Serum Ammonia in Cirrhosis: Clinical Impact of Hyperammonemia, Utility of Testing, and National Testing Trends

Efficacy of probiotics on improvement of health outcomes in cirrhotic liver disease patients: A systematic review and meta-analysis of randomised controlled trials

Liver cirrhosis is a chronic condition of the liver and is the 14th most common cause of death around the world; yet it remains an incurable disease. Probiotics have gained significant popularity as a potential treatment option for liver cirrhosis.

METHODS

A systematic review and meta-analysis was conducted to assess the effects of probiotics on liver cirrhosis. PubMed, Scopus, Cochrane Central Register for Controlled Trials (CENTRAL) and ProQuest Dissertation and Thesis were searched from 2000 to January 2024 for studies that evaluated the effects of probiotics on a variety of outcomes of liver disease.

RESULTS

A total of 22 randomised controlled trial studies were included in the meta-analysis. Probiotics significantly decreased Gamma-glutamyl transferase (effect size: 0.307, p = 0.024, 95% CI [-0.572, -0.040]) and Aspartate aminotransferase (p = 0.013, 95% CI [-17.927, -2.128]). Significant reduction in serum ammonia levels (effect size = -1.093, p = 0.000, 95% CI [-1.764, -0.423]) and endotoxin levels (effect size = -0.961, p = 0.000, 95% CI [-1.537, -0.385]) were also found.

SUMMARY

Overall probiotics could be recommended as a potential adjunct therapy for patients with cirrhosis, as they appear to have some benefit in improving liver function, and are well tolerated with minimal adverse effects. More comprehensive research with larger sample sizes is recommended to understand more about the widespread effects of probiotic use.

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.

Physiological network approach to prognosis in cirrhosis: A shifting paradigm

Decompensated liver disease is complicated by multi-organ failure and poor prognosis. The prognosis of patients with liver failure often dictates clinical management. Current prognostic models have focused on biomarkers considered as individual isolated units. Network physiology assesses the interactions among multiple physiological systems in health and disease irrespective of anatomical connectivity and defines the influence or dependence of one organ system on another. Indeed, recent applications of network mapping methods to patient data have shown improved prediction of response to therapy or prognosis in cirrhosis. Initially, different physical markers have been used to assess physiological coupling in cirrhosis including heart rate variability, heart rate turbulence, and skin temperature variability measures. Further, the parenclitic network analysis was recently applied showing that organ systems connectivity is impaired in patients with decompensated cirrhosis and can predict mortality in cirrhosis independent of current prognostic models while also providing valuable insights into the associated pathological pathways. Moreover, network mapping also predicts response to intravenous albumin in patients hospitalized with decompensated cirrhosis. Thus, this review highlights the importance of evaluating decompensated cirrhosis through the network physiologic prism. It emphasizes the limitations of current prognostic models and the values of network physiologic techniques in cirrhosis.

Digestive dynamics: Unveiling interplay between the gut microbiota and the liver in macronutrient metabolism and hepatic metabolic health

Although the liver is the largest metabolic organ in the body, it is not alone in functionality and is assisted by "an organ inside an organ," the gut microbiota. This review attempts to shed light on the partnership between the liver and the gut microbiota in the metabolism of macronutrients (i.e., proteins, carbohydrates, and lipids). All nutrients absorbed by the small intestines are delivered to the liver for further metabolism. Undigested food that enters the colon is metabolized further by the gut microbiota that produces secondary metabolites, which are absorbed into portal circulation and reach the liver. These microbiota-derived metabolites and co-metabolites include ammonia, hydrogen sulfide, short-chain fatty acids, secondary bile acids, and trimethylamine N-oxide. Further, the liver produces several compounds, such as bile acids that can alter the gut microbial composition, which can in turn influence liver health. This review focuses on the metabolism of these microbiota metabolites and their influence on host physiology. Furthermore, the review briefly delineates the effect of the portosystemic shunt on the gut microbiota-liver axis, and current understanding of the treatments to target the gut microbiota-liver axis.

Hepatic Encephalopathy-A Guide to Laboratory Testing

Hepatic encephalopathy (HE) remains both a clinical diagnosis and one of exclusion. Laboratory testing is largely focused on identifying precipitating factors. Ammonia levels in the blood can be helpful for the diagnosis of HE but are not required for confirmation. More recent literature is lending support to the prognostic capabilities of ammonia in cirrhosis, both in predicting future HE events and in determining outcomes in hospitalized patients. Accurate ammonia testing requires strict protocols to avoid common pitfalls in the measurement of this labile analyte. Future studies investigating the utility of other laboratory testing to diagnose, stage, or predict HE are encouraged.

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.

Gut-derived ammonia contributes to alcohol-related fatty liver development via facilitating ethanol metabolism and provoking ATF4-dependent de novo lipogenesis activation

BACKGROUND & AIMS

Dysbiosis contributes to alcohol-associated liver disease (ALD); however, the precise mechanisms remain elusive. Given the critical role of the gut microbiota in ammonia production, we herein aim to investigate whether and how gut-derived ammonia contributes to ALD.

METHODS

Blood samples were collected from human subjects with/without alcohol drinking. Mice were exposed to the Lieber-DeCarli isocaloric control or ethanol-containing diets with and without rifaximin (a nonabsorbable antibiotic clinically used for lowering gut ammonia production) supplementation for five weeks. Both in vitro (NH4Cl exposure of AML12 hepatocytes) and in vivo (urease administration for 5 days in mice) hyperammonemia models were employed. RNA sequencing and fecal amplicon sequencing were performed. Ammonia and triglyceride concentrations were measured. The gene and protein expression of enzymes involved in multiple pathways were measured.

RESULTS

Chronic alcohol consumption causes hyperammonemia in both mice and human subjects. In healthy livers and hepatocytes, ammonia exposure upregulates the expression of urea cycle genes, elevates hepatic de novo lipogenesis (DNL), and increases fat accumulation. Intriguingly, ammonia promotes ethanol catabolism and acetyl-CoA formation, which, together with ammonia, synergistically facilitates intracellular fat accumulation in hepatocytes. Mechanistic investigations uncovered that ATF4 activation, as a result of ER stress induction and general control nonderepressible 2 activation, plays a central role in ammonia-provoked DNL elevation. Rifaximin ameliorates ALD pathologies in mice, concomitant with blunted hepatic ER stress induction, ATF4 activation, and DNL activation.

CONCLUSIONS

An overproduction of ammonia by gut microbiota, synergistically interacting with ethanol, is a significant contributor to ALD pathologies.

Association between sarcopenia and hepatic encephalopathy after transjugular intrahepatic portosystemic shunt in patients with cirrhosis: a systematic review and meta-analysis

PURPOSE

The association between the presence of sarcopenia in patients with cirrhosis and the onset of hepatic encephalopathy (HE) after transjugular intrahepatic portosystemic shunt (TIPS) is yet to be established. We conducted a systematic review and meta-analysis to provide a thorough summary of the available evidence on this association.

METHODS

A thorough search of the literature was performed in the PubMed, EMBASE, and Web of Science databases. The protocol was duly registered on PROSPERO (CRD42023398856). The hazard ratio (HR) and corresponding 95% confidence intervals (CIs) for the occurrence of HE after TIPS were extracted from studies comparing cirrhotic patients with and without sarcopenia. These data were then combined using a random-effect model.

RESULTS

A total of 1135 patients from seven cohort studies that met our eligibility criteria were included in the meta-analysis. Our findings indicate a significantly higher risk of post-TIPS HE among cirrhotic patients with sarcopenia compared to those without sarcopenia (HR, 2.35; 95% CIs 1.32-4.19; p = 0.004; I2 = 75%). The findings remained consistent across subgroups stratified by liver disease etiology, study location, and severity of hepatic dysfunction.

CONCLUSION

The study demonstrated that sarcopenia was strongly linked to an increased likelihood post-TIPS HE among cirrhotic patients.

miRNA-ome plasma analysis unveils changes in blood-brain barrier integrity associated with acute liver failure in rats

BACKGROUND

Hepatic encephalopathy (HE) symptoms associated with liver insufficiency are linked to the neurotoxic effects of ammonia and other toxic metabolites reaching the brain via the blood-brain barrier (BBB), further aggravated by the inflammatory response. Cumulative evidence documents that the non-coding single-stranded RNAs, micro RNAs (miRs) control the BBB functioning. However, miRs' involvement in BBB breakdown in HE is still underexplored. Here, we hypothesized that in rats with acute liver failure (ALF) or rats subjected to hyperammonemia, altered circulating miRs affect BBB composing proteins.

METHODS

Transmission electron microscopy was employed to delineate structural alterations of the BBB in rats with ALF (thioacetamide (TAA) intraperitoneal (ip.) administration) or hyperammonemia (ammonium acetate (OA) ip. administration). The BBB permeability was determined with Evans blue dye and sodium fluorescein assay. Plasma MiRs were profiled by Next Generation Sequencing (NGS), followed by in silico analysis. Selected miRs, verified by qRT-PCR, were examined in cultured rat brain endothelial cells. Targeted protein alterations were elucidated with immunofluorescence, western blotting, and, after selected miR mimics transfection, through an in vitro resistance measurement.

RESULTS

Changes in BBB structure and increased permeability were observed in the prefrontal cortex of TAA rats but not in the brains of OA rats. The NGS results revealed divergently changed miRNA-ome in the plasma of both rat models. The in silico analysis led to the selection of miR-122-5p and miR-183-5p with their target genes occludin and integrin β1, respectively, as potential contributors to BBB alterations. Both proteins were reduced in isolated brain vessels and cortical homogenates in TAA rats. We documented in cultured primary brain endothelial cells that ammonia alone and, in combination with TNFα increases the relative expression of NGS-selected miRs with a less pronounced effect of TNFα when added alone. The in vitro study also confirmed miR-122-5p-dependent decrease in occludin and miR-183-5p-related reduction in integrin β1 expression.

CONCLUSION

This work identified, to our knowledge for the first time, potential functional links between alterations in miRs residing in brain endothelium and BBB dysfunction in ALF.

Serum ammonia variation predicts mortality in patients with hepatitis B virus-related acute-on-chronic liver failure

Background

Hyperammonemia is critical to the development of hepatic encephalopathy (HE) and is associated with mortality in end-stage liver disease. This study investigated the clinical value of ammonia variation in hepatitis B virus-related acute-on-chronic liver failure (HBV-ACLF) patients.

Methods

A total of 276 patients with HBV-ACLF were retrospectively recruited. Patients' ammonia levels were serially documented. Baseline ammonia, Peak ammonia (highest level), and Trough ammonia (lowest level) were particularly corrected to the upper limit of normal (AMM-ULN). The primary endpoint was 28-day mortality.

Results

The 28-day, 3-month, and 12-month mortality rates were 19.2, 25.7, and 28.2%, respectively. A total of 51 (18.4%) patients had overt HE (grade 2/3/4). Peak AMM-ULN was significantly higher in patients with overt HE and non-survivors compared with their counterparts (P < 0.001). Following adjustment for significant confounders, high Peak AMM-ULN was an independent predictor of overt HE (hazard ratio, 1.031, P < 0.001) and 28-day mortality (hazard ratio, 1.026, P < 0.001). The cut-off of Peak AMM-ULN was 1.8, determined by using the X-tile. Patients with Peak AMM-ULN appearing on days 1-3 after admission had a higher proportion of overt HE and mortality compared to other groups. Patients with decreased ammonia levels within 7 days had better clinical outcomes than those with increased ammonia.

Conclusion

Serum Peak ammonia was independently associated with overt HE and mortality in HBV-ACLF patients. Serial serum ammonia may have prognostic value.

Association of ADH1B rs1229984, ADH1C rs698, and ALDH2 rs671 with Alcohol abuse and Alcoholic Cirrhosis in People Living in Northeast Vietnam

OBJECTIVE

Alcohol abuse can cause developing cirrhosis, even liver cancer. Several single nucleotide polymorphisms (SNPs) of ADH1B, ADH1C, and ALDH2 genes have been reported to be associated with alcohol abuse and alcoholic cirrhosis (ALC). This study investigated the association between three SNPs of ADH1B rs1229984, ADH1C rs698, and ALDH2 rs671 with alcohol abuse and ALC in people living in the Northeast region of Vietnam.

METHODS

306 male participants were recruited including 206 alcoholics (106 ALC, 100 without ALC) and 100 healthy non-alcoholics. Clinical characteristics were collected by clinicians. Genotypes were identified by Sanger sequencing. Chi-Square (χ2) and Fisher-exact tests were used to assess the differences in age and clinical characteristics, Child-Pugh score, frequencies of alleles and genotypes.

RESULT

Our data showed that the frequency of ALDH2*1 was significantly higher in alcoholics (88.59%) and ALC groups (93.40%) than that of healthy non-alcoholics (78.50%) with p=0.0009 and non-ALC group (83.50%) with p=0.002, respectively. We detected opposite results when examined ALDH2*2. Frequency of combined genotypes with high acetaldehyde accumulation were significantly lower in alcoholics and ALC group than those of control groups with p=0.005 and p=0.008, respectively. Meanwhile, the proportion of combined genotypes with non-acetaldehyde accumulation were significantly two times higher in the ALC group (19.98%) than those of the non-ALC group (8%) with p=0.035. These combined genotypes showed a decreasing trend in the Child-Pugh score from likely phenotype causing risk for non-acetaldehyde accumulation to high acetaldehyde accumulation.

CONCLUSION

The ALDH2*1 allele was found as a risk factor for alcohol abuse and ALC, and combined genotypes of ADH1B rs1229984, ADH1C rs698, and ALDH2 rs671 with non-acetaldehyde accumulation increase ALC risk. In contrast, ALDH2*2 and the genotype combinations related to high acetaldehyde accumulation were protective factors against alcohol abuse and ALC.

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

BACKGROUND & AIMS

Hyperammonaemia is a key pathological feature of liver disease and the primary driver of hepatic encephalopathy (HE). However, the relative roles of increased ammonia production and reduced clearance are poorly understood as is the action of ammonia-targeting HE drugs. We aimed to quantify whole-body ammonia metabolism in healthy persons and patients with cirrhosis and to validate our method by examining the effects of glycerol phenylbutyrate and lactulose + rifaximin treatment.

METHODS

Ten healthy men and ten male patients with cirrhosis were investigated by 90-minute constant ammonia infusion to achieve steady-state plasma ammonia. Whole-body ammonia clearance was calculated as infusion rate divided by steady-state concentration increase and ammonia production as clearance times baseline ammonia concentration. Participants were re-investigated after the ammonia targeting interventions.

RESULTS

In healthy persons, ammonia clearance was 3.5 (3.1-3.9) L/min and production 49 (35-63) μmol/min. Phenylbutyrate increased clearance by 11% (4-19%, p=0.009). Patients with cirrhosis had a 20% decreased ammonia clearance of 2.7 (2.1-3.3) L/min (p = 0.02) and a nearly tripled production to 131 (102-159) μmol/min (p<0.0001). Lactulose + rifaximin reduced production by 20% (2-37%, p=0.03). The infusion was generally well-tolerated save one hyperammonaemic patient with cirrhosis with possible bleeding unrelated to the infusion who developed clinical HE that reverted when infusion was discontinued.

CONCLUSIONS

Whole-body ammonia clearance and production may be measured separately by the technique used. The method identified a lower clearance and a higher production in patients with cirrhosis, and showed that phenylbutyrate increases clearance, whereas lactulose + rifaximin reduces production. The method may be used to examine a range of questions related to normo-/pathophysiology and ammonia-targeting treatment mechanisms.

IMPACT AND IMPLICATIONS

High blood ammonia plays a key role in liver cirrhosis related brain dysfunction. However, the relative roles of increased ammonia production and reduced ammonia clearance are poorly understood as is the action of ammonia-targeting treatments. This study presents a relatively simple test to measure ammonia metabolism. By use of this test, it was possible to show that patients with liver cirrhosis have decreased ammonia clearance and increased ammonia production compared with healthy persons and to quantify distinctively different ammonia-targeting treatment effects. The test presented holds several perspectives for future studies of normal physiology and pathophysiology, not least in regard to elucidating effects of ammonia-targeting therapies.

CLINICAL TRIAL NUMBER

ClinicalTrials.gov (1-16-02-297-20).

The Ongoing Debate of Serum Ammonia Levels in Cirrhosis: the Good, the Bad, and the Ugly

Serum ammonia testing in hepatic encephalopathy (HE) has been long debated in the field of hepatology. Although central to the pathophysiology of HE, serum ammonia testing is fraught with complexities that can lead to challenges in laboratory collection and interpretation. Although there is some disagreement across guideline organizations regarding routine testing of ammonia in HE, all acknowledge that normal values, although possible in HE, may warrant reconsideration of the diagnosis. In this study, we propose a nuanced approach to ammonia testing in HE. Serum ammonia testing provides little additional benefit in clinical scenarios with a high or low pretest probability for HE. However, if the pretest probability for HE is uncertain, a low ammonia level may reduce the posttest probability of HE. In this scenario, other etiologies of altered mental status should be explored. Future research should focus on developing a standardized approach to serum ammonia collection, processing, and interpretation.

Role of Branched-Chain Amino Acids and Their Derivative β-Hydroxy-β-Methylbutyrate in Liver Cirrhosis

Branched-chain amino acids (BCAA) supplementation is used to promote protein synthesis in different clinical conditions in which proteolysis is increased. In addition, lower plasma BCAA levels have been related to an increased risk of hepatic encephalopathy in liver cirrhosis. In this article we will review the role of supplementation with BCAAs and BCAA derivative β-hydroxy-β-methylbutyrate (HMB) in liver cirrhosis, focusing on nutritional and clinical effects. Evidence shows that BCAA supplementation slightly increases muscle mass and body mass index, with an upward trend in muscular strength and no change in fat mass. Moreover, BCAA supplementation improves symptoms of hepatic encephalopathy, and is indicated as second-line therapy. The evidence is more limited for BCAA derivatives. HMB supplementation appears to increase muscle mass in chronic diseases associated with cachexia, although this effect has not yet been clearly demonstrated in liver cirrhosis studies. To date, HMB supplementation has no clinical indication in liver cirrhosis.

Missed diagnosis of cirrhosis in the inpatient setting

Cirrhosis accounts for a large number of deaths in the United States and worldwide, leading to an increasing burden on the healthcare system. Cirrhosis is, however, a progressive disease with different potential complications related to liver dysfunction and portal hypertension. Often, patients may present with complications of cirrhosis without having been diagnosed previously. It is pertinent that clinicians recognize these signs to place patients on an appropriate course of management to help delay or avoid further disease progression while avoiding deleterious outcomes and unnecessary utilization. We will discuss the epidemiology of liver disease, cirrhosis, and its complications (hepatic encephalopathy, ascites, and varices). In this study, we will discuss the rationale and impact of missing these diagnoses on the healthcare system and patient.