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

Area of Science:

• Radiobiology
• Cellular and Molecular Biology
• Radiation Oncology

Background:

• Bystander effects, where irradiated cells induce damage in neighboring non-irradiated cells, are well-documented for photon and alpha particle radiation.
• However, the induction of bystander effects by neutron irradiation remains less understood, particularly in normal human cells.

Purpose of the Study:

• To investigate whether fast neutrons induce bystander effects in normal human lymphoblastoid cell lines.
• To quantify genetic damage in unirradiated cells exposed to conditioned media from neutron-irradiated cells.
• To assess the role of contaminating photons in potential bystander responses.

Main Methods:

• Two normal human lymphoblastoid cell lines were exposed to fast neutrons (average 17 MeV).
• Irradiated-cell conditioned media (ICCM) was transferred to unirradiated cells.
• The cytokinesis-block micronucleus assay was used to measure genetic damage (micronuclei and nucleoplasmic bridges).
• Contaminating photon doses were simulated using cobalt-60 irradiation.

Main Results:

• No significant increase in micronuclei or nucleoplasmic bridges was observed in cells exposed to ICCM from neutron-irradiated cultures.
• Simulated photon contamination doses also did not induce bystander effects.
• High doses of cobalt-60 photons, however, induced a clear bystander effect, confirming assay sensitivity.
• Neutrons exhibited a relative biological effectiveness of 2.0 ± 0.13 for micronuclei and 5.8 ± 2.9 for bridges compared to cobalt-60.

Conclusions:

• Fast neutrons do not appear to induce bystander effects in the tested human lymphoblastoid cell lines.
• The study provides evidence that neutrons are not a significant source of radiation-induced bystander effects in these cell types.
• Findings are relevant for fast neutron therapy applications and the establishment of neutron radiation protection standards.