Chromosome Aberrations In Human Cells Research Articles

RITCARD: Radiation-Induced Tracks, Chromosome Aberrations, Repair and Damage.

Chromosome aberrations (CAs) are one of the effects of radiation exposure and can have implications for human health in the space environment, since they are related to cancer risk. In radiation research, chromosome aberrations are a convenient biomarker for carcinogenesis. To shed light on the formation and quality of chromosome aberrations in the space environment, many experiments and simulations have been performed using chromosome aberrations in human cells, induced by heavy ions, which are present in galactic cosmic rays (GCRs). In this work, the new simulation program, radiation-induced tracks, chromosome aberrations, repair and damage (RITCARD), is presented. This software program is based on the algorithm used in the NASA Radiation Track Image (NASARTI) model with some improvements. NASARTI and RITCARD are both comprised of four parts: a random walk (RW) algorithm for simulating chromosomes in a nucleus; a deoxyribonucleic acid (DNA) damage algorithm; a break repair process; and a function to assess and count chromosome aberrations. Prior to running RITCARD, the code, relativistic ion tracks (RITRACKS), is used to simulate detailed radiation track structure and calculate time-dependent differential voxel dose maps in a parallelepiped centered on a cell nucleus. The RITCARD program reads the pre-calculated voxel dose and locates the intersections between the voxels and the chromosomes that were simulated by random walk. Radiation-induced breaks occur strictly at these intersections with a probability that is a function of the voxel dose. When a break occurs in the random walk, the corresponding chromosome piece is cut into two fragments where each has a free end at the position of the break. RITCARD generates a collection of all fragments, free ends, and enlists free end pairs. In the next step, the algorithm simulates the time-dependent rejoining of free end pairs, using different probabilities for pairs originating from a given break (proper) or from different breaks (improper), which results in the formation of fragment sequences. By grouping these sequences, the program determines the number and types of aberrations, based on the same criteria used in our experiment. The new program is used to assess the yields of various types of chromosome aberrations in human fibroblast cells for several ions (1H+, 4He2+, 12C6+, 16O8+, 20Ne10+, 28Si14+, 48Ti22+ and 56Fe26+) with energies varying from 10 to 1,000 MeV/n. The results show linear and linear-quadratic dose dependence for most chromosome aberrations types. The calculation results were compared with those obtained by fluorescence in situ hybridization (FISH) experiments that were performed by our group. The simulations and experiments are in better agreement at lower LET. Regarding the simulation results, the coefficient of the linear part of the dose-dependence curve also peaks at an LET value of approximately 100 keV/lm, which evokes a relative biological effectiveness (RBE) peak found by other researchers.

Chromosomal Aberration Study of Human Lymphocytes exposed to Americium -241 in vitro

This study was intended to decide the impact of ?-partcales for acceptance of chromosome deviation. The venous blood sample was drawn from 30 years old healthy male donor. The blood sample after cultured in RPMI was divided into two groups, the first was as control and the second was exposed to radiation from Am-241 to detect the effect of it on chromosomal aberration (CA). The cultures exposed to Am-241 have dicentric (52.8%), breaks (20%) , fragments(18.5%) and (6.8%) ring chromosomes . There was significant differences (p ? 0.5 ) compared with control sample. Dicentric show high percentage of chromosomal aberration compared with other CA. The mean of mitotic index (MI) and stander deviation was (2.212±2.236) for radiation exposed sample higher than that of control was(1.565±1.581). It has been concluded the exposure to low ?-particales could caused chromosomal aberrations in human cells.

The Modifying Effect of Co-Mutagens on the Frequency and Spectrum of Radiation-Induced Chromosome Aberrations in Human Cells

We have studied the co-mutagenic effect of verapamil and ascorbic acid on formation of radiation-induced chromosomal aberrations in T-lymphocytes of peripheral blood (PBL) of healthy donors. Test system of PBL treated in vitro with subsequent metaphase analysis of chromosomal aberrations has been used. Cells were exposed to γ-ray radiation in G0- and G2- periods of cell cycle and treated with verapamil (1.5; 2 and 4.0 μg/ml of blood) and ascorbic acid (20; 40 and 80 μg/ml of blood). The post-irradiation treatment of PBL with ascorbic acid in concentrations of 40 and 80 μg/ml, which exceeded therapeutic concentration value 2 and 4 times, increased overall chromosome aberrations frequency in 1.4 times compared to low dose (0.3 Gy) radiation effect. Verapamil at a concentration of 4.0μg/ml also increased the damaging effect of low dose of radiation in 1.5 times. Modification of radiation-induced cytogenetic effects in human PBL treated with co-mutagens was dependent on the concentration of the drugs, the absorbed dose of radiation, as well as cell radiosensitivity. It could be concluded that high concentrations of comutagens potentiate the damaging effect of low doses of ionizing radiation.

Track structure based modelling of chromosome aberrations after photon and alpha-particle irradiation

A computational model of radiation-induced chromosome aberrations in human cells within the PARTRAC Monte Carlo simulation framework is presented. The model starts from radiation-induced DNA damage assessed by overlapping radiation track structures with multi-scale DNA and chromatin models, ranging from DNA double-helix in atomic resolution to chromatin fibre loops, heterochromatic and euchromatic regions, and chromosome territories. The repair of DNA double-strand breaks via non-homologous end-joining is followed. Initial spatial distribution and complexity, diffusive motion, enzymatic processing, synapsis and ligation of individual DNA ends from the breaks are simulated. To enable scoring of different chromosome aberration types resulting from improper joining of DNA fragments, the repair module has been complemented by tracking the chromosome origin of the ligated fragments and the positions of centromeres. The modelled motion of DNA ends has sub-diffusive characteristics and corresponds to measured chromatin mobility within time-scales of a few hours. The calculated formation of dicentrics after photon and α-particle irradiation in human fibroblasts is compared to experimental data (Cornforth et al., 2002, Radiat Res 158, 43). The predicted yields of dicentrics overestimate the measurements by factors of five for γ-rays and two for α-particle irradiation. Nevertheless, the observed relative dependence on radiation dose is correctly reproduced. Calculated yields and size distributions of other aberration types are discussed. The present work represents a first mechanistic approach to chromosome aberrations and their kinetics, combining full track structure simulations with detailed models of chromatin and accounting for the kinetics of DNA repair.

Biological Effectiveness of Accelerated Particles for the Induction of Chromosome Damage: Track Structure Effects

We have investigated how radiation quality affects the induction of chromosomal aberrations in human cells. Human lymphocytes were irradiated in vitro with various energies of accelerated high charge and energy (HZE) particles including oxygen, neon, silicon, titanium and iron. Chromosome damage was assessed using three-color FISH chromosome painting in chemically induced premature chromosome condensation samples collected at first cell division after irradiation. The LET values for these particles ranged from 30 to 195 keV/μm, and their energies ranged from about 55 MeV/u to more than 1,000 MeV/u. The 89 and 142 MeV/u neon particles produced the most simple-type reciprocal exchanges per unit dose. For complex-type exchanges, 64 MeV/u neon and 450 MeV/u iron were equally effective and induced the greatest amount of complex damage. Track structure models predict that at a fixed value of LET, particles with lower charge number (Z) will have a higher biological effectiveness compared to particles with a higher Z, and that a saturation cross section will be observed for different radiation qualities. Our results are consistent with model expectations within the limitation of experimental error, and provide the most extensive data that have been reported on the radiation quality dependences of chromosomal aberrations.

Computational Model of Chromosome Aberration Yield Induced by High- and Low-LET Radiation Exposures

We present a computational model for calculating the yield of radiation-induced chromosomal aberrations in human cells based on a stochastic Monte Carlo approach and calibrated using the relative frequencies and distributions of chromosomal aberrations reported in the literature. A previously developed DNA-fragmentation model for high- and low-LET radiation called the NASARadiationTrackImage model was enhanced to simulate a stochastic process of the formation of chromosomal aberrations from DNA fragments. The current version of the model gives predictions of the yields and sizes of translocations, dicentrics, rings, and more complex-type aberrations formed in the G(0)/G(1) cell cycle phase during the first cell division after irradiation. As the model can predict smaller-sized deletions and rings (<3 Mbp) that are below the resolution limits of current cytogenetic analysis techniques, we present predictions of hypothesized small deletions that may be produced as a byproduct of properly repaired DNA double-strand breaks (DSB) by nonhomologous end-joining. Additionally, the model was used to scale chromosomal exchanges in two or three chromosomes that were obtained from whole-chromosome FISH painting analysis techniques to whole-genome equivalent values.

Thresholds for indirect DNA damage across cellular barriers for orthopaedic biomaterials

Cobalt–chromium particles and ions can induce indirect DNA damage and chromosome aberrations in human cells on the other side of a cellular barrier in tissue culture. This occurs by intercellular signalling across the barrier. We now show that the threshold for this effect depends on the metal form and the particle composition. Ionic cobalt and chromium induced single strand breaks at concentrations equivalent to those found in the blood of patients with well functioning metal on metal hip prostheses. However, they only caused double strand breaks if the chromium was present as chromium (VI), and did not induce chromosome aberrations. Nanoparticles of cobalt–chromium alloy caused DNA double strand breaks and chromosome aberrations, of which the majority were tetraploidy. Ceramic nanoparticles induced only single strand breaks and/or alkaline labile sites when indirectly exposed to human fibroblasts. The assessment of reproductive risk from maternal exposure to biomaterials is not yet possible with epidemiology. Whilst the barrier model used here differs from the in vivo situation in several respects, it may be useful as a framework to evaluate biomaterial induced damage across physiological barriers.

The Fanconi anemia core complex is required for efficient point mutagenesis and Rev1 foci assembly

Fanconi anemia (FA) is a chromosome instability syndrome characterized by congenital abnormalities, cellular hypersensitivity to DNA crosslinking agents, and heightened cancer risk. Eight of the thirteen identified FA genes encode subunits of a nuclear FA core complex that monoubiquitinates FANCD2 and FANCI to maintain genomic stability in response to replication stress. The FA pathway has been implicated in the regulation of error-prone DNA damage tolerance via an undefined molecular mechanism. Here, we show that the FA core complex is required for efficient spontaneous and UVC-induced point mutagenesis, independently of FANCD2 and FANCI. Consistent with the observed hypomutability of cells deficient in the FA core complex, we also demonstrate that these cells are impaired in the assembly of the error-prone translesion DNA synthesis polymerase Rev1 into nuclear foci. Consistent with a role downstream of the FA core complex and like known FA proteins, Rev1 is required to prevent DNA crosslinker-induced chromosomal aberrations in human cells. Interestingly, proliferating cell nuclear antigen (PCNA) monoubiquitination, known to contribute to Rev1 recruitment, does not require FA core complex function. Our results suggest a role for the FA core complex in regulating Rev1-dependent DNA damage tolerance independently of FANCD2, FANCI, and PCNA monoubiquitination.

Genotoxic effects of particles of surgical cobalt chrome alloy on human cells of different age in vitro

Humans are exposed to metals from industry, the environment and from wear debris from worn orthopaedic joint replacements. Patients exposed to worn cobalt chrome hip replacements show an increase of chromosome aberrations in the bone marrow adjacent to the implant and an increase of chromosome translocations and aneuploidy in the peripheral blood. This study has tested whether particles of surgical cobalt chrome alloy are able to induce similar DNA damage and chromosome aberrations in human cells in vitro. Because increasingly young patients are receiving hip replacements it has also tested whether the response is altered at different cellular age in vitro. Primary human fibroblasts, were tested at different pre senescent population doublings (PD10 (young) and PD35 (older)) to particles of cobalt chrome alloy for up to 15 days. As in patients there was an increase of aneuploidy, chromosome translocations and DNA damage after exposure to the cobalt chrome particles in vitro. The overall level of DNA damage and numerical and structural aberrations was approximately the same in young and older cells. However, the cellular reaction to the DNA damage was different. Older cells showed a greater loss of viability and induction of senescence and a lesser rate of mitosis and cell growth than young cells. They showed less change in transcription, particularly of p38 and caspase 10 mRNA levels, than young cells. They showed more complex aneuploidy in association with unseparated or prematurely separated chromatids. This study suggests that at least part of the chromosome changes in patients with worn implants may be due to direct effects of the metal wear particles from the implant. It would be of interest to test whether the altered reaction of the human cells at different in vitro age might correspond with a different incidence of chromosome aberrations in patients at different ages.

Probing the chromosome 9p21 region susceptible to DNA double-strand breaks in human cells in vivo by restriction enzyme transfer

A restriction enzyme, MspI, was introduced into cultured human cells as a probe to detect genomic regions susceptible to DNA double-strand breaks (DSBs). A 2 h exposure to MspI at a concentration of 8 U/mul produced DSBs at MspI sites in more than 80% of HeLa cells. The sensitivity to digestion was examined on chromosomal DNAs for the region containing the p16 tumor suppressor gene and two other related genes, p14ARF and p15, by Southern blot hybridization analysis and linker-mediated capture of DNA fragments digested in vivo. DNAs for the promoter regions of the three genes, respectively, were sensitive to MspI digestion in HeLa cells, while DNA for the p16 promoter region was less sensitive in lung cancer cells with hypermethylation of the region. Breakpoints for interstitial 9p21 deletions removing the p16/p14ARF/p15 locus in a variety of human cancers were significantly over-represented in the three sensitive regions. The results suggest that the MspI sensitivity in vivo of each genomic region reflects its susceptibility to DSBs that trigger chromosome aberrations in human cells. This method could help us understand the pathogenic significance of differential susceptibility to DSBs among genomic regions in human carcinogenesis.

DNA adducts from acetaldehyde: implications for alcohol-related carcinogenesis

Alcoholic beverage consumption is classified as a known human carcinogen, causally related to an increased risk of cancer of the upper gastrointestinal tract. The formation of acetaldehyde from ethanol metabolism seems to be the major mechanism underlying this effect. Acetaldehyde is carcinogenic in rodents and causes sister chromatid exchanges and chromosomal aberrations in human cells. The best-studied DNA adduct from acetaldehyde is N 2 -ethyl-2′-deoxyguanosine, which is increased in liver DNA obtained from ethanol-treated rodents and in white blood cells obtained from human alcohol abusers. However, the carcinogenic relevance of this adduct is unclear in view of the lack of evidence that it is mutagenic in mammalian cells. A different DNA adduct, 1, N 2 -propano-2′-deoxyguanosine (PdG), can also be formed from acetaldehyde in the presence of histones and other basic molecules. PdG has been shown to be responsible for the genotoxic and mutagenic effects of crotonaldehyde. The PdG adduct can exist in either of two forms: a ring-closed form or a ring-opened aldehyde form. Whereas the ring-closed form is mutagenic, the aldehyde form can participate in the formation of secondary lesions, including DNA–protein cross-links and DNA interstrand cross-links. The formation of these types of complex secondary DNA lesions resulting from PdG may explain many of the observed genotoxic effects of acetaldehyde described above. Repair of PdG and its associated adducts is complex, involving multiple pathways. Inherited variation in the genes encoding the proteins involved in the repair of PdG and its secondary adducts may contribute to susceptibility to alcoholic beverage–related carcinogenesis.

Interstitial telomeric repeats are not preferentially involved in radiation-induced chromosome aberrations in human cells

Telomeric repeat sequences, located at the end of eukaryotic chromosomes, have been detected at intrachromosomal locations in many species. Large blocks of telomeric sequences are located near the centromeres in hamster cells, and have been reported to break spontaneously or after exposure to ionizing radiation, leading to chromosome aberrations. In human cells, interstitial telomeric sequences (ITS) can be composed of short tracts of telomeric repeats (less than twenty), or of longer stretches of exact and degenerated hexanucleotides, mainly localized at subtelomeres. In this paper, we analyzed the radiation sensitivity of a naturally occurring short ITS localized in 2q31 and we found that this region is not a hot spot of radiation-induced chromosome breaks. We then selected a human cell line in which approximately 800 bp of telomeric DNA had been introduced by transfection into an internal euchromatic chromosomal region in chromosome 4q. In parallel, a cell line containing the plasmid without telomeric sequences was also analyzed. Both regions containing the transfected plasmids showed a higher frequency of radiation-induced breaks than expected, indicating that the instability of the regions containing the transfected sequences is not due to the presence of telomeric sequences. Taken together, our data show that ITS themselves do not enhance the formation of radiation-induced chromosome rearrangements in these human cell lines.

Oncogenic transformation by BK virus and association with human tumors.

BK virus (BKV), a human polyomavirus closely related to JC virus and Simian Virus 40, is ubiquitous in human populations worldwide. After primary infection, BKV establishes a lifelong latent infection in many organs. BKV transforms rodent cells to the neoplastic phenotype and is highly oncogenic in rodents. This review considers the oncogenic potential of BKV in humans and its possible involvement in human tumors. BKV sequences and T antigen (Tag) are detected in several types of human neoplasms, although the viral load is generally low, with less than one copy of the viral genome per cell. The possible causative role of BKV in human oncogenesis rests on the ability of BKV Tag to inactivate the functions of tumor suppressor proteins p53 and pRB family as well as on its ability to induce chromosomal aberrations in human cells. A 'hit and run' mechanism and secretion of paracrine growth factors by BKV Tag-positive cells, recruiting into proliferation neighboring and distant cells, are discussed as possible BKV pathogenic elements in human oncogenesis.

Phenolphthalein induces chromosome aberrations in human and Chinese hamster liver cells (CHEL) cultured in vitro.

Phenolphthalein is a nonprescription laxative agent that has been widely used during this century. Recent studies in animal models have shown that phenolphthalein has carcinogenic activity. In order to assess cytogenetic effects on human cells in vitro, we tested phenolphthalein in a chromosome aberration assay in human embryo cells derived from amniotic fluid. Our results show that phenolphthalein induces a significant increase in the frequency of chromosome aberrations in human cells. The lowest dose level at which the clastogenic effect is evident is 23.2 microg/ml. Similar positive results were obtained in a Chinese hamster liver cell line, which is metabolically competent to activate different classes of promutagens and procarcinogens into biologically active metabolites. Instead, parallel experiments in Chinese hamster ovary cells did not show any clastogenic effect due to phenolphthalein. These latter data suggested that phenolphthalein acts as a promutagen and must be metabolically activated to exert its clastogenic effect. Teratogenesis Carcinog. Mutagen. 20:209-217, 2000.

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.

No increases in chromosome aberrations in human diploid fibroblasts following exposure to low concentrations of sodium fluoride for long times

To study whether exposure to fluoride at low concentrations for long times induces chromosome aberrations in human cells, human diploid fibroblasts in the quiescent phase were treated with sodium fluoride (NaF) at 1–10 μg/ml (equivalent to fluoride ion at 0.45–4.5 ppm) for 1–3 weeks. Quienscent cells were obtained by a 10-day culture in medium containing 1% serum following overnight incubation of cells in the logarithmic phase. Significant levels of cytotoxicity, as determined by a decrease in the number of cells, were not induced by treatment of the cells with NaF at 5 or 10 μg/ml for 1–3 weeks. No increase in the frequency of chromosome aberrations was elicited in cultures treated for 1–3 weeks with NaF over the range of doses examined. In contrast, a dose-dependent increase in the frequency of chromosome aberrations was observed in cultures treated with N-methyl- N′-nitro- N-nitrosoguanidine, used as a positive control. The results indicate that fluoride might be not clastogenic to human fibrobalsts when exposed at low levels, equivalent to those in the communal water supplies.

The Microdosimetric Regularities of Nanometre Regions

Abstract Regions with nanometre dimensions differ greatly from micrometre regions with regard to the contribution of delta rays to the fluctuation of energy deposition, because the fraction of delta rays escaping from their region of origin increases with decreasing size of the region. Under these geometric conditions, the delta ray term of the distribution of energy deposition in a nanometre region traversed by a primary particle is essentially determined by low energy delta rays originating and stopping within the region. This distribution is found to be practically independent of the mass and energy of the primary particle. The remaining primary-particle-dependent variable determining the fluctuation of energy deposition in the nanometre region is linear primary ionisation density or its energy equivalent, restricted LET. Restricted LET should therefore have the properties of a characteristic parameter of radiation quality. This fundamental conclusion is proven by evaluating the predictive potential of restricted LET for energy deposition fluctuation of electrons, protons and alpha particles in nanometre targets, and with regard to the yield coefficient a for radiation-induced chromosome aberrations in human cells. Methods for the determination of restricted LET are discussed briefly.

Definition of adenovirus type 5 functions involved in the induction of chromosomal aberrations in human cells

Infection of human embryonic kidney cells with adenovirus type 5 (Ad5) induces aberrations (gaps and breaks) in the cell chromosomes. We have conducted a study utilizing a large number of Ad5 mutants to identify the viral functions that are responsible for the occurrence of cytogenetic damage. The results of our investigation have indicated that expression of the gene products of the Ad5 early region 1A (E1A) is necessary for the induction of chromosomal aberrations and that other early viral gene products do not appear to contribute to this phenotype. We have also shown that expression of both the major E1A gene products, the 243 amino acid and the 289 amino acid proteins, is required for induction of damage at wild-type levels, although the 289 amino acid protein appears to retain detectable activity on its own. Lastly, we have observed that deletions in the amino-terminal region of the E1A proteins and in the transactivating domain of the 289 amino acid protein prevent the occurrence of cytogenetic damage, whereas mutations elsewhere in the proteins do not affect this process.

A modified host-mediated assay using cultured human lymphoid cells in diffusion chambers in mice and cytogenetic effects of cyclophosphamide

A modified host-mediated assay system using cultured human lymphoid cells as target cells is described. The human cells were cultured in diffusion chambers (DC) and implanted into C 3H St mice. Induction of chromosome aberrations in human cells in DC as well as host bone marrow cells was used as an index of mutagenicity of a given compound and its metabolites. The cells from six human lymphoid lines were studied for their growth potential in DC in mice. Cells from two lines, both derived from blood of normal persons, failed to grow. The other four lines proliferated well. The maximum number of cells per DC was reached from 3 to 5 days after implantation and the maximum cell density per DC varied from 4 to 15 times the initial cell concentration. The mitotic index in DC was high on the first and second days and then decreased gradually. There were mitoses in some DC more than 2 weeks after implantation. Cells from DC which had been in hosts for approximately 2 weeks were recultured. Several such cultures proliferated within a week. Cytogenetic effects of cyclophosphamide (CY) in cells from two lines in DC in mice and in host bone marrow were investigated. A high rate of human and mouse cells with chromosome aberrations caused by CY injection was observed.

Suppressive activity by fluoride on the induction of chromosome aberrations in human cells with alkylating agents in vitro

Suppressive activity by fluoride on the induction of chromosome aberrations in human cells with alkylating agents in vitro