Glutamine in the pathogenesis of acute hepatic encephalopathy

Set7/9 aggravates ischemic brain injury via enhancing glutamine metabolism in a blocking Sirt5 manner

The aberrant expression of methyltransferase Set7/9 plays a role in various diseases. However, the contribution of Set7/9 in ischemic stroke remains unclear. Here, we show ischemic injury results in a rapid elevation of Set7/9, which is accompanied by the downregulation of Sirt5, a deacetylase reported to protect against injury. Proteomic analysis identifies the decrease of chromobox homolog 1 (Cbx1) in knockdown Set7/9 neurons. Mechanistically, Set7/9 promotes the binding of Cbx1 to H3K9me2/3 and forms a transcription repressor complex at the Sirt5 promoter, ultimately repressing Sirt5 transcription. Thus, the deacetylation of Sirt5 substrate, glutaminase, which catalyzes the hydrolysis of glutamine to glutamate and ammonia, is decreased, promoting glutaminase expression and triggering excitotoxicity. Blocking Set7/9 eliminates H3K9me2/3 from the Sirt5 promoter and normalizes Sirt5 expression and Set7/9 knockout efficiently ameliorates brain ischemic injury by reducing the accumulation of ammonia and glutamate in a Sirt5-dependent manner. Collectively, the Set7/9-Sirt5 axis may be a promising epigenetic therapeutic target.

Residual Amino Acid Imbalance in Rats during Recovery from Acute Thioacetamide-Induced Hepatic Encephalopathy Indicates Incomplete Healing

The delayed consequences of the influence of hepatic encephalopathy (HE) on the metabolism of animals have not been studied enough. We have previously shown that the development of acute HE under the influence of the thioacetamide (TAA) toxin is accompanied by pathological changes in the liver, an imbalance in CoA and acetyl CoA, as well as a number of metabolites of the TCA cycle. This paper discusses the change in the balance of amino acids (AAs) and related metabolites, as well as the activity of glutamine transaminase (GTK) and ω-amidase enzymes in the vital organs of animals 6 days after a single exposure to TAA. The balance of the main AAs in blood plasma, liver, kidney, and brain samples of control (n = 3) and TAA-induced groups (n = 13) of rats that received the toxin at doses of 200, 400, and 600 mg/kg was considered. Despite the apparent physiological recovery of the rats at the time of sampling, a residual imbalance in AA and associated enzymes persisted. The data obtained give an idea of the metabolic trends in the body of rats after their physiological recovery from TAA exposure and may be useful for prognostic purposes when choosing the necessary therapeutic agents.

Blood Levels of Glutamine and Nitrotyrosine in Patients with Chronic Viral Hepatitis

Purpose

Oxidative stress is involved in pathogenesis of chronic viral hepatitis. Glutamine is an antioxidant, but there is a controversy about its risk-benefits. Nitrotyrosine is an oxidative stress marker. This observational cross-sectional study was designed to compare blood levels of glutamine and nitrotyrosine in treated versus untreated chronic viral hepatitis patients.

Patients and Methods

Five groups (n = 250) were included: hepatitis B untreated (HBV), hepatitis C untreated (HCV), HBV treated (HBVT), and HCV treated (HCVT) groups plus a normal control group. Liver function tests and blood levels of glutamine, nitrotyrosine, viral loads, and HBsAg were measured.

Results

Blood levels of glutamine and nitrotyrosine in all patient groups significantly increased compared with normal controls with non-significant differences in-between. Both tests showed significant large correlations with HBV-DNA or HCV-RNA test positivity, high accuracies, and cutoff scores with high sensitivities and specificities. The viral loads and HBsAg levels were significantly lower in treated versus untreated groups. However, they poorly correlated with levels of glutamine and nitrotyrosine in all patient groups.

Conclusion

Blood levels of glutamine and nitrotyrosine significantly increased in treated and untreated chronic viral hepatitis B and C patients compared with normal controls. Both tests showed high accuracies and cutoff scores with high sensitivities and specificities. However, they did not differ significantly in treated versus untreated patients. To our knowledge, this is the first data showing elevation of glutamine and nitrotyrosine in treated and untreated chronic viral hepatitis. A prospective longitudinal study with repeated measurements of glutamine and nitrotyrosine is recommended to verify if they can predict response to treatment. Study of other oxidative stress markers is also advised to clarify if the elevated nitrotyrosine could be an oxidative stress marker in these patients, and whether the increased glutamine could act as an antioxidant or as a predictive agent for deleterious consequences.

Plasma glutamine status at intensive care unit admission: an independent risk factor for mortality in critical illness

Background

A plasma glutamine concentration outside the normal range at Intensive Care Unit (ICU) admission has been reported to be associated with an increased mortality rate. Whereas hypoglutaminemia has been frequently reported, the number of patients with hyperglutaminemia has so far been quite few. Therefore, the association between hyperglutaminemia and mortality outcomes was studied in a prospective, observational study.

Patients and methods

Consecutive admissions to a mixed general ICU were eligible. Exclusion criteria were < 18 years of age, readmissions, no informed consent, or a ‘do not resuscitate’ order at admission. A blood sample was saved within one hour from admission to be analysed by high-pressure liquid chromatography for glutamine concentration. Conventional risk scoring (Simplified Acute Physiology Score and Sequential Organ Failure Assessment) at admission, and mortality outcomes were recorded for all included patients.

Results

Out of 269 included patients, 26 were hyperglutaminemic (≥ 930 µmol/L) at admission. The six-month mortality rate for this subgroup was 46%, compared to 18% for patients with a plasma glutamine concentration < 930 µmol/L (P = 0.002). A regression analysis showed that hyperglutaminemia was an independent mortality predictor that added prediction value to conventional admission risk scoring and age.

Conclusion

Hyperglutaminemia in critical illness at ICU admission was an independent mortality predictor, often but not always, associated with an acute liver condition. The mechanism behind a plasma glutamine concentration outside normal range, as well as the prognostic value of repeated measurements of plasma glutamine during ICU stay, remains to be investigated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03640-3.

Metabolism and Effects on Endogenous Metabolism of Paracetamol (Acetaminophen) in a Porcine Model of Liver Failure

The metabolic fate, toxicity, and effects on endogenous metabolism of paracetamol (acetaminophen, APAP) in 22 female Landrace cross large white pigs were evaluated in a model of acute liver failure (ALF). Anesthetized pigs were initially dosed at 250 mg/kg via an oroduodenal tube with APAP serum concentrations maintained above 300 mg/l using maintenance doses of 0.5–4 g/h until ALF. Studies were undertaken to determine both the metabolic fate of APAP and its effects on the endogenous metabolic phenotype of ALF in using ¹H NMR spectroscopy. Increased concentrations of citrate combined with pre-ALF increases in circulating lactate, pyruvate, and alanine in plasma suggest mitochondrial dysfunction and a switch in hepatic energy metabolism to glycolysis in response to APAP treatment. A specific liquid chromatography-tandem mass spectrometry assay was used to quantify APAP and metabolites. The major circulating and urinary metabolite of APAP was the phenolic glucuronide (APAP-G), followed by p-aminophenol glucuronide (PAP-G) formed from N-deacetylated APAP. The PAP produced by N-deacetylation was the likely cause of the methemoglobinemia and kidney toxicity observed in this, and previous, studies in the pig. The phenolic sulfate of APAP, and the glutathione-derived metabolites of the drug were only found as minor components (with the cysteinyl conjugate detected but not the mercapturate). Given its low sulfation, combined with significant capacity for N-deacetylation the pig may represent a poor translational model for toxicology studies for compounds undergoing significant metabolism by sulfation, or which contain amide bonds which when hydrolyzed to unmask an aniline lead to toxicity. However, the pig may provide a useful model where extensive amide hydrolysis is seen for drugs or environmental chemicals in humans, but not in, eg, the rat and dog which are the preclinical species normally employed for safety assessment.

Effects of erythropoietin on bile duct ligation-induced neuro-inflammation in male rats

Hepatic encephalopathy (HE) is a brain disorder as a result of liver failure. Previous studies have indicated that erythropoietin (EPO) has neuroprotective effects in different neurological diseases. This study addressed the therapeutic effect of a four-week treatment with EPO on neuronal damages in bile duct-ligated rats. Forty male Wistar rats (250-280 g) were used in the present study. The animals were randomly divided into four groups consisting of 10 animals each, including sham, sham + EPO, bile duct ligation (BDL), and BDL + EPO. EPO was intraperitoneally administered every other day (5,000 U/Kg) in the last four weeks after BDL. Biochemical and histological studies were performed to evaluate neurodegeneration. The results revealed that BDL increases the level of hepatic enzymes and total bilirubin. Furthermore, neurodegeneration was significantly increased in the BDL group compared to sham groups. EPO preserved hepatic enzymes and total bilirubin in the treated group. In addition, EPO significantly decreased the neurodegeneration in BDL + EPO compared to the BDL group. Results of this study showed that EPO has neuroprotective effects in the rat model of HE, possibly due to its anti-inflammatory and anti-oxidant properties. Complementary studies are required to clarify the exact mechanisms.

Astrocytes Maintain Glutamate Homeostasis in the CNS by Controlling the Balance between Glutamate Uptake and Release

Glutamate is one of the most prevalent neurotransmitters released by excitatory neurons in the central nervous system (CNS); however, residual glutamate in the extracellular space is, potentially, neurotoxic. It is now well-established that one of the fundamental functions of astrocytes is to uptake most of the synaptically-released glutamate, which optimizes neuronal functions and prevents glutamate excitotoxicity. In the CNS, glutamate clearance is mediated by glutamate uptake transporters expressed, principally, by astrocytes. Interestingly, recent studies demonstrate that extracellular glutamate stimulates Ca2+ release from the astrocytes' intracellular stores, which triggers glutamate release from astrocytes to the adjacent neurons, mostly by an exocytotic mechanism. This released glutamate is believed to coordinate neuronal firing and mediate their excitatory or inhibitory activity. Therefore, astrocytes contribute to glutamate homeostasis in the CNS, by maintaining the balance between their opposing functions of glutamate uptake and release. This dual function of astrocytes represents a potential therapeutic target for CNS diseases associated with glutamate excitotoxicity. In this regard, we summarize the molecular mechanisms of glutamate uptake and release, their regulation, and the significance of both processes in the CNS. Also, we review the main features of glutamate metabolism and glutamate excitotoxicity and its implication in CNS diseases.

Mechanistic insight, diagnosis, and treatment of ammonia-induced hepatic encephalopathy

Hepatic encephalopathy is a neuropsychological syndrome due to biochemical disturbance of brain function in advanced liver disease patients. Diagnosis and treatment of the condition is very demanding and has negative toll on finances with increased healthcare utilization. The pathophysiology is not completely understood; however, there is evidence that ammonia plays an important role in the etiology. Conventional methods of solely relying on blood ammonia level to diagnose hepatic encephalopathy did not help much; likewise, the use of lactulose alone in treating hepatic encephalopathy has also been discouraged. This paper analyzed the current knowledge regarding the mechanism of how ammonia disrupts the normal brain function as well as the use of latest diagnosing tools including those under development to evaluate the neuropsychiatric state of patients and their quality of life. The efficacies of lactulose and rifaximin combination for short-term and long-term treatment in addition to nutritional interventions and other drugs undergoing clinical trials were also reviewed.

Molecular and cellular physiology of sodium-dependent glutamate transporters

Glutamate is the major excitatory transmitter in the vertebrate brain. After its release from presynaptic nerve terminals, it is rapidly taken up by high-affinity sodium-dependent plasma membrane transporters. While both neurons and glial cells express these excitatory amino acid transporters (EAATs), the majority of glutamate uptake is accomplished by astrocytes, which convert synaptically-released glutamate to glutamine or feed it into their own metabolism. Glutamate uptake by astrocytes not only shapes synaptic transmission by regulating the availability of glutamate to postsynaptic neuronal receptors, but also protects neurons from hyper-excitability and subsequent excitotoxic damage. In the present review, we provide an overview of the molecular and cellular characteristics of sodium-dependent glutamate transporters and their associated anion permeation pathways, with a focus on astrocytic glutamate transport. We summarize their functional properties and roles within tripartite synapses under physiological and pathophysiological conditions, exemplifying the intricate interactions and interrelationships between neurons and glial cells in the brain.

Plasma Glutamine Concentrations in Liver Failure

Background

Higher than normal plasma glutamine concentration at admission to an intensive care unit is associated with an unfavorable outcome. Very high plasma glutamine levels are sometimes seen in both acute and chronic liver failure. We aimed to systematically explore the relation between different types of liver failure and plasma glutamine concentrations.

Methods

Four different groups of patients were studies; chronic liver failure (n = 40), acute on chronic liver failure (n = 20), acute fulminant liver failure (n = 20), and post-hepatectomy liver failure (n = 20). Child-Pugh and Model for End-stage Liver Disease (MELD) scores were assessed as indices of liver function. All groups except the chronic liver failure group were followed longitudinally during hospitalisation. Outcomes were recorded up to 48 months after study inclusion.

Results

All groups had individuals with very high plasma glutamine concentrations. In the total group of patients (n = 100), severity of liver failure correlated significantly with plasma glutamine concentration, but the correlation was not strong.

Conclusion

Liver failure, regardless of severity and course of illness, may be associated with a high plasma glutamine concentration. Further studies are needed to understand whether high glutamine levels should be regarded as a biomarker or as a contributor to symptomatology in liver failure.

Glutamine Synthetase: Role in Neurological Disorders

Glutamine synthetase (GS) is an ATP-dependent enzyme found in most species that synthesizes glutamine from glutamate and ammonia. In brain, GS is exclusively located in astrocytes where it serves to maintain the glutamate-glutamine cycle, as well as nitrogen metabolism. Changes in the activity of GS, as well as its gene expression, along with excitotoxicity, have been identified in a number of neurological conditions. The literature describing alterations in the activation and gene expression of GS, as well as its involvement in different neurological disorders, however, is incomplete. This review summarizes changes in GS gene expression/activity and its potential contribution to the pathogenesis of several neurological disorders, including hepatic encephalopathy, ischemia, epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, traumatic brain injury, Parkinson's disease, and astroglial neoplasms. This review also explores the possibility of targeting GS in the therapy of these conditions.

Ornithine transcarbamylase deficiency presenting with acute reversible cortical blindness

Acute focal neurologic deficits are a rare but known presentation of ornithine transcarbamylase deficiency, particularly in females. We describe here a 6-year-old girl with newly diagnosed ornithine transcarbamylase deficiency who presents with an episode of acute cortical blindness lasting for 72 hours in the absence of hyperammonemia. Her symptoms were associated with a subcortical low-intensity lesion with overlying cortical hyperintensity on fluid-attenuated inversion recovery magnetic resonance imaging (MRI) of the occipital lobes. Acute reversible vision loss with these MRI findings is an unusual finding in patients with ornithine transcarbamylase deficiency. Our findings suggest a role for oxidative stress and aberrant glutamine metabolism in the acute clinical features of ornithine transcarbamylase deficiency even in the absence of hyperammonemia.

Pathogenesis of brain edema and investigation into anti-edema drugs

Brain edema is a potentially fatal pathological state that occurs after brain injuries such as stroke and head trauma. In the edematous brain, excess accumulation of extracellular fluid results in elevation of intracranial pressure, leading to impaired nerve function. Despite the seriousness of brain edema, only symptomatic treatments to remove edema fluid are currently available. Thus, the development of novel anti-edema drugs is required. The pathogenesis of brain edema is classified as vasogenic or cytotoxic edema. Vasogenic edema is defined as extracellular accumulation of fluid resulting from disruption of the blood-brain barrier (BBB) and extravasations of serum proteins, while cytotoxic edema is characterized by cell swelling caused by intracellular accumulation of fluid. Various experimental animal models are often used to investigate mechanisms underlying brain edema. Many soluble factors and functional molecules have been confirmed to induce BBB disruption or cell swelling and drugs targeted to these factors are expected to have anti-edema effects. In this review, we discuss the mechanisms and involvement of factors that induce brain edema formation, and the possibility of anti-edema drugs targeting them.

Expression of glutamine transporter isoforms in cerebral cortex of rats with chronic hepatic encephalopathy

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs due to acute and chronic liver diseases, the hallmark of which is the increased levels of ammonia and subsequent alterations in glutamine synthesis, i.e. conditions associated with the pathophysiology of HE. Under physiological conditions, glutamine is fundamental for replenishment of the neurotransmitter pools of glutamate and GABA. The different isoforms of glutamine transporters play an important role in the transfer of this amino acid between astrocytes and neurons. A disturbance in the GABA biosynthetic pathways has been described in bile duct ligated (BDL) rats, a well characterized model of chronic HE. Considering that glutamine is important for GABA biosynthesis, altered glutamine transport and the subsequent glutamate/GABA-glutamine cycle efficacy might influence these pathways. Given this potential outcome, the aim of the present study was to investigate whether the expression of the glutamine transporters SAT1, SAT2, SN1 and SN2 would be affected in chronic HE. We verified that mRNA expression of the neuronal glutamine transporters SAT1 and SAT2 was found unaltered in the cerebral cortex of BDL rats. Similarly, no changes were found in the mRNA level for the astrocytic transporter SN1, whereas the gene expression of SN2 was increased by two-fold in animals with chronic HE. However, SN2 protein immuno-reactivity did not correspond with the increase in gene transcription since it remained unaltered. These data indicate that the expression of the glutamine transporter isoforms is unchanged during chronic HE, and thus likely not to participate in the pathological mechanisms related to the imbalance in the GABAergic neurotransmitter system observed in this neurologic condition.

Ammonia metabolism and hyperammonemic disorders

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.

Dysbalance of astrocyte calcium under hyperammonemic conditions

Increased brain ammonium (NH₄⁺/NH₃) plays a central role in the manifestation of hepatic encephalopathy (HE), a complex syndrome associated with neurological and psychiatric alterations, which is primarily a disorder of astrocytes. Here, we analysed the influence of NH₄⁺/NH₃ on the calcium concentration of astrocytes in situ and studied the underlying mechanisms of NH₄⁺/NH₃-evoked calcium changes, employing fluorescence imaging with Fura-2 in acute tissue slices derived from different regions of the mouse brain. In the hippocampal stratum radiatum, perfusion with 5 mM NH₄⁺/NH₃ for 30 minutes caused a transient calcium increase in about 40% of astrocytes lasting about 10 minutes. Furthermore, the vast majority of astrocytes (∼90%) experienced a persistent calcium increase by ∼50 nM. This persistent increase was already evoked at concentrations of 1–2 mM NH₄⁺/NH₃, developed within 10–20 minutes and was maintained as long as the NH₄⁺/NH₃ was present. Qualitatively similar changes were observed in astrocytes of different neocortical regions as well as in cerebellar Bergmann glia. Inhibition of glutamine synthetase resulted in significantly larger calcium increases in response to NH₄⁺/NH₃, indicating that glutamine accumulation was not a primary cause. Calcium increases were not mimicked by changes in intracellular pH. Pharmacological inhibition of voltage-gated sodium channels, sodium-potassium-chloride-cotransporters (NKCC), the reverse mode of sodium/calcium exchange (NCX), AMPA- or mGluR5-receptors did not dampen NH₄⁺/NH₃-induced calcium increases. They were, however, significantly reduced by inhibition of NMDA receptors and depletion of intracellular calcium stores. Taken together, our measurements show that sustained exposure to NH₄⁺/NH₃ causes a sustained increase in intracellular calcium in astrocytes in situ, which is partly dependent on NMDA receptor activation and on release of calcium from intracellular stores. Our study furthermore suggests that dysbalance of astrocyte calcium homeostasis under hyperammonemic conditions is a widespread phenomenon, which might contribute to the disturbance of neurotransmission during HE.

Effect of glutamine synthetase inhibition on brain and interorgan ammonia metabolism in bile duct ligated rats

Ammonia has a key role in the development of hepatic encephalopathy (HE). In the brain, glutamine synthetase (GS) rapidly converts blood-borne ammonia into glutamine which in high concentrations may cause mitochondrial dysfunction and osmolytic brain edema. In astrocyte-neuron cocultures and brains of healthy rats, inhibition of GS by methionine sulfoximine (MSO) reduced glutamine synthesis and increased alanine synthesis. Here, we investigate effects of MSO on brain and interorgan ammonia metabolism in sham and bile duct ligated (BDL) rats. Concentrations of glutamine, glutamate, alanine, and aspartate and incorporation of (15)NH(4)(+) into these amino acids in brain, liver, muscle, kidney, and plasma were similar in sham and BDL rats treated with saline. Methionine sulfoximine reduced glutamine concentrations in liver, kidney, and plasma but not in brain and muscle; MSO reduced incorporation of (15)NH(4)(+) into glutamine in all tissues. It did not affect alanine concentrations in any of the tissues but plasma alanine concentration increased; incorporation of (15)NH(4)(+) into alanine was increased in brain in sham and BDL rats and in kidney in sham rats. It inhibited GS in all tissues examined but only in brain was an increased incorporation of (15)N-ammonia into alanine observed. Liver and kidney were important for metabolizing blood-borne ammonia.

Ammonia toxicity to the brain

Hyperammonemia can be caused by various acquired or inherited disorders such as urea cycle defects. The brain is much more susceptible to the deleterious effects of ammonium in childhood than in adulthood. Hyperammonemia provokes irreversible damage to the developing central nervous system: cortical atrophy, ventricular enlargement and demyelination lead to cognitive impairment, seizures and cerebral palsy. The mechanisms leading to these severe brain lesions are still not well understood, but recent studies show that ammonium exposure alters several amino acid pathways and neurotransmitter systems, cerebral energy metabolism, nitric oxide synthesis, oxidative stress and signal transduction pathways. All in all, at the cellular level, these are associated with alterations in neuronal differentiation and patterns of cell death. Recent advances in imaging techniques are increasing our understanding of these processes through detailed in vivo longitudinal analysis of neurobiochemical changes associated with hyperammonemia. Further, several potential neuroprotective strategies have been put forward recently, including the use of NMDA receptor antagonists, nitric oxide inhibitors, creatine, acetyl-L-carnitine, CNTF or inhibitors of MAPKs and glutamine synthetase. Magnetic resonance imaging and spectroscopy will ultimately be a powerful tool to measure the effects of these neuroprotective approaches.

In vivo studies of brain metabolism in animal models of Hepatic Encephalopathy using ¹H Magnetic Resonance Spectroscopy

Hepatic encephalopathy (HE) is a common and severe neuropsychiatric complication present in acute and chronic liver disease. The unique advantages of high field (1)H MRS provide a method for assessing pathogenic mechanism, diagnosis and monitoring of HE, as well as for treatment assessment or recovery after liver transplantation, in a reproducible and reliable non-invasive way. The purpose of the present review is to present some new features of in vivo proton Magnetic Resonance Spectroscopy ((1)H MRS) at high magnetic fields combined with some basic requirements for reliable metabolic profiling. Finally, in vivo applications of (1)H MRS in different HE animal models are presented.

Acetyl-L-carnitine in hepatic encephalopathy

Hepatic encephalopathy is a common complication of hepatic cirrhosis. The clinical diagnosis is based on two concurrent types of symptoms: impaired mental status and impaired neuromotor function. Impaired mental status is characterized by deterioration in mental status with psychomotor dysfunction, impaired memory, and increased reaction time, sensory abnormalities, poor concentration, disorientation and coma. Impaired neuromotor function include hyperreflexia, rigidity, myoclonus and asterixis. The pathogenesis of hepatic encephalopathy has not been clearly defined. The general consensus is that elevated levels of ammonia and an inflammatory response work in synergy to cause astrocyte to swell and fluid to accumulate in the brain which is thought to explain the symptoms of hepatic encephalopathy. Acetyl-L-carnitine, the short-chain ester of carnitine is endogenously produced within mitochondria and peroxisomes and is involved in the transport of acetyl-moieties across the membranes of these organelles. Acetyl-L-carnitine administration has shown the recovery of neuropsychological activities related to attention/concentration, visual scanning and tracking, psychomotor speed and mental flexibility, language short-term memory, attention, and computing ability. In fact, Acetyl-L-carnitine induces ureagenesis leading to decreased blood and brain ammonia levels. Acetyl-L-carnitine treatment decreases the severity of mental and physical fatigue, depression cognitive impairment and improves health-related quality of life. The aim of this review was to provide an explanation on the possible toxic effects of ammonia in HE and evaluate the potential clinical benefits of ALC.

Update on cerebral uptake of blood ammonia

Ammonia is believed to play a key role in the development of hepatic encephalopathy (HE) with increased formation of glutamine playing a central role. It has been debated whether blood ammonia enters the brain by passive diffusion and/or active transport by ion-transporters and that changes in blood pH could affect the blood-to-brain transfer of ammonia. It has also been proposed that the permeability-surface area product for ammonia across the blood-brain barrier (PSBBB) should be increased in cirrhosis and HE. In the present paper it is argued that changes in blood pH does not alter PSBBB for ammonia and the question of passive diffusion versus active transport of ammonia remains unresolved. Furthermore, recent studies do not find evidence for increased PSBBB for ammonia in cirrhosis. The main determent for cerebral uptake of blood ammonia (i.e. flux) is the arterial blood ammonia concentration. This means that the only way to protect the brain from hyperammonemia is by lowering blood ammonia, inhibit cerebral uptake of ammonia, or by manipulating cerebral ammonia metabolism so that less glutamine is produced.

Novel nutritional substrates in surgery

Pharmaco-nutrients have beneficial effects on protective and immunological mechanisms in patients undergoing surgery, which are important for recovery after injury and in combating infectious agents. The aim of this review article was to outline the potential of the administration of nutritional substrates to surgical patients and the underlying mechanisms that make them particularly important in peri-operative care. Surgery causes a stress response, which has catabolic effects on the body's substrate stores. The amino acid glutamine is a stimulating agent for immune cells. It activates protective mechanisms through its role as a precursor for antioxidants and it improves the barrier function of the gut. Arginine also enhances the function of the immune system, since it is the substrate for T-lymphocytes. Furthermore, n-3 PUFA stabilise surgery-induced hyper-inflammation. Taurine is another substrate that may counteract the negative effects of surgical injury on acid–base balance and osmotic balance. These pharmaco-nutrients rapidly become deficient under the influence of surgical stress. Supplementation of these nutrients in surgical patients may restore their protective and immune-enhancing actions and improve clinical outcome. Moreover, pre-operative fasting is still common practice in the Western world, although fasting has a negative effect on the patient's condition and the recovery after surgery. This may be counteracted by a simple intervention such as administering a carbohydrate-rich supplement just before surgery. In conclusion, there are various nutritional substrates that may be of great value in improving the condition of the surgical patient, which may be beneficial for post-operative recovery.

Glutamine in the pathogenesis of hepatic encephalopathy: the trojan horse hypothesis revisited

Hepatic encephalopathy (HE) is major neuropsychiatric disorder occurring in patients with severe liver disease and ammonia is generally considered to represent the major toxin responsible for this condition. Ammonia in brain is chiefly metabolized ("detoxified") to glutamine in astrocytes due to predominant localization of glutamine synthetase in these cells. While glutamine has long been considered innocuous, a deleterious role more recently has been attributed to this amino acid. This article reviews the mechanisms by which glutamine contributes to the pathogenesis of HE, how glutamine is transported into mitochondria and subsequently hydrolyzed leading to high levels of ammonia, the latter triggering oxidative and nitrative stress, the mitochondrial permeability transition and mitochondrial injury, a sequence of events we have collectively termed as the Trojan horse hypothesis of hepatic encephalopathy.

Enzymatic analysis of α-ketoglutaramate--a biomarker for hyperammonemia

Two enzymatic assays were developed for the analysis of α-ketoglutaramate (KGM)-an important biomarker of hepatic encephalopathy and other hyperammonemic diseases. In both procedures, KGM is first converted to α-ketoglutarate (KTG) via a reaction catalyzed by ω-amidase (AMD). In the first procedure, KTG generated in the AMD reaction initiates a biocatalytic cascade in which the concerted action of alanine transaminase and lactate dehydrogenase results in the oxidation of NADH. In the second procedure, KTG generated from KGM is reductively aminated, with the concomitant oxidation of NADH, in a reaction catalyzed by L-glutamic dehydrogenase. In both assays, the decrease in optical absorbance (λ=340 nm) corresponding to NADH oxidation is used to quantify concentrations of KGM. The two analytical procedures were applied to 50% (v/v) human serum diluted with aqueous solutions containing the assay components and spiked with concentrations of KGM estimated to be present in normal human plasma and in plasma from hyperammonemic patients. Since KTG is the product of AMD-catalyzed hydrolysis of KGM, in a separate study, this compound was used as a surrogate for KGM. Statistical analyses of samples mimicking the concentration of KGM assumed to be present in normal and pathological concentration ranges were performed. Both enzymatic assays for KGM were confirmed to discriminate between the predicted normal and pathophysiological concentrations of the analyte. The present study is the first step toward the development of a clinically useful probe for KGM analysis in biological fluids.