Report of IRPA task group on issues and actions taken in response to the change in eye lens dose limit.

In 2018, the International Radiation Protection Association (IRPA) established its third task group (TG) on the implementation of the eye lens dose limit. To contribute to sharing experience and raising awareness within the radiation protection community about protection of workers in exposure of the lens of the eye, the TG conducted a questionnaire survey and analysed the responses. This paper provides an overview of the results of the questionnaire.

Report of IRPA task group on the impact of the eye lens dose limits.

In 2012 IRPA established a task group (TG) to identify key issues in the implementation of the revised eye lens dose limit. The TG reported its conclusions in 2013. In January 2015, IRPA asked the TG to review progress with the implementation of the recommendations from the early report and to collate current practitioner experience. This report presents the results of a survey on the view of the IRPA professionals on the new limit to the lens of the eye and on the wider issue of tissue reactions. Recommendations derived from the survey are presented. This report was approved by IRPA Executive Council on 31 January 2017.

Immunomodulation of classical and non-classical HLA molecules by ionizing radiation.

Radiotherapy has been employed for the treatment of oncological patients for nearly a century, and together with surgery and chemotherapy, radiation oncology constitutes one of the three pillars of cancer therapy. Ionizing radiation has complex effects on neoplastic cells and on tumor microenvironment: beyond its action as a direct cytotoxic agent, tumor irradiation triggers a series of alterations in tumoral cells, which includes the de novo synthesis of particular proteins and the up/down-regulation of cell surface molecules. Additionally, ionizing radiation may induce the release of "danger signals" which may, in turn lead to cellular and molecular responses by the immune system. This immunomodulatory action of ionizing radiation highlights the importance of the combined use (radiotherapy plus immunotherapy) for cancer healing. Major histocompatibility complex antigens (also called Human Leukocyte Antigens, HLA in humans) are one of those molecules whose expression is modulated after irradiation. This review summarizes the modulatory properties of ionizing radiation on the expression of HLA class I (classical and non-classical) and class II molecules, with special emphasis in non-classical HLA-I molecules.

HLA-G1 increases the radiosensitivity of human tumoral cells.

Different molecules regulate the response of tumoral tissues to ionizing radiation. The objective of this work was to determine if HLA-G1 expression modulates the radiosensitivity of human tumoral cell lines. To this end, human melanoma M8 and human erythroleukemia K562 cell lines, with their correspondent HLA-G1 negative and positive variants, were gamma irradiated and the survival frequency was determined by clonogenic assay. The survival fraction of HLA-G1 expressing cells was around 60% of HLA-G1 negative cells. The generation of acidic vesicular organelles was higher in HLA-G1 positive cells. Apoptosis levels showed statistically significant differences only in K562 cells, whereas the variation in G2/M cycle progression was only significant in M8 cells. In addition, irradiation diminished cell-surface HLA-G1 and increased soluble HLA-G1 levels. Soluble HLA-G1 has no influence on cell survival in any cell line. In summary, we could demonstrate that HLA-G1 confers higher radiosensitivity to HLA-G1 expressing cells.

Reactive species and apoptosis of neural precursor cells after gamma-irradiation.

This study addresses the participation of radiation-induced free radicals, mainly nitric oxide (NO), in modulating the apoptotic response in an in vitro model of neural cortical precursor cells exposed to gamma-radiation. Cortical cells obtained from rats at 17 gestational day (GD) were irradiated with a dose of 2 Gy. The percentage of apoptotic cells was significantly increased 4h post-irradiation (pi). NO content showed a significant increase after 30 min pi and the rate of generation reached a maximum 1h pi. Luminol-dependent chemiluminescence (CL) was significantly higher in cells after 2h pi as compared to control cells and this profile was maintained up to 4 h pi. Supplementation with L-NAME significantly increased light emission. Administration of superoxide dismutase (SOD) following L-NAME addition prevented the observed changes due to L-NAME administration. The caspase inhibitor zDEVD-fmk significantly reduced the radical generation. Moreover, the cellular decrease in NO content occurred coincidentally with the rise in oxygen radical generation and the activation of caspase-3. In vitro irradiation of neural precursor cells allowed us to suggest that an early radiation-induced generation of NO could exert a neuroprotective role. However, despite this NO initial protective effect and its role modulating the response against gamma-radiation, NO generation was not able of fully preventing radiation-induced apoptosis.

Increased activity and involvement of caspase-3 in radiation-induced apoptosis in neural cells precursors from developing rat brain.

Using primary cultures of neural precursor cells of cortex from developing rat brain, we demonstrated the involvement of caspase-3 in the apoptotic process induced by gamma irradiation. The precursor nature of cells was confirmed by nestin and GFAP immunoreactivity and by the capacity of differentiation in neuronal and glial cells after 5 days in culture. Neural precursors were irradiated with single doses ranging from 0.1 to 4Gy. Cellular death, determined 24 h post-irradiation (pi) was dose-dependent and the induction of apoptosis was confirmed by nuclear condensation, DNA fragmentation and hypodiploid DNA peak represented by the "sub G1" region. For the higher doses, apoptosis was evident after 4-6 h pi and increased during 24 h. Caspase-3 activity increased with doses and was maximal at 4-6 h pi with 3Gy and remained similar with 4Gy. The protection from radiation-induced apoptosis by caspase-3 inhibitor, zDEVD-fmk, confirmed that this enzyme is involved in the apoptotic mechanism in this system. The possibility of using this tissue culture system for studying the effects of ionizing radiation on morphological and molecular differentiation was considered.

The role of nitric oxide in the radiation-induced effects in the developing brain.

The immature and adult brain display clear differences in the way they respond to insults. The effects of prenatal irradiation on the developing brain are well known. Both epidemiological and experimental data indicate that ionizing radiation may disrupt developmental processes leading to deleterious effects on post-natal brain functions. A central role of reactive oxygen and nitrogen species (ROS/RNS) as important mediators in both neurotoxicity and neuroprotection has been demonstrated. However, data concerning the role of ROS/RNS in radiation-induced damage in the developing brain are scarce. The goal of this review was to summarize the current studies concerning the role of nitric oxide and its reactive intermediates in activation of signal transduction pathways involved in cellular radiation response, with particular focus on radiation-induced effects in the developing brain.

[Telomeres and genomic damage repair. Their implication in human pathology]. / Telómeros y reparación de daño genómico. Su implicancia en patología humana.

Telomeres, functional complexes that protect eukaryotic chromosome ends, participate in the regulation of cell proliferation and could play a role in the stabilization of genomic regions in response to genotoxic stress. Their significance in human pathology becomes evident in several diseases sharing genomic instability as a common trait, in which alterations of the telomere metabolism have been demonstrated. Many of them are also associated with hypersensitivity to ionizing radiation and cancer susceptibility. Besides the specific proteins belonging to the telomeric complex, other proteins involved in the DNA repair machinery, such as ATM, BRCA1, BRCA2, PARP/tankyrase system, DNA-PK and RAD50-MRE11-NBS1 complexes, are closely related with the telomere. This suggests that the telomere sequesters DNA repair proteins for its own structure maintenance, which could also be released toward damaged sites in the genomic DNA. This communication describes essential aspects of telomere structure and function and their links with homologous recombination, non-homologous end-joining (NHEJ), V(D)J system and mismatch-repair (MMR). Several pathological conditions exhibiting alterations in some of these mechanisms are also considered. The cell response to ionizing radiation and its relationship with the telomeric metabolism is particularly taken into account as a model for studying genotoxicity.

Ionizing radiation modulates the surface expression of human leukocyte antigen-G in a human melanoma cell line.

Human leukocyte antigen G (HLA-G) is a nonclassical HLA class I molecule involved in fetus protection from the maternal immune system, transplant tolerance, and viral and tumoral immune escape. Tumor-specific HLA-G expression has been described for a wide variety of malignancies, including melanomas. The aim of this study was to evaluate whether ionizing radiation (IR) could modulate the surface expression of HLA-G1 in a human melanoma cell line that expresses endogenously membrane-bound HLA-G1. For this purpose, cells were exposed to increasing doses of gamma-irradiation (0-20 Gy) and HLA-G1 levels at the plasma membrane were analyzed at different times postirradiation by flow cytometry. HLA-G total expression and the presence of the soluble form of HLA-G1 (sHLA-G1) in the culture medium of irradiated cells were also evaluated. IR was capable of downregulating cell surface and total HLA-G levels, with a concomitant increase of sHLA-G1 in the medium. These results could indicate that gamma-irradiation decreases HLA-G1 surface levels by enhancing the proteolytic cleavage of this molecule.

Biomarcadores de reação inflamatória crônica em pacientes com queimaduras radiológicas (síndrome cutânea da radiação) / Biomarkers of chronic inflammatory reaction in patients with radiological burns (cutaneous radiation syndrome)

Introdução: Os efeitos tardios da radiação geralmente são irreversíveis e podem ter efeitos devastadores sobre a qualidade de vida de pessoas expostas acidentalmente ou durante os tratamentos de radiação terapêutica. Apesar de diversas etiologias terem sido sugeridas em relação a essa toxicidade tardia, parâmetros inflamatórios envolvidos durante a fase tardia são menos conhecidos. Objetivo: O objetivo deste estudo foi analisar a resposta do sistema imunológico nas reações inflamatórias em pacientes com lesões de pele tardias após radioterapia ou procedimentos de fluoroscopia intervencionista. Métodos: O acompanhamento de 25 pacientes, dos 160 atendidos no Hospital de Queimados a partir de 1997, que demonstrou reações cutâneas tardias classificadas de acordo como sistema de RTOG/EORTC é relatado aqui. A expressão de moléculas de adesão ICAM1e 1-integrina em granulócitos e linfócitos, bem como alterações nas subpopulações dos linfócitos T, foram avaliadas por citometria de fluxo e o nível de proteína C-reativa, um marcador inflamatório bem estudado, foi quantificado por um ensaio imunoturbidimétrico. Resultados: Aanálise da expressão de moléculas de adesão revelou maior expressão de integrina 1em linfócitos de pacientes Grau IV em comparação a controles não-expostos. Observou-se, também, diminuição dos valores de sua expressão no acompanhamento de pacientes com boa resposta ao tratamento terapêutico. Isto foi acompanhado por uma tendência a diminuição na proporção T (CD4 +)/ T(CD8+) de pacientes com má evolução do G4 em comparação aos doentes do G4 com boa evolução. O nível de proteína C reativa (PCR) apresentou valores mais elevados em pacientes em fase aguda e pacientes com toxicidade tardia, mas em crise exacerbação.

Introduction: Late effects of radiation are generally irreversible and can have devastating effects on quality of life of people exposed either accidentally or during therapeutic radiation treatments. Although many etiologies have been suggested regarding these late toxicities, inflammatory parameters involved during the late phase are less known. Objective: The aim of this study was to analyze the response of the immune system in the inflammatory reactions in patients with late skin injuries after radiotherapy or interventional fluoroscopy procedures. Methods: The follow up of twenty five patients, out of 160 referred to Burn Hospital from 1997, that showed late cutaneous reactions graded according to the RTOG / EORTC system is reported here.The expression of adhesion molecules ICAM1 and 1-integrin on granulocytes and lymphocytes, as well as changes in subpopulations of T lymphocytes were evaluated by flow cytometry and the level of C-reactive protein, a well-studied inflammatory marker was quantified by an immunoturbidimetric assay. Results: The analysis of adhesion molecules expression revealed a higher expression of 1 Integrin on lymphocytes of Grade IV patients compared to non-exposed controls. It was also noted a decrease in its expression values in the follow up of patients with good response to therapeutic treatment. This was paralleled by a tendency to a decrease in the T(CD4+) / T(CD8+) ratio of G4 patients with bad evolution compared to G4 patients with good evolution.The level of C Reactive Protein (CRP) showed higher values in patients in acute phase and patients with late toxicity but in exacerbation crisis. Conclusions: The parameters analyzed, which require confirmation in a larger study, in combination with other inflammatory indicators, could be used as potential follow-up markers of the chronic radio-induced inflammation process just as its response to therapeutic treatments.

Genetic and epigenetic features in radiation sensitivity. Part II: implications for clinical practice and radiation protection.

Recent progress especially in the field of gene identification and expression has attracted greater attention to the genetic and epigenetic susceptibility to cancer, possibly enhanced by ionising radiation. This issue is especially important for radiation therapists since hypersensitive patients may suffer from adverse effects in normal tissues following standard radiation therapy, while normally sensitive patients could receive higher doses of radiation, offering a better likelihood of cure for malignant tumours. Although only a small percentage of individuals are "hypersensitive" to radiation effects, all medical specialists using ionising radiation should be aware of the aforementioned progress in medical knowledge. The present paper, the second of two parts, reviews human disorders known or strongly suspected to be associated with hypersensitivity to ionising radiation. The main tests capable of detecting such pathologies in advance are analysed, and ethical issues regarding genetic testing are considered. The implications for radiation protection of possible hypersensitivity to radiation in a part of the population are discussed, and some guidelines for nuclear medicine professionals are proposed.

Genetic and epigenetic features in radiation sensitivity Part I: cell signalling in radiation response.

Recent progress especially in the field of gene identification and expression has attracted greater attention to genetic and epigenetic susceptibility to cancer, possibly enhanced by ionising radiation. It has been proposed that the occurrence and severity of the adverse reactions to radiation therapy are also influenced by such genetic susceptibility. This issue is especially important for radiation therapists since hypersensitive patients may suffer from adverse effects in normal tissues following standard radiation therapy, while normally sensitive patients could receive higher doses of radiation offering a better likelihood of cure for malignant tumours. This paper, the first of two parts, reviews the main mechanisms involved in cell response to ionising radiation. DNA repair machinery and cell signalling pathways are considered and their role in radiosensitivity is analysed. The implication of non-targeted and delayed effects in radiosensitivity is also discussed.

Telómeros y reparación de daño genómico. Su implicancia en patologia humana / Telomeres and genomic damage repair. Their implication in human pathology

Los telómeros, complejos funcionales que protegen los extremos de los cromosomas eucariotes, participan en la regulación de la proliferación celular y pueden jugar un rol en la estabilización de cier-tas regiones del genoma en respuesta a estrés genotóxico. Su relevancia en patología humana se ha puesto de manifiesto en numerosas enfermedades que comparten como rasgo común la inestabilidad genómica, en las que se comprobaron alteraciones del metabolismo telomérico. Muchas de ellas se encuentran asociadas a hipersensi-bilidad a radiaciones ionizantes y susceptibilidad al cáncer. Además de las proteínas específicas que forman partedel complejo telomérico otras proteínas implicadas en la maquinaria de reparación del ADN tales como ATM,BRCA1, BRCA2 , sistema PARP/ tankirasa, complejo DNA-PK, y complejo RAD50- MRE11-NBS1, se encuentran en estrecha asociación con el mismo. Esto sugiere que el telómero secuestra proteínas de reparación para el mantenimiento de su propia estructura, las que podrían asimismo ser liberadas hacia sitios de daño en el ADN genómico. Esta comunicación describe los aspectos más relevantes de la estructura y función de los telómeros y su vinculación con los procesos de recombinación homóloga, recombinación no homóloga (NHEJ), sistema V(D)J y sistemas de reparación de apareamientos erróneos (MMR), considerando ciertas condiciones patológicas que exhiben alteraciones en algunos estos mecanismos. Se aborda en forma particular la respuesta celular a las ra-diaciones ionizantes y su relación con el metabolismo telomérico como un modelo de estudio de genotoxicidad