Randomized, double-blind, controlled study of glycerol phenylbutyrate in hepatic encephalopathy

Is it time to target gut dysbiosis and immune dysfunction in the therapy of hepatic encephalopathy?

The development of overt hepatic encephalopathy (HE) in a patient with cirrhosis confers a damning prognosis with a 1-year mortality approaching 64%. This complex neuropsychiatric syndrome arises as a consequence of a dysfunctional gut-liver-brain axis. HE has been largely neglected over the past 30 years, with the reliance on therapies aimed at lowering ammonia production or increasing metabolism following the seminal observation that the hepatic urea cycle is the major mammalian ammonia detoxification pathway and is key in the pathogenesis of HE. The relationship with ammonia is more clear-cut in acute liver failure; but in cirrhosis, it has become apparent that inflammation is a key driver and that a disrupted microbiome resulting in gut dysbiosis, bacterial overgrowth and translocation, systemic endotoxemia and immune dysfunction may be more important drivers. Therefore, it is important to re-focus our efforts into developing therapies that modulate the disrupted microbiome or alleviating its downstream consequences.

Progress in treatment of hepatic encephalopathy

Hepatic encephalopathy (HE) is a common complication of severe liver disease and a common cause of mortality. Clinical features range from clinically imperceptible symptoms in minimal HE which require neuropsychological testing to identify, to abnormal behavior, mental deterioration, and even coma or death. It is a reversible progressive neuropsychiatric disorder that is associated with a decrease in quality of life and an increase in rate of hospitalization and consequent costs because patients are at risk for recurrence. Unfortunately, the prevalence of HE continues to rise for several reasons. For one, patients with viral hepatitis are now developing cirrhosis. Additionally, we are currently in the midst of a global obesity epidemic, which fuels the metabolic syndrome and nonalcoholic fatty liver disease, and these patients are now presenting in larger numbers with complications of chronic liver disease such as HE. The high morbidity and mortality combined with the costs underline the importance to search the effective treatment for HE. This article reviews the progress in the treatment of HE.

Managing complications in cirrhotic patients

Liver cirrhosis is a serious and potentially life-threatening condition. This life-threatening condition usually arises from complications of cirrhosis. While variceal bleeding is the most acute and probably best studied, several other complications of liver cirrhosis are more insidious in their onset but nevertheless more important for the long-term management and outcome of these patients. This review summarizes the topics discussed during the UEG-EASL Hepatology postgraduate course of the United European Gastroenterology Week 2013 and discusses emergency surgical conditions in cirrhotic patients, the management of hepatic encephalopathy, ascites and hepatorenal syndrome, coagulation disorders, and liver cancer.

Hepatic encephalopathy in patients with acute decompensation of cirrhosis and acute-on-chronic liver failure

Hepatic encephalopathy in a hospitalized cirrhotic patient is associated with a high mortality rate and its presence adds further to the mortality of patients with acute-on-chronic liver failure (ACLF). The exact pathophysiological mechanisms of HE in this group of patients are unclear but hyperammonemia, systemic inflammation (including sepsis, bacterial translocation, and insulin resistance) and oxidative stress, modulated by glutaminase gene alteration, remain as key factors. Moreover, alcohol misuse, hyponatremia, renal insufficiency, and microbiota are actively explored. HE diagnosis requires exclusion of other causes of neurological, metabolic and psychiatric dysfunction. Hospitalization in the ICU should be considered in every patient with overt HE, but particularly if this is associated with ACLF. Precipitating factors should be identified and treated as required. Evidence-based specific management options are limited to bowel cleansing and non-absorbable antibiotics. Ammonia lowering drugs, such as glycerol phenylbutyrate and ornithine phenylacetate show promise but are still in clinical trials. Albumin dialysis may be useful in refractory cases. Antibiotics, prebiotics, and treatment of diabetes reduce systemic inflammation. Where possible and not contraindicated, large portal-systemic shunts may be embolized but liver transplantation is the most definitive step in the management of HE in this setting. HE in patients with ACLF appears to be clinically and pathophysiologically distinct from that of acute decompensation and requires further studies and characterization.

Ammonia metabolism and hyperammonemic disorders

Human adults produce around 1000 mmol of ammonia daily. Some is reutilized in biosynthesis. The remainder is waste and neurotoxic. Eventually most is excreted in urine as urea, together with ammonia used as a buffer. In extrahepatic tissues, ammonia is incorporated into nontoxic glutamine and released into blood. Large amounts are metabolized by the kidneys and small intestine. In the intestine, this yields ammonia, which is sequestered in portal blood and transported to the liver for ureagenesis, and citrulline, which is converted to arginine by the kidneys. The amazing developments in NMR imaging and spectroscopy and molecular biology have confirmed concepts derived from early studies in animals and cell cultures. The processes involved are exquisitely tuned. When they are faulty, ammonia accumulates. Severe acute hyperammonemia causes a rapidly progressive, often fatal, encephalopathy with brain edema. Chronic milder hyperammonemia causes a neuropsychiatric illness. Survivors of severe neonatal hyperammonemia have structural brain damage. Proposed explanations for brain edema are an increase in astrocyte osmolality, generally attributed to glutamine accumulation, and cytotoxic oxidative/nitrosative damage. However, ammonia neurotoxicity is multifactorial, with disturbances also in neurotransmitters, energy production, anaplerosis, cerebral blood flow, potassium, and sodium. Around 90% of hyperammonemic patients have liver disease. Inherited defects are rare. They are being recognized increasingly in adults. Deficiencies of urea cycle enzymes, citrin, and pyruvate carboxylase demonstrate the roles of isolated pathways in ammonia metabolism. Phenylbutyrate is used routinely to treat inherited urea cycle disorders, and its use for hepatic encephalopathy is under investigation.

Glycerol phenylbutyrate for the chronic management of urea cycle disorders

Glycerol phenylbutyrate (GPB) is a new generation ammonia scavenger drug that was recently approved by the US FDA for chronic management in patients with urea cycle defect disorders after multicenter clinical trials. GPB is composed of three molecules of phenylbutyrate (PB) that are esterified to a glycerol backbone. The active agent, phenylacetate, is generated through multiple metabolic steps including hydrolysis in the small intestine by pancreatic triglyceride lipases. Its pharmacokinetic pattern is characterized by a slower release of the active metabolite than unconjugated PB, which contributes to superior ammonia control and fewer episodes of hyperammonemia. GPB is well tolerated with fewer gastrointestinal complications compared with sodium benzoate or PB. These unique features suggest that it may enhance adherence and, potentially, in improved outcomes in urea cycle disorder patients. GPB may have therapeutic potential in additional conditions such as chronic hepatic encephalopathy or other inherited metabolic disorders.

Dietary management of hepatic encephalopathy revisited

PURPOSE OF REVIEW

The burden of hepatic encephalopathy on health services is increasing, and some degree of consensus in relation to drug therapy and prophylaxis has been reached. This review focuses on the role of nutritional interventions in the management of hepatic encephalopathy.

RECENT FINDINGS

A number of relatively new pieces of evidence are emerging in relation to nutrition and hepatic encephalopathy as follows: first, reduction of protein intake is not useful for hepatic encephalopathy, but protein selection should be considered; second, oral supplementation with branched chain amino acids has a role not only for its nutritional effect in cirrhosis per se, but also for its effect in reducing the risk of recurrence of hepatic encephalopathy; third, alterations in gut microbiota develop in parallel with decompensation of cirrhosis, and modulation of gut microbiota may be effective for treating and preventing hepatic encephalopathy; fourth, prebiotics and probiotics are potentially useful in this aim, thus further research or trials on prebiotics and probiotics are required; fifth, micronutrient deficiency, which is common in end-stage liver disease, has adverse effects on the brain and may either directly cause encephalopathy per se, or interact with the mechanisms leading to hepatic encephalopathy.

SUMMARY

Properly performed nutritional interventions are likely to be useful for patients with hepatic encephalopathy, but well conducted clinical trials are required.

VIDEO ABSTRACT

http://links.lww.com/COCN/A7.

Useful tests for hepatic encephalopathy in clinical practice

Hepatic encephalopathy (HE) is a serious complication of liver disease and portosystemic shunting that represents a continuum of neuropsychiatric changes and altered consciousness. It is classified as overt HE (OHE) when clinically apparent or as covert HE (CHE) in its mildest form. Progression of CHE to OHE and its impact of quality of life make its early diagnosis imperative. Several diagnostic techniques ranging from simple clinical scales to sophisticated computerized tests exist, yet diagnosis remains a challenge, due to the time, cost, and personnel involved. Psychometric tests appear promising due to their high sensitivity and low cost, but results are variable depending on age and education. The pros and cons of current diagnostic methods for OHE and CHE are reviewed, along with strategy for CHE testing.

Hepatic Encephalopathy: From the Pathogenesis to the New Treatments

Hepatic encephalopathy is a frequent and serious complication of liver cirrhosis; the pathophysiology of this complication is not fully understood although great efforts have been made during the last years. There are few prospective studies on the epidemiology of this complication; however, it is known that it confers with high short-term mortality. Hepatic encephalopathy has been classified into different groups depending on the degree of hepatic dysfunction, the presence of portal-systemic shunts, and the number of episodes. Due to the large clinical spectra of overt EH and the complexity of cirrhotic patients, it is very difficult to perform quality clinical trials for assessing the efficacy of the treatments proposed. The physiopathology, clinical manifestation, and the treatment of HE is a challenge because of the multiple factors that converge and coexist in an episode of overt HE.

Hepatic encephalopathy: how to test and treat

PURPOSE OF REVIEW

Hepatic encephalopathy causes significant cognitive impairment and morbidity in patients with cirrhosis; however, hepatic encephalopathy is considered a reversible syndrome once recognized clinically. Although hepatic encephalopathy is not a single clinical entity, the pathophysiology resulting in brain dysfunction is not fully understood, although it is believed that ammonia production is an important contributing factor. The purpose of this review is to highlight studies used to test for hepatic encephalopathy and those utilizing specific new treatments.

RECENT FINDINGS

A 'STROOP' smartphone app has been developed to allow clinicians to test for covert hepatic encephalopathy (CHE). Lactulose therapy was effective for cirrhotic patients as primary prophylaxis to prevent overt hepatic encephalopathy (OHE) episodes. In patients without prior OHE, probiotics can be useful in preventing OHE. Lactulose, probiotics, L-ornithine-L-aspartate, and potassium-iron-phosphate-citrate have been studied in the treatment of CHE. Rifaximin was found to be safe and well tolerated in long-term maintenance of remission from OHE; however, compared to lactulose therapy in CHE, it is not cost-effective.

SUMMARY

Refinement in clinical management strategies for patients with cirrhosis and hepatic encephalopathy appears to continue to contribute to improved patient outcomes.