Human-mouse comparison of the multistage nature of radiation carcinogenesis in a mathematical model.

Mouse models are vital for assessing risk from environmental carcinogens, including ionizing radiation, yet the interspecies difference in the dose response precludes direct application of experimental evidence to humans. Herein, we take a mathematical approach to delineate the mechanism underlying the human-mouse difference in radiation-related cancer risk. We used a multistage carcinogenesis model assuming a mutational action of radiation to analyze previous data on cancer mortality in the Japanese atomic bomb survivors and in lifespan mouse experiments. Theoretically, the model predicted that exposure will chronologically shift the age-related increase in cancer risk forward by a period corresponding to the time in which the spontaneous mutational process generates the same mutational burden as that the exposure generates. This model appropriately fitted both human and mouse data and suggested a linear dose response for the time shift. The effect per dose decreased with increasing age at exposure similarly between humans and mice on a per-lifespan basis (0.72- and 0.71-fold, respectively, for every tenth lifetime). The time shift per dose was larger by two orders of magnitude in humans (7.8 and 0.046 years per Gy for humans and mice, respectively, when exposed at ~35% of their lifetime). The difference was mostly explained by the two orders of magnitude difference in spontaneous somatic mutation rates between the species plus the species-independent radiation-induced mutation rate. Thus, the findings delineate the mechanism underlying the interspecies difference in radiation-associated cancer mortality and may lead to the use of experimental evidence for risk prediction in humans.

Design, synthesis and biological evaluation of 2-pyrrolone derivatives as radioprotectors.

It is known that p53 is an important transcription factor and plays a central role in ionizing radiation (IR)-induced DNA damage responses such as cell cycle arrest, DNA repair and apoptosis. We previously reported that regulating p53 protein is an effective strategy for modulating cell fate by reducing the acute side effects of radiation therapy. Herein, we report on the discovery of STK160830 as a new radioprotector from a chemical library at The University of Tokyo and the design, synthesis and biological evaluation of its derivatives. The radioprotective activity of STK160830 itself and its derivatives that were synthesized in this work was evaluated using a leukemia cell line, MOLT-4 cells as a model of normal cells that express the p53 protein in a structure-activity relationships (SAR) study. The experimental results suggest that a direct relationship exists between the inhibitory effect of these STK160830 derivatives on the expression level of p53 and their radioprotective activity and that the suppression of p53 by STK160830 derivatives contribute to protecting MOLT-4 cells from apoptosis that is induced by exposure to radiation.

A comparison of cerebral amyloid angiopathy in the cerebellum and CAA-positive occipital lobe of 60 brains from routine autopsies.

We semiquantitatively compared the frequency and severity of cerebral amyloid angiopathy (CAA) in the cerebellum and CAA-positive occipital lobe of 60 subjects from routine autopsies. In the 60 subjects with a CAA-positive occipital lobe, cerebellar CAA was observed in 29 subjects (48.3%), and the severity of cerebellar CAA was relatively mild compared with occipital lobe CAA. Capillary CAA was observed in the occipital lobe of 12 subjects and the cerebellum of three subjects. CAA-related vasculopathies were observed in the occipital lobe of 15 subjects and the cerebellum of two subjects. The severity of CAA-related vasculopathy was mild in both of these subjects. Amyloid-ß plaques were observed in the occipital lobe of 54 subjects (90%) and the cerebellum of 16 subjects (26.7%). The severity of amyloid-ß plaques in the cerebellum was mild compared with the occipital lobe. In summary, we confirmed that cerebellar CAA is frequently observed in the cerebellum but with a lower severity than CAA in the occipital lobe.

An autopsy case of amyloid angiopathy-related cerebellar hemorrhage.

An 80-year-old man with dementia demonstrated cerebellar hemorrhage. Autopsy revealed pathology compatible with Alzheimer's disease and cerebral amyloid angiopathy (CAA). CAA was more prevalent in the occipital lobe than in the frontal, parietal, and temporal lobes; however, amyloid-ß (Aß)-containing senile plaques were less abundant in the occipital cortex than in the other cortices. In the cerebellum, abundant CAA-involved vessels were observed in the subarachnoid space and molecular layer and to a lesser extent in the Purkinje and granule layers. On consecutive sections, Aß1-42 immunohistochemistry revealed senile plaques and CAA-involved vessels with strong immunoreactivity whereas Aß1-40 immunohistochemistry identfied CAA-involved vessels with strong immunoreactivity and senile plaques with weak immunoreactivity in the cerebellar cortices.

Longitudinal physiological remoulding of lower limb skin as a cause of diabetic foot ulcer: a histopathological examination.

OBJECTIVE: Diabetic foot ulcer (DFU) is recognised as a severe complication in patients with type 2 diabetes. With the increasing incidence of diabetes, it represents a major medical challenge. Several models have been proposed to explain its aetiology; however, they have never been assessed by longitudinal histopathological examination, which this study aims to address. METHOD: Multiplex-immunofluorescence analysis was carried out with lengthwise serial skin specimens obtained from the medial thigh, lower leg, ankle, dorsum of foot and acrotarsium close to the DFU region of a patient with type 2 diabetes receiving above the knee amputation. RESULTS: Proximal-to-distal gradual loss of peripheral nerve was demonstrated, accompanied by compromised capillaries in the superficial papillary plexus and distended CD31-positive capillaries in the dorsum of foot. Neural fibres and capillaries were also significantly compromised in the sweat gland acinus in the ankle and dorsum of foot. Injuries in the superficial papillary plexus, sweat gland acinus, and sweat gland-associated adipose tissues were accompanied by significant infiltration of macrophages. These results indicated that longitudinal impairment of local blood circulation could be the cause of peripheral neuropathy, which initiated ulcer formation. Resultant chronic inflammation, involving sweat gland-associated adipose tissue, gave rise to impairment of wound healing, and thus DFU formation. CONCLUSION: Longitudinal histopathological examination demonstrated that impairment of local microvascular circulation (rather than the systemic complication caused by type 2 diabetes) was considered the primary cause of peripheral neuropathy, which initiated ulceration. Together with chronic inflammation in the superficial papillary plexus and sweat gland-associated adipose tissue, it resulted in the development of a DFU. Although this is a study of just one individual's limb, our study provided a unique observation, contributing mechanistic insights into developing novel intervening strategies to prevent and treat DFUs.

Preoperative detection of the TERT promoter mutations in papillary thyroid carcinomas.

OBJECTIVE: Telomerase reverse transcriptase promoter (TERT-p) mutations are strongly associated with tumour aggressiveness and worse prognosis in papillary thyroid carcinomas (PTCs). Since the TERT-p mutations have been reported to be subclonal, it is unclear how accurately they can be detected by preoperative fine-needle aspiration (FNA). The objective of this study was to analyse the concordance rate of the TERT-p mutations between preoperative FNA and corresponding postoperative surgical specimens. DESIGN AND PATIENTS: Ninety-six cases of PTC aged 55 years or older were studied. The mutational status of TERT-p was detected by droplet digital polymerase chain reaction assay. RESULTS: The mutational status of the TERT-p in FNA samples was highly concordant with that in postoperative formalin-fixed and paraffin-embedded (FFPE) specimens. The TERT-p mutation was significantly associated with age, tumour size, extrathyroidal extension and the Ki-67 labelling index in multivariate analysis in both FNA and FFPE samples. CONCLUSIONS: The detection of the TERT-p mutations using FNA samples has a good ability to predict disease aggressiveness and, therefore, could be clinically useful in the determination of PTC management.

Cellular Mechanism Underlying Highly-Active or Antiretroviral Therapy-Induced Lipodystrophy: Atazanavir, a Protease Inhibitor, Compromises Adipogenic Conversion of Adipose-Derived Stem/Progenitor Cells through Accelerating ER Stress-Mediated Cell Death in Differentiating Adipocytes.

Lipodystrophy is a common complication in human immunodeficiency virus (HIV)-infected patients receiving highly active antiretroviral therapy (HAART) or antiretroviral therapy (ART). Previous studies demonstrated that endoplasmic reticulum (ER) stress-mediated unfolded protein response (UPR) is involved in lipodystrophy; however, the detailed mechanism has not been fully described in human adipogenic cell lineage. We utilized adipose tissue-derived stem cells (ADSCs) obtained from human subcutaneous adipose tissue, and atazanavir (ATV), a protease inhibitor (PI), was administered to ADSCs and ADSCs undergoing adipogenic conversion. Marked repression of adipogenic differentiation was observed when ATV was administered during 10 days of ADSC culture in adipogenic differentiation medium. Although ATV had no effect on ADSCs, it significantly induced apoptosis in differentiating adipocytes. ATV treatment also caused the punctate appearance of CCAAT-enhancer-binding (C/EBP) protein homologous protein (CHOP), and altered expression of CHOP and GRP78/Bip, which are the representation of ER stress, only in differentiating adipocytes. Administration of UPR inhibitors restored adipogenic differentiation, indicating that ER stress-mediated UPR was induced in differentiating adipocytes in the presence of ATV. We also observed autophagy, which was potentiated in differentiating adipocytes by ATV treatment. Thus, adipogenic cell atrophy leads to ATV-induced lipodystrophy, which is mediated by ER stress-mediated UPR and accelerated autophagy, both of which would cause adipogenic apoptosis. As our study demonstrated for the first time that ADSCs are unsusceptible to ATV and its deleterious effects are limited to the differentiating adipocytes, responsible target(s) for ATV-induced lipodystrophy may be protease(s) processing adipogenesis-specific protein(s).

Amyloid-ß plaques may be reduced in advanced stages of cerebral amyloid angiopathy in the elderly.

We examined 29 cases in which cerebral amyloid angiopathy (CAA) was detected among routine aged autopsies. Most cases with severe CAA had many amyloid-ß (Aß) plaques in the occipital cortex. Nonetheless, two cases had few Aß plaques with many small vessels and capillaries with CAA. In the two cases, severe CAA was widely distributed, except in the frontal lobes. Aß deposits in capillaries often showed the characteristic pattern of dysphoric amyloid angiopathy. A few naked plaques were present. Although Aß plaques were sparse near small vessels with CAA, there were many Aß plaques distant from small vessels with CAA. Some of the remaining plaques had a moth-eaten appearance. Based on Aß-positive star-like appearance and results of double immunohistochemistry for glial fibrillary acidic protein and Aß1-42 , some astrocytes appeared to contain Aß. Ionized calcium-binding adapter molecule 1 (Iba1)-positive microglia were scattered within the neuropil, with some present around small vessels with CAA. Iba1-positive microglia also seemed to phagocytose Aß in several senile plaques by double immunostaining. Neurons and neurites identified with a monoclonal antibody against phosphorylated tau (clone AT8) were occasionally detected in sparse plaque areas, with AT8-identified dot-like structures present around capillaries with CAA. Accumulation of T lymphocytes was detected around vessels in the subarachnoid space in one case. The morphological changes detected in our two cases were similar to those of morphological markers of plaque clearance after Aß immunotherapy. Nonetheless, our cases did not receive Aß immunotherapy, but similar pathologies were observed. Overall, advanced CAA cases, including our two cases, may be examples of plaque clearance without Aß immunotherapy. Further studies are needed to resolve the mechanism of Aß plaque clearance using these cases.

Astrocytic tau pathologies in aged human brain.

Argyrophilic and tau-positive abnormal structures in astrocytes are frequent in aged brains, with a new nomenclature of aging-related tau astrogliopathy (ARTAG) proposed. The two major cytomorphologies of ARTAG are thorn-shaped astrocytes (TSA) and granular or fuzzy tau immunoreactivity in processes of astrocytes (GFA). We selected 28 cases in which many AT8-identified astrocytic tauopathies were observed in the central nervous system from 330 routine aged autopsied cases, including Alzheimer's disease. AT8-identified and Gallyas silver staining-positive TSA were observed in subpial, subependymal, perivascular areas as well as white matter. These TSA were 4-repeat (4R) tau-positive. In contrast, 3-repeat (3R)-tau was negative in TSA, but positive in short thick cell processes, likely neuropil threads, in subpial and subependymal areas. The frequency of 3R-tau-positive processes was variable. Small dot-like AT8-identified astrocytic processes surrounding vessels in the neuropil were also positive for 4R-tau, but negative for 3R-tau. GFA in cerebral gray matter were AT8-identified and Gallyas-positive, and positive for 4R-tau but negative for 3R-tau. In this study, we did not identify 3R-tau+/4R-tau+ or 3R-tau+/4R-tau- astrocytes. Further studies are needed to clarify the nature and progression of glial tau-positive structures in ARTAG.

Biological Features Implies Potential Use of Autologous Adipose-Derived Stem/Progenitor Cells in Wound Repair and Regenerations for the Patients with Lipodystrophy.

A paradigm shift in plastic and reconstructive surgery is brought about the usage of cell-based therapies for wound healing and regeneration. Considering the imitations in the reconstructive surgeries in restoring tissue loss and deficiency, stem cell-based therapy, in particular, has been expected to pave the way for a new solution to the regenerative approaches. Limitations in the reconstructive surgeries in restoring tissue loss and deficiency have paved the way for new regenerative approaches. Among them, adipose-derived stem/progenitor cells (ADSCs)-based therapy could be the most promising clue, since ADSCs have pluripotent differentiation capabilities not only in adipocytes but also in a variety of cell types. Accumulating evidences have indicated that the unfavorable development of adipose-tissue damage, namely, lipodystrophy, is a systemic complication, which is closely related to metabolic abnormality. Considering ADSC-based regenerative medicine should be applied for the treatment of lipodystrophy, it is inevitable to ascertain whether the ADSCs obtained from the patients with lipodystrophy are capable of being used. It will be very promising and realistic if this concept is applied to lipoatrophy; one form of lipodystrophies that deteriorates the patients' quality of life because of excessive loss of soft tissue in the exposed areas such as face and extremities. Since lipodystrophy is frequently observed in the human immunodeficiency virus (HIV)-infected patients receiving highly active antiretroviral therapy (HAART), the present study aims to examine the biological potentials of ADSCs isolated from the HIV-infected patients with lipodystrophy associated with the HAART treatment. Growth properties, adipogenic differentiation, and mitochondrial reactive oxygen species (ROS) production were examined in ADSCs from HIV-infected and HIV-uninfected patients. Our results clearly demonstrated that ADSCs from both patients showed indistinguishable growth properties and potentials for adipocyte differentiation in vitro. Thus, although the number of cases were limited, ADSCs isolated from the patients with lipodystrophy retain sufficient physiological and biological activity for the reconstitution of adipose-tissue, suggesting that ADSCs from the patients with lipodystrophy could be used for autologous ADSC-based regenerative therapy.

Adult moyamoya disease associated with abundant phosphorylated tau accumulation in the brainstem: Report of a case with autopsy findings.

We report the case of a 72-year-old Japanese woman with moyamoya disease (MMD). She experienced her first intracerebral hemorrhage (ICH) at the age of 32 years, and had nine ICHs and/or intraventricular hemorrhages during the following 40 years. Cerebral angiograms and vascular pathologies at autopsy confirmed that the patient suffered from MMD. Macroscopically, there were brown-colored changes in the subarachnoid space, mainly at the base of the brain and around the cerebellar hemispheres. Microscopically, hemosiderin deposits were observed mainly in the old hemorrhagic lesions and on the surface of the brainstem and cerebellum. Many AT8-immunoreactive neurons and neurites were observed in the pons and midbrain, mainly in the locus ceruleus and reticular formation in the midbrain. Several AT8-immunoreactive neurons and neurites were positive for Gallyas silver staining. A few tiny and short AT8-immunoreactive processes were observed in the molecular, Purkinje cell and granular layers of the cerebellum. There were a few phosphorylated tau accumulations in the cerebrum without senile plaques. Lewy pathologies and transactive response DNA-binding protein 43 kDa proteinopathy were not detected. We suspect that oxidative stress after repeated bleedings with long-term courses in the ventricles and subarachnoid space may accelerate phosphorylated tau accumulation in the brainstem. To our knowledge, this is the first report of MMD with tauopathy in the brainstem.

Patterns of use of near-infrared spectroscopy in neonatal intensive care units: international usage survey.

AIM: To assess uptake and applications of near-infrared spectroscopy (NIRS) by neonatal intensive care units (NICUs). METHODS: A pre-piloted online questionnaire was distributed in May 2015 to 12 perinatal societies in Asia, Europe, Australasia, North America and Middle East for dissemination to NICUs. Questions surveyed demographics, NIRS research/clinical applications, usage frequency, training approaches and target infant populations. RESULTS: In total, 255 responses from 235 NICUs were obtained. Of these, 85 (36%) owned a NIRS device. Australian and New Zealand NICUs were more likely to own NIRS technology than Asian (OR 1.12, 95% CI: 0.38-3.37) and North American (OR 2.63, 95% CI: 1.07-6.45) NICUs. A total of 69 (71%) used NIRS within clinical or mixed clinical-research settings, however routine reliance for management and prognostication was low (9% and 3%, respectively). Of those without NIRS technology, 96 (64%) had no acquisition intentions. The main limiting factors were controversial evidence on efficacy (59%) and financial considerations (50%). About 51% of respondents received in-house NIRS training and 32% had access to written guidelines. CONCLUSION: There is considerable geographical variation in NIRS usage in NICUs that is, on the whole, limited by consumer perception of lack of evidence for its clinical utility. This knowledge gap should be addressed by future research.

What does the world think of ankyloglossia?

AIM: The diagnosis of tongue-tie (or ankyloglossia) has increased more than 10-fold in some countries. Whether this is a global phenomenon or related to cultural and professional differences is uncertain. METHODS: An online survey in English, Japanese, Chinese and Spanish was disseminated between May and November 2016 via 27 international professional bodies to >30 clinical professions chosen a priori to represent occupations involved in the management of neonatal ankyloglossia. RESULTS: A total of 1721 responses came from nursing (51%), medical (40%), dental (6%) and allied health (4%) clinicians. Nurses (40%) and allied health (34%) professionals were more likely than doctors (8%) to consider ankyloglossia as important for lactation problems, as were western (83%) compared to Asian (52%) clinicians. Referrals to clinicians for ankyloglossia management originated mainly from parents (38%). Interprofessional referrals were not clearly defined. Frenectomies were most likely to be performed by surgeons (65%) and dentists (35%), who were also less likely to be involved in lactation support. Clinicians performing frenectomies were more likely to consider analgesia as important compared to those not performing frenectomies. CONCLUSION: The diagnosis and treatment of ankyloglossia vary considerably around the world and between professions. Efforts to standardise management are required.

Characteristic phase distribution in the white matter of infants on phase difference enhanced imaging.

BACKGROUND AND PURPOSE: The infantile brain is continuously undergoing development. Non-invasive methods to assess the neurological development of infants are important for the early detection of abnormalities. Some microstructures in the brain have been demonstrated via phase difference-enhanced imaging (PADRE), which may reflect myelin-related microstructures. We aimed to assess the white matter (WM) signal distribution in infants using PADRE and compared it with that using T1-weighted images (T1WI) and diffusion tensor imaging (DTI) on magnetic resonance imaging (MRI). MATERIALS AND METHOD: This study included 18 infants (postmenstrual age at MRI, 37-40 weeks) without abnormal findings on MRI. Signal distribution using T1WI, a fractional anisotropy (FA) map and PADRE was assessed regarding the following intraparenchymal structures: the optic radiation (OR), internal capsule (IC), corpus callosum, corticospinal tract (CST), semiovale center and subcortical regions. RESULTS: We found that the signal distribution was significantly different (P<0.001) with a relatively large signal change found at the IC and CST across the three imaging methods. Signal changes were also greater at the OR and rolandic subcortical WM on PADRE, whereas these were smaller on T1WI and FA. CONCLUSION: PADRE demonstrated a characteristic phase shift distribution in infantile WM, which was different from that observed on T1WI and FA maps, and may demonstrate the developing myelin-related structures. PADRE can be a unique indicator of infantile brain development.

Comparison of AT8 immunoreactivity in the locus ceruleus and hippocampus of 154 brains from routine autopsies.

We compared semiquantitatively AT8 immunoreactivity in the locus ceruleus (LC) and hippocampus of 154 brains from routine autopsies to investigate the initial sites of phosphorylated tau (phospho-tau) development. The numbers of AT8-positive neurons and the severity of AT8-positive neuropil threads (NTs) in the LC were strongly associated: there were no cases with AT8-positive neurons that lacked NTs and 20 cases (13%) had only NTs in the LC. Phospho-tau pathologies in the LC were almost equally on both sides, although some cases (7.8%) showed unilateral predominance. The numbers of AT8-positive neurons in the LC and the numbers of AT8-positive neurons and NTs in the hippocampus were also strongly associated. There were only two cases with AT8-positive neurons in the LC that lacked phospho-tau pathology in the hippocampus, and 21 cases (13.6%) with phospho-tau pathology in the hippocampus that lacked AT8-positive neurons in the LC. The numbers of AT8-positive NTs in the LC and AT8-positive neurons and NTs in the hippocampus were also strongly associated. There were seven cases (4.5%) with AT8-positive NTs in the LC that lacked phospho-tau pathology in the hippocampus, and five cases (3.2 %) with phospho-tau pathologies in the hippocampus that lacked AT8-positive NTs in the LC. In this study, we could not confirm that phospho-tau pathologies begin in the LC. We suspect their simultaneous occurrences in both hippocampal regions and in LC.

Identification of DNA double strand breaks at chromosome boundaries along the track of particle irradiation.

Chromosomal translocations arise from misrejoining of DNA double strand breaks (DSBs) between loci located on two chromosomes. One current model suggests that spatial proximity of potential chromosomal translocation partners influences translocation probability. Ionizing radiation (IR) is a potent inducer of translocations. Accumulating evidence demonstrates that particle irradiation more frequently causes translocations compared with X-ray irradiation. This observation has led to the hypothesis that the high frequency of translocations after particle irradiation may be due to the formation of DSBs at chromosome boundaries along the particle track, because such DSBs can be misrejoined between distinct chromosomes. In this study, we simultaneously visualized the site of IR-induced DSBs and chromosome position by combining Immunofluorescence and fluorescence in situ hybridization. Importantly, the frequency of γH2AX foci at the chromosome boundary of chromosome 1 after carbon-ion irradiation was >4-fold higher than that after X-ray irradiation. This observation is consistent with the idea that particle irradiation generates DSBs at the boundaries of two chromosomes along the track. Further, we showed that resolution of γH2AX foci at chromosome boundaries is prevented by inhibition of DNA-PKcs activity, indicating that the DSB repair is NHEJ-dependent. Finally, we found that γH2AX foci at chromosome boundaries after carbon-ion irradiation contain DSBs undergoing DNA-end resection, which promotes repair utilizing microhomology mediated end-joining during translocation. Taken together, our study suggests that the frequency of DSB formation at chromosome boundaries is associated with the incidence of chromosomal translocations, supporting the notion that the spatial proximity between breaks is an important factor in translocation formation. © 2016 Wiley Periodicals, Inc.

Clinicians in 25 countries prefer to use lower levels of oxygen to resuscitate preterm infants at birth.

AIM: This study determined current international clinical practice and opinions regarding initial fractional inspired oxygen (FiO2 ) and pulse oximetry (SpO2 ) targets for delivery room resuscitation of preterm infants of less than 29 weeks of gestation. METHODS: An online survey was disseminated to neonatal clinicians via established professional clinical networks using a web-based survey programme between March 9 and June 30, 2015. RESULTS: Of the 630 responses from 25 countries, 60% were from neonatologists. The majority (77%) would target SpO2 between the 10th to 50th percentiles values for full-term infants. The median starting FiO2 was 0.3, with Japan using the highest (0.4) and the UK using the lowest (0.21). New Zealand targeted the highest SpO2 percentiles (median 50%). Most respondents agreed or did not disagree that a trial was required that compared the higher FiO2 of 0.6 (83%), targeting the 50th SpO2 percentile (60%), and the lower FiO2 of 0.21 (80%), targeting the 10th SpO2 percentile (78%). Most (65%) would join this trial. Many considered that evidence was lacking and further research was needed. CONCLUSION: Clinicians currently favour lower SpO2 targets for preterm resuscitation, despite acknowledging the lack of evidence for benefit or harm, and 65% would join a clinical trial.

Radiation signatures in childhood thyroid cancers after the Chernobyl accident: possible roles of radiation in carcinogenesis.

After the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant accident, cancer risk from low-dose radiation exposure has been deeply concerning. The linear no-threshold model is applied for the purpose of radiation protection, but it is a model based on the concept that ionizing radiation induces stochastic oncogenic alterations in the target cells. As the elucidation of the mechanism of radiation-induced carcinogenesis is indispensable to justify the concept, studies aimed at the determination of molecular changes associated with thyroid cancers among children who suffered effects from the Chernobyl nuclear accident will be overviewed. We intend to discuss whether any radiation signatures are associated with radiation-induced childhood thyroid cancers.

Dose and dose-rate effects of ionizing radiation: a discussion in the light of radiological protection.

The biological effects on humans of low-dose and low-dose-rate exposures to ionizing radiation have always been of major interest. The most recent concept as suggested by the International Commission on Radiological Protection (ICRP) is to extrapolate existing epidemiological data at high doses and dose rates down to low doses and low dose rates relevant to radiological protection, using the so-called dose and dose-rate effectiveness factor (DDREF). The present paper summarizes what was presented and discussed by experts from ICRP and Japan at a dedicated workshop on this topic held in May 2015 in Kyoto, Japan. This paper describes the historical development of the DDREF concept in light of emerging scientific evidence on dose and dose-rate effects, summarizes the conclusions recently drawn by a number of international organizations (e.g., BEIR VII, ICRP, SSK, UNSCEAR, and WHO), mentions current scientific efforts to obtain more data on low-dose and low-dose-rate effects at molecular, cellular, animal and human levels, and discusses future options that could be useful to improve and optimize the DDREF concept for the purpose of radiological protection.