Neuroactive amino acids in hepatic encephalopathy

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.

Effect of taurine on chronic and acute liver injury: Focus on blood and brain ammonia

Hyperammonemia is associated with chronic and acute liver injury. There is no promising therapeutic agent against ammonia-induced complications. Hence, finding therapeutic molecules with safe profile of administration has clinical value. The present study was conducted to evaluate the role of taurine (TA) administration on plasma and brain ammonia and its consequent events in different models of chronic and acute liver injury and hyperammonemia. Bile duct ligated (BDL) rats were used as a model of chronic liver injury. Thioacetamide and acetaminophen-induced acute liver failure were used as acute liver injury models. A high level of ammonia was detected in blood and brain of experimental groups. An increase in brain ammonia level coincided with a decreased total locomotor activity of animals and significant changes in the biochemistry of blood and also liver tissue. TA administration (500 and 1000 mg/kg, i.p), effectively alleviated liver injury and its consequent events including rise in plasma and brain ammonia and brain edema. The data suggested that TA is not only a useful and safe agent to preserve liver function, but also prevented hyperammonemia as a deleterious consequence of acute and chronic liver injury.

Implications and mechanism of action of gabapentin in neuropathic pain

Gabapentin is an anti-epileptic agent but now it is also recommended as first line agent in neuropathic pain, particularly in diabetic neuropathy and post herpetic neuralgia. α2δ-1, an auxillary subunit of voltage gated calcium channels, has been documented as its main target and its specific binding to this subunit is described to produce different actions responsible for pain attenuation. The binding to α2δ-1 subunits inhibits nerve injury-induced trafficking of α1 pore forming units of calcium channels (particularly N-type) from cytoplasm to plasma membrane (membrane trafficking) of pre-synaptic terminals of dorsal root ganglion (DRG) neurons and dorsal horn neurons. Furthermore, the axoplasmic transport of α2δ-1 subunits from DRG to dorsal horns neurons in the form of anterograde trafficking is also inhibited in response to gabapentin administration. Gabapentin has also been shown to induce modulate other targets including transient receptor potential channels, NMDA receptors, protein kinase C and inflammatory cytokines. It may also act on supra-spinal region to stimulate noradrenaline mediated descending inhibition, which contributes to its anti-hypersensitivity action in neuropathic pain.

Management of hepatic encephalopathy by traditional chinese medicine

In spite of the impressive progress in the investigation of hepatic encephalopathy (HE), the complex mechanisms underlying the onset and deterioration of HE are still not fully understood. Currently, none of the existing theories provide conclusive explanations on the symptoms that link liver dysfunction to nervous system disorders and clinical manifestations. This paper summarized the diagnostic and therapeutic approaches used for HE in modern medicine and traditional Chinese medicine and provided future perspective in HE therapies from the viewpoint of holistic and personalized Chinese medicine.

Two-dimensional MR spectroscopy of minimal hepatic encephalopathy and neuropsychological correlates in vivo

PURPOSE

To evaluate regional cerebral metabolic and structural changes in patients with minimal hepatic encephalopathy (MHE) using two-dimensional (2D) MR spectroscopy (MRS) and T( (1) )-weighted MRI, to correlate the observed MR changes with neuropsychological (NP) test scores, and to compare the diagnostic accuracy of MRI, 2D MRS, and NP tests in discriminating between patients and healthy subjects.

MATERIALS AND METHODS

Thirty-three MHE patients and 30 healthy controls were investigated. The 2D localized correlated spectroscopy (L-COSY) was performed in the frontal and occipital brain on a 1.5 Tesla (T) MR scanner. The NP test battery included 15 tests, grouped into 6 cognitive domains. Globus pallidus signal intensities were calculated from T(1)-weighted images.

RESULTS

The 2D MRS showed significant differences in ratios of the following metabolite(s) peaks with respect to creatine (Cr): decreased myo-inositol (mI), choline (Ch), mICh, and increased (glutamate plus glutamine) (Glx) in patients compared with healthy subjects in both occipital and frontal lobes. Frontal lobe taurine also showed a decline in patients. The NP test results revealed declines in cognitive speed, motor function, executive function, and global cognitive status. Significant correlations were found between the altered metabolites and NP tests. Alteration in the mICh/Cr ratio was noted as a powerful discriminant between healthy subjects and the patients.

CONCLUSION

The study demonstrates that relative metabolite levels determined by 2D MRS, in particular mICh/Cr, provide the best diagnostic prediction for MHE. The results suggest that depletions of myo-inositol, choline and taurine with respect to creatine correlate with measures of neuropsychological impairment.

Albumin dialysis has a favorable effect on amino acid profile in hepatic encephalopathy

According to one popular theory, hepatic encephalopathy (HE) is partly caused by an imbalance in plasma amino acid levels. The Fischer's ratio between branched chain amino acids (BCAAs) and aromatic amino acids (AAAs) correlates with the degree of HE; the lower Fischer's ratio, the higher the grade of HE. Extra-corporeal liver support systems, like MARS(R)-albumin dialysis (Molecular Adsorbents Recirculating System), can improve HE. The MARS(R) system uses a hyperosmolar albumin circuit to remove both water-soluble and albumin-bound substances. Plasma levels of neuroactive amino acids were analyzed in 82 consecutive patients with life-threatening liver failure admitted to our ICU. All patients fulfilled our indications for MARS treatment and most also fulfilled the criteria for liver transplantation (LTx). In patients with acute liver failure (ALF), as compared to those with acute decompensation of chronic liver failure (AcOChr), levels of leucine and isoleucine were significantly higher before MARS(R) treatment. In all patients, before MARS(R) treatment the higher the grade of HE grade the lower was the Fischer's ratio and higher were the levels of inhibitory neuroactive amino acids. During MARS(R) treatments the Fischer's ratio increased, and the grade of HE decreased. The increase in Fischer's ratio was mainly due to the decrease in AAAs. The plasma levels of neuroactive amino acids, methionine, glutamine, glutamate, histidine and taurine decreased during MARS(R)-treatment. In this study MARS(R)-albumin dialysis had a favorable effect on the plasma amino acid profile of patients with HE.

Flumazenil-Induced Improvement of the Central Dopaminergic System in Rats with Acute Hepatic Failure

Several reports have demonstrated the alleviation of hepatic encephalopathy by flumazenil, an antagonist of benzodiazepine receptors. As changes in central monoaminergic activity are involved in the mechanisms for hepatic encephalopathy, the effects of flumazenil on central monoaminergic activity were evaluated in acute hepatic failure produced by ischemia-reperfusion injury in rats. Eighteen male Wistar rats were evenly assigned to three groups: sham-operated group given saline, liver-ischemic group given saline, and liver-ischemic group given flumazenil. Flumazenil (1 mg/kg) or saline (10 mL/kg) was intraperitoneally administered three times, at 1, 6, and 24 hours after 90 minutes of liver ischemia produced by occlusion of the left portal vein. The extracellular concentrations of neurotransmitter amino acids, monoamines, and their metabolites were determined in the striatum using a microdialysis procedure. Another set of 12 rats was subjected to liver ischemia, and the effect of flumazenil on spontaneous motor activity was examined after 24 hours. The extracellular concentration of 3,4-dihydroxyphenylacetic acid, a metabolite of dopamine, decreased to 39% of that in sham-operated animals 24 hours after surgery (P < 0.05), although the dopamine level did not change. The treatment with flumazenil completely abolished the decrease in the metabolite (P < 0.05). Although the glutamate level in the injured animals decreased to 42% of that in sham-operated animals (P < 0.05), no remarkable increase in the glutamate level was observed in animals treated with flumazenil. Spontaneous motor activity decreased 24 hours after surgery in animals subjected to liver ischemia. Flumazenil led to improvement of spontaneous motor activity 5 minutes after administration, but this effect was not observed after 30 minutes. The restoration of the central dopaminergic function may be a contributing factor in the improvement of hepatic encephalopathy.

The relation between plasma tyrosine concentration and fatigue in primary biliary cirrhosis and primary sclerosing cholangitis

BACKGROUND

In primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) fatigue is a major clinical problem. Abnormal amino acid (AA) patterns have been implicated in the development of fatigue in several non-hepatological conditions but for PBC and PSC no data are available. This study aimed to identify abnormalities in AA patterns and to define their relation with fatigue.

METHODS

Plasma concentrations of tyrosine, tryptophan, phenylalanine, valine, leucine and isoleucine were determined in plasma of patients with PBC (n = 45), PSC (n = 27), chronic hepatitis C (n = 22) and healthy controls (n = 73). Fatigue and quality of life were quantified using the Fisk fatigue severity scale, a visual analogue scale and the SF-36.

RESULTS

Valine, isoleucine, leucine were significantly decreased in PBC and PSC. Tyrosine and phenylalanine were increased (p < 0.0002) and tryptophan decreased (p < 0.0001) in PBC. In PBC, but not in PSC, a significant inverse relation between tyrosine concentrations and fatigue and quality of life was found. Patients without fatigue and with good quality of life had increased tyrosine concentrations compared to fatigued patients. Multivariate analysis indicated that this relation was independent from disease activity or severity or presence of cirrhosis.

CONCLUSION

In patients with PBC and PSC, marked abnormalities in plasma AA patterns occur. Normal tyrosine concentrations, compared to increased concentrations, may be associated with fatigue and diminished quality of life.

Unusual manifestation of hepatic encephalopathy in two Irish wolfhound siblings

In hepatic encephalopathy the brain lesions are usually characterised by polymicrocavitation, preferentially in the white matter, and the occurrence of Alzheimer type II cells. This paper describes an unusual manifestation of hepatic encephalopathy in two Irish wolfhound siblings in which the white matter was not involved predominantly. Both puppies had developed progressive neurological disturbances and signs of blindness. Histologically, there were widespread spongiform changes in the neuropil and fibre bundles interspersed within the grey matter, and there were some neuronal vacuoles. In both animals, the regions of the brain mainly affected were the nucleus caudatus, amygdala, cerebellar nuclei, mesencephalon, thalamus, hypothalamus and medulla oblongata. An astrogliosis characterised by Alzheimer type II-like cells was also observed. Electron microscopy revealed a splitting of the myelin sheath. No infectious agents such as rabies virus, canine distemper virus or prion proteins were detected. The main findings in the portal regions of the liver consisted of a dilatation of the lymphatic vessels and increased numbers of small arteries, indicating that a portosystemic shunt was the probable cause of the spongiform brain lesions.

Neurophysiological evidence of cognitive impairment in patients without hepatic encephalopathy after transjugular intrahepatic portosystemic shunts

OBJECTIVES

We aimed to test the hypothesis that subclinical cognitive brain dysfunction in cirrhotic patients would deteriorate after a transjugular intrahepatic portosystemic shunt (TIPS) in the absence of clinically detectable hepatic encephalopathy.

METHODS

Out of 49 consecutive cirrhotic patients receiving elective TIPS for recurrent variceal hemorrhage, we identified 22 patients who were not encephalopathic and had not undergone liver transplantation at 6-month follow-up and confirmed TIPS patency by Doppler ultrasound. Patients were tested before and 6 months after TIPS implantation using event-related (P300) cognitive evoked potentials, late somatosensory median nerve (N70) potentials, and standard psychometric tests (Mini-Mental State and trailmaking test A). Twenty-two age-matched healthy subjects served as controls.

RESULTS

Relative to controls, patients showed significantly impaired P300 and N70 latencies and abnormal psychometric test results at baseline. Six months after the TIPS, a further impairment of P300 latency was observed (p = 0.005), whereas no relevant changes in N70 latency and psychometric test results occurred.

CONCLUSIONS

In cirrhotic patients with portal hypertension, neurophysiological signs of cognitive brain dysfunction are detectable in the absence of hepatic encephalopathy. A further subclinical deterioration of cognitive processing was observed 6 months after the TIPS. These findings demonstrate an aggravation of subclinical hepatic encephalopathy after a TIPS.

Pathogenesis of hepatic encephalopathy

Hepatic encephalopathy is considered to be a reversible metabolic encephalopathy, which occurs as a complication of hepatocellular failure and is associated with increased portal-systemic shunting of gut-derived nitrogenous compounds. Its manifestations are most consistent with a global depression of CNS function, which could arise as a consequence of a net increase in inhibitory neurotransmission, due to an imbalance between the functional status of inhibitory (e.g., GABA) and excitatory (e.g., glutamate) neurotransmitter systems. In liver failure, factors that contribute to increased GABAergic tone include increased synaptic levels of GABA and increased brain levels of natural central benzodiazepine (BZ) receptor agonists. Ammonia, present in modestly elevated levels, may also augment GABAergic tone by direct interaction with the GABAA receptor, synergistic interactions with natural central BZ receptor agonists, and stimulation of astrocytic synthesis and release of neurosteroid agonists of the GABAA receptor. Thus, there is a rationale for therapies of HE that lower ammonia levels and incrementally reduce increased GABAergic tone towards the physiologic norm.

Asterixis induced by gabapentin

We report the case of a patient with postherpetic neuralgia who developed asterixis while being treated with gabapentin. We discuss the possible mechanism of asterixis in this patient.

Neurologic complications in the intensive care unit

Neurologic complications resulting from critical illness and intensive care unit therapies are common, but frequently unrecognized because these patients are often intubated, sedated, and, occasionally, receiving neuromuscular blocking agents. Neurologic complications are associated with an increased intensive care unit mortality. This article discusses central nervous system complications that are secondary to critical illness or to therapeutic interventions in the critically ill patient.

Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist--a review of preclinical data

N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential in numerous CNS disorders ranging from acute neurodegeneration (e.g. stroke and trauma), chronic neurodegeneration (e.g. Parkinson's disease, Alzheimer's disease, Huntington's disease, ALS) to symptomatic treatment (e.g. epilepsy, Parkinson's disease, drug dependence, depression, anxiety and chronic pain). However, many NMDA receptor antagonists also produce highly undesirable side effects at doses within their putative therapeutic range. This has unfortunately led to the conclusion that NMDA receptor antagonism is not a valid therapeutic approach. However, memantine is clearly an uncompetitive NMDA receptor antagonist at therapeutic concentrations achieved in the treatment of dementia and is essentially devoid of such side effects at doses within the therapeutic range. This has been attributed to memantine's moderate potency and associated rapid, strongly voltage-dependent blocking kinetics. The aim of this review is to summarise preclinical data on memantine supporting its mechanism of action and promising profile in animal models of chronic neurodegenerative diseases. The ultimate purpose is to provide evidence that it is indeed possible to develop clinically well tolerated NMDA receptor antagonists, a fact reflected in the recent interest of several pharmaceutical companies in developing compounds with similar properties to memantine.

Amino acid metabolism in liver disease

The impairment of transsulphuration during methionine degradation in hepatic failure can be counteracted by treatment with S-adenosylmethionine. Regarding the pathogenesis of hepatic encephalopathy, no convincing evidence exists for tryptophan, glutamine or glutamate being involved. Portal-systemic shunting-induced hyperammonaemia may reduce plasma branched-chain amino acids. The glucose effect on urea synthesis does not exist in cirrhosis.

Improvement of chronic hepatic encephalopathy in dogs by the benzodiazepine-receptor partial inverse agonist sarmazenil, but not by the antagonist flumazenil

Therapeutic modulation of the increased GABAergic tone in chronic hepatic encephalopathy (HE) by the benzodiazepine receptor (BR) antagonist flumazenil (F) has led to conflicting results in humans and animal models for HE. The BR inverse agonist sarmazenil (S) has only been used in animal models of acute HE. Therefore we investigated the effects of intravenous injection of F and S in dogs with chronic HE 8 to 12 weeks after placement of a portocaval shunt and 40% hepatectomy (n=7), compared to sham-operated pair-fed controls (n=7). The HE dogs had hyperammonemia (298 +/- 48 microM v 33 +/- 3 before surgery (mean +/- SEM)) and signs of HE at the start of the experiments (0.9 +/- 0.1 (scale 0-4)). Three (S3) and 8 (S8) mg/kg of S resulted in a significant improvement of encephalopathy (grade 0.9 +/- 0.2 immediately before v 0.5 +/- 0.1 after injection (S3) and 0.7 +/- 0.1 v 0.3 +/- 0.1 (S8)) and increase in mean dominant frequency of the EEG (MDF; 9.1 +/- 0.7 Hz v 11.1 +/- 0.3 (S3) and 8.9 +/- 0.5 v 11.0 +/- 0.3 (S8)) in HE dogs, whereas 15 mg/kg of S, 3 and 8 mg/kg of F, and the vehicle had no significant effects. The efficacy of S in these dogs is consistent with an increased GABAergic tone in the pathogenesis of chronic HE. The lack of effects of F makes a role for endogenous benzodiazepines herein unlikely.

The influence of alcoholism and cirrhosis on benzodiazepine receptor function

In a previous study we reported that the affinity of the platelet benzodiazepine receptor was greater in alcoholic cirrhotic patients compared with normal controls and that there were detectable ligands for the neuronal benzodiazepine receptor in plasma from both alcoholic and nonalcoholic cirrhotic patients. The aim of the present study was to assess the separate contributions of alcoholism and cirrhosis to the presence of ligands in plasma for the neuronal and peripheral benzodiazepine receptors and to changes in peripheral benzodiazepine receptor binding in platelets. These parameters were measured in 10 alcoholic cirrhotics, 9 nonalcoholic cirrhotics, 7 alcoholics with a normal liver function, and 15 nonalcoholic subjects and normal liver function. Both groups of alcoholics had been abstinent for several months and the nonalcoholic groups had abstained for 24 h before the study. The concentration of ligands for the peripheral benzodiazepine receptor were significantly higher in both cirrhotic groups compared with the other two groups, suggesting that cirrhosis was responsible for this accumulation. Furthermore, the cirrhotic patients with detectable concentrations of these ligands had significantly poorer episodic memory than those without ligands. However, the presence of ligands for the peripheral benzodiazepine receptor did not correlate with the change in receptor affinity, which was increased in the alcoholic cirrhotic group compared with all other groups. Neither cirrhosis nor alcoholism altered the peripheral benzodiazepine receptor number. The cirrhotic patients with detectable ligands for the neuronal benzodiazepine receptor showed psychomotor slowing and executive dysfunction. The results suggest that the ligands for the peripheral benzodiazepine receptor may contribute to some of the cognitive deficits seen in hepatic encephalopathy, but are not responsible for the receptor affinity change seen in the alcoholic cirrhotics. This affinity change is not solely due to the effects of alcohol and could possibly serve as a marker for those at risk for developing alcoholic cirrhosis.