NCube/papyrus huggingface dataset:
Limited capacity for ammonia removal by brain in chronic liver failure: potential role of nitric oxide

Chronic liver failure leads to hyperammonemia and consequently increased brain ammonia concentrations, resulting in hepatic encephalopathy. When the liver fails to regulate ammonia concentrations, the brain, devoid of a urea cycle, relies solely on the amidation of glutamate to glutamine through glutamine synthetase, to efficiently clear ammonia. Surprisingly, under hyperammonemic conditions, the brain is not capable of increasing its capacity to remove ammonia, which even decreases in some regions of the brain. This non-induction of glutamine synthetase in astrocytes could result from possible limiting substrates or cofactors for the enzyme, or an indirect effect of ammonia on glutamine synthetase expression. In addition, there is evidence that nitration of the enzyme resulting from exposure to nitric oxide could also be implicated. The present review summarizes these possible factors involved in limiting the increase in capacity of glutamine synthetase in brain, in chronic liver failure.

Keyphrases: Ammonia, Ammoniac, Chronic liver failure, Glutamate-ammonia ligase, Glutamine synthetase, Hepatic encephalopathy, Maladie du foie en phase terminale, Monoxyde d'azote, Nitric oxide
Increase brain lactate in hepatic encephalopathy: Cause or consequence?

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome which develops as a result of liver failure or disease. Increased concentrations of brain lactate (microdialysate, cerebrospinal fluid, tissue) are commonly measured in patients with HE induced by either acute or chronic liver failure. Whether an increase in brain lactate is a cause or a consequence of HE remains undetermined. A rise in cerebral lactate may occur due to (1) blood-borne lactate (hyperlactataemia) crossing the blood-brain barrier, (2) increased glycolysis due to energy failure or impairment and (3) increased lactate production/release or decreased lactate utilization/uptake. This review explores the different reasons for lactate accumulation in the brain during liver failure and describes the possible roles of lactate in the pathogenesis of HE.

Keyphrases: Acide lactique, Encéphalopathie hépatique, Hepatic encephalopathy, Lactate
Acute insult of ammonia leads to calcium-dependent glutamate release from cultured astrocytes, an effect of pH

Hyperammonemia is a key factor in the pathogenesis of hepatic encephalopathy (HE) as well as other metabolic encephalopathies, such as those associated with inherited disorders of urea cycle enzymes and in Reye's syndrome. Acute HE results in increased brain ammonia (up to 5 mM), astrocytic swelling, and altered glutamatergic function. In the present study, using fluorescence imaging techniques, acute exposure (10 min) of ammonia (NH4+/NH3) to cultured astrocytes resulted in a concentration-dependent, transient increase in [Ca2+]i. This calcium transient was due to release from intracellular calcium stores, since the response was thapsigargin-sensitive and was still observed in calcium-free buffer. Using an enzyme-linked fluorescence assay, glutamate release was measured indirectly via the production of NADH (a naturally fluorescent product when excited with UV light). NH4+/NH3 (5 mM) stimulated a calcium-dependent glutamate release from cultured astrocytes, which was inhibited after preincubation with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester but unaffected after preincubation with glutamate transport inhibitors dihydrokainate and DL-threo-beta-benzyloxyaspartate. NH4+/NH3 (5 mM) also induced a transient intracellular alkaline shift. To investigate whether the effects of NH4+/NH3 were mediated by an increase in pH(i), we applied trimethylamine (TMA+/TMA) as another weak base. TMA+/TMA (5 mM) induced a similar transient increase in both pH(i) and [Ca2+]i (mobilization from intracellular calcium stores) and resulted in calcium-dependent release of glutamate. These results indicate that an acute exposure to ammonia, resulting in cytosolic alkalinization, leads to calcium-dependent glutamate release from astrocytes. A deregulation of glutamate release from astrocytes by ammonia could contribute to glutamate dysfunction consistently observed in acute HE.

Keyphrases: Acide glutamique, Ammonia, Ammoniac, Astrocytes, Calcium, Glutamate
Manganese deposition in basal ganglia structures results from both portal-systemic shunting and liver dysfunction

BACKGROUND & AIMS: Manganese (Mn) deposition could be responsible for the T(1)-weighted magnetic resonance signal hyperintensities observed in cirrhotic patients. These experiments were designed to assess the regional specificity of the Mn increases as well as their relationship to portal-systemic shunting or hepatobiliary dysfunction. METHODS: Mn concentrations were measured in (1) brain samples from basal ganglia structures (pallidum, putamen, caudate nucleus) and cerebral cortical structures (frontal, occipital cortex) obtained at autopsy from 12 cirrhotic patients who died in hepatic coma and from 12 matched controls; and from (2) brain samples (caudate/putamen, globus pallidus, frontal cortex) from groups (n = 8) of rats either with end-to-side portacaval anastomosis, with biliary cirrhosis, or with fulminant hepatic failure as well as from sham-operated and normal rats. RESULTS: Mn content was significantly increased in frontal cortex (by 38\%), occipital cortex (by 55\%), pallidum (by 186\%), putamen (by 66\%), and caudate (by 54\%) of cirrhotic patients compared with controls. Brain Mn content did not correlate with patient age, etiology of cirrhosis, or history of chronic hepatic encephalopathy. In cirrhotic and portacaval-shunted rats, Mn content was increased in pallidum (by 27\% and 57\%, respectively) and in caudate/putamen (by 57\% and 67\%, respectively) compared with control groups. Mn concentration in pallidum was significantly higher in portacaval-shunted rats than in cirrhotic rats. No significant changes in brain Mn concentrations were observed in rats with acute liver failure. CONCLUSIONS: These findings suggest that brain Mn deposition results both from portal-systemic shunting and from liver dysfunction.

Keyphrases: Anastomose chirurgicale portosystémique, Basal ganglia, Cirrhosis, Encéphalopathie hépatique, Fibrose, Hepatic encephalopathy, Imagerie par résonance magnétique, Manganese, Manganèse, Magnetic resonance imaging, Noyaux gris centraux, Portal-systemic shunting
Nothing New (Ethically) Under the Sun: Policy & Clinical
Implications of Nanomedicine

La recherche en nanotechnologie commence à recevoir une attention croissante dans les médias et la littérature de vulgarisation scientifique, mais les discussions sur les espoirs et les craintes concernant les nanotechnologies sont déjà polarisées par des visions utopiques et dystopiques. Par ailleurs, certaines discussions plus modérées se concentrent sur les applications à court terme des nanotechnologies, ainsi que sur leurs avantages et désavantages potentiels. Cependant, en explorant les implications sociales et éthiques des nanotechnologies (ou la nanomédecine, le but du présent document), d'importantes leçons devraient être tirées des expériences dans d'autres domaines. En particulier, les études sur les enjeux éthiques, légaux et sociaux (ELSI) de la recherche en génétique ont réussi à cartographier un grand nombre des questions (et des réponses sociales et politiques) qui se posent lorsque de nouvelles technologies sont déployées. Nous soutenons que, pour la plupart, les questions éthiques et sociales qui se posent dans la nanomédecine ne sont pas tout à fait nouvelles et ne nécessitent donc pas de nouveaux principes ou  cadres éthiques, ni un investissement massif dans la recherche « NELSI ». Au lieu de cela, nous avons besoin d'un soutien pour le développement d’une culture de l'éthique parmi les scientifiques et les cliniciens, des connaisances de base en science et médicine pour les bioéthiciens et une compétence sociale pour les citoyens pour qu’ils peut participer activement aux débats sur les répercussions des nouvelles technologies en général. Nanotechnology research is beginning to see widespread coverage in the media and popular science literatures, but discussions of hopes and fears about nanotechnology have already become polarised into utopian and dystopian visions. More moderate discussions focus on the near-term applications of nanotechnologies, and on potential benefits and harms. However, in exploring the social and ethical implications of nanotechnology (or nanomedicine, the focus of this paper), important lessons should be learned from experiences in other fields. In particular, studies of the ethical, legal, and social issues (ELSI) of genetics research have successfully mapped out many of the issues (and social and political responses) that arise when new technologies are deployed. It is our contention that, for the most part, the ethical and social issues arising in nanomedicine are not altogether new, and thus do not require novel ethical principles or frameworks, nor a massive investment in ‘NELSI’ research. Instead, what is needed is support for the development of a culture of ethics amongst scientists and clinicians, basic scientific and medical knowledge for bioethicists, and a social competency for citizens to participate actively in debates about the implications of new technologies in general.

Keyphrases: nanotechnologies, éthique, financement de recherche, politique, ELSI, nanotechnologies, nanotechnology, ethics, research financing, policy, ELSI
Role of manganese in the pathogenesis of portal-systemic encephalopathy

Amongst the potential neurotoxins implicated in the pathogenesis of hepatic encephalopathy, manganese emerges as a new candidate. In patients with chronic liver diseases, manganese accumulates in blood and brain leading to pallidal signal hyperintensity on T1-weighted Magnetic Resonance (MR) Imaging. Direct measurements in globus pallidus obtained at autopsy from cirrhotic patients who died in hepatic coma reveal 2 to 7-fold increases of manganese concentration. The intensity of pallidal MR images correlates with blood manganese and with the presence of extrapyramidal symptoms occurring in a majority of cirrhotic patients. Liver transplantation results in normalization of pallidal MR signals and disappearance of extrapyramidal symptoms whereas transjugular intrahepatic portosystemic shunting induces an increase in pallidal hyperintensity with a concomitant deterioration of neurological dysfunction. These findings suggest that the toxic effects of manganese contribute to extrapyramidal symptoms in patients with chronic liver disease. The mechanisms of manganese neurotoxicity are still speculative, but there is evidence to suggest that manganese deposition in the pallidum may lead to dopaminergic dysfunction. Future studies should be aimed at evaluating the effects of manganese chelation and/or of treatment of the dopaminergic deficit on neurological symptomatology in these patients.

Keyphrases: Affections des ganglions de la base, Anastomose portocave chirurgicale, Basal ganglia diseases, Encéphalopathie hépatique, Extrapyramidal disorders, Globus pallidus, Hepatic encephalopathy, Imagerie par résonance magnétique, Magnetic Resonance Imaging, Manganese, Manganèse, Portacaval shunt, Portal systemic encephalopathy
Induction of astrocytic cyclooxygenase-2 in epileptic patients with hippocampal sclerosis

Induction of cyclooxygenase-2 (COX-2) has been described in a wide range of neurological diseases including animal models of epilepsy. The present study was undertaken to assess COX-2 expression in hippocampal biopsies from patients with therapy-refractive temporal lobe epilepsy (TLE). For this purpose, hippocampal CA1 subfield was dissected from epileptic patients with (n=5) or without (n=2) hippocampal sclerosis (HS). COX-2 expression was investigated using immunohistochemistry and semi-quantitative RT-PCR. COX-2 immunoreactivity in TLE patient material in the absence of HS was restricted to a few neurons of the hippocampus. In the presence of HS, on the other hand, a significant induction of astrocytic COX-2 immunoreactivity associated with a concomitant increase in the steady-state level of COX-2 mRNA was observed in the CA1 subfield. These findings suggest that induction of astrocytic COX-2 is implicated in the pathogenesis of HS in TLE and is consistent with the previous findings of increased concentrations of prostaglandins in the cerebrospinal fluid of these patients.

Keyphrases: Astrocytes, Cyclooxygenase 2, Épilepsie temporale, Prostaglandines, Prostaglandins, Temporal lobe epilepsy
Effects of hypothermia on brain glucose metabolism in acute liver failure: a H/C-nuclear magnetic resonance study

Mild hypothermia has a protective effect on brain edema and encephalopathy in both experimental and human acute liver failure. The goals of the present study were to examine the effects of mild hypothermia (35°C) on brain metabolic pathways using combined 1H and 13C-Nuclear Magnetic Resonance (NMR) spectroscopy, a technique which allows the study not only of metabolite concentrations but also their de novo synthesis via cell-specific pathways in the brain. :1H and 13C NMR spectroscopy using [1-13C] glucose was performed on extracts of frontal cortex obtained from groups of rats with acute liver failure induced by hepatic devascularization whose body temperature was maintained either at 37°C (normothermic) or 35°C (hypothermic), and appropriate sham-operated controls.  At coma stages of encephalopathy in the normothermic acute liver failure animals, glutamine concentrations in frontal cortex increased 3.5-fold compared to sham-operated controls (P < 0.001). Comparable increases of brain glutamine were observed in hypothermic animals despite the absence of severe encephalopathy (coma). Brain glutamate and aspartate concentrations were respectively decreased to 60.9% ± 7.7% and 42.2% ± 5.9% (P < 0.01) in normothermic animals with acute liver failure compared to control and were restored to normal values by mild hypothermia. Concentrations of lactate and alanine in frontal cortex were increased to 169.2% ± 15.6% and 267.3% ± 34.0% (P < 0.01) respectively in normothermic rats compared to controls. Furthermore, de novo synthesis of lactate and alanine increased to 446.5% ± 48.7% and 707.9% ± 65.7% (P < 0.001), of control respectively, resulting in increased fractional 13C-enrichments in these cytosolic metabolites. Again, these changes of lactate and alanine concentrations were prevented by mild hypothermia. Mild hypothermia (35°C) prevents the encephalopathy and brain edema resulting from hepatic devascularization, selectively normalizes lactate and alanine synthesis from glucose, and prevents the impairment of oxidative metabolism associated with this model of ALF, but has no significant effect on brain glutamine. These findings suggest that a deficit in brain glucose metabolism rather than glutamine accumulation is the major cause of the cerebral complications of acute liver failure.

Keyphrases: Acute liver failure, Brain edema, Défaillance hépatique aigüe, Encéphalopathie hépatique, Glutamine, Hepatic encephalopathy, Hypothermia, Hypothermie, Nuclear magnetic resonance, Oedème cérébral
Effect of portacaval anastomosis on glutamine synthetase protein and gene expression in brain, liver and skeletal muscle

The effects of chronic liver insufficiency resulting from end-to-side portacaval anastomosis (PCA) on glutamine synthetase (GS) activities, protein and gene expression were studied in brain, liver and skeletal muscle of male adult rats. Four weeks following PCA, activities of GS in cerebral cortex and cerebellum were reduced by 32\% and 37\% (p<0.05) respectively whereas GS activities in muscle were increased by 52\% (p<0.05). GS activities in liver were decreased by up to 90\% (p<0.01), a finding which undoubtedly reflects the loss of GS-rich perivenous hepatocytes following portal-systemic shunting. Immunoblotting techniques revealed no change in GS protein content of brain regions or muscle but a significant loss in liver of PCA rats. GS mRNA determined by semi-quantitative RT-PCR was also significantly decreased in the livers of PCA rats compared to sham-operated controls. These findings demonstrate that PCA results in a loss of GS gene expression in the liver and that brain does not show a compensatory induction of enzyme activity, rendering it particularly sensitive to increases in ammonia in chronic liver failure. The finding of a post-translational increase of GS in muscle following portacaval shunting suggests that, in chronic liver failure, muscle becomes the major organ responsible for the removal of excess blood-borne ammonia.

Keyphrases: Ammonia, Ammoniac, Anastomose portocave chirurgicale, Encéphalopathie hépatique, Expression des gènes, Foie, Gene expression, Glutamine synthetase, Hepatic encephalopathy, Liver, Muscles squelettiques, Portacaval anastomosis, Skeletal muscle
Direct molecular and spectroscopic evidence for increased ammonia removal capacity of skeletal muscle in acute liver failure

BACKGROUND/AIMS: It has been proposed that, in acute liver failure, skeletal muscle adapts to become the principle organ responsible for removal of blood-borne ammonia by increasing glutamine synthesis, a reaction that is catalyzed by the cytosolic ATP-dependent enzyme glutamine synthetase. To address this issue, glutamine synthetase expression and activities were measured in skeletal muscle of rats with acute liver failure resulting from hepatic devascularization. METHODS: Glutamine synthetase protein and gene expression were investigated using immunoblotting and semi-quantitative RT-PCR analysis. Glutamine synthetase activity and glutamine de novo synthesis were measured using, respectively, a standard enzymatic assay and [13C]-nuclear magnetic resonance spectroscopy. RESULTS: Glutamine synthetase protein (but not gene) expression and enzyme activities were significantly up-regulated leading to increased de novo synthesis of glutamine and increased skeletal muscle capacity for ammonia removal in acute liver failure. In contrast to skeletal muscle, expression and activities of glutamine synthetase in the brain were significantly decreased. CONCLUSIONS: These findings demonstrate that skeletal muscle adapts, through a rapid induction of glutamine synthetase, to increase its capacity for removal of blood-borne ammonia in acute liver failure. Maintenance of muscle mass together with the development of agents with the capacity to stimulate muscle glutamine synthetase could provide effective ammonia-lowering strategies in this disorder.

Keyphrases: Acute liver failure, Ammonia, Ammoniac, Brain edema, Défaillance hépatique aigüe, Glutamate-ammonia ligase, Glutamine, Glutamine synthetase, Muscles squelettiques, Nuclear magnetic resonance spectroscopy, Oedème cérébral, Skeletal muscle, Spectroscopie par résonance magnétique
Mild hypothermia in the prevention of brain edema in acute liver failure: mechanisms and clinical prospects

Mild hypothermia (32 degrees C-35 degrees C) reduces intracranial pressure in patients with acute liver failure and may offer an effective adjunct therapy in the management of these patients. Studies in experimental animals suggest that this beneficial effect of hypothermia is the result of a decrease in blood-brain ammonia transfer resulting in improvement in brain energy metabolism and normalization of glutamatergic synaptic regulation. Improvement in brain energy metabolism by hypothermia may result from a reduction in ammonia-induced decrease of brain glucose (pyruvate) oxidation. Restoration of normal glutamatergic synaptic regulation by hypothermia may be the consequence of the removal of ammonia-induced decreases in expression of astrocytic glutamate transporters resulting in normal glutamate neurotransmitter inactivation in brain. Randomized controlled clinical trials of hypothermia are required to further evaluate its clinical impact.

Keyphrases: Acide glutamique, Acide lactique, Acute liver failure, Ammonia, Ammoniac, Brain edema, Cerebral blood flow, Défaillance hépatique aigüe, Glutamate, Glutamine, Hypothermia, Hypothermie, Lactate
Mild hypothermia prevents brain edema and attenuates up-regulation of the astrocytic benzodiazepine receptor in experimental acute liver failure

BACKGROUND/AIMS: Mild hypothermia has proven useful in the clinical management of patients with acute liver failure. Acute liver failure in experimental animals results in alterations in the expression of genes coding for astrocytic proteins including the "peripheral-type" (astrocytic) benzodiazepine receptor (PTBR), a mitochondrial complex associated with neurosteroid synthesis. To gain further insight into the mechanisms whereby hypothermia attenuates the neurological complications of acute liver failure, we investigated PTBR expression in the brains of hepatic devascularized rats under normothermic (37 degrees C) and hypothermic (35 degrees C) conditions. METHODS: PTBR mRNA was measured using semi-quantitative RT-PCR in cerebral cortical extracts and densities of PTBR sites were measured by quantitative receptor autoradiagraphy. Brain pregnenolone content was measured by radioimmunoassay. RESULTS: At coma stages of encephalopathy, animals with acute liver failure manifested a significant increase of PTBR mRNA levels. Brain pregnenolone content and [(3)H]PK 11195 binding site densities were concomitantly increased. Mild hypothermia prevented brain edema and significantly attenuated the increased receptor expression and pregnenolone content. CONCLUSIONS: These findings suggest that an attenuation of PTBR up-regulation resulting in the prevention of increased brain neurosteroid content represents one of the mechanisms by which mild hypothermia exerts its protective effects in ALF.

Keyphrases: Acute liver failure, Astrocytes, Brain edema, Défaillance hépatique aigüe, Encéphalopathie hépatique, Hepatic encephalopathy, Oedème cérébral, Peripheral-type benzodiazepine receptor, Pregnenolone, Prégnénolone, TSPO protein, human