Interorgan ammonia metabolism in liver failure: the basis of current and future therapies

Hepatic encephalopathy: experimental drugs in development and therapeutic potential

INTRODUCTION

Hepatic encephalopathy (HE) presents a complex pathophysiology, creating multiple potential treatment avenues. This review covers current and emerging treatments for HE.

AREAS COVERED

Standard therapies, including non-absorbable disaccharides and rifaximin, are widely used but show inconsistent efficacy. Alternatives such as polyethylene glycol and L-ornithine L-aspartate have been effective in certain cases. Advancements in understanding HE reveal a growing need for personalized treatments. Novel approaches targeting immune modulation and neuroinflammation are under investigation, though clinical translation is slow. Nutritional interventions and fecal microbiota transplantation show potential but lack robust evidence. Innovative therapies like gene and cell therapies, as well as extracellular vesicles from mesenchymal stem cells, present promising avenues for liver disease treatment, potentially benefiting HE.

EXPERT OPINION

A key challenge in HE research is the design of randomized clinical trials, which often suffer from small sample sizes, heterogeneity in patient population, and inconsistent blinding. Additionally, the multifactorial nature of HE, together with a high spontaneous response rate, complicates efforts to isolate treatment effects. Despite current limitations, ongoing research and technological advances hold promise for more effective and individualized HE treatments in the future.

Altered Mental Status in the Solid-Organ Transplant Recipient

Patients undergoing solid-organ transplantation (SOT) face a tumultuous journey. Prior to transplant, their medical course is characterized by organ dysfunction, diminished quality of life, and reliance on organ support, all of which are endured in hopes of reaching the haven of organ transplantation. Peritransplant altered mental status may indicate neurologic insults acquired during transplant and may have long-lasting consequences. Even years after transplant, these patients are at heightened risk for neurologic dysfunction from a myriad of metabolic, toxic, and infectious causes. This review provides a comprehensive examination of causes, diagnostic approaches, neuroimaging findings, and management strategies for altered mental status in SOT recipients. Given their complexity and the numerous etiologies for neurologic dysfunction, liver transplant patients are a chief focus in this review; however, we also review lesser-known contributors to neurological injury across various transplant types. From hepatic encephalopathy to cerebral edema, seizures, and infections, this review highlights the importance of recognizing and managing pre- and posttransplant neurological complications to optimize patient outcomes.

Liver assistive devices in acute liver failure: Current use and future directions

Acute liver failure (ALF) is a rare syndrome where rapid deterioration of liver function occurs after an acute insult in a patient without prior chronic liver disease and leads to jaundice, hepatic encephalopathy (HE), and oftentimes multiorgan failure (MOF). At this time, the only definitive treatment for ALF is LT but some patients, particularly APAP-induced ALF patients, may have ongoing regenerative capacity of the liver and may not require LT with ongoing supportive management. As a result, extracorporeal liver support (ECLS) has been a topic of interest both as a bridge to LT and as a bridge to spontaneous recovery and aims to remove damaging toxins that further aggravate liver failure, stimulate regeneration of the liver, and improve pathophysiologic consequences of liver failure. There are currently two categories of ECLS (artificial and bioartificial). Artificial ECLS does not incorporate active hepatocytes and are based on the principles of filtration and adsorption and includes renal replacement therapy (RRT), plasma adsorption including plasma exchange and Prometheus (Fractionated Plasma Separation and Adsorption), and albumin dialysis including MARS (Molecular Adsorbent Recirculating System) and SPAD (Single Pass Albumin Dialysis). Bioartificial ECLS incorporates active hepatocytes (human or porcine in origin) to improve liver detoxification capacity and to support hepatic synthetic function and includes ELAD (Extracorporeal Liver Assist Device) and HepatAssist.

Porous and Homogeneous Nanoheterojunction-Accumulating PdO@ZnO Structure for Exhaled Breath Ammonia Sensing

The functional gas sensor device plays a pivotal role in intelligent medical treatment, among which metal oxide semiconductors are widely studied because of their inexpensiveness and ease of fabrication. However, the metal oxide sensors present a significant challenge in detecting NH3 at ppm levels within complex exhaled gases. Herein, the ZnO/PdO-x series were prepared by in situ loading palladium particles and calcining using nano-ZIF-8 as a precursor, which not only provided more transport path for ammonia adsorption but also achieved homogeneous nanoheterojunction accumulation structure. The tailor-made ZnO/PdO-2 sensor exhibits the optimum gas sensitivity, with a response value of 5.56 for 100 ppm of NH3 at 160 °C and a lower detection limit of 0.75 ppm. Particularly, it has a clear quantitative response to the actual exhaled gas of liver and kidney patients. By elucidating the intrinsic link between the in situ loading of MOF templates and the sensing mechanism, it is expected to broaden the rational design of metal-oxide sensors and thus provide an effective method for clinical detection.

Ammonia in liver diseases: A glimpse into the controversies and consensus

Ammonia is a byproduct of the metabolism of nitrogen-containing micro and macromolecules. The key source of bodily ammonia in humans is the small intestine, from diet, luminal bacterial activity, and deamination of glutamine in enterocytes. It is disposed of from the system, mainly in the liver, through the urea cycle. Physiologically, ammonia plays a minor role in acid-base homeostasis. It is the critical molecule implicated in the pathogenesis of hepatic encephalopathy. Liver disease is the most common cause of hyperammonemia, while others include urea cycle defects, infections, and drugs. The diagnostic utility of ammonia in liver diseases has met with increasing skepticism but holds good in urea cycle defects. Additionally, the accuracy of ammonia assay depends on a myriad of patient and technical factors, making the test unreliable if not performed meticulously. Most scientific societies currently fall short of recommending ammonia for diagnostic purposes in chronic liver disease. Despite this fact, ammonia continues to be one of the most frequently requested assays in patients with suspected hepatic encephalopathy, contributing to significant non-productive health expenditure. However, ammonia level does have a prognostic role in liver diseases, especially in acute liver failure. Ammonia-lowering strategies are the cornerstone of the management of hepatic encephalopathy. These strategies include medications that attenuate ammoniagenesis and ammonia scavengers. This review examines the role of ammonia in hepatic encephalopathy, its diagnostic and prognostic implications in liver diseases, challenges associated with ammonia assay, and current therapeutic strategies for ammonia-lowering in clinical practice.

Ammonia and urea metabolism in acute liver failure: A multicentre cohort study

BACKGROUND & AIMS

Ammonia is metabolized into urea in the liver. In acute liver failure (ALF), ammonia has been associated with survival. However, urea variation has been poorly studied.

METHODS

Observational cohort including ALF patients from Curry Cabral Hospital (Lisbon, Portugal) and Clinic Hospital (Barcelona, Spain) between 10/2010 and 01/2023. The United States ALF Study Group cohort was used for external validation. Primary exposures were serum ammonia and urea on ICU admission. Primary endpoint was 30-day transplant-free survival (TFS). Secondary endpoint was explanted liver weight.

RESULTS

Among 191 ALF patients, median (IQR) age was 46 (32; 57) years and 85 (44.5%) were males. Overall, 86 (45.0%) patients were transplanted and 75 (39.3%) died. Among all ALF patients, following adjustment for age, sex, body weight, and aetiology, higher ammonia or lower urea was independently associated with higher INR on ICU admission (p < .009). Among all ALF patients, following adjustment for sex, aetiology, and lactate, higher ammonia was independently associated with lower TFS (adjusted odds ratio (95% confidence interval [CI]) = 0.991 (0.985; 0.997); p = .004). This model predicted TFS with good discrimination (area under receiver operating curve [95% CI] = 0.78 [0.75; 0.82]) and reasonable calibration (R2 of 0.43 and Brier score of 0.20) after external validation. Among transplanted patients, following adjustment for age, sex, actual body weight, and aetiology, higher ammonia (p = .024) or lower (p < .001) urea was independently associated with lower explanted liver weight.

CONCLUSIONS

Among ALF patients, serum ammonia and urea were associated with ALF severity. A score incorporating serum ammonia predicted TFS reasonably well.

Role of ammonia and glutamine in the pathogenesis and progression of metabolic dysfunction-associated steatotic liver disease: A systematic review

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects over 30% of the global population, with a significant risk of advancing to liver cirrhosis and hepatocellular carcinoma. The roles of ammonia and glutamine in MASLD's pathogenesis are increasingly recognized, prompting this systematic review. This systematic review was conducted through a meticulous search of literature on December 21, 2023, across five major databases, focusing on studies that addressed the relationship between ammonia or glutamine and MASLD. The quality of the included studies was evaluated using CASP checklists. This study is officially registered in the PROSPERO database (CRD42023495619) and was conducted without external funding or sponsorship. Following PRISMA guidelines, 13 studies were included in this review. The studies were conducted globally, with varying sample sizes and study designs. The appraisal indicated a mainly low bias, confirming the reliability of the evidence. Glutamine's involvement in MASLD emerged as multifaceted, with its metabolic role being critical for liver function and disease progression. Variable expressions of glutamine synthetase and glutaminase enzymes highlight metabolic complexity whereas ammonia's impact through urea cycle dysfunction suggests avenues for therapeutic intervention. However, human clinical trials are lacking. This review emphasizes the necessity of glutamine and ammonia in understanding MASLD and identifies potential therapeutic targets. The current evidence, while robust, points to the need for human studies to corroborate preclinical findings. A personalized approach to treatment, informed by metabolic differences in MASLD patients, is advocated, alongside future large-scale clinical trials for a deeper exploration into these metabolic pathways.

Biological ammonium transporters: evolution and diversification

Although ammonium is the preferred nitrogen source for microbes and plants, in animal cells it is a toxic product of nitrogen metabolism that needs to be excreted. Thus, ammonium movement across biological membranes, whether for uptake or excretion, is a fundamental and ubiquitous biological process catalysed by the superfamily of the Amt/Mep/Rh transporters. A remarkable feature of the Amt/Mep/Rh family is that they are ubiquitous and, despite sharing low amino acid sequence identity, are highly structurally conserved. Despite sharing a common structure, these proteins have become involved in a diverse range of physiological process spanning all domains of life, with reports describing their involvement in diverse biological processes being published regularly. In this context, we exhaustively present their range of biological roles across the domains of life and after explore current hypotheses concerning their evolution to help to understand how and why the conserved structure fulfils diverse physiological functions.

What every Intensivist should know about ... Ammonia in liver failure

PURPOSE

Acute liver failure (ALF) or acute-on-chronic liver failure (ACLF) patients have high short-term mortality and morbidity. In the context of liver failure, increased serum ammonia is associated with worse neurological outcomes, including high-grade hepatic encephalopathy (HE), cerebral edema, and intracranial hypertension. Besides its neurotoxicity, hyperammonemia may contribute to immune dysfunction and the risk of infection, a frequent trigger for multi-organ failure in these patients.

MATERIAL AND METHODS

We performed a literature-based narrative review. Publications available in PubMed® up to June 2023 were considered.

RESULTS

In the ICU management of liver failure patients, serum ammonia may play an important role. Accordingly, in this review, we focus on recent insights about ammonia metabolism, serum ammonia measurement strategies, hyperammonemia prognostic value, and ammonia-targeted therapeutic strategies.

CONCLUSIONS

Serum ammonia may have prognostic value in liver failure. Effective ammonia targeted therapeutic strategies are available, such as laxatives, rifaximin, L-ornithine-l-aspartate, and continuous renal replacement therapy.

Mitochondrial targets in hyperammonemia: Addressing urea cycle function to improve drug therapies

The urea cycle (UC) is a critically important metabolic process for the disposal of nitrogen (ammonia) produced by amino acids catabolism. The impairment of this liver-specific pathway induced either by primary genetic defects or by secondary causes, namely those associated with hepatic disease or drug administration, may result in serious clinical consequences. Urea cycle disorders (UCD) and certain organic acidurias are the major groups of inherited rare diseases manifested with hyperammonemia (HA) with UC dysregulation. Importantly, several commonly prescribed drugs, including antiepileptics in monotherapy or polytherapy from carbamazepine to valproic acid or specific antineoplastic agents such as asparaginase or 5-fluorouracil may be associated with HA by mechanisms not fully elucidated. HA, disclosing an imbalance between ammoniagenesis and ammonia disposal via the UC, can evolve to encephalopathy which may lead to significant morbidity and central nervous system damage. This review will focus on biochemical mechanisms related with HA emphasizing some poorly understood perspectives behind the disruption of the UC and mitochondrial energy metabolism, namely: i) changes in acetyl-CoA or NAD+ levels in subcellular compartments; ii) post-translational modifications of key UC-related enzymes, namely acetylation, potentially affecting their catalytic activity; iii) the mitochondrial sirtuins-mediated role in ureagenesis. Moreover, the main UCD associated with HA will be summarized to highlight the relevance of investigating possible genetic mutations to account for unexpected HA during certain pharmacological therapies. The ammonia-induced effects should be avoided or overcome as part of safer therapeutic strategies to protect patients under treatment with drugs that may be potentially associated with HA.

Inhibition of urease-mediated ammonia production by 2-octynohydroxamic acid in hepatic encephalopathy

Hepatic encephalopathy is a neuropsychiatric complication of liver disease which is partly associated with elevated ammonemia. Urea hydrolysis by urease-producing bacteria in the colon is often mentioned as one of the main routes of ammonia production in the body, yet research on treatments targeting bacterial ureases in hepatic encephalopathy is limited. Herein we report a hydroxamate-based urease inhibitor, 2-octynohydroxamic acid, exhibiting improved in vitro potency compared to hydroxamic acids that were previously investigated for hepatic encephalopathy. 2-octynohydroxamic acid shows low cytotoxic and mutagenic potential within a micromolar concentration range as well as reduces ammonemia in rodent models of liver disease. Furthermore, 2-octynohydroxamic acid treatment decreases cerebellar glutamine, a product of ammonia metabolism, in male bile duct ligated rats. A prototype colonic formulation enables reduced systemic exposure to 2-octynohydroxamic acid in male dogs. Overall, this work suggests that urease inhibitors delivered to the colon by means of colonic formulations represent a prospective approach for the treatment of hepatic encephalopathy.

L-Isoleucine reverses hyperammonemia-induced myotube mitochondrial dysfunction and post-mitotic senescence

Perturbations in the metabolism of ammonia, a cytotoxic endogenous metabolite, occur in a number of chronic diseases, with consequent hyperammonemia. Increased skeletal muscle ammonia uptake causes metabolic, molecular, and phenotype alterations including cataplerosis of (loss of tricarboxylic acid cycle (TCA) cycle intermediate) α-ketoglutarate (αKG), mitochondrial oxidative dysfunction, and senescence-associated molecular phenotype (SAMP). L-Isoleucine (Ile) is an essential, branched-chain amino acid (BCAA) that simultaneously provides acetyl-CoA as an oxidative substrate and succinyl-CoA for anaplerosis (providing TCA cycle intermediates). Our multiomics analyses in myotubes and skeletal muscle from hyperammonemic mice and human patients with cirrhosis showed perturbations in BCAA transporters and catabolism. We, therefore, determined if Ile reverses hyperammonemia-induced impaired mitochondrial oxidative function and SAMP. Studies were performed in differentiated murine C2C12 myotubes that were early passage, late passage (senescent), or those depleted of LAT1/SLC7A5 and human induced pluripotent stem cell-derived myotubes (hiPSCM). Ile reverses hyperammonemia-induced reduction in the maximum respiratory capacity, complex I, II, and III functions in early passage murine myotubes and hiPSCM. Consistently, low ATP content and impaired global protein synthesis (high energy requiring cellular process) during hyperammonemia are reversed by Ile in murine myotubes and hiPSCM. Lower abundance of critical regulators of protein synthesis in mTORC1 signaling, and increased phosphorylation of eukaryotic initiation factor 2α are also reversed by Ile. Genetic depletion studies showed that Ile responses are independent of the amino acid transporter LAT1/SLC7A5. Our studies show that Ile reverses the hyperammonemia-induced impaired mitochondrial oxidative function, cataplerosis, and SAMP in a LAT1/SLC7A5 transporter-independent manner.

The Management of Hepatic Encephalopathy from Ward to Domiciliary Care: Current Evidence and Gray Areas

Hepatic encephalopathy (HE) is a common complication of advanced liver disease and acute liver failure. It is a condition that features several neuropsychiatric symptoms that affect mortality, morbidity and the quality of patients' and caregivers' lives. An HE diagnosis is generally an exclusion diagnosis. Once the patient is admitted to the hospital, clinical examination, blood tests and eventually neuroimaging should be performed with the aim of ruling out other causes of acute brain dysfunction. Moreover, HE is recognized using various precipitants that can potentially promote its onset, alone or in combination, and must be identified. Once the diagnostic process is complete, a correct treatment should be started. The anti-HE treatment is based on a combination of the correction of precipitants; non-absorbable antibiotics, such as rifaximin; and non-absorbable disaccharides. Once the patient is discharged from the hospital, specific anti-HE therapy should be maintained in order to prevent other HE episodes.

Predicting disease progression in cirrhotic patients after transjugular intrahepatic portosystemic shunt implantation: A sex-stratified analysis

BACKGROUND

Transjugular intrahepatic portosystemic shunt (TIPS) has been extensively used to treat portal hypertension-associated complications, including cirrhosis. The prediction of post-TIPS prognosis is important for cirrhotic patients, as more aggressive liver transplantation is needed when the post-TIPS prognosis is poor.

AIM

To construct a nutrition-based model that could predict the disease progression of cirrhotic patients after TIPS implantation in a sex-dependent manner.

METHODS

This study retrospectively recruited cirrhotic patients undergoing TIPS implantation for analysis. Muscle quality was assessed by measuring the skeletal muscle index (SMI) by computed tomography. Multivariate Cox proportional hazard models were utilized to determine the association between SMI and disease progression in cirrhotic patients after TIPS implantation.

RESULTS

This study eventually included 186 cirrhotic patients receiving TIPS who were followed up for 30.5 ± 18.8 mo. For male patients, the 30-mo survival rate was significantly lower and the probability of progressive events was higher (3.257-fold) in the low-level SMI group than in the high-level SMI group. According to the multivariate Cox analysis of male patients, SMI < 32.8 was an independent risk factor for long-term adverse outcomes after TIPS implantation. A model was constructed, which involved creatinine, plasma ammonia, SMI, and acute-on-chronic liver failure and hepatic encephalopathy occurring within half a year after surgery. This model had an area under the receiver operating characteristic curve of 0.852, sensitivity of 0.926, and specificity of 0.652. According to the results of the DeLong test, this model outperformed other models (Child-Turcotte-Pugh, Model for End-Stage Liver Disease, and Freiburg index of post-TIPS survival) (P < 0.05).

CONCLUSION

SMI is strongly associated with poor long-term outcomes in male patients with cirrhosis who underwent TIPS implantation.

Nutritional therapy for persistent cognitive impairment after resolution of overt hepatic encephalopathy in patients with cirrhosis: A double-blind randomized controlled trial

BACKGROUND AND AIM

Minimal hepatic encephalopathy (MHE) reflects cognitive impairment in patients with liver cirrhosis and is associated with poor prognosis. We assessed the effects of nutritional therapy on cognitive functions, health-related quality of life (HRQOL), anthropometry, endotoxins, and inflammatory markers in cirrhotic patients with MHE.

METHODS

In a double-blind randomized controlled trial, cirrhotic patients with MHE were randomized to nutritional therapy (group I: 30-35 kcal/kg/day and 1.0-1.5 g of protein/kg/day) and no nutritional therapy (group II: diet as patients were taking before) for 6 months. MHE was diagnosed based on psychometric hepatic encephalopathy score (PHES). Anthropometry, ammonia, endotoxins, inflammatory markers, myostatin, and HRQOL were assessed at baseline and after 6 months. Primary endpoints were improvement or worsening in MHE and HRQOL.

RESULTS

A total of 150 patients were randomized to group I (n = 75, age 46.3 ± 12.5 years, 58 men) and group II (n = 75, age 45.2 ± 9.3 years, 56 men). Baseline PHES (-8.16 ± 1.42 vs -8.24 ± 1.43; P = 0.54) was comparable in both groups. Reversal of MHE was higher in group I (73.2% vs 21.4%; P = 0.001) than group II. Improvement in PHES (Δ PHES 4.0 ± 0.60 vs -4.18 ± 0.40; P = 0.001), HRQOL (Δ Sickness Impact Profile 3.24 ± 3.63 vs 0.54 ± 3.58; P = 0.001), anthropometry, ammonia, endotoxins, cytokines, and myostatin levels was also significantly higher in group I than group II. Overt hepatic encephalopathy developed in 6 patients in group I and 13 in group II (P = 0.04).

CONCLUSIONS

Nutritional therapy is effective in treatment of MHE and associated with improvement in nutritional status, HRQOL, ammonia, endotoxins, inflammatory markers, and myostatin levels.

Early serum ammonia variation in critically ill patients with cirrhosis: A multicentre cohort study

BACKGROUND

Serum ammonia variation in critically ill patients with cirrhosis has been poorly studied.

AIM

To describe and assess the impact of serum ammonia variation in these patients' outcomes.

METHODS

We studied patients ≥18 years old admitted to the intensive care units (ICUs) at University of Alberta Hospital (Edmonton, Canada) and Curry Cabral Hospital (Lisbon, Portugal; derivation cohort, n = 492) and Northwestern University Hospital (Chicago, USA; validation cohort, n = 600) between January 2010 and December 2021. Primary exposure was ICU days 1-3 serum ammonia. Primary endpoint was all-cause hospital mortality.

RESULTS

In the derivation cohort, 330 (67.1%) patients were male and median (IQR) age was 57 (50-63) years. On ICU day 1, median ammonia was higher in patients with grade 3/4 hepatic encephalopathy (HE) than those with grade 2 HE or grade 0/1 HE (112 vs. 88 vs. 77 μmoL/L, respectively; p < 0.001). Furthermore, medium ammonia was higher in hospital non-survivors than survivors (99 vs. 86 μmol/L; p < 0.030). Following adjustment for significant confounders (age, HE, vasopressor use and renal replacement therapy delivery), higher ICU day 2 ammonia was independently associated with higher hospital mortality (adjusted OR per each 10 μmoL/L increment [95% CI] = 1.11 [1.01-1.21]; p = 0.024). In the validation cohort, this model with serial ammonia (ICU days 1 and 3) predicted hospital mortality with reasonably good discrimination (c-statistic = 0.73) and calibration (R2  = 0.19 and Brier score = 0.17).

CONCLUSIONS

Among patients with cirrhosis in the ICU, early serum ammonia variation was independently associated with hospital mortality. In this context, serial serum ammonia may have prognostic value.

Sarcopenia in cirrhosis: Prospects for therapy targeted to gut microbiota

Decreased muscle mass and function, also known as sarcopenia, is common in patients with cirrhosis and is associated with a poor prognosis. Although the pathogenesis of this disorder has not been fully elucidated, a disordered gut-muscle axis probably plays an important role. Decreased barrier function of the gut and liver, gut dysbiosis, and small intestinal bacterial overgrowth (SIBO) can lead to increased blood levels of ammonia, lipopolysaccharides, pro-inflammatory mediators, and myostatin. These factors have complex negative effects on muscle mass and function. Drug interventions that target the gut microbiota (long-term use of rifaximin, lactulose, lactitol, or probiotics) positively affect most links of the compromised gut-muscle axis in patients with cirrhosis by decreasing the levels of hyperammonemia, bacterial translocation, and systemic inflammation and correcting gut dysbiosis and SIBO. However, although these drugs are promising, they have not yet been investigated in randomized controlled trials specifically for the treatment and prevention of sarcopenia in patients with cirrhosis. No data exist on the effects of fecal transplantation on most links of gut-muscle axis in cirrhosis; however, the results of animal experimental studies are promising.

Prokaryotic ammonium transporters: what has three decades of research revealed?

The exchange of ammonium across cellular membranes is a fundamental process in all domains of life. In plants, bacteria and fungi, ammonium represents a vital source of nitrogen, which is scavenged from the external environment. In contrast, in animal cells ammonium is a cytotoxic metabolic waste product and must be excreted to prevent cell death. Transport of ammonium is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. In addition to their function as transporters, Amt/Mep/Rh proteins play roles in a diverse array of biological processes and human physiopathology. Despite this clear physiological importance and medical relevance, the molecular mechanism of Amt/Mep/Rh proteins has remained elusive. Crystal structures of bacterial Amt/Rh proteins suggest electroneutral transport, whilst functional evidence supports an electrogenic mechanism. Here, focusing on bacterial members of the family, we summarize the structure of Amt/Rh proteins and what three decades of research tells us concerning the general mechanisms of ammonium translocation, in particular the possibility that the transport mechanism might differ in various members of the Amt/Mep/Rh superfamily.

Drug-induced hyperammonaemia

Hyperammonaemia (HA) as a consequence of numerous primary or secondary causes, gives rise to clinical manifestations due to its toxic effects on the brain. The neurological consequences broadly reflect the ammonia level, duration and age, with paediatric patients being more susceptible. Drug-induced HA may arise due to either decreased ammonia elimination or increased production. This is associated most frequently with use of valproate and presents a dilemma between ongoing therapeutic need, toxicity and the possibility of an alternative cause. As there is no specific test for drug-induced HA, prompt discussion with a metabolic physician is recommended, as the neurotoxic effects are time-dependent. Specific guidelines for managing drug-induced HA have yet to be published and hence the treatment approach outlined in this review reflects that outlined in relevant urea cycle disorder guidelines.

A multistrain probiotic increases the serum glutamine/glutamate ratio in patients with cirrhosis: a metabolomic analysis

To explore the potential mechanisms underlying the effects of a probiotic in cirrhotic patients, we analyzed the blood metabolome using proton nuclear magnetic resonance (1H-NMR) spectroscopy in 32 patients with cirrhosis and cognitive dysfunction or falls. Patients were randomized to receive a multistrain probiotic or placebo for 12 weeks. Among the 54 metabolites identified, the only significant changes in the probiotic group were an increase in glutamine, a decrease in glutamate, and an increase in the glutamine/glutamate ratio. In the placebo group, glutamate increased and the glutamine/glutamate ratio decreased. Our results suggest the multistrain probiotic could influence glutamine/glutamate metabolism, increasing the capacity of ammonia detoxification.

Hepatic encephalopathy - recent advances in treatment and diagnosis

INTRODUCTION

Hepatic encephalopathy (HE) is a peculiar kind of brain dysfunction typical of liver cirrhosis characterized by nonspecific neurological and psychiatric manifestations. HE ranges from minimal hepatic encephalopathy (MHE) to the most severe form characterized by alteration of consciousness or coma (overt HE, OHE). Once the diagnosis of OHE is made, every effort to identify and correct the precipitating cause is essential for the resolution of symptoms. Clinical studies that assessed the prevalence and incidence of any type of HE (MHE and OHE) in patients affected by cirrhosis were included in this review. No language, publication date, or publication status restrictions were imposed. The studies were identified by searching electronic databases (PubMed and SCOPUS).

AREAS COVERED

The most widely empirical pharmacological approach consists of non-absorbable antibiotics (rifaximin) and non-absorbable disaccharides (lactulose, lactitol per os and per enemas). Other agents (including branched-chain amino acids, probiotics, other antibiotics, or intravenous L-ornithine L-aspartate) are available, but the evidence supporting their efficacy remains under debate.

EXPERT OPINION

Gray areas and future needs remain the therapeutic approach to MHE and issues in the design of therapeutic studies for HE which have been extensively discussed in this review.

A double blind randomized controlled trial to assess efficacy of nutritional therapy for prevention of recurrence of hepatic encephalopathy in patients with cirrhosis

BACKGROUND AND AIM

Overt hepatic encephalopathy (OHE) has high risk of recurrence and is associated with poor survival. The role of nutrition therapy is well documented in cirrhosis, but its efficacy in preventing the recurrence of OHE has not been studied.

METHODS

In double blind RCT, we randomly assigned 150 patients with liver cirrhosis, with history of OHE in recent past to receive nutrition therapy (group I) or no nutrition therapy (group II) and followed up for 6 months. The primary efficacy end points were occurrence of breakthrough episodes and time to breakthrough episode of OHE. Secondary end points were OHE related hospitalizations and time to hospitalization involving OHE. Other parameters included anthropometry, changes in serum cytokines (IL-1, IL-6, IL-10, and TNF-α), endotoxin and myostatin.

RESULTS

There was significant reduction in occurrence of breakthrough episodes of OHE in group I [10 vs 36, hazard ratio 0.20; P < 0.001], OHE-related hospitalization [8 vs 24, hazard ratio 0.27; P < 0.001)]. Times to breakthrough episode of OHE and OHE-related hospitalization were longer in group I. At the end of 6 months, inflammatory and anthropometry parameters showed significant improvement in group I compared with worsening of serum albumin, anthropometric parameters, IL-6, IL-10 and TNF-α in group II. At the end of 6 months, ascites (50 vs 66, P = 0.01), gastrointestinal bleed (2 vs 11, P = 0.007), and jaundice (16 vs 41, P < 0.001) were lower in group I.

CONCLUSIONS

Treatment with nutrition therapy prevented recurrence of OHE and decreased OHE-related hospitalizations as compared with no nutrition therapy.

Old and New Precipitants in Hepatic Encephalopathy: A New Look at a Field in Continuous Evolution

Hepatic encephalopathy (HE) is a common complication in patients with advanced liver disease. It is a brain dysfunction characterized by neurological and psychiatric symptoms that significantly affects quality of life, morbidity and mortality of patients. HE has various precipitants that can potentially promote its onset, alone or in combination. Among the historically well-known precipitants, such as infections, gastrointestinal bleeding, dehydration, electrolyte disorders and constipation, recent studies have highlighted the role of malnutrition and portosystemic shunts as new precipitating factors of HE. The identification, management and correction of these factors are fundamental for effective HE treatment, in addition to pharmacological therapy with non-absorbable disaccharides and/or antibiotics.

Plasma ammonia levels predict hospitalisation with liver-related complications and mortality in clinically stable outpatients with cirrhosis

BACKGROUND & AIMS

Hyperammonaemia is central in the pathogenesis of hepatic encephalopathy. It also has pleiotropic deleterious effects on several organ systems, such as immune function, sarcopenia, energy metabolism and portal hypertension. This study was performed to test the hypothesis that severity of hyperammonaemia is a risk factor for liver-related complications in clinically stable outpatients with cirrhosis.

METHODS

We studied 754 clinically stable outpatients with cirrhosis from 3 independent liver units. Baseline ammonia levels were corrected to the upper limit of normal (AMM-ULN) for the reference laboratory. The primary endpoint was hospitalisation with liver-related complications (a composite endpoint of bacterial infection, variceal bleeding, overt hepatic encephalopathy, or new onset or worsening of ascites). Multivariable competing risk frailty analyses using fast unified random forests were performed to predict complications and mortality. External validation was carried out using prospective data from 130 patients with cirrhosis in an independent tertiary liver centre.

RESULTS

Overall, 260 (35%) patients were hospitalised with liver-related complications. On multivariable analysis, AMM-ULN was an independent predictor of both liver-related complications (hazard ratio 2.13; 95% CI 1.89-2.40; p <0.001) and mortality (hazard ratio 1.45; 95% CI 1.20-1.76; p <0.001). The AUROC of AMM-ULN was 77.9% for 1-year liver-related complications, which is higher than traditional severity scores. Statistical differences in survival were found between high and low levels of AMM-ULN both for complications and mortality (p <0.001) using 1.4 as the optimal cut-off from the training set. AMM-ULN remained a key variable for the prediction of complications within the random forests model in the derivation cohort and upon external validation.

CONCLUSION

Ammonia is an independent predictor of hospitalisation with liver-related complications and mortality in clinically stable outpatients with cirrhosis and performs better than traditional prognostic scores in predicting complications.

LAY SUMMARY

We conducted a prospective cohort study evaluating the association of blood ammonia levels with the risk of adverse outcomes in 754 patients with stable cirrhosis across 3 independent liver units. We found that ammonia is a key determinant that helps to predict which patients will be hospitalised, develop liver-related complications and die; this was confirmed in an independent cohort of patients.

Metabolomics profiles in acute-on-chronic liver failure: Unveiling pathogenesis and predicting progression

Acute-on-chronic liver failure (ACLF) usually develops based on acute decompensation (AD) of cirrhosis and is characterized by intense systemic inflammation, multiple organ failure, and high short-term mortality. Validated biomarkers for the diagnosis and prognosis of ACLF remain to be clarified. Metabolomics is an emerging method used to measure low-molecular-weight metabolites and is currently frequently implemented to understand pathophysiological processes involved in disease progression, as well as to search for new diagnostic or prognostic biomarkers of various disorders. The characterization of metabolites in ACLF has recently been described via metabolomics. The role of metabolites in the pathogenesis of ACLF deserves further investigation and improvement and could be the basis for the development of new diagnostic and therapeutic strategies. In this review, we focused on the contributions of metabolomics on uncovering metabolic profiles in patients with ACLF, the key metabolic pathways that are involved in the progression of ACLF, and the potential metabolite-associated therapeutic targets for ACLF.

The Effect of Glucagon on Protein Catabolism During Insulin Deficiency: Exchange of Amino Acids Across Skeletal Muscle and the Splanchnic Bed

Transient insulin deprivation with concurrent hyperglucagonemia is a catabolic state that can occur in type 1 diabetes. To evaluate glucagon's catabolic effect in the setting of its glucogenic effect, we measured the regional exchanges of amino acid metabolites (amino-metabolites) across muscle and splanchnic beds in 16 healthy humans during either somatostatin followed by glucagon or saline infusion alone. Despite a twofold or greater increase in the regional exchange of amino-metabolites by glucagon, whole-body kinetics and concentrations of amino acids (AA) remained stable. Glucagon increased the splanchnic uptake of not only gluconeogenic but also essential (EAA) AA while increasing their release from the muscle bed. Regional tracer-based kinetics and 3-methylhistidine release indicate that EAA release from muscle is likely caused by reduced protein synthesis rather than increased protein degradation. Furthermore, many metabolites known to affect insulin action and metabolism were altered by hyperglucagonemia including increase in branched-chain AA and keto acids of leucine and isoleucine in arterial plasma. Further, an increase in arterial concentrations of α-aminoadipic acid arising from increased conversion from lysine in the splanchnic bed was noted. These results demonstrate that hyperglucagonemia during hypoinsulinemia increases net muscle protein catabolism and substantially increases the exchange of amino metabolites across splanchnic and muscle beds.

Management of Hepatic Encephalopathy Associated with Advanced Liver Disease

Hepatic encephalopathy (HE) is a very prevalent condition in patients with advanced liver disease and has a high recurrence rate. The pathophysiology has a multifactorial origin where hyperammonaemia and inflammation become particularly relevant. There are no HE-specific diagnostic tests, and diagnosis is usually made by taking into account the presence of suggestive and compatible clinical symptoms, the existence of a predisposing liver condition and ruling out other causes with similar clinical manifestations. Once the diagnosis of HE is established, it is essential to carry out an adequate classification based on the underlying liver disease, the intensity of clinical manifestations, the temporal course of the disease and the presence or absence of precipitating factors. Treatment should be aimed at decreasing the duration, intensity and consequences of episodes, preventing recurrence and limiting the impact of the disease in patients and their relatives.

Catabolism in Critical Illness

OBJECTIVES

Ongoing risk of death and poor functional outcomes are important consequences of prolonged critical illness. Characterizing the catabolic phenotype of prolonged critical illness could illuminate biological processes and inform strategies to attenuate catabolism. We aimed to examine if urea-to-creatinine ratio, a catabolic signature of prolonged critical illness, was associated with mortality after the first week of ICU stay.

DESIGN

Reanalysis of multicenter randomized trial of glutamine supplementation in critical illness (REducing Deaths due to OXidative Stress [REDOXS]).

SETTING

Multiple adult ICUs.

PATIENTS

Adult patients admitted to ICU with two or more organ failures related to their acute illness and surviving to day 7.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The association between time-varying urea-to-creatinine ratio and 30-day mortality was tested using Bayesian joint models adjusted for prespecified-covariates (age, kidney replacement therapy, baseline Sequential Organ Failure Assessment, dietary protein [g/kg/d], kidney dysfunction, and glutamine-randomization). From 1,021 patients surviving to day 7, 166 (16.3%) died by day 30. After adjustment in a joint model, a higher time-varying urea-to-creatinine ratio was associated with increased mortality (hazard ratio [HR], 2.15; 95% credible interval, 1.66-2.82, for a two-fold greater urea-to-creatinine ratio). This association persisted throughout the 30-day follow-up. Mediation analysis was performed to explore urea-to-creatinine ratio as a mediator-variable for the increased risk of death reported in REDOXS when randomized to glutamine, an exogenous nitrogen load. Urea-to-creatinine ratio closest to day 7 was estimated to mediate the risk of death associated with randomization to glutamine supplementation (HR, 1.20; 95% CI, 1.04-1.38; p = 0.014), with no evidence of a direct effect of glutamine (HR, 0.90; 95% CI, 0.62-1.30; p = 0.566).

CONCLUSIONS

The catabolic phenotype measured by increased urea-to-creatinine ratio is associated with increased risk of death during prolonged ICU stay and signals the deleterious effects of glutamine administration in the REDOXS study. Urea-to-creatinine ratio is a promising catabolic signature and potential interventional target.

Treatment of Hyperammonemia by Transplanting a Symbiotic Pair of Intestinal Microbes

Hyperammonemia is a deleterious and inevitable consequence of liver failure. However, no adequate therapeutic agent is available for hyperammonemia. Although recent studies showed that the pharmabiotic approach could be a therapeutic option for hyperammonemia, its development is clogged with poor identification of etiological microbes and low transplantation efficiency of candidate microbes. In this study, we developed a pharmabiotic treatment for hyperammonemia that employs a symbiotic pair of intestinal microbes that are both able to remove ammonia from the surrounding environment. By a radioactive tracing experiment in mice, we elucidated how the removal of ammonia by probiotics in the intestinal lumen leads to lower blood ammonia levels. After determination of the therapeutic mechanism, ammonia-removing probiotic strains were identified by high-throughput screening of gut microbes. The symbiotic partners of ammonia-removing probiotic strains were identified by screening intestinal microbes of a human gut, and the pairs were administrated to hyperammonemic mice to evaluate therapeutic efficacy. Blood ammonia was in a chemical equilibrium relationship with intestinal ammonia. Lactobacillus reuteri JBD400 removed intestinal ammonia to shift the chemical equilibrium to lower the blood ammonia level. L. reuteri JBD400 was successfully transplanted with a symbiotic partner, Streptococcus rubneri JBD420, improving transplantation efficiency 2.3×10³ times more compared to the sole transplantation while lowering blood ammonia levels significantly. This work provides new pharmabiotics for the treatment of hyperammonemia as well as explains its therapeutic mechanism. Also, this approach provides a concept of symbiotic pairs approach in the emerging field of pharmabiotics.

The photodynamic/photothermal synergistic therapeutic effect of BODIPY-I-35 liposomes with urea

Phototherapy is a new treatment means for cancer which can reduce the side effects of traditional cancer treatments to humans. Urea is a naturally occurring metabolite in the human body. Some studies have shown that it can inhibit the proliferation of tumor cells and cause oxidative stress. In order to explore the application of urea in enhancing the phototherapy effect, we synthesized a new structure photosensitizer (BODIPY-I-35) with good phototherapeutic effect and encapsulated it in liposomes. Compared with free BODIPY-I-35, water-soluble nanoliposomes (LipoBOD) produced a huge redshift (> 122 nm) of fluorescence emission in solution. When LipoBOD was irradiated with 808 nm laser (1 W/cm²) for 10 min, the temperature contrast increased by 20 °C, which was 4 times higher than free BODIPY-I-35. Confocal microscopy showed appreciable accumulation of LipoBOD in HeLa cells. In addition, when LipoBOD was incubated with urea in HeLa cells, we found that urea not only obviously enhanced the production of ROS, but also increased the apoptosis of HeLa cells. The synergistic effect of LipoBOD (20 μg/mL, at BODIPY-I-35-eq) with urea (250 mM) showed significantly higher phototoxicity than LipoBOD alone. Low dose can reduce the cell viability to 10%. Therefore, we have obtained an effective method of using urea to enhance the phototherapy effect.

Impact of lifestyle interventions targeting physical exercise and caloric intake on cirrhosis regression in rats

In patients, advanced cirrhosis only regresses partially once the etiological agent is withdrawn. Animal models for advanced cirrhosis regression are missing. Lifestyle interventions (LIs) have been shown to improve steatosis, inflammation, fibrosis, and portal pressure (PP) in liver disease. We aimed at characterizing cirrhosis regression after etiological agent removal in experimental models of advanced cirrhosis and to study the impact of different LI on it. Advanced cirrhosis was induced in rats either by carbon tetrachloride (CCl4) or by thioacetamide (TAA) administration. Systemic and hepatic hemodynamics, liver fibrosis, hepatic stellate cell (HSC) activation, hepatic macrophage infiltration, and metabolic profile were evaluated after 48 h, 4 wk or 8 wk of etiological agent removal. The impact of LI consisting in caloric restriction (CR) or moderate endurance exercise (MEE) during the 8-wk regression process was analyzed. The effect of MEE was also evaluated in early cirrhotic and in healthy rats. A significant reduction in portal pressure (PP), liver fibrosis, and HSC activation was observed during regression. However, these parameters remained above those in healthy animals. During regression, animals markedly worsened their metabolic profile. CR although preventing those metabolic disturbances did not further reduce PP, hepatic fibrosis, or HSC activation. MEE also prevented metabolic disturbances, without enhancing, but even attenuating the reduction of PP, hepatic fibrosis, and HSC activation achieved by regression. MEE also worsened hepatic fibrosis in early-TAA cirrhosis and in healthy rats.NEW & NOTEWORTHY We have developed two advanced cirrhosis regression experimental models with persistent relevant fibrosis and portal hypertension and an associated deteriorated metabolism that mimic what happens in patients. LI, despite improving metabolism, did not enhance the regression process in our cirrhotic models. CR did not further reduce PP, hepatic fibrosis, or HSC activation. MEE exhibited a profibrogenic effect in the liver blunting cirrhosis regression. One of the potential explanations of this worsening could be ammonia accumulation.

Inhibition of histone deacetylation with vorinostat does not prevent tunicamycin-mediated acute kidney injury

Endoplasmic reticulum (ER) stress is associated with acute kidney injury (AKI) caused by various mechanisms, including antibiotics, non-steroidal anti-inflammatory drugs, cisplatin, and radiocontrast. Tunicamycin (TM) is a nucleoside antibiotic that induces ER stress and is a commonly used model of AKI. 4-phenylbutyrate (4-PBA) is a chemical chaperone and histone deacetylase (HDAC) inhibitor and has been shown to protect the kidney from ER stress, apoptosis, and structural damage in a tunicamycin model of AKI. The renal protection provided by 4-PBA is attributed to its ability to prevent misfolded protein aggregation and inhibit ER stress; however, the HDAC inhibitor effects of 4-PBA have not been examined in the TM-induced model of AKI. As such, the main objective of this study was to determine if histone hyperacetylation provides any protective effects against TM-mediated AKI. The FDA-approved HDAC inhibitor vorinostat was used, as it has no ER stress inhibitory effects and therefore the histone hyperacetylation properties alone could be investigated. In vitro work demonstrated that vorinostat inhibited histone deacetylation in cultured proximal tubular cells but did not prevent ER stress or protein aggregation induced by TM. Vorinostat induced a significant increase in cell death, and exacerbated TM-mediated total cell death and apoptotic cell death. Wild type male mice were treated with TM (0.5 mg/kg, intraperitoneal injection), with or without vorinostat (50 mg/kg/day) or 4-PBA (1 g/kg/day). Mice treated with 4-PBA or vorinostat exhibited similar levels of histone hyperacetylation. Expression of the pro-apoptotic protein CHOP was induced with TM, and not inhibited by vorinostat. Further, vorinostat did not prevent any renal damage or decline in renal function caused by tunicamycin. These data suggest that the protective mechanisms found by 4-PBA are primarily due to its molecular chaperone properties, and the HDAC inhibitors used did not provide any protection against renal injury caused by ER stress.

Usefulness of the Stroop Test in Diagnosing Minimal Hepatic Encephalopathy and Predicting Overt Hepatic Encephalopathy

Minimal hepatic encephalopathy (MHE) adversely affects the clinical outcomes of patients with liver cirrhosis. This prospective study aimed to evaluate the utility of the Stroop test in the diagnosis of MHE and prediction of overt hepatic encephalopathy (OHE) in Japanese patients with cirrhosis. We enrolled 152 patients who underwent the Stroop test between November 2018 and February 2020. MHE was diagnosed using a combination of neuropsychological tests as the gold standard. The enrolled patients were followed up prospectively until the occurrence of OHE or August 2020. The optimal cutoff value of the Stroop test measurements was determined by receiver operating characteristic (ROC) curve analysis, and its predictive ability was assessed using the area under the ROC curve (AUC). Among the 139 eligible patients, 50 (36%) were diagnosed with MHE. The OffTime+OnTime cutoff value of 218.3 seconds had the best discriminative ability for MHE diagnosis, with an AUC of 0.77, a sensitivity of 74%, and a specificity of 75%. During a median follow-up of 10.8 months, 6 (4%) patients developed OHE. The OffTime+OnTime cutoff value of 305.6 seconds had the highest predictive ability for OHE, with an AUC of 0.79, a sensitivity of 67%, and a specificity of 92%. This value predicted OHE occurrence independent of liver functional reserve and prior OHE (hazard ratio, 19.8; P = 0.003). These two cutoff values remained statistically significant even when patients with prior OHE were excluded from the analysis. Conclusion: The Stroop test was useful for diagnosing patients with MHE and predicting OHE in Japanese patients with cirrhosis.

Clinical outcomes and prognostic factors of mortality in liver cirrhosis patients on continuous renal replacement therapy in two tertiary hospitals in Korea

Background

Data on liver cirrhosis (LC) patients undergoing continuous renal replacement therapy (CRRT) are lacking despite of the dismal prognosis. We therefore evaluated clinical characteristics and predictive factors related to mortality in LC patients undergoing CRRT.

Methods

We performed a retrospective observational study at two tertiary hospitals in Korea. A total of 229 LC patients who underwent CRRT were analyzed. Patients were classified into survivor and non-survivor groups. We used multivariable Cox regression analyses to identify predictive factors of in-hospital mortality.

Results

During a median follow-up of 5 days (interquartile range, 1-19 days), in-hospital mortality rate was 66.4%. In multivariable analysis, the Acute Physiology and Chronic Health Evaluation II (APACHE II) score (hazard ratio [HR], 1.03; 95% confidence interval [CI], 1.01-1.06; p = 0.02), Model for End-Stage Liver Disease (MELD) score (HR, 1.08; 95% CI, 1.04-1.11; p > 0.001), and delivered CRRT dose (HR, 0.95; 95% CI, 0.92-0.98; p = 0.002) were significant risk factors for in-hospital mortality. Patients with a CRRT delivered dose < 25 mL/kg/hr had a higher mortality rate than those with a delivered dose > 35 mL/kg/hr (HR, 3.13; 95% CI, 1.62-6.05; p = 0.001). Subgroup analysis revealed that a CRRT delivered dose > 25 mL/kg/hr was a significant risk factor for in-hospital mortality among LC patients with a MELD score ≥ 30.

Conclusion

High APACHE II score, high MELD score, and low delivered CRRT dose were significant risk factors for in-hospital mortality. CRRT delivered dose impacted mortality significantly, especially in patients with a MELD score ≥ 30.

Comprehensive Analysis of Fecal Microbiome and Metabolomics in Hepatic Fibrosis Rats Reveal Hepatoprotective Effects of Yinchen Wuling Powder From the Host-Microbial Metabolic Axis

Hepatic fibrosis (HF) is a typical consequence in the development of multiple chronic liver diseases, which is intimately related to the composition and metabolic status of gut microbiota. A myriad of evidence has indicated that traditional Chinese medicine can treat HF by regulating gut microbiota. Yinchen Wuling powder (YCWLP) is a famous traditional Chinese medicine prescription, which has been used to relieve liver diseases for thousands of years. YCWLP has demonstrated protective function on HF, but its effect on the alterations of gut microbiota is still unclear, and its explicit therapeutic mechanism also needs to be further elucidated. In this study, 16S rRNA gene sequencing and fecal metabolomics analysis were combined to investigate the influence of YCWLP on gut microbiota in HF rats and the interactions between gut microbiota and host metabolism. The results showed that YCWLP treatment significantly improved the disorder of multiple organ indices, HF-related cytokines and plasma LPS induced by HF. Masson's trichrome stainings also showed that YCWLP treatment could significantly alleviate the severity of HF in rats. Additionally, YCWLP could reverse the significant changes in the abundance of certain genera closely related to HF phenotype, including Barnesiella [Ruminococcus] and Christensenella. Meanwhile, YCWLP significantly increased the abundance of Bifidobacterium, Coprococcus and Anaerostipes, which are closely related to butyrate production. Metabolomics and Spearman's correlation analysis showed that YCWLP could regulate the disorder of arginine biosynthesis, sphingolipid metabolism and alanine, aspartate and glutamate metabolism in HF rats, and these regulations were intimately related to Barnesiella, [Ruminococcus], Christensenella, Coprococcus and Anaerostipes. By explaining the biological significance of the above results, we concluded that YCWLP might ameliorate HF by regulating the imbalance of gut microbiota, increasing the abundance of butyrate-producing bacteria to reduce ammonia production, promote ammonia degradation, and regulate pro-inflammatory cytokines and immune function.

Pathophysiology of decompensated cirrhosis: Portal hypertension, circulatory dysfunction, inflammation, metabolism and mitochondrial dysfunction

Patients with acutely decompensated cirrhosis have a dismal prognosis and frequently progress to acute-on-chronic liver failure, which is characterised by hepatic and extrahepatic organ failure(s). The pathomechanisms involved in decompensation and disease progression are still not well understood, and as specific disease-modifying treatments do not exist, research to identify novel therapeutic targets is of the utmost importance. This review amalgamates the latest knowledge on disease mechanisms that lead to tissue injury and extrahepatic organ failure - such as systemic inflammation, mitochondrial dysfunction, oxidative stress and metabolic changes - and marries these with the classical paradigms of acute decompensation to form a single paradigm. With this detailed breakdown of pathomechanisms, we identify areas for future research. Novel disease-modifying strategies that break the vicious cycle are urgently required to improve patient outcomes.

Transient hyperammonaemia following epileptic seizures in cats

OBJECTIVES

The aim of this study was to determine whether transient postictal hyperammonaemia exists in cats.

METHODS

The medical records of all feline patients that presented at a Swedish veterinary hospital between 2008 and 2018 were retrospectively reviewed to find those that had a recent or ongoing epileptic seizure. To qualify for inclusion, the medical record had to include information on at least one ammonia value taken in close proximity to, or during, an active seizure, the cat must have exceeded the normal upper limit of blood ammonia concentration on initial testing (reference interval 0-95 μmol/l), and there needed to be a follow-up ammonia value available within a maximum of 3 days.

RESULTS

Five cats were included in the study, and they had blood ammonia concentrations on initial testing ranging from 146 to 195 µmol/l. They were all retested within a period of 2 h to 3 days of the original reading. All five cats had a spontaneous decrease in ammonia levels without any specific treatment for hyperammonaemia.

CONCLUSIONS AND RELEVANCE

Pursuant to the findings of this retrospective study, transient hyperammonaemia may be noted after epileptic seizure in cats. Consequently, a differential diagnostic list in feline patients with hyperammonaemia could, depending on the context, include non-hepatic-related pathologies, such as epileptic seizures.

Potassium deficiency decreases the capacity for urea synthesis and markedly increases ammonia in rats

Our study provides novel findings of experimental hypokalemia reducing urea cycle functionality and thereby severely increasing plasma ammonia. This is pathophysiologically interesting because plasma ammonia increases during hypokalemia by a hitherto unknown mechanism, which may be particular important in relation to the unexplained link between hypokalemia and hepatic encephalopathy. Potassium deficiency decreases gene expression, protein synthesis, and growth. The urea cycle maintains body nitrogen homeostasis including removal of toxic ammonia. Hyperammonemia is an obligatory trait of liver failure, increasing the risk for hepatic encephalopathy, and hypokalemia is reported to increase ammonia. We aimed to clarify the effects of experimental hypokalemia on the in vivo capacity of the urea cycle, on the genes of the enzymes involved, and on ammonia concentrations. Female Wistar rats were fed a potassium-free diet for 13 days. Half of the rats were then potassium repleted. Both groups were compared with pair- and free-fed controls. The following were measured: in vivo capacity of urea-nitrogen synthesis (CUNS); gene expression (mRNA) of urea cycle enzymes; plasma potassium, sodium, and ammonia; intracellular potassium, sodium, and magnesium in liver, kidney, and muscle tissues; and liver sodium/potassium pumps. Liver histology was assessed. The diet induced hypokalemia of 1.9 ± 0.4 mmol/L. Compared with pair-fed controls, the in vivo CUNS was reduced by 34% (P < 0.01), gene expression of argininosuccinate synthetase 1 (ASS1) was decreased by 33% (P < 0.05), and plasma ammonia concentrations were eightfold elevated (P < 0.001). Kidney and muscle tissue potassium contents were markedly decreased but unchanged in liver tissue. Protein expressions of liver sodium/potassium pumps were unchanged. Repletion of potassium reverted all the changes. Hypokalemia decreased the capacity for urea synthesis via gene effects. The intervention led to marked hyperammonemia, quantitatively explainable by the compromised urea cycle. Our findings motivate clinical studies of patients with liver disease.

Brain Herniation and Intracranial Hypertension

This article introduces the basic concepts of intracranial physiology and pressure dynamics. It also includes discussion of signs and symptoms and examination and radiographic findings of patients with acute cerebral herniation as a result of increased as well as decreased intracranial pressure. Current best practices regarding medical and surgical treatments and approaches to management of intracranial hypertension as well as future directions are reviewed. Lastly, there is discussion of some of the implications of critical medical illness (sepsis, liver failure, and renal failure) and treatments thereof on causation or worsening of cerebral edema, intracranial hypertension, and cerebral herniation.

A mathematical model of the rat kidney. III. Ammonia transport

Ammonia generated within the kidney is partitioned into a urinary fraction (the key buffer for net acid excretion) and an aliquot delivered to the systemic circulation. The physiology of this partitioning has yet to be examined in a kidney model, and that was undertaken in this work. This involves explicit representation of the cortical labyrinth, so that cortical interstitial solute concentrations are computed rather than assigned. A detailed representation of cortical vasculature has been avoided by making the assumption that solute concentrations within the interstitium and peritubular capillaries are likely to be identical and that there is little to no modification of venous composition as blood flows to the renal vein. The model medullary ray has also been revised to include a segment of proximal straight tubule, which supplies ammonia to this region. The principal finding of this work is that cortical labyrinth interstitial ammonia concentration is likely to be several fold higher than systemic arterial ammonia. This elevation of interstitial ammonia enhances ammonia secretion in both the proximal convoluted tubule and distal convoluted tubule, with uptake by Na⁺-K⁺-ATPases of both segments. Model prediction of urinary ammonia excretion was concordant with measured values, but at the expense of greater ammoniagenesis, with high rates of renal venous ammonia flux. This derives from a limited capability of the model medulla to replicate the high interstitial ammonia concentrations that are required to drive collecting duct ammonia secretion. Thus, renal medullary ammonia trapping appears key to diverting ammonia from the renal vein to urine, but capturing the underlying physiology remains a challenge.NEW & NOTEWORTHY This is the first mathematical model to estimate solute concentrations within the kidney cortex. The model predicts cortical ammonia to be several fold greater than in the systemic circulation. This higher concentration drives ammonia secretion in proximal and distal tubules. The model reveals a gap in our understanding of how ammonia generated within the cortex is channeled efficiently into the final urine.

Sunitinib-associated hyperammonemic encephalopathy successfully managed with higher intensity conventional hemodialysis: A case report

RATIONALE

Hyperammonemia encephalopathy is a rare but severe complication that has been reported in association with the use of sunitinib, a tyrosine kinase inhibitor. We report here a unique case of a patient with end stage renal disease that was initiated on sunitinib for metastatic renal cell carcinoma.

PATIENT CONCERNS

A 65-year-old man with end stage renal disease on maintenance conventional hemodialysis and had concomitant stable Child-Pugh class B liver cirrhosis consequent of hepatitis C infection was started on sunitinib for metastatic renal cell carcinoma. He developed confusion few weeks after starting therapy with no other indication of worsening liver dysfunction otherwise.

DIAGNOSIS

He was later diagnosed with hyperammonemia encephalopathy.

INTERVENTIONS

His treatment was discontinued and reinitiated at a lower dose after recovery and titrated according to tolerance. As ammonia is a very low molecular weight molecule and is cleared well with diffusive clearance, we intensified his dialysis regimen by increasing intensity for each session and frequency per week.

OUTCOMES

With this change in dialysis regimen, patient was able to continue treatment with sunitinib.

LESSONS

Clinicians prescribing sunitinib should be vigilant to monitor for this complication in patients receiving sunitinib, apart from the more usual presentation of hepatotoxicity. We found that a more intensive hemodialysis regimen consisting of 4× a week conventional high-flux hemodialysis (HD) can permit the continuation of treatment with sunitinib in an end stage renal disease (ESRD) patient with Child-Pugh class B liver cirrhosis.

The Role of Intestinal Bacteria and Gut-Brain Axis in Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a neurological disorder that occurs in patients with liver insufficiency. However, its pathogenesis has not been fully elucidated. Pharmacotherapy is the main therapeutic option for HE. It targets the pathogenesis of HE by reducing ammonia levels, improving neurotransmitter signal transduction, and modulating intestinal microbiota. Compared to healthy individuals, the intestinal microbiota of patients with liver disease is significantly different and is associated with the occurrence of HE. Moreover, intestinal microbiota is closely associated with multiple links in the pathogenesis of HE, including the theory of ammonia intoxication, bile acid circulation, GABA-ergic tone hypothesis, and neuroinflammation, which contribute to cognitive and motor disorders in patients. Restoring the homeostasis of intestinal bacteria or providing specific probiotics has significant effects on neurological disorders in HE. Therefore, this review aims at elucidating the potential microbial mechanisms and metabolic effects in the progression of HE through the gut-brain axis and its potential role as a therapeutic target in HE.

Interorgan Metabolism of Amino Acids in Human Health and Disease

Amino acids are integral for human health, influencing an array of physiological processes from gene expression to vasodilation to the immune response. In accordance with this expansive range of unique functions, the tissues of the body engage in a complex interplay of amino acid exchange and metabolism to respond to the organism's dynamic needs for a range of nitrogenous products. Interorgan amino acid metabolism is required for numerous metabolic pathways, including the synthesis of functional amino acids like arginine, glutamate, glutamine, and glycine. This physiological process requires the cooperative handling of amino acids by organs (e.g., the small intestine, skeletal muscle, kidneys, and liver), as well as the complete catabolism of nutritionally essential amino acids such as the BCAAs, with their α-ketoacids shuttled from muscle to liver. These exchanges are made possible by several mechanisms, including organ location, as well as the functional zonation of enzymes and the cell-specific expression of amino acid transporters. The cooperative handling of amino acids between the various organs does not appear to be under the control of any centralized regulation, but is instead influenced by factors such as fluctuations in nutrient availability, hormones, changes associated with development, and altered environmental factors. While the normal function of these pathways is associated with health and homeostasis, affected by physical activity, diet and body composition, dysregulation is observed in numerous disease states, including cardiovascular disease and cancer cachexia, presenting potential avenues for the manipulation of amino acid consumption as part of the therapeutic approach to these conditions in individuals.

Hepatic encephalopathy: Novel insights into classification, pathophysiology and therapy

Hepatic encephalopathy (HE) is a frequent and serious complication of both chronic liver disease and acute liver failure. HE manifests as a wide spectrum of neuropsychiatric abnormalities, from subclinical changes (mild cognitive impairment) to marked disorientation, confusion and coma. The clinical and economic burden of HE is considerable, and it contributes greatly to impaired quality of life, morbidity and mortality. This review will critically discuss the latest classification of HE, as well as the pathogenesis and pathophysiological pathways underlying the neurological decline in patients with end-stage liver disease. In addition, management strategies, diagnostic approaches, currently available therapeutic options and novel treatment strategies are discussed.

Ammonia uptake by transmembrane pH gradient poly(isoprene)-block-poly(ethylene glycol) polymersomes

Transmembrane pH gradient poly(isoprene)-block-poly(ethylene glycol) (PI-b-PEG) polymersomes were investigated for their potential use in the detoxification of ammonia, a metabolite that is excessively present in patients suffering from urea cycle disorders and advanced liver diseases, and which causes neurotoxic effects (e.g., hepatic encephalopathy). Polymers varying in PI and PEG block length were synthesized via nitroxide-mediated polymerization and screened for their ability to self-assemble into polymersomes in aqueous media. Ammonia sequestration by the polymersomes was investigated in vitro. While most vesicular systems were able to capture ammonia in simulated intestinal fluids, uptake was lost in partially dehydrated medium mimicking conditions in the colon. Polymeric crosslinking of residual olefinic bonds in the PI block increased polymersome stability, partially preserving the ammonia capture capacity in the simulated colon environment. These more stable vesicular systems hold promise for the chronic oral treatment of hyperammonemia.

Psoas Muscle Index Does Not Predict Post-Transplant Outcomes: A Series of 57 Liver Transplant Recipients

BACKGROUND

Sarcopenia is defined as the loss of muscle mass and function. Our aim is to evaluate the degree of sarcopenia by measuring the patients on the waiting list for liver transplantation and its influence on the different post-liver transplant outcomes in our group.

METHODS

The psoas muscle index (PMI, cm²/m²) was calculated (right psoas muscle area [cm²]/the square of the body height [m²]) in 57 patients on the waiting list for liver transplantation in our center, and the post-transplant variables relevant to our study were collected.

RESULTS

The 57 recipients had a mean age of 57 years (range, 35-73) and had a mean of 7.4 months (range, 0-39) on the liver transplant waiting list. The mean psoas muscle index was 2.39 (range, 1-4), and the mean body mass index was 28.01kg/m² (range, 22-36). After multivariate analysis we found a positive correlation between the PMI and the body mass index of the recipients (r = 0.320, P = .017), intensive care unit length of stay, and donor age (r = 0.319, P = .042), and between cold ischemia time and graft survival (r = 0.366, P = .009). We found no correlation in our sample between PMI and post-liver transplant complications either in terms of graft or patient survival.

CONCLUSION

PMI is not representative of total muscle mass and sarcopenia and is not effective in adequately predicting the survival of patients on the waiting list for liver transplantation.

Sarcopenia and cognitive impairment in liver cirrhosis: A viewpoint on the clinical impact of minimal hepatic encephalopathy

Minimal hepatic encephalopathy (MHE) represents the mildest type of hepatic encephalopathy (HE). MHE is considered as a preclinical stage of HE and is part of a wide spectrum of typical neurocognitive alterations characteristic of patients with liver cirrhosis, particularly involving the areas of attention, alertness, response inhibition, and executive functions. MHE can be detected by testing the patients’ psychometric performance, attention, working memory, psychomotor speed, and visuospatial ability, as well as by means of electrophysiological and other functional brain measures. MHE is very frequent, affecting from 20% up to 80% of patients tested, depending of the diagnostic tools used. Although subclinical, MHE is considered to be clinically relevant. In fact, MHE has been related to the patients’ falls, fitness to drive, and working ability. As a consequence, MHE affects the patients and caregivers lives by altering their quality of life and even their socioeconomic status. Recently sarcopenia, a very common condition in patients with advanced liver disease, has been shown to be strictly related to both minimal and overt HE. Aim of this review is to summarize the most recently published evidences about the emerging relationship between sarcopenia and cognitive impairment in cirrhotic patients and provide suggestions for future research.

Prognostic Role of Ammonia in Patients With Cirrhosis

Ammonia is thought to be central to the pathogenesis of hepatic encephalopathy (HE), but its prognostic role in patients with cirrhosis and acute decompensation is unknown. The aims of this study were to determine the relationship between ammonia levels and severity of HE and its association with organ dysfunction and short-term mortality. We identified 498 patients from two institutions as part of prospective observational studies in patients with cirrhosis. Plasma ammonia levels were measured on admission and Chronic Liver Failure-Sequential Organ Failure Assessment criteria were used to determine the presence of organ failures. The 28-day patient survival was determined. Receiver operating characteristic analysis was used to identify the cutoff points for ammonia values, and multivariable analysis was performed using the Cox proportional hazard regression model. The 28-day mortality was 43.4%. Plasma ammonia correlated with severity of HE (P < 0.001), was significantly higher in nonsurvivors (93 [73-121] versus 67 [55-89] µmol/L, P < 0.001), and was an independent predictor of 28-day mortality (hazard ratio, 1.009, P < 0.001). An ammonia level of 79.5 µmol/L had sensitivity of 68.1% and specificity of 67.4% for predicting 28-day mortality. An ammonia level of ≥79.5 µmol/L was associated with a higher frequency of organ failures (liver [P = 0.004], coagulation [P < 0.001], kidney [P = 0.004], and respiratory [P < 0.001]). Lack of improvement in baseline ammonia at day 5 was associated with high mortality (70.6%). Conclusion: Ammonia level correlates with not only the severity of HE but also the failure of other organs and is an independent risk factor for mortality; lack of improvement in ammonia level is associated with high risk of death, making it an important biomarker and a therapeutic target.

Tadalafil restores long-term memory and synaptic plasticity in mice with hepatic encephalopathy

BACKGROUND AND AIM

Tadalafil displays important neuroprotective effects in experimental models of neurodegenerative diseases, however its mechanisms of action remain poorly understood. The aim of the present study was to investigate the action of Tadalafil on learning and memory, neuroinflammation, glial cell activation and neuroprotection in the experimental model of hepatic encephalopathy (HE) induced by Thioacetamide (TAA) in mice.

METHODS

Mice received intraperitoneal injections of TAA, for 3 consecutive days, reaching the final dose of 600 mg/kg. Tadalafil 15 mg/kg body weight was administered by gavage during 15 days after TAA induction. Mice underwent a Barnes maze for learning and memory evaluation.

RESULTS

Animals with hepatic encephalopathy showed reduced learning and spatial memory in the Barnes Maze, presented astrocyte and microglia activation and increased neuroinflammatory markers such as TNF-α, IL-1β, IL-6, p-p38, p-ERK and p-NF-kB. In addition, the signaling pathway PKA/PKG/CREB/BDNF/NeuN/synaptophysin and glutamate receptors were deregulated by TAA. Tadalafil treatment regulated the inflammation signaling pathways restoring learning and spatial memory.

CONCLUSION

Tadalafil significantly reduced neuroinflammation, promoted neuroprotection and plasticity, regulated the expression of hippocampal glutamate receptor and restored spatial learning ability and memory.