Risks and Modeling at Low Doses

Sunday, October 16, 2005 3:00 PM-5:00 PM Exhibit Hall

(PP053) Comparison of the mitotic indices and dose prediction when using bromodeoxyuridine or cytochalasin B in the dicentric chromosome assay.

Thorleifson, Erika*,1, Segura, Tamika 2, Prud'homme-Lalonde, Louise2, Lachapelle, Sylvie2, Qutob, Sami1, Mullins, Dana 2, Wilkinson, Diana2, 1 Consumer and Clinical Radiation Protection, Ottawa, ON, Canada2 Radiological Analysis and Defence, Ottawa, ON, Canada

ABSTRACT- Differentiating between first and second mitosis in mitogen stimulated peripheral white bloods cells in the dicentric assay can be done using bromodeoxyuridine with fluorescence plus Giemsa staining or using cytochalasin B, to block cell division. The requirement for selective analysis of cells in first mitotic division arises in part from observations that individuals vary in their response time to mitogen stimulation and that radiation has a dose dependent effect on the lymphocyte proliferation rate. Much of the chromosome damage that is caused by radiation is terminal damage and can only be observed in cells in first metaphase. As part of technical improvements of chromosome aberration analysis for biological radiation dosimetry, we examined cytochalasin B and bromodeoxyuridine techniques for their effectiveness in identifying cells in first, second or third mitotic division. A single donor sample was separated into four fractions: 1) an un-irradiated control cultured in bromodeoxyuridine media, 2) an un-irradiated control cultured in cytochalasin B media, 3) one exposed to 3 Gy of gamma rays from a GB-150-C Co-60 source and cultured in bromodeoxyuridine media, and 4) one exposed to 3 Gy of gamma rays from a GB-150-C Co-60 source and cultured in cytochalasin B media. Each sample was then further fractionated into 4 cultures to be harvested at 48 hr, 52 hr, 56 hr, and 60 hr after stimulation with a mitogen, phytohaemaglutanin. The bromodeoxyuridine samples were cultured in complete media with 1mg/ml bromodeoxyuridine. The cytochalasin B samples were cultured in complete media for the first 24 hours at which point cytochalasin B was added to the media to a final concentration of 2.0 mL/mL. Four hours prior to the fixation time for each group, the cells were treated with colcemid. The M1, M2 and M3 mitotic indices were measured for each set of conditions and the dicentric chromosome assay was performed only on the cells found in first metaphase. The bromodeoxyuridine samples were more mitotically active than the corresponding cytochalasin B samples but both performed equally well for predicting dose with the dicentric chromosome assay.

Key words: biodosimetry, dicentric

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2005 RRS