Turnover of stable carbon and nitrogen isotopes in mammal tissues
Final Report Abstract
Knowledge on the isotope turnover is used for diet reconstruction in animal ecology, paleontology, forensics, and food authentication. In this project we (i) quantified the isotopic turnover by compartmental modeling of isotopic-switch experiments and validated the turnover information at different (dietary) conditions by forward modelling, (ii) applied inverse modelling of natural isotopic fluctuations to quantify isotopic turnover without systematic switch experiments, (iii) analyzed the effect of dietary protein content on isotopic turnover by piecewise linear/non-linear modeling and (iv) analyzed the nitrogen isotope turnover of amino acids. Carbon and nitrogen isotope compositions of the diet and of 28 tissues were available from three isotopic-switch experiments. These were whole milk, casein, lactose, milk fat, feces and hair from cow (Bos taurus) and urine, feces, plasma, liver, kidney, lung, spleen, brain, heart, muscle and twelve muscular amino acids from rat (Rattus norvegicus). The masses of organs were used to correct the isotopic turnover in case of growth. A delay between ingestion and first manifestation of dietary isotopes was considered during compartmental analysis. Overall, the delay in cow was ~12 h and the turnover was best represented by one-pool models, except for whole-milk, which was best represented with two pools. The two pools agreed with the turnover of its components (lactose, casein and fat). We could prove that the turnover information obtained from the diet-switch experiment allowed predicting the isotope fluctuations caused by fluctuations in isotope composition of natural grassland. Rat had a similar delay, and increasing dietary protein content increased isotopic turnover in all organs. The nitrogen in amino acids of rat muscle had a consistent turnover indicating coupling to muscle turnover, but differed in isotope value depending on the value in diet and the amino acids’ abilities of de novo synthesis and transamination. The results suggest that (i) delays should be considered in turnover estimation and are rather independent of the digestive system (monogaster vs ruminant), (ii) half-lives of different tissues within an animal cover about two orders of magnitude providing an isotopic clock for diet reconstruction, (iii) carbon and nitrogen half-lives are similar within the same material, and are similar for (experimental) single-switch and (natural) multiple-switch diets. The synopsis beyond species barriers revealed that the half-lives of organs of small model animals, like rats, can be used to predict the half-lives of organs of bigger animals, like cows.
Publications
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(2012): Quantification of isotopic turnover in agricultural systems. Geophysical Research Abstracts 14: EGU2012-158
Braun A., Auerswald K., Schnyder H.
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(2013): Dietary protein content affects isotopic carbon and nitrogen turnover. Rapid Commun. Mass Spectrom. 27: 2676–2684
Braun A, Auerswald K, Vikari A, Schnyder H
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(2013): Forward modeling of fluctuating dietary 13C signals to validate 13C turnover models of milk and milk components from a diet-switch experiment. PLoS ONE 8
Braun A, Schneider S, Auerswald K, Bellof G, Schnyder H
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(2014) Carbon and nitrogen isotope turnover in animals and animal products. Diss. Thesis, Technische Universität München
Braun A.
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(2014): Transamination governs nitrogen isotope heterogeneity of amino acids in rats. Journal of Agricultural and Food Chemistry 62: 8008 – 8013
Braun A, Vikari A, Windisch W, Auerswald K
