1.06.B–T01 - Iron Stable Isotope Composition as an Indicator of Iron Metabolism in Vertebrates

Abstract

Stable isotope ratios of metals in animal tissues reflect metal behavior under different biological conditions, such as health status or species differences. Iron is an essential trace element, and its stable isotope ratio (δ56Fe) fractionates in response to metabolic regulatioin, making it a promising tracer of iron metabolism across species. Previous studies suggest δ56Fe reflects storage iron levels, primarily iron bound to ferritin. To assess interspecies variation in δ56Fe and its link to storage iron level, we analyzed 14 vertebrate species (8 mammals, 2 birds, 2 reptiles, and 2 fish) and multiple tissues from mice (Mus musculus, Slc:ddY, male, n = 5).
Samples were sourced from Hokkaido University and the es-Bank at Ehime University. Iron speciation was determined using Fe K-edge X-ray absorption near edge structure (XANES) spectroscopy at the High Energy Accelerator Research Organization (KEK, Japan). Total iron and other elements were quantified by inductively coupled plasma mass spectrometry (ICP-MS; Agilent 7850). The δ56Fe values were measured using multicollector ICP-MS (MC-ICP-MS, Neptune Plus) after the addition of a double spike of 57Fe and 58Fe, with precision confirdmed using reference material (DOLT5, NRC Canada) and two in-house standards with known isotope ratios, with a maximum error of 0.2‰.
In mice, δ56Fe varied depending on the tissue type. The highest values were observed in the liver and spleen (－1.52‰ to －0.80‰, and －1.58‰ to －1.12‰), followed by the muscle (－1.87‰ to －1.23‰), testis (－1.88‰ to －2.07‰), kidney (－2.22‰ to －2.03‰), and red blood cells (－2.20‰ to －2.63‰). The δ56Fe of the diet (iron citrate) was －0.18‰, and the δ56Fe values of the stomach and intestinal contents were nearly identical to the dietary value. XANES revealed high ferritin-bound iron in the spleen and testis (64-89%, and 65-79%, respectively), followed by the liver (18-54%), muscle (32-33%), kidney (14-19%), and red blood cells (0%). The δ56Fe values positively correlated with ferritin-bound iron within mouse tissues (r = 0.55, p = 0.01), supporting preferential uptakes of heavy isotopes by ferritin.
Among species, liver δ56Fe was relatively high in mammals, intermediate in birds , and lower in reptiles. Diets or stomach contents among three domesticated animals (mouse, quail, and bovine) showed small δ56Fe variation (0.22 ± 0.89‰). Across species, liver δ56Fe value was negatively correlated with ferritin-bound iron (r = －0.42, p = 0.01), suggesting that higher storage iron may reflect selective uptake of lighter isotopes from diet due to lower iron absorption efficiency. These results indicate that δ56Fe values reflect interspecific difference in relation to iron uptake and storage. Further analyses may contribute to the development of a broad, non-invasive indicator of abnormal iron metabolism.
 

Author(s)

Presenter: Nanako, Hasegawa

Authors: 

Nanako Hasegawa Faculty of Veterinary Medicine, Hokkaido University Japan
Takaaki Itai Graduate School of Science, the University of Tokyo Japan
Yoshio Takahashi Graduate School of Science, the University of Tokyo Japan
Yuta Ijichi Japan Agency for Marine-Earth Science and Technology Japan
Teruhiko Kashiwabara Japan Agency for Marine-Earth Science and Technology Japan
Yared Yohannes Faculty of Veterinary Medicine, Hokkaido University Japan
Tatsuya Kunisue Ehime University Center for Marine Environmental Studies Japan
Kohei Ogasawara Faculty of Veterinary Medicine, Hokkaido University Japan
Yurika Tokunaga Faculty of Veterinary Medicine, Hokkaido University Japan
Yoshinori Ikenaka One Health Research Center, Hokkaido University Japan
Kunda Ndashe School of Veterinary Medicine, Univrsity of Zambia Zambia
Andrew Kataba School of Veterinary Medicine, Univrsity of Zambia Zambia
Rio Doya Faculty of Veterinary Medicine, Hokkaido University Japan
Koki Kotake Graduate School of Science, Nagoya University Japan
Hiroaki Norimoto Graduate School of Science, Nagoya University Japan
Shouta Nakayama Faculty of Veterinary Medicine, Hokkaido University Japan
Mayumi Ishizuka Faculty of Veterinary Medicine, Hokkaido University Japan