Vascular damage after fractionated whole-brain irradiation in rats

Whole-brain irradiation of animals and humans has been reported to lead to late delayed structural (vascular damage, demyelination, white matter necrosis) and functional (cognitive impairment) alterations. However, most of the experimental data on late delayed radiation-induced brain injury have been generated with large single doses or short fractionation schemes that may provide a less accurate indication of the events that occur after clinical whole-brain radiotherapy. The pilot study reported here investigates cerebral vascular pathology in male Fischer 344 rats after whole-brain irradiation with a fractionated total dose of 137Cs gamma rays that is expected to be biologically similar to that given to brain tumor patients. The brains of young adult rats (4 months old) were irradiated with a total dose of 40 Gy, given as eight 5-Gy fractions twice per week for 4 weeks. Brain capillary and arteriole pathology was studied using an alkaline phosphatase enzyme histochemistry method; vessel density and length were quantified using a stereology method with computerized image processing and analysis. Vessel density and length were unchanged 24 h after the last dose, but at 10 weeks postirradiation, both were substantially decreased. After 20 weeks, the rate of decline in the vessel density and length in irradiated rats was similar to that in unirradiated age-matched controls. No gross gliosis or demyelination was observed 12 months postirradiation using conventional histopathology techniques. We suggest that the early (10-week) and persistent vascular damage that occurs after a prolonged whole-brain irradiation fractionation scheme may play an important role in the development of late delayed radiation-induced brain injury.     

Local application of dimethyl sulfoxide at different concentrations to the prevention of radiation-induced damages in patient with cancer of the cervix uteri

OBJECTIVE: to study the efficacy of dimethyl sulfoxide ((DMSO) at different concentrations in preventing radiation-induced rectal and urinary bladder damages in patients with cervix uteri cancer (CUC). MATERIAL AND METHODS: combined radiation therapy (RT) was performed in 807 patients with CUC. In the control group (n = 221), RT was made, without applying radio-modified agents. An hour prior to a session of intracavitary irradiation, 10% DMSO solution was instilled into the rectum and urinary bladder in 113 patients and applications of metronidazole (MN) dissolved in 100% DSMO were made in 473 patients. Teleradiotherapy was performed, by using megavolt irradiation sources in the conventional fractionation mode; the total focal dose (TFD) was increased up to 40-46 Gy. Intracavitary irradiation was carried out on "AGAT-V" and "AGAT-VU" devices once weekly; the single focal dose in point A was 7 Gy; TFD was 49-56 Gy. RESULTS: 10% DMSO instillations reduced the incidence of late radiation-induced damages to the rectum and urinary bladder. In the control group, the incidence of these conditions was 19.0 and 9.5%, respectively; with the use of 10% DMSO, that was 8.8 and 7.1%. Applications of MN dissolved in 100% DMSO reduced the incidence of late radiation-induced damages to 1.7%. CONCLUSION: Local application of DMSO is a method for preventing late radiation-induced damages to the rectum and urinary bladder in patients with CUC. When the concentration of DMSO is increased, its preventive effect increases.     

Radiation factors and their influence on induction of oxygen resistance

Shortly after gamma irradiation, flour beetles exhibited a decline in resistance to oxygen toxicity. Then, about 2 weeks after irradiation, the 50% lethal dose (LD50) exposure time in pure oxygen was much greater than that of nonirradiated beetles, and this enhanced resistance persisted for about 6 months. The magnitude of the enhancement was a function of dose, decreased with increasing age at irradiation, and was modified by radiation factors. Both dose protraction and dose fractionation reduced the development of oxygen resistance to approximately the same degree that it reduced acute radiation lethality. This suggests that both the initial sensitization and the later enhancement of resistance are correlated with the residual biological damage rather than with the physical dose or initial damage.     

Effect of gemcitabine on the tolerance of the lung to single-dose irradiation in C3H mice.

In an early phase II trial combining gemcitabine (dFdC) and radiotherapy for lung carcinomas, severe pulmonary toxicity was observed. In this framework, the objective of this study was to investigate the effect of dFdC on the tolerance of the lungs of C3H mice to single-dose irradiation. The thoraxes of C3H mice were irradiated with a graded single dose of 8 MV photons; dFdC (150 mg/kg) or saline (control animals) was administered i.p. 3 or 48 h prior to irradiation. Lung tolerance was assessed by the LD50 at 7-180 days after irradiation. For irradiation alone, the LD50 reached 14.45 Gy (95% CI 13.33-15.66 Gy). With a 3-h interval between administration of dFdC and irradiation, the LD50 reached 13.29 (95% CI 12.26-14.44 Gy); the corresponding value with a 48-h interval reached 13.01 Gy (95% CI 11.92-14.20 Gy). Our data also suggested a possible effect of dFdC on radiation-induced esophageal toxicity. dFdC has a minimal effect on lung tolerance after single-dose irradiation. However, a proper phase I-II trial should be designed before any routine use of combined dFdC and radiotherapy in the thoracic region.     

Radioprotection by mangiferin in DBAxC57BL mice: a preliminary study

The radioprotective effects of various concentrations (0, 0.25, 0.5, 1, 2, 5, 10, 17.5, 25, 50, 75 and 100 mg/kg b.wt.) of mangiferin (MGN) was studied in the DBAxC57BL mice whole body exposed to 10 Gy of gamma-irradiation. Treatment of mice with different doses of MGN, one hour before irradiation reduced the symptoms of radiation sickness and delayed the onset of mortality when compared with the non-drug treated irradiated controls. The radioprotective action of MGN increased in a dose dependent manner up to 2mg/kg and declined thereafter. The highest radioprotective effect was observed at 2mg/kg MGN, where greatest number of animals survived against the radiation-induced mortality. The administration of 0.5, 1, 2, 5, 10 and 17.5 mg/kg MGN reduced the radiation-induced gastrointestinal death as evident by a greater number of survivors up to 10 days in this group when compared with the DDW + 10 Gy irradiation group. A similar effect of MGN was observed for the radiation-induced bone marrow deaths also. Our study demonstrates that mangiferin, a gluosylxanthone, present in the Mangifera indica protected mice against the radiation-induced sickness and mortality and the optimum protective dose of 2mg/kg was 1/200 of LD50 dose (400 mg/kg) of MGN. The administration of 400 mg/kg MGN induced 50% mortality, therefore LD50 of the drug was considered to be 400 mg/kg.     

Protective effect of corticosteroids on radiation pneumonitis in mice

We explored the protective effect of corticosteroids on the mortality of mice that received thoracic irradiation. Methylprednisolone, 100 mg/kg/week, given from 11 weeks after gamma irradiation of the thorax resulted in an increase in the LD50 (11-26 weeks) from 14.3 +/- 0.3 (mean +/- SE) Gy to 17.6 +/- 0.4 Gy, P less than 0.001, a protection factor of 1.2. Withdrawal of steroids at various times during the period of radiation pneumonitis resulted in accelerated mortality in the next 2-4 weeks, so that the cumulative mortality "caught up" with that of control animals by 4 weeks after steroid withdrawal. However, after the end of the usual period of pneumonitis withdrawal of steroids did not result in accelerated mortality, suggesting that the time when steroids are protective corresponds to the duration of pneumonitis. A smaller dose of steroids, 25 mg/kg/week, was found to be as protective as the larger dose used in the above experiments. The possibility that corticosteroids reduce mortality, even when given many weeks after radiation, may have important practical and theoretical implications.     

Tolerance of the vaginal vault to high-dose rate brachytherapy and concomitant chemo-pelvic irradiation: Long-term perspective

Aim/background

We sought to determine the tolerance level and complication rates of the vaginal vault to combined high-dose-rate intra-cavitary brachytherapy with concomitant chemo-radiotherapy.

Patients and methods

A retrospective review of medical records of all the patients who received definitive chemo-radiotherapy for cervical cancer between 1998 and 2002 was undertaken. The records were reviewed for doses and for radiation-associated early and late sequelae of the vagina, rectum and bladder. Cumulative biological effective dose was calculated for two reference vaginal surface points.

Results

Fifty patients were included. Average age at diagnosis was 54 years. Median follow-up was 59 months. There were no recorded instances of acute grade IV toxicity. Maximal high-dose-rate vaginal surface dose (upper central point) was 103 Gy, and maximal brachytherapy lateral surface dose was 70 Gy. Maximal cumulative biological effective dose for the lateral surface reference point was 465.5 Gy₃, and the maximal cumulative biological effective dose for the superior reference point was 878.6 Gy₃. There were no cases of vaginal necrosis or fistulas, and no cases of grade IV late vaginal, rectal or bladder toxicity. No correlation was found between the maximal vaginal surface dose and vaginal, rectal or bladder toxicity.

Conclusions

The maximal surface HDR brachytherapy dose of 103 Gy and the maximal cBED of 878.6 Gy₃ were not associated with fistula or necrosis or other grade 3–4 vaginal complications. Concomitant chemo-radiotherapy, including pelvic radiotherapy and high-dose-rate intracavitary brachytherapy, is relatively safe for cervical cancer patients.     

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.     

Relative cataractogenic effects of X rays, fission-spectrum neutrons, and 56Fe particles: a comparison with mitotic effects

The eyes of Sprague-Dawley rats were irradiated with doses of 2.5-10 Gy 250-kVp X rays, 1.25-2.25 Gy fission-spectrum neutrons (approximately 0.85 MeV), or 0.1-2.0 Gy 600-MeV/A 56Fe particles. Lens opacifications were evaluated for 51-61 weeks following X and neutron irradiations and for 87 weeks following X and 56Fe-particle irradiations. Average stage of opacification was determined relative to time after irradiation, and the time required for 50% of the irradiated lenses to achieve various stages (T50) was determined as a function of radiation dose. Data from two experiments were combined in dose-effect curves as T50 experimental values taken as percentages of the respective T50 control values (T50-% control). Simple exponential curves best describe dose responsiveness for both high-LET radiations. For X rays, a shallow dose-effect relationship (shoulder) up to 4.5 Gy was followed at higher doses by a steeper exponential dose-effect relationship. As a consequence, RBE values for the high-LET radiations are dose dependent. Dose-effect curves for cataracts were compared to those for mitotic abnormalities observed when quiescent lens epithelial cells were stimulated mechanically to proliferate at various intervals after irradiation. Neutrons were about 1.6-1.8 times more effective than 56Fe particles for inducing both cataracts and mitotic abnormalities. For stage 1 and 2 cataracts, the X-ray Dq was 10-fold greater and the D0 was similar to those for mitotic abnormalities initially expressed after irradiation.     

Radioprotective effect of rhizome extract of Zingiber montanum in Rattus norvegicus

The present study aims at determining the ability of 60% ethanol extract of the rhizome of Zingiber montanum (J. K?nig) A. Dietr. to protect bone marrow cells in vivo from radiation-induced chromosomal aberrations. Albino rats (Rattus norvegicus, 2n = 42) were used to carry out investigations on the radioprotective properties of Z. montanum. Acute toxicity of the extract was determined, and a suitable injectable dose was selected for intra-peritoneal administration. The LD(50) of the extract calculated for 72 h was 2.9 g/kg, and the calculated LD(10) dose was 1.7 g/kg. The calculated maximum tolerated dose of the rhizome extract was 1.3 g/kg. Rats were divided into 12 groups (with or without the administration of extract) and exposed to different radiation doses from 1 to 5 Gy. Whole-body irradiation of rats showed a significant dose-dependent increase in different types of chromosomal aberrations. The most common chromosomal aberrations were breaks, fragments, gaps, rings, endoreduplications and dicentric chromosomes. Ethanol extract of rhizome at a dose of 0.5 g/kg did not show any significant increase in chromosomal aberrations in unirradiated animals as compared to that of the control group. Intra-peritoneal administration of the extract at a dose of 0.5 g/kg considerably reduced the frequency of the aberrations stated above in irradiated animals with DMF value of 1.36 at 1 to 5 Gy dose range of gamma radiation. The incidence of micronucleated polychromatic erythrocytes and micronucleated normochromatic erythrocytes due to the radiation exposure was considerably reduced in extract-treated groups of animals with DMFs 1.34 and 1.17, respectively, as compared to that of the extract-untreated groups. Our results suggest that rhizome extract of Z. montanum may have a potential in protecting normal hematopoietic cells from radiation-induced damage.     

Mitigation of lung injury after accidental exposure to radiation

There is a serious need to develop effective mitigators against accidental radiation exposures. In radiation accidents, many people may receive nonuniform whole-body or partial-body irradiation. The lung is one of the more radiosensitive organs, demonstrating pneumonitis and fibrosis that are believed to develop at least partially because of radiation-induced chronic inflammation. Here we addressed the crucial questions of how damage to the lung can be mitigated and whether the response is affected by irradiation to the rest of the body. We examined the widely used dietary supplement genistein given at two dietary levels (750 or 3750 mg/kg) to Fischer rats irradiated with 12 Gy to the lung or 8 Gy to the lung + 4 Gy to the whole body excluding the head and tail (whole torso). We found that genistein had promising mitigating effects on oxidative damage, pneumonitis and fibrosis even at late times (36 weeks) when drug treatment was initiated 1 week after irradiation and stopped at 28 weeks postirradiation. The higher dose of genistein showed no greater beneficial effect. Combined lung and whole-torso irradiation caused more lung-related severe morbidity resulting in euthanasia of the animals than lung irradiation alone.     

Pharmacological Induction of Transforming Growth Factor-Beta1 in Rat Models Enhances Radiation Injury in the Intestine and the Heart

Radiation therapy in the treatment of cancer is dose limited by radiation injury in normal tissues such as the intestine and the heart. To identify the mechanistic involvement of transforming growth factor-beta 1 (TGF-β1) in intestinal and cardiac radiation injury, we studied the influence of pharmacological induction of TGF-β1 with xaliproden (SR 57746A) in rat models of radiation enteropathy and radiation-induced heart disease (RIHD). Because it was uncertain to what extent TGF-β induction may enhance radiation injury in heart and intestine, animals were exposed to irradiation schedules that cause mild to moderate (acute) radiation injury. In the radiation enteropathy model, male Sprague-Dawley rats received local irradiation of a 4-cm loop of rat ileum with 7 once-daily fractions of 5.6 Gy, and intestinal injury was assessed at 2 weeks and 12 weeks after irradiation. In the RIHD model, male Sprague-Dawley rats received local heart irradiation with a single dose of 18 Gy and were followed for 6 months after irradiation. Rats were treated orally with xaliproden starting 3 days before irradiation until the end of the experiments. Treatment with xaliproden increased circulating TGF-β1 levels by 300% and significantly induced expression of TGF-β1 and TGF-β1 target genes in the irradiated intestine and heart. Various radiation-induced structural changes in the intestine at 2 and 12 weeks were significantly enhanced with TGF-β1 induction. Similarly, in the RIHD model induction of TGF-β1 augmented radiation-induced changes in cardiac function and myocardial fibrosis. These results lend further support for the direct involvement of TGF-β1 in biological mechanisms of radiation-induced adverse remodeling in the intestine and the heart.     

Comparative kinetics of the early repair of intestines and lung in mice after fast neutron and gamma-ray irradiation

Early repair (Elkind) after d(50) + Be neutron and gamma irradiation is assessed by determining the additional dose Dr necessary to reach a given biological effect when a single fraction Ds is split into 2 equal fractions 2Di separated by a time interval "i". LD50 at 180 days after thoracic irradiation is used as an evaluation of late pulmonary tolerance; LD50 at 5 days after abdominal irradiation is used as an evaluation of early intestinal tolerance. Dr is reduced but still important after neutron irradiation as compared to gamma irradiation. For LD50/180, after fast neutron irradiation Dr reaches 66, 90, 64, 162, 195, 150 cGy for "i" = 1, 2, 3, 5, 4, 12, and 24 hours respectively; after gamma irradiation, Field and Hornsey reported Dr = 390, 530, and 376 cGy for "i" = 2, 6, and 24 hours respectively; after neutron irradiation, they reported Dr = 190 cGy for "i" = 24 hours. For LD50/5, after fast neutron irradiation, Dr = 14, 45, 43, and 133 cGy for "i" = 1,5, 3,5, 5,5 and 24 hours respectively. Early repair is faster after gamma irradiation: Dr reaches a maximum for "i" = 3-4 hours. For neutrons, Dr reaches its maximum at 24 hours for both criteria.     

Radiation-induced DNA double-stranded breaks and the dynamics of apoptotic death of human peripheral lymphocytes

DNA double-stranded breaks and their association with the development of radiation-induced peripheral lymphocyte apoptosis were studied in healthy donors exposed to in vitro gamma-irradiation in a dose of 1 Gy. It was shown that irradiation in 1-Gy dose caused a significant (p < 0.05) increase in the frequency of cells in late apoptosis 4 hours after irradiation and a rise in their frequency in early apoptosis 24 hours following this procedure. A significant correlation (r = 0.52, p < 0.05) was recorded between the primary level of radiation-induced DNA double-stranded breaks and the frequency of cells in late apoptosis following 4 hours, which suggests that DNA double-stranded breaks as a signal to trigger cell apoptotic death are of great importance.     

A decrease in the efficiency of radiation damage repair in HeLa tumor cells with their preliminary irradiation at low radiation doses (0.1 Gr)

In experiments with tumor HeLa cells, a study was made of the survival rate of both the whole population and individual clonogenic cells after irradiation within different regimes at a cumulative dose of 4 Gy. The results obtained prompt a conclusion that the preirradiation with a dose of 0.1 Gy decreases the efficiency of repair of radiation-induced damages to cells.     

Relationship between cell kinetics and radiation-induced arrest of proliferating cells in G2: relevance to efficacy of radiotherapy

Monitoring the radiation-induced G2-arrest with flow cytometry disclosed the relationship between the pattern of accumulation in G2 and the cell kinetics (Tc), as assessed with semi-continuous labelling. A close relationship between these two parameters was observed in a murine mammary tumour after high dose-rate irradiation and in human cervix tumours (xenografted and in patients) after low dose-rate irradiation. In inoperable tumours of the oral cavity, a G2-arrest, observed in the first two weeks of fractionated therapy, was found to predict a local cure. Consequently, it was concluded that the cells accumulated in G2 were not doomed cells. This process of radiation-induced synchronization might be exploited in fractionation schemes of which treatment intervals are adjusted to the Tc-related timing of the radiation-induced G2-arrest.     

Effect of exogenous melatonin on the ovarian follicles in gamma-irradiated mouse

The present study was performed to obtain the evidence of the radioprotective function of melatonin on gamma-radiation-induced follicular atresia in mouse ovary. Three-week-old immature mice received 10 and 100 microg of melatonin dissolved in 100 microl of the alcoholic saline. Two hours after the treatments, they were whole-body irradiated with a dose of LD(80(30)) (8.3 Gy). The ovaries were dissected out of the animals at -2, 2, 8, 14 h after the onset of irradiation. The total number of follicles including the normal and atretic follicles examined in the largest cross sections was 125. The number was reduced to 103 in the irradiated group. The number of primordial follicles of the irradiation group or the melatonin-treated group was smaller than that of the control group. However, the number of primary, preantral, and antral follicles was not different from that of the control group. In the group pretreated with 100 microg of melatonin before irradiation, the ratio of normal primordial follicles was significantly higher than that of the irradiation group at any time point after irradiation. The high concentration of melatonin also reduced the radiation-induced degeneration of the primary follicles at 14 h after irradiation. On the other hand, the pretreatment of 10 microg of melatonin had little or no effect on the radiation-induced degeneration of primary follicles. However, it gave a protective effect on the radiation-induced degeneration in the primordial follicles at 2 h after irradiation, and 14 h after irradiation in preantral and antral follicles. From the above results, it is concluded that the exogenous melatonin has different functions depending on the follicle stages, and that the radioprotective effect of exogenous melatonin on the follicular degeneration is related to its concentration.     

On the shape of neutron dose-effect curves for radiogenic cancers and life shortening in mice

Male and female hybrid BCF₁ (C57BL/6 BdxBALB/c Bd) were exposed to total neutron doses of 0.06, 0.12, 0.24, and 0.48 Gy in fractions over a period of 24 weeks. The fractionation regimens were: 24 weekly fractions of 0.0025 Gy, 12 fractions of 0.01 Gy every 2 weeks, 6 fractions of 0.04 Gy every 4 weeks, and 3 fractions of 0.16 Gy every 8 weeks. In order to detect any change in susceptibility with age over the period of exposures from 16 weeks to 40 weeks of age, mice were exposed to single doses of 0.025, 0.05, 0.10, and 0.2 Gy at 16 and 40 weeks of age. These experiments were designed to test whether the initial parts of the dose-response relationships for life shortening and cancer induction could be determined economically by using fractionated exposures and whether or not the initial slopes were linear. The conclusions were that for life shortening and most radiogenic cancers, the dose-effect curves are linear and that fractionation of the neutron dose has no effect on the magnitude of the response of equal total doses over the range of doses studied. The ratio of such initial slopes and comparable linear initial slopes for a reference radiation should provide maximum and constant relative biological effectiveness values.     

Activation of endogenous C-type retroviral genomes by internal alpha-irradiation of mice with224Radium

Sensitive cocultivation techniques were applied to study the radiation-induced activation of endogenous retroviral genomes in different mouse strains by the alpha-emitting radionuclide 224Radium. Activated infectious C-type retroviruses were detected in spleen, bone marrow and bone tissues of C57BL/6-, BALB/c- and NMRI mice. The titres of high-dose-irradiated animals were higher than those found in low-dose-irradiated animals. Infectious retrovirus could be detected with a dose of 13.2 rad (maximum dose rate 0.9 rad/day) in the skeleton, and a dose of 4.2 rad (maximum dose rate 0.3 rad/day) in the spleen. The virus activation pattern was different in the three mouse strains. These data indicate that activation of endogenous retroviral genomes by alpha-irradiation shows a dose-effect relationship and a dependence on the genetic background of the mouse.