Development of the irradiation method for the first instar silkworm larvae using locally targeted heavy-ion microbeam

Monte-Carlo dosimetry and real-time imaging of targeted irradiation consequences in 2-cell stage Caenorhabditis elegans embryo

Charged-particle microbeams (CPMs) provide a unique opportunity to investigate the effects of ionizing radiation on living biological specimens with a precise control of the delivered dose, i.e. the number of particles per cell. We describe a methodology to manipulate and micro-irradiate early stage C. elegans embryos at a specific phase of the cell division and with a controlled dose using a CPM. To validate this approach, we observe the radiation-induced damage, such as reduced cell mobility, incomplete cell division and the appearance of chromatin bridges during embryo development, in different strains expressing GFP-tagged proteins in situ after irradiation. In addition, as the dosimetry of such experiments cannot be extrapolated from random irradiations of cell populations, realistic three-dimensional models of 2 cell-stage embryo were imported into the Geant4 Monte-Carlo simulation toolkit. Using this method, we investigate the energy deposit in various chromatin condensation states during the cell division phases. The experimental approach coupled to Monte-Carlo simulations provides a way to selectively irradiate a single cell in a rapidly dividing multicellular model with a reproducible dose. This method opens the way to dose-effect investigations following targeted irradiation.

Heavy-Ion Microbeams for Biological Science: Development of System and Utilization for Biological Experiments in QST-Takasaki

Target irradiation of biological material with a heavy-ion microbeam is a useful means to analyze the mechanisms underlying the effects of heavy-ion irradiation on cells and individuals. At QST-Takasaki, there are two heavy-ion microbeam systems, one using beam collimation and the other beam focusing. They are installed on the vertical beam lines of the azimuthally-varying-field cyclotron of the TIARA facility for analyzing heavy-ion radiation effects on biological samples. The collimating heavy-ion microbeam system is used in a wide range of biological research not only in regard to cultured cells but also small individuals, such as silkworms, nematode C. elegans, and medaka fish. The focusing microbeam system was designed and developed to perform more precise target irradiation that cannot be achieved through collimation. This review describes recent updates of the collimating heavy ion microbeam system and the research performed using it. In addition, a brief outline of the focusing microbeam system and current development status is described.

Microbeam evolution: from single cell irradiation to pre-clinical studies

PURPOSE

This review follows the development of microbeam technology from the early days of single cell irradiations, to investigations of specific cellular mechanisms and to the development of new treatment modalities in vivo. A number of microbeam applications are discussed with a focus on pre-clinical modalities and translation towards clinical application.

CONCLUSIONS

The development of radiation microbeams has been a valuable tool for the exploration of fundamental radiobiological response mechanisms. The strength of micro-irradiation techniques lies in their ability to deliver precise doses of radiation to selected individual cells in vitro or even to target subcellular organelles. These abilities have led to the development of a range of microbeam facilities around the world allowing the delivery of precisely defined beams of charged particles, X-rays, or electrons. In addition, microbeams have acted as mechanistic probes to dissect the underlying molecular events of the DNA damage response following highly localized dose deposition. Further advances in very precise beam delivery have also enabled the transition towards new and exciting therapeutic modalities developed at synchrotrons to deliver radiotherapy using plane parallel microbeams, in Microbeam Radiotherapy (MRT).

Region-specific irradiation system with heavy-ion microbeam for active individuals of Caenorhabditis elegans

Radiation may affect essential functions and behaviors such as locomotion, feeding, learning and memory. Although whole-body irradiation has been shown to reduce motility in the nematode Caenorhabditis elegans, the detailed mechanism responsible for this effect remains unknown. Targeted irradiation of the nerve ring responsible for sensory integration and information processing would allow us to determine whether the reduction of motility following whole-body irradiation reflects effects on the central nervous system or on the muscle cells themselves. We therefore addressed this issue using a collimating microbeam system. However, radiation targeting requires the animal to be immobilized, and previous studies have anesthetized animals to prevent their movement, thus making it impossible to assess their locomotion immediately after irradiation. We developed a method in which the animal was enclosed in a straight, microfluidic channel in a polydimethylsiloxane chip to inhibit free motion during irradiation, thus allowing locomotion to be observed immediately after irradiation. The head region (including the central nervous system), mid region around the intestine and uterus, and tail region were targeted independently. Each region was irradiated with 12 000 carbon ions (12C; 18.3 MeV/u; linear energy transfer = 106.4 keV/μm), corresponding to 500 Gy at a φ20 μm region. Motility was significantly decreased by whole-body irradiation, but not by irradiation of any of the individual regions, including the central nervous system. This suggests that radiation inhibits locomotion by a whole-body mechanism, potentially involving motoneurons and/or body-wall muscle cells, rather than affecting motor control via the central nervous system and the stimulation response.

Advances in microbeam technologies and applications to radiation biology

Charged-particle microbeams (CPMs) allow the targeting of sub-cellular compartments with a counted number of energetic ions. While initially developed in the late 1990s to overcome the statistical fluctuation on the number of traversals per cell inevitably associated with broad beam irradiations, CPMs have generated a growing interest and are now used in a wide range of radiation biology studies. Besides the study of the low-dose cellular response that has prevailed in the applications of these facilities for many years, several new topics have appeared recently. By combining their ability to generate highly clustered damages in a micrometric volume with immunostaining or live-cell GFP labelling, a huge potential for monitoring radiation-induced DNA damage and repair has been introduced. This type of studies has pushed end-stations towards advanced fluorescence microscopy techniques, and several microbeam lines are currently equipped with the state-of-the-art time-lapse fluorescence imaging microscopes. In addition, CPMs are nowadays also used to irradiate multicellular models in a highly controlled way. This review presents the latest developments and applications of charged-particle microbeams to radiation biology.

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.

New challenges in radiobiology research with microbeams

There is a continuing interest in the use of microbeam systems designed to deliver ionizing radiation (both photons and particles) with a resolution of a few micrometers or less in biological targets. With more than 30 facilities currently in operation, several new research topics can be explored. In the 9th International Microbeam Workshop held in Darmstadt, Germany, in July 2010, several new ideas and results have been presented, indicating that microbeams will be increasingly important in radiobiology. Subnuclear targeting of single cells for DNA repair studies and microirradiation of 3D or small animal models are among the most promising new research perspectives.

Targeted heavy-ion microbeam irradiation of the embryo but not yolk in the diapause-terminated egg of the silkworm, bombyx mori, induces the somatic mutation

Using heavy-ion microbeam, we report target irradiation of selected compartments within the diapause-terminated egg and its mutational consequences in the silkworm, Bombyx mori. On one hand, carbon-ion exposure of embryo to 0.5-6 Gy increased the somatic mutation frequency, suggesting targeted radiation effects. On the other, such increases were not observed when yolk was targeted, suggesting a lack of nontargeted bystander effect.

Microbeam irradiation of the C. elegans nematode

The understanding of complex radiation responses in biological systems, such as non-targeted effects as represented by the bystander response, can be enhanced by the use of genetically amenable model organisms. Almost all bystander studies to date have been carried out by using conventional single-cell in vitro systems, which are useful tools to characterize basic cellular and molecular responses. A few studies have been reported in monolayer explants and bystander responses have been also investigated in a three-dimensional normal human tissue system. However, despite the well-know usefulness of in vitro models, they cannot capture the complexity of radiation responses of living systems such as animal models. To carry out in vivo studies on the bystander effect we have developed a new technique to expose living organisms using proton microbeams. We report the use of a nematode C. elegans strain with a Green Fluorescent Protein (GFP) reporter for the hsp-4 heat-shock gene as an in vivo model for radiation studies. Exposing animals to heat and chemicals stressors leads to whole body increases in the hsp-4 protein reflected by enhanced fluorescence. We report here that gamma-rays also can induce stress response in a dose dependent manner. However, whole body exposure to stress agents does not allow for evaluation of distance dependent response in non targeted tissues: the so-called bystander effect. We used the RARAF microbeam to site specifically deliver 3 MeV protons to a site in the tail of young worms. GFP expression was enhanced after 24 hours in a number dependent manner at distances > 100 microm from the site of irradiation.

Recent insights into the biological action of heavy-ion radiation

Biological effectiveness varies with the linear energy transfer (LET) of ionizing radiation. During cancer therapy or long-term interplanetary manned explorations, humans are exposed to high-LET energetic heavy ions that inactivate cells more effectively than low-LET photons like X-rays and gamma-rays. Recent biological studies have illustrated that heavy ions overcome tumor radioresistance caused by Bcl-2 overexpression, p53 mutations and intratumor hypoxia, and possess antiangiogenic and antimetastatic potential. Compared with heavy ions alone, the combination with chemical agents (a Bcl-2 inhibitor HA14-1, an anticancer drug docetaxel, and a halogenated pyrimidine analogue 5-iodo-2'-deoxyuridine) or hyperthermia further enhances tumor cell killing. Beer, its certain constituents, or melatonin ameliorate heavy ion-induced damage to normal cells. In addition to effects in cells directly targeted with heavy ions, there is mounting evidence for nontargeted biological effects in cells that have not themselves been directly irradiated. The bystander effect of heavy ions manifests itself as the loss of clonogenic potential, a transient apoptotic response, delayed p53 phosphorylation, alterations in gene expression profiles, and the elevated frequency of gene mutations, micronuclei and chromosome aberrations, which arise in nonirradiated cells having received signals from irradiated cells. Proposed mediating mechanisms involve gap junctional intercellular communication, reactive oxygen species and nitric oxide. This paper reviews briefly the current knowledge of the biological effects of heavy-ion irradiation with a focus on recent findings regarding its potential benefits for therapeutic use as well as on the bystander effect.

Heavy-ion microbeam system at JAEA-Takasaki for microbeam biology

Research concerning cellular responses to low dose irradiation, radiation-induced bystander effects, and the biological track structure of charged particles has recently received particular attention in the field of radiation biology. Target irradiation employing a microbeam represents a useful means of advancing this research by obviating some of the disadvantages associated with the conventional irradiation strategies. The heavy-ion microbeam system at JAEA-Takasaki, which was planned in 1987 and started in the early 1990's, can provide target irradiation of heavy charged particles to biological material at atmospheric pressure using a minimum beam size 5 mum in diameter. A variety of biological material has been irradiated using this microbeam system including cultured mammalian and higher plant cells, isolated fibers of mouse skeletal muscle, silkworm (Bombyx mori) embryos and larvae, Arabidopsis thaliana roots, and the nematode Caenorhabditis elegans. The system can be applied to the investigation of mechanisms within biological organisms not only in the context of radiation biology, but also in the fields of general biology such as physiology, developmental biology and neurobiology, and should help to establish and contribute to the field of "microbeam biology".