Opioid receptor ligands in human hepatic encephalopathy

Chronic opioid use is associated with altered gut microbiota and predicts readmissions in patients with cirrhosis

BACKGROUND

Opioid use is epidemic in cirrhosis, which could precipitate hepatic encephalopathy (HE) potentially through gut dysbiosis and inflammation.

AIM

To define the effect of opioids on readmissions and on gut microbiota composition and functionality.

METHODS

Cohort 1 had 200 cirrhotic in-patients (with/without opioid use) followed prospectively through the index hospitalisation and 6 months post discharge. Readmissions (HE-related/unrelated) were compared between patients discharged on opioids compared to the rest, including using a multi-variable analysis. Cohort 2 consisted of 72 cirrhotics on chronic opioids who were age/model for end-stage liver disease (MELD) and prior HE-balanced with 72 cirrhotics not on opioids. Stool microbiota composition (multi-tagged sequencing), predicted functionality (PiCRUST), endotoxemia and systemic inflammation (IL-6, IL-17) were compared.

RESULTS

Cohort 1: Chronic opioid use was statistically similar between those admitted with/without HE, and was judged to be an HE precipitant in <5% of cases during the index hospitalisation. Of the 144 patients alive at 6 months, 82 were readmitted. The opioid users had a significantly higher all cause (69% vs. 48%, P = 0.008), but not HE-related readmissions (30% vs. 41%, P = 0.30). On regression, opioid therapy and female gender were predictive of readmission independent of MELD score and previous HE. Cohort 2: Significant dysbiosis was noted in the opioid cohort, especially in HE+opioid patients with lower autochthonous taxa and Bacteroidaceae relative abundance. PiCRUST showed highest aromatic amino acid and endotoxin production in opioid users. Opioid users also had higher endotoxemia and IL-6 but not IL-17.

CONCLUSION

Chronic opioid use in cirrhosis is associated with increased endotoxemia, dysbiosis and all-cause readmissions.

Nitric oxide mediates effects of acute, not chronic, naltrexone on LPS-induced hepatic encephalopathy in cirrhotic rats

Recent studies suggest endogenous opioids and nitric oxide (NO) are involved in the pathophysiology of hepatic encephalopathy (HE). In this study, the interaction between the opioid receptor antagonist and NO was investigated on lipopolysaccharide (LPS)-induced HE in cirrhotic rats. Male rats were divided in the sham- and bile duct ligation (BDL)-operated groups. Animals were treated with saline; naltrexone (10 mg/kg, i.p.); or L-NAME (3 mg/kg, i.p.), alone or in combination with naltrexone. To induce HE, LPS (1 mg/kg, i.p.) was injected 1 h after the final drug treatment. HE scoring, hepatic histology, and plasma NO metabolites levels and mortality rate were recorded. Deteriorated level of consciousness and mortality after LPS administration significantly ameliorated following both acute and chronic treatment with naltrexone in cirrhotic rats. However, acute and chronic administration of L-NAME did not change HE scores in cirrhotic rats. The effects of acute but not chronic treatment of naltrexone on HE parameters were reversed by L-NAME. Plasma NO_x concentrations elevated in BDL rats, which were decreased after acute and chronic treatment by naltrexone or L-NAME, significantly. We suggest both acute and chronic treatment with naltrexone improved LPS-induced HE. But, only acute treatment with naltrexone may affect through NO pathway.

Recent advances in the understanding of the role of the endocannabinoid system in liver diseases

Endocannabinoids are ubiquitous signalling molecules that exert their effects through a number of specific cannabinoid receptors. Recent studies have indicated that this endocannabinoid system is involved in the pathophysiological processes associated with both acute and chronic liver diseases as well as in the complications that arise from these diseases such as hepatic encephalopathy and cardiac problems. Targeting this signalling system has been useful in ameliorating some of the symptoms and consequences in experimental models of these liver diseases. This review summarises the recent advances into our knowledge and understanding of endocannabinoids in liver diseases and highlights potential novel therapeutic strategies that may prove useful to treat these diseases.

Cannabidiol ameliorates cognitive and motor impairments in bile-duct ligated mice via 5-HT1A receptor activation

BACKGROUND AND PURPOSE

We aimed to demonstrate the involvement of 5-HT(1A) receptors in the therapeutic effect of cannabidiol, a non-psychoactive constituent of Cannabis sativa, in a model of hepatic encephalopathy induced by bile-duct ligation (BDL) in mice.

EXPERIMENTAL APPROACH

Cannabidiol (5 mg x kg(-1); i.p.) was administered over 4 weeks to BDL mice. Cognition and locomotion were evaluated using the eight-arm maze and the open field tests respectively. Hippocampi were analysed by RT-PCR for expression of the genes for tumour necrosis factor-alpha receptor 1, brain-derived neurotrophic factor (BDNF) and 5-HT(1A) receptor. N-(2-(4-(2-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N-(2-pyridyl) cyclohexanecarboxamide (WAY-100635), a 5-HT(1A) receptor antagonist (0.5 mg x kg(-1)), was co-administered with cannabidiol. Liver function was evaluated by measuring plasma liver enzymes and bilirubin.

KEY RESULTS

Cannabidiol improved cognition and locomotion, which were impaired by BDL, and restored hippocampal expression of the tumour necrosis factor-alpha receptor 1 and the BDNF genes, which increased and decreased, respectively, following BDL. It did not affect reduced 5-HT(1A) expression in BDL mice. All the effects of cannabidiol, except for that on BDNF expression, were blocked by WAY-100635, indicating 5-HT(1A) receptor involvement in cannabidiol's effects. Cannabidiol did not affect the impaired liver function in BDL.

CONCLUSIONS AND IMPLICATIONS

The behavioural outcomes of BDL result from both 5-HT(1A) receptor down-regulation and neuroinflammation. Cannabidiol reverses these effects through a combination of anti-inflammatory activity and activation of this receptor, leading to improvement of the neurological deficits without affecting 5-HT(1A) receptor expression or liver function. BDNF up-regulation by cannabidiol does not seem to account for the cognitive improvement.

Thyroid hormones alterations during acute liver failure: possible underlying mechanisms and consequences

Thyroid hormones are now recognized to change in different disease states with important consequences on severity and prognosis of disease. However, little is known about thyroid hormones' alterations in acute liver failure (ALF). To study the changes in thyroid hormones and cardiac thyroid receptors during ALF, we subjected seven female pigs to surgical liver devascularization. Liver function biochemical markers, thyroid hormones, endogenous opioids, malondialdehyde (MDA), and interleukins 1 and 6 were measured in serum for 24 h postoperatively. Heart biopsies were harvested at the end of the experiment. Baseline heart biopsies were taken from five additional animals. Serum thyroxin (T(4)) and triiodothyronine (T(3)) levels markedly decreased, whereas free-triiodothyronine and thyroxin-stimulating hormone levels did not change. T(4) and T(3) levels correlated with the degree of liver failure and with MDA and interleukin-6 levels. Beta-endorphin levels initially increased, whereas levels of leucine-enkephalin did not change. Thyroid hormone receptor-alpha1 protein expression in the heart decreased 1.6-fold after ALF, whereas myocardial myosin isoform expression remained unchanged. The downregulation of T(4) and T(3) levels during ALF seems to correlate well with the severity of disease. This downregulation related to inflammation and oxidative stress and resulted in changes in myocardial thyroid receptors.

Cholestasis and endogenous opioids: liver disease and exogenous opioid pharmacokinetics

A class of endogenous opioids is upregulated in liver disease particular to cholestasis, which contributes to symptoms in liver disease such as pruritus, hypotension and encephalopathy. Symptoms associated with cholestasis are reversed or at least ameliorated by mu opioid receptor antagonists. Palliation of symptoms related to cholestatic liver disease also involves bile acid binding agents. Opioid receptor antagonists, unlike bile acid binding agents, have been reported to relieve multiple symptoms, except for pruritus, and improve liver function as demonstrated in experimental cholestasis. Exogenous opioid pharmacology is altered by liver disease. Dose reduction or prolongation of dose intervals is necessary depending on the severity of liver disease.

Opioid system blockade decreases collagenase activity and improves liver injury in a rat model of cholestasis

BACKGROUND

Following bile duct ligation (BDL) endogenous opioids accumulate in plasma and play a role in the pathophysiology and manifestation of cholestasis. Evidence of centrally mediated induction of liver injury by exogenous opioid agonist administration, prompts the question of whether opioid receptor blockade by naltrexone can affect cholestasis-induced liver injury.

METHODS

Cholestasis was induced by BDL and cholestatic and sham-operated rats received either naltrexone or saline for 7 consecutive days. On the 7th day, liver samples were collected for determining matrix metalloproteinase-2 (MMP-2) activity, S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) content and blood samples were obtained for measuring plasma nitrite/nitrate and liver enzyme activities.

RESULTS

Naltrexone-treated BDL animals had a significant reduction in plasma enzyme activity and nitrite/nitrate level. Liver SAM : SAH ratio and SAM level improved by naltrexone treatment in cholestatic animals compared to saline-treated BDL ones. Naltrexone treatment in BDL rats led to a decrease in the level of liver MMP-2 activity, which had already increased during cholestasis.

CONCLUSION

Opioid receptor blockade improved the degree of liver injury in cholestasis, as assessed by plasma enzyme and liver MMP-2 activities. The beneficial effect of naltrexone may be due to its ability to increase liver SAM level and restore the SAM : SAH ratio.

Review article: the concept of entero-colonic encephalopathy, autism and opioid receptor ligands

There is growing awareness that primary gastrointestinal pathology may play an important role in the inception and clinical expression of some childhood developmental disorders, including autism. In addition to frequent gastrointestinal symptoms, children with autism often manifest complex biochemical and immunological abnormalities. The gut-brain axis is central to certain encephalopathies of extra-cranial origin, hepatic encephalopathy being the best characterized. Commonalities in the clinical characteristics of hepatic encephalopathy and a form of autism associated with developmental regression in an apparently previously normal child, accompanied by immune-mediated gastrointestinal pathology, have led to the proposal that there may be analogous mechanisms of toxic encephalopathy in patients with liver failure and some children with autism. Aberrations in opioid biochemistry are common to these two conditions, and there is evidence that opioid peptides may mediate certain aspects of the respective syndromes. The generation of plausible and testable hypotheses in this area may help to identify new treatment options in encephalopathies of extra-cranial origin. Therapeutic targets for this autistic phenotype may include: modification of diet and entero-colonic microbial milieu in order to reduce toxin substrates, improve nutritional status and modify mucosal immunity; anti-inflammatory/immunomodulatory therapy; and specific treatment of dysmotility, focusing, for example, on the pharmacology of local opioid activity in the gut.

Hepatic encephalopathy

In the last decade, a significant amount of research has been devoted to the pathogenesis and treatment of hepatic encephalopathy (HE). Non-invasive neuroimaging techniques such as magnetic resonance imaging and spectroscopy have become important research tools. The search for a suitable animal model of HE associated with cirrhosis is still ongoing. Moreover, consensus terminology and diagnostic criteria for HE in humans are badly needed.

Hepatic encephalopathy in liver cirrhosis: pathogenesis, diagnosis and management

The pathogenesis of hepatic encephalopathy (HE) is unknown. Many theories have been proposed. Most established therapies are based on such theories but since no theory has have ever been proved, therapies have to be considered empiric. The spectrum of HE ranges from minimal cerebral functional deficits, which can only be found by sensitive psychometric tests, to coma with signs of decerebration. HE has arbitrarily been divided into stages. A number of precipitating factors are known and the first line of therapy should always be the elimination of these factors. The differential diagnosis includes all states of impaired consciousness and deficits in cerebral function in patients with chronic liver disease, and clinical and biochemical tests to differentiate are indicated. The therapeutic options for HE include: protein restriction only for a limited time in comatous patients; nonabsorbable antibiotics (aminoglycosides), which because of adverse effects are also limited to higher grades of HE: intestinal cleansing which is applicable in all degrees of HE; lactulose, branched chain aminoacids and ornithin aspartate which have been proven to be effective and can be applied long term in patients with lower grades of HE.

Portal hypertension

Cirrhosis represents the end-stage of any chronic liver disease. Two major syndromes result from cirrhosis-portal hypertension and hepatic insufficiency. Additionally, vasodilatation and the hyperdynamic circulation are hemodynamic abnormalities typical of cirrhosis and portal hypertension. Complications of cirrhosis occur as a consequence of a combination of these factors. Gastroesophageal varices result almost solely from portal hypertension, although the hyperdynamic circulation contributes to variceal growth and hemorrhage. Ascites results from sinusoidal hypertension and sodium retention, which is, in turn, secondary to vasodilatation and activation of neurohumoral systems. Hepatorenal syndrome also results from severe peripheral vasodilatation that leads to renal vasoconstriction. Another complication of cirrhosis, portosystemic encephalopathy, is a consequence of both portal hypertension (shunting of blood through portosystemic collaterals) and hepatic insufficiency. In this article, recent advances in pathophysiology and management of the complications of cirrhosis and portal hypertension are reviewed.

Endogenous opiates: 1998

This paper is the twenty-first installment of our annual review of research concerning the opiate system. It summarizes papers published during 1998 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.

Combination treatment of hepatic encephalopathy due to thioacetamide-induced fulminant hepatic failure in the rat with benzodiazepine and opioid receptor antagonists

BACKGROUND/AIMS

Treatment of hepatic encephalopathy with drugs acting on the target organ of this syndrome, the brain, is unsatisfactory. Combination treatment with different neurotransmitter receptor antagonists may be a rational option to optimize treatment.

METHODS

The effects of various doses of the benzodiazepine receptor antagonist Ro 15-3505 and the opioid receptor antagonist naloxone, alone or in combination, were tested on hepatic encephalopathy in rats with thioacetamide-induced hepatic failure in an open-field activity meter. Comparison of single and combination treatment was also done using a neurological test battery. In addition, we compared survival of treatment-responder rats with treatment non-responders.

RESULTS

Naloxone dose dependently increased ambulatory activity and improved neurological score. Ro 15-3505 also improved ambulatory activity and neurological score; however, the improvement was less evident at higher doses. Combination treatment was not superior to single treatment. Survival was increased in treatment-responder rats.

CONCLUSIONS

The failure of combination treatment with Ro 15-3505 and naloxone to further improve hepatic encephalopathy may suggest that the two neurotransmitter systems are interrelated or that hepatic encephalopathy may not be further improved by drugs acting on the brain.