Brain tryptophan perturbation in hepatic encephalopathy: implications for effects by neuropsychoactive drugs in clinical practice

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.

Open-Field Behavioural Alterations in Liver-Impaired and Sham-Operated Rats after Acute Exposure to the Antidepressant Venlafaxine

Patients with chronic liver impairment often display symptoms of affective psychiatric nature where the choice for antidepressant treatment is rational. Since caution is recommended when these drugs are used in such patients, a dose reduction is usually performed. We have previously reported that a dose reduction to liver-impaired portacaval shunted rats has resulted in similar brain concentrations of venlafaxine as compared to sham-operated control rats that received a two times higher dose. The main aim of the present study was therefore to investigate if this "normalisation" in pharmacokinetics of the portacaval-shunted rats also was true for the pharmacodynamic response in terms of drug effect on spontaneous open-field behaviour. Thus, portacaval-shunted rats received a single reduced dose (5 mg/kg) of venlafaxine or saline, whereas sham-operated rats received either 10 mg/kg or saline. Thereafter, central and peripheral arena locomotor and rearing activities were recorded during 60 min. The venlafaxine-treated portacaval-shunted and sham rats displayed reduced and unchanged overall behavioural activities compared with corresponding controls, respectively. However, the ratios between centrally and peripherally performed behavioural activities were higher in the venlafaxine-treated sham rats, indicating an increase in central arena activity as compared to the sham-saline and portacaval-shunted rats. The present study indicates that, despite a 50% dose reduction, caution still is necessary when antidepressants are used in liver insufficient subjects. This study also shows the importance of detailed open-field behavioural studies in which both central and peripheral activities are recorded for measurement of open-field behavioural drug effects.

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.

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.

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.

Plasma and brain levels of oxindole in experimental chronic hepatic encephalopathy: effects of systemic ammonium acetate and L-tryptophan

It has previously been shown that the neurodepressant L-tryptophan metabolite oxindole is increased in the blood and brain of rats with fulminant hepatic failure and in the blood of cirrhotic patients affected by chronic hepatic encephalopathy. In the present investigation, we found that oxindole levels were significantly increased in the blood and brain of portacaval-shunted rats, an animal model of chronic hepatic encephalopathy, compared with sham-operated controls. A further increase in plasma and brain oxindole content was found after oral administration of L-tryptophan (300 mg/kg) to both portacaval-shunted or sham-operated animals, while intraperitoneal injection of the amino acid did not modify oxindole content either in brain or blood. Ammonium acetate administration (4.0 mmol/kg, intraperitoneal) reversibly deteriorated the neurological status of portacaval-shunted animals, but did not modify, in a directly related manner, plasma and brain oxindole content. The present findings are in line with the possibility that oxindole may be an additional L-tryptophan-related candidate in the pathogenesis of chronic hepatic encephalopathy.

Tryptamine-mediated stabilization of tryptophanyl-tRNA synthetase in human cervical carcinoma cell line

Tryptamine is an endogenous neuroactive metabolite of tryptophan. Interpretation of the function of this bioamine, however, is restricted to manipulation with tryptamine synthetic pathways. Meanwhile, tryptamine is a potent inhibitor of protein biosynthesis, via the competitive inhibition of tryptophanyl-tRNA synthetase (TrpRS). The influence of the persistent tryptamine inhibition on the half-life and cellular content of TrpRS was examined by chase labeling of HeLa cells and the tryptamine-resistant subline with [35S]methionine. The results indicate that long-term tryptamine treatment of HeLa cells led to a significant increase in the half-life of TrpRS while the content, in vivo phosphorylation and gene dose of TrpRS were unchanged. These findings suggest that survival of drug-resistant cells may not be due to TrpRS gene amplification, but to stabilization of TrpRS. It was shown that tryptamine is an effective inhibitor of HeLa cell growth. In contrast to the well-characterized antineoplastic compounds, conferring a many hundred-fold elevated drug resistance to tumor cells, resistance to tryptamine at very low levels was difficult to achieve, i.e. the 2-fold resistant subline was selected after 19 months of treatment of HeLa cells with gradually increasing concentrations of tryptamine. The tryptamine-resistant HeLa subline exhibited a slower growth rate than the original HeLa line when similar concentrations of both cell populations were seeded on the plates. A low tryptamine resistance and a lack of TrpRS gene amplification were observed in two tryptamine-resistant HeLa sublines and three Chinese hamster sublines. The role of TrpRS in oncogenesis and the perspective for tryptamine as a potential anti-cancer drug are discussed.

Psychiatric aspects of portal-systemic encephalopathy

This paper focuses on psychiatric aspects of portal-systemic encephalopathy (PSE) due to chronic liver disease and/or portal-systemic shunting. Clinical syndromes of PSE are discussed from the point of view of biological psychiatry, but, psychological consequences of concomitant cognitive disorders are also addressed. Psychiatric symptoms of early PSE and sleep disorders in patients with chronic liver disease are of specific interest.