gut flora as a source of BZR ligands. Rats received daily oral neomycin, vancomycin and metronidazole (AB +) or saline (AB -) before and concurrent with the induction of FHF with thioacetamide. BZR ligands were extracted from brain and plasma and quantified using radiometric techniques. Plasma BZR ligand concentrations in AB(+) and AB(-) rats with HE were higher than AB(+) and AB(-) control rats. Brain BZR ligand concentrations increased in AB(+) and AB(-) rats with HE. Stool cultures from antibiotic treated rats with HE indicated the presence of multidrug resistant Acinetobacter lwoffii. Although no significant concentrations of BZR ligands were detected in culture media inoculated with A. lwoffii, administering A. lwoffii to normal rats significantly elevated BZR ligand levels in brain, but not plasma. Thus, antibiotic treatment of rats is associated with the growth of a resistant strain of bacterium which produces an inactive BZR ligand precursor. BZR ligands may be synthesized from these precursors in the brain and efficiently cleared by a normal liver following brain-to-plasma transfer. Impairment of this clearance process in FHF facilitates their accumulation, enabling agonist BZR ligands to contribute to the pathogenesis of HE by further enhancing GABAergic neurotransmission.
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Affiliation(s)
- C Yurdaydin
- Liver Diseases Section, NIDDK, Bethesda, MD 20892, USA
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36
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Oja SS, Saransaari P, Wysmyk U, Albrecht J. Loss of GABAB binding sites in the cerebral cortex of rats with acute hepatic encephalopathy. Brain Res 1993; 629:355-7. [PMID: 8111641 DOI: 10.1016/0006-8993(93)91346-t] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The binding of [3H]GABA to GABAA and GABAB binding sites was measured in cerebral cortical membranes derived from control rats and rats with acute hepatic encephalopathy (HE) induced with a hepatotoxin, thioacetamide. HE did not affect the kinetic parameters (KD and Bmax) for the GABAA binding site. However, HE decreased Bmax (but not KD) for the GABAB binding site to 32% of the control level, indicating a substantial loss of GABAB receptors. Since GABAB receptors control the cerebral cortical release of the amino acid neurotransmitters glutamate and GABA, the loss of GABAB receptors is likely to contribute to the array of disturbances of glutamatergic and GABAergic neurotransmission known to accompany HE.
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Affiliation(s)
- S S Oja
- Department of Biomedical Sciences, University of Tampere, Finland
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