Reduced High-Dose Radiation-Induced Residual Genotoxic Damage by Induction of Radioadaptive Response and Prophylactic Mild Dietary Restriction in Mice

Radio-adaptive Response Induced by Low-dose Ionizing Radiation in Innate Immunity for Radiotherapy

ABSTRACT

Radio-adaptive response (RAR) is a mechanism by which low doses of ionizing radiation (IR) protect cells from subsequent high doses. This study aimed to compare the immuno-radiological effects of 0.25, 0.5, and 5 Gy to 0.25 or 0.5 Gy as priming and 5 Gy as challenging doses. Thirty-five rats were irradiated whole-body with 0.25 and 0.5 Gy followed by 5 Gy, and the same single IR doses with non-irradiated animals serving as controls. Serum interferon-gamma (INF-γ), interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), nitric oxide (NO), and malondialdehyde (MDA) levels were measured 4 d post both priming and challenge doses. A 0.25-Gy priming dose significantly (P < 0.05) reduced serum TNF-α, MDA, and NO levels compared to all single-irradiated groups. Surprisingly, there was no difference in IFN-γ serum levels between the RAR-induced and non-irradiated groups (P ≥ 0.05). Compared to the same low priming dose (0.25 and 0.5 Gy), the effect of the challenging dose (5 Gy) remains unchanged or decreases. Serum IFN-γ, MDA, and NO concentrations, on the other hand, were significantly (P < 0.05) lower in the 0.5 Gy pre-challenging dose, whereas IL1β had no effect (P ≥ 0.05) compared to 5 Gy alone. The post-RAR group had significantly (P < 0.05) lower oxidative stress indicators than the other irradiation groups. The findings suggested that priming with low IR could help mitigate the negative effects on the hematopoietic system. Finally, RAR has significantly impacted endogenous cytokines, oxidative stress biomarkers, and lipid peroxidation parameters. RAR can improve patients' radiological safety profiles by mitigating adverse radiotherapy effects.

Immune system modulation by low-dose ionizing radiation-induced adaptive response

OBJECTIVE

Hormesis or low-dose ionizing radiation is known to induce various biological responses, a subcategory of which is the adaptive response, which has been reported to protect against higher radiation doses via multiple mechanisms. This study investigated the role of the cell-mediated immunological component of low-dose ionizing radiation-induced adaptive response.

METHODS

Herein, male albino rats were exposed to whole-body gamma radiation, using a Cs¹³⁷ source with low-dose ionizing radiation doses of 0.25 and 0.5 Gray (Gy); 14 days later, another irradiation session at a dose level of 5 Gy was carried on. Four days post-irradiation at 5 Gy, rats were sacrificed. The low-dose ionizing radiation-induced immuno-radiological response has been assessed through the T-cell receptor (TCR) gene expression quantification. Also, the serum levels of each of interleukins-2 and -10 (IL-2, IL-10), transforming growth factor-beta (TGF-β), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were quantified.

RESULTS

Results indicated that priming low irradiation doses resulted in significant decrements in TCR gene expression and the serum levels of IL-2, TGF-β, and 8-OHdG with an increment in IL-10 expression compared to the irradiated group, which did not receive low priming doses.

CONCLUSION

The observed low-dose ionizing radiation-induced radio-adaptive response significantly protected against high irradiation dose injuries, through immune suppression, representing a promising pre-clinical protocol that would be applied to minimize radiotherapy side effects on normal but not against the tumor cells.

The radiation adaptive response and priming dose influence: the quantification of the Raper-Yonezawa effect and its three-parameter model for postradiation DNA lesions and mutations

The priming dose effect, called also the Raper-Yonezawa effect or simply the Yonezawa effect, is a special case of the radiation adaptive response phenomenon (radioadaptation), which refers to: (a) faster repair of direct DNA lesions (damage), and (b) DNA mutation frequency reduction after irradiation, by applying a small priming (conditioning) dose prior to the high detrimental (challenging) one. This effect is observed in many (but not all) radiobiological experiments which present the reduction of lesion, mutation or even mortality frequency of the irradiated cells or species. Additionally, the multi-parameter model created by Dr. Yonezawa and collaborators tried to explain it theoretically based on experimental data on the mortality of mice with chronic internal irradiation. The presented paper proposes a new theoretical approach to understanding and explaining the priming dose effect: it starts from the radiation adaptive response theory and moves to the three-parameter model, separately for two previously mentioned situations: creation of fast (lesions) and delayed damage (mutations). The proposed biophysical model was applied to experimental data-lesions in human lymphocytes and chromosomal inversions in mice-and was shown to be able to predict the Yonezawa effect for future investigations. It was also found that the strongest radioadaptation is correlated with the weakest cellular radiosensitivity. Additional discussions were focussed on more general situations where many small priming doses are used.

Mitigation of Iron Irradiation-Induced Genotoxicity and Genomic Instability by Postexposure Dietary Restriction in Mice

Background and Purpose. Postexposure onset of dietary restriction (DR) is expected to provide therapeutic nutritional approaches to reduce health risk from exposure to ionizing radiation (IR) due to such as manned space exploration, radiotherapy, or nuclear accidents as IR could alleviate radiocarcinogenesis in animal models. However, the underlying mechanisms remain largely unknown. This study is aimed at investigating the effect from postexposure onset of DR on genotoxicity and genomic instability (GI) induced by total body irradiation (TBI) in mice. Materials and Methods. Mice were exposed to 2.0 Gy of accelerated iron particles with an initial energy of 500 MeV/nucleon and a linear energy transfer (LET) value of about 200 keV/μm. After TBI, mice were either allowed to free access to a standard laboratory chow or treated under DR (25% cut in diet). Using micronucleus frequency (MNF) in bone marrow erythrocytes, induction of acute genotoxicity and GI in the hematopoietic system was, respectively, determined 1 and 2 months after TBI. Results and Conclusions. TBI alone caused a significant increase in MNF while DR alone did not markedly influence the MNF. DR induced a significant decrease in MNF compared to the treatment by TBI alone. Results demonstrated that postexposure onset of DR could relieve the elevated MNF induced by TBI with high-LET iron particles. These findings indicated that reduction in acute genotoxicity and late GI may be at least a part of the mechanisms underlying decreased radiocarcinogenesis by DR.