Relieved residual damage in the hematopoietic system of mice rescued by radiation-induced adaptive response (Yonezawa Effect)

0.5 Gy confers resistance to a subsequent high dose of γ-rays by modulating HO-1/Nrf2 and apoptosis pathways

Ionizing radiation, from the DNA centric view, elicits biological effects and health consequences solely through energy deposition events in the cell nucleus. At higher radiation doses, this is likely true; however, at low doses, non-targeted effects, a subcategory of which is the adaptive response, tend to dominate. Controversies exist over the definition of low dose. From a radiation therapy view, it is defined as 0.5-0.7 Gy. Therefore, we investigated the effects of exposure to ionizing radiation with or without a 0.5 Gy priming dose. Techniques including comet assay, flow cytometry, fluorescence microscopy, and real-time quantitative PCR were employed. In normal lung fibroblasts (WI-38), there was a statistically significant difference in mean normalized tail moments when comparing treatment with the challenge dose alone to treatment with a 0.5 Gy priming dose prior to the challenge dose (P < 0.05). Moreover, pretreatment with a 0.5 Gy priming dose reduced G1 phase cell cycle arrest and cell death-either through apoptosis or mitotic catastrophe-induced by the subsequent 2 Gy exposure. Similarly, A549 Cells pre-exposed to a 0.5 Gy priming dose before a 2 Gy exposure showed a lower percentage of apoptosis than those exposed to the 2 Gy alone. Mechanistically, cells responded to a priming 0.5 Gy by increasing the expression of HMOX1, SOD, and Bcl2 while decreasing of IL-1β and TNF-α. In conclusion, 0.5 Gy induces an adaptive response in lung normal and cancer cell against subsequent high doses of γ-rays. Modulation of the HO-1/Nrf2 and apoptosis pathways underlie the resistance observed in primed cells.

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.

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

Radioadaptive response (RAR) describes a phenomenon in a variety of in vitro and in vivo systems that a low-dose of priming ionizing radiation (IR) reduces detrimental effects of a subsequent challenge IR at higher doses. Among in vivo investigations, studies using the mouse RAR model (Yonezawa Effect) showed that RAR could significantly extenuate high-dose IR-induced detrimental effects such as decrease of hematopoietic stem cells and progenitor cells, acute radiation hematopoietic syndrome, genotoxicity and genomic instability. Meanwhile, it has been demonstrated that diet intervention has a great impact on health, and dietary restriction shows beneficial effects on numerous diseases in animal models. In this work, by using the mouse RAR model and mild dietary restriction (MDR), we confirmed that combination of RAR and MDR could more efficiently reduce radiogenotoxic damage without significant change of the RAR phenotype. These findings suggested that MDR may share some common pathways with RAR to activate mechanisms consequently resulting in suppression of genotoxicity. As MDR could also increase resistance to chemotherapy and radiotherapy in normal cells, we propose that combination of MDR, RAR, and other cancer treatments (i.e., chemotherapy and radiotherapy) represent a potential strategy to increase the treatment efficacy and prevent IR risk in humans.

Altered Response to Total Body Irradiation of C57BL/6-Tg (CAG-EGFP) Mice

Application of green fluorescent protein (GFP) in a variety of biosystems as a unique bioindicator or biomarker has revolutionized biological research and made groundbreaking achievements, while increasing evidence has shown alterations in biological properties and physiological functions of the cells and animals overexpressing transgenic GFP. In this work, response to total body irradiation (TBI) was comparatively studied in GFP transgenic C57BL/6-Tg (CAG-EGFP) mice and C57BL/6 N wild type mice. It was demonstrated that GFP transgenic mice were more sensitive to radiation-induced bone marrow death, and no adaptive response could be induced. In the nucleated bone marrow cells of GFP transgenic mice exposed to a middle dose, there was a significant increase in both the percentage of cells expressing pro-apoptotic gene Bax and apoptotic cell death. While in wild type cells, lower expression of pro-apoptotic gene Bax and higher expression of anti-apoptotic gene Bcl-2, and significant lower induction of apoptosis were observed compared to GFP transgenic cells. Results suggest that presence of GFP could alter response to TBI at whole body, cellular and molecular levels in mice. These findings indicate that there could be a major influence on the interpretation of the results obtained in GFP transgenic mice.

Reduction of Delayed Homologous Recombination by Induction of Radioadaptive Response in RaDR-GFP Mice (Yonezawa Effect): An Old Player With a New Role

Radiotherapy (RT) treats cancer effectively with high doses of ionizing radiation (IR) to killing cancer cells and shrinking tumors while bearing the risk of developing different side effects, including secondary cancer, which is most concerning for long-term health consequences. Genomic instability (GI) is a characteristic of most cancer cells, and IR-induced GI can manifest as delayed homologous recombination (HR). Radioadaptive response (RAR) is capable of reducing genotoxicity, cell transformation, mutation, and carcinogenesis, but the rational evidence describing its contributions to the reduction of radiation risk, in particular, carcinogenesis, remains fragmented. In this work, to investigate the impact of RAR on high-dose, IR-induced GI measured as delayed HR, the frequency of recombinant cells was comparatively studied under RAR-inducible and -uninducible conditions in the nucleated cells in hematopoietic tissues (bone marrow and spleen) using the Rosa26 Direct Repeat-green fluorescent protein (RaDR-GFP) homozygote mice. Results demonstrated that the frequency of recombinant cells was significantly lower in hematopoietic tissues under RAR-inducible condition. These findings suggest that reduction in delayed HR may be at least a part of the mechanisms underlying decreased carcinogenesis by RAR, and application of RAR would contribute to a more rigorous and scientifically grounded system of radiation protection in RT.

Differential radio-adaptive responses in BALB/c and C57BL/6 mice: pivotal role of calcium and nitric oxide signalling

Purpose: Our earlier studies demonstrated that transient radio-adaptive responses (RAR) in BALB/c mice were due to MAPK hyperactivation. The objective of this study was to determine the time duration of this low dose induced MAPK activation in BALB/c mice and to find out if similar adaptive responses are observed in C57BL/6 mice. Materials and methods: Mice were irradiated with 0.1 Gy priming dose (PD), 2 Gy challenge dose (CD) with an interval of 4 h (P + CD) and radiation induced immunosuppression in splenic lymphocytes was monitored as the endpoint for RAR. Results: Time kinetics following 0.1 Gy demonstrated persistence of MAPK hyperactivation till 48 h. Similar experiments in C57BL/6 mice indicated absence of RAR at 24 h following CD, in spite of MAPK activation which was also confirmed by time kinetics. Therefore, upstream activators of MAPK, viz., reactive oxygen and nitrogen species (ROS, RNS) and calcium levels were estimated. There was increased intracellular calcium (Ca²⁺) and nitric oxide (NO) in BALB/c and an increase in intracellular ROS in C57BL/6 mice 24 h after PD. Inhibition of NO and calcium chelation abrogated RAR in BALB/c mice. In vitro treatment of spleen cells with combination of NO donor and Ca²⁺ ionophore mimicked the effect of PD and induced adaptive response after 2 Gy not only in BALB/c but also in C57BL/6 mice confirming their crucial role in RAR. Conclusions: These results suggest that low dose induced differential induction of Ca²⁺ and NO signaling along with MAPK was responsible for contrasting RAR with respect to immune system of BALB/c and C57BL/6 mice. Abbreviations [³H]-TdR: ³H-methyl-thymidine; BAPTA: 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; CD: Challenge Dose; CFSE: Carboxy Fluorescein Succinamidyl Ester; on A: Concanavalin A; DAF-FM: 4-amino-5-methylamino-2',7'-difluorescein; DCF-DA: 2',7'-dichlorofluorescein diacetate; DSB: Double Strand Break; ELISA: Enzyme Linked ImmunoSorbent Assay; ERK: Extracellular signal-Regulated protein Kinase; FBS: Fetal Bovine Serum; HIF-1A: Hypoxia-Inducible Factor 1-alpha; LDR: Low Dose Radiation; MAPK: Mitogen Activated Protein Kinase; MAPKK/MKK: MAPK Kinase; MAPKKK: MAPK Kinase Kinase; NO: Nitric Oxide; NOS: Nitric Oxide Synthase; P + CD: Priming + Challenge dose; PBS: Phosphate Buffered Saline; PBST: Phosphate Buffered Saline-Tween 20; PD: Priming Dose; PI3K: Phosphatidyl Inositol 3-Kinase; PKC: Protein Kinase C; RAR: Radio Adaptive Response; RNS: Reactive Nitrogen Species; ROS: Reactive Oxygen Species; RPMI-1640: Roswell Park Memorial Institute-1640 medium; SAPK/JNK: Stress-Activated Protein Kinase/ c-Jun NH2-terminal Kinase; SEM: Standard Error of Mean; SNAP: S-nitro amino penicillamine; TP53: Tumor Protein 53; γ-H2AX: Gamma- H2A histone family member X; Th1: Type 1 helper T cell responses; Th2: Type 2 helper T cell responses.

Chronic restraint-induced stress has little modifying effect on radiation hematopoietic toxicity in mice

Both radiation and stresses cause detrimental effects on humans. Besides possible health effects resulting directly from radiation exposure, the nuclear plant accident is a cause of social psychological stresses. A recent study showed that chronic restraint-induced stresses (CRIS) attenuated Trp53 functions and increased carcinogenesis susceptibility of Trp53-heterozygous mice to total-body X-irradiation (TBXI), having a big impact on the academic world and a sensational effect on the public, especially the residents living in radioactively contaminated areas. It is important to investigate the possible modification effects from CRIS on radiation-induced health consequences in Trp53 wild-type (Trp53wt) animals. Prior to a carcinogenesis study, effects of TBXI on the hematopoietic system under CRIS were investigated in terms of hematological abnormality in the peripheral blood and residual damage in the bone marrow erythrocytes using a mouse restraint model. Five-week-old male Trp53wt C57BL/6J mice were restrained 6 h per day for 28 consecutive days, and TBXI (4 Gy) was given on the 8th day. Results showed that CRIS alone induced a marked decrease in the red blood cell (RBC) and the white blood cell (WBC) count, while TBXI caused significantly lower counts of RBCs, WBCs and blood platelets, and a lower concentration of hemoglobin regardless of CRIS. CRIS alone did not show any significant effect on erythrocyte proliferation and on induction of micronucleated erythrocytes, whereas TBXI markedly inhibited erythrocyte proliferation and induced a significant increase in the incidences of micronucleated erythrocytes, regardless of CRIS. These findings suggest that CRIS does not have a significant impact on radiation-induced detrimental effects on the hematopoietic system in Trp53wt mice.

In vivo radioadaptive response: a review of studies relevant to radiation-induced cancer risk

Radioadaptive response (RAR) describes phenomena where small conditioning doses of ionizing radiation (IR) reduce detrimental effects of subsequent higher IR doses. Current radiation protection regulations do not include RAR because of the large variability in expression among individuals and uncertainties of the mechanism. However, RAR should be regarded as an indispensable factor for estimation and control of individual IR sensitivity. In this article, RAR studies relevant to individual cancer risk are reviewed. Using various stains of mice, carcinogenic RAR has been demonstrated. Consistently much in vivo evidence for RAR with end points of DNA and chromosome damage is reported. Most in vivo RAR studies revealed efficient induction of RAR by chronic or repeated low-dose priming irradiation. Chronic IR-induced RAR was observed also in human individuals after environmental, occupational, and nuclear accident radiation exposure. These observations may be associated with an intrinsically distinct feature of in vivo experimental systems that mainly consist of nonproliferating mature cells. Alternatively, induction of RAR by gap junction-mediated bystander effects suggests that multicellular systems comprising densely communicating cells may be capable of responding to long-lasting low-dose-rate priming irradiation. Regulation by endocrine factors is also a plausible mechanism for RAR at an individual level. Emerging evidence suggests that glucocorticoids, known as stress hormones, participate in in vivo RAR induction following long-term low-dose-rate exposure to IR.

Role of DNA methylation in long-term low-dose γ-rays induced adaptive response in human B lymphoblast cells

PURPOSE

With widespread use of ionizing radiation, more attention has been attracted to low-dose radiation (LDR); however, the mechanisms of long-term LDR-induced bio-effects are unclear. Here, we applied human B lymphoblast cell line HMy2.CIR to monitor the effects of long-term LDR and the potential involvement of DNA methylation.

MATERIALS AND METHODS

HMy2.CIR cells were irradiated with 0.032 Gy γ-rays three times per week for 1-4 weeks. Some of these primed cells were further challenged with 2 Gy γ-rays. Cell proliferation, micronuclei formation, gene expression of DNA methyltransferases (DNMT), levels of global genomic DNA methylation and protein expression of methyl CpG binding protein 2 (MeCP2) and heterochromatin protein-1 (HP1) were measured.

RESULTS

Long-term LDR enhanced cell proliferation and clonogenicity and triggered a cellular adaptive response (AR). Furthermore, global genomic DNA methylation was increased in HMy2.CIR cells after long-term LDR, accompanied with an increase of gene expression of DNMT1 and protein expression of MeCP2 and HP1. After treatment with 5-aza-2'-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, the long-term LDR-induced global genomic DNA hypermethylation was decreased and the AR was eliminated.

CONCLUSION

Global genomic DNA hypermethylation accompanied with increases of DNMT1 and MeCP2 expression and heterochromatin formation might be involved in long-term LDR-induced adaptive response.

Sodium orthovanadate (vanadate), a potent mitigator of radiation-induced damage to the hematopoietic system in mice

Previous in vitro and in vivo studies have shown that sodium orthovanadate (vanadate), an inorganic vanadium compound, could effectively suppress radiation-induced p53-mediated apoptosis via both transcription-dependent and transcription-independent pathways. As a potent radiation protector administered at a dose of 20 mg/kg body weight (20 mg/kg) prior to total body irradiation (TBI) by intra-peritoneal (ip) injection, it completely protected mice from hematopoietic syndrome and partially from gastrointestinal syndrome. In the present study, radiation mitigation effects from vanadate were investigated by ip injection of vanadate after TBI in mice. Results showed that a single administration of vanadate at a dose of 20 mg/kg markedly improved the 30-day survival rate and the peripheral blood hemogram, relieved bone marrow aplasia and decreased occurrence of the bone marrow micronucleated erythrocytes in the surviving animals. The dose reduction factor was 1.2 when a single dose of 20 mg/kg was administered 15 min after TBI in mice using the 30-day survival test as the endpoint. Results also showed that either doubling the vanadate dose (40 mg/kg) in a single administration or continuing the vanadate treatment (after a single administration at 20 mg/kg) from the following day at a dose of 5 mg/kg per day for 4 consecutive days further significantly improved the efficacy for rescuing bone marrow failure in the 30-day survival test. Taken together, these findings indicate that vanadate would be a potent mitigator suppressing the acute lethality (hematopoietic syndrome) and minimizing the detrimental effects (anhematopoiesis and delayed genotoxic effects) induced by TBI in mice.