Monoamines and metabolites in autopsied brain tissue from cirrhotic patients with hepatic encephalopathy

A double-blind randomized controlled trial to assess efficacy of bromocriptine in cirrhotic patients with hepatic parkinsonism

BACKGROUND

Parkinsonism like features can be seen in cirrhotics, possibly related to alterations in brain dopamine metabolism, transport and receptor integrity at basal ganglia. Hepatic parkinsonism is often not suspected and only ammonia-reducing therapies are given to such patients. We investigated the efficacy and safety of bromocriptine, a dopaminergic agent, in patients with hepatic parkinsonism.

PATIENTS AND METHODS

Cirrhotics were screened for the presence of extrapyramidal symptoms and were diagnosed as hepatic parkinsonism if any two of tremor, bradykinesia and/or rigidity were present, supported by MRI brain showing T1 hyperintensities in basal ganglia and substantia nigra. Patients were randomized to receive placebo (Gr A, n = 22) or bromocriptine (Gr B, n = 24) for 12 weeks. Complete, partial and non-response were defined as 30%, 10%-30% and <10% reduction,respectively, in Unified Parkinson's Disease Rating Scale motor score.

RESULTS

Of 1016 cirrhotics, 50 (4.9%) had hepatic parkinsonism. Patients in two treatment groups were comparable for MELD score, arterial NH3 and frequency of portosystemic shunts. Bromocriptine therapy for 12 weeks resulted in improvement in rigidity, tremors, bradykinesia and gait compared to placebo with complete and partial response in seven vs none (29.1%, 0%, P < 0.01) and 12 vs one (50%, 4.5%, P < 0.01) patients. Prolonged and more severe motor symptoms were associated with non-response to bromocriptine therapy. There were no major side effects in either treatment group.

CONCLUSIONS

Hepatic parkinsonism is seen in ~5% cirrhotics. Bromocriptine is a safe and effective therapy for these patients and is more effective in mild to moderate hepatic parkinsonism.

Hashimoto encephalopathy with high plasma monoamine metabolite levels: a case report

Hashimoto encephalopathy (HE) is believed to be an immune-mediated disorder associated with Hashimoto's thyroiditis. It was suggested that neuropsychiatric symptoms, the presence of antithyroid antibody, and good response to steroids were important for the diagnosis of HE. It has been reported that homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), which are monoamine metabolites of dopamine and noradrenaline, respectively, are the possible biomarkers of neuropsychiatric diseases. We report a case of Hashimoto encephalopathy, in which we longitudinally measured the plasma levels of monoamine metabolites. A 52-year-old woman developed acute psychosis, and was admitted to the psychiatric ward of our hospital due to psychotic state, 6 days after a traffic accident. An extensive evaluation showed no remarkable findings, except an increase in antithyroglobulin antibodies. Plasma levels of HVA and MHPG were extremely high at 66.5 and 41.8 ng/mL, respectively. On day 16, 50 mg/day oral prednisolone was administered, which improved her psychotic symptoms. Plasma levels of HVA and MHPG decreased to 7.2 and 9.9 ng/mL, respectively, on day 19. After the temporary worsening of psychosis and increase in plasma levels of HVA and MHPG, the dosage of prednisolone was tapered and low-dose risperidone was started. Her psychiatric symptoms gradually improved and plasma monoamine metabolite levels decreased again (HVA: 17.9 ng/mL; MHPG: 7.7 ng/mL). Although autoimmune mechanism has been suggested to be involved in HE, neural mechanism and pathogenesis of HE remain unknown. Our findings suggest that monoaminergic neural activity might be associated with psychotic symptoms in patients with HE and plasma levels of monoamine metabolites might be useful as state markers.

Impact of depressive symptoms and hepatic encephalopathy on health-related quality of life in cirrhotic hepatitis C patients

Depression, common in chronic medical conditions, and hepatic encephalopathy (HE), a reversible neuropsychiatric syndrome due to liver dysfunction, are associated with impaired health-related quality of life (HRQOL) in cirrhosis and hepatitis C (HCV). This study investigated the impact of depression and HE on HRQOL in cirrhotic patients with HCV. A convenience sample of 43 ambulatory patients, with varying degrees of cirrhosis secondary to HCV, was prospectively enrolled in this study. Participants were assessed for any current depressive, fatigue, and daytime sleepiness symptoms and underwent a psychometric evaluation to determine the presence of HE symptoms. Participants reported current HRQOL on general health and liver disease-specific questionnaires. Diagnosis and current health status were confirmed via medical records. The associations between disease severity, depressive symptoms, HE, fatigue, and daytime sleepiness were measured. Predictors of HRQOL in this sample were determined. Depressive symptoms (70 %) and HE (77 %) were highly prevalent in this sample, with 58 % actively experiencing both conditions at the time of study participation. A significant positive association was found between depressive symptoms and HE severity (P = .05). Depressive symptoms were significantly associated with fatigue (P < .001), daytime sleepiness (P < .001), general HRQOL (P < .001), and disease-specific HRQOL (P < .001). HE was significantly associated with fatigue (P = .02), general HRQOL (P < .001), and disease-specific HRQOL (P < .001). Depressive symptoms and HE were significant predictors of reduced HRQOL (P < .001), with depressive symptoms alone accounting for 58.8 % of the variance. Depressive symptoms and HE accounted for 68.0 % of the variance. Findings suggest a possible pathophysiological link between depression and HE in cirrhosis, and potentially a wider-reaching benefit of treating minimal and overt HE than previously appreciated.

Differential regional responsiveness of astroglia in mild hepatic encephalopathy: An Immunohistochemical approach in bile duct ligated rat

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs in both acute and chronic liver failure. However, the pathomechanisms of the disease remains obscure. Neuropathological studies have demonstrated a primary gliopathy in humans as well as in animal models of chronic and acute liver failure. Here, we have investigated in an animal model of mild HE: the bile duct ligated rat (BDL) at the cirrhotic stage (4 weeks after surgery), the expression of the key marker of mature astrocytes; the glial fibrillary acidic protein (GFAP) in different brain areas such as: Substantia nigra pars compacta (SNc), Ventral tegmental area (VTA), hippocampus, dorsal striatum and brain cortex by means of immunohistochemistry. The immunohistochemical study showed, in BDL compared to the operated controls (shams), a diminished astrocyte reactivity corresponding to a loss of GFAP expression within SNc, VTA, hippocampus and dorsal striatum (p<0.05),whereas in the brain cortex astrocytes appeared strongly immunoreactive with increased GFAP expression (p<0.05) as compared to shams. Our finding demonstrated differential astroglial responses which depend to the specificity of the area investigated and its particular neuronal neighboring environment, and could have possible outcomes on the diverse neuronal functions especially those observed during the different episodes of hepatic encephalopathy.

Dopamine Burden Triggers Neurodegeneration via Production and Release of TNF-α from Astrocytes in Minimal Hepatic Encephalopathy

Dopamine (DA)-induced learning and memory impairment is well documented in minimal hepatic encephalopathy (MHE), but the contribution of DA to neurodegeneration and the involved underlying mechanisms are not fully understood. In this study, the effect of DA on neuronal apoptosis was initially detected. The results showed that MHE/DA (10 μg)-treated rats displayed neuronal apoptosis. However, we found that DA (10 μM) treatment did not induce evident apoptosis in primary cultured neurons (PCNs) but did produce TNF-α in primary cultured astrocytes (PCAs). Furthermore, co-cultures between PCAs and PCNs exposed to DA exhibited increased astrocytic TNF-α levels and neuronal apoptosis compared with co-cultures exposed to the vehicle, indicating the attribution of the neuronal apoptosis to astrocytic TNF-α. We also demonstrated that DA enhanced TNF-α production from astrocytes by activation of the TLR4/MyD88/NF-κB pathway, and secreted astrocytic TNF-α-potentiated neuronal apoptosis through inactivation of the PI3K/Akt/mTOR pathway. Overall, the findings from this study suggest that DA stimulates substantial production and secretion of astrocytic TNF-α, consequently and indirectly triggering progressive neurodegeneration, resulting in cognitive decline and memory loss in MHE.

Hepatic encephalopathy in alcoholic cirrhosis

Hepatic encephalopathy (HE) is a serious neuropsychiatric complication of cirrhosis in alcoholic patients that is characterized clinically by personality changes, sleep abnormalities, and impaired motor coordination, as well as cognitive dysfunction progressing to stupor and coma. Procedures used for diagnosis and grading of HE include neurologic assessment, electroencephalography, psychometric testing, and use of the critical flicker frequency test. Neuropathologically, HE in cirrhosis is principally a disorder of neuroglia characterized by Alzheimer type II astrocytosis and activation of microglia. However, thalamic and cerebellar neuronal pathologies have been noted as well as lesions to globus pallidus and substantia nigra, leading to a condition known as "parkinsonism in cirrhosis." Multiple mechanisms have been proposed to account for the pathogenesis of HE in cirrhosis, including the neurotoxic actions of ammonia and manganese (normally removed via the hepatobiliary route), impaired brain energy metabolism, central proinflammatory mechanisms, and alterations of both excitatory and inhibitory neurotransmission. Treatment of HE in cirrhosis continues to rely on ammonia-lowering strategies such as lactulose, antibiotics, probiotics and l-ornithine l-aspartate with nutritional management consisting of adequate (but not excessive) dietary protein and vitamin B1 supplements. l-DOPA may improve parkinsonian symptoms. Liver transplantation leads to recovery of central nervous system function in the majority of cases.

Loss of tyrosine hydroxylase expression within the nigro-striato-cortical pathways in the cirrhotic rat: the possible restorative effect of the neurosteroid dehydroepiandrosterone sulfate

Hepatic encephalopathy (HE) is a neuropsychiatric disorder occurring as a consequence of both acute and chronic liver failure. Advanced HE is generally accompanied with extrapyramidal symptoms including rigidity and tremor, which may reflect alterations of the dopaminergic system. Recently we reported a beneficial effect of the neuroactive steroid dehydroepiandrosterone sulfate (DHEAS) in cirrhotic rats, however the mechanisms of such an effect by DHEAS were not addressed. In the present study, we describe the changes of the dopaminergic system occurring in the cirrhotic rats and concomitantly we investigated the effect of DHEAS on this system in Sprague-Dawley rats using the expression of tyrosine hydroxylase (TH) as a neuronal marker. Rats were submitted to bile duct ligation (BDL) surgery and TH immunohistochemistry was assessed in the Substantia nigra pars compacta (SNc), striatum, ventral tegmental area (VTA) and the cortex. TH immunoreactivity showed a significant diminution in both SNc and VTA concomitantly with the cortical and the striatal outputs in the BDL rats vs. controls. Three daily injections of 5mg/kg of DHEAS to BDL rats significantly normalized TH expression decrease in both SNc and VTA as well as dopaminergic projections to the striatum and the cortex of BDL rats. The present data support an involvement of the dopaminergic system in mild HE and a possible beneficial effect of the neurosteroid DHEAS as a potential pharmacological treatment of mild HE.

Parkinsonism in cirrhosis: pathogenesis and current therapeutic options

Acquired hepatolenticular degeneration, also known as "Parkinsonism in cirrhosis" is characterized by extrapyramidal symptoms including hypokinesia, dystonia and rigidity that are rapidly progressive and may be independent of the severity of cognitive dysfunction. Magnetic resonance imaging reveals T1-weighted hyperintense signals in both globus pallidus and substantia nigra. Estimates of the prevalence of Parkinsonism in cirrhosis have been reported as high as 21 %. The cause of Parkinsonism in cirrhosis has been attributed to manganese deposition in basal ganglia structures, leading to the dysfunction of the dopaminergic neurotransmitter system. In particular, there is evidence from both spectroscopic and biochemical investigations for damage to (or dysfunction of) presynaptic dopamine transporters together with a loss of post-synaptic dopamine receptors in basal ganglia of affected patients. Therapeutic options are limited; ammonia-lowering strategies are without substantial benefit, and an effective manganese chelator is not available. In many patients, L-Dopa replacement therapy and the dopamine receptor agonist bromocriptine are beneficial, and liver transplantation is generally effective. However, reports of post-transplant residual extrapyramidal symptoms suggest an element of irreversibility in some cases.

Cirrhosis-related Parkinsonism: prevalence, mechanisms and response to treatments

BACKGROUND & AIMS

Extrapyramidal and cerebellar symptoms belong to the most prominent features of episodic hepatic encephalopathy, and usually decrease upon ammonia-lowering therapy. Rapidly progressing parkinsonian symptoms, which are unresponsive to treatment of hepatic encephalopathy, indicate cirrhosis-related Parkinsonism. This study aims at analyzing the prevalence of cirrhosis-related Parkinsonism in patients with liver cirrhosis, and to study the functional status of the striatal dopaminergic system in these patients.

METHODS

214 patients with liver cirrhosis who were consecutively seen at the out-patient clinic for liver transplant candidates and/or at the transplantation wards at Hannover Medical School, between August 1, 2008 and March 31, 2011, underwent a standardized neurological examination while on the waiting list or immediately after liver transplantation. Single photon emission computer tomography (SPECT) using (123)I-beta-CIT, for the evaluation of the striatal dopamine transporter function, and (123)I-IBZM for the evaluation of the striatal dopamine D2 receptor availability, was performed in 6 patients with cirrhosis-related Parkinsonism.

RESULTS

Cirrhosis-related Parkinsonism was diagnosed in 9 of 214 patients (4.2%). SPECT revealed significantly decreased dopamine receptor availability in 5 of 6 patients studied, and significantly decreased dopamine transporter availability in 3. Levodopa improved motor dysfunction in two of four patients treated, although only temporarily. Incomplete recovery was observed in two patients after liver transplantation.

CONCLUSIONS

Cirrhosis-related Parkinsonism is more frequent than presumed. The presented data suggest pre- and postsynaptic alteration of striatal dopaminergic neurotransmission as a possible cause of cirrhosis-related Parkinsonism and reveal the limited effects of dopaminergic therapy.

Neurotransmitter receptor alterations in hepatic encephalopathy: a review

Hepatic encephalopathy (HE), a complex neuropsychiatric syndrome with symptoms ranging from subtle neuropsychiatric and motor disturbances to deep coma and death, is thought to be a clinical manifestation of a low-grade cerebral oedema associated with an altered neuron-astrocyte crosstalk and exacerbated by hyperammonemia and oxidative stress. These events are tightly coupled with alterations in neurotransmission, either in a causal or a causative manner, resulting in a net increase of inhibitory neurotransmission. Therefore, research focussed mainly on the potential role of γ-aminobutyric acid-(GABA) or glutamate-mediated neurotransmission in the pathophysiology of HE, though roles for other neurotransmitters (e.g. serotonin, dopamine, adenosine and histamine) or for neurosteroids or endogenous benzodiazepines have also been suggested. Therefore, we here review HE-related alterations in neurotransmission, focussing on changes in the levels of classical neurotransmitters and the neuromodulator adenosine, variations in the activity and/or concentrations of key enzymes involved in their metabolism, as well as in the densities of their receptors.

Manganese and Parkinson's disease: a critical review and new findings

The goal of this review was to examine whether chronic Mn exposure produces dopamine neuron degeneration and PD or whether it has a distinct neuropathology and clinical presentation. I reviewed available clinical, neuroimaging, and neuropathological studies in humans and nonhuman primates exposed to Mn or other human conditions that result in elevated brain Mn concentrations. Human and nonhuman primate literature was examined to compare clinical, neuroimaging, and neuropathological changes associated with Mn-induced parkinsonism. Clinical, neuroimaging, and neuropathological evidence was used to examine whether Mn-induced parkinsonism involves degeneration of the nigrostriatal dopaminergic system as is the case in PD. The overwhelming evidence shows that Mn-induced parkinsonism does not involve degeneration of midbrain dopamine neurons and that l-dopa is not an effective therapy. New evidence is presented on a putative mechanism by which Mn may produce movement abnormalities. Confirmation of this hypothesis in humans is essential to make rational decisions about treatment, devise effective therapeutic strategies, and set regulatory guidelines.

Extent of reversibility of hepatic encephalopathy following liver transplantation

Although hepatic encephalopathy (HE) is prevalent in the cirrhotic population, it has also been considered a potentially reversible condition. Liver transplantation represents the ultimate reversal of the decompensated cirrhotic state and should provide the best option for the reversibility of HE. However, the neurologic compromise associated with HE in the cirrhotic patient may not be completely reversible. Theories regarding fixed structural and reversible metabolic deficits as well as persistence of the hyperdynamic state with continued portosystemic shunting have been proposed to explain this lack of complete reversibility. Whether this remnant neurologic deficit is clinically significant remains unclear.

A current review of the diagnostic and treatment strategies of hepatic encephalopathy

Hepatic encephalopathy (HE) is a serious and potentially fatal complication in patients with cirrhotic liver disease. It is a spectrum ranging from minimal hepatic encephalopathy (MHE) without recognizable clinical symptoms or signs, to overt HE with risk of cerebral edema and death. HE results in diminished quality of life and survival. The broad range of neuropsychiatric manifestations reflects the range of pathophysiological mechanisms and impairment in neurotransmission that are purported to cause HE including hyperammonemia, astrocyte swelling, intra-astrocytic glutamine, upregulation of 18-kDa translocator protein (TSPO) (formerly known as peripheral benzodiazepine receptor or PBTR), and manganese. There is a myriad of diagnostic tools including simple bedside clinical assessment, and more complex neuropsychological batteries and neurophysiological tests available today. Current treatment strategies are directed at reducing ammonia, with newer agents showing some early promise. This paper describes the pathophysiology of the disease and summarises current diagnostic and treatment therapies available.

Cerebral magnetic resonance imaging reveals marked abnormalities of brain tissue density in patients with cirrhosis without overt hepatic encephalopathy

BACKGROUND & AIMS

We applied advanced magnetic resonance imaging and Voxed based Morphometry analysis to assess brain tissue density in patients with cirrhosis.

METHODS

Forty eight patients with cirrhosis without overt hepatic encephalopathy (17 Child A, 13 Child B, and 18 Child C) and 51 healthy subjects were matched for age and sex. Seventeen patients had history of overt hepatic encephalopathy, eight of them had minimal hepatic encephalopathy at inclusion, 10 other patients had minimal hepatic encephalopathy at inclusion but without history of previous overt hepatic encephalopathy, and 21 patients had none of these features.

RESULTS

Patients with cirrhosis presented decreased brain density in many areas of the grey and white matter. The extension and size of the affected areas were greater in patients with alcoholic cirrhosis than in those with post-hepatitic cirrhosis and correlated directly with the degree of liver failure and cerebral dysfunction (as estimated by neuropsychological tests and the antecedent of overt hepatic encephalopathy). Twelve additional patients with cirrhosis who underwent liver transplantation were explored after a median time of 11months (7-50months) after liver transplant. At the time of liver transplantation, three patients belonged to class A of the Child-Pugh classification, five to class B and four to class C. Compared to healthy subjects, liver transplant patients showed areas of reduced brain density in both grey and white matter.

CONCLUSIONS

These results indicate that loss of brain tissue density is common in cirrhosis, progresses during the course of the disease, is greater in patients with history of hepatic encephalopathy, and persists after liver transplantation. The significance, physiopathology, and clinical relevance of this abnormality cannot be ascertained from the current study.

Manganese and Parkinson's disease: a critical review and new findings

BACKGROUND

Excess accumulation of manganese (Mn) in the brain results in a neurological syndrome with cognitive, psychiatric, and movement abnormalities. The highest concentrations of Mn in the brain are achieved in the basal ganglia, which may precipitate a form of parkinsonism with some clinical features that are similar and some that are different to those in Parkinson's disease (PD). Recently, scientists have debated the possibility that Mn may have an etiological role in PD or that it may accelerate the expression of PD.

OBJECTIVE

The goal of this review was to examine whether chronic Mn exposure produces dopamine neuron degeneration and PD or whether it has a distinct neuropathology and clinical presentation.

DATA SOURCE

I reviewed available clinical, neuroimaging, and neuropathological studies in humans and nonhuman primates exposed to Mn or other human conditions that result in elevated brain Mn concentrations.

DATA EXTRACTION

Human and nonhuman primate literature was examined to compare clinical, neuroimaging, and neuropathological changes associated with Mn-induced parkinsonism.

DATA SYNTHESIS

Clinical, neuroimaging, and neuropathological evidence was used to examine whether Mn-induced parkinsonism involves degeneration of the nigrostriatal dopaminergic system as is the case in PD.

CONCLUSIONS

The overwhelming evidence shows that Mn-induced parkinsonism does not involve degeneration of midbrain dopamine neurons and that l-dopa is not an effective therapy. New evidence is presented on a putative mechanism by which Mn may produce movement abnormalities. Confirmation of this hypothesis in humans is essential to make rational decisions about treatment, devise effective therapeutic strategies, and set regulatory guidelines.

Persistence of cognitive impairment after resolution of overt hepatic encephalopathy

BACKGROUND & AIMS

In patients with cirrhosis, hepatic encephalopathy (HE) has acute but reversible as well as chronic components. We investigated the extent of residual cognitive impairment following clinical resolution of overt HE (OHE).

METHODS

Cognitive function of cirrhotic patients was evaluated using psychometric tests (digit symbol, block design, and number connection [NCT-A and B]) and the inhibitory control test (ICT). Improvement (reduction) in ICT lures and first minus second halves (DeltaL(1-2)) were used to determine learning of response inhibition. Two cross-sectional studies (A and B) compared data from stable cirrhotic patients with or without prior OHE. We then prospectively assessed cognitive performance, before and after the first episode of OHE.

RESULTS

In study A (226 cirrhotic patients), 54 had experienced OHE, 120 had minimal HE, and 52 with no minimal HE. Despite normal mental status on lactulose after OHE, cirrhotic patients were cognitively impaired, based on results from all tests. Learning of response inhibition (DeltaL(1-2) > or =1) was evident in patients with minimal HE and no minimal HE but was lost after OHE. In study B (50 additional patients who developed > or =1 documented OHE episode during follow-up), the number of OHE hospitalizations correlated with severity of residual impairment, indicated by ICT lures (r = 0.5, P = .0001), digit symbol test (r = -0.39, P = .002), and number connection test-B (r = 0.33, P = .04). In the prospective study (59 cirrhotic patients without OHE), 15 developed OHE; ICT lure response worsened significantly after OHE (12 before vs 18 after, P = .0003), and learning of response inhibition was lost. The 44 patients who did not experience OHE did not have deteriorations in cognitive function in serial testing.

CONCLUSIONS

In cirrhosis, episodes of OHE are associated with persistent and cumulative deficits in working memory, response inhibition, and learning.

Persistence of cognitive impairment after resolution of overt hepatic encephalopathy

BACKGROUND & AIMS

In patients with cirrhosis, hepatic encephalopathy (HE) has acute but reversible as well as chronic components. We investigated the extent of residual cognitive impairment following clinical resolution of overt HE (OHE).

METHODS

Cognitive function of cirrhotic patients was evaluated using psychometric tests (digit symbol, block design, and number connection [NCT-A and B]) and the inhibitory control test (ICT). Improvement (reduction) in ICT lures and first minus second halves (DeltaL(1-2)) were used to determine learning of response inhibition. Two cross-sectional studies (A and B) compared data from stable cirrhotic patients with or without prior OHE. We then prospectively assessed cognitive performance, before and after the first episode of OHE.

RESULTS

In study A (226 cirrhotic patients), 54 had experienced OHE, 120 had minimal HE, and 52 with no minimal HE. Despite normal mental status on lactulose after OHE, cirrhotic patients were cognitively impaired, based on results from all tests. Learning of response inhibition (DeltaL(1-2) > or =1) was evident in patients with minimal HE and no minimal HE but was lost after OHE. In study B (50 additional patients who developed > or =1 documented OHE episode during follow-up), the number of OHE hospitalizations correlated with severity of residual impairment, indicated by ICT lures (r = 0.5, P = .0001), digit symbol test (r = -0.39, P = .002), and number connection test-B (r = 0.33, P = .04). In the prospective study (59 cirrhotic patients without OHE), 15 developed OHE; ICT lure response worsened significantly after OHE (12 before vs 18 after, P = .0003), and learning of response inhibition was lost. The 44 patients who did not experience OHE did not have deteriorations in cognitive function in serial testing.

CONCLUSIONS

In cirrhosis, episodes of OHE are associated with persistent and cumulative deficits in working memory, response inhibition, and learning.

Tryptophan metabolism in alcoholism

Acute and chronic alcohol (ethanol) intake and subsequent withdrawal exert major effects on tryptophan (Trp) metabolism and disposition in human subjects and experimental animals. In rats, activity of the rate-limiting enzyme of Trp degradation, liver Trp pyrrolase (TP), is enhanced by acute, but inhibited after chronic, ethanol administration, then enhanced during withdrawal. These changes lead to alterations in brain serotonin synthesis and turnover mediated by corresponding changes in circulating Trp availability to the brain. A low brain-serotonin concentration characterizes the alcohol-preferring C57BL/6J mouse strain and many alcohol-preferring rat lines. In this mouse strain, liver TP enhancement causes the serotonin decrease. In man, acute ethanol intake inhibits brain serotonin synthesis by activating liver TP. This may explain alcohol-induced depression, aggression and loss of control in susceptible individuals. Chronic alcohol intake in dependent subjects may be associated with liver TP inhibition and a consequent enhancement of brain serotonin synthesis, whereas subsequent withdrawal may induce the opposite effects. The excitotoxic Trp metabolite quinolinate may play a role in the behavioural disturbances of the alcohol-withdrawal syndrome. Some abstinent alcoholics may have a central serotonin deficiency, which they correct by liver TP inhibition through drinking. Further studies of the Trp and serotonin metabolic status in long-term abstinence in general and in relation to personality characteristics, alcoholism typology and genetic factors in particular may yield important information which should facilitate the development of more effective screening, and preventative and therapeutic strategies in this area of mental health.

Modification of sleep architecture in an animal model of experimental cirrhosis

AIM: To analyze the polygraphic sleep patterns during cirrhosis progression in a rat model by repeated CCl₄ administration.

METHODS: Male Wistar rats received three weekly injections of CCl₄ for 11 wk, and were analyzed before and during the induction of cirrhosis. Rats were implanted with electrodes to record their sleep patterns. Polygraph recordings were made weekly over 11 wk for 8 h, during the light period. After a basal recording, rats received three weekly injections of CCl₄. Histological confirmation of cirrhosis was performed after 11 wk.

RESULTS: The results showed a progressive decrease in total wake time that reached statistical significance from the second week of treatment. In addition, there was an increase in total time of slow wave sleep (SWS) II and rapid eye movement sleep (REM sleep) in most of the 11 wk. SWS I showed no significant variations. During the final weeks, a significant increase in REM sleep frequency was also observed. Histological analyses of the livers showed unequivocal signs of cirrhosis.

CONCLUSION: These data suggest that hepatic failure produced by CCl₄ administration is capable of modifying the sleep pattern even after only a few doses.

Selective alterations of brain dopamine D(2) receptor binding in cirrhotic patients: results of a (11)C-N-methylspiperone PET study

Alterations of the brain dopamine system have been implicated in the neurological complications of chronic liver failure. The present study was aimed at the measurement of dopamine D(2) binding sites in cirrhotic patients by positron emission tomography (PET) using (11)C-N-methylspiperone as ligand. The regions of interest (ROI) were designated on a three-dimensional stereotaxic ROI template (3DSRT). The pixel values of twelve ROIs corrected by the pixel value of the cerebellum after 80 min static scanning were used to quantitate changes in binding. D(2) binding sites were significantly decreased in the hippocampus and thalamus of cirrhotic patients and were positively correlated with serum bilirubin levels and Child-Pugh scores and were negatively correlated with prothrombin times (thalamus). Loss of D(2) sites was greater in thalamus and hippocampus of alcoholic cirrhotics compared to non-alcoholics. Statistically significant correlations were also observed between D(2) binding sites in hippocampus, thalamus and lenticular nuclei and history of overt encephalopathy. These findings suggest that D(2) receptor binding in some regions of brain in cirrhotic patients is influenced by factors such as the severity of liver damage and history of alcohol dependency or overt encephalopathy. Alterations of D(2) receptor sites indicative of dopaminergic synaptic dysfunction could play an important role in the pathogenesis of the cognitive and motor disturbances associated with chronic liver failure.

The inflammatory bases of hepatic encephalopathy

A hypothesis about the inflammatory etiopathogeny mediated by astroglia of hepatic encephalopathy is being proposed. Three evolutive phases are considered in chronic hepatic encephalopathy: an immediate or nervous phase with ischemia-reperfusion, which is associated with reperfusion injury, edema and oxidative stress; an intermediate or immune phase with microglia hyperactivity, which produces cytotoxic cytokines and chemokines and is involved in enzyme hyperproduction and phagocytosis; and a late or endocrine phase, in which neuroglial remodeling, with an alteration of angiogenesis and neurogenesis, stands out. The increasingly complex trophic meaning that the metabolic alterations have in the successive phases making up this chronic inflammation could explain the metabolic regression produced in acute and acute-on-chronic hepatic encephalopathy. In these two types of hepatic encephalopathy, characterized by edema, neuronal nutrition by diffusion would guarantee an appropriate support of substrates, in accordance with the reduced metabolic needs of the cerebral tissue.

Neural synchronization in hepatic encephalopathy

Hepatic encephalopathy (HE) is clinically characterized by a large variety of symptoms including motor symptoms, cognitive deficits, as well as changes in the level of alertness up to hepatic coma. A number of pathological processes affecting glial and neuronal function have been identified, including hyper-ammonia, changes within the excitatory and inhibitory transmitter systems, as well as osmolytic changes with consecutive cell swelling. One explanation how these pathological processes result in neurological deficits in HE is the concept of pathologically synchronized oscillations within and between relevant brain regions. A number of studies suggest that the cognitive deficits and the reduced level of alertness in patients with HE can be attributed to a significantly slowed and pathologically synchronized spontaneous oscillatory brain activity, depending on the grade of HE. Moreover, HE motor symptoms, like postural tremor called"mini asterixis," have recently been shown to be associated with abnormal thalamo-cortical and cortico-muscular synchronization. Indirect evidence exists from studies of processing and recognition of flicker stimuli that in HE slowing of oscillations also occurs in the visual system. Taken together, pathological synchronization of neuronal activity may turn out to be a promising pathophysiological concept for linking neuronal dysfunction to the diversity of clinical deficits in HE.

Hepatic encephalopathy: a dynamic or static condition

Hepatic encephalopathy (HE) is a neuropsychiatric disorder associated with portal hypertension. The mechanism of this disorder is still being characterized and the management has relied primarily on lowering the amount of ammonia present in the gastrointestinal tract or reversing liver disease by replacing the diseased liver. It is, however, not established that all the effects of hepatic encephalopathy are reversed by liver transplantation. In this review, we have outlined the mechanisms underlying HE and the pros and cons of reversibility of HE.

Increased oro-cecal transit time in grade I or II hepatic encephalopathy

The pathogenic mechanisms of hepatic encephalopathy remain to be elucidated. It has been suggested that a digestive motor disorder could promote the absorption of toxins produced within the lumen and thus enhance hepatic encephalopathy.

AIM

To evaluate oro-cecal transit time in cirrhotic patients with and without hepatic encephalopathy.

METHODS

Hospitalized patients with alcoholic cirrhosis without encephalopathy and with spontaneous grade I and II encephalopathy were included. Severity of hepatic encephalopathy was assessed clinically and the Child-Pugh score was used to describe cirrhosis severity. Nine healthy volunteers constituted a control group. Oro-cecal transit time was measured with the sulfasalazine test.

RESULTS

Twenty-eight patients (mean age 62.5 +/- 8.5 years) were included. Ten had hepatic encephalopathy of unknown cause and 18 were free of hepatic encephalopathy. Oro-cecal transit time was significantly longer in patients with hepatic encephalopathy (641 +/- 350 min) compared to patients without hepatic encephalopathy (298 +/- 96; P<0.05) and to controls (354 +/- 90; P<0.05). Oro-cecal transit time was comparable for each Child-Pugh score and was not different between the two grades of hepatic encephalopathy.

CONCLUSION

Oro-cecal transit time is longer in alcoholic cirrhosis patients with hepatic encephalopathy. This digestive motor disorder provides a partial explanation of hepatic encephalopathy of unknown etiology.

Increased brain serotonin turnover correlates with the degree of shunting and hyperammonemia in rats following variable portal vein stenosis

BACKGROUND/AIMS

Hepatic encephalopathy (HE) is a serious neuropsychiatric complication of chronic liver disease. Brain monoamines have been implicated in the pathogenesis of HE. We examined the relationship between monoamine dysfunction and the degree of portal-systemic shunting (PSS) in rats with varying degrees of PSS.

METHODS

Concentrations of catecholamines, serotonin, histamine, precursors and metabolites in frontal cortex of rats with varying degrees of PSS (9-99.8%) were measured by HPLC.

RESULTS

The concentrations of the serotonin precursor, tryptophan, and its metabolite, 5-HIAA were increased up to 4-fold in brains of rats with various degrees of PSS and were significantly correlated with the degree of shunting and with arterial ammonia levels. Brain levels of histamine, its precursor, l-histidine, and metabolite, tele-methylhistamine were significantly increased only following total shunting. Concentrations of catecholamines and their metabolites were not significantly correlated with degree of PSS or hyperammonemia.

CONCLUSIONS

Given the established role of the serotonin system in the regulation of sleep, circadian rhythmicity and locomotion these findings suggest that selective alterations of this system could be implicated in the pathogenesis of HE. Therapeutic approaches aimed at the normalization of serotonin turnover could be beneficial in the prevention and treatment of early neuropsychiatric symptoms of HE.

Hyperdynamic circulation and serotonin levels in patients with liver cirrhosis

Patients with liver cirrhosis and portal hypertension develop hyperdynamic state of circulation. Recent studies indicate that nitric oxide, prostaglandin's, endothelin-1 and serotonin are of major importance in the pathogenesis of portal hypertension and other hemodynamic complications. In our study we estimated the levels of serotonin in sera and 24h urine in 20 patients with liver cirrhosis, using original solid phase extraction procedure. Concentration of serotonin in sera was ranged from 18 to 270 nmol/L and in 24h urine ranged from 97 to 238 nmol/L/24h. In comparison with reference values (determined in range from 280 ?1300 nmol/L in sera and determined in the range from 157.8?1035.4 nmol/ L/24h in urine), a significant fall of serotonin concentration in sera, and urine was noted. A statistically significant correlation between serotonin levels in sera and platelet count was found (p = 0.017). Colour Doppler ultrasonography and peroral fiberpanendoscopy was applied in the whole series to evaluate degree of portal hypertension. The average diameter of portal vein was 16 mm (SD=1.36) and mean blood flow velocity in portal vein was 12 cm/s (SD=1.12). Splenomegaly was approved in the whole group and the mean splenic craniocaudal distance was 17.75 mm (SD=1.65). Esophageal varices grade I?II were detected in 8 (40%) of our patients and reamaining 12 (60%) were grade III?IV. In cirrhotic liver, the spleen congestion, result from platelet degradation. Serotonin, release in to spleen sinusoidal spaces, induces strong vasoconstriction response in portal venous circulation, which contributes to maintain portal hypertension. However, we consider that the decrease of serotonin levels in sera lead to development of hyperdynamic state of circulation.

Neurobiology of ammonia

Hyperammonemia resulting from inherited urea cycle enzyme deficiencies or liver failure results in severe central nervous system dysfunction including brain edema, convulsions and coma. Neuropathologic evaluation in these disorders reveals characteristic alterations of astrocyte morphology ranging from cell swelling (acute hyperammonemia) to Alzheimer Type II astrocytosis (chronic hyperammonemia). Having no effective urea cycle, brain relies on glutamine synthesis for the removal of excess ammonia and the enzyme responsible, glutamine synthetase, has a predominantly astrocytic localization. Accumulation of ammonia in brain results in a redistribution of cerebral blood flow and metabolism from cortical to sub-cortical structures. In addition to changes in astrocyte morphology, increased brain ammonia concentrations result in alterations in expression of key astrocyte proteins including glial fibrillary acidic protein, glutamate and glycine transporters and "peripheral-type" (mitochondrial) benzodiazepine receptors. Such changes result in alterations of astrocytic volume and increased extracellular concentrations of excitatory and inhibitory substances. In addition, the ammonium ion has direct effects on excitatory-inhibitory transmission via distinct mechanisms involving cellular chloride extrusion and postsynaptic receptor function. Acute ammonia exposure leads to activation of NMDA receptors and their signal transduction pathways. Chronic hyperammonemia also results in increased concentrations of neuroactive L-tryptophan metabolites including serotonin and quinolinic acid. Therapy in hyperammonemic syndromes continues to rely on ammonia-lowering strategies via peripheral mechanisms (reduction of ammonia production in the gastrointestinal tract, increased ammonia removal by muscle).

Reversible decrease of dopamine D2 receptor density in the striatum of rats with acute hepatic failure

The binding of a D2 receptor ligand, [3H]spiperone, was measured in striatal membranes derived from rats in which acute hepatic failure induced with thioacetamide (TAA) was associated with symptoms of hepatic encephalopathy (HE), and during recovery from HE. A 28% decrease of Bmax for the binding was measured in a symptomatic stage of HE, 1 day after TAA administration. The B(max) for [3H]spiperone binding was no longer different from control 7 days after TAA administration, when blood and brain biochemical correlates of HE were already absent. At 21 days after TAA administration, the B(max) was increased by 31% above the control level, consistent with other aspects of metabolic activation of the brain characteristic of the late recovery period from acute HE.

Striatal manganese accumulation induces changes in dopamine metabolism in the cirrhotic rat

Manganese (Mn) is an essential metal that, in excess, causes an extrapyramidal syndrome consisting in tremor, rigidity and akinesia. Recently, Mn was found to accumulate in brains of cirrhotic patients who also present motor abnormalities. Manganese alters dopaminergic transmission promoting an increase in the turnover of dopamine (DA). In this study, we studied the changes in dopamine and its main metabolite homovanillic acid (HVA) to evaluate DA turnover following administration of manganese to bile-duct obstructed rats. Some groups of rats were treated with manganese chloride in two concentrations: 0.5 and 1 mg/ml of Mn2+ in their drinking water. Four weeks after surgery and treatment with manganese, striatal Mn, DA and HVA were assessed. Marked increases (P<0.05) of striatal manganese content were observed in cirrhotic rats treated and untreated with manganese, these augments were dependent on the Mn concentration in water. Striatal contents of DA in cirrhotic rats diminished by 30% (P<0.05), administration of 0.5 mg/ml of manganese in drinking water to these rats returned dopamine to the basal level and 1 mg/ml of manganese increased dopamine content by 27%. The relationship of Mn content and DA turnover (HVA:DA) in the same animal showed a positive and statically significant correlation (P<0.05), with differences in slope for sham (b1=0.1528) and cirrhotic rats (b1=0.0174). These results suggest that manganese brain accumulation observed in liver failure could be a key element to understand dopamine metabolism in cirrhotic condition of humans.

Dynamic and kinetic effects of chronic citalopram treatment in experimental hepatic encephalopathy

Chronic hepatic encephalopathy (HE) is a neuropsychiatric syndrome that arises in liver-impaired subjects. Patients with HE display various neuropsychiatric symptoms including affective disturbances and may therefore likely receive treatment with novel thymoleptics like citalopram (CIT). The simultaneous pharmacokinetic and pharmacodynamic outcome of the commonly used serotonin-selective thymoleptic drugs in liver-impaired subjects with pending chronic HE is far from understood today. We therefore investigated the effects of chronic, body-weight-adjusted (10 mg x kg(-1) x day(-1)), treatment with CIT in rats with and without portacaval shunts (PCS). Open-field activity was monitored. The 5-HT, 5-HIAA, noradrenaline (NA), and dopamine (DA) output were assessed in the frontal neocortex. The racemic levels of CIT and its metabolites DCIT and DDCIT, including the S- and R-enantiomers, were determined in serum, brain parenchyma, and extracellular fluid. The rats with PCS showed higher (2-3-fold) levels of CIT than rats undergoing a sham treatment with CIT in all compartments investigated. The PCS rats also showed elevated levels of DCIT and DDCIT. No major differences in the S/R ratios between PCS rats and control rats could be detected. The CIT treatment resulted in neocortical output differences between PCS rats and control rats mainly within the 5-HT and DA systems but not within the NA system. For the 5-HT system, this change was further evidenced by outspoken elevation in 5-HT output after KCI-depolarizing challenges. Moreover, the CIT treatment to PCS rats was shown to "normalize" the metabolic turnover of 5-HT, measured as a profound lowering of a basal elevation in the 5-HIAA levels. The CIT treatment resulted in an increased or "normalized" behavioral activity in the PCS group. Therefore, a dose-equal chronic treatment with CIT in PCS rats produced pharmacokinetic and pharmacodynamic changes not observed in control rats. The results further support the contention of an altered 5-HT neurotransmission prevailing in the chronic HE condition. However, the tentatively beneficial behavioral response also seen following chronic CIT treatment to PCS rats in this study has to be viewed in relation to both the pharmacokinetic and pharmacodynamic changes observed.

Altered striatal dopamine D2 receptor density and dopamine transport in a patient with hepatic encephalopathy

A patient suffering from liver cirrhosis presented with a bradykinetic-rigid syndrome suspected as Parkinson's disease. A detailed work-up of the case revealed hepatic encephalopathy as the cause of the neurological symptomatology. An alteration of striatal dopamine D2 receptor binding and dopamine re-uptake sites was demonstrated by 123I-iodobenzamide (IBZM) and 123I-beta-CIT single photon emission computed tomography (SPECT), respectively. It is suggested that the alteration of the dopamine re-uptake in cirrhotics may be the cause of an increased catabolism of dopamine in HE.

Sleep disorders and portal-systemic encephalopathy following transjugular intrahepatic portosystemic stent shunt in patients with liver cirrhosis. Relation to plasma tryptophan

Neuropsychiatric symptoms due to any type of dysfunction and/or portal-systemic shunting are summarized as hepatic encephalopathy (HE). HE in the presence of liver cirrhosis and/or portal-systemic shunting has been termed portal-systemic encephalopathy (PSE). PSE is most frequent among the HE syndromes and is almost exclusively seen in patients with advanced cirrhosis and portal hypertension. Portal-systemic shunting either spontaneous due to portal hypertension, following surgical portocaval anastomosis, or subsequent to transjugular intrahepatic portosystemic stent-shunt (TIPSS) is regarded as the primary causative condition for PSE, not hepatic dysfunction per se. PSE may be considered as a disorder of multiple neurotransmitter systems among which derangements of the serotonergic system have been documented most consistently. Incipient PSE is frequently paralleled by the occurrence of sleep disorders, however, their relation to PSE remains unclear. We observed a transient increase of sleep disorders post-TIPSS, which were only in part correlated to other symptoms of PSE. Among the biochemical parameters studied only an association between arterial ammonia levels and sleep disorders became apparent, whereas no significant relation was observed for peripheral tryptophan.

Brain tryptophan/serotonin perturbations in metabolic encephalopathy and the hazards involved in the use of psychoactive drugs

Several combined pathogenetic factors such as hyperammonemia, different brain tryptophan metabolic disturbances and serotonin physiological/pharmacological alterations not yet defined in all details, will often give rise to the clinical neuropsychiatric condition known as hepatic encephalopathy (HE). Indeed, to this the probable exposure to novel potent CNS-monoamine acting drugs today may put such patients at certain risk for other pharmacodynamic (PD) responses than usually are expected from these "safe" drugs. Moreover, with a compromised liver function in HE, also pharmacokinetic (PK) features for the drugs are likely changed in these patients. Thus, the ultimate clinical outcome by this probable but unknown PD/PK-deviation for such psychoactive drugs when given to HE-patients needs further clarification. Accordingly, delineation of both PD- and PK-effects in experimental HE should shed light on this issue of relevance for monoamine-active drug safety as well as on some further details in the complex tryptophan/monoamine-related pathophysiology that comes into play in HE.

Complications of cirrhosis III. Hepatic encephalopathy

Hepatic encephalopathy (HE) is a major neuropsychiatric complication of cirrhosis. HE develops slowly in cirrhotic patients, starting with altered sleep patterns and eventually progressing through asterixis to stupor and coma. Precipitating factors are common and include an oral protein load, gastrointestinal bleeding and the use of sedatives. HE is common following transjugular intrahepatic portosystemic stent shunts (TIPS). Neuropathologically, HE in cirrhotic patients is characterized by astrocytic (rather than neuronal) changes known as Alzheimer type II astrocytosis and in altered expression of key astrocytic proteins. Magnetic resonance imaging in cirrhotic patients reveals bilateral signal hyperintensities particularly in globus pallidus on T1-weighted imaging, a phenomenon which may result from manganese deposition. Proton (1H) magnetic resonance spectroscopy shows increases in the glutamine resonance in brain, a finding which confirms previous biochemical studies and results no doubt from increased brain ammonia removal (glutamine synthesis). Additional evidence for increased brain ammonia uptake and removal in cirrhotic patients is provided by studies using positron emission tomography and 13NH3. Recent molecular biological studies demonstrate increased expression of genes coding for neurotransmitter-related proteins in chronic liver failure. Such genes include monoamine oxidase (MAO-A isoform), the peripheral-type benzodiazepine receptor and nitric oxide synthase (nNOS isoform). Activation of these systems has the potential to lead to alterations of monoamine and amino acid neurotransmitter function as well as modified cerebral perfusion in chronic liver failure. Prevention and treatment of HE in cirrhotic patients continues to rely on ammonia-lowering strategies which include assessment of dietary protein intake and the use of lactulose, neomycin, sodium benzoate and L-ornithine-aspartate. The benzodiazepine receptor antagonist flumazenil may be effective in certain cases. A more widespread use of central nervous system-acting drugs awaits a more complete understanding of the precise neurotransmitter systems involved in the pathogenesis of HE in chronic liver failure.

Nutritional support in hepatic encephalopathy

Hepatic encephalopathy (HE) is a syndrome of global cerebral dysfunction resulting from underlying liver disease or portal-systemic shunting. HE can present as one of four syndromes, depending on the rapidity of onset of hepatic failure and the presence or absence of preexisting liver disease. The precise pathogenesis is unknown but likely involves impaired hepatic detoxification of ammonia as well as alterations in brain transport and metabolism of amino acids and amines. The etiology of malnutrition in hepatic failure is multifactorial. Nutritional deficits may be clinically manifest as marasmus or kwashiorkor, or both. Nutritional support in HE is directed toward reducing morbidity related to underlying malnutrition and concurrent disease. However, reaching nutritional goals is often complicated by protein and carbohydrate intolerance. The use of protein restriction in HE is controversial. Modified formulas that are supplemented in branched chain amino acids may be of value in patients who exhibit protein intolerance with standard feeding solutions or in patients who present with advanced degrees of encephalopathy.

Alterations of neurotransmitter-related gene expression in human and experimental portal-systemic encephalopathy

Portal-systemic encephalopathy (PSE) is a serious neuropsychiatric condition that results from chronic liver failure and portal-systemic shunting of venous blood. PSE is particularly prevalent following treatment of portal hypertension or ascites by the TIPS procedure. Recent studies both in autopsied brain tissue from PSE patients as well as in experimental animal models of PSE reveal that chronic liver failure results in altered expression of several genes coding for proteins having key roles in the control of neuronal excitability. Such alterations include increased expression of monoamine oxidase (MAO-A isoform), the "peripheral-type" benzodiazepine receptor (PTBR) as well as constitutive, neuronal nitric oxide synthase (nNOS). Such changes result in altered protein expression and in increased degradation of monoamine neurotransmitters, increased synthesis of neurosteroids with inhibitory properties and increased production of nitric oxide (respectively) in brain in chronic liver failure. In the case of PTBR and nNOS, increases in expression result from exposure to ammonia and/or manganese, two neurotoxic agents shown previously to be increased in brain in chronic liver failure. Further elucidation of the consequences of neurotransmitter-related gene expression could identify new pathophysiologic mechanisms and result in new approaches to the prevention of PSE in chronic liver disease in humans.

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.

Opioid receptor ligands in human hepatic encephalopathy

BACKGROUND/AIMS

Opioid peptides may contribute to some of the manifestations of hepatic encephalopathy. To address the role of the opioid system in the pathogenesis of hepatic encephalopathy, three representative opioid ligands were measured in plasma and cerebrospinal fluid of patients with hepatic encephalopathy.

METHODS

Plasma and cerebrospinal fluid were obtained in three groups of patients: group 1: patients with hepatic encephalopathy; group 2: patients with lumbar back pain; group 3: healthy controls. Met-enkephalin, leu-enkephalin and beta-endorphin levels were measured in extracted plasma and cerebrospinal fluid samples by radioimmunoassay.

RESULTS

Plasma met-enkephalin levels were 656% (p<0.05) and 301% (p<0.05) and cerebrospinal fluid met-enkephalin levels were 1481% (p<0.01) and 645% (p<0.05) higher when compared to healthy control and pain control patients, respectively. Although plasma and cerebrospinal leu-enkephalin levels were elevated in patients with hepatic encephalopathy, the increases were not statistically significant. Plasma and cerebrospinal beta-endorphin levels were similar in the three study groups.

CONCLUSIONS

The results of this study support accumulating data on the role of the delta opioid receptor ligand met-enkephalin in the pathogenesis of hepatic encephalopathy, and provide a rationale for the use of opioid receptor antagonists in the treatment of hepatic encephalopathy.

Changes in the brain monoamine metabolism in acute liver failure produced by ischemia-reperfusion injury in rats

OBJECTIVE

To investigate the relationship between behavioral alterations and changes in monoaminergic systems provoked by ischemia-reperfusion liver injury in rats.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University animal laboratory.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

Acute liver failure was induced by occlusion of the left portal vein and the hepatic artery for 90 mins. Twenty animals were subjected to the behavioral examination. The brain water content was measured in 12 animals. Forty-two animals were used for the evaluation of brain monoamine turnover. Half of animals in each experiment were subjected to the ischemic operation.

MEASUREMENTS AND MAIN RESULTS

A step-through passive avoidance test was used for the behavioral evaluation 48 hrs after the ischemic operation. Then, plasma concentrations of amino acids were determined. The brain water content was measured with the dry weight method. The brain monoamine turnover was evaluated by the depletion of norepinephrine and dopamine induced by alpha-methyl-p-tyrosine, or the accumulation of 5-hydroxyindoleacetic acid induced by probenecid. In the plasma analysis performed 48 hrs after the operation, marked damage was found in animals subjected to liver ischemia. Injured rats demonstrated impairment in the passive avoidance test. The plasma concentrations of branch-chain amino acids were decreased, and the plasma concentrations of aromatic amino acids were increased. However, the brain water content was not changed by liver ischemia. The turnover of both norepinephrine in the cerebral cortex and dopamine in the striatum was decreased. The turnover of 5-hydroxytryptamine in the cerebral cortex was increased markedly.

CONCLUSION

In liver injury caused by liver ischemia, the excitatory neurotransmission by norepinephrine and dopamine is depressed and the inhibitory neurotransmission mediated by 5-hydroxytryptamine is facilitated, especially in the telencephalon.

Regional brain serotonin receptor changes in portacaval shunted rats

The pathogenesis of hepatic encephalopathy is unknown, but metabolic perturbations, including hyperammonaemia and increased brain turnover of serotonin (5-HT), have been identified. Possible alterations of 5-HT receptors in the brain have been rudimentarily studied. We therefore investigated the 5-HT1A, 5-HT1B and 5-HT2A receptor density in 18-22 different regions in the brain of portacaval shunted rats by means of radioligand binding with autoradiographical evaluation. The results revealed a decreased 5-HT1A receptor binding in seven serotonergic projection areas of the brain, and an increase in the nucleus accumbens, hypothalamus and subiculum. No changes in the raphe nuclei were observed. An increased 5-HT1B receptor binding was seen in five brain regions: basal ganglia, olfactorial regions, hippocampus, mid brain and thalamus. However, decreased binding was seen in three regions of cortical areas and hippocampus. The 5-HT2A receptor binding site density was essentially unaltered. These findings suggest that perturbations in the central serotonergic neurotransmission may play a functional role in chronic hepatic encephalopathy.

Effects of hyperammonaemia on brain function

Neuropsychiatric symptoms of hyperammonaemia include alterations of mood and personality, cognitive impairment, ataxia, convulsions and coma. The nature and severity of CNS dysfunction depend upon the aetiology and degree of hyperammonaemia, its acuteness of onset and the age of the patient. Neuropathological studies reveal Alzheimer type II astrocytosis in the adult hyperammonaemic patient, whereas hyperammonaemia in the infant resulting from congenital urea cycle disorders or Reye syndrome is accompanied by cerebral atrophy, neuronal loss and cerebral oedema. Several electrophysiological and biochemical mechanisms have been proposed to explain the deleterious effects of ammonia on CNS function. Such mechanisms include direct effects of the ammonium ion on excitatory and inhibitory neurotransmission and a deficit in cerebral energy metabolism due to ammonia-induced inhibition of alpha-ketoglutarate dehydrogenase. In addition, ammonia has been shown to interfere with normal processes of uptake, storage and release of various neurotransmitters. Ammonia disrupts monoamine storage, inhibits the high-affinity uptake of glutamate by both astrocytic and neuronal elements and activates 'peripheral-type' benzodiazepine receptors leading to the potential synthesis of neuroactive steroids in brain. On the basis of these actions, it has been proposed that ammonia disrupts neuron-astrocyte trafficking of amino acids and monoamines in brain. The increased formation of brain glutamine in hyperammonaemic syndromes could be responsible for the phenomenon of brain oedema in these disorders. Therapies aimed at either decreasing ammonia production in the gastrointestinal tract or increasing ammonia removal by liver or skeletal muscle are the mainstay in the prevention and treatment of the CNS consequences of hyperammonaemia. New therapeutic approaches aimed at correction of the neurotransmitter and cerebral energy deficits in these syndromes could hold promise for the future.

The portacaval-shunted rat: a new model for the study of the mechanisms controlling voluntary ethanol consumption and ethanol preference?

Portacaval anastomosis (PCA) is a surgical procedure whereby blood from the portal vein is shunted into the inferior vena cava. PCA in the rat results in a significant increase (from 0.77 +/- 0.26 to 3.51 +/- 0.37 g of ethanol/kg/day) in voluntary ethanol consumption in a free-choice paradigm between water and 5% ethanol solution. After PCA surgery, increased voluntary ethanol consumption starts abruptly at 6 to 7 days and is maintained for > 28 weeks. Voluntary ethanol consumption in rats after PCA results in blood ethanol levels up to 158 mg%. After PCA, the ethanol preference ratio (defined as the percentage of total fluid intake constituted by ethanol) increased from 19 +/- 2% to 78 +/- 2% (P < 0.001). Administration of the nonselective opioid receptor antagonist naloxone (5 mg/kg, sc) resulted in a significant 6-fold attenuation of voluntary ethanol consumption by rats with PCA, an effect that was not mediated by an effect on locomotor activity. These findings, together with previous reports of widespread alterations of the mu- and delta-opioid receptors in the brain after PCA, suggest that increased voluntary ethanol consumption and ethanol preference in PCA rats may result from activation of the endogenous opioid system. Preliminary studies suggest that rats with PCA manifest behavioral signs consistent with the development of dependence. The portacaval-shunted rat may provide a useful preparation for the study of mechanisms, in particular those involving the liver, implicated in the development of increased voluntary ethanol consumption and ethanol preference.

Release of [3H]dopamine from striatal and cerebral cortical slices from rats with thioacetamide-induced hepatic encephalopathy: different responses to stimulation by potassium ions and agonists of ionotropic glutamate receptors

The effects of depolarizing stimuli; high (50 mM) potassium ions and the glutamate receptor agonists N-methyl-D-aspartate, kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) on the release of newly-loaded [3H]dopamine were studied in frontal cortical and striatal slices from control rats and from rats with acute hepatic encephalopathy induced with a hepatotoxin, thioacetamide. Hepatic encephalopathy enhanced the stimulatory effect of potassium ions by 20% in striatal slices and by 34% in frontal cortical slices. In striatal slices the stimulatory effects of N-methyl-D-aspartate and kainate were depressed in hepatic encephalopathy by 46% and 21%, respectively, which may be taken to reflect impaired modulation of striatal dopamine release by glutamate acting at N-methyl-D-aspartate or kainate receptors. In frontal cortical slices, the stimulatory effect of kainate was enhanced by 35% in hepatic encephalopathy but N-methyl-D-aspartate-stimulated release was not affected. The release evoked by 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate was not affected in hepatic encephalopathy in either brain region. Stimulation of dopamine release in the frontal cortex by depolarization or glutamate acting at kainate receptors could inhibit the activity of descending corticostriatal glutamatergic pathways, further impairing regulation of dopamine release by glutamate in the striatum.

Ammonium acetate challenge in experimental chronic hepatic encephalopathy induces a transient increase of brain 5-HT release in vivo

Ammonia has been shown to cause release of neurotransmitters such as serotonin (5-hydroxytryptamine; 5-HT) from synaptosomal preparations in vitro. In the present study, frontal neocortical extracellular levels of 5-HT and its major metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were determined in vivo by the use of microdialysis in portacaval shunted (PCS) rats, an experimental model of chronic hepatic encephalopathy (HE), prior to and after an acute coma-inducing administration of ammonium acetate (NH4Ac; 5.2 mmol/kg, i.p.). PCS rats displayed elevated (P < 0.01) 5-HIAA but unaltered 5-HT extracellular levels compared with controls, supporting the contention of an increased neocortical 5-HT metabolism but unaltered neuronal 5-HT output in chronic HE. However, a transient elevation of extracellular 5-HT levels was observed when PCS-NH4Ac rats were in coma. Increased brain ammonia may thus augment neuronal 5-HT release in chronic HE, which in turn could be a causative for precipitation of more severe stages of HE.