Free amino acids in plasma and skeletal muscle of patients with liver cirrhosis

Biomarker Discovery in Liver Disease Using Untargeted Metabolomics in Plasma and Saliva

Chronic liver diseases, including non-alcoholic fatty liver disease (NAFLD), cirrhosis, and hepatocellular carcinoma (HCC), continue to be a global health burden with a rise in incidence and mortality, necessitating a need for the discovery of novel biomarkers for HCC detection. This study aimed to identify novel non-invasive biomarkers for these different liver disease states. We performed untargeted metabolomics in plasma (Healthy = 9, NAFLD = 14, Cirrhosis = 10, HCC = 34) and saliva samples (Healthy = 9, NAFLD = 14, Cirrhosis = 10, HCC = 22) to test for significant metabolite associations with each disease state. Additionally, we identified enriched biochemical pathways and analyzed correlations of metabolites between, and within, the two biofluids. We identified two salivary metabolites and 28 plasma metabolites significantly associated with at least one liver disease state. No metabolites were significantly correlated between biofluids, but we did identify numerous metabolites correlated within saliva and plasma, respectively. Pathway analysis revealed significant pathways enriched within plasma metabolites for several disease states. Our work provides a detailed analysis of the altered metabolome at various stages of liver disease while providing some context to altered pathways and relationships between metabolites.

Serum Branched-Chain Amino Acids and Long-Term Complications of Liver Cirrhosis: Evidence from a Population-Based Prospective Study

BACKGROUND AND AIMS

The role of serum branched-chain amino acids (BCAAs) in long-term liver cirrhosis complication events remains unclear. We aimed to evaluate the associations between serum BCAAs and the risk of liver-related events.

METHODS

We included a total of 64,005 participants without liver cirrhosis complication events at baseline from the UK Biobank. Cox proportional hazards regression models were utilized to estimate multivariable hazard ratios (HRs) and 95% CIs for the incidence of liver cirrhosis complication events, adjusting for potential confounders, including sociodemographic and lifestyle factors. Relationships between serum BCAAs and liver cirrhosis complications were examined using nonparametrically restricted cubic spline regression.

RESULTS

During a median follow-up of 12.7 years, 583 participants developed liver cirrhosis complication events. The multivariable Cox regression model suggested that total BCAAs (HR  =  0.88, 95% CI 0.82-0.95), serum leucine (HR  =  0.88, 95% CI 0.81-0.95), serum isoleucine (HR  =  0.88, 95% CI 0.82-0.96), and serum valine (HR  =  0.87, 95% CI 0.82-0.96) were all independent protective factors for liver cirrhosis complications after adjustment for sociodemographic and lifestyle factors. Cox models with restricted cubic splines showed U-shaped associations between serum valine and liver cirrhosis complication incidence. Serum total BCAA and isoleucine concentrations might reduce the risk of liver cirrhosis complications by raising the risk of (type 2 diabetes mellitus) T2DM.

CONCLUSION

Lower serum BCAA levels exacerbate the long-term risk of liver cirrhosis complications. Future studies should confirm these findings and identify the biological pathways of these associations.

Quick and easy assessment of sarcopenia in cirrhosis: Can ultrasound be the solution?

Cirrhosis is frequently associated with sarcopenia, with reported rates of over 80% in patients with decompensated alcohol-related liver disease. Sarcopenia negatively impacts the prognosis of cirrhotic patients and affects the response to treatment of patients with hepatocellular carcinoma (HCC). For these reasons, identifying an easy-to-perform method to assess sarcopenia in is a key element in the optimization of care in this patient population. Assessment of muscle mass by computed tomography is considered the standard of care for the diagnosis of sarcopenia, but exposure to radiation and high costs limit its application in this setting, especially for repeated assessments. We believe that ultrasound, a cheap and harmless technique also used for HCC screening in cirrhotic patients, could have an expanding role in the diagnosis and follow-up of sarcopenia in these patients.

Association between frailty and hepatic fibrosis in NAFLD among middle-aged and older adults: results from NHANES 2017-2020

Background

Although previous studies found that frailty is prevalent in NAFLD patients with advanced liver fibrosis and cirrhosis, studies examining the relationship are spare.

Aim

Our study aspires to investigate the potential correlation between the Frailty Index (FI) and hepatic fibrosis among middle-aged and older adults with NAFLD.

Methods

Data from the 2017-2020.03 National Health and Nutrition Examination Survey (NHANES) were utilized for this study, with a final of 2,383 participants aged 50 years and older included. The quantification of frailty was executed employing a 49-item frailty index. The recognition of hepatic steatosis and fibrosis was accomplished through the utilization of the controlling attenuation parameter (CAP) and transient elastography (TE). The relationship between the FI and hepatic fibrosis were investigated employing univariable and multivariable-adjusted logistic regression analyses. A subgroup analysis was conducted, dividing the subjects based on gender, Body Mass Index (BMI), and the presence of hyperlipidemia.

Results

The findings demonstrated a positive correlation between the FI and significant hepatic fibrosis in NAFLD, even after using multivariate logistic regression models adjusting for potential confounding factors (OR = 1.022, 95% CI, 1.004-1.041) and in tertiles (Q3vs Q1: OR = 2.004, 95% CI, 1.162-3.455). In the subgroup analysis, the correlation was more statistically significant in male (OR = 1.046, 95% CI, 1.022-1.071), under/normal weight (OR = 1.077, 95% CI, 1.009-1.150), overweight (OR = 1.040, 95% CI, 1.010-1.071), and subjects without hyperlipidemia (OR = 1.054, 95% CI, 1.012-1.097). The area under the Receiver Operating Characteristic (ROC) curve for the FI in assessing the existence of substantial fibrosis in NAFLD was 0.612 (95% CI, 0.596-0.628).

Conclusion

This study demonstrated a positive correlation between significant hepatic fibrosis and frailty, particularly among males aged 50 years and older, who were non-obese and did not have hyperlipidemia with NAFLD. Additional studies are required to further validate these findings.

Integrated Amino Acids and Transcriptome Analysis Reveals Arginine Transporter SLC7A2 Is a Novel Regulator of Myogenic Differentiation

Skeletal muscle differentiation is a precisely coordinated process. While many of the molecular details of myogenesis have been investigated extensively, the dynamic changes and functions of amino acids and related transporters remain unknown. In this study, we conducted a comprehensive analysis of amino acid levels during different time points of C2C12 myoblast differentiation using high-performance liquid chromatography (HPLC). Our findings revealed that the levels of most amino acids exhibited an initial increase at the onset of differentiation, reaching their peak typically on the fourth or sixth day, followed by a decline on the eighth day. Particularly, arginine and branched-chain amino acids showed a prominent increase during this period. Furthermore, we used RNA-seq analysis to show that the gene encoding the arginine transporter, Slc7a2, is significantly upregulated during differentiation. Knockdown of Slc7a2 gene expression resulted in a significant decrease in myoblast proliferation and led to a reduction in the expression levels of crucial myogenic regulatory factors, hindering the process of myoblast differentiation, fusion, and subsequent myotube formation. Lastly, we assessed the expression level of Slc7a2 during aging in humans and mice and found an upregulation of Slc7a2 expression during the aging process. These findings collectively suggest that the arginine transporter SLC7A2 plays a critical role in facilitating skeletal muscle differentiation and may hold potential as a therapeutic target for sarcopenia.

Outpatient screening with the Royal Free Hospital-Nutrition Prioritizing Tool for patients with cirrhosis at risk of malnutrition

OBJECTIVES

Malnutrition is common among inpatients with cirrhosis. However, data on the prevalence of malnutrition among stable ambulatory patients with cirrhosis is lacking. We sought to investigate the prevalence of patents at risk of malnutrition (ARMN) among ambulatory patients with cirrhosis using the Royal Free Hospital-Nutrition Prioritizing Tool (RFH-NPT) and the Malnutrition Universal Screening Tool (MUST) and compare their correlation to clinical outcomes.

METHODS

Patients attending an outpatient liver cirrhosis clinic at a tertiary hospital were screened for ARMN using both the RFH-NPT and MUST (defined by a score of ≥2 for either tool). Differences in clinical outcomes after 6 mo were compared.

RESULTS

There were 134 patients recruited. The RFH-NPT identified more ARMN patients compared with MUST (32.8% versus 8.2%; P < 0.01; Cohen κ, 0.27 [95% CI, 0.12-0.42]; P < 0.001). Fluid overload at recruitment was the only independent predictor of disagreement between the RFH-NPT and MUST (odds ratio [OR], 43.14; 95% CI, 8.70-214.00; P < 0.001). There was a trend toward an increased risk of mortality for ARMN patients by the RFH-NPT (hazard ratio, 3.58; 95% CI, 0.81-15.83; P = 0.06) but not by the MUST (P = 0.62). The incidence of hospital admissions in ARMN patients was higher by the RFH-NPT, with an incidence rate ratio of 13.27 (95% CI, 5.11-43.70; P < 0.001), but not in ARMN patients by the MUST (P = 0.85). Being ARMN by the RFH-NPT was the only independent predictor of hospital admissions (OR, 15.08; 95% CI, 2.47-91.98; P = 0.003).

CONCLUSIONS

The RFH-NPT identified more ARMN patients when compared with the MUST, especially among patients with fluid overload. Patients at risk of malnutrition were at an increased risk of hospital admissions and possibly death.

Skeletal muscle protein turnover responses to parenteral nutrition in patients with alcoholic liver cirrhosis and sarcopenia

Alcoholic liver cirrhosis (ALC) is accompanied by sarcopenia. The aim of this study was to investigate the acute effects of balanced parenteral nutrition (PN) on skeletal muscle protein turnover in ALC. Eight male patients with ALC and seven age- and sex-matched healthy controls were studied for 3 h of fasting followed by 3 h of intravenous PN (SmofKabiven 1,206 mL: amino acid = 38 g, carbohydrates = 85 g, and fat = 34 g) 4 mL/kg/h. We measured leg blood flow and sampled paired femoral arteriovenous concentrations and quadriceps muscle biopsies while providing a primed continuous infusion of [ring-2d5]-phenylalanine to quantify muscle protein synthesis and breakdown. Patients with ALC exhibited shorter 6-min walking distance (ALC: 487 ± 38 vs. controls: 722 ± 14 m, P < 0.05), lower hand-grip strength (ALC: 34 ± 2 vs. controls: 52 ± 2 kg, P < 0.05), and computed tomography (CT)-verified leg muscle loss (ALC: 5,922 ± 246 vs. controls: 8,110 ± 345 mm2, P < 0.05). Net leg muscle phenylalanine uptake changed from negative (muscle loss) during fasting to positive (muscle gain) in response to PN (ALC: -0.18 ± +0.01 vs. 0.24 ± 0.03 µmol/kg muscle·min-1; P < 0.001 and controls: -0.15 ± 0.01 vs. 0.09 ± 0.01 µmol/kg muscle·min-1; P < 0.001) but with higher net muscle phenylalanine uptake in ALC than controls (P < 0.001). Insulin concentrations were substantially higher in patients with ALC during PN. Our results suggest a higher net muscle phenylalanine uptake during a single infusion of PN in stable patients with ALC with sarcopenia compared with healthy controls.NEW & NOTEWORTHY Muscle protein turnover responses to parenteral nutritional (PN) supplementation have not previously been studied in stable alcoholic liver cirrhosis (ALC). We applied stable isotope tracers of amino acids to directly quantify net muscle protein turnover responses to PN in sarcopenic males with ALC and healthy controls. We found a higher net muscle protein gain in ALC during PN, thereby providing the physiological rationale for future clinical trials of PN as a potential countermeasure to sarcopenia.

From Listing to Recovery: A Review of Nutritional Status Assessment and Management in Liver Transplant Patients

Liver transplantation (LT) is a complex surgical procedure requiring thorough pre- and post-operative planning and care. The nutritional status of the patient before, during, and after LT is crucial to surgical success and long-term prognosis. This review aims to assess nutritional status assessment and management before, during, and after LT, with a focus on patients who have undergone bariatric surgery. We performed a comprehensive topic search on MEDLINE, Ovid, In-Process, Cochrane Library, EMBASE, and PubMed up to March 2023. It identifies key factors influencing the nutritional status of liver transplant patients, such as pre-existing malnutrition, the type and severity of liver disease, comorbidities, and immunosuppressive medications. The review highlights the importance of pre-operative nutritional assessment and intervention, close nutritional status monitoring, individualised nutrition care plans, and ongoing nutritional support and monitoring after LT. The review concludes by examining the effect of bariatric surgery on the nutritional status of liver transplant recipients. The review offers valuable insights into the challenges and opportunities for optimising nutritional status before, during, and after LT.

Multiomics-Identified Intervention to Restore Ethanol-Induced Dysregulated Proteostasis and Secondary Sarcopenia in Alcoholic Liver Disease

BACKGROUND/AIMS

Signaling and metabolic perturbations contribute to dysregulated skeletal muscle protein homeostasis and secondary sarcopenia in response to a number of cellular stressors including ethanol exposure. Using an innovative multiomics-based curating of unbiased data, we identified molecular and metabolic therapeutic targets and experimentally validated restoration of protein homeostasis in an ethanol-fed mouse model of liver disease.

METHODS

Studies were performed in ethanol-treated differentiated C2C12 myotubes and physiological relevance established in an ethanol-fed mouse model of alcohol-related liver disease (mALD) or pair-fed control C57BL/6 mice. Transcriptome and proteome from ethanol treated-myotubes and gastrocnemius muscle from mALD and pair-fed mice were analyzed to identify target pathways and molecules. Readouts including signaling responses and autophagy markers by immunoblots, mitochondrial oxidative function and free radical generation, and metabolic studies by gas chromatography-mass spectrometry and sarcopenic phenotype by imaging.

RESULTS

Multiomics analyses showed that ethanol impaired skeletal muscle mTORC1 signaling, mitochondrial oxidative pathways, including intermediary metabolite regulatory genes, interleukin-6, and amino acid degradation pathways are β-hydroxymethyl-butyrate targets. Ethanol decreased mTORC1 signaling, increased autophagy flux, impaired mitochondrial oxidative function with decreased tricarboxylic acid cycle intermediary metabolites, ATP synthesis, protein synthesis and myotube diameter that were reversed by HMB. Consistently, skeletal muscle from mALD had decreased mTORC1 signaling, reduced fractional and total muscle protein synthesis rates, increased autophagy markers, lower intermediary metabolite concentrations, and lower muscle mass and fiber diameter that were reversed by β-hydroxymethyl-butyrate treatment.

CONCLUSION

An innovative multiomics approach followed by experimental validation showed that β-hydroxymethyl-butyrate restores muscle protein homeostasis in liver disease.

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.

S-Adenosylmethionine Deficiency and Brain Accumulation of S-Adenosylhomocysteine in Thioacetamide-Induced Acute Liver Failure

BACKGROUND

Acute liver failure (ALF) impairs cerebral function and induces hepatic encephalopathy (HE) due to the accumulation of neurotoxic and neuroactive substances in the brain. Cerebral oxidative stress (OS), under control of the glutathione-based defense system, contributes to the HE pathogenesis. Glutathione synthesis is regulated by cysteine synthesized from homocysteine via the transsulfuration pathway present in the brain. The transsulfuration-transmethylation interdependence is controlled by a methyl group donor, S-adenosylmethionine (AdoMet) conversion to S-adenosylhomocysteine (AdoHcy), whose removal by subsequent hydrolysis to homocysteine counteract AdoHcy accumulation-induced OS and excitotoxicity.

METHODS

Rats received three consecutive intraperitoneal injections of thioacetamide (TAA) at 24 h intervals. We measured AdoMet and AdoHcy concentrations by HPLC-FD, glutathione (GSH/GSSG) ratio (Quantification kit).

RESULTS

AdoMet/AdoHcy ratio was reduced in the brain but not in the liver. The total glutathione level and GSH/GSSG ratio, decreased in TAA rats, were restored by AdoMet treatment.

CONCLUSION

Data indicate that disturbance of redox homeostasis caused by AdoHcy in the TAA rat brain may represent a deleterious mechanism of brain damage in HE. The correction of the GSH/GSSG ratio following AdoMet administration indicates its therapeutic value in maintaining cellular redox potential in the cerebral cortex of ALF rats.

Muscle wasting and branched-chain amino acid, alpha-ketoglutarate, and ATP depletion in a rat model of liver cirrhosis

The aim of the study was to examine whether a rat model of liver cirrhosis induced by carbon tetrachloride (CCl4) is a suitable model of muscle wasting and alterations in amino acid metabolism in cirrhotic humans. Rats were treated by intragastric gavage of CCl4 or vehicle for 45 days. Blood plasma and different muscle types-tibialis anterior (mostly white fibres), soleus (red muscle) and extensor digitorum longus (white muscle) - were analysed at the end of the study. Characteristic biomarkers of impaired hepatic function were found in the plasma of cirrhotic animals. The weights and protein contents of all muscles of CCl4-treated animals were lower when compared with controls. Increased concentrations of glutamine (GLN) and aromatic amino acids (phenylalanine and tyrosine) and decreased concentrations of branched-chain amino acids (BCAA), glutamate (GLU), alanine and aspartate were found in plasma and muscles. In the soleus muscle, GLN increased more and GLU and BCAA decreased less than in the extensor digitorum and tibialis muscles. Increased chymotrypsin-like activity (indicating enhanced proteolysis) and decreased α-ketoglutarate and ATP levels were found in muscles of cirrhotic animals. ATP concentration also decreased in blood plasma. It is concluded that a rat model of CCl4-induced cirrhosis is a valid model for the investigation of hepatic cachexia that exhibits alterations in line with a theory of role of ammonia in pathogenesis of BCAA depletion, citric cycle and mitochondria dysfunction, and muscle wasting in cirrhotic subjects. The findings indicate more effective ammonia detoxification to GLN in red than in white muscles.

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.

Role of Nutrition and Muscle in Cirrhosis

OPINION STATEMENT

Most widely recognized complications in cirrhotic patients include ascites, hepatic encephalopathy, variceal bleeding, kidney dysfunction, and hepatocellular carcinoma; however, malnutrition and muscle wasting (sarcopenia) constitute common complications which negatively impact survival, quality of life, and response to stressors, such as infection and surgery in patients with cirrhosis. Despite the important role that malnutrition and sarcopenia play in the prognosis of patients with cirrhosis, they are frequently overlooked, in part because nutritional assessment can be a difficult task in patients with cirrhosis due to fluid retention and/or overweight. Moreover, patients with cirrhosis may develop simultaneous loss of skeletal muscle and gain of adipose tissue, culminating in the condition of "sarcopenic obesity." In addition, muscle depletion is characterized by both a reduction in muscle size and increased proportion of intermuscular and intramuscular fat-denominated "myosteatosis." Sarcopenia in cirrhotic patients has been associated with increased mortality, sepsis complications, hyperammonemia, overt hepatic encephalopathy, and increased length of stay after liver transplantation. Muscularity assessment with cross-sectional imaging studies has become an attractive index of nutritional status evaluation in cirrhosis, as sarcopenia reflects a chronic detriment in general physical condition, rather than acute severity of the liver disease. In this review, we discuss the current diagnostic methods to evaluate malnutrition and muscle abnormalities in cirrhosis and also analyze the current knowledge regarding incidence and clinical impact of malnutrition and muscle abnormalities in cirrhosis and their impact after liver transplantation. We also discuss existing and potential novel therapeutic strategies for malnutrition in cirrhosis, emphasizing the recognition of sarcopenia in cirrhosis in an effort to improve survival and reduce morbidity related to cirrhosis. Finally, we analyze new studies including sarcopenia with the MELD score that seems to allow better prediction of mortality among cirrhotic patients waiting for liver transplantation.

Elevation of branched-chain amino acid levels in diabetes and NAFL and changes with antidiabetic drug treatment

Diabetes mellitus (DM), non-alcoholic fatty liver (NAFL), and obesity are associated with elevated branched-chain amino acid (BCAA) levels, but the mechanism and significance of this has not been elucidated. Eighty-four subjects were enrolled including 43 with DM. Serum BCAA levels were positively correlated with waist-hip ratio and ALT. Serum BCAA levels in subjects with DM were higher than non-DM and those in subjects with NAFL were also higher than non-NAFL. Treatment with pioglitazone and alogliptin (19 of 43 DM subjects) improved serum haemoglobin A1c and decreased BCAA levels. The decrease in BCAAs with improved glucose metabolism suggests that abnormal glucose metabolism is also a factor in elevated BCAA levels.

A metabonomic analysis of serum from rats treated with ricinine using ultra performance liquid chromatography coupled with mass spectrometry

A metabonomic approach based on ultra performance liquid chromatography coupled with mass spectrometry (UPLC/MS) was used to study the hepatotoxicity of ricinine in rats. Potential biomarkers of ricinine toxicity and toxicological mechanism were analyzed by serum metabonomic method. The significant differences in the metabolic profiling of the control and treated rats were clear by using the principal components analysis (PCA) of the chromatographic data. Significant changes of metabolite biomarkers like phenylalanine, tryptophan, cholic acid, LPC and PC were detected in the serum. These biochemical changes were related to the metabolic disorders in amino acids and phospholipids. This research indicates that UPLC/MS-based metabonomic analysis of serum samples can be used to predict the hepatotoxicity and further understand the toxicological mechanism induced by ricinine. This work shows that metabonomics method is a valuable tool in drug mechanism study.

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.

(1)H NMR spectroscopy of ascitic fluid: discrimination between malignant and benign ascites and comparison of the results with conventional methods

It is often difficult to distinguish benign ascites from malignant ascites by conventional examination of ascitic fluid. Therefore, (1)H NMR spectroscopy of ascitic fluid specimens was explored as a one-shot experiment to identify potentially interesting metabolic indices that might help to differentiate between the two. Seventy ascitic fluid specimens (15 cytologically positive for malignant cells, eight cytologically negative for malignant cells but remaining suspicious for malignant ascites, and 47 due to liver cirrhosis) were subjected to (1)H NMR spectroscopy for quantitative estimation of 14 metabolites. Mean concentrations of the metabolites were compared with the Mann-Whitney U test. Multivariate discriminant function analysis was performed to determine important descriptors in the discrimination process. The sensitivity and specificity of the proposed model were compared with conventional methods using ascitic fluid protein and serum ascitic albumin gradient. Then, probable predictions for the doubtful cases were made using the proposed model. Patients with malignant ascites had significantly higher mean concentrations (microM) of beta-hydroxybutyrate (594 vs 61), lactate (5384 vs 2104), acetone (136 vs 69), and acetoacetate (122 vs 48) than patients with cirrhotic ascites, and significantly lower concentrations of glutamine (359 vs 615), citrate (62 vs 118), glucose (4933 vs 8411), tyrosine (44 vs 124), and phenylalanine (51 vs 93) (P < 0.05 for all). In the discriminant function analysis model, the best discrimination (P < 0.001) was achieved when beta-hydroxybutyrate, lactate, citrate and tyrosine were considered together as markers. Sensitivity and specificity of the proposed model, ascitic fluid protein and serum ascitic albumin gradient were found to be 100% and 97.9%, 53.3% and 76.6%, and 60% and 87.2%, respectively. The proposed model put five of the eight doubtful cases in the malignant group. This is encouraging and may provide useful information for clinical purposes.

The essentiality of sulfur is closely related to nitrogen metabolism: a clue to hyperhomocysteinaemia

N and S metabolisms are closely interwoven throughout both the plant and animal kingdoms. The essentiality of S relates to its participation in the structure of S-containing amino acids (SAA), to its inclusion in many sulfonated molecules, and to a myriad of metabolic and catalytic reactions of vital importance. Methionine (Met) is the indispensable SAA supplied by food proteins and its plasma homeostasis is achieved via a number of highly efficient regulatory mechanisms. In all conditions characterised by a negative body protein balance such as in dietary restriction or cytokine-induced hypercatabolic losses, N and S endogenous pools manifest parallel tissue depletion rates. Adaptive conservation of N and S body stores is reached by a functional restraint of the trans-sulfuration cascade, through the depression of cystathionine β-synthase activity. As a result, upstream accumulation of homocysteine favours its re-methylation conversion to Met which helps maintain metabolic pathways of survival value. In addition to the measurement of vitamin indices, that of plasma transthyretin, a sensitive marker of protein nutritional status, is proposed to identify the fluctuations of the total body N component accountable for the alterations of homocysteine concentrations in body fluids.

Role of meal carbohydrate content for the imbalance of plasma amino acids in patients with liver cirrhosis

BACKGROUND AND AIM

Imbalance of circulating branched chain amino acids (BCAA) versus aromatic amino acids (AAA) and hyperinsulinemia are common metabolic alterations in patients with liver cirrhosis. The aim of this study was to characterize the effect of the carbohydrate component of a protein-rich mixed meal on postprandial plasma concentrations of 21 amino acids, insulin and C-peptide in patients with compensated liver cirrhosis. Furthermore, the effect of a dietary intervention on the metabolic alterations in cirrhotic patients was examined.

METHODS

Eighteen patients with cirrhosis and 12 healthy volunteers received a protein-rich meal (pork filet 200 g) with or without carbohydrates (bread 50 g, glucose 20 g). A subgroup of four cirrhotic patients received an isoenergetic (117 kJ/kg bw) carbohydrate-enriched (60%) and -restricted (20%) diet for 7 days each.

RESULTS

In the cirrhotic patients, basal plasma insulin and C-peptide concentrations were significantly elevated. The ingestion of a protein-rich meal without additional carbohydrates led to a significantly greater increase of insulin and C-peptide in the cirrhotic patients compared to controls. Postprandial increases of leucine and isoleucine were reduced, whereas those of phenylalanine were higher in cirrhotic patients. The addition of carbohydrates led to higher insulin and C-peptide plasma concentrations in cirrhotic patients. Postprandial BCAA increases were more impaired in the cirrhotic group after additional carbohydrate ingestion (46%vs 82%). After the carbohydrate-restricted diet for 7 days BCAA plasma levels increased but the BCAA/AAA ratio remained unaltered.

CONCLUSIONS

The carbohydrate content of a meal enhances reduction of BCAA plasma concentrations in clinically stable cirrhotic patients. An imbalanced BCAA/AAA ratio cannot be avoided by a carbohydrate-reduced diet alone, supporting mandatory BCAA supplementation.

Altered expression of genes regulating skeletal muscle mass in the portacaval anastomosis rat

We examined the temporal relationship between portacaval anastomosis (PCA), weight gain, changes in skeletal muscle mass and molecular markers of protein synthesis, protein breakdown, and satellite cell proliferation and differentiation. Male Sprague-Dawley rats with end to side PCA (n=24) were compared with sham-operated pair-fed rats (n=24). Whole body weight, lean body mass, and forelimb grip strength were determined at weekly intervals. The skeletal muscle expression of the ubiquitin proteasome system, myostatin, its receptor (the activin 2B receptor) and its signal, cyclin-dependent kinase inhibitor (CDKI) p21, insulin-like growth factor (IGF)-I and its receptor (IGF-I receptor-alpha), and markers of satellite cell proliferation and differentiation were quantified. PCA rats did not gain body weight and had lower lean body mass, forelimb grip strength, and gastrocnemius muscle weight. The skeletal muscle expression of the mRNA of ubiquitin proteasome components was higher in PCA rats in the first 2 wk followed by a lower expression in the subsequent 2 wk (P<0.01). The mRNA and protein of myostatin, activin 2B receptor, and CDKI p21 were higher, whereas IGF-I and its receptor as well as markers of satellite cell function (proliferating nuclear cell antigen, myoD, myf5, and myogenin) were lower at weeks 3 and 4 following PCA (P < 0.05). We conclude that PCA resulted in uninhibited proteolysis in the initial 2 wk. This was followed by an adaptive response in the later 2 wk consisting of an increased expression of myostatin that may have contributed to reduced muscle protein synthesis, impaired satellite cell function, and lower skeletal muscle mass.

Altered alanine plasma levels despite normalized hepatic alanine extraction in the long-term course after liver transplantation

BACKGROUND

The amino acid (AA) metabolism in cirrhosis is deranged, reflected by an altered plasma AA profile. Alanine is a unique AA with predominant production by muscle and the highest hepatic extraction rate.

METHODS

We studied circulating levels and hepatic alanine extraction in 52 patients with advanced cirrhosis, 16 stable patients more than 6 months after orthotopic liver transplant (OLT), and 50 controls. In addition, hepatic hemodynamics (portal pressure, hepatic blood flow, and splanchnic percent indocyanine green extraction) and parameters of hepatic metabolism (splanchnic oxygen uptake and splanchnic glucose production) were assessed.

RESULTS

Circulating alanine levels decreased independently of the clinical stage in cirrhosis (262+/-15 micromol/L vs. 330+/-14 micromol/L in controls, P<0.001) and decreased even further after OLT (209+/-10 micromol/L, P<0.001). Hepatic alanine extraction decreased dependently on the clinical stage in cirrhosis (59+/-7 micromol/min) and was normalized after OLT (100+/-10 micromol/min, P<0.001), indicating that decreased plasma alanine levels in OLT patients are the result of changes in extrahepatic metabolism. Hepatic alanine extraction correlated with splanchnic oxygen uptake (r=0.64, P<0.001) and hepatic glucose production (r=0.65, P<0.001).

CONCLUSIONS

These results demonstrate that significant alterations in muscular AA metabolism persist even in the clinically stable long-term course after OLT when the hepatic AA metabolism is normalized.

Altered amino acid metabolism in chronic obstructive pulmonary disease: new therapeutic perspective?

PURPOSE OF REVIEW

Wasting of muscle mass, commonly present in patients with chronic obstructive pulmonary disease, is a complex process involving changes in the control of intermediary metabolism as well as in muscle cell status. Although research exploring intermediary metabolism in chronic obstructive pulmonary disease is still in its infancy, there is an increased interest in a potential role for amino acids in modulating muscle anabolism. This review aims at summarizing and critically evaluating the available clinical studies examining alterations in amino acid profile in plasma and skeletal muscle of patients with chronic obstructive pulmonary disease.

RECENT FINDINGS

All studies show pronounced alterations in plasma and muscle amino acid status in patients with chronic obstructive pulmonary disease but no consistent "disease specific" pattern for most amino acids. Variability is likely influenced by the heterogeneity of the disease with respect to lung function and nutritional state. Nevertheless, general consistency exists in chronic obstructive pulmonary disease with respect to (1) a reduced plasma branched-chain amino acid level, and (2) a decreased muscle glutamate concentration. Alterations in branched-chain amino acid metabolism appear to be influenced by the degree of muscle wasting, while the reduction in muscle glutamate is related to the diffusing capacity as a hallmark of emphysema. The reduction in glutamate status is associated with reduced muscle glutathione levels and appears to be linked to enhanced glycolysis as evidenced from an accelerated increase in plasma lactate during exercise.

SUMMARY

Underlying mechanisms of the observed alterations in amino acid profile in chronic obstructive pulmonary disease, and the influences of disease associated mediators such as chronic low-grade inflammation and (chronic and intermittent) hypoxia are speculative and need to be explored in experimental study designs.

S-Adenosyl-L-methionine and alcoholic liver disease in animal models: implications for early intervention in human beings

In patients with severe alcoholic liver disease (i.e., cirrhosis), a deficiency of S-adenosylmethionine (SAMe) develops as a result of decreased SAMe synthetase activity. Whether a sizeable SAMe depletion occurs already at earlier stages of alcoholic liver disease has been the subject of debate. To address this issue, rats were fed alcohol (or isocaloric carbohydrate) in Lieber-DeCarli liquid diets containing adequate amounts of protein, vitamins, and lipotropic factors, including methionine. Alcohol feeding resulted in hepatic steatosis (without fibrosis) and unchanged SAMe synthetase activity, yet SAMe concentration was already greatly decreased. This most likely resulted from oxidative stress associated with the metabolism of alcohol and the induction of cytochrome P4502E1 (CYP2E1), which generates free radicals. Indeed, the decrease in hepatic SAMe correlated with parameters of oxidative stress, such as increased 4-hydroxynonenal (measured by gas chromatography-mass spectrometry) and diminished glutathione (GSH). Decreased GSH, occurring as a result of excessive GSH consumption caused by the oxidative stress, probably generated by enhanced utilization of SAMe, a precursor of GSH, thereby explaining the depletion of SAMe. In view of the known differences between rodents and primates in the metabolism of lipotropes, my colleagues and I have also studied the interaction between alcohol and SAMe in baboons and found again that, at early stages preceding the development of cirrhosis, there was already a significant lowering of hepatic SAMe concentration, associated with a striking oxidative stress documented by decreased levels and accelerated turnover of GSH. This was associated with increased lipid peroxidation and damage to cellular membranes, including those of the mitochondria, assessed by electron microscopy. Oral administration of SAMe resulted in its hepatic repletion with a corresponding attenuation of the ethanol-induced oxidative stress and liver injury, with significantly less GSH depletion, less increases in plasma aspartate aminotransferase (AST) levels, less leakage of mitochondrial glutamic dehydrogenase into the plasma, and fewer megamitochondria. In conclusion, (1) both in rodents and in non-human primates, significant SAMe depletion occurs already at early stages of alcoholic liver disease, despite the consumption of adequate diets; (2) the decreased hepatic SAMe concentration and the associated liver lesions, including mitochondrial injury, can be corrected with SAMe supplementation; and (3) accordingly, therapeutic administration of SAMe should be the subject of a comprehensive clinical trial to assess its capacity to attenuate early stages of alcoholic liver injury in human beings.

Plasma amino acids in cirrhosis and after liver transplantation: influence of liver function, hepatic hemodynamics and circulating hormones

Liver cirrhosis is characterized by substantial changes in amino acid (AA) metabolism, resulting in a deranged plasma AA profile. To investigate the effect of liver transplantation (OLT), we studied arterial AA profiles in 52 patients with advanced cirrhosis, 16 stable patients over 6 months after OLT and 48 controls. Changes in AA levels were correlated with portal pressure (hepatic venous pressure gradient), functional hepatic blood flow (indocyanine green extraction) and circulating hormone levels (catecholamines, insulin, C-peptide). Fourteen of 18 measured AA were significantly altered in cirrhosis and 11 of 18 remained abnormal after OLT compared with controls. Aromatic AA (AAA) and methionine were elevated in cirrhosis (p < 0.001 each), increasing with disease stage, and normalized after OLT. Branched chain AA (BCAA) levels were decreased in cirrhosis (p < 0.001) and were unrelated to disease stage. After OLT, BCAA levels remained subnormal (p < 0.01), although higher than in cirrhosis (p < 0.001). AAA levels increased with decreasing functional hepatic blood flow (r = -0.67; p < 0.001) and increasing portal pressure (r = 0.59; p < 0.001). BCAA levels decreased with increasing catecholamine (r = - 0.54, p < 0.001) and insulin levels (r = - 0.40, p = 0.001). We conclude that despite normal liver function, AA metabolism is only partially normalized after OLT. AAA levels mainly determined by hepatic metabolic function and functional liver blood flow return to normal, while BCAA levels remain subnormal, indicating persistent changes in muscular AA metabolism after OLT.

Glycine N-methyltransferase deficiency: a novel inborn error causing persistent isolated hypermethioninaemia

This paper reports clinical and metabolic studies of two Italian siblings with a novel form of persistent isolated hypermethioninaemia, i.e. abnormally elevated plasma methionine that lasted beyond the first months of life and is not due to cystathionine beta-synthase deficiency, tyrosinaemia I or liver disease. Abnormal elevations of their plasma S-adenosylmethionine (AdoMet) concentrations proved they do not have deficient activity of methionine adenosyltransferase I/III. A variety of studies provided evidence that the elevations of methionine and AdoMet are not caused by defects in the methionine transamination pathway, deficient activity of methionine adenosyltransferase II, a mutation in methylenetetrahydrofolate reductase rendering this activity resistant to inhibition by AdoMet, or deficient activity of guanidinoacetate methyltransferase. Plasma sarcosine (N-methylglycine) is elevated, together with elevated plasma AdoMet in normal subjects following oral methionine loads and in association with increased plasma levels of both methionine and AdoMet in cystathionine beta-synthase-deficient individuals. However, plasma sarcosine is not elevated in these siblings. The latter result provides evidence they are deficient in activity of glycine N-methyltransferase (GNMT). The only clinical abnormalities in these siblings are mild hepatomegaly and chronic elevation of serum transaminases not attributable to conventional causes of liver disease. A possible causative connection between GNMT deficiency and these hepatitis-like manifestations is discussed. Further studies are required to evaluate whether dietary methionine restriction will be useful in this situation.

ALCOHOL: its metabolism and interaction with nutrients

In the past, alcoholic liver disease was attributed exclusively to dietary deficiencies, but experimental and judicious clinical studies have now established alcohol's hepatotoxicity. Despite an adequate diet, it can contribute to the entire spectrum of liver diseases, mainly by generating oxidative stress through its microsomal metabolism via cytochrome P4502E1 (CYP2E1). It also interferes with nutrient activation, resulting in changes in nutritional requirements. This is exemplified by methionine, one of the essential amino acids for humans, which needs to be activated to S-adenosylmethionine (SAMe), a process impaired by liver disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. In baboons, SAMe attenuated mitochondrial lesions and replenished glutathione; it also significantly reduced mortality in patients with Child A or B cirrhosis. Similarly, decreased phosphatidylethanolamine methyltransferase activity is associated with alcoholic liver disease, resulting in phosphatidylcholine depletion and serious consequences for the integrity of membranes. This can be offset by polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines comprising dilinoleoylphosphatidylcholine (DLPC), which has high bioavailability. PPC (and DLPC) opposes major toxic effects of alcohol, with down-regulation of CYP2E1 and reduction of oxidative stress, deactivation of hepatic stellate cells, and increased collagenase activity, which in baboons, results in prevention of ethanol-induced septal fibrosis and cirrhosis. Corresponding clinical trials are ongoing.

Factors contributing to alterations in skeletal muscle and plasma amino acid profiles in patients with chronic obstructive pulmonary disease

BACKGROUND

There is increasing evidence of abnormal protein metabolism in patients with chronic obstructive pulmonary disease (COPD), as reflected by lower plasma branched-chain amino acid (BCAA) concentrations and different muscle amino acid (AA) patterns than in age-matched control subjects.

OBJECTIVE

We examined whether the low plasma BCAA concentrations in COPD reflect an imbalance between anabolic and catabolic processes as evidenced by a low fat-free mass (FFM) and alterations in the anabolic hormone insulin and whether discrepancies in muscle AA concentrations between studies are related to different patient characteristics.

DESIGN

AA profiles in arterial plasma and quadriceps femoris muscle and insulin concentrations in venous plasma were analyzed in 28 postabsorptive COPD patients (14 with and 14 without macroscopic emphysema) and in 28 control subjects. FFM was measured by dual-energy X-ray absorptiometry.

RESULTS

The lower sum of plasma BCAAs in the COPD group than in the control subjects was the result of a lower leucine concentration (P: < 0.001); no significant difference in valine and isoleucine was found between the groups. In the COPD group, the lower leucine concentrations were associated with low FFM (P: < 0.01). Compared with the control group, the muscle-to-plasma leucine gradient was higher in the COPD group (P: < 0.001) and was associated with a higher insulin concentration (P: < 0.01). Several muscle AA concentrations were higher or tended to be higher in the group without emphysema than in the control group, whereas nearly all AA concentrations were lower in the group with emphysema.

CONCLUSIONS

Leucine metabolism is altered in COPD patients and is associated with low FFM and high insulin concentrations. There were striking differences in the skeletal muscle AA profile between the COPD subtypes.

Alcoholic liver disease: new insights in pathogenesis lead to new treatments

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in improvement of prevention and therapy, with promising prospects for even more effective treatments. The most successful approaches that one can expect to evolve are those that deal with the fundamental cellular disturbances resulting from excessive alcohol consumption. Two pathologic concepts are emerging as particularly useful therapeutically. Whereas it continues to be important to replenish nutritional deficiencies, when present, it is crucial to recognize that because of the alcohol-induced disease process, some of the nutritional requirements change. This is exemplified by methionine, which normally is one of the essential amino acids for humans, but needs to be activated to S-adenosylmethionine (SAMe), a process impaired by the disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. Indeed, SAMe was found to attenuate mitochondrial lesions in baboons, replenish glutathione, and significantly reduce mortality in patients with Child A or B cirrhosis. Similarly, polyenylphosphatidylcholine (PPC) corrects the ethanol-induced hepatic phospholipid depletion as well as the decreased phosphatidylethanolamine methyltransferase activity and opposes oxidative stress. It also deactivates hepatic stellate cells, whereas its dilinoleoyl species (DLPC) increases collagenase activity, resulting in prevention of ethanol-induced septal fibrosis and cirrhosis in the baboon. Clinical trials with PPC are ongoing in patients with alcoholic liver disease. Furthermore, enzymes useful for detoxification, such as CYP2E1, when excessively induced, become harmful and should be downregulated. PPC is one of the substances with anti-CYP2E1 properties that is now emerging. Another important aspect is the association of alcoholic liver disease with hepatitis C: a quarter of all patients with alcoholic liver disease also have markers of HCV infection, with an even higher incidence in some urban areas but, at present, no specific therapy is available since interferon is contraindicated in that population. However, in addition to antiviral medications, agents that oppose oxidative stress and fibrosis should also be tested for hepatitis C treatment since these two processes contribute much to the pathology and mortality associated with the virus. In addition to antioxidants (such as PPC, silymarin, alpha-tocopherol and selenium), anti-inflammatory medications (corticosteroids, colchicine, anticytokines) are also being tested as antifibrotics. Transplantation is now accepted treatment in alcoholics who have brought their alcoholism under control and who benefit from adequate social support but organ availability is still the major limiting factor and should be expanded more aggressively. Finally, abstinence from excessive drinking is always indicated; it is difficult to achieve but agents that oppose alcohol craving are becoming available and they should be used more extensively.

Characteristics of nitrogen metabolism in rats with thioacetamide-induced liver cirrhosis

Female Sprague-Dawley rats were given 0.03% thioacetamide (TAA) in their drinking water daily for 4 or 12 weeks, and were then given normal water for 4 weeks after the end of a 12-week TAA treatment to investigate amino acid metabolism. In the malnourished precirrhotic stage (stage 1) and the malnourished cirrhotic stage (stage 2), the aromatic amino acids (AAA), Glu, Asp, Orn, Arg and Cit increased, and the branched-chain amino acids (BCAA) decreased slightly. Because these changes normalized in the well-nourished cirrhotic stage (stage 3), they might have resulted from impairment of hepatocytes and malnutrition. The net uptake of BCAA into the liver increased in stage 2, but the AAA uptake did not exceed that in normal controls. Portal venous plasma AAA increased to the same level as arterial plasma AAA. These results suggest that the decrease in BCAA was partially due to liver uptake and that the increase in AAA was induced by reduction of liver uptake and overproduction in extrahepatic tissues. The liver contents of BCAA and AAA were unchanged in all stages, so were fully utilized in the impaired liver. The increases in Glu, Asp, Orn and Cit might have resulted from overproduction in the liver, because these contents of the liver increased in stage 2. In conclusion, the changes in amino acid metabolism in rats with cirrhosis induced by TAA closely resemble those seen in human liver cirrhosis.

Abnormalities in branched-chain amino acid metabolism in cirrhosis: influence of hormonal and nutritional factors and directions for future research

Plasma branched-chain amino acid (BCAA) levels are decreased in patients with liver cirrhosis, owing to an increase in BCAA tissue uptake and/or catabolism and a decrease in BCAA production from proteins. Non-specific factors such as malnutrition worsen this picture. Studies of BCAA fluxes and protein turnover in cirrhotic patients have given conflicting results due to patient heterogeneity, differences in method and bias in the expression of results. In well compensated cirrhosis, muscle wasting is moderate and probably due more to decreased protein synthesis than to increased protein catabolism. Hyperinsulinemia has been suggested as the main cause of decreased BCAA levels, by increasing BCAA uptake in muscle and additionally in adipose tissue. However, as depletion of fat stores is frequent in cirrhosis, this effect is certainly quantitatively weak. Also, there is no correlation between state of hyperinsulinemia and decrease in BCAA levels. An effect of cytokines (IL1 and TNF) on muscle BCAA catabolism is a possibility. Until recently, the contribution of the liver to abnormal BCAA metabolism has been underestimated. In cirrhotic liver an increase in liver transamination of branched-chain keto acids (BCKAs) has been suggested and may result from inhibition of liver BCKA dehydrogenase. A modification of protein turnover in cirrhotic liver must be also considered. Lastly, the contribution of non-hepatocyte liver cells, which are activated in cirrhosis, remains to be assessed.

Hyperammonemia-induced depletion of glutamate and branched-chain amino acids in muscle and plasma

BACKGROUND/AIMS

Exogenous hyperammonemia is known to decrease the plasma levels of branched-chain amino acids (BCAA). To investigate whether changes in intracellular amino acid concentrations of muscle are associated with and may, at least in part, mediate this effect, experiments were carried out on a total of 60 male Wistar rats.

METHODS

Five groups were formed in a randomized manner. Group A: no treatment; groups B1 and B2: 2-hour and 6-hour continuous central-venous infusions, respectively, of sodium salts; groups C1 and C2: 2-hour and 6-hour infusions of ammonium salts. We obtained venous blood samples and muscle biopsies. Plasma ammonia, whole blood glucose, serum insulin, blood pH, and amino acids in plasma as well as in the intracellular water of muscle were measured.

RESULTS

As compared with control group A, groups C1 and C2 displayed a 3.3- and a 4-fold increase, respectively, in the plasma ammonium concentration. Regarding insulin, the ammonium-infused rats were similar to group A but not to the sodium-infused B groups, which had significantly lower insulin concentrations. Administering ammonium brought about a decline in BCAA concentrations in plasma after 2 hours and in muscle after 6 hours. The ammonium-induced fall in intracellular BCAA values was preceded by an increase of glutamine as well as by a decrease of glutamate and alanine in both plasma and muscle.

CONCLUSIONS

It is pointed out that the inter-group differences in serum insulin, although possibly accounting for some of the findings, can by no means explain the entire pattern of amino acid concentrations seen after the ammonium infusions. Instead, our results agree with the hypothesis that hyperammonemia indirectly lowers the plasma levels of BCAA by stimulating glutamine synthesis, thus reducing the intracellular glutamate pool, which is likely to be restored, at least in part, by an intensified BCAA transamination. Clarification is needed as to whether carbon skeletons derived from valine and isoleucine additionally contribute to replenishing the glutamate pool.

Body composition in nonalcoholic cirrhosis: the effect of disease etiology and severity on nutritional compartments

BACKGROUND/AIMS

Previous studies of body composition in cirrhosis have either measured only one body compartment, used alcoholic subjects, or not corrected body composition for physical characteristics. The aim of this study was to perform a detailed analysis of body composition in subjects with nonalcoholic cirrhosis.

METHODS

Simultaneous measurements of total body potassium and total body water were performed and values of body cell mass and body fat were corrected for physical characteristics.

RESULTS

Child's class C patients had a significantly lower mean total body potassium index (i.e., percent observed value/expected value) and body fat index than class A or B patients. Eighty-one percent of class C patients had simultaneous reductions in body fat and body cell mass, and 71% of patients with class A disease had a significant reduction in either or both compartments. Nine patients showed the pattern of tissue loss seen with short-term starvation. Fourteen patients showed the pattern of tissue loss seen in physiological stress.

CONCLUSIONS

Severe liver disease is characterized by significant reductions in body fat and body cell mass, most class A patients have a significant reduction in some nutritional compartments, and the pattern of tissue loss may reflect mechanisms of tissue wasting.

Mechanisms of ethanol-drug-nutrition interactions

Mechanisms of the toxicologic manifestations of ethanol abuse are reviewed. Hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive hepatic generation of nicotinamide adenine dinucleotide and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) pathway, the microsomal ethanol-oxidizing system, which involves a specific cytochrome P450. It generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications and carcinogens. The contribution of gastric alcohol dehydrogenase to the first pass metabolism of ethanol and alcohol-drug interactions is now recognized. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta-carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other supernutrients include polyenylphosphatidylcholine, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in non-human primates. Thus, a better understanding of the pathology induced by ethanol has now generated improved prospects for therapy.

Leucine and phenylalanine kinetics in compensated liver cirrhosis: effects of insulin

BACKGROUND

The pathogenesis of the altered ratio of branched-chain amino acid to aromatic amino acid concentration in liver cirrhosis is poorly known. We explored the possible link between altered amino acid concentrations and kinetics in cirrhosis.

METHODS

Post-absorptive leucine and phenylalanine rates of appearance (Ra) and their response to insulin were studied in patients with compensated, nondiabetic cirrhosis and in controls.

RESULTS

In the cirrhotics, concentration of postabsorptive phenylalanine was greater and that of alpha-ketoisocaproate lower than in controls, whereas concentration of leucine was comparable. Leucine Ra was lower, phenylalanine Ra was greater, and the ratio of leucine Ra to phenylalanine Ra was markedly decreased (P < 0.001) in patients vs. controls (2.40 +/- 0.23 vs. 3.67 +/- 0.19, respectively). During an euglycemic-hyperinsulinemic clamp, glucose disposal was reduced and leucine Ra was suppressed more profoundly in cirrhotics than in controls, whereas suppression of phenylalanine Ra was comparable.

CONCLUSIONS

In compensated liver cirrhosis, postabsorptive phenylalanine Ra is increased with respect to leucine Ra, suggesting the existence either of altered amino acid pools and/or transport or of abnormally sequenced proteins and/or peptides. Insulin resistance is restricted to glucose, but not to amino acid metabolism.

Effect of S-adenosyl-L-methionine administration on plasma levels of sulphur-containing amino acids in patients with liver cirrhosis

An impaired transsulphuration pathway has been described in patients with liver cirrhosis. The defective metabolic step is located at the site of S-adenosyl-L-methionine (SAMe) formation from methionine. In a placebo-controlled study, we measured the fasting plasma levels of sulphur-containing amino-acids in cirrhotic patients with hypermethioninemia and/or severe hepatocellular failure, during treatment with exogenous SAMe (1.2 g i.v. for 3 days, followed by an oral administration of 1.2 g for an additional 30 days; 8 cases) or saline and placebo tablets (8 cases). All subjects were initially treated during hospital admission, and completed the oral study as out-patients. In patients given SAMe, long-term treatment doubled the plasma concentration of the secondary sulphur-containing amino acid cystine (from 36 [SD 18] mumol.l(-1) to 67 [36]) and taurine (from 42 [13] mumol.l(-1) to 89 [33]), which were on average low-normal at baseline, without any change in the concentration of methionine, of neutral amino acids, and of polyamines. No changes in plasma amino acids were observed in the control group. Two-factor, repeated measures of analysis of variance revealed differences between SAMe- and placebo-treated patients, consistent with an effect of long-term SAMe administration on secondary sulphur-containing amino acids. The potential therapeutic advantage of such treatment remains to be determined in clinical studies.

In vivo differences between the turnover rates of leucine and leucine's ketoacid in stable cirrhosis

Based on urinary nitrogen excretion, previous studies have indicated increased protein breakdown rates in cirrhosis. However, studies using [1-13C]-leucine infusion methodology have found normal protein breakdown rates. Because abnormal partitioning between extracellular and intracellular leucine exists in cirrhosis, plasma enrichment of leucine's keto acid (KIC), a marker of intracellular leucine, may more accurately reflect protein metabolism than plasma [1-13C]leucine enrichment. Therefore, protein breakdown and oxidation were calculated using both [1-13C]leucine and [1-13C]KIC and compared with urinary nitrogen excretion in seven cirrhotics and seven matched controls after an overnight fast. The ratio of KIC and leucine plasma enrichment was decreased (P less than 0.001) in cirrhosis because of lower KIC enrichment (P less than 0.006). Cirrhotics had increased rates of protein breakdown (P less than 0.006) and protein oxidation (P less than 0.05) based on KIC (P less than 0.006) but not leucine enrichment. In controls, protein oxidation calculated from urinary nitrogen excretion did not differ from KIC results (0.88 +/- 0.08 vs. 0.83 +/- 0.06) but was higher than the leucine method (0.88 +/- 0.08 vs. 0.73 +/- 0.05; P less than 0.01). However, in cirrhotics protein oxidation based on urinary nitrogen was lower than the KIC methodology (P less than 0.01). Therefore, cirrhotics have accelerated rates of protein breakdown and oxidation associated with increased extrarenal nitrogen loss. Furthermore, these results suggest abnormal leucine transport across cell membranes.

Measurements of total body and extracellular water in cirrhotic patients with and without ascites

Using H2[18O] tracer isotope dilution and corrected bromide space as standard reference techniques, we determined total body water and extracellular water in cirrhotic patients with (four men and four women) and without (seven men and six women) ascites and compared them with a normal control group (eight men and six women). These results were then compared with calculations of total body and extracellular water determined by the bioelectrical impedance analysis technique. According to H2[18(O)] dilution, total body water was similar in cirrhotic patients without ascites and in controls (60.8% +/- 2.1% vs. 60.3% +/- 1.4% body wt), but was increased in patients with ascites (69.7% +/- 1.2% body wt; p less than 0.002). Correlation was excellent between the H2[18(O)] dilution and bioelectrical impedance measurements of total body water in controls and cirrhotic patients without ascites (r = 0.98; p less than 0.0001). However, this correlation was poor in cirrhotic patients with ascites (r = 0.17; not significant). According to the bromide space, extracellular water (expressed as a percentage of total body water) was increased in cirrhotic patients with (57.8% +/- 1.8%; p less than 0.001) and without (44.0% +/- 1.2%; p less than 0.001) ascites compared with controls (36.6% +/- 1.0%). A poor correlation (r = 0.41; p less than 0.13) was seen for extracellular water measurements between the bromide space method and the bioelectrical impedance method, which failed to detect the differences among the three groups observed with the bromide space technique. Furthermore, bioelectrical impedance failed to detect any change in total body or extracellular water after paracentesis, with a degree of inaccuracy that increased linearly as the amount of ascitic fluid removed increased (r = 0.97; p less than 0.001). All these intergroup comparisons remained the same, whether the analysis was of both men and women combined or for each gender individually. However, we saw differences between men and women in the control group and cirrhotic group without ascites. These results demonstrate that abnormalities in water homeostasis and compartmentalization between intracellular (the difference between total body and extracellular water fluid) and extracellular water may exist in cirrhosis whether or not fluid accumulation is clinically evident. These data further indicate that alterations in the metabolically active body cell mass (as represented by intracellular water) in cirrhosis may occur independently of total body water and calculated fat-free body mass. In addition, gender is an important variable to control for in studies of this type.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitation of tryptophan and other plasma amino acids by automated pre-column o-phthaldialdehyde derivatization high-performance liquid chromatography: improved sample preparation

Pre-column derivatization with o-phthaldialdehyde is a rapid and sensitive method for the quantitation of amino acids in biological fluids. This method uses acetonitrile as a deproteinizing reagent which gives improved recovery of tryptophan compared with 5-sulfosalicylic acid and permits the measurement of aspartic acid which coelutes with 5-sulfosalicylic acid. The method is automated to increase reproducibility and convenience. Mean coefficients of variation for peak areas relative to internal standard were 3.2 and 5.2% for amino acid standards and plasma samples, respectively. The presence of nitrilotriacetic acid stabilized the o-phthaldialdehyde reagent which is important in an automated system. The method is suitable for the analysis of large numbers of plasma samples where total tryptophan and aspartic acid are of interest.

Attenuation of alcohol-induced hepatic fibrosis by polyunsaturated lecithin

Characteristic features of alcoholic liver injury include fibrosis and striking membrane alterations, with associated phospholipid changes. To offset some of these abnormalities, a 10-yr study was conducted in baboons: 12 animals (eight females, four males) were fed a liquid diet supplemented with polyunsaturated lecithin (4.1 mg/kcal) for up to 8 yr, with either ethanol (50% of total energy) or isocaloric carbohydrate. They were compared with another group of 18 baboons fed an equivalent amount of the same diet (with or without ethanol), but devoid of lecithin. In the two groups, comparable increases in lipids developed in the ethanol-fed animals, but striking differences in the degree of fibrosis were seen. Whereas at least septal fibrosis (with cirrhosis in two) and transformation of their lipocytes into transitional cells developed in seven of the nine baboons fed the regular diet with ethanol, septal fibrosis did not develop in any animals fed lecithin (p less than 0.005). They did not progress beyond the stage of perivenular fibrosis (sometimes associated with pericellular and perisinusoidal fibrosis) and had a significantly lesser activation of lipocytes to transitional cells. Furthermore, when three of these animals were taken off lecithin, but continued on the same amount of the ethanol-containing diet, they rapidly (within 18 to 21 mo) progressed to cirrhosis, accompanied by an increased transformation of their lipocytes to transitional cells. These results indicate that some component of lecithin exerts a protective action against the fibrogenic effects of ethanol. Because we had previously found that choline, in amounts present in lecithin, has no comparable action, the polyunsaturated phospholipids themselves might be responsible for the protective effect.

S-adenosyl-L-methionine attenuates alcohol-induced liver injury in the baboon

Chronic ethanol consumption by baboons (50% of energy from a liquid diet) for 18 to 36 mo resulted in significant depletion of hepatic S-adenosyl-L-methionine concentration: 74.6 +/- 2.4 nmol/gm vs. 108.9 +/- 8.2 nmol/gm liver in controls (p less than 0.005). The depletion was corrected with S-adenosyl-L-methionine (0.4 mg/kcal) administration (102.1 +/- 15.4 nmol/gm after S-adenosyl-L-methionine-ethanol, with 121.4 +/- 11.9 nmol/gm in controls). Ethanol also induced a depletion of glutathione (2.63 +/- 0.13 mumol/gm after ethanol vs. 4.87 +/- 0.36 mumol/gm in controls) that was attenuated by S-adenosyl-L-methionine (3.89 +/- 0.51 mumol/gm in S-adenosyl-L-methionine-methanol vs. 5.22 +/- 0.53 mumol/gm in S-adenosyl-L-methionine controls). There was a significant correlation between hepatic S-adenosyl-L-methionine and glutathione level (r = 0.497; p less than 0.01). After the baboons received ethanol, we observed the expected increase in circulating levels of the mitochondrial enzyme glutamic dehydrogenase: 95.1 +/- 21.4 IU/L vs. 13.4 +/- 1.8 IU/L; p less than 0.001, whereas in a corresponding group of animals given S-adenosyl-L-methionine with ethanol, the values were only 30.3 +/- 7.1 IU/L (vs. 9.6 +/- 0.7 IU/L in the S-adenosyl-L-methionine controls). This attenuation by S-adenosyl-L-methionine of the ethanol-induced increase in plasma glutamic dehydrogenase (p less than 0.005) was associated with a decrease in the number of giant mitochondria (assessed in percutaneous liver biopsy specimens), with a corresponding change in the activity of succinate dehydrogenase, a mitochondrial marker enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)