Neutron exposures in human cells: bystander effect and relative biological effectiveness

• Published in: PloS one 2014-06, Vol.9 (6), p.e98947-e98947
• Main Authors: Seth, Isheeta, Schwartz, Jeffrey L, Stewart, Robert D, Emery, Robert, Joiner, Michael C, Tucker, James D
• Format: Article
• Language: English
• Subjects: Alpha rays; Ataxia; Atoms & subatomic particles; Biological effects; Biology and Life Sciences; Biotechnology; Bystander Effect - radiation effects; Cancer; Cell cycle; Cell Line; Cell Nucleus Division - radiation effects; Cells (Biology); Chromosome aberrations; Cobalt; Cobalt Radioisotopes; Conditioning; Contamination; Cytokinesis; Deoxyribonucleic acid; DNA; DNA Damage; Drug dosages; Exposure; Fast neutrons; Fibroblasts; Humans; Ionizing radiation; Irradiated; Irradiation; Kinases; Laboratories; Lymphoblastoid cell lines; Mammalian cells; Medicine and Health Sciences; Micronuclei; Micronuclei, Chromosome-Defective - radiation effects; Micronucleus Tests - methods; Mutagenesis; Neutron beams; Neutron irradiation; Neutron radiation; Neutrons; Nuclear energy; Nuclear power plants; Oncology; Photons; Proteins; Proton beams; Radiation; Radiation damage; Radiation protection; Radiation standards; Radiation therapy; Regulatory agencies; Relative Biological Effectiveness; Relative biological effectiveness (RBE); Tumors; α Radiation
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0098947

Bystander effects have been observed repeatedly in mammalian cells following photon and alpha particle irradiation. However, few studies have been performed to investigate bystander effects arising from neutron irradiation. Here we asked whether neutrons also induce a bystander effect in two normal human lymphoblastoid cell lines. These cells were exposed to fast neutrons produced by targeting a near-monoenergetic 50.5 MeV proton beam at a Be target (17 MeV average neutron energy), and irradiated-cell conditioned media (ICCM) was transferred to unirradiated cells. The cytokinesis-block micronucleus assay was used to quantify genetic damage in radiation-naïve cells exposed to ICCM from cultures that received 0 (control), 0.5, 1, 1.5, 2, 3 or 4 Gy neutrons. Cells grown in ICCM from irradiated cells showed no significant increase in the frequencies of micronuclei or nucleoplasmic bridges compared to cells grown in ICCM from sham irradiated cells for either cell line. However, the neutron beam has a photon dose-contamination of 5%, which may modulate a neutron-induced bystander effect. To determine whether these low doses of contaminating photons can induce a bystander effect, cells were irradiated with cobalt-60 at doses equivalent to the percent contamination for each neutron dose. No significant increase in the frequencies of micronuclei or bridges was observed at these doses of photons for either cell line when cultured in ICCM. As expected, high doses of photons induced a clear bystander effect in both cell lines for micronuclei and bridges (p