Possible mechanisms of the occurrence of chromosome aberrations. I. Patterns in the occurrence of aberrations induced by ultraviolet irradiation

The frequency of chromosome aberrations induced by UV light at wavelengths 254, 265, 280 and 302 using doses 2-10 J/m2 in the primary culture of mouse embryonic fibroblasts during the G1, S and G2 phases was studied at metaphase of the first mitosis. Two classes of chromosome aberrations were distinguished. These classes differ in the time intervals of the final establishment of the cell cycle. The aberrations of the class 1 emerge before the beginning of prometaphase (possibly, at interphase). Formation of the second class aberrations is completed during the metaphase. It is shown that the class 1 aberrations occur with almost the same rate in approx. 7% of cells, irrespective of the cell cycle, irradiation dose and wavelength. It is suggested that these aberrations arise as a result of indirect UV action on the chromosome structures; the mechanism of their emergence does not depend on DNA replication. The class 2 aberrations do not appear after UV irradiation during the post-DNA-synthetic G2 phase of the cell cycle. However, after UV treatment at the G1 or S periods, they represent the majority of aberrations and their rate increases almost monotonously with the radiation dose. The UV action spectrum for these aberrations coincides with the adsorption spectrum of thymidine and the action spectrum for DNA cross-links. Thus, it may be inferred that formation of DNA cross-links following thymine dimerization is the first step in formation of UV-induced aberrations of the class 2. The passage of cells through DNA replication is a very important step in the process of their emergence.     

A study of the effect of low-intensity laser radiation of the blue, green, and red spectral regions on the healing of experimental skin wounds in rats

The effect of low-intensity laser radiation of the blue (441.2 nm), green (532 nm), and red (632.8 nm) spectral regions on the healing of experimental skin wounds in rats has been studied. The effect of the traditionally applied laser radiation in the red region has been compared with the effect of laser radiation in the other spectral regions, assuming that, upon irradiation of wounds by lasers emitting in the blue and green regions, a similar effect can be achieved at lower doses. The following parameters characterizing the healing of experimental wounds were used: the functional activity of phagocytes of wound exudates, which was determined by luminol-dependent chemiluminescence, and their number; the antioxidant activity of wound exudates; and the rate of healing, which was determined as a change in the wound area. It was shown that irradiation with laser accelerated the healing of wounds in all cases. The exposure to laser radiations in the red (1.5 J/cm), blue, and green (0.75 J/cm2) spectral regions shortened the time of wound healing from 22 to 17 and 19 days, respectively. The functional activity of leukocytes after the exposure increased on day 5 after the infliction of the wound, whereas in the control it decreased. The superoxide dismutase activity increased in all experimental groups by day 5 after the operation. A maximum increase in the superoxide dismutase activity occurred after the exposure to laser radiation in the red region at a dose of 1.5 J/cm and in the blue and green spectral regions at a dose of 0.75 J/cm2.     

Alteration of intracellular pH of macrophages after UV-irradiation

It was shown that in vitro exposuse of mice peritoneal middle-wave ultraviolet radiation (lambdamax = 306 nm) in doses which don't damage to cause plasma membrane caused dose-dependent decreasing of their intracellular pH. After exposure of cells to 0.5 J/cm2 it was detected an acidification of intracellular contents followed by an increase of intracellular pH up to control level (after 40 min of incubation) and then above it (on 45 min of incubation). An increase of irradiation dose was accompanied by more evident reduction of intracellular pH and lack of its restoration on 45 min of postradiational incubation under irradiation with a dose of 3 J/cm2.     

Effect of preliminary chronic irradiation and alpha-tocopherol on the frequency of chromosome aberrations in mouse bone marrow cells, induced by exposure to acute gamma-irradiation

The incidence of chromosome aberrations in bone marrow cells of femur did not exceed the spontaneous one in CBA mice exposed, during 70 days, to gamma-radiation at dose--rates of 33.7-35.8 nA/kg and cumulative dose of 2.75 Gy. A single acute exposure of intact animals to a dose of 2.98 Gy increased significantly the mutation level. Preirradiation with small doses increased the resistance of hereditary structures to sublethal radiation doses. Exogenous alpha-tocopherol (0.06 mg/20 g mass) protected the genetic apparatus of cells from total-body irradiation and was an additional factor decreasing the mutation level after acute exposure of mice at the background of long-term irradiation with small doses.     

The cytogenetic effects of low doses of accelerated charged particles in human blood lymphocytes in vitro

The aim of the investigation was the study of cytogenetic effects in human blood lymphocytes of low doses of ionizing radiation in vitro. The analysis of unstable chromosome aberrations in human lymphocytes after irradiation by the accelerated ions 12C with the energy 500 MeV/nucleon and LET 10.7 keV/microm was carried out. Blood samples were irradiated on Nuclotron of the High Energy Laboratory of the Joint Institute for Nuclear Research. The doses of irradiation were in the range from 0.05 up to 1.0 Gy. Was shown that the frequency of unstable chromosome aberrations depends from the dose of ionizing radiation and can be described by linear function. At the doses 0.25-0.50 Gy the dose-independent curve was obtained for dicentrics and centric rings. The frequencies of dicentrics and centric rings as markers of the radiation action were slightly different for different donors that could be explained by different radiosensitivity. Using the calibration curve obtained earlier for gamma-rays coefficients of relative biological efficiency of accelerated 12C with the energy 500 MeV/nucleon were defined: they varied from 1.0 at the doses (0.5-1.0 Gy) up to 3.2 at the lower doses (0.05-0.25 Gy).     

578.2 nm激光照射对兔视网膜的损伤效应研究

研究578.2 nm激光照射对兔视网膜的作用特点,以新西兰白兔5只10眼为实验对象,铜蒸汽激光(578.2 nm)通过裂隙灯照射兔视网膜后极部,照射时间为100 s,光斑直径为2 mm,照射剂量分别为60 J/cm2、80 J/cm2、100 J/cm2、120 J/cm2、160 J/cm2、200 J/cm2,每组4个光斑。照后1 h及24 h进行眼底照相及光镜观察。照光后可见,随激光功率密度的增加,兔视网膜的损伤也逐渐加重,并且照后24 h的损伤要重于照后1h。80 J/cm2和60 J/cm2在照后1 h和24 h均未发现明显改变。578.2 nm激光照射白兔后的主要病理学改变位于脉络膜。因此,以578.2 nm激光作为光动力治疗眼底疾病的光源时,照射剂量不宜超过80 J/cm2。     

Radioadaptation in Indian muntjac fibroblast cells induced by low intensity laser irradiation.

Earlier reports have indicated that an adaptive, protective response to ionizing radiation is inducible by pre-treatment with low intensity laser irradiation (LILI). We have investigated the potential of LILI to induce an adaptive response against the damaging effects of ionizing radiation in Indian muntjac fibroblasts. LILI at 660, but not 820 nm, at 11.5 and 23.0 J/cm2, induced an apparent adaptive response in the form of a reduction in the frequency of radiation-induced chromosome aberrations, but not in cell survival. There was also a trend towards a reduction in the level of single-stranded and double-stranded DNA breaks induced by ionizing radiation when cells were preconditioned with LILI. However, this did not contribute to the reduced chromosome aberration frequency. Further analysis revealed that the reduced aberration frequency was caused by a laser-induced extension of G2 delay. The adaptive response was therefore the result of cell cycle modulation by LILI, at a wavelength where there is no known DNA damaging effect to induce the checkpoint mechanisms that are normally responsible for altering cell cycle progression.     

Chromosome aberration frequencies and chromosome instability in mice after long-term exposure to low-dose-rate gamma-irradiation

Chronological changes of chromosome aberration rates related to accumulated doses in chronically exposed humans and animals at a low-dose-rate have not been well studied. C3H female specific pathogen-free mice (8 weeks of age) were chronically irradiated. Chromosome aberration rate in mouse splenocytes after long-term exposure to low-dose-rate (LDR) gamma-rays was serially determined by conventional Giemsa method. Incidence of dicentrics and centric rings increased almost linearly up to 8000 mGy following irradiation for about 400 days at a LDR of 20 mGy/day. Clear dose-rate effects were observed in the chromosome aberration frequencies between dose rates of 20 mGy/day and 200 Gy/day. Furthermore, the frequencies of complex aberrations increased as accumulated doses increased in LDR irradiation. This trend was also observed for the incidences of micronuclei and trisomies of chromosomes 5, 13 and 18 in splenocytes, detected by micronucleus assay and metaphase fluorescence in situ hybridization (FISH) method, respectively. Incidences of 2-4 micronuclei and trisomy increased in mouse splenocytes after irradiation of 8000 mGy at a LDR of 20 mGy/day. These complex chromosome aberrations and numerical chromosome aberrations seem to be induced indirectly after radiation exposure and thus the results indicate that continuous gamma-ray irradiation for 400 days at LDR of 20 mGy/day induced chromosomal instability in mice. These results are important to evaluate the biological effects of long-term exposure to LDR radiation in humans.     

Characteristic cytogenetic effects of small doses of ionizing radiation

A study was made of the frequency of chromosome aberrations in human lymphocyte culture after gamma-irradiation (60Co) with doses ranging from 0.05 to 1.0 Gy at dose--rates of 0,005, 0.05 and 0.5 Gy/min. The frequency of structural changes in chromosomes at low doses was higher than it was expected in the case of extrapolating the effect produced by high to low doses of radiation; within the dose range from 0.1 to 0.5 Gy a plateau was registered for aberrations of the exchange type (dicentrics and rings). The abnormal character of the dose dependence of the yield of chromosome aberrations persisted with all three dose - rates under study.     

Chromosome aberration frequencies produced by a 70-MeV proton beam

The effectiveness of a 70-MeV proton beam in the induction of chromosome aberrations was studied. We employed peripheral lymphocytes and analyzed the frequencies of dicentrics and rings after irradiation at doses ranging from 0.1 to 8.0 Gy at various depths within a Lucite phantom. The frequency of chromosome aberrations after irradiation with an unmodulated proton beam at 5 mm showed a dose-response relationship similar to that of 60Co gamma rays. However, irradiation at greater depths with the spread-out Bragg peak induced higher aberration frequencies at doses lower than those with gamma rays. Furthermore, the distribution curve of chromosome aberration frequencies as a function of depth was found to be slightly different from the physically measured depth-dose curve. With the spread-out Bragg peak the biological effects were more marked at greater depths, resulting in a distribution of relative biological effectiveness values. The results obtained from chromosome aberration analysis may not be related directly to those for the relationship between dose and cell killing. Slight differences in values for relative biological effectiveness due to the change of dose and site of proton beam irradiation may not be important for practical proton beam therapy, but may be important in the prevention of late radiation injuries.     

Melanin decreases clastogenic effects of ionizing radiation in human and mouse somatic cells and modifies the radioadaptive response

Melanin’s influence on the chromosome aberration frequency induced by radiation in human lymphocytes and mouse bone marrow cells has been studied. We revealed earlier that melanin significantly decreases the frequencies of different radiation-induced mutations in animal germ cells. Melanin protection in somatic cells has been found to be less effective. The melanin effect in somatic cells depends on radiation dose: the lower the damage level, the better the melanin protection. In order to determine the influence of melanin at low radiation doses, the adaptive response was investigated in mouse bone marrow cells in vivo. The level of chromosome aberrations in these cells after fractionated irradiation of 0.2 Gy+1.5 Gy with a 4-h interval was about half that after a single dose of 1.7 Gy. If melanin was injected prior to irradiation, the aberration level decreased by a factor of about two in both cases. This observed result may be due to the potential radioprotective effect of melanin and to the absence of any adaptive response, whereas in the case of melanin application between the priming and challenge doses, the combined effect of the adaptive response as well as melanin protection resulted in a 4-fold decrease of chromosome aberrations. These results allow us to draw the following conclusions: adaptive response can be prevented by a radioprotector such as melanin, and melanin is capable of completely removing low-dose radiation effects. Received: 2 December 1998 / Accepted in revised form: 15 September 1999     

Observations on the effect of X-ray alone and in combination with ultrasound on human chromosomes

Summary Human peripheral blood was treated with ultrasound either before or after irradiation, and chromosome aberrations in lymphocytes of peripheral blood cultures compared to those resulting from an equivalent dose of irradiation given alone.When peripheral blood is sonicated at a high intensity (3 W/cm²) for 10 min after irradiation, there is an increase in aberration frequency as compared to control samples receiving the equivalent radiation dose alone. However, should the blood be sonicated at the same frequency and for the same time period before radiation there is no significant increase in total chromosome aberrations over the irradiated controls. On the contrary a significant decreases occurs in certain classes of aberration.When sonification with a lower intensity (20 mW/cm²) was used in combination with irradiation the reverse effect was noted. Ultrasound administered for 10 min after radiation caused no significant increase in aberrations. On the contrary increasing the period of sonification to one hour resulted in a lowering of all types of aberration, significant in the case of dicentrics and total chromosome aberrations, when compared to irradiation alone. Reversing the order of treatment again resulted in the opposite effect to that achieved with comparable experiments at high intensities of sonification. Ultrasound before radiation did not produce lower breakage rates. Instead, when the period of sonification was increased to one hour, the number of aberrant cells, fragments, and total aberrations rose significantly over controls.It is suggested that sonification produces chemical changes affecting cellular repair systems, which when combined with ionising radiation, results in an increased or decreased repair effect depending on the dose, duration, and order of treatment.Dedicated to Prof. Dr. Felix Mainx on the occasion of his 80th birthday     

Anticlastogenic effects of a polyvitamin product, 'Pharmavit', on gamma-ray induction of somatic and germ cell chromosome aberrations in the mouse.

The polyvitamin product 'Pharmavit' (Pv), comprising vitamins A, D2, B1, B2, B6, C, E, nicotinamide, and calcium pantothene, was tested for anticlastogenic properties against gamma-rays in mice. Pretreatment with Pv consisted of daily administration by gavage for 30 days at dose levels corresponding to clinical recommendations for an adult human, as recalculated in terms of mg/kg. Findings indicated a reduction of chromosome aberrations in bone marrow cells from mice exposed to 3.0 Gy 137Cs gamma-rays; the reduction concerned predominantly fragments of the chromatid type. Furthermore, a reduction factor of 1.6 was obtained for the frequency of reciprocal translocations induced by spermatogonial irradiation in mice exposed to 4.0 Gy gamma-rays. Pretreatment with vitamin C alone, at the dose present in Pv, proved nearly ineffective in protecting from chromosome aberrations in bone marrow cells. Pharmavit is believed to be a promising agent for application to human populations exposed to the carcinogenic and genetic hazards of ionizing radiation.     

Radioprotective effect of rhizome extract of Zingiber montanum in Rattus norvegicus

The present study aims at determining the ability of 60% ethanol extract of the rhizome of Zingiber montanum (J. K?nig) A. Dietr. to protect bone marrow cells in vivo from radiation-induced chromosomal aberrations. Albino rats (Rattus norvegicus, 2n = 42) were used to carry out investigations on the radioprotective properties of Z. montanum. Acute toxicity of the extract was determined, and a suitable injectable dose was selected for intra-peritoneal administration. The LD(50) of the extract calculated for 72 h was 2.9 g/kg, and the calculated LD(10) dose was 1.7 g/kg. The calculated maximum tolerated dose of the rhizome extract was 1.3 g/kg. Rats were divided into 12 groups (with or without the administration of extract) and exposed to different radiation doses from 1 to 5 Gy. Whole-body irradiation of rats showed a significant dose-dependent increase in different types of chromosomal aberrations. The most common chromosomal aberrations were breaks, fragments, gaps, rings, endoreduplications and dicentric chromosomes. Ethanol extract of rhizome at a dose of 0.5 g/kg did not show any significant increase in chromosomal aberrations in unirradiated animals as compared to that of the control group. Intra-peritoneal administration of the extract at a dose of 0.5 g/kg considerably reduced the frequency of the aberrations stated above in irradiated animals with DMF value of 1.36 at 1 to 5 Gy dose range of gamma radiation. The incidence of micronucleated polychromatic erythrocytes and micronucleated normochromatic erythrocytes due to the radiation exposure was considerably reduced in extract-treated groups of animals with DMFs 1.34 and 1.17, respectively, as compared to that of the extract-untreated groups. Our results suggest that rhizome extract of Z. montanum may have a potential in protecting normal hematopoietic cells from radiation-induced damage.     

The protective effect of newly synthesized compounds against the action of UV-C irradiation on human lymphocytes in vitro

In this work we present our data about the protective effect of the newly synthesized compound 1-(4-fluorphenyltioureido)-4-methyl-piperazyne (FTMP) against high doses UV-C irradiation using human lymphocytes in vitro as a model system. The endpoint used was chromosome aberrations. The genotoxic effect of different UV-C doses in the range from 10 J/m2 to 200 J/m2 was evaluated. Studying the protective effect of FTMP, it was obtained that a low, adaptive concentration (10(-6) mol/l) applied before harmful doses of UV-C irradiation (100 J/M2 and 150 J/M2) induces the yield of chromosome aberrations lower than theoretical, estimated as a sum of single effects of both agents. A tendency for reducing the damage effect of UV-C irradiation was established. The effect is the most clear when a 4-hour interval between the treatments was used. The mitotic index was not affected. These results pointed out the ability of FTMP to decrease the damaging effect of UV-C irradiation in this type of cells and possess the potential to induce the adaptive response against the damaging effect of UV-C irradiation.     

Effect of copper vapor laser on the microrelief and ultrastructure of gastric mucosal glandulocytes

It was investigated the influence of low intensive irradiation by the copper++ vapor laser (lambda-510.6 nm) on the glandulocytes of gastric mucosa of 28 white rats. The doses of endogastric irradiation were 6.78, 20.34 and 33.90 J/cm2. It has been shown that after irradiation of gastric mucosa with the copper++ vapor laser the microrelief and ultrastructure of glandulocytes changes testified to stimulation of specific secret function. This changes took place under irradiation doses from 6.78 to 20.34 J/cm2. The doses exceeded 20.34 J/cm2 caused the alterations of the epitheliocytes. Thus it is necessary to take into account that during laser therapy of the ulcers with copper++ vapor laser, doses of 20.34 J/cm2 caused the alterative effect on the epitheliocytes.     

Improvement of stored turkey semen quality as a result of He-Ne laser irradiation

Two experiments were carried out to evaluate the effects of He-Ne laser irradiation at various energy doses on the quality of stored turkey semen. Four semen pools were used in Experiment 1. Each pool was divided into 10 aliquots, nine of which were irradiated with energy doses ranging from 0.144 to 10.8 J/cm2 while the tenth one was not irradiated (control). Each sample was evaluated for motility immediately after irradiation, 24 and 48 h later. Energy doses ranging from 3.24 to 5.4 J/cm2 had higher (P <0.01) sperm motility index (SMI) value compared to the control and samples irradiated with lower and higher laser doses. The energy dose of 3.96 J/cm2 was selected for Experiment 2 to obtain further insight on its effects on turkey sperm preservation for up to 60 h. Each pool of four semen was divided into two aliquots: one represented the control and the other one was irradiated with He-Ne laser at an energy dose of 3.96 J/cm2. Each sample was evaluated for motility and viability immediately after irradiation and then at 12 h intervals up to 60 h. The cell energy charge was also measured by HPLC. Exposure to 3.96 J/cm2 increased the SMI and viability of turkey semen stored for 60 h compared to the control (P <0.05). The cell energy charge of irradiated samples was 200% higher than in the control. Laser irradiation increased the longevity of stored turkey spermatozoa, and might be a useful technique to enhance semen quality in long-term storage.     

Time dependence of chromosomal aberrations induced in human and monkey lymphocytes by acute and fractionated exposure to 60Co

Changes in the numbers of peripheral lymphocytes with chromosome aberrations were observed in cynomolgus monkeys after fractionated or acute 60Co irradiation at the same total doses. Immediately after irradiation, the yield of dicentrics decreased when the dose was fractionated but remained constant for 20 to 80 days, depending on the dose, when irradiation was acute. Lymphopenia was greater than expected when the dose was fractionated. The kinetics of the loss of chromosome aberrations and the changes in peripheral lymphocyte count occurring in monkeys after acute irradiation were compared to those observed in accidentally irradiated men.     

Orange-red light reduces the inhibition by UV-A of the proliferation of rat fibroblasts and influences their attachment in a dose-dependent fashion

The effects of ultraviolet-A (UV-A, lambdam = 365 nm) and orange-red light (lambdam = 625 nm) on the attachment and proliferation of embryonic skin-muscle rat fibroblasts were investigated. It was found that orange-red light (ORL) produces both the stimulatory and inhibitory actions on the attachment and proliferation of fibroblasts, whereas UV-A radiation caused only the inhibition of the processes. Upon consecutive irradiation in both variants: ORL --> UV and UV --> ORL, the synergistic effect of the inhibitory action in both spectral regions was observed. Conversely, upon simultaneous irradiation with ORL (dose 3.6 J/cm2) and UV-A (dose 1.8 J/cm2), the inhibitory effect of ORL and UV-A weakened. Possible mechanisms of the effects are analyzed.     

Biological indication and dosimetry of unstable chromosome aberration frequencies in human lymphocytes

Review is devoted to the problems of biological (cytogenetic) dosimetry and indication of degree of radiation lesions based on analysis of unstable chromosome aberrations in lymphocytes of human peripheral blood. Effects of radiation in low doses on human chromosomes and methodology of interpretation of the character of dose cytogenetic curves are discussed. Traditional cytogenetic analysis remains the basic one for monitoring in groups of people with accidental irradiation.