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Badawy AA, Elghaba R, Soliman M, Hussein AM, AlSadrah SA, Awadalla A, Abulseoud OA. Chronic Valproic Acid Administration Increases Plasma, Liver, and Brain Ammonia Concentration and Suppresses Glutamine Synthetase Activity. Brain Sci 2020; 10:brainsci10100759. [PMID: 33096612 PMCID: PMC7589689 DOI: 10.3390/brainsci10100759] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 10/07/2020] [Accepted: 10/15/2020] [Indexed: 01/09/2023] Open
Abstract
Asymptomatic valproic acid (VPA)-induced hyperammonemia in the absence of liver impairment is fairly common. However, the underlying mechanisms through which VPA causes elevation in plasma ammonia (NH4) remains under investigation. Male Sprague Dawley rats (n = 72) were randomly allocated to receive VPA 400 mg/kg, 200 mg/kg, or vehicle IP daily for either 8, 14, or 28 consecutive days. The behavioral effects of VPA were assessed. Plasma, liver, and prefrontal cortex (PFC), striatum (Str), and cerebellum (Cere) were collected 1 h post last injection and assayed for NH4 concentration and glutamine synthetase (GS) enzyme activity. Chronic VPA treatment caused attenuation of measured behavioral reflexes (p < 0.0001) and increase in plasma NH4 concentration (p < 0.0001). The liver and brain also showed significant increase in tissue NH4 concentrations (p < 0.0001 each) associated with significant reduction in GS activity (p < 0.0001 and p = 0.0003, respectively). Higher tissue NH4 concentrations correlated with reduced GS activity in the liver (r = −0.447, p = 0.0007) but not in the brain (r = −0.058, p = 0.4). Within the brain, even though NH4 concentrations increased in the PFC (p = 0.001), Str (p < 0.0001), and Cere (p = 0.01), GS activity was reduced only in the PFC (p < 0.001) and not in Str (p = 0.2) or Cere (p = 0.1). These results suggest that VPA-induced elevation in plasma NH4 concentration could be related, at least in part, to the suppression of GS activity in liver and brain tissues. However, even though GS is the primary mechanism in brain NH4 clearance, the suppression of brain GS does not seem to be the main factor in explaining the elevation in brain NH4 concentration. Further research is urgently needed to investigate brain NH4 dynamics under chronic VPA treatment and whether VPA clinical efficacy in treating seizure disorders and bipolar mania is impacted by its effect on GS activity or other NH4 metabolizing enzymes.
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Affiliation(s)
- Abdelnaser A. Badawy
- Department of Biochemistry, Faculty of Medicine, Northern Border University, Arar 73213, Saudi Arabia;
- Department of Biochemistry, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt
| | - Rasha Elghaba
- Department of Medical Physiology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt;
| | - Mohamed Soliman
- Department of Microbiology, Faculty of Medicine, Northern Border University, Arar 73213, Saudi Arabia;
| | - Abdelaziz M. Hussein
- Department of Medical Physiology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt;
- Correspondence: (A.M.H.); (O.A.A.)
| | - Sana A. AlSadrah
- Department of Preventive Medicine, Governmental Hospital Khobar, Health Centers in Khobar, Ministry of Health, Khobar 34446, Saudi Arabia;
| | - Amira Awadalla
- Center of Excellence and Cancer Genome, Mansoura Urology and Nephrology Center, Mansoura 35516, Egypt;
| | - Osama A. Abulseoud
- Neuroimaging Research Branch, IRP, National Institute on Drug Abuse, National Institutes of Health, Biomedical Research Center, Baltimore, MD 21224, USA
- Correspondence: (A.M.H.); (O.A.A.)
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Acanthopanax senticosus reduces brain injury in mice exposed to low linear energy transfer radiation. Biomed Pharmacother 2018; 99:781-790. [DOI: 10.1016/j.biopha.2018.01.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 12/25/2017] [Accepted: 01/03/2018] [Indexed: 11/16/2022] Open
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Díez-Fernández C, Hu L, Cervera J, Häberle J, Rubio V. Understanding carbamoyl phosphate synthetase (CPS1) deficiency by using the recombinantly purified human enzyme: effects of CPS1 mutations that concentrate in a central domain of unknown function. Mol Genet Metab 2014; 112:123-32. [PMID: 24813853 DOI: 10.1016/j.ymgme.2014.04.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Revised: 04/11/2014] [Accepted: 04/11/2014] [Indexed: 01/02/2023]
Abstract
Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is an inborn error of the urea cycle that is due to mutations in the CPS1 gene. In the first large repertory of mutations found in CPS1D, a small CPS1 domain of unknown function (called the UFSD) was found to host missense changes with high frequency, despite the fact that this domain does not host substrate-binding or catalytic machinery. We investigate here by in vitro expression studies using baculovirus/insect cells the reasons for the prominence of the UFSD in CPS1D, as well as the disease-causing roles and pathogenic mechanisms of the mutations affecting this domain. All but three of the 18 missense changes found thus far mapping in this domain in CPS1D patients drastically decreased the yield of pure CPS1, mainly because of decreased enzyme solubility, strongly suggesting misfolding as a major determinant of the mutations negative effects. In addition, the majority of the mutations also decreased from modestly to very drastically the specific activity of the fraction of the enzyme that remained soluble and that could be purified, apparently because they decreased V(max). Substantial although not dramatic increases in K(m) values for the substrates or for N-acetyl-L-glutamate were observed for only five mutations. Similarly, important thermal stability decreases were observed for three mutations. The results indicate a disease-causing role for all the mutations, due in most cases to the combined effects of the low enzyme level and the decreased activity. Our data strongly support the value of the present expression system for ascertaining the disease-causing potential of CPS1 mutations, provided that the CPS1 yield is monitored. The observed effects of the mutations have been rationalized on the basis of an existing structural model of CPS1. This model shows that the UFSD, which is in the middle of the 1462-residue multidomain CPS1 protein, plays a key integrating role for creating the CPS1 multidomain architecture leading us to propose here a denomination of "Integrating Domain" for this CPS1 region. The majority of these 18 mutations distort the interaction of this domain with other CPS1 domains, in many cases by causing improper folding of structural elements of the Integrating Domain that play key roles in these interactions.
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Affiliation(s)
| | - Liyan Hu
- University Children's Hospital, Zurich and Children's Research Center, Zurich, Switzerland
| | - Javier Cervera
- Instituto de Biomedicina de Valencia of the CSIC, Valencia, Spain; Group 739 of the Centro de Investigación Biomédica en Red sobre Enfermedades Raras (CIBERER) del Instituto de Salud Carlos III, Spain
| | - Johannes Häberle
- University Children's Hospital, Zurich and Children's Research Center, Zurich, Switzerland.
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia of the CSIC, Valencia, Spain; Group 739 of the Centro de Investigación Biomédica en Red sobre Enfermedades Raras (CIBERER) del Instituto de Salud Carlos III, Spain.
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Diez-Fernandez C, Martínez AI, Pekkala S, Barcelona B, Pérez-Arellano I, Guadalajara AM, Summar M, Cervera J, Rubio V. Molecular Characterization of Carbamoyl-Phosphate Synthetase (CPS1) Deficiency Using Human Recombinant CPS1 as a Key Tool. Hum Mutat 2013; 34:1149-59. [DOI: 10.1002/humu.22349] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Accepted: 04/18/2013] [Indexed: 12/30/2022]
Affiliation(s)
- Carmen Diez-Fernandez
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Centro de Investigación Príncipe Felipe; Valencia Spain
| | | | - Satu Pekkala
- Centro de Investigación Príncipe Felipe; Valencia Spain
| | - Belén Barcelona
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Centro de Investigación Príncipe Felipe; Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | - Isabel Pérez-Arellano
- Centro de Investigación Príncipe Felipe; Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | | | - Marshall Summar
- Childrens National Medical Center; Washington District of Columbia
| | - Javier Cervera
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Centro de Investigación Príncipe Felipe; Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
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Giannola LI, De Caro V, Severino A. Carnauba Wax Microspheres Loaded with Valproic Acid: Preparation and Evaluation of Drug Release. Drug Dev Ind Pharm 2008. [DOI: 10.3109/03639049509069246] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Gerstner T, Bell N, König S. Oral valproic acid for epilepsy--long-term experience in therapy and side effects. Expert Opin Pharmacother 2008; 9:285-92. [PMID: 18201150 DOI: 10.1517/14656566.9.2.285] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Valproic acid (VPA) is considered to be a drug of first choice and one of the most frequently-prescribed antiepileptic drugs worldwide for the therapy of generalized and focal epilepsies, including special epileptic. It is a broad-spectrum antiepileptic drug and is usually well tolerated. Rarely, serious complications may occur in some patients, including hemorrhagic pancreatitis, coagulopathies, bone marrow suppression, VPA-induced hepatotoxicity and encephalopathy, but there is still a lack of knowledge about the incidence and occurrence of these special side effects. Additionally, the consequences for VPA therapy and indication are more or less unclear. By literature review and own data this review addresses some of the challenges of VPA therapy and its side effects, which are not unique to epilepsy in childhood.
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Affiliation(s)
- Thorsten Gerstner
- University Children's Hospital, Neuropediatric Unit, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
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Gerstner T, Bauer MO, Longin E, Bell N, Koenig SA. Reversible hepatotoxicity, pancreatitis, coagulation disorder and simultaneous bone marrow suppression with valproate in a 2-year-old girl. Seizure 2007; 16:554-6. [PMID: 17493839 DOI: 10.1016/j.seizure.2007.04.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2007] [Revised: 03/27/2007] [Accepted: 04/16/2007] [Indexed: 11/17/2022] Open
Abstract
Valproic acid (VPA) is considered to be a drug of first choice for the therapy of generalized and focal epilepsies, including special epileptic syndromes like the WEST-syndrome. The drug is usually well tolerated; rare serious complications may occur in some patients, including haemorrhagic pancreatitis, coagulapathies, bone marrow suppression, VPA-induced hepatotoxicity and encephalopathy. We report a case of combined appearance of several severe VPA-associated side effects in a two- and a half-year-old girl with lissencephaly.
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Affiliation(s)
- Thorsten Gerstner
- University Children's Hospital, Theodor-Kutzer-Ufer 1-3, 69167 Mannheim, Germany.
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8
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Gerstner T, Buesing D, Longin E, Bendl C, Wenzel D, Scheid B, Goetze G, Macke A, Lippert G, Klostermann W, Mayer G, Augspach-Hofmann R, Fitzek S, Haensch CA, Reuland M, Koenig SA. Valproic acid induced encephalopathy – 19 new cases in Germany from 1994 to 2003 – A side effect associated to VPA-therapy not only in young children. Seizure 2006; 15:443-8. [PMID: 16787750 DOI: 10.1016/j.seizure.2006.05.007] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Revised: 05/10/2006] [Accepted: 05/23/2006] [Indexed: 01/26/2023] Open
Abstract
Valproic acid (VPA) is a broad-spectrum antiepileptic drug and is usually well-tolerated. Rare serious complications may occur in some patients, including haemorrhagic pancreatitis, bone marrow suppression, VPA-induced hepatotoxicity and VPA-induced encephalopathy. The typical signs of VPA-induced encephalopathy are impaired consciousness, sometimes marked EEG background slowing, increased seizure frequency, with or without hyperammonemia. There is still no proof of causative effect of VPA in patients with encephalopathy, but only of an association with an assumed causal relation. We report 19 patients with VPA-associated encephalopathy in Germany from the years 1994 to 2003, none of whom had been published previously.
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Affiliation(s)
- Thorsten Gerstner
- University Children's Hospital Mannheim, Neuropediatric Unit, Theodor-Kutzer-Ufer 1-3, 69167 Mannheim, Germany
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9
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Sztajnkrycer MD. Valproic acid toxicity: overview and management. JOURNAL OF TOXICOLOGY. CLINICAL TOXICOLOGY 2002; 40:789-801. [PMID: 12475192 DOI: 10.1081/clt-120014645] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Acute valproic acid intoxication is an increasing problem, accounting for more than 5000 calls to the American Association of Poison Control Centers in 2000. The purpose of this paper is to review the pharmacology and toxicology of valproic acid toxicity. Unlike earlier antiepileptic agents, valproic acid appears to function neither through sodium channel inhibition nor through direct gamma-aminobutyric acid agonism, but through an indirect increase in regional brain gamma-aminobutyric acid levels. Manifestations of acute valproic acid toxicity are myriad, and reflect both exaggerated therapeutic effect and impaired intermediary metabolism. Central nervous system depression is the most common finding noted in overdose, and may progress to coma and respiratory depression. Cerebral edema has also been observed. Although hepatotoxicity is rare in the acute overdose setting, pancreatitis and hyperammonemia have been reported. Metabolic and hematologic derangements have also been described. Management of acute valproic acid ingestion requires supportive care and close attention to the airway. The use of controversial adjunctive therapies, including extracorporeal drug elimination and L-carnitine supplementation, will be discussed.
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10
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Krikorian A, Sharara AI, Khalifeh RR. Valproic Acid-Induced Hyperammonemic Encephalopathy. J Pharm Technol 2002; 18:70-74. [DOI: 10.1177/875512250201800204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/07/2023] Open
Abstract
ObjectiveTo review the relevant literature concerning the biochemical mechanism(s) of valproic acid (VPA)-induced hyperammonemia in an attempt to present a unifying pathogenetic hypothesis.Data SourcesThe MEDLINE database (1966–July 2001) was searched for English-language articles and abstracts on VPA-induced hyperammonemia. References cited in relevant primary articles were also reviewed.Study SelectionMore than 150 original and review articles were evaluated, and the most relevant were selected.Data ExtractionClinically significant hyperammonemia is a rare adverse effect of VPA therapy. The exact pathogenesis of VPA-induced hyperammonemia remains unclear, but is likely to involve a variety of contributing and possibly overlapping biochemical steps. These include VPA drug concentration, indirect inhibition of ureagenesis by valproyl coenzyme A (CoA), direct suppression of the urea cycle enzymes, depletion of mitochondrial acetyl CoA and decreased production of N-acetylglutamate, depletion of carnitine stores, and increased glutamate dehydrogenase activity.ConclusionsHyperammonemic encephalopathy is a rare, but clinically important, adverse effect of VPA therapy. The biochemical basis for this association remains unclear. Awareness of this adverse reaction by healthcare personnel is important in early recognition, treatment, and prevention.
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Affiliation(s)
| | - Ala I Sharara
- Department of Medicine, American University of Beirut Medical Center
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Wirshing WC, Ames D, Bisheff S, Pierre JM, Mendoza A, Sun A. Hepatic encephalopathy associated with combined clozapine and divalproex sodium treatment. J Clin Psychopharmacol 1997; 17:120-1. [PMID: 10950478 DOI: 10.1097/00004714-199704000-00013] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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12
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Abstract
The effects of valproate on brain energy and lipid metabolism is reviewed. Increasing evidence suggests that valproate uses the monocarboxylic acid carrier in order to cross the blood brain barrier (BBB) and the neural cell plasma membranes. The uptake of valproate into the brain through this mechanism would compete with the uptake of energy precursors, such as the monocarboxylic acids 3-hydroxybutyrate, lactate or pyruvate and with some amino acids, but not with glucose. This could impair brain fuel utilization, specially during the neonatal period or childhood, when lactate or 3-hydroxybutyrate furnishes alternative substrates to glucose for the brain. It is concluded that valproate interference with energy metabolism may have implications for the therapeutic action of the drug, stressing the possibility that valproate-mediated alterations in brain lipid synthesis may contribute to the pharmacological action of the drug.
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Affiliation(s)
- J P Bolaños
- Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia,Universidad de Salamanca, Spain
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13
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Abstract
The aim of the study was to investigate the effect of carnitine supplementation of valproic acid (VPA) treated patients presenting with increased plasma ammonia concentrations. Plasma ammonia concentrations were recorded in 69 children and young adults on VPA monotherapy (25.6 +/- 9.2 mg VPA/kg per day; mean plasma VPA concentration 68.8 +/- 27.6 mg/l). Their mean plasma ammonia concentration was 80.2 +/- 32.1 micrograms/dl (median 73.1 microgram/dl). A total of 24 patients (35.3%) presenting with ammonia concentrations > 80 microgram/dl were considered hyperammonaemic. Of these, 15/24 (22.1%) showed ammonia concentrations > 100 microgram/dl, even up to 194 micrograms/dl. In 48/69 patients, plasma carnitine concentrations could be determined. The plasma total carnitine (TC) concentrations were rather low (26.9 +/- 8.8 mumol/1) compared to normal values obtained in our laboratory (40.9 +/- 7.2 mumol/1). The percentage of free carnitine was considered decreased (< 75% TC) in 13/48 samples (27%). Fourteen hyperammonaemic patients and one with a plasma ammonia level of 60 micrograms/dl agreed to be supplemented with L-carnitine (1 g/m2 per day divided into two equal doses). Their plasma ammonia and carnitine concentrations were re-evaluated after a mean of 9.1 +/- 4.0 days (median 9.0 days) and in 9 patients again after a mean of 79.6 +/- 30.1 days (median 75 days) of L-carnitine supplementation. Plasma ammonia concentrations decreased in all 15 patients. The decrease was 25.4 +/- 11.2% (median 28.3%) after a mean of 9.1 +/- 4.0 days and amounted to 46.0 +/- 17.2% (median 48%) after 79.6 +/- 30.1 days. L-Carnitine supplementation led to an increase in plasma free carnitine of 11.6 +/- 13.0% (median 15.6%) and to a further increase of 11.1 +/- 8.4% (median 11.5%) when re-evaluated a second time. The plasma ammonia concentrations were significantly correlated with the percentage of free plasma carnitine (r = -0.67; p < 0.0001). The results show that carnitine supplementation is a means of normalizing elevated plasma ammonia concentrations. However, we cannot conclude from our results whether this lowers the risk of developing a VPA-induced Reye's-like syndrome.
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Affiliation(s)
- H Böhles
- Zentrum der Kinderheilkunde, Johann Wolfgang Goethe-Universität Frankfurt, FRG
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Grisolía S, Miñana MD, Grau E, Felipo V. Control of urea synthesis and ammonia detoxification. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 341:1-12. [PMID: 7906913 DOI: 10.1007/978-1-4615-2484-7_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- S Grisolía
- Instituto de Investigaciones Citologicas, Amadeo de Saboya, Valencia, Spain
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Horiuchi M, Imamura Y, Nakamura N, Maruyama I, Saheki T. Carbamoylphosphate synthetase deficiency in an adult: deterioration due to administration of valproic acid. J Inherit Metab Dis 1993; 16:39-45. [PMID: 8487502 DOI: 10.1007/bf00711313] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A 24-year-old patient had symptoms of lethargy, convulsions and hyperammonaemia during valproic acid therapy. Cessation of valproic acid treatment brought about an improvement both of the symptoms and of the hyperammonaemia. However, enzymatic analysis after the cessation of valproic acid therapy revealed a complete absence of carbamoylphosphate synthetase (CPS) activity in liver biopsy. A unique polypeptide band, corresponding to the control CPS protein in molecular weight ('CPS-like' protein), was found in normal amounts in the patient's liver on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. This CPS-like protein seemed to be more labile than the control, because the polypeptide band became faint after freeze-thawing. Intravenous administration of L-alanine resulted in a significant increase of serum urea and a transient increase of blood ammonia concentrations. These results strongly suggest that the patient has a labile CPS protein with no activity in vitro but some activity in vivo. We consider that valproic acid may have disrupted some metabolic adaptation by reducing N-acetylglutamate in the liver, which in combination with CPS deficiency induced severe hyperammonaemia.
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Affiliation(s)
- M Horiuchi
- Department of Internal Medicine, Faculty of Medicine, Kogoshima University, Japan
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García-España A, Alonso E, Rubio V. Influence of anions on the activation of carbamoyl phosphate synthetase (ammonia) by acetylglutamate: implications for the activation of the enzyme in the mitochondria. Arch Biochem Biophys 1991; 288:414-20. [PMID: 1898038 DOI: 10.1016/0003-9861(91)90214-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Rat liver carbamoyl phosphate synthetase is shown to be inhibited by anions competitively with acetylglutamate (the allosteric activator of the enzyme) with a potency decreasing in the order NO3- greater than SO4(2-) greater than Cl- approximately HCO3-. Inhibition by chloride accounts for most of the inhibition reported [Lund, P., and Wiggins, D. (1987) Biochem. J. 243, 273-276] in Tris buffer. Mes, acetate, and isethionate give little or no inhibition and phosphate inhibits noncompetitively. Plots of the KA value for acetylglutamate versus the concentration of chloride or nitrate are curved upward and binding assays demonstrate that the inhibitory anions displace acetylglutamate from the enzyme. Thus, the anions may compete with the carboxyls of acetylglutamate for positive charges at the binding site. Of the organic anions found in the mitochondrial matrix, alpha-ketoglutarate, malate, succinate, and citrate increase substantially the KA for acetylglutamate. Changes in the concentrations of ATP, HCO3-, NH4+, and Mg2+, and high concentrations of protein (60 mg/ml serum albumin) influence the KA value. Changes in the concentration of the enzyme have no effect. Under assay conditions approaching the ionic, buffer, and substrate concentrations expected to occur in the mitochondrial matrix, the KA value for acetylglutamate is 27 microM and the Vmax is decreased about 50%. These results indicate that physiological changes in the level of acetylglutamate significantly influence the degree of activation of carbamoyl phosphate synthetase in vivo.
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Affiliation(s)
- A García-España
- Laboratory of Cell Chemistry, Instituto de Investigaciones Citológicas de la Caja de Ahorros de Valencia (Centro Asociado del CSIC), Spain
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Alonso E, García-Pérez MA, Bueso J, Rubio V. N-acetyl-L-glutamate in brain: assay, levels, and regional and subcellular distribution. Neurochem Res 1991; 16:787-94. [PMID: 1944768 DOI: 10.1007/bf00965688] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
N-Acetyl-L-glutamate (NAG), the activator of mitochondrial carbamoyl phosphate synthetase (CPS), is demonstrated by several methods, including a new HPLC assay, in the brain of mammals and of chicken. The brain levels of NAG are 200-300 times lower than the levels of N-acetyl-L-aspartate (NAA), and are similar to the levels of NAG in rat liver. The NAG levels in chicken liver are very low. Although NAG is mitochondrial in the liver, it is cytosolic in brain. Using enzyme activity and immuno assays we did not detect CPS in brain (detection limit, 12.5 micrograms/g brain), excluding that brain NAG is involved in citrullinogenesis. The regional distribution of brain NAG differs from that of NAA and resembles that of N-acetyl-L-aspartyl-L-glutamate (NAAG), suggesting that NAG and NAAG are related. NAG might be involved in the modulation of NAAG degradation.
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Affiliation(s)
- E Alonso
- Department of Biochemistry and Molecular Biology, Facultad de Medicina, Universidad de Valencia, Spain
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18
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Felipo V, Miñana MD, Grisolía S. Control of urea synthesis and ammonia utilization in protein deprivation and refeeding. Arch Biochem Biophys 1991; 285:351-6. [PMID: 1680307 DOI: 10.1016/0003-9861(91)90371-o] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Rats were fed a standard diet (20% protein) or a protein-free diet for up to 65 days. After 20 days on the protein-free diet some rats were refed the standard diet. By the 20th day the rats fed the protein-free diet showed a blood ammonia level approximately 70% higher than controls and urea excretion decreased approximately 20-fold. At this time the liver acetylglutamate decreased to approximately one-fifth of the initial and control levels, returning to normal after 3 days of refeeding the standard diet, with a concomitant increase in urea excretion. The protein-deficient diet resulted in decreased activities of liver enzymes related to ammonia metabolism. All enzyme activities assayed returned to normal values rapidly upon refeeding the standard diet, except hepatic carbamylphosphate synthetase, glutamine synthetase, and glutaminase, which took approximately 1 month to return to control values. The findings presented here are consistent with the view that urea production is controlled, at least under certain conditions, by acetylglutamate, the physiological activator of carbamylphosphate synthetase.
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Affiliation(s)
- V Felipo
- Instituto de Investigaciones Citológicas de la Caja de Ahorros de Valencia, Centro Asociado del CSIC, Spain
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Abstract
1. Amino acid metabolism was studied in control virgin rats, lactating rats and virgin rats protein-pair-fed with the lactating rats (high-protein virgin rats). 2. Urinary excretion of nitrogen and urea was higher in lactating than in control virgin rats, and in high-protein virgin rats it was higher than in lactating rats. 3. The activities of urea-cycle enzymes (units/g) were higher in high-protein virgin than in lactating rats, except for arginase. In lactating rats the activities of carbamoyl-phosphate synthase, ornithine carbamoyltransferase and argininosuccinate synthase were lower than in control virgin rats. When the liver size is considered, the activities in lactating rats were similar to those in high-protein virgin rats, except for arginase. 4. N-Acetylglutamate content was higher in high-protein virgin rats than in the other two groups. 5. The rate of urea synthesis from precursors by isolated hepatocytes was higher in high-protein virgin rats than in the other two groups. 6. The flooding-dose method (L-[4-3H]phenylalanine) for measuring protein synthesis was used. The absolute synthesis rates of mammary gland, liver and small-intestinal mucosa were higher in lactating rats than in the other two groups, and in high-protein virgin rats than in control virgin rats 7. These results show that the increased needs for amino acids during lactation are met by hyperphagia and by a nitrogen-sparing mechanism.
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