Novel use of zebrafish as a vertebrate model to screen radiation protectors and sensitizers

Ecotoxicity and environmental safety assessment of two-dimensional niobium carbides (MXenes)

Two-dimensional (2D) MXenes have gained great interest in water treatment, biomedical, and environmental applications. The antimicrobial activity and cell toxicity of several MXenes including Nb4C3Tx and Nb2CTx have already been explored. However, potential side effects related to Nb-MXene toxicity, especially on aquatic pneuma, have rarely been studied. Using zebrafish embryos, we investigated and compared the potential acute toxicity between two forms of Nb-MXene: the multilayer (ML-Nb4C3Tx, ML-Nb2CTx) and the delaminated (DL-Nb2CTx, and DL-Nb4C3Tx) Nb-MXene. The LC50 of ML-Nb4C3Tx, ML-Nb2CTx, DL-Nb2CTx, and DL-Nb4C3Tx were estimated to be 220, 215, 225, and 128 mg/L, respectively. Although DL-Nb2CTx, and DL-Nb4C3Tx derivatives have similar sizes, DL-Nb4C3Tx not only shows the higher mortality (LC50 = 128 mg/L Vs 225 mg/L), but also the highest teratogenic effect (NOEC = 100 mg/L Vs 200 mg/L). LDH release assay suggested more cell membrane damage and a higher superoxide anion production in DL-Nb4C3Tx than DL-Nb2CTx,. Interestingly, both DL-Nb-MXene nanosheets showed insignificant cardiac, hepatic, or behavioral toxic effects compared to the negative control. Embryos treated with the NOEC of DL-Nb2CTx presented hyperlocomotion, while embryos treated with the NOEC of DL-Nb4C3Tx presented hyperlocomotion, suggesting developmental neurotoxic effect and muscle impairment induced by both DL-Nb-MXene. According to the Fish and Wildlife Service (FSW) Acute Toxicity Rating Scale, all tested Nb-MXene nanosheets were classified as "Practically not toxic". However, DL-Nb4C3Tx should be treated with caution as it might cause a neurotoxic effect on fauna when it ends up in wastewater in high concentrations.

Changes in repair pathways of radiation-induced DNA double-strand breaks at the midblastula transition in Xenopus embryo

Ionizing radiation (IR) causes DNA damage, particularly DNA double-strand breaks (DSBs), which have significant implications for genome stability. The major pathways of repairing DSBs are homologous recombination (HR) and nonhomologous end joining (NHEJ). However, the repair mechanism of IR-induced DSBs in embryos is not well understood, despite extensive research in somatic cells. The externally developing aquatic organism, Xenopus tropicalis, serves as a valuable model for studying embryo development. A significant increase in zygotic transcription occurs at the midblastula transition (MBT), resulting in a longer cell cycle and asynchronous cell divisions. This study examines the impact of X-ray irradiation on Xenopus embryos before and after the MBT. The findings reveal a heightened X-ray sensitivity in embryos prior to the MBT, indicating a distinct shift in the DNA repair pathway during embryo development. Importantly, we show a transition in the dominant DSB repair pathway from NHEJ to HR before and after the MBT. These results suggest that the MBT plays a crucial role in altering DSB repair mechanisms, thereby influencing the IR sensitivity of developing embryos.

Dose and dose rate dependence of the tissue sparing effect at ultra-high dose rate studied for proton and electron beams using the zebrafish embryo model

PURPOSE

A better characterization of the dependence of the tissue sparing effect at ultra-high dose rate (UHDR) on physical beam parameters (dose, dose rate, radiation quality) would be helpful towards a mechanistic understanding of the FLASH effect and for its broader clinical translation. To address this, a comprehensive study on the normal tissue sparing at UHDR using the zebrafish embryo (ZFE) model was conducted.

METHODS

One-day-old ZFE were irradiated over a wide dose range (15-95 Gy) in three different beams (proton entrance channel, proton spread out Bragg peak and 30 MeV electrons) at UHDR and reference dose rate. After irradiation the ZFE were incubated for 4 days and then analyzed for four different biological endpoints (pericardial edema, curved spine, embryo length and eye diameter).

RESULTS

Dose-effect curves were obtained and a sparing effect at UHDR was observed for all three beams. It was demonstrated that proton relative biological effectiveness and UHDR sparing are both relevant to predict the resulting dose response. Dose dependent FLASH modifying factors (FMF) for ZFE were found to be compatible with rodent data from the literature. It was found that the UHDR sparing effect saturates at doses above ∼ 50 Gy with an FMF of ∼ 0.7-0.8. A strong dose rate dependence of the tissue sparing effect in ZFE was observed. The magnitude of the maximum sparing effect was comparable for all studied biological endpoints.

CONCLUSION

The ZFE model was shown to be a suitable pre-clinical high-throughput model for radiobiological studies on FLASH radiotherapy, providing results comparable to rodent models. This underlines the relevance of ZFE studies for FLASH radiotherapy research.

Imaging the radioprotective effect of amifostine in the developing brain using an apoptosis-reporting transgenic zebrafish

PURPOSE

Normal tissue radioprotectants alleviate radiation-induced damages and preserve critical organ functions. Investigating their efficacy in vivo remains challenging, especially in enclosed organs like the brain. An animal model that enables direct visualization of radiation-induced apoptosis while possessing the structural complexity of a vertebrate brain facilitates these studies in a precise and effective manner.

MATERIALS AND METHODS

We employed a secA5 transgenic zebrafish expressing secreted Annexin V fused with a yellow fluorescent protein to visualize radiation-induced apoptosis in vivo. We developed a semi-automated imaging method for standardized acquisition of apoptosis signals in batches of zebrafish larvae. Using these approaches, we studied the protective effect of amifostine (WR-2721) in the irradiated zebrafish larval brain.

RESULTS

Upon 2 Gy total-body 137Cs irradiation, increased apoptosis could be visualized at high resolution in the secA5 brain at 2, 24, and 48 hour post irradiation (hpi). Amifostine treatment (4 mM) during irradiation reduced apoptosis significantly at 24 hpi and preserved Wnt active cells in the larval brain. When the 2 Gy irradiation was delivered in combination with cisplatin treatment (0.1 mM), the radioprotective effect of amifostine was also observed.

CONCLUSIONS

Our study reveals the radioprotective effect of amifostine in the developing zebrafish larval brain, and highlights the utility of secA5 transgenic zebrafish as a novel system for investigating normal tissue radioprotectants in vivo.

Radiation Sensitivity: The Rise of Predictive Patient-Derived Cancer Models

Patient-derived cancer models have been used for decades to improve our understanding of cancer and test anticancer treatments. Advances in radiation delivery have made these models more attractive for studying radiation sensitizers and understanding an individual patient's radiation sensitivity. Advances in the use of patient-derived cancer models lead to a more clinically relevant outcome, although many questions remain regarding the optimal use of patient-derived xenografts and patient-derived spheroid cultures. The use of patient-derived cancer models as personalized predictive avatars through mouse and zebrafish models is discussed, and the advantages and disadvantages of patient-derived spheroids are reviewed. In addition, the use of large repositories of patient-derived models to develop predictive algorithms to guide treatment selection is discussed. Finally, we review methods for establishing patient-derived models and identify key factors that influence their use as both avatars and models of cancer biology.

In Vivo Imaging of Radiation-Induced Apoptosis at Single-Cell Resolution in Transgenic Zebrafish Embryos

Among the various types of cell death induced by ionizing radiation, apoptosis is a highly regulated and well-characterized form. Investigating radiation-induced apoptosis in an intact organism offers advantages in capturing the dynamics of apoptosis under preserved physiology, although high resolution imaging remains challenging. Owing to their optical transparency and genetic amenability, zebrafish is an ideal animal model for research into this aspect. In this study, we present a secA5 transgenic zebrafish expressing genetically encoded secreted ANNEXIN V fused with mVenus, a yellow fluorescent protein that enables reporting of radiation-induced apoptosis. Using in vivo imaging approach, we show that after 2 Gy total-body irradiation, apoptosis could be visualized at single-cell resolution in different cell types throughout the embryo. Elevated apoptosis could be imaged and quantified in the neuroepithelium of the embryonic brain, as well as the proliferative zone and parenchyma of the larval brain. In addition, clearance of apoptotic cells by microglia, the professional phagocytes residing in the brain, could be imaged at single-cell resolution in irradiated larvae. These results establish transgenic secA5 zebrafish as a useful and versatile in vivo system for investigating the dynamic process of radiation-induced apoptosis.

Zebrafish as a Mainstream Model for In Vivo Systems Pharmacology and Toxicology

Pharmacology and toxicology are part of a much broader effort to understand the relationship between chemistry and biology. While biomedicine has necessarily focused on specific cases, typically of direct human relevance, there are real advantages in pursuing more systematic approaches to characterizing how health and disease are influenced by small molecules and other interventions. In this context, the zebrafish is now established as the representative screenable vertebrate and, through ongoing advances in the available scale of genome editing and automated phenotyping, is beginning to address systems-level solutions to some biomedical problems. The addition of broader efforts to integrate information content across preclinical model organisms and the incorporation of rigorous analytics, including closed-loop deep learning, will facilitate efforts to create systems pharmacology and toxicology with the ability to continuously optimize chemical biological interactions around societal needs. In this review, we outline progress toward this goal.

Responses of hematopoietic cells after ionizing-irradiation in anemic adult medaka (Oryzias latipes)

PURPOSE

Hematopoietic tissues of vertebrates are highly radiation sensitive and the effects of ionizing radiation on the hematopoiesis have been studied in mammals and teleosts for decades. In this study, radiation responses in the kidney, the main hematopoietic organ in teleosts, were investigated in Japanese medaka (Oryzias latipes), which has been a model animal and a large body of knowledge has been accumulated in radiation biology.

METHODS

Kidney, the main hematopoietic tissue of adult medaka fish, was locally irradiated using proton and carbon ion beams irradiation system of Takasaki Ion Accelerator for Advanced Radiation Application (TIARA), QST, and the effects on peripheral blood cells and histology of the kidney were investigated.

RESULTS

When only kidneys were locally irradiated with proton or carbon ion beam (15 Gy), the hematopoietic cells in the irradiated kidney and cell density in the peripheral blood decreased 7 days after the irradiation in the same manner as after the whole-body irradiation with γ-rays (15 Gy). These results demonstrate that direct irradiation of the hematopoietic cells in the kidney induced cell death and/or cell cycle arrest and stopped the supply of erythroid cells. Then, the cell density in the peripheral blood recovered to the control level within 4 days and 7 days after the γ-ray and proton beam irradiation (15 Gy), respectively, while the cell density in the peripheral blood did not recover after the carbon ion beam irradiation (15 Gy). The hematopoietic cells in the irradiated kidneys temporarily decreased and recovered to the control level within 21 days after the γ-ray or proton beam irradiation (15 Gy), while it did not recover after the carbon ion beam irradiation (15 Gy). In contrast, the recovery of the cell density in the peripheral blood delayed when anemic medaka were irradiated 1 day after the administration of phenylhydrazine. With and without γ-ray irradiation, a large number of hematopoietic cells was still proliferating in the kidney 7 days after the anemia induction.

CONCLUSIONS

The results obtained strongly suggest that the hematopoietic stem cells in medaka kidney prioritize to proliferate and increase peripheral blood cells to eliminate anemia, even when they are damaged by high-dose irradiation.

Radioprotective effect of mistletoe extract on intestinal toxicity: in vivo study using adult zebrafish

PURPOSE

The intestine is a dose-limiting organ in the treatment of intra-abdominal cancer. We previously reported that the extract of mistletoe parasites on Quercus had a more potent radioprotective effect than amifostine in reducing the developmental toxicities of zebrafish embryos. In this study, radioprotection against intestinal toxicity was investigated in adult zebrafish.

METHODS

Wild-type adult AB zebrafish were exposed to 45-50 Gy of photon beam irradiation and/or treated with mistletoe extract orally 1 h before. The main endpoints of the study were survival and degree of deformation of the intestinal villi.

RESULTS

The median follow-up period was 10 d post-irradiation (range: 7-11 d). A total of 105 zebrafish were used, including 42 in the radiation alone, 42 in the radiation and mistletoe arms, and 21 control subjects (mistletoe alone, mock-irradiated arm). The rate of both significant deformity and death was 53% in the radiation-alone arm, whereas the corresponding rate was 30% in the radiation and mistletoe arms. Significant deformity-free survival rates at 10 d post-irradiation in the radiation alone, and radiation and mistletoe arms were 44.7% (95% confidence interval [CI]:20-54.3) and 68.4% (95% CI:53.8-86.8), respectively (p=.046). The radiation and mistletoe arms showed decreased expression of two of three inflammatory genes (IL-1β and IL-6) compared to the radiation alone group (p<.05).

CONCLUSION

The radioprotective effect against intestinal toxicity was successfully shown in an adult zebrafish model. This result suggests the possibility of clinical use of mistletoe extract for the treatment of abdominal cancers.

Metaphase-Based Cytogenetic Approach Identifies Radiation-Induced Chromosome and Chromatid Aberrations in Zebrafish Embryos

Metaphase-based cytogenetic methods based on scoring of chromosome aberrations for the estimation of the radiation dose received provide a powerful approach for evaluating the associated risk upon radiation exposure and form the bulk of our current knowledge of radiation-induced chromosome damages. They mainly rely on inducing quiescent peripheral lymphocytes into proliferation and blocking them at metaphases to quantify the damages at the chromosome level. However, human organs and tissues demonstrate various sensitivity towards radiation and within them, self-proliferating progenitor/stem cells are believed to be the most sensitive populations. The radiation-induced chromosome aberrations in these cells remain largely unknown, especially in the context of an intact living organism. Zebrafish is an ideal animal model for research into this aspect due to their small size and the large quantities of progenitor cells present during the embryonic stages. In this study, we employ a novel metaphase-based cytogenetic approach on zebrafish embryos and demonstrate that chromosome-type and chromatid-type aberrations could be identified in progenitor cells at different cell-cycle stages at the point of radiation exposure. Our work positions zebrafish at the forefront as a useful animal model for studying radiation-induced chromosome structural changes in vivo.

A versatile, automated and high-throughput drug screening platform for zebrafish embryos

Zebrafish provide a unique opportunity for drug screening in living animals, with the fast-developing, transparent embryos allowing for relatively high-throughput, microscopy-based screens. However, the limited availability of rapid, flexible imaging and analysis platforms has limited the use of zebrafish in drug screens. We have developed an easy-to-use, customisable automated screening procedure suitable for high-throughput phenotype-based screens of live zebrafish. We utilised the WiScan® Hermes High Content Imaging System to rapidly acquire brightfield and fluorescent images of embryos, and the WiSoft® Athena Zebrafish Application for analysis, which harnesses an Artificial Intelligence-driven algorithm to automatically detect fish in brightfield images, identify anatomical structures, partition the animal into regions and exclusively select the desired side-oriented fish. Our initial validation combined structural analysis with fluorescence images to enumerate GFP-tagged haematopoietic stem and progenitor cells in the tails of embryos, which correlated with manual counts. We further validated this system to assess the effects of genetic mutations and X-ray irradiation in high content using a wide range of assays. Further, we performed simultaneous analysis of multiple cell types using dual fluorophores in high throughput. In summary, we demonstrate a broadly applicable and rapidly customisable platform for high-content screening in zebrafish. This article has an associated First Person interview with the first author of the paper.

Models for Translational Proton Radiobiology-From Bench to Bedside and Back

The number of proton therapy centers worldwide are increasing steadily, with more than two million cancer patients treated so far. Despite this development, pending questions on proton radiobiology still call for basic and translational preclinical research. Open issues are the on-going discussion on an energy-dependent varying proton RBE (relative biological effectiveness), a better characterization of normal tissue side effects and combination treatments with drugs originally developed for photon therapy. At the same time, novel possibilities arise, such as radioimmunotherapy, and new proton therapy schemata, such as FLASH irradiation and proton mini-beams. The study of those aspects demands for radiobiological models at different stages along the translational chain, allowing the investigation of mechanisms from the molecular level to whole organisms. Focusing on the challenges and specifics of proton research, this review summarizes the different available models, ranging from in vitro systems to animal studies of increasing complexity as well as complementing in silico approaches.

Radioprotective Effects of Kelulut Honey in Zebrafish Model

Large doses of ionizing radiation can damage human tissues. Therefore, there is a need to investigate the radiation effects as well as identify effective and non-toxic radioprotectors. This study evaluated the radioprotective effects of Kelulut honey (KH) from stingless bee (Trigona sp.) on zebrafish (Danio rerio) embryos. Viable zebrafish embryos at 24 hpf were dechorionated and divided into four groups, namely untreated and non-irradiated, untreated and irradiated, KH pre-treatment and amifostine pre-treatment. The embryos were first treated with KH (8 mg/mL) or amifostine (4 mM) before irradiation at doses of 11 Gy to 20 Gy using gamma ray source, caesium-137 (137Cs). Lethality and abnormality analysis were performed on all of the embryos in the study. Immunohistochemistry assay was also performed using selected proteins, namely γ-H2AX and caspase-3, to investigate DNA damages and incidences of apoptosis. KH was found to reduce coagulation effects at up to 20 Gy in the lethality analysis. The embryos developed combinations of abnormality, namely microphthalmia (M), body curvature and microphthalmia (BM), body curvature with microphthalmia and microcephaly (BMC), microphthalmia and pericardial oedema (MO), pericardial oedema (O), microphthalmia with microcephaly and pericardial oedema (MCO) and all of the abnormalities (AA). There were more abnormalities developed from 24 to 72 h (h) post-irradiation in all groups. At 96 h post-irradiation, KH was identified to reduce body curvature effect in the irradiated embryos (up to 16 Gy). γ-H2AX and caspase-3 intensities in the embryos pre-treated with KH were also found to be lower than the untreated group at gamma irradiation doses of 11 Gy to 20 Gy and 11 Gy to 19 Gy, respectively. KH was proven to increase the survival rate of zebrafish embryos and exhibited protection against organ-specific abnormality. KH was also found to possess cellular protective mechanism by reducing DNA damage and apoptosis proteins expression.

Radiopharmaceutical Validation for Clinical Use

Radiopharmaceuticals are reemerging as attractive anticancer agents, but there are no universally adopted guidelines or standardized procedures for evaluating agent validity before early-phase trial implementation. To validate a radiopharmaceutical, it is desirous for the radiopharmaceutical to be specific, selective, and deliverable against tumors of a given, molecularly defined cancer for which it is intended to treat. In this article, we discuss four levels of evidence—target antigen immunohistochemistry, in vitro and in vivo preclinical experiments, animal biodistribution and dosimetry studies, and first-in-human microdose biodistribution studies—that might be used to justify oncology therapeutic radiopharmaceuticals in a drug-development sequence involving early-phase trials. We discuss common practices for validating radiopharmaceuticals for clinical use, everyday pitfalls, and commonplace operationalizing steps for radiopharmaceutical early-phase trials. We anticipate in the near-term that radiopharmaceutical trials will become a larger proportion of the National Cancer Institute Cancer Therapy Evaluation Program (CTEP) portfolio.

High-throughput preparation of radioprotective polymers via Hantzsch's reaction for in vivo X-ray damage determination

Radioprotectors for acute injuries caused by large doses of ionizing radiation are vital to national security, public health and future development of humankind. Here, we develop a strategy to explore safe and efficient radioprotectors by combining Hantzsch's reaction, high-throughput methods and polymer chemistry. A water-soluble polymer with low-cytotoxicity and an excellent anti-radiation capability has been achieved. In in vivo experiments, this polymer is even better than amifostine, which is the only approved radioprotector for clinical applications, in effectively protecting zebrafish embryos from fatally large doses of ionizing radiation (80 Gy X-ray). A mechanistic study also reveals that the radioprotective ability of this polymer originates from its ability to efficiently prevent DNA damage due to high doses of radiation. This is an initial attempt to explore polymer radioprotectors via a multi-component reaction. It allows exploiting functional polymers and provides the underlying insights to guide the design of radioprotective polymers.

Stage-Specific Effects of Ionizing Radiation during Early Development

Early embryonic cells are sensitive to genotoxic stressors such as ionizing radiation. However, sensitivity to these stressors varies depending on the embryonic stage. Recently, the sensitivity and response to ionizing radiation were found to differ during the preimplantation period. The cellular and molecular mechanisms underlying the change during this period are beginning to be elucidated. In this review, we focus on the changes in radio-sensitivity and responses to ionizing radiation during the early developmental stages of the preimplantation (before gastrulation) period in mammals, Xenopus, and fish. Furthermore, we discuss the underlying cellular and molecular mechanisms and the similarities and differences between species.

A feasibility study of zebrafish embryo irradiation with laser-accelerated protons

The development from single shot basic laser plasma interaction research toward experiments in which repetition rated laser-driven ion sources can be applied requires technological improvements. For example, in the case of radio-biological experiments, irradiation duration and reproducible controlled conditions are important for performing studies with a large number of samples. We present important technological advancements of recent years at the ATLAS 300 laser in Garching near Munich since our last radiation biology experiment. Improvements range from target positioning over proton transport and diagnostics to specimen handling. Exemplarily, we show the current capabilities by performing an application oriented experiment employing the zebrafish embryo model as a living vertebrate organism for laser-driven proton irradiation. The size, intensity, and energy of the laser-driven proton bunches resulted in evaluable partial body changes in the small (<1 mm) embryos, confirming the feasibility of the experimental system. The outcomes of this first study show both the appropriateness of the current capabilities and the required improvements of our laser-driven proton source for in vivo biological experiments, in particular the need for accurate, spatially resolved single bunch dosimetry and image guidance.

Adverse effects induced by chronic gamma irradiation in progeny of adult fish not affecting parental reproductive performance

Multigenerational studies have become of great interest in ecotoxicology since the consequence of parental exposure to contaminants on offspring generations was established in situ or in laboratory conditions. The present study mainly examined the chronic effects of external Cs-137 gamma irradiation exposure at 4 dose rates (control, 0.5, 5, and 50 mGy h^-1 ) on adult zebrafish (F0) exposed for 10 d and their progeny (F1) exposed or unexposed for 4 to 5 d. The main endpoints investigated included parental reproductive performance, embryo-larval survival, DNA alterations, and reactive oxygen species (ROS) production in F0 and F1. No effects on reproductive success, fecundity, or egg fertilization rate were observed. However, drastic effects were observed on F1 exposed to 50 mGy h^-1 , resulting in a mortality rate of 100%. The drastic effects were also observed when the progeny was not irradiated. It was demonstrated that the sensitivity of the embryos was mainly attributable to parental irradiation. Moreover, these drastic effects induced by adult irradiation disappeared over time when 10 d-irradiated adults were placed in a nonirradiated condition. Alterations in larval DNA were observed for the 3 dose rates, and an increase of ROS production was also shown for the 2 lowest dose rates. The present study improves our understanding of the consequences of parental exposure conditions to the progeny. Furthermore, it provides an incentive to take transmitted generational effects into account in ecological risk assessments. Environ Toxicol Chem 2019;38:2556-2567. © 2019 SETAC.

Characterization of the adenosinergic system in a zebrafish embryo radiotherapy model

Adenosine is a nucleoside that acts as a signaling molecule by activating P1 purinergic receptors (A₁, A_2A, A_2B and A₃). This activation is involved in immune responses, inflammation, and tissue remodeling and tumor progression. Gamma rays are a type of ionizing radiation widely adopted in radiotherapy of tumors. Although it brings benefits to the success of the therapeutic scheme, it can trigger cellular damages, inducing a perpetual inflammatory response that culminates in adverse effects and severe toxicity. Our study aims to characterize the adenosinergic system in a zebrafish embryo radiotherapy model, relating the adenosine signaling to the changes elicited by radiation exposure. To standardize the radiotherapy procedure, we established a toxicological profile after exposure. Zebrafish were irradiated with different doses of gamma rays (2, 5, 10, 15 and 20 Gy) at 24 hpf. Survival, hatching rate, heartbeats, locomotor activity and morphological changes were determined during embryos development. Although without significant difference in survival, gamma-irradiated embryos had their heartbeats increased and presented decreased hatching time, changes in locomotor activity and important morphological alterations. The exposure to 10 Gy disrupted the ecto-5'-nucleotidase/CD73 and adenosine deaminase/ADA enzymatic activity, impairing adenosine metabolism. We also demonstrated that radiation decreased A_2B receptor gene expression, suggesting the involvement of extracellular adenosine in the changes prompted by radiotherapy. Our results indicate that the components of the adenosinergic system may be potential targets to improve radiotherapy and manage the tissue damage and toxicity of ionizing radiation.

Radioprotective effects of mistletoe extract in zebrafish embryos in vivo

Introduction: Radioprotectors can enhance the efficacy of cancer radiotherapy, but their clinical use remains uncommon. The present study aimed to assess the radioprotective potential of mistletoe extract (commercial name: Abnoba Viscum), a well-known complementary cancer medicine, in zebrafish larvae. Materials and methods: Wild-type AB zebrafish embryos at 4 h-post-fertilization were exposed to 5 Gy 9-MeV electron beam irradiation after being treated for 1 h with 4 mMl/L amifostine or 0.2 mg/ml Abnoba Viscum A, F, M, or Q. Primary endpoints were abnormality-free survival and abnormality-free rates among survivors at 5 days-post-fertilization. Results: The crude abnormality-free survival rates were 33.7%, 49.0%, 38.8%, 43.9%, 38.1%, and 52.6%, whereas abnormality-free rates among survivors were 36.4%, 49.6%, 37.8%, 45.6%, 52.0%, and 62.8% for the control (with no pharmacologic treatment), amifostine, Abnoba Viscum A, F, M, and Q groups, respectively. Abnormality-free survival rates in the amifostine and Abnoba Viscum Q groups were significantly different from those in the control (p = .040 and .012, respectively), with an odds ratio (OR) of 1.90 [95% confidence interval (CI): 1.03-3.51] and 2.20 (95% CI: 1.19-4.08), respectively. Abnormality-free rates among survivors in the amifostine and Abnoba Viscum M and Q groups were significantly different from those in the control group (p = .048, .042, and <.001, respectively), with an OR of 1.79 (95% CI: 1.00-3.20), 1.82 (95% CI: 1.02-3.26), and 2.98 (1.67-5.33), respectively. Conclusion: Abnoba Viscum Q has at least a similar radioprotective effect to that of amifostine. Mistletoe extracts have been clinically applied for a long time and their effectiveness and feasibility have been verified. Abnoba Viscum Q might be a new candidate radioprotectant to enhance cancer radiotherapy efficacy.

Cellular responses to ionizing radiation change quickly over time during early development in zebrafish

Animal cells constantly receive information about and respond to environmental factors, including ionizing radiation. Although it is crucial for a cell to repair radiation-induced DNA damage to ensure survival, cellular responses to radiation exposure during early embryonic development remain unclear. In this study, we analyzed the effects of ionizing radiation in zebrafish embryos and found that radiation-induced γH2AX foci formation and cell cycle arrest did not occur until the gastrula stage, despite the presence of major DNA repair-related gene transcripts, passed on as maternal factors. Interestingly, P21/WAF1 accumulation began ∼6 h post-fertilization, although p21 mRNA was upregulated by irradiation at 2 or 4 h post-fertilization. These results suggest that the cellular responses of zebrafish embryos at 2 or 4 h post-fertilization to radiation failed to overcome P21 protein accumulation and further signaling. Regulation of P21/WAF1 protein stabilization appears to be a key factor in the response to genotoxins during early embryogenesis.

An IRAK1-PIN1 signalling axis drives intrinsic tumour resistance to radiation therapy

Drug-based strategies to overcome tumour resistance to radiotherapy (R-RT) remain limited by the single-agent toxicity of traditional radiosensitizers (e.g., platinums) and a lack of targeted alternatives. In a screen for compounds that restore radiosensitivity in p53 mutant zebrafish while tolerated in non-irradiated wild-type animals, we identified the benzimidazole anthelmintic, oxfendazole. Surprisingly, oxfendazole acts via inhibition of IRAK1, a kinase otherwise involved in Interleukin-1 and Toll-like receptor (IL-1R/TLR) immune responses. IRAK1 drives R-RT in a pathway involving IRAK4 and TRAF6 but not the IL-1R/TLR—IRAK adaptor MyD88. Rather than stimulating NF-κB, radiation-activated IRAK1 acts to prevent apoptosis mediated by the PIDDosome complex (PIDD/RAIDD/caspase-2). Countering this pathway with IRAK1 inhibitors suppresses R-RT in tumour models derived from cancers in which TP53 mutations predict R-RT. Lastly, IRAK1 inhibitors synergize with inhibitors of PIN1, a prolyl isomerase essential for IRAK1 activation in response to pathogens and, as shown here, ionizing radiation. These data identify an IRAK1 radiation-response pathway as a rational chemo-RT target.

Radiobiological effects and proton RBE determined by wildtype zebrafish embryos

The increasing use of proton radiotherapy during the last decade and the rising number of long-term survivors has given rise to a vital discussion on potential effects on normal tissue. So far, deviations from clinically applied generic RBE (relative biological effectiveness) of 1.1 were only obtained by in vitro studies, whereas indications from in vivo trials and clinical studies are rare. In the present work, wildtype zebrafish embryos (Danio rerio) were used to characterize the effects of plateau and mid-SOBP (spread-out Bragg peak) proton radiation relative to that induced by clinical MV photon beam reference. Based on embryonic survival data, RBE values of 1.13 ± 0.08 and of 1.20 ± 0.04 were determined four days after irradiations with 20 Gy plateau and SOBP protons relative to 6 MV photon beams. These RBE values were confirmed by relating the rates of embryos with morphological abnormalities for the respective radiation qualities and doses. Besides survival, the rate of spine bending, as one type of developmental abnormality, and of pericardial edema, as an example for acute radiation effects, were assessed. The results revealed that independent on radiation quality both rates increased with time approaching almost 100% at the 4th day post irradiation with doses higher than 15 Gy. To sum up, the applicability of the zebrafish embryo as a robust and simple alternative model for in vivo characterization of radiobiological effects in normal tissue was validated and the obtained RBE values are comparable to previous finding in animal trials.

A novel vertebrate system for the examination and direct comparison of the relative biological effectiveness for different radiation qualities and sources

PURPOSE

The recent rapid increase of hadron therapy applications requires the development of high performance, reliable in vivo models for preclinical research on the biological effects of high linear energy transfer (LET) particle radiation.

AIM

The aim of this paper was to test the relative biological effectiveness (RBE) of the zebrafish embryo system at two neutron facilities.

MATERIAL AND METHODS

Series of viable zebrafish embryos at 24-hour post-fertilization (hpf) were exposed to single fraction, whole-body, photon and neutron (reactor fission neutrons (<En = 1 MeV>) and (p (18 MeV)+Be, <En> = 3.5 MeV) fast neutron) irradiation. The survival and morphologic abnormalities of each embryo were assessed at 24-hour intervals from the point of fertilization up to 192 hpf and then compared to conventional 6 MV photon beam irradiation results.

RESULTS

The higher energy of the fast neutron beams represents lower RBE (ref. source LINAC 6 MV photon). The lethality rate in the zebrafish embryo model was 10 times higher for 1 MeV fission neutrons and 2.5 times greater for p (18 MeV)+Be cyclotron generated fast neutron beam when compared to photon irradiation results. Dose-dependent organ perturbations (shortening of the body length, spine curvature, microcephaly, micro-ophthalmia, pericardial edema and inhibition of yolk sac resorption) and microscopic (marked cellular changes in eyes, brain, liver, muscle and the gastrointestinal system) changes scale together with the dose response.

CONCLUSION

The zebrafish embryo system is a powerful and versatile model for assessing the effect of ionizing radiation with different LET values on viability, organ and tissue development.

Radio-Protective Effects of Octopus ocellatus Meat Consisted of a Plentiful Taurine Against Damages Caused by Gamma Ray Irradiation

Gamma ray irradiation causes immune suppressive responses by inducing oxidative stress such as reduction of cell viability and damages in immune cells. In this present study, we investigated whether Octopus ocellatus meet (OM) consisted of a plentiful taurine has protective effects against damages caused by oxidative stress in murine splenocytes. First of all, we prepared the aqueous extract from OM (OMA) and identified it contained a plentiful taurine content. The result also showed that OMA exhibited the antioxidant activity by scavenging DPPH and ABTS+ radicals and hydrogen peroxide. In addition, OMA improved the cell viability without cytotoxicity in gamma ray-irradiated murine splenocytes. Moreover, OMA significantly reduced the production of reactive oxygen species (ROS) in gamma ray-irradiated splenocytes. In further study, we identified that OMA protected zebrafish embryo via improving the reduced survival rate and decreasing the formation of deformity caused by the exposure of gamma ray irradiation. Also, OMA decreased the production of NO and ROS in gamma ray-irradiated zebrafish embryos as well as the induction of cell death. In these results, this study suggests that the consumption of taurine-rich foods, such as O. ocellatus, may be useful for the useful material for the protection against oxidative stress.

Early embryonic exposure of ionizing radiations disrupts zebrafish pigmentation

Studies have demonstrated that zebrafish are powerful tools for monitoring environmental toxicity, including radiation hazard. Here we investigated the developmental toxicity of ionizing radiation (IR) in an in vivo embryonic zebrafish model. The effects of heavy ion (¹² C⁶⁺ ), proton, and X-ray radiation on early zebrafish embryos were determined. A similar dose-dependent decrease in the hatch and survival rate of zebrafish embryos was observed after exposure to these irradiations. Exposure of zebrafish embryos to 1-4 Gy IR caused significant loss of pigmentation. Quantitative real-time reverse transcription polymerase chain reaction, western blot analysis, and in situ hybridization (ISH) experiment revealed that atp5α1 was markedly upregulated in irradiated zebrafish embryos. In addition, IR resulted in a rapid decrease in total adenosine triphosphate (ATP) generation. With dual functions of synthesizing or hydrolyzing ATP, ATP synthase regulated H⁺ transport crossing the mitochondrial inner. Administration of the mitochondrial ATP synthase inhibitor, oligomycin, partially restored pigmentation in irradiated zebrafish embryos, but the ATPase inhibitor, BTB06584, had no effect. Taken together, these results showed that IR exposure downregulated zebrafish pigmentation through regulation of H⁺ ion transport in mitochondria.

Uranium mining wastes: The use of the Fish Embryo Acute Toxicity Test (FET) test to evaluate toxicity and risk of environmental discharge

Active and abandoned uranium mining sites often create environmentally problematic situations, since they cause the contamination of all environmental matrices (air, soil and water) with stable metals and radionuclides. Due to their cytotoxic, genotoxic and teratogenic properties, the exposure to these contaminants may cause several harmful effects in living organisms. The Fish Embryo Acute Toxicity Test (FET) test was employed to evaluate the genotoxic and teratogenic potential of mine liquid effluents and sludge elutriates from a deactivated uranium mine. The aims were: a) to determine the risk of discharge of such wastes in the environment; b) the effectiveness of the chemical treatment applied to the uranium mine water, which is a standard procedure generally applied to liquid effluents from uranium mines and mills, to reduce its toxicological potential; c) the suitability of the FET test for the evaluation the toxicity of such wastes and the added value of including the evaluation of genotoxicity. Results showed that through the FET test it was possible to determine that both elutriates and effluents are genotoxic and also that the mine effluent is teratogenic at low concentrations. Additionally, liquid effluents and sludge elutriates affect other parameters namely, growth and hatching and that water pH alone played an important role in the hatching process. The inclusion of genotoxicity evaluation in the FET test was crucial to prevent the underestimation of the risks posed by some of the tested effluents/elutriates. Finally, it was possible to conclude that care should be taken when using benchmark values calculated for specific stressors to evaluate the risk posed by uranium mining wastes to freshwater ecosystems, due to their chemical complexity.

Parental gamma irradiation induces reprotoxic effects accompanied by genomic instability in zebrafish (Danio rerio) embryos

Gamma radiation represents a potential health risk to aquatic and terrestrial biota, due to its ability to ionize atoms and molecules in living tissues. The effects of exposure to ⁶⁰Co gamma radiation in zebrafish (Danio rerio) were studied during two sensitive life stages: gametogenesis (F0: 53 and 8.7mGy/h for 27 days, total doses 31 and 5.2Gy) and embryogenesis (9.6mGy/h for 65h; total dose 0.62Gy). Progeny of F0 exposed to 53mGy/h showed 100% mortality occurring at the gastrulation stage corresponding to 8h post fertilization (hpf). Control and F0 fish exposed to 8.7mGy/h were used to create four lines in the first filial generation (F1): control, G line (irradiated during parental gametogenesis), E line (irradiated during embryogenesis) and GE line (irradiated during parental gametogenesis and embryogenesis). A statistically significant cumulative mortality of GE larva (9.3%) compared to controls was found at 96 hpf. E line embryos hatched significantly earlier compared to controls, G and GE (48-72 hpf). The deformity frequency was higher in G and GE, but not E line compared to controls at 72 hpf. One month after parental irradiation, the formation of reactive oxygen species (ROS) was increased in the G line, but did not significantly differ from controls one year after parental irradiation, while at the same time point it was significantly increased in the directly exposed E and GE lines from 60 to 120 hpf. Lipid peroxidation (LPO) was significantly increased in the G line one year after parental irradiation, while significant increase in DNA damage was detected in both the G and GE compared to controls and E line at 72 hpf. Radiation-induced bystander effects, triggered by culture media from tissue explants and observed as influx of Ca²⁺ ions through the cellular membrane of the reporter cells, were significantly increased in 72 hpf G line progeny one month after irradiation of the parents. One year after parental irradiation, the bystander effects were increased in the E line compared to controls, but not in progeny of irradiated parents (G and GE lines). Overall, this study showed that irradiation of parents can result in multigenerational oxidative stress and genomic instability in irradiated (GE) and non-irradiated (G) progeny of irradiated parents, including increases in ROS formation, LPO, DNA damage and bystander effects. The results therefore highlight the necessity for multi- and transgenerational studies to assess the environmental impact of gamma radiation.

Effects of gamma radiation on the early developmental stages of Zebrafish (Danio rerio)

The zebrafish is gaining importance as a popular vertebrate model organism and is widely employed in ecotoxicological studies, especially for the biomonitoring of pollution in water bodies. There is limited data on the genetic mechanisms governing the adverse health effects in regards to an early developmental exposure to gamma radiation. In the present study zebrafish (Danio rerio) embryos were exposed to 1, 2.5, 5, 7.5 and 10Gy of gamma radiation at 3h post fertilization (hpf). Different developmental toxicity endpoints were investigated. Further, expression of genes associated with the development and DNA damage i.e. (sox2 sox19a and p53) were evaluated using Quantitative PCR (qPCR). The significant changes in the expression of sox2 sox19a and p53 genes were observed. This data was supported the developmental defects observed in the zebrafish embryo exposed to gamma radiation such as i.e. increased DNA damage, decreased hatching rate, increase in median hatching time, decreased body length, increased mortality rate, increased morphological deformities. Further, study shows that the potential ecotoxicological threat of gamma radiation on the early developmental stages of zebrafish. Further, it revealed that the above parameters can be used as predictive biomarkers of gamma radiation exposure.

Dose-dependent effects of gamma radiation on the early zebrafish development and gene expression

Ionizing radiation from natural sources or anthropogenic activity has the potential to cause oxidative stress or genetic damage in living organisms, through the ionization and excitation of molecules and the subsequent production of free radicals and reactive oxygen species (ROS). The present work focuses on radiation-induced biological effects using the zebrafish (Danio rerio) vertebrate model. Changes in developmental traits and gene expression in zebrafish were assessed after continuous external gamma irradiation (0.4, 3.9, 15 and 38 mGy/h) with corresponding controls, starting at 2.5 hours post fertilization (hpf) and lasting through embryogenesis and the early larval stage. The lowest dose rate corresponded to recommended benchmarks at which adverse effects are not expected to occur in aquatic ecosystems (2-10 mGy/day). The survival observed at 96 hours post fertilization (hpf) in the 38 mGy/h group was significantly lower, while other groups showed no significant difference compared to controls. The total hatching was significantly lower from controls in the 15 mGy/h group and a delay in hatching onset in the 0.4 mGy/h group was observed. The deformity frequency was significantly increased by prolonged exposure duration at dose rates ≥ 0.4 mGy/h. Molecular responses analyzed by RNA-seq at gastrulation (5.5 hpf transcriptome) indicate that the radiation induced adverse effects occurred during the earliest stages of development. A dose-response relationship was found in the numbers of differentially regulated genes in exposure groups compared to controls at a total dose as low as 1.62 mGy. Ingenuity Pathway Analysis identified retinoic acid receptor activation, apoptosis, and glutathione mediated detoxification signaling as the most affected pathways in the lower dose rate (0.54 mGy/h), while eif2 and mTOR, i.e., involved in the modulation of angiogenesis, were most affected in higher dose rates (5.4 and 10.9 mGy/h). By comparing gene expression data, myc was found to be the most significant upstream regulator, followed by tp53, TNF, hnf4a, TGFb1 and cebpa, while crabp2b and vegfab were identified as most frequent downstream target genes. These genes are associated with various developmental processes. The present findings show that continuous gamma irradiation (≥ 0.54 mGy/h) during early gastrula causes gene expression changes that are linked to developmental defects in zebrafish embryos.

Effect of Photon Hormesis on Dose Responses to Alpha Particles in Zebrafish Embryos

Photon hormesis refers to the phenomenon where the biological effect of ionizing radiation with a high linear energy transfer (LET) value is diminished by photons with a low LET value. The present paper studied the effect of photon hormesis from X-rays on dose responses to alpha particles using embryos of the zebrafish (Danio rerio) as the in vivo vertebrate model. The toxicity of these ionizing radiations in the zebrafish embryos was assessed using the apoptotic counts at 20, 24, or 30 h post fertilization (hpf) revealed through acridine orange (AO) staining. For alpha-particle doses ≥ 4.4 mGy, the additional X-ray dose of 10 mGy significantly reduced the number of apoptotic cells at 24 hpf, which proved the presence of photon hormesis. Smaller alpha-particle doses might not have inflicted sufficient aggregate damages to trigger photon hormesis. The time gap T between the X-ray (10 mGy) and alpha-particle (4.4 mGy) exposures was also studied. Photon hormesis was present when T ≤ 30 min, but was absent when T = 60 min, at which time repair of damage induced by alpha particles would have completed to prevent their interactions with those induced by X-rays. Finally, the drop in the apoptotic counts at 24 hpf due to photon hormesis was explained by bringing the apoptotic events earlier to 20 hpf, which strongly supported the removal of aberrant cells through apoptosis as an underlying mechanism for photon hormesis.

Exogenous Nitric Oxide Suppresses in Vivo X-ray-Induced Targeted and Non-Targeted Effects in Zebrafish Embryos

The present paper studied the X-ray-induced targeted effect in irradiated zebrafish embryos (Danio rerio), as well as a non-targeted effect in bystander naïve embryos partnered with irradiated embryos, and examined the influence of exogenous nitric oxide (NO) on these targeted and non-targeted effects. The exogenous NO was generated using an NO donor, S-nitroso-N-acetylpenicillamine (SNAP). The targeted and non-targeted effects, as well as the toxicity of the SNAP, were assessed using the number of apoptotic events in the zebrafish embryos at 24 h post fertilization (hpf) revealed through acridine orange (AO) staining. SNAP with concentrations of 20 and 100 µM were first confirmed to have no significant toxicity on zebrafish embryos. The targeted effect was mitigated in zebrafish embryos if they were pretreated with 100 µM SNAP prior to irradiation with an X-ray dose of 75 mGy but was not alleviated in zebrafish embryos if they were pretreated with 20 µM SNAP. On the other hand, the non-targeted effect was eliminated in the bystander naïve zebrafish embryos if they were pretreated with 20 or 100 µM SNAP prior to partnering with zebrafish embryos having been subjected to irradiation with an X-ray dose of 75 mGy. These findings revealed the importance of NO in the protection against damages induced by ionizing radiations or by radiation-induced bystander signals, and could have important impacts on development of advanced cancer treatment strategies.

l-Alpha Glycerylphosphorylcholine as a Potential Radioprotective Agent in Zebrafish Embryo Model

This work establishes the zebrafish embryo model for ionizing radiation (IR) modifier research and also evaluates the protective effect of l-alpha glycerylphosphorylcholine (GPC). Embryos were exposed to a single-fraction whole-body gamma irradiation (5, 10, 15, and 20 Gy) at different postfertilization time points and were serially assessed for viability and macro- and micromorphologic abnormalities. After toxicity evaluation, 194 μM of GPC was added for certain groups with 3-h incubation before the radiation. Nuclear factor kappa B (NF-κB) and interleukin-1β (IL-1β) expression changes were measured using quantitative real-time polymerase chain reaction. A higher sensitivity could be observed at earlier stages of the embryogenesis. The lethal dose (LD₅₀) for 6 hours postfertilization (hpf) embryos was 15 Gy and for 24 hpf was 20 Gy on day 7, respectively. GPC administration resulted in a significant improvement in both the distortion rate and survival of the 24 hpf embryos. Qualitative evaluation of the histological changes confirmed the protective effect of GPC. IL-1β and NF-κB overexpression due to 10 Gy irradiation was also reduced by GPC. GPC exhibited promising radioprotective effects in our zebrafish embryo model, decreasing the irradiation-induced morphological damage and lethality with significant reduction of IR-caused pro-inflammatory activation.

Lanthanide Hydroxide Nanoparticles Induce Angiogenesis via ROS-Sensitive Signaling

Recent studies suggest that the nanorods consisting of europium hydroxide could promote angiogenesis. In this study, it is sought to determine if additional types of nanoparticles are capable of enhancing angiogenesis and in addition, understand the underlying mechanisms. For this reason, a method is employed that combines a high throughput in vitro cell based screen coupled with an in vivo validation using vascular specific green fluorescent protein reporter transgenic zebrafish for examining proangiogenesis activity. After screening multiple types of nanoparticles, it is discovered that four of them, Eu(III) (OH)3 rods (Eu rods), Eu(III) (OH)3 spheres (Eu spheres), Tb(III) (OH)3 rods (Tb rods), and Tb(III) (OH)3 spheres (Tb spheres), are the most effective in promoting angiogenesis. It is also showed that ionic forms of europium nitrate [Eu(NO3 )3 ] (Eu) and terbium nitrate [Tb(NO3 )3 ] (Tb), the two lanthanide elements for these four nanoparticles, are also capable of enhancing angiogenesis. However, this effect is further enhanced by nanoparticle synthesis. Finally, it is demonstrated that reactive oxygen species H2 O2 is a key factor in the process of proangiogenesis by lanthanide elemental nanoparticles.

Non-induction of radioadaptive response in zebrafish embryos by neutrons

In vivo neutron-induced radioadaptive response (RAR) was studied using zebrafish (Danio rerio) embryos. The Neutron exposure Accelerator System for Biological Effect Experiments (NASBEE) facility at the National Institute of Radiological Sciences (NIRS), Japan, was employed to provide 2-MeV neutrons. Neutron doses of 0.6, 1, 25, 50 and 100 mGy were chosen as priming doses. An X-ray dose of 2 Gy was chosen as the challenging dose. Zebrafish embryos were dechorionated at 4 h post fertilization (hpf), irradiated with a chosen neutron dose at 5 hpf and the X-ray dose at 10 hpf. The responses of embryos were assessed at 25 hpf through the number of apoptotic signals. None of the neutron doses studied could induce RAR. Non-induction of RAR in embryos having received 0.6- and 1-mGy neutron doses was attributed to neutron-induced hormesis, which maintained the number of damaged cells at below the threshold for RAR induction. On the other hand, non-induction of RAR in embryos having received 25-, 50- and 100-mGy neutron doses was explained by gamma-ray hormesis, which mitigated neutron-induced damages through triggering high-fidelity DNA repair and removal of aberrant cells through apoptosis. Separate experimental results were obtained to verify that high-energy photons could disable RAR. Specifically, 5- or 10-mGy X-rays disabled the RAR induced by a priming dose of 0.88 mGy of alpha particles delivered to 5-hpf zebrafish embryos against a challenging dose of 2 Gy of X-rays delivered to the embryos at 10 hpf.

A Drosophila model to investigate the neurotoxic side effects of radiation exposure

Children undergoing cranial radiation therapy (CRT) for pediatric central nervous system malignancies are at increased risk for neurological deficits later in life. We have developed a model of neurotoxic damage in adult Drosophila following irradiation during the juvenile stages with the goal of elucidating underlying neuropathological mechanisms and of ultimately identifying potential therapeutic targets. Wild-type third-instar larvae were irradiated with single doses of γ-radiation, and the percentage that survived to adulthood was determined. Motor function of surviving adults was examined with a climbing assay, and longevity was assessed by measuring lifespan. Neuronal cell death was assayed by using immunohistochemistry in adult brains. We also tested the sensitivity at different developmental stages by irradiating larvae at various time points. Irradiating late third-instar larvae at a dose of 20 Gy or higher impaired the motor activity of surviving adults. A dose of 40 Gy or higher resulted in a precipitous reduction in the percentage of larvae that survive to adulthood. A dose-dependent decrease in adult longevity was paralleled by a dose-dependent increase in activated Death caspase-1 (Dcp1) in adult brains. Survival to adulthood and adult lifespan were more severely impaired with decreasing larval age at the time of irradiation. Our initial survey of the Drosophila Genetic Reference Panel demonstrated that differences in genotype can confer phenotypic differences in radio-sensitivity for developmental survival and motor function. This work demonstrates the usefulness of Drosophila to model the toxic effects of radiation during development, and has the potential to unravel underlying mechanisms and to facilitate the discovery of novel therapeutic interventions.

Highlighted Article: To model delayed neurological deficits resulting from pediatric cranial radiation therapy, neurotoxic damage in adult Drosophila is assessed following larval irradiation with the goal of elucidating underlying pathological mechanisms.

External gamma irradiation-induced effects in early-life stages of zebrafish, Danio rerio

In the general context of validation of tools useful for the characterization of ecological risk linked to ionizing radiation, the effects of an external gamma irradiation were studied in zebrafish larvae irradiated for 96 h with two dose rates: 0.8 mGy/d, which is close to the level recommended to protect ecosystems from adverse effects of ionizing radiation (0.24 mGy/d) and a higher dose rate of 570 mGy/d. Several endpoints were investigated, such as mortality, hatching, and some parameters of embryo-larval development, immunotoxicity, apoptosis, genotoxicity, neurotoxicity and histological alterations. Results showed that an exposure to gamma rays induced an acceleration of hatching for both doses and a decrease of yolk bag diameter for the highest dose, which could indicate an increase of global metabolism. AChE activity decreased with the low dose rate of gamma irradiation and alterations were also shown in muscles of irradiated larvae. These results suggest that gamma irradiation can induce damages on larval neurotransmission, which could have repercussions on locomotion. DNA damages, basal ROS production and apoptosis were also induced by irradiation, while ROS stimulation index and EROD biotransformation activity were decreased and gene expression of acetylcholinesterase, choline acetyltransferase, cytochrome p450 and myeloperoxidase increased. These results showed that ionizing radiation induced an oxidative stress conducting to DNA damages. This study characterized further the modes of action of ionizing radiation in fish.

Some properties of the signals involved in unirradiated zebrafish embryos rescuing α-particle irradiated zebrafish embryos

PURPOSE

The in vivo radiation-induced bystander effect (RIBE) and radiation-induced rescue effect (RIRE) induced between embryos of the zebrafish (Danio rerio) by alpha-particle irradiation were studied through the number of apoptotic signals revealed at 24 h post fertilization (hpf) through vital dye acridine orange staining.

MATERIALS AND METHODS

RIBE and RIRE were verified through the significant increase and decrease in apoptotic signals in the partnered bystander and irradiated embryos, respectively.

RESULTS

The medium transfer experiment where irradiated zebrafish embryos were rescued through immersion in the medium previously conditioned by a larger number of irradiated zebrafish embryos showed (a) the involvement of a released stress signal in the induction of RIRE, and (b) RIBE and RIRE signals had the same function. With the help of 500 μM of the specific nitric oxide (NO) scavenger cPTIO (2-(4carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide), NO was confirmed as an essential signaling molecule for inducing both the RIBE and RIRE. On the other hand, the treatment with 20 μM of the carbon monoxide (CO) releasing chemical CORM-3 (tricarbonylchloro(glycinato)ruthenium (II)) suppressed the manifestations of RIBE but did not suppress RIRE.

CONCLUSIONS

In conclusion, unirradiated zebrafish embryos need NO but not NO-induced damages to rescue α-particle irradiated zebrafish embryos.

Rescue effects: irradiated cells helped by unirradiated bystander cells

The rescue effect describes the phenomenon where irradiated cells or organisms derive benefits from the feedback signals sent from the bystander unirradiated cells or organisms. An example of the benefit is the mitigation of radiation-induced DNA damages in the irradiated cells. The rescue effect can compromise the efficacy of radioimmunotherapy (RIT) (and actually all radiotherapy). In this paper, the discovery and subsequent confirmation studies on the rescue effect were reviewed. The mechanisms and the chemical messengers responsible for the rescue effect studied to date were summarized. The rescue effect between irradiated and bystander unirradiated zebrafish embryos in vivo sharing the same medium was also described. In the discussion section, the mechanism proposed for the rescue effect involving activation of the nuclear factor κB (NF-κB) pathway was scrutinized. This mechanism could explain the promotion of cellular survival and correct repair of DNA damage, dependence on cyclic adenosine monophosphate (cAMP) and modulation of intracellular reactive oxygen species (ROS) level in irradiated cells. Exploitation of the NF-κB pathway to improve the effectiveness of RIT was proposed. Finally, the possibility of using zebrafish embryos as the model to study the efficacy of RIT in treating solid tumors was also discussed.

Effects of depleted uranium on the reproductive success and F1 generation survival of zebrafish (Danio rerio)

Despite the well-characterized occurrence of uranium (U) in the aquatic environment, very little is known about the chronic exposure of fish to low levels of U and its potential effect on reproduction. Therefore, this study was undertaken to investigate the effects of environmental concentrations of depleted U on the reproductive output of zebrafish (Danio rerio) and on survival and development of the F1 embryo-larvae following parental exposure to U. For that purpose, sexually mature male and female zebrafish were exposed to 20 and 250 μg/L of U for 14 days and allowed to reproduce in clean water during a further 14-day period. At all sampling times, whole-body vitellogenin concentrations and gonad histology were analyzed to investigate the effects of U exposure on these reproductive endpoints. In addition, accumulation of U in the gonads and its genotoxic effect on male and female gonad cells were quantified. The results showed that U strongly affected the capability of fish to reproduce and to generate viable individuals as evidenced by the inhibition of egg production and the increased rate of mortality of the F1 embryos. Interestingly, U exposure resulted in decreased circulating concentrations of vitellogenin in females. Increased concentrations of U were observed in gonads and eggs, which were most likely responsible for the genotoxic effects seen in fish gonads and in embryos exposed maternally to U. Altogether, these findings highlight the negative effect of environmentally relevant concentrations of U which alter the reproductive capability of fish and impair the genetic integrity of F1 embryos raising further concern regarding its effect at the population level.

Embryonic ionizing radiation exposure results in expression alterations of genes associated with cardiovascular and neurological development, function, and disease and modified cardiovascular function in zebrafish

The relationship between ionizing radiation (IR) and carcinogenesis is long established, but recently the association between IR and other diseases is starting to be recognized. Currently, there is limited information on the genetic mechanisms governing the role of IR in non-cancer related adverse health effects and in regards to an early developmental exposure. In this study, zebrafish embryos were exposed to a range of IR doses (0, 1, 2, 5, 10 Gy) at 26 h post fertilization (hpf). No significant increase in mortality or hatching rate was observed, but a significant decrease in total larval length, head length, and eye diameter was observed in the 10 Gy dose. Transcriptomic analysis was conducted at 120 hpf to compare gene expression profiles between the control and highest IR dose at which no significant differences were observed in morphological measurements (5 Gy). 253 genes with well-established function or orthology to human genes were significantly altered. Gene ontology and molecular network analysis revealed enrichment of genes associated with cardiovascular and neurological development, function, and disease. Expression of a subset of genetic targets with an emphasis on those associated with the cardiovascular system was assessed using Quantitative PCR (qPCR) to confirm altered expression at 5 Gy and then to investigate alterations at lower doses (1 and 2 Gy). Strong correlation between microarray and qPCR expression values was observed, but zebrafish exposed to 1 or 2 Gy resulted in a significant expression alteration in only one of these genes (LIN7B). Moreover, heart rate was analyzed through 120 hpf following IR dosing at 26 hpf. A significant decrease in heart rate was observed at 10 Gy, while a significant increase in heart rate was observed at 1, 2, and 5 Gy. Overall these findings indicate IR exposure at doses below those that induce gross morphological changes alters heart rate and expression of genes associated with cardiovascular and neurological functions.

Protective effects of Korean red ginseng against radiation-induced apoptosis in human HaCaT keratinocytes

Radiation-induced oral mucositis is a dose-limiting toxic side effect for patients with head and neck cancer. Numerous attempts at improving radiation-induced oral mucositis have not produced a qualified treatment. Ginseng polysaccharide has multiple immunoprotective effects. Our aim was to investigate the effectiveness of Korean red ginseng (KRG) on radiation-induced damage in the human keratinocyte cell line HaCaT and in an in vivo zebrafish model. Radiation inhibited HaCaT cell proliferation and migration in a cell viability assay and wound healing assay, respectively. KRG protected against these effects. KRG attenuated the radiation-induced embryotoxicity in the zebrafish model. Irradiation of HaCaT cells caused apoptosis and changes in mitochondrial membrane potential (MMP). KRG inhibited the radiation-induced apoptosis and intracellular generation of reactive oxygen species (ROS), and stabilized the radiation-induced loss of MMP. Western blots revealed KRG-mediated reduced expression of ataxia telangiectasia mutated protein (ATM), p53, c-Jun N-terminal kinase (JNK), p38 and cleaved caspase-3, compared with their significant increase after radiation treatment. The collective results suggest that KRG protects HaCaT cells by blocking ROS generation, inhibiting changes in MMP, and inhibiting the caspase, ATM, p38 and JNK pathways.

The effects of x-ray radiation on the eye development of zebrafish

The toxic effects of x-ray radiation on eye development was measured using zebrafish as a model organism. Zebrafish embryos at 8 h post-fertilization (hpf) were irradiated using X-rays at doses of 1, 2, 4, and 8 Gy. At 24 and 48 hpf, x-ray radiation induced a significant increase in reactive oxygen species (ROS) content and cell apoptotic signals. Both of these increases were dose dependent and there were significant positive relationships between them at 24 hpf. At 48 and 72 hpf, the increase of ROS concentration can be eliminated by increasing activities of superoxide dismutase and catalase. Although the ROS generated by x-ray radiation caused a significant increase in cell apoptosis at 24 and 48 hpf, the cellular layers of the retina and lens formation in the irradiated groups were not significantly disrupted at 144 hpf compared with the control group, with the exception of a heterogeneous distribution of the cells in inner nuclear cell layer and a significant decrease in the diameters of whole eyes after 8 Gy irradiation. X-Ray radiation at later stages of gastrulation may not cause distinct optic complications; however, there is still a risk of microophthalmia at high doses of irradiation.

Embryos of the zebrafish Danio rerio in studies of non-targeted effects of ionizing radiation

The use of embryos of the zebrafish Danio rerio as an in vivo tumor model for studying non-targeted effects of ionizing radiation was reviewed. The zebrafish embryo is an animal model, which enables convenient studies on non-targeted effects of both high-linear-energy-transfer (LET) and low-LET radiation by making use of both broad-beam and microbeam radiation. Zebrafish is also a convenient embryo model for studying radiobiological effects of ionizing radiation on tumors. The embryonic origin of tumors has been gaining ground in the past decades, and efforts to fight cancer from the perspective of developmental biology are underway. Evidence for the involvement of radiation-induced genomic instability (RIGI) and the radiation-induced bystander effect (RIBE) in zebrafish embryos were subsequently given. The results of RIGI were obtained for the irradiation of all two-cell stage cells, as well as 1.5 hpf zebrafish embryos by microbeam protons and broad-beam alpha particles, respectively. In contrast, the RIBE was observed through the radioadaptive response (RAR), which was developed against a subsequent challenging dose that was applied at 10 hpf when <0.2% and <0.3% of the cells of 5 hpf zebrafish embryos were exposed to a priming dose, which was provided by microbeam protons and broad-beam alpha particles, respectively. Finally, a perspective on the field, the need for future studies and the significance of such studies were discussed.

Effect of radiation dose-rate on hematopoietic cell engraftment in adult zebrafish

Although exceptionally high radiation dose-rates are currently attaining clinical feasibility, there have been relatively few studies reporting the biological consequences of these dose-rates in hematopoietic cell transplant (HCT). In zebrafish models of HCT, preconditioning before transplant is typically achieved through radiation alone. We report the comparison of outcomes in adult zebrafish irradiated with 20 Gy at either 25 or 800 cGy/min in the context of experimental HCT. In non-transplanted irradiated fish we observed no substantial differences between dose-rate groups as assessed by fish mortality, cell death in the kidney, endogenous hematopoietic reconstitution, or gene expression levels of p53 and ddb2 (damage-specific DNA binding protein 2) in the kidney. However, following HCT, recipients conditioned with the higher dose rate showed significantly improved donor-derived engraftment at 9 days post transplant (p ≤ 0.0001), and improved engraftment persisted at 31 days post transplant. Analysis for sdf-1a expression, as well as transplant of hematopoietic cells from cxcr4b -/- zebrafish, (odysseus), cumulatively suggest that the sdf-1a/cxcr4b axis is not required of donor-derived cells for the observed dose-rate effect on engraftment. Overall, the adult zebrafish model of HCT indicates that exceptionally high radiation dose-rates can impact HCT outcome, and offers a new system for radiobiological and mechanistic interrogation of this phenomenon. Key words: Radiation dose rate, Total Marrow Irradiation (TMI), Total body irradiation (TBI), SDF-1, Zebrafish, hematopoietic cell transplant.

Long-term effects of ionizing radiation on gene expression in a zebrafish model

Understanding how initial radiation injury translates into long-term effects is an important problem in radiation biology. Here, we define a set of changes in the transcription profile that are associated with the long-term response to radiation exposure. The study was performed in vivo using zebrafish, an established radiobiological model organism. To study the long-term response, 24 hour post-fertilization embryos were exposed to 0.1 Gy (low dose) or 1.0 Gy (moderate dose) of whole-body gamma radiation and allowed to develop for 16 weeks. Liver mRNA profiles were then analyzed using the Affymetrix microarray platform, with validation by quantitative PCR. As a basis for comparison, 16-week old adults were exposed at the same doses and analyzed after 4 hours. Statistical analysis was performed in a way to minimize the effects of multiple comparisons. The responses to these two treatment regimes differed greatly: 360 probe sets were associated primarily with the long-term response, whereas a different 2062 probe sets were associated primarily with the response when adults of the same age were irradiated 4 hours before exposure. Surprisingly, a ten-fold difference in radiation dose (0.1 versus 1.0 Gy) had little effect. Analysis at the gene and pathway level indicated that the long-term response includes the induction of cytokine and inflammatory regulators and transcription and growth factors. The acute response includes the induction of p53 target genes and modulation of the hypoxia-induced transcription factor-C/EBP axis. Results help define genes and pathways affected in the long-term, low and moderate dose radiation response and differentiate them from those affected in an acute response in the same tissue.

Bystander effect between zebrafish embryos in vivo induced by high-dose X-rays

We employed embryos of the zebrafish, Danio rerio, for our studies on the in vivo bystander effect between embryos irradiated with high-dose X-rays and naive unirradiated embryos. The effects on the naive whole embryos were studied through quantification of apoptotic signals at 25 h post fertilization (hpf) through the terminal dUTP transferase-mediated nick end-labeling (TUNEL) assay followed by counting the stained cells under a microscope. We report data showing that embryos at 5 hpf subjected to a 4-Gy X-ray irradiation could release a stress signal into the medium, which could induce a bystander effect in partnered naive embryos sharing the same medium. We further demonstrated that this bystander effect (induced through partnering) could be successfully suppressed through the addition of the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) into the medium but not through the addition of the CO liberator tricarbonylchloro(glycinato)ruthenium(II) (CORM-3). This shows that NO was involved in the bystander response between zebrafish embryos induced through X-ray irradiation. We also report data showing that the bystander effect could be successfully induced in naive embryos by introducing them into the irradiated embryo conditioned medium (IECM) alone, i.e., without partnering with the irradiated embryos. The IECM was harvested from the medium that had conditioned the zebrafish embryos irradiated at 5 hpf with 4-Gy X-ray until the irradiated embryos developed into 29 hpf. NO released from the irradiated embryos was unlikely to be involved in the bystander effect induced through the IECM because of the short life of NO. We further revealed that this bystander effect (induced through IECM) was rapidly abolished through diluting the IECM by a factor of 2× or greater, which agreed with the proposal that the bystander effect was an on/off response with a threshold.