Publications (3)16.04 Total impact
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Article: New insights in the methodological issues of the indicator amino acid oxidation (IAAO) method in preterm neonates.
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ABSTRACT: Background:We determined the effect of adaptation to the study diet on the oxidation of the indicator amino acid and the required tracer washout time in preterms.Methods:Subjects received a study diet for 6d that entailed a 50% reduction in leucine. Tracer studies using enterally infused [(13)C]bicarbonate and [1-(13)C]phenylalanine were performed on days 1, 2, 4 and 6. Breath samples containing (13)CO(2) were collected during steady state, measured by infrared spectrometric analysis and the fraction of (13)CO(2) recovery from (13)C oxidation (F(13)CO(2)) was calculated.Results:Preterm infants (n=11, birth weight 1.9 ± 0.1 kg, gestational age 32.6 ± 1.5 wks) received 166 mg∙kg(-1)∙d(-1) of leucine. Baseline enrichment changed significantly at day 1 of the study diet. F(13)CO(2) did not change significantly between days 2 and 4 but was significantly lower at day 6. The tracer washout time was determined 7.5 h using a biphasic regression analysis.Conclusion:One day of adaptation to a new diet is necessary to adapt to the (13)C enrichment of the study formula before starting infant requirement studies. Adaptation for a period of 5 d results in a protein sparing response. The minimal time between two studies within the same subject is 7.5 h.Pediatric Research (2013); doi:10.1038/pr.2013.31.Pediatric Research 02/2013; · 2.70 Impact Factor -
Article: Methionine requirement of the enterally fed term infant in the first month of life in the presence of cysteine.
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ABSTRACT: The essential amino acid methionine can be used for protein synthesis but also serves as a precursor for homocysteine and cysteine. The objective of this study was to determine the minimal obligatory methionine requirement of infants in the presence of excess cysteine (91 mg ⋅ kg(-1) ⋅ d(-1)) by using the indicator amino acid oxidation (IAAO) method with l-[1-(13)C]phenylalanine as the indicator. Fully enterally fed term infants <1 mo of age were randomly assigned to methionine intakes that ranged from 3 to 59 mg ⋅ kg(-1) ⋅ d(-1) as part of an elemental formula. After 1 d of adaptation to the test diet, [(13)C]bicarbonate and l-[1-(13)C]phenylalanine tracers were given enterally. Breath samples were collected at baseline and during isotopic plateaus. The mean methionine requirement was determined by using biphasic linear regression crossover analysis on the fraction of (13)CO(2) recovery from l-[1-(13)C]phenylalanine oxidation (F(13)CO(2)). Data are presented as means ± SDs. Thirty-three neonates (gestational age: 39 ± 1 wk) were studied at 13 ± 6 d. With increasing methionine intakes, F(13)CO(2) decreased until a methionine intake of 38 mg ⋅ kg(-1) ⋅ d(-1); additional increases in methionine intake did not affect F(13)CO(2). The mean methionine requirement was determined at 38 mg ⋅ kg(-1) ⋅ d(-1), and the upper and lower CIs were 48 and 27 mg ⋅ kg(-1) ⋅ d(-11), respectively (P < 0.0001, r(2) = 0.59). Although the current recommended methionine intake of 28 mg ⋅ kg(-1) ⋅ d(-1) is within the CIs of our study, the estimated mean requirement is substantially higher. However, most of the infant formulas provide a methionine intake of 49-80 mg ⋅ kg(-1) ⋅ d(-1), which is above the upper CI of our study. This trial was registered at www.trialregister.nl as NTR1610.American Journal of Clinical Nutrition 04/2012; 95(5):1048-54. · 6.67 Impact Factor -
Article: Lysine requirement of the enterally fed term infant in the first month of life.
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ABSTRACT: Infant nutrition has a major impact on child growth and functional development. Low and high intakes of protein or amino acids could have a detrimental effect. The objective of the study was to determine the lysine requirement of enterally fed term neonates by using the indicator amino acid oxidation (IAAO) method. L-[1-(13)C]phenylalanine was used as an indicator amino acid. Twenty-one neonates were randomly assigned to lysine intakes that ranged from 15 to 240 mg · kg(-1) · d(-1). Breath, urine, and blood samples were collected at baseline and during the plateau. The mean lysine requirement was determined by using biphasic linear regression crossover analysis on the fraction of (13)CO(2) recovery from L-[1-(13)C]phenylalanine oxidation (F(13)CO(2)) and phenylalanine oxidation rates calculated from the L-[1-(13)C]phenylalanine enrichment of urine and plasma. The mean (±SD) phenylalanine flux calculated from urine and plasma L-[1-(13)C]phenylalanine enrichment data were 88.3 ± 6.9 and 84.5 ± 7.4 μmol · kg(-1) · h(-1), respectively. Graded intakes of lysine had no effect on phenylalanine fluxes. The mean lysine requirement determined by F(13)CO(2) was 130 mg · kg(-1) · d(-1) (upper and lower CIs: 183.7 and 76.3 mg · kg(-1) · d(-1), respectively). The mean requirement was identical to the requirement determined by using phenylalanine oxidation rates in urine and plasma. The mean lysine requirement of enterally fed term neonates was determined by using F(13)CO(2) and phenylalanine oxidation rates calculated from the L-[1-(13)C]phenylalanine enrichment of urine and plasma. These methods yielded a similar result of 130 mg lysine · kg(-1) · d(-1). This study demonstrates that sampling of (13)CO(2) in expired air is sufficient to estimate the lysine requirement by using the IAAO method in infants. This trial was registered at www.trialregister.nl as NTR1610.American Journal of Clinical Nutrition 11/2011; 94(6):1496-503. · 6.67 Impact Factor
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2011–2013
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Erasmus MC
Rotterdam, South Holland, Netherlands
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