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Udo Wendel – One of the best experts on this subject based on the ideXlab platform.

  • Significance of L-Alloisoleucine in Plasma for Diagnosis of Maple Syrup Urine Disease
    , 2015
    Co-Authors: Peter Schadewaldt, Annette Bodner-leidecker, Hans-werner Hammen, Udo Wendel

    Abstract:

    leucine, which is derived from L-isoleucine in vivo, for diagnosis of maple syrup urine disease (MSUD) was examined. Methods: Branched-chain L-amino acids were measured by automatic amino acid analysis. Results: Alloisoleucine reference values in plasma were established in healthy adults [1.9 6 0.6 mmol/L (mean 6 SD); n 5 35], children 3–11 years (1.6 6 0.4 mmol/L; n 5 17), and infants <3 years (1.3 6 0.5 mmol/L; n 5 37). The effect of dietary isoleucine was assessed in oral loading tests. In controls receiving 38 mmol (n 5 6; low dose) and 1527 mmol (n 5 3; high dose) of L-isoleucine per kilo-gram of body weight, peak increases of plasma isoleu-cine were 78 6 24 and 1763 6 133 mmol/L, respectively; the peak increase of Alloisoleucine, however, was neg

  • Formation of L-Alloisoleucine In Vivo : An L-[^13C]Isoleucine Study in Man
    Pediatric Research, 2000
    Co-Authors: Peter Schadewaldt, Annette Bodner-leidecker, Hans-werner Hammen, Udo Wendel

    Abstract:

    L-Alloisoleucine (2 S , 3 R ), a diastereomer of L-isoleucine (2 S , 3 S ), is a normal constituent of human plasma. Considerable amounts accumulate in maple syrup urine disease, in which the branched-chain 2-oxo acid dehydrogenase step is impaired. The mechanism of L-Alloisoleucine formation, however, is unclear. We addressed this issue by performing oral L-[1-^13C]isoleucine loading (38 μmol/kg body wt, 50% 1-^13C) in overnight-fasted healthy subjects ( n = 4) and measuring the 3-h kinetics of ^13C-label incorporation into L-isoleucine plasma metabolites. Compared with L-isoleucine, the time course of ^13C-enrichment in the related 2-oxo acid, S -3-methyl-2-oxopentanoate, was only slightly delayed. Peak values, amounting to 18 ± 4 and 17 ± 3 mol percent excess, respectively, were reached within 35 and 45 min, respectively. The kinetics of ^13C-enrichment in S – and R -3-methyl-2-oxopentanoate enantiomorphs were similar and linearly correlated ( p ≪ 0.001). In L-Alloisoleucine, however, ^13C-label accumulated only gradually and in minor amounts. Our results indicate that R -3-methyl-2-oxopentanoate is an immediate and inevitable byproduct of L-isoleucine transamination and further suggest that Alloisoleucine is primarily formed via retransamination of 3-methyl-2-oxopenanoate in vivo .

  • Formation of L-Alloisoleucine in vivo: an L-[13C]isoleucine study in man.
    Pediatric research, 2000
    Co-Authors: Peter Schadewaldt, Annette Bodner-leidecker, Hans-werner Hammen, Udo Wendel

    Abstract:

    L-Alloisoleucine (2 S, 3 R), a diastereomer of L-isoleucine (2 S, 3 S), is a normal constituent of human plasma. Considerable amounts accumulate in maple syrup urine disease, in which the branched-chain 2-oxo acid dehydrogenase step is impaired. The mechanism of L-Alloisoleucine formation, however, is unclear. We addressed this issue by performing oral L-[1-13C]isoleucine loading (38 μmol/kg body wt, 50% 1-13C) in overnight-fasted healthy subjects (n = 4) and measuring the 3-h kinetics of 13C-label incorporation into L-isoleucine plasma metabolites. Compared with L-isoleucine, the time course of 13C-enrichment in the related 2-oxo acid, S-3-methyl-2-oxopentanoate, was only slightly delayed. Peak values, amounting to 18 ± 4 and 17 ± 3 mol percent excess, respectively, were reached within 35 and 45 min, respectively. The kinetics of 13C-enrichment in S- and R-3-methyl-2-oxopentanoate enantiomorphs were similar and linearly correlated (p 0.001). In L-Alloisoleucine, however, 13C-label accumulated only gradually and in minor amounts. Our results indicate that R-3-methyl-2-oxopentanoate is an immediate and inevitable byproduct of L-isoleucine transamination and further suggest that Alloisoleucine is primarily formed via retransamination of 3-methyl-2-oxopenanoate in vivo.

Peter Schadewaldt – One of the best experts on this subject based on the ideXlab platform.

  • Significance of L-Alloisoleucine in Plasma for Diagnosis of Maple Syrup Urine Disease
    , 2015
    Co-Authors: Peter Schadewaldt, Annette Bodner-leidecker, Hans-werner Hammen, Udo Wendel

    Abstract:

    leucine, which is derived from L-isoleucine in vivo, for diagnosis of maple syrup urine disease (MSUD) was examined. Methods: Branched-chain L-amino acids were measured by automatic amino acid analysis. Results: Alloisoleucine reference values in plasma were established in healthy adults [1.9 6 0.6 mmol/L (mean 6 SD); n 5 35], children 3–11 years (1.6 6 0.4 mmol/L; n 5 17), and infants <3 years (1.3 6 0.5 mmol/L; n 5 37). The effect of dietary isoleucine was assessed in oral loading tests. In controls receiving 38 mmol (n 5 6; low dose) and 1527 mmol (n 5 3; high dose) of L-isoleucine per kilo-gram of body weight, peak increases of plasma isoleu-cine were 78 6 24 and 1763 6 133 mmol/L, respectively; the peak increase of Alloisoleucine, however, was neg

  • Formation of L-Alloisoleucine In Vivo : An L-[^13C]Isoleucine Study in Man
    Pediatric Research, 2000
    Co-Authors: Peter Schadewaldt, Annette Bodner-leidecker, Hans-werner Hammen, Udo Wendel

    Abstract:

    L-Alloisoleucine (2 S , 3 R ), a diastereomer of L-isoleucine (2 S , 3 S ), is a normal constituent of human plasma. Considerable amounts accumulate in maple syrup urine disease, in which the branched-chain 2-oxo acid dehydrogenase step is impaired. The mechanism of L-Alloisoleucine formation, however, is unclear. We addressed this issue by performing oral L-[1-^13C]isoleucine loading (38 μmol/kg body wt, 50% 1-^13C) in overnight-fasted healthy subjects ( n = 4) and measuring the 3-h kinetics of ^13C-label incorporation into L-isoleucine plasma metabolites. Compared with L-isoleucine, the time course of ^13C-enrichment in the related 2-oxo acid, S -3-methyl-2-oxopentanoate, was only slightly delayed. Peak values, amounting to 18 ± 4 and 17 ± 3 mol percent excess, respectively, were reached within 35 and 45 min, respectively. The kinetics of ^13C-enrichment in S – and R -3-methyl-2-oxopentanoate enantiomorphs were similar and linearly correlated ( p ≪ 0.001). In L-Alloisoleucine, however, ^13C-label accumulated only gradually and in minor amounts. Our results indicate that R -3-methyl-2-oxopentanoate is an immediate and inevitable byproduct of L-isoleucine transamination and further suggest that Alloisoleucine is primarily formed via retransamination of 3-methyl-2-oxopenanoate in vivo .

  • Formation of L-Alloisoleucine in vivo: an L-[13C]isoleucine study in man.
    Pediatric research, 2000
    Co-Authors: Peter Schadewaldt, Annette Bodner-leidecker, Hans-werner Hammen, Udo Wendel

    Abstract:

    L-Alloisoleucine (2 S, 3 R), a diastereomer of L-isoleucine (2 S, 3 S), is a normal constituent of human plasma. Considerable amounts accumulate in maple syrup urine disease, in which the branched-chain 2-oxo acid dehydrogenase step is impaired. The mechanism of L-Alloisoleucine formation, however, is unclear. We addressed this issue by performing oral L-[1-13C]isoleucine loading (38 μmol/kg body wt, 50% 1-13C) in overnight-fasted healthy subjects (n = 4) and measuring the 3-h kinetics of 13C-label incorporation into L-isoleucine plasma metabolites. Compared with L-isoleucine, the time course of 13C-enrichment in the related 2-oxo acid, S-3-methyl-2-oxopentanoate, was only slightly delayed. Peak values, amounting to 18 ± 4 and 17 ± 3 mol percent excess, respectively, were reached within 35 and 45 min, respectively. The kinetics of 13C-enrichment in S- and R-3-methyl-2-oxopentanoate enantiomorphs were similar and linearly correlated (p 0.001). In L-Alloisoleucine, however, 13C-label accumulated only gradually and in minor amounts. Our results indicate that R-3-methyl-2-oxopentanoate is an immediate and inevitable byproduct of L-isoleucine transamination and further suggest that Alloisoleucine is primarily formed via retransamination of 3-methyl-2-oxopenanoate in vivo.

Marcus J. Miller – One of the best experts on this subject based on the ideXlab platform.

  • Rapid quantification of underivatized Alloisoleucine and argininosuccinate using mixed-mode chromatography with tandem mass spectrometry
    Journal of chromatography. B Analytical technologies in the biomedical and life sciences, 2019
    Co-Authors: Chandler Griffin, Zineb Ammous, Gail H. Vance, Brett H. Graham, Marcus J. Miller

    Abstract:

    Abstract Plasma elevations of the amino acids Alloisoleucine and argininosuccinic acid (ASA) are pathognomonic for maple syrup urine disease and argininosuccinate lyase deficiency, respectively. Reliable detection of these biomarkers is typically achieved using methods with tedious sample preparations or long chromatographic separations, and many published amino acid assays report poor specificity and/or sensitivity for one or both of these compounds. This report describes a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) method that provides rapid quantification of Alloisoleucine and ASA in human plasma. The basis of this method is a mixed-mode solid phase separation that achieves baseline resolution of Alloisoleucine from isobaric interferents without the use of derivatization or ion pairing agents. The inject-to-inject time is 6 min including elution, column washing and re-equilibration. Validation studies demonstrate excellent limits of quantification (1 μmol/L), linearity (r = 0.999 from 1 to 250 μmol/L), accuracy (bias = −3.8% and −10.1%), and inter-assay imprecision (CV