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In 2021, over three million children interacted with the child welfare system and over six hundred thousand were in foster care. These child welfare systems, striving as they may to help children and families in crisis, are themselves in crisis. Seeking relief from these dysfunctional state systems, children and advocacy groups have turned to the federal courts for relief. These plaintiffs have challenged almost every aspect of state child welfare systems, from initial investigation to discharge, and have asked federal courts to mandate everything from targeted reforms to complete overhauls of state systems. But because child welfare systems are often run by, through, and with the oversight of state courts, the Younger abstention doctrine has posed an early obstacle to some of these suits. Courts considering whether to abstain have split on almost every point of Younger’s analysis: whether state courts provide an adequate opportunity to raise federal claims, whether a federal challenge would interfere with the state court proceedings, and whether child welfare proceedings are the kind of proceedings to which Younger applies. While the literature on Younger abstention is expansive, this last question—whether child welfare proceedings are the kind of proceedings to which Younger applies—has largely been ignored by scholars. This Note fills that gap. Part I details the development of the Younger doctrine. Part II introduces the child welfare system and explores how courts have applied Younger in this context, beginning with an overview of child welfare systems and concluding with an in-depth look at recent decisions by the Seventh and Fourth Circuits. Part III analyzes child welfare proceedings within the Younger/Sprint framework. It argues that certain portions of child welfare proceedings are quasi-criminal, that the extent to which a proceeding is quasi-criminal varies across and within cases, and that neither the Seventh nor the Fourth Circuit has adequately accounted for this heterogeneity. Finally, Part IV offers a solution, proposing that courts should take a piecemeal approach to Younger in the child welfare space. [ABSTRACT FROM AUTHOR]

The article reports that The COVID-19 pandemic created a renewed interest and acceptance towards study participation in clinical trial research. This is an exciting time for the industry. With more capabilities than ever before – an explosion of data sources, insight from increasingly important stakeholders, and a variety of technologies and service providers – creating a trial around the patient and their needs, while also benefiting operationally, is achievable.

Intercellular induction of apoptosis (IIA) represents a well-defined signaling model by which precancerous cells are selectively eradicated through reactive oxygen/nitrogen species and cytokine signaling from neighbour normal cells. Previously, we demonstrated that the IIA process could be enhanced by exposure of normal cells to very low doses of ionizing radiation as a result of perturbing the intercellular signaling. In this study, we investigate the kinetic behaviour of both autocrine destruction (AD) and IIA as a function of cell density of both precancerous and normal cells using an insert co-culture system and how exposure of normal cells to ionizing radiation influence the kinetics of apoptosis induction in precancerous cells. Increasing the seeding density of transformed cells shifts the kinetics of AD towards earlier times with the response plateauing only at high seeding densities. Likewise, when co-culturing precancerous cells with normal cells, increasing the seeding density of either normal or precancerous cells also shifts the kinetics of IIA response towards earlier times and plateau only at higher seeding densities. Irradiation of normal cells prior to co-culture further enhances the kinetics of IIA response, with the degree of enhancement dependent on the relative cell densities. These results demonstrate the pivotal role of the cell seeding density of normal and precancerous cells in modulating both AD and IIA. These results further support the proposition that ionizing radiation could result in an enhancement in the rate of removal of precancerous cells through the IIA process. [ABSTRACT FROM AUTHOR]

To reduce the amount of nonclimatic biases of air temperature in each weather station's record by comparing it with neighboring stations, global land surface air temperature datasets are routinely adjusted using statistical homogenization to minimize such biases. However, homogenization can unintentionally introduce new nonclimatic biases due to an oftenoverlooked statistical problem known as "urban blending" or "aliasing of trend biases." This issue arises when the homogenization process inadvertently mixes urbanization biases of neighboring stations into the adjustments applied to each station record. As a result, urbanization biases of the original unhomogenized temperature records are spread throughout the homogenized data. To evaluate the extent of this phenomenon, the homogenized temperature data for two countries (Japan and the United States) are analyzed. Using the Japanese stations in the widely used Global Historical Climatology Network (GHCN) dataset, it is first confirmed that the unhomogenized Japanese temperature data are strongly affected by urbanization bias (possibly ~60% of the long-term warming). The U.S. Historical Climatology Network (USHCN) dataset contains a relatively large amount of long, rural station records and therefore is less affected by urbanization bias. Nonetheless, even for this relatively rural dataset, urbanization bias could account for ~20%of the long-term warming. It is then shown that urban blending is a major problem for the homogenized data for both countries. The IPCC's estimate of urbanization bias in the global temperature data based on homogenized temperature records may have been low as a result of urban blending. Recommendations on how future homogenization efforts could be modified to reduce urban blending are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] A dL lesion is not repaired as effectively as an AP site. [•] The repair of a cluster with dL and 8-oxodGuo lesions is compromised. [•] Delayed repair of the cluster leads to an increase in mutation frequency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitric oxide reacts with hydroxyl radical-induced adenine radicals to form hypoxanthine and 8-azaadenine. [•] Radiosensitization of cells by nitric oxide increases cellular DNA double strand breaks. [•] Nitric oxide induced DNA damage may result in replication-induced double strand breaks. [Copyright &y& Elsevier]

Abstract: Nitric oxide (•NO) is a very effective radiosensitizer of hypoxic mammalian cells. In vivo •NO may have effects on tumor vasculature and hence on tumor oxygenation and it may also interact with radiation-produced radicals to modify DNA lesions. Few studies have addressed this last aspect, and we report here specific base modifications that result from reaction of •NO with radicals in DNA bases and in plasmid DNA after irradiation. 2′-Deoxyxanthosine monophosphate and 2′-deoxy-8-azaguanosine monophosphate (8azadGMP) are formed upon γ-irradiation of 2′-deoxyguanosine monophosphate (dGMP) in the presence of micromolar levels of •NO in anoxia. In addition, the presence of •NO at physiological pH inhibits the formation of the well-described •OH-induced oxidation product of dGMP, 8-oxo-2′-deoxyguanosine monophosphate. Single-strand breaks are induced in plasmid DNA when γ-irradiated in anoxia, whereas in the presence of •NO the number of breaks is reduced by approximately threefold, and evidence is shown for the formation of 8azadGMP in these plasmids. The consequence of the base modifications by •NO are as yet unknown although additional breaks are revealed in irradiated plasmid DNA after treatment with glycosylases involved in base excision repair. V79-4 cells irradiated in anoxia show an enhancement in the number of γH2AX foci when •NO is present, particularly evident a few hours postirradiation, indicative of the formation of replication-induced DNA damage. We propose that the consequence of •NO-induced base modifications in anoxia contributes to its radiosensitization of cells. [Copyright &y& Elsevier]

Abstract: A signature of ionizing radiation exposure is the induction of DNA clustered damaged sites, defined as two or more lesions within one to two helical turns of DNA by passage of a single radiation track. Clustered damage is made up of double strand breaks (DSB) with associated base lesions or abasic (AP) sites, and non-DSB clusters comprised of base lesions, AP sites and single strand breaks. This review will concentrate on the experimental findings of the processing of non-DSB clustered damaged sites. It has been shown that non-DSB clustered damaged sites compromise the base excision repair pathway leading to the lifetime extension of the lesions within the cluster, compared to isolated lesions, thus the likelihood that the lesions persist to replication and induce mutation is increased. In addition certain non-DSB clustered damaged sites are processed within the cell to form additional DSB. The use of E. coli to demonstrate that clustering of DNA lesions is the major cause of the detrimental consequences of ionizing radiation is also discussed. The delayed repair of non-DSB clustered damaged sites in humans can be seen as a “friend”, leading to cell killing in tumour cells or as a “foe”, resulting in the formation of mutations and genetic instability in normal tissue. [Copyright &y& Elsevier]

This brief report describes a writing-in-the-disciplines collaboration between the Write Now CETL and the Department of Art, Media and Design at London Metropolitan University. The project, writing design, aims to enable year one design practice-based students to write critically, confidently and effectively about design and design practice in its historical and theoretical contexts. ‘ writing design’ involved curricular change, embedded writing workshops and staff development to achieve these goals. [ABSTRACT FROM AUTHOR]

Abstract: Clustered DNA damage induced by a single radiation track is a unique feature of ionizing radiation. Using a plasmid-based assay in Escherichia coli, we previously found significantly higher mutation frequencies for bistranded clusters containing 7,8-dihydro-8-oxoguanine (8-oxoG) and 5,6-dihydrothymine (DHT) than for either a single 8-oxoG or a single DHT in wild type and in glycosylase-deficient strains of E. coli. This indicates that the removal of an 8-oxoG from a clustered damage site is most likely retarded compared to the removal of a single 8-oxoG. To gain further insights into the processing of bistranded base lesions, several potential repair intermediates following 8-oxoG removal were assessed. Clusters, such as DHT+apurinic/apyrimidinic (AP) and DHT+GAP have relatively low mutation frequencies, whereas clusters, such as AP+AP or GAP+AP, significantly reduce the number of transformed colonies, most probably through formation of a lethal double strand break (DSB). Bistranded AP sites placed 3′ to each other with various interlesion distances also blocked replication. These results suggest that bistranded base lesions, i.e., single base lesions on each strand, but not clusters containing only AP sites and strand breaks, are repaired in a coordinated manner so that the formation of DSBs is avoided. We propose that, when either base lesion is initially excised from a bistranded base damage site, the remaining base lesion will only rarely be converted into an AP site or a single strand break in vivo. [Copyright &y& Elsevier]

The widely used Global Historical Climatology Network (GHCN) monthly temperature dataset is available in two formats—non-homogenized and homogenized. Since 2011, this homogenized dataset has been updated almost daily by applying the "Pairwise Homogenization Algorithm" (PHA) to the non-homogenized datasets. Previous studies found that the PHA can perform well at correcting synthetic time series when certain artificial biases are introduced. However, its performance with real world data has been less well studied. Therefore, the homogenized GHCN datasets (Version 3 and 4) were downloaded almost daily over a 10-year period (2011–2021) yielding 3689 different updates to the datasets. The different breakpoints identified were analyzed for a set of stations from 24 European countries for which station history metadata were available. A remarkable inconsistency in the identified breakpoints (and hence adjustments applied) was revealed. Of the adjustments applied for GHCN Version 4, 64% (61% for Version 3) were identified on less than 25% of runs, while only 16% of the adjustments (21% for Version 3) were identified consistently for more than 75% of the runs. The consistency of PHA adjustments improved when the breakpoints corresponded to documented station history metadata events. However, only 19% of the breakpoints (18% for Version 3) were associated with a documented event within 1 year, and 67% (69% for Version 3) were not associated with any documented event. Therefore, while the PHA remains a useful tool in the community's homogenization toolbox, many of the PHA adjustments applied to the homogenized GHCN dataset may have been spurious. Using station metadata to assess the reliability of PHA adjustments might potentially help to identify some of these spurious adjustments. [ABSTRACT FROM AUTHOR]

Purpose: This article seeks to illustrate some contributions of radiation chemistry to radiobiology and related science, and to draw attention to examples where radiation chemistry is central to our knowledge of specific aspects. Radiation chemistry is a mature branch of radiation science which is continually evolving and finding wider applications. This is particularly apparent in the study of the roles of free radicals in biology generally, and radiation biology specifically. The chemical viewpoint helps unite the spatial and temporal insight coming from radiation physics with the diversity of biological responses. While historically, the main application of radiation chemistry of relevance to radiation biology has been investigations of the free-radical processes leading to radiation-induced DNA damage and its chemical characterization, two features of radiation chemistry point to its wider importance. First, its emphasis on quantification and characterization at the molecular level helps provide links between DNA damage, biochemical repair processes, and mutagenicity and radiosensitivity. Second, its central pillar of chemical kinetics aids understanding of the roles of 'reactive oxygen species' in cell signalling and diverse biological effects more generally, and application of radiation chemistry in the development of drugs to enhance radiotherapy and as hypoxia-specific cytotoxins or diagnostic agents. The illustrations of the broader applications of radiation chemistry in this article focus on their relevance to radiation biology and demonstrate the importance of synergy in the radiation sciences. Conclusions: The past contributions of radiation chemistry to radiation biology are evident, but there remains considerable potential to help advance future biological understanding using the knowledge and techniques of radiation chemistry. [ABSTRACT FROM AUTHOR]

Overexpression of extracellular matrix metalloproteinase inducer (EMMPRIN or CD147), a member of the immunoglobulin family and a glycoprotein enriched on the surface of tumor cells, promotes invasion, metastasis, and growth and survival of malignant cells and confers resistance to some chemotherapeutic drugs. However, the molecular mechanisms underlying the actions of EMMPRIN are not fully understood. In this study we sought to determine whether EMMPRIN contributes to the malignant phenotype of breast cancer by inhibiting anoikis, a form of apoptosis induced by loss or alteration of cell-cell or cell-matrix anchorage, and to explore the signaling pathways involved. We found that in the absence of attachment, human breast carcinoma cells expressing high levels of EMMPRIN formed less compact aggregates with larger surface area and less fibronectin matrix assembly, had higher viability, and were resistant to anoikis. Knockdown of EMMPRIN expression by RNA interference (small interfering RNA or short hairpin RNA) sensitized cancer cells to anoikis, as demonstrated by activation of caspase-3, increased DNA fragmentation, and decreased cellular viability. Furthermore, we observed that the accumulation of Bim, a proapoptotic BH3-only protein, was reduced in EMMPRIN-expressing cells and that silencing of EMMPRIN expression elevated Bim protein levels and enhanced cellular sensitivity to anoikis. Treatment of cells with a MEK inhibitor (U0126) or proteasome inhibitor (epoxomicin) also up-regulated Bim accumulation and rendered cells more sensitive to anoikis. These results indicated that expression of EMMPRIN protects cancer cells from anoikis and that this effect is mediated at least in part by a MAP kinase-dependent reduction of Bim. Because anoikis deficiency is a key feature of neoplastic transformation and invasive growth of epithelial cancer cells, our study on the role of EMMPRIN in anoikis resistance and the mechanism involved underscores the potential of EMMPRIN expression as a prognostic marker and novel target for cancer therapy. [ABSTRACT FROM AUTHOR]

Offers a close analysis of the usage of the term circulus to refer to groups of Romans gathered together for various reasons. Importance of a more general culture of popular sociability at Rome; Examination of the representation of circuli and circulators, a showman, by ancient authors; Strategies developed by the Roman elite to represent popular activity.

Wireless in Local Loop (WiLL), a radio communications solution with implica tions for the provision of cheaper telephony in urban and rural areas, has become a topic of a debate in India over what has become known as the 'Poor Man's Mobile Phone'. This paper examines access to 'telematics' (not simple phone ownership), the validity of 'teledensity' as a statistical tool, the view that rural people are too poor to justify phone infrastructure, and the validity of cross-subsidy arguments from city to rural areas. The need to seek overseas investment is questioned, since developing countries can avoid expensive foreign telecommunications equipment through low-cost, high-quality, indigenous telematics equipment production. India, for instance, has installed more than 20 million such indigenous phone lines, saving billions of dollars. Internet, not just phone, connectivity, is essential for rural people to increase earnings. Politics, price, technical differences, and internet access are examined in relation to two competing WiLL products: India's corDECT, and the American/South Korean CDMA. Finally, it is suggested that the information gap cannot be 'bridged'. Instead, developing countries will have to wrest control of the web for their own regions. [ABSTRACT FROM AUTHOR]

Radiation-induced degradation of protein or DNA samples by synchrotron radiation is an inherent problem in X-ray crystallography, especially at the 'brighter' light sources. This short review gives a radiation chemical perspective on some of the physical and chemical processes that need to be considered in understanding potential pathways leading to the gradual degradation of the samples. Under the conditions used for X-ray crystallography at a temperature of <100 K in the presence of cryoprotectant agents, the majority of radiation damage of the protein samples arises from direct ionization of the amino acid residues and their associated water molecules. Some of the chemical processes that may occur at these protein centres, such as bond scission, are discussed. Several approaches are discussed that may reduce radiation damage, using agents known from radiation chemistry to minimize radical-induced degradation of the sample. [ABSTRACT FROM AUTHOR]

A recent paper in Cell by Ma et al. [Cell 8 (2002) 781] showed that the protein Artemis cleaves a hairpin intermediate during V(D)J recombination. Peter O’Neill and Penny Jeggo discuss this finding in the light of evidence that Artemis also functions to repair radiation damage [Cell 105 (2001) 177]. The findings suggest that Artemis may function in double strand break repair by “tidying up” double strand ends with associated base damage. The development of genetic diversity during immune development, therefore, seems to exploit damage response mechanisms that function to maintain genetic stability in other cell lineages. [ABSTRACT FROM AUTHOR]

The provision of complex electronic assistive technology systems for people with severe physical disabilities requires a structured process of assessment, prescription and follow-up. The provision framework developed in Barnsley includes a long-term iterative process of continuing follow-up and optimisation of the prescribed system. A computer-based integrated assistive system has been developed, which includes a software tool to log usage. The expectation is that the information available from data logging will supplement information from communication with the users and carers, and observational data, to give feedback on the success of the prescription that is more objective, comprehensive and easy to collect. Approaches to analysis of the logged data are presented and illustrated by a case study. The results demonstrate that, when usage data are logged within an integrated assistive system, the data can be analysed and presented to give meaningful feedback on the fit of the system to user requirements. [ABSTRACT FROM AUTHOR]

Describes the base excision repair (BER) mechanism involved in the processing of clustered lesions in DNA. Effect of ionizing radiation on DNA; Discussion on the BER pathways; Effect of closely opposed single-strand breaks or base lesions on DNA glycosulase and abasic site endonuclease activities; Mechanism for orchestrating BER of clustered lesions.

Focuses on thermosonic wirebonding and the challenges it face in the integrated circuits (IC) industry. Uses of gold ball wirebonding; History of thermosonic wirebonding technology; Implications of interconnect development for wirebonding.

Reports developments related to medical science. Legislation to reduce road deaths in Australia; Compensation for HIV contaminated French victims through transfusion; Increase number of admitted patients in emergency rooms in New York.

This paper discusses the Clean Power Plan (CPP) legislation and its repeal on the emissions from electricity generation sources. Demand side management (DSM) is probed to illustrate an alternative technique to achieve lower emissions goals. This work discusses the Climate Action Plan (CAP) corresponding to Fort Collins, Colorado, U.S. and its timeline targets. Therefore, the paper provides a technique for prioritizing DSM options through a Multi-Criteria Decision-Making (MCDM). In that regard, a framework is created to examine several options of DSM in reducing carbon footprints. The algorithm states that affecting Greenhouse Gases (GHG) in electric power system is the main goal and this can be achieved by implementing DSM technologies in distribution systems. MCDM algorithms have been proposed to prioritize alternatives and select the ones that achieve suitable emissions reduction. The findings from Analytic Hierarchy Process (AHP) show that the “communication and intelligence” option has a global priority of 0.341 making it the potential optimal alternative in achieving the goal. The second alternative is “electric stationary storage” with global priority of 0.207. The results obtained from Analytic Network Process (ANP) suggest that “communication and intelligence” is the optimum technology to reach the target with a priority of 0.284. [ABSTRACT FROM AUTHOR]

Discusses the measurement of single- and double-strand breaks in DNA after exposure to monoenergetic photons. Details on the process which lowered the energy of electrons incident on DNA; Information on the damage to the genome of a living cell by sparsely ionizing radiation; Mechanisms that explain radical migration in DNA.

Reports the rate of abortion in Europe. Inadequacy of family planning services; Association between abortion and contraception; Use of mini aspiration vacuum techniques in abortion.

An introduction is presented in which the editors discuss various reports within the issue concerning professor Clemens von Sonntag's research in radiation sciences including DNA radicals, protein damage, and translational aspects of therapy.

Purpose: Nitric oxide (NO) radiosensitizes mammalian cells significantly more efficiently than oxygen but the mechanism of this effect is unknown. We have studied the effect of NO on radiation-induced single strand breaks in plasmid DNA, changes to DNA bases, cellular double strand breaks and cell survival to gain further information into the mechanisms of radiosensitization. Results: The yields of plasmid DNA strand breaks are reduced in the presence of NO when compared with the yield induced by hydroxyl radical alone – post-irradiation treatment with DNA glycosylases however revealed that damaged nucleotides are formed in the presence of NO as seen through the formation of additional strand breaks. NO reacts with radiation-induced dGMP (2’-deoxyguanosine monophosphate) radicals to produce specific guanine modifications. Chemical mechanisms for these changes have been proposed. V79-4 cells are radiosensitized by NO more efficiently in exponential growth; these cells also exhibit enhanced γH2AX staining, a marker for double strand breaks (DSB). The maximum numbers of foci are formed later and remain longer after NO damage relative to DSB generated in anoxia, suggesting formation of replication-induced DSB. Conclusions: It is tentatively proposed that NO may radiosensitize cells by causing specific DNA damage which is difficult to repair - future studies will focus on identifying NO-induced DNA lesions in irradiated cells and increasing our understanding into how these lesions may enhance DNA damage following replication and repair. [Copyright &y& Elsevier]

Introduction: A never event is the most egregious of patient safety incidents. It refers to events that should theoretically never happen, such amputating the wrong limb. The term "never event" is used around the world by a variety of medical and patient safety organizations and is synonymous with sentinel events and serious reportable events. Unfortunately, there is little consensus about which events, in particular, are never events. These differing lists hinder potential collaboration or large-scale analyses. A recent systematic review by Hegarty et al. (2020) identified the need for a standardized definition for serious reportable events. The objective of our systematic review is to build on this by identifying which events are consistently or frequently identified as never events in order to isolate those which are core never events. Materials and methods: A systematic review will be conducted using Medline, Medline in Process, Scopus, PsychINFO, Embase via OVID, and CINAHL via EBSCO databases, as well as grey literature. We will include articles of any study design that discuss never events or one of its synonymous terms in the context of medical care. Four independent reviewers will conduct the title and abstract as well as the full-text screening, and 2 reviewers will abstract data. Data will be analyzed using narrative synthesis. Results will be categorized by year and geographic location, and by other factors determined during full-text screening. Discussion and conclusion: The lack of consensus regarding never events hinders progress in reducing their occurrence. Differing data sources makes comparison challenging, and limits the ability for patient safety groups to work collaboratively and share learnings with others. Identifying a core set of never events will serve as a first step to focus our efforts to reduce these harmful incidents. [ABSTRACT FROM AUTHOR]

Reports developments related to health in as of March 1990. Vaccination against hepatitis B virus in Western Europe; Impact of sex tourism on the tourism industry in Bangkok, Thailand; Accessibility of migrants on mental health services.

Informs that United Nations Conference on Trade and Development is to launch a program to help scientists in the former Soviet republics to negotiate with foreign companies interested in licensing their research results. Benefits to be provided by the program; Slowing down of the flow of funding for science.

focuses on the concern of delegates to the world summit of national academies of science on the suspension of the Australian government of funds for family planning. Denial of reproductive health to women in developed countries; Retardation of economic development through high population growth; Concern of international scientific opinion on science and humanity.

Examines the risk of lead-based paint poisoning in Europe. Risk of children on the poisoning; Cause of acute lead poisoning; Death of two children in Paris.

Non-homologous end joining (NHEJ) is the dominant DNA double strand break (DSB) repair pathway and involves several repair proteins such as Ku, DNA-PKcs, and XRCC4. It has been experimentally shown that the choice of NHEJ proteins is determined by the complexity of DSB. In this paper, we built a mathematical model, based on published data, to study how NHEJ depends on the damage complexity. Under an appropriate set of parameters obtained by minimization technique, we can simulate the kinetics of foci track formation in fluorescently tagged mammalian cells, Ku80-EGFP and DNA-PKcs-YFP for simple and complex DSB repair, respectively, in good agreement with the published experimental data, supporting the notion that simple DSB undergo fast repair in a Ku-dependent, DNA-PKcs-independent manner, while complex DSB repair requires additional DNA-PKcs for end processing, resulting in its slow repair, additionally resulting in slower release rate of Ku and the joining rate of complex DNA ends. Based on the numerous experimental descriptions, we investigated several models to describe the kinetics for complex DSB repair. An important prediction of our model is that the rejoining of complex DSBs is through a process of synapsis formation, similar to a second order reaction between ends, rather than first order break filling/joining. The synapsis formation (SF) model allows for diffusion of ends before the synapsis formation, which is precluded in the first order model by the rapid coupling of ends. Therefore, the SF model also predicts the higher number of chromosomal aberrations observed with high linear energy transfer (LET) radiation due to the higher proportion of complex DSBs compared to low LET radiation, and an increased probability of misrejoin following diffusion before the synapsis is formed, while the first order model does not provide a mechanism for the increased effectiveness in chromosomal aberrations observed. [ABSTRACT FROM AUTHOR]

Abstract: When cells are exposed to radiation serious lesions are introduced into the DNA including double strand breaks (DSBs), single strand breaks (SSBs), base modifications and clustered damage sites (a specific feature of ionizing radiation induced DNA damage). Radiation induced DNA damage has the potential to initiate events that can lead ultimately to mutations and the onset of cancer and therefore understanding the cellular responses to DNA lesions is of particular importance. Using γH2AX as a marker for DSB formation and RAD51 as a marker of homologous recombination (HR) which is recruited in the processing of frank DSBs or DSBs arising from stalled replication forks, we have investigated the contribution of SSBs and non-DSB DNA damage to the induction of DSBs in mammalian cells by ionizing radiation during the cell cycle. V79-4 cells and human HF19 fibroblast cells have been either irradiated with 0–20Gy of γ radiation or, for comparison, treated with a low concentration of hydrogen peroxide, which is known to induce SSBs but not DSBs. Inhibition of the repair of oxidative DNA lesions by poly(ADP ribose) polymerase (PARP) inhibitor leads to an increase in radiation induced γH2AX and RAD51 foci which we propose is due to these lesions colliding with replication forks forming replication induced DSBs. It was confirmed that DSBs are not induced in G1 phase cells by treatment with hydrogen peroxide but treatment does lead to DSB induction, specifically in S phase cells. We therefore suggest that radiation induced SSBs and non-DSB DNA damage contribute to the formation of replication induced DSBs, detected as RAD51 foci. [ABSTRACT FROM AUTHOR]

Purpose: To characterize the complexity of DNA damage through determination of the yields of single (SSB) and double strand breaks (DSB), base lesions and clustered damage sites induced in fully hydrated plasmid DNA by direct radiation effects as a function of the ionizing density of the radiation using 4He2+ ion irradiation with linear energy-transfer (LET) values in the range 19 to 148 keV/μm. Materials and methods: Hydrated plasmid DNA (pUC18) containing 34.5 water molecules/nucleotide was irradiated with He2+ ions with LET values of 19, 63, 95, 121 and 148 keV/μm. From quantification of the conformational changes of the irradiated samples (closed circular, open or linear forms) analyzed by agarose gel electrophoresis, the yields of SSB and DSB were obtained. Base lesions were visualized as additional strand breaks by treatment with base excision repair enzymes (endonuclease III (Nth) and formamidpyrimidine DNA glycosylase (Fpg)). Results: The yield of prompt SSB does not depend significantly on LET of the 4He2+ ions, whereas the yield of prompt DSB increases with increasing LET. The yields of isolated base lesions, revealed by Nth and Fpg as additional SSB, decrease drastically with increasing LET. The sum of the yields of DSB and additional DSB revealed by Nth and Fpg increase with increasing LET of the 4He2+ ions except at the highest LET investigated. Conclusion: The yields of clustered damage, revealed as DSB and non-DSB clustered damage sites, but not isolated lesions, namely SSB, increase with increasing ionization density of the 4He2+ ions except at the highest LET investigated. [ABSTRACT FROM AUTHOR]

Abstract: Ionizing radiation induces clustered DNA damaged sites, defined as two or more lesions formed within one or two helical turns of the DNA through passage of a single radiation track. It is now established that clustered DNA damage sites are found in cells and present a challenge to the repair machinery of the cell but to date, most studies have investigated the effects of bi-stranded lesions. A subset of clustered DNA damaged sites exist in which two or more lesions are present in tandem on the same DNA strand. In this study synthetic oligonucleotides containing an AP site 1, 3 or 5 bases 5′ or 3′ to 8-oxo-7,8-dihydroguanine (8-oxoG) on the same DNA strand were synthesized as a model of a tandem clustered damaged sites. It was found that 8-oxoG retards the incision of the AP site by exonuclease III (Xth) and formamidopyrimidine DNA glycosylase (Fpg). In addition the rejoining of the AP site by xrs5 nuclear extracts is impaired by the presence of 8-oxoG. The mutation frequency arising from 8-oxoG within a tandem clustered site was determined in both wild type and mutant E. coli backgrounds. In wild-type, nth, fpg and mutY null E. coli, the mutation frequency is slightly elevated when an AP site is in tandem to 8-oxoG, compared with when 8-oxoG is present as a single lesion. Interestingly, in the double mutant mutY/fpg null E. coli, the mutation frequency of 8-oxoG is reduced when an AP site is present in tandem compared with when 8-oxoG is present as a single lesion. This study demonstrates that tandem lesions can present a challenge to the repair machinery of the cell. [Copyright &y& Elsevier]

Clustered DNA damage, where two or more lesions are located proximal to each other on the same or opposite DNA strands, is frequently produced as a result of exposure to ionising radiation. It has been suggested that such complex damaged sites pose problems for repair pathways. In this study, we addressed the question of how two 8-oxoguanine lesions, located two nucleotides apart on the same DNA strand, are repaired. We find that in human cell extracts repair of either of the 8-oxoguanine lesions within a tandem damaged site is initiated randomly and that the majority of the initiated repair proceeds to completion. However, a fraction of the initiated repair is delayed at the stage of an incised AP site and the rate of further processing of this incised AP site is dependent on the position of the remaining 8-oxoguanine. If the remaining 8-oxoguanine residue is located near the 5′ terminus of the incised abasic site, repair continues as efficiently as repair of a single 8-oxoguanine residue. However, repair is delayed after the incision step when the remaining 8-oxoguanine residue is located near the 3′ terminus. Although the presence of the 8-oxoguanine residue near the 3′ terminus did not affect either DNA polymerase β activity or poly(ADP)ribose polymerase-1 affinity and turnover on an incised AP site, we find that 8-oxoguanine-DNA glycosylase has reduced ability to remove an 8-oxoguanine residue located near the 3′ terminus of the incised AP site. We find that binding of the 8-oxoguanine-DNA glycosylase to this 8-oxoguanine residue inhibits DNA repair synthesis by DNA polymerase β, thus delaying repair. We propose that interference between a DNA glycosylase and DNA polymerase during the repair of tandem lesions may lead to accumulation of the intermediate products that contain persisting DNA strand breaks. [Copyright &y& Elsevier]