Lesion evolution after gamma knife irradiation observed by magnetic resonance imaging

PURPOSE: Our study is focused on the magnetic resonance imaging (MRI) observation of lesion development and hippocampus related functional impairments in rats after irradiation with a Leksell Gamma knife (LGK). MATERIALS AND METHODS: We exposed 32 three-month-old Long-Evans rats to various radiation doses (25 Gy, 50 Gy or 75 Gy). The rats were scanned by a 4.7 T magnetic resonance (MR) spectrometer at several timepoints (1 - 18 months) after irradiation. The lesion size was evaluated by manual segmentation; the animals were behaviorally tested in a Morris water maze and examined histologically. RESULTS: We found that a dose of 25 Gy induced no edema, necrosis or behavioral change. The response of the rats to higher doses was not uniform; the first occurrence of lesions in the rat brains irradiated with 50 and 75 Gy was detected six months post-irradiation. Functional impairment correlated well with the lesion size and histology. CONCLUSIONS: Rat brains showed the development of expanding delayed lesions after 50 or 75 Gy doses from the LGK during the first year after irradiation.     

Development of a small-animal focal brain irradiation model to study radiation injury and radiation-injury modifiers

Abstract

Purpose: Our aim was to establish an effective small-animal focal brain radiation model for research on brain injuries.

Material and methods: Groups of up to six rats were exposed to a range of doses from 120–40 Gy, at 10 intervals of a 6 MeV electron beam. Open-field motor functions and water maze learning-memory tests were performed after the irradiation at two-week intervals. Morphological changes were detected through repeated magnetic resonance imaging (MRI) monthly and were compared with the histopathological findings to determine if they predicted late microscopic changes.

Results: The development of necrosis proved to be dose-dependent. 120 Gy resulted in serious deterioration within 4 weeks in all rats. Localized necrosis in one hemisphere was detected 2 months after the irradiation with ≥ 70 Gy, and 3 months after 40–60 Gy consistent for all animals. The Morris water maze (MWM) tests proved to be the most sensitive tool for the early detection of a brain functional impairment. MRI screening provided useful information on the development of radiation necrosis, which defined the time point for histological examinations.

Conclusions: The described method permits accurate dose delivery to a definite part in one hemisphere of the brain for six rats at a time. Following complex examinations, a dose of 40 Gy and a follow-up time of 4 months are proposed for investigations on neuroradiation modifiers.     

Enhanced survival from radiation pneumonitis by combined irradiation to the skin

Abstract

Purpose: To develop mitigators for combined irradiation to the lung and skin.

Methods: Rats were treated with X-rays as follows: (1) 12.5 or 13 Gy whole thorax irradiation (WTI); (2) 30 Gy soft X-rays to 10% area of the skin only; (3) 12.5 or 13 Gy WTI + 30 Gy skin irradiation after 3 hours; (4) 12.5 Gy WTI + skin irradiation and treated with captopril (160 mg/m²/day) started after 7 days. Our end points were survival (primary) based on IACUC euthanization criteria and secondary measurements of breathing intervals and skin injury. Lung collagen at 210 days was measured in rats surviving 13 Gy WTI.

Results: After 12.5 Gy WTI with or without skin irradiation, one rat (12.5 Gy WTI) was euthanized. Survival was less than 10% in rats receiving 13 Gy WTI, but was enhanced when combined with skin irradiation (p < 0.0001). Collagen content was increased at 210 days after 13 Gy WTI vs. 13 Gy WTI + 30 Gy skin irradiation (p < 0.05). Captopril improved radiation-dermatitis after 12.5 Gy WTI + 30 Gy skin irradiation (p = 0.008).

Conclusions: Radiation to the skin given 3 h after WTI mitigated morbidity during pneumonitis in rats. Captopril enhanced the rate of healing of radiation-dermatitis after combined irradiations to the thorax and skin.     

Radiation tolerance in the tardigrade Milnesium tardigradum

Purpose: Tardigrades are known to survive high doses of ionizing radiation. However, there have been no reports about radiation effects in tardigrades under culture conditions. In this study, we investigated tolerance of the tardigrade, Milnesium tardigradum, against gamma-rays and heavy ions by determining short-term or long-term survival, and reproductive ability after irradiation.

Materials and methods: Hydrated and anhydrobiotic animals were exposed to gamma-rays (1000 – 7000 Gy) or heavy ions (1000 – 8000 Gy) to evaluate short-term survival at 2, 24 and 48 h post-irradiation. Long-term survival and reproduction were observed up to 31 days after irradiation with gamma-rays (1000 – 4000 Gy).

Results: At 48 h after irradiation, median lethal doses were 5000 Gy (gamma-rays) and 6200 Gy (heavy ions) in hydrated animals, and 4400 Gy (gamma-rays) and 5200 Gy (heavy ions) in anhydrobiotic ones. Gamma-irradiation shortened average life span in a dose-dependent manner both in hydrated and anhydrobiotic groups. No irradiated animals laid eggs with one exception in which a hydrated animal irradiated with 2000 Gy of gamma-rays laid 3 eggs, and those eggs failed to hatch, whereas eggs produced by non-irradiated animals hatched successfully.

Conclusion: M. tardigradum survives high doses of ionizing radiation in both hydrated and anhydrobiotic states, but irradiation with >1000 Gy makes them sterile.     

Effects of dexpanthenol with or without Aloe vera extract on radiation-induced oral mucositis: Preclinical studies

Purpose: To define the effect of dexpanthenol with or without Aloe vera extract on radiation-induced oral mucositis.

Materials and methods: Mouse tongue mucosal ulceration was analysed as the clinically relevant endpoint. Graded single or fractionated dose irradiation (10 x 3?Gy/2 weeks, graded test doses on day 14) were combined with topical administration of dexpanthenol or a base, with or without Aloe vera extract. The formulations were applied for 14 days (single dose) or 24 days after the first fraction.

Results: Single dose irradiation resulted in an ED₅₀ (dose at which a positive mucosal response was expected in 50% of the animals irradiated) of 11.9?±?1.2?Gy. None of the formulations yielded a significant change in incidence or time course of ulceration. Test irradiation after 10 x 3?Gy gave an ED₅₀ of 9.0?±?0.1?Gy. Base treatment increased the ED₅₀-values to 10.5?±?0.8?Gy (p?=?0.0095) and 9.9?±?0.7?Gy (p?=?0.0445) without or with Aloe vera. Dexpanthenol resulted in ED₅₀ values of 9.5?±?0.1?Gy without Aloe vera (p?>?0.05), and of 10.9?±?0.9?Gy (p?=?0.0035) with Aloe vera. The latent time to ulceration was prolonged, compared to the control (6.3 days) without Aloe vera (8.0?–?8.2 days, p?<?0.001) and with dexpanthenol and Aloe vera (7.3 days, p?=?0.0239).

Conclusions: With single dose irradiation, neither dexpanthenol nor Aloe vera extract significantly changed the oral mucosal radiation response. With fractionated irradiation, drug administration significantly increased the isoeffective radiation doses, independent of dexpanthenol or Aloe vera content. Neither dexpanthenol nor Aloe vera display a prophylactic potential.     

基于小动物精准放疗平台构建Wistar大鼠急性放射性食管炎动物模型

目的 基于小动物精准放疗平台(SARRP)建立Wistar大鼠急性放射性食管炎体内模型。方法 将36只Wistar大鼠按照随机数表法分为对照组、40、60和75 Gy组,每组9只。基于SARRP结合照射前磁共振图像(MRI)勾画大鼠食管靶区并制定计划,每次分别照射0、8、12和15 Gy,连续照射5 d,观察大鼠体重、进食量、食管病理和磁共振图像改变。结果 75 Gy组大鼠在照后第6天体重最先出现明显降低(P<0.05),照后第9天各照射组大鼠食管较对照组增粗(F=14.20,P<0.05)。照后第9天HE染色显示,40 Gy组放射性食管炎形成率为4/5,60 Gy 组食管炎形成率为5/5,且以轻度食管炎为主,75 Gy组食管炎形成率为5/5,其中3/5表现为重度。照后第9天各组大鼠病理损伤评分[M(Q₁, Q₃)]为0、1.0(0.5, 2.5)、1.0(1.0, 2.5)和4.0(1.5, 6.0),75 Gy组与对照组相比,差异有统计学意义(H=12.69,P<0.05)。动态监测颈部MRI图像后发现,照后第9天时各照射组大鼠食管信号增强变宽。结论 本实验基于小动物精准放疗平台结合MRI成功建立大鼠的急性放射性食管炎动物模型,75 Gy是最佳照射剂量,且第9天是最佳观察时间点。     

Persistence of genetic damage in mice exposed to low dose of X rays

Purpose:?The aim of this work was to evaluate the persistence of genetic damage in CBA/J mice treated with a single irradiation of 0.1 or 1 Gy of X rays.

Materials and methods:?Peripheral blood was collected from irradiated and control mice after 30 min, 24 h, 7 days, 1, 3 and 6 months from exposure and analysed by comet assay. To investigate if the whole-body irradiation affect DNA repair, half of the sampled blood cells were in vitro-irradiated with additional 4 Gy and immediately analysed. Six months from exposure haematopoietic organs were sampled for measuring apoptotic index.

Results:?In mice exposed to 1 Gy genetic damage was initially high and decreased during the experimental-time, while in the 0.1 Gy group damage, at first low, persisted and slightly increased. The 0.1 Gy-irradiated mice showed also a time-dependent increasing sensitivity to the in vitro-irradiation. Six months after whole-body irradiation, the percentage of apoptotic cells observed in haematopoietic compartments from 0.1 Gy-irradiated mice was significantly higher compared to controls and to 1 Gy mice.

Conclusions:?Results demonstrated that a single exposure to low-dose might induce long-term damage. Persistence of genetic damage might have relevant implications for estimating risk for low doses.     

Reduction of oral mucositis by palifermin (rHuKGF): Dose-effect of rHuKGF

Purpose: The aim of the present study was to determine the dose effect of palifermin (recombinant human keratinocyte growth factor, rHuKGF) for reduction of the response of oral mucosa to fractionated radiotherapy in a mouse model.

Material and methods: Ulceration (confluent mucositis) of mouse tongue epithelium was analysed as the clinically relevant endpoint. Palifermin at doses from 1 – 30 mg/kg was administered before the onset (day ?3), at the end of the first (day +4) or the second week of irradiation (day +11) with 5 × 3 Gy/week. Each protocol was terminated by graded radiation test (top-up) doses. In a further experiment, optimally effective doses were given on days ?3 and +4, or ?3, +4 and +11.

Results: Single dose irradiation of mouse mucosa yielded an ED50 (dose inducing ulcer in 50% of the mice) of 10.7 ± 1.0 Gy. With fractionated irradiation for 1 week an ED50 for test irradiation (day +7) of 5.1 ± 1.9 Gy was observed. After 2 weeks (day +14), the ED50 was 7.3 ± 1.9 Gy. Palifermin significantly increased the ED50 values in all protocols tested. Maximally effective doses for single injections were 15.0 mg/kg (day ?3, +11) or 22.5 mg/kg (day +4), which yielded ED50 values of 12.1 ± 1.3 Gy, 13.7 ± 1.5 Gy and 14.4 ± 1.3 Gy, respectively. Higher palifermin doses did not further increase the ED50. Repeated injections on days ?3 and +4 did not increase the ED50 beyond the value obtained with injections on day +4 alone. An additional injection on day +11 increased the ED50 further to 15.1 ± 0.1 Gy.

Conclusions: A significant palifermin dose-effect was seen at doses below 15 mg/kg. However, a significant increase in oral mucosal radiation tolerance by palifermin over untreated control tissue was observed already with low doses of 1 mg/kg. This indicates that in clinical studies with palifermin, the dose of the growth factor may be of minor relevance over a wide dose range.     

Combined gamma‐irradiation and subsequent cisplatin treatment in human squamous carcinoma cell lines sensitive and resistant to cisplatin

Purpose: To investigate the effects of combined radiation and subsequent cisplatin treatment on the human squamous carcinoma cell line SCC‐25 and its cisplatin‐resistant derivative SCC‐25/CP.

Materials and methods: SCC‐25 and SCC‐25/CP cells were treated with various gamma‐ray doses (5?cGy–7?Gy) followed 60?min later by cisplatin treatment and subsequently assayed for survival using a conventional colony assay. For SCC‐25, the subsequent cisplatin treatment was 0.1, 1, 10 and 20?µM for 1?h. For the more cisplatin‐resistant SCC‐25/CP cells, the subsequent cisplatin treatment was 10 and 50?µM for 1?h.

Results: The cisplatin‐resistant SCC‐25/CP cells were not cross‐resistant to gamma‐irradiation. Subsequent treatment with an LD₅₀ concentration of cisplatin (10 and 50?µM for SCC‐25 and SCC‐25/CP, respectively) resulted in radiosensitization for SCC‐25/CP but not for SCC‐25 cells. Gamma‐irradiation of SCC‐25/CP cells followed by treatment with 10 and 50?µM cisplatin for 1?h resulted in radiation survival curves displaying a significant low‐dose hypersensitive region followed by increased radioresistance at higher doses. A total of 10?µM cisplatin resulted in radiosensitization confined to the low‐dose region (0.05 and 0.25?Gy), whereas the higher cisplatin treatment of 50?µM resulted in the appearance of a hypersensitive region together with a reduction of the increased radioresistance region. In contrast, cisplatin treatment (0.1, 1, 10 and 20?µM for 1?h) of SCC‐25 cells had no significant effect on survival following 2.5 or 7.0?Gy and actually resulted in an increased low‐dose radiation survival (0.05, 0.25 and 1?Gy) when survival was corrected for cisplatin treatment (p<0.01 for all cisplatin concentrations tested).

Conclusions: The significant radiosensitization for SCC‐25/CP given subsequent treatment with 50?µM cisplatin indicates cisplatin can inhibit the increased radioresistance response in SCC‐25/CP cells. In contrast, the subsequent cisplatin treatment of SCC‐25 cells can enhance their survival following low radiation doses.     

Dose-dependent histological alterations in the rat lung following intravenous application of Re-188-labeled microspheres

Abstract

Purpose: The objective of this study was to determine the dose-effect correlation of pneumopathy after application of Rhenium-188 microspheres (Re-188 MS) in an animal model using histological changes as an end-point.

Methods and materials: Wistar rats received an intravenous injection of Re-188 MS yielding doses that ranged from ? 2 to ? 55 Gy. Lungs were removed after ? 25 weeks and prepared for histology. Sections were evaluated using a semi-quantitative 5-tiered score. Dose groups of 10 Gy intervals were statistically analyzed using the Chi-square test with respect to grade and extent of connective tissue accumulation, thickness of vessel walls and accumulation of alveolar macrophages (AM).

Results: There was a statistically significant increase in connective tissue content and extent in all dose groups compared to control lungs and at least between each other dose group. The steepest increase in connective tissue was at doses higher than 40 Gy. Starting from that dose, a statistically significant increase of AM accumulation and vessel wall thickness occurred.

Conclusions: There was a clear dose-effect correlation between radiation dose and histological changes. These findings allow an estimation of potential normal tissue damage especially during tumor treatments of liver lesions with radioactive particles in patients with significant liver-to-lung shunts.     

Attenuation of radiation-induced gastrointestinal damage by epidermal growth factor and bone marrow transplantation in mice

Purpose: We examined the effect of epidermal growth factor (EGF) and bone marrow transplantation (BMT) on gastrointestinal damage after high-dose irradiation of mice.

Material and methods: C57Black/6 mice were used. Two survival experiments were performed (12 and 13 Gy; ⁶⁰Co, 0.59–0.57 Gy/min). To evaluate BMT and EGF action, five groups were established – 0 Gy, 13 Gy, 13 Gy + EGF (at 2 mg/kg, first dose 24 h after irradiation and then every 48 h), 13 Gy + BMT (5 × 10⁶ cells from green fluorescent protein [GFP] syngenic mice, 4 h after irradiation), and 13 Gy + BMT + EGF. Survival data, blood cell counts, gastrointestine and liver parameters and GFP positive cell migration were measured.

Results: BMT and EGF (three doses, at 2 mg/kg, administered 1, 3 and 5 days after irradiation) significantly increased survival (13 Gy). In blood, progressive cytopenia was observed with BMT, EGF or their combination having no improving effect early after irradiation. In gastrointestinal system, BMT, EGF and their combination attenuated radiation-induced atrophy and increased regeneration during first week after irradiation with the combination being most effective. Signs of systemic inflammatory reaction were observed 30 days after irradiation.

Conclusions: Our data indicate that BMT together with EGF is a promising strategy in the treatment of high-dose whole-body irradiation damage.     

Low-dose hyperradiosensitivity of human glioblastoma cell lines in vitro does not translate into improved outcome of ultrafractionated radiotherapy in vivo

Purpose: Low dose hyperradiosensitivity (HRS) has been observed in HGL21- and T98G human glioblastoma cells in vitro. The present study investigates whether these effects translate into improved outcome of ultrafractionated irradiation (UF) in vivo.

Material and methods: T98G or HGL21 were transplanted on the hind leg of nude mice. Tumours were irradiated with UF (3 fractions of 0.4 Gy per day, interval 4 h, 7 days per week) or with conventional fractionation (CF; 1 fraction of 1.68 Gy per day, 5 days per week) over 2 or 4 weeks in HGL21 and 2,4 or 6 weeks in T98G. In HGL21, graded top-up doses under clamped hypoxia were applied after 4 weeks of fractionated irradiation. Additional groups of animals were irradiated with single doses under clamp hypoxic conditions with or without whole body irradiation (WBI) before tumour transplantation. Experimental endpoints were growth delay (time to 5-fold starting volume, GD_V5) and local tumour control.

Results: In T98G tumours median relative GD_V5 was 1.2 [95%C.I. 0.96; ∞] in the CF and 0.8 [0.7; 1.02] in the UF arm (p = 0.009) indicating that ultrafractionation is less efficient than conventional fractionation. The TCD₅₀ value of 33.5 Gy [22; 45] after UF was higher than TCD₅₀ of 23.6 Gy [16; 31] after CF (p = 0.15). In HGL21 the median relative GD_V5 was not significantly different between CF and UF. The top-up TCD₅₀ value of 16.1 Gy [95% C.I. 9; 23 Gy] after CF was significantly lower than the corresponding value of 33.2 Gy [23; 44] after UF irradiation (p = 0.007), indicating a higher efficacy of CF compared to UF.

Conclusion: The results on human T98G and HGL21 glioblastoma do not support the hypothesis that HRS in vitro translates into improved outcome of ultrafractionated irradiation in vivo.     

Mitochondrial DNA deletions in tissues of mice after ionizing radiation exposure

Purpose: The objective of the study was to estimate the presence of large mtDNA deletions in brain and spleen tissues of mice four months after exposure to 2 and 5?Gy.

Materials and methods: The male BALB/c mice underwent X-ray total-body acute radiation. Four months after irradiation, the mice were decapitated, and the samples of spleen and brain tissues were examined. A long-distance PCR was used to detect mtDNA deletions and their levels in samples of brain and spleen tissues.

Results: Four months after irradiation the levels of mtDNA deletions in the brain and spleen tissues were higher in animals exposed to 5?Gy than in animals at an irradiation dose of 2?Gy and in control mice. The levels of deletions in the mice brain tissues were higher 4 months than 1 month after X-ray exposure to both doses (2 and 5?Gy). In spleen tissues, a higher level of deletions was observed only at an irradiation dose of 5?Gy.

Conclusions: Our data have shown that ionizing radiation induces an increase of mtDNA copies with deletions in tissues of mice four months after the post-irradiation period. The level of deletions depends on the animal age, type of tissue, irradiation dose and length of the post-irradiation period.     

Differential response to acute low dose radiation in primary and immortalized endothelial cells

Abstract

Purpose: The low dose radiation response of primary human umbilical vein endothelial cells (HUVEC) and its immortalized derivative, the EA.hy926 cell line, was evaluated and compared.

Material and methods: DNA damage and repair, cell cycle progression, apoptosis and cellular morphology in HUVEC and EA.hy926 were evaluated after exposure to low (0.05–0.5 Gy) and high doses (2 and 5 Gy) of acute X-rays.

Results: Subtle, but significant increases in DNA double-strand breaks (DSB) were observed in HUVEC and EA.hy926 30 min after low dose irradiation (0.05 Gy). Compared to high dose irradiation (2 Gy), relatively more DSB/Gy were formed after low dose irradiation. Also, we observed a dose-dependent increase in apoptotic cells, down to 0.5 Gy in HUVEC and 0.1 Gy in EA.hy926 cells. Furthermore, radiation induced significantly more apoptosis in EA.hy926 compared to HUVEC.

Conclusions: We demonstrated for the first time that acute low doses of X-rays induce DNA damage and apoptosis in endothelial cells. Our results point to a non-linear dose-response relationship for DSB formation in endothelial cells. Furthermore, the observed difference in radiation-induced apoptosis points to a higher radiosensitivity of EA.hy926 compared to HUVEC, which should be taken into account when using these cells as models for studying the endothelium radiation response.     

A biosafety evaluation of synchrotron radiation X-ray to skin and bone marrow: single dose irradiation study of rats and macaques

Purpose: Very limited experimental data is available regarding the safe dosages related to synchrotron radiation (SR) procedures. We used young rats and macaques to address bone marrow and skin tolerance to various doses of synchrotron radiation.

Methods: Rats were subjected to 0, 0.5, 2.5, 5, 25 or 100?Gy local SR X-ray irradiation at left hind limb. Rat blood samples were analyzed at 2–90 days after irradiation. The SR X-ray irradiated skin and tibia were sectioned for morphological examination. For non-human primate study, three male macaques were subjected to 0.5 or 2.5?Gy SR X-ray on crus. Skin responses of macaques were observed.

Results: All rats that received SR X-ray irradiation doses greater than 2.5?Gy experienced hair loss and bone-growth inhibition, which were accompanied by decreased number of follicles, thickened epidermal layer, and decreased density of bone marrow cells (p?<?0.05). Macaque skin could tolerate 0.5?Gy SR X-ray but showed significant hair loss when the dose was raised above 2.5?Gy.

Conclusion: The safety threshold doses of SR X-ray for rat skin, bone marrow and macaque skin are between 0.5 and 2.5?Gy. Our study provided essential information regarding the biosafety of SR X-ray irradiation.     

Irradiation dose-dependent oxidative changes in red blood cells for transfusion

Abstract

Purpose: To investigate the extent of γ-irradiation-induced oxidative protein and lipid damage in long-term (up to 21 days) cold stored (4°C) erythrocytes (RBC) and in plasma from whole blood anticoagulated with acid-citrate-dextrose (ACD-A).

Materials and methods: Lipid peroxidation, protein carbonyl group (CO) and thiol levels were quantified by the amount of thiobarbituric acid-reactive substances (TBARS), enzyme-linked immunosorbent assay (ELISA) and with Ellman reagent, respectively.

Results: Irradiation (40–50 Gy) enhanced lipid peroxidation in the RBC membrane (at day 1 and after 21 storage days); the increase was storage time-dependent. In pre-irradiated (30–50 Gy) and long-term stored RBC membrane protein CO level was higher vs. non-irradiated. Irradiation resulted in RBC membrane protein thiol level elevation, most likely being a result of conformational changes and/or the polypeptide chain fragmentation. Similar to RBC, irradiation of plasma resulted in the increased TBARS generation. In plasma, significant protein CO elevation (at dose of 50 Gy) and protein thiol reduction (30–50 Gy) was observed.

Conclusion: These findings clearly indicate that irradiation at clinically relevant doses enhances the degree of lipid peroxidation and oxidative protein damage in the membranes of stored RBC. The oxidative stress markers may be considered as additional parameters for RBC quality assessment in the blood banks.     

IL‐1β, TNFα and IL‐6 induction in the rat brain after partial‐body irradiation: role of vagal afferents

Purpose: To evaluate the central nervous system neuroimmune and inflammatory responses during the prodromal phase of the acute irradiation syndrome in rat brains after partial‐body exposure (head‐protected) and to investigate the potential neural signalling pathways from the irradiated periphery to the non‐irradiated brain.

Material and methods: The study included four groups of rats: one irradiated group and one sham irradiated group, each containing non‐vagotomized and vagotomized rats. In vagotomized rat groups, the subdiaphragmatic vagal section surgery was carried out 45 days before the irradiation exposure. The rats were partial‐body irradiated with the head shielded with ⁶⁰Co γ‐rays to a dose of 15?Gy. They were sacrificed 6?h after the end of exposure. The hypothalamus, hippocampus, thalamus and cortex were then collected, and the concentrations of IL‐1β, TNFα and IL‐6 in each were measured by ELISA assays.

Results: Six hours after irradiation, IL‐1β levels had increased in the hypothalamus, thalamus and hippocampus, and TNFα and IL‐6 levels had increased significantly in the hypothalamus. Vagotomy before irradiation prevented these responses.

Conclusions: It was concluded that the hypothalamus, hippocampus, thalamus and cortex react rapidly to peripheral irradiation by releasing pro‐inflammatory mediators. The results also show that the vagus nerve is one of the major ascending pathways for rapid signalling to the brain with respect to partial body irradiation.     

Radioprotective combination of α-tocopherol and ascorbic acid promotes apoptosis that is evident by release of low-molecular weight DNA fragments into circulation

Abstract

Purpose: Genotoxic stresses, including irradiation, lead to the apoptosis of damaged cells and the release of DNA fragments into circulation. Both α-tocopherol acetate and ascorbic acid possess antioxidant and radioprotective properties. Interestingly, depending on a particular experimental system, the treatment with vitamins may demonstrate either apoptosis-promoting or apoptosis-suppressing effects.

Materials and methods: Adult Wistar male rats received total body irradiation with 2–100 Gy doses, while non-irradiated rats served as controls. Oral gavages with vitamins were administered either 10 min or 1 h before irradiation. Control groups were similarly treated with water. Blood samples were collected at 5 h post irradiation. The levels and the composition of circulating DNA were profiled. Chromosomal aberrations were assessed 24 h after irradiation.

Results: A substantial dose-dependent increase in circulating low-molecular weight (LMW) DNA levels was observed after whole body irradiation. An order-of-magnitude increase in the proportion of bone marrow cells with chromosomal abnormalities was observed after irradiation at 2 Gy. Single vitamin preparations were not protective, while the combination of α-tocopherol (10?mg/kg) and ascorbic acid (20?mg/kg) displayed a protective effect evident from marked decrease in chromosomal aberrations. In animals treated with a combination of the vitamins only, substantial increases in the release of LMW DNA were observed.

Conclusions: Radioprotective combination of α-tocopherol and ascorbic acid promotes apoptosis that is evident by release of low-molecular weight DNA into circulation. We hypothesize that the pretreatment with vitamins provides radioprotection, at least in part, by aiding non-inflammatory, apoptotic elimination of most damaged cells. The microevolutionary nature of observed adaptive response provides mechanistic foundation for the phenomenon of hormesis.