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.

Signaling factors for irradiated glioma cells induced bystander responses in fibroblasts

The aim of this study was to investigate the signaling factor and its pathway involved in the targeted irradiation-induced bystander response from glioblastoma cells to primary fibroblasts. After co-culturing with a glioblastoma T98G population where a fraction of cells had been individually irradiated with a precise number of helium particles, additional micronucleus (MN) were induced in the non-irradiated human fibroblasts AG01522 cells and its yield was independent of irradiation dose. This bystander MN induction was eliminated by treating the cells with either aminoguanidine (AG), an iNOS inhibitor, or anti-transforming growth factor-beta 1 (anti-TGF-beta 1). In addition, TGF-beta 1 could be released from irradiated T98G cells but this release was inhibited by AG. In consistent, TGF-beta 1 could also be induced from T98G cells treated with diethylamine nitric oxide (DEANO), a donor of nitric oxide (NO). Moreover, the effect of TGF-beta 1 on bystander AG01522 cells was investigated. It was found that reactive oxygen species (ROS) and MN were induced in AG01522 cells after TGF-beta 1 treatment. Our results indicate that, downstream of NO, TGF-beta 1 plays an important role in the targeted T98G cells induced bystander response to AGO cells by further causing DNA damage in vicinal fibroblasts through a ROS related pathway. This study may have implications for properly evaluating the secondary effects of radiotherapy. (C) 2007 Elsevier B.V. All rights reserved.

Bystander effects induced by diffusing mediators after photodynamic stress.

The bystander effect, whereby cells that are not traversed by ionizing radiation exhibit various responses when in proximity to irradiated cells, is well documented in the field of radiation biology, Here we demonstrate that considerable bystander responses are also observed after photodynamic stress using the membrane-localizing dye deuteroporphyrin (DP). Using cells of a WTK1 human lymphoblastoid cell line in suspension and a transwell insert system that precludes contact between targeted and bystander cells, we have shown that the bystander signaling is mediated by diffusing species. The extranuclear localization of the photosensitizer used suggests that primary DNA damage is not the trigger for initiating these bystander responses, which include elevated oxidative stress, DNA damage (micronucleus formation), mutagenesis and decreased clonogenic survival. In addition, oxidative stress in the bystander population was reduced by the presence of the membrane antioxidant vitamin E in the targeted cells, suggesting that lipid peroxidation may play a key role in mediating these bystander effects. The fluence responses for these bystander effects are non-linear, with larger effects seen at lower fluences and toxicity to the target cell population. Hence, when considering outcomes of photodynamic action in cells and tissue, bystander effects may be significant, especially at sublethal fluences.

Differential modulation of a radiation-induced bystander effect in glioblastoma cells by pifithrin-alpha and wortmannin

The implication of radiation-induced bystander effect (RIBE) for both radiation protection and radiotherapy has attracted significant attention, but a key question is how to modulate the RIBE. The present study found that, when a fraction of glioblastoma cells in T98G population were individually targeted with precise helium particles through their nucleus, micronucleus (MN) were induced and its yield increased non-linearly with radiation dose. After co-culturing with irradiated cells, additional MN could be induced in the non-irradiated bystander cells and its yield was independent of irradiation dose, giving direct evidence of a RIBE. Further results showed that the RIBE could be eliminated by pifithrin-alpha (p53 inhibitor) but enhanced by wortmannin (PI3K inhibitor). Moreover, it was found that nitric oxide (NO) contributed to this RIBE, and the levels of NO of both irradiated cells and bystander cells could be extensively diminished by pifithrin-alpha but insignificantly reduced by wortmannin. Our results indicate that RIBE can be modulated by p53 and PI3K through a NO-dependent and NO-independent pathway, respectively. (C) 2009 Elsevier B.V. All rights reserved.

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