A simple method for simultaneous interphase-metaphase chromosome analysis in biodosimetry

PURPOSE

To find a simple protocol for measuring chromosome damage both in G1 and in G2/M chromosomes, to overcome problems related to low mitotic index and cell-cycle alterations in biodosimetric tests.

MATERIALS AND METHODS

The protocol is based on the use of calyculin A to induce premature chromosome condensation in human peripheral blood lymphocytes in different phases of the cell cycle. Chromosome exchanges were measured by fluorescence in situ hybridization (chromosomes 2 and 4) in lymphocytes from four different donors. Cells were exposed to 4Gy X-rays and the results were compared to aberrations in M phase (colcemid block) and G0 (premature chromosome condensation induced by fusion to mitotic hamster cells).

RESULTS

Treatment with calyculin A produced a high fraction of chromosome condensation in different phases of the cell cycle. Cells in G1 and G2/M could be scored simultaneously for biodosimetry by chromosome painting. The condensation index was 5-20 times higher than the mitotic index (colcemid alone). The calyculin A treatment did not produce a significant increase in the background of chromosomal aberrations or modify the yield of chromosomal aberrations scored after exposure to X-rays.

CONCLUSIONS

Induction of chromosome condensation by calyculin A is a powerful biodosimetric tool, which provides a high number of spreads for analysis and overcomes problems related to poor in vitro growth or cell-cycle alterations.

Autonomic modulation of heart rate and blood pressure in hypertensive subjects with symptoms of anxiety

1. The influence of anxiety symptoms on autonomic nervous system cardiovascular control has never been studied in hypertensive subjects. This study was designed to verify the presence of sympathetic hyperactivity in hypertension associated with anxiety symptoms. 2. Neuroautonomic cardiovascular control was evaluated using short-time power spectral analysis of RR and arterial pressure variability at baseline and after the head-up tilt test. The two spectral components principally influenced by the autonomic nervous system are the low-frequency (LF) component, mainly though not exclusively due to sympathetic modulation, and the high-frequency (HF) component, due to parasympathetic activity. The ratio of LF to HF powers (LF:HF) provides an index of the sympathovagal sinus balance. 3. We studied 33 hypertensive subjects (mean age 47+/-1 years; M:F=19:14) and 37 normotensive control subjects (mean age: 47+/-2 years; M:F=20:17) divided into four subgroups: hypertensive subjects who scored 2 or more on a 5-item anxiety symptom scale, hypertensive subjects who scored 0, normotensive controls who scored 2 or more and normotensive controls who scored 0. LF:HF and LF during rest were significantly higher (P<0.05) in hypertensive and normotensive groups with an anxiety score of 2 or more compared with the two groups who scored 0. HF of systolic blood pressure was significantly lower in the hypertensive group who scored 2 or more than in the hypertensive group who scored 0 (P<0.05). Tilt in both hypertensive groups reporting anxiety symptoms left the indexes of sympathetic modulation unchanged. Tilt in hypertensive subjects reporting anxiety symptoms also induced a significant fall in arterial pressure (P<0.05). The mean left ventricular mass index was significantly higher in the hypertensive subjects who had anxiety scores of 2 or more than in those scoring 0 (144.7+/-3.0 versus 133. 4+/-2.31, P<0.05). 4. In conclusion, normotensive and hypertensive subjects reporting anxiety symptoms showed increased sympathetic modulation of heart rate at rest. Higher anxiety scores seem to be associated with the development of left ventricular hypertrophy.

Rejoining and misrejoining of radiation-induced chromatin breaks. IV. Charged particles

We have recently reported the kinetics of chromosome rejoining and exchange formation in human lymphocytes exposed to gamma rays using the techniques of fluorescence in situ hybridization (FISH) and premature chromosome condensation (PCC). In this paper, we have extended previous measurements to cells exposed to charged particles. Our goal was to determine differences in chromatin break rejoining and misrejoining after exposure to low- and high-linear energy transfer (LET) radiation. Cells were irradiated with hydrogen, neon, carbon or iron ions in the LET range 0.3-140 keV/microm and were incubated at 37 degrees C for various times after exposure. Little difference was observed in the yield of early prematurely condensed chromosome breaks for the different ions. The kinetics of break rejoining was exponential for all ions and had similar time constants, but the residual level of unrejoined breaks after prolonged incubation was higher for high-LET radiation. The kinetics of exchange formation was also similar for the different ions, but the yield of chromosome interchanges measured soon after exposure was higher for high-LET particles, suggesting that a higher fraction of DNA breaks are misrejoined quickly. On the other hand, the rate of formation of complete exchanges was slightly lower for densely ionizing radiation. The ratios between the yields of different types of aberrations observed at 10 h postirradiation in prematurely condensed chromosome preparations were dependent on LET. We found significant differences between the yields of aberrations measured in interphase (after repair) and metaphase for densely ionizing radiation. This difference might be caused by prolonged mitotic delay and/or interphase death. Overall, the results point out significant differences between low- and high-LET radiation for the formation of chromosome aberrations.

Effects of melanin on high- and low- linear energy transfer (LET) radiation response of human epithelial cells

The search for effective radioprotectors is of major concern in the medical, military, environmental, and space sciences. Conventional radioprotectors are generally effective only during a single irradiation and display their radioprotective properties only at high, toxic concentrations. In addition, they reduce somatic radiation effects but are poorly efficient in protecting from hereditary stochastic radiation effects. In this respect, the pigment melanin merits attention. Experiments referring to potential melanin effects on the ionising radiation response have been carried out with different biological systems, both in vivo and in vitro. In this paper, we present results on the response to high- and low-linear energy transfer (LET) radiation of a human mammary epithelial cell line, H184B5 F5-1 M/10, supplemented by melanin. The incorporation of auto-oxidative (L-dopa) melanin was linear for concentrations from 3 to 10 micrograms/ml in the growth medium. Concentrations of up to 250 micrograms/ml did not significantly impair the cells proliferative ability. No significant protective effect of melanin on the survival of cultured cells after exposure to alpha-particles (130 keV/micron) or x-rays was observed.

The effect of track structure on the induction of chromosomal aberrations in murine cells

PURPOSE

To measure chromosome aberrations in C3H 10T1/2 mouse fibroblasts using FISH painting at the first mitosis following exposure to 30 keV/microm hydrogen or neon ions.

MATERIALS AND METHODS

Cells in plateau-phase were irradiated with 0.86 MeV protons at the TTT-3 Tandem accelerator in Naples (Italy), or with 400 MeV/n Ne ions at the HIMAC accelerator in Chiba (Japan). Colcemid-blocked cells were harvested at the first mitosis following exposure, and chromosome spreads were hybridized in situ with a fluorescein-labelled composite mouse DNA probe specific for chromosomes 2 and 8.

RESULTS

Protons were more efficient than neon ions at the same LET in the induction of chromosome interchanges and breaks. Yields of complex exchanges were similar for both particles at the same dose, but protons produced mostly insertions, while with Ne exposure non-reciprocal exchanges were the most frequent complex-type exchange.

CONCLUSIONS

Charged particles with the same LET produce different yields of chromosome aberrations, and some observed differences can be explained based on the available track-structure models.

Biodosimetry of heavy ions by interphase chromosome painting

We report measurements of chromosomal aberrations in peripheral blood lymphocytes from cancer patients undergoing radiotherapy treatment. Patients with cervix or esophageal cancer were treated with 10 MV X-rays produced at a LINAC accelerator, or high-energy carbon ions produced at the HIMAC accelerator at the National Institute for Radiological Sciences (NIRS) in Chiba. Blood samples were obtained before, during, and after the radiation treatment. Chromosomes were prematurely condensed by incubation in calyculin A. Aberrations in chromosomes 2 and 4 were scored after fluorescence in situ hybridization with whole-chromosome probes. Pre-treatment samples were exposed in vitro to X-rays, individual dose-response curves for the induction of chromosomal aberrations were determined, and used as calibration curves to calculate the effective whole-body dose absorbed during the treatment. This calculated dose, based on the calibration curve relative to the induction of reciprocal exchanges, has a sharp increase after the first few fractions of the treatment, then saturates at high doses. Although carbon ions are 2-3 times more effective than X-rays in tumor sterilization, the effective dose was similar to that of X-ray treatment. However, the frequency of complex-type chromosomal exchanges was much higher for patients treated with carbon ions than X-ray.

Rejoining and misrejoining of radiation-induced chromatin breaks. III. Hypertonic treatment

It has been shown that treatment in anisotonic medium modifies rejoining of radiation-induced breaks in interphase chromosomes. In previous work, we have demonstrated that formation of exchanges in human lymphocytes has a slow component (half-time of 1-2 h), but a fraction of exchanges are also observed in samples assayed soon after exposure. In this paper we studied the effect of hypertonic treatment on rejoining and misrejoining of radiation-induced breaks using fluorescence in situ hybridization of prematurely condensed chromosomes in human lymphocytes. Isolated lymphocytes were irradiated with 7 Gy gamma rays, fused to mitotic hamster cells and incubated in hypertonic solution (0.5 M NaCl) for the period normally allowed for interphase chromosome condensation to occur. The data from hypertonic treatment experiments indicate the presence of a class of interphase chromosome breaks that rejoin and misrejoin very quickly (half-time of 5-6 min). The fast misrejoining of these lesions is considered to be responsible for the initial level of exchanges which we reported previously. No significant effect of hypertonic treatment on the yield of chromosome aberrations scored at the first postirradiation mitosis was detected.

Biodosimetry of ionizing radiation by selective painting of prematurely condensed chromosomes in human lymphocytes

Painting of interphase chromosomes can be useful for biodosimetric purposes in particular cases such as radiation therapy, accidental exposure to very high radiation doses and exposure to densely ionizing radiation, for example during space missions. Biodosimetry of charged-particle radiation is analyzed in the present paper. Target cells were human peripheral blood lymphocytes irradiated in vitro with gamma rays, protons and iron ions. After exposure, lymphocytes were incubated for different times to allow repair of radiation-induced damage and then fused to mitotic hamster cells to promote premature condensation in the interphase chromosomes. Chromosome spreads were then hybridized with whole-chromosome DNA probes labeled with fluorescent stains. Dose-response curves for the induction of chromatin fragments shortly after exposure, as well as the kinetics of rejoining and misrejoining, were not markedly dependent on linear energy transfer. However, after exposure to heavy ions, more aberrations were scored in the interphase cells after incubation for repair than in metaphase samples harvested at the first postirradiation mitosis. On the other hand, no significant differences were observed in the two samples after exposure to sparsely ionizing radiation. These results suggest that interphase chromosome painting can be a useful tool for biodosimetry of particle radiation.

Induction of chromosome aberrations in human cells by charged particles

Chromosome aberrations induced by high-energy charged particles in normal human lymphocytes and human fibroblasts have been investigated. The charged particles included 250 MeV/nucleon protons, 290 MeV/nucleon carbon ions and 1 GeV/nucleon iron ions. The energies of the charged particles were higher than in most of the studies reported in the literature. Lymphocytes were stimulated to grow immediately after irradiation, while fibroblasts were incubated at 37 degrees C for 24 h for repair. Chromosomes were collected at the first mitosis after irradiation and chromosome aberrations were scored using the fluorescence in situ hybridization (FISH) technique with a whole-chromosome 4 probe. Chromosome aberrations were classified as reciprocal exchanges, incomplete exchanges, deletions and complex exchanges. The relative biological effectiveness (RBE) for each type of aberration was calculated by dividing a dose of 4 Gy by the dose of the charged particles producing the same effect as 4 Gy of gamma rays. Results of this study showed that complex aberrations have the highest RBE for radiation of high linear energy transfer (LET) for human lymphocytes, but for fibroblasts, the greatest effect was for incomplete exchanges. For both lymphocytes and fibroblasts, iron ions induced a similar fraction of aberrant cells.

Biodosimetry results from space flight Mir-18

Astronauts are classified as radiation workers due to the presence of ionizing radiation in space. For the assessment of health risks, physical dosimetry has been indispensable. However, the change of the location of dosimeters on the crew members, the variation in dose rate with location inside the spacecraft and the unknown biological effects of microgravity can introduce significant uncertainties in estimating exposure. To circumvent such uncertainty, a study on the cytogenetic effects of space radiation in human lymphocytes was proposed and conducted for Mir-18, a 115-day mission. This study used fluorescence in situ hybridization (FISH) with whole-chromosome painting probes to score chromosomal exchanges and the Giemsa staining method to determine the frequency of dicentrics. The growth kinetics of cells and sister chromatid exchanges (SCEs) were examined to ensure that chromosomal aberrations were scored in the first mitosis and were induced primarily by space radiation. Our results showed that the frequency of chromosomal aberrations increased significantly in postflight samples compared to samples drawn prior to flight, and that the frequency of SCEs was similar for both pre- and postflight samples. Based on a dose-response curve for preflight samples exposed to gamma rays, the absorbed dose received by crew members during the mission was estimated to be about 14.75 cSv. Because the absorbed dose measured by physical dosimeters is 5.2 cGy for the entire mission, the RBE is about 2.8.

Inactivation of individual mammalian cells by single alpha-particles

PURPOSE

To measure clonogenic death of Chinese hamster V79 cells following exposure to a defined number of 4.3 MeV alpha-particles (track-averaged LET = 105 keV/micron).

MATERIALS AND METHODS

Cells were irradiated at the radiobiological facility installed at the TTT-3 Tandem accelerator in Naples by using a 'Biostack' approach, which allows the positions of incident tracks relative to cells to be carefully determined. Subcellular structure was identified by fluorescence microscopy, while tracks were visualized by LR-115 solid state nuclear track detectors.

RESULTS

Particle hits in the cytoplasm did not significantly affect cell survival, yet survival probability decreased exponentially as a function of the number of nuclear traversals. Measured probability of surviving to exactly one 4.3 MeV alpha-particle traversal in the cell nucleus was 0.67 +/- 0.10. Inactivation cross-section was substantially higher than expected from conventional survival curves. However, folding of the data with Poisson statistics showed that survival level expected if a mean of one alpha-particle goes through a nucleus is higher than the measured value after exactly one particle traversal.

CONCLUSIONS

V79 cells have about 67% probability to survive a single alpha-particle traversal in the cell nucleus. Single-particle survival curves are consistent with conventional dose-survival relationships, once Poisson distribution of traversals is taken into account.

Initiation of oncogenic transformation in human mammary epithelial cells by charged particles

Experimental studies have shown that high linear-energy transfer (LET) charged particles can be more effective than x-rays and gamma-rays in inducing oncogenic transformation in cultured cells and tumors in animals. Based on these results, experiments were designed and performed with an immortal human mammary epithelial cell line (H184B5), and several clones transformed by heavy ions were obtained. Cell fusion experiments were subsequently done, and results indicate that the transforming gene(s) is recessive. Chromosome analysis with fluorescence in situ hybridization (FISH) techniques also showed additional translocations in transformed human mammary epithelial cells. In addition, studies with these cell lines indicate that heavy ions can effectively induce deletion, break, and dicentrics. Deletion of tumor suppressor gene(s) and/or formation of translocation through DNA double strand breaks is a likely mechanism for the initiation of oncogenic transformation in human mammary epithelial cells.

A thermal denaturation study of macronuclear chromatin in Blepharisma japonicum (Protozoa, Ciliophora, Heterotrichida)

The macronuclear chromatin of the ciliate Blepharisma japonicum, in two starvation states, was studied by thermal denaturation analysis. The behaviour of B. japonicum chromatin, native and reconstituted with Tetrahymena pyriformis H1 histone, was analysed. The data obtained are consistent with the hypothesis that B. japonicum macronuclear chromatin contains a H1-like peptide associated with the linker DNA, although this peptide is reduced in amount and/or chromatin stabilising ability when compared to Tetrahymena macronuclear H1.

Centric rings, acentric rings and excess acentric fragments based on a random-walk interphase chromosome model

Excess acentric fragments, consisting of acentric rings and acentric linear fragments, are among the most frequent kinds of chromosome-type aberrations produced by radiation. The frequency of acentric rings cannot be obtained directly by experiment but is estimated here from the ratio of acentric to centric rings, evaluated using a random-walk model for the organization of chromatin during interphase and an assumption that the probability of an exchange formation is proportional to the rate of collision between two DSB. This ratio is calculated to be 2.5 in low-LET irradiated human fibroblasts, significantly greater than the ratio if proximity effects are not considered. The calculated frequency of acentric rings is insufficient to account for all the observed excess acentric fragments. Assuming that the rest of the excess acentric fragments are due to incomplete exchanges, all possible recombinations between two DSB that result in acentric rings and acentric linear fragments have been identified. From the chromosome aberration data, the incompleteness parameter has been estimated. Intra-arm chromosome exchanges, either complete or incomplete, were estimated to account for more than 50% of the excess acentric fragments in human fibroblasts.

Cytogenetic effects of space radiation in lymphocytes of MIR-18 crews

For assessing health risk, the measurement of physical dose received during a space mission, as well as the LETs, energies and charges of particles is important. It is also important to obtain quantitative information regarding the effectiveness of space radiation in causing damage to critical biological targets, e.g., chromosomes, since at present the estimated uncertainty of biological effects of space radiation is more than a factor of two. Such large uncertainty makes accurate health risk assessment very difficult. For this very reason, a study on cytogenetic effects of space radiation in human lymphocytes was proposed and done for MIR-18 mission. This study used FISH technique to score chromosomal translocations and C-banding method to determine dicentrics. Growth kinetics of cells and SCE were examined to ensure that chromosomal aberrations were scored in first mitosis and were induced not by chemical mutagens. Our results showed that chromosomal aberration frequency of post-flight samples was significantly higher than that of pre-flight ones and that SCE frequency was similar between pre- and post-flight samples. Based on a dose-response curve of preflight samples exposed to gamma rays, the absorbed dose received by crews during the mission was estimated to be about 14.5 cSv. Because the absorbed dose measured by physical dosimeters is 4.16 cGy for the entire mission, the RBE is about 3.5.

Heart rate and blood pressure variabilities in salt-sensitive hypertension

In salt-sensitive hypertension, a high sodium intake causes plasma catecholamines to rise and pulmonary baroreceptor plasticity to fall. In salt-sensitive and salt-resistant hypertensive subjects during low and high sodium intakes, we studied autonomic nervous system activity by power spectral analysis of heart rate and arterial pressure variabilities and baroreceptor sensitivity. In all subjects, high sodium intake significantly enhanced the low-frequency power of heart rate and arterial pressures at rest and after sympathetic stress. It also increased heart rate and arterial pressure variabilities. During high sodium intake, salt-sensitive hypertensive subjects had significantly higher low-frequency powers of systolic arterial pressure (7.5 mm Hg2, P < .05) and of heart rate at rest (59.2 +/- 2.4 normalized units [NU], P < .001) than salt-resistant subjects (6.6 +/- 0.3 mm Hg2, 55.0 +/- 3.2 NU) and normotensive control subjects (5.1 +/- 0.5 mm Hg2, 41.6 +/- 2.9 NU). In salt-sensitive subjects, low sodium intake significantly reduced low-frequency normalized units (P < .001) and the ratio of low- to high-power frequency (P < .001). High-sodium intake significantly increased baroreflex sensitivity in control subjects (from 10.0 +/- 0.7 to 17.5 +/- 0.7 ms/mm Hg, P < .001) and salt-resistant subjects (from 6.9 +/- 0.7 to 13.9 +/- 0.9, P < .05) but not in salt-sensitive subjects (7.4 +/- 0.3 to 7.9 +/- 0.4). In conclusion, a high sodium intake markedly enhances cardiac sympathetic activity in salt-sensitive and salt-resistant hypertension. In contrast, although reduced sodium intake lowers arterial pressure and sympathetic activity, it does so only in salt-sensitive subjects. Hence, in salt-resistant subjects, neither arterial pressure nor sympathetic activity depends on salt intake. During a high sodium intake in normotensive subjects and salt-resistant hypertensive subjects, increased sympathetic activity is probably compensated by enhanced baroreflex sensitivity.

Nuclear DNA changes within Helianthus annuus L.: variations in the amount and methylation of repetitive DNA within homozygous progenies

Complex alterations in the redundancy and methylation of repeated DNA sequences were shown to differentiate the nuclear genome of individuals belonging to single progenies of homozygous plants of the sunflower. DNA was extracted from seedlings obtained from seeds collected at the periphery of flowering heads (P DNA) or from seedlings obtained from seeds collected in their middle (M DNA). Three fractions of repeated sequences were isolated from genomic DNA: a highly repetitive fraction (HR), which reassociates within an equivalent Cot of about 2 × 10(-1), and two medium repetitive fractions (MR1 and MR2) having Cot ranges of about 2 × 10(-1)-2 and 2-10(2), respectively. Denaturation kinetics allowed different sequence families to be recognized within each fraction of repetitive DNA, and showed significant differences in sequence redundancy to occur between P and M DNA, particularly as far as the MR2 fraction is concerned. Most DNA sequence families are more represented in P DNA than in M DNA. However, the redundancy of certain sequences is greater in the latter than in the former. Each repetitive DNA fraction was hybridized to Southern blots of genomic P or M DNA which was digested to completion by three pairs of isoschizomeric restriction endonucleases which are either insensitive or sensitive to the methylation of a cytosine in the recognition site. The results obtained showed that the repetitive DNA of H. annuus is highly methylated. Clear-cut differences in the degree of methylation of P and M DNA were found, and these differences were particularly apparent in the MR2 fraction. It is suggested that alterations in the redundancy of given DNA sequences and changes in their methylation patterns are complementary ways to produce continuous genotypic variability within the species which can be exploited in environmental adaptation.

Rejoining and misrejoining of radiation-induced chromatin breaks. I. experiments with human lymphocytes

Fluorescence in situ hybridization with a composite probe for human chromosome 4 and a probe that stained all centromeres was used to study gamma-ray induced breakage, rejoining and misrejoining in prematurely condensed chromosomes in human lymphocytes. Dose-response curves for the induction of all types of aberrations in prematurely condensed human chromosomes 4 were determined immediately after irradiation and after 8 h postirradiation incubation. In addition, aberrations were measured after various incubation times from 0 to 18 h after a dose of 7 Gy. Unrejoined chromosome breaks were the most frequent type of aberration observed immediately after irradiation. Approximately 15% of total aberrations observed were chromosome exchanges. After 8 h postirradiation incubation, the frequency of breaks in prematurely condensed chromosomes declined to about 20% of the initial value, and chromosomal exchanges became the most frequent aberration. Results of metaphase analysis were similar to those for prematurely condensed chromosomes after 8 h incubation with the exception that a significantly lower frequency of fragments was observed. Symmetrical and asymmetrical interchanges were found at similar frequencies at all doses. No complex exchanges were observed in lymphocyte chromosomes immediately after exposure. They accounted for about 1% of total exchanges in metaphase chromosomes at doses <3 Gy and about 14% at 7 Gy. Incomplete exchanges amounted to approximately 15% of total exchanges at all doses. The kinetics of break rejoining was exponential, and the frequency of exchanges increased with kinetics similar to that observed for the rejoining of the breaks. This increase in the total exchanges as a function of the time between irradiation and fusion was due to a rapid increase in reciprocal interchanges, and a slower increase in complex exchanges; the frequency of incomplete exchanges increased initially, then decreased with prolonged incubation to the level observed in metaphase. It is concluded that the formation of each kind of chromosome aberrations follows different kinetics.

Rejoining and misrejoining of radiation-induced chromatin breaks. II. Biophysical Model

A biophysical model for the kinetics of the formation of radiation-induced chromosome aberrations is developed to account for the recent experimental results obtained with a combination of the premature chromosome condensation (PCC) and fluorescence in situ hybridization (FISH) techniques. In this model, we consider the broken ends of DNA double-strand breaks (DSBs) to be reactant and make use of the interaction distance hypothesis. The repair/misrepair process between broken ends is suggested to consist of two steps; the first step represents the two break ends approaching each other, and the second step represents the enzymatic processes leading to DNA end-to-end rejoining. Only the second step is reflected in the kinetics observed in experiments using PCC. The model appears to be able to fit existing data for human cells. It is shown that the kinetics of the formation of chromosome aberrations can be explained by a single rate that characterizes both rejoining and misrejoining of DSBs, suggesting that repair and misrepair share the same mechanism. Fast repair (completed in minutes) in a subset of DSBs is suggested as an explanation of the complete exchanges observed with PCC in human lymphocytes immediately after irradiation. The fast repair component seems to be absent in human fibroblasts.

Radiation-induced chromosomal instability in human mammary epithelial cells

Karyotypes of human cells surviving X- and alpha-irradiation have been studied. Human mammary epithelial cells of the immortal, non-tumorigenic cell line H184B5 F5-1 M/10 were irradiated and surviving clones isolated and expanded in culture. Cytogenetic analysis was performed using dedicated software with an image analyzer. We have found that both high- and low-LET radiation induced chromosomal instability in long-term cultures, but with different characteristics. Complex chromosomal rearrangements were observed after X-rays, while chromosome loss predominated after alpha-particles. Deletions were observed in both cases. In clones derived from cells exposed to alpha-particles, some cells showed extensive chromosome breaking and double minutes. Genomic instability was correlated to delayed reproductive death and neoplastic transformation. These results indicate that chromosomal instability is a radiation-quality-dependent effect which could determine late genetic effects, and should therefore be carefully considered in the evaluation of risk for space missions.

Biological dosimetry by interphase chromosome painting

Both fluorescence in situ hybridization of metaphase spreads with whole-chromosome probes and premature chromosome condensation in interphase nuclei have been used in the past to estimate the radiation dose to lymphocytes. We combined these techniques to evaluate the feasibility of using painted interphase chromosomes for biodosimetry. Human peripheral lymphocytes were exposed to gamma rays and fused to mitotic Chinese hamster cells either immediately after irradiation or after 8 h incubation at 37 degrees C. Interphase or metaphase human chromosomes were hybridized with a composite probe specific for human chromosomes 3 and 4. The dose-response curve for fragment induction immediately after irradiation was linear; these results reflected breakage frequency in the total genome in terms of DNA content per chromosome. At 8 h after irradiation, the dose-response curve for chromosome interchanges, the prevalent aberration in interphase chromosomes, was linear-quadratic and similar to that observed for metaphase chromosomes. These results suggest that painting prematurely condensed chromosomes can be useful for biological dosimetry when blood samples are available shortly after the exposure, or when interphase cells are to be scored instead of mitotic cells.

Power spectral analysis of heart rate in elderly hypertensive subjects with or without silent coronary disease

Much evidence indicates an involvement of the sympathetic nervous system in the genesis of silent myocardial ischemia. The authors assessed autonomic system activity by power spectrum analysis of heart rate variability in 21 elderly hypertensive men with and without angiographically confirmed coronary artery disease and compared the results with those from an age-matched control group. In the analysis an autoregressive algorithm was used to determine the power spectrum from an electrocardiographic recording of 512 consecutive RR intervals. The autonomic nervous system induces two distinct sinusoids: a low-frequency signal attributable to sympathetic activity and a high-frequency vagal response. In the hypertensive patients with coronary disease the authors also evaluated sympathetic activation after double-blind, placebo-controlled administration of metoprolol (100 mg/day), followed by amlodipine (10 mg/day), quinapril (20 mg/day), and amlodipine (5 mg/day) plus quinapril (10 mg/day).

The quality of DNA double-strand breaks: a Monte Carlo simulation of the end-structure of strand breaks produced by protons and alpha particles

The quality of DNA damage induced by protons and alpha-particles of various linear energy transfer (LET) was studied. The aim was to single out specific lesions in the DNA molecule that might lead to biological endpoints such as inactivation. A DNA model coupled with a track structure code (MOCA-15) were used to simulate the lesions induced on the two helixes. Four categories of DNA breaks were considered: single-strand breaks (ssb), blunt-ended double-strand breaks (dsb, with no or few overlapping bases), sticky-ended double-strand breaks (with cohesive free ends of many bases), and deletions (complex lesions which involve at least two dsb within a small number of base pairs). Calculations were carried out assuming various sets of parameters characterizing the production of these different DNA breaks. No large variations in the yields of ssb and blunt- or sticky-ended dsb were found in the LET range between 10 and 200 keV/mu m. On the other hand, the yield of deletions increases up to about 100 keV/mu m and seems to reach a plateau at higher LET values. In the LET interval from 30 to 60 keV/mu m, protons proved to be more efficient than alpha-particles in inducing deletions. The induction of these complex lesions is thus dependent not simply on LET but also on the characteristics of the track structure. Comparison with RBE values for cell killing shows that this special class of dsb might play an important role in radiation-induced cell inactivation.

Radiogenic cell transformation and carcinogenesis

Radiation carcinogenesis is one of the major biological effects considered important in the risk assessment for space travel. Various biological model systems, including both cultured cells and animals, have been found useful for studying the carcinogenic effects of space radiations, which consist of energetic electrons, protons and heavy ions. The development of techniques for studying neoplastic cell transformation in culture has made it possible to examine the cellular and molecular mechanisms of radiation carcinogenesis. Cultured cell systems are thus complementary to animal models. Many investigators have determined the oncogenic effects of ionizing and nonionizing radiation in cultured mammalian cells. One of the cell systems used most often for radiation transformation studies is mouse embryonic cells (C3H10T1/2), which are easy to culture and give good quantitative dose-response curves. Relative biological effectiveness (RBE) for heavy ions with various energies and linear energy transfer (LET) have been obtained with this cell system. Similar RBE and LET relationship was observed by investigators for other cell systems. In addition to RBE measurements, fundamental questions on repair of sub- and potential oncogenic lesions, direct and indirect effect, primary target and lesion, the importance of cell-cell interaction and the role of oncogenes and tumor suppressor genes in radiogenic carcinogenesis have been studied, and interesting results have been found. Recently several human epithelial cell systems have been developed, and ionizing radiation have been shown to transform these cells. Oncogenic transformation of these cells, however, requires a long expression time and/or multiple radiation exposures. Limited experimental data indicate high-LET heavy ions can be more effective than low-LET radiation in inducing cell transformation. Cytogenetic and molecular analyses can be performed with cloned transformants to provide insights into basic genetic mechanism(s) of radiogenic transformation of human epithelial cells.

Effects of alpha-particles on survival and chromosomal aberrations in human mammary epithelial cells

We have studied the radiation responses of a human mammary epithelial cell line, H184B5 F5-1 M/10. This cell line was derived from primary mammary cells after treatment with chemicals and heavy ions. The F5-1 M/10 cells are immortal, density-inhibited in growth, and non-tumorigenic in athymic nude mice and represent an in vitro model of the human epithelium for radiation studies. Because epithelial cells are the target of alpha-particles emitted from radon daughters, we concentrated our studies on the efficiency of alpha-particles. Confluent cultures of M/10 cells were exposed to accelerated alpha-particles [beam energy incident at the cell monolayer = 3.85 MeV, incident linear energy transfer (LET) in cell = 109 keV/microns] and, for comparison, to 80 kVp x-rays. The following endpoints were studied: (1) survival, (2) chromosome aberrations at the first postirradiation mitosis, and (3) chromosome alterations at later passages following irradiation. The survival curve was exponential for alpha-particles (D0 = 0.73 +/- 0.04 Gy), while a shoulder was observed for x-rays (alpha/beta = 2.9 Gy; D0 = 2.5 Gy, extrapolation number 1.6). The relative biological effectiveness (RBE) of high-LET alpha-particles for human epithelial cell killing was 3.3 at 37% survival. Dose-response curves for the induction of chromosome aberrations were linear for alpha-particles and linearquadratic for x-rays. The RBE for the induction of chromosome aberrations varied with the type of aberration scored and was high (about 5) for chromosome breaks and low (about 2) for chromosome exchanges.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiation-induced chromosomal aberrations in mouse 10T1/2 cells: dependence on the cell-cycle stage at the time of irradiation

Cell-cycle stage radiosensitivity for the induction of chromosome aberrations has been investigated in C3H 10T1/2 cells. Exponentially growing cells were irradiated with 3 Gy X-rays (80 kVp) or 0.6 Gy alpha-particles (LET = 101 keV/micron). The two doses produce the same survival level (37%) in the asynchronous population. Cells were harvested at four different times following irradiation and cell-cycle phase at the time of irradiation was assessed by using the differential replication staining technique. The frequency of chromosome aberrations produced in a given stage of the cell cycle was not constant as a function of the sampling time, but this could not be simply related to the existence of subphases exhibiting different radiosensitivity, because of cell-cycle perturbation introduced by radiation. X-radiation induced more exchanges than deletions, whereas a predominance of isochromatid deletions was observed after alpha-irradiation. This can be interpreted on the basis of the different patterns of energy deposition of densely- and sparsely-ionizing radiation. Both X- and alpha-rays produced a significant increase in the frequency of Robertsonian translocations when cells were exposed in G1 or S phase, but not in G2 phase.

The induction of Robertsonian translocations by X-rays and mitomycin C in mouse cells

The induction of Robertsonian translocations in murine C3H 10T1/2 embryo fibroblasts after exposure to X-rays and mitomycin C has been investigated. Cells were irradiated in log-phase and harvested at different times for chromosome analysis. The stage of the cell cycle of individual cells at the time of irradiation could be determined by differential replication staining. A dose-dependent delay in the progression through S- and G2-phase has been observed. X-rays produced an increase in the frequency of Robertsonian translocations when cells were exposed in G1- or S-phase, but not in G2. The dose-response curve for the induction of Robertsonian translocations both in G1 and S peaked at 2 Gy and slightly declined at higher doses. For G2 cells, an increase compared to the control level was observed only after 1 Gy. Mitomycin C induced chromosomal aberrations and Robertsonian translocations in 10T1/2 cells, but no significant interaction between ionizing radiation and the alkylating agent was observed for these two endpoints. However, the combined exposure caused satellite associations of chromosomes. Both the number of satellite associations/metaphase (five times the frequency observed after mitomycin C alone) and the number of chromosomes/satellite (up to 10 chromosomes were observed in satellite associations) were greatly enhanced compared to X-rays and mitomycin C alone.

Heavy-ion induced genetic changes and evolution processes

On Moon and Mars, there will be more galactic cosmic rays and higher radiation doses than on earth. Our experimental studies showed that heavy ion radiation can effectively cause mutation and chromosome aberrations and that high-LET heavy-ion induced mutants can be irreversible. Chromosome translocations and deletions are common in cells irradiated by heavy particles, and ionizing radiations are effective in causing hyperploidy. The importance of the genetic changes in the evolution of life is an interesting question. Through evolution, there is an increase of DNA content in cells from lower forms of life to higher organisms. The DNA content, however, reached a plateau in vertebrates. By increasing DNA content, there can be an increase of information in the cell. For a given DNA content, the quality of information can be changed by rearranging the DNA. Because radiation can cause hyperploidy, an increase of DNA content in cells, and can induce DNA rearrangement, it is likely that the evolution of life on Mars will be effected by its radiation environment. A simple analysis shows that the radiation level on Mars may cause a mutation frequency comparable to that of the spontaneous mutation rate on Earth. To the extent that mutation plays a role in adaptation, radiation alone on Mars may thus provide sufficient mutation for the evolution of life.

Nuclear DNA changes within Helianthus annum L.: changes within single progenies and their relationships with plant development

The variations in the basic nuclear DNA content, which previous results indicated to occur within one and the same progeny of Helianthus annuus, were studied in detail and correlated with certain developmental features of the plants. The size and organization of the genome of seedlings obtained from seeds (achenes) collected at the periphery (P-seedlings) or in the middle (M-seedlings) of the flowering heads of plants belonging to a line selfed for 10 years were compared. Cytophotometric determinations indicated that the nuclear DNA content of P-seedlings is 14.7% higher than that of M-seedlings. Thermal denaturation and reassociation kinetics of extracted DNAs showed that variations in the redundancy of repetitive DNA, in particular of a family of medium repeated sequences with a Cot range of 2-100, account for the differences in genome size. These findings were confirmed by the results of molecular hybridizations (slot blots), which also indicated a higher amount of ribosomal DNA in the P-seedlings than in the M-seedlings. Cell proliferation is affected by DNA content, and mitotic cycle time is 1h30' longer in the P-seedlings. By studying mature plants, positive correlations were also found between genome size and both the surface area of leaf epidermal cells (P≤0.01) and flowering time (P≤0.001). It is suggested that the variations of nuclear DNA content and organization observed play a role in determining developmental variability in plant populations, which may be of importance in buffering the effects of changing environmental conditions.

DNA variations in regenerated plants of pea (Pisum sativum L.)

The aim of this study was to determine whether DNA variations could be detected in regenerated pea plants. Two different genotypes were analyzed by cytogenetic and molecular techniques: the "Dolce Provenza" cultivar and the "5075" experimental line. "Dolce Provenza" regenerated plants showed a reduction in DNA content, particularly at the level of unique sequences and ribosomal genes. Moreover, regeneration was associated with an increase in DNA methylation of both internal and external cytosines of the CCG sequence. On the other hand, the DNA content of the "5075" line remained stable after regeneration. DNA reduction was found only in "5075" plants regenerated from callus cultures maintained for long incubation periods (about a year). The DNA variations observed are discussed both in relation to the genotype source and the role of tissue-culture stress.

Differences in membrane electrical properties between C3H 10T1/2 mouse embryo fibroblasts and their ionizing radiation and chemically transformed counterparts

Membrane electrical properties of mouse embryo fibroblasts and their ionizing radiation and chemically transformed counterparts were investigated using dielectric relaxation measurements in the radio frequency range. This determination is possible because, in the radio frequency range, suspensions of cells in an electrolyte buffer show a conductivity dispersion due to interfacial polarization. An analysis of the experimental data based on a "single-shell" model showed that conductivity and permittivity of the membranes of both radiation and chemically transformed fibroblasts were lower than in normal cells. In addition, the conductivity of the cytoplasm was higher in both transformed cell types than in the normal mouse fibroblasts. We discuss the significance of these findings in view of the possible structural and functional modifications brought about by the process of neoplastic transformation.

Genetic changes in mammalian cells transformed by helium ions

Midterm Syrian Hamster embryo (SHE) cells were employed to study high LET-radiation induced tumorigenesis. Normal SHE cells (secondary passage) were irradiated with accelerated helium ions at an incident energy of 22 MeV/u (9-10 keV/micrometer). Transformed clones were isolated after growth in soft agar of cells obtained from the foci of the initial monolayer plated postirradiation. To study the progression process of malignant transformation, the transformed clones were followed by monolayer subculturing for prolonged periods of time. Subsequently, neoplasia tests in nude mice were done. In this work, however, we have focused on karyotypic changes in the banding patterns of the chromosomes during the early part of the progressive process of cell transformation for helium ion-induced transformed cells.

Differences in membrane order between C3H 10 T1/2 cells and their transformed counterparts as measured by EPR

Membrane order of mouse embryo fibroblasts and their ionizing radiation and chemically transformed counterparts was investigated using EPR spectroscopy after labeling the membrane of the cells with the fatty acid spin label, 5-nitroxy stearic acid. The EPR spectra were recorded at temperatures ranging from 18 to 38 degrees C for both control and transformed cells. The distance between the outer hyperfine splitting (2T' parallel), which is used as indicator of membrane order, varies in these two cell types. Below 28 degrees C. 2T' parallel is higher in transformed fibroblasts than in normal cells, whereas above this temperature membrane order is the same. Lipid analysis as carried out by the measurement of the cholesterol/membrane proteins and sphingomyelin/lecithin ratios, showed no difference in the amounts of the main membrane rigidifiers. These findings suggest that cell transformation of mouse fibroblasts induced by radiation or chemicals may produce alterations in the cell membrane, as evidenced by variations in its order at low temperature. These measured differences are presumably not attributable to its fatty acids composition but to its glycoproteins content, since changes in membrane rigidifiers were not observed between normal and transformed cells.

Efficacy and acceptability of transdermal estradiol in the treatment of postmenopausal bone loss

In order to assess the effects and acceptability of transdermal estradiol on the prevention of the loss of bone mass, the Authors administered transdermal estradiol (ETTS 50 mcgr/day) for 3 weeks and, cyclically, medroxyprogesterone 10/mg/day from day 10 to day 21 of each cycle for 12 months, to 20 operated patients for bilateral ovariectomy. Primary markers of the bone turnover (hydroxyproline urinary, osteocalcin, PTH) were estimated before therapy and after 3, 6, 9, 12 months. The BMD was evaluated before therapy and after 6 and 12 months. Our study clearly shows that the transdermal administration of estradiol prevents the postmenopausal bone loss, also in postmenopausal women at higher risk of developing osteoporosis as those evaluated in our study.

Repair of potentially lethal damage by introduction of T4 DNA ligase in eucaryotic cells

The bacterial enzyme PvuII, which generates blunt-ended DNA double-strand breaks, and T4 DNA ligase, which seals adjacent DNA fragments in coupling to ATP cleavage, were introduced in mouse C3H10T1/2 fibroblasts using osmolytic shock of pinocytic vesicles. Cells were then assayed for their clonogenic ability. In agreement with previous studies by others, we find that the PvuII restriction endonuclease simulates ionizing radiation effects by causing a dose-dependent loss of reproductive capacity. Here we show that the concomitant treatment with DNA ligase considerably increases cell survival. Survival curves were shown to be dependent on the ligase enzyme dose and on ATP concentration in the hypertonic medium. We conclude that T4 DNA ligase is able to repair some of the potentially lethal damage produced by restriction endonucleases in eucaryotic cells.

Modulation of membrane potential in algal cells by temperature gradients. A thermodynamic approach

The aim of the present study is to ascertain whether transmembrane temperature gradients couple with transport of electric charge in living cells of Valonia utricularis and eventually measure the thermodynamic coupling coefficient (s). Simple experimental procedures are described that allow generation of temperature gradients of predetermined sense and intensity across the cell membrane. Simultaneous measurement of the potential difference is ensured by standard electrophysiological methods. The mathematical expressions that allow quantitative treatment of experimental results are indicated in the article and are based on standard nonequilibrium thermodynamic and electrophysiological formalism. The value of the coupling coefficient between temperature gradient and flow of electric charge is indicated and concisely discussed in terms of possible mechanisms of ionic membrane transport.

Non-random alkylation of DNA sequences induced in vivo by chemical mutagens

Previous studies of the interaction of alkylating agents on the eukaryotic genome support the idea that induction of DNA adducts is at specific genomic sites. Here we show molecular and cytological evidence that alkylation is rather specific. Mammalian cell cultures were exposed to different doses of mutagens and the DNA was analyzed by density gradient ultracentrifugation, hydroxylapatite fractionation, and by restriction enzyme analysis. Studies with the labelled mutagens N-ethyl-N-nitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine show that there is a non-random distribution of the adducts. The adducts are found more frequently in A-T, G-C rich satellite DNA and highly repetitive sequences. Analysis with restriction enzymes shows that both methyl and ethyl groups influence the restriction patterns of the enzymes HpaII and MspI that recognize specific endogenous DNA methylation. These data suggest, as a subsequent mechanism, a modification in the pattern of the normal endogenous methylation of 5-methylcytosine.

5-azacytidine-induced tumorous transformation and DNA hypomethylation in Nicotiana tissue cultures

The phenomenon of habituation is considered in plant tissue cultures to be a real process of chemical tumorogenesis; the cultures acquire the capacity of autonomous growth in a hormone-free medium under the influence of a variety of chemical and physical agents. Treatments with 5-azacytidine (AzaC) of in vitro cultured cells of the Nicotiana glauca x N. langsdorffii nontumorous hybrid (NNT) during the culture cycle led to the induction of a habituated phenotype. The repetitive DNA sequences showed a significant lower level of endogenous methylation in the treated cells in comparison with the normal ones. It is worth noting that it was impossible until now to habituate this strain by conventional methods and that the treatments were effective only in the first 5 days of subculturing; various evidence (cytological and biochemical) pointed out a phenomenon of DNA amplification, occurring in the same period. Moreover, analysis of DNA from control and treated cells shows the induction of variations in the endogenous methylation pattern by AzaC in a critical period of cell culture. These results suggest that demethylation can act as a switch from hormone-dependent to autonomous proliferation by activation of genes coding for or regulating the synthesis of growth factors.

Distribution of 5-methylcytosine-rich regions in the polytene chromosomes of Phaseolus coccineus embryo suspensor as shown by the immunoperoxidase technique

5-Methylcytosine (5-mC) has been visualized in polytene chromosomes of Phaseolus coccineus, scarlet bean using specific antibodies to 5-mC and the immunoperoxidase technique. The results obtained indicate that most heterochromatic regions are methylated, even though the frequency of methylation is highly variable and sometimes low. A preferential binding of anti-5-mC to centromeric heterochromatic blocks was observed. Comparison between anti-5-mC binding and the results of hybridization with highly repetitive DNA and satellite DNA shows, moreover, that centrometric heterochromatic regions hybridize in particular with both DNAs. This finding is consistent with the fact that repetitive DNA and satellite DNA are methylated to a considerably greater extent than main band DNA, in line with many data to be found in the literature. The binding pattern of anti-5-mC that we observed also suggests that methylation does not occur in all classes of repetitive DNA. The high variability of band methylation frequency is discussed in relation to a possible characteristic DNA composition of the band.

5'-Methyl-cytosine in the macronuclear DNA of Blepharisma japonicum

Brief report on the presence of 5'-methyl-cytosine as a minor base (0.56%) in the macronuclear DNA of the ciliate protozoan Blepharisma japonicum. The evidence comes from electrophoresis of macronuclear DNA digested by appropriate restriction endonucleases and high-performance liquid chromatography.