Role of N-acetylglutamate and acetyl-CoA in the inhibition of ureagenesis by isovaleric acid in isolated rat hepatocytes.

1 and 10 mmol/l isovalerate strongly inhibited urea synthesis in isolated rat hepatocytes incubated with 10 mmol/l alanine and 3 mmol/l ornithine. Isovalerate also markedly decreased N-acetylglutamate levels, and the decrease correlated with the inhibition of urea synthesis by isovalerate. This compound also lowered cellular levels of acetyl-CoA, a substrate of N-acetylglutamate synthase (EC 2.3.1.1). Isovalerate did not significantly affect the cellular levels of ATP and had no direct effect on N-acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by isovalerate is due to decrease in N-acetylglutamate levels.

Nutritional effects of feeding a ketoanalogue mixture in growing and adult uremic rats.

Insufficient protein diets supplemented with ketoanalogue/essential amino acid (KA/EAA) mixtures are proposed to maintain nutrition and to retard renal deterioration. We compared in growing and in adult uremic rats diets containing limited or usual amounts of protein (12%, 20% for growing rats, and 10% and 16% for adult rats) with diets containing 50% or 60% less casein plus a KA/EAA mixture providing KA at an equimolar amount of removed EAA or at higher amounts. The latter supplement caused stunting, the former caused no anorexia, a slight growth deficit when added to the lowest basal casein diets, and almost normal growth when added to higher casein diets. Growth was normal with EAA supplements. The plasma EAA changes were unrelated to intake and to growth. Thus, KA utilization is maximal, provided that basal protein is sufficient and KA are not in excess.

Optimal dietary substitution of racemic ketoanalogues for isoleucine in growing normal and uremic rats.

Dietary ketoanalogues (KAs) were shown to replace their essential amino acids with a 50% efficiency for valine and leucine. We determined the optimal concentration of the racemic KA of isoleucine (KMVA) in uremic and control rats: nutrition responses were compared between a diet containing optimal isoleucine concentration and diets containing various KMVA concentrations. Isomolar replacement of isoleucine produced anorexia, stunting, and poor nitrogen balance. Doubling KMVA partially improved these indices. Tripling KMVA lessened urea production and improved growth up to that obtained with the isoleucine diet in uremic but not in control rats (20% lower). A further KMVA increase produced no further benefit. Among plasma branched-chain amino acids, only alloisoleucine was affected; it increased with increasing KMVA concentration, being maximum after tripling KMVA. Racemic KMVA could replace isoleucine with a 35% efficiency but supported no growth acceleration in uremic rats and no maximal growth in control rats. Plasma alloisoleucine rose without adverse nutrition effects.

Amino acid handling in uremic rats: citrulline, a reliable marker of renal insufficiency and proximal tubular dysfunction.

The kidney is involved in amino acid reabsorption and metabolism; consequently, in renal insufficiency, these important functions are disturbed, as has been reported in animals and patients. In a first experimental series, rats were subjected to degrees of nephrectomy (NX) varying between 10% and 90%. Three weeks later, amino acid levels were measured in plasma to correlate the levels with the degree of NX. The results indicate that in the range of 33% to 74% NX, the plasma concentration of only three to four amino acids was modified, whereas in rats with 84% NX, the concentration of 11 amino acids was disturbed, compared with sham-operated rats. Citrullinemia was enhanced in uremic rats and correlated with the degree of NX. More interestingly, citrullinemia was increased in the range of 10% to 33% NX without any changes in uremia and creatininemia, two well-known markers of uremic states. A second experimental series was designed to study the time course of changes in aminoacidemia to find a marker for the onset of renal failure. Rats were subjected to 36% NX for a period of 1 to 21 days. Uremia and creatininemia peaked 24 to 48 hours after NX, and creatinine clearance (Clcreat) concomitantly diminished. Unfortunately, these three markers of uremic states returned to control values during the next few days before increasing during the last 2 weeks. In contrast, citrullinemia increased twofold 48 hours after NX and plateaued over the next 20 days. We conclude that in rats, citrullinemia could be used (1) to detect acute and chronic renal failure, (2) as a specific marker of normal function of the proximal tubule, and (3) to estimate the degree of renal damage. From this study, renal insufficiency might be easily detected by measuring citrullinemia.

A scheme for the interpretation of primary and secondary disturbances of plasma and urinary amino acid profiles. A possible way to an expert system.

A general scheme for the interpretation of primary and secondary abnormalities of plasma and urine amino acid concentrations is described. The key steps of this scheme are: analytical assessment of the measurements, comparison of results obtained with the reference values expressed in absolute and/or relative concentrations and identification of abnormally increased ninhydrin-positive compounds. The interpretation of results takes account of the various abnormalities induced by drugs or diet. The origins of these abnormalities are ordered by their frequency. A part of the proposed scheme is now computerized as the first step in the development of an expert system.

Ion-exchange chromatography and clinical criteria in the screening of the aminoacidopathies.

By a retrospective study on a two-year period (1494 patients) we have obtained evidence that the best method of screening aminoacidopathies is given by the ion-exchange chromatography of amino acids. This method gave the highest rates of diagnosis and allowed diagnosis of aminoacidopathies that other techniques such as thin-layer chromatography would fail to detect because the concentrations of some amino acids, although pathological, were too low. The diagnostic rate was markedly improved by a skilled clinical selection of the population studied.

Early alterations of plasma free amino acids in chronic renal failure.

In order to assess the influence of renal failure and nutritional status on the fasting concentrations of free plasma amino acids, we studied 81 ambulatory adult patients with varying degrees of chronic renal failure. Each of the patients was in good general and nutritional condition. Compared to 33 healthy controls, patients with mild renal failure (Ccr greater than 25 ml/mn) exhibited significantly (p less than 0.01, Student's t test) raised concentrations of cystine, citrulline, ornithine, taurine and 3-methyl-histidine and low level of serine. Concentrations of cystine, citrulline, and 3-methyl-histidine in plasma but not of taurine or ornithine rose in parallel with the progression of renal failure. A significant, but moderate decrease in valine, leucine and isoleucine concentrations was observed in patients with the most marked degree of renal failure (Ccr less than 10 ml/mn). We conclude that changes in the plasma concentration of several non essential amino acids are already present in the early stage of renal failure in patients with no sign of protein malnutrition: these may result from altered metabolic pathways of amino acids related to uremia and/or nephron loss per se whereas the moderate decrease in branched-chain amino acids that is observed only in the advanced stage of renal failure may be, at least in part, nutritional in origin.

Blood and urinary amino acids in children receiving total parenteral nutrition.

Plasma concentrations and urinary outputs of amino acids were estimated in nineteen patients receiving intravenous hyperalimentation to evaluate the adequacy of dosage and composition of the infusates for the maintenance of normal blood concentrations of essential amino acids. The use of high concentrations of branched chain amino acids seems to be appropriate for valine and isoleucine but not for leucine. The high concentration of cysteine in the infusates used induces a very high urinary excretion of cysteine and cystine and are ineffective to bring the decreased plasma cystine levels back to normal.

Assay of tissue free cystine: application to the diagnosis of cystinosis.

A fast method for the determination of tissue free cystine is shown. Its usefulness for free cystine assays in leucocytes and muscle biopsies is discussed. The use of muscle biopsy as a means of diagnosis is proposed.

[A decision tree for abnormalities of plasma and urine lysine level]. / 'Un arbre de décision pour les anomalies de concentration de la lysine plasmatique et urinaire.

Variations of plasma lysine were divided in four situations: decreased, slightly decreased to normal, normal to slightly increased and always very increased. From each of these situations, and with the concentrations of urinary lysine; a flow chart is proposed for aminoacidopathies and organic acidurias in which lysine metabolism is primarily or secondarily disturbed.

[Methodological errors in amino acid assay in biological fluids]. / Les erreurs méthodologiques dans l'analyse des acides aminés des liquides biologiques.

Numerous methodological errors have been observed in the measurement of free-amino acids in the biological fluids. Some of them are related to the presence or the formation of amino acids or ninhydrin-positive compounds in tubes or anticoagulants used for the blood sampling. Hemolysis or blood clotting modify the concentration of some amino acids in plasma. A special error observed with the capillary blood is related to the amino acids present on area of the skin. Bacterial contamination of urines or buffers used for the analysis can also modify the results of the amino acids assays.

[Hyperlysinemia and hyperammonemia]. / Hyperlysinémie et hyperammoniémie.

A quite important increase of plasma lysine was often reported in different cases of hyperammonemia. This retrospective study of patients with different types of hyperammonemia shows that hyperlysinemia is not automatically associated to hyperammonemia (lysinemia is expressed as the percent of total aminoacidemia). Hyperlysinemia was observed with neonatal propionic and methylmalonic acidurias. Reye's syndrome and to a less extent with ornithine transcarbamylase deficiency.

[Rapid column chromatography of blood amino-acids from a paper sample (author's transl)]. / Chromatographie rapide sur colonne des acides aminés sanguins à partir d'un prélèvement sur papier.

Authors propose a method permitting rapide quantitative analysis of blood amino-acids from a blood sample on paper. The amino-acid analyser was equiped with two columns of different lenght and diameter, one (0.5 x 30 cm) permitting rapid detection (complete chromatography in 110 minutes), the other (0.63 x 35 cm) permitting a quantitative study of amino-acidopathies (complete chromatography in 240 minutes). The apparatus and the program of elution proposed have the advantage of being adaptable without any other modification than the time of passage of the reagents to very rapid analysis of amino-acid groups and classical analysis of samples of serum and urine.

[Free amino acids in fetal urine and prognosis of renal function in bilateral obstructive uropathies]. / Acides aminés libres de l'urine foetale et pronostic de la fonction rénale dans les uropathies obstructives bilatérales.

In order to evaluate renal function, fetal urine was sampled in 27 fetuses with urinary tract obstruction diagnosed by ultrasonography. Amino acid concentrations were measured retrospectively. On histological examination performed after termination of pregnancy, five fetuses were found to have bilateral renal dysplasia (group 1). Eleven fetuses developed renal failure after birth: at one year, plasma creatinine concentration was over 50 mumol/l (group 2). Renal function was normal in the 11 other infants (group 3, plasma creatinine concentration at one year < 50 mumol-1). Statistically significant between-group differences were seen in fetal urine amino acids concentrations. However, there was an overlap of values in the three groups and individual amino acid concentrations could not be used predictively.

[Variation of amino acids in relation to age in Down syndrome subjects]. / Variation des acides aminés en fonction de l'âge chez des sujets trisomiques 21.

BACKGROUND: A preliminary study of plasma and urinary amino acid concentration in Down's syndrome subjects had shown some impairments. PATIENTS AND METHODS: A comparative study of the variations of amino acid concentration with age in Down's syndrome subjects aged 0 to 60 years and in control subjects aged 0 to 94 years was made in order to determine whether these impairments could be explained by generalized premature aging, or by a specific gene dosage effect. RESULTS: Two major changes (P < 0.001) were found in Down's syndrome: a decrease in plasma concentration of serine at any age, which could be due to a dosage effect of cytathionine-beta-synthase, and an increase in plasma lysine concentration in patients above 10 year's old, probably due to premature aging. Other minor changes were also present in plasma and urine, also possibly explained by premature aging. CONCLUSIONS: Other studies are necessary to evaluate possible consequences of such changes in the amino acid profiles.