D.W. van Bekkum

Radiation Sensitivity of the Hemopoietic Stem Cell

VAN BEKKUM, D. W. Radiation Sensitivity of the Hemopoietic Stem Cell. Radiat. Res. 128, S4-S8 (1991). The LD50o/3 after total-body irradiation (TBI) indicates the radiosensitivity of any animal species and is determined by the number and radiosensitivity of the hemopoietic stem cells, in particular those that are pluripotent. The most extensive information exists for the mouse because in the species the pluripotential stem cells can be enumerated by the spleen colony assay. Stem cells of various species can also be quantified in vitro by the CFU-S and CFU-C assays. With the latter assay, the reported values for Do and N vary by factors of 2-3 and up to 5, respectively. In both assays the upper level of the range of doses is about 5 Gy. A theoretical approach for the calculation of the Do of hemopoietic stem cells was previously developed by comparing the number of autologous or syngeneic bone marrow cells required to protect 50% of supralethally irradiated animals with the known LDo/3o of the species and the estimates of total number of bone marrow cells present before irradiation. Using the rate of repopulation of peripheral blood cells in monkeys following high-dose TBI and the repopulation of the spleen and the bone marrow in mice, we have derived estimates of the surviving fractions of hemopoietic stem cells at radiation doses between 5 and 10 Gy. The resulting data suggest, among other possibilities, the presence of a small subpopulation of hemopoietic stem cells with higher radioresistance than the majority of the stem cells. It was postulated that this small subpopulation may exist under hypoxic conditions. To test this hypothesis, RBEs for fission neutrons have been determined for CFU-S survival and for LDso/3o in BCBA mice. Both RBEs were very similar, which proves that the radioresistance of the subpopulation responsible for survival at high doses is not due to hypoxic con

The Prevention of Pseudomonas aeruginosa Infections in Irradiated Mice and Rats

In several studies of endogenous postirradiation infection in mice a varying incidence of Pseudomonas aeruginosa bacteremia has been reported (1-3). Since this organism has occasionally been found in the intestine, the occurrence of Pseudomonas bacteremia seemed to be in accord with other data suggesting the enteric origin of the invading organisms (1). It was soon found, however, that Pseudomonas, in contrast to other intestinal organisms, may be rapidly fatal for irradiated mice. Epizootics were encountered which significantly modified the course of the radiation sickness and made it necessary to dispose of all stock animals. Carriers appeared to be a constant source of infection for their cagemates (4). In our experience infection with Pseudomonas constitutes a troublesome complication of irradiation experiments; constant careful epidemiological survey was found to be indispensable for its control. In this paper details will be given of procedures which led to the virtual disappearance of Pseudomonas infections. The origin of these infections has been traced to both animal and human carriers, and the ways of propagation will be discussed.

Relative Biological Effectiveness for Neutron Carcinogenesis in Monkeys and Rats

The risks of total-body irradiation with large doses of X rays (average dose 6.7 Gy) and fission neutrons (average dose 3.4 Gy) were investigated by keeping a group of long-term surviving monkeys from an experiment on acute effects under continuous observation. On the basis of the number of animals developing tumors in each group as a function of the total observation period and the average absorbed dose, relative biological effectiveness (RBE) values between 4 and 5 have been derived at these high dose levels. In experiments on mammary carcinogenesis in rats the highest RBE values are observed for neutrons with energies of 0.43 to 1 MeV as produced by the p + T reaction or by the fission process. Based upon linear dose-response curves for neutrons and X rays, a maximum RBE value of 15 was observed for induction of adenocarcinomas in WAG/Rij rats. Appreciably higher RBE values would be obtained if the results of the gamma-ray exposure, indicating a nearly quadratic dose-response relationship, were used as a baseline. For radiation protection applications it should be realized, however, that such an increase will be caused by the lower efficiency of low-linear-energy-transfer radiation rather than by an increase in efficiency of the neutron irradiation at low doses.

The effect of X-rays on phosphorylations in vivo

Abstract The incorporation of 32 P into ATP and ADP of spleen and thymus was measured shortly after the intravenous administration of radioactive inorganic phosphate to rats. 4 hours after total body X-irradiation with a dose of 700 r, both the specific activity and the relative specific activity of the ADP and ATP of the spleen were significantly decreased. Similar results were obtained with the thymus. These changes may result from an inhibition of the phosphorylation in the irradiated tissues.

Induction of mammary tumors in rats by single-dose gamma irradiation at different ages.

The effect of age at exposure on induction of mammary tumors was studied in female rats of the inbred WAG/Rij strain. Groups of 40 animals were exposed to a single total-body dose of 1 or 2 Gy of 137Cs gamma radiation at ages of 8, 12, 16, 22, 36 or 64 weeks and were observed for life. Mammary tumors, identified as nodules persisting and growing for 6 weeks, were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in a group of 120 unirradiated control rats, using lifetime statistical analysis with both parametric and nonparametric methods. The excess normalized risk of carcinoma was 0.9 for 1 Gy and 2.2 for 2 Gy in age groups 8-36 weeks, with no significant differences between the age groups. However, irradiation at 64 weeks yielded fewer carcinomas than in the controls, the excess normalized risk being -0.7 and -0.3 for 1 and 2 Gy, respectively. The occurrence of one or more fibroadenomas did not influence the incidence of carcinoma. The present data agree closely with the results reported previously for rats irradiated at age 8 or 17 weeks with a dose of 1.2 Gy. The reduced risk of radiation exposure at midlife is consistent with the available epidemiological data for exposed women. Although our findings have been obtained with a single total-body dose that is several orders of magnitude higher than the multiple doses delivered to the mammary gland during mammography, it is suggested that radiological screening for mammary cancer after the age of menopause will not increase the normal incidence of breast cancer.

The oxidative phosphorylation by mitochondria isolated from the spleen of rats after total body exposure to X rays.

1. The oxidative phosphorylation of isolated rat spleen mitochondria has been measured following a total body X irradiation of 1100 r. 2. Four hours after irradiation, the phosphorylation, oxygen uptake and P/O ratio are significantly reduced. 3. This effect has been observed with succinate as well as with α-ketoglutarate as a substrate.

Protection of the infant thyroid from radioactive contamination by the administration of stable iodide. An experimental evaluation in chimpanzees

Protection of the thyroid from radioactive contamination by the administration of stable iodide was investigated in chimpanzees aged 2 to 98 weeks. The uptake of iodide in the thyroid was measured with 123I-. The animals were subjected to a control measurement first, and subsequently the thyroid uptake of 123I- was determined twice; once at the start and once at the end of 11 days of ingestion of 0.5, 1.5 or 5.0 mg of stable iodide per kg body weight per day. The three doses of iodide reduced the control thyroid iodide uptake of 10 to 30% to lower than 1% when ingested 1 h before exposure to the tracer and to 2-4% when ingested 20 h before exposure. In the latter experiments 0.5 mg iodide/kg was less effective than doses of 1.5 mg/kg or higher. The physiological state of the thyroid of control infant chimpanzees does not differ from that of human infants. Incidentally, an increased level of TSH was found during the ingestion of iodide, but with unaltered thyroxine levels. Therefore, it is concluded that a daily dose of 1.5 mg stable iodide/kg body weight and higher offers optimal protection of the thyroid against exposure to radioactive iodine in infants and that, when used during 10 days, it leaves the thyroid unaffected.

Protection of the maternal and fetal thyroid from radioactive contamination by the administration of stable iodide during pregnancy. An experimental evaluation in chimpanzees

The safety and efficacy of the administration of stable iodide to protect the fetal thyroid from exposure to radioactive iodide were investigated in chimpanzees in weeks 19 to 21 of pregnancy. The mean 24-h uptake of iodide in the fetal thyroid, determined with 123I-, was 1.8%. Administration of stable potassium iodide (KI), 0.65, 1.95 or 6.5 mg per kg body weight, 1 h before tracer injection reduced the fetal uptake satisfactorily. Only the higher doses were effective after 20 h. Excess iodide may impair a childs thyroid status. However, adverse effects were not found during the 11 days the animals ingested these doses. Tracer concentrations in the amniotic fluid were 30- to 130-fold lower than in the urine. The dose to the fetus from radioactivity in the maternal bladder was estimated by computer simulation. The potential increment of the risk from this dose during the ingestion of stable iodide is smaller than the reduction of risk achieved by inhibiting the uptake of radioactive iodide by the fetal thyroid. The conclusion of the experiments is that stable iodide can be used safely and effectively to protect the fetal thyroid against contamination with radioactive iodine.

Lasting engraftment of histoincompatible bone marrow cells in dogs.

Conditioning protocols were tested for their efficacy in increasing the incidence of engraftment of histoincompatible dog bone marrow cells. Cyclophosphamide and total body irradation (TBI), Corynebacterium parvum and TBI, a 3- or 5-day delayed transfusion of bone marrow cells after TBI, or an increase in the number of donor bone marrow cells or lymphocytes appeared to be ineffective. These protocols were previously reported to promote recovery of splenic hemopoiesis in mice in short-term assays. The noted discrepancy between studies with mice and dogs invalidated allogeneic resistance as measured in the mouse spleen assay as a model for bone marrow allograft rejection. Intravenous treatment with silica particles or L-asparaginase did improve the engraftment rate after 7.5 Gy TBI. Low efficiency and significant extra toxicity restrict the applicability of these procedures. The most promising conditioning schedule found appeared to be two fractions of 6.0 Gy TBI separated by a 72-hr interval. Prolonged survival was noted after transplantation of bone marrow cells from a one-DLA haplo-type-mismatched donor. Possibilities for further improvement of this protocol are discussed.

LESIONS OF THE TONGUE IN IRRADIATED MICE

Postmortem examination of nearly 700 CBA and C57BL mice that died after total-body exposure to 675 and 750 r reveal~ macroscopic lesions of the tongue in 23% of the cases. Microscopic lesions were found to be much more frequent. The lesions resemble an abscess or an ulcer and consist of a heavily infected necrotic mass. Cellular reaction is absent. The possibility that the lesions are the portal of entry for microorganisms in the development of the bacteremia associated with the bone marrow syndrome is discussed. (auth)