Lack of bystander effects from high-LET radiation for early cytogenetic end points.
The aim of this work was to study radiation-induced bystander effects for early cytogenetic end points in various cell lines using the medium transfer technique after exposure to high- and low-LET radiation. Cells were exposed to 20 MeV/ nucleon nitrogen ions, 968 MeV/nucleon iron ions, or 575 MeV/nucleon iron ions followed by transfer of the conditioned medium from the irradiated cells to unirradiated test cells. The effects studied included DNA double-strand break induction, gamma-H2AX focus formation, induction of chromatid breaks in prematurely condensed chromosomes, and micronucleus formation using DNA repair-proficient and -deficient hamster and human cell lines (xrs6, V79, SW48, MO59K and MO59J). Cell survival was also measured in SW48 bystander cells using X rays. Although it was occasionally possible to detect an increase in chromatid break levels using nitrogen ions and to see a higher number of gamma-H2AX foci using nitrogen and iron ions in xrs6 bystander cells in single experiments, the results were not reproducible. After we pooled all the data, we could not verify a significant bystander effect for any of these end points. Also, we did not detect a significant bystander effect for DSB induction or micronucleus formation in these cell lines or for clonogenic survival in SW48 cells. The data suggest that DNA damage and cytogenetic changes are not induced in bystander cells. In contrast, data in the literature show pronounced bystander effects in a variety of cell lines, including clonogenic survival in SW48 cells and induction of chromatid breaks and micronuclei in hamster cells. To reconcile these conflicting data, it is possible that the epigenetic status of the specific cell line or the precise culture conditions and medium supplements, such as serum, may be critical for inducing bystander effects.
Groesser
Torsten
T
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. tgroesser@lbl.gov
Cooper
Brian
B
Rydberg
Bjorn
B
D000818:Animals; D024201:Bystander Effect / Q000528:radiation effects*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D002842:Chromatids / Q000378:metabolism / Q000528:radiation effects; D020732:Cytogenetic Analysis; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D023381:Endpoint Determination; D005434:Flow Cytometry; D006657:Histones / Q000378:metabolism; D006801:Humans; D018499:Linear Energy Transfer; D013194:Staining and Labeling
D006657:Histones