Support for the "Vancouver call for action to strengthen expertise in radiological protection worldwide": the position of organisations in formal relations with the International Commission on Radiological Protection (ICRP).

The International Commission on Radiological Protection (ICRP), recently expressed concern that "a shortage of investment in training, education, research, and infrastructure seen in many sectors and countries may compromise society's ability to properly manage radiation risks" and in 2022 announced the "Vancouver call for action to strengthen expertise in radiological protection worldwide". As representatives of organisations in formal relations with ICRP, we decided to promote this position paper to declare and emphasise that strengthening the expertise in radiological protection is a collective priority for all of us.

Experiences in transitioning a testing laboratoryto the new ISO/IEC 17025:2017 standard.

Since its inception, the international quality standard ISO/IEC 17025 has been revised twice. The most recent edition adopted a new structure to align with other conformity assessment and quality management standards, harmonized the terminology with the International Vocabulary of Metrology and introduced the concept of risk-based thinking. This paper disseminates the experience of the IAEA Radiation Safety Technical Services Laboratory in successful transition and re-accreditation to ISO/IEC 17025:2017. It covers all stages of the transition cycle: from conducting a gap analysis between the existing quality system and the requirements in the revised standard, updating the corresponding quality documents, developing training and communication plans for laboratory personnel, to monitoring the changes and improving the system through auditing, management review and participation in proficiency testing schemes. Lessons learned about building operational resilience and maintaining a business continuity management system to prepare for, respond to, and recover from disruptions are considered.

ICRP workshop on the review and revision of the system of radiological protection: a focus on research priorities-feedback from the international community.

In September 2022, the International Commission on Radiological Protection (ICRP) organised a workshop in Estoril, Portugal, on the 'Review and Revision of the System of Radiological Protection: A Focus on Research Priorities'. The workshop, which was a side event of the European Radiation Protection Week, offered an opportunity to comment on a recent paper published by ICRP on areas of research to support the System of Radiological Protection. Altogether, about 150 individuals participated in the workshop. After the workshop, 16 of the 30 organisations in formal relations with ICRP provided written feedback. All participants and organisations followed ICRP's view that further research in various areas will offer additional support in improving the System in the short, medium, and long term. In general, it was emphasised that any research should be outcome-focused in that it should improve protection of people or the environment. Many research topics mentioned by the participants were in line with those already identified by ICRP in the paper noted above. In addition, further ideas were expressed such as, for example, that lessons learned during the COVID-19 pandemic with regards to the non-radiological social, economic and environment impacts, should be analysed for their usefulness to enhance radiological protection, and that current protection strategies and application of current radiological protection principles may need to be adapted to military scenarios like those observed recently during the military conflict in the Ukraine or the detonation of a nuclear weapon. On a broader perspective, it was discussed how radiation research and radiological protection can contribute towards the Sustainable Development Goals announced by the United Nations in 2015. This paper summarises the views expressed during the workshop and the major take home messages identified by ICRP.

The Inter-Agency Committee on Radiation Safety-30 years of international coordination of radiation protection and safety matters.

The Inter-Agency Committee on Radiation Safety (IACRS) was constituted in 1990, as a forum for collaboration and coordination between international bodies with regards to radiation safety. It consists today of representatives of eight intergovernmental member organizations (the European Commision, Food and Agriculture Organization, International Atomic Energy Agency (IAEA), International Labour Office, Organisation for Economic Co-operation and Development/ Nuclear Energy Agency (OECD/NEA), Pan American Health Organization, United Nations Scientific Committee on the Effects of Atomic Radiation and the World Health Organization) and five observer non-governmental organizations (International Commission on Radiological Protection, International Commission on Radiation Units & Measurements, International Electrotechnical Commission, International Radiation Protection Association and International Organization for Standardization). The IACRS provides a platform for interaction between these relevant international bodies to contribute to a common understanding of the scientific basis and legal framework for the application of the system of radiation protection, towards global harmonisation of radiation safety standards. The IACRS played a key role in the development of the International Basic Safety Standards (BSS) in 1996 and in its revision in 2014. Further, an IACRS specific Task Group-chaired by the IAEA-fosters the implementation of the BSS in a consistent and coherent manner in all Member States of the United Nations. The IACRS operates via a standing secretariat jointly provided by the IAEA and OECD/NEA and is chaired by one of its member organizations on a rotating basis for periods of about 18 months. This approach has proved to be effective and was the foundation for ensuring continuity of the work of the committee and at the same time allowing a rotating leadership for all member organizations. Currently, the IACRS is chaired by the WHO. The International Radiation Safety Framework under which the IACRS works is structured around four main areas: (a) science; (b) principles; (c) standards; and (d) practice. This paper presents briefly the mandates, roles and functions of the various international bodies that are relevant to the four above mentioned areas of work, discusses how these bodies coordinate their actions and complement each other to enhance radiation protection and safety worldwide and describes their contribution to the achievement of the Sustainable Development Goals. The paper also provides an overview of the main accomplishments of the IACRS since its inception 30 years ago, and an outlook on key challenges for its future activities.

How often does it happen? A review of unintended, unnecessary and unavoidable high-dose radiation exposures.

High-dose radiation exposures of humans occur every year around the world, and may lead to harmful tissue reactions. This review aims to look at the available information sources that can help answering the question of how often these events occur yearly on a global scale. In the absence of comprehensive databases of global occurrence, publications on radiation accidents in all uses of radiation and on rates of high-dose events in different medical uses of radiation have been reviewed. Most high-dose radiation exposures seem to occur in the medical uses of radiation, reflecting the high number of medical exposures performed. In therapeutic medical uses, radiation doses are purposely often given at levels known to cause deterministic effects, and there is a very narrow range in which the medical practitioner can operate without causing severe unacceptable outcomes. In interventional medical uses, there are scenarios in which the radiation dose given to a patient may reach or exceed a threshold for skin effects, where this radiation dose may be unavoidable, considering all benefits and risks as well as benefits and risks of any alternative procedures. Regardless of if the delivered dose is unintended, unnecessary or unavoidable, there are estimates published of the rates of high-dose events and of radiation-induced tissue injuries occurring in medical uses. If this information is extrapolated to a global scenario, noting the inherent limitations in doing so, it does not seem unreasonable to expect that the global number of radiation-induced injuries every year may be in the order of hundreds, likely mainly arising from medical uses of radiation, and in particular from interventional fluoroscopy procedures and external beam radiotherapy procedures. These procedures are so frequently employed throughout the world that even a very small rate of radiation-induced injuries becomes a substantial number when scaled up to a global level.

A possible overestimation of the effect of acetylation on lysine residues in KQ mutant analysis.

Acetylation of lysine residues, one of the most common protein post-transcriptional modifications, is thought to regulate protein affinity with other proteins or nucleotides. Experimentally, the effects of acetylation have been studied using recombinant mutants in which lysine residues (K) are substituted with glutamine (Q) as a mimic of acetyl lysine (KQ mutant), or with arginine (R) as a mimic of nonacetylated lysine (KR mutant). These substitutions, however, have not been properly validated. The effects lysine acetylation on Ku, a multifunctional protein that has been primarily implicated in DNA repair and cell survival, are characterized herein using a series of computer simulations. The binding free energy was reduced in the KQ mutant, while the KR mutant had no effect, which is consistent with previous experimental results. Unexpectedly, the binding energy between Ku and DNA was maintained at almost the same level as in the wild type protein despite full acetylation of the lysine residues. These results suggest that the effects of acetylation may be overestimated when the KQ mutant is used as a mimic of the acetylated protein.

DNA strand break: structural and electrostatic properties studied by molecular dynamics simulation.

Due to their lethal consequences and a relatively high probability of introduction of repair errors and mutations, single and double strand breaks are among the most important and dangerous DNA lesions. However, the mechanisms of their recognition and repair processes are only poorly known at present. This work defines and analyzes a DNA with single strand break as a template study for future complex analyses of biologically serious double strand break damage and its enzymatic repair mechanisms. Besides a non-damaged DNA serving as a reference system with no surprising results, system with open valences of the atoms at the strand break ends as well as a system with filled valences were simulated. In both cases during the first few nanoseconds the broken ends of strand breaks are significantly exposed to the outside of the molecule. However, with increasing time, the system with single strand break with open valences is partially disrupted. On the contrary, the system with filled valences shows stable conformation with newly created hydrogen bond between the two strand break endings. Moreover, these endings are steadily situated in the inner part of the molecule, thus making the recognition and docking process of a repair enzyme more complicated in the case of filled valences.

Molecular dynamics simulation of clustered DNA damage sites containing 8-oxoguanine and abasic site.

Clustered DNA damage sites induced by ionizing radiation have been suggested to have serious consequences to organisms, such as cancer, due to their reduced probability to be repaired by the enzymatic repair machinery of the cell. Although experimental results have revealed that clustered DNA damage sites effectively retard the efficient function of repair enzymes, it remains unclear as to what particular factors influence this retardation. In this study, approaches based on molecular dynamics (MD) simulation have been applied to examine conformational changes and energetic properties of DNA molecules containing clustered damage sites consisting of two lesioned sites, namely 7,8-dihydro-8-oxoguanine (8-oxoG) and apurinic/apyrimidinic (AP) site, located within a few base pairs of each other. After 1 ns of MD simulation, one of the six DNA molecules containing a clustered damage site develops specific characteristic features: sharp bending at the lesioned site and weakening or complete loss of electrostatic interaction energy between 8-oxoG and bases located on the complementary strand. From these results it is suggested that these changes would make it difficult for the repair enzyme to bind to the lesions within the clustered damage site and thereby result in a reduction of its repair capacity.

Theoretical study of the human DNA repair protein HOGG1 activity.

We have examined the role of the catalytic lysine (Lys 249) in breaking the glycosidic bond of 8-oxoguanine in the enzyme human 8-oxoguanine DNA glycosylase. Until quite recently it has been assumed that this lysine acts as a nucleophile in an S(N)2 type of reaction after being activated through a donation of a proton to a strictly conserved aspartate, also located in the active site. However, evidence from crystallographic, as well as biochemical studies, questions this assumption mainly because the lysine is not ideally positioned for such an attack. In addition, the catalytic activity is preserved even after that aspartate is mutated to a residue not accepting protons, but still keeping the interactions in the active site. In this study, we have investigated several different reaction mechanisms to discover plausible ways where the lysine could assist in breaking the glycosidic bond. We use hybrid density functional theory to characterize both associative and dissociative pathways. We find that the smallest energetical barrier involves an S(N)1 type of mechanism where the lysine electrostatically stabilizes the dissociating base and then donates a proton with a very small barrier and then finally attacks the sugar ring to create the covalently bound protein-DNA intermediate complex. The S(N)2 mechanism also has a lower barrier than the "spontaneous" bond breaking but considerably above that of the S(N)1 reaction. However, in current conditions, the reactants placed in a conformation posed for an S(N)2 reaction is substantially more stable than if posed for the S(N)1 reaction, indicating that the active site has to bind stronger to the latter in order to achieve a full catalytic effect. An analysis of the polarization of the transition states shows that the polarization is largest for the S(N)1 reaction, indicating that this path will gain most by being placed in a prepolarized active site. These findings give further support to the hypothesis that a dissociative mechanism may be the preferred mode of action for this type of enzymes.

Electrostatic energy analysis of 8-oxoguanine DNA lesion-molecular dynamics study.

One nanosecond molecular dynamics (MD) simulation was performed for two DNA segments each composed of 30 base pairs. In one DNA segment the native guanines at nucleotides positions 17 and 19 were replaced with two 8-oxoguanines (8-oxoG) (8-oxoG is mutagenic DNA oxo-lesion). The analysis of results was focused on the electrostatic energy that is supposed to be significant factor causing the disruption of DNA base stacking in DNA duplex and may also serve as a signal toward the repair enzyme informing the presence of the lesion. The repulsive interaction between 8-oxoG and the entire DNA molecule was observed, which caused the extrahelical position of 8-oxoG (position 19). The repulsive electrostatic interaction between both 8-oxoG lesions contributed to the flipping out of one 8-oxoG and to the local instability of the lesioned DNA region. The electrostatic potential at the surface of DNA close to the lesions has more negative value than the same region on the native DNA. This electrostatic potential may signal presence of the lesion to the repair enzyme. In the simulation of native DNA segment, no significant structural changes were observed and B-DNA structure was well preserved throughout the MD simulation.

8-oxoguanine lesioned B-DNA molecule complexed with repair enzyme hOGG1: a molecular dynamics study.

The molecular dynamics (MD) simulation of DNA mutagenic oxidative lesion, 7,8-dihydro-8-oxoguanine (8-oxoG), complexed with the repair enzyme, human oxoguanine glycosylase 1 (hOGG1), was performed for 1 nanosecond (ns) in order to describe the dynamical process of DNA-enzyme complex formation. After 900 picoseconds of MD the lesioned DNA and enzyme formed a complex that lasted until the end of the simulation at 1 ns. The complex was mainly represented by the overlapping van der Waals surfaces of DNA and enzyme molecules. The amino group of arginine 324 was located close to the phosphodiester bond of the nucleotide with 8-oxoG enabling chemical reactions between amino acid and lesion. The broken hydrogen bonds resulting in locally collapsed B-DNA structure were observed at the lesion site. The phosphodiester bond at C5' of 8-oxoG was displaced to the position close to the amino group of arginine 324. The water-mediated hydrogen bond network was formed in each contact area between DNA and enzyme, further enhancing the stability of the complex. In the background simulation of the identical molecular system with the native DNA, neither the complex nor the water- mediated hydrogen bond network was observed.

Molecular dynamics simulation of thymine glycol-lesioned DNA reveals specific hydration at the lesion.

One nanosecond molecular dynamics (MD) simulation of a thymine glycol (TG)-lesioned part of human lymphoblast AG9387 was performed to determine structural changes in DNA molecule caused by the presence of a lesion. These changes can be significant for proper recognition of lesions by a repair enzyme. Thymine glycol is the DNA oxidative lesion formed by addition of OH radicals to C5 and C6 atoms of the thymine base. This lesion is known as causing Cockayne Syndrome-inherited genetic disorder. Distribution of water molecules in a hydration shell around the DNA molecule was analyzed for its contribution to the recognition of the TG lesion by the repair enzyme. The results of MD simulation show there is a specific DNA structural configuration formed at the lesion. After 500 ps the DNA is bent in a kink at the TG site. This change dislocates the glycosyl bond at C5' to a position closer to the DNA surface, and thus its atoms are more exposed to the surrounding water shell. The increased number of water molecules that are close to the TG site indicates that the glycosyl bond may be easily contacted by the repair enzyme. In addition, the higher number of water molecules at the TG site substantiates the importance of water-mediated hydrogen bonds created between the repair enzyme and the DNA upon formation of the complex. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1723-1731, 2001