Radiocesium Concentration in Commercially-Available Foods Produced in Japan: 2017-2019.

We investigated the concentration of radioactive cesium (r-Cs: 134Cs and 137Cs) in commercially-available foods to confirm the effectiveness of pre-shipment radioactive material inspections mainly conducted by local governments. We focused on selected production areas and foods with high probability of r-Cs detection. To this end, we evaluated 715, 685, and 683 samples using scintillation spectrometer and high-purity germanium γ-spectrometer in fiscal years 2017, 2018, and 2019, respectively. The results accounted for 9 samples (1.3%), 10 samples (1.5%), and 5 samples (0.7%) for each fiscal year exceeded the standard limit of radioactive material (100 Bq/kg as r-Cs concentration for general foods). Although we selected and evaluated foods with high probability of r-Cs detection, percentage of samples exceeding the standard limit in each fiscal year was very low, less than 2% to be exact. This suggests that food management system, including pre-shipment inspections, were effectively functioning. In addition, samples exceeding the standard limit were bound to edible wild plants and wild mushrooms, and log-cultivated mushrooms. The former is consider to be difficult for cultivation/feeding control, and the latter was know to be parts of foods greatly affected by radioactive materials. This suggests that the concentration of r-Cs in these items remains at relatively high levels. In contrast, r-Cs was not detected in items with controalble cultivation/feeding. Based on these observations, it is better to be inspected on more difficult-to-cotrol cultivation/feeding items, in order to achieve further streamlining and improving of inspection efficiency. Our results indicate that r-Cs concentration in commercially-available foods of easy-to cultivation/feeding control, such as general vegetables, fruits, and meat, have been well-controlled in Japan, however, difficult-to-cultivation/feeding control items need to be more paid attention to r-Cs concentrations.

Continuous Estimation of Annual Committed Effective Dose of Radioactive Cesium by Market Basket Study in Japan from 2013 to 2019 after Fukushima Daiichi Nuclear Power Plant Accident.

Radionuclide contamination in foods has been a great concern after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. To estimate time trends of daily intake and annual committed effective dose of radionuclides after the accident, radioactive cesium (r-Cs; 134Cs and 137Cs) and potassium-40 (40K) in market basket (MB) samples prepared at 6-month intervals in periods from September 2013 to March 2019 in 15 regions of Japan were analyzed using γ-ray spectrometry. The annual committed effective dose of r-Cs, calculated at non-detected radionuclide levels assumed to be half the limit of detection (LOD), appeared to decrease gradually in 11 regions close to the FDNPP that were more likely to be affected by the accident. Differences in doses among the 15 regions were large just after the accident, but gradually decreased. In particular, 134Cs has not been detected in any MB sample in any region since September 2018, and annual committed effective dose from 134Cs in all regions was mostly constant at around 0.3 µSv/year (given the respective LODs). The maximum annual committed effective dose of r-Cs in this study was decreased from 2.7 µSv/year in September 2013 to 1.0 µSv/year in March 2019. In contrast, the range of annual committed effective dose of 40K varied from approximately 150 to 200 µSv/year during that time frame and did not change much throughout the period of this study. Although annual committed effective doses of r-Cs in regions close to the FDNPP appeared to be higher than in regions far from the FDNPP, doses in all regions are remaining at a much lower levels than the intervention exemption level, 1 mSv/year, in foods in Japan.

[Concentration of Radioactive Cesium in Domestic Foods Collected from the Japanese Market in Fiscal Years 2014-2016].

Between fiscal years 2014 and 2016, we surveyed the concentration of radioactive cesium in commercial foods produced in areas where there is a risk of radiation contamination due to the Fukushima Daiichi nuclear disaster. The number of samples with a concentration of radioactive cesium that exceeded the regulatory limit （100 Bq/kg for general foods） was 9 out of 1,516 （0.6％） in fiscal 2014, 12 out of 900 （1.3％） in fiscal 2015, and 10 out of 654 （1.5％） in fiscal 2016. Even though some samples were expected to be contaminated with radioactive cesium, because wild mushrooms and edible wild plants were intentionally included in this survey, the percentage of samples that exceeded the regulatory limit was only around 1％. The surveillance results confirmed that the pre-shipment food monitoring conducted by local governments was properly and efficiently performed, although continuous monitoring of the concentration of radioactive cesium in cultivated and wild mushrooms, edible wild plants, and wild animal meats is still required.

Polyamines stimulate the CHSY1 synthesis through the unfolding of the RNA G-quadruplex at the 5'-untraslated region.

Glycosaminoglycans (GAGs), a group of structurally related acidic polysaccharides, are primarily found as glycan moieties of proteoglycans (PGs). Among these, chondroitin sulfate (CS) and dermatan sulfate, side chains of PGs, are widely distributed in animal kingdom and show structural variations, such as sulfation patterns and degree of epimerization, which are responsible for their physiological functions through interactions with growth factors, chemokines and adhesion molecules. However, structural changes in CS, particularly the ratio of 4-O-sulfation to 6-O-sulfation (4S/6S) and CS chain length that occur during the aging process, are not fully understood. We found that 4S/6S ratio and molecular weight of CS were decreased in polyamine-depleted cells. In addition, decreased levels of chondroitin synthase 1 (CHSY1) and chondroitin 4-O-sulfotransferase 2 proteins were also observed on polyamine depletion. Interestingly, the translation initiation of CHSY1 was suppressed by a highly structured sequence (positions -202 to -117 relative to the initiation codon) containing RNA G-quadruplex (G4) structures in 5'-untranslated region. The formation of the G4s was influenced by the neighboring sequences to the G4s and polyamine stimulation of CHSY1 synthesis disappeared when the formation of the G4s was inhibited by site-directed mutagenesis. These results suggest that the destabilization of G4 structures by polyamines stimulates CHSY1 synthesis and, at least in part, contribute to the maturation of CS chains.

Polyamines release the let-7b-mediated suppression of initiation codon recognition during the protein synthesis of EXT2.

Proteoglycans (PGs), a family of glycosaminoglycan (GAG)-protein glycoconjugates, contribute to animal physiology through interactions between their glycan chains and growth factors, chemokines and adhesion molecules. However, it remains unclear how GAG structures are changed during the aging process. Here, we found that polyamine levels are correlated with the expression level of heparan sulfate (HS) in human skin. In cultured cell lines, the EXT1 and EXT2 enzymes, initiating HS biosynthesis, were stimulated at the translational level by polyamines. Interestingly, the initiation codon recognition by 43S preinitiation complex during EXT2 translation is suppressed by let-7b, a member of the let-7 microRNA family, through binding at the N-terminal amino acid coding sequence in EXT2 mRNA. Let-7b-mediated suppression of initiation codon depends on the length of 5'-UTR of EXT2 mRNA and its suppression is inhibited in the presence of polyamines. These findings provide new insights into the HS biosynthesis related to miRNA and polyamines.

Spermidine and Ca(2+), but not Na(+), can permeate NMDA receptors consisting of GluN1 and GluN2A or GluN2B in the presence of Mg(2+).

N-Methyl-D-aspartate receptors (NMDA receptors) are known to be permeable to Na(+) and Ca(2+) ions. In this study, we tested whether polyamines (putrescine, spermidine, spermine), organic cations found in cells, can permeate NMDA receptors expressed in Xenopus laevis oocytes and HEK293 cells. It was found that polyamines, especially spermidine, can permeate NMDA channels expressed from GluN1/GluN2A or GluN1/GluN2B activated by glycine and glutamate. Furthermore, spermidine and Ca(2+) influx through NMDA receptors was observed in the presence of Mg(2+), although Na(+) influx was strongly inhibited by Mg(2+). The Km values for spermidine influx through GluN1/GluN2A and GluN1/GluN2B were 2.2 mM and 2.7 mM, respectively in the presence of isotonic extracellular ion solutions. Spermidine uptake by NMDA receptors was dependent on the presence of glycine and glutamate, and inhibited by Ca(2+) and by memantine, an NMDA receptor channel blocker. The Km values for Ca(2+) influx through GluN1/GluN2A and GluN1/GluN2B were 4.6 mM and 3.3 mM, respectively, under the same ionic conditions. The results indicate that spermidine and Ca(2+), but not Na(+), can permeate NMDA receptors in the presence of Mg(2+). Spermidine, if released locally from presynaptic terminals (where its concentration is high in synaptosomes and synaptic vesicles) could permeate NMDA receptors and play a role in synaptic plasticity mediated by NMDA receptors together with Ca(2+).

Identification of functional amino acid residues involved in polyamine and agmatine transport by human organic cation transporter 2.

Polyamine (putrescine, spermidine and spermine) and agmatine uptake by the human organic cation transporter 2 (hOCT2) was studied using HEK293 cells transfected with pCMV6-XL4/hOCT2. The Km values for putrescine and spermidine were 7.50 and 6.76 mM, and the Vmax values were 4.71 and 2.34 nmol/min/mg protein, respectively. Spermine uptake by hOCT2 was not observed at pH 7.4, although it inhibited both putrescine and spermidine uptake. Agmatine was also taken up by hOCT2, with Km value: 3.27 mM and a Vmax value of 3.14 nmol/min/mg protein. Amino acid residues involved in putrescine, agmatine and spermidine uptake by hOCT2 were Asp427, Glu448, Glu456, Asp475, and Glu516. In addition, Glu524 and Glu530 were involved in putrescine and spermidine uptake activity, and Glu528 and Glu540 were weakly involved in putrescine uptake activity. Furthermore, Asp551 was also involved in the recognition of spermidine. These results indicate that the recognition sites for putrescine, agmatine and spermidine on hOCT2 strongly overlap, consistent with the observation that the three amines are transported with similar affinity and velocity. A model of spermidine binding to hOCT2 was constructed based on the functional amino acid residues.