Amino acid specific carbon and nitrogen stable isotope ratios - role of nutritional and physiological conditions in humans
Final Report Abstract
Bulk natural 15N and 13C stable isotope abundances of hair can be used as nutritional biomarker. The use of stable isotope ratios as physiological biomarker and research of amino acids at the compound-specific level is uncommon in human studies. Changes of amino acid specific stable isotope signatures during pregnancy and its complications are unknown. We suspected influences due to strongly increased requirements for amino acids during pregnancy, changes in amino acid metabolism, and influences by pathophysiological complications such as nausea and vomiting. We measured for the first time compound specific the δ15N and δ13C stable isotope abundances of amino acids of hair protein hydrolysates during pregnancy. Samples were obtained from subjects after normal pregnancy during complications such as nutritional stress and diabetes. Hair samples were collected after birth and studied longitudinal from before conception until after birth in 1 cm segments each representing a 4 week period of pregnancy or hair growth. The measurements were performed by GC/C/IRMS using N-pivaloyl-i-propyl esters detecting 15 of the proteinogenic amino acids. The stable isotope patterns differed in a characteristic way between individual amino acids. The δ values of threonine were found to be depleted in 15N (-9.5 ± 1.1 ‰ vs. AIR-N2) and those of glycine were enriched in 13C (-5.7 ± 5.2 ‰ vs. V-PDB) in comparison to other amino acids detected. Furthermore, significantly higher δ15N and lower δ13C values were obtained in amino acids of US subjects compared with German subjects. We suggest that these differences can be related to consumption of regionally different food protein sources. Plots of δ15N against δ13C values of individual amino acids confirmed the distinct differences between indispensable and dispensable amino acids. There revealed no significant and systematic drift of amino acid specific δ13C values of hair protein during pregnancy. In contrast, the δ15N values of specific hair protein amino acids clearly changes during pregnancy. The extent of an increase of the δ15N values in phases of nutritional stress can amount to more than 3 ‰ for a specific amino acid such as proline. Amino acids which are dispensable or which participate in the metabolic amino nitrogen pool by transamination (e.g. glutamic acid, proline, and leucine) show increased δ15N values during stress or in catabolic state. As opposed to this the δ15N values can decrease during an anabolic state by more than 1 ‰ during the last trimester of normal pregnancy or after recovery from nutritional stress. Significantly reduced or enhanced δ15N values of amino acids carrying the dispensable nitrogen moiety such as leucine or proline can indicate positive or negative nitrogen balances, respectively, and showed a strongly negative correlation with body weight gain during nutritional stress. Interestingly and contrasting to dispensable amino acid nitrogen, the δ15N values of the indispensable amino acid threonine can decrease during nutritional stress and correlated with body weight gain. Moreover, we computed differences of up to 28 ‰ δ15N between proline and threonine (∆δ15NPro-Thr) in phases of nutritional stress or in subjects suffering from gestational diabetes. It is likely that this spacing could be used as a marker to distinguish between physiological and nutritional or trophic influences. Furthermore, this could be a marker with important impact for the interpretation of stable isotope data in archaeological and forensic studies provided that this model can be confirmed in future studies. Possible biochemical reasons responsible for modifications of the amino acid specific natural δ15N values are discussed. Particularly the unique function of depletion in threonine N concentrations during nutritional stress and a possible negative trophic effect of this indispensable amino acid were stressed. However, further studies are required to confirm that the ∆δ15NPro-Thr value can be used as a pathophysiological marker. The results of this project are highly interdisciplinary and will have important implications in nutrition, forensics, archaeology, and ecology. As a first application we examined hair of a late medieval female bog body found in Bavaria. A drop in amino acid specific δ15N values during the last months after a slight increase following suspected conception were interpreted as changes based on metabolic conditions during pregnancy.
Publications
- Advances in natural stable isotope ratio analysis of human hair to determine nutritional and metabolic status. Current opinion in clinical nutrition and metabolic care 2010;13(5):532-40
Petzke KJ, Fuller BT, Metges CC
- 15N and 13C abundances of individual amino acids of hair during pregnancy. JESIUM 2012, Leipzig, UFZ conference center ‘Leipziger KUBUS’, Germany, September 2–7, 2012
Petzke KJ, Fuller BT
- Stable isotope ratio analysis in human hair. In: Preedy, V. (ed.) Handbook of hair in health and disease. Wageningen Academic Publishers, pp 333-351 (2012)
Petzke K J, Fuller B T
- Was Rosalinde a pregnant foreigner? Isotope analysis of H, C, N, S and Sr in hair strands of a late medieval bog body from Upper Bavaria. In: JESIUM 2012, Leipzig, UFZ conference center ‘Leipziger KUBUS’, Germany, September 2–7, 2012
Lehn C, Haas-Gebhard B, Graw M, Rossmann A, Rummel S, Hölzl S, Fuller BT, Petzke KJ
- Natural abundances of 15N and 13C values of single amino acids in human hair are modified during pregnancy and nutritional stress. AMINO ACIDS (Vol. 48, No. 2, pp. 625-626). 2016. SACHSENPLATZ 4-6, PO BOX 89, A-1201 WIEN, AUSTRIA: SPRINGER WIEN
Fuller BT, Petzke KJ
