55. Induction of Micronuclei in Rat Alveolar Epithelial Cell Line by Alpha Particle Irradiation
Yutaka Yamada, Yoichi Oghiso, Hiroko Enomoto and Nobuhito Ishigure
Keywords: micronucleus, alpha particle, rat, alveolar type II cell line, biodosimetry
A life-span study has been conducted on rats that inhaled plutonium dioxide aerosols and it was observed that plutonium deposited in lung induces lung tumors in a dose-dependent manner. The absorbed dose in lung was calculated from radioactivity in thorax by whole body counting procedure, but the absorbed dose in target cells' level remains unclear. The lung model of ICRP publication 66 describes cells at risk of respiratory tract tissues as secretory and basal cells in bronchial airways, and Clara and Type II cells in the alveolar interstitial region. Therefore, dose estimations in the tissue layers containing the target cells are required in the model. Recently, a biodosimetric approach has been developed and applied to estimate absorbed dose in respiratory cells. In the biodosimetry, responses of isolated cells that have been previously exposed to alpha emitters in vivo are compared to the responses obtained from similar populations of cells that were irradiated in vitro using alpha sources. As a preliminary experiment for biodosimetry in respiratory epithelial cells of rat, the dose-response relationships of radiation-induced micronucleus formation were investigated utilizing an immortalized rat alveolar Type II cell line (SV40T2).
The SV40T2 cells were exposed to either alpha particles (241Am: 3.2 MeV, 128 keV/µm, 0.093 Gy/min at cell-Mylar interface) or X-rays (200 kVp, 1 Gy/min). The frequency of micronucleus formation was 1.6 - 3.0% for unirradiated subjects but increased for irradiated ones in a dose-dependent manner. A linear relationship between the dose and the micronucleus formation was observed until 1 Gy for alpha particles and 4 Gy for X-rays. The linear slope for alpha particles was 28.5 % per Gy and the relative biological effectiveness (RBE) was 4.3, as calculated from the slopes. The slope for alpha particles was dependent on the energy of the alpha particles. These results indicate that the micronucleus assay is available for biodosimetry of alpha particle irradiation in the rat alveolar epithelial cells.
Publications:
Yamada, Y., Oghiso, Y., Enomoto, H. and Ishigure, N.: Radiation Protection Dosimetry, 99, 219-221, 2002.