Plasma and CSF benzodiazepine receptor ligand concentrations in cirrhotic patients with hepatic encephalopathy: relationship to severity of encephalopathy and to pharmaceutical benzodiazepine intake

MetaboRank: network-based recommendation system to interpret and enrich metabolomics results

Motivation

Metabolomics has shown great potential to improve the understanding of complex diseases, potentially leading to therapeutic target identification. However, no single analytical method allows monitoring all metabolites in a sample, resulting in incomplete metabolic fingerprints. This incompleteness constitutes a stumbling block to interpretation, raising the need for methods that can enrich those fingerprints. We propose MetaboRank, a new solution inspired by social network recommendation systems for the identification of metabolites potentially related to a metabolic fingerprint.

Results

MetaboRank method had been used to enrich metabolomics data obtained on cerebrospinal fluid samples from patients suffering from hepatic encephalopathy (HE). MetaboRank successfully recommended metabolites not present in the original fingerprint. The quality of recommendations was evaluated by using literature automatic search, in order to check that recommended metabolites could be related to the disease. Complementary mass spectrometry experiments and raw data analysis were performed to confirm these suggestions. In particular, MetaboRank recommended the overlooked α-ketoglutaramate as a metabolite which should be added to the metabolic fingerprint of HE, thus suggesting that metabolic fingerprints enhancement can provide new insight on complex diseases.

Availability and implementation

Method is implemented in the MetExplore server and is available at www.metexplore.fr. A tutorial is available at https://metexplore.toulouse.inra.fr/com/tutorials/MetaboRank/2017-MetaboRank.pdf.

Supplementary information

Supplementary data are available at Bioinformatics online.

Benzodiazepines and risk for hepatic encephalopathy in patients with cirrhosis and ascites

Background

There is limited evidence to support the belief that benzodiazepines increase cirrhosis patients' risk of hepatic encephalopathy (HE).

Objective

We aimed to examine the association between benzodiazepine use and HE development in cirrhosis patients.

Methods

We used data on 865 cirrhosis patients with ascites from three trials to study the effect of benzodiazepine use on development of first-time HE. For each patient, we classified periods of benzodiazepine use by the number of days since initiation. We used Cox regression to compare the risk of HE in current benzodiazepine users vs. non-users adjusting for confounders.

Results

Cirrhosis patients were not at increased risk of HE for the first two days of benzodiazepine use, but then faced a five-fold increased risk of HE during days 3 to 10 of benzodiazepine use. The risk of HE was not increased for those who had been using benzodiazepines for more than 28 days.

Conclusion

Cirrhosis patients who had begun using benzodiazepines between 3 and 10 days previously had a markedly increased risk of developing first-time HE. Cirrhosis patients who had been using benzodiazepines for just one or two days or continued use for more than 28 days did not have such an excess risk.

GABAergic transmission in hepatic encephalopathy

Hepatic encephalopathy (HE)(1) is a neuropsychiatric disorder caused by chronic or acute liver failure. Nearly thirty years ago a hypothesis was formulated explaining the neuropathology of HE by increased GABAergic tone. Recent progress in the GABAA-receptor (GABAAR) molecular pharmacology and biochemistry as well as the physiology of GABAergic transmission provided better understanding of GABA's role in health and disease. A detailed analysis of neuronal populations and their GABAergic afferents affected in HE is still missing. The slow progress in understanding the pathology of GABAergic transmission in HE is due to the high complexity of brain circuitries controlled by multiple types of GABAergic interneurons and the large variety of GABAAR, which are differently affected by pathological conditions and not yet fully identified. The mechanisms of action of the GABAAR agonist taurine, allosteric positive modulators (inhibitory neurosteroids, anaesthetics, benzodiazepines and histamine) and inhibitors of the GABAAR (excitatory neurosteroids, Ro15-4513) are discussed with respect to HE pathophysiology. Perspectives for GABAergic drugs in the symptomatic treatment of HE are suggested.

Increased levels of pregnenolone and its neuroactive metabolite allopregnanolone in autopsied brain tissue from cirrhotic patients who died in hepatic coma

It has been suggested that neurosteroids with agonist properties at the central GABA-A receptor are implicated in the pathogenesis of hepatic encephalopathy (HE) in chronic liver disease. In order to address this issue, gas chromatography/mass spectrometry was used to measure the neurosteroids pregnenolone, allopregnanolone, and tetrahydrodeoxycorticosterone (THDOC) in postmortem brain tissue from controls, cirrhotic patients who died without HE, a patient who died in uremic coma, and cirrhotic patients who died in hepatic coma. Exposure of rat cerebral cortical membranes to brain extracts from hepatic coma patients resulted in a 53% (p < 0.001) increase in binding of [3H]muscimol, a GABA-A receptor ligand. Subsequent GC/MS analysis showed that concentrations of the GABA-A receptor agonist neurosteroid allopregnanolone were significantly increased in brain tissue from hepatic coma patients compared to patients without HE or controls (p < 0.001). Brain allopregnanolone concentrations were significantly correlated with the magnitude of induction of [3H]muscimol binding (r2 = 0.82, p < 0.0001). Concentrations of allopregnanolone comparable to those observed in hepatic coma brains are pathophysiologically relevant. Concentrations of the neurosteroid precursor pregnenolone were also increased in brain tissue from hepatic coma patients, while those of a second neurosteroid THDOC were below the levels of detection in all groups. Brain concentrations of benzodiazepine receptor ligands estimated by radioreceptor assay were not significantly increased in cirrhotic patients with or without hepatic coma. These findings suggest that increased levels of allopregnanolone rather than "endogenous benzodiazepines" offer a cogent explanation for the phenomenon of "increased GABAergic tone" previously proposed in HE.

Role of endogenous benzodiazepine ligands and their GABA-A--associated receptors in hepatic encephalopathy

Benzodiazepine receptor ligands are suggested to play a role in the pathogenesis of hepatic encephalopathy (HE). Accumulation of these ligands in brain was suggested to explain in part the notion of"increased GABAergic tone," the rational for which arose initially from reports of a beneficial effect of the selective benzodiazepine antagonist flumazenil in HE patients. It was suggested on the basis of the effect of flumazenil in human HE that liver failure may result in alterations of the density and/or affinity of the benzodiazepine-associated GABA-A receptor site. Subsequent controlled-clinical trials showed that fumazenil had a transient beneficial effect in only a subpopulation of HE patients. In contrast to the antagonists, partial inverse agonists of the benzodiazepine receptor have unequivocal beneficial effects on behavioral and electro-physiological performance in all experimental models of HE studied so far. Benzodiazepine-associated GABA-A receptors have consistently been demonstrated to be unaltered in both human and experimental HE. Contrary to initial reports, the so-called "endogenous benzodiazepines" do not appear to be significantly related to the pathogenesis of HE. On the other hand, nonbenzodiazepine GABA-A receptor complex modulators, such as neuro-steroids, recently identified in brain in human and experimental HE, may provide a new mechanistic basis for this disorder and lead to novel treatments for human HE.

Pathophysiology of hepatic encephalopathy: a new look at GABA from the molecular standpoint

Hepatic encephalopathy (HE) is a neuropsychiatric disorder associated with either acute or chronic liver failure. More than two decades ago, the role of altered GABAergic neurotransmission was proposed following evidence of "increased GABAergic tone" in HE. Increased GABAergic tone was based on several observations: (i) Similarity of visual evoked response potential patterns between rabbits with galactosamine-induced fulminant hepatic failure and animals treated with various allosteric agonists of the GABA receptor complex (GRC). (ii) Spontaneous activities of isolated Purkinje neurons from rabbits with galactosamine-induced fulminant hepatic failure are more depressed by GRC modulator compounds compared to normal animals. (iii) Flumazenil, a high selective benzodiazepine antagonist at the GRC, ameliorates behavioral symptoms and EEG activity in some HE patients. Pathophysiological mechanisms put forward to explain increased GABAergic tone in HE include (1) increase in brain GABA content due to increased brain GABA uptake through altered permeability of the blood brain barrier, (2) alteration of the integrity of constituents of the GRC, and (3) increase of endogenous GRC modulators such as benzodiazepines (and more recently neurosteroids) with potent agonist properties at the GRC. Studies performed subsequently excluded alterations of either GABA content or GRC integrity in favor of increased brain concentrations of endogenous agonists. While the role of endogenous benzodiazepines remains controversial, the presence of neurosteroids with GABA agonist properties affords a plausible explanation for increased GABAergic tone in HE.

Role of circulating neurotoxins in the pathogenesis of hepatic encephalopathy: potential for improvement following their removal by liver assist devices

Both acute and chronic liver failure result in impaired cerebral function known as hepatic encephalopathy (HE). Evidence suggests that HE is the consequence of the accumulation in brain of neurotoxic and/or neuroactive substance including ammonia, manganese, aromatic amino acids, mercaptans, phenols, short-chain fatty acids, bilirubin and a variety of neuroactive medications prescribed as sedatives to patients with liver failure. Brain ammonia concentrations may attain levels in excess of 2 mm, concentrations which are known to adversely affect both excitatory and inhibitory neurotransmission as well as brain energy metabolism. Manganese exerts toxic effects on dopaminergic neurones. Prevention and treatment of HE continues to rely heavily on the reduction of circulating ammonia either by reduction of gut production using lactulose or antibiotics or by increasing its metabolism using L-ornithine-L-aspartate. No specific therapies have so far been designed to reduce circulating concentrations of other toxins. Liver assist devices offer a potential new approach to the reduction of circulating neurotoxins generated in liver failure. In this regard, the Molecular Adsorbents Recirculating System (MARS) appears to offer distinct advantages over hepatocyte-based systems.

Normal coupling of brain benzodiazepine and neurosteroid modulatory sites on the GABA-A receptor complex in human hepatic encephalopathy

To assess the possible implication of the allosteric coupling of different modulatory sites at the GABA-A receptor complex in hepatic encephalopathy (HE), we investigated in autopsied frontal cortex of six cirrhotic patients and six appropriately-matched controls, the modulatory effects of the benzodiazepine site agonist flunitrazepam on the binding of [3H]muscimol and the effect of the neurosteroid site agonist allopregnanolone (5alpha-pregnan-3alpha-ol-20-one) on the binding of [3H]muscimol and [3H]flunitrazepam. There were no significant differences in either the magnitude E(max): 11.5+/-1.1% (controls) versus 10.2+/-2.2% (HE patients) or the efficacy EC(50): 20.2+/-5.5 nM (controls) versus 17.7+/-6.2 nM (HE patients) of flunitrazepam modulation of [3H]muscimol binding. Allopregnanolone also showed modulation of both sites to a comparable extent in brain tissue from cirrhotic patients and controls E(max): [3H]muscimol, 15.1+/-2.8% (controls) versus 13.8+/-1.9% (HE patients); [3H]flunitrazepam, 17.9+/-2.3% (controls) versus 19.1+/-2.3% (HE patients), EC(50): [3H]muscimol, 386.5+/-25.8 nM (controls) versus 373.8+/-13.1 nM (HE patients); [3H]flunitrazepam, 49.8+/-22.9 nM (controls) versus 55.5+/-14.0 nM (HE patients). These findings demonstrate unequivocally that the GABA-A sites and their benzodiazepine and neurosteroid modulatory sites manifest normal allosteric coupling in brain in human HE. Therefore, if increased "GABAergic tone" is implicated in the pathophysiology of HE, this must be the consequence of increased brain concentrations of endogenous benzodiazepine and/or neurosteroid ligands for components of the GABA-A receptor complex rather than alterations of the receptor proteins themselves.

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).

Concomitant overdosing of other drugs in patients with paracetamol poisoning

AIMS

Paracetamol is frequently involved in intended self-poisoning, and concomitant overdosing of other drugs is commonly reported. The purpose of the study was to investigate further concomitant drug overdose in patients with paracetamol poisoning and to evaluate its effects on the outcome of the paracetamol intoxication.

METHODS

Six hundred and seventy-one consecutive patients admitted with paracetamol poisoning were studied and concomitant drug intake was recorded. The relative risk of hepatic encephalopathy, death or liver transplantation, hepatic dysfunction, liver cell damage, and renal dysfunction associated with concomitant overdosing of other drugs was evaluated by multivariate analysis.

RESULTS

Concomitant drug overdose was found in 207 patients (31%, 95% confidence interval [CI] 27, 34%). Concomitant overdosing of benzodiazepines (99 cases), opioid analgesics (38 cases), acetylsalicylic acid (33 cases), and NSAID (32 cases) predominated. Concomitant benzodiazepine overdose was an independent risk factor in the development of hepatic encephalopathy (odds ratio [OR] 1.91; CI 1.00, 3.65) and renal dysfunction (OR 1.81; CI 1.00, 3.22). Concomitant overdosing of opioid analgesics was a protective factor in the development of hepatic encephalopathy (OR 0.26; CI 0.07, 0.96). Concomitant acetylsalicylic acid overdose was a risk factor in the development of hepatic encephalopathy (OR 4.87; CI 1.52, 15.7) and death or liver transplantation (OR 6.04; CI 1.69, 21.6). A tendency towards a more favourable outcome was observed in patients with concomitant NSAID overdose.

CONCLUSIONS

Concomitant overdosing of benzodiazepines or analgesics is frequent in patients admitted with paracetamol poisoning. Concomitant benzodiazepine or acetylsalicylic acid overdose was associated with more severe toxicity, whereas concomitant overdosing of opioid analgesics was associated with less toxicity.