Modelling Spatial Scales of Dose Deposition and Radiolysis Products from Gold Nanoparticle Sensitisation of Proton Therapy in A Cell: From Intracellular Structures to Adjacent Cells

Gold nanoparticle (GNP) enhanced proton therapy is a promising treatment concept offering increased therapeutic effect. It has been demonstrated in experiments which provided indications that reactive species play a major role. Simulations of the radiolysis yield from GNPs within a cell model were performed using the Geant4 toolkit. The effect of GNP cluster size, distribution and number, cell and nuclear membrane absorption and intercellular yields were evaluated. It was found that clusters distributed near the nucleus increased the nucleus yield by 91% while reducing the cytoplasm yield by 7% relative to a disperse distribution. Smaller cluster sizes increased the yield, 200 nm clusters had nucleus and cytoplasm yields 117% and 35% greater than 500 nm clusters. Nuclear membrane absorption reduced the cytoplasm and nucleus yields by 8% and 35% respectively to a permeable membrane. Intercellular enhancement was negligible. Smaller GNP clusters delivered near sub-cellular targets maximise radiosensitisation. Nuclear membrane absorption reduces the nucleus yield, but can damage the membrane providing another potential pathway for biological effect. The minimal effect on adjacent cells demonstrates that GNPs provide a targeted enhancement for proton therapy, only effecting cells with GNPs internalised. The provided quantitative data will aid further experiments and clinical trials.

Potential TSPO Ligand and Photooxidation Quencher Isorenieratene from Arctic Ocean Rhodococcus sp. B7740

Due to its special aromatic structure, isorenieratene is thought to be an active natural antioxidant and photo/UV damage inhibitor. In this work, isorenieratene that was extracted from Rhodococcus sp. B7740 isolated from the Arctic Ocean, showed excellent scavenging ability of both singlet oxygen and hydroxyl radical in the UVB-induced auto-oxidation process using the EPR method. Within an ARPE-19 cell model damaged by UVB radiation, isorenieratene showed fine protective effects (1.13 ± 0.03 fold) compared with macular xanthophylls (MXs) through upregulating of tspo. The molecular docking was firstly performed to investigate the interaction of isorenieratene with TSPO as a special ligand. Results showed isorenieratene might form a better binding conformation (S-score −8.5438) than MXs and indicate that isorenieratene not only can function as a direct antioxidant but also activate tspo in ARPE-19 cells. Thus, isorenieratene might ease the UV-related damages including age-related macular degeneration (AMD).

Towards predicting intracellular radiofrequency radiation effects

Recent experiments have reported an effect of weak radiofrequency magnetic fields in the MHz-range on the concentrations of reactive oxygen species (ROS) in living cells. Since the energy that could possibly be deposited by the radiation is orders of magnitude smaller than the energy of molecular thermal motion, it was suggested that the effect was caused by the interaction of RF magnetic fields with transient radical pairs within the cells, affecting the ROS formation rates through the radical pair mechanism. It is, however, at present not entirely clear how to predict RF magnetic field effects at certain field frequency and intensity in nanoscale biomolecular systems. We suggest a possible recipe for interpreting the radiofrequency effects in cells by presenting a general workflow for calculation of the reactive perturbations inside a cell as a function of RF magnetic field strength and frequency. To justify the workflow, we discuss the effects of radiofrequency magnetic fields on generic spin systems to particularly illustrate how the reactive radicals could be affected by specific parameters of the experiment. We finally argue that the suggested workflow can be used to predict effects of radiofrequency magnetic fields on radical pairs in biological cells, which is specially important for wireless recharging technologies where one has to know of any harmful effects that exposure to such radiation might cause.

Optoregulated Biointerfaces to Trigger Cellular Responses

Optoregulated biointerfaces offer the possibility to manipulate the interactions between cell membrane receptors and the extracellular space. This Invited Feature Article summarizes recent efforts by our group and others during the past decade to develop light-responsive biointerfaces to stimulate cells and elicit cellular responses using photocleavable protecting groups (PPG) as our working tool. This article begins by providing a brief introduction to available PPGs, with a special focus on the widely used o-nitrobenzyl family, followed by an overview of molecular design principles for the control of bioactivity in the context of cell-material interactions and the characterization methods to use in following the photoreaction at surfaces. We present various light-guided cellular processes using PPGs, including cell adhesion, release, migration, proliferation, and differentiation, both in vitro and in vivo. Finally, this Invited Feature Article closes with our perspective on the current status and future challenges of this topic.

Dose calculations in a cell monolayer for high-throughput irradiation with proton beams generated by PW lasers for space applications

One of the specific properties of laser-driven radiation is a broadband energy spectrum, which is also a feature of the space radiation fields. This property can be used in materials science studies or radiobiology experiments to simulate the energy spectrum of space radiation exposures in a ground-based laboratory. However, the differences in effects between the higher dose rates of laser generated radiation and the lower dose rates of space radiation have to be investigated in separate, prior studies. A design for a high-throughput irradiation experiment and the associated Monte Carlo dose calculations for a broadband energy proton beam depositing energy in a cell monolayer is presented. Dose control and dose uniformity in the cell monolayer was achieved in the simulations using a variable thickness Ni attenuator. A set of target doses from 0.2 Gy to 4 Gy was obtained and dose uniformity was optimized to less than 4% variability. This work opens the possibility of single or multiple exposures, controllable, high-throughput irradiation experiments on biological samples or materials, using broadband energy particle beams generated by lasers, with relevance for space applications.

Sacrificial-layer free transfer of mammalian cells using near infrared femtosecond laser pulses

Laser-induced cell transfer has been developed in recent years for the flexible and gentle printing of cells. Because of the high transfer rates and the superior cell survival rates, this technique has great potential for tissue engineering applications. However, the fact that material from an inorganic sacrificial layer, which is required for laser energy absorption, is usually transferred to the printed target structure, constitutes a major drawback of laser based cell printing. Therefore alternative approaches using deep UV laser sources and protein based acceptor films for energy absorption, have been introduced. Nevertheless, deep UV radiation can introduce DNA double strand breaks, thereby imposing the risk of carcinogenesis. Here we present a method for the laser-induced transfer of hydrogels and mammalian cells, which neither requires any sacrificial material for energy absorption, nor the use of UV lasers. Instead, we focus a near infrared femtosecond (fs) laser pulse (λ = 1030 nm, 450 fs) directly underneath a thin cell layer, suspended on top of a hydrogel reservoir, to induce a rapidly expanding cavitation bubble in the gel, which generates a jet of material, transferring cells and hydrogel from the gel/cell reservoir to an acceptor stage. By controlling laser pulse energy, well-defined cell-laden droplets can be transferred with high spatial resolution. The transferred human (SCP1) and murine (B16F1) cells show high survival rates, and good cell viability. Time laps microscopy reveals unaffected cell behavior including normal cell proliferation.

Oxidative stress response in SH-SY5Y cells exposed to short-term 1800 MHz radiofrequency radiation

The exact mechanism that could explain the effects of radiofrequency (RF) radiation exposure at non-thermal level is still unknown. Increasing evidence suggests a possible involvement of reactive oxygen species (ROS) and development of oxidative stress. To test the proposed hypothesis, human neuroblastoma cells (SH-SY5Y) were exposed to 1800 MHz short-term RF exposure for 10, 30 and 60 minutes. Electric field strength within Gigahertz Transverse Electromagnetic cell (GTEM) was 30 V m^-1 and specific absorption rate (SAR) was calculated to be 1.6 W kg^-1. Cellular viability was measured by MTT assay and level of ROS was determined by fluorescent probe 2',7'-dichlorofluorescin diacetate. Concentrations of malondialdehyde and protein carbonyls were used to assess lipid and protein oxidative damage and antioxidant activity was evaluated by measuring concentrations of total glutathione (GSH). After radiation exposure, viability of irradiated cells remained within normal physiological values. Significantly higher ROS level was observed for every radiation exposure time. After 60 min of exposure, the applied radiation caused significant lipid and protein damage. The highest GSH concentration was detected after 10 minute-exposure. The results of our study showed enhanced susceptibility of SH-SY5Y cells for development of oxidative stress even after short-term RF exposure.

Guiding cellular activity with polarized light

Actin, cytoskeleton protein forming microfilaments, play a crucial role in cellular motility. Here we show that exposure to very low levels of polarized light guide their orientation in-vivo within the live cell. Using a simple model to describe the role of actin-filament orientation in directional cellular motion, we demonstrate that the actin polymerization/depolymerization mechanism develops primarily along this direction and, under certain conditions, can lead to guidance of the cell movement. Our results also show a dose dependent increase in actin activity in direct correspondence to the level of laser irradiance. We found that total expression of Tau protein, which stabilize microtubules, was decreased by the irradiance, indicating that exposure to the light may change the activity of kinase, leading to increased cell activity.

No adaptive response is induced by chronic low-dose radiation from Ra-226 in the CHSE/F fish embryonic cell line and the HaCaT human epithelial cell line

PURPOSE

To determine whether chronic low-dose α-particle radiation from Ra-226 over multiple cell generations can lead to an adaptive response in CHSE/F fish embryonic cells or HaCaT human epithelial cells receiving subsequent acute high-dose γ-ray radiation.

METHODS

CHSE/F and HaCaT cells were exposed to very low doses of Ra-226 in medium for multiple generations prior to being challenged by a higher dose γ-ray radiation. The clonogenic assay was used to test the clonogenic survival of cells with or without being pretreated by radiation from Ra-226.

RESULTS

In general, pretreatment with chronic radiation has no significant influence on the reaction of cells to the subsequent challenge radiation. Compared to unprimed cells, the change in clonogenic survival of primed cells after receiving challenge radiation is mainly due to the influence of the chronic exposure, and there's little adaptive response induced. However at several dose points, pretreatment of CHSE/F fish cells with chronic radiation resulted in a radiosensitive response to a challenge dose of γ-ray radiation, and pretreatment of HaCaT cells resulted in no effect except for a slightly radioresistant response to the challenge radiation which was not significant.

CONCLUSION

The results suggest that chronic low-dose radiation is not effective enough to induce adaptive response. There was a difference between human and fish cells and it may be important to consider results from multiple species before making conclusions about effects of chronic or low doses of radiation in the environment. The term "radiosensitive" or "adaptive" make no judgment about whether such responses are ultimately beneficial or harmful.

The Effect of Electron Beam Irradiation in Environmental Scanning Transmission Electron Microscopy of Whole Cells in Liquid

Whole cells can be studied in their native liquid environment using electron microscopy, and unique information about the locations and stoichiometry of individual membrane proteins can be obtained from many cells thus taking cell heterogeneity into account. Of key importance for the further development of this microscopy technology is knowledge about the effect of electron beam radiation on the samples under investigation. We used environmental scanning electron microscopy (ESEM) with scanning transmission electron microscopy (STEM) detection to examine the effect of radiation for whole fixed COS7 fibroblasts in liquid. The main observation was the localization of nanoparticle labels attached to epidermal growth factor receptors (EGFRs). It was found that the relative distances between the labels remained mostly unchanged (<1.5%) for electron doses ranging from the undamaged native state at 10 e-/Å2 toward 103 e-/Å2. This dose range was sufficient to determine the EGFR locations with nanometer resolution and to distinguish between monomers and dimers. Various different forms of radiation damage became visible at higher doses, including severe dislocation, and the dissolution of labels.

Modeling cell response to low doses of photon irradiation--Part 1: on the origin of fluctuations

Intra- and inter-individual variability is a well-known aspect of biological responses of cells observed at low doses of radiation, whichever the phenomenon considered (adaptive response, bystander effects, genomic instability, etc.). There is growing evidence that low-dose phenomena are related to cell mechanisms other than DNA damage and misrepair, meaning that other cellular structures may play a crucial role. Therefore, in this study, a series of calculations at low doses was carried out to study the distribution of specific energies from different irradiation doses (3, 10 and 30 cGy) in targets of different sizes (0.1, 1 and 10 μm) corresponding to the dimensions of different cell structures. The results obtained show a strong dependence of the probability distributions of specific energies on the target size: targets with dimensions comparable to those of the cell show a Gaussian-like distribution, whereas very small targets are very likely to not be hit. A statistical analysis showed that the level of fluctuations in the fraction of aberrant cells is only related to the fraction of aberrant cells and the number of irradiated cells, regardless of, for instance, the heterogeneity in cell response.

Single proton counting at the RIKEN cell irradiation facility

We present newly developed tapered capillaries with a scintillator window, which enable us to count single protons at the RIKEN cell irradiation setup. Their potential for performing single proton irradiation experiments at our beamline setup is demonstrated with CR39 samples, showing a single proton detection fidelity of 98%.

Effects of ionizing radiation on biological molecules--mechanisms of damage and emerging methods of detection

SIGNIFICANCE

The detrimental effects of ionizing radiation (IR) involve a highly orchestrated series of events that are amplified by endogenous signaling and culminating in oxidative damage to DNA, lipids, proteins, and many metabolites. Despite the global impact of IR, the molecular mechanisms underlying tissue damage reveal that many biomolecules are chemoselectively modified by IR.

RECENT ADVANCES

The development of high-throughput "omics" technologies for mapping DNA and protein modifications have revolutionized the study of IR effects on biological systems. Studies in cells, tissues, and biological fluids are used to identify molecular features or biomarkers of IR exposure and response and the molecular mechanisms that regulate their expression or synthesis.

CRITICAL ISSUES

In this review, chemical mechanisms are described for IR-induced modifications of biomolecules along with methods for their detection. Included with the detection methods are crucial experimental considerations and caveats for their use. Additional factors critical to the cellular response to radiation, including alterations in protein expression, metabolomics, and epigenetic factors, are also discussed.

FUTURE DIRECTIONS

Throughout the review, the synergy of combined "omics" technologies such as genomics and epigenomics, proteomics, and metabolomics is highlighted. These are anticipated to lead to new hypotheses to understand IR effects on biological systems and improve IR-based therapies.

Synergistic dual-modality in vivo upconversion luminescence/X-ray imaging and tracking of amine-functionalized NaYbF(4):Er nanoprobes

In this work, the amine-functionalized NaYbF4:Er nanoparticles were developed as dual-modal nanoprobes for synergistic upconversion (UC) luminescence and X-ray imaging in a single system by a simple one-step method of simultaneous synthesis and surface modification. The water-soluble NaYbF4:Er nanoparticles present excellent green and dominant red UC emissions. The in vitro cell imaging shows that the high-contrast green and intense red UC emissions can be observed from HeLa cells treated with these nanoparticles, indicating the successful labeling of HeLa cells. Moreover, the localized spectra measured from HeLa cells and background presented significant green and dominant red UC emissions with the absence of any autofluorescence, further verifying that these nanoparticles can be successfully used as ideal probes for optical UC bioimaging with high contrast and non-autofluorescence. In addition, the amine-functionalized NaYbF4:Er nanoparticles maintained low cell toxicity in HeLa cells evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. More importantly, these amine-functionalized NaYbF4:Er nanoparticles can also be used as X-ray imaging, owing to the large X-ray absorption efficiency of the Yb ion. The synergistic in vivo UC and X-ray imaging present significant UC luminescence and X-ray signals in the same region of a nude mouse, and the two signals are matched very well, which provides direct evidence for simultaneous UC luminescence and X-ray imaging in a single compound of lanthanide-doped material. Moreover, ex vivo UC imaging shows that these nanoparticles are first accumulated in the lung and gradually translocated from the lung into the liver. These results demonstrate that the amine-functionalized NaYbF4:Er nanoparticles presented here are very attractive nanoprobes for dual-modal UC luminescence and X-ray imaging with low cytotoxicity, autofluorescence free, and synergistic combination of the advantages of the two imaging modalities.

Certitudes and controversies regarding the deleterious effects of low doses ionizing radiation

The problem of the deleterious effects of ionizing radiation must be a constant preoccupation of the medical staff. We must never forget that radiations can cure (by increasing the diagnostic accuracy and by the benefic use of radiotherapy), but can also generate cancer and genomic instability. All the governments have the desire to use the "cheap" (it's cheap when you do not take into consideration all the spenditures regarding the monitorisation of radiation workers and the cost of decontamination) nuclear energy. We must underline, also, the fact that a too frequent exposure to ionizing radiation (especially by CT examinations) is generating undesired consequences, and that the direct irradiation and the bystander effect can create a genomic instability that is "transferred" to the following generation. As, nowadays, it is almost impossible to live in an environment devoid of risks, we must try to reduce them significantly.

Microdosimetry of alpha particles for simple and 3D voxelised geometries using MCNPX and Geant4 Monte Carlo codes

Microdosimetry using Monte Carlo simulation is a suitable technique to describe the stochastic nature of energy deposition by alpha particle at cellular level. Because of its short range, the energy imparted by this particle to the targets is highly non-uniform. Thus, to achieve accurate dosimetric results, the modelling of the geometry should be as realistic as possible. The objectives of the present study were to validate the use of the MCNPX and Geant4 Monte Carlo codes for microdosimetric studies using simple and three-dimensional voxelised geometry and to study their limit of validity in this last case. To that aim, the specific energy (z) deposited in the cell nucleus, the single-hit density of specific energy f(1)(z) and the mean-specific energy were calculated. Results show a good agreement when compared with the literature using simple geometry. The maximum percentage difference found is <6 %. For voxelised phantom, the study of the voxel size highlighted that the shape of the curve f(1)(z) obtained with MCNPX for <1 µm voxel size presents a significant difference with the shape of non-voxelised geometry. When using Geant4, little differences are observed whatever the voxel size is. Below 1 µm, the use of Geant4 is required. However, the calculation time is 10 times higher with Geant4 than MCNPX code in the same conditions.

A new device to expose cells to changing dose rates of ionising radiation

In many exposure scenarios to ionising radiation, the dose rate is not constant. Despite this, most in vitro studies aimed at investigating the effects of ionising radiation are carried out exposing samples at constant dose rates. Consequently, very little data exist on the biological effects of exposures to changing dose rates. This may be due to technical limitations of standard irradiation facilities, but also to the fact that the importance of research in this area has not been appreciated. We have recently shown that cells exposed to a decreasing dose rate suffer higher levels of cytogenetic damage than do cells exposed to an increasing or a constant dose rate. To further study the effects of changing dose rates, a new device was constructed that permits the exposure of cell samples in tubes, flasks or Petri dishes to changing dose rates of X-rays. This report presents the technical data, performance and dosimetry of this novel device.

Current progress of the biological single-ion microbeam at FUDAN

A biological microbeam for precisely positioned single-ion/single cell irradiation is built in the Institute of Modern Physics in Fudan University, Shanghai, China, based on the tandem accelerator (2 × 3MV) in the laboratory. In this paper, the developing progress of the FUDAN microbeam is reported, including the newly constructed beam line, the microbeam collimator, the ion detection system, and the cell-imaging and targeting systems. Statistical models are proposed for evaluating the spatial resolution and dosage precision of the microbeam. By taking the collimated ions as a Gaussian beam, the spatial resolution can be evaluated by the full width at half maximum of the 2-D Gaussian distribution, which is determined by fitting the proportions of peripheral pits outside specific radii in the pit clusters etched on ion track detectors to a 2-D Gaussian distribution. In the preset hitting of defined ion number, by taking the real delivered number of ions as an independent identically distributed random variable (iidrv), according to the Law of Large Numbers and Central Limit Theorem, the expected value μ and standard deviation σ of the real delivered ion number in a preset N-ion hitting can be determined by approaching the normal distribution of N (μ, σ (2)/n) with the proportions of the mean counts of pits in multiple pit clusters on ion track detectors. By the values of μ, σ and additional assumptions, statistical dosage precision evaluations can be made on the preset hitting. From the linear fit curve of μ(N) and the power function fit curve of σ(N) on different preset ion numbers, characteristic factors k, b, A, p can be extracted for a precision evaluation independent of the specific preset ion number.

Natural agents: cellular and molecular mechanisms of photoprotection

The skin is the largest organ of the body that produces a flexible and self-repairing barrier and protects the body from most common potentially harmful physical, environmental, and biological insults. Solar ultraviolet (UV) radiation is one of the major environmental insults to the skin and causes multi-tiered cellular and molecular events eventually leading to skin cancer. The past decade has seen a surge in the incidence of skin cancer due to changes in life style patterns that have led to a significant increase in the amount of UV radiation that people receive. Reducing excessive exposure to UV radiation is desirable; nevertheless this approach is not easy to implement. Therefore, there is an urgent need to develop novel strategies to reduce the adverse biological effects of UV radiation on the skin. A wide variety of natural agents have been reported to possess substantial skin photoprotective effects. Numerous preclinical and clinical studies have elucidated that natural agents act by several cellular and molecular mechanisms to delay or prevent skin cancer. In this review article, we have summarized and discussed some of the selected natural agents for skin photoprotection.

The impact of adaptive and non-targeted effects in the biological responses to low dose/low fluence ionizing radiation: the modulating effect of linear energy transfer

A large volume of laboratory and human epidemiological studies have shown that high doses of ionizing radiation engender significant health risks. In contrast, the health risks of low level radiation remain ambiguous and have been the subject of intense debate. To reduce the uncertainty in evaluating these risks, research advances in cellular and molecular biology are being used to characterize the biological effects of low dose radiation exposures and their underlying mechanisms. Radiation type, dose rate, genetic susceptibility, cellular redox environment, stage of cell growth, level of biological organization and environmental parameters are among the factors that modulate interactions among signaling processes that determine short- and long-term outcomes of low dose exposures. Whereas, recommended radiation protection guidelines assume a linear dose-response relationship in estimating radiation cancer risk, in vitro and in vivo investigations of phenomena such as adaptive responses and non-targeted effects, namely bystander effects and genomic instability, suggest that low dose/low fluence-induced signaling events act to alter linearity of the dose-response relation as supported by the biophysical argument. The latter predicts that increases in dose simply increase the probability that a given cell in a tissue will be intersected by an electron track, and by corollary, each unit of radiation, no matter how small would increases risk. These predictions assume that similar molecular events mediate both low and high dose radiobiological effects, and the cumulative risk from two sequential radiation exposures can never be less than one alone.

Radiation-induced genomic instability

Radiation induced genomic instability can be observed in the progeny of irradiated cells multiple generations after irradiation of parental cells. The phenotype is well established both in vivo (Morgan 2003) and in vitro (Morgan 2003), and may be critical in radiation carcinogenesis (Little 2000, Huang et al. 2003). Instability can be induced by both the deposition of energy in irradiated cells as well as by signals transmitted by irradiated (targeted) cells to non-irradiated (non-targeted) cells (Kadhim et al. 1992, Lorimore et al. 1998). Thus both targeted and non-targeted cells can pass on the legacy of radiation to their progeny. However the radiation induced events and cellular processes that respond to both targeted and non-targeted radiation effects that lead to the unstable phenotype remain elusive.

Far-field superposition method for three-dimensional computation of light scattering from multiple cells

A linear coherent superposition method for estimating the plane wave far-field scattering pattern from multiple biological cells computed by the finite-difference time-domain (FDTD) method is presented. The method enables the FDTD simulation results of scattering from a small number of complex scatterers, such as biological cells, to be used to estimate the far-field pattern from a large group of those same scatterers. The superposition method can be used to reduce the computational cost of FDTD simulations by enabling a single large scattering problem to be broken into smaller problems with more practical computational requirements. It is found that the method works best in cases where there is little multiple scattering interaction between adjacent cells, so the far-field pattern of multicell geometry can simply be calculated as a phase-adjusted linear superposition of the scattering from individual cells. A strategy is also presented for choosing the minimum number of cells in cases with significant multiple scattering interactions between cells.

Optofluidic chip for single cell trapping and stretching fabricated by a femtosecond laser

The authors present the design and optimization of an optofluidic monolithic chip, able to provide optical trapping and controlled stretching of single cells. The chip is fabricated in a fused silica glass substrate by femtosecond laser micromachining which can produce both optical waveguides and microfluidic channels with great accuracy. A new fabrication procedure adopted in this work allows the demonstration of microchannels with a square cross-section, thus guaranteeing an improved quality of the trapped cell images. Femtosecond laser micromachining emerges as a promising technique for the development of multifunctional integrated biophotonic devices that can be easily coupled to a microscope platform, thus enabling a complete characterization of the cells under test.

Optical manipulation for single-cell studies

In the last decade optical manipulation has evolved from a field of interest for physicists to a versatile tool widely used within life sciences. This has been made possible in particular due to the development of a large variety of imaging techniques that allow detailed information to be gained from investigations of single cells. The use of multiple optical traps has high potential within single-cell analysis since parallel measurements provide good statistics. Multifunctional optical tweezers are, for instance, used to study cell heterogeneity in an ensemble, and force measurements are used to investigate the mechanical properties of individual cells. Investigations of molecular motors and forces on the single-molecule level have led to discoveries that would have been difficult to make with other techniques. Optical manipulation has prospects within the field of cell signalling and tissue engineering. When combined with microfluidic systems the chemical environment of cells can be precisely controlled. Hence the influence of pH, salt concentration, drugs and temperature can be investigated in real time. Fast advancing technical developments of automated and user-friendly optical manipulation tools and cross-disciplinary collaboration will contribute to the routinely use of optical manipulation techniques within the life sciences.

Picosecond acoustics in vegetal cells: non-invasive in vitro measurements at a sub-cell scale

A 100 fs laser pulse passes through a single transparent cell and is absorbed at the surface of a metallic substrate. Picosecond acoustic waves are generated and propagate through the cell in contact with the metal. Interaction of the high frequency acoustic pulse with a probe laser light gives rise to Brillouin oscillations. The measurements are thus made with lasers for both the opto-acoustic generation and the acousto-optic detection, and acoustic frequencies as high as 11 GHz can be detected, as reported in this paper. The technique offers perspectives for single cell imaging. The in-plane resolution is limited by the pump and probe spot sizes, i.e. approximately 1 microm, and the in-depth resolution is provided by the acoustic frequencies, typically in the GHz range. The effect of the technique on cell safety is discussed. Experiments achieved in vegetal cells illustrate the reproducibility and sensitivity of the measurements. The acoustic responses of cell organelles are significantly different. The results support the potentialities of the hypersonic non-invasive technique in the fields of bio-engineering and medicine.

Calculation of cellular oxygen concentration for photodynamic therapy in vitro

In vitro photodynamic therapy experiments are usually performed by irradiating cells in confluent or nearly confluent monolayer cultures. Oxygen is consumed in the monolayer by photodynamic reactions and cellular respiration and is supplied by diffusion from the overlying medium. Calculations of oxygen concentration by numerical solution of the time-dependent diffusion equation show that hypoxia can be induced in the monolayer under typical PDT conditions and that this will limit the total treatment effect. There is an optimum fluence rate at which the greatest singlet oxygen dose can be delivered before hypoxia becomes limiting. It is recommended that researchers use these calculations to avoid hypoxia or confirm that fortuitous oxygen transport by other mechanisms (e.g., convection) is adequate to prevent it.

Variations in radiosensitivity among individuals: a potential impact on risk assessment?

To have an impact on risk assessment for purposes of radiation protection recommendations, significantly broad variations in carcinogenic radiosensitivity would have to exist in significant proportions in the human population. Even if we knew all the genes where mutations would have major effects, individual genome sequencing does not seem useful, since we do not know all these genes, nor can we be certain of the phenotypic effect of polymorphisms discovered. Further, sequencing would not reveal epigenetic changes in gene expression. Another approach to develop phenotypic biomarkers for cells or tissues for which variations in radiation response may reflect the variations in carcinogenic sensitivity. To be useful, experimental evidence for such a correlation would be crucial, and it is also evident that correlations may be tissue or tumor specific. Some cellular markers are discussed that have shown promise in this regard. They include chromosome aberration induction and DNA repair assays that are sufficiently sensitive to measure after modest or low doses or dose rates. To this end we summarize here some of these assays and review the results of a number of experiments from our laboratory that show clear differences in DNA repair capacity reflected by gamma-H2AX foci formation in cells from a high proportion (perhaps 1/3) of apparently normal individuals. A low dose-rate assay was used to amplify such differences. Another promising assay combines G(2) chromosomal radiosensitivity with the above gamma-H2AX foci on mitotic chromosomes. There are other potentially useful assays as well.

Flow cytometry with gold nanoparticles and their clusters as scattering contrast agents: FDTD simulation of light-cell interaction

The formulation of the finite-difference time-domain (FDTD) approach is presented in the framework of its potential applications to in-vivo flow cytometry based on light scattering. The consideration is focused on comparison of light scattering by a single biological cell alone in controlled refractive-index matching conditions and by cells labeled by gold nanoparticles. The optical schematics including phase contrast (OPCM) microscopy as a prospective modality for in-vivo flow cytometry is also analyzed. The validation of the FDTD approach for the simulation of flow cytometry may open up a new avenue in the development of advanced cytometric techniques based on scattering effects from nanoscale targets.

Radon: Current Challenges in Cellular Radiobiology

Radon is by far the most important contributor to the collective dose equivalent. Most of what is known about the hazards of radon daughters comes from epidemiological studies of miners. There are a few well defined areas in which in vitro research can complement such studies: First, more data on the relative effects of differing energy (LET) alpha-particles would help: (1) understand the significance of the depth of sensitive cells in the bronchial epithelium--which varies between individuals, as well as between smokers and non-smokers, and between miners and non-miners; (2) understand the relative hazards of radon and thoron daughters. Second, reliable methods for predicting high LET responses from low LET response, would enable Japanese A-bomb survivor data to be applied with confidence. Third, understanding the effects of single-particle traversals of cells relative to multiple traversals could allow reliable extrapolation of epidemiological miner data to low exposures. Fourth, a better understanding of the nature of the interaction between tobacco and radiation damage would help predict the effect of radon on non-smokers.

Cell response to ionising radiation analysed by gene expression patterns

Following ionising radiation exposure of living cells several mechanisms are activated through gene modulations. The measurement of these modifications can be done with QT-PCR and, since about 10 years, microarray technique. The latter approach has the advantage to allow a global monitoring of the complex cellular responses to radiation-induced stress and has been proposed to be used for dose assessment. Even if some publications have identified sets of genes specific to given doses, and that some of the genes have an induction proportional to the dose, a precise estimation of the received dose seems difficult with gene expression, at least in the near future. Nevertherless, in vivo studies have shown that gene profiles of individuals chronically exposed to a cumulative dose of more than 10 mSv are significantly modified. This highlights the great potential of microarray approaches in the detection of low dose exposure.

Cellular automaton model of cell response to targeted radiation

It has been shown that the response of cells to low doses of radiation is not linear and cannot be accurately extrapolated from the high dose response. To investigate possible mechanisms involved in the behaviour of cells under very low doses of radiation, a cellular automaton (CA) model was created. The diffusion and consumption of glucose in the culture dish were computed in parallel to the growth of cells. A new model for calculating survival probability was introduced; the communication between targeted and non-targeted cells was also included. Early results on the response of non-confluent cells to targeted irradiation showed the capability of the model to take account for the non-linear response in the low-dose domain.

Lethal events in V79 cells irradiated by low-energy protons and correlations with distribution patterns of energy deposition, radical concentration and DNA damage

Published survival data of V79 cells irradiated by 0.5-5.0 MeV (7-40 keV/microm) protons have been analyzed with a detailed radiobiological model to estimate the per-track yields of lethal lesions. Their correlations with distribution patterns of deposited energy, radical concentrations and with the yields of specific classes of DNA damage have been studied. The observed correlations indicate a potential interpretation of DNA damage lethal for the cell and the initial physical and chemical processes leading to such damage.

Oscillations and bistability in the stochastic model of p53 regulation

The p53 regulatory pathway controls cell responses, which include cell cycle arrest, DNA repair, apoptosis and cellular senescence. We propose a stochastic model of p53 regulation, which is based on two feedback loops: the negative, coupling p53 with its immediate downregulator Mdm2, and the positive, which involves PTEN, PIP3 and Akt. Existence of the negative feedback assures homeostasis of healthy cells and oscillatory responses of DNA-damaged cells, which are persistent when DNA repair is inefficient and the positive feedback loop is broken. The positive feedback destroys the negative coupling between Mdm2 and p53 by sequestering most of Mdm2 in cytoplasm, so it may no longer prime the nuclear p53 for degradation. It works as a clock, giving the cell some time for DNA repair. However, when DNA repair is inefficient, the active p53 rises to a high level and triggers transcription of proapoptotic genes. As a result, small DNA damage may be repaired and the cell may return to its initial "healthy" state, while the extended damage results in apoptosis. The stochasticity of p53 regulation, introduced at the levels of gene expression, DNA damage and repair, leads to high heterogeneity of cell responses and causes cell population split after irradiation into subpopulations of apoptotic and surviving cells, with fraction of apoptotic cells growing with the irradiation dose.

Cellular low-dose effects of ionizing radiation

The most important physical quantity used to define the deposition of energy in organs and tissues from ionizing radiation is the absorbed dose, but this measure does not characterize the fluctuation of energy absorption resulting from the stochastic nature of the energy deposition events in individual cells. The fluctuation in the energy deposition between cells in a tissue is generally disregarded, but can be significant when the possible effects of ionizing radiation on cells at low doses are considered. Current models of radiation effects in cellular systems are based on direct damage to nuclear DNA being an initiating event in the carcinogenic process. For a given type of radiation, DNA damage is induced in proportion to dose, which implies a linear relationship between cancer induction and dose in the low-dose region. These models have been challenged with a range of studies showing effects in the absence of direct DNA damage due to energy deposition. A range of new observed non-targeted effects of biological responses to radiation shows other mechanisms of action: genomic instability, low dose hypersensitivity, adaptive responses, inverse dose-rate and bystander effects. They are important in determining the biological responses at low doses of radiation and have the potential to influence the shape of the dose-effect relationship by a saturating response above a threshold dose. There is convincing epidemiological evidence that doses of ionizing radiation above about a few tens of mGy cause a small but significant increase in cancer risk.

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".

Cell Type Specific Redox Status is Responsible for Diverse Electromagnetic Field Effects

Epidemiologic and experimental research on the potential carcinogenic effects of extremely low frequency electromagnetic fields (ELF-EMF) has been performed for a long time. Epidemiologic studies regarding ELF-EMF-exposure have focused primarily on leukaemia development due to residential sources in children and adults, and from occupational exposure in adults, but also on other kinds of cancer. Genotoxic investigations of EMF have shown contradictory results, a biological mechanism is still lacking that can explain the link between cancer development and ELF-EMF-exposure. Recent laboratory research has attempted to show general biological effects, and such that could be related to cancer development and/or promotion. Metabolic processes which generate oxidants and antioxidants can be influenced by environmental factors, such as ELF-EMF. Increased ELF-EMF exposure can modify the activity of the organism by reactive oxygen species leading to oxidative stress. It is well established that free radicals can interact with DNA resulting in single strand breaks. DNA damage could become a site of mutation, a key step to carcinogenesis. Furthermore, different cell types react differently to the same stimulus, because of their cell type specific redox status. The modulation of cellular redox balance by the enhancement of oxidative intermediates, or the inhibition or reduction of antioxidants, is discussed in this review. An additional aspect of free radicals is their function to influence other illnesses such as Parkinson's and Alzheimer's diseases. On the other hand, modulation of antioxidants by ELF-EMF can lower the intracellular defence activity promoting the development of DNA damage. It has also been demonstrated that low levels of reactive oxygen species trigger intracellular signals that involve the transcription of genes and leading to responses including cell proliferation and apoptosis. In this review, a general overview is given about oxidative stress, as well as experimental studies are reviewed as they are related to changes in oxidant and antioxidant content after ELF-EMF exposure inducing different biological effects. Finally, we conclude from our review that modulations on the oxidant and antioxidant level through ELF-EMF exposure can play a causal role in cancer development.

Cellular metabolic responses of PET radiotracers to (188)Re radiation in an MCF7 cell line containing dominant-negative mutant p53

We investigated the relations between the cell uptakes of metabolic radiotracers and beta-radiation pretreatment using a dominant mutant p53 (p53mt) cell line to evaluate the effects of p53 genes on (18)F labeled positron emission tomography (PET) radiotracer uptakes.

METHODS

pCMV-Neo-Bam (control), which contains a neo-resistance marker, and p53 dominant-negative mutant expression constructs were stably transfected into MCF7 cell line. Cells were plated in 24-well plates at 1.0x10(5) cells for 18 h. Rhenium-188 ((188)Re) (a beta emitter) was added to the medium (3.7, 18.5, 37 MBq) and incubated for 24 h. We performed gamma-counting to determine the cellular uptakes of 2-[(18)F]fluoro-2-deoxy-d-glucose (FDG), o-(2-[(18)F]fluoroethyl)-l-tyrosine (FET) and 2'-[(18)F]fluoro-2'-deoxythymidine (FLT) (370 kBq, 60 min). Cell viabilities were determined by trypan blue staining and flow cytometry.

RESULTS

p53mt cells showed 1.5-2-fold higher FDG uptake than wild-type p53 cells in basal condition, and the difference of FDG uptake was greater after (188)Re treatment (P<.01). FET uptake increased with (188)Re dose without a significant difference between p53 statuses. p53mt cells showed lower FLT uptake than wild-type p53 cells in basal condition, and the difference of FLT uptake was greater after (188)Re treatment. By cell viability testing and FACS analysis, p53mt cells showed lower viability and a larger apoptotic fraction (sub-G1) than wild-type p53 cells after (188)Re treatment.

CONCLUSION

We speculate that p53 dysfunction increases glucose and decreases thymidine metabolism in cancer cells and that this may be exaggerated by (188)Re beta-radiation. Our findings suggest that FDG could reflect tumor viability and malignant potential after (188)Re beta-radiation treatment, whereas FLT could be a more useful PET radiotracer for assessing therapeutic response to beta-radiation, especially in cancer cells with an altered function of p53.

[Vector potential as a channel of informational effect on living objects]

The physical properties of the vector potential were considered in terms of the problem of bioactivity of electromagnetic fields. A possible primary mechanism underlying the effect of vector potentials on elementary processes of charge transport were considered by analogy with the well-known Aharonov-Bohms and Josephsons effects. The possibility of using the curl-free vector potential for "force-free" information effect on biochemical processes in the living cell was grounded. The technical possibilities of creation of vector potential free of magnetic field in laboratory are discussed.

Investigating Relaxation Processes in Cells and Developing Organisms: From Cell Ablation to Cytoskeleton Nanosurgery

Dynamic microscopy of living cells and organisms alone does not reveal the high level of complexity of cellular and subcellular organization. All observable processes rely on the activity of biochemical and biophysical processes and many occur at a physiological equilibrium. Experimentally, it is not trivial to apply a perturbation that targets a specific process without perturbing the overall equilibrium of a cell. Drugs and more recently RNAi certainly have general and undesired effects on cell physiology and metabolism. In particular, they affect the entire cell. Pulsed lasers allow to severe biological tissues with a precision in the range of hundreds of nanometers and to achieve ablation on the level of a single cell or a subcellular compartment. In this chapter, we present an efficient implementation of a picosecond UV-A pulsed laser-based nanosurgery system and review the different mechanisms of ablation that can be achieved at different levels of cellular organization. We discuss the performance of the ablation process in terms of the energy deposited onto the sample and compare our implementation to others recently employed for cellular and subcellular surgery. Above the energy threshold of ionization, we demonstrate how to achieve single-cell ablation through the induction of mechanical perturbation and cavitation in living organisms. Below this threshold, we induce cytoskeleton severing inside live cells. By combining nanosurgery with fast live-imaging fluorescence microscopy, we show how the apparent equilibrium of the cytoskeleton can be perturbed regionally inside a cell.