Radiation induced bystander signals are independent of DNA damage and DNA repair capacity of the irradiated cells.

Evidence is accumulating that irradiated cells produce signals, which interact with non-exposed cells in the same population. Here, we analysed the mechanism for bystander signal arising in wild-type CHO cells and repair deficient varients, focussing on the relationship between DNA repair capacity and bystander signal arising in irradiated cells. In order to investigate the bystander effect, we carried out medium transfer experiments after X-irradiation where micronuclei were scored in non-targeted DSB repair deficient xrs5 cells. When conditioned medium from irradiated cells was transferred to unirradiated xrs5 cells, the level of induction was independent of whether the medium came from irradiated wild-type, ssb or dsb repair deficient cells. This result suggests that the activation of a bystander signal is independent of the DNA repair capacity of the irradiated cells. Also, pre-treatment of the irradiated cells with 0.5% DMSO, which suppresses micronuclei induction in CHO but not in xrs5 cells, suppressed bystander effects completely in both conditioned media, suggesting that DMSO is effective for suppression of bystander signal arising independently of DNA damage in irradiated cells. Overall the work presented here adds to the understanding that it is the repair phenotype of the cells receiving bystander signals, which determines overall response rather than that of the cell producing the bystander signal.

Radiation-induced bystander and adaptive responses in cell and tissue models.

The use of microbeam approaches has been a major advance in probing the relevance of bystander and adaptive responses in cell and tissue models. Our own studies at the Gray Cancer Institute have used both a charged particle microbeam, producing protons and helium ions and a soft X-ray microprobe, delivering focused carbon-K, aluminium-K and titanium-K soft X-rays. Using these techniques we have been able to build up a comprehensive picture of the underlying differences between bystander responses and direct effects in cell and tissue-like models. What is now clear is that bystander dose-response relationships, the underlying mechanisms of action and the targets involved are not the same as those observed for direct irradiation of DNA in the nucleus. Our recent studies have shown bystander responses even when radiation is deposited away from the nucleus in cytoplasmic targets. Also the interaction between bystander and adaptive responses may be a complex one related to dose, number of cells targeted and time interval.

The use of microbeams to investigate radiation damage in living cells.

The micro-irradiation technique continues to be highly relevant to a number of radiobiological studies in vitro. In particular, studies of the bystander effect show that direct damage to cells is not the only trigger for radiation-induced effects, but that unirradiated cells can also respond to signals from irradiated neighbours. Furthermore, the bystander response can be initiated even when no energy is deposited in the genomic DNA of the irradiated cell (i.e. by targeting just the cytoplasm).

Radiowave propagation from a tissue-implanted source at 418 MHz and 916.5 MHz

Tissue-implanted ultra-high frequency (UHF) radio devices are being employed in both humans and animals for telemetry and telecommand applications, This paper describes the experimental measurement and electromagnetic modeling of propagation from 418-MHz and 916.5-MHz sources placed in the human vagina. Whole-body homogeneous and semi-segmented software models were constructed using data from the Visible Human Project. Bodyworn radiation efficiencies for a vaginally placed 418-MHz source were calculated using finite-difference time-domain and ranged between 1.6% and 3.4% (corresponding to net body losses of between 14.7 and 18.0 dB), Greater losses were encountered at 916.5 MHz, with efficiencies between 0.36% and 0.46% (net body loss ranging between 23.4 and 24.4 dB), Practical measurements were in good agreement with simulations, to within 2 dB at 418 MHz and 3 dB at 916.5 MHz. The degree of tissue-segmentation for whole-body models was found to have a minimal effect on calculated azimuthal radiation patterns and bodyworn radiation efficiency, provided the region surrounding the implanted source was sufficiently detailed.

Control of leaky-mode propagation and radiation properties in hybrid dielectric-waveguide printed-circuit technology: Experimental results

Experimental results are presented to show how a planar circuit, printed on a laterally shielded dielectric waveguide, can induce and control the radiation from a leaky-mode. By studying the leaky-mode complex propagation constant, a desired radiation pattern can be synthesized, controlling the main radiation characteristics (pointing direction, beamwidth, sidelobes level) for a given frequency, This technique leads to very flexible and original leaky-wave antenna designs. The experiments show to be in very good agreement with the leaky-mode theory.

Visible and Near-Infrared Emission by Samarium(III)-Containing Ionic Liquid Mixtures

Highly luminescent anionic samarium(III) beta-diketonate and dipicolinate complexes were dissolved in the imidazolium ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(6)mim][Tf2N]. The solubility of the complexes in the ionic liquid was ensured by a careful choice of the countercation of the samarium(III) complex. The samarium(III) complexes that were considered are [C(6)mim][SM(tta)(4)], where tta is 2-thenoyltrifluoroacetonate; [C(6)mim][Sm(nta)(4)], where nta is 2-naphthoyltrifluoroacetonate; [C(6)mim][Sm(hfa)(4)], where hfa is hexafluoroacetylacetonate; and [choline](3)-[Sm(dpa)(3)], where dpa is pyridine-2,6-dicarboxylate (dipicolinate) and [choline](+) is (2-hydroxyethyl)trimethyl ammonium. The crystal structures of the tetrakis samarium(III) P-diketonate complexes revealed a distorted square antiprismatic coordination for the samarium(III) ion in all three cases. Luminescence spectra were recorded for the samarium(III) complexes dissolved in the imidazolium ionic liquid as well as in a conventional solvent, that is, acetonitrile or water for the beta-diketonate and dipicolinate complexes, respectively. These experiments demonstrate that [C(6)mim][Tf2N] is a suitable spectroscopic solvent for studying samarium(III) luminescence. High-luminescence quantum yields were observed for the samarium(III) beta-diketonate complexes in solution.