Visual evoked potentials in encephalopathy induced by galactosamine, ammonia, dimethyldisulfide, and octanoic acid

Possible Association Between DHEA and PKCε in Hepatic Encephalopathy Amelioration: A Pilot Study

Objective: Hepatic encephalopathy (HE) is a neuropsychiatric syndrome caused by liver failure and by an impaired neurotransmission and neurological function caused by hyperammonemia (HA). HE, in turn, decreases the phosphorylation of protein kinase C epsilon (PKCε), contributing to the impairment of neuronal functions. Dehydroepiandrosterone (DHEA) exerts a neuroprotective effect by increasing the GABAergic tone through GABA_A receptor stimulation. Therefore, we investigated the protective effect of DHEA in an animal model of HE, and the possible modulation of PKCε expression in different brain area.

Methods: Fulminant hepatic failure was induced in 18 male, Sprague–Dawley rats by i.p. administration of 3 g/kg D-galactosamine, and after 30 min, a group of animals received a subcutaneous injection of 25 mg/kg (DHEA) repeated twice a day (3 days). Exploratory behavior and general activity were evaluated 24 h and 48 h after the treatments by the open field test. Then, brain cortex and cerebellum were used for immunoblotting analysis of PKCε level.

Results: DHEA administration showed a significant improvement of locomotor activity both 24 and 48 h after D-galactosamine treatment (^****p < 0.0001) but did not ameliorate liver parenchymal degeneration. Western blot analysis revealed a reduced immunoreactivity of PKCε (^*p < 0.05) following D-galactosamine treatment in rat cortex and cerebellum. After the addition of DHEA, PKCε increased in the cortex in comparison with the D-galactosamine-treated (^***p < 0.001) and control group (^*p < 0.05), but decreased in the cerebellum (^*p < 0.05) with respect to the control group. PKCε decreased after treatment with NH₄Cl alone and in combination with DHEA in both cerebellum and cortex (^****p < 0.0001). MTS assay demonstrated the synergistic neurotoxic action of NH₄Cl and glutamate pretreatment in cerebellum and cortex along with an increased cell survival after DHEA pretreatment, which was significant only in the cerebellum (^*p < 0.05).

Conclusion: An association between the DHEA-mediated increase of PKCε expression and the improvement of comatose symptoms was observed. PKCε activation and expression in the brain could inhibit GABA-ergic tone counteracting HE symptoms. In addition, DHEA seemed to ameliorate the symptoms of HE and to increase the expression of PKCε in cortex and cerebellum.

Hepatic encephalopathy: from pathophysiology to therapeutic management

Hepatic encephalopathy is a complex and potentially reversible neuropsychiatric syndrome complicating acute or chronic liver disease. Clinical manifestations are multiple and varied, ranging from minimal neurological changes to coma. Ammonia is the main toxic substance involved in the pathogenesis of hepatic encephalopathy, although other mechanisms, such as modifications of the blood-brain barrier, disruptions in neurotransmission and abnormalities in GABAergic and benzodiazepine pathways may also play a role. The identification and treatment of precipitating factors is crucial in the management of patients with hepatic encephalopathy. Current treatments are based on reducing intestinal ammonia load by agents such as antibiotics or disaccharides, although their efficacy is yet to be clearly established.

Natural endogenous ligands for benzodiazepine receptors in hepatic encephalopathy

Benzodiazepines of natural origin (NBZDs) have been found in human blood and brains as well as in medicinal plants and foods. In plasma and brain tissue there are i.e. diazepam and nordiazepam equal to commercial drugs but there are also other benzodiazepine-like compounds termed "endozepines", which act as agonists at the benzodiazepine receptors of central type (CBR). A synthetic pathway for the production of NBZDs has not yet been found, but it has been suggested that micro-organisms may synthesize molecules with benzodiazepine-like structures. Hence NBZDs could be of both endogenous and exogenous source and be considered as natural anxyolitic and sedative. Interestingly there are also natural compounds, such as the polypeptide Diazepam Binding Inhibitor (DBI) acting as an "inversive agonist" implicated in fair and panic disorders. It has been suggested that NBZDs may play a role in the pathogenesis of hepatic encephalopathy (HE). Multidirectional studies evaluated NBZDs levels (1) in the blood of normal subjects, of cirrhotic with or without HE and in commercial benzodiazepine consumers; (2) in the blood of cirrhotic treated or not with a non-absorbable antibiotic; (3) in several constituents of our diet. In conclusion, NBZDs increase sometime in cirrhotics with or without HE but they reach concentrations not higher than those found in commercial benzodiazepines consumers. Hence NBZDs must be considered as occasional precipitating factor of HE and benzodiazepine antagonists only symptomatic drugs. The finding that NBZDs may be in part synthesized by intestinal bacterial flora and in part constituent of our diet underlines the importance to feed cirrhotic patients with selected food.

Management of hepatic encephalopathy: role of rifaximin

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome, which develops in patients with acute or chronic liver failure. It is widely accepted to be due to impairment of hepatic clearance of toxic products from the gut such as ammonia. Accumulation of ammonia induces a glutamate neurotoxicity leading to an increased tone of the gamma-aminobutyric acid A (GABA-A) receptor system in the brain which results in HE. Factors either increasing the ammonia levels (protein load, constipation, sepsis, or gastrointestinal bleeding) or potentiating the functional activity of the GABAergic system [natural benzodiazepine-like compounds (NBZDs) or exogenous benzodiazepines] may act as precipitating factors of HE. NBZDs are present in trace amounts in the blood of normal subjects and have been found to be increased in the blood of patients with liver cirrhosis, with or without HE. These compounds may derive either from the diet since they have been found in plants, vegetables and animals or from gut bacteria. The observation that intestinal bacterial flora is involved in the production of both primary agent of HE (ammonia) and precipitating factors (NBZDs) suggests that the use of nonabsorbable antibiotics such as rifaximin may be useful in preventing episodes of HE in patients with liver cirrhosis.

The effect of Helicobacter pylori eradication on gastric juice and blood ammonia concentrations and on visual evoked potentials in cirrhotics

BACKGROUND

The primary source of ammonia is the gut. Ammonia can also be generated by the urease activity of Helicobacter pylori in the gastric mucosa. The aim of this study was to investigate the effect of H. pylori eradication on blood and gastric juice ammonia levels and on visual evoked potential (VEP) recordings in cirrhotic patients.

MATERIALS AND METHODS

Male patients with cirrhosis and H. pylori infection were prospectively evaluated. All patients were given triple regimen for eradication for 10 days. Gastroscopy together with gastric juice sampling for ammonia and mucosal sampling for H. pylori status was performed before and after therapy. Gastric juice and blood ammonia levels were measured and VEP recordings were obtained before and after treatment.

RESULTS

Twenty-seven patients were included in the study. Patients with overt clinical hepatic encephalopathy were excluded from the study. Twenty-four out of twenty-seven patients became H. pylori-negative after the treatment. Ammonia measurements and VEP recordings were evaluated in the 24 patients in whom eradication was successful. A slight but statistically significant decrease in blood and a considerable decrease in gastric juice ammonia levels were observed after treatment [from 44.23 micromol/l to 41.6 micromol/l compared with 3234 micromol/l to 2709 micromol/l, respectively (p <.05)] in patients in whom H. pylori was eradicated. VEP recordings were abnormal in 14 out of 24 patients before the treatment. Only four of these 14 patients with abnormal recordings showed improvement. (p > .05).

CONCLUSIONS

Helicobacter pylori eradication in cirrhotics decreases blood and gastric juice ammonia concentrations whereas it does not provide an improvement in VEP recordings.

Evoked potentials in liver diseases

Evoked potentials are objective and quantitative methods capable of evaluating functions of both peripheral and central nervous systems (PNS and CNS). During the past 8 years, we have been using somatosensory, brainstem auditory, and pattern-reversal visual evoked potentials (SEP, BAEP, VEP) to study hepatic encephalopathy (HE) as well as functional status of the PNS and CNS in various liver diseases including viral hepatitis B, alcoholic liver disease and Wilson's disease (WD). In HE irrespective of its etiologies, there is a sequential prolongation and eventual disappearance of cortical components of the median nerve evoked SEP while there is no change in BAEP, suggesting that HE is primarily due to a disturbance in cerebral cortical function and that median SEP may be used for early detection of HE and for monitoring its clinical course. In addition, absence of the N20-P25 component, or presence of only the N20 component of the wave complex in fulminant hepatic failure is associated with high mortality, whereas presence of late cortical components in HE is usually associated with reversibility of clinical course. Central conduction time (CCT) of the BAEP is prolonged in patients with WD, alcoholic liver disease and liver cirrhosis due to hepatitis B. Furthermore, BAEP abnormality is most severe in WD, followed by alcoholic liver disease, and finally hepatitis B. Peripheral nerve conduction as determined by the N9 latency of SEP is slowed in alcoholic liver disease and liver cirrhosis of chronic hepatitis B, but normal in WD. Our studies, therefore, suggest that evoked potentials may be useful in the evaluation of both CNS and PNS functions in various liver diseases and also in the diagnosis and monitoring of HE.

New aspects on etiology, biochemistry, and therapy of portal systemic encephalopathy: a critical survey

There is scientific agreement that portal systemic encephalopathy (PSE) is caused morphologically by portal systemic shunts and biochemically by constituents of the portal venous blood. Ammonium has a key role in the pathogenesis of PSE. Direct correlations with the degree of PSE have been established exclusively with glutamine, i.e. the terminal product of the peripheral detoxification of ammonium. In PSE, ammonium is probably responsible for damage to astrocytic and neuronal cells. Ammonium's toxic effect is due to the intracerebral glutamine synthesis. After several metabolic steps, which will be discussed in detail, brain cell damage is caused directly or indirectly (exitotoxically) by energy deficiency. Hyperammonemia and PSE are each well defined though different forms of disturbance. Therefore, ammonium is not the sole decisive factor in the pathogenesis of PSE. We performed a detailed and critical analysis of all studies on amino acid therapy of PSE, especially those that were randomized and controlled. This analysis revealed a close and direct correlation between qualitative and quantitative dosages of amino acids on one hand, and parallel improvements of amino acid imbalance (essentially associated with PSE) and degree of PSE on the other. A close and direct dose/efficacy correlation must be assumed. Disturbed plasmatic amino acid homeostasis and cerebral monoaminergic neurotransmission are probably important pathogenic factors of PSE. A fundamental cofactor in the efficacy of each adequate amino acid therapy might be a substantial decrease of endogenous ammonium production. Physiologic benzodiazepines may also have an important function in the pathogenesis of PSE: not so, however, the glutamate-ergic and GABA-ergic neurotransmission, which are disturbed principally in PSE. In close correlation to pathogenesis, established and proposed therapies of PSE are critically discussed.

Increased brain concentrations of polyamines in rats with encephalopathy due to a galactosamine-induced fulminant hepatic failure

Polyamine concentrations including putrescine, spermidine and spermine were documented in two brain areas of rats with mild and severe stages of hepatic encephalopathy (HE) due to fulminant hepatic failure induced by galactosamine HC1 injection (3 g kg-1 i.p.). In the mild stage of HE putrescine increased by 3-4 times whereas spermidine and spermine showed a slight increase. The scenario, however, was found to be changed going from the mild to the severe stage of HE, since in this last stage spermidine and spermine showed a further rise while putrescine was found to be significantly lower than in the mild stage of HE in both the brain areas studied. The changes in the ratio among the three polyamines with an enhanced prevalence in the severe stage of HE of spermidine and spermine are likely to be related to the exhaustion of the synthetic pathway of putrescine or to a reduction of the interconversion to this polyamine from spermidine and spermine. Considering that these last two polyamines potentiate the N-methyl-D-aspartate glutamate receptor mediated toxicity and that they might exert neurotoxic effects per se, there are clear reasons for suspecting an implication of the described changes of polyamines in the neurochemical mechanism which sustain HE and to surmise a potential therapeutic effect in this pathology of non-competitive antagonists of polyamine-site on N-methyl-D-aspartate glutamate receptors.

The effect of oral-administered lactulose on colonic nitrogen metabolism and excretion

The influence of lactulose on organic acid fermentation, nitrogen metabolism and excretion in the colon associated with its mechanism of action on hepatic encephalopathy was investigated. Orally administered lactulose in increasing amounts (0 to 20 to 40 to 80 to 160 gm/day) to 12 healthy volunteers decreased ammonia production in 16.6% fecal homogenates incubated 6 hr and 24 hr at 37 degrees C (mean +/- S.E.M.: from 7 +/- 1 to 0 +/- 0 and from 13 +/- 2 to 0 +/- 0 mmol/L, respectively). Every dose of lactulose was given for 3 days with intervals of 1 to 2 wk, and 24-hr stools were collected on day 3. Fecal concentrations of ammonia decreased (from 50 +/- 9 to 11 +/- 3 mmol/L), but ammonia excretions increased (from 6 +/- 2 to 17 +/- 4 mmol/24 hr). Total fecal concentrations of nitrogen decreased (from 1,043 +/- 78 to 300 +/- 136 mmol/L), but excretions of nitrogen increased fourfold (from 111 +/- 21 to 457 +/- 113 mmoL/24 hr) because of the increase in stool mass. Fecal pH declined (from 6.9 +/- 0.1 to 4.9 +/- 0.1), but total organic acids (short-chain fatty acids and DL-lactate; range = 105 to 148 mmol/L) and osmolality in feces (417 to 450 mOsm/L) did not change, although the colonic fermentation of lactulose had a major impact on the proportions between the nontoxic acetate (increased from 65% +/- 2% to 89% +/- 3%) and the potentially neurotoxic 3-6-carbon fatty acids (decreased from 35% +/- 2% to 11% +/- 2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Globus pallidus alterations and brain atrophy in liver cirrhosis patients with encephalopathy: an MR imaging study

Brain magnetic resonance (MR) was performed in 29 liver cirrhosis patients without (N = 10) and with hepatic encephalopathy (HE) of chronic recurrent (N = 10) and of chronic persistent (N = 9) type. Sixty percent of the patients with chronic recurrent HE and 100% of the patients with chronic persistent HE showed a bilateral and symmetrical hyperintensity of the globus pallidus in the T1-weighted images while the T2-weighted images were normal, suggesting the possibility of the accumulation of a paramagnetic compound in this brain area during HE. Other findings of the study were evidence of brain atrophy of mild or moderate degree in 70% of patients with chronic recurrent HE and in 77% with chronic persistent HE and patients with liver cirrhosis without HE appeared normal on MR examination.

Reversal of the behavioral and electrophysiological abnormalities of an animal model of hepatic encephalopathy by benzodiazepine receptor ligands

Behavioral and electrophysiological evidence implicating the GABA-benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy was obtained using an improved rat model of hepatic encephalopathy caused by thioacetamide-induced fulminant hepatic failure. After the administration of thioacetamide together with supportive therapy, acute hepatocellular failure developed in rats as a result of massive hepatocellular necrosis without evidence of renal failure or hypoglycemia. The evolution of hepatic encephalopathy in this model was sufficiently slow to readily permit the staging of the syndrome. Prominent features of the encephalopathy include a marked reduction in open field activity and an abnormal visual evoked response. Both the deficits in spontaneous motor function and visual evoked response abnormalities of rats in stages III to IV hepatic encephalopathy were significantly improved after the administration of the benzodiazepine receptor ligands flumazenil or Ro 15-4513. Doses of flumazenil or Ro 15-4513 that produced these effects in rats with hepatic encephalopathy had no detectable action on either the behavior or the visual evoked responses of normal rats. The ability of benzodiazepine receptor ligands to ameliorate both the behavioral depression and the visual evoked response abnormalities associated with hepatic encephalopathy in the thioacetamide-induced rat model suggest an involvement of the GABA/benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy. In addition, the similarity of these observations to those in rabbits with hepatic encephalopathy caused by galactosamine-induced fulminant hepatic failure is compatible with the hypothesis that the mechanisms of hepatic encephalopathy in these two distinct models share a common final pathway, the allosteric enhancement of GABAergic tone through the benzodiazepine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Supersensitivity of GABA-A receptors in hepatic encephalopathy

During the past decade a new approach to pathogenetic studies of hepatic encephalopathy has been undertaken to identify the neurochemical alterations which characterize the syndrome. Using animal models of hepatic encephalopathy electrophysiological, behavioral, pharmacological and biochemical evidence were provided of an increased functional activity of the GABA-A receptors, including the Benzodiazepine site. These demonstrations seem to explain the increased sensitivity of patients with acute or chronic liver disease to sedative administration. The described increased tone of the GABAergic receptor complex seems to play a key role in the generalized depression of the central nervous system which characterizes hepatic encephalopathy, but other factors seem to contribute to the neuronal derangement present in this syndrome leading to an imbalance between inhibitory and excitatory receptor systems in the brain. Based on these findings a new symptomatic treatment with anti-benzodiazepine compounds which seem temporarily to counteract the symptoms of hepatic encephalopathy, was introduced.

Hepatic encephalopathy, GABA-ergic neurotransmission and benzodiazepine receptor ligands

Evidence compatible with increased GABAergic tone contributing to the manifestations of hepatic encephalopathy (HE) in animal models of fulminant hepatic failure (FHF) includes: (i) increased resistance to drugs which induce seizures by reducing GABAergic tone; (ii) abnormalities of visual evoked responses (VERs) which resemble those induced by drugs which augment GABAergic tone; (iii) increased sensitivity of CNS neurons to a GABA agonist; and (iv) ameliorations of the encephalopathy induced by a GABA receptor antagonist. Evidence compatible with a benzodiazepine (BZ) receptor ligand with agonist properties contributing to increased GABAergic tone in animal models of FHF includes: (i) abnormalities of VERs which resemble those in BZ agonist-induced coma; (ii) increased sensitivity of CNS neurons to a BZ receptor agonist; (iii) excitation of CNS neurons induced by BZ receptor antagonists; (iv) reversal of the increased sensitivity of CNS neurons to a GABA agonist by a BZ receptor antagonist; (v) presence of a ligand(s) in brain which displaces a radiolabeled ligand from BZ receptors; and (vi) increased affinity of this ligand(s) for BZ receptors in the presence of GABA ("positive GABA shift").

Neurotransmission in hepatic encephalopathy

After a careful characterization, a rat model of fulminant hepatic failure galactosamine-induced was utilized in order to evaluate the neurochemical changes and the histological alterations which occur during the developing of the encephalopathy. Following these studies, normal rats were treated with toxins claimed to be the primary agents of hepatic encephalopathy to recognize those which are able to mimic the behavioral, electrophysiological and neurochemical changes found in the rat model of fulminant hepatic failure. With the limit due to informations coming from an experimental model, the symptoms of HE seem to be attributable to neurotoxic agents such as ammonia. The toxicity of ammonia does not seem to be due to a mere decrease of general brain metabolism, but seems rather to be mediated by an increase, at least in some compartment, of neurotoxic amino acids such as glutamate. Both accumulation of ammonia and the neurotoxic effect of glutamate seem to be potentiated by the described zinc depletion (both in liver and in brain). Hence the final effect of these phenomena is the development of the symptoms of encephalopathy triggered by an imbalance between inhibitory and excitatory receptor systems in the brain associated with neuronal alterations which take place early and before the appearance of brain edema.

Visual evoked potential--a tool in the diagnosis of hepatic encephalopathy?

Visual evoked potentials (VEP) have been suggested to be of value in the diagnosis of subclinical and mild hepatic encephalopathy. In the present study, a comparison between VEP and four psychometric tests (number connection test A and B, digit symbol and word memory test) was performed in 42 cirrhotic patients, 17 of whom had clinical signs of encephalopathy. The results were compared to sex- and age-matched healthy controls. The VEP latencies for P2 (the second positive wave) and N3 (the third negative wave) were 11% and 26% longer (P less than 0.01-0.001) in the patients than in the controls. Moreover, the latencies for N2 (the second negative wave) and P2 were longer in the encephalopathic as compared to the non-encephalopathic patients (P less than 0.05). There was a significant correlation between the latencies for N2 and number connection tests A and B and digit symbol test. However, of the patients with clinical encephalopathy, less than half had VEP latencies longer than the mean +/- 2 S.D. above those for the controls. In contrast, none of the encephalopathic patients had normal results on the psychometric tests. This study demonstrates that although statistically significant differences exist between groups of cirrhotic patients and controls, VEP is not a reliable tool for the diagnosis of encephalopathy in the individual patient.

Hepatic encephalopathy

Hepatic encephalopathy (HE) is a complex reversible syndrome that can progress to coma. Recently, behavioral and electrophysiologic ameliorations of HE have been reported to occur in animal models of fulminant hepatic failure (FHF) and, in uncontrolled studies, in a majority of patients with FHF or cirrhosis following the intravenous administration of the benzodiazepine (BZ) receptor antagonist, flumazenil. These observations, while not excluding a role for other mechanisms in the mediation of HE, raise the possibility that an endogenous BZ receptor ligand with agonist properties may contribute to the manifestations of HE by allosterically potentiating GABA-mediated neurotransmission.

Assessment of hepatic encephalopathy with visual evoked potentials compared with conventional methods

Thirty-six patients with advanced chronic liver disease of predominantly alcoholic etiology and with a documented history or current physical evidence of hepatic encephalopathy were studied and compared to 30 healthy controls. Assessment was made of their mental state, number connection test, venous blood ammonia, electroencephalography and visual evoked potentials with both pattern reversal and flash stimuli. Because of considerable inter- and intraindividual variation in waveform, visual evoked potentials from flash stimuli were considered unreliable. In pattern reversal visual evoked potentials, the latency of the N1 and P1 waves was significantly longer (p less than 0.05) in patients than in controls; however, the wave latencies did not correlate with the mental state score. The mental state score correlated with the number connection test (r = 0.69, p less than 0.001), asterixis (r = 0.36, p less than 0.05), electroencephalography mean dominant frequency (r = 0.44, p less than 0.01) and blood ammonia (r = 0.60, p less than 0.01). In 14 patients studied sequentially, change in the mental state score correlated with change in the number connection test (r = 0.80, p less than 0.01) and asterixis (r = 0.75, p less than 0.01) but not with change in the electroencephalography, blood ammonia or visual evoked potential wave latencies. Although visual evoked potentials are abnormal in patients with alcoholic cirrhosis and encephalopathy, they are less accurate in assessing the level of consciousness than simple bedside evaluation with a number connection test.

Could an endogenous benzodiazepine ligand contribute to hepatic encephalopathy?

High affinity recognition sites for benzodiazepines are part of the gamma-aminobutyric acid (GABA) supramolecular complex on the plasma membrane of neurons in the mammalian brain. Synthetic agonist benzodiazepines promote GABA-ergic neurotransmission, and hence the hypnotic and anxiolytic effects of this class of drugs, by binding to these sites. A normal physiological role for these binding sites is unknown, and an endogenous ligand for benzodiazepine receptors has not been definitely identified in normal animals. In animals and human beings with hepatic encephalopathy, however, benzodiazepine receptor antagonists have induced amelioration of the encephalopathy, and an endogenous substance that competitively binds to benzodiazepine receptors has been found in cerebrospinal fluid. These findings suggest that an endogenous ligand for the benzodiazepine receptor with agonist properties contributes to hepatic encephalopathy by promoting GABA-ergic neurotransmission.

Hepatic encephalopathy. Application of visual evoked responses to test hypotheses of its pathogenesis in rats

A previous study of the patterns of visual evoked responses (VERs) in rats was interpreted as providing support for the synergistic neurotoxins hypothesis of the pathogenesis of hepatic encephalopathy (HE) due to fulminant hepatic failure (FHF). In contrast, other studies of the patterns of VERs in rabbits with different encephalopathies were interpreted as providing support for the concept that increased GABA-ergic tone may contribute to the neural inhibition of HE due to FHF. To attempt to resolve the discordant findings in these studies, additional studies of VERs have been undertaken in rats. To induce increased tissue levels of ammonia, mercaptans and fatty acids which are found in HE due to FHF, carefully predetermined doses of urease, dimethyldisulphide and octanoic acid were administered. The (pre-seizure) encephalopathy induced by these three agents was associated with abnormalities of the VER waveform that were fundamentally different from the abnormalities of the VER waveform associated with HE due to thioacetamide-induced FHF. However, the VER waveform in this model of HE due to FHF resembled closely that associated with pentobarbital-induced encephalopathy. These findings are in satisfactory agreement with those in the previous analogous studies in rabbits. They do not provide support for the synergistic neurotoxins hypothesis of the pathogenesis of HE, but are entirely consistent with increased GABA-ergic tone contributing to the neural inhibition of HE due to FHF.

Brainstem auditory evoked potentials in hepatic encephalopathy

Brainstem auditory evoked potentials were obtained from 30 patients primarily with viral hepatitis to determine the functional status of the brainstem in hepatic encephalopathy. The patients were divided into four groups: Group 1 with compensated hepatic diseases; Group 2 with hepatic failure but no hepatic encephalopathy; Group 3 with Grade 1 or 2 hepatic encephalopathy, and Group 4 with Grade 3 or 4 hepatic encephalopathy. The brainstem auditory evoked potential central conduction times (I-V interval) of four patient groups were not significantly different from that of the age-matched control group. The present data suggest that the brainstem auditory pathways remain undisturbed in hepatic encephalopathy.

Somatosensory evoked potentials: monitoring cerebral functions following liver transplantation

Serial somatosensory evoked potentials (SEPs) were obtained from a patient with Wilson's disease who had had liver transplantation. Correlating with recovery of hepatic encephalopathy and liver functions following the surgery, SEPs showed progressive normalization of peak latencies and waveforms. The data indicate that SEP may be a useful objective method in assessing recovery of cerebral functions following liver transplantation.

Somatosensory evoked potentials in hepatic encephalopathy

Median nerve somatosensory evoked potentials were recorded from 33 patients with various degrees of hepatic failure and from 10 age-matched controls. Within 20 ms poststimulation, one negative peak (N13) could be recorded from the middle of the back of the patient's neck at the C2 vertebral level. Within 150 ms, three negative and three positive peaks, sequentially designated as N1, P1, N2, P2, N3, and P3, could be recorded from the scalp over the contralateral sensory cortex. There was a progressive prolongation of peaks and interpeak latencies correlating with the severity of hepatic encephalopathy. In 10 patients with hepatic failure but no clinical evidence of hepatic encephalopathy, latencies of peak N3 and P3 were delayed and N1-N3 interpeak latencies were prolonged. Thirteen patients with grade 1 or 2 hepatic encephalopathy showed further delayed latencies of peaks P2, N3, and P3, further prolonged N1-N3, N1-P2 interpeak latencies, and distortion of waveforms. Peaks N2, P2, N3, and P3 were further delayed, and even disappeared in 10 patients with grade 3 or 4 hepatic encephalopathy. However, central conduction time (N13-N1 interpeak latency) was not prolonged in all stages of hepatic failure. In addition, serial somatosensory evoked potential studies correlated well with the clinical course. The present data suggest that somatosensory evoked potential recording is a reliable objective method in the early assessment and monitoring of hepatic encephalopathy.

Octanoic acid-induced coma and reticular formation energy metabolism

The medium chain fatty acid octanoic acid was injected i.p. into 20-22 g Swiss-Albino mice at a dose of 15 mumol/g. This dose produced a reproducible response consisting of a 3-4 min period of drowsiness, followed by coma. These mice as well as suitable controls were sacrificed by rapid submersion in liquid N2, or by microwave irradiation in a 7.3 kW microwave oven. Tissue from the reticular formation and the inferior colliculus was prepared for microanalysis of the energy metabolites glucose, glycogen, ATP and phosphocreatine. Results from this study showed a selective effect on energy metabolism in cells of the reticular formation. Both glucose and glycogen were elevated in the coma and precoma state. In addition, ATP and phosphocreatine were decreased in the reticular formation during coma. These results show a selective effect of octanoic acid on energy metabolism in the reticular formation both in the precoma stage, and during overt coma. The selective vulnerability of the reticular formation to metabolic insult may act in a beneficial manner to the animal by inducing coma. This lowers the overall demand for energy, thereby placing the animal in a milieu in which there is an increased chance for correction of the perturbation.

Evidence that 2-phenylpyrazolo[4,3-c]-quinolin-3(5H)-one antagonises pharmacological, electrophysiological and biochemical effects of diazepam in rats

The effects of the acute administration of 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one on diazepam-induced behaviour and electrophysiological activity were studied in rat. The compound, in doses of 5-10 mg/kg (i.p.), which per se did not induce alterations in spontaneous locomotor activity, antagonised the sedative effect induced by 5-10 mg/kg (i.p.) of diazepam. The injection of diazepam in rats, induced a profound reduction in the first negative wave of the recording of the visual evoked potential used as a sensitive electrophysiological test, in vivo. 2-Phenylpyrazolo[4,3-c]quinolin-3(5H)-one (10 mg/kg, i.p.) caused a recovery of the amplitude of the first negative wave within a few minutes. This result was confirmed by the finding that 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one, injected acutely in rats, pretreated with diazepam exhibited the capacity to antagonise the binding of [3H]diazepam determined in vitro on synaptic membrane preparations from cortex. The comparison of the pattern of the visual-evoked potential, recorded after the injection of 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one (50 mg/kg) with the patterns recorded after the injection of ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazolo(1,5a) (1,4)benzodiazepine-3-carboxylate (50 mg/kg) and ethyl-beta-carboline-3-carboxylate and 1-methyl-beta-carboline demonstrated that 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one is devoid of intrinsic activity.

Hepatic encephalopathy. Experimental studies in a rat model of fulminant hepatic failure

A new approach to pathogenetic study of hepatic encephalopathy was recently undertaken in order to identify the neurological alterations of the brain which characterize the coma. In this study attention was firstly addressed to a correct and objective evaluation of the comatose state in rats with fulminant hepatic failure induced by galactosamine. For this purpose visual evoked potentials were utilized since this electrophysiological test proved reliable and sensitive on the basis of an extensive pharmacological study. Two different stages of coma were identified in the rat and they were named mild and severe. Receptor binding studies performed on brain membranes of these rats show in the mild stage an increased number of low and high affinity GABA receptors and a decreased affinity of dopamine receptors. The severe stage is characterized by the persistence of only high affinity GABA receptors and a reduced number of dopamine receptors. This imbalance between inhibitory and excitatory receptor systems may explain the generalized central nervous system depression which characterizes the hepatic encephalopathy while the increased number of benzodiazepine receptors found in both stages of coma may account for the brain supersensitivity to sedative administration of patients with liver disease and for the sedative-induced episodes of coma. These receptor alterations may be attributed to a disuse and/or a partial degeneration of nerve terminals due to peripheral neurotoxins (i.e., ammonia, mercaptans, short chain fatty acids) and the decrease of glutamate decarboxylase activity and of zinc levels in brain tissues seems to be respectively a direct and an indirect demonstration of this phenomenon. Bearing in mind the supersensitivity of the GABA-benzodiazepine receptor system and their reciprocal interaction, a benzodiazepine antagonist was administered to rats in mild stage of encephalopathy. Electrophysiological and benzodiazepine binding studies demonstrated that this treatment can temporarily counteract some of the neurological disturbances of the earlier stage of coma and act as antidote of the sedative-induced episodes of coma.

Toxins in hepatic encephalopathy: the role of the synergistic effect of ammonia, mercaptans and short chain fatty acids

Evidence has been recently produced that neurological changes which characterize hepatic encephalopathy due to fulminant hepatic failure in rats are linked with a pathology of GABA receptors. In the search for the peripheral toxins responsible for the CNS impairment present in hepatic encephalopathy it has been shown that the administration of ammonia and mercaptans and octanoic acid in normal rats reproduced behavioural and electrophysiological changes similar to those seen in galactosamine induced encephalopathy. The present report shows that a subacute administration of the above toxins induced a marked alteration of the GABA receptor complex which may account for the CNS derangement of hepatic encephalopathy.