Gene Expression Changes in the Spleen, Lungs, and Liver of Wistar Rats Exposed to β-Emitted 31SiO2 Particles

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 <i>Ccng1</i>, <i>Cdkn1a</i>, and <i>Phlda3</i>, was measured in the spleen, lungs, and liver. Furthermore, the expressions of pathophysiological marker genes, including <i>Aqp1</i>, <i>Aqp5</i>, and <i>Smad7</i> in the lungs and <i>Cth</i>, <i>Ccl2</i>, and <i>Nfkb1</i> in the liver, were determined. Impacts of ³¹SiO₂ exposure were observed mainly in the liver, where the expression of <i>Cth</i> 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.