Abstract:
To understand the biological effects of residual radioactivity after the atomic
bomb explosion in Hiroshima and Nagasaki, we previously investigated the effects of
56Mn, a major residual radioisotope. Our rat study demonstrated that inhalation exposure
to 56MnO2 microparticles affected gene expression in the lungs, testes, and liver, despite
the low radiation doses. Because 56Mn is a β- and γ-emitter, the differential effects between β- and γ-rays should be clarified. In this study, 31Si, a β-emitter with a radioactive
half-life similar to that of 56Mn, was used to determine its effects. Male Wistar rats were
exposed to sprayed neutron-activated 31SiO2 microparticles, stable SiO2 microparticles, or
X-rays. The animals were examined on days 3 and 14 after irradiation. The expression of
radiation-inducible marker genes, including Ccng1, Cdkn1a, and Phlda3, was measured in
the spleen, lungs, and liver. Furthermore, the expressions of pathophysiological marker
genes, including Aqp1, Aqp5, and Smad7 in the lungs and Cth, Ccl2, and Nfkb1 in the liver,
were determined. Impacts of 31SiO2 exposure were observed mainly in the liver, where the
expression of Cth markedly increased on post-exposure days 3 and 14. Our data suggest
that internal exposure to β-emitted microparticles has significant biological effects and its
possible roles as residual radiation after atomic bombing.
