[CYTOGENETIC EFFECTS IN MICE BONE MARROW AFTER IRRADIATION BY FAST NEUTRONS].

Mechanisms of damaging mice bone marrow cells by 1.5 MeV neutrons at the dose of 25-250 cGy, dose rate of 23.9 cGy/s and γ-quants 6°Co as a standard radiation were studied. The mitotic index and aberrant mitoses in marrow preparations were counted in 24 and 72 hours after irradiation. Coefficients of relative biological effectiveness (RBE) of fast neutrons 24 and 72 hours post irradiation calculated from mitotic index reduction and aberrant mitoses formation were within the range from 4.1 ± 0.1 to 7.3 ± 0.1. Mean time of the existence of chromosomal aberrations in marrow cells was determined. For the specified doses from γ-rays, the period of aberrations existence was 1.4-1.1 cycles and for neutrons, 1.0-0.6 cycles. Morphologic analysis of neutron-induced damages and ratio of the most common breaks demonstrated a high production of bridges, which outnumbered cells with fragments in 3 to 4 times suggesting a more destructive effect on the genetic structures of cells. RBE of fast neutrons is a variable that grows with a radiation dose. Moreover, RBE estimated after 72 hours exceeded values it had 24 hours after irradiation.

Early Response of Mouse Bone Mrrow Cells to Short-Term Irradiation in a Wide Range of Doses.

Experiments on mice irradiated with γ-rays in a wide range of doses, from 0.5 to 400 cGy and the bone marrow have shown cytogenetic and cytological effects ranging from I cGy dose 24 hours after exposure to radiation. Dose-independent reduction of the number of nucleated cells in the bone marrow, normal or even elevated levels of mitotic activity, and extreme dependence of the type of chromosomal aberrations on the radiation dose with the maximum in the region of 7.5 cGy were observed in the dose range from 1 to 20 cGy. A linear dose-dependent decrease of the cell.number in the bone marrow, a decreased mitotic activity and increased number of aberrant mitosis were marked in the dose range from 20 to 400 cGy. The findings are discussed in terms of their application for explaining the mechanisms of hormesis, adaptive response, as well as the appropriateness of accounting the parameters studied for solving problems of regulation of permissible doses.

[DEMONSTRATION OF LIKELIHOOD OF THE NEGATIVE EFFECT OF PHYSICAL PROTECTION DURING TOTAL PROTON IRRADIATION OF MICE].

The experiments were performed with outbred CD-1 male mice (SPF category). Total irradiation at 1.0; 2.5 and 5.0 Gy by protons with the average energy of 170 MeV was conducted in a level medical beam of the phasotron at the Joint Institute of Nuclear Investigations. Targets were 2 points of in-depth dose distribution, i.e. beam entrance of the object, and modified Bragg peak. As a physical protector, the comb filter increases linear energy transfer (LET) of 170 MeV entrance protons from 0.49 keV/µm to 1.6 keV/µm and, according to the bone marrow test, doubles the biological effectiveness of protons when comparing radiation doses that cause 37% inhibition of blood cell formation in the bone marrow. Physical protection increases dose rate from 0.37 Gy/min for entrance protons to 0.8 Gy/min for moderated protons which more than in thrice reduces time of irradiation needed to reach an equal radiobiological effect.

[CYSTEAMINE-INDUCED MODIFICATION OF CYTOGENETIC DAMAGES TO THE CORNEAL EPITHELIUM OF MICE EXPOSED TO CORPUSCULAR RADIATION WITH VARYING LINEAR TRANSFER ENERGIES].

Cytogenetic damages to cells of the corneal epithelium were studied in mice exposed to protons (10, 25, 50 and 645 MeV), ions of boron, carbon and neon, and X-rays (180 keV) within the dose range from 25 to 750 cGy and injected with a radioprotector. Animals were subjected to a single exposure. The protective effect of ß-mercaptoethylamine was tested in the experiment. The radioprotector (0.2 ml) was introduced intraperitoneally 30 minutes before exposure in 350 mI/kg dose. Control animals received the same amount of sodium chloride solution. The animals were sacrificed by cervical dislocation in 24 and 72 hrs. after exposure. It was shown that cysteamine effectively protects in vivo corneal epithelium cells of mice exposed to electromagnetic radiation or protons in a broad energy spectrum (10 to 645 MeV), and to a broad range of radiation doses (25 to 750 cGy), as judged from levels of aberrant mitosis and mitotic activity. The radioprotector exhibited the highest effectiveness in animals exposed to the doses of 50 to 300 cGy. These findings prove that cysteamine may potentially be used for pharmacological protection from protons. The radioprotector failed to prevent chromosomal aberrations after exposure to heavy charged particles of boron, carbon and neon, which implies the need to design radioprotectors against this type of corpuscular radiation specifically.

[Cytogenetic damage to the corneal epithelium of mice due to the in vivo exposure to ionizing radiation with different levels of linear energy transfer].

Damages to corneal epithelium cells were studied in mice irradiated by protons with the energies of 10, 25, 50 and 645 MeV, 60Co γ-quanta and accelerated ions of boron, carbon and neon with the energies of 7.5; 2.5 and 6.0 MeV/nucleon, respectively. X-rays (180 keV) were used as a standard radiation. Animals were exposed to a single dose in the range from 25 to 760 cGy. The mitotic index and aberrant mitoses were counted in corneal preparations in 24 hrs after irradiation. No matter the type of radiation, the mitotic index had an inverse dose dependence, i.e. the higher the dose, the lower the mitotic index. Exposure to all types of radiation resulted in a sharp increase in the number of chromosomal aberrations in the corneal epithelium; frequency of aberrations was a function of dose and type of radiation. The number of chromosomal aberrations displayed a peculiar direct dose dependence irrespective of type of radiation; however, heavy ions of carbon and boron are the most damaging to the cytogenetic apparatus of epithelial cells. Protons at the Bragg peak and ensuing fall, and of 50 MeV also contribute to the production of chromosomal aberrations as compared with sparsely ionizing gamma- and X-rays and high-energy protons with low linear energy transfer. Coefficients of relative biological effectiveness were calculated based on the mitotic index and evidence of aberrant mitosis.

[Modification of the cytogenetic effects of irradiation by water with the reduced content of deuterium and heavy isotopes of oxygen].

The influence of light water with the reduced content of heavy stable isotopes of oxygen and hydrogen (deuterium) on the cytogenetic status of irradiated animals was investigated. In mice, hybrids of the first generation (CBA x C57B1) F1, the increase in the output (two-fold at the dose of 2 Gy) of aberrant mitoses in the cells of bone marrow and the decrease in the duration of the mitotic index of the first cellular cycle occurred under the influence of the two week maintenance before the irradiation on light water with ppm 35 obtained by the method of rectification as compared with the irradiated animals that were kept on the distilled water. It has been discovered that 24 h after irradiation the number of leukocytes in the group which consumed light water is lower than that in the animals that were contained on the distilled water. Moreover, the cellularity of the bone marrow in the group which consumed light water was higher than that in the animals that were contained on distilled water. The prolonged application of light water before irradiation (for 14 days) led to an increase in the sensitivity of the chromosomal apparatus of mice to γ-irradiation against the background of an increase in the mitotic activity of cells.

[Mitigation of mice radiation damage after acute and prolonged γ-irradiation by a laser device].

Effects of 7 Gy 60Co γ-radiation (acute and prolonged exposure), and combined exposure to 650 nm laser and γ-radiation on survival, peripheral blood, karyocyte count and mitotic index of bone marrow cells were studied in young C57BL/6 mice. All mice died following acute γ-irradiation at the dose rate of 1.14 Gy/min for 5 days or combined exposure for 11 days. Thirty percent survival from prolonged exposure to the dose rate of 0.027 Gy/min was observed after 19-day γ- and 38-day combined irradiation. Peripheral blood parameters did not differ significantly after acute and prolonged exposure; however, hyperchromemia was observed in mice after 24 hours of acute γ-irradiation. The count of mitoses per 1000 nucleus-containing BM cells evidenced that BM was virtually collapsed after 72 hours since the acute γ-exposure. It was demonstrated that laser can manage protection from a broad range of ionizing radiation doses and mitigate the adverse effects of equally acute and prolonged radiation exposure.

[Radiobiological effects of total mice irradiation with Bragg's peak protons].

Outbred CD-1 female mice were irradiated in a proton beam (171 MeV, 5 Gy) on the phasotron at the Joint Institute of Nuclear Research (Dubna, Russia). Radiation was delivered in two points of the depth dose distribution: at the beam entry and on Bragg's peak. Technical requirements for studying the effects of Bragg's peak protons on organism of experimental animals were specified. It was recognized that protons with high linear energy transfer (mean LET = 1.6 keV/microm) cause a more severe damaging effect to the hemopoietic system and cytogenetic apparatus in bone marrow cells as compared with entry protons and 60Co gamma-quanta. It was shown that recovery of the main hemopoietic organs and immunity as well as elimination of chromosomal aberrations take more time following irradiation with Bragg's peak protons but not protons with the energy of 171 MeV.

[Light-isotope water as a therapeutic agent for acute radiation disease].

Eighty outbred CD-I male and female mice (initial body mass of 31-34 g) and 40 male Wistar rats (initial body mass of 280-360 g) were randomly distributed into the experimental and control groups by sex and body mass. According to the results of experiments, consumption of rectified light-isotope water over 30 days immediately after irradiation by gamma-quanta 60Co at 5 Gy and 6.5 Gy can increase survivability rate significantly, accelerate hemopoiesis recovery and prevent body mass loss in irradiated animals. Therefore, light-isotope water can be considered as an effective agent for treatment of the bone marrow syndrome.

[Effect of a mineral organic complex on mice radioresistance].

Experiments showed that drinking water supplemented with a complex of 12 microelements and organic acids stimulates body mass gain and strengthening of radioresistance in mice. Obviously, availability of water with the mineral and organic complex before and after irradiation was the factor in survival of a part of mice exposed to the absolutely lethal dose (7.6 Gy from gamma-quanta 60Co) and reduction of chromosomal aberrations rate in bone marrow cells in consequence of nonlethal (1 Gy) irradiation.

[Dynamics of chromosomal aberrations in primates subject to continuous and fractionated gamma-irradiation by equally effective residual doses].

The paper deals with a comparative study of two regimens of Macaca mulatta continuous 2-week gamma- and double fractionated acute irradiation by the total absorbed doses of 250 and 132 cGy, respectively; data about chromosomal aberration rates in peripheral lymphocytes were correlated. Based on calculations it was hypothesized that, regardless of regimen, by day-12 of irradiation the effective residual dose would be same, i.e. approximately 100 cGy. Analysis of instable aberration chromosomes showed similarity of the effect of gamma-irradiation by 137Cs at earlier time points (on days 2-21). In primates with the gamma-irradiation profile close to chronic (Gamma 25) the total rate of chromosomal aberrations and rate of radiation markers remain high, whereas animals exposed to fractionated radiation (Gamma 66) displayed a statistically significant (p < 0.05) reduction in cytogenetic parameters on days 36, 50 and 85. Cytogenetic analysis of peripheral lymphocytes permits the conclusion that though markedly different in dose values and rates, both regimens produce an essentially equal early damaging effect.

[Cytological and cytogenetic studies of cells of Mongolian gerbils' retinal epithelium and marrow following 12-day space flight].

The paper report the results of studying mitotic activity and cytogenetic disorders in marrow and retinal epithelium cells of Mongolian gerbils in 21 - 23 hrs. of landing space apparatus Foton-M3, and the animals of synchronous and vivarium controls. Cells of the space flown gerbils displayed a statistically significant (p < 0.05) gain in the ratio of mitosis prophases and metaphases to the sum of ana- and telophases (1.7 +/- 0.3 and 2 +/- 0.1, respectively) as compared to these parameters in the synchronous and vivarium controls, where the ratio made up 0.6 +/- 0.1 and 0.7 +/- 0.1, respectively. Frequency of aberrant mytoses in the form of bridges was increased equally in both types of cells. Patterns of chromosome damages occurred in flight infer that the major portion of changes was not due to chromosome breakage but adhesion and ensuing wrong disjunction. These results seem to have been caused by acute g-stress to organism during re-entry and return from micro-g to the normal gravity.

[Chromosomal aberrations upon isolated and combined exposures to chemical substances and ionizing irradiation].

The partial summation of biological effects evaluated by the anaphasic chromosomal aberration test in the bone marrow karyocytes of mice was determined when the animals were concurrently exposed to chemical substances (acetone, acetaldehyde, ammonia, and ethanol) at low concentrations and gamma-irradiation in a total dose of 30 Gy. Qualitative analysis of chromosomal aberrations in the karyocytes of the bone marrow (ponses, fragments) has indicated that upon combined exposure of the animals to the chemical substances and gamma-irradiation, the chemical factor is dominant since upon combined radiochemical exposure, the number of chromosomal aberration increases mainly at the expense of fragments (91.2%), as does upon isolated exposure to chemical substances (96.4%).

[Investigation of the processes of post-radiation reparation of the corneal epithelium cells of mice irradiated by helium ions with various LET values].

Biological effectiveness and post-radiation recovery of corneal epithelium cells of mice were studied. Mice were exposed to a broad range of doses from accelerated helium ions with the energy of 4 MeV/nucleon and 4 GeV/nucleon once and twice with a 24-hr. interval. LET values for these energies were 120 and 0.88 keV/microm, respectively. Gamma-source 137Cs (LET = 0.3 keV/microm) was used as a radiation standard. Animals irradiated by 25-400 sGy were sacrificed in 24 and 72 hrs. by way of cervical dislocation. Total corneal preparations made from enucleated eyeballs were analyzed for the mitotic index and aberrant mitoses using the anaphase method. High damaging properties of accelerated helium ions with the energy of 4 MeV/nucleon were manifested by a considerable reduction of the mitotic index and a more marked rise in the number of aberrant mitoses following the single and repeated exposure. Fractional irradiation by helium ions with the energy of 4 MeV/nucleon resulted in inhibition and even arrest of reparation suggesting additivity of separate radiation fractions. From the dose values that produced the double reduction of the mitotic index, coefficients of the relative biological effectiveness (RBE) for helium ions with the energy of 4 MeV/nucleon and 4 GeV/nucleon were estimated to be 5.3-8.6 and 1.3-1.8, respectively. In the context of the number of aberrant mitoses, RBE coefficients were significantly lower ranging 2.3-3.5 and 1.1-1.3 for these energies, respectively.

[Cytogenetic and biochemical reactions of experimental animals to combined exposure to low-intensity radiation and chemical factors].

Combined exposure of mice to a mixture of chemicals in small quantities and gamma-radiation at a total dose of 30 sGy cause partial summation of biological effects assessed by cytogenetic disorders in nuclear cells of the bone marrow and changes in erythrocyte metabolism. The level of cytogenetic damages in bone marrow cells remained increased till day 14 of recovery, whereas following exposure to chemicals or radiation alone the number of chromosomal aberrations (ChA) was nearly same as in control at this point of recovery The anaphase method showed prevalence of ChA in the form of fragments over bridges in marrow karyocites. The combination of factors suppressed energy-producing processes in erythrocytes (reliable reductions in lactate dehydrogenase and lactate) and activated oxidation processes (reliable decrease in reduced glutathione). Functional shifts in erythrocyte metabolism persisted till day 30 of recovery Based on results of the investigation, functional status of organism following low-intensity exposures can be assessed, along with cytogenetic, also by indices of erythrocyte metabolism.

[Relative biological effectiveness of accelerated heavy ions and fast neutrons estimated from frequency of aberration mytoses in the retinal epithelium].

Analyzed was the literature and authors' experimental data concerning lesion and recovery of epithelium cells of mice retina immediately and long after irradiation at different sources including single and partly fractionated irradiation by gamma- and X-rays, accelerated protons, helium, carbon and boron ions, and fast neutrons of the reactor range in a large spectrum of doses and LET. Reviewed are some new techniques of determining the RBE coefficient for these types of radiation; large values of the RBE coefficients for accelerated ions and neutrons (5-10 times higher than RBE coefficients calculated for the next day following irradiation) are a result of integration into calculation of the available data about the delayed disorders in retinal epithelium cell regeneration.

[Cytogenetic and biochemical assay of an unidirectional effect of chronic combined exposure of laboratory animals to isoeffective concentrations of chemical substances].

Chronic combined exposure to low concentrations of chemical substances (equal to the maximal admissible limits for space vehicles) is fraught with an increase in chromosomal aberrations in bone marrow cells as compared with the spontaneous chromosome aberration rate. In addition to the cytogenetic evidence, there were also statistical phase shifts in metabolic parameters of erythrocytes (enzymes involved in the basal metabolism and a number of metabolites), leukocyte count in peripheral blood, and the total quantity of karyocytes in the bone marrow. No significant changes were found in organs of the immune and reproductive systems.

[Experimental studies of the relative biological effectiveness of accelerated charged particles varying in energy].

Experimental results and literary data were analyzed for the relative biological effectiveness of heavy charged particles in a broad range of energy and LET to cells of humans and other mammals in culture, whole body of laboratory animals, microorganisms, bacteriophages, and plants. Analyzed were data obtained with the use of a diversity of tests of acute and delayed lesions induced by ionizing radiation, cancers and cataracts, specifically. Non-parametric methods are applied in parallel to the classic method of calculating the coefficients of relative biological effectiveness by correlating the equal-effective doses of the standard and a given radiation. Consideration is given to factors that may modify RBE values estimated for different types of radiation.

[The influence of the water with decreased content of heavy stable hydrogen and oxygen (18O) isotope on development of radiation injuries at gamma-radiation in low dose].

The investigations of the water with decreased content of heavy stable hydrogen and of oxygen (18O) isotope received by the method of rectification were conducted on development of radiation injuries in organisms of the experimental animals. The objects of the investigation were male mice of Balb/c line. The animals were irradiated at the unit PX-gamma-30 with the gamma-radiation source 60Co in the dose of 25 sGy. It was observed that the water with decreased content of heavy stable hydrogen and of oxygen (18O) isotope influences positively the processes of restoration. It was manifested in decrease of the degree of gravity of radiation injuries in immune system organs (thymus and spleen), peripheral blood and marrow cells.

[Cytogenetic changes in cells of mammals after irradiation by protons with an energy of 1000 MeV and gamma-rays 137CS].

The purpose was to investigate cytological and cytogenetic disorders in cornea epithelium and bone marrow cells of mice after different periods since irradiation by protons at an energy of 1000 MeV and gamma doses of 25 to 400 cGy (137Cs). Suppression of the mitotic activity of cells by ionizing radiations was a function of dose value. In addition, the rate of aberrant mitoses was dependent on the type of radiation and time elapsed after exposure. Coeffcients of the relative biological effectiveness of protons with an energy of 1000 MeV in 24, 72 and 120 hrs. after irradiation were calculated based on comparison of doses compromising mitosis in 50% of differentiating cells. For the cornea epithelium cell the coefficients amounted to 1.3; 1.2 and 1.1, respectively; for the bone marrow cells they were 1.2; 1.1 and 0.9, respectively. The fingerprint of the proton biological effect is a higher production of exchange aberrations suggesting more severe damages to the hereditary cells.