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

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.

Keywords: 31Si; 31SiO2 microparticles; atomic bomb; internal irradiation; residual radiation.

Figure 1

Relative mRNA levels of Cdkn1a, Ccng1, and Phlda3 in the spleen, lungs, and liver 3 and 14 days after exposure to nonradioactive SiO₂ particles (Cold-Si), ³¹SiO₂ particles (31Si), or 2 Gy of X-rays (X-ray). Each bar indicates mean ± standard error of the mean (n = 5, each group). * p < 0.05 or ** p < 0.01 versus control. # p < 0.05 versus control or Cold-Si (paired comparison). X-rays increased the expression of all three marker genes on day 3, except for Ccng1 in the lung. ³¹SiO₂ exposure increased splenic Phlda3 and hepatic Ccng1 expressions on day 3.

Figure 2

Relative mRNA levels of Aqp1, Aqp5, and Smad7 in the lungs 3 and 14 days after exposure to nonradioactive SiO₂ particles (Cold-Si), ³¹SiO₂ particles (31Si), or 2 Gy of X-rays (X-ray). Each bar indicates mean ± standard error of the mean (n = 5, each group). # p < 0.05 versus control (paired comparison). X-rays reduced the expression of Smad7.

Figure 3

Relative mRNA levels of Cth, Ccl2, and Nfkb1 in the liver 3 and 14 days after exposure to nonradioactive SiO₂ particles (Cold-Si), ³¹SiO₂ particles (31Si), or 2 Gy of X-rays (X-ray). Each bar indicates mean ± standard error of the mean (n = 5, each group). * p < 0.05 or ** p < 0.01 versus control. # p < 0.05 versus control (paired comparison). The expression of Cth was increased in the ³¹Si and X-ray groups on post-exposure days 3 and 14. The expression of Ccl2 was increased in the X-ray group on day 3.