Adaptive responses were observed using the micronucleus frequency in bullfrog tadpoles. In tanks in which control tadpoles were placed in contact with tadpoles that were previously housed in tritiated water (3.0× 104 Bq/L), the cells from all animals responded as though they were “adapted”. This suggests that direct exposure to 3.0× 104 Bq/L tritium contributes to an increased resistance to a h...

A number of studies in the field of radiobiology contradict the Linear Non-Threshold model in the low dose range. These observations indicate that there may be more harmful effects for cells exposed to low dose irradiation than would be predicted by extrapolation from high dose data. For the last 20 years a new phenomenon in the area of the radiobiological effects has been described. A radiatio...

Radiation-induced bystander effects have been observed in vitro and in cell and tissue culture models, however, there are few reported studies showing these effects in vivo. To our knowledge, this is the first reported study on bystander effects induced by microbeam irradiation in an intact living mammal. The mouse ear was used to investigate radiation-induced bystander effects in keratinocytes...

There is strong evidence that biological response to ionizing radiation has a contribution from unirradiated "bystander" cells that respond to signals emitted by irradiated cells. We discuss here an approach incorporating a radiobiological bystander response, superimposed on a direct response due to direct energy deposition in cell nuclei. A quantitative model based on this approach is describe...

Bystander and low-dose-rate effects influence the dose-response relationship in a manner not predicted by current dosimetric methodologies. Radiation-induced bystander effects refer to biologic responses in cells that are not traversed by an ionizing radiation track and, thus, not subject to direct energy deposition; that is, the responses occur in nonirradiated cells. Low-dose-rate hypersensit...

Direct cellular DNA damage may lead to genome destabilization in unexposed, bystander, cells sharing the same milieu with directly damaged cells by means of the bystander effect. One proposed mechanism involves double strand break (DSB) formation in S phase cells at sites of single strand lesions in the DNA of replication complexes, which has a more open structure compared with neighboring DNA....

Cells without intact mitochondrial DNA have been shown to lack the bystander effect, which is an energy-dependent process. We hypothesized that cells harboring mutations in mitochondrial genes responsible for ATP synthesis would show a decreased bystander effect compared to normal cells. Radiation-induced bystander effects were analyzed in two normal and four mitochondrial mutant human lymphobl...

background: in this study, the bystander effect of radiation was evaluated on the regulation of cox-2, inos, and 8-ohdg in the lung tissues of sprague-dawley rats with and without pre-administration of melatonin. materials and methods: a 2×2 cm area of the pelvis of male sprague-dawley rats with and without pre-administration of melatonin (100 mg/kg) by oral and ip injection was irradiated with...

Radiation induced bystander effects and adaptive responses are two phenomena that modulate cellular responses to low doses of ionizing radiation. Bystander effects generally exaggerate the effects of low doses of radiation by eliciting detrimental effects in nonirradiated cells, thus making the target for radiation effects greater than the volume irradiated. Adaptive responses on the other hand...

Small interfering RNAs (siRNAs) represent a new class of antigene agents, which has emerged as a powerful tool for functional genomics and might serve as a potent therapeutic approach. However, several studies have showed that they could trigger several bystander effects, including immune activation and inhibition of unintended target genes. Although activation of innate immunity by siRNAs migh...