The Fukushima-Daiichi Nuclear Power Plant (FNPP) accident in March of 2011 released substantial amounts of radionuclides into the environment. We collected 4,957 deciduous teeth formed in children before the Fukushima accident to obtain precise control data for teeth formed after the accident. Radioactivity was measured using imaging plates (IP) and epidemiologically assessed using multivariate regression analysis. Additionally, we measured ⁹⁰Sr, ¹³⁷Cs, and natural radionuclides which might be present in teeth. Epidemiological studies of IP showed that the amount of radioactivity in teeth from Fukushima prefecture was similar to that from reference prefectures. We found that artificial radionuclides of ⁹⁰Sr and ¹³⁷Cs, which were believed to have originated from past nuclear disasters, and natural radionuclides including ⁴⁰ K and daughter nuclides in the ²³⁸U and ²³²Th series contributed to the generation of radioactivity in teeth. We also found no evidence to suggest that radionuclides originating from the FNPP accident significantly contaminated pre-existing teeth. This is the first large-scale investigation of radioactivity and radionuclides in teeth. The present findings will be indispensable for future studies of teeth formed after the FNPP accident, which will fall out over the next several years and might be more contaminated with radionuclides.

Bisphosphonates (BPs) are classified into two groups, according to their side chain structures, as nitrogen-containing BPs (NBPs) and non-nitrogen-containing BPs (non-NBPs). In this study, we examined the effects of NBPs and non-NBPs on inflammatory responses, by quantifying the inflammatory mediators, prostaglandin E₂ (PGE₂) and nitric oxide (NO), in cultured neonatal mouse calvaria. All examined NBPs (pamidronate, alendronate, incadronate, risedronate, zoledronate) stimulated lipopolysaccharide (LPS)-induced PGE₂ and NO production by upregulating COX-2 and iNOS mRNA expression, whereas non-NBPs (etidronate, clodronate, tiludronate) suppressed PGE₂ and NO production, by downregulating gene expression. Additionally, [4-(methylthio) phenylthio] methane bisphosphonate (MPMBP), a novel non-NBP with an antioxidant methylthio phenylthio group in its side chain, exhibited the most potent anti-inflammatory activity among non-NBPs. Furthermore, results of immunohistochemistry showed that the nuclear translocation of NF-κB/p65 and tyrosine nitration of cytoplasmic protein were stimulated by zoledronate, while MPMBP inhibited these phenomena, by acting as a superoxide anion (O₂⁻) scavenger. These findings indicate that MPMBP can act as an efficacious agent that causes fewer adverse effects in patients with inflammatory bone diseases, including periodontitis and rheumatoid arthritis.

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, great attention has been paid to the impact of chronic low-dose-rate (LDR) radiation exposure on biological systems. The reproductive system is sensitive to radiation, with implications connected to infertility. We investigated the testis ultrastructure of the wild large Japanese field mouse (Apodemus speciosus) from three areas contaminated after the FDNPP accident, with different levels of LDR radiation (0.29 µSv/h, 5.11 µSv/h, and 11.80 µSv/h). Results showed good preservation of the seminiferous tubules, comparable to the unexposed animals (controls), except for some ultrastructural modifications. Increases in the numerical density of lipid droplet clusters in spermatogenic cells were found at high levels of LDR radiation, indicating an antioxidant activity rising due to radiation recovery. In all groups, wide intercellular spaces were found between spermatogenic cells, and cytoplasmic vacuolization increased at intermediate and high levels and vacuolated mitochondria at the high-level. However, these findings were also related to the physiological dynamics of spermatogenesis. In conclusion, the testes of A. speciosus exposed to LDR radiation associated with the FDNPP accident showed a normal spermatogenesis, with some ultrastructural changes. These outcomes may add information on the reproductive potential of mammals chronically exposed to LDR radiation.

To apply electron spin resonance (ESR) dosimetry to wild Japanese macaques captured in the ex-evacuation area during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the improvement of the detection limit is crucial. In this study, we optimized the microwave power in ESR measurements to suppress the noise of native radicals and enhanced the signals of radiation-induced carbonate radicals. Tooth enamels of a Japanese macaque captured in a control area were prepared and irradiated with gamma rays from ⁶⁰Co source. The ESR spectra of the enamel samples with different absorbed doses ranging from 0 to 1800 mGy were measured with varying microwave power. The ESR spectra were analyzed by an in-house multi-component decomposition code using a simulated annealing method. Intensities of both components originating from carbonate and native radicals saturated and decayed as the microwave power increased. The intensity ratio of carbonate radicals to native radicals, i.e., signal to noise ratio, increased monotonically at microwave powers below 30 mW. We also examined the linearity of the intensity of carbonate radicals against the absorbed doses and recommended a microwave power range of 5-25 mW. In this study, we showed that optimizing the microwave power is an effective way to improve the quantitation accuracy of carbonate radicals in samples with low absorbed doses. The improved measurement conditions will expand the applicable range of ESR dosimetry for research on the effects of radiation on wild animals related to the FDNPP accident.

The Fukushima-Daiichi Nuclear Power Plant (FNPP) accident in March 2011 released substantial amounts of radionuclides into the environment. We collected 4,957 deciduous teeth formed in children before the Fukushima accident to obtain precise control data for teeth formed after the accident. Radioactivity was measured using imaging plates (IP) and epidemiologically assessed using multivariate regression analysis. Additionally, we measured ⁹⁰Sr, ¹³⁷Cs, and natural radionuclides which might be present in teeth. Epidemiological studies of IP showed that the amount of radioactivity in teeth from Fukushima prefecture was similar to that from reference prefectures. We found that artificial radionuclides of ⁹⁰Sr and ¹³⁷Cs, which were believed to have originated from past nuclear disasters, and natural radionuclides including ⁴⁰K and daughter nuclides in the ²³⁸U and ²³²Th series contributed to the generation of radioactivity in teeth. We also found no evidence to suggest that radionuclides originating from the FNPP accident significantly contaminated pre-existing teeth. This is the first large-scale investigation of radioactivity and radionuclides in teeth. The present findings will be indispensable for future studies of teeth formed after the FNPP accident, which will fall out over the next several years and might be more contaminated with radionuclides.