Recent developments in the assessment of chromosomal damage

Assessment of genotoxic potential of the treated hospital wastewater using cytogenetic assays

The cytogenetic study using hospital effluent was carried out engaging three cytogenetic end points—chromosomal aberration (CA) assay, mitotic indices (MIs), and micronucleus (MN) Analysis. These bioassays were performed in hematopoietic bone marrow cells of Mus musculus. The experiment commenced with the collection of hospital effluent from the final outlet when wastewater gets collected after undergoing treatment by a multistep process. The pure treated sample water was collected at different times between March 2019 to January 2020 and was given ad libitum to mice at its low (90% dilution) and high (pure form), i.e. 100% concentration for 3 different durations i.e. 7, 15, and 30 days, respectively. The results indicated a significant (P < 0.01) decrease in the MI in all the groups but was more pronounced in the group which was given 100% concentrated sample water collected in the month of March 2019. Besides this, the major finding was presence of CAs like breaks, fragments, rings, and pulverization in bone marrow cells in different groups; however, the frequency of these aberrations varied from group to group. A significant (P < 0.01) increase in MN Induction and decreased ratio (P < 0.01) of polychromatic to normonochromatic erythrocytes were observed in samples collected in month of March both at 10% and 100% concentrations. However, decrease in the ratio was observed in the samples of September and January at low-concentration sample water. The results thus indicated that there was some lacuna in the treatment process earlier in the month of March, which was rectified to some extent in the subsequent months. Hence, the treated wastewater collected in the month of January next year was more suitable for its use than other samples. Summary: These findings thus draw attention toward ensuring efficiency of the treatment plant and quality of water by the hospital management before it being disposed off into the municipal supply; a step that can help society to live a healthy life. With these findings, it is conveyed that all the hospitals, diagnostic labs, and other health care establishments must pay utmost attention at liquid waste disposal mechanism to make environment pollution-free.

Fluoride and endosulfan together potentiate cytogenetic effects in Swiss albino mice bone marrow cells

In this study, the cytotoxic potential of fluoride and endosulfan in combination was investigated in Swiss albino mice bone marrow cells using the chromosomal aberration (CA) and micronucleus (MN) test systems. Fluoride (25.1 mg kg^-1 body weight [bw] in water) and endosulfan (1.8 mg kg^-1 bw by oral intubation) were administered orally alone and in combination (fluoride 25.1 mg kg^-1 bw + endosulfan 1.8 mg kg^-1 bw) to male Swiss albino mice daily for 30 days. A significant (p < 0.01) increase in micronuclei (MNs) induction and decreased ratio (p < 0.01) of polychromatic to normonochromatic erythrocytes (indicators of cytotoxicity) were observed compared with saline controls when animals were given the combination of fluoride and endosulfan. A significant (p < 0.01) increase in MNs induction and no change in the polychromatic erythrocytes to erythrocyte ratio were also observed when endosulfan was given alone. CAs such as gaps, breaks, fragments, rings, exchanges, and polyploidy were recorded in the bone marrow cells. The mean percent frequency of CAs was increased (p < 0.01) in all the treated groups compared with the control saline group. In the combination group (F + E), the percent frequencies of CAs were significantly higher (13.875%) compared with those in the individual treatment groups of fluoride (4.375%) and endosulfan (6.25%). The mitotic index was calculated as percentage of dividing cells. A significant (p < 0.01) decrease in mitotic index was observed in all treated groups compared with controls. In the combination group (F + E), mitotic index was significantly less than (p < 0.01; 4.1 ± 0.49) the saline control (10.8 ± 0.98). These results indicated that repeated intake of endosulfan through various sources in fluoride affected areas resulted in increased cytotoxic effects. The greater effect in the combination group indicated additive interaction of fluoride and endosulfan in inducing cytotoxicity in Swiss albino mice.

Use of human lymphocyte G0 PCCs to detect intra- and inter-chromosomal aberrations for early radiation biodosimetry and retrospective assessment of radiation-induced effects

A sensitive biodosimetry tool is required for rapid individualized dose estimation and risk assessment in the case of radiological or nuclear mass casualty scenarios to prioritize exposed humans for immediate medical countermeasures to reduce radiation related injuries or morbidity risks. Unlike the conventional Dicentric Chromosome Assay (DCA), which takes about 3–4 days for radiation dose estimation, cell fusion mediated Premature Chromosome Condensation (PCC) technique in G0 lymphocytes can be rapidly performed for radiation dose assessment within 6–8 hrs of sample receipt by alleviating the need for ex vivo lymphocyte proliferation for 48 hrs. Despite this advantage, the PCC technique has not yet been fully exploited for radiation biodosimetry. Realizing the advantage of G0 PCC technique that can be instantaneously applied to unstimulated lymphocytes, we evaluated the utility of G0 PCC technique in detecting ionizing radiation (IR) induced stable and unstable chromosomal aberrations for biodosimetry purposes. Our study demonstrates that PCC coupled with mFISH and mBAND techniques can efficiently detect both numerical and structural chromosome aberrations at the intra- and inter-chromosomal levels in unstimulated T- and B-lymphocytes. Collectively, we demonstrate that the G0 PCC technique has the potential for development as a biodosimetry tool for detecting unstable chromosome aberrations (chromosome fragments and dicentric chromosomes) for early radiation dose estimation and stable chromosome exchange events (translocations) for retrospective monitoring of individualized health risks in unstimulated lymphocytes.

History and evolution of cytogenetic techniques: Current and future applications in basic and clinical research

Chromosomes are the vehicles of genes, which are the functional units of a cell's nucleus. In humans, there are more than 20,000 genes that are distributed among 46 chromosomes in somatic cells. The study of chromosome structure and function is known as cytogenetics which is historically a field of hybrid science encompassing cytology and genetics. The field of cytogenetics has undergone rapid developments over the last several decades from classical Giemsa staining of chromosomes to 3-dimensional spatial organization of chromosomes with a high resolution mapping of gene structure at the nucleotide level. Improved molecular cytogenetic techniques have opened up exciting possibilities for understanding the chromosomal/molecular basis of various human diseases including cancer and tissue degeneration. This review summaries the history and evolution of various cytogenetic techniques and their current and future applications in diverse areas of basic research and medical diagnostics.

Inhibition of radiation-induced DNA damage by jamun, Syzygium cumini, in the cultured splenocytes of mice exposed to different doses of γ-radiation

The radioprotective property of 50 mg/kg body weight jamun (Syzygium cumini) extract was studied in the cultured splenocytes of mice exposed to 0, 0.5, 1, 2, 3, or 4 Gy of γ-radiation. The spleens of irradiated mice were removed aseptically and the splenocytes were extracted from the individual spleens and cultured. The micronuclei were prepared 72 hours after irradiation in binucleate splenocytes by blocking cytokinesis with cytochalasin-B. Irradiation of mice resulted in a dose-dependent elevation in the micronucleated splenocytes. The exposure of mice not only elevated splenocytes bearing one micronucleus but also cells bearing 2 and multiple (>2) micronuclei indicating induction of complex DNA damage after irradiation. Oral treatment of mice with 50 mg/kg body weight of jamun leaf extract protected against the radiation-induced micronuclei formation. Jamun extract also protected against the formation of 2 and multiple micronuclei indicating repair or inhibition of complex DNA damage. The assessment of lipid peroxidation in mice brain homogenate has indicated a concentration dependent inhibition of lipid peroxidation by jamun extract. Studies in a cell free system revealed that jamun extract inhibited the formation of OH, O(2)-, DPPH, and ABTS(+) free radicals in a concentration dependent manner. Our study demonstrates that jamun extract protected mice against the radiation-induced DNA damage and inhibition of radiation-induced free radical formation may be one of the mechanisms of radioprotection.

Different DNA-PKcs functions in the repair of radiation-induced and spontaneous DSBs within interstitial telomeric sequences

Interstitial telomeric sequences (ITSs) in hamster cells are hot spots for spontaneous and induced chromosome aberrations (CAs). Most data on ITS instability to date have been obtained in DNA repair-proficient cells. The classical non-homologous end joining repair pathway (C-NHEJ), which is the principal double strand break (DSB) repair mechanism in mammalian cells, is thought to restore the morphologically correct chromosome structure. The production of CAs thus involves DNA-PKcs-independent repair pathways. In our current study, we investigated the participation of DNA-PKcs from the C-NHEJ pathway in the repair of spontaneous or radiation-induced DSBs in ITSs using wild-type and DNA-PKcs mutant Chinese hamster ovary cells. Our data demonstrate that DNA-PKcs stabilizes spontaneous DSBs within ITSs from the chromosome 9 long arm, leading to the formation of terminal deletions. In addition, we show that DNA-PKcs-dependent C-NHEJ is employed following radiation-induced DSBs in other ITSs and restores morphologically correct chromosomes, whereas DNA-PKcs independent mechanisms co-exist in DNA-PKcs proficient cells leading to an excess of CAs within ITSs.

Detection of premature segregation of centromeres in persons exposed to ionizing radiation

We have analyzed the frequency of premature centromeric division (PCD) in medical personnel professionally exposed to low doses of radiation. They had chromosome aberrations (CAs) involving dicentric chromosomes, ring chromosomes, acentric fragments, chromosome breaks, and chromatid breaks. The study included 30 exposed subjects and 23 controls who were each analyzed by a conventional cytogenetics procedure and subsequently by fluorescent in situ hybridization (FISH). The latter was applied particularly in order to verify PCD in a specific chromosome (chromosome 18) in both metaphases and interphase nuclei. The results revealed a significant difference (p < 0.001) in frequencies between the two groups (exposed and controls) for all the observed variables (CAs), metaphases with PCD (MPCD), total number of chromosomes with PCD (TPCD), number of PCD metaphases in acrocentric chromosomes (MAPCD), and the total number of acrocentric chromosomes with PCD (TAPCD). The doses of ionizing radiation absorbed by the subjects' bodies were measured with thermoluminescent dosimeters once a month during the duration of occupational exposure. They were expressed in mSv, as mean annual effective doses for the period of exposure. The Spearman rank test showed a high positive correlation between total life effective dose and frequency of CAs and PCD. Based on the results obtained in this study, we suggest that PCD, as a phenomenon manifesting chromosomal instability (CIN), should be considered as a suitable cytogenetic biomarker for individuals occupationally exposed to ionizing radiation.

Treatment of mice with stem bark extract ofAphanamixis polystachyareduces radiation-induced chromosome damage

PURPOSE

Normal tissue radiosensitivity is the major limiting factor in radiotherapy of cancer. The use of phytochemicals may reduce the adverse effects of radiation in normal tissue. The effect of ethyl acetate fraction of Aphanamixis polystachya (EAP) was investigated on the radiation-induced chromosome damage in the bone marrow cells of Swiss albino mice exposed to various doses of gamma-radiation.

MATERIALS AND METHODS

The mice were divided into two groups, one group was exposed to 0, 1, 2, 3, 4 or 5 Gy of gamma-radiation, while another group received 7.5 mg/kg body weight (BW) of EAP 1 h before exposure to 0, 1, 2, 3, 4 or 5 Gy of gamma-radiation. Various asymmetrical chromosome aberrations were studied in the bone marrow cells of mice at 12, 24 or 48 h post-irradiation. To understand the mechanism of action of the free radical scavenging activity of 0, 5, 10, 20, 30, 40, 50, 60 or 70 microg/ml EAP, assays were carried out in vitro.

RESULTS

Irradiation of mice to different doses of gamma radiation caused a dose dependent elevation in the frequency of aberrant cells and chromosome aberrations like chromatid breaks, chromosome breaks, dicentrics, acentric fragments and total aberrations at all the post-irradiation times studied. The maximum asymmetrical aberrations were scored at 24 h post-irradiation except chromatid breaks that were highest at 12 h post-irradiation. A maximum number of polyploid and severely damaged cells (SDC) were recorded at 24 h post-irradiation in the SPS+irradiation group. Treatment of mice with 7.5 mg/kg BW of EAP before exposure to 1-5 Gy of whole body gamma-radiation significantly reduced the frequencies of aberrant cells and chromosomal aberrations like acentric fragments, chromatid and chromosome breaks, centric rings, dicentrics and total aberrations at all post-irradiation scoring times (p<0.01). The EAP showed a concentration dependent scavenging of hydroxyl, superoxide, 2,2'-diphenyl-1-picryl hydrazyl (DPPH) radicals and the 2,2-azino-bis-3-ethyl benzothiazoline-6-sulphonic acid (ABTS) cation radicals in vitro. EAP treatment also reduced lipid peroxidation in bone marrow cells in a concentration dependent manner.

CONCLUSION

Our study demonstrates that EAP protects mouse bone marrow cells against radiation-induced chromosomal aberrations and this reduction in radiation-induced chromosome damage may be due to free radical scavenging and reduction in lipid peroxidation. The radioprotection by EAP is best comparable to that of protection demonstrated by the grape fruit flavonone, naringin, in our earlier studies in mouse bone marrow cells.

Studies on radiation-induced apoptosis in G0human lymphocytes

PURPOSE

To determine the relationships between the frequencies of radiation-induced chromosomal alterations and the extent of apoptosis in G0 human lymphocytes.

MATERIAL AND METHODS

G0 human peripheral blood lymphocytes (HPBL) were X or gamma-irradiated, in the presence or absence of the repair inhibitor cytosine arabinoside (Ara-C). Directly after irradiation, a part of the lymphocytes were stimulated to grow while the rest were stimulated 48 h after irradiation. These lymphocyte cultures were analysed for induction of chromosomal aberrations. A subset of lymphocytes was kept in G0 and analysed for cell viability, apoptosis and p53 expression.

RESULTS

The fraction of cells bearing dicentrics was reduced in lymphocytes stimulated to grow 48 h post irradiation as compared to lymphocytes stimulated immediately after irradiation. The decrease in the frequency of dicentrics correlated with the increase in the number of apoptotic cells. The operative apoptotic pathway in irradiated Go lymphocytes was dependent on the expression of p53.

CONCLUSIONS

The radiation-induced apoptotic response of G0 lymphocytes is p53 dependent and increases with the time they are held in G0. When mitogen was added 48 h after irradiation, cells with dicentrics were either preferentially eliminated or did not enter mitosis. Thus the radiation-induced damage can be underevaluated depending on the time between radiation exposure and the induction of proliferation. These results may have relevance for biodosimetry studies or for evaluations of the efficacy of radiotherapy which are based on the frequencies of chromosomal aberrations.

Activation of telomerase by ionizing radiation: differential response to the inhibition of DNA double-strand break repair by abrogation of poly (ADP-ribosyl)ation, by LY294002, or by Wortmannin

PURPOSE

Telomerase activity represents a radiation-inducible function, which may be targeted by a double-strand break (DSB)-activated signal transduction pathway. Therefore, the effects of DNA-PK inhibitors (Wortmannin and LY294002) on telomerase upregulation after irradiation were studied. In addition, the role of trans-dominant inhibition of poly(ADP-ribosyl)ation, which strongly reduces DSB rejoining, was assessed in comparison with 3-aminobenzamide.

METHODS AND MATERIALS

COM3 rodent cells carry a construct for the dexamethasone-inducible overexpression of the DNA-binding domain of PARP1 and exhibit greatly impaired DSB rejoining after irradiation. Telomerase activity was measured using polymerase chain reaction ELISA 1 h after irradiation with doses up to 10 Gy. Phosphorylation status of PKB/Akt and of PKCalpha/beta(II) was assessed by western blotting.

RESULTS

No telomerase upregulation was detectable for irradiated cells with undisturbed DSB rejoining. In contrast, incubation with LY294002 or dexamethasone yielded pronounced radiation induction of telomerase activity that could be suppressed by Wortmannin. 3-Aminobenzamide not only was unable to induce telomerase activity but also suppressed telomerase upregulation upon incubation with LY294002 or dexamethasone. Phospho-PKB was detectable independent of irradiation or dexamethasone pretreatment, but was undetectable upon incubations with LY294002 or Wortmannin, whereas phospho-PKC rested detectable.

CONCLUSIONS

Telomerase activation postirradiation was triggered by different treatments that interfere with DNA DSB processing. This telomerase upregulation, however, was not reflected by the phosporylation status of the putative mediators of TERT activation, PKB and PKC. Although an involvement of PKB in TERT activation is not supported by the present findings, a respective role of PKC isoforms other than alpha/beta(II) cannot be ruled out.

An extract of Phyllanthus amarus protects mouse chromosomes and intestine from radiation induced damages

We reported earlier on our preliminary study of the radioprotective effect of Phyllanthus amarus (P.amarus) in mice. P.amarus was found to inhibit the myelosuppression and elevated the levels of antioxidant enzymes in the blood and liver. In the present study we have evaluated the protective effect of P.amarus against radiation-induced changes in the intestine and mouse chromosomal damage. P.amarus at concentrations of 250 & 750 mg/Kg. b. wt were found to elevate the antioxidant enzymes in the intestine and decrease the lipid peroxidation levels. Histopathological evaluations of the intestine revealed decreased damage to intestinal cells, demonstrating that P.amarus protected the intestine. The genotoxic effects of radiation on mouse chromosomes were evaluated by assaying the micronuclei formation and chromosomal aberrations. P.amarus was found to protect the clastogenic effects of radiation as seen from decreased number of micronuclei. The administration of P.amarus was also found to decrease the percentage of chromosomal aberrations. Based on our present and previous reports it could be concluded that P.amarus extract has significant radioprotective activity.

Efficient repair of bleomycin-induced double-strand breaks in barley ribosomal genes

Ability of barley ribosomal genes to cope with damage produced in vivo by the radiomimetic agent bleomycin was investigated. Repair kinetics of bleomycin-induced double-strand breaks in ribosomal and total genomic DNA was compared. Induction and repair of double-strand breaks in defined regions of the ribosomal genes was also analyzed. Preferential sensitivity of barley linker DNA towards bleomycin treatment in vivo was established. Relatively higher yield of initially induced double-strand breaks in genomic DNA in comparison to ribosomal DNA was also found. Fragments containing intergenic spacers of barley rRNA genes displayed higher sensitivity to bleomycin than the coding sequences. No heterogeneity in the repair of DSB between transcribed and non-transcribed regions of ribosomal genes was detected. Data indicate that DSB repair in barley rDNA, although more efficient than in genomic DNA, does not correlate with the activity of nucleolus organizer regions.

Chromosome breakpoint distribution of damage induced in peripheral blood lymphocytes by densely ionizing radiation

PURPOSE

To assess the chromosomal breakpoint distribution in human peripheral blood lymphocytes (PBL) after exposure to a low dose of high linear energy transfer (LET) alpha-particles using the technique of multiplex fluorescence in situ hybridization (m-FISH).

MATERIALS AND METHODS

Separated PBL were exposed in G0 to 0.5 Gy 238Pu alpha-particles, stimulated to divide and harvested approximately 48 - 50 hours after exposure. Metaphase cells were assayed by m-FISH and chromosome breaks identified. The observed distribution of breaks were then compared with expected distributions of breaks, calculated on the assumption that the distribution of breaks is random with regard to either chromosome volume or chromosome surface area.

RESULTS

More breaks than expected were observed on chromosomes 2 and 11, however no particular region of either chromosome was identified as significantly contributing to this over-representation. The identification of hot or cold chromosome regions (pter,p,cen,q,qter) varied depending on whether the data were compared according to chromosome volume or surface area.

CONCLUSIONS

A deviation from randomness in chromosome breakpoint distribution was observed, and this was greatest when data were compared according to the relative surface area of each individual chromosome (or region). The identification of breaks by m-FISH (i.e., more efficient observation of interchanges than intrachanges) and importance of territorial boundaries on interchange formation are thought to contribute to these differences. The significance of the observed non-random distribution of breaks on chromosomes 2 and 11 in relation to chromatin organization is unclear.

Simple biodosimetry method for cases of high-dose radiation exposure using the ratio of the longest/shortest length of Giemsa-stained drug-induced prematurely condensed chromosomes (PCC)

The aim was to develop a simple biodosimetry method for as rapid as possible estimation of absorbed radiation doses in victims of radiation accidents, in particular after high-dose exposure. Human peripheral blood lymphocytes (PBL) were gamma-irradiated in vitro with several doses up to 40 Gy stimulated with phytohaemagglutinin-P (PHA-P) for 2 days and their chromosomes condensed prematurely using 50 nm calyculin A. Chromosome lengths of Giemsa-stained G2 prematurely condensed chromosomes (PCC) were measured using image analysing software and the ratio of the longest/shortest chromosome length was calculated. The length ratio (LR) of the longest/shortest Giemsa-stained chromosome s increased with a good correlation to the square root of the radiation dose (D) up to 40 Gy, i.e. LR = (4.90 x D0.5) + 2.14. The LR of the longest/shortest chromosome might be used as an index for estimating the radiation dose. The blood samples should not be cooled until the start of separation/stimulation of the lymphocytes. A rapid and easy estimation of large doses after whole-body exposure was identified by measuring the ratio of the longest/shortest length of Giemsa-stained G2-PCC induced by calyculin A. This simple protocol will be particularly useful for making therapy decisions for victims of ionizing radiation exposure and has potential for use as a biodosimeter for partial-body exposure accidents.

Preferential reduction of dicentrics in reciprocal exchanges due to the combination of the size of broken chromosome segments by radiation

Induction rates of the dicentrics and translocations involving chromosomes 2 and 4 in peripheral lymphocytes irradiated with X-rays at a dose of 3 Gy were examined using a conventional Giemsa staining method and a chromosome painting method. In total, 228 reciprocal exchanges detected in 982 metaphases were classified into three groups according to the break points of the original chromosomes. The incidence of both acentric fragments being larger than half of the original chromosome (combination 1) was only seven (3%) and did not contribute significantly to induction rates. When the broken acentric fragments of two affected chromosomes were smaller than half of the original chromosomes (combination 2), which was found in 175 (77%) rearrangements, the induction rates of dicentrics and translocations were about the same (86:89). But if the sizes of the broken segments were unequal in both chromosomes (combination 3: one with a larger acentric part and the other with a smaller acentric part), the yield of dicentrics was significantly lower than that of translocations (16:30). It was suggested that there was a special mechanism causing preferential reduction of dicentrics in reciprocal exchanges originated from the heteromorphic size of broken chromosomes in the last combination.

A combination of the micronucleus assay and a FISH technique for evaluation of the genotoxicity of 1,2,4-benzenetriol

The cytokinesis-block micronucleus (CBMN) assay has emerged as one of the preferred methods for assessing chromosome damage. Micronuclei (MN) are small, extranuclear bodies that are formed in mitosis from acentric chromosomal fragments or chromosomes that are not included in each daughter nucleus. Thus, MN contain either chromosomal fragments or whole chromosomes. The CBMN assay, together with a fluorescence in situ hybridization (FISH) technique using specific centromeric probes for chromosomes 7 and 8, were employed in mitogen-stimulated human lymphocytes pretreated with the benzene metabolite, 1,2,4-benzenetriol (BT). Treatment of human lymphocytes resulted in the induction of MN in a dose-dependent manner. The frequency of MN in control lymphocytes was 4.5 per 1000 binucleated (BN) cells and this increased to 9.5, 14, 28 and 40 per 1000 BN cells at 10, 25, 50 and 100 microM BT, respectively. The frequency of aneuploidy 7 and 8 in BN cells also increased at each concentration. Aneuploidy 8 was more frequent than aneuploidy 7, suggesting that chromosome 8 is more sensitive to aneuploidy induction by BT. The frequency of MN containing centromere positive signals for chromosomes 7 and 8 increased with the concentration of BT. The frequency of MN with centromere positive signals was higher for chromosome 8 than for chromosome 7, also suggesting a greater sensitivity of chromosome 8 to this agent. These results suggest that combined application of the CBMN assay with a FISH technique, using chromosome-specific centromeric probes, would allow the detection of aneuploidy in human lymphocytes and identify the mechanistic origin of MN induced by a clastogen or aneugen.

Bone marrow stromal cells regulate caspase 3 activity in leukemic cells during chemotherapy

The interaction between leukemic cells and stromal cells of the bone marrow microenvironment has been shown to enhance leukemic cell survival during exposure to chemotherapeutic agents. In the current study we investigated whether association of B lineage acute lymphoblastic leukemic cells with human bone marrow stromal cells altered caspase activation during chemotherapy treatment. Following treatment with Ara-C or VP-16 in vitro, caspase 3 activity in leukemic cells was consistently reduced by co-culture of leukemic cells with human bone marrow stromal cell layers. These observations suggest that the protective effect of the bone marrow microenvironment on leukemic cells may be due, in part, to regulation of caspase 3 activity.

Chromosome nondisjunction and loss induced by protons and X rays in primary human fibroblasts: role of centromeres in aneuploidy

To study the origin of micronuclei induced in human primary fibroblasts by low-energy protons (7.7 and 28.5 keV/microm) and X rays, we have developed a combined antikinetochore-antibody (CREST) and FISH staining with pancentromeric probes. This technique allowed us to analyze the integrity of the kinetochore and centromeric DNA structures and to assess their role in induced aneuploidy. The effect of LET on radiation-induced chromosome nondisjunction was studied in binucleated cells with centromeric-specific DNA probes for chromosomes 7 and 11. Our results indicate that, though more than 90% of radiation-induced micronuclei were CREST(-)/FISH(-), 28.5 keV/microm protons and X rays were also able to induce statistically significant increases in the number of micronuclei that were CREST(-)/FISH(+) and CREST(+)/FISH(+), respectively. One interpretation of these results could be that the protons induced chromosome loss by kinetochore detachment or by breakage in the centromeric DNA region, whereas X rays induced aneuploidy through a non-DNA damage mechanism. Nondisjunction appears to be a far more important mechanism leading to radiation-induced aneuploidy. Irrespective of the higher frequency of micronuclei induced by 28.5 keV/microm protons, the frequency of chromosome loss was markedly higher for X rays than for 28.5 keV/microm protons, strengthening the hypothesis that non-DNA targets, such as components of the mitotic spindle apparatus, may be involved in aberrations in chromosome segregation after X irradiation.

Induction of telomerase activity by irradiation in human lymphoblasts

Neuhof, D., Ruess, A., Wenz, F. and Weber, K. J. Induction of Telomerase Activity by Irradiation in Human Lymphoblasts. Radiat. Res. 155, 693-697 (2001). Telomerase activity is a radiation-inducible function, which suggests a role of this enzyme in DNA damage processing. Since the tumor suppressor TP53 plays a central role in the regulation of the cellular response to DNA damage, our study explored the ability of ionizing radiation to change telomerase activity and telomere length in two closely related human lymphoblast cell lines with different TP53 status. TK6 cells (wild-type TP53) and WTK1 cells (mutated TP53) were exposed to different doses of X rays, and telomerase activity was measured by PCR ELISA at different times after irradiation. A dose-dependent increase in telomerase activity was observed. One hour after irradiation with 4 Gy, TK6 and WTK1 cells showed an approximately 2.5-fold increase; for lower doses (0.1 to 1 Gy), telomerase induction was seen only in TK6 cells. Telomerase induction was observed by 0.5 h after irradiation, with a further increase up to 24 h. Irradiated TK6 and WTK1 cells had longer telomeres (+1.3 kb) than unirradiated cells 14 days after exposure. Our data demonstrate a dose-dependent induction of telomerase activity and lengthening of telomeres by ionizing radiation in human lymphoblasts. Induction of telomerase activity by radiation does not generally appear to be controlled by the TP53-dependent DNA damage response pathway. However, for low doses, induction of telomerase requires wild-type TP53.

Frequencies of X-ray induced chromosome aberrations in lymphocytes of xeroderma pigmentosum and Fanconi anemia patients estimated by Giemsa and fluorescence in situ hybridization staining techniques

Blood lymphocytes from xeroderma pigmentosum (XP) and Fanconi anemia (FA) patients were assessed for their sensitivity to ionizing radiation by estimating the frequency of X-ray (1 and 2 Gy)-induced chromosome aberrations (CA). The frequencies of aberrations in the whole genome were estimated in Giemsa-stained preparations of lymphocytes irradiated at G0 or G2 stages. The frequencies of translocations and dicentrics involving chromosomes 1 and 3 as well as the X-chromosome were determined in slides stained by fluorescence in situ hybridization (FISH) technique. An increase in all types of CA was observed in XP and FA lymphocytes irradiated at G0 when compared to controls. The frequency of dicentrics and rings was 6 to 27% higher (at 1 and 2 Gy) in XP lymphocytes and 37% higher (at 2 Gy) in FA lymphocytes than in controls, while chromosome deletions were higher in irradiated (30% in 1 Gy and 72% in 2 Gy) than in control XP lymphocytes and 28 to 102% higher in FA lymphocytes. In G2-irradiated lymphocytes the frequency of CA was 24 to 55% higher in XP lymphocytes than in controls. In most cases the translocation frequencies were higher than the frequencies of dicentrics (21/19).

Analysis of X-ray-induced aberrations in human chromosome 5 using high-resolution multicolour banding FISH (mBAND)

Peripheral lymphocytes were exposed to 4 Gy X-rays and aberrations were analysed in human chromosome 5 using high-resolution multicolour banding fluorescence in-situ hybridization (mBAND). This method is suited to detect simple and complex aberrations including peri- and paracentric inversions and exchanges between both chromosomes 5. Additionally, breakpoints carr be assigned to specific regions in chromosome 5. Quantitative relationships of induced aberration types are discussed.

The influence of radiation and chemotherapy-related DNA strand breaks on carcinogenesis: an evaluation

PURPOSE

DNA strand breaks are believed to induce carcinogenesis. This study was conducted to analyze induction and repair of irradiation- and chemotherapy-related strand breaks in vitro.

METHODS

Friend Leukemia cells were exposed to irradiation and various chemotherapeutic agents at different doses and concentrations. Occurrence of strand breaks was determined fluorometrically, measuring the rate of DNA unwinding immediately after exposure and 24 hours later.

RESULTS

The amount of double-stranded DNA decreased significantly for irradiation, doxorubicin, dactinomycin and etoposide (p < or = 0.05, t-test). After 24 hours free of exposure, the persistent damage was detectable for all of these agents but not for irradiated cells, with DNA strand breaks being decreased for etoposide, unchanged for doxorubicin and increased for methotrexate as well as for dactinomycin.

CONCLUSIONS

Severe DNA damage is induced by various chemotherapeutic agents and by irradiation. While repair of chemotherapy-related strand breaks may remain incomplete or prolonged for some chemotherapeutic agents, repair of radiation induced strand breaks is faster and more complete. Therefore chemotherapy-related carcinogenesis may partially be explained by prolonged persistence of DNA strand breaks.

Analysis by FISH of the spectrum of chromosome aberrations induced by X-rays in G0 human lymphocytes and their fate through mitotic divisions in culture

The induction, distribution, and persistence of chromosome aberrations in human lymphocytes exposed to X-rays in G0 were analyzed in 48-, 70-, and 94-hr cultures by conventional metaphase analysis and painting of chromosomes 1, 2, and 4 by FISH. All cells that had been scored by FISH were relocated to determine by differential staining of chromatids whether they had passed through 1, 2, or > or =3 divisions. FISH revealed a dose-dependent induction of stable and unstable aberrations, while chromatid labeling showed mitotic lag caused by irradiation in G0. Relative to their DNA contents, there was a small but significant overrepresentation of chromosome 4 and underrepresentation of chromosome 2 among the aberrations involving chromosomes 1, 2, and 4. FISH slightly underestimated the genomic frequency of unstable aberrations measured by conventional metaphase analysis. There was a slight excess of translocations relative to dicentrics, but the data are compatible with the 1:1 ratio expected from cytogenetic theory. Many of the translocations were apparently incomplete (i.e., nonreciprocal). Incomplete translocations were more frequent at higher X-ray dose and in first division, suggesting that they may be associated with complex damage and are more apt to be lost in mitosis than complete translocations. Among the incomplete translocations, t(Ab) outnumbered t(Ba) -- a difference ascribable to the FISH technique. Aberration frequencies declined as the cells divided in culture. The overall decline in the frequency of aberrant cells (approximately 29% per cell generation) reflects a rapid decline in dicentrics and fragments (approximately 60% per cell generation) and the relative stability of translocations. The frequency of translocation-bearing cells underwent a modest decline in culture (approximately 13% per cell generation).

Molecular epidemiology in cancer research

The use of molecular biomarkers in epidemiological investigations brings clear advantages of economy, speed and precision. Epidemiology--the study of the factors that control the patterns of incidence of disease--normally requires large numbers of subjects and/or long periods of time, because what is measured (the occurrence of disease) is a rare event. Biomarkers are measurable biological parameters that reflect, in some way, an individual's risk of disease-because they indicate exposure to a causative (or protective) agent, or because they represent an early stage in development of the disease, or because they allow an assessment of individual susceptibility. Biomarkers must be usable on one of the few materials available for biomonitoring of humans, i.e. blood, urine, exfoliated epithelial cells and, with some difficulty, biopsies. The approach of molecular epidemiology has a great potential is several areas of cancer research: investigating the aetiology of the disease; monitoring cancer risk in people exposed to occupational or environmental carcinogens; studying factors that protect from cancer; and assessing intrinsic factors that might predispose to cancer. The biomarkers most commonly employed in cancer epidemiology include: measurements of DNA damage--DNA breaks, altered bases, bulky adducts--in lymphocytes; the surrogate marker of chemical modifications to blood proteins, caused by agents that also damage DNA; the presence of metabolites of DNA-damaging agents (or the products of DNA damage themselves) in urine; chromosome alterations, including translocations, micronuclei and sister chromatid exchange, resulting from DNA damage; mutations in marker genes; DNA repair; and the differential expression of a variety of enzymes, involved in both activation and detoxification of carcinogens, that help to determine individual susceptibility. The molecular approach has been enthusiastically employed in several studies of occupational/environmental exposure to carcinogens. While the estimation of biological markers of exposure has certainly shown the expected effects in terms of DNA damage and adducts, the detection of the biological effects of exposure (e.g. at the level of chromosome alterations) has not been so clear-cut. This is true also when smokers are examined as a group compared with non-smokers. Several markers (especially of chromosome damage and mutation) show a strong correlation with age-indicating either an increasing susceptibility to damage with age, or an accumulation of long-lived changes. DNA repair--a crucial player in the removal of damage before it can cause mutation--may vary between individuals, and may be modulated by intrinsic or extrinsic factors, but limited data are available because of the lack of a reliable assay. Information on other enzymes determining individual susceptibility does exist, and some significant effects of phenotypic or genotypic polymorphisms have emerged, although the interactions between various enzymes make the situation very complex. The important question of whether oxidative DNA damage in normal cells is decreased by dietary antioxidants (vitamin C, carotenoids etc., from fruit and vegetables) has been tackled in antioxidant supplementation experiments. The use of poorly validated assays for base oxidation has not helped us to reach a definitive answer; it seems that, in any case, the level of oxidative damage has been greatly exaggerated. DNA-damaging agents lead to characteristic kinds of base changes (transitions, transversions, deletions). The investigation of the spectrum of mutations in cancer-related genes studied in tumour tissue should lead to a better understanding of the agents ultimately responsible for inducing the tumour. Similarly, studying mutations in a neutral marker gene (not involved in tumorigenesis) can tell us about the origins of the 'background' level of mutations. So far, interpretation of the growing databases is largely speculative. (ABSTRACT

Mechanisms of the origin of chromosomal aberrations

This manuscript gives a selective survey of some aspects of the origin of chromosomal aberrations (CA). The following topics are discussed: heterogeneity regarding the induction of initial DNA lesions and their repair among chromosomes or regions of the same chromosome, ratio between symmetrical and asymmetrical exchanges, influence of DNA repeats, chromatin condensation and cell-cycle checkpoints on the formation of chromosome alterations.

137Cesium-induced chromosome aberrations analyzed by fluorescence in situ hybridization: eight years follow up of the Goiânia radiation accident victims

The radiation accident in focus here occurred in a section of Goiânia (Brazil) where more than a hundred individuals were contaminated with 137Cesium on September 1987. In order to estimate the absorbed radiation doses, initial frequencies of dicentrics and rings were determined in 129 victims [A.T. Ramalho, PhD Thesis, Subsidios a tecnica de dosimetria citogenetica gerados a partir da analise de resultados obtidos com o acidente radiologico de Goiânia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, 1992]. We have followed some of these victims cytogenetically over the years seeking for parameters that could be used as basis for retrospective radiation dosimetry. Our data on translocation frequencies obtained by fluorescence in situ hybridization (FISH) could be directly compared to the baseline frequencies of dicentrics available for those same victims. Our results provided valuable information on how precise these estimates are. The frequencies of translocations observed years after the radiation exposure were two to three times lower than the initial dicentrics frequencies, the differences being larger at higher doses (>1 Gy). The accuracy of such dose estimates might be increased by scoring sufficient amount of cells. However, factors such as the persistence of translocation carrying lymphocytes, translocation levels not proportional to chromosome size, and inter-individual variation reduce the precision of these estimates.

A high yield of translocations parallels the high yield of sister chromatid exchanges in the CHO mutant EM9

The fluorescence plus Giemsa (FPG) and fluorescence in situ hybridization (FISH) techniques have been used to determine, respectively, the frequencies of sister chromatid exchanges (SCEs) and stable chromosome aberrations (translocations) induced by different concentrations of BrdU in the Chinese hamster ovary cell mutant EM9 and its parental line AA8. The results indicate that BrdU induced a high frequency of SCEs and translocations in EM9 as compared with AA8, and that the translocation/dicentric ratio was also higher in the mutant cell line than in the parental cell line in both untreated and BrdU-treated cultures. These observations may indicate a possible relationship between the molecular mechanisms involved in the formation of SCEs and translocations.

Evaluation of bleomycin-induced chromosome aberrations under simulated microgravity conditions in human lymphocytes using "FISH" techniques

In the present investigation we report the effects of simulated microgravity conditions (clinostat) on the induction of chromosomal aberrations in human lymphocytes in vitro by (R) Bleomycin. Chromosomal aberrations have been analysed by means of fluorescent in situ hybridisation (FISH) and chromosome-specific composite DNA probes (chromosome painting). The results obtained show that, under simulated microgravity conditions, the levels of both symmetrical and asymmetrical (dicentrics, rings), the number of cells bearing "complex" aberrations and hence the total numbers of aberrations were significantly elevated at any of the dose-levels assayed, compared to the parallel treatments performed as 1g control ("ground"). Furthermore, the ratio symmetrical:asymmetrical translocations was markedly elevated under simulated microgravity conditions, compared to the findings usually observed under "normal" 1g conditions. On these bases, we are much inclined to believe that simulated microgravity, rather than limiting the resealing of DNA double strand breaks (DSB's) induced by genotoxic agents is influencing in terms of enhancement the misrejoining of DSB's which is actually responsible for the fixation of the original lesions to DNA into chromosomal aberrations. In addition, the possible different misrepair processes leading to the formation of symmetrical and asymmetrical translocations might be differentially influenced by microgravity being the symmetrical translocations significantly more represented.

Review: proximity effects in the production of chromosome aberrations by ionizing radiation

After ionizing radiation has induced double-strand DNA breaks (dsb), misrejoining produces chromosome aberrations. Aberration yields are influenced by "proximity' effects, i.e., by the dependence of misrejoining probabilities on initial dsb separations. We survey proximity effects, emphasizing implications for chromosome aberration-formation mechanisms, for chromatin geometry, and for dose-response relations. Evidence for proximity effects comes from observed biases for centric rings and against three-way interchanges, relative to dicentrics or translocations. Other evidence comes from the way aberration yields depend on radiation dose and quality, tightly bunched ionizations being relatively effective. We concludes (1) that misrejoining probabilities decrease as the distance between dsb at the time of their formation increases, and almost all misrejoining occurs among dsb initially separated by < 1/3 of a cell nucleus diameter; (2) that chromosomes occupy (irregular) territories during the G0/G1 phase of the cell cycle, having dimensions also roughly 1/3 of a cell nucleus diameter, (3) that proximity effects have the potential to probe how much different chromosomes intertwine on move relative to each other: and (4) that incorporation of proximity effects into the classic random breakage-and-reunion model allows quantitative interrelation of yields for many different aberration types and of data obtained with various FISH painting methods or whole-genome scoring.

Paternally inherited chromosomal structural aberrations detected in mouse first-cleavage zygote metaphases by multicolour fluorescence in situ hybridization painting

We describe a fluorescence in situ hybridization (FISH) procedure for assessing zygotic risk of paternal exposure to endogenous or exogenous agents. The procedure employs multicolour FISH with chromosome-specific DNA painting probes plus DAPI staining for detecting both balanced and unbalanced chromosomal aberrations in mouse first-cleavage (1-Cl) zygote metaphases. Four composite probes specific for chromosomes 1, 2, 3 or X, each labelled with biotin, plus a composite probe specific for chromosome Y labelled with digoxigenin, were used. We applied this method to evaluate the effects of paternal exposure to acrylamide, a model germ cell clastogen. First-cleavage zygote metaphases, collected from untreated females mated to males whose sperm or late spermatids were treated with acrylamide, were scored for the induction of structural aberrations using both chromosome painting (PAINT analysis) and DAPI analysis. Structural chromosomal aberrations were observed in the sperm-derived, but not in the egg-derived, pronuclei. While 59.4% of the zygotes had structural aberrations by DAPI analysis, 94.1% of the same zygotes had structural aberrations by PAINT analysis (P < 0.001), illustrating the increased sensitivity for detecting translocations and insertions obtained by adding chromosome painting. These findings show that FISH painting of mouse 1-Cl zygotes when used in conjunction with DAPI analysis is a powerful model for investigating the cytogenetic defects transmitted from father to offspring.

Chromosome analysis in X-irradiated primary cells of a human squamous cell carcinoma by fluorescence in situ hybridization

Chromosomes in primary tumour cells derived from a squamous cell carcinoma of the gingival mucosa were analysed. The ploidy of individual chromosomes and the frequencies of reciprocal translocations in unirradiated and irradiated cells were assessed by the method of fluorescence in situ hybridization. Hybridization probes for whole chromosomes 1, 2, 3, 4, 9 and 12 were used. The analysis was carried out in early (1st-3rd) passage cells and for comparison, in late (25th-30th) passage cells. A radiation-induced polyploidy of all analysed chromosomes was observed in irradiated (D = 4 Gy) early as well as late passage cells, with the exception of chromosome 4 in late passage cells. Ploidy of chromosomes 1 and 4 was studied at lower doses (1-3 Gy), too. Polyploidy was observed for doses >2 Gy. Some of the analysed chromosomes showed a high 'spontaneous' translocation frequency in both types of cells. The frequencies of radiation-induced translocations were similar in early and late cells and these frequencies were not always proportional to the length of the chromosomes studied. The radiosensitivity of individual chromosomes was not correlated with the level of spontaneous translocation frequency.

Theoretical predictions on the equality of radiation-produced dicentrics and translocations detected by chromosome painting

Existing models of chromosome aberrations produced by ionizing-radiation predict equal numbers of dicentrics and translocations if the dose is so low that complex aberrations can be ignored. We show that, for a specific subset of aberrations detected by FISH, dicentric/translocation equality is predicted even at higher doses. Assuming one-colour whole-chromosome painting (with unpainted chromosomes counterstained and centromeres recognizable) the relevant restriction is that the final metaphase pattern be, in the terminology of Simpson and Savage, 'apparently simple'. This means that the painted pattern is required to have the colour/centromere appearance corresponding to a single complete reciprocal exchange but its actual formation, as reflected for example in lengths, is allowed to be more complicated. The restriction to apparent simplicity is significantly less limiting than ignoring all complex aberrations. Our analysis of predicted dicentric/translocation equality in this case uses examples, a combinatorial counting method, Monte Carlo computer programs, and a duality proof. However, we argue that for 'visibly complex' dicentrics or translocations, no similar equality is expected in general. Corresponding experimental results are briefly surveyed. Checking dicentric/translocation equality experimentally can provide a significant test of current chromosome aberration models.

Reciprocal translocation frequency in irradiated sensitive and resistant human tumor cells in correlation with clonogenic in vitro cell survival: a possibility of tumor radiosensitivity prediction?

We have investigated the yields of radiation-induced translocations in several human tumor cell lines and in normal diploid human fibroblasts by fluorescence in situ hybridization. The translocation yields were determined with respect to chromosome no. 1 in all cell lines investigated, and moreover in chromosomes nos. 2, 4 and 9 in fibroblasts and one tumor cell line. The chromosomes were "painted' with fluorescent whole chromosome-hybridization probes. The clonogenic survival of the studied cell lines was determined by standard colony-formation assay. We observed a higher frequency of reciprocal translocations in the radiosensitive cells MCF-7 and MDA-MB-436 as compared with the radioresistant cells CaSki and normal skin fibroblasts. Thus, the results suggest a possibility to predict the intrinsic tumor radiosensitivity on the basis of reciprocal translocation yield determined in cells irradiated in vitro. The correlation was observed in spite of the trisomy no. 1 which occurred in all three investigated tumor cell lines. On the other hand, the results obtained with different chromosomes in MCF-7 cells suggest that only chromosomes with relatively low "spontaneous' translocation yields are suitable for this kind of analysis.

Comparison of gamma-ray induced dicentric yields in human lymphocytes measured by conventional analysis and FISH

In an earlier work stable aberrations and dicentrics were determined by fluorescence in situ hybridization (FISH) after various doses of 137Cs gamma-rays. No corresponding calibration curve for dicentrics is available for determinations in terms of the conventional analysis as performed in our laboratory. In view of the potential for the application of chromosome painting to human biological dosimetry, it is desirable to determine such a calibration curve and this and the comparison of the resulting data to those obtained in terms of the FISH method is the objective of the present communication. In the study it is found that the linear-quadratic dose response curves for dicentrics, that are determined by the two methods, are significantly different, although the different target sizes are accounted for. A similar problem was found earlier for X-rays. It does not appear that the difference is due to technical difficulties in the FISH method, that has been improved by employing in addition to the whole chromosome DNA probes, a pan-centromeric DNA probe.

Frequencies of complex chromosome exchange aberrations induced by 238Pu alpha-particles and detected by fluorescence in situ hybridization using single chromosome-specific probes

We undertook an analysis of chromosome-type exchange aberrations induced by alpha-particles using fluorescence in situ hybridization (FISH) with whole chromosome-specific probes for human chromosomes 1 or 4, together with a pan-centromeric probe. Contact-inhibited primary human fibroblasts (in G1) were irradiated with 0.41-1.00 Gy 238Pu alpha-particles and aberrations were analysed at the next mitosis following a single chromosome paint. Exchange and aberration painting patterns were classified according to Savage and Simpson (1994a). Of exchange aberrations, 38-47% were found to be complex derived, i.e. resulting from three or more breaks in two or more chromosomes, and the variation with dose was minimal. The class of complex aberrations most frequently observed were insertions, derived from a minimum of three breaks in two chromosomes. There was also an elevated frequency of rings. The high level of complex aberrations observed after alpha-particle irradiation indicates that, when chromosome domains are traversed by high linear energy transfer alpha-particle tracks, there is an enhanced probability of production of multiple localized double-strand breaks leading to more complicated interactions.

Use of multicolour chromosome painting to identify chromosomal rearrangements in human lymphocytes exposed to bleomycin: a comparison with conventional cytogenetic analysis of Giemsa-stained chromosomes

Exchange aberrations induced by bleomycin were identified by multicolour fluorescence in situ hybridisation (FISH) with probes for chromosomes 1, 2, and 3. The frequency and distribution of aberration types were compared to conventional metaphase analysis of Giemsa-stained chromosomes from the same human lymphocyte cultures. The total percentage of exchanges detectable by painting three pairs of chromosomes with separate colours was calculated as 40%. Giemsa staining revealed predominantly asymmetric chromosome exchanges, which are expected to comprise 50% of the total induced exchanges. Genomic exchange frequencies were, therefore, determined by multiplying the observed frequencies from FISH analysis by 2.5 and the number of asymmetric exchanges identified in Giemsa-stained slides by 2.0. By these calculations, the genomic exchange frequency calculated from chromosome painting exceeded that estimated by Giemsa-staining. This difference was due to the identification by chromosome painting of a unique class of cells in which chromosomes had undergone complex exchanges (nonreciprocal exchanges involving multiple mutual sites). The percentage of cells exhibiting exchanges was similar for both methods.