Cytogenetic analysis of radiation-induced leukemia in Trp53-deficient C3H/He mice

C3H/He mice develop acute myeloid leukemia (AML) after whole-body irradiation, but the strain becomes highly susceptible to stem cell leukemia (SCL) when a null mutation is introduced into the Trp53 gene. To examine the etiology of SCL and the influence of chromosomal instability on leukemogenesis, 12 SCLs and two AMLs arising from Trp53-deficient C3H/He mice were investigated cytogenetically. Each SCL demonstrated cell-to-cell variation in the number and structural integrity of their chromosomes, indicating chromosomal instability. Typical deletion of chromosome 2 was observed in the two AML cases, while most SCL cells did not display this aberration. Deletions and rearrangements of chromosome 11 were noticeable in SCLs from Trp53 heterozygotes but not in AMLs. Analysis of loss of heterozygosity revealed that aberrations involving chromosome 11 in SCLs resulted in loss of the wild-type Trp53 allele. These results suggest that loss of Trp53 function triggers the tumorigenic process leading toward SCL through the induction of chromosomal instability, and that SCL and AML are distinct varieties of leukemia.     

The adaptive response modifies latency for radiation-induced myeloid leukemia in CBA/H mice.

We have investigated the effect of the adaptive response on acute myeloid leukemia (AML) induced in CBA/Harwell mice by a chronic radiation exposure. Groups of mice irradiated with a total dose of 1. 0 Gy at two different chronic dose rates (0.5, 0.004 Gy/h) had similar frequencies of AML. Compared to control animals that did not develop AML, irradiation at either of these dose rates did not change the longevity of the mice that did not die of leukemia. The survival rates of irradiated mice that did develop leukemia in the two groups were not different from each other, indicating that the dose rates produced similar responses and therefore were both chronic exposures. We then tested the ability of a chronic 10-cGy (0. 5 Gy/h) exposure to ionizing radiation, mild hyperthermia (40.5 degrees C whole-body, 60 min) or treatment with interleukin-1 (1500 U i.p.) to induce an adaptive response and modify the frequency or latency of AML which resulted from a subsequent (24 h later) 1.0-Gy (0.5 Gy/h) chronic radiation exposure. The frequency of radiation-induced leukemia was not changed in mice given any of the three adapting treatments 24 h prior to the chronic 1.0-Gy dose that induced leukemia. However, the latent period for development of AML was significantly increased by both the prior low radiation dose and mild hyperthermia treatment. Injection of interleukin-1, in contrast, may have reduced the latent period. Similar to the single 1.0-Gy chronic exposure alone, none of the adapting treatments prior to that exposure influenced the survival of animals that did not develop AML. These results indicate that an earlier exposure to a small adapting dose of radiation or to a mild heat stress can influence secondary steps in radiation-induced carcinogenesis.     

Oxalomalate regulates ionizing radiation-induced apoptosis in mice

Ionizing radiation induces the production of reactive oxygen species, which play an important causative role in apoptotic cell death. Recently, we demonstrated that the control of mitochondrial redox balance and the cellular defense against oxidative damage are primary functions of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm) by supplying NADPH for antioxidant systems. In this paper, we demonstrate that modulation of IDPm activity in the kidneys of mice regulates ionizing radiation-induced apoptosis. When oxalomalate, a competitive inhibitor of IDPm, was administered to mice, inhibition of IDPm and enhanced susceptibility of apoptosis reflected by DNA fragmentation, the changes in mitochondria function, and the modulation of apoptotic marker proteins were observed upon exposure to 2 Gy of gamma-irradiation. We also observed a significant difference in the mitochondrial redox status between the kidneys of the control and the oxalomalate-administered mice. This study indicates that IDPm may play an important role in regulating the apoptosis induced by ionizing radiation, presumably, through acting as an antioxidant enzyme.     

Ultraviolet radiation-induced immunosuppression of delayed-type hypersensitivity in mice

Ultraviolet (UV) radiation present in sunlight plays a critical role in the initiation and promotion of nonmelanoma skin carcinogenesis and immune suppression. The immune suppressive effects of UV have been identified as a risk factor for skin cancer induction. For these reasons, scientists have focused on elucidating the mechanisms of UV-induced immune suppression to better understand the pathogenesis of skin cancer induction. A hallmark of UV-induced immune suppression is the generation of antigen-specific suppressor T cells. These suppressor cells have been shown to suppress antitumor immunity as well as other cell-mediated responses such as delayed-type hypersensitivity (DTH) reactions. Due to the excessive cost and time involved in traditional UV carcinogenic experiments, scientists have opted to use UV-induced suppression of DTH reactions as a surrogate model. DTH has been, and continues to be, a widely used assay system to measure in vivo immune function. Although somewhat unsophisticated by today's standards, this assay has great advantages because it presents a fast, inexpensive, and reliable model system to help dissect the mechanisms involved in UV-induced immune suppression. Furthermore, the murine model of DTH enables scientists to perform additional procedures, such as adoptive transfer studies with suppressor T cells, which are currently unavailable with human subjects.     

RF radiation-induced changes in the prenatal development of mice

The possible effects of radiofrequency (RF) radiation on prenatal development has been investigated in mice. This study consisted of RF level measurements and in vivo experiments at several places around an “antenna park.” At these locations RF power densities between 168 nW/cm² and 1053 nW/cm² were measured. Twelve pairs of mice, divided in two groups, were placed in locations of different power densities and were repeatedly mated five times. One hundred eighteen newborns were collected. They were measured, weighed, and examined macro- and microscopically. A progressive decrease in the number of newborns per dam was observed, which ended in irreversible infertility. The prenatal development of the newborns, however, evaluated by the crown-rump length, the body weight, and the number of the lumbar, sacral, and coccygeal vertebrae, was improved. Bioelectromagnetics 18:455–461, 1997. © 1997 Wiley-Liss, Inc.     

Role of radioadaptation on radiation-induced thymic lymphoma in mice

Thymic lymphoma (TL) was observed in different stages of development in 46% of male mice (23/50) following exposure to an acute challenge dose of 2 Gy ⁶⁰Co γ-rays. With an adapting dose of 1 cGy 24 h prior to the challenge dose of 2 Gy, similar growth of TL was seen in 42.5% of mice (17/40). TL was not found in unirradiated control mice (0/50) or in the group treated with 1 cGy (0/50). Multiple adapting doses for 5 or 10 consecutive days induced TL in 8/50 and 9/50 mice, respectively (17% in average). When multiple adapting doses were followed by the challenge dose, the yield of TL was much lower, 16% (8/50) and 30% (15/30), respectively. By 15, 30, 60, 90, and 120 days after exposure with 3 Gy of ⁶⁰Co γ-rays, TL developed in 30, 70, 70, 80 and 85% of the female mice, respectively. When mice were conditioned with an adapting dose of 1 cGy 24 h prior to the challenge dose, TL was not found 15 days post-irradiation, while about a 25% reduction in the occurrence of TL was noticed at all other intervals. The results suggested that an adapting dose could play a role in bringing about a change in terms of delay and inhibition of the acute effects of radiation, i.e., the onset of TL in mice.     

Chemical protection and cell-cycle effects on radiation-induced mutagenesis

Chinese hamster ovary cells in the exponential phase of growth were harvested and separated by the method of centrifugal elutriation into subpopulations enriched with up to 95% G1 phase, 70% S phase and 65% G2 + M phase cells. Cell cycle distributions were routinely monitored by flow cytometry. Following elutriation, aliquots of cells from each of the enriched cell fractions were incubated in the presence or absence of 4 mM of 2-[(aminopropyl)amino] ethanethiol (WR-1065) for 30 min at 37 degrees C. The cells were then irradiated with 60Co gamma-rays or fission-spectrum neutrons from the JANUS research reactor. Both cell killing and mutagenesis were determined. Regardless of the radiation quality used, cells enriched in G1 phase were the most sensitive to radiation-induced mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase locus. The relative magnitude of protection exerted by WR-1065 differed for each of the elutriator separated cell populations. The greatest magnitude of protection, however, was observed for G1-enriched populations, regardless of the radiation quality used or the biological end-point tested.     

Effect of sesamol on radiation-induced cytotoxicity in Swiss albino mice

The radio-protective ability of sesamol (SM) at various doses viz., 0, 10, 25, 40, 50, 70 and 100 mg/kg bw, administered intraperitoneally 30 min prior to 9.5 Gy whole-body γ-irradiation was studied in Swiss albino mice. Radiation toxicity and mortality were observed during a period of 30 days and the percentage mortality was calculated. SM pretreatment with 50 mg/kg bw was found to be the most effective dose in maintaining body weight and in reducing the percentage mortality, while 100 mg/kg bw was found to be more effective in maintaining the spleen index and in stimulation of endogenous spleen colony-forming units. Pretreatment with SM (50 mg/kg bw) in mice irradiated with 15 Gy significantly reduced dead, inflammatory, mitotic and goblet cells in irradiated jejunum. SM at 50 mg/kg bw also increased crypt cells, maintained villus height, and prevented mucosal erosion. Nuclear enlargement in epithelial cells was found less in SM-treated mice compared with the irradiated control. The radiation-induced decrease in endogenous antioxidant enzymes (GSH, GST, catalase) and the increase in lipid peroxidation were also reduced by pretreatment with SM [50 and 100 mg/kg bw] at all monitored post-irradiation intervals. There was no protection at a dose less than 25 mg/kg bw.     

Effect of sesamol on radiation-induced cytotoxicity in Swiss albino mice

The radio-protective ability of sesamol (SM) at various doses viz., 0, 10, 25, 40, 50, 70 and 100mg/kg bw, administered intraperitoneally 30min prior to 9.5Gy whole-body gamma-irradiation was studied in Swiss albino mice. Radiation toxicity and mortality were observed during a period of 30 days and the percentage mortality was calculated. SM pretreatment with 50mg/kg bw was found to be the most effective dose in maintaining body weight and in reducing the percentage mortality, while 100mg/kg bw was found to be more effective in maintaining the spleen index and in stimulation of endogenous spleen colony-forming units. Pretreatment with SM (50mg/kg bw) in mice irradiated with 15Gy significantly reduced dead, inflammatory, mitotic and goblet cells in irradiated jejunum. SM at 50mg/kg bw also increased crypt cells, maintained villus height, and prevented mucosal erosion. Nuclear enlargement in epithelial cells was found less in SM-treated mice compared with the irradiated control. The radiation-induced decrease in endogenous antioxidant enzymes (GSH, GST, catalase) and the increase in lipid peroxidation were also reduced by pretreatment with SM [50 and 100mg/kg bw] at all monitored post-irradiation intervals. There was no protection at a dose less than 25mg/kg bw.     

New class of leukemogenic ecotropic recombinant murine leukemia virus isolated from radiation-induced thymomas of C57BL/6 mice

We previously reported the establishment of several lymphoid cell lines from X-ray-induced thymomas of C57BL/Ka mice, and all, except one, produce retroviruses (P. Sankar-Mistry and P. Jolicoeur, J. Virol.35:270-275, 1980). Biological characterization of five of these new primary radiation leukemia viruses (RadLVs) indicated that they had a B-tropic, fibrotropic, and ecotropic host range and were leukemogenic when reinjected into C57BL/Ka newborn mice. The leukemogenic potential of one isolate (G(6)T(2)) was further assessed and shown to be retained after prolonged passaging on fibroblasts in vitro. Restriction endonuclease analysis of the DNA of four of our new RadLV isolates (G(6)T(2), Ti-7, Ti-8, and Ti-9) revealed that G(6)T(2) and Ti-7 murine leukemia virus (MuLV) genomes had identical restriction maps, whereas Ti-8 and Ti-9 genomes were different from each other and from the G(6)T(2) and Ti-7 genomes. The physical maps of these genomes were similar to that of known ecotropic MuLV genomes (including the C57BL/Ka endogenous ecotropic MuLV) within their long terminal repeats, env, the right portion of pol, and the left portion of gag. However, a region covering the end of gag and the beginning of pol was different and showed several similarities with xenotropic MuLV genomes of BALB/c, AKR, and C58 mice previously mapped. Our results suggest that these primary RadLV genomes are recombinants between the parental ecotropic MuLV genome and a nonecotropic (xenotropic) sequence. This nonecotropic gag-pol region might be important in conferring the leukemogenic potential to these isolates. Therefore, these RadLVs appear to form a new class of leukemogenic recombinant MuLVs recovered from leukemic tissues of mice. They appear to be distinct from the recombinant AKR mink cell focus-inducing MuLVs which have a dual-tropic host range and harbor xenotropic env sequences. To further study the leukemogenic potential of these RadLVs, the genome of one of them (G(6)T(2)) was cloned in Charon 21A as an infectious molecule.     

Efficacy of radioprotection in the prevention of radiation-induced craniofacial bone growth inhibition

It has been reported that radiotherapy-induced craniofacial deformities can occur in 66 to 100 percent of survivors of childhood head and neck cancers. Recent interest in the effectiveness of radioprotectors in the protection of normal tissue against radiation injury led us to investigate a possible role of radioprotection in the prevention of radiation-induced craniofacial bone growth inhibition. Therefore, the objective of this study was to use the radioprotective agent amifostine (Ethyol, WR-2721) as a probe to determine the effectiveness of radioprotection in the prevention of radiation-induced craniofacial bone growth inhibition after single-dose orthovoltage radiation to the infant rabbit orbital-zygomatic complex. Seven-week-old male New Zealand white rabbits were randomized into three groups (n = 10 each): group 1, 0 Gy (sham radiation); group 2, 35-Gy single-dose orthovoltage radiation; and group 3, 35-Gy single-dose orthovoltage radiation and amifostine (300 mg/kg intravenously, given 20 minutes before radiation). Serial radiographs and computed tomographic scans were obtained for cephalometric analysis, bone volume, and bone density measurements until skeletal maturity at 21 weeks. Significant (p < 0.05) reductions in orbital-zygomatic complex linear bone growth, bone volume, and bone density were observed after 35-Gy radiation compared with nonirradiated controls. No significant differences were noted between groups in cephalometric analysis of the nontreated (nonirradiated) left orbital-zygomatic complex, indicating no crossover effect from the radiation beam. However, pretreatment with amifostine, 20 minutes before 35-Gy radiation, resulted in significant (p < 0.05) preservation of linear bone growth, bone volume, and bone mineral density in the rabbit orbital-zygomatic complex compared with controls. This study demonstrated for the first time the effectiveness of a radioprotector in the prevention of radiation-induced craniofacial bone growth inhibition, and it paves the way for investigation into the pathogenic mechanism and prevention of radiotherapy-induced craniofacial deformities.