Utilization of alpha-ketoisocaproate for synthesis of hepatic export proteins and peripheral proteins in normal and cirrhotic subjects

Hepatic encephalopathy

Hepatic encephalopathy (HE) is a syndrome of neuropsychiatric dysfunction caused by portosystemic venous shunting, with or without intrinsic liver disease. Patients with hepatic encephalopathy often present with the onset of mental status changes ranging from subtle psychologic abnormalities to profound coma. Several hypotheses have been proposed to explain the mental impairment associated with portosystemic shunting and liver disease. Clinicians diagnosing HE frequently have the opportunity to intervene and reverse severe HE, even hepatic coma. The recent advances in understanding and management of HE are the subject of this article.

Splanchnic bed utilization of enteral alpha-ketoisocaproate in humans

The branched-chain ketoacids (BCKAs) are used as dietary supplements to spare essential amino acid nitrogen, yet little is known about their absorption and utilization in the body. To study the fate of enterally delivered alpha-ketoisocaproate (KIC), seven healthy adults were infused in the postabsorptive state with [1-(13)C]KIC and [phenyl-2H5]phenylalanine intravenously (NGI) and with [5,5,5-2H3]KIC by nasogastric tube (NG). After 3.5 hours, the routes of tracer infusion were switched for an additional 3.5 hours. Each subject received a second infusion study on a different day with the order of tracer infusion reversed. KIC and phenylalanine kinetics and first-pass uptake and disposal of the enteral tracer by the splanchnic bed were calculated from the tracer enrichments measured in plasma KIC, leucine, and phenylalanine and breath CO2. Phenylalanine flux was 39.5 +/- 1.2 micromol/kg/h during the i.v. infusion periods. KIC flux was 33.1 +/- 1.8 and 30.4 +/- 1.4 micromol/kg/h measured with 13C- and 2H3-KIC, respectively, and these values were significantly different. The fraction of enterally delivered tracer sequestered by the splanchnic bed on the first pass was 30.9% +/- 2.0%, 30.0% +/- 1.4%, and 30.7% +/- 2.7% for 13C-KIC, 2H3-KIC, and 2H5-phenylalanine, respectively. The fraction of infused 13C-KIC tracer recovered as 13CO2 was 27.1% +/- 1.2% and 24.0% +/- 0.9% during i.v. and NG infusion, respectively. From these data, the fraction of ng KIC tracer extracted and oxidized on the first pass was calculated to be 5.1% +/- 1.1%. This fraction was greater than that previously reported for leucine extraction and oxidation (2%), but it was still only a small fraction of the overall extraction (5/30 = 16%). Because the only two fates of the KIC tracer extracted by the splanchnic bed are oxidation or transamination to leucine, the majority (84%) of the KIC tracer was extracted and converted to leucine. These results demonstrate that KIC delivered enterally to postabsorptive humans is rapidly extracted and predominantly converted to leucine by the splanchnic bed. This leucine appears to be available for use by both the splanchnic bed and the whole body.

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.

Malnutrition in children with chronic liver disease accepted for liver transplantation: clinical profile and effect on outcome

The nutritional profiles of 37 children (aged 0.5-14.0 years) with chronic liver disease at the time of acceptance for orthotopic liver transplantation (OLTP) have been evaluated using clinical, biochemical and body composition methods. Nutritional progress while waiting for a donor has been related to outcome, whether transplanted or not. At the time of acceptance, most children were underweight (mean standard deviation (s.d.) weight = -1.4 +/- 0.2) and stunted (mean s.d. height = -2.2 +/- 0.4), had low serum albumin (27/35) and had reduced body fat and depleted body cell mass (measured by total body potassium--mean % expected for age = 58 +/- 5%, n = 15). Mean ad libitum nutrient intake was 63 +/- 5% of recommended daily intake (RDI). Those who died while waiting (n = 8) had significantly lower mean initial s.d. weight compared with those transplanted. The overall actuarial 1 year survival of those who were transplanted (mean waiting time = 75 days) was 81% but those who were initially well nourished (s.d. weight greater than -1.0) had an actuarial 1 year survival of 100%. There were no significant differences in actuarial survival in relationship to age, type of transplant (whole liver or segmental), liver biochemistry or the presence or absence of ascites. Of the total group accepted for OLTP, whether transplanted or not, the overall 1 year survival for those who were relatively well nourished was 88% and for those undernourished (initial s.d. weight less than -1.0) was 38% (P less than 0.003). Declining nutritional status during the waiting period also adversely affected outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Pre-operative nutritional support in children with end-stage liver disease accepted for liver transplantation: an approach to management

Pre-operative nutritional support was studied in 28 children with end-stage liver disease awaiting orthotopic liver transplantation. Nasogastric supplemental administration of a standard semi-elemental enteral nutritional formula was compared with a similar formula enriched with branched chain amino acids, and with a group receiving oral nutrition only. The duration of treatment in all groups was similar (mean 90 days). Energy intakes in the supplemented groups were 120-150% of recommended daily intakes (RDI), whereas ad libitum intakes in the oral group ranged 58-100% RDI. A significant improvement in mean Z-score for body weight (denoting catch-up) was noted only in those children who received nasogastric supplements enriched with branched-chain amino acids. The standard enterally-fed group maintained their body weight and Z-scores did not change significantly. In contrast, body weight Z-scores in those fed orally declined significantly. Nutritional supportive therapy of malnourished children with end-stage liver disease can minimize or improve nutritional status in children awaiting liver transplantation. The use of nutritional formulae rich in branched-chain amino acids may have nutritional advantages in children with chronic liver disease which require further study and evaluation.

Plasma reciprocal pool specific activity predicts that of intracellular free leucine for protein synthesis

We previously proposed that, during the infusion of either labeled leucine or its alpha-ketoacid, alpha-ketoisocaproate (KIC), the plasma specific activity (SA) of the transaminated product of the infused tracer ("reciprocal pool SA") may better reflect the intracellular leucine SA than the plasma SA of either infused tracer ("primary pool SA"). To test this hypothesis, 14 dogs were simultaneously infused intravenously with [3H]leucine and [14C]KIC, and blood and tissue compartments were sampled. The ratios of [3H]-leucine to [14C]leucine [( 3H]/[14C]leucine) in mixed tissue proteins and in the intracellular space of striated muscle were the same as the ratio of the isotope infusion rates and similar, although slightly lower (P less than 0.01), than [3H]KIC/[14C]leucine SA (ratio of reciprocal pool SA) in plasma. Plasma [3H]KIC/[14C]leucine SA were essentially identical to the [3H]/[14C] of leucine in 1) mixed liver proteins, 2) intrahepatic free leucine, and 3) fibrin. The [3H]/[14C]leucine in mixed renal proteins and in the intracellular space of kidney and erythrocytes were similar to those of the venous plasma [3H]/[14C]leucine SA. The plasma [3H]KIC and [14C]leucine SA (the reciprocal pool SA) were similar to the SA of [3H]- and [14C]leucine in the intracellular space of all organs investigated with the exception of kidney. Therefore, in postabsorptive dogs, the plasma SA of the transaminated product of the infused labeled KIC or leucine is an excellent predictor of the intracellular leucine SA in all tissues investigated with the exception of kidney.

Utilization for protein synthesis in individual rat organs of extracellular 2-ketoisocaproate relative to utilization of extracellular leucine

Rats were given constant intravenous infusions of [3H]-leucine plus [1-14C]-2-ketoisocaproate (KIC). Specific activities of plasma leucine and plasma KIC reached plateaus by two to three hours. 3H specific activity of KIC was 85% +/- 2% of that in leucine. 14C specific activity of leucine was 36% +/- 2% of that in KIC. The 14C/3H ratios in leucine and KIC were constant from the earliest sampling time (one hour) at 0.65 +/- 0.03 and 2.20 +/- 0.07, respectively. In various tissues, 14C/3H in free leucine and in tissue protein were approximately equal, but in most organs these ratios were significantly greater than the ratio 14C/3H in plasma leucine. From these data we estimate that the fraction of leucine incorporated into protein in individual organs derived from extracellular KIC rather than extracellular leucine varies from zero (in liver and bone marrow) to 35% to 45% (in brain and heart), and comprises 12% in the body as a whole.

Rate of whole-body protein synthesis in the rat as calculated from fractional oxidation of leucine, valine, or methionine

In the steady state, the ratio of the rate of utilization for whole-body protein synthesis of any essential amino acid to its rate of oxidation should be the same as the ratio of the peak fraction of a dose of tracer incorporated into protein (F) to the fraction oxidized (1-F) provided that negligible tracer remains in the free amino acid pool or remains unabsorbed in the gut. The total rate of amino acid catabolism (C) can be estimated from the rate of urinary excretion of urea nitrogen (N) plus ammonia N. Hence the rate of whole-body protein synthesis (S) can be estimated as CF/(1-F). This method, which is not new, was explored as follows: (1) Radioactivity in the leucine of whole-body protein of rats after intravenous (IV) injection of labeled leucine was shown to plateau from three to nine hours. (2) The fractions of labeled leucine, valine, and methionine remaining in the gut six hours after enteral injection were 1.2 +/- 0.4% (SD), 1.2 +/- 0.4%, and 7.1 +/- 2.9%, respectively; thus, enterally administered methionine cannot be used for this purpose. (3) Oxidation of [1-14C]-labeled leucine or valine, measured from 14CO2 excretion, was found to be the same whether these isotopes were given IV or enterally. (4) Negligible radioactivity remained in the free leucine of plasma within one hour after injection of labeled leucine.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of branched-chain amino acids and branched-chain keto acids on protein synthesis in isolated hepatocytes

We investigated the effects of the branched-chain amino acids--valine, leucine and isoleucine--or their keto analogs, the branched-chain keto acids--alpha-ketoisovaleric acid, alpha-ketoisocaproic acid and alpha-keto-beta-methylvaleric acid--on protein synthesis and secretion by monolayers of rabbit hepatocytes incubated with [35S] methionine in pulse-chase and steady-state experiments. The branched-chain amino acids (2.0 mM or 1.0 mM), in the presence or absence of insulin (2 X 10(-4) IU per dish) and in both types of experiments, reduced the trichloroacetic acid-precipitable 35S-protein secreted into the medium. The branched-chain keto acids (2.0 mM or 1.0 mM) had a stimulatory effect on secreted trichloroacetic acid-precipitable 35S-protein which was observed only by the pulse-chase technique in the presence of insulin. Immunoaffinity chromatography of medium demonstrated a slight inhibition by branched-chain amino acids and a slight stimulation by branched-chain keto acids on secretion of 35S-albumin and no effect of either treatment on secretion of 35S-fibrinogen. ELISA analysis of total (i.e., 35S-labeled and unlabeled) secreted albumin revealed an inhibitory effect of the branched-chain amino acids in both pulse-chase and steady-state experiments, and a small stimulatory effect, in steady-state experiments, of the branched-chain keto acids; both effects were insulin-dependent. Total secreted fibrinogen, under steady-state conditions, was increased by the branched-chain keto acids in the presence of insulin, while transferrin production was unaffected by any treatment.(ABSTRACT TRUNCATED AT 250 WORDS)