Hepatic encephalopathy: experimental studies on the pathogenesis

Aims of this thesis: 1. To study, in rabbits, the suitability of experimental acute liver failure and acute hyperammonemia simulating acute liver failure for the study of hepatic encephalopathy and ammonia toxicity. 2. To study glutamate neurotransmission in rabbits with acute liver failure and acute hyperammonentia. 3. To determine the role of the changes in glutamate neurotransntission found in 2 in the development of hepatic encephalopathy. 18The pathogenesis of hepatic encephalopathy is largely unknown. Ammonia was the flrst toxin seriously considered to be of importance in the pathogenesis, has been subsequently rejected, but now appears to return to the forefront of "hepatic neurochemistry" (58). In theory, hyperammonemia can disturb normal brain ftmction through interference with basic cell metabolism (e.g. pH-regulation and water and energy balance)(59-61), electrophysiologic membrane ftmction (depending on ion pumps)(62) and biochemical communication between neurons, i.e. neurotransmission (depending on neurotransmitters). With regard to neurotransmission, one of the current opinions on the pathogenesis of hepatic encephalopathy is a dysbalance between neuro-inhibitory and neuro-excitatory neurotransmitters (63). Several groups have proposed that neuroinhibition via GABA or endogenous benzodiazepines is enhanced; we are investigating whether excitatory neurotransmission -especially glutamate neurotransmission- is altered during hepatic

45CaCl2 autoradiography in brain from rabbits with encephalopathy from acute liver failure or acute hyperammonemia

In experimental hepatic encephalopathy and hyperammonemia, extracellular levels of glutamate are increased in hippocampus and cerebral cortex. It has been suggested that overstimulation of glutamate receptors causes a pathological entry of calcium into neurons via receptor-operated (NMDA- and AMPA-type) or voltage-dependent calcium channels leading to calcium overload and cell death. Neurodegeneration as a result of exposure to excitotoxins, including glutamate, can be localized and quantified using45CaCl2 autoradiography. This approach was used to study cerebral calcium accumulation in rabbits with acute liver failure and acute hyperammonemia. Acute liver failure was induced in 6 rabbits, acute hyperammonemia in 4 rabbits; 4 control rabbits received sodium-potassium-acetate. At the start of the experiment 500 µCi45CaCl2 was given intravenously. After development of severe encephalopathy, the animals were killed by decapitation. All rabbits with acute liver failure or acute hyperammonemia developed severe encephalopathy, after 13.2±1.7 and 19.3±0.5 hours respectively (mean±SEM). Plasma ammonia levels were 425±46 and 883±21 µmol/l, respectively (p<0.05). Control rabbits maintained normal plasma ammonia levels (13±5 µmol/l), demonstrated normal behaviour throughout the study and were sacrificed after 16 hours.45Ca2+-autoradiograms of 40 µm brain sections were analyzed semiquantitatively using relative optical density and computerized image analysis. As compared to background levels45Ca was not increased in hippocampus or any other brain area of rabbits with severe encephalopathy from acute liver failure or acute hyperammonemia. This suggests that, despite increased extracellular brain glutamate levels in these conditions, glutamate neurotoxicity was not important for the development of encephalopathy in these rabbits

Management of Thrombocytopenia in Chronic Liver Disease: Focus on Pharmacotherapeutic Strategies

Thrombocytopenia (platelet count <150 × 109/L) often complicates chronic liver disease, impeding optimal management of these patients. The prevalence of this manifestation ranges from 6 % among non-cirrhotic patients with chronic liver disease to 70 % among patients with liver cirrhosis. It has also been shown that the severity of liver disease is associated with both prevalence and level of thrombocytopenia. Its development is often multifactorial, although thrombopoietin is thought to be a major factor. The discovery of and ability to clone thrombopoietin led to new treatment opportunities for this clinical manifestation. This review discusses data on the three most important thrombopoietin receptor agonists: eltrombopag, avatrombopag, and romiplostim. Currently, only eltrombopag is approved for usage among patients with thrombocytopenia and chronic hepatitis C virus infection in order to initiate and maintain interferon-based antiviral treatment. Nevertheless, the optimal management of hematologic abnormalities among patients with chronic liver disease, and its risk for bleeding complications, is still a matter of discussion. Thrombocytopenia definitely contributes to hemostatic defects but is often counterbalanced by the enhanced presence of procoagulant factors. Therefore, a thorough assessment of the patient's risk for thrombotic events is essential when the use of thrombopoietin receptor agonists is considered among patients with chronic liver disease and thrombocytopenia

The treatment of hepatitis C: history, presence and future

The treatment of chronic hepatitis C has made remarkable progress over the past two decades. For interferon-alpha monotherapy, sustained virological response rates were between 2 and 9% in genotype 1 and between 16 and 23% in genotypes 2 and 3. By adjusting treatment duration up to 48 weeks for genotype 1 and combining regular interferon-alpha with ribavirin, sustained response rates could be improved to 28 to 31% in genotype 1 and around 65% in genotypes 2 and 3. Attempts to further increase efficacy included the addition of amantadine without conclusive evidence up till now. With the recent introduction of long-acting pegylated interferon-alpha in combination with ribavirin, sustained virological response rates of 8o% can be obtained in genotypes 2 and 3. However, sustained virological response rates for patients with either genotype 1, nonresponse to prior treatment, cirrhosis or a combination of these characteristics are still less than 50%. In view of results with daily high-dose interferon-alpha induction in combination with prolongation of treatment duration up to 18 months, such patients might benefit from induction and prolonged PEG-IFN-alpha treatment and should be treated in an experimental setting

Serum levels of caspase-cleaved cytokeratin 18 (CK18-Asp396) predict severity of liver disease in chronic hepatitis B

Background and aim: Caspase-cleaved cytokeratin 18 (CK18-Asp396) is a potential clinically useful biomarker in liver disease as it is released from hepatocytes during apoptosis. In this study, we investigated serum CK18-Asp396 levels in chronic hepatitis B (CHB). Patients and methods: Overall, 163 patients with CHB were included. Serum CK18-Asp396 levels were determined by enzyme-linked immunosorbent assay (ELISA), and results were related to steatosis grade, histological activity index, inflammation score, and METAVIR fibrosis grade as well as to viral load, serum levels of liver enzymes, and albumin. Receiver operating characteristic analysis was used to evaluate the diagnostic performance of serum CK18-Asp396 levels for assessing disease activity. Results: A higher level of serum CK 18 concentrations was found in patients with significant inflammation vs no significant inflammation (378.5 [interquartile range {IQR}: 173.2-629.6] vs 137.3 [87.5-197.7], P < 0.05; approximately threefold increase) and in patients with significant fibrosis vs no significant fibrosis (177.8 [IQR: 120.8-519.1] vs 142.7 [IQR: 88.8-214.4], P < 0.05; 1.25-fold increase). There was no differential CK 18 level by degree of steatosis. CK 18 was an independent predictor of significant inflammation with an 82% specificity and a 94% negative predictive value. We found the strongest correlation of CK 18 with alanine aminotransferase and aspartate aminotransferase (both r = 0.52; P < 0.001), but less with albumin (r = -0.24; P < 0.05) and viral load (log) (r = 0.19; P < 0.05). Conclusion: CHB appears to be accompanied by continuous high levels of hepatocyte apoptosis as judged from serum CK 18, suggesting that elimination of the infected compartment constitutes a defensive strategy against disease. Accordingly, CK 18 works as an independent predictor of significant inflammation with a high specificity

Flumazenil does not improve hepatic encephalopathy associated with acute ischemic liver failure in the rabbit

The effect of flumazenil, a benzodiazepine antagonist, on hepatic encephalopathy was studied in rabbits with acute hepatic failure induced by a two-stage liver devascularization procedure. The rabbits were randomized for treatment with 5 mg/kg of flumazenil or the placebo. The drug was administered at two easily recognizable time points in the course of the encephalopathy: first, when the righting reflex was disturbed, and second, when the animal could no longer achieve to the sitting position. The response after flumazenil did not differ from that after the placebo, as measured by clinical evaluation and automated EEG analysis. Furthermore, the progression of the encephalopathy, as measured by the survival time after the first injection, was not affected by flumazenil

Binding of the ligand [3H]MK-801 to the MK-801 binding site of the N-methyl-D-aspartate receptor during experimental encephalopathy from acute liver failure and from acute hyperammonemia in the rabbit

Binding of the ligand [3H]MK-801 to the MK-801 binding site of the N-methyl-D-aspartate (NMDA) receptor population on brain homogenates in rabbits was studied during experimental encephalopathy from acute liver failure and from acute hyperammonemia in the rabbit. Homogenates were prepared from brain cortex, hippocampus and striatum. Hepatic encephalopathy was induced by a two-stage liver devascularization procedure and acute hyperammonemia by a prolonged ammonium-acetate infusion; rabbits receiving a sodium-potassium-acetate infusion served as controls. In these animal models extracellular brain glutamate levels are known to be elevated. However no significant alterations in the number nor the affinity of the MK-801 binding sites of the NMDA receptors were found during acute liver failure and acute hyperammonemia. These findings suggest that the NMDA receptor population remains unaltered in experimental encephalopathy from acute liver failure and acute hyperammonemia, desp

Negative Regulation of Hepatitis C Virus Specific Immunity Is Highly Heterogeneous and Modulated by Pegylated Interferon-Alpha/Ribavirin Therapy

Specific inhibitory mechanisms suppress the T-cell response against the hepatitis C virus (HCV) in chronically infected patients. However, the relative importance of suppression by IL-10, TGF-β and regulatory T-cells and the impact of pegylated interferon-alpha and ribavirin (PegIFN-α/ribavirin) therapy on these inhibitory mechanisms are still unclear. We revealed that coregulation of the HCV-specific T-cell responses in blood of 43 chronic HCV patients showed a highly heterogeneous pattern before, during and after PegIFN-α/ribavirin. Prior to treatment, IL-10 mediated suppression of HCV-specific IFN-γ production in therapy-naive chronic HCV patients was associated with higher HCV-RNA loads, which suggests that protective antiviral immunity is controlled by IL-10. In addition, as a consequence of PegIFN-α/ribavirin therapy, negative regulation of especially HCV-specific IFN-γ production by TGF-β and IL-10 changed dramatically. Our findings emphasize the importance of negative regulation for the dysfunctional HCV-specific immunity, which should be considered in the design of future immunomodulatory therapies