Katarzyna M. Romek 1,2, Maxime Julien 2, Marine Frasquet-Darrieux 3, Illa Tea 2, Ingrid Antheaume 2, Régis Hankard 3 and Richard J. Robins 2 Protein intake plays a key role in fetal and post-natal growth. A number of studies have shown the importance of balanced protein intake in infancy and intra-uterine growth. [2],[3] However, the present work shows 15 N-isotope values of human baby hair are not dictated by 15 N-isotope values of mother’s breast-milk. Is it the infant nitrogen metabolism dominating over nutrient source? References: [1] Romek K.M., Julien M., Frasquet-Darrieux M., Tea I., Antheaume I., Hankard R. and Robins R. J., Natural-abundance 15 N-isotope values of human baby hair protein are not dictated by 15 N-isotope values of mother’s breast-milk: infant nitrogen metabolism dominates over nutrient source. AJCN, 2013 [2] Paolini C, Marconi A, Ronzoni S, et al. Placental transport of leucine, phenylalanine, glycine, and proline in intrauterine growth-restricted pregnancies. J Clin Endocrinol Metab 2001;86: [3] Tea I, Le Gall G, Küster A, et al. 1 H-NMR-based metabolic profiling of maternal and umbilical cord blood indicates altered materno-foetal nutrient exchange in preterm infants. PloS One 2012;7:e29947 (12 pages) 2D isotope plot for δ 13 C g and δ 15 N g (‰) values for total hair and milk solids. Each data point represents one mother-infant pair, analyzed by EA-irm-Ms. Comparison of δ 15 N values obtained by EA and obtained by calculation based on the individual δ 15 N and quantities from irm-MS; values from milk and hair the same mother-infant pairs. Low values of δ 13 C could be explained by the high fat content in milk causing those differences. In the case of δ 15 N values – high metabolic rate of baby and/or differences in amino acids between milk and hair could be the cause. Correlations between isotopic values of δ 15 N (‰) for hair and milk proteins for individual amino acid in the mother-infant pairs Differences in global δ 15 N-isotope values tend to confirm lower level of enrichment of human milk. Existence of other nitrogenous compounds may be the major reason. Isotope distribution in infant protein is dictated by its intrinsic nitrogen metabolism and is not determined by δ 15 N of the amino acids provided in mother’s milk. Metabolism has a much greater influence than does nurture. Isotope ratios δ 15 N and δ 13 C (‰) were significantly higher in infant hair than in breast milk. Likewise, δ 15 N (‰) of amino acid fraction obtained from infant hair was also significantly higher than from maternal milk. 1. Laboratory for Isotope Effects Studies, Department of Chemistry, Institute of Applied Radiation Chemistry, Technical University, Zeromskiego 116, Łodź, Poland, 2. Elucidation of Biosynthesis by Isotopic Spectrometry Group, CEISAM, University of Nantes–CNRS UMR6230, France. 3. Inserm, CIC 0802, University of Poitiers and CHU Poitiers, PoiAtiers, F-86000, France. EA-irm-MS GC-irm-MS ANALYSIS δ 15 N and δ 13 C obtained from whole samples δ 15 N, concentration and quantity of amino acids in samples RESULTS Horizontal and vertical shift between hair and milk δ 15 N and δ 13 C values In order to relate different sets of data to a standard set of conditions, values for analytes were normalized. After first correction, further ones were applied so as to compare fully results obtained in EA-irms-MS and GC-irms-MS. δ 15 N GC-Acor = δ 15 N GC-A + δ 15 N EA-A. [1] Number of pairs analyzed. If N < 11, then the peak area was insufficient in one or more samples Total number of mother–infant pairs analyzed for correlations of unhydrolyzed hair and milk proteins and determined by EA-irm-MS Correlation of the isotope values for the mother milk and infant hair (A) δ 15 N values and (B) δ 13 C values. Each data point represents one mother– infant pair, analyzed by EA-irm-MS. The amino acid composition of hair and milk proteins did not account for the observed difference in isotope content. For milk, the difference (Calc δ 15 N; EA δ 15 N) = 0,95 ‰ The difference for hair (Calc δ 15 N; EA δ 15 N) = 1,29 ‰. This demonstrates a regular shift in the values obtained by the two different methods. It should also be noted that the (Hair- Milk) difference based on the Calc δ 15 N values of 3.26 ‰ is the same....as that based on the EA- IRMS δ 15 N values of 3.59 ‰. δ 15 N shift is consistent whether obtained by EA measurement or obtained on the basis of the individual amino acids. ASSAY