Hyperammonemia results in reduced muscle function independent of muscle mass

The Story of Ammonia in Liver Disease: An Unraveling Continuum

Hyperammonemia and liver disease are closely linked. Most of the ammonia in our body is produced by transamination and deamination activities involving amino acid, purine, pyrimidines, and biogenic amines, and from the intestine by bacterial splitting of urea. The only way of excretion from the body is by hepatic conversion of ammonia to urea. Hyperammonemia is associated with widespread toxicities such as cerebral edema, hepatic encephalopathy, immune dysfunction, promoting fibrosis, and carcinogenesis. Over the past two decades, it has been increasingly utilized for prognostication of cirrhosis, acute liver failure as well as acute on chronic liver failure. The laboratory assessment of hyperammonemia has certain limitations, despite which its value in the assessment of various forms of liver disease cannot be negated. It may soon become an important tool to make therapeutic decisions about the use of prophylactic and definitive treatment in various forms of liver disease.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Clinical practice guidelines for nutritional assessment and monitoring of adult ICU patients in China

The Chinese Society of Critical Care Medicine (CSCCM) has developed clinical practice guidelines for nutrition assessment and monitoring for patients in adult intensive care units (ICUs) in China. This guideline focuses on nutrition evaluation and metabolic monitoring to achieve optimal and personalized nutrition therapy for critically ill patients. This guideline was developed by experts in critical care medicine and evidence-based medicine methodology and was developed after a thorough review of the system and a summary of relevant trials or studies published from 2000 to July 2023. A total of 18 recommendations were formed and consensus was reached through discussions and reviews by expert groups in critical care medicine, parenteral and enteral nutrition, and surgery. The recommendations are based on currently available evidence and cover several key fields, including screening and assessment, evaluation and assessment of enteral feeding intolerance, metabolic and nutritional measurement and monitoring during nutrition therapy, and organ function evaluation related to nutrition supply. Each question was analyzed according to the Population, Intervention, Comparison, and Outcome (PICO) principle. In addition, interpretations were provided for four questions that did not reach a consensus but may have potential clinical and research value. The plan is to update this nutrition assessment and monitoring guideline using the international guideline update method within 3-5 years.

Sleep disturbances in chronic liver disease

Sleep disturbances are common in chronic liver disease and significantly impact patient outcomes and quality of life. The severity and nature of sleep disturbances vary by liver disease etiology and severity. While there is ongoing research into the association between liver disease and sleep-wake dysfunction, the underlying pathophysiology varies and, in many cases, is poorly understood. Liver disease is associated with alterations in thermoregulation, inflammation, and physical activity, and is associated with disease-specific complications, such as HE, that may directly affect sleep. In this article, we review the relevant pathophysiologic processes, disease-specific sleep-wake disturbances, and clinical management of CLD-associated sleep-wake disturbances.

Expression of miR-let7b and miR-19b in progressive familial intrahepatic cholestasis (PFIC) children

BACKGROUND

MicroRNAs (miRNAs) are a group of small non-coding RNAs that bind to the target mRNA and regulate gene expression. Recently circulating microRNAs were investigated as markers of diseases and therapeutic targets. Although various studies analyze the miRNA expression in liver disease, these studies on PFIC are few. Progressive familial intrahepatic cholestasis (PFIC) is a rare liver disease with autosomal recessive inheritance. Most children with PFIC progress to cirrhosis and liver failure and consequently need to have a liver transplant. The aim of this study is the investigation of the miR-19b and miR-let7b expression levels in Iranian PFIC children.

METHODS

25 PFIC patients, 25 healthy children and 25 Biliary Atresia patients were considered as case and two control groups respectively. Blood samples were obtained and Liver function tests (LFTs) were measured. After RNA extraction and cDNA synthesis, quantitative PCR was performed using specific primers for miR-19b and miR-let7b. The U6 gene is used as an internal control.

RESULTS

qPCR on PFIC patients' samples demonstrated that the miR-19b and the miR-let7b expression were significantly decreased in patients compared to the control groups, with a p-value<0.0001 and p-value=0.0006 receptively.

CONCLUSION

In conclusion, circulating micro-RNA like miR-19b and miR-let7b have a potential opportunity to be a non-invasive diagnostic marker or therapeutic target for PFIC in the future.

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.

Multiple ammonia-induced episodes of hepatic encephalopathy provoke neuronal cell loss in bile-duct ligated rats

Background & Aims

Hepatic encephalopathy (HE) is defined as a reversible syndrome and therefore should resolve following liver transplantation (LT). However, neurological complications have been reported in up to 47% of LT recipients, which have been documented to be associated with a history of overt HE pre-LT. We hypothesise that multiple episodes of HE lead to permanent cell injury and exacerbate neurological dysfunction. Our goal was to evaluate the impact of cumulative HE episodes on neurological status and brain integrity in rats with chronic liver disease.

Methods

Episodes of overt HE (loss of righting reflex) were induced following injection of ammonium acetate in bile duct ligation (BDL) rats (BDL-Ammonia) every 4 days starting at week 3 post-BDL. Neurobehaviour was evaluated after the last episode. Upon sacrifice, plasma ammonia, systemic oxidative stress, and inflammation markers were assessed. Neuronal markers including neuron-specific nuclear antigen and SMI311 (anti-neurofilament marker) and apoptotic markers (cleaved caspase-3, Bax, and Bcl2) were measured. Total antioxidant capacity, oxidative stress marker (4-hydroxynonenal), and proinflammatory cytokines (tumour necrosis factor-alpha and interleukin-1β) were measured in brain (hippocampus, frontal cortex, and cerebellum). Proteomic analysis was conducted in the hippocampus.

Results

In hippocampus of BDL-Ammonia rats, cleaved caspase-3 and Bax/Bcl2 ratio were significantly increased, whereas NeuN and SMI311 were significantly decreased compared with BDL-Vehicle rats. Higher levels of oxidative stress-induced post-translational modified proteins were found in hippocampus of BDL-Ammonia group which were associated with a lower total antioxidant capacity.

Conclusions

Ammonia-induced episodes of overt HE caused neuronal cell injury/death in BDL rats. These results suggest that multiple bouts of HE can be detrimental on the integrity of the brain, translating to irreversibility and hence neurological complications post-LT.

Impact and implications

Hepatic encephalopathy (HE) is defined as a reversible neuropsychiatric syndrome resolving following liver transplantation (LT); however, ∼47% of patients demonstrate neurological impairments after LT, which are associated with a previous history of overt HE pre-LT. Our study indicates that multiple episodes of overt HE can cause permanent neuronal damage which may lead to neurological complications after LT. Nevertheless, preventing the occurrence of overt HE episodes is critical for reducing the risk of irreversible neuronal injury in patients with cirrhosis.

Transjugular intrahepatic portosystemic shunt insertion improves muscle mass but not muscle function or frailty measures

INTRODUCTION

Sarcopenia in cirrhosis is associated with poor outcomes. While transjugular intrahepatic portosystemic shunt (TIPS) insertion improves radiological measures of muscle mass, its impact on muscle function, performance and frailty has not been evaluated.

METHODS

Patients with cirrhosis referred for TIPS were prospectively recruited and followed for 6 months. L3 CT scans were used to calculate skeletal muscle and adipose tissue parameters. Handgrip strength, Liver Frailty Index and short physical performance battery were serially monitored. Dietary intake, insulin resistance, insulin-like growth factor (IGF)-1, and immune function using QuantiFERON Monitor (QFM) were measured.

RESULTS

Twelve patients completed the study with a mean age of 58 ± 9 years and model for end-stage liver disease score of 16 ± 5. At 6 months post-TIPS, skeletal muscle area increased from 139.33 cm 2  ± 22.72 to 154.64 ± 27.42 ( P  = 0.012). Significant increases were observed in the subcutaneous fat area ( P  = 0.0076) and intermuscular adipose tissue ( P  = 0.041), but not muscle attenuation or visceral fat. Despite marked changes in muscle mass, no improvements were observed in handgrip strength, frailty, or physical performance. At 6 months post-TIPS, IGF-1 ( P  = 0.0076) and QFM ( P  = 0.006) increased compared to baseline. Nutritional intake, hepatic encephalopathy measures, insulin resistance and liver biochemistry were not significantly impacted.

CONCLUSION

Muscle mass increased following TIPS insertion as did IGF-1, a known driver of muscle anabolism. The lack of improvement in muscle function was unexpected and may relate to impairment in muscle quality and the effects of hyperammonaemia on muscle contractile function. Improvements in QFM, a marker of immune function, may suggest a reduction in infection susceptibility in this at-risk population and requires further evaluation.

Handgrip strength is associated with 12-month survival in male patients suffering with advanced chronic liver disease

BACKGROUND

Advanced chronic liver disease (ACLD) patients are usually malnourished, and both conditions in combination increase the likelihood of unfavourable clinical outcomes. Handgrip strength (HGS) has been suggested as a relevant parameter for nutritional assessment and predictor of adverse clinical outcomes in ACLD. However, the HGS cut-off values for ACLD patients have not yet been reliably established. The aims of this study were to preliminarily identify HGS reference values in a sample population of ACLD male patients and to assess their association with survival over a 12-month follow-up period.

METHODS

This was a prospective observational study with preliminary analysis of outpatients and inpatients. A total of 185 male patients with a medical diagnosis of ACLD met the inclusion criteria and were invited to participate in the study. The physiological variation in muscle strength related to the age of the individuals included in the study was considered to obtain cut-off values.

RESULTS

After categorising HGS by age group (adults: 18-60 years; elderly: ≥60 years), the reference values obtained were 32.5 kg for the adults and 16.5 kg for the elderly. During the 12-month follow-up, 20.5% of the patients died, and 76.3% of those had been identified with reduced HGS.

CONCLUSIONS

Patients with adequate HGS showed significantly higher 12-month survival than those with reduced HGS within the same period. Our findings show that HGS is an important predictive parameter for clinical and nutritional follow-up in ACLD male patients.

Liver transplantation in the patient with physical frailty

Frailty is a decline in functional reserve across multiple physiological systems. A key component of frailty is sarcopenia, which denotes a loss of skeletal muscle mass and impaired contractile function that ultimately result in physical frailty. Physical frailty/sarcopenia are frequent and contribute to adverse clinical outcomes before and after liver transplantation. Frailty indices, including the liver frailty index, focus on contractile dysfunction (physical frailty), while cross-sectional image analysis of muscle area is the most accepted and reproducible measure to define sarcopenia. Thus, physical frailty and sarcopenia are interrelated. The prevalence of physical frailty/sarcopenia is high in liver transplant candidates and these conditions have been shown to adversely impact clinical outcomes including mortality, hospitalisations, infections, and cost of care both before and after transplantation. Data on the prevalence of frailty/sarcopenia and their sex- and age-dependent impact on outcomes are not consistent in patients on the liver transplant waitlist. Physical frailty and sarcopenic obesity are frequent in the obese patient with cirrhosis, and adversely affect outcomes after liver transplantation. Nutritional interventions and physical activity remain the mainstay of management before and after transplantation, despite limited data from large scale trials. In addition to physical frailty, there is recognition that a global evaluation including a multidisciplinary approach to other components of frailty (e.g., cognition, emotional, psychosocial) also need to be addressed in patients on the transplant waitlist. Recent advances in our understanding of the underlying mechanisms of sarcopenia and contractile dysfunction have helped identify novel therapeutic targets.

Diet was less significant than physical activity in the prognosis of people with sarcopenia and metabolic dysfunction-associated fatty liver diseases: Analysis of the National Health and Nutrition Examination Survey III

BACKGROUND

Sarcopenia is prevalent in metabolic dysfunction-associated fatty liver diseases (MAFLD), and the primary treatment for both diseases is lifestyle modification. We studied how dietary components and physical activity affect individuals with sarcopenia and MAFLD.

MATERIALS AND METHODS

We conducted a study utilizing National Health and Nutrition Examination Survey (NHANES) III (1988-1994) data with Linked Mortality file (through 2019). The diagnosis of fatty liver disease (FLD) was based on ultrasound images revealing moderate and severe steatosis. Using bioelectrical measures, sarcopenia was assessed. Using self-report data, dietary intake and physical activity levels were evaluated.

RESULTS

Among 12,259 participants, 2,473 presented with MAFLD, and 290 of whom had sarcopenia. Higher levels of physical activity (odds ratio [OR] = 0.51 [0.36-0.95]) and calorie (OR = 0.58 [0.41-0.83]) intake reduced the likelihood of sarcopenia in MAFLD patients. During a median follow-up period of 15.3 years, 1,164 MAFLD and 181 MAFLD patients with sarcopenia perished. Increased activity levels improved the prognosis of patients with sarcopenia (Insufficiently active, HR = 0.75 [0.58-0.97]; Active, HR = 0.64 [0.48-0.86]), which was particularly pronounced in older patients.

CONCLUSION

In the general population, hyperglycemia was highly related to MAFLD prognosis. Physical inactivity and a protein-restricted diet corresponded to sarcopenia, with physical inactivity being connected to poor outcomes. Adding protein supplements would be beneficial for older people with sarcopenia who are unable to exercise due to frailty, while the survival benefits were negligible.

Understanding the role of smoking and chronic excess alcohol consumption on reduced caloric intake and the development of sarcopenia

This narrative review provides mechanistic insight into the biological link between smoking and/or chronic excess alcohol consumption, and increased risk of developing sarcopenia. Although the combination of excessive alcohol consumption and smoking is often associated with ectopic adipose deposition, this review is focused on the context of a reduced caloric intake (leading to energy deficit) that also may ensue due to either lifestyle habit. Smoking is a primary cause of periodontitis and chronic obstructive pulmonary disease that both induce swallowing difficulties, inhibit taste and mastication, and are associated with increased risk of muscle atrophy and mitochondrial dysfunction. Smoking may contribute to physical inactivity, energy deficit via reduced caloric intake, and increased systemic inflammation, all of which are factors known to suppress muscle protein synthesis rates. Moreover, chronic excess alcohol consumption may result in gut microbiota dysbiosis and autophagy-induced hyperammonemia, initiating the up-regulation of muscle protein breakdown and down-regulation of muscle protein synthesis via activation of myostatin, AMPK and REDD1, and deactivation of IGF-1. Future research is warranted to explore the link between oral healthcare management and personalised nutrition counselling in light of potential detrimental consequences of chronic smoking on musculoskeletal health outcomes in older adults. Experimental studies should investigate the impact of smoking and chronic excess alcohol consumption on the gut-brain axis, and explore biomarkers of smoking-induced oral disease progression. The implementation of behavioural change interventions and health policies regarding smoking and alcohol intake habits may mitigate the clinical and financial burden of sarcopenia on the healthcare system.

Shared and unique phosphoproteomics responses in skeletal muscle from exercise models and in hyperammonemic myotubes

Skeletal muscle generation of ammonia, an endogenous cytotoxin, is increased during exercise. Perturbations in ammonia metabolism consistently occur in chronic diseases, and may blunt beneficial skeletal muscle molecular responses and protein homeostasis with exercise. Phosphorylation of skeletal muscle proteins mediates cellular signaling responses to hyperammonemia and exercise. Comparative bioinformatics and machine learning-based analyses of published and experimentally derived phosphoproteomics data identified differentially expressed phosphoproteins that were unique and shared between hyperammonemic murine myotubes and skeletal muscle from exercise models. Enriched processes identified in both hyperammonemic myotubes and muscle from exercise models with selected experimental validation included protein kinase A (PKA), calcium signaling, mitogen-activated protein kinase (MAPK) signaling, and protein homeostasis. Our approach of feature extraction from comparative untargeted "omics" data allows for selection of preclinical models that recapitulate specific human exercise responses and potentially optimize functional capacity and skeletal muscle protein homeostasis with exercise in chronic diseases.

Impact of L-ornithine L-aspartate on non-alcoholic steatohepatitis-associated hyperammonemia and muscle alterations

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) is the most common chronic liver disease in the world. Progression toward non-alcoholic steatohepatitis (NASH) is associated with alterations of skeletal muscle. One plausible mechanism for altered muscle compartment in liver disease is changes in ammonia metabolism. In the present study, we explored the hypothesis that NASH-associated hyperammonemia drives muscle changes as well as liver disease progression.

MATERIALS AND METHODS

In Alms1-mutant mice (foz/foz) fed a 60% fat diet (HFD) for 12 weeks; we investigated hepatic and muscular ammonia detoxification efficiency. We then tested the effect of an 8 week-long supplementation with L-ornithine L-aspartate (LOLA), a known ammonia-lowering treatment, given after either 4 or 12 weeks of HFD for a preventive or a curative intervention, respectively. We monitored body composition, liver and muscle state by micro computed tomography (micro-CT) as well as muscle strength by four-limb grip test.

RESULTS

According to previous studies, 12 weeks of HFD induced NASH in all foz/foz mice. Increase of hepatic ammonia production and alterations of urea cycle efficiency were observed, leading to hyperammonemia. Concomitantly mice developed marked myosteatosis. First signs of myopenia occurred after 20 weeks of diet. Early LOLA treatment given during NASH development, but not its administration in a curative regimen, efficiently prevented myosteatosis and muscle quality, but barely impacted liver disease or, surprisingly, ammonia detoxification.

CONCLUSION

Our study confirms the perturbation of hepatic ammonia detoxification pathways in NASH. Results from the interventional experiments suggest a direct beneficial impact of LOLA on skeletal muscle during NASH development, though it does not improve ammonia metabolism or liver disease.

Implications of pre-transplant sarcopenia and frailty in patients with non-alcoholic steatohepatitis and alcoholic liver disease

Frailty manifesting as sarcopenia is an independent risk factor for mortality in cirrhosis, and often presents in low model for end-stage liver disease (MELD) patients. Its etiology is multifactorial, but key physiologic changes culminate in altered energy utilization in the fasting state, preferentially utilizing muscle amino acids for gluconeogenesis thereby promoting sarcopenia. Hyperammonemia alters the circulating amino acid profile, diminishing pro-muscle branched-chain amino acids like leucine. The metabolic syndrome worsens sarcopenia through multi-tissue insulin resistance. Alcohol also exacerbates sarcopenia as a direct muscle toxin and inhibitor of growth signaling. Therapy is aimed at alcohol cessation, frequent high-protein meals, branched-chain amino acid supplementation, and diminished time spent fasting. Moderate exercise can improve muscle mass and muscle quality, though precise exercise regimens have not yet been explicitly determined. Studies are ongoing into the effects of myostatin antagonists and insulin sensitizers. The Liver Frailty Index can predict patients most at risk of poor outcome and should be considered in the management of all cirrhotic patients. Specialty testing like dual-energy X-ray absorptiometry (DEXA) scanning and cross-sectional estimates of muscle mass are areas of active research and may play a future role in clinical risk-stratification.

Nutritional priorities in patients with severe COVID-19

PURPOSE OF REVIEW

The COVID-19 pandemic has altered the profile of critical care services internationally, as professionals around the globe have struggled to rise to the unprecedented challenge faced, both in terms of individual patient management and the sheer volume of patients that require treatment and management in intensive care. This review article sets out key priorities in nutritional interventions during the patient journey, both in the acute and recovery phases.

RECENT FINDINGS

The current review covers the care of the acutely unwell patient, and the evidence base for nutritional interventions in the COVID-19 population. One of the biggest differences in caring for critically ill patients with acute respiratory failure from COVID-19 is often the time prior to intubation. This represents specific nutritional challenges, as does nursing patients in the prone position or in the setting of limited resources. This article goes on to discuss nutritional support for COVID-19 sufferers as they transition through hospital wards and into the community.

SUMMARY

Nutritional support of patients with severe COVID-19 is essential. Given the longer duration of their critical illness, combined with hypermetabolism and energy expenditure, patients with COVID-19 are at increased risk for malnutrition during and after their hospital stay.

Survival benefit of L-carnitine supplementation in patients with cirrhosis

BACKGROUND

L-carnitine supplementation is effective in improving muscle cramps, hyperammonemia, and hepatic encephalopathy in patients with cirrhosis. However, limited evidence is available on the effect of L-carnitine supplementation on the survival of patients with cirrhosis.

METHODS

In this retrospective study, 674 patients with cirrhosis admitted to Gifu University Hospital or Chuno Kosei Hospital between October 2011 and December 2018 were enrolled. L-carnitine supplementation was defined as the use of L-carnitine for more than 30 consecutive days during the follow-up period. Propensity score matching was applied to create comparable groups between L-carnitine-treated and untreated patients. Mortality was evaluated using the Cox proportional hazards model.

RESULTS

Among the patients, 93 were excluded. Of the remaining 581 patients, 71 (12%) received L-carnitine supplementation. Propensity matching identified 189 patients (63 L-carnitine-treated and 126 untreated patients) with comparable baseline characteristics in both groups. Of the matched patients, 33 (52%) L-carnitine-treated and 74 (59%) untreated patients died during the median follow-up period of 36.3 months. Overall survival was significantly higher in L-carnitine-treated patients than in untreated patients (hazard ratio [HR], 0.66; 95% confidence interval [CI], 0.43-0.99). A subgroup analysis showed that the survival benefit of L-carnitine supplementation was prominent in patients with Child-Pugh class B or C (HR, 0.39; 95% CI, 0.23-0.68), albumin levels ≤3.5 g/dL (HR, 0.59; 95% CI, 0.37-0.95), and ammonia levels ≥90 μg/dL (HR, 0.50; 95% CI, 0.26-0.97) and those without sarcopenia (HR, 0.56; 95% CI, 0.35-0.90).

CONCLUSION

L-carnitine supplementation may improve survival in patients with cirrhosis.

CLINICAL RELEVANCY STATEMENT

Carnitine is a vitamin-like compound that regulates lipid and energy metabolism. Although it has been recognized that L-carnitine supplementation improves hyperammonemia, hepatic encephalopathy, sarcopenia, and frailty in patients with cirrhosis, the relationship between L-carnitine supplementation mortality remains unknown. The results of our study provide the first evidence that L-carnitine supplementation may improve survival in patients with cirrhosis. L-carnitine supplementation may shed a new light on the nutritional intervention for patients with cirrhosis. This article is protected by copyright. All rights reserved.

Ammonia and the Muscle: An Emerging Point of View on Hepatic Encephalopathy

In the last years the link between the presence of muscular alterations and hepatic encephalopathy (HE), both minimal and overt, has been deeply studied. The pathophysiological background supporting the relationship between muscle depletion, and HE is characterized by an imbalance between the capacity of muscle in ammonia metabolism and trafficking and the inability of the liver in removing ammonia through urea synthesis due to liver failure and/or the presence of porto-systemic shunts. This review will focus on the clinical burden, the physio pathological mechanisms understanding the liver muscle axis and principles of management of muscular alterations in cirrhosis.

Metabolic reprogramming during hyperammonemia targets mitochondrial function and postmitotic senescence

Ammonia is a cytotoxic metabolite with pleiotropic molecular and metabolic effects, including senescence induction. During dysregulated ammonia metabolism, which occurs in chronic diseases, skeletal muscle becomes a major organ for nonhepatocyte ammonia uptake. Muscle ammonia disposal occurs in mitochondria via cataplerosis of critical intermediary metabolite α-ketoglutarate, a senescence-ameliorating molecule. Untargeted and mitochondrially targeted data were analyzed by multiomics approaches. These analyses were validated experimentally to dissect the specific mitochondrial oxidative defects and functional consequences, including senescence. Responses to ammonia lowering in myotubes and in hyperammonemic portacaval anastomosis rat muscle were studied. Whole-cell transcriptomics integrated with whole-cell, mitochondrial, and tissue proteomics showed distinct temporal clusters of responses with enrichment of oxidative dysfunction and senescence-related pathways/proteins during hyperammonemia and after ammonia withdrawal. Functional and metabolic studies showed defects in electron transport chain complexes I, III, and IV; loss of supercomplex assembly; decreased ATP synthesis; increased free radical generation with oxidative modification of proteins/lipids; and senescence-associated molecular phenotype–increased β-galactosidase activity and expression of p16^INK, p21, and p53. These perturbations were partially reversed by ammonia lowering. Dysregulated ammonia metabolism caused reversible mitochondrial dysfunction by transcriptional and translational perturbations in multiple pathways with a distinct skeletal muscle senescence-associated molecular phenotype.

Novel methods to identify and measure catabolism

PURPOSE OF REVIEW

Assess current potential catabolism-biomarkers to characterize patients developing prolonged critical illness.

RECENT FINDINGS

A raised urea-to-creatinine ratio (UCR) during critical illness is negatively associated with muscle mass with greater increases in UCR seen patients developing persistent critical illness. Similarly, sarcopenia index (a ratio of creatinine to cystatin-c concentrations) correlates well to muscle mass in intensive care populations. Elevated growth/differentiation factor-15 (GDF-15) has been inconsistently associated with muscle loss. Although GDF-15 was a poor marker of feeding tolerance, it has been associated with worse prognosis in intensive care.

SUMMARY

UCR is an available and clinically applicable biomarker of catabolism. Similarly, sarcopenia index can be used to assess muscle mass and indirectly measure catabolism based on readily available biochemical measurements. The utility of novel biomarkers, such as GDF-15 is less established.

Should nutritional therapy be modified to account for mitochondrial dysfunction in critical illness?

Metabolic dysfunction, and its associated muscle atrophy, remains the most common complication of critical care. At the centre of this is mitochondrial dysfunction, secondary to hypoxia and systemic inflammation. This leads to a bioenergetic crisis, with decreased intramuscular adenosine tri-phosphate content and a reduction in the highly energy dependent process of protein synthesis. Numerous methods have been studied to try and reduce these effects, with only limited success. Trials investigating the use of increased calorie and protein administration have instead found a decrease in relative lean body mass, and a potential increase in morbidity and mortality. Ketone bodies have been proposed as alternative substrates for metabolism in critical illness, with promising results seen in animal models. They are currently being investigated in critical care patients in the Alternative Substrates in the Critically Ill Subjects trial. The evidence to date suggests that individualised feeding regimens may be key in the nutritional approach to critical illness. Consideration of individual patient factors will need to be combined with personalised protein content, total energy load received, and the timings of such feeds. This review covers mitochondrial dysfunction in critical illness, and how it contributes to muscle wasting and the resultant morbidity and mortality and the scientific basis of why current nutritional approaches to date have not been successful in negating this effect. These two factors underpin the need for consideration of alternative nutritional strategies in the critically ill patient. This article is protected by copyright. All rights reserved.

Russian Consensus “Hyperammonemia in Adults” (Version 2021)

Justification Given the large number of reports on the peculiarities of liver lesions during the Sars-Cov-2 infection [1], a team of experts who participated in the 23rd Congress of the Scientific Society of Gastroenterologists of Russia and 15 National Congress of Therapists of November 19, 2020 decided to make additions to the Russian Consensus of “Hyperammonemia in Adults” published early 2020 [2, 3].

An Overview of the Molecular Mechanisms Contributing to Musculoskeletal Disorders in Chronic Liver Disease: Osteoporosis, Sarcopenia, and Osteoporotic Sarcopenia

The prevalence of osteoporosis and sarcopenia is significantly higher in patients with liver disease than in those without liver disease and osteoporosis and sarcopenia negatively influence morbidity and mortality in liver disease, yet these musculoskeletal disorders are frequently overlooked in clinical practice for patients with chronic liver disease. The objective of this review is to provide a comprehensive understanding of the molecular mechanisms of musculoskeletal disorders accompanying the pathogenesis of liver disease. The increased bone resorption through the receptor activator of nuclear factor kappa (RANK)-RANK ligand (RANKL)-osteoprotegerin (OPG) system and upregulation of inflammatory cytokines and decreased bone formation through increased bilirubin and sclerostin and lower insulin-like growth factor-1 are important mechanisms for osteoporosis in patients with liver disease. Sarcopenia is associated with insulin resistance and obesity in non-alcoholic fatty liver disease, whereas hyperammonemia, low amount of branched chain amino acids, and hypogonadism contributes to sarcopenia in liver cirrhosis. The bidirectional crosstalk between muscle and bone through myostatin, irisin, β-aminoisobutyric acid (BAIBA), osteocalcin, as well as the activation of the RANK and the Wnt/β-catenin pathways are associated with osteosarcopenia. The increased understandings for these musculoskeletal disorders would be contributes to the development of effective therapies targeting the pathophysiological mechanism involved.

Malnourished cirrhotic patient: what should we do?

Malnutrition and sarcopenia have a high prevalence in cirrhotic patients. Frailty generally overlaps with malnutrition and sarcopenia in cirrhosis, leading to increased morbidity and mortality. Rapid nutritional screening assessment should be performed in all patients with cirrhosis, and more specific tests for sarcopenia should be performed in those at high risk. The pathogenesis of malnutrition in cirrhosis is complex and multifactorial and it is not just due to reduction in protein and calorie intake. Nutritional management in malnourished patients with cirrhosis should be undertaken by a multidisciplinary team to achieve adequate protein/calorie intake. While the role of branched-chained amino acids remains somewhat contentious in achieving a global benefit of decreasing mortality- and liver-related events, these latter and vitamin supplements, are recommended for those with advanced liver disease. Novel strategies to reverse sarcopenia such as hormone supplementation, long-term ammonia-lowering agents and myostatin antagonists, are currently under investigation. Malnutrition, sarcopenia and frailty are unique, inter-related and multidimensional problems in cirrhosis which require special attention, prompt assessment and appropriate management as they significantly impact morbidity and mortality.

Compound Sarcopenia in Hospitalized Patients with Cirrhosis Worsens Outcomes with Increasing Age

Background: There are limited data on outcomes of older patients with chronic diseases. Skeletal muscle loss of aging (primary sarcopenia) has been extensively studied but the impact of secondary sarcopenia of chronic disease is not as well evaluated. Older patients with chronic diseases have both primary and secondary sarcopenia that we term compound sarcopenia. We evaluated the clinical impact of compound sarcopenia in hospitalized patients with cirrhosis given the increasing number of patients and high prevalence of sarcopenia in these patients. Design: The Nationwide Inpatients Sample (NIS) database (years 2010–2014) was analyzed to study older patients with cirrhosis. Since there is no universal hospital diagnosis code for “muscle loss”, we used a comprehensive array of codes for “muscle loss phenotype” in the international classification of diseases-9 (ICD-9). A randomly selected 2% sample of hospitalized general medical population (GMP) and inpatients with cirrhosis were stratified into 3 age groups based on age-related changes in muscle mass. In-hospital mortality, length of stay (LoS), cost of hospitalization (CoH), comorbidities and discharge disposition were analyzed. Results. Of 517,605 hospitalizations for GMP and 106,835 hospitalizations for treatment of cirrhosis or a cirrhosis-related complication, 207,266 (40.4%) GMP and 29,018 (27.7%) patients with cirrhosis were >65 years old, respectively. Muscle loss phenotype in both GMP and inpatients with cirrhosis 51–65 years old and >65 years old was significantly (p < 0.001 for all) associated with higher mortality, LoS, and CoH compared to those ≤50 years old. Patients >65 years old with cirrhosis and muscle loss phenotype had higher mortality (adjusted OR: 1.06, 95% CI [1.04, 1.08] and CoH (adjusted odds ratio (OR): 1.10, 95% confidence interval (CI) [1.04, 1.08])) when compared to >65 years old GMP with muscle loss phenotype. Muscle loss in younger patients with cirrhosis (≤50 years old) was associated with worse outcomes compared to GMP >65 years old. Non-home discharges (nursing, skilled, long-term care) were more frequent with increasing age to a greater extent in patients with cirrhosis with muscle loss phenotype for each age stratum. Conclusion: Muscle loss is more frequent in older patients with cirrhosis than younger patients with cirrhosis and older GMP. Younger patients with cirrhosis had clinical outcomes similar to those of older GMP, suggesting an accelerated senescence in cirrhosis. Compound sarcopenia in older patients with cirrhosis is associated with higher inpatient mortality, increased LoS, and CoH compared to GMP with sarcopenia.

Treatment on the Spleen Prevents the Progression of Secondary Sarcopenia in Patients With Liver Cirrhosis

Hyperammonemia is an important stimulator of myostatin expression, a negative regulator of muscle growth. After splenectomy or partial splenic artery embolization (PSE), hyperammonemia often improves. Thus, we investigated changes in skeletal muscle index (SMI) in patients following an operation on the spleen and in patients who did not undergo an operation on their spleen. The study was designed retrospectively, in which we analyzed data collected between January 2000 and December 2015. Patients were assigned to the splenectomy/PSE or nontreatment group. Changes in SMI (ΔSMI), ammonia (Δammonia), myostatin (Δmyostatin), irisin (Δirisin), and branched‐chain amino acids/tyrosine molar ratio (ΔBTR) were analyzed between baseline and 5‐year follow‐up both before and after inverse probability of treatment weighting adjustment (IPTW). Patients (102) were enrolled (splenectomy/PSE, n = 45; nontreatment group, n = 57) before IPTW adjustment: ΔSMI (2.6 cm²/m² vs. −8.8 cm²/m², respectively) (P < 0.001), Δmyostatin (−867 vs. −568, respectively) (P < 0.001), Δammonia (−34 and 16, respectively) (P < 0.001), and ΔBTR (0.89 and −0.665, respectively) (P < 0.001). There were no differences between splenectomy and PSE regarding these factors. Moreover, after IPTW adjustment, significant differences were observed between the splenectomy/PSE and nontreatment group for the median ΔBTR (0.89 and −0.64, respectively) (P < 0.001), Δammonia (−33 and 16, respectively) (P < 0.001), Δmyostatin (−894 and 504, respectively) (P < 0.001), and ΔSMI (1.8 cm²/m² and −8.2 cm²/m², respectively) (P < 0.001). Conclusions: Both splenectomy and PSE were associated with the prevention of secondary sarcopenia in patients with LC. Moreover, it can be expected that muscle volume loss is reduced by splenectomy or PSE in patients with hyperammonemia.

Non-Lactulose Medication Therapies for the Management of Hepatic Encephalopathy: A Literature Review

OBJECTIVE

The most appropriate medication regimen to mitigate the consequences hepatic encephalopathy remains inconclusive. This review seeks to serve as a reference for clinicians to help guide therapy decisions with regard to hepatic encephalopathy.

METHODS

A comprehensive literature review between August 2018 and April 2019 was accomplished with the assistance of a medical librarian. Sources of literature review include PubMed, MEDLINE, SCOPUS, ProQuest Central, CINAHL, and ProQuest Dissertations. The authors selected randomized clinical and double-blind cross-over trials evaluating probiotics, zinc, polyethylene glycol, rifaximin, and flumazenil. Sixteen clinical trials are discussed in this review. Pertinent safety, efficacy, and statistical and clinical outcomes are summarized by the authors.

CONCLUSIONS

The most appropriate regimen to mitigate the consequences of hepatic encephalopathy remains elusive; however, the agents discussed within this review offer alternative options for patients unresponsive to or intolerant of traditional lactulose therapy. This review seeks to serve as a repository for relevant clinical trials, and as a reference for clinicians to help guide therapy decisions.

Important Unresolved Questions in the Management of Hepatic Encephalopathy: An ISHEN Consensus

Management of hepatic encephalopathy (HE) remains challenging from a medical and psychosocial perspective. Members of the International Society for Hepatic Encephalopathy and Nitrogen Metabolism recognized 5 key unresolved questions in HE management focused on (i) driving, (ii) ammonia levels in clinical practice, (iii) testing strategies for covert or minimal HE, (iv) therapeutic options, and (v) nutrition and patient-reported outcomes. The consensus document addresses these topical issues with a succinct review of the literature and statements that critically evaluate the current science and practice, laying the groundwork for future investigations.

Exercise and physical activity in cirrhosis: opportunities or perils

Reduced exercise capacity and impaired physical performance are observed in nearly all patients with liver cirrhosis. Physical activity and exercise are physiological anabolic stimuli that can reverse dysregulated protein homeostasis or proteostasis and potentially increase muscle mass and contractile function in healthy subjects. Cirrhosis is a state of anabolic resistance, and unlike the beneficial responses to exercise reported in physiological states, there are few systematic studies evaluating the response to exercise in cirrhosis. Hyperammonemia is a mediator of the liver-muscle axis with net skeletal muscle ammonia uptake in cirrhosis causing signaling perturbations, mitochondrial dysfunction with decreased ATP content, modifications of contractile proteins, and impaired ribosomal function, all of which contribute to anabolic resistance in cirrhosis and have the potential to impair the beneficial responses to exercise. English language-publications in peer-reviewed journals that specifically evaluated the impact of exercise in cirrhosis were reviewed. Most studies evaluated responses to endurance exercise, and readouts included peak or maximum oxygen utilization, grip strength, and functional capacity. Endurance exercise for up to 12 wk is clinically tolerated in well-compensated cirrhosis. Data on the safety of resistance exercise are conflicting. Nutritional supplements enhance the benefits of exercise in healthy subjects but have not been evaluated in cirrhosis. Whether the beneficial physiological responses with endurance exercise and increase in muscle mass with resistance exercise that occur in healthy subjects also occur in cirrhotics is not known. Specific organ-system responses, changes in body composition, or improved long-term clinical outcomes with exercise in cirrhosis need evaluation.

[Ornitine-dependent mechanisms of muscle fatigue correction and recovery from physical activity]

The article analyzes the literature data characterizing modern concepts of the mechanisms of muscle fatigue and metabolic features of recovery processes after exhausting loads. The significance of transient hyperammonium in the formation of the developed complex of fatigue manifestations in the central and peripheral links of motor units, its pathogenetic links with oxygen debt, lactacidosis, violation of ATP resynthesis, deficiency of energy-supplying substrates in working skeletal muscles, damage to muscle fibre structures, and dysfunction of various parts of the CNS is shown. The necessity of correction of hyperammoniemia associated with physical activity has been confirmed to reduce the speed of formation and expression of fatigue feeling, to reduce the risks of development of fatigue and overtraining states in sportsmen and to ensure effective course of recovery processes after exhausting physical activity. It was revealed that ornithine-containing preparations can be used for correction of post-load hyperammonium and acceleration of recovery processes. The data characterizing the high efficiency of L-ornitine-L-aspartate in sports medicine practice are presented.

Review article: malnutrition/sarcopenia and frailty in patients with cirrhosis

BACKGROUND

Malnutrition/sarcopenia and frailty are common in patients with cirrhosis and are associated with poor outcomes.

AIM

To provide an overview of data on the importance, assessment and management of malnutrition/sarcopenia and frailty in cirrhosis.

METHODS

A literature search was conducted in PubMed and other sources, using the search terms "sarcopenia," "muscle," "malnutrition," "cirrhosis," "liver" and "frailty" from inception to April 2019, to identify the relevant studies and international guidelines.

RESULTS

The prevalence of malnutrition/sarcopenia in cirrhosis is 23%-60%. Frailty generally overlaps with malnutrition/sarcopenia in cirrhosis, leading to increased morbidity and mortality. Rapid nutritional screening assessment should be performed in all patients with cirrhosis, and more specific tests for sarcopenia should be performed in those at high risk. The pathogenesis of malnutrition/sarcopenia in cirrhosis is complex/multifactorial and not just reduction in protein/calorie intake. Hyperammonemia appears to be the main driver of sarcopenia in cirrhosis through several molecular signalling pathways. Nutritional management in malnourished patients with cirrhosis should be undertaken by a multidisciplinary team to achieve adequate protein/calorie intake. While the role of branched-chained amino acids remains somewhat contentious in achieving a global benefit of decreasing mortality- and liver-related events, they, and vitamin supplements, are recommended for those with advanced liver disease. Novel strategies to reverse sarcopenia such as hormone supplementation, long-term ammonia-lowering agents and myostatin antagonists, are currently under investigation.

CONCLUSIONS

Malnutrition/sarcopenia and frailty are unique, inter-related and multi-dimensional problems in cirrhosis which require special attention, prompt assessment and appropriate management as they significantly impact morbidity and mortality.

Reduced handgrip strength is predictive of poor survival among patients with liver cirrhosis: A sex-stratified analysis

AIM

Handgrip strength (HGS) is a marker of sarcopenia and has been used to stratify an individual's risk of death. We aimed to assess the prognostic significance of HGS in patients with liver cirrhosis.

METHODS

In this retrospective study, we collated data of 563 consecutive patients admitted to our hospital with cirrhosis (375 men). A dynamometer was used to measure HGS. Body composition (including skeletal muscle and adipose tissue volumes) was estimated using computed tomography. Predictors of mortality were identified using sex-stratified multivariate analyses.

RESULTS

After adjustments for age, cirrhosis etiology, Child-Pugh score, and other confounding variables, HGS, but not body composition, was independently associated with mortality in male patients (hazard ratio [HR], 0.96; 95% confidence interval [CI], 0.94-0.99; P < 0.01) and female patients (HR, 0.91; 95% CI, 0.84-0.99; P = 0.02). Men with low HGS (<30 kg) had a higher risk of mortality (HR, 2.09; 95% CI, 1.39-3.17; P < 0.001), as did women with low (<15 kg) HGS (HR, 2.14; 95% CI, 1.16-4.01; P = 0.02). We could stratify the sex-specific risk of mortality in cirrhotic patients using HGS, regardless of coexistent hepatocellular carcinoma and the Child-Pugh class.

CONCLUSIONS

Reduced HGS, rather than skeletal muscle and adipose tissue volumes, is associated with an increased risk of mortality in patients of both sexes with liver cirrhosis. Measurement of HGS is a simple, cost-effective, and appropriate bedside assessment for the prediction of survival in patients with cirrhosis.

Impaired Ribosomal Biogenesis by Noncanonical Degradation of β-Catenin during Hyperammonemia

Increased ribosomal biogenesis occurs during tissue hypertrophy, but whether ribosomal biogenesis is impaired during atrophy is not known. We show that hyperammonemia, which occurs in diverse chronic disorders, impairs protein synthesis as a result of decreased ribosomal content and translational capacity. Transcriptome analyses, real-time PCR, and immunoblotting showed consistent reductions in the expression of the large and small ribosomal protein subunits (RPL and RPS, respectively) in hyperammonemic murine skeletal myotubes, HEK cells, and skeletal muscle from hyperammonemic rats and human cirrhotics. Decreased ribosomal content was accompanied by decreased expression of cMYC, a positive regulator of ribosomal biogenesis, as well as reduced expression and activity of β-catenin, a transcriptional activator of cMYC. However, unlike the canonical regulation of β-catenin via glycogen synthase kinase 3β (GSK3β)-dependent degradation, GSK3β expression and phosphorylation were unaltered during hyperammonemia, and depletion of GSK3β did not prevent ammonia-induced degradation of β-catenin. Overexpression of GSK3β-resistant variants, genetic depletion of IκB kinase β (IKKβ) (activated during hyperammonemia), protein interactions, and in vitro kinase assays showed that IKKβ phosphorylated β-catenin directly. Overexpressing β-catenin restored hyperammonemia-induced perturbations in signaling responses that regulate ribosomal biogenesis. Our data show that decreased protein synthesis during hyperammonemia is mediated via a novel GSK3β-independent, IKKβ-dependent impairment of the β-catenin-cMYC axis.

Effect of untreated pharmaceutical plant effluent on cardiac Na+-K+- ATPase and Ca2+-Mg2+-ATPase activities in mice (Mus Musculus)

Cardiovascular diseases are major causes of non-communicable diseases (NCDs)-related throughout the world. Water pollution has been linked with the high global NCD burden but no report exists on the cardiotoxicity of untreated or poorly treated pharmaceutical effluent, despite its indiscriminate discharge into the aquatic environment in Nigeria, as in many other locations of the world. Thus, this study investigated the cardiotoxic effect of oral exposure to pharmaceutical effluent in mice. Thirty (30) male mice (Mus musculus) were randomly divided into 6 groups. Group A (control) received 0.2 ml distilled water, while groups B-F were treated with 0.2 ml 2.5%, 5.0%, 10.0%, 20.0% and 40% concentrations (v/v, effluent/distilled water) of the effluent respectively, for 28 days. Significant reductions (p<0.05) in heart weight and cardiac weight index were observed in the groups treated with 5%, 10%, 20% and 40% concentrations of the effluent, without significant change in body weight. Similarly, 28 day administration of the effluent showed significant decrease in cardiac Na+-K+-ATPase activity (p<0.05) at concentrations 10% and above, in a concentration dependent manner. However, there was insignificant decrease in cardiac Ca2+-Mg2+-ATPase activity of the exposed mice, when compared with the control group. This study provides novel information on the cardiotoxic effects of oral exposure to untreated pharmaceutical effluent, showing reduced Na+-K+-ATPase activity and decreseased myocardial atrophy. Therefore, drinking water contaminated with pharmaceutical effluent may promote the incidence of cardiovascular diseases. Further studies on the exact mechanistic routes of the induced cardiotoxicity are recommended.

Sarcopenia: Ammonia metabolism and hepatic encephalopathy

Sarcopenia (loss of muscle mass and/or strength) frequently complicates liver cirrhosis and adversely affects the quality of life; cirrhosis related liver decompensation and significantly decreases wait-list and post-liver transplantation survival. The main therapeutic strategies to improve or reverse sarcopenia include dietary interventions (supplemental calorie and protein intake), increased physical activity (supervised resistance and endurance exercises), hormonal therapy (testosterone), and ammonia lowering agents (L-ornithine L-aspartate, branch chain amino acids) as well as mechanistic approaches that target underlying molecular and metabolic abnormalities. Besides other factors, hyperammonemia has recently gained attention and increase sarcopenia by various mechanisms including increased expression of myostatin, increased phosphorylation of eukaryotic initiation factor 2a, cataplerosis of α ketoglutarate, mitochondrial dysfunction, increased reactive oxygen species that decrease protein synthesis and increased autophagy-mediated proteolysis. Sarcopenia contributes to frailty and increases the risk of minimal and overt hepatic encephalopathy.

Progressive resistance training prevents loss of muscle mass and strength in bile duct-ligated rats

BACKGROUND

Loss of muscle mass and strength is common in cirrhosis and increases the risk of hyperammonaemia and hepatic encephalopathy. Resistance training optimizes muscle mass and strength in several chronic diseases. However, the beneficial effects of resistance training in cirrhosis remain to be investigated. Bile duct-ligated (BDL) rats develop chronic liver disease, hyperammonaemia, reduced muscle mass and strength. Our aim was to test the effects of resistance training on muscle mass, function and ammonia metabolism in BDL-rats.

METHODS

A group of BDL-rats underwent a progressive resistance training programme and a group of non-exercise BDL-rats served as controls. Resistance training comprised of ladder climbing with a progressive increase in carrying weights attached to the tail. Training was performed 5 days a week during 4 weeks. Muscle strength and body composition were assessed using grip strength and EchoMRI. Weight and circumference of the gastrocnemius muscle (normalized to bodyweight), plasma ammonia and glutamine synthetase protein expression and activity were assessed.

RESULTS

BDL + exercise rats had significantly larger gastrocnemius circumference compared to non-exercise BDL-rats: ratio 0.082 vs 0.075 (P < 0.05). Gastrocnemius muscle weight was higher in exercisers than controls: 0.006 vs 0.005 (P < 0.05). A tendency towards a lower plasma ammonia in the exercise group compared to controls was observed (P = 0.10). There were no differences in lean body mass, GS protein expression and activity between the groups.

CONCLUSION

Resistance training in rats with chronic liver disease beneficially effects muscle mass and strength. The effects were followed by non-significant reduction in blood ammonia; however, a tendency was observed.

Ethanol sensitizes skeletal muscle to ammonia-induced molecular perturbations

Ethanol causes dysregulated muscle protein homeostasis while simultaneously causing hepatocyte injury. Because hepatocytes are the primary site for physiological disposal of ammonia, a cytotoxic cellular metabolite generated during a number of metabolic processes, we determined whether hyperammonemia aggravates ethanol-induced muscle loss. Differentiated murine C2C12 myotubes, skeletal muscle from pair-fed or ethanol-treated mice, and human patients with alcoholic cirrhosis and healthy controls were used to quantify protein synthesis, mammalian target of rapamycin complex 1 (mTORC1) signaling, and autophagy markers. Alcohol-metabolizing enzyme expression and activity in mouse muscle and myotubes and ureagenesis in hepatocytes were quantified. Expression and regulation of the ammonia transporters, RhBG and RhCG, were quantified by real-time PCR, immunoblots, reporter assays, biotin-tagged promoter pulldown with proteomics, and loss-of-function studies. Alcohol and aldehyde dehydrogenases were expressed and active in myotubes. Ethanol exposure impaired hepatocyte ureagenesis, induced muscle RhBG expression, and elevated muscle ammonia concentrations. Simultaneous ethanol and ammonia treatment impaired protein synthesis and mTORC1 signaling and increased autophagy with a consequent decreased myotube diameter to a greater extent than either treatment alone. Ethanol treatment and withdrawal followed by ammonia exposure resulted in greater impairment in muscle signaling and protein synthesis than ammonia treatment in ethanol-naive myotubes. Of the three transcription factors that were bound to the RhBG promoter in response to ethanol and ammonia, DR1/NC2 indirectly regulated transcription of RhBG during ethanol and ammonia treatment. Direct effects of ethanol were synergistic with increased ammonia uptake in causing dysregulated skeletal muscle proteostasis and signaling perturbations with a more severe sarcopenic phenotype.

EASL Clinical Practice Guidelines on nutrition in chronic liver disease

A frequent complication in liver cirrhosis is malnutrition, which is associated with the progression of liver failure, and with a higher rate of complications including infections, hepatic encephalopathy and ascites. In recent years, the rising prevalence of obesity has led to an increase in the number of cirrhosis cases related to non-alcoholic steatohepatitis. Malnutrition, obesity and sarcopenic obesity may worsen the prognosis of patients with liver cirrhosis and lower their survival. Nutritional monitoring and intervention is therefore crucial in chronic liver disease. These Clinical Practice Guidelines review the present knowledge in the field of nutrition in chronic liver disease and promote further research on this topic. Screening, assessment and principles of nutritional management are examined, with recommendations provided in specific settings such as hepatic encephalopathy, cirrhotic patients with bone disease, patients undergoing liver surgery or transplantation and critically ill cirrhotic patients.

Hyperammonemia and proteostasis in cirrhosis

PURPOSE OF REVIEW

Skeletal muscle loss or sarcopenia is a frequent complication of cirrhosis that adversely affects clinical outcomes. As skeletal muscle is the largest store of proteins in the body, proteostasis or protein homeostasis is required for maintenance of muscle mass. This review will focus on disordered skeletal muscle proteostasis in liver disease.

RECENT FINDINGS

Increased skeletal muscle uptake of ammonia initiates responses that result in disordered proteostasis including impaired protein synthesis and increased autophagy. The cellular response to the stress of hyperammonemia (hyperammonemic stress response, HASR) involves the coordinated action of diverse signaling pathways targeting the molecular mechanisms of regulation of protein synthesis. Transcriptional upregulation of myostatin, a TGFβ superfamily member, results in impaired mTORC1 signaling. Phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α) also relates to decreased global protein synthesis rates and mTORC1 signaling. Ammonia also causes mitochondrial and bioenergetic dysfunction because of cataplerosis of α-ketoglutarate. Lowering ammonia, targeting components of HASR and regulating cellular amino acid levels can potentially restore proteostasis.

SUMMARY

Signaling via myostatin and eIF2α phosphorylation causes decreases in protein synthesis and mTORC1 activity with a parallel mitochondrial dysfunction and increased autophagy contributing to proteostasis perturbations during skeletal muscle hyperammonemia of liver disease.

Sarcopenia in Liver Disease: Current Evidence and Issues to Be sResolved

Sarcopenia is a common clinical symptom in aging and patients with wasting diseases, characterized by a decreased skeletal muscle mass. As a consequence of lifestyle change, the nonalcoholic fatty liver disease (NAFLD) presents a rising trend. In the past three decades, increasing evidence has proved that sarcopenia is related to NAFLD. In this chapter, we will summarize the emerging evidence of the predictive role of sarcopenia in NAFLD and review the diagnosis value, feasible mechanism, and therapy strategies of sarcopenia in NAFLD. Sarcopenia is a potential risk factor for NAFLD, and targeting sarcopenia can benefit NAFLD to some extent.

Nutrition and Muscle in Cirrhosis

As the cirrhosis progresses, development of complication like ascites, hepatic encephalopathy, variceal bleeding, kidney dysfunction, and hepatocellular carcinoma signify increasing risk of short term mortality. Malnutrition and muscle wasting (sarcopenia) is yet other complications that negatively impact survival, quality of life, and response to stressors, such as infection and surgery in patients with cirrhosis. Conventionally, these are not routinely looked for, because nutritional assessment can be a difficult especially if there is associated fluid retention and/or obesity. Patients with cirrhosis may have a combination of loss of skeletal muscle and gain of adipose tissue, culminating in the condition of "sarcopenic obesity." Sarcopenia in cirrhotic patients has been associated with increased mortality, sepsis complications, hyperammonemia, overt hepatic encephalopathy, and increased length of stay after liver transplantation. Assessment of muscles with cross-sectional imaging studies has become an attractive index of nutritional status evaluation in cirrhosis, as sarcopenia, the major component of malnutrition, is primarily responsible for the adverse clinical consequences seen in patients with liver disease. Cirrhosis is a state of accelerated starvation, with increased gluconeogenesis that requires amino acid diversion from other metabolic functions. Protein homeostasis is disturbed in cirrhosis due to several factors such as hyperammonemia, hormonal, and cytokine abnormalities, physical inactivity and direct effects of ethanol and its metabolites. New approaches to manage sarcopenia are being evolved. Branched chain amino acid supplementation, Myostatin inhibitors, and mitochondrial protective agents are currently in various stages of evaluation in preclinical studies to prevent and reverse sarcopenia, in cirrhosis.

In vitro contraction protects against palmitate-induced insulin resistance in C2C12 myotubes

We are interested in understanding mechanisms that govern the protective role of exercise against lipid-induced insulin resistance, a key driver of type 2 diabetes. In this context, cell culture models provide a level of abstraction that aid in our understanding of cellular physiology. Here we describe the development of an in vitro myotube contraction system that provides this protective effect, and which we have harnessed to investigate lipid-induced insulin resistance. C2C12 myocytes were differentiated into contractile myotubes. A custom manufactured platinum electrode system and pulse stimulator, with polarity switching, provided an electrical pulse stimulus (EPS) (1 Hz, 6-ms pulse width, 1.5 V/mm, 16 h). Contractility was assessed by optical flow flied spot noise mapping and inhibited by application of ammonium acetate. Following EPS, myotubes were challenged with 0.5 mM palmitate for 4 h. Cells were then treated with or without insulin for glucose uptake (30 min), secondary insulin signaling activation (10 min), and phosphoinositide 3-kinase-α (PI3Kα) activity (5 min). Prolonged EPS increased non-insulin-stimulated glucose uptake (83%, P = 0.002), Akt (Thr308) phosphorylation (P = 0.005), and insulin receptor substrate-1 (IRS-1)-associated PI3Kα activity (P = 0.048). Palmitate reduced insulin-specific action on glucose uptake (-49%, P < 0.001) and inhibited insulin-stimulated Akt phosphorylation (P = 0.049) and whole cell PI3Kα activity (P = 0.009). The inhibitory effects of palmitate were completely absent with EPS pretreatment at the levels of glucose uptake, insulin responsiveness, Akt phosphorylation, and whole cell PI3Kα activity. This model suggests that muscle contraction alone is a sufficient stimulus to protect against lipid-induced insulin resistance as evidenced by changes in the proximal canonical insulin-signaling pathway.

Sarcopenia in Alcoholic Liver Disease: Clinical and Molecular Advances

Despite advances in treatment of alcohol use disorders that focus on increasing abstinence and reducing recidivism, alcoholic liver disease (ALD) is projected to be the major cause of cirrhosis and its complications. Malnutrition is recognized as the most frequent complication in ALD, and despite the high clinical significance, there are no effective therapies to reverse malnutrition in ALD. Malnutrition is a relatively imprecise term, and sarcopenia or skeletal muscle loss, the major component of malnutrition, is primarily responsible for the adverse clinical consequences in patients with liver disease. It is, therefore, critical to define the specific abnormality (sarcopenia) rather than malnutrition in ALD, so that therapies targeting sarcopenia can be developed. Skeletal muscle mass is maintained by a balance between protein synthesis and proteolysis. Both direct effects of ethanol (EtOH) and its metabolites on the skeletal muscle and the consequences of liver disease result in disturbed proteostasis (protein homeostasis) and consequent sarcopenia. Once cirrhosis develops in patients with ALD, abstinence is unlikely to be effective in completely reversing sarcopenia, as other contributors including hyperammonemia, hormonal, and cytokine abnormalities aggravate sarcopenia and maintain a state of anabolic resistance initiated by EtOH. Cirrhosis is also a state of accelerated starvation, with increased gluconeogenesis that requires amino acid diversion from signaling and substrate functions. Novel therapeutic options are being recognized that are likely to supplant the current "deficiency replacement" approach and instead focus on specific molecular perturbations, given the increasing availability of small molecules that can target specific signaling components. Myostatin antagonists, leucine supplementation, and mitochondrial protective agents are currently in various stages of evaluation in preclinical studies to prevent and reverse sarcopenia, in cirrhosis in general, and ALD, specifically. Translation of these data to human studies and clinical application requires priority for allocation of resources.

Ammonia lowering reverses sarcopenia of cirrhosis by restoring skeletal muscle proteostasis

Sarcopenia or skeletal muscle loss is a frequent, potentially reversible complication in cirrhosis that adversely affects clinical outcomes. Hyperammonemia is a consistent abnormality in cirrhosis that results in impaired skeletal muscle protein synthesis and breakdown (proteostasis). Despite the availability of effective ammonia-lowering therapies, whether lowering ammonia restores proteostasis and increases muscle mass is unknown. Myotube diameter, protein synthesis, and molecular responses in C2C12 murine myotubes to withdrawal of ammonium acetate following 24-hour exposure to 10 mM ammonium acetate were complemented by in vivo studies in the hyperammonemic portacaval anastomosis rat and sham-operated, pair-fed Sprague-Dawley rats treated with ammonia-lowering therapy by l-ornithine l-aspartate and rifaximin orally for 4 weeks. We observed reduced myotube diameter, impaired protein synthesis, and increased autophagy flux in response to hyperammonemia, which were partially reversed following 24-hour and 48-hour withdrawal of ammonium acetate. Consistently, 4 weeks of ammonia-lowering therapy resulted in significant lowering of blood and skeletal muscle ammonia, increase in lean body mass, improved grip strength, higher skeletal muscle mass and diameter, and an increase in type 2 fibers in treated compared to untreated portacaval anastomosis rats. The increased skeletal muscle myostatin expression, reduced mammalian target of rapamycin complex 1 function, and hyperammonemic stress response including autophagy markers normally found in portacaval anastomosis rats were reversed by treatment with ammonia-lowering therapy. Despite significant improvement, molecular and functional readouts were not completely reversed by ammonia-lowering measures.

CONCLUSION

Ammonia-lowering therapy results in improvement in skeletal muscle phenotype and function and molecular perturbations of hyperammonemia; these preclinical studies complement previous studies on ammonia-induced skeletal muscle loss and lay the foundation for prolonged ammonia-lowering therapy to reverse sarcopenia of cirrhosis. (Hepatology 2017;65:2045-2058).

Ammonia promotes endothelial cell survival via the heme oxygenase-1-mediated release of carbon monoxide

Although endothelial cells produce substantial quantities of ammonia during cell metabolism, the physiologic role of this gas in these cells is not known. In this study, we investigated if ammonia regulates the expression of heme oxygenase-1 (HO-1), and if this enzyme influences the biological actions of ammonia on endothelial cells. Exogenously administered ammonia, given as ammonium chloride or ammonium hydroxide, or endogenously generated ammonia stimulated HO-1 protein expression in cultured human and murine endothelial cells. Dietary supplementation of ammonia also induced HO-1 protein expression in murine arteries. The increase in HO-1 protein by ammonia in endothelial cells was first detected 4h after ammonia exposure and was associated with the induction of HO-1 mRNA, enhanced production of reactive oxygen species (ROS), and increased expression and activity of NF-E2-related factor-2 (Nrf2). Ammonia also activated the HO-1 promoter and this was blocked by mutating the antioxidant responsive element or by overexpressing dominant-negative Nrf2. The induction of HO-1 expression by ammonia was dependent on ROS formation and prevented by N-acetylcysteine or rotenone. Finally, prior treatment of endothelial cells with ammonia inhibited tumor necrosis factor-α-stimulated cell death. However, silencing HO-1 expression abrogated the protective action of ammonia and this was reversed by the administration of carbon monoxide but not bilirubin or iron. In conclusion, this study demonstrates that ammonia stimulates the expression of HO-1 in endothelial cells via the ROS-Nrf2 pathway, and that the induction of HO-1 contributes to the cytoprotective action of ammonia by generating carbon monoxide. Moreover, it identifies ammonia as a potentially important signaling gas in the vasculature that promotes endothelial cell survival.

Sarcopenia from mechanism to diagnosis and treatment in liver disease

Sarcopenia or loss of skeletal muscle mass is the major component of malnutrition and is a frequent complication in cirrhosis that adversely affects clinical outcomes. These include survival, quality of life, development of other complications and post liver transplantation survival. Radiological image analysis is currently utilized to diagnose sarcopenia in cirrhosis. Nutrient supplementation and physical activity are used to counter sarcopenia but have not been consistently effective because the underlying molecular and metabolic abnormalities persist or are not influenced by these treatments. Even though alterations in food intake, hypermetabolism, alterations in amino acid profiles, endotoxemia, accelerated starvation and decreased mobility may all contribute to sarcopenia in cirrhosis, hyperammonemia has recently gained attention as a possible mediator of the liver-muscle axis. Increased muscle ammonia causes: cataplerosis of α-ketoglutarate, increased transport of leucine in exchange for glutamine, impaired signaling by leucine, increased expression of myostatin (a transforming growth factor beta superfamily member) and an increased phosphorylation of eukaryotic initiation factor 2α. In addition, mitochondrial dysfunction, increased reactive oxygen species that decrease protein synthesis and increased autophagy mediated proteolysis, also play a role. These molecular and metabolic alterations may contribute to the anabolic resistance and inadequate response to nutrient supplementation in cirrhosis. Central and skeletal muscle fatigue contributes to impaired exercise capacity and responses. Use of proteins with low ammoniagenic potential, leucine enriched amino acid supplementation, long-term ammonia lowering strategies and a combination of resistance and endurance exercise to increase muscle mass and function may target the molecular abnormalities in the muscle. Strategies targeting endotoxemia and the gut microbiome need further evaluation.

Metabolic adaptation of skeletal muscle to hyperammonemia drives the beneficial effects of l-leucine in cirrhosis

BACKGROUND & AIMS

Increased skeletal muscle ammonia uptake with loss of muscle mass adversely affects clinical outcomes in cirrhosis. Hyperammonemia causes reduced protein synthesis and sarcopenia but the cellular responses to impaired proteostasis and molecular mechanism of l-leucine induced adaptation to ammonia induced stress were determined.

METHODS

Response to activation of amino acid deficiency sensor, GCN2, in the skeletal muscle from cirrhotic patients and the portacaval anastomosis (PCA) rat were quantified. During hyperammonemia and l-leucine supplementation, protein synthesis, phosphorylation of eIF2α, mTORC1 signaling, l-leucine transport and response to l-leucine supplementation were quantified. Adaptation to cellular stress via ATF4 and its target GADD34 were also determined.

RESULTS

Activation of the eIF2α kinase GCN2 and impaired mTORC1 signaling were observed in skeletal muscle from cirrhotic patients and PCA rats. Ammonia activated GCN2 mediated eIF2α phosphorylation (eIF2α-P) and impaired mTORC1 signaling that inhibit protein synthesis in myotubes and MEFs. Adaptation to ammonia induced stress did not involve translational reprogramming by activation transcription factor 4 (ATF4) dependent induction of the eIF2α-P phosphatase subunit GADD34. Instead, ammonia increased expression of the leucine/glutamine exchanger SLC7A5, l-leucine uptake and intracellular l-leucine levels, the latter not being sufficient to rescue the inhibition of protein synthesis, due to potentially enhanced mitochondrial sequestration of l-leucine. l-leucine supplementation rescued protein synthesis inhibition caused by hyperammonemia.

CONCLUSIONS

Response to hyperammonemia is reminiscent of the cellular response to amino acid starvation, but lacks the adaptive ATF4 dependent integrated stress response (ISR). Instead, hyperammonemia-induced l-leucine uptake was an adaptive response to the GCN2-mediated decreased protein synthesis.

LAY SUMMARY

Sarcopenia or skeletal muscle loss is the most frequent complication in cirrhosis but there are no treatments because the cause(s) of muscle loss in liver disease are not known. Results from laboratory experiments in animals and muscle cells were validated in human patients with cirrhosis to show that ammonia plays a key role in causing muscle loss in patients with cirrhosis. We identified a novel stress response to ammonia in the muscle that decreases muscle protein content that can be reversed by supplementation with the amino acid l-leucine.