Biological impacts on the lungs in rats internally exposed to radioactive 56MnO2 particle

Abstract

To understand the radiation effects of the atomic bombing of Hiroshima and Nagasaki among the survivors, radiation from neutron-induced radioisotopes in soil should be considered in addition to the initial radiation directly received from the bombs. 56Mn, which emits both β particles and γ-rays, is one of the dominant radioisotopes created in soil by neutrons from the bomb. Thus we investigated the biological effects of internal exposure to 56MnO2 particle in the lung of male Wistar rats comparing to the effects of external 60Co-γ irradiation. Absorbed doses of internal irradiation of lungs were between 25 and 65 mGy in 56MnO2-exposed animals, while the whole body doses were between 41 and 100 mGy. Animals were examined on days 3 and 61 after the exposure. There were no remarkable pathological changes related to 56MnO2 particle exposure. However, mRNA and protein expressions of aquaporin 5 increased significantly in the lung tissue on day 3 postexposure in 56MnO2 groups (by 1.6 and 2.9 times, respectively, in the highest dose group). Smad7 mRNA expression was also significantly elevated by 30% in the highest dose group of 56MnO2. Our data demonstrated that internal exposure to 56MnO2 induced significant biological responses including gene expression changes in the lungs, while external 60Co-γ irradiation of 2 Gy did not show any changes.

The overview of neutron-induced 56Mn radioactive microparticle effects in experimental animals and related studies

“…However, other studies report conflicting findings, which therefore require further investigation. It was also found that there was a difference in RNA expression between external exposure to 60 Co gamma rays and internal exposure to 56 Mn [ 39–41 ]. Research should continue on gene expression.…”

“…However, later studies by Fujimoto et al. [ 39 , 40 ] reported that such strong differences of the pathological effects were not observed. Shichijo et al .…”

“…With a lack of proper control groups, the results were inconclusive. Recently, we conducted new experiments in rats exposed to 56 MnO 2 with the appropriate control groups to further examine the effects of 56 MnO 2 on the lungs by determining the gene and protein expression changes [ 39 ]. Absorbed doses from internal irradiation of the lungs ranged from 25 to 65 mGy for animals exposed to 56 MnO 2 and from 41 to 100 mGy for the whole body [ 39 ].…”

“…Recently, we conducted new experiments in rats exposed to 56 MnO 2 with the appropriate control groups to further examine the effects of 56 MnO 2 on the lungs by determining the gene and protein expression changes [ 39 ]. Absorbed doses from internal irradiation of the lungs ranged from 25 to 65 mGy for animals exposed to 56 MnO 2 and from 41 to 100 mGy for the whole body [ 39 ]. Animals were examined on days 3 and 61 post-irradiation, where no significant pathological changes associated with exposure to 56 MnO 2 microparticles were observed.…”

A combined scientific and public health approach is needed to evaluate the health impacts of internal exposure to radiation

“…There are numerous aspects of the health impacts of internal radiation exposure that are still unknown. One study indicated that internal exposure to radioactive material poses a greater health risk than that posed by external exposure [3] . The physical and mental health impacts of internal exposure as a result of the dropping of atomic bombs on Hiroshima and Nagasaki, the Chernobyl accident, the Semipalatinsk Nuclear Test Site, the Fukushima Daiichi Nuclear Power Plant accident, and other incidents involving radiation must be accurately ascertained scientifically.…”