Genomic instability in Chinese hamster cells after exposure to X rays or alpha particles of different mean linear energy transfer

Evidence has accumulated that radiation induces a transmissible persistent destabilization of the genome, which mag. result in effects arising in the progeny of irradiated but surviving cells. An enhanced death rate among the progeny of cells surviving irradiation persists for many generations in the form of a reduced plating efficiency. Such delayed reproductive death is correlated with an increased occurrence of micronuclei. Since it has been suggested that radiation-induced chromosomal instability might depend on the radiation quality, we investigated the effects of alpha particles of different LET by looking at the frequency of delayed micronuclei in Chinese hamster V79 cells after cytochalasin-induced block of cell division, A dose-dependent increase in the frequency of micronuclei was found in cells assayed 1 week postirradiation or later. Also, there was a persistent increase in the frequency of dicentrics in surviving irradiated cells, Moreover, we found an increased micronucleus frequency in all of the 30 clones isolated from individual cells which had been irradiated with doses equivalent to either one, two or three alpha-particle traversals per cell nucleus, We conclude that the target for genomic instability in Chinese hamster cells must be larger than the cell nucleus. (C) 1997 by Radiation Research Society

A charged-particle microbeam .1. Development of an experimental system for targeting cells individually with counted particles

Charged-particle microbeams provide a unique opportunity to control precisely, the dose to individual cells and the localization of dose within the cell. The Gray Laboratory is now routinely operating a charged-particle microbeam capable of delivering targeted and counted particles to individual cells, at a dose-rate sufficient to permit a number of single-cell assays of radiation damage to be implemented. By this means, it is possible to study a number of important radiobiological processes in ways that cannot be achieved using conventional methods. This report describes the rationale, development and current capabilities of the Gray Laboratory microbeam.

A study of DNA fragmentation patterns in cells irradiated with charged particles: evidence for non-random distributions

Many studies have shown that the effectiveness of radiations of varying LET is similar when yields of dsb have been measured, despite large differences in biological response. Recent evidence has suggested however, that current techniques underestimate the yields of dsb. By monitoring the fragmentation of DNA over a wide range of fragment sizes ( 6 Mbp) by pulsed field electrophoresis, RBE values greater than 1.0 for radiations of around 100 keV/mm have been determined. The data provide evidence for the production of correlated breaks produced within cells as particle tracks traverse the nucleus. The highly ordered structure of DNA within mammalian cells may lead to clustering of breaks over distances related to the repeating unit structures of the chromatin. As well as these regionally damaged sites, a major contributor to radiation effectiveness will be the localised clustering of damage in the 1 - 20 bp region. A major effort is required to elucidate the relative importance of these levels of clustering and their importance in biological response.

Delayed lethality, apoptosis and micronucleus formation in human fibroblasts irradiated with X-rays or alpha-particles

Purpose: To determine the yields of cell lethality and micronucleus formation measured immediately after irradiation or at delayed times in primary human fibroblasts exposed to X-rays or alpha-particles.

The role of higher-order chromatin structure in the yield and distribution of DNA double-strand breaks in cells irradiated with X-rays or alpha-particles

Purpose: To determine whether the non-random distributions of DNA double-strand breaks in cells observed after alpha-particle irradiation are related to the higher-order structure of the chromatin within the nucleus.

The relationship between the RBE of alpha particles and the radiosensitivity of different mutations of Chinese hamster cells

The RBE of alpha -particles in different mutations of Chinese hamster cells was determined with the aim of identifying differences in the sensitivity to x-ray and alpha -particle-induced DNA damage. Two parental lines of Chinese hamster cells and four radiosensitive mutants were irradiated with different single doses of x-rays and alpha -particles and clonogenic cell survival was determined. Radiosensitivity to x-rays varied by a factor of 5 between the cell strains whereas sensitivity to alpha -particle irradiation was almost identical among all strains. The RBE is only determined by the sensitivity of the cells towards x-rays. Since cells with different defects of repair or cell cycle control have different radiosensitivities, we conclude that the effects of x-ray irradiation and the RBE are mostly determined by the activity of repair processes.

Genomic instability in human lymphocytes irradiated with individual charged particles: Involvement of tumor necrosis factor a in irradiated cells but not bystander cells

Exposure to ionizing radiation can increase the risk of cancer, which is often characterized by genomic instability. In environmental exposures to high-LET radiation (e.g. Ra-222), it is unlikely that many cells will be traversed or that any cell will be traversed by more than one alpha particle, resulting in an in vivo bystander situation, potentially involving inflammation. Here primary human lymphocytes were irradiated with precise numbers of He-3(2+) ions delivered to defined cell population fractions, to as low as a single cell being traversed, resembling in vivo conditions. Also, we assessed the contribution to genomic instability of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFA). Genomic instability was significantly elevated in irradiated groups ( greater than or equal totwofold over controls) and was comparable whether cells were traversed by one or two He-3(2+) ions. Interestingly, substantial heterogeneity in genomic instability between experiments was observed when only one cell was traversed. Genomic instability was significantly reduced (60%) in cultures in which all cells were irradiated in the presence of TNFA antibody, but not when fractions were irradiated under the same conditions, suggesting that TNFA may have a role in the initiation of genomic instability in irradiated cells but not bystander cells. These results have implications for low-dose exposure risks and cancer. (C) 2005 by Radiation Research Society.

Nonlinear Field Line Random Walk and Generalized Compound Diffusion of Charged Particles

A new nonlinear theory for the perpendicular transport of charged particles is presented. This approach is based on an improved nonlinear treatment of field line random walk in combination with a generalized compound diffusion model. The generalized compound diffusion model is much more systematic and reliable, in comparison to previous theories. Furthermore, the new theory shows remarkably good agreement with test-particle simulations and heliospheric observations.

Assessing the occupational risk of dust particles in the Kenyan tanning industry using rapid image processing and microscopy techniques

The purpose of this study was to investigate the occupational hazards within the tanning industry caused by contaminated dust. A qualitative assessment of the risk of human exposure to dust was made throughout a commercial Kenyan tannery. Using this information, high-risk points in the processing line were identified and dust sampling regimes developed. An optical set-up using microscopy and digital imaging techniques was used to determine dust particle numbers and size distributions. The results showed that chemical handling was the most hazardous (12 mg m(-3)). A Monte Carlo method was used to estimate the concentration of the dust in the air throughout the tannery during an 8 h working day. This showed that the high-risk area of the tannery was associated with mean concentrations of dust greater than the UK Statutory Instrument 2002 No. 2677. stipulated limits (exceeding 10 mg m(-3) (Inhalable dust limits) and 4 mg m(-3) (Respirable dust limits). This therefore has implications in terms of provision of personal protective equipment (PPE) to the tannery workers for the mitigation of occupational risk.

Simulations of magnetic microstructure in thin film elements used for programmable motion of magnetic particles

The results of two-dimensional micromagnetic modeling of magnetization patterns in Permalloy ellipses under the influence of rotating constant-amplitude magnetic fields are discussed. Ellipses of two different lateral sizes have been studied, 0.5m x 1.5m and 1m x 3m. The amplitude of the rotating magnetic field was varied between simulations with the condition that it must be large enough to saturate or nearly saturate the ellipse with the field applied along the long axis of the ellipse. For the smaller ellipse size it is found that the magnetization pattern forms an S state and the direction of the net magnetization lags behind the direction of the applied field. At a critical angle of the rotating magnetic field the direction of the magnetization switches by a large angle to a new S state. Both the critical angle and the angle interval of the switch depend on field amplitude. For this new state, it is instead the applied field direction that lags behind the magnetization direction. The transient magnetization patterns correspond to multi-domain patterns including two vortices, but this state never exists for the equilibrated magnetization patterns. The behavior of the larger ellipse in rotating field is different. With the field applied along the long-axis of the ellipse, the magnetization of the ellipse is nearly saturated with a vortex close to each apex of the ellipse. As the field is rotated, this magnetization pattern remains and the net-magnetization direction lags behind the direction of the field until for a certain angle of the applied field an equilibrium multi-domain state is created. Comparisons are made with corresponding experimental results obtained by performing in-field magnetic force microscopy on Permalloy ellipses.