Bystander effects induced by serum from survivors of the Chernobyl accident

Environmentally relevant mixed exposures to radiation and heavy metals induce measurable stress responses in Atlantic salmon

These experiments were designed to identify stress effects in 3 key organs in Atlantic Salmon (Salmo salar, L.) after exposure in vivo to very low doses of radiation, and subtoxic levels of aluminum (Al) and cadmium (Cd) alone or in combination. Six fish per group were sacrificed after exposure and the anterior kidney, fin, and gill were dissected and sentfor assay of bystander signal production as a stress response end point. Radiation doses as low as 4 mGy delivered over 5 h, alone or in combination with Cd and/or Al, caused bystander signals to be produced in tissues harvested from in vivo exposed salmon. The effects vary among different organs and are not consistently additive or synergistic for a given treatment although gill cells do show high degrees of synergism between radiation and metal exposure. Data for individual fish did not suggest any systemic sensitivity to the stressors. Interestingly, the data for Cd suggest that lower toxicity is found when the metal is used in combination with radiation exposure. Expression of two proteins associated with survival responses (Bcl-2) or death responses (cmyc) after radiation was measured in the tissue cultures and showed a highly significant correlation with response outcome. The results, although complex, indicate that these stress signal responses may aid in the mechanistic investigation of mixed contaminant effects in fish exposed to metals and radiation.

In vivo bystander effect: cranial X-irradiation leads to elevated DNA damage, altered cellular proliferation and apoptosis, and increased p53 levels in shielded spleen

PURPOSE

It is well accepted that irradiated cells may "forward" genome instability to nonirradiated neighboring cells, giving rise to the "bystander effect" phenomenon. Although bystander effects were well studied by using cell cultures, data for somatic bystander effects in vivo are relatively scarce.

METHODS AND MATERIALS

We set out to analyze the existence and molecular nature of bystander effects in a radiation target-organ spleen by using a mouse model. The animal's head was exposed to X-rays while the remainder of the body was completely protected by a medical-grade shield. Using immunohistochemistry, we addressed levels of DNA damage, cellular proliferation, apoptosis, and p53 protein in the spleen of control animals and completely exposed and head-exposed/body bystander animals.

RESULTS

We found that localized head radiation exposure led to the induction of bystander effects in the lead-shielded distant spleen tissue. Namely, cranial irradiation led to increased levels of DNA damage and p53 expression and also altered levels of cellular proliferation and apoptosis in bystander spleen tissue. The observed bystander changes were not caused by radiation scattering and were observed in two different mouse strains; C57BL/6 and BALB/c.

CONCLUSION

Our study proves that bystander effects occur in the distant somatic organs on localized exposures. Additional studies are required to characterize the nature of an enigmatic bystander signal and analyze the long-term persistence of these effects and possible contribution of radiation-induced bystander effects to secondary radiation carcinogenesis.

Epigenetic changes and nontargeted radiation effects--is there a link?

It is now well accepted that the effects of ionizing radiation (IR) exposure can be noticed far beyond the borders of the directly irradiated tissue. IR can affect neighboring cells in the proximity, giving rise to a bystander effect. IR effects can also span several generations and influence the progeny of exposed parents, leading to transgeneration effects. Bystander and transgeneration IR effects are linked to the phenomenon of the IR-induced genome instability that manifests itself as chromosome aberrations, gene mutations, late cell death, and aneuploidy. While the occurrence of the above-mentioned phenomena is well documented, the exact mechanisms that lead to their development have still to be delineated. Evidence suggests that the IR-induced genome instability, bystander, and transgeneration effects may be epigenetically mediated. The epigenetic changes encompass DNA methylation, histone modification, and RNA-associated silencing. Recent studies demonstrated that IR exposure alters epigenetic parameters in the directly exposed tissues and in the distant bystander tissues. Transgeneration radiation effects were also proposed to be of an epigenetic nature. We will discuss the role of the epigenetic mechanisms in radiation responses, bystander effects, and transgeneration effects.