Quantitative regularities and peculiarities of the development of the cerebral form of radiation sickness at fractionated irradiation

Several peculiarities in manifestations of cerebral form of radiation sickness have been revealed at a fractionated double irradiation with equal and unequal doses per fraction and different intervals between the fractions. A reliable increase in average lifespan of rats irradiated with (100 + 100 Gy) equal doses at 10 and 60 min intervals between two fractions compared to the single radiation exposure to 200 Gy has been obtained. Lifespan of rats irradiated with a total dose greater than 200 Gy in most cases of double exposures with 10 min interval was reliably less than that for animals after a single exposure. The influence of the first dose on the reduction of animal average lifespan increased with fraction dose increasing from 150 to 300 Gy and was most pronounced at the total exposure dose of 400 Gy. Reaction of rats on the repeated irradiation was significantly weakened in comparison with the reaction on the first exposure. At a study of capacitation the interval of 30 min appeared to be more favorable compared to 10 min interval. Importance of a dose value in the first fraction has been demonstrated: the higher this value the worse the capacity of the rats 3 hours after the repeated exposure.     

Unstable Chromosome Aberrations Do Not Accumulate in Normal Human Fibroblast after Fractionated X-Irradiation

We determined the frequencies of dicentric chromosomes per cell in non-dividing confluent normal human fibroblasts (MRC-5) irradiated with a single 1 Gy dose or a fractionated 1 Gy dose (10X0.1 Gy, 5X0.2 Gy, and 2X0.5 Gy). The interval between fractions was between 1 min to 1440 min. After the completion of X-irradiation, the cells were incubated for 24 hours before re-plating at a low density. Then, demecolcine was administrated at 6 hours, and the first mitotic cells were collected for 42 hours. Our study demonstrated that frequencies of dicentric chromosomes in cells irradiated with a 1 Gy dose at different fractions were significantly reduced if the fraction interval was increased from 1 min to 5 min (p<0.05, χ²-test). Further increasing the fraction interval from 5 up to 1440 min did not significantly affect the frequency of dicentric chromosomes. Since misrejoining of two independent chromosome breaks introduced in close proximity gives rise to dicentric chromosome, our results indicated that such circumstances might be quite infrequent in cells exposed to fractionated X-irradiation with prolonged fraction intervals. Our findings should contribute to improve current estimation of cancer risk from chronic low-dose-rate exposure, or intermittent exposure of low-dose radiation by medical exposure.     

Late sequelae of exposure to ionizing radiation with various LET's. Effect of dose rate and fractionation on changes in the life span of rats

In experiments with 2120 albino mongrel rats their life span was followed up after the effect of various types of radiation (for instance, gamma-neutron radiation of 0.9 MeV and gamma- and X-rays) at different exposure schedules (that is, whole-body irradiation with doses from LD0/30 to LD100/30 and fractionated at 24 and 72 hour intervals and dose--rates varying from 0.00042 Gy/min to 1.02 Gy/min). The type of radiation, the dose--rate, single and cumulative doses, the number of fractions and the interval between them were estimated with respect to their contribution to life span shortening.     

Effects of topically-applied olive oil on the response of hamster skin to single or multiple doses of 230kV X-rays.

The effects of topically-applied olive oil on the response of hamster skin to single or multiple doses of X-rays has been studied. The olive oil was applied either 15 min or 1 hour before the radiation exposures. The treatment did not alter the temporal pattern of development and recovery from the radiation injury. For single exposers, olive oil did not alter the 1- to 30-day average skin response. However, when it was administered at each treatment when three radiation fractions were given over a 4-day interval (3 fractions/4 days), a significant increase in the amount of dose recovered was found compared with control irradiated animals. For controls, the average amount of dose recovered per fractionation interval, (Dn-D1)/(n-1), was about 505 rad. For animals treated with olive oil 15 min before irradiation, it was about 720 rad; and for those treated 1 hour before irradiation, it was 782 rad. The data indicate a definite radioprotective effect of topical administration of olive oil, but at present the mechanism is not known.     

Specific-locus mutation response to unequal, 1 + 9 Gy X-ray fractionations at 24-h and 4-day fraction intervals

The specific-locus mutation frequency obtained from mouse spermatogonial stem cells following unequal, 1 + 9 Gy X-ray fractionation with a 24-h fractionation interval is low, and consistent with the two fractions acting additively. The response is therefore markedly different from the augmented mutation frequencies obtained with 500 + 500 R and 100 + 500 R, 24-h fractionations. The lower yield compared with the 100 + 500 R response also indicates a clear difference from the translocation data which demonstrate increases in yield with increasing second dose over the same dose range. The decline in specific locus mutation yield with the increase in the second dose from 500 R to 9 Gy suggests that the stem cells surviving the first fraction are heterogeneous in their sensitivities to this class of genetic damage. A similar, additive specific locus mutation frequency is obtained with unequal, 1 + 9 Gy X-irradiation when the interval between fractions is 4 days. This is consistent with 500 + 500 R, 4-day and 7-day interval responses obtained previously but again differs from the sub-additive translocation responses obtained with such X-ray fractionation. Taken together with the data from previous studies the present results suggest that (1) 24 h after the first fraction, (a) the surviving stem cell have two components; survivors of the formerly radiosensitive, cycling component of the normal stem cell population and the formerly radioresistant, G0 or arrested G1 cells, which are being 'triggered' into a rapid cell cycle to achieve repopulation of the testis; (b) these two components are of near-equal sensitivity to translocation induction and cell killing, hence the additive translocation yields with equal X-ray fractionations and yields consistent with those extrapolated from lower doses with higher, unequal fractionations, e.g. 1 + 7 Gy, 1 + 9 Gy; but (c) the formerly radioresistant, triggered component is much more sensitive than the surviving cycling component to specific locus mutation and cell killing, hence the augmented mutation response with 500 + 500 R fractionation and the drop in yield with 1 + 9 Gy compared with 100 + 500 R X-irradiation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Early changes in intracellular ATP concentration after 5 Gy irradiation by routine regimen and regimen modified by low doses (0.1+4.9 Gy)]

Comparative studies were made of immediate (within the first minutes) changes in intracellular ATP concentration after irradiation by different regimens. ATP concentration in cells at a stationary phase of growth increased immediately after irradiation with a dose of 5 Gy, reaching its maximum within 30-40 min. Irradiation with the same total dose, by the regimen of 0.1 + 4.9 Gy at a 3-minute interval between the doses, did not cause alterations in the ATP content in cells. It is concluded that the absence of the increase in the parameter under study (ATP) after irradiation by the latter regimen indicates that preirradiation at a dose of 0.1 Gy inhibits the adequate development of an early response to irradiation with a dose of 4.9 Gy.     

Tissue repair and repopulation in the tumor bed effect

These experiments were designed to study the kinetics and magnitude of cell repair and repopulation in tissues whose damage results in the tumor bed effect. The right hind thighs of mice were irradiated with single doses or two equal gamma-ray fractions. Interfraction intervals ranging from 30 min to 24 h (to measure the kinetics of repair from sublethal damage) and 6 and 12 weeks (to determine the extent of repopulation) were used. One day after the second radiation dose 5 X 10(5) FSA tumor cells were inoculated into the center of the irradiated field. Radiation dose-response curves were obtained by calculating the time required for tumors to reach 12 mm diameter. No recovery occurred within 6 h of the radiation delivery as measured by this assay. Some recovery, 3.2-4.6 Gy above a single radiation dose, occurred when the interval between two fractions was 24 h. With increasing interfraction intervals of 6 and 12 weeks further dose sparing occurred in the amount of 5.0-6.9 and 7.5-8.3 Gy, respectively. The data suggest that repopulation is the major contributor to the radiation dose-sparing recovery of stromal tissue and that some proliferative response may occur as early as 1 day after the first irradiation.     

Peculiarities of the ovary structure in the rat offspring developing under conditions of the removed thyroid gland of female rat with the thyroxine replacement therapy and external radiation exposure in utero

The influence of a single external gamma-radiation at a dose of 1.0 Gy (dose rate 9.08 x 10(-4) Gy/sec) on the 15th day of gestation in case of the removed complex of thyroid and parathyroid glands (thyroidparathyroidectomy) on the first day of gestation, as well as introduction of thyroxin and CaC12 on the structure of offspring ovary in postnatal ontogenesis (30-day old animals) was studied. It has been shown that thyroidparathyroidectomy of a female mother rat with thyroxine replacement therapy and irradiation, as well as the combination of these factors disturb the structure of ovarian tissues of the offspring. A single external irradiation on the 15th day of embryogenesis causes death of a considerable part of primordial follicles in the offspring ovary and growth of follicular layers in the secondary follicles. Thyroidparathyroidectomy of female rat on the first day of gestation with thyroxine replacement therapy causes delay in the development of follicles in the ovary at the early stages of maturation of 30-day old animals. The radiosensitivity of the ovarian tissues of the offspring that has been developed under the combined effect of the factors studied increases and results in an almost full loss of pool cells in the ovary of infant rats.     

Effects of split-dose X irradiation on rat salivary gland function.

The effect of a single local dose of 15 Gy on salivary gland function in male Albino Wistar rats was compared with the effect of two doses of 7.5 Gy. The intervals chosen were 0-24 h and 1 week. Before and 1-30 days after the last radiation dose, samples of parotid and submandibular saliva were collected simultaneously after stimulation of the glands with pilocarpine. Irradiation with the single dose resulted in an increased lag phase and potassium concentration, and a decreased flow rate and sodium concentration. The rate of secretion of amylase was decreased during Days 1-6, increased at Day 10, and was decreased again at Day 30. With two dose fractions, substantial dose-sparing effects on lag phase, flow rate, and secretion of amylase were observed for both the very early (0-6 days postirradiation) and later (6-30 days postirradiation) effects. These effects were maximal when the interval between the fractions was 6 h. A significant dose-sparing effect on electrolytes was observed for the later effects only, again with a maximum for the 6-h interval. The dose-sparing observed for the very early effects cannot be explained satisfactorily by repair of sublethal damage (SLD), redistribution of cells over the cell cycle, or repopulation of salivary gland tissue between the doses. In contrast to the earlier dose-sparing effects, the split-dose recovery seen for later damage may be attributed, in part, to SLD repair in providing for greater reproductive survival of intercalated ductal cells and enhanced tissue regeneration.     

Changes in bromodeoxyuridine labeling index during radiation treatment of an experimental tumor

Cell proliferation kinetics in a spontaneous mouse fibrosarcoma (FSaII) growing in C3H mice has been studied by in vivo pulse labeling of cells synthesizing DNA with bromodeoxyuridine (BrdUrd). A monoclonal antibody to BrdUrd and flow cytometry were used to quantify these cells. Labeling indices (LI) were measured before and after radiation. Unirradiated 10-mm tumors had a mean LI of 17.5%. After a single dose of 20 Gy there was depression of LI after 1 day followed by a rapid increase to greater than control values after 5 days. Analysis performed after five fractions showed that LI was dependent on the dose per fraction and interval between fractions. After 5 and 7 Gy/fraction LI remained similar to control values during daily fractionation but was significantly depressed after twice daily fractionation. With doses greater than 10 Gy/fraction there was marked depression of LI using both fractionation schedules. These changes in LI correlated well with changes in tumor volume after radiation. Tumors were also biopsied after 5 fractions of a 20-fraction course to see if LI would predict for tumor control. LIs of greater than or equal to 10% were associated with lack of tumor control at 90 days while all controlled tumors had a significant depression of LI. Changes in LI after radiation were a reasonable indication of the amount of repopulation occurring and might be useful in selecting patients for altered fractionation schedules.     

Myeloid progenitors: a radiation countermeasure that is effective when initiated days after irradiation

The aim of this study was to elucidate the potential of mouse myeloid progenitor cells (mMPC) to mitigate lethal doses of (60)Co γ radiation and X rays in various strains of mice. Different cell doses of pooled allogeneic mMPC generated ex vivo from AKR, C57Bl/6, and FVB mice were transfused intravenously into haplotype-mismatched recipient Balb/c or CD2F1 mice at various times after irradiation to assess their effect on 30-day survival. Our results show that cryopreserved allogeneic mMPC significantly improve survival in both strains of mice irradiated with lethal doses of (60)Co γ radiation (CD2F1, 9.2 Gy) and X-ray exposures (Balb/c, 9 Gy) that are known to cause acute radiation syndrome in hematopoietic tissues. Survival benefit was mMPC-dose dependent and significant even when mMPC administration was delayed up to 7 days after irradiation. We further show that mMPC administration mitigates death from acute radiation syndrome at radiation doses of up to 15 Gy ((60)Co γ radiation, CD2F1), which are radiation exposure levels that cause mice to succumb to multi-organ failure, and determined that the dose-reduction factor of 5 million mMPC administered 24 h after irradiation of CD2F1 mice is 1.73. Even at high doses of up to 14 Gy (60)Co γ radiation, mMPC administration could be delayed up to 5 days in CD2F1 mice and still provide significant benefit to 30-day survival. These results demonstrate that mMPC are a promising radiation countermeasure with the potential to mitigate radiation injury in unmatched recipients across a broad range of lethal radiation doses, even when administration is delayed days after radiation exposure. With respect to efficacy, timing, and practicality of administration, mMPC appear to be a very promising radiation countermeasure for acute radiation syndrome among all candidate therapeutics currently under development.     

Adaptive response and split-dose effect of radiation on the survival of mice

Although the importance of radiation-induced adaptive response has been recognized in human health, risk assessment and clinical application, the phenomenon has not been understood well in terms of survival of animals. To examine this aspect Swiss albino mice were irradiated with different doses (2–10 Gy) at 0015 Gy/s dose rate and observed on a regular basis for 30 days. Since almost 50% lethality was seen with 8 Gy, it was selected as the challenging dose for further studies. Irradiation of mice with conditioning doses (0.25 or 0.5 Gy) and subsequent exposure to 8 Gy caused significant increase in the survival of mice compared to irradiated control. The splitting of challenging dose did not influence the efficiency of conditioning doses (0.25 Gy and 0.5 Gy) to induce an adaptive response. However conditioning doses given in fractions (0.25 Gy + 0.25 Gy) or (0.5 Gy + 0.5 Gy) were able to modulate the response of challenging dose of 8 Gy. These results clearly showed the occurrence of adaptive response in terms of survival of animals. The conditioning dose given in small fractions seemed to be more effective. The findings have been discussed from a mechanistic point of view. The possible biological implications, potential medical benefits, uncertainties and controversies related to adaptive response have also been addressed     

A test of equal effect per fraction in the kidney of the mouse.

Measurements of renal damage in the mouse were made to determine if there was an equal effect per fraction during a course of repeated 240-kVp X-ray doses. An X-ray dose of 2 Gy was given 2, 8, 14, or 20 times with interfraction intervals of 12 h. Some animals were also irradiated with twenty 2-Gy doses using a 5-h interfraction interval. The underlying effect per fraction (-logeSF of the notional target cell population) was determined from the additional top-up dose of d(4)-Be neutrons needed to produce measurable renal impairment assessed by decreased clearance from the plasma of [51Cr]EDTA and by a reduction in the hematocrit at 25, 29, 33, and 39 weeks after treatment. There was no significant influence of the time of assay on the values of underlying effect measured. A mean value of underlying effect was therefore calculated for the two different assays of each mouse, from the measurements at the four times. This gave approximately 40 estimates (one for each animal assessed) with each assay of the effectiveness of 2-Gy fractions in each of the four fractionation schedules, a total of 321 determinations in the study with 12-h intervals. Regression analysis showed that there was no significant trend in underlying effect per fraction with number of fractions, i.e., the damage per fraction was constant regardless of the number of fractions used. With underlying effect normalized to 1 unit of damage for a single 2-Gy dose, the slope of this plot was -0.0013 per fraction2 +/- 0.0097 (95% CL). The assumption of equal effect per fraction was therefore not invalidated in the kidney of the mouse. With a 5- instead of a 12-h interfraction interval, the 20-fraction schedule was 7% more effective as measured by the two assays analyzed together; this was significant at P = 0.0001. This shows that 5 h is not sufficient time between fractions for full repair to occur in the kidney, and underlines the need for intervals of at least 6 h between the doses in clinical radiotherapy using more than one fraction per day. The data are consistent with an alpha/beta ratio approximately 1.6 Gy, with a repair half-time approximately 1.3 h. However, these experiments were not designed to determine these parameters and their values should be regarded only as rough estimates.     

In vivo radioprotection by 5-aminosalicylic acid

The radioprotective effect of 5-aminosalicylic acid (5ASA) was investigated in mouse bone marrow. The present study was aimed at investigating the radioprotective effect of pre-irradiation treatment with 5ASA against a range of whole-body lethal (8-11 Gy) and sublethal (1-4 Gy) doses of gamma-radiation (RT) in adult Swiss albino mice. Protection against lethal irradiation was evaluated from 30-day mouse survival and against sublethal doses was assessed from chromosomal aberrations in the bone marrow 24 h after irradiation. An intraperitoneal injection of 5ASA at a dose of 25mg/kg body weight (b. wt.) 30 min before lethal RT increased survival, giving a dose modification factor (DMF) of 1.08. Injection of 5ASA (25 mg/kg b. wt.) 60 or 30 min before or within 15 min after 3 Gy whole body RT resulted in a significant decrease in the radiation-induced aberrant metaphases, at 24 h post-irradiation. Maximum effect was seen when the drug was administered 30 min before irradiation. 5ASA (25 mg/kg b. wt.) significantly reduced the number of aberrant metaphases and the different types of aberrations at all the radiation doses (1-4 Gy) tested, giving a DMFs of 1.43 for number of aberrant metaphases. 5ASA pretreatment also significantly enhanced the endogenous spleen colonies in mouse exposed to 11 Gy RT. Pretreatment with 5ASA, protected plasmid DNA (pGEM-7Zf) against breakage induced by RT and Fenton reactants. Using nanosecond pulse radiolysis technique, the bimolecular rate constant of the reaction of 5ASA with hydroxyl radical was found to be 6.7x10(9)M(-1)s(-1). The p53 and p21 protein levels of bone marrow and spleen were evaluated to identify the specific molecular mechanisms. Both p53 and p21 increased 24h after 6 Gy irradiation, while treatment with 5ASA inhibited this RT-induced increase. Therefore, the present data suggest that 5ASA pretreatment decreases death caused by RT-induced gastrointestinal and hemopoeitic syndromes. The proposed mechanism of radioprotection by 5ASA is through the inhibition of damage to DNA, lipids, and proteins; and prevention of RT-induced increased expression of p53 and p21.     

Increase in endogenous spleen colonies without recovery of blood cell counts in radioadaptive survival response in C57BL/6 mice

The radioadaptive survival response induced by a conditioning exposure to 0.45 Gy and measured as an increase in 30-day survival after mid-lethal X irradiation was studied in C57BL/6N mice. The acquired radioresistance appeared on day 9 after the conditioning exposure, reached a maximum on days 12-14, and disappeared on day 21. The conditioning exposure 14 days prior to the challenge exposure increased the number of endogenous spleen colonies (CFU-S) on days 12-13 after the exposure to 5 Gy. On day 12 after irradiation, the conditioning exposure also increased the number of endogenous CFU-S to about five times that seen in animals exposed to 4.25-6.75 Gy without preirradiation. The effect of the interval between the preirradiation and the challenge irradiation on the increase in endogenous CFU-S was also examined. A significant increase in endogenous CFU-S was observed when the interval was 14 days, but not 9 days. This result corresponded to the increase in survival observed on day 14 after the challenge irradiation. Radiation-inducted resistance to radiation-induced lethality in mice appears to be closely related to the marked recovery of endogenous CFU-S in the surviving hematopoietic stem cells that acquired radioresistance by preirradiation. Preirradiation enhanced the recovery of the numbers of erythrocytes, leukocytes and thrombocytes very slightly in mice exposed to a sublethal dose of 5 Gy, a dose that does not cause bone marrow death. There appears to be no correlation between the marked increase in endogenous CFU-S and the slight increase or no increase in peripheral blood cells induced by the radioadaptive response. The possible contribution by some factor, such as Il4 or Il11, that has been reported to protect irradiated animals without stimulating hematopoiesis is discussed.     

The induction of chromosome aberrations during the course of radiation therapy for morbus Hodgkin

In a patient with Morbus Hodgkin, structural aberrations of the chromosome type in peripheral lymphocytes were analyzed during radiation therapy (accumulated target dose 44.6 Gy: 22 fractions of 1.8 Gy each and 2 fractions of 2.5 Gy each at the end of the therapy). The blood was sampled about 5 min after a fraction and/or 24, 48, or 72 h thereafter. The frequency of dicentric chromosomes:acentric fragments:centric ring chromosomes is 37:14:1 throughout the therapy. Independent of the time of blood sampling after a fraction, the distributions of dicentrics and acentrics are overdisperse and represent negative binomial distributions. The yields from these aberrations, as determined during the course of radiotherapy, are best fitted to a linear-quadratic function with a negative quadratic term. The two dose-effect curves (blood sampling about 5 min and 24 to 72 h after a fraction) of dicentrics and acentrics do not differ significantly. Up to an accumulated target dose of about 20 Gy the percentages of cells with chromosome aberrations increase to about 48 to 65% and, at this level, remain constant until the end of therapy.     

Effects of autotransplantation of minced muscle tissue and subsequent laser therapy on recovery of the muscle injured by irradiation

A comparative histological investigation of posttraumatic regeneration in irradiated with 30 or 40 Gy and cross-sectioned musculus gastrocnemius of rats after autotransplantation into muscle defect of non-irradiated minced muscle tissue and laser therapy of hind limb in post-operative period was conducted. The obtained results showed that in irradiated with 30 Gy sectioned muscle (control series) the inflammatory reaction, resorption of fibrin in the area of trauma were inhibited and proliferation of muscle tissue from proximal and distal stump was suppressed. The rough connective tissue scar was formed. In experimental series for stimulation of regeneration the method of autografting minced muscle tissue into the defect of irradiated (30 or 40 Gy) cross-sectioned muscle and combination of this method with helium-neon laser rays exposition was used. The more marked recovery was obtained in irradiated with 30 Gy operated muscle after a 10-day treatment of limb with laser rays.     

Comparative radiosensitivity of CFUs of the mouse bone marrow and embryonal liver forming 7- and 11-day colonies

The authors studied the radiosensitivity of CFU-s, forming 7- and 11-day colonies from fetal liver (FL) of 14 and 17 day gestation and bone marrow (BM) of adult mice. The index of D0 for 7-day colonies, formed by CFU-s from 14-day, 17-day FL and BM was 2.02; 1.57 and 0.78 Gy, accordingly. 11-day CFU-s both from FL, and from BM did not distinguish statistically at their radiosensitivity (their D0 was 1.25 Gy).     

Survival of irradiated animals and the preservation of CFUs after the administration of various radioprotectors

The comparative data are presented concerning the 30-day restoration of the bone marrow cellularity and the number of endogenous colonies in the spleen of the control animals and of those treated with the radioprotective agents after irradiation with doses from 4.5 to 8.1 Gy. There was a good agreement between the results of studies in the integrity of the haemopoietic system on day 9 after irradiation and the 30-day survival of animals.     

The individual and combined effects of X-irradiation and hyperthermia on early somite mouse embryos in culture.

The effects of 1) X-irradiation and 2) hyperthermia at a temperature of 43 degrees C individually and in combination have been investigated using cultured 8-day mouse embryos. B6C3F1 embryos were exposed to 0.3-2.0 Gy of X-rays, 5-20 min of heating, or 5 min of heating and irradiation at 0.3, 0.6, and 0.9 Gy. Irradiation alone at 0.3 Gy showed no apparent effect on embryonic development, but irradiation at 0.6-2.0 Gy caused a dose-dependent increase in malformed embryos. Heating alone for 5 min produced no malformed embryos, while heating for 10-20 min caused malformations as a function of heating time. Combined treatments produced higher frequencies (22.2-100%) of malformations than those of the sum of the separate treatments (0-41.7%). Malformations observed were primarily microphthalmia, microcephaly, and open neural tubes. The results indicate that in cultured mouse embryos irradiation combined with a "nonteratogenic dose" of hyperthermia directly exerts an additive effect on formation of the malformed embryos. In addition, a single occurrence of left-sided tail was produced by hyperthermia alone, while four occurrences were produced in combination with radiation.