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1. Estimation of dietary 14C dose coefficient using 13C-labelled compound administration analysis

Author

Toshitada Yoshioka, Yuichi Takaku, Hiroshi Takeda, Shun'ichi Hisamatsu, Tsuyoshi Masuda, Yasuhiro Tako, Tomoyuki Takahashi, Hideo Hatta, and Kensaku Matsushita

Subjects
Adult, Male, lcsh:Medicine, Food Contamination, Effective dose (radiation), Article, 030218 nuclear medicine & medical imaging, Excretion, 03 medical and health sciences, 0302 clinical medicine, Animal science, Nutrient, Monosaccharide, Humans, Carbon Radioisotopes, Amino Acids, lcsh:Science, chemistry.chemical_classification, Carbon Isotopes, Multidisciplinary, Chemistry, Radiation dose, lcsh:R, Fatty Acids, Nuclear energy, Metabolism, Middle Aged, Diet, Nuclear facilities, 030220 oncology & carcinogenesis, lcsh:Q, Female
Abstract

Carbon-14 released from nuclear facilities has been assessed to contribute significantly to the radiation dose that people are exposed to through the food chain. However, the current dose coefficient for members of public, which is the ratio of the 50-year committed effective dose to ingested 1 Bq 14C, recommended by the International Commission on Radiological Protection (ICRP) is not based on experimental human metabolic data for 14C in nutrients and diet. Therefore, to validate the coefficient, we administered 13C-labelled nutrients consisting of four amino acids, three fatty acids, and one monosaccharide to volunteers as substitutes for 14C labelled nutrients and measured the 13C concentration in various excreta samples. Although metabolic models were constructed from the excretion data, a significant fraction of administered 13C was not recovered from some nutrients. The dose coefficients of 14C in uniformly labelled Japanese diet, which were estimated under several assumptions about the unrecoverable fraction, varied from (6.2 ± 0.9) × 10–11 to (8.9 ± 4.4) × 10–10 Sv Bq−1 and were approximately comparable to the current value of 5.8 × 10–10 Sv Bq−1 recommended by the ICRP. Further studies are necessary to elucidate the metabolism of 14C in various nutrients in the unrecoverable fraction.

Published
2020

2. Biokinetics of 13C in the human body after oral administration of 13C-labeled glucose as an index for the biokinetics of 14C.

Author

Tsuyoshi Masuda, Yasuhiro Tako, Kensaku Matsushita, Hiroshi Takeda, Masahiro Endo, Yuji Nakamura, and Shun’ichi Hisamatsu

Subjects
*ORAL drug administration, *CHEMICAL kinetics, *RADIOISOTOPES, *RADIATION doses, *GLUCOSE metabolism
Abstract

The retention of 13C in the human body after oral administration of 13C-labeled glucose was studied in three healthy volunteer subjects to estimate the 50 year cumulative body burden for 13C as an index of the committed dose of the radioisotope 14C. After administration of 13C-labeled glucose, the volunteers ingested controlled diets with a fixed number of calories for 112 d. Samples of breath and urine were collected up to 112 d after administration. Samples of feces were collected up to 14 d after administration. Hair samples were obtained at 119 d after administration and analyzed as a representative index of the rate of excretion of organic 13C via pathways such as skin cell exfoliation and mucus secretion. All samples were analyzed for 13C/12C atomic ratio to determine the rate of excretion via each pathway. We then constructed a metabolic model with a total of four pathways (breath, urine, feces, and other) comprising seven compartments. We determined the values of the biokinetic parameters in the model by using the obtained excretion data. From 74% to 94% of the 13C administered was excreted in breath, whereas  <2% was excreted in urine and feces. In the other pathway, the excretion rate constant in the compartment with the longest residence time stretched to hundreds of days but the rate constant for each subject was not statistically significant (P value  >  0.1). In addition, the dataset for one of the three subjects was markedly different from those of the other two. When we estimated the 50 year cumulative body burden for 13C by using our model and we included non-statistically significant parameters, a considerable cumulative body burden was found in the compartments excreting to the other pathway. Although our results on the cumulative body burden of 13C from orally administered carbon as glucose were inconclusive, we found that the compartments excreting to the other pathway had a markedly long residence time and therefore should be studied further to clarify the fate of carbon in the human body. In addition to excreta, data for serum and blood cell samples were also collected from the subjects to examine the metabolism of 13C in human body. [ABSTRACT FROM AUTHOR]

Published
2016
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