Glycerol Phenylbutyrate in Patients With Cirrhosis and Episodic Hepatic Encephalopathy: A Pilot Study of Safety and Effect on Venous Ammonia Concentration

Nontraditional Treatment of Hepatic Encephalopathy

The pathophysiology of hepatic encephalopathy (HE) is complex, with hyperammonemia playing a central role in its development. Traditional therapies for HE have targeted ammonia and include medications such as lactulose and rifaximin. Although these agents are considered standard of care, nontraditional treatments seek to affect other factors in the pathogenesis of HE. Finally, procedural therapies include albumin dialysis, shunt closure, and the ultimate cure for HE, which is liver transplant. The treatments discussed provide alternative options for patients who have failed standard of care. However, more high-quality studies are needed to routinely recommend many of these agents.

Hepatic Encephalopathy: Current and Emerging Treatment Modalities

Hepatic encephalopathy (HE) is a potentially reversible neurocognitive complication of cirrhosis. It has been reported in at least 30% of patients with cirrhosis and imposes a significant economic burden on caregivers and the healthcare system. Ammonia has been recognized as the culprit in HE development, and all the currently approved treatments mostly act on this toxin to help with HE resolution. After a brief overview of HE characteristics and pathophysiology, this review explores the current accepted treatments for this debilitating complication of cirrhosis. This is followed by an overview of the novel available therapies and a brief focus on future treatment modalities for HE.

Novel Agents in the Management of Hepatic Encephalopathy: A Review

Hepatic encephalopathy is an often devastating complication of chronic liver disease, associated with high mortality and increased burden on patients and healthcare systems. Current agents (such as nonabsorbable disaccharides and oral antibiotics) are often only partially effective and associated with unpleasant side effects. With our improved understanding of the pathophysiology of hepatic encephalopathy, multiple treatment modalities have emerged with promising results when used alone or as an adjunct to standard medications. The mechanisms of these agents vary greatly, and include the manipulation of gut microbial composition, reduction of oxidative stress, inhibition of inflammatory mediators, protection of endothelial integrity, modulation of neurotransmitter release and function, and other novel methods to reduce blood ammonia and neurotoxins. Despite their promising results, the studies assessing these treatment modalities are often limited by study design, sample size, outcome assessment heterogeneity, and paucity of data regarding their safety profiles. In this article, we discuss these novel agents in depth and provide the best evidence supporting their use, along with a critical look at their limitations and future directions.

Pharmacologic Management of Hepatic Encephalopathy

Pharmacologic management of hepatic encephalopathy includes a broad range of therapies. This article covers the specific mainstays of therapies, such as antimicrobials and laxatives, with an established evidence base. This article also covers newer modalities of therapies, such as fecal microbiota transplant, probiotics, bioartificial support systems, small molecular therapies such as l-ornithine l-aspartate, branched chain amino acids, l-carnitine, zinc, and other forms of therapy currently under review.

Ammonia Levels Do Not Guide Clinical Management of Patients With Hepatic Encephalopathy Caused by Cirrhosis

INTRODUCTION

Ammonia appears to play a major role in the pathophysiology of hepatic encephalopathy (HE), but its role in guiding management is unclear. We aimed to understand the impact of ammonia levels on inpatient HE management, hypothesizing that patients with elevated ammonia levels would receive more aggressive lactulose therapy than patients with normal ammonia or no ammonia level drawn.

METHODS

We examined patients with cirrhosis older than 18 years admitted for management of HE from 2005 to 2015. We additionally used propensity matching to control for confounding by the severity of underlying disease. Patients with an ammonia level taken at time of HE diagnosis were further separated into those with normal or elevated ammonia levels. The primary endpoint was the total lactulose (mL) amount (or dose) given in the first 48 hours of HE management.

RESULTS

One thousand two hundred two admissions with HE were identified. Ammonia levels were drawn in 551 (46%) patients; 328 patients (60%) had an abnormal ammonia level (>72 μmol/L). There were no significant differences in the Child-Pugh score, MELD, or Charlson Comorbidity Index in those with and without ammonia levels drawn. The average total lactulose dose over 48 hours was 167 and 171 mL in the no ammonia vs ammonia groups, respectively (P = 0.42). The average lactulose dose in patients with an elevated ammonia level was 161 mL, identical to the lactulose dose in patients with a normal ammonia level. There was no correlation between lactulose dose and ammonia level (R = 0.0026).

DISCUSSION

Inpatient management of HE with lactulose was not influenced by either the presence or level of ammonia level, suggesting that ammonia levels do not guide therapy in clinical practice.

Novel Therapies in Hepatic Encephalopathy

Despite widespread use of lactulose and rifaximin for the treatment of hepatic encephalopathy, this complication of advanced liver disease remains a major burden on the health care system in the United States and continues to predispose to high morbidity and mortality. Several agents have surfaced over recent years with promise to treat hepatic encephalopathy and mitigate the cognitive impairment associated with this disease process. The purpose of this article is to highlight the leading emerging therapies in hepatic encephalopathy as well as their therapeutic targets.

Pharmacotherapies that specifically target ammonia for the prevention and treatment of hepatic encephalopathy in adults with cirrhosis

BACKGROUND

Hepatic encephalopathy is a common complication of cirrhosis, with high related morbidity and mortality. Its presence is associated with a wide spectrum of change ranging from clinically obvious neuropsychiatric features, known as 'overt' hepatic encephalopathy, to abnormalities manifest only on psychometric or electrophysiological testing, 'minimal' hepatic encephalopathy. The exact pathogenesis of the syndrome is unknown but ammonia plays a key role. Drugs that specifically target ammonia include sodium benzoate, glycerol phenylbutyrate, ornithine phenylacetate, AST-120 (spherical carbon adsorbent), and polyethylene glycol.

OBJECTIVES

To evaluate the beneficial and harmful effects of pharmacotherapies that specifically target ammonia versus placebo, no intervention, or other active interventions, for the prevention and treatment of hepatic encephalopathy in people with cirrhosis.

SEARCH METHODS

We searched the Cochrane Hepato-Biliary Controlled Trials Register, CENTRAL, MEDLINE, Embase, and three other databases to March 2019. We also searched online trials registries such as ClinicalTrials.gov, European Medicines Agency, WHO International Clinical Trial Registry Platform, and the Food and Drug Administration for ongoing or unpublished trials. In addition, we searched conference proceedings, checked bibliographies, and corresponded with investigators.

SELECTION CRITERIA

We included randomised clinical trials comparing sodium benzoate, glycerol phenylbutyrate, ornithine phenylacetate, AST-120, and polyethylene glycol versus placebo or non-absorbable disaccharides, irrespective of blinding, language, or publication status. We included participants with minimal or overt hepatic encephalopathy or participants who were at risk of developing hepatic encephalopathy.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data from the included reports. The primary outcomes were mortality, hepatic encephalopathy, and serious adverse events. We undertook meta-analyses and presented results using risk ratios (RR) or mean differences (MD), both with 95% confidence intervals (CIs), and I² statistic values as a marker of heterogeneity. We assessed bias control using the Cochrane Hepato-Biliary domains and the certainty of the evidence using GRADE.

MAIN RESULTS

We identified 11 randomised clinical trials that fulfilled our inclusion criteria. Two trials evaluated the prevention of hepatic encephalopathy while nine evaluated the treatment of hepatic encephalopathy. The trials assessed sodium benzoate (three trials), glycerol phenylbutyrate (one trial), ornithine phenylacetate (two trials), AST-120 (two trials), and polyethylene glycol (three trials). Overall, 499 participants received these pharmacotherapies while 444 participants received a placebo preparation or a non-absorbable disaccharide. We classified eight of the 11 trials as at 'high risk of bias' and downgraded the certainty of the evidence to very low for all outcomes.Eleven trials, involving 943 participants, reported mortality data, although there were no events in five trials. Our analyses found no beneficial or harmful effects of sodium benzoate versus non-absorbable disaccharides (RR 1.26, 95% CI 0.49 to 3.28; 101 participants; 2 trials; I² = 0%), glycerol phenylbutyrate versus placebo (RR 0.65, 95% CI 0.11 to 3.81; 178 participants; 1 trial), ornithine phenylacetate versus placebo (RR 0.73, 95% CI 0.35 to 1.51; 269 participants; 2 trials; I² = 0%), AST-120 versus lactulose (RR 1.05, 95% CI 0.59 to 1.85; 41 participants; 1 trial), or polyethylene glycol versus lactulose (RR 0.50, 95% CI 0.09 to 2.64; 190 participants; 3 trials; I² = 0%).Seven trials involving 521 participants reported data on hepatic encephalopathy. Our analyses showed a beneficial effect of glycerol phenylbutyrate versus placebo (RR 0.57, 95% CI 0.36 to 0.90; 178 participants; 1 trial; number needed to treat for an additional beneficial outcome (NNTB) 6), and of polyethylene glycol versus lactulose (RR 0.19, 95% CI 0.08 to 0.44; 190 participants; 3 trials; NNTB 4). We did not observe beneficial effects in the remaining three trials with extractable data: sodium benzoate versus non-absorbable disaccharides (RR 1.22, 95% CI 0.51 to 2.93; 74 participants; 1 trial); ornithine phenylacetate versus placebo (RR 2.71, 95% CI 0.12 to 62.70; 38 participants; 1 trial); or AST-120 versus lactulose (RR 1.05, 95% CI 0.59 to 1.85; 41 participants; 1 trial).Ten trials, involving 790 participants, reported a total of 130 serious adverse events. Our analyses found no evidence of beneficial or harmful effects of sodium benzoate versus non-absorbable disaccharides (RR 1.08, 95% CI 0.44 to 2.68; 101 participants; 2 trials), glycerol phenylbutyrate versus placebo (RR 1.63, 95% CI 0.85 to 3.13; 178 participants; 1 trial), ornithine phenylacetate versus placebo (RR 0.92, 95% CI 0.62 to 1.36; 264 participants; 2 trials; I² = 0%), or polyethylene glycol versus lactulose (RR 0.57, 95% CI 0.18 to 1.82; 190 participants; 3 trials; I² = 0%). Likewise, eight trials, involving 782 participants, reported a total of 374 non-serious adverse events and again our analyses found no beneficial or harmful effects of the pharmacotherapies under review when compared to placebo or to lactulose/lactitol.Nine trials, involving 733 participants, reported data on blood ammonia. We observed significant reductions in blood ammonia in placebo-controlled trials evaluating sodium benzoate (MD -32.00, 95% CI -46.85 to -17.15; 16 participants; 1 trial), glycerol phenylbutyrate (MD -12.00, 95% CI -23.37 to -0.63; 178 participants; 1 trial), ornithine phenylacetate (MD -27.10, 95% CI -48.55 to -5.65; 231 participants; 1 trial), and AST-120 (MD -22.00, 95% CI -26.75 to -17.25; 98 participants; 1 trial). However, there were no significant differences in blood ammonia concentrations in comparison with lactulose/lactitol with sodium benzoate (MD 9.00, 95% CI -1.10 to 19.11; 85 participants; 2 trials; I² = 0%), AST-120 (MD 5.20, 95% CI -2.75 to 13.15; 35 participants; 1 trial), and polyethylene glycol (MD -29.28, 95% CI -95.96 to 37.39; 90 participants; 2 trials; I² = 88%).

FUNDING

Five trials received support from pharmaceutical companies while four did not; two did not provide this information.

AUTHORS' CONCLUSIONS

There is insufficient evidence to determine the effects of these pharmacotherapies on the prevention and treatment of hepatic encephalopathy in adults with cirrhosis. They have the potential to reduce blood ammonia concentrations when compared to placebo, but their overall effects on clinical outcomes of interest and the potential harms associated with their use remain uncertain. Further evidence is needed to evaluate the potential beneficial and harmful effects of these pharmacotherapies in this clinical setting.

Pathophysiology of hepatic encephalopathy and future treatment options

Understanding of the pathophysiology of hepatic encephalopathy has conditioned new treatment options. Ammonia detoxification in hepatic encephalopathy is regulated by two enzymes: glutaminase or glutamine synthetase. The first produces ammonia and the second detoxifies the ammonia, which is why treatments are aimed at glutaminase inhibition or glutamine synthetase activation. At present, we know that both enzymes are found not only in the liver, but also in the muscle, intestine, kidney, and brain. Therefore, current treatments can be directed at each enzyme at different sites. Awareness of those potential treatment sites makes different options of approach possible in the patient with hepatic encephalopathy, and each approach should be personalized.

Identification of modules of hepatic encephalopathy based on protein-protein network and gene expression data

Hepatic encephalopathy (HE) is regarded as a complication of liver cirrhosis, and 50–75% of patients who have been diagnosed with cirrhosis have HE syndrome. The aim of this study was to identify genes and pathways associated with HE alcoholics. Human protein-protein interactions were downloaded from the STRING database. Gene expression data were downloaded from EMBL-EBI. Combined score and Pearson's correlation coefficient were calculated to construct differential co-expression networks. Graph-theoretical measure was used to calculate the module connectivity dynamic score of multiple differential modules. In total, 11,134 genes were obtained after mapping between probes and genes. Then, 501,736 pairs and 16,496 genes were obtained to form background protein-protein interaction networks, 1,435 edges and 460 nodes were obtained constituting differential co-expression networks. Twenty-three seed genes and 10 significantly differential modules were identified. Four significantly differential modules which had larger connectivity alternation were observed. The identified seed genes and significantly differential modules offer novel understanding and molecular targets for the treatment of HE alcoholics.

Safety, tolerability, and pharmacokinetics of l-ornithine phenylacetate in patients with acute liver injury/failure and hyperammonemia

Cerebral edema remains a significant cause of morbidity and mortality in patients with acute liver failure (ALF) and has been linked to elevated blood ammonia levels. l-ornithine phenylacetate (OPA) may decrease ammonia by promoting its renal excretion as phenylacetylglutamine (PAGN), decreasing the risk of cerebral edema. We evaluated the safety, tolerability, and pharmacokinetics of OPA in patients with ALF and acute liver injury (ALI), including those with renal failure. Forty-seven patients with ALI/ALF and ammonia ≥60 μM were enrolled. Patients received OPA in a dose escalation scheme from 3.3 g every 24 hours to 10 g every 24 hours; 15 patients received 20 g every 24 hours throughout the infusion for up to 120 hours. Plasma phenylacetate (PA) concentrations were uniformly below target (<75 μg/mL) in those receiving 3.3 g every 24 hours (median [interquartile range] 5.0 [5.0] μg/mL), and increased to target levels in all but one who received 20 g every 24 hours (150 [100] μg/mL). Plasma [PAGN] increased, and conversion of PA to PAGN became saturated, with increasing OPA dose. Urinary PAGN clearance and creatinine clearance were linearly related (r = 0.831, P < 0.0001). Mean ammonia concentrations based on the area under the curve decreased to a greater extent in patients who received 20 g of OPA every 24 hours compared with those who received the maximal dose of 3.3 or 6.7 g every 24 hours (P = 0.046 and 0.022, respectively). Of the reported serious adverse events (AEs), which included 11 deaths, none was attributable to study medication. The only nonserious AEs possibly related to study drug were headache and nausea/vomiting.

CONCLUSION

OPA was well-tolerated in patients with ALI/ALF, and no safety signals were identified. Target [PA] was achieved at infusion rates of 20 g every 24 hours, leading to ammonia excretion in urine as PAGN in proportion to renal function. Randomized, controlled studies of high-dose OPA are needed to determine its use as an ammonia-scavenging agent in patients with ALF. (Hepatology 2018;67:1003-1013).

Hepatic Encephalopathy: An Update on the Pathophysiology and Therapeutic Options

Hepatic encephalopathy is a spectrum of reversible neuropsychiatric abnormalities, seen in patients with liver dysfunction and/or portosystemic shunting. One of the most debilitating complications of cirrhosis, encephalopathy affects 30-45% of cirrhotics. In addition to significantly affecting the lives of patients and their caregivers, it is also associated with increased morbidity and mortality as well as significant utilization of health care resources. In this paper, we provide an overview on the pathophysiology, diagnosis, management and newer therapies of hepatic encephalopathy.

A morphological method for ammonia detection in liver

Hyperammonemia is a metabolic condition characterized by elevated levels of ammonia and a common event in acute liver injury/failure and chronic liver disease. Even though hepatic ammonia levels are potential predictive factors of patient outcome, easy and inexpensive methods aiming at the detection of liver ammonia accumulation in the clinical setting remain unavailable. Thus, herein we have developed a morphological method, based on the utilization of Nessler´s reagent, to accurately and precisely detect the accumulation of ammonia in biological tissue. We have validated our method against a commercially available kit in mouse tissue samples and, by using this modified method, we have confirmed the hepatic accumulation of ammonia in clinical and animal models of acute and chronic advanced liver injury as well as in the progression of fatty liver disease. Overall, we propose a morphological method for ammonia detection in liver that correlates well with the degree of liver disease severity and therefore can be potentially used to predict patient outcome.

Impact of ornithine phenylacetate (OCR-002) in lowering plasma ammonia after upper gastrointestinal bleeding in cirrhotic patients

BACKGROUND

Ornithine phenylacetate (OP) has been proven effective in lowering ammonia plasma levels in animals, and to be well tolerated in cirrhotic patients. A trial to assess OP efficacy in lowering plasma ammonia levels versus placebo in cirrhotic patients after an upper gastrointestinal bleeding was performed. The primary outcome was a decrease in venous plasma ammonia at 24 hours.

METHODS

A total of 38 consecutive cirrhotic patients were enrolled within 24 hours of an upper gastrointestinal bleed. Patients were randomized (1:1) to receive OP (10 g/day) or glucosaline for 5 days.

RESULTS

The primary outcome was not achieved. A progressive decrease in ammonia was observed in both groups, being slightly greater in the OP group, with significant differences only at 120 hours. The subanalysis according to Child-Pugh score showed a statistically significant ammonia decrease in Child-Pugh C-treated patients at 36 hours, as well as in the time-normalized area under the curve (TN-AUC) 0-120 hours in the OP group [40.16 μmol/l (37.7-42.6); median (interquartile range) (IQR)] versus placebo group [65.5 μmol/l (54-126);p = 0.036]. A decrease in plasma glutamine levels was observed in the treated group compared with the placebo group, and was associated with the appearance of phenylacetylglutamine in urine. Adverse-event frequency was similar in both groups. No differences in hepatic encephalopathy incidence were observed.

CONCLUSIONS

OP failed to significantly decrease plasma ammonia at the given doses (10 g/day). Higher doses of OP might be required in Child-Pugh A and B patients. OP appeared well tolerated.

Fasting Blood Ammonia Predicts Risk and Frequency of Hepatic Encephalopathy Episodes in Patients With Cirrhosis

BACKGROUND & AIMS

There is controversy over the use of measuring blood levels of ammonia (NH3) in the management of patients with overt hepatic encephalopathy (HE).

METHODS

We performed a retrospective analysis of data from a randomized, double-blind study of 178 patients with cirrhosis given glycerol phenylbutyrate (an NH3-lowering agent) or placebo for 16 weeks. Blood samples were collected at baseline and on study days 7 and 14 and NH3 levels were measured. The probabilities of having an HE episode, based on ammonia values, were modeled using binary logistic regression. A Cox proportional model was used to determine the risk of HE episodes in patients with baseline fasting NH3 levels ≤1.5-fold the upper limit of normal (ULN) versus patients with fasting NH3 levels >1.5-fold the ULN.

RESULTS

The risk and frequency of HE episodes and HE-related hospitalizations correlated with baseline (mean, 51 ± 6 μmol/L; ULN, 35 μmol/L) and on-study fasting levels of NH3, and increased sharply at levels >1.5-fold the ULN. Regardless of baseline level, NH3 exposure and the relative risk of HE episodes were decreased by glycerol phenylbutyrate.

CONCLUSIONS

In analysis of data from a phase 2 study of the effects of glycerol phenylbutyrate in patients with cirrhosis, we found that fasting levels of NH3 in blood can identify patients at risk for HE-related morbidity. Patients with HE might benefit from NH3-lowering therapy. ClinicalTrials.gov no: NCT 00999167.

Novel Ammonia-Lowering Agents for Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a common complication of cirrhosis, leading to frequent hospitalizations. Because ammonia is thought to play an important role in the pathogenesis of HE, therapies specifically aimed at reducing ammonia levels have been developed for conditions causing hyperammonemia, including HE. Ammonia scavengers have been used in HE patients, leading to improvements in symptoms. Bowel cleansing with polyethylene glycol has also been studied recently, resulting in more rapid improvement in acute HE compared with lactulose. Extracorporeal devices have been used in cases of refractory HE but currently are used primarily in research settings and not approved for clinical management for HE.

Recent insights into the pathogenesis of hepatic encephalopathy and treatments

Hepatic encephalopathy (HE) encompasses a spectrum of neuropsychiatric disorders related to liver failure. The development of HE can have a profound impact on mortality as well as quality of life for patients and carers. Ammonia is central in the disease process contributing to alteration in neurotransmission, oxidative stress, and cerebral edema and astrocyte swelling in acute liver failure. Inflammation in the presence of ammonia coactively worsens HE. Inflammation can result from hyperammonemic responses, endotoxemia, innate immune dysfunction or concurrent infection. This review summarizes the current processes implicated in the pathogenesis of HE, as well as current and potential treatments. Treatments currently focus on reducing inflammation and/or blood ammonia levels and provide varying degrees of success. Optimization of current treatments and initial testing of novel therapies will provide the basis of improvement of care in the near future.

Elevated phenylacetic acid levels do not correlate with adverse events in patients with urea cycle disorders or hepatic encephalopathy and can be predicted based on the plasma PAA to PAGN ratio

BACKGROUND

Phenylacetic acid (PAA) is the active moiety in sodium phenylbutyrate (NaPBA) and glycerol phenylbutyrate (GPB, HPN-100). Both are approved for treatment of urea cycle disorders (UCDs) - rare genetic disorders characterized by hyperammonemia. PAA is conjugated with glutamine in the liver to form phenylacetyleglutamine (PAGN), which is excreted in urine. PAA plasma levels ≥ 500 μg/dL have been reported to be associated with reversible neurological adverse events (AEs) in cancer patients receiving PAA intravenously. Therefore, we have investigated the relationship between PAA levels and neurological AEs in patients treated with these PAA pro-drugs as well as approaches to identifying patients most likely to experience high PAA levels.

METHODS

The relationship between nervous system AEs, PAA levels and the ratio of plasma PAA to PAGN were examined in 4683 blood samples taken serially from: [1] healthy adults [2], UCD patients of ≥ 2 months of age, and [3] patients with cirrhosis and hepatic encephalopathy (HE). The plasma ratio of PAA to PAGN was analyzed with respect to its utility in identifying patients at risk of high PAA values.

RESULTS

Only 0.2% (11) of 4683 samples exceeded 500 μg/ml. There was no relationship between neurological AEs and PAA levels in UCD or HE patients, but transient AEs including headache and nausea that correlated with PAA levels were observed in healthy adults. Irrespective of population, a curvilinear relationship was observed between PAA levels and the plasma PAA:PAGN ratio, and a ratio>2.5 (both in μg/mL) in a random blood draw identified patients at risk for PAA levels>500 μg/ml.

CONCLUSIONS

The presence of a relationship between PAA levels and reversible AEs in healthy adults but not in UCD or HE patients may reflect intrinsic differences among the populations and/or metabolic adaptation with continued dosing. The plasma PAA:PAGN ratio is a functional measure of the rate of PAA metabolism and represents a useful dosing biomarker.