Stem Cells in Bone and Bone Marrow after Contamination with Bone-seeking Radionuclides

Summary

The effects of time, mass and oxidation state on plutonium gastrointestinal absorption and tooth adsorption were studied during and after chronic ingestion of plutonium-238 (IV) or (VI) (1·55–15·60 kBq/ml) in 6·5 mm bicarbonate medium by fed rats via drinking water for 8 days to 3 months. Animals were killed during the ingestion to follow the kinetics of whole-body storage and clearance of plutonium. At 1·55 kBq/ml the amount of plutonium retained in the skeleton increased continuously during the 85 days of ingestion and reached a plateau thereafter. This plutonium retention was therefore dependent on the total mass administered but not proportional to this mass, as the fraction of administered plutonium retained decreased during the first 22 days of ingestion and then stabilized. This is reflected by the gastrointestinal transfer (f₁), which had risen to (3·80 ± 0·82) × 10^?5 on Day 3 of ingestion and then decreased to a stabilized value of (1·07 ± 0·06) × 10^?5 from Day 30 to the end of the ingestion period. In the liver, the amount of plutonium retained reached a plateau, which lasted from Day 30 to the end of ingestion. The kidneys and spleen were also found to be retention sites. By Day 3 of ingestion, for a mass ingested of 5 × 10^?7 g/kg of body mass, the maximum mean value of f₁ we found was smaller than the 10^?4 recommended by ICRP Report 30. The oxidation state had no effect on f₁. Large plutonium deposition was observed on the teeth. For both oxidation states (IV) and (VI), about 0·10% of the administered dose was deposited on the teeth after 3 days of ingestion, whatever the plutonium concentration administered. However, whereas the amount of plutonium (IV) deposited did not change throughout the ingestion period, tooth deposition of plutonium (VI) decreased.     

Induction and Repair of DNA Strand Breaks in X-irradiated Proliferating and Quiescent CHO Cells

Summary

Induction and repair of DNA strand breaks was studied in X-irradiated proliferating and quiescent CHO cells using the alkaline unwinding technique. The results showed that induction of strand breaks is identical for both states of proliferation, whereas repair is different. The decrease in the number of DNA strand breaks with incubation time at 37°C is best described by a sum of three exponential components I, II and III. The half-times of component I were similar (τ_Ip = 1·73 min versus τ_Iq = 1·66 min) whereas strand breaks comprising component II were repaired slightly faster (τ_IIp = 17·0 min versus τ_IIq = 14·2 min) and those comprising component III were repaired significantly faster (τ_IIIp = 218 min versus τ_IIIq = 113 min) in quiescent as compared with proliferating cells. In contrast, the initial fractions, f, of the three components were closely similar for both states of growth (proliferating cells: f_I = 0·69, f_II = 0·25, f_III = 0·06; quiescent cells: f_I = 0·65, f_II = 0·29, f_III = 0·06). Radiosensitivity as assayed by colony formation was found to be lower for quiescent cells than for proliferating cells. By fitting the survival data to the linear-quadratic equation, ?ln(S/S₀) = αD + βD², the ratios α_p/α_q = 1·7 and β_p/β_q = 1·2 were obtained, which are similar to the ratios of the half-times of components III and II (τ_IIIp/τ_IIIq = 1·9; τ_IIp/τ_IIq = 1·2). This result indicates that the DNA damage represented by components II and III might be involved in cell killing.     

Long-term Changes in Mouse Lung Following Inhalation of a Fibrosis-inducing Dose of 239PuO2: Changes in Collagen Synthesis and Degradation Rates

Summary

Mice were exposed by nose-only inhalation to ²³⁹PuO₂, which resulted in an IAD of 1110 ± 29 Bq. At various times after exposure, rates of collagen metabolism were measured using validated in vivo methods based on the administration of radiolabelled proline, together with a large flooding dose of unlabelled proline and measurement of its incorporation into lung collagen as hydroxyproline. Dramatic increases in both synthesis and degradation rates of collagen were observed. At 54 days after exposure the fractional synthesis rates in experimental mice were almost five times those in controls (control: 3·2 ± 0·6%/day, ²³⁹PuO₂-exposed: 14·5 ± 0·4%/day) and by 300 days synthesis rates, although declining, were still more than double the control values. A similar pattern of change was observed for collagen degradation. The combination of changes in synthesis and degradation rates led to a 60% increase in lung collagen content by 300 days (control: 3·05 ± 0·24 mg/lung, ²³⁹PuO₂-exposed: 4·88 ± 0·42 mg/lung). The data suggest that extensive remodelling of the lung connective tissue matrix occurs during development of fibrosis and that, over long periods of time, small imbalances between synthesis and degradation may result in quite large increases in protein content.     

One-electron Reduction of 8-hydroxy-5-deazaisoalloxazine in Aqueous Solution: A Pulse Radiolysis Study

Summary

The one-electron reduction of 8-hydroxy-5-deazaisoalloxazine (HMDI) has been studied in aqueous solution in the acidity range pH0 to 13 using the reducing species CO₂·^?, e^?_aq and (CH₃)₂COH radicals. The spectral and other properties of the HMDI radicals were found to be independent of the reductant used. Four protolytic forms of the radical were distinguished with associated pK_a values of 2·3 ± 0·3, 6·0 ± 0·3 and 10·1 ± 0·3.     

One-electron Reduction of 5-deazalumiflavin in Aqueous Solution: A Pulse Radiolysis Study

Summary

The one-electron reduction of 5-deazalumiflavin has been studied in aqueous solution in the acidity range H₀ = ?1 to pH 13 using the reducing species CO₂^?, e^?_aq and (CH₃)₂?OH radicals. The spectral and other properties of the deazaflavin radicals formed were found to be independent of the reductant used. Four protolytic forms of the radical were distinguished with associated pK_a values of 1·3 ± 0·3, 6·0 ± 0·3 and 10·7 ± 0·3.     

Interactions of Drugs and Radiation in Haemopoietic Tissue Assessed by Lethality of Mice after Whole-body Irradiation

Summary

Drug-radiation interactions in haemopoietic tissue were assessed as the lethality of mice within 7–28 days after whole-body irradiation. The investigated drugs were adriamycin (ADM), bleomycin (BLM), cyclophosphamide (CTX), 5-fluorouracil (5-FU), methotrexate (MTX), mitomycin C (MM-C) and cis-diamminedichloroplatinum II (cis-DDP). The drugs were administered as single doses 15 min before graded doses of whole-body irradiation or at different intervals from 7 days before to 7 days after fixed radiation doses. ADM, CTX, 5-FU, MM-C and cis-DDP enhanced the radiation response when administered 15 min before irradiation. The dose effect factor (DEF) was 9·11 for 5-FU and in the range 1·25–1·59 for the other drugs. MTX administration 15 min before irradiation had no effect (DEF 1·00). However, MTX increased lethality if given 1–3 days after irradiation (DEF 1·21–1·76) and protected against lethality if given 1–3 days before irradiation (DEF 0·83). A similar time dependence was observed for ADM, CTX, 5-FU, MM-C and cis-DDP. Protection against lethality was not observed but in all these cases the lethality was significantly lower at administration 1–3 days before than 1–3 days after irradiation. A proper investigation of the effect of BLM was not possible as the combination of this drug and whole-body irradiation caused a high rate of gastrointestinal deaths.     

Response of Human Bone Marrow Progenitor Cells to X-rays in Vitro

Summary

In 25 out of 33 cases the survival response of myeloid progenitor cells from fresh human bone marrows, X-irradiated in vitro in phosphate-buffered saline at 23°C, was characterized by a two-term exponential relationship, with D₀ values of 0·42 ± 0·19 Gy and 1·38 ± 0·37 Gy, respectively. In the remaining eight cases for which the colony-forming efficiency was 10 times lower, survival followed a single exponential function with D₀ = 1·18 ± 0·15 Gy. The biphasic response at 23°C became a single exponential response when the temperature at irradiation was 30 or 37°C.     

Three Classes of DNA Strand Breaks Induced by X-irradiation and Internal β-rays

Summary

Repair kinetics of DNA strand breaks were investigated after exposing exponentially growing CHO cells to X-radiation or to internal β-rays from incorporated tritium, respectively. DNA strand breaks were analysed by the alkaline unwinding technique followed by chromatography on hydroxyapatite. For either type of radiation, the repair kinetics are statistically best described by a sum of three exponential components. The half-times determined are τ_I ～ 2 min, τ_II ～ 20 min and τ_III ～ 170 min; they are identical for both types of radiation. But the initial fractions of the components are different for X- and internal β-rays; X-rays: f_I = 0·70, f_II = 0·25, f_III = 0·05; internal β-rays: f_I = 0·40, f_II = 0·40, f_III = 0·20. Components I and II are considered to represent the repair of two different classes of single-strand breaks and component III the repair of double-strand breaks. Two alternative interpretations for the occurrence of the two classes of single-strand breaks are discussed.     

Micronuclei in Cytokinesis-blocked Lymphocytes of Cancer Patients Following Fractionated Partial-body Radiotherapy

Summary

We applied the cytokinesis-block micronucleus assay to measure chromosome damage in lymphocytes of 11 cancer patients undergoing fractionated partial-body irradiation. Measurements performed before, during and after cessation of radiotherapy showed a dose-related increase in micronucleus frequency in each of the patients studied. When the results for micronucleus frequency (Y) were plotted against the estimated equivalent whole-body dose (X) the dose-response relationship obtained was Y = 75·8X + 49·5 (r = 0·783, P < 0·0001). A general decline in MN frequency was observed during the post-treatment period down to 57 per cent (± 10) after 12 months but there was considerable variation between individuals. The advantages and disadvantages of the application of the cytokinesis-block micronucleus assay as a biological dosemeter for lymphocytes irradiated in vivo are discussed.     

In Vitro Studies of the Sensitivity of Canine Bone-marrow Erythroid Burst-forming Units (BFU-E) and Fibroblast Colony-forming Units (CFU-F) to X-irradiation

Summary

The radiosensitivity of the early erythroid progenitor cells (BFU-E) and the progenitor cells of the stroma (CFU-F) in canine bone marrow was studied under steady-state conditions by in vitro irradiation with 280 kV X-rays. The dose—effect relationship for colony formation was determined for BFU-E obtained from the iliac crest marrow, and for CFU-F in bone marrow collected from the iliac crest and the humerus of adult beagles. The BFU-E were adequately stimulated with serum from lethally irradiated dogs to obtain a source of BPA (burst-promoting activity). The BFU-E proved to be extremely radiosensitive, and the survival curve was exponential (D₀ = 15·3 ± 1·8 cGy). We showed that buffy-coat leukocytes separated from bone marrow leukocytes obtained by aspiration were an optimum source of CFU-F. A curve was fitted to the data obtained for CFU-F obtained from the iliac crest or the humerus, resulting in D₀ = 241 ± 38 cGy and an extrapolation number n = 1·38 ± 0·62 or D₀ = 261 ± 40 cGy and n = 1·04 ± 0·42, respectively. According to these findings, and other published data, we conclude that the canine bone marrow BFU-E are presently the most radiosensitive hemopoietic cells detected among all hemopoietic cells of different mammals.     

The Incorporation of Plutonium by the Embryo and Fetus of Rats and Guinea-pigs

Summary

The transfer of ²³⁸Pu from the maternal circulation to the developing embryo and fetus was studied in rats and guinea-pigs to provide data for the development of dosimetric models for the human embryo and fetus. Following administration at different stages of gestation, measurements were made after 3 days in the rat and 7 days in guinea-pigs. The amount transferred was greater after administration at later stages of gestation, up to a maximum of about 0·8–0·9% of the injected activity per fetoplacental unit (FPU) and about 0·2% per fetus in both species. In advanced gestation the yolk sac, the initial site of haemopoietic stem cells, contained up to 80% of the total activity in the FPU in rats, compared with about 25% for the guinea-pig; retention in placental trophoblast was greater in the guinea-pig. The concentrations of ²³⁸Pu in the yolk sac were generally about two to three orders of magnitude greater than fetal concentrations and of the same order as in maternal liver and bone. In both species, concentrations in the embryo and fetus were greatest after injection early in gestation, reached their lowest around mid-organogenesis and increased again in later gestation. The fetus:mother whole-body concentration ratios in late gestation were about 0·1 and 0·05 in rats and guinea-pigs, respectively. Measurements were also made of the ²³⁸Pu retention in neonates at birth. In guinea-pigs the liver accounted for about 6–9% of retained activity; similar values for femora indicated skeletal retention of about 60–80%. For administration at each stage of gestation, and particularly at early stages, transfer of ²³⁸Pu to the fetus continued throughout gestation but concentrations decreased due to fetal growth.     

Biexponential diffusion attenuation in various states of brain tissue: Implications for diffusion-weighted imaging

Diffusion-weighted single voxel experiments conducted at b-values up to 1 × 10⁴ smm⁻² yielded biexponential signal attenuation curves for both normal and ischemic brain. The relative fractions of the rapidly and slowly decaying components (f₁, f₂)are f₁ = 0.80 ± 0.02, f₂ = 0.17 ± 0.02 in healthy adult rat brain and f₁ = 0.90 ± 0.02, f₂ = 0.11 ± 0.01 in normal neonatal rat brain, whereas the corresponding values for the postmortem situation are f₁ = 0.69 ± 0.02, f₂ = 0.33 ± 0.02. It is demonstrated that the changes in f₁ and f₂ occur simultaneously to those in the extracellular and intracellular space fractions (f_ex, f_in) during: (i) cell swelling after total circulatory arrest, and (ii) the recovery from N-methyl-D-aspartate induced excitotoxic brain edema evoked by MK-801, as measured by changes in the electrical impedance. Possible reasons for the discrepancy between the estimated magnitude components and the physiological values are presented and evaluated. Implications of the biexponential signal attenuation curves for diffusion-weighted imaging experiments are discussed.     

Induction of Cytogenetic Adaptive Response of Somatic and Germ Cells in Vivo and in Vitro by Low-dose X-irradiation

Summary

The cytogenetic adaptive response induced by low-level radiation was studied using human and rabbit lymphocytes in vitro and bone marrow cells and germ cells in vivo. The inductive dose of X-rays was 10 mGy for the in vitro studies at a dose rate of 10 mGy/min, and 2, 10, 50, 75 and 100 mGy for the in vivo studies at a dose rate of 50 mGy/min. The challenging dose was 1·5 Gy X-rays for the in vitro experiments and 0·65 or 0·75 Gy for the in vivo experiments at a dose rate of 0·44 Gy/min. The results reported here, in addition to those that have appeared in the literature, show the following characteristics documented for the first time: (1) 10 mGy could induce the adaptive response in human as well as rabbit lymphocytes irradiated not only in G₁, S and G₂ phases, but also in the G₀ state; (2) although the induced adaptive response could only last three cell cycles, it could be revived when the inductive dose was repeated after the third cell cycle; (3) the adaptive response could be induced by low-dose X-rays in somatic cells, both in vitro (lymphocytes) and in vivo (bone marrow cells), and also in germ cells (spermatocytes); (4) the magnitude of the adaptive response induced by whole-body irradiation was found to be dose-dependent–the lower the inductive dose the more the reduction of the frequency of chromatid aberrations following the challenging dose.     

Enhancement by Hyperthermia of the ‘Early Delayed’ and ‘Late Delayed’ Radiation Response of the Rat Cervical Spinal Cord

Summary

The cervical spinal cord (C5–T5) of female Wistar WU rats was irradiated with 250 kV X-rays (15–32 Gy). Heat was applied at approximately the same site 7 ± 1 min after X-rays. ‘Early delayed’ paralysis of the forelegs was observed 5–10 months after treatment. The ED₅₀ (± SE) after single-dose irradiation alone was 25·8 ± 0·4 Gy. ‘Late delayed’ paralysis and paresis were observed 11–21 months after irradiation with an ED₅₀ (X-rays alone) of 22·7 ± 0·6 Gy. The data for late paralysis, late paresis and minor neurological symptoms were pooled resulting in an ED₅₀ (± SE) of 20·6 ± 0·7 Gy. Hyperthermia enhanced the radiation response. Thermal enhancement ratios (TER) in the ‘early delayed’ response after a 30 min treatment with 41·1 ± 0·4°C, 42·1 ± 0·4°C and 42·9 ± 0·4°C were 1·07 ± 0·08, 1·17 ± 0·08 and 1·12 ± 0·04 respectively. For the ‘late delayed’ radiation response concerning paralysis and paresis the TER after 30 min at 41·1°C and 42·1°C were 1·25 ± 0·10 and 1·31 ± 0·07, respectively. The latent period for paralysis was not significantly affected. Pathological examination of the spinal cord after combined treatment of X-rays and hyperthermia showed focal demyelination with white matter necrosis and vascular injury in animals as an indication of ‘early delayed’ and ‘late delayed’ paralysis, respectively. This was not different from histopathological changes observed after irradiation alone.     

Effects of Monoenergetic X-rays with Resonance Energy of Bromine K-absorption Edge on Bromouracil-labelled E. Coli Cells

Summary

In order to examine enhanced killing that might be induced by Auger cascades in the incorporated atoms in cells, bromouracil(BrU)-labelled E. coli cells were irradiated with monoenergetic X-rays at 13·49 and 12·40 keV, just above and below the K-absorption edge of bromine. In both cases BrU-labelled cells were more sensitive for killing than were normal cells. However, when the degree of BrU-sensitization was compared between the two energies of X-rays, the enhanced killing at 13·49 keV was only small, 2 ± 8 per cent based on the D₀ value in saline. By the addition of DMSO, which is believed to suppress radical-mediated effects, killing of BrU-labelled cells was enhanced at 13·49 keV by 8 ± 4 per cent as compared with 12·40 keV, based on D₀. These results have been examined in terms of absorbed energy in BrU-labelled cells and in terms of the number of induced Auger events.     

Radioprotective Effect of an Acute Non-specific Inflammation in Mice

Summary

Protection against 8·7 Gy whole-body γ-irradiation (lethal in 100 per cent of mice by 30 days) was observed in 90 per cent of mice bearing a one-day-old granuloma induced by polyacrylamide beads. When the inflammatory reaction was induced sooner or later a lower or null protection was obtained. A dose-effect relationship between the volume of injected beads and resulting radioprotection was established. The radioprotective effect depends only on the acute non-specific inflammation since hydrocortisone acetate injected into mice before the beads abolished this protection. This inflammatory pattern led to a dose reduction factor of 1·36 ± 0·08 (P < 0·05) for LD 50/30. A 90 per cent survival was observed in mice bearing a one-day-old granuloma when they were injected 1 h before 10 Gy with the granuloma acellular eluate (P < 0·02 compared to a 50 per cent survival observed with polyacrylamide beads alone). Substances with a molecular weight higher than 300 000 are involved in the synergistic radioprotective effect of the granuloma-eluate association.     

The Kinetics of Repair in Mouse Lung after Fractionated Irradiation

Summary

The kinetics of repair of sublethal damage in mouse lung was studied after fractionated doses of ¹³⁷Cs γ-rays. A wide range of doses per fraction (1·7–12 Gy) was given with interfraction intervals ranging from 0·5 to 24 h. The data were analysed by a direct method of analysis using the incomplete repair model. The half-time of repair (T_1/2) was 0·76 h for the pneumonitis phase of damage (up to 8 months) and 0·65 h for the later phase of damage up to 12 months. The rate of repair was dependent on fraction size for both phases of lung damage and was faster after large dose fractions than after small fractions. The T_1/2 was 0·6 h (95 per cent c.1. 0·53, 0·69) for doses per fraction greater than 5 Gy and 0·83 h (95 per cent c.1. 0·76, 0·92) for doses per fraction of 2 Gy. Repair was nearly complete by 6 h, at least for the pneumonitis phase of damage. To the extent that extrapolation of these data to humans may be valid, these results imply that treatments with multiple fractions per day that involve the lung will not be limited by the necessity for interfraction intervals much longer than 6 h.     

Lung Tumour Induction in Mice after X-rays and Neutrons

Summary

Dose–response curves were determined for pulmonary adenomas and adenocarcinomas in mice after single acute doses of 200 kVp X-rays and cyclotron neutrons (E¯ = 7·5 MeV). A serial-killing experiment established that the radiation induction of chromosome aberrations. The validity of the concept of PLD neous cancers. The dose versus incidence (I) of tumours in male and female mice for X-ray doses between 0·25 and 7·5 Gy is ‘bell-shaped’ and best fitted with a purely quadratic induction and exponential inactivation terms, i.e. I = A + BD²e^?αD. In contrast, the tumour dose–response after 0·1–4·0 Gy of neutrons is best fitted by I = A + BD e^?αD and is steeply linear ≤ 1 Gy, peaks between 1 and 3 Gy and sharply declines at 4·0 Gy. The data for the female mice ≤ 1 Gy neutrons are best fitted to the square root of the dose.

A major objective of the experiments was to derive neutron RBE values. Because of the differences between the X-ray (quadratic) and neutron (linear) curves, the RBE_n will vary inversely with decreasing X-ray dose. The RBE values at 1 Gy of X-rays derived from the B coefficients in the above equations are 7·4 ± 3·2 (male and female); 8·6 ± 3·6 (female) and 4·7 ± 1·8 (male). These are high values and imply even higher values at the doses of interest to radiation protection. If, however, one restricts the analysis to the initial, induction side of the response (≤ 1 Gy neutrons, ≤ 3 Gy X-rays) then good linear fits are obtainable for both radiations and indicate neutron RBE values of 7·4 ± 2·3 for female mice and 4·5 ± 1·8 for males, and these are independent of dose level.     

Effect of acute exercise-induced fatigue on maximal rate of heart rate increase during submaximal cycling

Different mathematical models were used to evaluate if the maximal rate of heart rate (HR) increase (rHRI) was related to reductions in exercise performance resulting from acute fatigue. Fourteen triathletes completed testing before and after a 2-h run. rHRI was assessed during 5 min of 100-W cycling and a sigmoidal (rHRI_sig) and exponential (rHRI_exp) model were applied. Exercise performance was assessed using a 5-min cycling time-trial. The run elicited reductions in time-trial performance (1.34 ± 0.19 to 1.25 ± 0.18 kJ · kg^?1, P < 0.001), rHRI_sig (2.25 ± 1.0 to 1.14 ± 0.7 beats · min^?1 · s^?1, P < 0.001) and rHRI_exp (3.79 ± 2.07 to 1.98 ± 1.05 beats · min^?1 · s^?1, P = 0.001), and increased pre-exercise HR (73.0 ± 8.4 to 90.5 ± 11.4 beats · min^?1, P < 0.001). Pre-post run difference in time-trial performance was related to difference in rHRI_sig (r = 0.58, P = 0.04 and r = 0.75, P = 0.003) but not rHRI_exp (r = ?0.04, P = 0.9 and r = 0.27, P = 0.4) when controlling for differences in pre-exercise and steady-state HR. rHRI_sig was reduced following acute exercise-induced fatigue, and correlated with difference in performance.     

Determination and validation of peak fat oxidation in endurance‐trained men using an upper body graded exercise test

Peak fat oxidation rate (PFO) and the intensity that elicits PFO (Fat_max) are commonly determined by a validated graded exercise test (GE) on a cycling ergometer with indirect calorimetry. However, for upper body exercise fat oxidation rates are not well elucidated and no protocol has been validated. Thus, our aim was to test validity and inter‐method reliability for determination of PFO and Fat_max in trained men using a GE protocol applying double poling on a ski‐ergometer. PFO and Fat_max were assessed during two identical GE tests (GE1 and GE2) and validated against separated short continuous exercise bouts (SCE) at 35%, 50%, and 65% of V?O_2peak on the ski‐ergometer in 10 endurance‐trained men (V?O_2peak: 65.1 ± 1.0 mL·min^?1·kg^?1, mean ± SEM). Between GE tests no differences were found in PFO (GE1: 0.42 ± 0.03; GE2: 0.45 ± 0.03 g·min^?1, P = .256) or Fat_max (GE1: 41 ± 2%; GE2: 43 ± 3% of V?O_2peak, P = .457) and the intra‐individual coefficient of variation (CV) was 8 ± 2% and 11 ± 2% for PFO and Fat_max, respectively. Between GE and SCE tests, PFO (GE_avg: 0.44 ± 0.03; SCE; 0.47 ± 0.06 g·min^?1, P = .510) was not different, whereas a difference in Fat_max (GE_avg: 42 ± 2%; SCE: 52 ± 4% of V?O_2peak, P = .030) was observed with a CV of 17 ± 4% and 15 ± 4% for PFO and Fat_max, respectively. In conclusion, GE has a high day‐to‐day reliability in determination of PFO and Fat_max in trained men, whereas it is unclear if PFO and Fat_max determined by GE reflect continuous exercise in general.