Effect of ozone oxidative preconditioning in preventing early radiation-induced lung injury in rats

Abstract

Ionizing radiation causes its biological effects mainly through oxidative damage induced by reactive oxygen species. Previous studies showed that ozone oxidative preconditioning attenuated pathophysiological events mediated by reactive oxygen species. As inhalation of ozone induces lung injury, the aim of this study was to examine whether ozone oxidative preconditioning potentiates or attenuates the effects of irradiation on the lung. Rats were subjected to total body irradiation, with or without treatment with ozone oxidative preconditioning (0.72 mg/kg). Serum proinflammatory cytokine levels, oxidative damage markers, and histopathological analysis were compared at 6 and 72 h after total body irradiation. Irradiation significantly increased lung malondialdehyde levels as an end-product of lipoperoxidation. Irradiation also significantly decreased lung superoxide dismutase activity, which is an indicator of the generation of oxidative stress and an early protective response to oxidative damage. Ozone oxidative preconditioning plus irradiation significantly decreased malondialdehyde levels and increased the activity of superoxide dismutase, which might indicate protection of the lung from radiation-induced lung injury. Serum tumor necrosis factor alpha and interleukin-1 beta levels, which increased significantly following total body irradiation, were decreased with ozone oxidative preconditioning. Moreover, ozone oxidative preconditioning was able to ameliorate radiation-induced lung injury assessed by histopathological evaluation. In conclusion, ozone oxidative preconditioning, repeated low-dose intraperitoneal administration of ozone, did not exacerbate radiation-induced lung injury, and, on the contrary, it provided protection against radiation-induced lung damage.

Figure 1. Serum tumor necrosis factor alpha (TNF-α) levels of control, saline-treated+ionizing radiation (IR), or ozone oxidative preconditioning (OOP)+IR groups decapitated at 6 or 72 h after irradiation. Each group consisted of 8 rats. *P=0.001 compared to control group; ⁺P=0.001 compared to saline-treated group (Mann-Whitney U-test).

Figure 2. Serum interleukin-1β (IL-1β) levels of control, saline-treated+ionizing radiation (IR), or ozone oxidative preconditioning (OOP)+IR groups decapitated at 6 or 72 h after irradiation. Each group consisted of 8 rats. *P=0.001 compared to control group; ⁺P=0.001 compared to saline-treated group (Mann-Whitney U-test).

Figure 3. Malondialdehyde (MDA) levels in the lung tissues of control, saline-treated+ionizing radiation (IR), or ozone oxidative preconditioning (OOP)+IR groups decapitated at 6 or 72 h after irradiation. Each group consisted of 8 rats. Circle: outlier. *P=0.001 compared to control group; ⁺P=0.001 compared to saline-treated group (Mann-Whitney U-test).

Figure 4. Superoxide dismutase (SOD) activity in the lung tissues of control, saline-treated+ionizing radiation (IR), or ozone oxidative preconditioning (OOP)+IR groups decapitated at 6 or 72 h after irradiation. Each group consisted of 8 rats. *P=0.001 compared to control group; ⁺P=0.001 compared to saline-treated group (Mann-Whitney U-test).

Figure 5. Histopathological findings of the groups. A, Normal lung parenchyma in the control group [hematoxylin-eosin (HE), 100X]. B, Alveolar area reduction (thin arrow) and alveolar hemorrhage (thick arrow) in radiation-treated group at 6 h (HE, 200X). C, Severe alveolar hemorrhage (thick arrow), alveolar area reduction (thin arrow), interstitial congestion, and edema in the radiation-treated group at 72 h (HE, 200X). D, Reduced interstitial congestion and alveolar hemorrhage (thick arrow) and expanded alveolar area (thin arrow) in ozone-treated groups at 6 h (HE, 200X). E, Clearly reduced interstitial congestion and alveolar hemorrhage and re-established alveolar structure (arrows) in ozone-treated groups at 72 h (HE, 200X).