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Weinstein AM. A mathematical model of the rat kidney. III. Ammonia transport. Am J Physiol Renal Physiol 2021; 320:F1059-F1079. [PMID: 33779315 DOI: 10.1152/ajprenal.00008.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ammonia generated within the kidney is partitioned into a urinary fraction (the key buffer for net acid excretion) and an aliquot delivered to the systemic circulation. The physiology of this partitioning has yet to be examined in a kidney model, and that was undertaken in this work. This involves explicit representation of the cortical labyrinth, so that cortical interstitial solute concentrations are computed rather than assigned. A detailed representation of cortical vasculature has been avoided by making the assumption that solute concentrations within the interstitium and peritubular capillaries are likely to be identical and that there is little to no modification of venous composition as blood flows to the renal vein. The model medullary ray has also been revised to include a segment of proximal straight tubule, which supplies ammonia to this region. The principal finding of this work is that cortical labyrinth interstitial ammonia concentration is likely to be several fold higher than systemic arterial ammonia. This elevation of interstitial ammonia enhances ammonia secretion in both the proximal convoluted tubule and distal convoluted tubule, with uptake by Na+-K+-ATPases of both segments. Model prediction of urinary ammonia excretion was concordant with measured values, but at the expense of greater ammoniagenesis, with high rates of renal venous ammonia flux. This derives from a limited capability of the model medulla to replicate the high interstitial ammonia concentrations that are required to drive collecting duct ammonia secretion. Thus, renal medullary ammonia trapping appears key to diverting ammonia from the renal vein to urine, but capturing the underlying physiology remains a challenge.NEW & NOTEWORTHY This is the first mathematical model to estimate solute concentrations within the kidney cortex. The model predicts cortical ammonia to be several fold greater than in the systemic circulation. This higher concentration drives ammonia secretion in proximal and distal tubules. The model reveals a gap in our understanding of how ammonia generated within the cortex is channeled efficiently into the final urine.
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Affiliation(s)
- Alan M Weinstein
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York.,Department of Medicine, Weill Medical College of Cornell University, New York, New York
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2
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Zhou Y, Eid T, Hassel B, Danbolt NC. Novel aspects of glutamine synthetase in ammonia homeostasis. Neurochem Int 2020; 140:104809. [DOI: 10.1016/j.neuint.2020.104809] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Revised: 07/08/2020] [Accepted: 07/09/2020] [Indexed: 02/07/2023]
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Abstract
This article reviews hepatic encephalopathy (HE) in companion animals. Clinical signs and categories of hepatic disease likely to cause HE are discussed. Ammonia has a key role in pathogenesis and current concepts in body ammonia metabolism are reviewed. Inflammation and manganese accumulation are also thought to be important in pathogenesis. Treatment of HE in acute and chronic cases is discussed along with the rationale for current treatment recommendations. Potential avenues for new treatments and human treatments, which may be transferable to companion animals, are reviewed.
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Affiliation(s)
- Adam G Gow
- Hospital for Small Animals, Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush, Edinburgh EH25 9RG, Scotland.
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4
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Chandar J, Garcia J, Jorge L, Tekin A. Transplantation in autosomal recessive polycystic kidney disease: liver and/or kidney? Pediatr Nephrol 2015; 30:1233-42. [PMID: 25115876 DOI: 10.1007/s00467-014-2887-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 05/13/2014] [Accepted: 06/11/2014] [Indexed: 12/19/2022]
Abstract
Autosomal recessive polycystic kidney disease (ARPKD) is characterized by enlarged kidneys with dilated collecting ducts and congenital hepatic fibrosis. There is a variable rate of progression of kidney and liver disease. Portal hypertension and Caroli's disease occur from liver involvement that contributes to morbidity and mortality. Approximately 40 % of patients have a severe disease phenotype leading to rapid onset of end-stage kidney disease (ESKD) and signs of portal hypertension and the rest may have predominant involvement of either the kidney or liver. It is important for the physician to establish the extent of organ involvement before deciding on the ultimate plan of management, especially when transplantation is required. Isolated renal transplantation can be considered when liver involvement is minimal. If hepatobiliary disease is prominent, and kidney function is preserved, management options are based on individual characteristics. In the presence of significant liver disease and ESKD, consideration should be given to combined liver kidney transplantation, which can be beneficial in eliminating the consequences of both kidney and liver disease. However, this is a complex surgical procedure that needs to be performed at experienced transplant centers. Improvement in surgical techniques has considerably improved short-term graft survival with the added advantage of the liver offering immunologic protection to the kidney allograft.
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Affiliation(s)
- Jayanthi Chandar
- Department of Pediatrics, Division of Pediatric Nephrology, Holtz Children's Hospital, University of Miami Miller School of Medicine, PO Box 016960 (M-714), Miami, FL, 33101, USA,
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Abstract
Human adults produce around 1000 mmol of ammonia daily. Some is reutilized in biosynthesis. The remainder is waste and neurotoxic. Eventually most is excreted in urine as urea, together with ammonia used as a buffer. In extrahepatic tissues, ammonia is incorporated into nontoxic glutamine and released into blood. Large amounts are metabolized by the kidneys and small intestine. In the intestine, this yields ammonia, which is sequestered in portal blood and transported to the liver for ureagenesis, and citrulline, which is converted to arginine by the kidneys. The amazing developments in NMR imaging and spectroscopy and molecular biology have confirmed concepts derived from early studies in animals and cell cultures. The processes involved are exquisitely tuned. When they are faulty, ammonia accumulates. Severe acute hyperammonemia causes a rapidly progressive, often fatal, encephalopathy with brain edema. Chronic milder hyperammonemia causes a neuropsychiatric illness. Survivors of severe neonatal hyperammonemia have structural brain damage. Proposed explanations for brain edema are an increase in astrocyte osmolality, generally attributed to glutamine accumulation, and cytotoxic oxidative/nitrosative damage. However, ammonia neurotoxicity is multifactorial, with disturbances also in neurotransmitters, energy production, anaplerosis, cerebral blood flow, potassium, and sodium. Around 90% of hyperammonemic patients have liver disease. Inherited defects are rare. They are being recognized increasingly in adults. Deficiencies of urea cycle enzymes, citrin, and pyruvate carboxylase demonstrate the roles of isolated pathways in ammonia metabolism. Phenylbutyrate is used routinely to treat inherited urea cycle disorders, and its use for hepatic encephalopathy is under investigation.
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Affiliation(s)
- Valerie Walker
- Department of Clinical Biochemistry, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom.
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Cui X, Geffers L, Eichele G, Yan J. A computational approach to estimate interorgan metabolic transport in a mammal. PLoS One 2014; 9:e100963. [PMID: 24971892 PMCID: PMC4074118 DOI: 10.1371/journal.pone.0100963] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2014] [Accepted: 06/02/2014] [Indexed: 11/18/2022] Open
Abstract
In multicellular organisms metabolism is distributed across different organs, each of which has specific requirements to perform its own specialized task. But different organs also have to support the metabolic homeostasis of the organism as a whole by interorgan metabolite transport. Recent studies have successfully reconstructed global metabolic networks in tissues and cell types and attempts have been made to connect organs with interorgan metabolite transport. Instead of these complicated approaches to reconstruct global metabolic networks, we proposed in this study a novel approach to study interorgan metabolite transport focusing on transport processes mediated by solute carrier (Slc) transporters and their couplings to cognate enzymatic reactions. We developed a computational approach to identify and score potential interorgan metabolite transports based on the integration of metabolism and transports in different organs in the adult mouse from quantitative gene expression data. This allowed us to computationally estimate the connectivity between 17 mouse organs via metabolite transport. Finally, by applying our method to circadian metabolism, we showed that our approach can shed new light on the current understanding of interorgan metabolite transport at a whole-body level in mammals.
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Affiliation(s)
- Xiao Cui
- Functional Genomics Group, CAS-MPG Partner Institute for Computational Biology, Shanghai, China
| | - Lars Geffers
- Department of Genes and Behavior, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Gregor Eichele
- Department of Genes and Behavior, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Jun Yan
- Functional Genomics Group, CAS-MPG Partner Institute for Computational Biology, Shanghai, China
- * E-mail:
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7
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Affiliation(s)
- HJ Lee
- CT2 Core Medical Trainee, Southend University Hospital NHS Foundation Trust, Essex SS0 0RY
| | - N Halliday
- ST3 in Gastroenterology, Southend University Hospital NHS Foundation Trust, Essex SS0 0RY
| | - GP Bray
- Consultant Gastroenterologist and Hepatologist, Department of Gastroenterology, Southend University Hospital NHS Foundation Trust, Essex SS0 0RY
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8
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Sturgeon JP, Shawcross DL. Recent insights into the pathogenesis of hepatic encephalopathy and treatments. Expert Rev Gastroenterol Hepatol 2014; 8:83-100. [PMID: 24236755 DOI: 10.1586/17474124.2014.858598] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hepatic encephalopathy (HE) encompasses a spectrum of neuropsychiatric disorders related to liver failure. The development of HE can have a profound impact on mortality as well as quality of life for patients and carers. Ammonia is central in the disease process contributing to alteration in neurotransmission, oxidative stress, and cerebral edema and astrocyte swelling in acute liver failure. Inflammation in the presence of ammonia coactively worsens HE. Inflammation can result from hyperammonemic responses, endotoxemia, innate immune dysfunction or concurrent infection. This review summarizes the current processes implicated in the pathogenesis of HE, as well as current and potential treatments. Treatments currently focus on reducing inflammation and/or blood ammonia levels and provide varying degrees of success. Optimization of current treatments and initial testing of novel therapies will provide the basis of improvement of care in the near future.
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Affiliation(s)
- Jonathan P Sturgeon
- Institute of Liver Studies, King's College London School of Medicine at King's College Hospital, Denmark Hill, London, SE5 9RS, UK
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Mpabanzi L, van den Broek MAJ, Visschers RGJ, van de Poll MCG, Nadalin S, Saner FH, Dejong CHC, Malago M, Olde Damink SWM. Urinary ammonia excretion increases acutely during living donor liver transplantation. Liver Int 2011; 31:1150-4. [PMID: 21745291 DOI: 10.1111/j.1478-3231.2011.02544.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
INTRODUCTION Arterial ammonia concentrations increase acutely during the anhepatic phase of a liver transplantation (LTx) and return to baseline within 1 h after reperfusion of a functioning liver graft. So far, this return to baseline has solely been attributed to hepatic ammonia clearance. No data exist on the potential contribution of altered renal ammonia handling to peritransplantation ammonia homoeostasis. AIM The present study investigated the consequences of a hepatectomy and subsequent implantation of a partial liver graft on arterial ammonia concentrations and urinary ammonia excretion during a living donor liver transplantation (LDLTx). METHODS Patients with end-stage liver disease undergoing LDLTx were selected. Samples of arterial blood and urine were taken before, during and 2 h after the anhepatic phase. Differences were tested using Wilcoxon's test. Results are given as median and range. RESULTS Eleven adult patients undergoing an LDLTx were included. Before hepatectomy, arterial ammonia concentrations were 89 μM (40-156 μM), increasing to 146 μM (102-229 μM) (P<0.001) during the anhepatic phase and returning to 79 μM (46-111 μM) (P<0.01) after reperfusion. Urinary ammonia excretion was initially 1.06 mmol/h (0.02-6.00 mmol/h), increasing to 3.81 mmol/h (0.32-12.55 mmol/h) (P=0.004) during the anhepatic phase and further increasing to 4.00 mmol/h (0.79-9.51 mmol/h) (P=0.013) after reperfusion. CONCLUSION The kidney significantly increased urinary ammonia excretion during the anhepatic phase, which was sustained after reperfusion, contributing to the rapid decrease of ammonia concentrations. Accordingly, the plasma ammonia concentrations measured directly after LTx cannot simply be used as a read-out of initial liver graft function.
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Affiliation(s)
- Liliane Mpabanzi
- Department of Surgery, Maastricht University, Maastricht, the Netherlands
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10
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Jalan R, Olde Damink SWM, Ter Steege JC, Redhead DN, Lee A, Hayes PC, Deutz NEP. Acute endotoxemia following transjugular intrahepatic stent-shunt insertion is associated with systemic and cerebral vasodilatation with increased whole body nitric oxide production in critically ill cirrhotic patients. J Hepatol 2011; 54:265-71. [PMID: 21067839 DOI: 10.1016/j.jhep.2010.06.042] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 06/03/2010] [Accepted: 06/20/2010] [Indexed: 12/18/2022]
Abstract
BACKGROUND & AIMS Transjugular intrahepatic stent-shunt (TIPSS) insertion, in patients with uncontrolled gastro-intestinal bleeding, often results in worsening of the systemic hemodynamics which can be associated with intracranial hypertension but the underlying mechanisms are unclear. This study explored the hypothesis that TIPSS insertion results in acute endotoxemia which is associated with increased nitric oxide production resulting in systemic and cerebral vasodilatation. METHODS Twelve patients with cirrhosis who were undergoing TIPSS for uncontrolled variceal bleeding were studied prior to and 1-h after TIPSS insertion. Changes in cardiac output (CO) and cerebral blood flow (CBF) were measured. NO production was measured using stable isotopes using l-[guanidino-(15)N(2)] arginine and l-[ureido-(13)C;5,5-(2)H(2)] citrulline infusion. The effect of pre- and post-TIPSS plasma on nitric oxide synthase (NOS) activity on human endothelial cell-line (HUVEC) was measured. RESULTS TIPSS insertion resulted in a significant increase in CO and CBF. Endotoxin and induced neutrophil oxidative burst increased significantly without any significant changes in cytokines. Whole body NO production increased significantly and this was associated with increased iNOS activity in the HUVEC lines. The change in NO production correlated with the changes in CO and CBF. Brain flux of ammonia increased without significant changes in arterial ammonia. CONCLUSIONS In conclusion, the insertion of TIPSS results in acute endotoxemia which is associated with increased nitric oxide production possibly through an iNOS dependent mechanism which may have important pathophysiological and therapeutic relevance to understanding the basis of circulatory failure in the critically ill cirrhotic patient.
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Affiliation(s)
- R Jalan
- Liver Failure Group, UCL Hepatology, Upper Third Medical School, UCL Medical School, Rowland Hill Street, Royal Free Hospital, London NW3 2PF, UK.
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Wright G, Noiret L, Olde Damink SWM, Jalan R. Interorgan ammonia metabolism in liver failure: the basis of current and future therapies. Liver Int 2011; 31:163-75. [PMID: 20673233 DOI: 10.1111/j.1478-3231.2010.02302.x] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Hepatic encephalopathy complicates the course of both acute and chronic liver disease and its treatment remains an unmet clinical need. Ammonia is thought to be central in its pathogenesis and remains an important target of current and future therapeutic approaches. In liver failure, the main detoxification pathway of ammonia metabolism is compromised leading to hyperammonaemia. In this situation, the other ammonia-regulating pathways in multiple organs assume important significance. The present review focuses upon interorgan ammonia metabolism in health and disease describing the role of the key enzymes, glutamine synthase and glutaminase. Better understanding of these alternative pathways are leading to the development of new therapeutic approaches.
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Affiliation(s)
- Gavin Wright
- UCL Institute of Hepatology, Division of Medicine, University College London, London, UK
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12
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Guevara M, Baccaro ME, Ríos J, Martín-Llahí M, Uriz J, Ruiz del Arbol L, Planas R, Monescillo A, Guarner C, Crespo J, Bañares R, Arroyo V, Ginès P. Risk factors for hepatic encephalopathy in patients with cirrhosis and refractory ascites: relevance of serum sodium concentration. Liver Int 2010; 30:1137-42. [PMID: 20602681 DOI: 10.1111/j.1478-3231.2010.02293.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Hyponatraemia is common in patients with advanced cirrhosis and is associated with remarkable changes in brain cells, particularly a reduction in myoinositol and other intracellular organic osmolytes related to the hypo-osmolality of the extracellular fluid. It has been recently suggested that hyponatraemia may be an important factor associated with the development of overt hepatic encephalopathy (HE). To test this hypothesis, we retrospectively analysed the incidence and predictive factors of overt HE using a database of 70 patients with cirrhosis included in a prospective study comparing transjugular intrahepatic portosystemic shunts (TIPS) vs large-volume paracentesis in the management of refractory of ascites. Variables used in the analysis included age, sex, previous history of HE, treatment assignment (TIPS vs large volume paracentesis plus albumin), treatment with diuretics, serum bilirubin, serum creatinine and serum sodium concentration. Laboratory parameters were measured at entry, at 1 month and every 3 months during follow-up and at the time of development of HE in patients who developed this complication. During a mean follow-up of 10 months, 50 patients (71%) developed 117 episodes of HE. In the whole population of patients, the occurrence of HE was independently associated with serum hyponatraemia, serum bilirubin and serum creatinine. In conclusion, in patients with refractory ascites, the occurrence of HE is related to the impairment of liver and renal function and presence of hyponatraemia.
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Affiliation(s)
- Mónica Guevara
- Liver Unit Hospital Clínic, Universitat de Barcelona, Barcelona, Spain.
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Olde Damink SWM, Jalan R, Dejong CHC. Interorgan ammonia trafficking in liver disease. Metab Brain Dis 2009; 24:169-81. [PMID: 19067143 DOI: 10.1007/s11011-008-9122-5] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [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: 12/25/2022]
Abstract
Patients with liver disease have reduced urea synthesis capacity resulting in reduced capacity to detoxify ammonia in the liver. The contribution of the gut to the hyperammonemic state observed during liver failure is mainly due to portacaval shunting and not the result of changes in the metabolism of ammonia in the gut. Small intestinal synthesis of ammonia is related to amino acid breakdown, predominantly glutamine, whereas large bowel ammonia production is caused by bacterial breakdown of amino acids and urea. The kidneys produce ammonia but adapt to liver failure in experimental portacaval shunting by reducing ammonia release into the systemic circulation. The kidneys have the ability to switch from net ammonia production to net ammonia excretion. Data from recent studies in patients with cirrhosis of the liver show that the kidneys have a major role in post upper gastrointestinal bleeding hyperammonemia. During hyperammonemia muscle takes up ammonia and plays a major role in (temporarily) detoxifying ammonia to glutamine. Net uptake of ammonia by the brain occurs in patients and experimental animals with acute and chronic liver failure. Insight will be given in recent developments on ammonia lowering therapies which are based on the information of interorgan ammonia trafficking.
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Affiliation(s)
- Steven W M Olde Damink
- Department of Surgery, Maastricht University Medical Center, PO Box 5800, Maastricht, AZ, 6202 The Netherlands.
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Transjugular intrahepatic portosystemic shunts in hemodialysis-dependent patients and patients with advanced renal insufficiency: safety, caution, and encephalopathy. J Vasc Interv Radiol 2008; 19:516-20. [PMID: 18375295 DOI: 10.1016/j.jvir.2007.11.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Revised: 11/11/2007] [Accepted: 11/15/2007] [Indexed: 01/31/2023] Open
Abstract
PURPOSE To retrospectively determine the acute safety and chronic outcomes of transjugular intrahepatic portosystemic shunt (TIPS) creation in patients with hemodialysis-dependent end-stage renal disease for control of bleeding and refractory ascites. MATERIALS AND METHODS Four dialysis-dependent patients and one renal transplant recipient (glomerular filtration rate, 27 mL/min) underwent TIPS creation for treatment of refractory ascites (n = 3) and recurrent portal hypertensive bleeding (n = 1). A sixth patient developed unrelated renal failure 3 years after initial TIPS formation and presented with encephalopathy at that time. All had nearly normal liver function test results and no previous baseline encephalopathy. Three dialysis recipients underwent dialysis immediately after the TIPS procedure in an intensive care unit; one did not. RESULTS There were no complications of fluid overload or pulmonary edema after TIPS creation in the patients who immediately underwent dialysis. The one patient in whom dialysis was delayed developed respiratory failure and shock liver (ie, ischemic hepatitis). Ascites resolved in all three patients, and no recurrent variceal bleeding occurred during a mean follow-up of 17 months. Severe, grade 2-4 hepatic encephalopathy developed in all patients; in one patient, its onset was delayed until the onset of renal failure 3 years after the original TIPS procedure. Shunt reduction was required in four cases and competitive variceal embolization was required in one to reduce portosystemic diversion. No less than grade 1 episodic baseline encephalopathy was present in all patients despite continued use of the maximum prescribed medical therapy thereafter. CONCLUSIONS TIPS creation is effective in controlling ascites and bleeding in functionally anephric patients, but at the cost of marked and disproportionate hepatic encephalopathy. Prompt, acute postprocedural dialysis and fluid management is critical for safe creation of a TIPS in dialysis-dependent patients.
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Vissers YLJ, Debats IBJG, Luiking YC, Jalan R, van der Hulst RRWJ, Dejong CHC, Deutz NEP. Pros and cons of L-arginine supplementation in disease. Nutr Res Rev 2007; 17:193-210. [DOI: 10.1079/nrr200490] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The amino acid arginine and one of its metabolites NO have gathered broad attention in the last decade. Although arginine is regarded as a conditionally essential amino acid in disease, L-arginine supplementation in severe illness has not found its way into clinical practice. This might be due to the invalid interpretation of results from studies with immune-enhancing diets containing L-arginine amongst other pharmaconutrients. However, not much attention is given to research using L-arginine as a monotherapy and the possibility of the alternative hypothesis: that L-arginine supplementation is beneficial in disease. The present review will discuss data from studies in healthy and diseased animals and patients with monotherapy of L-arginine to come to an objective overview of positive and negative aspects of L-arginine supplementation in disease with special emphasis on sepsis, cancer, liver failure and wound healing.
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Abstract
OBJECTIVE Cognitive impairment is a common problem in patients with liver cirrhosis. Its pathogenesis is multifactorial and ammonia is considered to play a central role. Renal function has been shown to be important for ammonia metabolism in cirrhosis. Although renal dysfunction is common in cirrhotic patients, its effect on cognitive function is largely unexplored. MATERIAL AND METHODS A total of 128 consecutive cirrhotic patients were prospectively evaluated for the presence of cognitive dysfunction according to the West-Haven criteria and by means of two psychometric tests. Serum creatinine, sodium and potassium as well as plasma ammonia concentrations were assessed. Glomerular filtration rate was also measured by (51)Cr- EDTA clearance in a subgroup of patients. RESULTS Forty-one patients (32%) were found to have cognitive dysfunction (clinical evaluation and/or psychometric tests). Sixteen patients (13%) found with serum creatinine levels above reference values had cognitive dysfunction more frequently than patients with creatinine within the normal range (69% versus 31%; p = 0.001), but did not differ in aetiology or severity of cirrhosis (p >0.1). Patients with loop diuretics versus without did not differ in creatinine values (p >0.1). Multivariate analysis showed that cognitive dysfunction was related to hospital admission at inclusion in the study, international normalized ratio and serum creatinine (p <0.05 for all), but not to potassium or sodium levels. Plasma ammonia concentration was related to serum creatinine (r = 0.26, p = 0.004) and the glomerular filtration rate (r = -0.44, p = 0.023). CONCLUSIONS Renal dysfunction seems to be related to cognitive impairment in patients with liver cirrhosis and might be implicated in the pathogenesis of hepatic encephalopathy.
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Affiliation(s)
- Evangelos Kalaitzakis
- Section of Gastroenterology and Hepatology, Department of Internal Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden.
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17
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Dejong CHC, van de Poll MCG, Soeters PB, Jalan R, Olde Damink SWM. Aromatic amino acid metabolism during liver failure. J Nutr 2007; 137:1579S-1585S; discussion 1597S-1598S. [PMID: 17513430 DOI: 10.1093/jn/137.6.1579s] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Liver failure is associated with hepatic encephalopathy (HE). An imbalance in plasma levels of aromatic amino acids (AAA) phenylalanine, tyrosine, and tryptophan and branched chain amino acids (BCAA) and their BCAA/AAA ratio has been suggested to play a causal role in HE by enhanced brain AAA uptake and subsequently disturbed neurotransmission. Until recently, data on this subject and the role of the liver and splanchnic bed were scarce, particularly in humans, due to inaccessibility of portal and hepatic veins. Here, we discuss, against a background of relevant literature, data obtained in patients undergoing liver resection or with a transjugular intrahepatic portasystemic stent shunt (TIPSS), where these veins are accessible. The BCAA/AAA ratio remained unchanged after major liver resection, but plasma AAA levels were inversely correlated (P < 0.001) with residual liver volume, in keeping with the observed hepatic AAA uptake. In patients with stable cirrhosis and a TIPSS, the plasma BCAA/AAA ratio was lower than in controls (1.19 +/- 0.09 vs. controls: 3.63 +/- 0.34). Gastrointestinal bleeding in cirrhotics with a TIPSS induced disturbances in BCAA levels and the BCAA/AAA ratio and induced catabolism, which could partly be corrected by isoleucine administration. AAA may be important in the pathogenesis of HE, but it is unlikely that they are the sole factors. HE most likely is a syndrome with multifactorial pathogenesis, where hyperammonemia, AAA/BCAA imbalances, inflammation, brain edema, and neurotransmitter changes interact. Novel therapies to normalize AAA levels in patients with liver failure (such as the molecular adsorbent recirculating system dialysis device) should probably be combined with supplementation of e.g. isoleucine and enhancing ammonia excretion by the kidneys.
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Affiliation(s)
- Cornelis H C Dejong
- Department of Surgery, Nutrition and Toxicology Institute Maastricht, Maastricht University, the Netherlands.
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18
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Olde Damink SWM, Dejong CHC, Deutz NEP, Redhead DN, Hayes PC, Soeters PB, Jalan R. Kidney plays a major role in ammonia homeostasis after portasystemic shunting in patients with cirrhosis. Am J Physiol Gastrointest Liver Physiol 2006; 291:G189-94. [PMID: 16455791 DOI: 10.1152/ajpgi.00165.2005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The kidney plays an important role in ammonia metabolism. In this study the hypothesis was tested that the kidney can acutely diminish ammonia release after portacaval shunting. Thirteen patients with cirrhosis (6 female/7 male, age 54.4 +/- 3.3 yr) were studied. Blood was sampled prior to and 1 h after transjugular intrahepatic stent-shunt (TIPSS) insertion from the portal vein, a hepatic vein, the right renal vein, and the femoral vein, and renal and liver plasma flow were measured. Prior to TIPSS, renal ammonia release was significantly higher than ammonia release from the splanchnic region, which was not significantly different from zero. TIPSS insertion did not change arterial ammonia concentration or ammonia release from the splanchnic region but reduced renal ammonia release into the circulation (P < 0.05) to values that were not different from zero. TIPSS resulted in a tendency toward increased venous-arterial ammonia concentration differences across leg muscle. Post-TIPSS ammonia efflux via portasystemic shunts was estimated to be seven times higher than renal efflux. Kidneys have the ability to acutely diminish systemic ammonia release after portacaval shunting. Diminished renal ammonia release and enhanced muscle ammonia uptake are important mechanisms by which the cirrhotic patient maintains ammonia homeostasis after portasystemic shunting.
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van de Poll MCG, Soeters PB, Deutz NEP, Fearon KCH, Dejong CHC. Renal metabolism of amino acids: its role in interorgan amino acid exchange. Am J Clin Nutr 2004; 79:185-97. [PMID: 14749222 DOI: 10.1093/ajcn/79.2.185] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The kidneys play a role in the synthesis and interorgan exchange of several amino acids. The quantitative importance of renal amino acid metabolism in the body is not, however, clear. We review here the role of the kidney in the interorgan exchange of amino acids, with emphasis on quantitative aspects. We reviewed relevant literature by using a computerized literature search (PubMed) and checking relevant references from the identified articles. Our own data are discussed in the context of the literature. The kidney takes up glutamine and metabolizes it to ammonia. This process is sensitive to pH and serves to maintain acid-base homeostasis and to excrete nitrogen. In this way, the metabolism of renal glutamine and ammonia is complementary to hepatic urea synthesis. Citrulline, derived from intestinal glutamine breakdown, is converted to arginine by the kidney. Renal phenylalanine uptake is followed by stoichiometric tyrosine release, and glycine uptake is accompanied by serine release. Certain administered oligopeptides (eg, glutamine dipeptides) are converted by the kidneys to their constituent components before they can be used in metabolic processes. The kidneys play an important role in the interorgan exchange of amino acids. Quantitatively, for several important amino acids, the kidneys are as important as the gut in intermediary metabolism. The kidneys may be crucial "mediators" of the beneficial effects of specialized, disease-specific feeding solutions such as those enriched in glutamine dipeptides.
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Olde Damink SWM, Jalan R, Redhead DN, Hayes PC, Deutz NEP, Soeters PB. Interorgan ammonia and amino acid metabolism in metabolically stable patients with cirrhosis and a TIPSS. Hepatology 2002; 36:1163-71. [PMID: 12395326 DOI: 10.1053/jhep.2002.36497] [Citation(s) in RCA: 149] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ammonia is central to the pathogenesis of hepatic encephalopathy. This study was designed to determine the quantitative dynamics of ammonia metabolism in patients with cirrhosis and previous treatment with a transjugular intrahepatic portosystemic stent shunt (TIPSS). We studied 24 patients with cirrhosis who underwent TIPSS portography. Blood was sampled and blood flows were measured across portal drained viscera, leg, kidney, and liver, and arteriovenous differences across the spleen and the inferior and superior mesenteric veins. The highest amount of ammonia was produced by the portal drained viscera. The kidneys also produced ammonia in amounts that equaled total hepatosplanchnic area production. Skeletal muscle removed more ammonia than the cirrhotic liver. The amount of nitrogen that was taken up by muscle in the form of ammonia was less than the glutamine that was released. The portal drained viscera consumed glutamine and produced ammonia, alanine, and citrulline. Urea was released in the splenic and superior mesenteric vein, contributing to whole-body ureagenesis in these cirrhotic patients. In conclusion, hyperammonemia in metabolically stable, overnight-fasted patients with cirrhosis of the liver and a TIPSS results from portosystemic shunting and renal ammonia production. Skeletal muscle removes more ammonia from the circulation than the cirrhotic liver. Muscle releases excessive amounts of the nontoxic nitrogen carrier glutamine, which can lead to ammonia production in the portal drained viscera (PDV) and kidneys. Urinary ammonia excretion and urea synthesis appear to be the only way to remove ammonia from the body.
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Olde Damink SWM, Deutz NEP, Dejong CHC, Soeters PB, Jalan R. Interorgan ammonia metabolism in liver failure. Neurochem Int 2002; 41:177-88. [PMID: 12020618 DOI: 10.1016/s0197-0186(02)00040-2] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
In the post-absorptive state, ammonia is produced in equal amounts in the small and large bowel. Small intestinal synthesis of ammonia is related to amino acid breakdown, whereas large bowel ammonia production is caused by bacterial breakdown of amino acids and urea. The contribution of the gut to the hyperammonemic state observed during liver failure is mainly due to portacaval shunting and not the result of changes in the metabolism of ammonia in the gut. Patients with liver disease have reduced urea synthesis capacity and reduced peri-venous glutamine synthesis capacity, resulting in reduced capacity to detoxify ammonia in the liver. The kidneys produce ammonia but adapt to liver failure in experimental portacaval shunting by reducing ammonia release into the systemic circulation. The kidneys have the ability to switch from net ammonia production to net ammonia excretion, which is beneficial for the hyperammonemic patient. Data in experimental animals suggest that the kidneys could have a major role in post-feeding and post-haemorrhagic hyperammonemia.During hyperammonemia, muscle takes up ammonia and plays a major role in (temporarily) detoxifying ammonia to glutamine. Net uptake of ammonia by the brain occurs in patients and experimental animals with acute and chronic liver failure. Concomitant release of glutamine has been demonstrated in experimental animals, together with large increases of the cerebral cortex ammonia and glutamine concentrations. In this review we will discuss interorgan trafficking of ammonia during acute and chronic liver failure. Interorgan glutamine metabolism is also briefly discussed, since glutamine synthesis from glutamate and ammonia is an important alternative pathway of ammonia detoxification. The main ammonia producing organs are the intestines and the kidneys, whereas the major ammonia consuming organs are the liver and the muscle.
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Chakrabarti P, Zullo A, Hassan C, Pandit A, Chowdhury A, Santra A, Hazra B, Morini S, Roy T. Helicobacter pylori, gastric juice, and arterial ammonia levels in patients with cirrhosis. J Clin Gastroenterol 2002; 34:578-81. [PMID: 11960074 DOI: 10.1097/00004836-200205000-00020] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Helicobacter pylori urease activity is a potential source of ammonia in the stomach of patients with cirrhosis. However, the possible role of H. pylori in the pathogenesis of hepatic encephalopathy deserves further investigations. The current study evaluates the relationship among H. pylori infection, gastric juice ammonia concentrations, and arterial ammonia levels in patients with cirrhosis. Overall, 14 patients with cirrhosis with overt hepatic encephalopathy, 19 with subclinical hepatic encephalopathy, and 13 without encephalopathy were enrolled. All patients underwent upper endoscopy, and gastric biopsy specimens were taken for H. pylori assessment (rapid urease test, histology, and culture). A gastric juice sample and an arterial blood sample were obtained for ammonia level assessment. Patients with overt encephalopathy had both higher arterial ammonia levels and a more severe hepatic impairment than the remaining patients, whereas gastric juice ammonia concentrations did not differ among the three groups. H. pylori prevalence was similar among groups. Patients with H. pylori infection had significantly higher gastric juice ammonia concentrations than those without infection (2.3 +/- 1.3 vs. 0.9 +/- 0.6 mmol/L, respectively; p = 0.003); however, no difference in arterial ammonia levels emerged between the two groups (37.7 +/- 18.6 vs. 37.6 +/- 18.8 micromol/L, respectively). No significant correlation was found between gastric juice ammonia concentrations and arterial ammonia levels. The data suggest that liver impairment remains crucial in ammonia disposal in patients with cirrhosis, whereas H. pylori infection does not seem to play a major role in the pathogenesis of hyperammonemia in these patients.
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Affiliation(s)
- Prantar Chakrabarti
- Department of Medicine, Institute of Post Graduate Medical Education and Research, Calcutta, India
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Hallemeesch MM, Cobben DC, Dejong CH, Soeters PB, Deutz NE. Renal amino acid metabolism during endotoxemia in the rat. J Surg Res 2000; 92:193-200. [PMID: 10896821 DOI: 10.1006/jsre.2000.5867] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND The kidney has an important function in the exchange of nitrogenous metabolites. Glutamine is the most important substrate for renal ammoniagenesis and thus plays a crucial role in acid-base homeostasis. Furthermore, the kidney is the main endogenous source for de novo arginine production from citrulline, which in turn is derived from intestinal glutamine metabolism. Sepsis is a condition in which glutamine availability is reduced, whereas the need for arginine biosynthesis may be increased. Limited bioavailability of glutamine may affect arginine synthesis, which may have consequences for nitric oxide (NO) synthesis. Therefore, we studied renal glutamine and arginine metabolism in a rat model of endotoxemia and related this to NO metabolism. MATERIALS AND METHODS Rats were subject to double hit endotoxemia, and control rats received 0.9% NaCl. Renal blood flow was measured using para-aminohippuric acid. Concentrations of plasma amino acids and nitrate were measured in the aorta and renal vein to calculate net renal uptake or release of amino acids and address NO production. RESULTS The arterial concentrations of glutamine and ammonia were not changed in endotoxemic rats. Although renal glutamine uptake was reduced, total renal ammonia production was not changed during endotoxemia. The arterial concentration of citrulline and renal citrulline uptake was not altered in endotoxin-treated rats, but renal arginine production was increased. However, no effect was observed on nitric oxide production. CONCLUSIONS Although the kidney has very important functions in the excretion of waste products and in interorgan metabolism, this study suggests that the kidney has a limited role in glutamine, arginine, and NO metabolism during late endotoxemia in rats.
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Affiliation(s)
- M M Hallemeesch
- Department of Surgery, Maastricht University, Maastricht, The Netherlands
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Hallemeesch MM, Soeters PB, Deutz NE. Tracer methodology in whole body and organ balance metabolic studies: plasma sampling is required. A study in post-absorptive rats using isotopically labeled arginine, phenylalanine, valine and leucine. Clin Nutr 2000; 19:157-63. [PMID: 10895105 DOI: 10.1054/clnu.1999.0116] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
BACKGROUND AND AIMS Radioactive and stable amino acid isotopes are frequently used in metabolic research. Blood cells contain amino acid transporters, which may influence tracer distribution in blood. The aim of this study was to determine whether plasma or whole blood specific activity or enrichment of amino acid tracers should be used in the calculation of whole body and organ production rates. METHODS Seven male Wistar rats were infused with L-[2,3-(3)H]-Arginine, L-[2, 6-(3)H]-Phenylalanine, L-[3,4-(3)H]-Valine, and [L-[4,5-(3)H]-Leucine. Whole body and portal drained visceral, hepatic and renal production rates of arginine, phenylalanine, valine and leucine were determined in plasma and in whole blood. RESULTS Amino acid tracers that equilibrate well between plasma and blood cells (for instance phenylalanine, valine and leucine) yield similar whole body production rates when whole blood or plasma is sampled. Also, organ production rates measured using these amino acid tracers are consistent. However, a discrepancy exists between the whole body production rate and the sum of PDV, hepatic and renal production rates. When tracers are used that do not equilibrate well between plasma and blood cells (for instance arginine) the use of whole blood specific activity in the calculations yield overestimations of whole body and organ production rates. CONCLUSION From our data we recommend plasma sampling and strongly advise against whole blood sampling in metabolic organ balance studies in which amino acid tracers are used.
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Affiliation(s)
- M M Hallemeesch
- Department of Surgery, Maastricht University, Maastricht, The Netherlands
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Abstract
BACKGROUND/AIMS The intake of dietary protein has been associated with increased arterial ammonia levels. However, the origin of this rise in ammonia levels is unknown. This study was designed to examine whether this increase is caused by ammonia formed by the gut escaping hepatic clearance, or ammonia formed by the kidney and subsequently released into the circulation. METHODS Splanchnic and renal fluxes of ammonia and amino acids were studied in 10 pigs that were fed in a randomized cross-over design with a protein meal (n = 8), a meal with an equimolar amount of free amino acids (n = 8) or an iso-osmolar NaCl solution (n = 6). RESULTS After the protein meal, and less pronounced after the amino acid meal, arterial ammonia levels increased from approximately 25 to 75 micromol/l. Arterial pH changes and splanchnic ammonia release were negligible. The renal vein ammonia efflux increased after the protein meal (0.67+/-0.10 to 1.94+/-0.35 micromol/kg bw/min) and to a lesser degree after the amino acid meal (to 1.20+/-0.39 micromol/kg bw/ min). Renal uptake of alanine, and not glutamine, increased stoichiometrically, paralleling the enhanced renal vein ammonia efflux. CONCLUSIONS Arterial ammonia increases after a meal in pigs, coinciding with a negligible splanchnic ammonia release, but increased renal vein ammonia efflux. Thus, post-prandial plasma ammonia levels appear to be mainly related to renal ammoniagenesis. Alanine appears to be the main precursor for this renal ammoniagenesis in the pig.
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Affiliation(s)
- C F Welters
- Department of Surgery, Catharina Hospital, Eindhoven, The Netherlands
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Zullo A, Rinaldi V, Meddi P, Hassan C, Winn S, Attili AF. Helicobacter pylori infection, plasma ammonia levels, and psychometric testing in cirrhotic patients. Am J Gastroenterol 1999; 94:2214-8. [PMID: 10445552 DOI: 10.1111/j.1572-0241.1999.01295.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
OBJECTIVE The role of Helicobacter pylori (H. pylori) infection as a cause of hepatic encephalopathy is still debated. This study focused on the relationship between H. pylori, plasma ammonia levels, and intellectual function in cirrhotic patients. METHODS Forty-seven cirrhotics with latent or mild hepatic encephalopathy were enrolled in the study, upon H. pylori assessment at endoscopy. Plasma ammonia level determinations and psychometric testing were performed at entry in all patients. Patients with H. pylori infection received a 2-wk standard dual therapy and bacterial eradication was assessed at endoscopy 6-8 wk later. On this occasion, plasma ammonia levels and psychometric assessments were repeated. Patients without H. pylori infection at entry were also studied after 6-8 wk for ammonia level assessment and psychometric testing, as a control group. Patients receiving lactulose therapy and those without therapy were grouped separately for statistical analysis. RESULTS Among 21 patients without lactulose therapy (group A), basal plasma ammonia levels and psychometric testing scores did not significantly differ between 13 infected and eight uninfected patients. Similarly, among 26 patients undergoing lactulose therapy (group B), basal plasma ammonia concentration and psychometric testing scores did not significantly differ between 13 infected and 13 uninfected patients. Moreover, in group B, both the prevalence of previous overt hepatic encephalopathy episodes and the mean daily dose of lactulose therapy were similar between infected and uninfected patients. In addition, no significant reduction in the plasma ammonia concentrations and in psychometric testing scores emerged in both groups A and B after bacterial eradication. CONCLUSIONS This study failed to find a relationship between H. pylori, plasma ammonia levels, and psychometric testing scores in cirrhotic patients with latent or mild hepatic encephalopathy.
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Affiliation(s)
- A Zullo
- Department of Clinical Medicine, Gastroenterology II, La Sapienza University, Rome, Italy
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van der Hulst RR, von Meyenfeldt MF, Deutz NE, Soeters PB. Glutamine extraction by the gut is reduced in depleted [corrected] patients with gastrointestinal cancer. Ann Surg 1997; 225:112-21. [PMID: 8998127 PMCID: PMC1190613 DOI: 10.1097/00000658-199701000-00013] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE AND SUMMARY BACKGROUND DATA Glutamine is an important fuel for the intestinal mucosa. However, glutamine pools may become depleted in the cancer-bearing host as a result of tumor consumption and diminished production due to nutritional depletion. As human data are lacking, the authors investigated glutamine extraction by different sites of the human intestine, including tumor and the potential relation with the degree of nutritional depletion. METHODS Thirty-two patients with gastrointestinal malignancies were studied. Blood from an artery and veins draining jejunum, ileum, colon, or tumor were sampled. Depletion was estimated by the percentage ideal body weight. RESULTS Fractional glutamine extraction rate in the jejunum was 24%, three times higher than in ileum and colon. Percentage ideal body weight correlated with arterial glutamine levels (r = 0.5275, p = 0.003). In addition, arterial glutamine concentrations were correlated with extraction in the ileum (r = -0.8411, p < 0.001). Colon-containing tumor did not extract more glutamine than did nontumor-containing colon. CONCLUSIONS Glutamine is a quantitatively more important substrate for the proximal intestine than for the distal gut. Nutritional depletion results in decreased arterial glutamine concentration, which in turn results in diminished extraction. Colon cancer does not function as a glutamine trap and does not contribute to glutamine depletion.
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Affiliation(s)
- R R van der Hulst
- Department of Surgery, University Hospital Maastricht, Maastricht, The Netherlands
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Dejong CH, Deutz NE, Soeters PB. Ammonia and glutamine metabolism during liver insufficiency: the role of kidney and brain in interorgan nitrogen exchange. SCANDINAVIAN JOURNAL OF GASTROENTEROLOGY. SUPPLEMENT 1996; 218:61-77. [PMID: 8865453 DOI: 10.3109/00365529609094733] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND During liver failure, urea synthesis capacity is impaired. In this situation the most important alternative pathway for ammonia detoxification is the formation of glutamine from ammonia and glutamate. Information is lacking about the quantitative and qualitative role of kidney and brain in ammonia detoxification during liver failure. METHODS This review is based on own experiments considered against literature data. RESULTS AND CONCLUSIONS Brain detoxifies ammonia during liver failure by ammonia uptake from the blood, glutamine synthesis and subsequent glutamine release into the blood. Although quantitatively unimportant, this may be qualitatively important, because it may influence metabolic and/or neurotransmitter glutamate concentrations. The kidney plays an important role in adaptation to hyperammonaemia by reversing the ratio of ammonia excreted in the urine versus ammonia released into the blood from 0.5 to 2. Thus, the kidney changes into an organ that netto removes ammonia from the body as opposed to the normal situation in which it adds ammonia to the body pools.
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Affiliation(s)
- C H Dejong
- Dept. of Surgery, University Hospital Maastricht, The Netherlands
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Nomura F, Ohnishi K, Terabayashi H, Nakai T, Isobe K, Takekoshi K, Okuda K. Effect of intrahepatic portal-systemic shunting on hepatic ammonia extraction in patients with cirrhosis. Hepatology 1994; 20:1478-81. [PMID: 7982647 DOI: 10.1002/hep.1840200616] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Increased plasma ammonia levels in patients with advanced cirrhosis have been attributed to reduced conversion of enteric ammonia to urea by the diseased liver and to entry of enteric ammonia into systemic circulation by way of portal-systemic shunts. Because single-pass extraction is high for portal venous ammonia, reduction of portal blood supply to hepatocytes may have detrimental effects on the hepatic extraction of ammonia. To assess how the development of intrahepatic portal-systemic shunts alters hepatic ammonia metabolism, we determined portal and hepatic venous ammonia levels along with measurements of intrahepatic portal-systemic shunts using 99mTc-macroaggregated albumin in 46 patients with portal hypertension. Hepatic venous ammonia levels in the groups of patients with idiopathic portal hypertension, Child class A cirrhosis and Child class B or C cirrhosis were 36 +/- 17, 75 +/- 26 and 93 +/- 52 micrograms/dl, respectively, in increasing order, and portal venous ammonia extraction rates as calculated with the equation (portal venous ammonia-hepatic venous ammonia)/portal venous ammonia x 100% were decreased in the same order (77% +/- 14%, 50% +/- 21%, 40% +/- 25%, respectively). Furthermore, we noted a significant negative correlation between the intrahepatic shunt indexes as calculated by counts per minute in lungs/counts per minute in lungs and liver x 100% and the ammonia extraction rates. It was noteworthy that among Child class C patients, the ammonia extraction rates were significantly lower in patients with high intrahepatic shunt indexes than in those with low shunt indexes. These results demonstrate a significant direct relationship between hepatic ammonia extraction rates and intrahepatic shunting in cirrhosis.
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Affiliation(s)
- F Nomura
- Department of Clinical Pathology, Tsukuba University, Ibaraki, Japan
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Abstract
The aim of this study was to investigate the role of skeletal muscle in ammonia and glutamine metabolism during chronic hyperammonemia induced by liver insufficiency. The hindquarter ammonia and amino acid fluxes and muscle tissue concentrations were studied in two rat models of chronic liver insufficiency, portacaval shunting and portacaval shunting plus bile-duct ligation, as well as in sham-operated animals, 7 and 14 days after surgery, and in normal, unoperated rats. To reduce nutritional influences, portacaval-shunted rats and sham-operated rats were pair-fed to portacaval shunt biliary obstruction rats. Arterial ammonia levels were elevated in both liver insufficiency groups. In the portacaval shunting plus bile-duct ligation group, arterial glutamine levels were elevated compared with sham-operated controls. No net hind-quarter ammonia uptake was observed in any of the groups, despite hyperammonemia in the chronic liver insufficiency groups. Hindquarter glutamine release was always increased in the liver insufficiency groups compared with sham-operated controls, despite similar muscle glutamine levels in the sham-operated and hyperammonemic groups, suggesting enhanced muscle glutamine synthesis in the latter groups. Muscle ammonia levels were always increased and muscle glutamate decreased in the hyperammonemic groups, probably indicating glutamate consumption by enhanced glutamine synthesis. The increased phenylalanine tissue concentrations and efflux in portacaval shunt/biliary obstruction rats suggest that enhanced net muscle protein breakdown, amino acid catabolism and transamination, rather than ammonia uptake from the blood furnish amino acids and ammonia for enhanced glutamine synthesis. These experiments suggest that nutritional factors are important in explaining altered muscle metabolism during chronic liver insufficiency.
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Affiliation(s)
- C H Dejong
- Department of Surgery, University of Limburg, Maastricht, The Netherlands
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Heeneman S, Dejong CH, Deutz NE. Effects of methionine sulphoximine treatment on renal amino acid and ammonia metabolism in rats. Pflugers Arch 1994; 427:524-32. [PMID: 7971151 DOI: 10.1007/bf00374270] [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: 01/28/2023]
Abstract
Renal glutamine metabolism in relation to ammoniagenesis has been extensively studied during chronic metabolic acidosis, when arterial glutamine levels are reduced. However, little is known about the effects of reduced glutamine delivery on renal glutamine and ammonia metabolism at physiological systemic pH values. Therefore, a model of decreased arterial glutamine concentrations at normal pH values was developed using methionine sulphoximine (MSO). Renal glutamine and ammonia metabolism was measured by determining fluxes and intracellular concentrations after an overnight fast in ether anaesthetized normal rats, MSO-treated rats and their pair-fed controls. Moreover, fluxes and intracellular concentrations of several other amino acids were determined concomitantly. After 2 and 4 days of MSO treatment, arterial glutamine concentrations were reduced to 55%, while arterial ammonia concentrations increased by 70%. Kidney glutamine uptake reduced, but systemic pH was unchanged. Fractional extraction of glutamine remained unchanged, suggesting that also in vivo net uptake of glutamine by the kidney at subnormal levels is related to arterial glutamine concentrations. As a result, at day 2 but not at day 4, the kidney reduced the net release of ammonia into the renal vein and thus reduced net renal ammonia addition to body ammonia pools. Therefore at day 2, the kidney seems to play an important role in adaptation to both hyperammonaemia and hypoglutaminaemia.
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Affiliation(s)
- S Heeneman
- Department of Surgery, University of Limburg, Maastricht, The Netherlands
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