Department of Pediatrics, Division of Neonatology, Medical Centre-Sophia Children's Hospital, Rotterdam, Netherlands.
Am J Clin Nutr. 2012 May;95(5):1048-54. doi: 10.3945/ajcn.111.028779. Epub 2012 Apr 4.
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.
必需氨基酸蛋氨酸可用于蛋白质合成，但也可作为同型半胱氨酸和半胱氨酸的前体。
本研究旨在通过使用 l-[1-(13)C]苯丙氨酸作为指示剂的指示氨基酸氧化（IAAO）方法，确定在过量半胱氨酸（91mg ⋅ kg(-1) ⋅ d(-1)）存在下婴儿的最低必需蛋氨酸需求量。
小于 1 个月龄的完全肠内喂养足月婴儿被随机分配到蛋氨酸摄入量为 3 至 59mg ⋅ kg(-1) ⋅ d(-1)的范围内，作为元素配方的一部分。适应试验饮食 1 天后，经肠内给予 [(13)C]碳酸氢盐和 l-[1-(13)C]苯丙氨酸示踪剂。在基线和同位素平台期采集呼吸样本。通过使用双相线性回归交叉分析 l-[1-(13)C]苯丙氨酸氧化的（13）CO（2）回收率的分数（F（13）CO（2））来确定平均蛋氨酸需求量。数据以平均值 ± 标准差表示。
33 名新生儿（胎龄：39 ± 1 周）在 13 ± 6 天时进行了研究。随着蛋氨酸摄入量的增加，F（13）CO（2）下降，直到蛋氨酸摄入量为 38mg ⋅ kg(-1) ⋅ d(-1)；进一步增加蛋氨酸摄入量不会影响 F（13）CO（2）。平均蛋氨酸需求量为 38mg ⋅ kg(-1) ⋅ d(-1)，上下置信区间分别为 48 和 27mg ⋅ kg(-1) ⋅ d(-1)（P<0.0001，r(2)=0.59）。
尽管目前推荐的 28mg ⋅ kg(-1) ⋅ d(-1)的蛋氨酸摄入量在我们研究的置信区间内，但估计的平均需求量要高得多。然而，大多数婴儿配方奶粉提供的蛋氨酸摄入量为 49-80mg ⋅ kg(-1) ⋅ d(-1)，高于我们研究的上限置信区间。本试验在 www.trialregister.nl 注册为 NTR1610。
