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PubMed1990

Amino acid metabolism during exercise and following endurance training.

Exercise results in marked alterations in amino acid metabolism within the body. The branched-chain amino acids, especially leucine, are particularly important since they contribute as energy substrates and as nitrogen donors in the formation of alanine, glutamine and aspartate. Leucine oxidation increases during whole-body exercise. Nonetheless, leucine's contribution as a muscle energy substrate is amll, being 3 to 4% at rest, and even lower (1%) during exercise. Traditional energy substrates (carbohydrates, lipid) remain most important. These rates of leucine oxidation can be readily attributed to skeletal muscle. Following endurance training, whole-body leucine oxidation is increased at rest and during exercise. Since its oxidation by muscle is not augmented, this whole-body increase is not due to muscle. Thus, other tissues within the body (i.e. liver) must account for this. Comparisons of leucine oxidation in rats and humans indicate that species differences exist. Much larger increases in leucine oxidation are brought about by exercise in humans. Calculations based on steady-state rates of leucine oxidation at rest and during exercise indicate that the recommended dietary intake of leucine is inadequate, since it is lower than measured whole-body rates of leucine oxidation. This inadequacy is exacerbated in individuals who are physically active.

Amino Acids↗
PubMed1988

Influence of leupeptin on protein and amino-acid metabolism in septic rats.

We investigated the influence of leupeptin (LP) intraperitoneal injection (40 mumol/2 days) on protein and amino-acid metabolism of septic rats (cecal ligation). All septic rats lost weight (-17 +/- 4 g), which was not prevented by LP administration (-24 +/- 1.8 g, n.s.). LP injection evoked weight loss even in normal rats (p less than 0.05 vs controls). Weight loss was accompanied by enhanced urinary nitrogen losses in all three groups. LP reduced food intake for 47% in control rats. Cecal ligation, and also the administration of LP, led to alterations of amino-acid metabolism. The most important changes were found in muscle free amino-acid concentrations with highly decreased levels of free glutamine. A glutamine deficiency is known to be related to a decreased rate of protein synthesis. The proteolytic rate in incubated soleus muscle was increased for 11.5% and even higher in LP-treated septic rats (+22%). It is concluded that the administration of LP cannot reverse protein catabolism in sepsis--possibly because LP does not influence those enzymes or proteases involved in tissue loss, or LP is inactivated by enzymes in rat tissues.

Amino Acids↗
PubMed1986

Defective suppression by insulin of leucine-carbon appearance and oxidation in type 1, insulin-dependent diabetes mellitus. Evidence for insulin resistance involving glucose and amino acid metabolism.

To determine whether a resistance to insulin in type 1, insulin-dependent diabetes mellitus (IDDM) is extended to both glucose and amino acid metabolism, six normal subjects and five patients with IDDM, maintained in euglycemia with intravenous insulin administration, were infused with L-[4,5-3H]leucine (Leu) and [1-14C]alpha ketoisocaproate (KIC). Steady-state rates of leucine-carbon appearance derived from protein breakdown (Leu + KIC Ra) and KIC (approximately leucine) oxidation were determined at basal and during sequential euglycemic, hyperinsulinemic (approximately 40, approximately 90 and approximately 1,300 microU/ml) clamps. In the euglycemic postabsorptive diabetic patients, despite basal hyperinsulinemia (24 +/- 6 microU/ml vs. 9 +/- 1 microU/ml in normals, P less than 0.05), Leu + KIC Ra (2.90 +/- 0.18 mumol/kg X min), and KIC oxidation (0.22 +/- 0.03 mumol/kg X min) were similar to normal values (Leu + KIC Ra = 2.74 +/- 0.25 mumol/kg X min) (oxidation = 0.20 +/- 0.02 mumol/kg X min). During stepwise hyperinsulinemia, Leu + KIC Ra in normals decreased to 2.08 +/- 0.19, to 2.00 +/- 0.17, and to 1.81 +/- 0.16 mumol/kg X min, but only to 2.77 +/- 0.16, to 2.63 +/- 0.16, and to 2.39 +/- 0.08 mumol/kg X min in the diabetic patients (P less than 0.05 or less vs. normals at each clamp step). KIC oxidation decreased in normal subjects to a larger extent than in the diabetic subjects. Glucose disposal was reduced at all insulin levels in the patients. In summary, in IDDM: (a) Peripheral hyperinsulinemia is required to normalize both fasting leucine metabolism and blood glucose concentrations. (b) At euglycemic hyperinsulinemic clamps, lower glucose disposal rates and a defective suppression of leucine-carbon appearance and oxidation were observed. We conclude that in type 1 diabetes a resistance to the metabolic effects of insulin on both glucose and amino acid metabolism is present.

Adult↗
PubMed1982

The pancreatic beta cell fraction in children with errors of amino acid metabolism.

Blocks of pancreas were obtained from the following cases of errors of amino acid metabolism: eight cystinosis, eight tyrosinosis, five phenylketonuria, three hypermethioninemia, two hyperprolinemia and two maple syrup urine disease. Blocks were also obtained from four cases of homocystinuria and 72 control patients of the same age range who had died from a variety of conditions believed not to affect the pancreas. Sections were cut from each pancreatic block and stained with haematoxylin or for insulin and pancreatic polypeptide (PP) by the immunoperoxidase method. Measurements were performed separately in the PP rich and the PP poor regions of all sections. The fractional surface area of section occupied by insulin stained cells (%) and the cellular density (nuclei/100 microgram2) of each specimen were estimated. The beta cell fractional area in the PP poor region of the experimental cases was plotted against the logarithm of gestational age and compared to a reference grid of the 10th, 50th and 90th centile estimates of the control cases (Fig. 1). The distribution of results from the cases of tyrosinosis, phenylketonuria and cystinosis were skewed positively; four of eight tyrosinosis and three of five phenylketonuria cases lying above the 90th centile (P less than 0.001). The beta cell fractional area of the cystinosis cases was also significantly increased (Table 1, P less than 0.05). The results from the cases dying from maple syrup urine disease, hyperprolinemia, hypermethioninemia or homocystinuria were distributed as might be expected to occur by chance.

Amino Acid Metabolism, Inborn Errors↗
PubMed1996

Enumeration of human colonic bacteria producing phenolic and indolic compounds: effects of pH, carbohydrate availability and retention time on dissimilatory aromatic amino acid metabolism.

Concentrations of phenolic compounds in human gut contents were more than fourfold higher in the distal colon (6.2 mmol kg-1) compared to the proximal bowel (1.4 mmol kg-1). Tryptophan metabolites were never found in more than trace amounts in large intestinal contents and phenol substituted fatty acids were the major products of aromatic amino acid fermentation that accumulated in the proximal colon, whereas phenol and p-cresol were more important in the distal gut, accounting for 70% of all products of dissimilatory aromatic amino acid metabolism. In vitro incubations of colonic material showed that phenol was produced most rapidly (1.0 mumol g-1 h-1), whereas indole was formed comparatively slowly (0.06 mumol g-1 h-1). Most probable number (MPN) estimations demonstrated that large populations of phenol and indole producing bacteria occur in the large intestine (range log10 9.8-11.5 (g dry wt faeces)-1, mean 10.6, N = 7). With respect to phenolic compounds, phenylacetate and phenylpropionate producers predominated, while indoleacetate-forming bacteria were the major tryptophan-utilizing organisms. Quantitation of products of dissimilatory aromatic amino acid metabolism in MPN tubes showed that phenol and phenylpropionate mainly accumulated at low sample dilutions, whereas phenylacetate, p-cresol, indoleacetate and indolepropionate were formed in greatest amounts at high sample dilutions. The significance of pH and carbohydrate availability with respect to aromatic amino acid metabolism was shown in batch culture fermentation studies, where net production of phenolic compounds by mixed populations of intestinal bacteria was reduced by approximately 33% during growth at pH 5.5 compared to pH 6.8, and by 60% in the presence of a fermentable carbohydrate. Experiments with 16 species of intestinal bacteria belonging to six different genera showed that environmental factors such as low pH and high carbohydrate availability markedly reduced dissimilatory aromatic amino acid metabolism in some organisms, but stimulated this process in others. A three-stage continuous culture model of the colon was used to investigate the effect of system retention time (27.1 or 66.7 h) on aromatic amino acid fermentation. Qualitative and quantitative increases in phenol production occurred from vessel 1 to vessel 3 in this model. Concentrations of phenolic compounds in vessel 3 were three times greater at R = 66.7 h compared to R = 27.1 h. Phenol and p-cresol were not detected in vessel 1, though formation of these metabolites increased from vessel 2 to vessel 3, in a pattern similar to that observed in the distal colon.

Amino Acids↗
PubMed2001

Amino acid metabolism during total parenteral nutrition in healthy volunteers: evaluation of a new amino acid solution.

The aim of this study was to determine the metabolism and the tolerance of a new amino acid (AA) solution administered under conditions mimicking cyclical parenteral nutrition (PN) in humans. Eight healthy volunteers received peripheral PN for 10 h providing 10.5 mg N x kg(-1) x h(-1) and 2.0 kcal x kg(-1) x h(-1) (glucose-to-lipids ratio: 70/30%). For adaptation, a non-protein energy intake was increased progressively for 90 min; thereafter, AA infusion was started and maintained at a constant rate for 10 h. Plasma and urine concentrations of all the AAs were measured before, during and after the PN. For each given AA, the relation between plasma variations at the steady-state and infusion rate, plasma clearance (Cl), renal clearance (Clr), re-absorption rate (Reab) and, retention rate (Reten) were determined. The nitrogen balance (DeltaN) was calculated during the PN period. The results are presented as means+/-sem. All plasma AA concentrations decreased during the starting period of non-protein energy intake. The plasma AA concentrations reached a steady-state within 3 h upon AA infusion, except for glycine and lysine (6 h). At the steady state, the plasma concentrations of the infused AAs were closely correlated to their infusion rate (y= -18.3+1.5x, r(2)=0.92). The plasma glutamine concentration was maintained during the PN, which indicates that the solution might stimulate the de novo synthesis of this AA. When the PN was stopped, plasma levels of the AAs decreased, most of them returning to their basal levels, or significantly below for lysine (P<0.05), alanine (P<0.05), proline (P<0.01) and glutamine (P<0.05). No volunteer showed any adverse effect during the infusion period. DeltaN was: 0.8+/-0.5 gN/10 h. Metabolic characteristics for essential AAs were: Cl<0.5 l min(-1), Clr <1.5 ml x min(-1) Reab >or= 99%, Reten >or=99% and for non-essential AAs: Cl <0.6 l x min(-1) except aspartate (2.8+/-0.3 l x min(-1)), Clr < 3 ml x min(-1) except glycine (6.8+/-0.7), aspartate (8.2+/-3.5) and histidine (8.8+/-1.3); Reab >or= 98% except glycine (95+/-1), aspartate (94+/-2) and histidine (94+/-1), Reten >or=97% except histidine (94+/-1), glycine (95+/-3). These results indicate that in healthy subjects, the amounts of AAs provided by the new solution were well balanced for an intravenous administration, and so were well utilized without excessive urinary excretion. The present study provides useful metabolic parameters for a further evaluation in disease.

Adult↗
PubMed1988

Hepatic cysteine dioxygenase activity and sulfur amino acid metabolism in rats: possible indicators in the evaluation of protein quality.

Experiments were carried out to examine the possibility that the sulfur amino acid metabolism of rats may be an indicator of the nutritional value of dietary protein. Rats were fed diets containing 8, 16 or 24% of gluten, soy protein or casein for 3 wk. Hepatic cysteine dioxygenase activity, hepatic concentration of glutathione, cysteine and taurine and urinary taurine were examined. In addition, the sulfur amino acid metabolism of rats fed these diets fortified with the appropriate first limiting amino acid for 7 d was also examined. High urinary taurine excretion was observed in the three gluten groups, whereas very low urinary taurine excretion was observed with up to 24% soy protein or up to 16% casein. The hepatic hepatic cysteine dioxygenase activities of the gluten diet groups were higher than those of corresponding soy protein or casein diet groups, except that of rats fed the 24% casein diet. The hepatic concentrations of both glutathione and cysteine in gluten diet groups were also higher than those of corresponding soy protein or casein diet groups, except 24% soy protein and 16 and 24% casein diet groups. In rats fed the casein or soy protein diets urinary taurine excretion and hepatic cysteine dioxygenase activity increased with increasing methionine supplementation, the first limiting amino acid. Conversely, in rats fed the gluten diet both urinary taurine excretion and hepatic cysteine dioxygenase activity decreased with increasing lysine supplementation, the first limiting amino acid. These findings suggest that urinary taurine excretion and hepatic cysteine dioxygenase activity may be useful as sensitive indicators of the nutritional value of dietary protein.

Amino Acids, Sulfur↗
PubMedDate not supplied

[Amino acid metabolism in long-term nutrition with dehydrated products and in the modelling of space-flight factors].

Forty-two healthy volunteers, aged 19 to 49, participated in three bed rest studies of 69 to 180 days in duration. The test subjects were kept on the diet consisting of dehydrated foods: fresh, stored for up to 2 years, and exposed to proton irradiation at a dose of 24,000 rad. Metabolism of amino acids was investigated under these conditions. It was concluded that during prolonged storage and irradiation proteins of dehydrated foods retained their biological value. This allows their use in long-term space flights.

Adult↗
PubMed1990

Hepatic sulfur amino acid metabolism in rats with chronic renal failure.

We recently demonstrated elevated plasma amino acid concentrations and abnormal responses to amino acid supplementation (e.g., elevated methionine and phenylalanine) in children with chronic renal failure (CRF). We also recently developed an improved model of CRF in which animals manifest abnormal tissue amino acid levels, marked anorexia and growth failure. The objective of the current study was to determine the etiology of elevations of sulfur amino acids in animals with chronic renal failure. Chronic renal failure, defined as creatinine clearance less than 30% of control values, was induced in male rats in a two-stage surgical procedure. Four groups were studied over 2, 4 and 6 wk: control (non-operated) control (sham-operated), pair-fed (sham-operated and pair-fed with uremics) and CRF. Animals with CRF were anorexic and growth-retarded. Although plasma sulfur amino acid levels tended to be lower in the uremic animals than in controls, hepatic tissue concentrations were higher. Methionine adenosyltransferase was higher, but cystathione synthase and cystathionase activities were not significantly different in rats with CRF compared to pair-fed controls. We conclude that uremia, not malnutrition, affected sulfur amino acid metabolism and that with CRF, a normal adaptive response to elevated methionine levels was occurring, sufficient to normalize sulfur amino acid pool size. Alternative causes of elevated sulfur amino acids must be sought.

Amino Acids, Sulfur↗
PubMed2004

Effect of treatment with the Molecular Adsorbents Recirculating System on arterial amino acid levels and cerebral amino acid metabolism in patients with hepatic encephalopathy.

BACKGROUND: Liver failure is associated with low concentrations of branched-chain amino acids and high concentrations of most other amino acids. In this study the effect of treatment with the Molecular Adsorbents Recirculating System (MARS) on arterial amino acid levels and cerebral amino acid metabolism was examined in patients with severe hepatic encephalopathy. METHODS: The study included seven patients with hepatic encephalopathy from fulminant hepatic failure (FHF) and five patients with hepatic encephalopathy from acute-on-chronic liver failure (AoCLF). Cerebral blood flow and cerebral arteriovenous differences in amino acids were measured before and after 6 h of treatment with MARS. RESULTS: During MARS treatment, the total arterial amino acid concentration decreased by 20% from 8.92 +/- 7.79 mmol/L to 7.16 +/- 5.64 mmol/L (P < 0.05). The concentration decreased in all amino acids with the exception of the branched-chain amino acids. Fischer's ratio of branched-chain to aromatic amino acids increased from 0.73 +/- 0.47 to 0.91 +/- 0.54 (P < 0.05). A net cerebral efflux of amino acids in patients with FHF (8.94 +/- 8.34 micromol/100 g/min) as well as AoCLF (7.35 +/- 24.97 micromol/100 g/min) was not affected by the MARS treatment. MARS had no effect on the cerebral metabolic rate of any single amino acid in either group. CONCLUSIONS: MARS treatment tends to normalize the arterial amino acid concentrations in patients with hepatic encephalopathy. Even though the overall reduction in plasma amino acids and improvement in amino acid dysbalance may well be beneficial, it was not accompanied by any immediate improvement in cerebral amino acid metabolism in patients with FHF or AoCLF.

Adult↗
PubMed1999

Muscle protein degradation and amino acid metabolism during prolonged knee-extensor exercise in humans.

The aim of this study was to investigate whether prolonged one-leg knee-extensor exercise enhances net protein degradation in muscle with a normal or low glycogen content. Net amino acid production, as a measure of net protein degradation, was estimated from leg exchange and from changes in the concentrations of amino acids that are not metabolized in skeletal muscle. Experiments were performed at rest and during one-leg knee-extensor exercise in six subjects having one leg with a normal glycogen content and the other with a low glycogen content. Exercise was performed for 90 min at a workload of 60-65% of maximal one-leg power output, starting either with the normal-glycogen or the low-glycogen leg, at random. The net production of threonine, lysine and tyrosine and the sum of the non-metabolized amino acids were 9-20-fold higher (P<0.05) during exercise of the normal-glycogen leg than at rest. Total amino acid production was also 10-fold higher during exercise compared with that at rest (difference not significant). The net production rates of threonine, glycine and tyrosine and of the sum of the non-metabolized amino acids were about 1.5-2.5-fold higher during exercise with the leg with a low glycogen content compared with the leg with a normal glycogen content (P<0.05). Total amino acid production was 1.5-fold higher during exercise for the low-glycogen leg compared with the normal-glycogen leg (difference not significant). These data indicate that prolonged one-leg knee-extensor exercise leads to a substantial increase in net muscle protein degradation, and that a lowering of the starting muscle glycogen content leads to a further increase. The carbon atoms of the branched-chain amino acids (BCAA), glutamate, aspartate and asparagine, liberated by protein degradation, and the BCAA and glutamate extracted in increased amounts from the blood during exercise, are used for the synthesis of glutamine and for tricarboxylic-acid cycle anaplerosis.

Adult↗
PubMed1990

Sulfur amino acid metabolism in cystinuria: a biochemical and clinical study of patients.

Sulfur amino acid metabolism was studied in 26 homozygotic cystinuric patients, some of whom received D-penicillamine, 2-mercaptopropionylglycine or N-acetylcysteine treatments in order to evaluate signs of cyst(e)ine deficiency. Decreased leukocyte glutathione and taurine levels, plasma cyst(e)ine and taurine concentrations and urinary inorganic sulfate, taurine, mercaptolactate and thiosulfate outputs were found in cystinuric patients, probably reflecting intracellular cyst(e)ine deficiency. An increased mercaptoacetate-cysteine mixed disulfide output was found, probably as result of a poor tubular reabsorption of this compound, as well as for cystine. Normal retinal function was recorded in all patients. During drug treatments, the excretion of most of the sulfur compounds in cystinurics was as those found in controls, probably reflecting an increased mobilization of cysteine. N-acetylcysteine treatment increased the excretion of cyst(e)ine and can thus not be recommended as stone preventive therapy in cystinuria.

Acetylcysteine↗
PubMed1984

Sulfur amino acid metabolism in juvenile-onset nonketotic and ketotic diabetic patients.

Sulfur amino acid metabolism was studied in non-fasting nonketotic and ketotic juvenile-onset diabetic children and the results were compared to age-matched healthy children on an ordinary diet. An increased excretion of total sulfur and inorganic sulfate was found in diabetic children, probably a result of a decreased protein-serum synthesis and/or increased endogenous protein catabolism, although as a result of hyperglycemia a decreased tubular reabsorption may also have contributed. All diabetics showed a normal excretion of methionine. For cyst(e)ine and taurine an increased excretion was seen in ketotic diabetics, probably also a consequence of an increased endogenous protein degradation. As a sign of the latter, an increased output of 3-methylhistidine was also observed, a confirmation of earlier reports. The increased output of mercaptolactate and mercaptoacetate found in ketotic patients, was probably also a result of enhanced endogenous protein degradation. An increased urinary excretion of N-acetylcysteine was seen in diabetic children, which may reflect an enhanced availability to acetyl coenzyme A.

Adolescent↗
PubMed1991

[The effect of metabolic acidosis on amino acid and keto acid metabolism in chronic renal failure].

The effect of metabolic acidosis (MA) on amino acid and keto acid metabolism was studied in fourteen patients with chronic renal failure (CRF) under the low protein diet (0.6-0.8 g/kgBW). The comparative study of five patients with renal tubular acidosis was carried out. Each patient was investigated before [MA(+)period] and after correction with sodium bicarbonate administration lasting 10 days [MA(-)period]. The correction of MA improved nitrogen balance and elevated plasma branched-chain amino acids (BCAA), keto acids (BCKA), glutamine and alanine concentrations. No effect was however, observed in change of plasma insulin and glucagon. Oral administration of the keto-analogues of BCKA [0.1 g/kgBW of alpha-ketoisovalerates (KIV) and alpha-keto-isocaproic acid (KIC)] is made for the purpose of investigating the change in the metabolic conversion rate to amino acids. As a result, MA (+) suppressed an increase in plasma KIV and KIC concentrations. Moreover, an increase in plasma valine and leucine concentrations were suppressed by MA (+). These results suggested that MA stimulates BCKA oxidation and suppresses the protein sparing effect of leucine and KIC, and accelerates the catabolism in CRF under the low protein diet. The correction of MA is ineffective in severe renal failure (serum creatinine above 10.0 mg/dl), because the other uremic factors appear to be affecting protein and amino acid metabolism. Therefore, it might be concluded that MA should be corrected at an earlier stage of CRF.

Acidosis, Renal Tubular↗
PubMed1980

[Amino acid metabolism in Pasteurella multocida studied using thin-layer chromatography].

Amino asid metabolism was studied by thin layer chromatography in 25 Pasteurella multocida strains isolated from various manifestations of the disease chicken septicemia. Six amino acids were used: DL-ornithin, L-cystein, L-asparagin, DL-serin, L-arginin and Acidum glutaminicum. The Pasteurella strains studied include in their metabolism the amino acid asparagin, but serin and cystein are excluded. The strains isolated from birds suffering from acute and atypical septicemia do not metabolize ornithin, while these isolated from birds having wattles oedema or from calves suffering from arthritis metabolize it. The reaction of Pasteurellae to arginin and glutamic acid varies and no regularity in this respect is observed. Strains isolated from calves suffering from bronchopneumonia do not include in their metabolism any one of the named amino acids. As a result of the test applied a correlation between the Pasteurella multocida biotypes assessed by the authors and the amino acid metabolism was established. This is one proof more that the isolated pasteurellae can be groupped in two big biotypes by the tests for virulence in birds and including in their metabolism the amino acid ornithin.

Amino Acids↗