Effects of Internal Exposure of Radioactive 56MnO2 Particles on the Lung in C57BL Mice

Abstract

The investigation of the radiation effects of the atomic bombing in Hiroshima and Nagasaki has revealed concerns about the impact of the residual radioactive dust produced in the soil. Manganese-56 is one of the major radioisotopes produced by neutrons from the bomb; hence, we previously examined the biological effects of manganese dioxide-56 (56MnO2) in Wistar rats, in which significant changes were found in the lung. In the present study, ten-week-old male C57BL mice were exposed to three doses of radioactive 56MnO2, stable MnO2 particles, or external γ-rays (2 Gy) to further examine the effects of 56MnO2 in a different species. The estimated absorbed radiation doses from 56MnO2 were 26, 96, and 250 mGy in the lung. The animals were examined at 3, 14, and 70 days post exposure. Histologically, no exposure-related changes were found in the lungs of any group. However, pulmonary mRNA expression of aquaporin 1, which is a useful marker for lung pathophysiology, was significantly elevated at 14 and 70 days, although no such changes were found in the mice exposed to external γ-rays (2 Gy). These data indicated that the inhalation exposure to 56MnO2 particles, with <250 mGy of organ doses, produced significant biological responses in the lung.

Effects of Radioactive 56MnO2 Particle Inhalation on Mouse Lungs: A Comparison between C57BL and BALB/c

“…The gene expression of Aqp1 increased in pulmonary edema models, whereas the expression of Aqp1 and Aqp5 decreased in acute lung injury models [31][32][33]. In our previous study in-volving C57BL mice, 56 MnO 2 exposure resulted in a late increase in the expression of Aqp1, indicating pathophysiological alterations without obvious histological changes [5]. This study confirmed the late effects of 56 MnO 2 exposure on Aqp1 expression as Aqp1 increased 65 days after exposure in the Mn56 × 3 group but not in the Co60 group.…”

“…Possible radionuclides activated by atomic bombs' neutron beams are 24 Na, 28 Al, 31 Si, 32 P, and 56 Mn [4]. Because 56 Mn is a significant residual radiation source produced by atomic bombs, we investigated the biological effects of 56 MnO 2 on laboratory rats and mice [5,6]. Our studies suggested that exposure to 56 MnO 2 particles induced more prominent physiological responses than external γ-irradiation in both rats and mice, although mice were less sensitive to internal exposure than rats [5].…”

“…Manganese 56 ( 56 Mn) is a primary radioisotope produced in the soil after an atomic bomb explosion [4]. We thus investigated the biological effects of 56 MnO 2 particles on laboratory rats (Wistar) and mice (C57BL) [5,6]. The effects of these particles on the lung, a primary target organ of inhalation, were examined.…”

“…No pathological alterations related to 56 MnO 2 particle exposure were observed in either species. However, the expression of pulmonary genes, including aquaporins (AQPs), which are pathophysiological markers of lung function, was altered by 56 MnO 2 exposure, suggesting that internal exposure to residual radioactive particles has significant biological effects [5,6].…”