Leucine Metabolism Research Articles

Subclinical infection with the nematode Trichostrongylus colubriformis increases gastrointestinal tract leucine metabolism and reduces availability of leucine for other tissues.

Gastrointestinal (GI) tract leucine metabolism was measured in 6- to 9-mo-old lambs subjected to trickle infection with Trichostrongylus colubriformis larvae and in separate animals that were not infected. Animals prepared with a jejunal catheter and with indwelling catheters into the aorta and the portal- (PDV) and mesenteric- (MDV) drained viscera were infused simultaneously with [1-13C] and [5,5,5-2H3] leucine to determine GI tract sequestration of leucine from arterial and luminal amino acid pools by tracer and tracee arteriovenous concentration differences. Leucine oxidative losses and net fluxes were also determined across the GI tract. Infection had no detectable effect on whole-body leucine flux, but it increased total GI tract leucine sequestration by 24% (P<.05) and GI tract oxidative losses of leucine by 22 to 41% (P<.01). Net PDV fluxes of leucine were decreased by 20 to 32% during the infection. The infection did not alter either the proportion of precursor leucine used by GI tract metabolism that was derived from the arterial leucine pool (.84 to .88) or the proportional sequestration of digesta-derived leucine during "first pass" absorptive metabolism (.12 to .18). These findings help to elucidate the metabolic basis for the reduced growth rates and nitrogen retention observed when animals are subjected to subclinical nematode infection.

Effects of an amino acid dialysate on leucine metabolism in continuous ambulatory peritoneal dialysis patients

Protein-energy malnutrition is frequent in continuous ambulatory peritoneal dialysis (CAPD) patients. The use of amino acids in the dialysate could improve the protein balance, especially if associated to a concomitant energy intake. A 1.1% amino acid solution for peritoneal dialysis was administered to CAPD patients over 30 minutes during concomitant absorption of 600 ml water (control study) or of a 600 kcal meal/600 ml. Leucine metabolism was studied using the combination of intravenous [2H3] and intraperitoneal [13C] leucine. The rate of leucine appearance was stimulated by 56 and 53% (control and meal) at 45 minutes. The rates of leucine appearance and disappearance were lower from 180 to 300 minutes during the meal versus control study (P < 0.05). Proteolysis was unaffected during the control study and was inhibited by 25% during the meal study (P < 0.05). During the five-hour cycle dialysis with or without a meal, 80% of the leucine administered into the peritoneum was absorbed. Forty-one percent was retained in the splanchnic bed. Forty-three percent was used for protein synthesis, and 16% was oxidized. This amino acids solution is efficaciously utilized for protein synthesis in CAPD patients with no effect on protein breakdown. The concomitant ingestion of a carbohydrate-lipid meal inhibits protein breakdown and reinforces a positive effect of the amino acids solution on protein balance.

Elucidation of carbon sources used for the biosynthesis of fatty acids and sterols in the trypanosomatid Leishmania mexicana

Sterols are necessary for the growth of trypanosomatid protozoans; sterol biosynthesis is a potential target for the use and development of drugs to treat the diseases caused by these organisms. This study has used (14)C-labelled substrates to investigate the carbon sources utilized by promastigotes and amastigotes of Leishmania mexicana for the production of sterol [mainly ergosta-5,7,24(24(1))-trien-3beta-ol] and the fatty acid moieties of the triacylglycerol (TAG) and phospholipid (PL) of the organism. The isoprenoid precursor mevalonic acid (MVA) was incorporated into the sterols, and the sterol precursor squalene, by the promastigotes of L. mexicana. However, acetate (the precursor to MVA in most organisms) was a very poor substrate for sterol production but was readily incorporated into the fatty acids of TAG and PL. Other substrates (glucose, palmitic acid, alanine, serine and isoleucine), which are metabolized to acetyl-CoA, were also very poor precursors to sterol but were incorporated into TAG and PL and gave labelling patterns of the lipids similar to those of acetate. In contrast, the amino acid leucine was the only substrate to be incorporated efficiently into the squalene and sterol of L. mexicana promastigotes. Quantitative measurements revealed that at least 70-80% of the sterol synthesized by the promastigotes of L. mexicana is produced from carbon provided by leucine metabolism. Studies with the amastigote form of L. mexicana showed that in this case leucine was again the major sterol precursor, whereas acetate was utilized for fatty acid production.

Factors influencing leucine catabolism by a strain of Staphylococcus carnosus

The metabolism of leucine by resting cells of Staphylococcus carnosus 833 was studied according to three physico-chemical factors: preculture condition (defined medium; complex medium), nitrate concentration (0% and 0.03%) and stirring condition (static or shaking). A factorial design was set up to test the effects of these factors, each at two levels. The results showed that resting cells of S. carnosus 833 produced 3-methyl butanal, 3-methyl butanol and 3-methyl butanoic acid from leucine. Whatever the incubation conditions, there was greater quantity of 3-methyl butanoic acid than 3-methyl butanal and 3-methyl butanol. The preculture and incubation conditions influenced the level of production of the 3 metabolites. The highest overall production of the 3 metabolites was observed when cells were incubated without nitrate in the reaction mixture. 3-methylbutanoic acid production was enhanced when S. carnosus 833 was precultivated in complex medium. 3-methylbutanal was only detected when cells were precultivated in defined medium. Stirring condition had no effect on leucine catabolism of S. carnosus 833.

Effects of Insulin and Amino Acids on Glucose and Leucine Metabolism in CAPD Patients

This study investigates the basal and insulin-stimulated glucose metabolism, substrate utilization, and protein turnover in eight patients maintained on continuous ambulatory peritoneal dialysis (CAPD) (mean age 39+/-5 yr, body mass index [BMI] 108+/-6) and 14 control subjects (mean age 33+/-4 yr, BMI 103+/-3). Euglycemic insulin clamp studies (180 min) were performed in combination with continuous indirect calorimetry and 1-14C leucine infusion (study I). Postabsorptive glucose oxidation was higher (1.75+/-0.18 versus 1.42+/-0.14 mg/kg per min) and lipid oxidation was lower (0.43+/-0.09 versus 0.61+/-0.12 mg/kg per min) in CAPD patients than in control subjects (P<0.05 versus control subjects). During the last 60 min of euglycemic hyperinsulinemia, the total rate of glucose metabolism was similar in CAPD and control subjects (6.33+/-0.51 versus 6.54+/-0.62 mg/kg per min). Both insulin-stimulated glucose oxidation (2.53+/-0.27 versus 2.64+/-0.37 mg/kg per min) and glucose storage (3.70+/-0.48 versus 3.90+/-0.58 mg/kg per min) were similar in CAPD and control subjects. Basal leucine flux (an index of endogenous proteolysis) was significantly lower in CAPD patients than in control subjects (1.21+/-0.15 versus 1.65+/-0.07 micromol/kg per min). Leucine oxidation (0.13+/-0.02 versus 0.26+/-0.02 micromol/kg per min) and nonoxidative leucine disposal (an index of protein synthesis) (1.09+/-0.16 versus 1.35+/-0.05 micromol/kg per min) were also reduced in CAPD compared with control subjects (P<0.01 versus control subjects). In response to insulin (study I), endogenous leucine flux decreased to 0.83+/-0.08 and 1.05+/-0.05 micromol/kg per min in CAPD and control subjects, respectively (all P<0.01 versus basal). Leucine oxidation declined to 0.06+/-0.01 and to 0.19+/-0.02 micromol/kg per min in CAPD and control subjects, respectively (P<0.01 versus basal). A second insulin clamp was performed in combination with an intravenous amino acid infusion (study II). During insulin plus amino acid administration, nonoxidative leucine disposal rose to 1.23+/-0.17 and 1.42+/-0.09 micromol/kg per min in CAPD and control subjects, respectively (both P<0.05 versus basal, P = NS versus control subjects), and leucine balance, an index of the net amino acid flux into protein, become positive in both groups (0.30+/-0.05 versus 0.40+/-0.07 micromol/kg per min in CAPD and control subjects, respectively) (both P<0.01 versus basal, P = NS versus control subjects). In summary, in CAPD patients: (1) basal glucose oxidation is increased; (2) basal lipid oxidation is decreased; (3) insulin-mediated glucose oxidation and storage are normal; (4) basal leucine flux is reduced; (5) the antiproteolitic action of insulin is normal; and (6) the anabolic response to insulin plus amino acid administration is normal. Uremic patients maintained on CAPD treatment show a preferential utilization of glucose as postabsorptive energy substrate; however, their anabolic response to substrate administration and the sensitivity to insulin are normal.

Leucine metabolism in preterm infants receiving parenteral nutrition with medium-chain compared with long-chain triacylglycerol emulsions

Although medium-chain triacylglycerols (MCTs) may be utilized more efficiently than long-chain triacylglycerols (LCTs), their effect on protein metabolism remains controversial. The aim of the study was to compare the effects of mixed MCT-LCT and pure LCT emulsions on leucine metabolism in preterm infants. Fourteen preterm [gestational age: 30+/-1 wk; birth weight: 1409+/-78 g (x +/- SE)] neonates were randomly assigned to receive, from the first day of life, either a 50:50 MCT-LCT (mixed MCT group; n = 7) or an LCT (LCT group; n = 7) lipid emulsion as part of an isonitrogenous, isoenergetic total parenteral nutrition program. On the fourth day, infants received intravenous feeding providing 3 g lipid, 15 g glucose, and 3 g amino acids kg(-1) x d(-1) and underwent 1) indirect calorimetry and 2) a primed, 2-h infusion of H13CO3Na to assess the recovery of 13C in breath, immediately followed by 3) a 3-h infusion of L-[1-13C]leucine. The respiratory quotient tended to be slightly but not significantly higher in the mixed MCT than in the LCT group (0.96+/-0.06 compared with 0.93+/-0.03). We did not detect a significant difference between the mixed MCT and LCT groups with regard to release of leucine from protein breakdown (B; 309+/-40 compared with 257+/-46 micromol x kg(-1) x h(-1)) and nonoxidative leucine disposal (NOLD; 296+/-36 compared with 285+/-49 micromol x kg(-1) x h(-1)). In contrast, leucine oxidation was greater in the mixed MCT than in the LCT group (113+/-10 compared with 67+/-10 micromol x kg(-1) x h(-1); P = 0.007). Net leucine balance (NOLD - B) was less positive in the mixed MCT than in the LCT group (-14+/-9 compared with 28+/-10 micromol x kg(-1) x h(-1); P = 0.011). Mixed MCTs may not be as effective as LCT-containing emulsions in promoting protein accretion in parenterally fed preterm neonates.

Isolated Isobutyryl-CoA Dehydrogenase Deficiency: An Unrecognized Defect in Human Valine Metabolism

A 2-year-old female was well until 12 months of age when she was found to be anemic and had dilated cardiomyopathy. Total plasma carnitine was 6 μM and acylcarnitine analysis while receiving carnitine supplement revealed an increase in the four-carbon species. Urine organic acids were normal.In vitroanalysis of the mitochondrial pathways for beta oxidation, and leucine, valine, and isoleucine metabolism was performed in fibroblasts using stable isotope-labeled precursors to these pathways followed by acylcarnitine analysis by tandem mass spectrometry. 16-2H3-palmitate was metabolized normally down to the level of butyryl-CoA thus excluding SCAD deficiency.13C6-leucine and13C6-isoleucine were also metabolized normally.13C5-valine incubation revealed a significant increase in13C4-isobutyrylcarnitine without any incorporation into propionylcarnitine as is observed normally. These same precursors were also evaluated in fibroblasts with proven ETF-QO deficiency in which acyl-CoA dehydrogenase deficiencies in each of these pathways was clearly identified. These results indicate that in the human, there is an isobutyryl-CoA dehydrogenase which exists as a separate enzyme serving only the valine pathway in addition to the 2-methyl branched-chain dehydrogenase which serves both the valine and the isoleucine pathways in both rat and human.

Role of hyperglucagonemia in catabolism associated with type 1 diabetes: effects on leucine metabolism and the resting metabolic rate.

The catabolic state of poorly controlled type 1 diabetes has largely been attributed to insulin deficiency. However, the role of hyperglucagonemia, which occurs concomitantly with insulin deficiency, has not been fully investigated. We studied the effects of hyperglucagonemia during insulin deprivation on energy expenditure (using indirect calorimetry) and protein metabolism (using L-[1-(13)C,15N]leucine and L-[1-(13)C]leucine as tracers) in 12 type 1 diabetic subjects. Five protocols were used: insulin treatment, insulin deprivation, insulin deprivation with suppression of endogenous glucagon with somatostatin (SRIH) and growth hormone replacement, insulin deprivation with endogenous glucagon suppression with SRIH (no growth hormone replacement), and insulin deprivation with SRIH and a high level of glucagon replacement (no growth hormone replacement). It was observed that leucine oxidation and the resting metabolic rate (RMR) were significantly lower during insulin treatment and insulin deprivation with concomitant SRIH infusion (lowering glucagon) than during insulin deprivation alone. Replacement of glucagon at a high level during SRIH infusion in the insulin-deprived state increased leucine oxidation and the RMR. Hyperglucagonemia was also associated with a trend for decreased protein synthesis. Hyperglucagonemia did not affect leucine transamination. Insulin replacement decreased leucine flux and oxidation. Leucine oxidation (R2 = 0.79) and the RMR (R2 = 0.81) were seen, by multiple regression analysis, to correlate with glucagon levels and not with other hormones. We conclude that while insulin deficiency increases protein breakdown, hyperglucagonemia is primarily responsible for the increased leucine oxidation and RMR seen during insulin deprivation.

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.

O.34 Effects of meals on leucine metabolism: investigation on mechanism involved in improving leucine balance during feeding

O.34 Effects of meals on leucine metabolism: investigation on mechanism involved in improving leucine balance during feeding

Leucine metabolism in rat liver after a bolus injection of endotoxin

To evaluate the contribution of hepatic tissue to alterations in the metabolism of proteins and the branched-chain amino acids (BCAA) leucine, isoleucine, and valine in systemic inflammatory response syndrome, we studied the changes of leucine metabolism in isolated perfused liver (IPL) of endotoxin-treated rats. Male albino rats were injected with the endotoxin of Salmonella enteritidis (5 mg · kg −1) or saline (control). Four hours later, leucine and ketoisocaproate (KIC) oxidation and incorporation into liver proteins were determined in IPL using the single-pass liver perfusion technique. l-[1- 14C]leucine and α-keto[1- 14C]isocaproic acid were used as a tracer in two separate experiments. Endotoxin treatment resulted in a decrease of plasma BCAA levels, an increase of leucine oxidation, and a decrease of KIC oxidation by IPL. Leucine incorporation into liver proteins was lower in endotoxin-treated rats, and we did not find measurable incorporation of the labeled carbon of KIC in liver proteins in either group of animals. The sum of individual amino acid concentrations in the effluent perfusate was higher in endotoxin-treated animals, although only leucine and phenylalanine increased significantly. The decrease in KIC oxidation indicates a decreased capacity of hepatic tissue to oxidize branched-chain ketoacids (BCKA). The increase in leucine oxidation by IPL of endotoxin-treated rats indicates an increase in BCAA aminotransferase activity. These changes demonstrate an important response of the body that enables the resynthesis of essential BCAA from their ketoanalogs delivered to the liver from peripheral tissues, particularly muscle.

Phenylbutyrate-induced glutamine depletion in humans: effect on leucine metabolism.

The present study was designed to determine whether sodium phenylbutyrate (phi B) acutely induces a decrease in plasma glutamine in healthy humans, and, if so, will decrease estimates of whole body protein synthesis. In a first group of three healthy subjects, graded doses (0, 0.18, and 0.36 g.kg-1.day-1) of phi B were administered for 24 h before study: postabsorptive plasma glutamine concentration declined in a dose-dependent manner, achieving an approximately 25% decline for a dose of 0.36 g phi B.kg-1.day-1. A second group of six healthy adults received 5-h infusions of L-[1-14C]leucine and L-[1-13C]glutamine in the postabsorptive state on two separate days: 1) under baseline conditions and 2) after 24 h of oral treatment with phi B (0.36 g.kg-1.day-1) in a randomized order. The 24-h phenylbutyrate treatment was associated with 1) an approximately 26% decline in plasma glutamine concentration from 514 +/- 24 to 380 +/- 15 microM (means +/- SE; P < 0.01 with paired t-test) with no change in glutamine appearance rate or de novo synthesis; 2) no change in leucine appearance rate (Ra), an index of protein breakdown (123 +/- 7 vs. 117 +/- 5 mumol.kg-1.h-1; not significant); 3) an approximately 22% rise in leucine oxidation (Ox) from 23 +/- 2 to 28 +/- 2 mumol.kg-1.h-1 (P < 0.01), resulting in an approximately 11% decline in nonoxidative leucine disposal (NOLD = Ra-Ox), an index of protein synthesis, from 100 +/- 6 to 89 +/- 5 mumol.kg-1.h-1 (P < 0.05). The data suggest that, in healthy adults, 1) large doses of oral phenylbutyrate can be used as a "glutamine trap" to create a model of glutamine depletion; 2) a moderate decline in plasma glutamine does not enhance rates of endogenous glutamine production; and 3) a short-term depletion of plasma glutamine decrease estimates of whole body protein synthesis.

Arginine (Arg) Turnover and Oxidation in Neonates Receiving Total Parenteral Nutrition (TPN) • 1497

In human, Arg is generally considered a dispensable amino acid. However, it has been proposed that Arg may be an indispensable amino acid in neonates after an increase in blood ammonia level was observed when arginine was removed from amino acid solution used in parenteral nutrition.Method: In order to estimate net de novo synthesis, in vivo, in neonates fed parenterally, I evaluated Arg and citrulline (Cit) metabolism measuring respective plasma amino acids fluxes and whole-body rate of Arg oxidation based on a single pool model (Beaumier, 1995). Rate of conversion of plasma Cit to Arg was also measured using the Clarke and Bier equation (1982). Protein turnover was also measured usingα-ketoisocaproic acid (α-KIC) as representative metabolite of leucine metabolism (Matthews 1982). Experiments: After being on TPN for 4-5 days, providing 3 gm of protein/kg/day and a minimum of 120 kcal/kg/day, a known primed constant infusion of [5-13C] Arg,[15N2-guanidino] Arg, [5,5-2H2, 13C-ureido] Cit and [5,5,5-2H2] leucine was given for five hours. Blood and breath samples were taken once before and twice, at 30 minute intervals, at the end of the infusion. Expired 13CO2 was corrected for under-recovery of 13C-label from infused [5-13C] ornithine. Isotopic abundance of amino acids and α-KIC was measured by GC/MS as methyl ester-TFA and t-BDMS derivatives, respectively. Results: Under these conditions, plasma Arg and Cit flux were measured at 209 ± 17 and 37± 3 μmol/kg/h, respectively. Arg oxidation was measured at 76± 6 with a dietary Arg intake was 69 ± 10 μmol/kg/h. Rate of conversion of plasma Cit into Arg was 15 ± 3 μmol/kg/h. The small excess in Arg oxidation and the low rate of conversion support the concept that neonates have a very limited rate of Arg de novo synthesis. Leucine appearance from protein breakdown was 141 ± 18 μmol/kg/h, which represents 9.4 ± 1.2 g/kg/day of protein. Conclusion: Net rate of endogenous Arg synthesis is measurable in neonates receiving TPN but remains relatively small in comparison to the whole-body turnover of the amino acid. These results are consistent with a limiting capacity for neonates to synthesize arginine supporting the recommendation that Arg is an indispensable amino acid in neonates fed a parenteral solution.

Catabolism Dominates the First-Pass Intestinal Metabolism of Dietary Essential Amino Acids in Milk Protein-Fed Piglets

To investigate the extent of first-pass intestinal metabolism of dietary amino acids, seven female pigs (28 d old, 8.0 kg) were implanted with arterial, venous, portal and gastric catheters and with an ultrasonic portal blood flow probe. The pigs were fed a milk-based diet once hourly and infused intragastrically with [U-13C]algal protein. On average, 56% of the essential amino acid (EAA) intake appeared in the portal blood. However, the net portal balance of methionine (48% of intake) and threonine (38% of intake) tended (P = 0.08) to be lower than the mean of all EAA. The net portal balance (expressed as a percentage of intake) of alanine (205%), tyrosine (167%) and arginine (137%) exceeded their intake. Net portal outflow of ammonia accounted for 18% of total amino acid nitrogen intake. As a percentage of the enteral tracer input, there was substantial first-pass metabolism of lysine (35%), leucine (32%), phenylalanine (35%) and threonine (61%). However, only 18, 21, 18 and 12% of the total first-pass metabolism of lysine, leucine, phenylalanine and threonine, respectively, were recovered in mucosal protein. We conclude that roughly one third of dietary intake of EAA is consumed in first-pass metabolism by the intestine and that amino acid catabolism by the mucosal cells is quantitatively greater than amino acid incorporation into mucosal protein.

Leucine metabolism across the gastrointestinal tract of sheep infected with Trichostrongylus colubriformis

In previous studies where sheep were subjected to experimental subclinical Trichostrongylus colubriformis infections, protein metabolism was seriously impaired during both the initial infection (5-7 weeks at early dosing) and the subsequent immune response (11-13 weeks of dosing) periods (see MacRae, 1993). Symonds and Jones (1983) reported that T. colubriformis infection increased the rates of protein synthesis in the small and large intestines of guinea pigs by 24 and 70% respectively, however there are no equivalent data in farm animals. In the present study trans-organ catheterisation procedures have been coupled with mass isotope tracer kinetics to examine leucine metabolism across the gastrointestinal (g.i.) tract of lambs subjected to subclinical T. colubriformis infection.

Leucine metabolism across the gastrointestinal tract of sheep infected with Trichostrongylus colubriformis

In previous studies where sheep were subjected to experimental subclinical Trichostrongylus colubriformis infections, protein metabolism was seriously impaired during both the initial infection (5-7 weeks at early dosing) and the subsequent immune response (11-13 weeks of dosing) periods (see MacRae, 1993). Symonds and Jones (1983) reported that T. colubriformis infection increased the rates of protein synthesis in the small and large intestines of guinea pigs by 24 and 70% respectively, however there are no equivalent data in farm animals. In the present study trans-organ catheterisation procedures have been coupled with mass isotope tracer kinetics to examine leucine metabolism across the gastrointestinal (g.i.) tract of lambs subjected to subclinical T. colubriformis infection.

Leucine metabolism in TNF-alpha- and endotoxin-treated rats: contribution of hepatic tissue.

The effects of tumor necrosis factor-alpha (TNF-alpha; cachectin) and lipopolysaccharide of Salmonella enteritidis (LPS; endotoxin) on leucine metabolism in rats were evaluated in the whole body using intravenous infusion of L-[1-14C]leucine and in isolated perfused liver (IPL) using the single-pass perfusion technique with alpha-keto[1-14C]isocaproate as a tracer for measurement of ketoisocaproic acid (KIC) oxidation, and the recirculation technique for measurement of hepatic amino acid exchanges. The data obtained in TNF-alpha and LPS groups were compared with those obtained in controls. Both TNF-alpha and LPS treatment induced an increase of whole body leucine turnover, oxidation, and clearance. As the result of a higher increase of leucine oxidation than of incorporation into the pool of body proteins, the fractional oxidation of leucine was increased. The fractional rate of protein synthesis increased significantly in the spleen (both in TNF-alpha and LPS rats), in blood plasma, liver, colon, kidneys, gastrocnemius muscle (in LPS rats), and in lungs (TNF-alpha-treated rats), whereas it decreased in the jejunum (LPS rats). In IPL of TNF-alpha- and LPS-treated rats a decrease of KIC oxidation and higher uptake of branched-chain amino acids (BCAA; valine, leucine, and isoleucine) were observed when compared with control animals. We hypothesize that the negative consequences of increased whole body proteolysis and of increased oxidation of BCAA induced by TNF-alpha and/or LPS are reduced by decreased activity of hepatic branched-chain ketoacid dehydrogenase that can help resupply BCAA to the body.

A 13C Nuclear Magnetic Resonance Investigation of the Metabolism of Leucine to Isoamyl Alcohol in Saccharomyces cerevisiae

The metabolism of leucine to isoamyl alcohol in yeast was examined by 13C nuclear magnetic resonance spectroscopy. The product of leucine transamination, alpha-ketoisocaproate had four potential routes to isoamyl alcohol. The first, via branched-chain alpha-keto acid dehydrogenase to isovaleryl-CoA with subsequent conversion to isovalerate by acyl-CoA hydrolase operates in wild-type cells where isovalerate appears to be an end product. This pathway is not required for the synthesis of isoamyl alcohol because abolition of branched-chain alpha-keto acid dehydrogenase activity in an lpd1 disruption mutant did not prevent the formation of isoamyl alcohol. A second possible route was via pyruvate decarboxylase; however, elimination of pyruvate decarboxylase activity in a pdc1 pdc5 pdc6 triple mutant did not decrease the levels of isoamyl alcohol produced. A third route utilizes alpha-ketoisocaproate reductase (a novel activity in Saccharomyces cerevisiae) but with no role in the formation of isoamyl alcohol from alpha-hydroxyisocaproate because cell homogenates could not convert alpha-hydroxyisocaproate to isoamyl alcohol. The final possibility was that a pyruvate decarboxylase-like enzyme encoded by YDL080c appears to be the major route of decarboxylation of alpha-ketoisocaproate to isoamyl alcohol although disruption of this gene reveals that at least one other unidentified decarboxylase can substitute to a minor extent.

O.69 Phenylbutyrate-induced glutamine depletion in healthy humans: effect on leucine metabolism

O.69 Phenylbutyrate-induced glutamine depletion in healthy humans: effect on leucine metabolism

Ovine fetal metabolism during norepinephrine infusion.

Although stress in fetal life not only increases fetal catecholamine concentration but also decreases fetal growth, there have been few studies that define the specific role of catecholamines in mediating the fetal response to stress. None, however, have investigated effects on fetal amino acid or protein metabolism, processes that should be affected during aberrant fetal growth. Therefore, hormone concentrations as well as oxygen, glucose, lactate, and amino nitrogen, leucine, and protein metabolism were measured with and without norepinephrine infusion in fetuses of eight pregnant ewes (118-125 days of gestation). Transumbilical uptake of oxygen increased during norepinephrine infusion, whereas uptake of glucose remained constant and that of lactate and amino acids fell. The proportion of fetal oxidative metabolism that could be supported by transplacental uptake of exogenous substrates was < 1, indicating that endogenous substrates were used to maintain fetal oxidative metabolism and therefore that fetal growth was diminished. Both fetal leucine uptake and oxidation decreased during norepinephrine infusion, as did fetal protein synthesis and proteolysis. Fetal protein synthesis fell more than proteolysis, however. Consequently, fetal protein accretion, a variable closely related to fetal growth, also fell. Thus the effects of norepinephrine infusion in fetuses suggest that fetal catecholamines play an important role not only in altering fetal metabolism but also in regulating fetal growth.