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Abstract
We have studied the biological effects of the internal exposure to radioactive manganese-56 dioxide (56MnO2), the major radioisotope dust found in soil after atomic bomb explosions. Our previous study of blood chemistry indicated a possible adverse effect of 56MnO2 on the liver. In the present study, we further examined the effects on the liver by determining changes in hepatic gene expressions. Male Wistar rats were exposed to 56MnO2 particles (three groups with the whole-body doses of 41, 90, and 100 mGy), stable MnO2 particles, or external 60Co γ-rays (2 Gy), and were examined together with the non-treated control group on postexposure day 3 and day 61. No histopathological changes were observed in the liver. The mRNA expression of a p53-related gene, the cyclin-dependent kinase inhibitor 1A, increased in 56MnO2 as well as in γ-ray irradiated groups on postexposure day 3 and day 61. The expression of a stress-responsive gene, nuclear factor κB, was also increased by 56MnO2 and γ-rays on postexposure day 3. However, the expression of cytokine genes (interleukin-6 or chemokine ligand 2) or fibrosis-related TGF-β/Smad genes (Tgfb1, Smad3, or Smad4) was not altered by the exposure. Our data demonstrated that the internal exposure to 56MnO2 particles at less than 0.1 Gy significantly affected the short-term gene expressions in the liver in a similar manner with 2 Gy of external γ-irradiation. These changes may be adaptive responses because no changes occurred in cytokine or TGF-β/Smad gene expressions.
Highlights
Main radioisotopes produced in soil by the neutron from the atomic bomb explosions included 24 Na, 42 K, and 56 Mn [2]
To understand the biological effects of residual radiation after the atomic bomb explosion, the hepatic gene expression in the rats exposed to 56 MnO2, one of the major radioactive compounds produced in soil by the atomic bomb, was investigated
The short-term upregulation of Cdkn1A, BCL2 Associated X (Bax), and Nfkb1 gene expressions was found by the exposure to both 60 Co-γ rays and 56 MnO2 particles on day 3 postexposure, while Cdkn1A
Summary
At the atomic bombing of Hiroshima and Nagasaki, Japan, initial radiation directly from the explosions caused major biological impacts. People who entered these cities soon after the detonations and who did not receive any direct radiation were reported to suffer from acute radiation syndrome, such as nausea, vomiting, and diarrhea [1]. These people might have inhaled residual radioactive dust and may have been exposed to radiation. Main radioisotopes produced in soil by the neutron from the atomic bomb explosions included 24 Na, 42 K, and 56 Mn [2].
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