Effect of high linear energy transfer radiation on biological membranes

Cellular membranes are vital elements, and their integrity is extremely essential for the viability of the cells. We studied the effects of high linear energy transfer (LET) radiation on the membranes. Rabbit erythrocytes (1×10⁷ cells/ml) and microsomes (0.6 mg protein/ml) prepared from liver of rats were irradiated with ⁷Li ions of energy 6.42 MeV/u and ¹⁶O ions of energy 4.25 MeV/u having maximum LET values of 354 keV/μm and 1130 keV/μm, respectively. ⁷Li- and ¹⁶O-induced microsomal lipid peroxidation was found to increase with fluence. The ¹⁶O ions were more effective than ⁷Li ions, which could be due to the denser energy distribution in the track and the yield of free radicals. These findings suggested that the biological membranes could be peroxidized on exposure to high-LET radiation. Inhibition of the lipid peroxidation was observed in the presence of a membrane-active drug, chlorpromazine (CPZ), which could be due to scavenging of free radicals (mainly HO⋅ and ROO⋅), electron donation, and hydrogen transfer reactions. The ⁷Li and ¹⁶O ions also induced hemolysis in erythrocytes. The extent of hemolysis was found to be a function of time and fluence, and showed a characteristic sigmoidal pattern. The ¹⁶O ions were more effective in the lower fluence range than ⁷Li ions. These results were compared with lipid peroxidation and hemolysis induced by gamma-radiation. Received: 10 March 1998 / Accepted in revised form: 6 July 1998     

A comparison of low and high dose-rate radiation for recipient mice in spleen-colony studies

Over the last 15 years, endogenous spleen-colony formation in our mice, following lethal irradiation, has increased to an unacceptable level. It has been found necessary, therefore, to introduce a new method of preparing recipient mice for spleen-colony studies. Irradiation with low dose-rate 60Cobalt gamma rays has been compared with high dose-rate linear accelerator electrons, and their effects on endogenous spleen colony formation compared with earlier X and gamma ray dose-response data. It was found that a large dose (13.5 Gy) of gamma rays results in fewer endogenous colonies than 8.5 Gy of electrons, yet because of its low dose rate (14.1 X 10(-3) Gy/min) it has a marked sparing of the intestinal tissue as measured by the intestinal microcolony technique. This in turn permits better survival and, therefore, a 'healthier' animal for spleen-colony work. Exogenous colony formation is also lower in the low dose-rate, gamma-irradiated recipients and this is shown to be due to a reduced spleen-seeding efficiency. It is concluded that very low dose-rate radiation is preferable for haemopoietic ablation, that a mouse colony requires constant monitoring for changes of endogenous spleen-colony formation and that the spleen-seeding efficiency of CFU-s depends on the irradiation technique used--there is no absolute value for a given strain of mouse.     

Critical target and dose and dose-rate responses for the induction of chromosomal instability by ionizing radiation.

To investigate the critical target, dose response and dose-rate response for the induction of chromosomal instability by ionizing radiation, bromodeoxyuridine (BrdU)-substituted and unsubstituted GM10115 cells were exposed to a range of doses (0.1-10 Gy) and different dose rates (0.092-17.45 Gy min(-1)). The status of chromosomal stability was determined by fluorescence in situ hybridization approximately 20 generations after irradiation in clonal populations derived from single progenitor cells surviving acute exposure. Overall, nearly 700 individual clones representing over 140,000 metaphases were analyzed. In cells unsubstituted with BrdU, a dose response was found, where the probability of observing delayed chromosomal instability in any given clone was 3% per gray of X rays. For cells substituted with 25-66% BrdU, however, a dose response was observed only at low doses (<1.0 Gy); at higher doses (>1.0 Gy), the incidence of chromosomal instability leveled off. There was an increase in the frequency and complexity of chromosomal instability per unit dose compared to cells unsubstituted with BrdU. The frequency of chromosomal instability appeared to saturate around approximately 30%, an effect which occurred at much lower doses in the presence of BrdU. Changing the gamma-ray dose rate by a factor of 190 (0.092 to 17.45 Gy min(-1)) produced no significant differences in the frequency of chromosomal instability. The enhancement of chromosomal instability promoted by the presence of the BrdU argues that DNA comprises at least one of the critical targets important for the induction of this end point of genomic instability.     

Radioadaptive response: An implication for the biological consequences of low dose-rate exposure to radiations

Radioadaptive response provides a considerable impact on the risk assessment of low-dose and low dose-rate exposures to ionizing radiations. The cells previously exposed to low doses of radiations become resistant to the induction of mutations, chromosome aberrations and cell killing by the subsequent doses but more susceptible to malignant transformation. The reaction kinetics of radioadaptive response were incorporated into a modelling of biological consequences of protracted low dose-rate exposures to radiations. The model is also consistent with the low dose-rate effects on spermatogonial mutations and translocations in the experimental animals and inverse dose-rate effects of morphological transformation in cultured cells.     

Characteristics of DNA-binding proteins determine the biological sensitivity to high-linear energy transfer radiation

Non-homologous end-joining (NHEJ) and homologous recombination repair (HRR), contribute to repair ionizing radiation (IR)-induced DNA double-strand breaks (DSBs). Mre11 binding to DNA is the first step for activating HRR and Ku binding to DNA is the first step for initiating NHEJ. High-linear energy transfer (LET) IR (such as high energy charged particles) killing more cells at the same dose as compared with low-LET IR (such as X or γ rays) is due to inefficient NHEJ. However, these phenomena have not been demonstrated at the animal level and the mechanism by which high-LET IR does not affect the efficiency of HRR remains unclear. In this study, we showed that although wild-type and HRR-deficient mice or DT40 cells are more sensitive to high-LET IR than to low-LET IR, NHEJ deficient mice or DT40 cells are equally sensitive to high- and low-LET IR. We also showed that Mre11 and Ku respond differently to shorter DNA fragments in vitro and to the DNA from high-LET irradiated cells in vivo. These findings provide strong evidence that the different DNA DSB binding properties of Mre11 and Ku determine the different efficiencies of HRR and NHEJ to repair high-LET radiation induced DSBs.     

A polymer, random walk model for the size-distribution of large DNA fragments after high linear energy transfer radiation

DNA double-strand breaks (DSBs) produced by densely ionizing radiation are not located randomly in the genome: recent data indicate DSB clustering along chromosomes. Stochastic DSB clustering at large scales, from >100 Mbp down to <0.01 Mbp, is modeled using computer simulations and analytic equations. A random-walk, coarse-grained polymer model for chromatin is combined with a simple track structure model in Monte Carlo software called DNAbreak and is applied to data on alpha-particle irradiation of V-79 cells. The chromatin model neglects molecular details but systematically incorporates an increase in average spatial separation between two DNA loci as the number of base-pairs between the loci increases. Fragment-size distributions obtained using DNAbreak match data on large fragments about as well as distributions previously obtained with a less mechanistic approach. Dose-response relations, linear at small doses of high linear energy transfer (LET) radiation, are obtained. They are found to be non-linear when the dose becomes so large that there is a significant probability of overlapping or close juxtaposition, along one chromosome, for different DSB clusters from different tracks. The non-linearity is more evident for large fragments than for small. The DNAbreak results furnish an example of the RLC (randomly located clusters) analytic formalism, which generalizes the broken-stick fragment-size distribution of the random-breakage model that is often applied to low-LET data. Received: 19 July 1999 / Accepted in revised form: 10 December 1999     

Quantitative analysis of biological responses to ionizing radiation, including dose, irradiation time, and dose rate

Because biological responses to radiation are complex processes that depend on both irradiation time and total dose, consideration of both dose and dose rate is necessary to predict the risk from long-term irradiations at low dose rates. Here we mathematically and statistically analyzed the quantitative relationships between dose, dose rate and irradiation time using micronucleus formation and inhibition of proliferation of human osteosarcoma cells as indicators of biological response. While the dose-response curves did not change with exposure times of less than 20 h, at a given dose, both biological responses clearly were reduced as exposure time increased to more than 8 days. These responses became dependent on dose rate rather than on total dose when cells were irradiated for 20 to 27 days. Mathematical analysis demonstrates that the relationship between effective dose and dose rate is well described by an exponential function when the logarithm of effective dose is plotted as a function of the logarithm of dose rate. These results suggest that our model, the modified exponential (ME) model, can be applied to predict the risk from exposure to low-dose/low-dose-rate radiation.     

Electron paramagnetic resonance radiation dose assessment in fingernails of the victim exposed to high dose as result of an accident

In this paper, we report results of radiation dose measurements in fingernails of a worker who sustained a radiation injury to his right thumb while using 130 kVp X-ray for nondestructive testing. Clinically estimated absorbed dose was about 20–25 Gy. Electron paramagnetic resonance (EPR) dose assessment was independently carried out by two laboratories, the Naval Dosimetry Center (NDC) and French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The laboratories used different equipments and protocols to estimate doses in the same fingernail samples. NDC used an X-band transportable EPR spectrometer, e-scan produced by Bruker BioSpin, and a universal dose calibration curve. In contrast, IRSN used a more sensitive Q-band stationary spectrometer (EMXplus) with a new approach for the dose assessment (dose saturation method), derived by additional dose irradiation to known doses. The protocol used by NDC is significantly faster than that used by IRSN, nondestructive, and could be done in field conditions, but it is probably less accurate and requires more sample for the measurements. The IRSN protocol, on the other hand, potentially is more accurate and requires very small amount of sample but requires more time and labor. In both EPR laboratories, the intense radiation-induced signal was measured in the accidentally irradiated fingernails and the resulting dose assessments were different. The dose on the fingernails from the right thumb was estimated as 14 ± 3 Gy at NDC and as 19 ± 6 Gy at IRSN. Both EPR dose assessments are given in terms of tissue kerma. This paper discusses the experience gained by using EPR for dose assessment in fingernails with a stationary spectrometer versus a portable one, the reasons for the observed discrepancies in dose, and potential advantages and disadvantages of each approach for EPR measurements in fingernails.     

Transposition of chromosome loci in bystander cells upon exposure to an adaptive dose of ionizing radiation

During the process of the realization of the bystander effect the trans of the Signal from irradiated cells to the intact cell (bystander cells) happens. So both type of cells (irradiated and intact cells) have the same damages and reactions. There are new data about bystander effect as the transduction mechanism of the adaptive response and we have investigated this phenomenon. There are an incubation of the intact (bystander cells) and the exposed (X-radiation of 10 cGy) human lymphocytes and we analyze the location of the centromeric loci of the first chromosome. We observed hat for the first time that after X-ray exposition of the adaptive doses the transposition of the chromosome loci from the peripheral to the central parts of the nucleus in intact (bystander cell) G0-lymphocytes which were incubated in the growth environment cells with irradiated cells removal. We support that the starting states of the adaptive response is the loci extrication of the matrix, the transposition and the approach homologous chromosomes. This process is necessary for the DNA double strand breaks reparation (in the case of injured dose X-radiation) with the participation of the homologous recombination.     

Functional and morphological characterization of rat thyroid gland at remote periods following single high and low dose radiation exposure

A study of the morphological structure and functional activity of the rat thyroid gland was carried out after 22 months following a single exposure to external radiation. The 3-month-old animals were irradiated with doses of 0.25, 0.5, 1.0, 2.0 and 5.0 Gy. Blood was assayed for thyroxin (T4) and triiodothyronine (T3) levels, while liver tissue--for NADP-MDH activity and thyroid tissue--for thyroperoxidase activity. The thyroid was studied histologically, morphometrically and by electron microscope. The decreased T4 concentrations 2.59-fold in the 5.0 Gy group, the increased T3/T4 in the 2.0 and 0.25 Gy groups, the reduced diameter of cellular nuclei and follicles, the flat follicular epithelium and diminished number of thyrocyte ultrastructures indicate thyroid hypofunction in the irradiated animals. The morphological changes are characterized by enhanced diffuse and focal sclerotic changes in thyroid, most pronounced at high irradiation doses (1.0-5.0 Gy), whereas the hemosiderosis foci suggest that the structural changes are consequences of radiation-induced destructive injuries in the gland parenchyma. Two of the thyroids (0.5 Gy) demonstrate foci with pronounced lymphoid infiltration, while follicular carcinomas were detected in 4 thyroids (2.0 Gy), and in one thyroid (0.5 Gy) in one thyroid (5.0 Gy). The remote effects of radiation were dose-dependent destructive, sclerotic and atrophic processes, decreased functional activity, stimulation of development of autoimmune aggression and carcinogenesis in thyroid.     

Cerenkov radiation energy transfer (CRET) imaging: a novel method for optical imaging of PET isotopes in biological systems

Background

Positron emission tomography (PET) allows sensitive, non-invasive analysis of the distribution of radiopharmaceutical tracers labeled with positron (β⁺)-emitting radionuclides in small animals and humans. Upon β⁺ decay, the initial velocity of high-energy β⁺ particles can momentarily exceed the speed of light in tissue, producing Cerenkov radiation that is detectable by optical imaging, but is highly absorbed in living organisms.

Principal Findings

To improve optical imaging of Cerenkov radiation in biological systems, we demonstrate that Cerenkov radiation from decay of the PET isotopes ⁶⁴Cu and ¹⁸F can be spectrally coupled by energy transfer to high Stokes-shift quantum nanoparticles (Qtracker705) to produce highly red-shifted photonic emissions. Efficient energy transfer was not detected with ^99mTc, a predominantly γ-emitting isotope. Similar to bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET), herein we define the Cerenkov radiation energy transfer (CRET) ratio as the normalized quotient of light detected within a spectral window centered on the fluorophore emission divided by light detected within a spectral window of the Cerenkov radiation emission to quantify imaging signals. Optical images of solutions containing Qtracker705 nanoparticles and [¹⁸F]FDG showed CRET ratios in vitro as high as 8.8±1.1, while images of mice with subcutaneous pseudotumors impregnated with Qtracker705 following intravenous injection of [¹⁸F]FDG showed CRET ratios in vivo as high as 3.5±0.3.

Conclusions

Quantitative CRET imaging may afford a variety of novel optical imaging applications and activation strategies for PET radiopharmaceuticals and other isotopes in biomaterials, tissues and live animals.     

Using lanthanide-based resonance energy transfer for in vitro and in vivo studies of biological processes

This review describes key directions in the development of different probes based on complex compounds of lanthanides for in vitro and in vivo researches. The role of microsecond fluorescence of lanthanides for overcoming problems of background fluorescence is considered. The basic classes of synthetic and genetically encoded complex compounds of lanthanides are summarized. Main principles of designing lanthanide-based molecular sensors, including FRET sensors based on lanthanides and colored fluorescent proteins are described. Their applications in bioanalytical research and cellular bioimaging are described. The main principles of cellular bioimaging using lanthanides are formulated, questions of their delivery into cells are considered, and the problem of their potential toxicity for living organisms is discussed. A technique using multiphoton excitation of lanthanides is described.     

Quantitative regularities for clinical manifestations of radiation injury in large-sized laboratory animals exposed to supralethal radiation doses Gamma-neutron and electron biological effectiveness as influenced by exposure conditions and dose distribution in the animal body

The damaging effect of gamma-neutron radiation over a wide neutron-energy range, with average values of 0.37 and 1.2 MeV, and that of electrons with an average electron energy of 25 MeV have been compared in dogs and two monkey species exposed to a broad range of supralethal doses. An analysis of absorbed dose distribution in critical organs and systems has shown the highest effect of gamma-neutron radiation with an average neutron energy of 1.2 MeV. With severity of early clinical manifestations of damage as a criterion, electrons have appeared the most effective. The radiosensitivity of animals grew in the order as follows: dog-->M. fascicularis-->P. hamadryas.     

Biologically based analysis of the data for the Colorado uranium miners cohort: age, dose and dose-rate effects.

This study is a comprehensive analysis of the latest follow-up of the Colorado uranium miners cohort using the two-stage clonal expansion model with particular emphasis on effects related to age and exposure. The model provides a framework in which the hazard function for lung cancer mortality incorporates detailed information on exposure to radon and radon progeny from hard rock and uranium mining together with information on cigarette smoking. Even though the effect of smoking on lung cancer risk is explicitly modeled, a significant birth cohort effect is found which shows a linear increase in the baseline lung cancer risk with birth year of the miners in the cohort. The analysis based on the two-stage clonal expansion model suggests that exposure to radon affects both the rate of initiation of intermediate cells in the pathway to cancer and the rate of proliferation of intermediate cells. However, in contrast to the promotional effect of radon, which is highly significant, the effect of radon on the rate of initiation is found to be not significant. The model is also used to study the inverse dose-rate effect. This effect is evident for radon exposures typical for mines but is predicted to be attenuated, and for longer exposures even reversed, for the more protracted and lower radon exposures in homes. The model also predicts the drop in risk with time after exposure ceases. For residential exposures, lung cancer risks are compared with the estimates from the BEIR VI report. While the risk estimates are in agreement with those derived from residential studies, they are about two- to fourfold lower than those reported in the BEIR VI report.     

A field trial of the effectiveness of a feline Toxoplasma gondii vaccine in reducing T. gondii exposure for swine

A 3-yr field trial was conducted on 8 commercial swine farms in Illinois to determine the effectiveness of a feline Toxoplasma gondii vaccine in reducing the exposure of swine to T. gondii. A vaccine consisting of live bradyzoites of the mutant T-263 strain, capable of preventing oocyst shedding by cats, was used in this study. Each farm was visited 3 times in 1994, 3 times in 1995, and once in 1996. Cats were trapped and inoculated with the T-263 oral vaccine during 1994 and 1995. On each visit, the following samples were collected: blood from pigs, cats, and mice for detection of serum antibodies to T. gondii, feces from cats to detect oocysts, and heart and brain tissues from rodents to determine the presence of T. gondii tissue cysts. The modified agglutination test (MAT), with a positive titer set at the 1:25 dilution, was used to determine serum antibodies. At first capture, 72.6% (61/84) of juvenile cats and 32.6% (31/95) of adult cats had no detectable antibodies (seronegative), indicating no prior exposure to T. gondii when they received their first vaccine. Of these first-time seronegative cats, 58.1% (18/31) of adult and 45.9% (28/61) of juvenile cats were recaptured and received a second dose of vaccine. Changes in the prevalence of T. gondii infection were evaluated from the prevaccination (1992, 1993) to the postvaccination (1996) period. Eleven cats (5%) were detected shedding oocysts between 1994 and 1996, of which 10 (90.1%) shed during 1994. The last detection of oocyst shedding by cats was during the first farm visit in 1995. There was a significant decrease in T. gondii seroprevalence for finishing pigs (P < 0.05, Wilcoxon sign rank test). There was a positive correlation (Spearman's p = 1.0, P < 0.0001) between the change in prevalence in juvenile cats and the change in prevalence in finishing pigs. The seropositivity rate (MAT > or = 1:25) in mice among all farms decreased from 4% in 1992-1993 to 0% in 1996. The mean prevalence of T. gondii tissue cyst isolation for mice on all farms decreased from 1.1% in 1994, to 0.8% in 1995, and to 0.5% in 1996. The results of this study suggest that the reduced exposure of pigs to T. gondii was due to the administration of the T. gondii vaccine to cats.