Gastrointestinal Acute Radiation Syndrome: Mechanisms, Models, Markers, and Medical Countermeasures

There have been a number of reported human exposures to high dose radiation, resulting from accidents at nuclear power plants (e.g., Chernobyl), atomic bombings (Hiroshima and Nagasaki), and mishaps in industrial and medical settings. If absorbed radiation doses are high enough, evolution of acute radiation syndromes (ARS) will likely impact both the bone marrow as well as the gastrointestinal (GI) tract. Damage incurred in the latter can lead to nutrient malabsorption, dehydration, electrolyte imbalance, altered microbiome and metabolites, and impaired barrier function, which can lead to septicemia and death. To prepare for a medical response should such an incident arise, the National Institute of Allergy and Infectious Diseases (NIAID) funds basic and translational research to address radiation-induced GI-ARS, which remains a critical and prioritized unmet need. Areas of interest include identification of targets for damage and mitigation, animal model development, and testing of medical countermeasures (MCMs) to address GI complications resulting from radiation exposure. To appropriately model expected human responses, it is helpful to study analogous disease states in the clinic that resemble GI-ARS, to inform on best practices for diagnosis and treatment, and translate them back to inform nonclinical drug efficacy models. For these reasons, the NIAID partnered with two other U.S. government agencies (the Biomedical Advanced Research and Development Authority, and the Food and Drug Administration), to explore models, biomarkers, and diagnostics to improve understanding of the complexities of GI-ARS and investigate promising treatment approaches. A two-day workshop was convened in August 2022 that comprised presentations from academia, industry, healthcare, and government, and highlighted talks from 26 subject matter experts across five scientific sessions. This report provides an overview of information that was presented during the conference, and important discussions surrounding a broad range of topics that are critical for the research, development, licensure, and use of MCMs for GI-ARS.

Advanced Technologies in Radiation Research

The U.S. Government is committed to maintaining a robust research program that supports a portfolio of scientific experts who are investigating the biological effects of radiation exposure. On August 17 and 18, 2023, the Radiation and Nuclear Countermeasures Program, within the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), partnered with the National Cancer Institute, NIH, the National Aeronautics and Space Administration, and the Radiation Injury Treatment Network to convene a workshop titled, Advanced Technologies in Radiation Research (ATRR), which focused on the use of advanced technologies under development or in current use to accelerate radiation research. This meeting report provides a comprehensive overview of the research presented at the workshop, which included an assembly of subject matter experts from government, industry, and academia. Topics discussed during the workshop included assessments of acute and delayed effects of radiation exposure using modalities such as clustered regularly interspaced short palindromic repeats (CRISPR) - based gene editing, tissue chips, advanced computing, artificial intelligence, and immersive imaging techniques. These approaches are being applied to develop products to diagnose and treat radiation injury to the bone marrow, skin, lung, and gastrointestinal tract, among other tissues. The overarching goal of the workshop was to provide an opportunity for the radiation research community to come together to assess the technological landscape through sharing of data, methodologies, and challenges, followed by a guided discussion with all participants. Ultimately, the organizers hope that the radiation research community will benefit from the workshop and seek solutions to scientific questions that remain unaddressed. Understanding existing research gaps and harnessing new or re-imagined tools and methods will allow for the design of studies to advance medical products along the critical path to U.S. Food and Drug Administration approval.

Radiation-induced multi-organ injury

PURPOSE

Natural history studies have been informative in dissecting radiation injury, isolating its effects, and compartmentalizing injury based on the extent of exposure and the elapsed time post-irradiation. Although radiation injury models are useful for investigating the mechanism of action in isolated subsyndromes and development of medical countermeasures (MCMs), it is clear that ionizing radiation exposure leads to multi-organ injury (MOI).

METHODS

The Radiation and Nuclear Countermeasures Program within the National Institute of Allergy and Infectious Diseases partnered with the Biomedical Advanced Research and Development Authority to convene a virtual two-day meeting titled 'Radiation-Induced Multi-Organ Injury' on June 7-8, 2022. Invited subject matter experts presented their research findings in MOI, including study of mechanisms and possible MCMs to address complex radiation-induced injuries.

RESULTS

This workshop report summarizes key information from each presentation and discussion by the speakers and audience participants.

CONCLUSIONS

Understanding the mechanisms that lead to radiation-induced MOI is critical to advancing candidate MCMs that could mitigate the injury and reduce associated morbidity and mortality. The observation that some of these mechanisms associated with MOI include systemic injuries, such as inflammation and vascular damage, suggests that MCMs that address systemic pathways could be effective against multiple organ systems.

Immune Dysfunction from Radiation Exposure

Exposure to ionizing radiation causes acute damage and loss of bone marrow and peripheral immune cells that can result in high mortality due to reduced resistance to infections and hemorrhage. Besides these acute effects, tissue damage from radiation can trigger inflammatory responses, leading to progressive and chronic tissue damage by radiation-induced loss of immune cell types that are required for resolving tissue injuries. Understanding the mechanisms involved in radiation-induced immune system injury and repair will provide new insights for developing medical countermeasures that help restore immune homeostasis. For these reasons, The Radiation and Nuclear Countermeasures Program (RNCP) and the Basic Immunology Branch (BIB) under the Division of Allergy, Immunology, and Transplantation (DAIT) within the National Institute of Allergy and Infectious Diseases (NIAID) convened a two-day workshop, along with partners from the Biomedical Advanced Research and Development Authority (BARDA), and the Radiation Injury Treatment Network (RITN). This workshop, titled "Immune Dysfunction from Radiation Exposure," was held virtually on September 9-10, 2020; this Commentary provides a high-level overview of what was discussed at the meeting.

Immune Dysfunction from Radiation Exposure

The hematopoietic system is highly sensitive to ionizing radiation. Damage to the immune system may result in opportunistic infections and hemorrhage, which could lead to mortality. Inflammation triggered by tissue damage can also lead to additional local or widespread tissue damage. The immune system is responsible for tissue repair and restoration, which is made more challenging when it is in the process of self-recovery. Because of these challenges, the Radiation and Nuclear Countermeasures Program (RNCP) and the Basic Immunology Branch (BIB) under the Division of Allergy, Immunology, and Transplantation (DAIT) within the National Institute of Allergy and Infectious Diseases (NIAID), along with partners from the Biomedical Advanced Research and Development Authority (BARDA), and the Radiation Injury Treatment Network (RITN) sponsored a two-day meeting titled Immune Dysfunction from Radiation Exposure held on September 9-10, 2020. The intent was to discuss the manifestations and mechanisms of radiation-induced immune dysfunction in people and animals, identify knowledge gaps, and discuss possible treatments to restore immune function and enhance tissue repair after irradiation.

The NIAID/RNCP Biodosimetry Program: An Overview

Established in 2004, the Radiation and Nuclear Countermeasures Program (RNCP), within the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health has the central mission to advance medical countermeasure mitigators/therapeutics, and biomarkers and technologies to assess, triage, and inform medical management of patients experiencing acute radiation syndrome and/or the delayed effects of acute radiation exposure. The RNCP biodosimetry mission space encompasses: (1) basic research to elucidate novel approaches for rapid and accurate assessment of radiation exposure, (2) studies to support advanced development for US Food and Drug Administration (FDA) clearance of promising triage or treatment devices/approaches, (3) characterization of biomarkers and/or assays to determine degree of tissue or organ dose that can predict outcome of radiation injuries (i.e., organ failure, morbidity, and/or mortality), and (4) outreach efforts to facilitate interactions with researchers developing cutting edge biodosimetry approaches. Thus far, no biodosimetry device has been FDA cleared for use during a radiological/nuclear incident. At NIAID, advancement of radiation biomarkers and biodosimetry approaches is facilitated by a variety of funding mechanisms (grants, contracts, cooperative and interagency agreements, and Small Business Innovation Research awards), with the objective of advancing devices and assays toward clearance, as outlined in the FDA's Radiation Biodosimetry Medical Countermeasure Devices Guidance. The ultimate goal of the RNCP biodosimetry program is to develop and establish accurate and reliable biodosimetry tools that will improve radiation preparedness and ultimately save lives during a radiological or nuclear incident.

Minimum reporting standards should be expected for preclinical radiobiology irradiators and dosimetry in the published literature

The cornerstones of science advancement are rigor in performing scientific research, reproducibility of research findings and unbiased reporting of design and results of the experiments. For radiation research, this requires rigor in describing experimental details as well as the irradiation protocols for accurate, precise and reproducible dosimetry. Most institutions conducting radiation biology research in in vitro or animal models do not have describe experimental irradiation protocols in sufficient details to allow for balanced review of their publication nor for other investigators to replicate published experiments. The need to increase and improve dosimetry standards, traceability to National Institute of Standards and Technology (NIST) standard beamlines, and to provide dosimetry harmonization within the radiation biology community has been noted for over a decade both within the United States and France. To address this requirement subject matter experts have outlined minimum reporting standards that should be included in published literature for preclinical irradiators and dosimetry.

Considerations of Medical Preparedness to Assess and Treat Various Populations During a Radiation Public Health Emergency

During a radiological or nuclear public health emergency, given the heterogeneity of civilian populations, it is incumbent on medical response planners to understand and prepare for a potentially high degree of interindividual variability in the biological effects of radiation exposure. A part of advanced planning should include a comprehensive approach, in which the range of possible human responses in relation to the type of radiation expected from an incident has been thoughtfully considered. Although there are several reports addressing the radiation response for special populations (as compared to the standard 18-45-year-old male), the current review surveys published literature to assess the level of consideration given to differences in acute radiation responses in certain sub-groups. The authors attempt to bring clarity to the complex nature of human biology in the context of radiation to facilitate a path forward for radiation medical countermeasure (MCM) development that may be appropriate and effective in special populations. Consequently, the focus is on the medical (as opposed to logistical) aspects of preparedness and response. Populations identified for consideration include obstetric, pediatric, geriatric, males, females, individuals of different race/ethnicity, and people with comorbidities. Relevant animal models, biomarkers of radiation injury, and MCMs are highlighted, in addition to underscoring gaps in knowledge and the need for consistent and early inclusion of these populations in research. The inclusion of special populations in preclinical and clinical studies is essential to address shortcomings and is an important consideration for radiation public health emergency response planning. Pursuing this goal will benefit the population at large by considering those at greatest risk of health consequences after a radiological or nuclear mass casualty incident.

Animal Care in Radiation Medical Countermeasures Studies

Animal models are necessary to demonstrate the efficacy of medical countermeasures (MCM) to mitigate/treat acute radiation syndrome and the delayed effects of acute radiation exposure and develop biodosimetry signatures for use in triage and to guide medical management. The use of animal models in radiation research allows for the simulation of the biological effects of exposure in humans. Robust and well-controlled animal studies provide a platform to address basic mechanistic and safety questions that cannot be conducted in humans. The U.S. Department of Health and Human Services has tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- through advanced-stage MCM development for radiation-induced injuries; and advancement of biodosimetry platforms and exploration of biomarkers for triage, definitive dose, and predictive purposes. Some of these NIAID-funded projects may transition to the Biomedical Advanced Research and Development Authority (BARDA), a component of the Office of the Assistant Secretary for Preparedness and Response in the U.S. Department of Health and Human Services, which is tasked with the advanced development of MCMs to include pharmacokinetic, exposure, and safety assessments in humans. Guided by the U.S. Food and Drug Administration's (FDA) Animal Rule, both NIAID and BARDA work closely with researchers to advance product and device development, setting them on a course for eventual licensure/approval/clearance of their approaches by the FDA. In August 2020, NIAID partnered with BARDA to conduct a workshop to discuss currently accepted animal care protocols and examine aspects of animal models that can influence outcomes of studies to explore MCM efficacy for potential harmonization. This report provides an overview of the two-day workshop, which includes a series of special topic presentations followed by panel discussions with subject-matter experts from academia, industry partners, and select governmental agencies.

Development of Biomarkers for Radiation Biodosimetry and Medical Countermeasures Research: Current Status, Utility, and Regulatory Pathways

Biomarkers are important indicators of biological processes in health or disease. For this reason, they play a critical role in advanced development of radiation biodosimetry tools and medical countermeasures (MCMs). They can aid in the assessment of radiation exposure level, extent of radiation-induced injury, and/or efficacy of an MCM. This meeting report summarizes the presentations and discussions from the 2020 workshop titled, "Biomarkers in Radiation Biodosimetry and Medical Countermeasures," sponsored by the Radiation and Nuclear Countermeasures Program (RNCP) at the National Institute of Allergy and Infectious Diseases (NIAID). The main goals of this meeting were to: 1. Provide an overview on biomarkers and to focus on the state of science with regards to biomarkers specific to radiation biodosimetry and MCMs; 2. Understand developmental challenges unique to the role of biomarkers in the fields of radiation biodosimetry and MCM development; and 3. Identify existing gaps and needs for translational application.

Acute Radiation Syndrome and the Microbiome: Impact and Review

Study of the human microbiota has been a centuries-long endeavor, but since the inception of the National Institutes of Health (NIH) Human Microbiome Project in 2007, research has greatly expanded, including the space involving radiation injury. As acute radiation syndrome (ARS) is multisystemic, the microbiome niches across all areas of the body may be affected. This review highlights advances in radiation research examining the effect of irradiation on the microbiome and its potential use as a target for medical countermeasures or biodosimetry approaches, or as a medical countermeasure itself. The authors also address animal model considerations for designing studies, and the potential to use the microbiome as a biomarker to assess radiation exposure and predict outcome. Recent research has shown that the microbiome holds enormous potential for mitigation of radiation injury, in the context of both radiotherapy and radiological/nuclear public health emergencies. Gaps still exist, but the field is moving forward with much promise.

Commonalities Between COVID-19 and Radiation Injury

As the multi-systemic components of COVID-19 emerge, parallel etiologies can be drawn between SARS-CoV-2 infection and radiation injuries. While some SARS-CoV-2-infected individuals present as asymptomatic, others exhibit mild symptoms that may include fever, cough, chills, and unusual symptoms like loss of taste and smell and reddening in the extremities (e.g., "COVID toes," suggestive of microvessel damage). Still others alarm healthcare providers with extreme and rapid onset of high-risk indicators of mortality that include acute respiratory distress syndrome (ARDS), multi-organ hypercoagulation, hypoxia and cardiovascular damage. Researchers are quickly refocusing their science to address this enigmatic virus that seems to unveil itself in new ways without discrimination. As investigators begin to identify early markers of disease, identification of common threads with other pathologies may provide some clues. Interestingly, years of research in the field of radiation biology documents the complex multiorgan nature of another disease state that occurs after exposure to high doses of radiation: the acute radiation syndrome (ARS). Inflammation is a key common player in COVID-19 and ARS, and drives the multi-system damage that dramatically alters biological homeostasis. Both conditions initiate a cytokine storm, with similar pro-inflammatory molecules increased and other anti-inflammatory molecules decreased. These changes manifest in a variety of ways, with a demonstrably higher health impact in patients having underlying medical conditions. The potentially dramatic human impact of ARS has guided the science that has identified many biomarkers of radiation exposure, established medical management strategies for ARS, and led to the development of medical countermeasures for use in the event of a radiation public health emergency. These efforts can now be leveraged to help elucidate mechanisms of action of COVID-19 injuries. Furthermore, this intersection between COVID-19 and ARS may point to approaches that could accelerate the discovery of treatments for both.

Metabolomics in Radiation Biodosimetry: Current Approaches and Advances

Triage and medical intervention strategies for unanticipated exposure during a radiation incident benefit from the early, rapid and accurate assessment of dose level. Radiation exposure results in complex and persistent molecular and cellular responses that ultimately alter the levels of many biological markers, including the metabolomic phenotype. Metabolomics is an emerging field that promises the determination of radiation exposure by the qualitative and quantitative measurements of small molecules in a biological sample. This review highlights the current role of metabolomics in assessing radiation injury, as well as considerations for the diverse range of bioanalytical and sampling technologies that are being used to detect these changes. The authors also address the influence of the physiological status of an individual, the animal models studied, the technology and analysis employed in interrogating response to the radiation insult, and variables that factor into discovery and development of robust biomarker signatures. Furthermore, available databases for these studies have been reviewed, and existing regulatory guidance for metabolomics are discussed, with the ultimate goal of providing both context for this area of radiation research and the consideration of pathways for continued development.

An in vitro DNA double-strand break repair assay based on end-joining of defined duplex oligonucleotides

DNA double-strand breaks (DSBs) are caused by endogenous cellular processes such as oxidative metabolism, or by exogenous events like exposure to ionizing radiation or other genotoxic agents. Repair of these DSBs is essential for the maintenance of cellular genomic integrity. In human cells, and cells of other higher eukaryotes, DSBs are primarily repaired by the nonhomologous end-joining (NHEJ) DSB repair pathway. Most in vitro assays that have been designed to measure NHEJ activity employ linear plasmid DNA as end-joining substrates, and such assays have made significant contributions to our understanding of the biochemical mechanisms of NHEJ. Here we describe an in vitro end-joining assay employing linear oligonucleotides that has distinct advantages over plasmid-based assays for the study of structure-function relationships between the proteins of the NHEJ pathway and synthetic DNA end-joining substrates possessing predetermined DSB configurations and chemistries.

Base damage immediately upstream from double-strand break ends is a more severe impediment to nonhomologous end joining than blocked 3'-termini

Radiation-induced DNA double-strand breaks (DSBs) are critical cytotoxic lesions that are typically repaired by nonhomologous end joining (NHEJ) in human cells. Our previous work indicated that the highly cytotoxic DSBs formed by (125)I decay possess base damage clustered within 8 to 10 bases of the break and 3'-phosphate (P) and 3'-OH ends. This study examined the effect of such structures on NHEJ in in vitro assays employing either (125)I decay-induced DSB linearized plasmid DNA or structurally defined duplex oligonucleotides. Duplex oligonucleotides that possess either a 3'-P or 3'-phosphoglycolate (PG) or a ligatable 3'-OH end with either an AP site or an 8-oxo-dG 1 nucleotide upstream (-1n) from the 3'-terminus have been examined for reparability. Moderate to severe end-joining inhibition was observed for modified DSB ends or 8-oxo-dG upstream from a 3'-OH end. In contrast, abolition of end joining was observed with duplexes possessing an AP site upstream from a ligatable 3'-OH end or for a lesion combination involving 3'-P plus an upstream 8-oxo-dG. In addition, base mismatches at the -1n position were also strong inhibitors of NHEJ in this system, suggesting that destabilization of the DSB terminus as a result of base loss or improper base pairing may play a role in the inhibitory effects of these structures. Furthermore, we provide data indicating that DSB end joining is likely to occur prior to removal or repair of base lesions proximal to the DSB terminus. Our results show that base damage or base loss near a DSB end may be a severe block to NHEJ and that complex combinations of lesions presented in the context of a DSB may be more inhibitory than the individual lesions alone. In contrast, blocked DSB 3'-ends alone are only modestly inhibitory to NHEJ. Finally, DNA ligase activity is implicated as being responsible for these effects.

Radiation-generated short DNA fragments may perturb non-homologous end-joining and induce genomic instability

Cells exposed to densely ionizing radiation (high-LET) experience more severe biological damage than do cells exposed to sparsely ionizing radiation (low-LET). The prevailing hypothesis is that high-LET radiations induce DNA double strand-breaks (DSB) that are more complex and clustered, and are thereby more challenging to repair. Here, we present experimental data obtained by atomic force microscopy imaging, DNA-dependent protein kinase (DNA-PK) activity determination, DNA ligation assays, and genomic studies to suggest that short DNA fragments are important products of radiation-induced DNA lesions, and that the lengths of DNA fragments may be significant in the cellular responses to ionizing radiation. We propose the presence of a subset of short DNA fragments that may affect cell survival and genetic stability following exposure to ionizing radiation, and that the enhanced biological effects of high-LET radiation may be explained, in part, by the production of increased quantities of short DNA fragments.

Coincident In Vitro Analysis of DNA-PK-Dependent and -Independent Nonhomologous End Joining

In mammalian cells, DNA double-strand breaks (DSBs) are primarily repaired by nonhomologous end joining (NHEJ). The current model suggests that the Ku 70/80 heterodimer binds to DSB ends and recruits DNA-PK_cs to form the active DNA-dependent protein kinase, DNA-PK. Subsequently, XRCC4, DNA ligase IV, XLF and most likely, other unidentified components participate in the final DSB ligation step. Therefore, DNA-PK plays a key role in NHEJ due to its structural and regulatory functions that mediate DSB end joining. However, recent studies show that additional DNA-PK-independent NHEJ pathways also exist. Unfortunately, the presence of DNA-PK_cs appears to inhibit DNA-PK-independent NHEJ, and in vitro analysis of DNA-PK-independent NHEJ in the presence of the DNA-PK_cs protein remains problematic. We have developed an in vitro assay that is preferentially active for DNA-PK-independent DSB repair based solely on its reaction conditions, facilitating coincident differential biochemical analysis of the two pathways. The results indicate the biochemically distinct nature of the end-joining mechanisms represented by the DNA-PK-dependent and -independent NHEJ assays as well as functional differences between the two pathways.

DNA-PKcs deficiency leads to persistence of oxidatively induced clustered DNA lesions in human tumor cells

DNA-dependent protein kinase (DNA-PK) is a key non-homologous-end-joining (NHEJ) nuclear serine/threonine protein kinase involved in various DNA metabolic and damage signaling pathways contributing to the maintenance of genomic stability and prevention of cancer. To examine the role of DNA-PK in processing of non-DSB clustered DNA damage, we have used three models of DNA-PK deficiency, i.e., chemical inactivation of its kinase activity by the novel inhibitors IC86621 and NU7026, knockdown and complete absence of the protein in human breast cancer (MCF-7) and glioblastoma cell lines (MO59-J/K). A compromised DNA-PK repair pathway led to the accumulation of clustered DNA lesions induced by gamma-rays. Tumor cells lacking protein expression or with inhibited kinase activity showed a marked decrease in their ability to process oxidatively induced non-DSB clustered DNA lesions measured using a modified version of pulsed-field gel electrophoresis or single-cell gel electrophoresis (comet assay). In all cases, DNA-PK inactivation led to a higher level of lesion persistence even after 24-72h of repair. We suggest a model in which DNA-PK deficiency affects the processing of these clusters first by compromising base excision repair and second by the presence of catalytically inactive DNA-PK inhibiting the efficient processing of these lesions owing to the failure of DNA-PK to disassociate from the DNA ends. The information rendered will be important for understanding not only cancer etiology in the presence of an NHEJ deficiency but also cancer treatments based on the induction of oxidative stress and inhibition of cluster repair.

In vitro non-homologous DNA end joining assays--the 20th anniversary

DNA double-strand breaks (DSBs) are the most serious forms of DNA damage in cells. Unrepaired or misrepaired DSBs account for some of the genetic instabilities that lead to mutations or cell death, and consequently, to cancer predisposition. In human cells non-homologous DNA end joining (NHEJ) is the main repair mechanism of these breaks. Systems for DNA end joining study have been developing during the last 20 years. New assays have some advantages over earlier in vitro DSBs repair assays because they are less time-consuming, allow the use of clinical material and examination of the joining DNA ends produced physiologically in mammalian cells. Proteins involved in NHEJ repair pathway can serve as biomarkers or molecular targets for anticancer drugs. Results of studies on NHEJ in cancer could help to select potent repair inhibitors that may selectively sensitize tumor cells to ionizing radiation (IR) and chemotherapy. Here, we review the principles and practice of in vitro NHEJ assays and provide some insights into the future prospects of this assay in cancer diagnosis and treatment.

Determination and analysis of site-specific 125I decay-induced DNA double-strand break end-group structures

End groups contribute to the structural complexity of radiation-induced DNA double-strand breaks (DSBs). As such, end-group structures may affect a cell's ability to repair DSBs. The 3'-end groups of strand breaks caused by gamma radiation, or oxidative processes, under oxygenated aqueous conditions have been shown to be distributed primarily between 3'-phosphoglycolate and 3'-phosphate, with 5'-phosphate ends in both cases. In this study, end groups of the high-LET-like DSBs caused by 125I decay were investigated. Site-specific DNA double-strand breaks were produced in plasmid pTC27 in the presence or absence of 2 M DMSO by 125I-labeled triplex-forming oligonucleotide targeting. End-group structure was assessed enzymatically as a function of the DSB end to serve as a substrate for ligation and various forms of end labeling. Using this approach, we have demonstrated 3'-hydroxyl (3'-OH) and 3'-phosphate (3'-P) end groups and 5'-ends (> or = 42%) terminated by phosphate. A 32P postlabeling assay failed to detect 3'-phosphoglycolate in a restriction fragment terminated by the 125I-induced DNA double-strand break, and this is likely due to restricted oxygen diffusion during irradiation as a frozen aqueous solution. Even so, end-group structure and relative distribution varied as a function of the free radical scavenging capacity of the irradiation buffer.

Molecular analysis of base damage clustering associated with a site-specific radiation-induced DNA double-strand break

Base damage flanking a radiation-induced DNA double-strand break (DSB) may contribute to DSB complexity and affect break repair. However, to date, an isolated radiation-induced DSB has not been assessed for such structures at the molecular level. In this study, an authentic site-specific radiation-induced DSB was produced in plasmid DNA by triplex forming oligonucleotide-targeted (125)I decay. A restriction fragment terminated by the DSB was isolated and probed for base damage with the E. coli DNA repair enzymes endonuclease III and formamidopyrimidine-DNA glycosylase. Our results demonstrate base damage clustering within 8 bases of the (125)I-targeted base in the DNA duplex. An increased yield of base damage (purine > pyrimidine) was observed for DSBs formed by irradiation in the absence of DMSO. An internal control fragment 1354 bp upstream from the targeted base was insensitive to enzymatic probing, indicating that the damage detected proximal to the DSB was produced by the (125)I decay that formed the DSB. Gas chromatography-mass spectrometry identified three types of damaged bases in the approximately 32-bp region proximal to the DSB. These base lesions were 8-hydroxyguanine, 8-hydroxyadenine and 5-hydroxycytosine. Finally, evidence is presented for base damage >24 bp upstream from the (125)I-decay site that may form via a charge migration mechanism.

Characterization of complex apurinic/apyrimidinic-site clustering associated with an authentic site-specific radiation-induced DNA double-strand break

Radiation lethality is largely attributed to radiation-induced DNA double-strand breaks (DSBs). A range of structural complexity is predicted for radiation-induced DSBs. However, this lesion has never been analyzed in isolation at the molecular level. To address this problem, we have created authentic site-specific radiation-induced DSBs in plasmid DNA by triplex-forming oligonucleotide-targeted 125I decay. No significant difference in DSB yield was observed after irradiation in the presence or absence of the radical scavenger DMSO, suggesting that DSB formation is a result of the direct effect of the radiation. A restriction fragment terminated by the DSB was isolated and probed with the Escherichia coli DNA repair enzyme endonuclease IV (endo IV), which recognizes apurinic/apyrimidinic (AP) sites. Enzymatic probing demonstrated clustering of AP sites within 10 bases of the 125I-targeted base in the DNA duplex. Our results suggest scavengeable radicals may not play a large role in the generation of AP sites associated with DSB formation, because at least 30% of all fragments have endo IV-sensitive sites, regardless of irradiation conditions. An internal control fragment recovered from the 125I linearized plasmid did not exhibit endo IV sensitivity in excess of that observed for a similar fragment recovered from an undamaged plasmid. Thus, AP site clustering proximal to the DSB resulted from the 125I decays responsible for DSB formation and was not due to untargeted background irradiation.

Characterization of a complex 125I-induced DNA double-strand break: implications for repair

PURPOSE

To examine the role of radiation-induced DNA double-strand break (DSB) structural organization in DSB repair, and characterize the structural features of 125I-induced DSBs that may impact the repair process.

METHODS

Plasmid DNA was linearized by sequence-specific targeting using an 125I-labeled triplex-forming oligonucleotide (TFO). Following isolation from agarose gels, base damage structures associated with the DSB ends in plasmids linearized by the 125I-TFO were characterized by probing with the E. coli DNA damage-specific endonuclease and DNA-glycosylases, endonuclease IV (endo IV), endonuclease III (endo III), and formamidopyrimidine-glycosylase (Fpg).

RESULTS

Plasmid DNA containing DSBs produced by the high-LET-like effects of 125I-TFO has been shown to support at least 2-fold lower end joining than gamma-ray linearized plasmid, and this may be a consequence of the highly complex structure expected near an 125I-induced DSB end. Therefore, to determine if a high density of base damage exists proximal to the DSBs produced by 125I-TFOs, short fragments of DNA recovered from the DSB end of 125I-TFO-linearized plasmid were enzymatically probed. Base damage and AP site clustering was demonstrated within 3 bases downstream and 7 bases upstream of the targeted base. Furthermore, the pattern and extent of base damage varied depending upon the presence or absence of 2 M DMSO during irradiation.

CONCLUSIONS

125I-TFO-induced DSBs exhibit a high degree of base damage clustering proximal to the DSB end. At least 60% of the nucleotides within 10 bp of the 125I decay site are sensitive to cleavage by endo IV, endo III, or Fpg following damage accumulation in the presence of DMSO, whereas > or = 80% are sensitive in the absence of DMSO. The high degree of base damage clustering associated with the 125I-TFO-induced DSB end may be a major factor leading to its negligible in vitro repair by the non-homologous end-joining pathway (NHEJ).

In vitro effects of soy phytoestrogens on rat L6 skeletal muscle cells

Soy isoflavones display estrogenic activity in humans and animals, and thus are referred to as phytoestrogens. This study was performed to observe the effects of the soy isoflavones genistein, daidzein, and glycitein on cell cultures of rat skeletal muscles. [3H]Thymidine incorporation was used to determine cell proliferation, while protein synthesis and degradation were determined by tracking radiolabeled leucine. For the proliferation studies, insulin, estradiol, genistein, daidzein, or glycitein was supplemented at 0, 0.04, 0.08, 0.16, 0.31, 0.63, 1.25, 2.5, 5, 10, or 20 microM, respectively, or in combinations with final concentrations of 0, 0.1, 1, or 10 microM. Genistein reacted most similarly to estradiol, inhibiting proliferation at > or = 1 microM (P < .001). A combination of phytoestrogens resulted in significant inhibition of cell proliferation, but not to the extent observed with genistein alone. For the protein synthesis and degradation experiments, treatments of 0.1 microM dexamethasone or 1 microM concentrations of insulin, genistein, daidzein, or glycitein were used. Phytoestrogens did not inhibit or stimulate protein degradation or synthesis (P > .05). A one-tailed univariate analysis of variance revealed a trend (P < or = .1) in protein stimulation with genistein and glycitein treatments. These results suggest that the tyrosine kinase inhibiting activity of genistein may be affecting phosphorylation of the mitosis-promoting factor, preventing the advancement of the mitotic cell cycle. In addition, at higher total combined concentrations, daidzein and glycitein may be able to outcompete genistein for receptor sites. These results suggest that soy isoflavones in the diet may potentially modulate normal growth and development in humans and animals that ingest soy-based products.

Effects of Soy-derived diets on plasma and liver lipids, glucose tolerance, and longevity in normal, long-lived and short-lived mice

We examined the effects of diets based on a low isoflavone or a high isoflavone soy protein isolates in normal, growth-hormone receptor knockout and Ames dwarf, and Prop 1 (df) mice that are hypoinsulinemic, insulin-sensitive, and exceptionally long-lived, as well as in growth hormone transgenic mice that are hyperinsulinemic, insulin-resistant, dyslipidemic, and short-lived. Soybean diets tended to normalize plasma cholesterol levels in dwarf and transgenic mice, while low isoflavone diet reduced plasma triglycerides in most of the examined genotypes. The effects of low isoflavone and high isoflavone diets on the levels of free and esterified cholesterol in the liver were strongly genotype-dependent. Fasting blood glucose levels were reduced and glucose tolerance improved by both low isoflavone and high isoflavone diets in growth hormone-transgenic mice and in their normal siblings. Glucose tolerance was also improved by high-isoflavone diet in growth hormone receptor knockout mice. Lifespan was increased by low isoflavone diet in normal mice from two of the examined stocks. High isoflavone diet increased lifespan in normal animals from one line, but reduced lifespan of normal mice from a different line. We conclude that dietary soy protein intake can improve plasma and hepatic lipid profiles, reduce fasting glucose, enhance capacity for glucose tolerance, and prolong life, but all of these effects are strongly genotype-dependent.

DNA uptake and repair enzyme access to transfected DNA is under reported by gene expression

Gene expression is the typical biological end point of interest following transfection. However, transcription may not accurately assess DNA uptake, or the ability of transfected DNA to be acted on by other enzymatic pathways. We have compared DNA uptake to gene expression and the unrelated enzymatic process of DNA double strand break (DSB) repair. Transfection efficiency (at limiting DNA concentration) was assessed as a function of DNA uptake and gene expression in the DSB repair proficient WI38VA13 and MO59K cell lines and the DSB repair defective cell line MO59J, by comparing eGFP expression from the pHygEGFP expression vector with uptake of rhodamine labeled linear pSP189 plasmid (3:1). Repair proficient cells expressed eGFP most efficiently, but never approached DNA uptake levels (>or=90%). Although transfected DNAs were stable in repair proficient cells and degraded in MO59J cells, most cells did not express eGFP, but in the repair proficient cells linear DNA did undergo DSB repair.

Repair of radiation-induced DNA double-strand breaks is dependent upon radiation quality and the structural complexity of double-strand breaks

Mammalian cells primarily repair DSBs by nonhomologous end joining (NHEJ). To assess the ability of human cells to mediate end joining of complex DSBs such as those produced by chemicals, oxidative events, or high- and low-LET radiation, we employed an in vitro double-strand break repair assay using plasmid DNA linearized by these various agents. We found that human HeLa cell extracts support end joining of complex DSBs and form multimeric plasmid products from substrates produced by the radiomimetic drug bleomycin, 60Co gamma rays, and the effects of 125I decay in DNA. End joining was found to be dependent on the type of DSB-damaging agent, and it decreased as the cytotoxicity of the DSB-inducing agent increased. In addition to the inhibitory effects of DSB end-group structures on repair, NHEJ was found to be strongly inhibited by lesions proximal to DSB ends. The initial repair rate for complex non-ligatable bleomycin-induced DSBs was sixfold less than that of similarly configured (blunt-ended) but less complex (ligatable) restriction enzyme-induced DSBs. Repair of DSBs produced by gamma rays was 15-fold less efficient than repair of restriction enzyme-induced DSBs. Repair of the DSBs produced by 125I was near the lower limit of detection in our assay and was at least twofold lower than that of gamma-ray-induced DSBs. In addition, DSB ends produced by 125I were shown to be blocked by 3'-nucleotide fragments: the removal of these by E. coli endonuclease IV permitted ligation.

In vitro repair of complex unligatable oxidatively induced DNA double-strand breaks by human cell extracts

We describe a new assay for in vitro repair of oxidatively induced DNA double-strand breaks (DSBs) by HeLa cell nuclear extracts. The assay employs linear plasmid DNA containing DNA DSBs produced by the radiomimetic drug bleomycin. The bleomycin-induced DSB possesses a complex structure similar to that produced by oxidative processes and ionizing radiation. Bleomycin DSBs are composed of blunt ends or ends containing a single 5'-base overhang. Regardless of the 5'-end structure, all bleomycin-induced DSBs possess 3'-ends blocked by phosphoglycolate. Cellular extraction and initial end joining conditions for our assay were optimized with restriction enzyme-cleaved DNA to maximize ligation activity. Parameters affecting ligation such as temperature, time, ionic strength, ATP utilization and extract protein concentration were examined. Similar reactions were performed with the bleomycin-linearized substrate. In all cases, end-joined molecules ranging from dimers to higher molecular weight forms were produced and observed directly in agarose gels stained with Vistra Green and imaged with a FluorImager 595. This detection method is at least 50-fold more sensitive than ethidium bromide and permits detection of </=0.25 ng double-stranded DNA per band in post-electrophoretically stained agarose gels. Consequently, our end-joining reaction requires </=100 ng substrate DNA and >/=50% conversion of substrate to product is achieved with simple substrates such as restriction enzyme-cleaved DNA. Using our assay we have observed a 6-fold lower repair rate and a lag in reaction initiation for bleomycin-induced DSBs as compared to blunt-ended DNA. Also, end joining reaction conditions are DSB end group dependent. In particular, bleomycin-induced DSB repair is considerably more sensitive to inhibition by increased ionic strength than repair of blunt-ended DNA.

Gene targeted agents: new opportunities for rational drug development

In addition to traditional drug development methods designed to modulate the activity of protein targets, knowledge of disease gene DNA sequences provides an opportunity for the highly rational design of therapeutic agents that act at the DNA level through sequence-specific interactions. Among the ligands capable of binding DNA in a precise, sequence-specific manner are oligonucleotides, peptide nucleic acids and polyamides. Various strategies employing these agents to either transiently or permanently alter gene expression have been investigated over the past decade. During the past two to three years, important steps have been taken to illustrate the therapeutic potential of these ligands. Triple-helix (triplex) forming oligonucleotides have been particularly effective DNA-targeting agents with a wide range of applications, including the positive and negative transcriptional regulation of target genes, as well as the controlled delivery of site-specific mutations. This review will focus upon recent advances involving the use of sequence-specific DNA-binding ligands to modify gene expression and/or structure, with particular emphasis on the use of triplex-forming oligonucleotides in these roles.

Development of DNA-based radiopharmaceuticals carrying Auger-electron emitters for anti-gene radiotherapy

Targeting of radiation damage to specific DNA sequences is the essence of antigene radiotherapy. This technique also provides a tool to study molecular mechanisms of DNA repair on a defined, single radiodamaged site. We achieved such sequence-specific radiodamage by combining the highly localized DNA damage produced by the decay of Auger-electron-emitters such as 125I with the sequence-specific action of triplex-forming oligonucleotides (TFO). TFO complementary to polypurine-polypyrimidine regions of human genes were synthesized and labeled with 125I-dCTP by the primer extension method. 125I-TFO were delivered into cells with several delivery systems. In addition, human enzymes capable of supporting DNA single-strand-break repair were isolated and assessed for their role in the repair of this lesion. Also, the mutagenicity and repairability of 125I-TFO-induced double strand breaks (DSB) were assessed by repair of a plasmid possessing a site-specific DSB lesion. Using plasmids containing target polypurine-polypyrimidine tracts, we obtained the fine structure of sequence-specific DNA breaks produced by decay of 125I with single-nucleotide resolution. We showed that the designed 125I-TFO in nanomolar concentrations could bind to and introduce double-strand breaks into the target sequences in situ, i.e., within isolated nuclei and intact digitonin-permeabilized cells. We also showed 125I-TFO-induced DSB to be highly mutagenic lesions resulting in a mutation frequency of nearly 80%, with deletions comprising the majority of mutations. The results obtained demonstrate the ability of 125I-TFO to target specific sequences in their natural environment--within eucaryotic nucleus. Repair of 125I-TFO-induced DNA damage should typically result in mutagenic gene inactivation.

A cooperative interaction between soy protein and its isoflavone-enriched fraction lowers hepatic lipids in male obese Zucker rats and reduces blood platelet sensitivity in male Sprague-Dawley rats

Soy protein diets lower plasma cholesterol in hyperlipoproteinemic human subjects, as well as in animal models. We fed 7-wk-old male obese (fa/fa) and lean Zucker rats a modified AIN-76 diet (20 g protein/kg diet) containing casein (C), low isoflavone soy protein (38 mg isoflavones/kg diet; LI), or high isoflavone soy protein (578 mg isoflavones/kg diet; HI) for 70 d. In obese rats, plasma total cholesterol was 21 and 29% lower in the LI and HI groups, respectively, than in the C group (P: </= 0.004). Liver weight and liver triglyceride and cholesteryl ester concentrations were 27, 33 and 46% lower, respectively, in the LI group than in the C group (P: < 0.003). These liver measurements were 23, 24 and 57% lower, respectively, in the HI group than in the LI group (P: < 0.05). In a complementary study, 5-wk-old male Sprague-Dawley rats were fed the same C, LI and HI diets for 42 d. Thrombin-mediated platelet serotonin release in vitro was 13% lower in the HI group than in the C group (P: = 0.003). In a third study, 7-wk-old male Sprague-Dawley rats were fed either a modified AIN-76 control diet or a high fat casein-based atherogenic diet (140 g fat, 12 g cholesterol, and 2 g cholic acid/kg diet) with or without a soy isoflavones extract (983 mg isoflavones/kg diet) for 63 d. Addition of the isoflavones extract to the atherogenic diet lowered the liver triglyceride concentration by 33% relative to the atherogenic diet without isoflavones (P: = 0.0001). Our studies suggest that the hypocholesterolemic mechanism of dietary soy protein involves a cooperative interaction between the protein and isoflavone-enriched fraction that lowers hepatic lipid concentrations. We speculate that modulation of liver and plasma lipid homeostasis can also lower blood platelet sensitivity.

Absolute structure determination of the highly biologically active bisdehydrodoisynolic acids

In a project designed to relate the unexpected in vivo and in vitro properties exhibited by (+)- and (-)-bisdehydrodoisynolic acid with their absolute stereochemical structure, an X-ray crystal-structure analysis was undertaken of the highly estrogenic, poorly binding (-) enantiomer. (1) and (13)C NMR spectra are also reported for the first time. The crystal structure shows the cis juxtaposition of the carboxyl and ethyl groups, which are separated by a large torsion angle, and that only the carbon atom holding the carboxyl group is out of the plane in which the remainder of the fused three-ring moiety lies. The crystal structure, which unequivocally characterizes the (-) enantiomer as cis-13(S),14(R) and, implicitly, the (+) enantiomer as cis-13(R),14(S), will be useful in continued studies aimed at explaining the selective estrogen receptor modulation (SERM) of these enantiomers which, in some cases, produces significantly different end-organ effects compared to those of estradiol, in both males and females, affording the promise of a variety of therapeutic and pharmacologic applications.

Ovarian follicle apoptosis in bovine growth hormone transgenic mice

Growth hormone directly or via insulin like-growth factor-I has been shown to inhibit preovulatory follicle apoptosis, which is the underlying mechanism of follicular atresia. We studied the levels of apoptosis in the ovaries of transgenic mice expressing bovine growth hormone. Female bovine growth hormone transgenic mice (n = 10) and nontransgenic litter mates (n = 8) were killed at early proestrus. Ovaries were collected, sectioned, and processed using a nonradioactive in situ method for apoptosis detection. Follicles were classified and counted on the basis of size and level of apoptosis. Our results demonstrate that the percentage of ovarian follicles containing apoptotic cells was lower in transgenic versus normal mice (30% vs. 46%; P < 0.05). The percentage of follicles undergoing heavy apoptosis was lower (P < 0.05) in transgenic versus control animals in preovulatory and early antral follicles, but it was not different in preantral follicles. The percentage of healthy preovulatory follicles was also higher in transgenic versus normal mice (7.4% vs. 4.3%; P < 0.05). These results indicate that growth hormone overexpression in transgenic mice significantly decreases follicle apoptosis, and thus atresia in the mouse ovary, therefore leading to increased propensity for ovulation in these animals.

Effects of growth hormone overexpression and growth hormone resistance on neuroendocrine and reproductive functions in transgenic and knock-out mice

Transgenic mice overexpressing growth hormone (GH) exhibit alterations in the function of the hypothalamic-pituitary-gonadal (HPG) axis and the H-P-adrenal axis. Alterations in the turnover of hypothalamic neurotransmitters, in plasma hormone levels, and in regulation of their release are associated with reproductive deficits, particularly in females. Results reported after publication of our minireview on this subject provided evidence that GH-transgenic mice have increased binding of GH to GH binding proteins in plasma, are hyperinsulinemic and insulin resistant, and have major alterations in energy budgets with increased allocation to growth. Reduced life span and fertility of these animals may be related to insufficient allocation of energy to reproduction and maintenance. Growth hormone resistance induced by transgenic expression of an antagonistic bGH analog or by targeted disruption (knock-out, KO) of the GH receptor (GH-R) gene leads to dramatic suppression of plasma levels of insulin-like growth factor-1 (IGF-1), and dwarf phenotype due to reduced growth and increased adiposity. In both models of GH resistance, there are marked reproductive deficits in females, decline of breeding performance of males, and alterations in the function of the HPG axis. In GH-R-KO females, puberty is delayed, and litter size is reduced. Fetal weights are reduced whereas placental weights are increased, and the weight of newborn pups is reduced despite an increase in the length of gestation. In GH-R-KO males, copulatory behavior and fertility are reduced, plasma PRL is elevated, and responses to luteinizing hormone releasing hormone (LHRH) in vivo and to LH in vitro are suppressed. However, reproductive deficits in GH-R-KO mice are very mild when compared to those described previously in IGF-KO animals. Apparently, the amounts of IGF-1 that may be produced locally in the absence of GH stimulation are sufficient for sexual maturation and fertility in both sexes, whereas quantitative deficits in reproductive function reflect absence of GH-dependent IGF-1 production and other consequences of eliminating GH signaling. The reproduction phenotype of the GH-R-KO mice is also mild when compared to dwarf mice that lack GH, prolactin (PRL), and thyroid stimulating hormone (TSH). This is presumably related to the presence of redundant mechanisms in the stimulatory control of the gonads by the pituitary and the ability of animals capable of producing PRL and TSH to compensate partially for the absence of GH signaling.

Gene targeted DNA double-strand break induction by (125)I-labeled triplex-forming oligonucleotides is highly mutagenic following repair in human cells

A parallel binding motif 16mer triplex-forming oligonucleotide (TFO) complementary to a polypurine-polypyrimidine target region near the 3'-end of the SupF gene of plasmid pSP189 was labeled with [5-(125)I]dCMP at position 15. Following triplex formation and decay accumulation, radiation-induced site-specific double-strand breaks (DSBs) were produced in the pSP189 SupF gene. Bulk damaged DNA and the isolated site-specific DSB-containing DNA were separately transfected into human WI38VA13 cells and allowed to repair prior to recovery and analysis of mutants. Bulk damaged DNA had a relatively low mutation frequency of 2.7 x 10(-3). In contrast, the isolated linear DNA containing site-specific DSBs had an unusually high mutation frequency of 7.9 x 10(-1). This was nearly 300-fold greater than that observed for the bulk damaged DNA mixture, and >1.5 x 10(4)-fold greater than background. The mutation spectra displayed a high proportion of deletion mutants targeted to the(125)I binding position within the SupF gene for both bulk damaged DNA and isolated linear DNA. Both spectra were characterized by complex mutations with mixtures of changes. However, mutations recovered from the linear site-specific DSB-containing DNA presented a much higher proportion of complex deletion mutations.

Determination of human DNA polymerase utilization for the repair of a model ionizing radiation-induced DNA strand break lesion in a defined vector substrate

Human DNA polymerase and DNA ligase utilization for the repair of a major class of ionizing radiation-induced DNA lesion [DNA single-strand breaks containing 3'-phosphoglycolate (3'-PG)] was examined using a novel, chemically defined vector substrate containing a single, site-specific 3'-PG single-strand break lesion. In addition, the major human AP endonuclease, HAP1 (also known as APE1, APEX, Ref-1), was tested to determine if it was involved in initiating repair of 3'-PG-containing single-strand break lesions. DNA polymerase beta was found to be the primary polymerase responsible for nucleotide incorporation at the lesion site following excision of the 3'-PG blocking group. However, DNA polymerase delta/straightepsilon was also capable of nucleotide incorporation at the lesion site following 3'-PG excision. In addition, repair reactions catalyzed by DNA polymerase beta were found to be most effective in the presence of DNA ligase III, while those catalyzed by DNA polymerase delta/straightepsilon appeared to be more effective in the presence of DNA ligase I. Also, it was demonstrated that the repair initiating 3'-PG excision reaction was not dependent upon HAP1 activity, as judged by inhibition of HAP1 with neutralizing HAP1-specific polyclonal antibody.

Comparative effects of the selective estrogen receptor modulators (-)-, (+)- and (+/-)-Z bisdehydrodoisynolic acids on metabolic and reproductive parameters in male and female rats

Doisynolic acids are non-steroidal estrogenic compounds originally obtained from alkali fusion of estrone and equilenin. Z-bisdehydrodoisynolic acids (Z-BDDA) exhibit a low binding affinity accompanied by a disproportionately high biologic activity. Two experiments were designed to investigate the chronic effects of (+)-, (-)- and (+/-)-Z-BDDA and (+)-17beta-estradiol (E2) in male and female rats. The (+)-, (-)- and (+/-)-forms Z-BDDA were prepared and injected, daily for four to six weeks into male and female rats and changes in body weight, food intake, metabolic parameters, and reproductive parameters were investigated. Results from both experiments demonstrate that in male and female rats, (+)- and (+/-)-Z-BDDA had similar estrogenic effects on reproductive organ weight. Surprisingly, (-)-Z-BDDA did not induce the increase in uterine weight observed with (+)- and (+/-)-Z-BDDA and E2, demonstrating selective estrogen receptor modulation (SERM). Beneficial metabolic effects, although compound- and gender-specific, included a significant weight repression, reduction in cholesterol, reduction in blood glucose, and positive alterations in body fat distribution. Future research defining the optimal dosages of (-)-Z-BDDA that will maximize beneficial effects and minimize undesirable effects on reproductive tissues will lead to more efficacious treatment options for endocrine-responsive conditions in males and females.

Mutation of the uracil DNA glycosylase gene detected in glioblastoma

Despite extensive characterization of genetic changes in gliomas, the underlying etiology of these tumors remains largely unknown. Spontaneous DNA damage due to hydrolysis, methylation, and oxidation is a frequent event in the brain. Failure of DNA repair following this damage may contribute to tumorigenesis of gliomas. Uracil DNA glycosylase (UDG), an enzyme which excises uracil from DNA, is an important component of the base excision repair pathway. The sequence of a human homologue of uracil DNA glycosylase gene (UNG) has been recently identified. We performed PCR-based SSCP mutational analysis of UNG in 11 sporadic gliomas (six glioblastomas, two anaplastic astrocytomas, and three oligodendrogliomas) and eight glioblastoma cell lines. One out of six sporadic glioblastomas had a point mutation in exon 3, which resulted in a missense mutation in codon 143. None of the eight glioblastoma cell lines or the five non-glioblastoma sporadic gliomas showed a mutation. Genetic alterations of UNG may play a role in the development of a subset of primary glioblastomas.

In situ amplification of the cytochrome P-450 cholesterol side-chain cleavage enzyme mRNA in single porcine granulosa cells by IGF-1 and FSH acting alone or in concert

To investigate the cellular mechanisms and cell-cell heterogeneity of the actions of insulin-like growth factor-1 (IGF-1) and follicle-stimulating hormone (FSH) exerted alone and in combination on ovarian cholesterol side-chain cleavage gene expression (P450scc mRNA) in (pig) granulosa cells, we implemented semiquantitative in situ molecular hybridization at the single target-cell level. To this end, a 1-kb cDNA specific to the catalytic region of porcine p450scc gene was subcloned into pGEM-3 and directionally transcribed in vitro in the presence of 35S-dUTP to yield radiolabeled antisense (and sense, negative control) cRNA hybridization probes. Swine granulosa cells harvested nonenzymatically from immature (1-5 mm) Graafian follicles were anchored on eight-chamber multiwell slides and treated with control solvent, human recombinant IGF-1 (10nM), ovine FSH (10nM), or both hormones, for 48 h to stimulate progestin biosynthesis maximally. After appropriate cellular permeabilization, cRNA hybridization, and solvent washes, granulosa cells were exposed to Kodak NTB-2 emulsion for 6 wk. Semiquantitative automated image analysis software (NIH IMAGE 1.5) was used to evaluate the number of silver grains deposited/20,000 square pixels. Specificity controls included labeled sense riboprobe, pretreatment with RNase, and 100-fold molar excess unlabeled cRNA. Grain counts and their distributions were examined by ANOVA and the Wilcoxon nonparametric test. The mean number of silver grains deposited per granulosa cell increased over control (reflecting specific P450scc mRNA expression) in granulosa cells pretreated with IGF-1, FSH, or IGF-1 + FSH (p < 0.05 by ANOVA). The rank order of abundance of expression of P450scc mRNA (grains/ovarian cell) was (IGF-1 + FSH) > FSH > IGF-1 > control treatment. Distributional analysis showed that each treatment introduced skewed distributions toward granulosa cells expressing more P450scc per cell than controls (p < 0.01). The median grain count of granulosa cells treated with FSH was significantly increased over that of IGF-1 treatment (p < 0.05). Treatment with both IGF-1 and FSH further shifted the grain count distribution per cell to favor granulosa cells expressing more P450scc mRNA compared to IGF-1 or FSH treatment alone (p < 0.05). Accordingly, a demonstrable mechanism of IGF-1 and FSH's regulation of specific P450scc gene expression at the single granulosa cell level is amplification in the number of target ovarian cells expressing this enzymatically rate-determining gene transcript. Interestingly, the induction of P450scc mRNA is not sufficient to explain fully the synergistic increases in progesterone accumulation driven by combined treatment with IGF-1 and FSH, thus suggesting that other steroidogenic control points are also targets of IGF-1/FSH action.

Identification of defective illegitimate recombinational repair of oxidatively-induced DNA double-strand breaks in ataxia-telangiectasia cells

Ataxia-telangiectasia (A-T) is an autosomal-recessive lethal human disease. Homozygotes suffer from a number of neurological disorders, as well as very high cancer incidence. Heterozygotes may also have a higher than normal risk of cancer, particularly for the breast. The gene responsible for the disease (ATM) has been cloned, but its role in mechanisms of the disease remain unknown. Cellular A-T phenotypes, such as radiosensitivity and genomic instability, suggest that a deficiency in the repair of DNA double-strand breaks (DSBs) may be the primary defect; however, overall levels of DSB rejoining appear normal. We used the shuttle vector, pZ189, containing an oxidatively-induced DSB, to compare the integrity of DSB rejoining in one normal and two A-T fibroblast cells lines. Mutation frequencies were two-fold higher in A-T cells, and the mutational spectrum was different. The majority of the mutations found in all three cell lines were deletions (44-63%). The DNA sequence analysis indicated that 17 of the 17 plasmids with deletion mutations in normal cells occurred between short direct-repeat sequences (removing one of the repeats plus the intervening sequences), implicating illegitimate recombination in DSB rejoining. The combined data from both A-T cell lines showed that 21 of 24 deletions did not involve direct-repeats sequences, implicating a defect in the illegitimate recombination pathway. These findings suggest that the A-T gene product may either directly participate in illegitimate recombination or modulate the pathway. Regardless, this defect is likely to be important to a mechanistic understanding of this lethal disease.

Nature of endothelin binding in the porcine ovary

We investigated the nature of endothelin (ET) binding in the porcine ovary. We demonstrated the presence of high affinity (Kd = 0.72; 95% confidence interval = 0.43-1.1 nM) binding sites for ET-1 in the porcine ovary. The binding capacity for this ET-1-specific binding site was 97 pmol/micrograms DNA (95% confidence interval = 90-107). Autoradiographic studies showed that putative ET receptors reside in the granulosa cell layer of the maturing Graafian follicle and in the vascular components of the corpora lutea. The relative abundance of ET receptors was greatest in granulosa cells of large antral follicles, whereas ET binding was absent in granulosa cells of preantral follicles and in luteal cells. ET binding by cultured granulosa cells was further characterized by RRA and shown to exhibit a rank order of binding affinities for different ET isopeptides. The observed rank order indicates that the ET receptors present on granulosa cells are of the ET(A) receptor subtype. The radioreceptor studies also indicated that granulosa cells collected from large antral follicles (9-10 mm in diameter) have a greater binding capacity for [125I]ET-1 in culture than granulosa cells collected from smaller follicles. When cultured granulosa cells were exposed to 100 nM ET-1 or 14 nM 12-O-tetradecanoylphorbol 13-acetate overnight, the percentage of specific [125I]ET-1 binding was reduced (12% and 50%, respectively), indicating a down-regulation of the ET receptor by these treatments. In summary, we have characterized the distribution, isopeptide specificity, relative abundance, and down-regulation of putative ovarian endothelin receptors of subtype ET(A) on swine granulosa cells. Such results in conjunction with other available literature strongly suggest that granulosa cells of maturing Graafian follicles are targeted by ET-1. An additional physiological role for ET-1 in the ovary is suggested by the presence of putative ET receptors in the vasculature of the corpus luteum.

Removal of 3'-phosphoglycolate from DNA strand-break damage in an oligonucleotide substrate by recombinant human apurinic/apyrimidinic endonuclease 1

A recombinant human AP endonuclease, HAP1, was constructed and characterized with respect to its ability to recognize and act upon a model double-stranded 39-mer oligodeoxyribonucleotide substrate containing a strand break site with 3'-phosphoglycolate and 5'-phosphate end-group chemistries. This oligodeoxyribonucleotide substrate exactly duplicates the chemistry and configuration of a major DNA lesion produced by ionizing radiation. HAP1 was found to recognize the strand break, and catalyze the release of the 3'-phosphoglycolate as free phosphoglycolic acid. The enzyme had a Vmax of 0.1 fmole/min/pg of HAP1 protein, and a Km of 0.05 microM for the 3'-phosphoglycolate strand break lesion. The mechanism of catalysis was hydrolysis of the phosphate ester bond between the 3'-phosphoglycolate moiety and the 3'-carbon of the adjacent dGMP moiety within the oligonucleotide. The resulting DNA contained a 3'-hydroxyl which supported nucleotide incorporation by E. coli DNA polymerase I large fragment. AP endonucleolytic activity of HAP1 was examined using an analogous double-stranded 39-mer oligodeoxyribonucleotide substrate, in which the strand break site was replaced by an apyrimidinic site. The Vmax and Km for the AP endonuclease reaction were 68 fmole/min/pg of HAP1 protein and 0.23 microM, respectively.

Purification and characterization of the herpes simplex virus type 2-encoded uracil-DNA glycosylase

The herpes simplex virus type 2 (HSV-2) uracil-DNA glycosylase (UNG) was from the nuclei of infected KB cells using ion exchange, affinity, and chromatofocusing chromatography techniques. Chromatography on DNA cellulose revealed two distinct HSV-2-encoded UNGs. One species, designated A, was purified approximately 324-fold, while the second species, designated B, was purified approximately 130-fold. The HSV UNG species B was observed to unidirectionally convert to the A species, suggesting that the B species binding to DNA cellulose may be the result of an association with other DNA binding proteins. SDS-PAGE demonstrated that both species A and B had molecular weights of 32,000. The HSV-2-encoded UNGs could be distinguished from the cellular nuclear UNG based upon differences in their behavior on the chromatography matrixes and by their molecular weights. There were no significant differences in the biochemical properties of the HSV-2-encoded or nuclear UNGs. Furthermore, all of these UNGs reacted with a monoclonal antibody produced against the human placental UNG. These data support recent studies, at both the DNA and the amino acid levels, which have demonstrated that this enzyme is highly conserved between species.

Ontogeny of the epidermal growth factor receptor during development of the fetal bovine mesonephros and associated organs of the urogenital tract

A primary cell culture system was developed to study the epidermal growth factor (EGF) receptor in the fetal bovine mesonephros and its urogenital derivatives. Radioreceptor assays demonstrated EGF binding as early as Day 37 in mesonephric cells and in cells derived from the fetal reproductive ducts, gonads, and metanephros--all mesonephric derivatives. Immunocytochemical studies revealed that EGF receptors were localized in the ductal and tubular epithelium of these urogenital organs. EGF induced DNA synthesis and tyrosine phosphorylation in the bovine mesonephric cells, suggesting that EGF receptors detected in these cells were functional. In addition, transforming growth factor alpha, the putative fetal ligand for the EGF receptor, was found to specifically compete for EGF binding to the receptor, as well as to induce DNA synthesis in a manner similar to that of EGF. Estrogen did not regulate EGF receptors or specifically bind to bovine mesonephric cells. The development of estrogen receptors in the bovine species occurs markedly later than that of the EGF receptor, in contrast to the mouse, where both receptors are observed at very early stages of reproductive tract development.