Effects of branched-chain amino acid infusion on protein metabolism in rats with acute hepatic failure

Effect of Hemodiabsorption and Sorbent-Based Pheresis on Amino Acid Levels in Hepatic Failure

Changes in plasma amino acid concentrations were measured in patients with hepatic failure during extracorporeal hemodiabsorption (using the Liver Dialysis Unit, “the Unit”) or hemodiabsorption plus sorbent-based pheresis treatment (using the Liver Dialysis Plasmafilter Unit, “the PF-Unit”) Systems.

Eight patients with hepatic failure, grade 3 or 4 encephalopathy, elevated bilirubin and/or creatinine levels and respiratory or renal failure were treated for 1–3 days with the Unit alone. Three of these were also treated with the Unit containing 10 g of BCAA in the sorbent suspension. Four patients with hepatic failure treated with the PF Unit also had 10 g of branched chain amino acid (BCAA) added to the sorbents of the Unit portion of this device. Pre- and post-plasma samples were drawn and high performance liquid chromatography (HPLC) was used to separate and detect amino acids in the plasma.

Both the Unit and the PF-Unit have the capability to selectively remove various amino acids, especially aromatic amino acids (AAA). The pre-treatment amino acid profiles of plasma were typical for hepatic failure, with abnormally high levels of phenylalanine, tyrosine, tryptophan, and methionine and decreased levels of valine, leucine and isolucine.

The average pre-treatment Fischer ratio (BCAA/AAA) for both Unit and PF-Unit patients was 1.43 (±0.58). Treatments by both systems resulted in an increase of BCAA levels in blood and concomitant decrease of AAA levels, with an average Fischer ratio improvement of 30–38% for the Unit and PF-Unit without BCAA. The Fischer ratio improved by 90% (average) for the Unit with BCAA. Levels of many other amino acids (such as alanine, glycine, proline or lysine) increased during both Unit and PF-Unit treatments. The removal of strongly protein-bound toxin and amino acids such as tryptophan and sulphydryl amino acids was more effective by the PF-Unit.

Both the Unit and the PF-Unit have the unique capability to remove toxic aromatic amino acids while increasing BCAA levels in patient. The increase in many amino acid levels may be related to the removal of toxins that interfere with normal amino acid metabolism. The addition of the PF module improves the removal of bilirubin and similarly protein-bound chemicals. Changes in amino acid profiles by the Unit and the PF-Unit contrast markedly with other extracorporeal devices.

Biochemistry of uridine in plasma

Uridine is a pyrimidine nucleoside that plays a crucial role in synthesis of RNA, glycogen, and biomembrane. In humans, uridine is present in plasma in considerably higher quantities than other purine and pyrimidine nucleosides, thus it may be utilized for endogenous pyrimidine synthesis. Uridine has a number of biological effects on a variety of organs with or without disease, such as the reproductive organs, central and peripheral nervous systems, and liver. In addition, it is used in clinical situations as a rescue agent to protect against the adverse effects of 5-fluorouracil. Since the biological actions of uridine may be related to its plasma concentration, it is important to examine factors that have effects on that concentration. Factors associated with an increase in plasma concentration of uridine include enhanced ATP consumption, enhanced uridine diphosphate (UDP)-glucose consumption via glycogenesis, inhibited uridine uptake by cells via the nucleoside transport pathway, increased intestinal absorption, and increased 5-phosphribosyl-1-pyrophosphate and urea synthesis. In contrast, factors that decrease the plasma concentration of uridine are associated with accelerated uridine uptake by cells via the nucleoside transport pathway and decreased pyrimidine synthesis.

Metabolic profiling analysis of a D-galactosamine/lipopolysaccharide-induced mouse model of fulminant hepatic failure

The purpose of this study was to characterize the changes in metabolic intermediates and to investigate the metabolic profile of a mouse model of fulminant hepatic failure (FHF), induced by D-galactosamine/lipopolysaccharide (GalN/LPS). Plasma metabolite levels were detected using gas chromatography/time-of-flight mass spectrometry, and the acquired data were transferred into Simca-P and processed using principal components analysis (PCA). In total, 45 metabolites were identified from the 267 distinct compounds found in the study. Whereas significant differences were noted in the plasma levels of the control and FHF groups, no differences in gluconeogenesis or glycolysis were noted following GalN/LPS treatment. Our data also suggest that the production of ketone bodies, and the tricarboxylic acid and urea cycles, was inhibited. PCA data suggest that 5-hydroxyindoleacetic acid, glucose, beta-hydroxybutyrate, and phosphate parameters had the highest weights on each of the principal components, and that they were the most important metabolites contributing to the separation of groups. In conclusion, this metabonomic approach can be used as a powerful tool to characterize changes in metabolic intermediates and to search for metabolic markers under certain pathophysiological conditions, such as FHF. Our data also demonstrate that a combination of 5-hydroxyindoleacetic acid, glucose, beta-hydroxybutyrate, and phosphate concentrations in the plasma is a potential marker for FHF, as well as for the early prognosis of FHF.

[Acute liver failure]

Acute liver failure is characterized by a dynamic clinical course associated with high mortality. The main prognostic determinant is the development of extrahepatic complications. Close monitoring is mandatory, and prophylactic measures to avoid complications should be initiated. In case of complications, early and aggressive treatment is indicated. To date, artificial liver support devices are still in the experimental phase. Liver transplantation should be considered in patients with predictors of a poor spontaneous prognosis. Therefore, a transplant center should be contacted in every case of acute liver failure.

Branched-chain amino acids: a role in skeletal muscle proteolysis in catabolic states?

A 48-h starvation period resulted in a great increase in muscle proteolysis-as measured following the release of tyrosine into the medium-in incubated isolated rat extensor digitorum longus (EDL) muscles. We have quantified the contribution of the different proteolytic systems to the increased protein degradation and observed a considerable activation in the ATP-dependent proteolytic (60%) and in the calcium-dependent (125%) systems, while no increases were observed in lysosomal proteolysis. The addition of 10 mM leucine to the incubation medium did not result in any changes in either total proteolytic rate or the activity rates of any of the different systems studied. In addition, the presence of the amino acid did not influence the levels of mRNA for the different genes studied-ubiquitin, C8 proteasome subunit, E2 conjugating enzyme, m-calpain, and cathepsin B. In a similar way, as observed during starvation, tumor growth resulted in increased protein degradation in incubated isolated EDL muscles from animals bearing the Yoshida AH-130 ascites hepatoma. The increased rate of protein degradation affected all the proteolytic systems studied: ATP- and calcium-dependent and lysosomal. Finally, leucine addition (10 mM), although not able to revert the increased proteolytic rate, resulted in a decrease in the gene expression for ubiquitin, C8 proteasome subunit and cathepsin B.

Effects of leucine supplemented diet on intestinal absorption in tumor bearing pregnant rats

BACKGROUND

It is known that amino acid oxidation is increased in tumor-bearing rat muscles and that leucine is an important ketogenic amino acid that provides energy to the skeletal muscle.

METHODS

To evaluate the effects of a leucine supplemented diet on the intestinal absorption alterations produced by Walker 256, growing pregnant rats were distributed into six groups. Three pregnant groups received a normal protein diet (18% protein): pregnant (N), tumor-bearing (WN), pair-fed rats (Np). Three other pregnant groups were fed a diet supplemented with 3% leucine (15% protein plus 3% leucine): leucine (L), tumor-bearing (WL) and pair-fed with leucine (Lp). Non pregnant rats (C), which received a normal protein diet, were used as a control group. After 20 days, the animals were submitted to intestinal perfusion to measure leucine, methionine and glucose absorption.

RESULTS

Tumor-bearing pregnant rats showed impairment in food intake, body weight gain and muscle protein content, which were less accentuated in WL than in WN rats. These metabolic changes led to reduction in both fetal and tumor development. Leucine absorption slightly increased in WN group. In spite of having a significant decrease in leucine and methionine absorption compared to L, the WL group has shown a higher absorption rate of methionine than WN group, probably due to the ingestion of the leucine supplemented diet inducing this amino acid uptake. Glucose absorption was reduced in both tumor-bearing groups.

CONCLUSIONS

Leucine supplementation during pregnancy in tumor-bearing rats promoted high leucine absorption, increasing the availability of the amino acid for neoplasic cells and, mainly, for fetus and host utilization. This may have contributed to the better preservation of body weight gain, food intake and muscle protein observed in the supplemented rats in relation to the non-supplemented ones.

Prognostic value of energy metabolism in patients with viral liver cirrhosis

The effect of energy malnutrition on survival in patients with non-alcoholic viral liver cirrhosis has not been well defined. We characterized energy metabolism at study entrance and prospectively analyzed its effect on subsequent survival in cirrhotics. One hundred nine consecutive patients with viral liver cirrhosis and 22 healthy control subjects participated in the study. By indirect calorimetry after overnight bedrest and fasting, resting energy expenditure (REE) was measured and non-protein respiratory quotient (npRQ) was calculated. Survival of cirrhotics were followed for up to 8 y. Survival rate was estimated with the Kaplan-Meier method. REE at entrance was significantly higher than the predicted basal metabolic rate (BMR) in cirrhotics (P < 0.001). NpRQ was significantly lower in cirrhotics than in controls (P < 0.001). Survival rate was significantly lower in patients with low npRQ ( < 0.85) than in patients with scores above 0.85 (P < 0.01) and was significantly higher in normal metabolic patients (0.9 < REE/BMR < 1.1) than in hypometabolic (REE/BMR < 0.9) or hypermetabolic (1.1 < REE/BMR) patients (P < 0.05). The proportional hazards model showed that npRQ (relative risk = 0.0003, 95% confidence interval = 0.0000-0.0970), REE/BMR (0.0199, 0.0007-0.5652), prothrombin time, and ammonia were independent significant factors determining survival. Thus evaluation of energy metabolism can be used to predict survival in patients with viral liver cirrhosis.

Effects of prostaglandin E(1) on the efficacy of xenogeneic extracorporeal pig liver perfusion in a canine model of acute liver failure

Xenogeneic extracorporeal liver perfusion (ECLP) has the potential to become an important tool in the management of patients with severe liver failure. We previously showed that xenogeneic pig liver perfusion may be prolonged for up to 9 hours by the administration of prostaglandin E(1) (PGE(1)). In this study, we used a canine model of acute liver failure to evaluate the effects of PGE(1) on the efficacy of ECLP as a liver-assist device. Liver failure was surgically induced in 12 beagle dogs, with a control group (group 1, n = 4) not connected to the ECLP circuit. Direct cross-circulation between the dogs and the ECLP circuit using a pig liver was performed without (group 2, n = 4) or with (group 3, n = 4) continuous administration of PGE(1) through the portal vein of the pig liver. The duration of cross-circulation in group 3 (9.4 +/- 1.2 hours) was significantly longer than in group 2 (4.3 +/- 1.0 hours). In addition, elevation of blood ammonia, total bile acid, and hyaluronic acid levels was less marked in group 3 compared with the other 2 groups. The ratio of branched-chain amino acids to aromatic amino acids was also improved in group 3. The mean survival time in group 3 (26.6 +/- 0.4 hours) was significantly longer than in group 1 (15.5 +/- 1.3 hours) or group 2 (17.1 +/- 2.9 hours). Continuous administration of PGE(1) to xenogeneic ECLP resulted in a significant improvement in both liver function and survival time of dogs with surgically induced liver failure.

Branched-chain amino acids inhibit proteolysis in rat skeletal muscle: mechanisms involved

Incubation of isolated rat soleus and EDL muscles in the presence of 10 mM leucine resulted in a decreased proteolytic rate as measured by the release of tyrosine into the incubation medium. The effect of this branched-chain amino acid (BCAA) is associated with a decreased activity of the lysosomal proteases and a decreased expression of the genes of the ATP-ubiquitin-dependent proteolysis (ubiquitin and C8). Incubation of muscles in the presence of actinomycin D revealed that the effects of the amino acid can be accounted for by an inhibition of the transcription rate. The presence of leucine did not influence the gene expression of other nonlysosomal (m-calpain) and lysosomal (cathepsin B) proteolytic systems. It is concluded that the well-known effect of BCAA on muscle proteolysis is mediated, in the short term, by the inhibition of lysosomal proteolysis. In a longer period, based on the inhibition of gene transcription observed, an involvement of the ATP-dependent proteolytic system is also likely to occur.

Effect of branched-chain amino acids on the plasma concentration of uridine does not occur via the action of glucagon or insulin

To examine whether branched-chain amino acids affect the plasma concentration of uridine, we administered branched-chain amino acids (L-isoleucine, 2.85 g, L-leucine 5.71 g, and L-valine, 3.43 g) orally to 6 healthy subjects. Plasma uridine and glucose decreased by 44% and 12%, respectively, together with an increase in plasma isoleucine, leucine, and valine 90 minutes after administration. However, branched-chain amino acids did not affect the plasma concentration and urinary excretion of purine bases (hypoxanthine, xanthine, and uric acid) and uridine or the plasma concentration of insulin, glucagon, and cyclic adenosine monophosphate (cAMP). Since small amounts of regular insulin, which were found to decrease plasma glucose more than the amino acids, did not decrease the plasma concentration of uridine, these results suggest that plasma uridine was decreased by a direct effect of the branched-chain amino acids on the cellular uptake and/or release of uridine.

Nutritional modulation of liver regeneration by carbohydrates, lipids, and amino acids: a review

The survival of patients after a life-threatening hepatic injury of varying etiology depends on the ability of the remaining hepatocytes to regenerate. Thus, the stimulation of hepatic regeneration can have tremendous therapeutic relevance. Experimental studies--performed mostly on a model of regenerating rat liver after partial hepatectomy--indicate that glucose administration inhibits, whereas infusion of a lipid emulsion can enhance, the rate of liver regeneration. However, the inhibitory effect of glucose on liver regeneration is not observed when glucose is administered together with other nutrients. The results further indicate that administration of a standard amino acid mixture without energy substrate has an inhibitory effect and that development of liver regeneration can be favorably influenced by branched-chain amino acids (valine, leucine, and isoleucine) and glutamine.

Leucine metabolism in partially hepatectomized rats

BACKGROUND/AIMS

We hypothesized that the decrease in plasma branched-chain amino acids (i.e. valine, leucine and isoleucine) and the increase in the oxidized leucine fraction demonstrated in cirrhotic rats in our previous study were caused by the reduced liver cell mass. In the present study we have evaluated the influence of the loss of a substantial amount of the hepatic tissue on changes in leucine metabolism.

METHODS

A two-thirds partial hepatectomy (PH) was performed in male Wistar rats, weighing 210-250 g. Sham-operated rats served as controls. Whole-body leucine kinetics and ketoisocaproate oxidation rates in the isolated perfused liver were investigated using continuous infusion of [1-14C]leucine and alpha-keto[1-14C]ketoisocaproate at 0 h, 24 h and 72 h after surgery. All groups were compared by analysis of variance, and differences were considered significant at the p < 0.05 level.

RESULTS

A significant decrease in the sum of branched-chain amino acids in blood plasma was observed at 24 h after PH. The decrease in whole-body leucine utilization in protein synthesis observed at 24 h after PH was associated with a decrease in protein synthesis in the gastrocnemius muscle, in the small intestine and in the liver remnant (although protein synthesis per mg of liver protein was higher than in sham-treated animals). In contrast, the rate of whole-body leucine oxidation increased immediately after PH (PH: 4.5 +/- 0.7 vs. sham: 2.4 +/- 0.4; mumol .100 g b.w.-1.h-1). As a result of the opposite changes in protein synthesis and leucine oxidation, marked increases in oxidized leucine fraction were observed immediately (14.6 +/- 1.5%) and 24 h (15.1 +/- 1.6%) after PH in comparison to the sham-treated rats (7.1 +/- 0.8%). In isolated perfused livers of PH rats, an increase in ketoisocaproate oxidation per liver weight unit was observed at 24 h and 72 h in comparison to the sham group. The loss of liver capacity for ketoisocaproate oxidation was restored at 72 h after PH, although the liver weight did not reach the preoperative value.

CONCLUSIONS

We conclude that the loss of hepatic tissue results in an increase in leucine oxidized fraction that is caused by both a decrease in protein synthesis and an increase in leucine oxidation. Both the liver remnant and the extrahepatic tissues are involved in this response.