Differences in amino acid kinetics in cirrhosis

Protein tolerance to standard and high protein meals in patients with liver cirrhosis

AIM

To investigate the plasma amino acid response and tolerance to normal or high protein meals in patients with cirrhosis.

METHODS

The plasma amino acid response to a 20 g mixed protein meal was compared in 8 biopsy-proven compensated cirrhotic patients and 6 healthy subjects. In addition the response to a high protein meal (1 g/kg body weight) was studied in 6 decompensated biopsy-proven cirrhotics in order to evaluate their protein tolerance and the likelihood of developing hepatic encephalopathy (HE) following a porto-caval shunt procedure. To test for covert HE, the “number connection test” (NCT) was done on all patients, and an electroencephalogram was recorded in patients considered to be at Child-Pugh C stage.

RESULTS

The changes in plasma amino acids after a 20 g protein meal were similar in healthy subjects and in cirrhotics except for a significantly greater increase (P < 0.05) in isoleucine, leucine and tyrosine concentrations in the cirrhotics. The baseline branched chain amino acids/aromatic amino acids (BCAA/AAA) ratio was higher in the healthy persons and remained stable-but it decreased significantly after the meal in the cirrhotic group. After the high protein meal there was a marked increase in the levels of most amino acids, but only small changes occurred in the levels of taurine, citrulline, cysteine and histidine.The BCAA/AAA ratio was significantly higher 180 and 240 min after the meal. Slightly elevated basal plasma ammonia levels showed no particular pattern. Overt HE was not observed in any patients.

CONCLUSION

Patients with stable liver disease tolerate natural mixed meals with a standard protein content. The response to a high protein meal in decompensated cirrhotics suggests accumulation of some amino acids but it did not precipitate HE. These results support current nutritional guidelines that recommend a protein intake of 1.2-1.5 g/kg body weight/day for patients with cirrhosis.

Nutrition and chronic liver disease

Nutritional abnormalities almost uniformly accompany the metabolic disturbances of severe chronic liver disease and may adversely affect patient well-being and survival, especially surrounding liver transplantation surgery. The exact metabolic alterations responsible for malnutrition and its consequences in these patients have been debated and are a focus of this review. Disturbances in energy production and utilization, as well as macro- and micronutrient metabolism have been appreciated but are not always easily identified or quantifiable. Interestingly, the manifestations of poor nutritional status can vary substantially between patients, even in those having the same etiology and severity of illness. Proper assessment of patients with liver disease for malnutrition carries its own challenges, but some of the more easily applied techniques, such as anthropometry, can be comparable in accuracy to more sophisticated measuring tools. Gaining an appreciation and understanding of how nutritional disturbances develop and can contribute to morbidity and mortality will help combat inappropriate nutritional losses in this specialized group of patients. In many instances, simple adjustments in diet can offset losses and stabilize or improve the patient's nutritional status.

Enhanced levels of whole-body protein turnover in patients with chronic obstructive pulmonary disease

A substantial number of patients with chronic obstructive pulmonary disease (COPD) are characterized by fat-free mass wasting and altered muscle and plasma amino acid levels, suggesting changes in protein metabolism. In the present study, we examined whether whole-body protein breakdown (PB) and synthesis (PS) differ between 14 stable patients with COPD and 8 healthy controls. Whole-body PB, PS, and net PB (= PB-PS) were measured by the combined infusion of the stable isotopes L-[ring-(2)H(5)]phenylalanine (Phe) and L-[ring-(2)H(2)]tyrosine. Because there is evidence for specific disturbances in leucine (Leu) metabolism, the PB values were compared with those obtained when infusing L-[1-(13)C]Leu tracer. In arterialized-venous plasma and in vastus lateralis muscle, the isotope enrichment values and amino acid concentrations were measured. Whole-body PS and PB, assessed by Phe and Tyr tracer, were higher in the COPD group than in the control group (p < 0.05), indicating an elevated protein turnover. Net PB was increased in both groups, indicating a comparable degree of protein catabolism in the postabsorptive state. In contrast, whole-body PB determined by Leu tracer was not different between the groups. As a consequence, the ratio of Leu to Phe breakdown was reduced in the COPD group (p < 0.001). Moreover, in the COPD group a higher muscle-to-plasma gradient was found for Leu (p < 0.001) but not for Phe. The present study reveals elevated levels for protein turnover in patients with COPD, and indicates that infusion of the Leu tracer gives a reflection of Leu metabolism but not of whole-body protein metabolism in these patients.

Effect of mesocaval interposition shunting and repeated sclerotherapy on blood levels of gastrointestinal regulatory peptides, amino acids, and lysosomal enzymes--a prospective randomised trial

AIMS/BACKGROUND

Patients with liver cirrhosis and portal hypertension frequently exhibit a multitude of alterations of hormones and metabolism, but the relation of these alterations to liver function, degree of blood shunting, and hepatic encephalopathy remains unclear.

METHODS

Twenty-four patients were randomised to mesocaval interposition shunt (MIS) and 21 patients to repeated sclerotherapy (ST). Several peptide hormones, amino acids and lysosomal enzymes were monitored during a 4 year follow-up period.

RESULTS

Insulin and glucagon levels were elevated in the MIS group compared to pre-therapy levels, whereas the gastrin level was significantly higher in the ST group. Pancreatic polypeptide, somatostatin and vasoactive intestinal peptide levels were not affected by either treatment. The branched chain amino acids valine, leucine and isoleucine serum levels were all elevated after ST, and the arginine, proline and tyrosine levels were higher in the MIS group at follow-up. Other amino acids were not changed, neither were the lysosomal enzymes beta-hexosaminidase nor beta-glucoronidase during this longterm follow-up.

CONCLUSION

MIS or repeated ST treatment only affected serum levels of hormones, amino acids and lysosomal enzymes to a limited extent. In this trial, the type of treatment had only a small influence on these parameters during long term follow-up.

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.

Defective nonoxidative leucine degradation and endogenous leucine flux in cirrhosis during an amino acid infusion

The metabolic fate of leucine's first and second carbon may be different depending on the tissue in which leucine is metabolized, as well as the prevailing hormonal milieu of that tissue. However, previous studies of leucine kinetics in humans have used only leucine labeled (as tracer) at the first carbon position. Because cirrhosis is associated with factors (such as insulin resistance and altered fuel substrate utilization) that may influence how leucine is degraded, the kinetics of leucine's first and second carbon using a simultaneous infusion of [1-14C] leucine and [2-13C] leucine were studied in the postabsorptive state and during an amino acid infusion in 6 stable cirrhotic patients and 6 matched controls. The data were normalized for different body compartments that were quantified from the dilution of H2 [180] and bromide. The body cell mass, but not body weight or fat-free body mass, was decreased in cirrhosis (P < .001). In response to the amino acid infusion, total leucine appearance from proteolysis and leucine's incorporation into protein increased significantly in both groups, but were higher in cirrhotic patients. Endogenous protein breakdown decreased in normals but remained unchanged in cirrhosis. These alterations in leucine metabolism became more prominent when data were expressed based on the body cell mass rather than on body weight. The oxidation of leucine's first carbon (C1) was decreased in cirrhosis, but the oxidation of leucine's second carbon (C2) did not differ between groups during both the postabsorptive period and the amino acid infusion, while nonoxidative leucine degradation [the difference between the oxidation of leucine's (C1) and (C2)] was also decreased in cirrhosis. In addition, there was a positive correlation between nonoxidative leucine degradation (which represents leucine incorporation into fat), and the respiratory quotient obtained from indirect calorimetry (r = .87; P < .001). These data suggest that the extent of leucine carbon oxidation is dependent on whether fat or carbohydrate is the prevailing fuel substrate. In addition, cirrhotic patients have decreased nonoxidative leucine degradation and are unable to suppress endogenous protein breakdown normally in response to amino acid administration. These abnormalities may contribute to the diminished fat stores and body cell mass commonly observed in cirrhosis.

Metabolic effects of liver transplantation in cirrhotic patients

To assess whether liver transplantation (LTx) can correct the metabolic alterations of chronic liver disease, 14 patients (LTx-5) were studied 5+/-1 mo after LTx, 9 patients (LTx-13) 13+/-1 mo after LTx, and 10 patients (LTx-26) 26+/-2 months after LTx. Subjects with chronic uveitis (CU) and healthy volunteers (CON) were also studied. Basal plasma leucine and branched-chain amino acids were reduced in LTx-5, LTx-13, and LTx-26 when compared with CU and CON (P < 0.01). The basal free fatty acids (FFA) were reduced in LTx-26 with respect to CON (P < 0.01). To assess protein metabolism, LTx-5, LTx-13, and LTx-26 were studied with the [1-14C]leucine turnover combined with a 40-mU/m2 per min insulin clamp. To relate changes in FFA metabolism to glucose metabolism, eight LTx-26 were studied with the [1-14C]palmitate and [3-3H]glucose turnovers combined with a two-step (8 and 40 mU/m2 per min) euglycemic insulin clamp. In the postabsorptive state, LTx-5 had lower endogenous leucine flux (ELF) (P < 0.005), lower leucine oxidation (LO) (P < 0.004), and lower non-oxidative leucine disposal (NOLD) (P < 0.03) with respect to CON (primary pool model). At 2 yr (LTx-26) both ELF (P < 0.001 vs. LTx-5) and NOLD (P < 0.01 vs. LTx-5) were normalized, but not LO (P < 0.001 vs. CON) (primary and reciprocal pool models). Suppression of ELF by insulin (delta-reduction) was impaired in LTx-5 and LTx-13 when compared with CU and CON (P < 0.01), but normalized in LTx-26 (P < 0.004 vs. LTx-5 and P = 0.3 vs. CON). The basal FFA turnover rate was decreased in LTx-26 (P < 0.01) and CU (P < 0.02) vs. CON. LTx-26 showed a lower FFA oxidation rate than CON (P < 0.02). Tissue glucose disposal was impaired in LTx-5 (P < 0.005) and LTx-13 (P < 0.03), but not in LTx-26 when compared to CON. LTx-26 had normal basal and insulin-modulated endogenous glucose production. In conclusion, LTx have impaired insulin-stimulated glucose, FFA, and protein metabolism 5 mo after surgery. Follow-up at 26 mo results in (a) normalization of insulin-dependent glucose metabolism, most likely related to the reduction of prednisone dose, and, (b) maintenance of some alterations in leucine and FFA metabolism, probably related to the functional denervation of the graft and to the immunosuppressive treatment.

Effect of long-term refeeding on protein metabolism in patients with cirrhosis of the liver

Patients with cirrhosis of the liver require an increased amount of protein to achieve N balance. However, the utilization of protein with increased protein intake, i.e. the slope from regression analysis of N balance v. intake, is highly efficient (Nielsen et al. 1995). In the present study, protein requirement and protein utilization were investigated further by measuring protein synthesis and degradation. In two separate studies, five or six patients with cirrhosis of the liver were refed on a balanced diet for an average of 2 or 4 weeks. Protein and energy intakes were doubled in both studies. Initial and final whole-body protein metabolism was measured in the fed state by primed continuous [15N]glycine infusion. Refeeding caused a statistically significant increase of about 30% in protein synthesis in both studies while protein degradation was only slightly affected. The increase in protein synthesis was associated with significant increases in plasma concentrations of total amino acids (25%), leucine (58%), isoleucine (82%), valine (72%), proline (48%) and triiodothyronine (27%) while insulin, growth hormone, insulin-like growth factor (IGF)-I and IGF-binding protein-3 were not changed significantly. The results indicate that the efficient protein utilization is due to increased protein synthesis, rather than decreased protein degradation, and suggest that increases in plasma amino acids may be responsible for the increased protein synthesis. A comparison of the patients who had a normal protein requirement with the patients who had an increased protein requirement suggests that the increased protein requirement is due to a primary increase in protein degradation. It is speculated that this is due to low levels of IGF-I secondary to impaired liver function, since initial plasma concentration of IGF-I was about 25% of control values and remained low during refeeding.

Short-term changes in energy metabolism after 1 month of a regular oral diet in severely malnourished cirrhotic patients

Malnutrition in patients with liver cirrhosis is currently associated with abnormal fuel metabolism. The aim of this study was to evaluate changes in energy production and substrate oxidation rates in a group of 26 nonanorectic severely malnourished cirrhotic patients in stable clinical condition after 1 month of an oral diet. Child-Pugh score, nutritional status, energy expenditure, rates of nutrient oxidation, and plasma levels of intermediary metabolites in the postabsorptive phase were assessed before and after 1 month of oral nutrition. Upon entry onto the study, caloric and protein intakes were 40.1 +/- 2.0 kcal/kg and 1.44 +/- 0.8 g/kg, respectively. The Child-Pugh score did not change during the study, whereas nutritional status improved as shown by increased muscular midarm circumference, ([MMAC] P < .02), height-creatinine index (P < .05), triceps skinfold thickness ([TST] P < .01), and fat mass (P < .001). Inflammatory state improved during the study, as shown by the decrease of C-reactive protein ([CRP] P < .01) and orosomucoid (P < .001). The ratio of caloric intake to resting energy expenditure (REE) increased (1.53 +/- 0.06 v 1.66 +/- 0.07, P < .05), as well as the rate of glucose oxidation ([Gox] 73.6 +/- 9.9 v 128.1 +/- 10.3 mg/min, P < .001) and urine nitrogen excretion (6.69 +/- 0.47 v 7.96 +/- 0.48 g/d, P < .02). On the other hand, the rate of lipid oxidation (Lox) decreased (67.3 +/- 3.9 v 47.3 +/- 4.9 mg/min, P < .001) and was correlated with the decrease of free fatty acid (FFA) levels (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)