Amino acid, ammonia and neurotransmitter concentrations in hepatic encephalopathy: serial analysis in plasma and cerebrospinal fluid during treatment with an adapted amino acid solution

The critical role of hippocampal dopamine in the pathogenesis of hepatic encephalopathy

The pathogenesis of hepatic encephalopathy (HE) has been generally linked to blood ammonia, gamma-aminobutyric acid and serotonin. However, the exact mechanism remains unclear. In the present study, we aimed to explore the role of hippocampal dopamine (DA) and its receptors in the pathogenesis of HE through the use of behavioral testing, western blotting, and immunofluorescence staining in normal rats, HE model rats and rats treated with the DA precursor-levodopa (L-DOPA). HE model rats manifested fibrotic livers and showed serious behavioral disorders. They also had significantly lower hippocampal DA content and increased expression of both D1 and D2 receptors relative to normal rats. After treatment with L-DOPA, the HE model rats showed normal behavior and expression of D1 returned to normal levels. Furthermore, pretreatment with the D1 antagonist SCH23390 blocked the therapeutic effect of L-DOPA on behavior in HE model rats. Taken together, these results clarify that the decrease in hippocampal DA plays a role in the pathogenesis of HE and that this effect is mediated by D1. These findings provide new evidence for the pathogenesis of HE.

Simultaneous determination of thirteen substances related to NAFLD in mouse brain tissue using 3-aminobutyric acid as internal standard by HPLC-FLD

Disorders of certain branched-chain amino acids may be associated with the occurrence and development of non-alcoholic fatty liver disease. Measurement of related branched-chain amino acid levels could provide a reference for the clinical and scientific research of the non-alcoholic fatty liver disease. An established HPLC-FLD method was used to quantify aspartic acid, glutamate, glutamine, glycine, taurine, tyrosine, 4-amino butanoic acid, tryptophan, methionine, valine, phenylalanine, isoleucine and leucine in mouse brain tissue. Brain tissue samples mixed with internal standard (3-aminobutyric acid) were processed, then derivatized with 2-O-phthaldialdehyde, and finally separated on an ODS2 column through gradient elution at a flow rate of 1.0 ml·min^-1 . The excitation and emission wavelengths were set at 340 and 455 nm, respectively. The mobile phase A was 100% methanol and the mobile phase B consisted of 30 mmol·L^-1 sodium acetate (pH 6.8). The injection volume was 20 μl and the single run time was 45 min. Several parameters, accuracy, precision, and stability, were verified and the results showed the established method had good sensitivity and resolution for all of the 13 compounds and internal standard in mouse brain.

A Metabonomics Approach to Drug Toxicology in Liver Disease and its Application in Traditional Chinese Medicine

BACKGROUND

The progression of liver disease causes metabolic transformation in vivo and thus affects corresponding endogenous small molecular compounds. Metabonomics is a powerful technology which is able to assess global low-molecular-weight endogenous metabolites in a biological system. This review is intended to provide an overview of a metabonomics approach to the drug toxicology of diseases of the liver.

METHODS

The regulation of, and relationship between, endogenous metabolites and diseases of the liver is discussed in detail. Furthermore, the metabolic pathways involved in drug interventions of liver diseases are reviewed. Evaluation of the protective mechanisms of traditional Chinese medicine in liver diseases using metabonomics is also reviewed. Examples of applications of metabolite profiling concerning biomarker discovery are highlighted. In addition, new developments and future prospects are described.

RESULTS

Metabonomics can measure changes in metabolism relating to different stages of liver disease, so metabolic differences can provide a basis for the diagnosis, treatment and prognosis of various diseases.

CONCLUSION

Metabonomics has great advantages in all aspects of the therapy of liver diseases, with good prospects for clinical application.

Ingestion of Lactobacillus strain reduces anxiety and improves cognitive function in the hyperammonemia rat

Evidence suggests that the hyperammonemia (HA)-induced neuroinflammation and alterations in the serotonin (5-HT) system may contribute to cognitive decline and anxiety disorder during hepatic encephalopathy (HE). Probiotics that maintain immune system homeostasis and regulate the 5-HT system may be potential treatment for HA-mediated neurological disorders in HE. In this study, we tested the efficacy of probiotic Lactobacillus helveticus strain NS8 in preventing cognitive decline and anxiety-like behavior in HA rats. Chronic HA was induced by intraperitoneal injection of ammonium acetate for four weeks in male Sprague-Dawley rats. HA rats were then given Lactobacillus helveticus strain NS8 (10(9) CFU mL(-1)) in drinking water as a daily supplementation. The Morris water maze task assessed cognitive function, and the elevated plus maze test evaluated anxiety-like behavior. Neuroinflammation was assessed by measuring the inflammatory markers: inducible nitric oxide synthase, prostaglandin E2, and interleukin-1 β in the brain. 5-HT system activity was evaluated by measuring 5-HT and its metabolite, 5-HIAA, and the 5-HT precursor, tryptophan. Probiotic treatment of HA rats significantly reduced the level of inflammatory markers, decreased 5-HT metabolism, restored cognitive function and improved anxiety-like behavior. These results indicate that probiotic L. helveticus strain NS8 is beneficial for the treatment of cognitive decline and anxiety-like behavior in HA rats.

Three targets of branched-chain amino acid supplementation in the treatment of liver disease

The article explains the pathogenesis of disturbances in branched-chain amino acid (BCAA; valine, leucine, and isoleucine) and protein metabolism in various forms of hepatic injury and it is suggested that the main cause of decrease in plasma BCAA concentration in liver cirrhosis is hyperammonemia. Three possible targets of BCAA supplementation in hepatic disease are suggested: (1) hepatic encephalopathy, (2) liver regeneration, and (3) hepatic cachexia. The BCAA may ameliorate hepatic encephalopathy by promoting ammonia detoxification, correction of the plasma amino acid imbalance, and by reduced brain influx of aromatic amino acids. The influence of BCAA supplementation on hepatic encephalopathy could be more effective in chronic hepatic injury with hyperammonemia and low concentrations of BCAA in blood than in acute hepatic illness, where hyperaminoacidemia frequently develops. The favorable effect of BCAA on liver regeneration and nutritional state of the body is related to their stimulatory effect on protein synthesis, secretion of hepatocyte growth factor, glutamine production and inhibitory effect on proteolysis. Presumably the beneficial effect of BCAA on hepatic cachexia is significant in compensated liver disease with decreased plasma BCAA concentrations, whereas it is less pronounced in hepatic diseases with inflammatory complications and enhanced protein turnover. It is concluded that specific benefits associated with BCAA supplementation depend significantly on the type of liver disease and on the presence of inflammatory reaction. An important task for clinical research is to identify groups of patients for whom BCAA treatment can significantly improve the health-related quality of life and the prognosis of hepatic disease.

New concepts in the mechanism of ammonia-induced astrocyte swelling

It is generally accepted that astrocyte swelling forms the major anatomic substrate of the edema associated with acute liver failure (ALF) and that ammonia represents a major etiological factor in its causation. The mechanisms leading to such swelling, however, remain elusive. Recent studies have invoked the role of oxidative stress in the mechanism of hepatic encephalopathy (HE), as well as in the brain edema related to ALF. This article summarizes the evidence for oxidative stress as a major pathogenetic factor in HE/ALF and discusses mechanisms that are triggered by oxidative stress, including the induction of the mitochondrial permeability transition (MPT) and activation of signaling kinases. We propose that a cascade of events initiated by ammonia-induced oxidative stress results in cell volume dysregulation leading to cell swelling/brain edema. Blockade of this cascade may provide novel therapies for the brain edema associated with ALF.

Sustained citalopram treatment in experimental hepatic encephalopathy: effects on entrainment to the light-dark cycle and melatonin

Patients with chronic hepatic encephalopathy often display altered diurnal rhythm as well as other affective disturbances which motivate treatment with antidepressants. We investigated the effects of sustained treatment with citalopram (10 mg/kg daily, 10 days) on 24-hr behavioural open-field activities in portacaval-shunted (PCS) rats and sham-operated control rats. In addition, the daytime and nighttime serum melatonin levels, as well as the serum concentrations of the enantiomers of citalopram and its metabolites, were analyzed. Untreated PCS rats showed reduced locomotor and rearing activities during nighttime. Citalopram treatment resulted in elevated behavioural activity in the PCS rats during night, indicative of an improved entrainment to the light-dark cycle, whereas no behavioural effect could be observed in sham rats. Higher melatonin levels in both PCS and sham rats were observed during nighttime compared with daytime, but the untreated PCS rats also showed higher daytime melatonin level than the corresponding sham group. Citalopram treatment seemed not to have any major effect on the melatonin levels. Higher serum levels of both citalopram and metabolites were observed in PCS rats as compared to sham rats. An altered ratio between the S- and R-enantiomers could also be observed in the PCS rats. In conclusion, the present data support the contention of a disturbed diurnal rhythm, and that the melatonin activity may be altered, in chronic hepatic encephalopathy. The citalopram treatment resulted in similar behavioural performances and daytime serum melatonin levels in PCS rats and controls, although pharmacokinetic differences were present between the groups.

Glutamine: a Trojan horse in ammonia neurotoxicity

Mechanisms involved in hepatic encephalopathy still remain to be defined. Nonetheless, it is well recognized that ammonia is a major factor in its pathogenesis, and that the astrocyte represents a major target of its CNS toxicity. In vivo and in vitro studies have shown that ammonia evokes oxidative/nitrosative stress, mitochondrial abnormalities (the mitochondrial permeability transition, MPT) and astrocyte swelling, a major component of the brain edema associated with fulminant hepatic failure. How ammonia brings about these changes in astrocytes is not well understood. It has long been accepted that the conversion of glutamate to glutamine, catalyzed by glutamine synthetase, a cytoplasmic enzyme largely localized to astrocytes in brain, represented the principal means of cerebral ammonia detoxification. Yet, the "benign" aspect of glutamine synthesis has been questioned. This article highlights evidence that, at elevated levels, glutamine is indeed a noxious agent. We also propose a mechanism by which glutamine executes its toxic effects in astrocytes, the "Trojan horse" hypothesis. Much of the newly synthesized glutamine is subsequently metabolized in mitochondria by phosphate-activated glutaminase, yielding glutamate and ammonia. In this manner, glutamine (the Trojan horse) is transported in excess from the cytoplasm to mitochondria serving as a carrier of ammonia. We propose that it is the glutamine-derived ammonia within mitochondria that interferes with mitochondrial function giving rise to excessive production of free radicals and induction of the MPT, two phenomena known to bring about astrocyte dysfunction, including cell swelling. Future therapeutic approaches might include controlling excessive transport of newly synthesized glutamine to mitochondria and its subsequent hydrolysis.

Effects of sorbent suspension dialysis on plasma amino acid levels in cirrhotic patients with refractory hepatic encephalopathy

In cirrhotic patients, plasma amino acid levels are severely deranged. A decreased ratio of branched-chain to aromatic amino acids (Fischer ratio) has been implicated in the pathogenesis of hepatic encephalopathy. In this prospective study, we investigated the effects of extracorporeal detoxification on amino acid levels using a sorbent suspension dialysis system. Twenty patients with documented cirrhosis and hepatic encephalopathy grade II-III not responding to standard treatment were randomized to receive either six hours of sorbent dialysis and standardized conventional medical treatment or ongoing medical treatment alone. In contrast to previous uncontrolled studies, no significant effect on amino acid levels, Fischer ratio or clinical grade of hepatic encephalopathy was detected in either treatment group. In conclusion, a 6-hour treatment with sorbent dialysis did not significantly influence plasma levels of amino acids and did not ameliorate the clinical grade of hepatic encephalopathy.

Cerebrospinal fluid glutamine, tryptophan, and tryptophan metabolite concentrations in dogs with portosystemic shunts

OBJECTIVE

To determine whether glutamine (GLN), tryptophan (TRP), and tryptophan metabolite concentrations are higher in cerebralspinal fluid (CSF) dogs with naturally occurring portosystemic shunts (PSS), compared with control dogs.

ANIMALS

11 dogs with confirmed PSS and 12 control dogs fed low- and high-protein diets.

PROCEDURE

Cerebrospinal fluid and blood samples were collected from all dogs. Serum and CSF concentrations of GLN, alanine, serine, TRP, 5-hydroxyindoleacetic acid (5-HIAA), and quinolinic acid (QUIN) were measured.

RESULTS

Cerebrospinal fluid concentrations of GLN, TRP, and 5-HIAA were significantly higher in PSS dogs, compared with control dogs fed high- or low-protein diets. Cerebrospinal fluid QUIN concentration was significantly higher in PSS dogs, compared with control dogs fed the low-protein diet. Serum QUIN concentration was significantly lower in PSS dogs, compared with control dogs fed either high- or low-protein diets.

CONCLUSIONS AND CLINICAL RELEVANCE

An increase in CNS GLN concentration is associated with high CSF concentrations of TRP and TRP metabolites in dogs with PSS. High CSF 5-HIAA concentrations indicate an increased flux of TRP through the CNS serotonin metabolic pathway, whereas high CSF QUIN concentrations indicate an increased metabolism of TRP through the indolamine-2,3-dioxygenase pathway. The high CSF QUIN concentrations in the face of low serum QUIN concentrations in dogs with PSS indicates that QUIN production from TRP is occurring in the CNS. High concentrations of QUIN and other TRP metabolites in the CNS may contribute to neurologic abnormalities found in dogs with PSS and hepatic encephalopathy.

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.

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.

Cerebral changes in hepatic encephalopathy

Hepatic encephalopathy (HE) accompanied by an impairment of consciousness from orientation disorder (grade II) to coma (grade IV) is considered to be overt HE and is treated as an emergency. However, subclinical hepatic encephalopathy (SHE) can be detected by sensitive and quantitative neuropsychological examinations in cirrhotic patients without overt HE. The introduction of the SHE concept is clinically important for preventing the deterioration of SHE (grades 0 and I) to overt HE (grade II and more severe), prolonging the compensated state of cirrhosis without its deterioration to hepatic failure, and the continuation of patient treatment at home. We developed a new diagnostic method for SHE using a quantitative neuropsychological test, with the computerization of all operations. Evaluations of cerebral function and morphology are useful for the determination of the pathophysiology of HE, and assist the diagnosis of SHE. The latencies of the P3 wave in the visually evoked potential and the P300 wave in the event-related potential are prolonged in cirrhotic patients with SHE and are well expressed in three-dimensional coloured topograms (brain mapping). Automated polysomnographic analysis is useful for continuous-monitoring electroencephalograms (EEG) and for the detection of the sleep disturbance observed in cirrhotic patients with SHE. Brain atrophy in computed tomography (CT), magnetic resonance imaging (MRI) and high signals in the basal ganglia in the MR-T1-weighted images have frequently been observed in patients with SHE. The reduction of regional cerebral blood flow (rCBF) by 99mtechnetium-1, 1-ethylcysteinate dimer (99mTc-ECD)-single photon emission computed tomography (SPECT) and the choline/N-acetylaspartic acid ratio by proton-magnetic resonance spectroscopy (1H-MRS) were observed in the hippocampus in patients with SHE. These approaches (cerebral function tests and imaging diagnoses of the brain) can also be used to evaluate the effectiveness of treatments for HE; for example, branched-chain amino acid (BCAA) was shown by automated continuous polysomnographic analysis to be a psychotropic drug which acts directly on the central nervous system and the clinical significance of choline administration to HE patients is now being evaluated by 1H-MRS and neuropsychological tests.

Overtraining and the BCAA hypothesis

The purpose of this review was to give an answer to the question whether there are convincing data to support the hypothesis of an amino acid imbalance as one possible mechanism to explain overtraining syndrome. Animal studies point to an enhanced synthesis of the neurotransmitter 5-hydroxytryptamine through an amino acid imbalance at the blood-brain barrier with a preferable tryptophan uptake into the brain, resulting in premature fatigue. Human studies, however, show contradictory results, mainly because of nonstandardized methodology, so that a final conclusion cannot be made at present. BCAA supplementation in addition to standard carbohydrate ingestion during sustained exercise seems to be of no eminent advantage to delay fatigue. The overall results concerning the BCAA hypothesis to explain overtraining are inconclusive and require more controlled experimental research.

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 an infusion of branched-chain amino acids on neurophysiological and psychometric testings in cirrhotic patients with mild hepatic encephalopathy

Psychotropic action of a branched-chain-enriched amino acid solution (Aminoleban) was quantitatively and visually examined in six cirrhotic patients with mild hepatic encephalopathy (grades I and II) using electrophysiological and psychometric methods. Neurophysiological effects of the amino acid solution were observed by comparing topographic spectrum analyses of electroencephalography (EEG) before and immediately after an intravenous 3 h infusion of the solution. The delta wave in the frontal region diminished from 61 +/- 13 to 12 +/- 4% (P < 0.01) and the alpha wave in the occipital region increased from 11 +/- 3 to 51 +/- 11% (P < 0.01). Latencies of the P3 wave in visual evoked potentials, which were topographically recorded in the occipital region, shortened from 220 +/- 32 to 148 +/- 19 ms (P < 0.01). Latencies of the P300 wave in event-related potentials, which were topographically recorded in the centro-temporal region, shortened from 493 +/- 81 to 360 +/- 93 ms (P < 0.05). Topographic reaction pattern of P300 was irregular toward the occipital or parietal region in cirrhotic patients. The EEG frequency power spectrum, illustrated by the colour density spectral array of computer-aided polysomnography analysis, clearly showed a gradual increase of the alpha wave spectrum and a gradual decrease of the delta wave spectrum after initiation of the infusion. These immediate neurophysiological changes were confirmed by improvement of quantitative psychometric tests including number connection test, reaction time to sound, and digit symbol and block design tests of Wechsler Adult Intelligence Scale.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperammonemia and hepatic encephalopathy stimulate rat cerebral synaptic mitochondrial glutamate dehydrogenase activity specifically in the direction of glutamate oxidation

The effects of hepatic encephalopathy (HE) due to thioacetamide (TAA)-induced liver failure and hyperammonemia (HA) produced by repeated i.p. administration of ammonium acetate on the activity of glutamate dehydrogenase (GlDH) in the direction of glutamate (Glu) synthesis from--(GlDH-NADH) or its oxidation to alpha-ketoglutarate (alpha-KG) (GlDH-NAD), respectively, were examined in non-synaptic and synaptic mitochondria from rat cerebral hemispheres. In non-synaptic mitochondria, HE and HA stimulated the GlDH-NADH activity by, respectively, 33% and 49%, but neither condition affected the GlDH-NAD activity. In synaptic mitochondria, HE and HA decreased the GlDH-NADH activity by, respectively, 31% and 28%, but stimulated the GlDH-NAD activity by as much as 90% (HE) and 100% (HA). Kinetic assays revealed that HA increased the Vmax of the synaptic mitochondrial GLDH-NAD by 105%, without affecting the Km for Glu. The stimulation of GlDH-NAD favors the oxidation of synaptic Glu to alpha-KG, and may represent an adaptive response serving to counteract hyperammonemia-induced decrease of cerebral alpha-KG production in other metabolic pathways.

Hepatic Encephalopathy

Hepatic encephalopathy occurs in a number of different species as a result of either congenital portacaval shunts or acquired liver disease. Despite intensive research, the neurochemical basis of the disorder has not been defined. Theories to explain the cerebral dysfunction that accompanies acute or chronic hepatic failure include 1) ammonia acting as the putative neurotoxin, 2) perturbed monoamine neurotransmission as a result of altered plasma amino acid metabolism, 3) an imbalance between excitatory amino acid neurotransmission, mediated by glutamate, and inhibitory amino acid neurotransmission, mediated by gamma-aminobutyric acid, and 4) increased cerebral concentrations of an endogenous benzodiazepine-like substance.

Characteristics of large neutral amino acid-induced release of preloaded L-glutamine from rat cerebral capillaries in vitro: Effects of ammonia, hepatic encephalopathy, and ?-glutamyl transpeptidase inhibitors

The release of newly loaded L-[14C]glutamine (L-Gln) from rat cerebral cortical capillaries was stimulated by L-transport system substrates: tryptophan (TRY), leucine (leu), and nonlabeled L-Gln, respectively, by 32, 50, and 40% above the basal release resulting from superfusion with standard Krebs-Henseliet buffer. However, no stimulation was observed upon treatment with D-Gln or L-glutamate (L-Glu), which are not the L-system substrates, or with ammonium chloride. The stimulatory effect of TRY was temperature dependent but sodium independent, and was abolished in the presence of a sulfhydryl reagent N-ethylmaleimide (NEM). The results support the view that the L-Gln-stimulated uptake of large neutral amino acids (LNAA) across the blood-brain barrier involves the L-system mediated Gln-LNAA exchange. The TRY-stimulated Gln release was enhanced in vitro by simultaneous addition of ammonium chloride, and in capillaries derived from rats with acute hepatic encephalopathy (HE). These results confirm the role of Gln-LNAA exchange in the excessive accumulation of LNAA in brain observed in a variety of hyperammonemic conditions. Superfusion of L-Gln-loaded capillaries in a buffer containing gamma-glutamyl transpeptidase (GGT) inhibitors, serine borate (SB) or 6-diazo-5-oxo-L-norleucine (DON), increased the basal L-Gln release and made it irresponsive to subsequent treatment with TRY. However, the basal release was also increased by superfusion with serine alone or Leu, and this treatment abolished the subsequent effect of TRY as well. Moreover, DON stimulated L-Gln release from capillaries superfused in a standard way, and the effects of DON and TRY were additive. Hence, in the present conditions, SB and DON acted as L-system substrates rather than as GGT inhibitors. Taken together, the results do not support the concept that GGT mediates the Gln-LNAA exchange.

The effects of ammonia tolerance tests on the cerebrospinal fluid concentrations of amino acids and indoleamines in patients with liver cirrhosis

To study the effect of ammonia administration on amino acids and indoleamines in cerebrospinal fluid (CSF) and on amino acids, insulin, and glucagon in plasma in humans with liver cirrhosis, we performed seven ammonia tolerance tests on six patients with stable liver cirrhosis. The grade of encephalopathy was determined by psychometric tests. Only one of the patients had pronounced encephalopathy. The other patients had no or only slight encephalopathy. The plasma concentrations of valine, leucine, isoleucine, phenylalanine, tyrosine, and methionine decreased after the ammonia load, whereas no changes were found in the plasma concentrations of glucagon and insulin. In CSF the concentrations of glutamine, aromatic amino acids, and indoleamines increased only in the patient who had pronounced encephalopathy, whereas no changes were found in the other patients. The effect of an ammonia load on the concentrations of neutral amino acids in CSF in patients with pronounced encephalopathy remains to be demonstrated.

The effect of blood ingestion on brain serotonin synthesis in portacaval-shunted rats

In rats with a portacaval shunt (PCS), the effect on the serotonin metabolism in the brain after oral administration of blood, a mixed amino acid solution (Vamin 14; KabiVitrum, Sweden) or a 10% glucose solution was studied. One week after PCS, the animals were fed with a gastric tube for 8 h and thereafter tested for behavioral abnormalities before decapitation at 12 h. The concentration of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were analyzed chromatographically (HPLC technique with electrochemical detection) in different regions of the brain. Estimation of synthetic rates of 5-hydroxyindoles was facilitated by aromatic aminoacid decarboxylase inhibition (m-hydroxybenzyl-hydrazine; NSD 1015). The brain concentrations of 5-HTP, 5-HT, and 5-HIAA were increased in all shunted rats as compared with sham-operated animals. Whether animals received blood, glucose, or aminoacid solution made no differences in the brain concentrations of 5-HTP and 5-HT. Concentrations of 5-HIAA were lower in those animals receiving blood as compared with the other shunted groups. No reproducible differences in the behavior of the animals were observed. These results suggest that massive blood administration 1 week after PCS in rats has no influence on the rate of brain indole synthesis. While alterations in serotonin metabolism may play a role in some forms of encephalopathy, this study implies that the behavioral and neurologic disorders which follow gastrointestinal tract hemorrhage in patients with liver failure may have other etiologies.

The effect of liver ischaemia on brain monoamine synthesis in the rat

Subtotal or total liver ischaemia was induced in the rat by dividing the hepatic artery (Expt. I) or by total dearterialisation of the liver (Expt. II) 2 days after porta-caval shunt (PCS). The animals received i.v. a 10% glucose infusion for 5 h after the last operation and were killed by decapitation. At the end of the experiment all animals with liver ischaemia were in Grade III coma. In different regions of the CNS 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), were analysed by HPLC-technique with electrochemical detection, while dihydroxyphenylalanine (DOPA), dopamine (DA) and norepinephrine (NE) were analysed with a radio enzymatic method after blocking the decarboxylation of 5-HTP to 5-HT and DOPA to DA by inhibition of the aromatic amino acid decarboxylase enzyme with m-hydroxybenzylhydrazine (NSD 1015) in order to estimate the synthesis rate of 5-hydroxyindoles and catecholamines. In Expt. I concentrations of 5-HTP in animals with PCS were increased as compared to sham operation. In animals with liver ischaemia, 5-HTP concentrations were increased as compared to sham operation but similar to those in animals with PCS alone. These results suggest that ligation of the hepatic artery for 5 h in PCS animals does not further accelerate the rate of brain indole synthesis. In Expt. II, the 5-HTP concentrations were increased in PCS animals as compared to sham operation. Animals with total liver dearterialisation exhibited decreased 5-HTP levels as compared to PCS, suggesting a decreased brain indole synthesis after severe liver ischaemia. In Expt. II, CNS concentrations of DOPA following PCS were unaltered as compared with sham-operated animals. In animals with total liver dearterialisation, DOPA levels were increased, suggesting an augmented catecholamine synthesis. The NE levels were lower than in PCS and in sham-operated animals.

Morphometric and densitometric investigations of protoplasmic astrocytes and neurons in human hepatic encephalopathy

Morphometric and densitometric evaluations were made of nuclei of astrocytes and nerve cells of 49 cases with chronic liver diseases and of 9 control cases. The data measured from Nissl-stained specimens of putamen were compared with clinical degrees of encephalopathy and with blood ammonia levels. The parameters measured included nuclear area and optical density of nuclei. The nuclear area of astrocytes (AAREA), on average, was found to grow significantly along with aggravation of encephalopathy, that growth being from 39 micron 2 in the control group to about 60 micron 2 in cases of severe encephalopathy. Furthermore the proportion of astrocyte nuclei with an area above 70 micron 2 (ALRG) and the proportion of the optical light area of the total nuclear area (AHOLE) rises. Mean compactness (ACEXT) and mean extinction of astrocyte nuclei (AMEXT) dropped along with growing severity of encephalopathy. Mean blood ammonia levels rose from 42 mumol/l in cases with no microscopically detectable signs of encephalopathy to about six times higher values in cases with severe encephalopathy. Optical density of astrocyte nuclei was negatively correlated and mean nuclear area positively correlated to blood ammonia levels. No characteristic morphometric and densitometric changes of nerve cell nuclei were recordable from the putamen.

The disposition of intravenous L-tryptophan in healthy subjects and in patients with liver disease

The disposition of free and of total tryptophan following an intravenous load of 1.5 g of L-tryptophan was evaluated in eight patients with non-cirrhotic liver disease, 40 patients with cirrhosis of the liver (21 Child's A, 15 Child's B, 4 Child's C) and in 14 healthy subjects. Cirrhosis affected disposition of tryptophan by (a) decreasing the clearance of both free and total tryptophan by 64% (P less than 0.001) and 34% (P less than 0.01), respectively, (b) by increasing the apparent volume of distribution of total tryptophan by 42% (P less than 0.01) by expansion of the peripheral compartment, resulting in (c) a threefold increase in the half-life of tryptophan. Apart from a reduction in free tryptophan clearance, these changes in tryptophan disposition were not apparent in patients with non-cirrhotic liver disease. Elevated fasting free tryptophan plasma concentrations are an indicator of impaired tryptophan metabolism in cirrhosis. They result from a decreased hepatic clearance of tryptophan rather than from a reduction in tryptophan protein binding. This study emphasises the markedly differing pharmacokinetic behaviour of tryptophan in cirrhotic patients compared with normal subjects and with patients with non-cirrhotic liver disease.

[Tryptophan metabolism in liver diseases: a pharmacokinetic and enzymatic study]

Tryptophan is considered to be one of the agents involved in the pathogenesis of hepatic encephalopathy. In our study, we evaluated tryptophan metabolism in liver disease. A bolus of 1.5 g of L-tryptophan was administered intravenously to 14 patients with noncirrhotic liver disease, 40 patients with liver cirrhosis, and 8 healthy volunteers. As pharmacokinetic parameters, the half life, clearance, and volume of distribution of free and total tryptophan were determined using a biexponential formula. In addition, the activity of liver tryptophan pyrrolase, the key enzyme of tryptophan metabolism, was measured in liver biopsy specimens of 15 patients with noncirrhotic liver disease, 8 patients with cirrhosis of the liver, and 4 patients with histologically normal livers. Healthy subjects and patients with noncirrhotic liver disease both showed similar results in measured and calculated data. In contrast, patients with cirrhosis revealed significant alterations of the pharmacokinetic parameters of free and total tryptophan: the half-life was increased by 195% and 176%, the clearance was decreased by 73% and 34%, respectively, and the activity of tryptophan pyrrolase was decreased by 22%. The tryptophan transfer in cirrhosis amounted to only 0.75 +/- 0.03 g per 24 h compared with 2.6 +/- 0.34 g per 24 h in healthy individuals. The findings demonstrate that patients with cirrhosis show a marked reduction in their ability to metabolize tryptophan. This should be taken into account in the oral and parenteral nutrition of those patients.