Novel Drugs for the Management of Hepatic Encephalopathy: Still a Long Journey to Travel

Abstract

Hepatic encephalopathy (HE) is one of the reversible complications of chronic liver disease, associated with a higher mortality rate. In current clinical practice, treatment with rifaximin and lactulose/lactitol is the first line of treatment in HE. With the advance in pathophysiology, a new class of ammonia lowering drugs has been revealed to overcome the hurdle and disease burden. The mechanism of the novel agents differs significantly and includes the alteration in intestinal microbiota, intestinal endothelial integrity, oxidative stress, inflammatory markers, and modulation of neurotoxins. Most of the trials have reported promising results in the treatment and prevention of HE with fecal microbiota transplantation, albumin, probiotics, flumazenil, polyethylene glycol, AST-120, glycerol phenylbutyrate, nitazoxanide, branched-chain amino acid, naloxone, and acetyl-l-carnitine. However, their clinical use is limited due to the presence of major drawbacks in their study design, sample size, safety profile, bias, and heterogenicity. This study will discuss the novel therapeutic targets for HE in liver cirrhosis patients with supporting clinical trial data.

Hepatic encephalopathy (HE) is one of the serious complications of liver dysfunction, encircling an extensive range of reversible neurological and psychomotor dysfunction varying from confusion to coma.¹ Based on etiology, it is categorized into three main categories: type A (resulting from acute liver failure), type B (with underlying portosystemic shunt), and type C (due to liver cirrhosis).² A high mortality rate that is, 65% in one year was found to be associated with liver cirrhosis induced HE.³ Additionally, HE also affects patients’ quality of life and has a major effect on disease burden.⁴ Successful treatment of HE starts with the detection of the main cause of precipitating events along with ruling out alternating causes and starting the appropriate treatment.

Pathophysiology of hepatic encephalopathy

Intestinal enterocytes and bacteria play a crucial role in the formation of ammonia and later, it is converted into glutamine by the liver.⁵ Due to impaired hepatic function in chronic liver disease and portosystemic shunt, the concentration of nitrogenous toxins including ammonia increased in the body that acts neurotoxins (inhibit both inhibitory and excitatory pathways in postsynaptic potential) linked to the HE. Putative neurotoxins include ammonia, short-chain fatty acids, mercaptans, false neurotransmitters (e.g., tyramine, octopamine, β-phenylethanolamines), manganese, and GABA, though ammonia is the most widely recognized. It is established that ammonia crosses the blood–brain barrier (BBB) and has both direct and indirect effects on the brain. Many studies have reported that hyperammonemia-induced astrocytes inflammation is correlated with HE in patients with liver cirrhosis.6, 7, 8, 9 Increased ammonia in the brain is associated with swelling of astrocytes due to increased glutamine, inflammation, oxidative stress ultimately leading to mitochondrial dysfunction causing brain edema. In addition to increased ammonia, systemic inflammation, oxidative stress, and increased manganese levels, bile acids and lactate also influence the BBB increasing its permeability.

Alterations of cerebrospinal fluid (CSF) metabolites, as well as alterations in neurotransmission such as increased GABergic tone potentiated with neurosteroids and glutamate-induced N-methyl-d-aspartate (NMDA) stimulation, are observed. Neuroinflammation and microglial activation are significant modulators in the onset of neurological decline. Astrocyte senescence, as well as neuronal cell death, may be key features in the irreversibility of HE. Blood derived increase in brain ammonia is central in the pathophysiological mechanisms underlying the development of HE.

Few studies have reported a significantly increased level of glutamine in acute liver failure by biochemical or proton magnetic resonance spectroscopy in brain biopsy samples.^10,11 In addition to hyperammonemia, an added hepatic insult with superimposed inflammation leads to worsening of brain edema. This is seen frequently in patients with acute-on-chronic liver failure, where inflammation, hyponatremia, and effects of hyperammonemia play a vast role in the development of HE, compared to those in cirrhosis of the liver. In the present scenario, the treatment, which is currently approved, aims to reduce or decrease the absorption of ammonia by lactulose and/or rifaximin. Several trials are undergoing to find out the novel drug or novel therapeutic targets to treat the HE by altering the gut microbiota, endothelial integration, and modifying neuronal response. This review will discuss the novel treatment for HE.

Old-town Therapy for HE

Lactulose and Lactitol Therapy (nonabsorbable disaccharides)

Lactulose and lactitol are synthetic nonabsorbable disaccharides that are given orally or rectally in patients with HE. Due to the absence of hydrolytic disaccharidase in the human intestinal enterocytes, lactulose and lactitol cannot be absorbed which in turn allow the access of lactulose and lactitol into the colon, where they endure bacterial fermentation which results in the acidification of luminal content. Due to a decrease in intestinal pH, ammonia is changed into ammonium ions which cannot be absorbed thus confining ammonia within the colon.^12,13 Moreover, lactulose and lactitol exhibit a cathartic effect on gastrointestinal tract time which further reduces ammonia absorption.¹⁴ Few studies have reported that lactulose and lactitol can decrease the formation of harmful fatty acids and ammonia in the colon and also increase the concentration of total fecal nitrogen excretion.^15,16 A recent meta-analysis comprising 38 randomized control trials showed improvement of HE in 1/3 of the patients and a decrease in mortality by 50% utilizing nonabsorbable disaccharides.¹⁷ The results were more noticeable in overt HE when compared to patients with minimal HE.^18,19 However, included randomized control trials did not measure the confounding impact of the precipitant factor for HE. Moreover, the use of lactulose and lactitol was found to be associated with increased non-serious adverse events like bloating, diarrhea, and nausea.^20,21 This group forms the first line as conventional therapy of HE.

L-Ornithine L-Aspartate

In the liver, ammonia is detoxified mainly via ureagenesis in periportal hepatocytes (i.e., in zone 1) and via glutamine synthesis in perivenous hepatocytes (in zone 3). Whereas in the periphery, ammonia is taken up and converted to glutamine in skeletal muscles.²² l-Ornithine l-aspartate (LOLA) is a combination of endogenous amino acids that are metabolized in periportal and perivenous hepatocytes. l-Ornithine acts as a substrate and activator in a urea cycle and carbamoyl phosphate synthetase, respectively. LOLA also promotes glutamine synthesis (by raising the glutamine synthetase activity), which results in the possible anabolic effect of protein in skeletal muscles, thus reducing nitrogen load in the body. Multiple randomized studies have reported the effectiveness of oral and intravenous LOLA compared to placebo or standard treatment.²³ Meta-analysis of these trials showed improvement in ammonia level and hepatic encephalopathy grade.²³ Clinical trials reported that the effectiveness of LOLA is sometimes the least equivalent to other treatments. However, compared to others like antibiotics, lactulose, and lactitol, LOLA is well tolerated and linked with better health-related quality of life in patients with HE.²⁴ Despite these benefits, trials associated with LOLA endure numerous biases associated with inadequate blinding, pharmaceutical funding, inadequate data, and selection bias.²⁵ A recent randomized control trial from India to assess the role of intravenous LOLA therapy on hepatic encephalopathy among 140 participants with liver cirrhosis equally divided into a case (LOLA + lactulose + rifaximin) and control (placebo + rifaximin + lactulose) group. The study reported a significant improvement in blood ammonia, IL-6, TNF-α, recovery time, 28 days mortality, and hepatic encephalopathy grade in the LOLA group.²⁶ However, intravenous use of LOLA is not yet approved by Food and Drug Administration (FDA), although it is advised by the American Association of Study of Liver Disease (AASLD) guidelines for patients with conventional therapy failure.²⁷ In Europe, LOLA is a commonly used treatment for HE, but it is not available in the United States.

Antibiotic Therapy

Rifaximin is one of the most commonly used drugs for HE, usually as an aide therapy to nonabsorbable disaccharides (lactulose and lactitol). Rifaximin is not well absorbed in the intestine and is responsible for the alteration of microbiota functions and exerts an anti-inflammatory effect in patients with liver cirrhosis.²⁸ Jiang et al in 2008 evaluated five randomized trials in a meta-analysis comparing rifaximin with nonabsorbable disaccharides. In the study, rifaximin was found to have similar efficacy as nonabsorbable disaccharides.²⁹ Bass et al. (2010) performed a placebo-controlled trial to assess the efficacy of rifaximin in the anticipation of future events of HE in patients with a past medical record of HE. This showed reduced incidence and hospital admissions by more than half in the rifaximin group (49.5% in placebo developed breakthrough HE compared to 22.1 and among rifaximin group).³⁰ Few problems with the study were noticed like confounding factors of trans jugular intrahepatic portosystemic shunt and surgical portosystemic shunt³⁰; absence of HE scales.³⁰ In 2014, a meta-analysis reported benefits and reduction in the rate of mortality with rifaximin usage in patients with HE.³¹ European Association for the Study of the Liver (EASL) and AASLD recommended the use of rifaximin as “add-on” therapy with lactulose in a patient with HE and also as a prophylaxis for recurrence of HE.³² Other antibiotics such as neomycin, metronidazole, and vancomycin have been studied for the management of HE, but due to the lack of safety data, their use is limited in a patient with liver cirrhosis.33, 34, 35, 36

Novel Drugs for Hepatic Encephalopathy

Many novel therapeutic drugs were identified with potential therapeutic action against HE and they are as follows (Figure 1).

Figure 1.

Novel therapeutic targets for hepatic encephalopathy (developed by freepik), Legends: ALC, Acetyl-l-carnitine; BCAA, branched-chain amino acid; FMT, fecal microbiota transplantation; GPB, glycerol phenylbutyrate; LOLA, l-ornithine l-aspartate; MARS, molecular absorbent recirculating system; NH₃, ammonia; NTZ, nitazoxanide.

Fecal Microbiota Transplantation

Few studies have shown the differences in microbiota in cirrhotic patients with HE when compared to the control group (normal individual and cirrhosis without HE). Khoruts and Sadowsky reported the possible mechanism of action behind fecal microbiota transplantation (FMT). FMT is based on the theory of bacterial intrusion, that is, using innocuous bacteria to replace pathogenic organisms, such as by competitive niche exclusion.³⁷ Cross-sectional data on stool genomics convinced that genomic species are either over or under-expressed in decompensated cirrhosis when compared to compensated cirrhosis.³⁸ Patients with HE were found to have a lower prevalence of Lachnospiraceae and Ruminococcaceae (responsible for the formation of short-chain fatty acid) and higher Enterobacteriaceae, respectively (Table 2).^39,40 Bajaj et al (2017) performed an open-label randomized trial with 20 cirrhotic patients having multiple episodes of HE, using Lachnospiraceae and Ruminococcaceae enema in the intervention arm compared with standard care. Reduction in hospitalization and improvement in cognition was noticed with the use of fecal microbiota transplantation was reported with no adverse events or bacterial infections with the use of FMT. Less number of participants, short-term follow-up, and absence of a placebo group were the major limitations of this trial.⁴¹ In 2019, they conducted another study comparing FMT [capsule rich in Lachnospiraceae and Ruminococcaceae (dose of 15 capsules at a time) with a placebo group in patients with cirrhosis having recurrent episodes of HE and noted that there was an improvement in microbiota, inflammatory markers, and the cognitive scores (Table 1).⁴² Currently, two trials are under process to evaluate the therapeutic effect of FMT in HE.^43,44

Table 2.

Characteristics of Other Studies.

Author	Type of Study	Methodology	Results
Fecal microbiota transplantation (FMT)
Yanfei Chen40 – China	Prospective	36 and 24 cirrhotic and control participants were registered, respectively. Fecal microbial communities were explored by 454 pyrosequencing of 16s ribosomal RNA V3 followed by RT-qPCR	•In cirrhosis patients, Bacteroidetes were considerably decreased while Proteobacteria and Fusobacteria were significantly high •Significant prevalence of Enterobacteriaceae, Veillonellaceae, and Streptococcaceae were found in a patient with cirrhosis
Probiotics
Rohan Dalal46	Cochrane review	21 RCTs with probiotics as intervention and placebo (14 studies)/standard care (7 studies) were included with a total of 1420 participants. Range of probiotics was used, VSL#3 was most commonly used.	•No effect on all-cause mortality •Probiotics improved QOL •The probiotic group reported improvement in plasma ammonia levels •The author reported a high risk of systematic and random error in most of the included trial
Arturo J Marti Carvajal72	Cochrane review	RCTs with ALC as the intervention were included. Five trials were included with a total of 398 participants.	•Significant improvement in serum ammonia levels in the case group.
Flumazenil
Goh ET76	Cochrane review	A sum of 14 RCTs was included with 867 participants with cirrhosis and HE. Flumazenil (any dose) and placebo or usual care was used as case and control intervention respectively.	•Flumazenil showed short term benefit on HE, but no evidence on all-cause mortality
Nitazoxanide (NTZ)
Basu P Patrick91 – NY	Prospective pilot study	A sum of 20 patients with cirrhosis was enrolled. The intervention included the use of NTZ 500 mg BD and Lactulose 30 ml BD for 14 days	•Reported improvement in MED and ORT score
A.Elrakaybi92 – Egypt	Open-label, RCT pilot study	A sum of 34 patients was enrolled and randomized into three groups. Nitazoxanide 500 mg BD (12), Metronidazole 250 mg TID (11) and Rifaximin 200 mg TID (11). Lactulose 30–60 ml TID was the common intervention.	•Serum ammonia level in all groups. •NTZ group showed significant improvement in CLDQ and fatigue score
Branched-Chain Amino Acid (BCAA)
Lise Lotte Gluud99	Cochrane review	A sum of 16 RCTs consisting of 827 participants was included. Among 16, 08 trials were with BCAA supplements, and 07 trials were with IV BCAA. The Control group received a placebo in 02 trials, a diet in 10 trials, lactulose in 02 trials, and neomycin in 02 trials.	•Results showed a beneficial effect of BCAA on HE •No significant change in mortality, QOL, and nutritional parameters.
Naloxone (Nal)
Q. Jiang102	Meta-analysis	A sum of 17 RCTs consisting of 1197 participants was included irrespective of language, medication dose, route of administration, blinding, and publication status. Nal (any dose) and placebo or usual care was used as case and control intervention respectively.	•Nal group showed significant improvement in HE •Nal was well tolerated, few patients had episodes of nausea and vomiting

ALC, acetyl-l-carnitine; BCAA, branched-chain amino acid; BD, twice a day; CHESS, Clinical Hepatic Encephalopathy Staging Scale; CLDQ, Chronic Liver Disease Questionnaire; MED, Modified Encephalopathy Scale; Nal, naloxone; ORT, object recognition test; QOL, quality of life; RCT, randomized control trial; RT-qPCR, real-time quantitative polymerase chain reaction; TID, three times a day; VSL#3, high concentration probiotic preparation.

Table 1.

Characteristics of Randomized Control Trials.

First Author [R] – Country	Study Type	Treatment		Sample Size			Encepha–lopathy Scale or Another Tool	Publication Year/Status	Outcomes
		Case	Control	Case	Control
Fecal Microbiota Transplantation (FMT)
Jasmohan S Bajaj41 – USA	Open label, RCT	FMT enema	Standard care	20	10		•PHES •EncephalApp Stroop	2017	•Significant improvement in cognitive and MELD score in FMT group •In the FMT group, microbiota improvement was observed
Jasmohan S Bajaj42 – USA	Phase 1, RCT	FMT capsules	Placebo	10	10		EncephalApp Stroop	2019	•In the FMT group, duodenal microbiota diversity was improved •Serum LBP and IL-6 decreased in the FMT group •Encephalopathy outcomes improved in the FMT group
Raymond Chung (responsible party)43 – USA	Phase 2, RCT	FMT Capsule	Placebo oral capsule	10 patients for the pilot study and 20 patients for RCT			•PHES •SF-36	On-going	•Primary outcome: change in PHES score •Secondary outcomes: monitoring AEs, HRQOL, ammonia level, and microbial engraftment
Radha K Dhiman (responsible party)44 – India	Open-label, RCT	FMT	Placebo	36 participants			–	On-going	•Primary outcomes: change in Survival rates •Secondary outcomes: change in MELD, MELD Na, ammonia level, IL level, the incidence of hepatic encephalopathy and variceal bleed
Probiotics
Radha K Dhiman45 – India	Double blind trial	VSL #3, 9, 10 (11)	Placebo	66		64	–	2014	•Significant improvement in CTP and MELD score in case group •Decreased HE related hospitalization in case group
Nazaril Kobylaik (responsible party)47 – Ukraine	Open label, RCT	Dietary supplement: E. coli Nissle 1917	Lactulose and Rifaximin	42 participants			–	On-going	•Primary outcomes: change in Stroop test and serum ammonia level •Secondary outcomes: changes in serum level of IL-6, IL-8, INF, and bacteria culture
Mariquit Sendelbach (responsible party)49 – USA	Double blind, RCT	Probiotic supplements	Placebo	80 participants			–	On-going	•Primary outcomes: effect on liver fibrosis •Secondary outcomes: effect on a liver enzyme, diabetic marker, BMI, and LDL
Aleksander Krag (responsible party)50 – Denmark	Open-label, RCT	Profermin Plus®	Fresubin®	56 participants			–	On-going	•Primary outcomes: to evaluate hepatic stellate cell activity •Secondary outcomes: assessment of hepatic a-SMA, hepatic inflammation, alfa smooth muscle actin concentration, hepatic venous pressure gradient, reduction in non-invasive fibrosis score, gut dysbiosis, liver vein outflow, metabolic changes
Albumin
Macarena Simon Talero54 – Spain	Double-blind, RCT	Albumin (1.5  g/kg on day 1 and 1 g/kg on day 3)	Saline and usual treatment	26	30		–	2013	•Significant decrease in mortality rate was found in the albumin group •No significant difference was found with respect to liver function and in HE development
Barjesh Chander Sharma55 – India	RCT	Albumin 1.5 /kg/day and lactulose 30–60 lml TID	Lactulose 30–60 lml TID	60	60		West Haven Criteria	2017	•A significant reduction in mortality rate was noticed in the case group. •No significant reduction in arterial ammonia level, IL-6, IL-8, TNF-α was noticed
Paolo Caraceni56 – Italy	Open label RCT	Standard treatment + albumin infusion 40 g twice weekly for 2 weeks followed by 40 g once a week	Standard treatment	218	213		–	2018	•Significant improvement in survival rate was found in the case group
Louise China57 – UK	Open label, RCT	Albumin 20% for 14 days or until discharge	Standard care	380	397		–	2021	•Targeting the level of albumin at ≥30  g/l did not show advantages compared to standard care
Hunter Holmes Mcguire Veteran Affairs Medical Center (responsible party)58 – USA	Double-blind, RCT	Albumin 25% IV weekly for 4 weeks	Saline	48 participants			•PHES •EncephalApp Stroop	On-going	•Primary outcomes: change in a psychometric score, and critical flicker frequency •Secondary outcomes: to evaluate sickness impact factor, change in PHES score, CFF, and SIP
Hospital Universitati Vall d’Hebron Research Institute (responsible party)59 – Spain	Double-blind, RCT	Albumin 1–2 days after hospitalization and at 48 ± 24 h after the first dose	Saline	128 participants			–	On-going	•Survival rate at 90 and 180 days
Aleksander Krag (responsible party)60 – Denmark	Double-blind, RCT	Albumin 20% high expected effect and albumin 20% low expected effect	Saline	240 participants			–	On-going	•To evaluate liver-related clinical outcomes
AST-120
Bajaj JS66 – USA	Double blind, RCT	AST-120 12 g (50) and AST-120 6 g (50)	Placebo	100	48		RBANS	2013	•No significant cognitive improvement was found at the end of 8 weeks
Acetyl-l-Carnitine (ALC)
Mariano Malaguarnera68 – Italy	Double blind, RCT	ALC 2 g BD for 90 days	Placebo	60	55		MMSE	2008	•Significant reduction in prothrombin time, serum bilirubin, fasting serum ammonia •Significant improvement in albumin level, MMSE score, auditory verbal learning
Mariano Malaguarnera69 – Italy	Double-blind, RCT	ALC 2 g BD for 90 days	Placebo	33	34		•PHES •BDI	2011	•Significant improvement in social, emotional, physical, and general health •Significant improvement in PHES and BDI
Michele Malaguarnera70 – Italy	Double blind, RCT	ALC 2 g BD for 90 days	Placebo	61	60		–	2011	•The trial reported significant improvement in ammonia level, liver functions, and neurophysiological function
Mariano Malaguarnera71 – Italy	Double blind, RCT	ALC	Placebo	13	11		–	2006	•Significant improvement in serum ammonia, BUN, Glasgow, and EEG was observed
Glycerol Phenyl Butyrate
Don C Rocky82 – USA	Double blind, RCT	6 lml GPB BD orally for 16 weeks	Placebo	90	88		–	2014	•The study showed a significant improvement in plasma ammonia concentration and safety profile
Polyethylene Glycol (PEG)
Mohammadreza Naderian85 – Iran	RCT	PEG-lactulose	Lactulose	21	19		HESA	2017	•Significant decrease in blood ammonia level and length of hospital stays •Subgroup analysis showed PEG lactulose can decrease the length of hospital stay more significantly in women compared to males
Om Parkash (responsible party)88 – Pakistan	Double-blind, RCT	PEG 3 or 4 sachets in 750 lml water TID until patient discharge	Lactulose 90 ml in 750 ml water TID up to 72 h or until discharge	102 participants			HESA	On-going	•Primary outcome: improvement in HE •Secondary outcome: length of hospital stays
Radha K Dhiman (responsible party)89 – India	Open-label, RCT	PEG and lactulose Q12h	Lactulose 30 ml QID	60 participants				On-going	•Primary outcomes: survival benefit, improvement in HE grades •Secondary outcomes: Reduction in seizure, ammonia, mortality, cerebral edema
Ahmed Syed86 – India	RCT	PEG 3350 and lactulose Q12h	Lactulose 30–60 ml TID	29	31		HESA	2020	•Significant reduction in HESA score in PEG group •No significant improvement in ammonia levels in both groups. Although improvement in hepatic encephalopathy was better in the PEG group
Waseem Raja87 – India	RCT	PEG 3350	Lactulose	25	25		HESA	2019	•A significant change in HESA score in the PEG group within 24 h •No significant changes in serum ammonia levels and length of hospital stay in both the groups
Nitazoxanide (NTZ)
Abd-Elsalam93 – Egypt	RCT	NTZ and lactulose	Placebo and lactulose	60	60		CHESS	2019	•Results demonstrated significant advancement in CHESS score and mental status (alertness, orientation, response to stimulation) in the NTZ group
Abd-Elsalam (responsible party)94 – Egypt	RCT	NTZ 500 mg for 6 months	Rifaximin 550 mg BD for 6 months	60 participants			–	On-going	•Primary outcome: to assess the number of encephalopathy episodes
Branched-Chain Amino Acid (BCAA)
Madhumita Premkumar (responsible party)100 – India	RCT	IV BCAA 500 ml OD for 3 days and lactulose	Lactulose	68 participants			–	On-going	•Primary outcomes: improvement in survival and encephalopathy •Secondary outcomes: reduction in ammonia, recovery time, cerebral edema, and change in mortality rate

ALC, acetyl-l-carnitine; BD, twice a day; BCAA, branched-chain amino acid; BDI, Beck Depression Inventory; BUN, blood urea nitrogen; CHESS, Clinical Hepatic Encephalopathy Staging Scale; ECT, estimated completion time; EEG, electroencephalogram; FMT, fecal microbiota transplantation; GPB, glycerol phenylbutyrate; HESA, Hepatic Encephalopathy Scoring Algorithm; HRQOL, health-related quality of life; IV, intravenous; MELD, Model for End-stage Liver Disease; MMSE, Mini-Mental State Examination; NTZ, nitazoxanide; OD, once a day; PEG, polyethylene glycol; QID, four times a day; RBNS, Repeatable Battery for the Assessment of Neuropsychological Status; RCT, randomized control trial; TID, three times a day.

Probiotics

Probiotics were found to have a beneficial effect in a patient with cirrhosis-induced HE by causing a reduction in ammonia absorption and ammonia-producing bacteria. Probiotics are also found to be involved in alteration of the gastrointestinal environment such as permeability, enzyme composition, and pH hence reducing the absorption of ammonia. Dhiman et al, 2014 performed a double-blind randomized control trial among 130 liver cirrhosis patients recovered from hepatic encephalopathy by using VSL #3, 9, 10 (11). Study reported significant improvement in Child Turcotte Pugh (CTP) and Model for End-stage Liver Disease (MELD) score and reduced risk of HE-related hospitalization (Table 1).⁴⁵ Cochrane review of 21 trials with 1420 patients demonstrates no effect in all-cause mortality when compared to placebo (14 trials) or lactulose (7 trials). However, the use of probiotics when compared to placebo was found to be associated with higher recovery from HE, improved quality of life, and ammonia concentration in patients with HE. However, on comparing with lactulose, these events were not significant. Whether probiotics are better than lactulose for hepatic encephalopathy is uncertain because the quality of the available evidence is very low.⁴⁶ High risk of bias, low-quality evidence, the different strains of probiotics used, and heterogenicity in the outcomes were the major drawbacks among the included trials (Table 2). Multiple trials are under process to assess the therapeutic role of probiotics (different strains) in cirrhotic patients (Table 1).47, 48, 49, 50

Albumin

Albumin is produced and secreted by the liver. In a patient with cirrhosis, albumin production decreases by 60–80% leading to hypoalbuminemia. Few experimental studies have demonstrated the role of albumin in neutralizing oxygen reactive species, reduction of the inflammatory arbitrator, and endothelial dysfunction. Albumin was also found to have a role in regulating oncotic pressure in cirrhosis patients. Intravenous 20% albumin has been shown to improve reaction to diuretics, avert circulatory dysfunction after large-volume paracentesis and have a role in the prevention and treatment of the hepatorenal syndrome.51, 52, 53 Many trials have shown encouraging outcomes with the use of albumin. In a multicentric, double-blind randomized control trial among acute HE patients with the use of intravenous albumin versus isotonic saline with standard treatment. Although no substantial change was found with respect to HE outcome on day 4, a considerable reduction in the rate of mortality was found on day 90 (Table 1).⁵⁴ In 2017, Sharma et al performed a randomized control trial with 120 patients with overt HE, with the use of lactulose + albumin in the treatment group versus lactulose in the control group for 10 days. Combination therapy was found to be more beneficial in terms of complete recovery from HE, shorter hospital stays, and lower mortality rates. Furthermore, a substantial reduction in IL-6, IL-18, and TNF-α was found. Small sample size and open-label study design were the key drawbacks of the study (Table 1).⁵⁵

cANSWER, a multicenter, randomized open-label trial with 440 patients with cirrhosis and uncomplicated ascites, tolerant to diuretics with the intervention group receiving standard care and albumin and control group receiving standard care. The survival rate was found to be considerably higher in the albumin group with a decrease in rates of hospitalization, severe encephalopathy, and the future need of therapeutic paracentesis, renal dysfunction, and the hepatorenal syndrome were also noticed.⁵⁶ Open-label study and the absence of blinding were the major limitations of the study (Table 1).⁵⁴ Recently in 2021, another randomized, open-label, multicentric trial with 777 hospitalized patients with decompensated liver cirrhosis with the intervention group receiving 20% albumin till discharge compared to standard medical care found no clinical difference among the two groups. The study concluded that targeting the level of albumin at ≥30  g/l is not advantageous when equated to standard care.⁵⁷ Many trials are under process to appraise the possible use of albumin in HE patients.58, 59, 60

AST-120

AST-120 is a synthetic activated carbon with a large area and high adsorptive capacity. Due to restricted gastrointestinal absorption, AST-120 can trap organic neuro and hepato-toxic substances <10 kDa.⁶¹ Some studies have shown the role of AST-120 in the reduction of blood ammonia levels, oxidative stress in animal models.^61,62 A phase II multicentric randomized control trial was conducted with 41 patients with low-grade HE with the use of AST-120 or lactulose for 4 weeks. The study revealed no significant difference in primary (change in West Haven scale) and secondary (change in HESA, venous ammonia level, bile acid, clinical laboratory test, and reduction in itching) outcomes.^63,64 Nevertheless, fewer episodes of diarrhea and flatulence were observed in patients with AST-120.

ASTUTE, multicentric, double-blind, randomized control trial with 148 patients with compensated cirrhosis, comparing AST-120 and placebo found no significant difference in the neurocognitive parameters or rate of HE episodes among two groups at 8 weeks of the trial. However, improvement in ammonia concentration was observed in the intervention group independent of neurocognitive changes.^65,66

Acetyl-L-carnitine

Carnitine is one of the essential nutrients that play a significant role in the transfer of fatty acid in the hepatocytes. In chronic liver disease patients, diminished metabolism of carnitine is observed. Acetyl-l-carnitine (ALC) is an ester of carnitine that is endogenously formed within mitochondria and peroxisomes in the liver, brain, and kidney by the enzyme acetyl-l-carnitine transferase.⁶⁷ The role of ALC in the treatment of HE is hypothesized to be connected to the decrease in serum ammonia by increasing ureagenesis.⁶⁷ In addition to enhancing the production of acetylcholine in the brain and stimulating protein and phospholipid synthesis, all of which upsurge cellular energy production and decrease neuronal toxicity in patients with HE.^67,68 The majority of the findings come from the four small randomized trials, though all studies showed the benefit of carnitine over the control group. Reduction of ammonia concentration,⁶⁸ improvement in cognitive function, energy level and emotional health⁶⁸ (Table 1), improvement in cognitive and EEG findings,⁷⁰ and improvement in neurological functions⁷¹ were the major findings of these studies. Recently, a Cochrane review that assessed five randomized control trials showed no improvement in clinical outcomes or reduction of ammonia level with the help of acetyl-l-carnitine (Table 2).⁷² Adverse events with acetyl-l-carnitine were not described, making the potential harm of the drug unknown. This study suggests the need for a large sample, double-blind, randomized control trial to determine the potential safety and therapeutic profile of ALC.

Flumazenil

Flumazenil is well known as a benzodiazepine antagonist with the potential to bind with γ-aminobutyric acid receptors.⁷³ Few studies have reported the GABA-A upregulation and augmented tone of GABAergic tone in patients with HE.^74,75 Upregulation of GABAergic neurons performs a vital role in the alteration of neurocognitive outcomes in patients with HE. Recently a Cochrane review which assessed twelve randomized trials showed significant improvement in patients with HE, with no significant difference with respect to all-cause mortality. Short follow-up (few studies had a follow-up of less than one day), risk of bias, cross-over design, and limited conclusions were the major drawback of the included trials (Table 2).⁷⁶ This study suggests the need for more randomized control trials with flumazenil, as the majority of the studies were from before the 2000s.

Glycerol phenyl-butyrate

Glycerol phenyl-butyrate (GPB) is a triglyceride in which three molecules of phenylbutyrate are connected to a glycerol backbone. In the current scenario, the use of GPB is certified in the United States and Europe in patients with urea cycle disorders and for those patients in which hyperammonemia cannot be controlled by dietary protein constraints.77, 78, 79, 80 Phenylacetic acid is one of the metabolites of phenyl butyric acid, and through acetylation, it is found to be in a conjugated state with glutamine to form phenylacetylglutamine. Phenylacetylglutamine is water-soluble and plays a crucial role in decreasing blood ammonia and nitrogenous waste and is eliminated in urine.^78,80,81 A pilot study was conducted with 15 patients with HE followed by a randomized control trial with 178 patients with a record of recurrent episodes of HE. The intervention included the use of GPB 6 ml BD orally for four months or a placebo. When compared to placebo, GPB showed a significant decrease in HE-associated events, HE-related hospitalization, and blood ammonia level.⁸² The small sample size and the large number of patients who withdrew prematurely in the GPB group were the major drawbacks of the study. Stopping rule, withdrawing consent, adverse events, non-compliance, and investigator decision were the major reason for prematurely withdrawing. At the time of randomization total of 59 patients were on rifaximin that indicates a refractory state. But authors reported GPB-associated benefits after controlling the rifaximin use.

Polyethylene Glycol

Polyethylene glycol (PEG) is a cathartic agent that is responsible for reducing intestinal transient time for ammonia absorption. PEG and nonabsorbable disaccharides share the same mechanism of action but unlike nonabsorbable disaccharides, PEG does not have a carbohydrate group and is not metabolized by the colonic bacteria.⁸³ HELP, the first randomized control trial to assess the efficacy of PEG in 50 patients with cirrhosis-induced HE. When compared to lactulose, the study revealed significant improvement in HE outcomes (improved HESA score) in a shorter median time. However, patients with PEG experienced more episodes of diarrhea while bloating was more in the lactulose group.⁸⁴ Another non-inferiority trial reported evaluating the use of lactulose and PEG combination therapy in 40 patients with cirrhosis and HE compared to lactulose monotherapy. It showed significant improvement in HESA score within 24 h and shorter hospital days among combination groups. No substantial change was seen with respect to blood ammonia level.⁸⁵ However, non-blinding, less sample size was the major drawback of the trials. Two Indian randomized control trials reported significant improvement of HESA score in the PEG group when compared to lactulose.^86,87 Currently, two trials are under process to access the therapeutic use of PEG in HE.^88,89

Nitazoxanide

Nitazoxanide (NTZ) is a broad-spectrum thiazolide antiparasitic agent which has an action against many anaerobic bacteria, protozoa, and helminthic species. Currently, nitazoxanide is approved for the treatment of infectious diarrhea caused by crytpsporidiumparvum and giardia lamblia. Nitazoxanide is also found to have peripheral and central anti-inflammatory effects.⁹⁰ Basu P et al, 2008,⁹¹ conducted a pilot study in cirrhotic patients comparing nitazoxanide and lactulose. The study reported significant improvement in mental status and quality of life (Table 2). Similarly, Elrakaybu et al (2015)⁹² conducted an open-label randomized control trial with severe HE patients, comparing nitazoxanide, metronidazole, and rifaximin. The trial reported significant improvement in the nitazoxanide group. However, no significant improvement was found with respect to the ammonia concentration. Recently, Abd-Elsalam et al, 2019⁹³ reported a trial on HE patients, comparing nitazoxanide + lactulose and lactulose. The trial reported significant improvement in CHESS score in the case group (Table 1).⁹³ The open-label study, study duration, and small sample size were the major drawbacks of the included trials. Currently, one trial is ongoing to assess the potential use of nitazoxanide in HE patients (Table 1).⁹⁴

Branched-chain Amino Acid

Branched-chain amino acid (BCAA) provides carbon skeletons to muscle tissue for replenishment of α-ketoglutarate, which was found to be reduced during hyperammonemia all through with increased amination to glutamate. In patients with liver cirrhosis, the concentration of BCAA and glutamate is found to be decreased in muscle and plasma and elimination of ammonia from muscle is proportional to the elimination of BCAA. Several studies have shown the role of BCAA in the augmentation of ammonia detoxification by skeletal muscle.^95,96 BCAA supplements may revert the muscle loss and breakdown of the protein in liver disease patients which in turn will increase the extrahepatic ammonia detoxification.^97,98 In 2017, the Cochrane review assessed 16 randomized control trials that showed a positive effect on HE. However, no significant effect was observed with respect to mortality, quality of life, and nutritional status (Table 2).⁹⁹ Currently, one randomized control trial is under process to evaluate the potential therapeutic uses of intravenous BCAA among patients with ACLF (Table 1).¹⁰⁰

Naloxone

Naloxone (Nal) is one of the commonly used opioid receptor antagonists with a higher affinity for the Mu opioids receptor. In patients with HE, higher ammonia concentration is found to be associated with a functional change in various neurotransmitters like opioids, serotonin, and noradrenergic. In both acute and chronic liver failure patients, plasma opioid peptides concentration was found to be elevated, which in turn can modulate the effect of various neurotransmitters.¹⁰¹ In 2010, Q. Jiang et al¹⁰² performed a meta-analysis with 17 randomized control trials. Study reported a significant improvement in HE (Table 2). Limited study design details, randomization technique, allocation, and blinding of outcome assessment were the major drawback of the included studies. This study suggests the need for a more randomized control trial with naloxone to evaluate the potential therapeutic use in HE.

Artificial Liver Support System

The primary objective of artificial and bioartificial liver support systems is to bridge patients with liver failure to transplantation or recovery. Molecular Absorbent Recirculating System (MARS) is one of the artificial liver support systems and has been extensively studied in patients with ALF. The use of extracorporeal albumin dialysis by the MARS has been shown to remove protein-bound substances including toxins and decrease the plasma concentrations of bilirubin, ammonium, and creatinine in patients with ACLF. In a trial done in 2007, 70 patients were randomized to extracorporeal albumin dialysis with SMT (n = 39) and SMT alone (n = 31). The use of albumin dialysis was associated with an earlier and more frequent improvement of HE.¹⁰³ Another observational study showed that albumin dialysis resulted in a significant decrease in circulating phenolic aromatic amino acids and improvement of hepatic encephalopathy in patients with severe liver failure among patients with alcoholic hepatitis.¹⁰⁴ RELIEF trial showed that with the use of MARS, there is a non-significant improvement in hepatic encephalopathy when compared to standard medical therapy.¹⁰⁵

Clinical management of HE is complex, and treatment starts with the detection of the leading precipitating cause of the disease. In the current scenario, guideline-based treatment is followed. However, although many potential novel therapies are available for HE, very few have been found to have clinical benefits. Many trials are under process to assess the possible use of novel treatment. In contrast, due to several drawbacks, the majority of the reported trials need further evaluation before clinical use.

Credit authorship contribution statement

Siddheesh Rajpurohit: Conceptualization, Investigation, Writing Review and Editing Balaji Musunuri: Writing Review and Editing, supervision Shailesh: Writing Review and Editing, visualization Pooja Basthi Mohan: Writing Review and Editing, visualization Shiran Shetty: Writing Review and Editing, supervision.

Conflicts of interest

The authors have none to declare.

Acknowledgment

None.

Funding

None.