Radiation induced bystander effects in the spleen of cranially-irradiated rats

Abstract

Objective: To investigate the radiation-induced abscopal effect in terms of oxidative stress, apoptosis and DNA damage in the spleen cells following cranial X-rays irradiation of rats.

Methods: Rats were cranially irradiated using 2 Gy X-rays. Another group was whole-body irradiated with 2 Gy X-rays and a third group was exposed to scattered radiation (measured to be 3 mGy). 24 hours following irradiation, sections from the spleen of the rats were dissected as well as plasma samples. The samples were examined for the desired endpoints.

Results: The cranially irradiated animals showed a significant increase in the levels of glutathione, superoxide dismutase and catalase with no significant change in the lipid peroxidation product in the spleen cells with a significant increase in the C-reactive protein level the plasma. Apoptotic cell death in the spleen cells was demonstrated as indicated by the decrease of Bcl-2; the increase of p53, Bax, caspase-3 and caspase-8 and induction of DNA damage in the spleen in both of the cranially irradiated rats and whole body exposed rats. The exposure to 3 mGy scattered radiation increased the plasma level of C-RP and also induced apoptosis in the spleen cells.

Conclusion: Cranial irradiation-induced abscopal effect in distant spleen cells. Very low doses of radiation can induce apoptosis in the spleen cells. Advances in knowledge: This paper provides an evidence on the incidence of radiation abscopal effect. Also, the results shed light of the effect very low doses of radiation as low as 3 mGy.

Figure 1.

Changes in the levels of the lipid peroxidation product MDA (nmol/g tissue) (a), superoxide dismutase (SOD; U/g tissue) (b), and catalase (CAT; U/g tissue) (c) and glutathione (GSH; ng/g tissue) (d) in the spleens of sham-irradiated, 2 Gy whole-body irradiated, 2 Gy cranially irradiated animals and animals exposed to scattered radiation only (measured to be 3 mGy). The values are expressed as the means ± SEM (n = 5). *Significant at p < 0.05, **significant at p < 0.01 and ***significant at p < 0.001 with respect to the sham-irradiated group. CAT, catalase; GSH, glutathione; MDA, malondialdehyde; SOD, superoxide dismutase.

Figure 2.

Changes in the BCL-2, Bax, caspase-8, caspase-3 and p53 levels in spleen cells of the sham-irradiated, 2 Gy whole-body irradiated, 2 Gy cranially irradiated animals and animals exposed to scattered radiation only (measured to be 3 mGy). The values are expressed as the means ± SEM (n = 5). *Significant at p < 0.05 and ***significant at p < 0.001 with respect to the sham-irradiated group.

Figure 3.

Changes in the apoptosis levels in spleen cells of the sham-irradiated, 2 Gy whole-body irradiated, 2 Gy cranially irradiated animals and animals exposed to scattered radiation only (measured to be 3 mGy). The values are expressed as the means ± SEM (n = 5). *Significant at p > 0.05, **significant at p > 0.01, and ***significant at p > 0.001 with respect to the sham-irradiated group.

Figure 4.

Changes in the percentage of DNA damage in the spleen cells of the sham irradiated, 2 Gy whole-body irradiated, 2 Gy cranially irradiated animals and animals exposed to scattered radiation only (measured to be ~3 mGy) using the alkali comet assay that detects DNA single-strand breaks. (a) Percent of tail DNA, (b) tail length and (c) tail moment. The appearance of the microscopic images of representative comets for the different groups is shown at the bottom of histograms. The values are expressed as the means ± SEM (n = 2). *Significant at p > 0.05, ** significant at p > 0.01, and ***significant at p > 0.001 with respect to the sham-irradiated group.