Long-lasting depression of rabbit aortic prostacyclin formation by single-dose irradiation

Male rabbits were exposed to a single irradiation dose of 1000-5000 rad when 12, 15, 16, and 17 months old and were killed when 18 months old (i.e., 1, 2, 3, and 6 months after irradiation). Even after this long interval after irradiation, abdominal aortic prostacyclin formation was significantly depressed, whereas the nonirradiated thoracic aortic segment exhibited no significant alteration in vascular PGI2 generation. The data show that the severe decrease in PGI2 synthesis was not caused by deendothelialization induced by irradiation alone. The data support the view that a deterioration in the prostaglandin system regulating hemostatic balance is an important determinant in the development of radiation-induced vasculopathy.     

Bone marrow toxicity of total-body irradiation combined with radiosensitizers

The effect of the addition of radiosensitizers to low-dose total-body irradiation was studied. SR2508 (1 g/kg) or misonidazole (0.35 g/kg) was given 30 min prior to single-dose total-body irradiation, delivered at 0.1 Gy/min. Six dogs received either SR2508 or misonidazole and 2 Gy irradiation, and 14 dogs served as controls, receiving no drug and either 2 or 3 Gy of total-body irradiation. All dogs had a decline in their white blood cell and platelet counts and were supported with prophylactic antibiotics and platelet transfusions. High plasma levels of both radiosensitizers were achieved. The degree of cytopenia with 2 Gy total-body irradiation when combined with either radiosensitizer was not significantly greater than that seen with 2 Gy alone, and the neutropenia was significantly less than that seen with 3 Gy alone. The only observed toxicity of the drugs was vomiting, which started shortly after the infusion of SR2508 and before the radiation treatment. A single high-dose infusion of a radiosensitizer combined with total-body irradiation appears to cause a mild increase in bone marrow toxicity but is otherwise well tolerated.     

Antioxidant-chemoprevention diet ameliorates late effects of total-body irradiation and supplements radioprotection by MnSOD-plasmid liposome administration

Abstract Many acute and chronic effects of ionizing radiation are mediated by reactive oxygen species and reactive nitrogen species, which deplete antioxidant stores, leading to cellular apoptosis, stem cell depletion and accelerated aging. C57BL/6NHsd mice receiving intravenous MnSOD-PL prior to 9.5 Gy total-body irradiation (TBI) show increased survival from the acute hematopoietic syndrome, and males demonstrated improved long-term survival (Epperly et al., Radiat. Res. 170, 437-444, 2008). We evaluated the effect of an antioxidant-chemopreventive diet compared to a regular diet on long-term survival in female mice. Twenty-four hours before the LD(50/30) dose of 9.5 Gy TBI, subgroups of mice were injected intravenously with MnSOD-PL (100 μg plasmid DNA in 100 μl of liposomes). Mice on either diet treated with MnSOD-PL showed decreased death after irradiation compared to irradiated mice on the house diet alone (P = 0.031 for the house diet plus MnSOD-PL or 0.015 for antioxidant diet plus MnSOD-PL). The mice on the antioxidant-chemoprevention diet alone or with MnSOD-PL that survived 30 days after irradiation had a significant increase in survival compared to mice on the regular diet (P = 0.04 or 0.01, respectively). In addition, mice treated with MnSOD-PL only and surviving 30 days after radiation also had increased survival compared to those on the regular diet alone (P = 0.02). Survivors of acute ionizing radiation damage have ameliorated life shortening if they are fed an antioxidant-chemopreventive diet.     

Comparison of the gastrointestinal syndrome after total-body or total-abdominal irradiation

In pathogen-free mice, but not standard conventionally housed laboratory rodents, two distinctly different modes of early radiation lethality can be identified by modifying the irradiation technique (total-body versus abdominal irradiation) or by therapeutic intervention such as rescue of total-body-irradiated mice with syngeneic bone marrow or spleen. While damage to the gastrointestinal tract is usually designated as the predominant cause of death occurring within 10 days of radiation exposure, it was demonstrated that damage to the hematopoietic/lymphopoietic system can result in animal lethality over the same period as the gastrointestinal syndrome and that this target cell population is more radiation-sensitive than the gastrointestinal epithelium.     

Radiation damage in patients treated by total-body irradiation, bone marrow grafting, and cyclosporin

The bone marrow (BM) and peripheral blood (PB) from 63 patients were assessed for the presence of chromosomal aberrations after bone marrow transplantation (BMT) following total body irradiation (TBI) for leukemia. Forty-one patients showed no abnormalities in either BM or PB, and 22 had aberrations in either BM or PB or both. Only stable aberrations were found in the BM, but both stable and unstable abnormalities were present in the PB, the majority showing only unstable aberrations. Among the 25 patients who had a leukemic relapse, clonal chromosomal abnormalities were found in the BM of 12 out of the 16 cases for whom marrow was studied at the time of the relapse. A statistically significant negative correlation between leukemic relapse and graft versus host disease (GvHD) was found, but the relationships between chromosome damage and leukemic relapse, GvHD, and the pretransplant radiation dose and between the radiation dose and both leukemic relapse and GvHD were not significant.     

Captopril protects mice bone marrow cells against genotoxicity induced by gamma irradiation

The radioprotective effects of captopril were investigated by using the micronucleus test for anticlastogenic and cell proliferation activity. A single intraperitoneal administration of captopril at doses of 10, 25 and 50 mg/kg 1 h prior to gamma irradiation (2 Gy) reduced the frequencies of micronuleated polychromatic erythrocytes (MnPCEs). All three doses of captopril significantly reduced the frequencies of MnPCEs and increased polychromatic erythrocytes (PCE)/PCE+NCE (normochromatic erythrocyte) ratio in mice bone marrow compared to the non-drug-treated irradiated control (p < 0.001). The optimum dose for protection in mouse was 10 mg/kg to protect mice bone marrow 2.18-fold against the clastogenic effects of gamma-irradiation with respect to the non-drug-treated irradiated control. There was a drug dose-response effect of captopril in increasing the PCE/PCE+NCE ratio in bone marrow cells. The maximum protective effect of captopril was at a dose of 25 mg/kg for increasing the PCE/PCE + NCE ratio. Captopril exhibited concentration-dependent antioxidant activity, scavenging > 96% of the 1,1-diphenyl-2-picryl hydrazyl free radicals when used at a concentration of 0.2 mM. In this study captopril reduced lipid peroxidation induced by hydrogen peroxide in mice liver. It appears that captopril, due to its free radical scavenging properties, protects mice bone marrow cells from radiation-induced DNA damage and genotoxicity.     

Effect of losartan and enalapril on cognitive deficit caused by Goldblatt induced hypertension

The present study was designed to evaluate the learning and memory, in an altered physiological state associated with increased blood pressure and activated renin angiotensin system in Wistar rats. The role of angiotensin in cognitive function was assessed by treatment with angiotensin converting enzyme (ACE) inhibitor enalapril (2 mg/kg), angiotensin 1 receptor (AT(1)) antagonist losartan (5 mg/kg) and their combination. The experimental renal hypertension was induced by the method of Goldblatt. Learning and memory was assessed using the radial arm maze test. Acetylcholine esterase (AChE) levels in the pons medulla, hippocampus, striatum and frontal cortex were measured as a cholinergic marker of learning and memory. Results indicate that in comparison to normotensive rats, renal hypertensive rats committed significantly higher number of errors and took more trials and days to learn the radial arm maze learning and exhibited memory deficit in the radial arm maze retrieval after two weeks of retention interval, indicating impaired acquisition and memory. Treatment with enalapril, losartan and their combination attenuated the observed memory deficits indicating a possible role of renin angiotensin system in cognitive function. AChE level was reduced in hippocampus and frontal cortex of renal hypertensive rats which could be attributed to the observed memory deficit in hypertensive rats. It can be concluded that, renal hypertensive rats had a poor acquisition, retrieval of the learned behavior, perhaps a possible disturbance in memory consolidation process and that this state was reversed with ACE inhibitor enalapril and AT 1 receptor antagonist losartan.     

Dietary antioxidants protect hematopoietic cells and improve animal survival after total-body irradiation

The purpose of this study was to determine whether a dietary supplement consisting of L-selenomethionine, vitamin C, vitamin E succinate, alpha-lipoic acid and N-acetyl cysteine could improve the survival of mice after total-body irradiation. Antioxidants significantly increased the 30-day survival of mice after exposure to a potentially lethal dose of X rays when given prior to or after animal irradiation. Pretreatment of animals with antioxidants resulted in significantly higher total white blood cell and neutrophil counts in peripheral blood at 4 and 24 h after 1 Gy and 8 Gy. Antioxidants were effective in preventing peripheral lymphopenia only after low-dose irradiation. Antioxidant supplementation was also associated with increased bone marrow cell counts after irradiation. Supplementation with antioxidants was associated with increased Bcl2 and decreased Bax, caspase 9 and TGF-beta1 mRNA expression in the bone marrow after irradiation. Maintenance of the antioxidant diet was associated with improved recovery of the bone marrow after sublethal or potentially lethal irradiation. Taken together, oral supplementation with antioxidants appears to be an effective approach for radioprotection of hematopoietic cells and improvement of animal survival, and modulation of apoptosis is implicated as a mechanism for the radioprotection of the hematopoietic system by antioxidants.     

Uptake of carbon monoxide by C3H mice following X irradiation of lung only or total-body irradiation with 60Co

Carbon monoxide uptake (Vco) and ventilation rate (VR) of C3H mice were determined at 14 weeks following either X irradiation of lungs only or total-body irradiation with 60Co at different dose rates. Following localized X irradiation of lung at 97 cGy/min there was a reduction in Vco, which was inversely related to radiation dose, with a small reduction below control levels being detected at 7 Gy, the lowest dose tested. An increase in VR could be detected only at doses of 11 Gy, or more. Another group of animals received 11.5 Gy total-body irradiation at either 26.2 or 4.85 cGy/min followed by transplantation with syngeneic bone marrow. Following total-body irradiation, Vco was significantly reduced by about 37% at the higher dose rate and 23% at the lower dose rate. In contrast, a trend toward elevated VR was detected only at the higher dose rate. The results indicate that Vco is a sensitive indicator of radiation-induced lung injury and that under the experimental conditions used Vco is a more sensitive indicator of radiation-induced lung injury in C3H mice than VR.