Clearance and production of ammonia quantified in humans by constant ammonia infusion - the effects of cirrhosis and ammonia targeting treatments

Management of hepatic encephalopathy following transjugular intrahepatic portosystemic shunts: Current strategies and future directions

Transjugular intrahepatic portosystemic shunts (TIPSs) are generally used for the management of complications of portal hypertension in patients with decompensated cirrhosis. However, hepatic encephalopathy (HE), which impairs neuropsychiatric function and motor control, remains the primary adverse effect of TIPS, limiting its utility. Prompt prevention and treatment of post-TIPS HE are critical, as they are strongly associated with readmission rates and poor quality of life. This review focuses on the main pathophysiological mechanisms underlying post-TIPS HE, explores advanced biomarkers and predictive tools, and discusses current management strategies and future directions to prevent or reverse HE following TIPS. These strategies include preoperative patient assessment, individualized shunt diameter optimization, spontaneous portosystemic shunt embolization during the TIPS procedure, postoperative preventive and therapeutic measures such as nutrition management, medical therapy, fecal microbiota transplantation, and stent reduction.

Chinese Guidelines on the Management of Hepatic Encephalopathy in Cirrhosis (2024)

With progress in basic and clinical research on hepatic encephalopathy in cirrhosis worldwide, the Chinese Society of Hepatology of the Chinese Medical Association has invited experts in relevant fields to revise the 2018 "Chinese Guidelines on the Management of Hepatic Encephalopathy in Cirrhosis." The updated guidelines provide recommendations for the clinical diagnosis, treatment, and both primary and secondary prevention of hepatic encephalopathy in cirrhosis.

Hepatic encephalopathy: risk identification and prophylaxis approaches

Hepatic encephalopathy (HE) is a debilitating neurological condition associated with cirrhosis, characterized by cognitive impairment ranging from minimal to overt symptoms. It significantly impacts patients' quality of life and substantially burdens healthcare systems. This review examines current prophylactic strategies for HE, focusing on established treatments, emerging therapies, and predictive tools to identify high-risk patients. Traditional treatments such as lactulose and rifaximin remain the cornerstone of HE management, effectively reducing ammonia levels and preventing recurrence. However, novel approaches like L-ornithine L-aspartate, albumin infusions, and antioxidants like resveratrol show promise in further improving outcomes by addressing underlying pathophysiological mechanisms, including systemic inflammation and gut dysbiosis. Developing predictive models, such as the AMMON-OHE score and clinical-genetic risk assessments, enhances the ability to tailor preventive interventions to individual patient profiles. These advancements are crucial in mitigating the incidence of overt HE, reducing hospital admissions, and improving patient survival rates. The future of HE management lies in personalized medicine, targeting specific inflammatory and metabolic pathways, with the potential integration of genetic manipulation. Continued research is essential to refine these strategies, ultimately aiming to improve the prognosis and quality of life for cirrhotic patients at risk of HE.

Microbiota transplant for hepatic encephalopathy in cirrhosis: The THEMATIC trial

BACKGROUND & AIMS

Preventing hepatic encephalopathy (HE) recurrence in cirrhosis, which is associated with an altered gut-liver-brain axis, is an unmet need. Benefits of fecal microbiota transplantation (FMT) have been shown in phase I studies, but route and dose-related questions remain.

METHODS

We performed a phase II randomized, placebo-controlled, double-blind, clinical trial of capsule and enema FMT in patients with cirrhosis and HE on lactulose and rifaximin. Participants were randomized into four groups (3 active doses; 2 active and 1 placebo dose; 1 active and 2 placebo doses; 3 placebo doses). Each patient received two capsules and one enema (either placebo or FMT) and were followed for 6 months. The primary outcome was FMT-related (serious) adverse events ([s]AEs)/AEs using intention-to-treat analysis. Secondary outcomes were HE recurrence, all-cause hospitalizations, death, donor engraftment, and quality-of-life. FMT was from a vegan or omnivorous donor.

RESULTS

We enrolled 60 patients (15/group) with similar baseline characteristics. FMT was safe without any FMT-related SAEs/AEs. Overall SAEs (p = 0.96) or death (p = 1.0) were similar. There were significant differences in HE recurrence between groups (p = 0.035, Cramer's V = 0.39). On post hoc analysis, recurrence was highest in the all-placebo vs. any FMT group (40% vs. 9%; odds ratio 0.15, 95% CI 0.04-0.64). Within the FMT groups, HE recurrence rates were similar regardless of route, doses, or donor type. Quality of life improved in FMT-recipient groups. Engraftment was highest in those with high pre-FMT Lachnospiraceae and lower in those whose HE recurred.

CONCLUSIONS

In patients with cirrhosis and HE on maximal therapy, FMT regardless of dose, route, or donor was safe without any FMT-related AEs. On post hoc analysis, HE recurrence was highest in the placebo-only group and linked with lower baseline Lachnospiraceae and reduced donor engraftment.

IMPACT AND IMPLICATIONS

Patients with hepatic encephalopathy (HE) already on maximal therapy could have recurrences, which worsen prognosis and are not prioritized for liver transplant. In this phase II, double-blind, randomized, placebo-controlled trial in patients with cirrhosis and prior overt HE, we found that fecal microbiota transplant (FMT) was safe and well tolerated regardless of route of delivery (oral or enema), number of doses (1 through 3), or donor type (vegan or omnivorous). HE recurrence, which was a key secondary endpoint, was different between groups and, on post hoc analysis, lowest in groups that received any FMT. Donor engraftment was higher in those with higher relative abundance of Lachnospiraceae, which was associated with lower HE recurrence.

Down the road towards hepatic encephalopathy. The elusive ammonia- what determines the arterial concentration?

Elevated arterial ammonia is associated with several complications of liver disease as it predicts mortality for in-patients and decompensation, hospitalization and death in out-patients with cirrhosis. In this review, our aim was to estimate how the individual organs contribute to arterial ammonia based on published data from human studies. The brain removes ammonia from arterial blood in a concentration-dependent fashion. Ammonia that is released from the gut to portal blood is mainly from metabolism of glutamine in the enterocytes using this as a source of energy. Ammonia produced by bacterial metabolism of urea and proteins only partially reach portal blood and is likely recycled into bacterial proteins. In general, the liver efficiently removes ammonia from arterial or portal blood in proportion to the delivered concentration. As a result,- and in some contrast to conventional wisdom-, the hepato-splanchnic region only contributes marginally to arterial ammonia; even during a simulated upper GI bleed. The only exception is acute liver failure where hepatocyte necrosis allows large quantities of portal ammonia to pass. The kidneys release ammonia from glutamine metabolism into systemic blood. The renal ammonia release increases during a simulated upper GI bleed or hypokalemia where it becomes a major source of elevated arterial ammonia. In the resting state, muscles remove ammonia in a concentration-dependent manner and muscles are the primary ammonia lowering organ in most situations with elevated arterial ammonia. During strenuous exercise, muscles produce large amounts of ammonia into systemic blood. Thus, the complete pattern of ammonia metabolism is very dynamic and illustrates the difficulties in designing ammonia lowering therapies.

Down the road towards hepatic encephalopathy. Urea synthesis - the liver workhorse of nitrogen metabolism

Urea synthesis is an irreversible, essential for maintenance of health and life, and highly regulated liver function with a very high capacity for production of the end-product urea-nitrogen. The set-point of urea synthesis in relation to its overall substrate, the prevailing blood concentration of L-α-amino acids, contributes to determine whole-body nitrogen balance and the size and composition of the plasma free amino acid pool. Ammonia is definitively eliminated from the body by urea synthesis. Ammonia is released by all tissues as part of their nitrogen metabolism and accumulation of ammonia to supranormal levels is toxic, particularly to the brain where it gives rise to the devastating complication to liver diseases, hepatic encephalopathy. The first line ammonia scavenging has an efficiently high clearance several times over hepatic blood flow and close to cardiac output, under normal conditions securing rapid neutralization of ammonia by synthesis of amino acids and glutamine. This scavenging has a much lower capacity than urea synthesis. Maintenance of the scavenging system, therefore, relies on subsequent definitive depletion and elimination of amino- and amide-nitrogen to urea-nitrogen. In liver diseases, the capacity for urea synthesis is deficient due to reduced functional liver mass and dysregulation, which eventually delays the scavenging so that ammonia overflows. Considering the key role of ammonia in hepatic encephalopathy, this indirect relationship implies that deficient urea synthesis is a prerequisite for development of hyperammonemia and hepatic encephalopathy. This is in accordance with the definition of hepatic encephalopathy as being caused by liver insufficiency, where the insufficiency more specifically likely is deficiency of the urea synthesis.

Blood ammonia concentration measurement - effects of sampling site and cirrhosis during induced hyperammonaemia

BACKGROUND

Ammonia is implicated in hepatic encephalopathy (HE) and prognostic in cirrhosis. Venous ammonia concentration, yielding similar correlation with HE grades as arterial, has become the preferred practise but comparative data are limited.

AIM

To quantify effect of sampling site on ammonia concentration in healthy persons and patients with cirrhosis.

METHODS

Ammonia concentrations were measured by arterial and femoral venous blood sampling in ten healthy men and ten male patients with cirrhosis before and during hyperammonaemia induced by ammonia infusion. Cubital vein samples were included during the infusion.

RESULTS

At baseline, arterial-venous concentration gaps were similar (p = 0.15) in healthy persons [14 (10-19) and 8 (4-12) µmol/L] and patients with cirrhosis [53 (32-74) and 40 (23-57) µmol/L]. Ammonia infusion increased arterial-venous concentration gaps in both groups [115 (97-133) and 61 (31-90) vs. 175 (123-227) and 134 (65-203) µmol/L]. Mean ammonia concentration difference between groups during hyperammonaemia was 72 (42-103) µmol/L (p < 0.001) and independent of sampling site. Cubital and femoral vein concentrations were comparable (p = 0.26). In cirrhosis, calculated upper limit normal values (ULN) were comparable for arterial and venous blood at baseline [2.0 (1.2-2.8) and 2.1 (1.2-3.0), p = 0.74] and during hyperammonaemia [6.7 (4.7-8.7) and 6.2 (4.4- 8.1), p = 0.44].

CONCLUSIONS

We found clinically meaningful intra-individual arterial-venous concentration gaps in both healthy persons and patients with cirrhosis at any ammonia concentration. Inter-group concentration differences after induced hyperammonaemia were relatively constant across sampling sites which supports clinical use of venous sampling. ULN-normalised ammonia concentrations were valid for both arterial and venous sampling.

Ammonia-induced stress response in liver disease progression and hepatic encephalopathy

Ammonia levels are orchestrated by a series of complex interrelated pathways in which the urea cycle has a central role. Liver dysfunction leads to an accumulation of ammonia, which is toxic and is strongly associated with disruption of potassium homeostasis, mitochondrial dysfunction, oxidative stress, inflammation, hypoxaemia and dysregulation of neurotransmission. Hyperammonaemia is a hallmark of hepatic encephalopathy and has been strongly associated with liver-related outcomes in patients with cirrhosis and liver failure. In addition to the established role of ammonia as a neurotoxin in the pathogenesis of hepatic encephalopathy, an increasing number of studies suggest that it can lead to hepatic fibrosis progression, sarcopenia, immune dysfunction and cancer. However, elevated systemic ammonia levels are uncommon in patients with metabolic dysfunction-associated steatotic liver disease. A clear causal relationship between ammonia-induced immune dysfunction and risk of infection has not yet been definitively proven. In this Review, we discuss the mechanisms by which ammonia produces its diverse deleterious effects and their clinical relevance in liver diseases, the importance of measuring ammonia levels for the diagnosis of hepatic encephalopathy, the prognosis of patients with cirrhosis and liver failure, and how our knowledge of inter-organ ammonia metabolism is leading to the development of novel therapeutic approaches.

Hepato-splanchnic fluxes during exercise in patients with cirrhosis-a pilot study

In cirrhotic patients, compromised hepatocyte function combined with disturbed hepatic blood flow could affect hepato-splanchnic substrate and metabolite fluxes and exacerbate fatigue during exercise. Eight cirrhotic patients performed incremental cycling trials (3 × 10 min; at light (28 [19-37] W; median with range), moderate (55 [41-69] W), and vigorous (76 [50-102] W) intensity). Heart rate increased from 68 (62-74) at rest to 95 (90-100), 114 (108-120), and 140 (134-146) beats/min (P < 0.05), respectively. The hepatic blood flow, as determined by constant infusion of indocyanine green with arterial and hepatic venous sampling, declined from 1.01 (0.75-1.27) to 0.69 (0.47-0.91) L/min (P < 0.05). Hepatic glucose output increased from 0.6 (0.5-0.7) to 1.5 (1.3-1.7) mmol/min, while arterial lactate increased from 0.8 (0.7-0.9) to 9.0 (8.1-9.9) mmol/L (P < 0.05) despite a rise in hepatic lactate uptake. Arterial ammonia increased in parallel to lactate from 47.3 (40.1-54.5) to 144.4 (120.5-168.3) μmol/L (P < 0.05), although hepatic ammonia uptake increased from 19.5 (12.4-26.6) to 69.5 (46.5-92.5) μmol/min (P < 0.05). Among the 14 amino acids measured, glutamate was released in the liver, while the uptake of free fatty acids decreased. During exercise at relatively low workloads, arterial lactate and ammonia levels were comparable to those seen in healthy subjects at higher workloads, while euglycemia was maintained due to sufficient hepatic glucose production. The accumulation of lactate and ammonia may contribute to exercise intolerance in patients with cirrhosis.

NMR-based metabolomics for investigating urinary profiles of metal carpentry workers exposed to welding fumes and volatile organic compounds

Introduction

Metal carpentry includes a wide range of work activities such as welding and cutting metallic components, use of solvents and paints. Therefore, the employees in these types of activities are mainly exposed to welding fumes and volatile organic solvents. Here, we present an NMR-based metabolomic approach for assessing urinary profiles of workers in the same company that are exposed to two different risk factors.

Methods

The study enrolled 40 male subjects exposed to welding fumes, 13 male subjects exposed to volatile organic compounds of a metal carpentry company, and 24 healthy volunteers. All samples were collected, in the middle of the working week at fast. Thirty-five urinary metabolites belonging to different chemical classes such as amino acids, organic acids and amines were identified and quantified. Results were processed by multivariate statistical analysis for identifying significant metabolites for each working group examined, compared to controls.

Results

Workers exposed to welding fumes displayed urinary increase in glutamine, tyrosine, taurine, creatine, methylguanidine and pseudouridine associated to oxidative impairment, while workers exposed to volatile organic compounds showed higher urinary levels of branched chain aminoacids.

Conclusion

Our work identified specific urinary profile related to each occupational exposure, even if it is below the threshold limit values.

The Value of Ammonia as a Biomarker in Patients with Cirrhosis

Ammonia is a product of amino acid metabolism that accumulates in the blood of patients with cirrhosis and plays a pivotal role in the pathogenesis of hepatic encephalopathy (HE). Despite being one of the main drivers of brain dysfunction, for many years international societies stated that increased blood ammonia does not add any diagnostic, staging, or prognostic value for HE in patients with cirrhosis. Nonetheless, in the last decades, evidence is emerging that supports the utility of ammonia for risk stratification, but its role in guiding HE diagnosis, staging, and treatment is unclear and there is equipoise in its use in clinical practice. This review provides the latest evidence on the value of ammonia as a biomarker in patients with cirrhosis. Although correct measurement of ammonia requires disciplined sample collection, it provides extremely useful clinical guidance for the diagnosis of HE, offers prognostic information, and it defines a therapeutic target.

Substitution of One Meat-Based Meal With Vegetarian and Vegan Alternatives Generates Lower Ammonia and Alters Metabolites in Cirrhosis: A Randomized Clinical Trial

INTRODUCTION

Diet can affect ammoniagenesis in cirrhosis and hepatic encephalopathy (HE), but the impact of dietary preferences on metabolomics in cirrhosis is unclear. As most Western populations follow meat-based diets, we aimed to determine the impact of substituting a single meat-based meal with an equal protein-containing vegan/vegetarian alternative on ammonia and metabolomics in outpatients with cirrhosis on a meat-based diet.

METHODS

Outpatients with cirrhosis with and without prior HE on a stable Western meat-based diet were randomized 1:1:1 into 3 groups. Patients were given a burger with 20 g protein of meat, vegan, or vegetarian. Blood for metabolomics via liquid chromatography-mass spectrometry and ammonia was drawn at baseline and hourly for 3 hours after meal while patients under observation. Stool microbiome characteristics, changes in ammonia, and metabolomics were compared between/within groups.

RESULTS

Stool microbiome composition was similar at baseline. Serum ammonia increased from baseline in the meat group but not the vegetarian or vegan group. Metabolites of branched chain and acylcarnitines decreased in the meat group compared with the non-meat groups. Alterations in lipid profile (higher sphingomyelins and lower lysophospholipids) were noted in the meat group when compared with the vegan and vegetarian groups.

DISCUSSION

Substitution of a single meat-based meal with a non-meat alternatives results in lower ammoniagenesis and altered serum metabolomics centered on branched-chain amino acids, acylcarnitines, lysophospholipids, and sphingomyelins in patients with cirrhosis regardless of HE or stool microbiome. Intermittent meat substitution with vegan or vegetarian alternatives could be helpful in reducing ammonia generation in cirrhosis.

Possible pathogenetic role of ammonia in liver cirrhosis without hyperammonemia of venous blood: The so-called latency period of abnormal ammonia metabolism

Ammonia plays a crucial role in the pathogenesis of hepatic encephalopathy. Ammonia is also involved in many other pathological conditions seen in cirrhosis, such as sarcopenia, liver fibrosis, hepatocellular injury, immune dysfunction, and hyperammonemia. Furthermore, the ammonia level of the veins is a useful prognostic factor for cirrhosis. In cirrhosis without hyperammonemia of the vein, however, covert hepatic encephalopathy has been reported. This discrepancy is because of the anatomical features of ammonia metabolism. There are two systems in the body for detoxifying ammonia: one is the urea cycle in the liver, and the other is the glutamine synthesis pathway in skeletal muscle and other tissues. The blood processed in the liver's urea cycle is then transported via arteries to various organs. Further processing occurs in the brain and skeletal muscle's glutamine synthesis pathway before entering the veins. When the urea cycle function decreases in cirrhosis, the ammonia levels in the artery increase. In response, the glutamine synthesis pathway compensates by increasing the capacity to process ammonia. Therefore, the ammonia concentration in the veins downstream of skeletal muscles does not increase immediately. However, the brain and skeletal muscles, which receive arterial blood, might be exposed to high ammonia concentrations. In addition, branched-chain amino acids in venous blood decrease. This period is the transition phase from early- to late-phase cirrhosis, and understanding the pathophysiology during this stage is extremely important for preventing the progression of cirrhosis.

Can rifaximin for hepatic encephalopathy be discontinued during broad-spectrum antibiotic treatment?

Hepatic encephalopathy (HE) is a formidable complication in patients with decompensated cirrhosis, often necessitating the administration of rifaximin (RFX) for effective management. RFX, is a gut-restricted, poorly-absorbable oral rifamycin derived antibiotic that can be used in addition to lactulose for the secondary prophylaxis of HE. It has shown notable reductions in infection, hospital readmission, duration of hospital stay, and mortality. However, limited data exist about the concurrent use of RFX with broad-spectrum antibiotics, because the patients are typically excluded from studies assessing RFX efficacy in HE. A pharmacist-driven quasi-experimental pilot study was done to address this gap. They argue against the necessity of RFX in HE during broad-spectrum antibiotic treatment, particularly in critically ill patients in intensive care unit (ICU). The potential for safe RFX discontinuation without adverse effects is clearly illuminated and valuable insight into the optimization of therapeutic strategies is offered. The findings also indicate that RFX discontinuation during broad-spectrum antibiotic therapy was not associated with higher rates of delirium or coma, and this result remained robust after adjustment in multivariate analysis. Furthermore, rates of other secondary clinical and safety outcomes, including ICU mortality and 48-hour changes in vasopressor requirements, were comparable. However, since the activity of RFX is mainly confined to the modulation of gut microbiota, its potential utility in patients undergoing extensive systemic antibiotic therapy is debatable, given the overlapping antibiotic activity. Further, this suggests that the action of RFX on HE is class-specific (related to its activity on gut microbiota), rather than drug-specific. A recent double-blind randomized controlled (ARiE) trial provided further evidence-based support for RFX withdrawal in critically ill cirrhotic ICU patients receiving broad-spectrum antibiotics. Both studies prompt further discussion about optimal therapeutic strategy for patients facing the dual challenge of HE and systemic infections. Despite these compelling results, both studies have limitations. A prospective, multi-center evaluation of a larger sample, with placebo control, and comprehensive neurologic evaluation of HE is warranted. It should include an exploration of longer-term outcome and the impact of this protocol in non-critically ill liver disease patients.