Isoleucine infusion during "simulated" upper gastrointestinal bleeding improves liver and muscle protein synthesis in cirrhotic patients

Associations of Serum Isoleucine with Mild Cognitive Impairment and Alzheimer's Disease

BACKGROUND

Advances in blood biomarker discovery have enabled the improved diagnosis and prognosis of Alzheimer's disease (AD). Most branched-chain amino acids, except isoleucine (Ile), are correlated with both mild cognitive impairment (MCI) and AD. Therefore, this study investigated the association between serum Ile levels and MCI/AD.

METHODS

This study stratified 700 participants from the Alzheimer's Disease Neuroimaging Initiative database into four diagnostic groups: cognitively normal, stable MCI, progressive MCI, and AD. Analysis of covariance and chi-square analyses were used to test the demographic data. Receiver operating curve analyses were used to calculate the diagnostic accuracy of different biomarkers and were compared by MedCalc 20. Additionally, Cox proportional hazards models were used to measure the ability of serum Ile levels to predict disease conversion. Finally, a linear mixed-effects model was used to evaluate the associations between serum Ile levels and cognition, brain structure, and metabolism.

RESULTS

Serum Ile concentration was decreased in AD and demonstrated significant diagnostic efficacy. The combination of serum Ile and cerebrospinal fluid (CSF) phosphorylated tau (P-tau) improved the diagnostic accuracy in AD compared to total tau (T-tau) alone. Serum Ile levels significantly predicted the conversion from MCI to AD (cutoff value of 78.3 μM). Finally, the results of this study also revealed a correlation between serum Ile levels and the Alzheimer's Disease Assessment Scale cognitive subscale Q4.

CONCLUSIONS

Serum Ile may be a potential biomarker of AD. Ile had independent diagnostic efficacy and significantly improved the diagnostic accuracy of CSF P-tau in AD. MCI patients with a lower serum Ile level had a higher risk of progression to AD and a worse cognition assessment.

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.

Metabolomic Investigation of Ultraviolet Ray-Inactivated White Spot Syndrome Virus-Induced Trained Immunity in Marsupenaeus japonicus

Trained immunity is driven by metabolism and epigenetics in innate immune cells in mammals. The phenomenon of trained immunity has been identified in invertebrates, including shrimp, but the underlying mechanisms remain unclear. To elucidate mechanisms of trained immunity in shrimp, the metabolomic changes in hemolymph of Marsupenaeus japonicus trained by the UV-inactivated white spot syndrome virus (UV-WSSV) were analyzed using tandem gas chromatography-mass/mass spectrometry. The metabolomic profiles of shrimp trained with UV-WSSV followed WSSV infection showed significant differences comparison with the control groups, PBS injection followed WSSV infection. 16 differential metabolites in total of 154 metabolites were identified, including D-fructose-6-phosphate, D-glucose-6-phosphate, and D-fructose-6-phosphate, and metabolic pathways, glycolysis, pentose phosphate pathway, and AMPK signaling pathway were enriched in the UV-WSSV trained groups. Further study found that histone monomethylation and trimethylation at H3K4 (H3K4me1 and H3K4me3) were involved in the trained immunity. Our data suggest that the UV-WSSV induced trained immunity leads to metabolism reprogramming in the shrimp and provide insights for WSSV control in shrimp aquaculture.

Mass spectrometry imaging of L-[ring-13C6]-labeled phenylalanine and tyrosine kinetics in non-small cell lung carcinoma

BACKGROUND

Metabolic reprogramming is a common phenomenon in tumorigenesis and tumor progression. Amino acids are important mediators in cancer metabolism, and their kinetics in tumor tissue are far from being understood completely. Mass spectrometry imaging is capable to spatiotemporally trace important endogenous metabolites in biological tissue specimens. In this research, we studied L-[ring-¹³C₆]-labeled phenylalanine and tyrosine kinetics in a human non-small cell lung carcinoma (NSCLC) xenografted mouse model using matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry imaging (MALDI-FTICR-MSI).

METHODS

We investigated the L-[ring-¹³C₆]-Phenylalanine (¹³C₆-Phe) and L-[ring-¹³C₆]-Tyrosine (¹³C₆-Tyr) kinetics at 10 min (n = 4), 30 min (n = 3), and 60 min (n = 4) after tracer injection and sham-treated group (n = 3) at 10 min in mouse-xenograft lung tumor tissues by MALDI-FTICR-MSI.

RESULTS

The dynamic changes in the spatial distributions of 19 out of 20 standard amino acids are observed in the tumor tissue. The highest abundance of ¹³C₆-Phe was detected in tumor tissue at 10 min after tracer injection and decreased progressively over time. The overall enrichment of ¹³C₆-Tyr showed a delayed temporal trend compared to ¹³C₆-Phe in tumor caused by the Phe-to-Tyr conversion process. Specifically, ¹³C₆-Phe and ¹³C₆-Tyr showed higher abundances in viable tumor regions compared to non-viable regions.

CONCLUSIONS

We demonstrated the spatiotemporal intra-tumoral distribution of the essential aromatic amino acid ¹³C₆-Phe and its de-novo synthesized metabolite ¹³C₆-Tyr by MALDI-FTICR-MSI. Our results explore for the first time local phenylalanine metabolism in the context of cancer tissue morphology. This opens a new way to understand amino acid metabolism within the tumor and its microenvironment.

Applications of stable isotopes in MALDI imaging: current approaches and an eye on the future

Matrix-assisted laser desorption/ionisation-imaging mass spectrometry (MALDI-IMS) is now an established imaging modality with particular utility in the study of biological, biomedical and pathological processes. In the first instance, the use of stable isotopically labelled (SIL) compounds in MALDI-IMS has addressed technical barriers to increase the accuracy and versatility of this technique. This has undoubtedly enhanced our ability to interpret the two-dimensional ion intensity distributions produced from biological tissue sections. Furthermore, studies using delivery of SIL compounds to live tissues have begun to decipher cell, tissue and inter-tissue metabolism while maintaining spatial resolution. Here, we review both the technical and biological applications of SIL compounds in MALDI-IMS, before using the uptake and metabolism of glucose in bovine ocular lens tissue to illustrate the current limitations of SIL compound use in MALDI-IMS. Finally, we highlight recent instrumentation advances that may further enhance our ability to use SIL compounds in MALDI-IMS to understand biological and pathological processes. Graphical Abstract.

Isoleucine increases muscle mass through promoting myogenesis and intramyocellular fat deposition

Isoleucine (Ile), as a branched-chain amino acid (BCAA), has a vital role in regulating body weight and muscle protein synthesis. However, the regulatory effect of Ile on muscle mass under high-fat diet (HFD) conditions and intramyocellular lipid deposition remains largely unclear. In this study, a feeding experiment with HFD with or without 25 g L^-1 Ile was performed using 32 wild male C57BL/6J mice randomly divided into two groups. The results showed that Ile significantly increased both muscle and fat mass, as well as causing insulin resistance and meanwhile upregulating the levels of key adipogenic and myogenic proteins. More importantly, Ile damaged the mitochondrial function by vacuolation, swelling and cristae fracture in the gastrocnemius (GAS) and tibialis anterior (TA) with downregulation of mitochondrial function-related genes. Furthermore, Ile promoted myogenesis and more lipid droplet accumulation in myotubes. Compared with the control, the protein levels of myosin heavy chain (MyHC), myoblast determination protein 1 (MyoD), myogenin (MyoG), peroxisome proliferator-activated receptor gamma (PPARg) and fatty acid synthase (FAS) were upregulated in the Ile group, whereas the protein levels of adipose triglyceride lipase (ATGL) and lipoprotein lipase (LPL) were downregulated. Collectively, Ile increased muscle mass through myogenesis and intramyocellular lipid deposition. Our findings provide a new perspective for not only improving the lean juiciness of farm animals by increasing intramyocellular lipid accumulation, but also modulating myopathies under obesity.

Isoleucine Plays an Important Role for Maintaining Immune Function

Branched chain amino acids are the essential nutrients for humans and many animals. As functional amino acids, they play important roles in physiological functions, including immune functions. Isoleucine, as one of the branched chain amino acids, is also critical in physiological functions of the whole body, such as growth, immunity, protein metabolism, fatty acid metabolism and glucose transportation. Isoleucine can improve the immune system, including immune organs, cells and reactive substances. Recent studies have also shown that isoleucine may induce the expression of host defense peptides (i.e., β-defensins) that can regulate host innate and adaptive immunity. In addition, isoleucine administration can restore the effect of some pathogens on the health of humans and animals via increasing the expression of β-defensins. Therefore, the present review will emphatically discuss the effect of isoleucine on immunity while summarizing the relationship between branched chain amino acids and immune functions.

ESPEN guideline on clinical nutrition in liver disease

This update of evidence-based guidelines (GL) aims to translate current evidence and expert opinion into recommendations for multidisciplinary teams responsible for the optimal nutritional and metabolic management of adult patients with liver disease. The GL was commissioned and financially supported by ESPEN. Members of the guideline group were selected by ESPEN. We searched for meta-analyses, systematic reviews and single clinical trials based on clinical questions according to the PICO format. The evidence was evaluated and used to develop clinical recommendations implementing the SIGN method. A total of 85 recommendations were made for the nutritional and metabolic management of patients with acute liver failure, severe alcoholic steatohepatitis, non-alcoholic fatty liver disease, liver cirrhosis, liver surgery and transplantation as well as nutrition associated liver injury distinct from fatty liver disease. The recommendations are preceded by statements covering current knowledge of the underlying pathophysiology and pathobiochemistry as well as pertinent methods for the assessment of nutritional status and body composition.

Nutritional Intervention in Chronic Liver Failure

Patients suffering from chronic liver failure (CLF) frequently are malnourished and do not achieve an adequate intake of nutrients, in particular protein. Low protein intake and loss of muscle mass and function, termed sarcopenia, are indicators of a poor outcome. CLF patients, therefore, should be screened for risk of malnutrition using a validated tool, and if positive, full assessment of nutritional status is mandatory including search for sarcopenia. The main goal of nutritional intervention is to provide enough protein (1.2–1.5 g × kg^–1 × day^–1) and to ensure adequate energy intake (total energy 30 kcal × kg^–1 × day^–1; 1.3 × resting energy expenditure). Livers of CLF patients are deplete in glycogen and, therefore, prolonged periods of fasting (>12 h) must be avoided in order to prevent further breakdown of muscle protein for gluconeogenesis. Therefore, late evening snacks or even nocturnal oral nutritional supplements improve total body ­protein status and thus, are recommended. Nutrition intervention should be stepped up from nutrition counselling to oral nutritional supplements, to enteral tube feeding, or to parenteral nutrition as appropriate. As in other malnourished patients, the prevention of refeeding syndrome or vitamin/trace element deficiency should be taken care of.

Detection of Localized Hepatocellular Amino Acid Kinetics by using Mass Spectrometry Imaging of Stable Isotopes

Mass spectrometry imaging (MSI) simultaneously detects and identifies the spatial distribution of numerous molecules throughout tissues. Currently, MSI is limited to providing a static and ex vivo snapshot of highly dynamic systems in which molecules are constantly synthesized and consumed. Herein, we demonstrate an innovative MSI methodology to study dynamic molecular changes of amino acids within biological tissues by measuring the dilution and conversion of stable isotopes in a mouse model. We evaluate the method specifically on hepatocellular metabolism of the essential amino acid l-phenylalanine, associated with liver diseases. Crucially, the method reveals the localized dynamics of l-phenylalanine metabolism, including its in vivo hydroxylation to l-tyrosine and co-localization with other liver metabolites in a time course of samples from different animals. This method thus enables the dynamics of localized biochemical synthesis to be studied directly from biological tissues.

Protein Requirements for Critically Ill Patients With Renal and Liver Failure

Diseases leading to critical illness induce proteolysis resulting in muscle wasting and negative nitrogen balance. Muscle wasting has been associated with poor intensive care unit (ICU)-related outcomes, including an increased risk for mortality. Acute kidney injury (AKI) represents a common organ dysfunction associated with ICU-related disorders, such as sepsis, trauma, and respiratory failure. AKI and renal replacement therapy lead to amino acid loss. Decompensated liver cirrhosis (DLC) and acute liver failure (ALF) represent more severe forms of liver dysfunction leading to ICU admission. DLC and ALF are associated with proteolysis and amino acid loss. AKI, DLC, and ALF uniquely contribute to negative nitrogen balance. The purpose of this review is to outline proteolysis associated with critical illness; define specific protein abnormalities in AKI, DLC, and ALF; define protein requirements in AKI, DLC, and ALF; and discuss barriers associated with optimal protein supplementation in these disorders.

Nutrition and Alcoholic Liver Disease: Effects of Alcoholism on Nutrition, Effects of Nutrition on Alcoholic Liver Disease, and Nutritional Therapies for Alcoholic Liver Disease

Malnutrition is the most frequent and nearly universal consequence in alcoholic liver disease (ALD) that adversely affects clinical outcomes. Sarcopenia or skeletal muscle loss is the major component of malnutrition in liver disease. There are no effective therapies to prevent or reverse sarcopenia in ALD because the mechanisms are not well understood. Consequences of liver disease including hyperammonemia, hormonal perturbations, endotoxemia and cytokine abnormalities as well as the direct effects of alcohol and its metabolites contribute to sarcopenia in ALD. This article focuses on the prevalence, methods to quantify malnutrition, specifically sarcopenia and potential therapies including novel molecular targeted treatments.

Plasma Amino Acid Concentrations Predict Mortality in Patients with End-Stage Liver Disease

BACKGROUND

The liver plays a key role in amino acid metabolism. In former studies, a ratio between branched-chain and aromatic amino acids (Fischer's ratio) revealed associations with hepatic encephalopathy. Furthermore, low concentrations of branched-chain amino acids were linked to sarcopenia in literature. Encephalopathy and sarcopenia are known to dramatically worsen the prognosis. Aim of this study was to investigate a complex panel of plasma amino acids in the context of mortality in patients with end-stage liver disease.

METHODS

166 patients evaluated for orthotopic liver transplantation were included. 19 amino acids were measured from citrated plasma samples using mass spectrometry. We performed survival analysis for plasma amino acid constellations and examined the relationship to established mortality predictors.

RESULTS

33/166 (19.9%) patients died during follow-up. Lower values of valine (p<0.001), Fischer's ratio (p<0.001) and valine to phenylalanine ratio (p<0.001) and higher values of phenylalanine (p<0.05) and tyrosine (p<0.05) were significantly associated with mortality. When divided in three groups, the tertiles discriminated cumulative survival for valine (p = 0.016), phenylalanine (p = 0.024) and in particular for valine to phenylalanine ratio (p = 0.003) and Fischer's ratio (p = 0.005). Parameters were also significantly correlated with MELD and MELD-Na score.

CONCLUSIONS

Amino acids in plasma are valuable biomarkers to determine increased risk of mortality in patients with end-stage liver disease. In particular, valine concentrations and constellations composed of branched-chain and aromatic amino acids were strongly associated with prognosis. Due to their pathophysiological importance, the identified amino acids could be used to examine individual dietary recommendations to serve as potential therapeutic targets.

Serum Ammonia is Associated With Transplant-free Survival in Hospitalized Patients With Acutely Decompensated Cirrhosis [corrected]

BACKGROUND

As ammonia metabolism is a complex multiorgan process, we sought to determine whether serum ammonia concentrations were associated with transplant-free survival in patients with acutely decompensated cirrhosis and acute-on-chronic liver failure (ACLF).

METHODS

We studied 494 consecutive patients hospitalized with cirrhosis between April 2007 and September 2012 with venous ammonia measured on hospital admission. The primary outcome was transplant-free survival.

RESULTS

Overall, rates of death or transplant within 30 and 90 days were 23.1% (n=114) and 37.7% (n=186), respectively. Forty-six patients (9.2%) underwent liver transplantation within 90 days. In a multivariate Cox proportional hazards model, ammonia concentration was independently associated with death or transplantation within 30 and 90 days after adjusting for model for end-stage liver disease, sodium, white blood cells, and number of ACLF organ failures; every doubling of ammonia was associated with respective hazard ratios of 1.22 (95% confidence interval, 1.03-1.38) and 1.21 (95% confidence interval, 1.04-1.44) for 90- and 30-day transplant or mortality. Notably, after adjusting for ammonia, organ failures were not predictive of outcomes. In a Kaplan-Meier analysis, patients with admission ammonia concentrations >60 μmol/L had significantly lower 90-day transplant-free survival (P=0.0004). Patients with admission ammonia concentrations >60 μmol/L had higher 90- and 30-day risk of death or transplantation (45.2% vs. 31.2%, P=0.001; and 31.6% vs. 15.7%, P<0.0001, respectively).

CONCLUSION

For patients with acutely decompensated cirrhosis, an elevated serum ammonia concentration on admission is associated with reduced 90-day transplant-free survival after adjusting for established predictors.

Refining the ammonia hypothesis: a physiology-driven approach to the treatment of hepatic encephalopathy

Hepatic encephalopathy (HE) is one of the most important complications of cirrhosis and portal hypertension. Although the etiology is incompletely understood, it has been linked to ammonia directly and indirectly. Our goal is to review for the clinician the mechanisms behind hyperammonemia and the pathogenesis of HE to explain the rationale for its therapy. We reviewed articles collected through a search of MEDLINE/PubMed, Cochrane Database of Systematic Reviews, and Google Scholar between October 1, 1948, and December 8, 2014, and by a manual search of citations within retrieved articles. Search terms included hepatic encephalopathy, ammonia hypothesis, brain and ammonia, liver failure and ammonia, acute-on-chronic liver failure and ammonia, cirrhosis and ammonia, portosytemic shunt, ammonia and lactulose, rifaximin, zinc, and nutrition. Ammonia homeostatsis is a multiorgan process involving the liver, brain, kidneys, and muscle as well as the gastrointestinal tract. Indeed, hyperammonemia may be the first clue to poor functional reserves, malnutrition, and impending multiorgan dysfunction. Furthermore, the neuropathology of ammonia is critically linked to states of systemic inflammation and endotoxemia. Given the complex interplay among ammonia, inflammation, and other factors, ammonia levels have questionable utility in the staging of HE. The use of nonabsorbable disaccharides, antibiotics, and probiotics reduces gut ammoniagenesis and, in the case of antibiotics and probiotics, systemic inflammation. Nutritional support preserves urea cycle function and prevents wasting of skeletal muscle, a significant site of ammonia metabolism. Correction of hypokalemia, hypovolemia, and acidosis further assists in the reduction of ammonia production in the kidney. Finally, early and aggressive treatment of infection, avoidance of sedatives, and modification of portosystemic shunts are also helpful in reducing the neurocognitive effects of hyperammonemia. Refining the ammonia hypothesis to account for these other factors instructs a solid foundation for the effective treatment and prevention of hepatic encephalopathy.

Activity of MMP1 and MMP13 and amino acid metabolism in patients with alcoholic liver cirrhosis

Background

Alcoholic liver disease remains one of the most common causes of chronic liver disease worldwide.

The aim of this study was to assess the usefulness of metalloproteinases (MMP1 and MMP13) as diagnostic markers of alcoholic liver disease and to determine the changes in free amino acid profile in the patients with alcoholic liver cirrhosis.

Material/Methods

Sixty patients with alcoholic liver cirrhosis treated in various hospitals of the Lublin region were randomly enrolled. The control group consisted of 10 healthy individuals without liver disease, who did not drink alcohol. Additionally, a group of alcoholics (22 persons) without liver cirrhosis was included in the study. The activity of MMP-1 and MMP-13 in blood plasma of patients and controls was measured using the sandwich enzyme immunoassay technique with commercially available quantitative ELISA test kits. Amino acids were determined by automated ion-exchange chromatography.

Results

No significant differences were observed in the activity of MMP-1 in alcoholics with or without liver cirrhosis or in controls. Increased serum MMP-13 was found in patients with liver cirrhosis (stage A, B, C) compared to the control group. Patients with alcoholic liver cirrhosis (stage A, B, C) demonstrated reduced concentrations of glutamic acid and glutamine compared to the control group. Plasma levels of valine, isoleucine, leucine, and tryptophan were significantly lower in patients with alcoholic liver cirrhosis (stage C) than in controls.

Conclusions

MMP-13 can be useful to confirm the diagnosis of alcoholic liver cirrhosis, but levels of MMP-1 are not significantly increased in patients with liver cirrhosis compared to controls. The serum branched-chain amino acid (BCAA) is markedly reduced in patients with stage C alcoholic liver cirrhosis.

Expression of NAD(H) kinase and glucose-6-phosphate dehydrogenase improve NADPH supply and L-isoleucine biosynthesis in Corynebacterium glutamicum ssp. lactofermentum

Corynebacterium glutamicum is the workhorse for the production of amino acids, including L-isoleucine (Ile). During Ile biosynthesis, NADPH is required as a crucial cofactor. In this study, four NADPH-supplying strategies based on NAD kinase, NADH kinase, glucose-6-phosphate dehydrogenase, and NAD kinase coupling with glucose-6-phosphate dehydrogenase were compared, and their influences on Ile biosynthesis were examined. PpnK is a NAD kinase of C. glutamicum ssp. lactofermentum JHI3-156 that predominantly phosphorylates NAD(+) to produce NADP(+). Pos5 is a NADH kinase of Saccharomyces cerevisiae that predominantly phosphorylates NADH to produce NADPH. Zwf is a glucose-6-phosphate dehydrogenase of JHI3-156. The ppnK, POS5, zwf, and zwf-ppnK genes were overexpressed in the Ile-producing strain JHI3-156. The expression of all four genes increased intracellular NADPH concentration and Ile production. The increase of NADPH concentration and Ile production in a POS5-expressing strain (229 and 75.6 %, respectively) was higher than that in a ppnK-expression strain. The expression of zwf also increased NADPH supply and Ile biosynthesis, but the constitutive expression of zwf was not as effective as the inducible expression of zwf. Coexpression of zwf and ppnK genes greatly enhanced NADPH supply and thus improved Ile production by up to 85.9 %, indicating that this strategy was the most effective one. These results are helpful for improving Ile biosynthesis and other biosynthetic processes.

[Nutrition and liver failure]

In the critically ill liver patient, nutrition support is not very different from that given for other illnesses. In hyperacute liver failure, nutrition support is of less importance than in the other subtypes of acute liver failure that take a more protracted course. Nasoenteral tube feeding using a polymeric standard formula should be the first-line approach, while parenteral nutrition giving glucose, fat, amino acids, vitamins, and trace elements is initiated when enteral nutrition is insufficient or impracticable. In chronic liver disease, notably cirrhosis, there is frequently protein malnutrition indicating a poor prognosis and requiring immediate initiation of nutrition support. Enteral nutrition ensuring an adequate provision of energy and protein should be preferred. Particular care should be taken to avoid refeeding syndrome and to treat vitamin and trace element deficiency.

Nutritional support for liver disease

BACKGROUND

Weight loss and muscle wasting are commonly found in patients with end-stage liver disease. Since there is an association between malnutrition and poor clinical outcome, such patients (or those at risk of becoming malnourished) are often given parenteral nutrition, enteral nutrition, or oral nutritional supplements. These interventions have costs and adverse effects, so it is important to prove that their use results in improved morbidity or mortality, or both.

OBJECTIVES

To assess the beneficial and harmful effects of parenteral nutrition, enteral nutrition, and oral nutritional supplements on the mortality and morbidity of patients with underlying liver disease.

SEARCH METHODS

The following computerised databases were searched: the Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE, EMBASE, and Science Citation Index Expanded (January 2012). In addition, reference lists of identified trials and review articles and Clinicaltrials.gov were searched. Trials identified in a previous systematic handsearch of Index Medicus were also considered. Handsearches of a number of medical journals, including abstracts from annual meetings, were done. Experts in the field and manufacturers of nutrient formulations were contacted for potential references.

SELECTION CRITERIA

Randomised clinical trials (parallel or cross-over design) comparing groups of patients with any underlying liver disease who received, or did not receive, enteral or parenteral nutrition or oral nutritional supplements were identified without restriction on date, language, or publication status. Six categories of trials were separately considered: medical or surgical patients receiving parenteral nutrition, enteral nutrition, or supplements.

DATA COLLECTION AND ANALYSIS

The following data were sought in each report: date of publication; geographical location; inclusion and exclusion criteria; the type of nutritional support and constitution of the nutrient formulation; duration of treatment; any nutrition provided to the controls; other interventions provided to the patients; number, sex, age of the study participants; hospital or outpatient status; underlying liver disease; risks of bias (sequence generation, allocation concealment, blinding, incomplete outcome reporting, intention-to-treat analysis, selective outcome reporting, others (vested interests, baseline imbalance, early stopping)); mortality; hepatic morbidity (development or resolution of ascites or hepatic encephalopathy, occurrence of gastrointestinal bleeding); quality of life scores; adverse events; infections; lengths of stay in the hospital or intensive care unit; costs; serum bilirubin; postoperative complications (surgical trials only); and nutritional outcomes (nitrogen balance, anthropometric measurements, body weight). The primary outcomes of this review were mortality, hepatic morbidity, quality of life, and adverse events. Data were extracted in duplicate; differences were resolved by consensus.Data for each outcome were combined in a meta-analysis (RevMan 5.1). Estimates were reported using risk ratios or mean differences, along with the 95% confidence intervals (CI). Both fixed-effect and random-effects models were employed; fixed-effect models were reported unless one model, but not the other, found a significant difference (in which case both were reported). Heterogeneity was assessed by the Chi(2) test and I(2) statistic. Subgroup analyses were planned to assess specific liver diseases (alcoholic hepatitis, cirrhosis, hepatocellular carcinoma), acute or chronic liver diseases, and trials employing standard or branched-chain amino acid formulations (for the hepatic encephalopathy outcomes). Sensitivity analyses were planned to compare trials at low and high risk of bias and trials reported as full papers. The following exploratory analyses were undertaken: 1) medical and surgical trials were combined for each nutritional intervention; 2) intention-to-treat analyses in which missing dichotomous data were imputed as best- and worst-case scenarios; 3) all trials were combined to assess mortality; 4) effects were estimated by absolute risk reductions.

MAIN RESULTS

Thirty-seven trials were identified; only one was at low risk of bias. Most of the analyses failed to find any significant differences. The significant findings that were found were the following: 1) icteric medical patients receiving parenteral nutrition had a reduced serum bilirubin (mean difference (MD) -2.86 mg%, 95% CI -3.82 mg% to -1.89 mg%, 3 trials) and better nitrogen balance (MD 3.60 g/day, 95% CI 0.86 g/day to 6.34 g/day, 1 trial); 2) surgical patients receiving parenteral nutrition had a reduced incidence of postoperative ascites only in the fixed-effect model (RR 0.65, 95% CI 0.48 to 0.87, 2 trials, I(2) = 70%) and one trial demonstrated a reduction in postoperative complications, especially infections (pneumonia in particular); 3) enteral nutrition may have improved nitrogen balance in medical patients (although a combination of the three trials was not possible); 4) one surgical trial of enteral nutrition found a reduction in postoperative complications; and 5) oral nutritional supplements had several effects in medical patients (reduced occurrence of ascites (RR 0.57, 95% CI 0.37 to 0.88, 3 trials), possibly (significant differences only seen in the fixed-effect model) reduced rates of infection (RR 0.49, 95% CI 0.24 to 0.99, 3 trials, I(2) = 14%), and improved resolution of hepatic encephalopathy (RR 3.75, 95% CI 1.15 to 12.18, 2 trials, I(2) = 79%). While there was no overall effect of the supplements on mortality in medical patients, the one low risk of bias trial found an increased risk of death in the recipients of the supplements. Three trials of supplements in surgical patients failed to show any significant differences. No new information was derived from the various subgroup or sensitivity analyses. The exploratory analyses were also unrevealing except for a logical conundrum. There was no difference in mortality when all of the trials were combined, but the trials of parenteral nutrition found that those recipients had better survival (RR 0.53, 95% CI 0.29 to 0.98, 10 trials). Either the former observation represents a type II error or the latter one a type I error.

AUTHORS' CONCLUSIONS

The data do not compellingly justify the routine use of parenteral nutrition, enteral nutrition, or oral nutritional supplements in patients with liver disease. The fact that all but one of these trials were at high risks of bias even casts doubt on the few benefits that were demonstrated. Data from well-designed and executed randomised trials that include an untreated control group are needed before any such recommendation can be made. Future trials have to be powered adequately to see small, but clinically important, differences.

Nutritional support for liver disease

BACKGROUND

Weight loss and muscle wasting are commonly found in patients with end-stage liver disease. Since there is an association between malnutrition and poor clinical outcome, such patients (or those at risk of becoming malnourished) are often given parenteral nutrition, enteral nutrition, or oral nutritional supplements. These interventions have costs and adverse effects, so it is important to prove that their use results in improved morbidity or mortality, or both.

OBJECTIVES

To assess the beneficial and harmful effects of parenteral nutrition, enteral nutrition, and oral nutritional supplements on the mortality and morbidity of patients with underlying liver disease.

SEARCH METHODS

The following computerised databases were searched: the Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE, EMBASE, and Science Citation Index Expanded (January 2012). In addition, reference lists of identified trials and review articles and Clinicaltrials.gov were searched. Trials identified in a previous systematic handsearch of Index Medicus were also considered. Handsearches of a number of medical journals, including abstracts from annual meetings, were done. Experts in the field and manufacturers of nutrient formulations were contacted for potential references.

SELECTION CRITERIA

Randomised clinical trials (parallel or cross-over design) comparing groups of patients with any underlying liver disease who received, or did not receive, enteral or parenteral nutrition or oral nutritional supplements were identified without restriction on date, language, or publication status. Six categories of trials were separately considered: medical or surgical patients receiving parenteral nutrition, enteral nutrition, or supplements.

DATA COLLECTION AND ANALYSIS

The following data were sought in each report: date of publication; geographical location; inclusion and exclusion criteria; the type of nutritional support and constitution of the nutrient formulation; duration of treatment; any nutrition provided to the controls; other interventions provided to the patients; number, sex, age of the study participants; hospital or outpatient status; underlying liver disease; risks of bias (sequence generation, allocation concealment, blinding, incomplete outcome reporting, intention-to-treat analysis, selective outcome reporting, others (vested interests, baseline imbalance, early stopping)); mortality; hepatic morbidity (development or resolution of ascites or hepatic encephalopathy, occurrence of gastrointestinal bleeding); quality of life scores; adverse events; infections; lengths of stay in the hospital or intensive care unit; costs; serum bilirubin; postoperative complications (surgical trials only); and nutritional outcomes (nitrogen balance, anthropometric measurements, body weight). The primary outcomes of this review were mortality, hepatic morbidity, quality of life, and adverse events. Data were extracted in duplicate; differences were resolved by consensus.Data for each outcome were combined in a meta-analysis (RevMan 5.1). Estimates were reported using risk ratios or mean differences, along with the 95% confidence intervals (CI). Both fixed-effect and random-effects models were employed; fixed-effect models were reported unless one model, but not the other, found a significant difference (in which case both were reported). Heterogeneity was assessed by the Chi(2) test and I(2) statistic. Subgroup analyses were planned to assess specific liver diseases (alcoholic hepatitis, cirrhosis, hepatocellular carcinoma), acute or chronic liver diseases, and trials employing standard or branched-chain amino acid formulations (for the hepatic encephalopathy outcomes). Sensitivity analyses were planned to compare trials at low and high risk of bias and trials reported as full papers. The following exploratory analyses were undertaken: 1) medical and surgical trials were combined for each nutritional intervention; 2) intention-to-treat analyses in which missing dichotomous data were imputed as best- and worst-case scenarios; 3) all trials were combined to assess mortality; 4) effects were estimated by absolute risk reductions.

MAIN RESULTS

Thirty-seven trials were identified; only one was at low risk of bias. Most of the analyses failed to find any significant differences. The significant findings that were found were the following: 1) icteric medical patients receiving parenteral nutrition had a reduced serum bilirubin (mean difference (MD) -2.86 mg%, 95% CI -3.82 mg% to -1.89 mg%, 3 trials) and better nitrogen balance (MD 3.60 g/day, 95% CI 0.86 g/day to 6.34 g/day, 1 trial); 2) surgical patients receiving parenteral nutrition had a reduced incidence of postoperative ascites only in the fixed-effect model (RR 0.65, 95% CI 0.48 to 0.87, 2 trials, I(2) = 70%) and one trial demonstrated a reduction in postoperative complications, especially infections (pneumonia in particular); 3) enteral nutrition may have improved nitrogen balance in medical patients (although a combination of the three trials was not possible); 4) one surgical trial of enteral nutrition found a reduction in postoperative complications; and 5) oral nutritional supplements had several effects in medical patients (reduced occurrence of ascites (RR 0.57, 95% CI 0.37 to 0.88, 3 trials), possibly (significant differences only seen in the fixed-effect model) reduced rates of infection (RR 0.49, 95% CI 0.24 to 0.99, 3 trials, I(2) = 14%), and improved resolution of hepatic encephalopathy (RR 3.75, 95% CI 1.15 to 12.18, 2 trials, I(2) = 79%). While there was no overall effect of the supplements on mortality in medical patients, the one low risk of bias trial found an increased risk of death in the recipients of the supplements. Three trials of supplements in surgical patients failed to show any significant differences. No new information was derived from the various subgroup or sensitivity analyses. The exploratory analyses were also unrevealing except for a logical conundrum. There was no difference in mortality when all of the trials were combined, but the trials of parenteral nutrition found that those recipients had better survival (RR 0.53, 95% CI 0.29 to 0.98, 10 trials). Either the former observation represents a type II error or the latter one a type I error.

AUTHORS' CONCLUSIONS

The data do not compellingly justify the routine use of parenteral nutrition, enteral nutrition, or oral nutritional supplements in patients with liver disease. The fact that all but one of these trials were at high risks of bias even casts doubt on the few benefits that were demonstrated. Data from well-designed and executed randomised trials that include an untreated control group are needed before any such recommendation can be made. Future trials have to be powered adequately to see small, but clinically important, differences.

Overexpression of NAD kinases improves the L-isoleucine biosynthesis in Corynebacterium glutamicum ssp. lactofermentum

NADPH is the key cofactor in L-isoleucine (Ile) biosynthetic pathway. To increase the Ile biosynthesis in Corynebacterium glutamicum ssp. lactofermentum JHI3-156, NADPH supply needs to be enhanced. Here NAD kinase, the key enzyme for the de novo biosynthesis of NADP(+) and NADPH, were cloned and expressed in JHI3-156, and their influences on Ile production were analysed. Meanwhile, enzyme properties of NAD kinase from JHI3-156 (CljPpnK) were compared with that from C. glutamicum ssp. lactofermentum ATCC 13869 (ClPpnK). Four variations existed between CljPpnK and ClPpnK. Both PpnKs were poly(P)/ATP-dependent NAD kinases that used ATP as the preferred phosphoryl donor and NAD(+) as the preferred acceptor. CljPpnK exhibited a higher activity and stability than ClPpnK and less sensitivity towards the effectors NADPH, NADP(+), and NADH, partly due to the variations between them. The S57P variation decreased their activity. Expression of CljppnK and ClppnK in JHI3-156 increased the ATP-NAD(+) kinase activity by 69- and 47-fold, respectively, the intracellular NADP(+) concentration by 36% and 101%, respectively, the NADPH concentration by 95% and 42%, respectively, and Ile production by 37% and 24%, respectively. These results suggest that overexpressing NAD kinase is a useful metabolic engineering strategy to improve NADPH supply and isoleucine biosynthesis.

Ornithine phenylacetate prevents disturbances of motor-evoked potentials induced by intestinal blood in rats with portacaval anastomosis

BACKGROUND & AIMS

Ornithine phenylacetate (OP) is a new drug that has been proposed for the treatment of hepatic encephalopathy (HE) because it decreases plasma ammonia. We performed a study to assess if OP would impact on neuronal function.

METHODS

Motor-evoked potentials (MEP), a surrogate of hepatic encephalopathy, were assessed (without anesthesia) in rats with portacaval anastomosis (PCA) that received gastrointestinal blood (GIB). Rats were pre-treated with OP prior to GIB. Ammonia and related metabolites (plasma, urine, and brain microdialysis) were assessed by HPLC and mass spectroscopy.

RESULTS

OP (one dose or 3 days) prevented disturbances in MEP induced by GIB in PCA rats. In rats treated with OP for 3 days, the amplitude and latency of MEP remained stable (-1% and +1%), while in the control group the amplitude decreased -21% and the latency increased +12% (p<0.01). OP attenuated the rise of ammonia in plasma by 45%, ammonia in brain microdialysate by 48%, induced a faster glutamine rise and the appearance of phenylacetylglutamine in plasma and urine. In addition, OP was associated with a lower concentration of ammonia and glutamate in brain microdialysate (approx. 50%).

CONCLUSIONS

OP prevents abnormalities in MEP precipitated by GIB in a model of HE. This is probably due to the enhancement of glutamine synthesis and metabolism, which results in a lower rise of plasma ammonia and the prevention of changes in glutamate in microdialysate. Thus, OP may be a good drug to prevent HE precipitated by gastrointestinal bleeding.

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

Hepatic encephalopathy complicates the course of both acute and chronic liver disease and its treatment remains an unmet clinical need. Ammonia is thought to be central in its pathogenesis and remains an important target of current and future therapeutic approaches. In liver failure, the main detoxification pathway of ammonia metabolism is compromised leading to hyperammonaemia. In this situation, the other ammonia-regulating pathways in multiple organs assume important significance. The present review focuses upon interorgan ammonia metabolism in health and disease describing the role of the key enzymes, glutamine synthase and glutaminase. Better understanding of these alternative pathways are leading to the development of new therapeutic approaches.

Branched-chain amino acids in liver disease: new aspects of long known phenomena

PURPOSE OF REVIEW

To provide an overview of findings on the role of branched-chain amino acids (BCAAs) in the pathophysiology, pathobiochemistry, and treatment of liver cirrhosis and its complications that have been published since or were not included in the last review on this topic in 2007 in this journal.

RECENT FINDINGS

There has been continued interest in the potential of oral BCAA supplements in improving energy metabolism, nitrogen metabolism, carbohydrate metabolism, insulin resistance, severity of liver disease, serum albumin levels, quality of serum albumin, or postoperative complication rates. Unfortunately, many trials suffer from lacking or inadequate controls or small sample size. In a fine example of scientific perseverance, Dutch researchers uncovered the long-known phenomenon of ingested blood being highly comagenic in patients with cirrhosis to be due to the low biologic value of blood protein. The absence of isoleucine and the abundance of leucine in the hemoglobin molecule by way of BCAA antagonism leads to impaired protein synthesis and azotemia paving the way for hepatic encephalopathy.

SUMMARY

Recognizing hypoisoleucinemia and BCAA antagonism following gastrointestinal bleeding, and its successful treatment by isoleucine infusion has advanced our understanding of the role of BCAA in liver cirrhosis.

ESPEN Guidelines on Parenteral Nutrition: hepatology

Parenteral nutrition (PN) offers the possibility to increase or to ensure nutrient intake in patients, in whom sufficient nutrition by oral or enteral alone is insufficient or impossible. Complementary to the ESPEN guideline on enteral nutrition of liver disease (LD) patients the present guideline is intended to give evidence-based recommendations for the use of PN in LD. For this purpose three paradigm conditions of LD were chosen: alcoholic steatohepatitis (ASH), liver cirrhosis and acute liver failure. The guideline was developed by an interdisciplinary expert group in accordance with officially accepted standards and is based on all relevant publications since 1985. The guideline was presented on the ESPEN website and visitors' criticism and suggestions were welcome and included in the final revision. PN improves nutritional state and liver function in malnourished patients with ASH. PN is safe and improves mental state in patients with cirrhosis and severe HE. Perioperative (including liver transplantation) PN is safe and reduces the rate of complications. In acute liver failure PN is a safe second-line option to adequately feed patients in whom enteral nutrition is insufficient or impossible.

Review article: hyperammonaemic and catabolic consequences of upper gastrointestinal bleeding in cirrhosis

BACKGROUND

Upper gastrointestinal (UGI) bleeding in patients with cirrhosis of the liver induces hyperammonaemia and leads to a catabolic cascade that precipitates life-threatening complications. The haemoglobin molecule is unique because it lacks the essential amino acid isoleucine and contains high amounts of leucine and valine. UGI bleed therefore presents the gut with protein of very low biologic value, which may be the stimulus to induce net catabolism.

AIM

To describe the hyperammonaemic and catabolic consequences of UGI bleeding in cirrhosis.

METHODS

A semi-structured literature search was performed using PubMed and article references.

RESULTS

It has recently been proven that ('simulation of ') a UGI bleed in patients with cirrhosis leads to impaired protein synthesis that can be restored by intravenous infusion of isoleucine. This may have therapeutic implications for the function of rapidly dividing cells and short half-life proteins such as clotting factors. Renal and small bowel ammoniagenesis were shown to be the most prominent causes for the hyperammonaemia that resulted from a UGI bleed. This provides an explanation for the therapeutic failure of the current clinical therapies that are aimed at large bowel-derived ammonia production. Isoleucine infusion did not diminish renal ammoniagenesis.

CONCLUSIONS

New pharmacological therapies to diminish postbleeding hyperammonaemia should target the altered inter-organ ammonia metabolism and promote ammonia excretion and/or increase the excretion of precursors of ammoniagenesis, e.g. l-ornithine-phenylacetate.

Protein synthesis is severely diminished following a simulated upper GI bleed in patients with cirrhosis

BACKGROUND/AIMS

An upper gastrointestinal (GI) bleed in cirrhotic patients has been hypothesised to induce catabolism due to the absence of the essential branched chain amino acid (BCAA) isoleucine and an abundance of the BCAA leucine in haemoglobin. We tested whether an upper GI bleed produces hypoisoleucinemia via BCAA antagonism and impairs protein synthesis.

METHODS

Isoleucine turnover and oxidation was studied in 5 metabolically stable patients with cirrhosis during a 4-h period of intragastric saline infusion followed by a 4-h period in which an upper GI bleed was simulated by an amino acid solution mimicking haemoglobin.

RESULTS

The simulated upper GI bleed induced hypoisoleucinemia (26% of initial values) and an increase in leucine (400%) and valine (350%) concentrations. Isoleucine flux and isoleucine oxidation decreased to a third of initial values following a simulated bleed, but the fraction of isoleucine flux used for oxidation did not change. Consequently, the non-oxidative portion of isoleucine flux, representing protein synthesis, decreased similarly.

CONCLUSIONS

The present study shows that a simulated upper GI bleed induces hypoisoleucinemia and decreases protein synthesis markedly. The fact that the percentage of isoleucine flux that was oxidized was not influenced by the hypoisoleucinemic state can only be explained by BCAA antagonism.

Aromatic amino acid metabolism during liver failure

Liver failure is associated with hepatic encephalopathy (HE). An imbalance in plasma levels of aromatic amino acids (AAA) phenylalanine, tyrosine, and tryptophan and branched chain amino acids (BCAA) and their BCAA/AAA ratio has been suggested to play a causal role in HE by enhanced brain AAA uptake and subsequently disturbed neurotransmission. Until recently, data on this subject and the role of the liver and splanchnic bed were scarce, particularly in humans, due to inaccessibility of portal and hepatic veins. Here, we discuss, against a background of relevant literature, data obtained in patients undergoing liver resection or with a transjugular intrahepatic portasystemic stent shunt (TIPSS), where these veins are accessible. The BCAA/AAA ratio remained unchanged after major liver resection, but plasma AAA levels were inversely correlated (P < 0.001) with residual liver volume, in keeping with the observed hepatic AAA uptake. In patients with stable cirrhosis and a TIPSS, the plasma BCAA/AAA ratio was lower than in controls (1.19 +/- 0.09 vs. controls: 3.63 +/- 0.34). Gastrointestinal bleeding in cirrhotics with a TIPSS induced disturbances in BCAA levels and the BCAA/AAA ratio and induced catabolism, which could partly be corrected by isoleucine administration. AAA may be important in the pathogenesis of HE, but it is unlikely that they are the sole factors. HE most likely is a syndrome with multifactorial pathogenesis, where hyperammonemia, AAA/BCAA imbalances, inflammation, brain edema, and neurotransmitter changes interact. Novel therapies to normalize AAA levels in patients with liver failure (such as the molecular adsorbent recirculating system dialysis device) should probably be combined with supplementation of e.g. isoleucine and enhancing ammonia excretion by the kidneys.