Frequency of Acentric Fragments Are Associated with Cancer Risk in Subjects Exposed to Ionizing Radiation.

BACKGROUND/AIM: Biomonitoring is currently applied in the estimation of health risks after overexposure to ionizing radiation (IR). The aim of this study was to compare the association of dicentric chromosomes and acentric fragments (AF) with cancer risk in subjects exposed to IR, as well as in control subjects. MATERIALS AND METHODS: The study was performed on 3,574 subjects (2,030 subjects exposed to IR and 1,544 control subjects). The mean follow-up period was 8 years. RESULTS: In subjects reporting exposure to IR, the presence of AFs and dicentric chromosomes was associated with a significant increase in cancer risk, hazard ratio (HR)=1.78 (95% confidence interval (CI)=1.01-3.13) and HR=1.73 (95% CI=1.03-2.90), respectively. CONCLUSION: AFs are associated with cancer risk and have a similar sensitivity to dicentric chromosomes in subjects exposed to IR. Because automated AF scoring can be easily introduced using fast flow cytometry combined with the pan-centromere staining, this biomarker may hold promise as a potential sensitive biomarker of exposure to IR and cancer risk.

Effect of occupational exposure to multiple pesticides on translocation yield and chromosomal aberrations in lymphocytes of plant workers.

Employees handling pesticides are simultaneously exposed to different active substances. Occurring multiple chemical exposures may pose a higher risk than it could be deduced from studies evaluating the effect of a single substance. This study comprised 32 pesticide plantworkers exposed to carbofuran, chlorpyrifos, metalaxyl, and dodine and an equal number of control subjects. Groups were matched by age (43.8 +/- 10.16 vs 41.8 +/- 7.42, respectively), sex (14 females; 18 males), and smoking (11 smokers; 21 nonsmokers). Chromosome aberration and translocation frequencies were determined using a standard aberration assay and fluorescent in situ hybridization (FISH) by applying painting probes for chromosomes 1, 2, and 4. Although significant, an observed increase in chromatid breaks (5.2 +/- 2.49) compared to controls (2.1 +/- 0.87), p(PostHoc) = 0.000001 is biologically irrelevant. Genomic frequency of translocations was also significantly elevated (exposed 0.0165 +/- 0.0070; control 0.0051 +/- 0.0023, P(PostHoc) = 0.000004). The distribution of translocations among chromosomes 1, 2, and 4 did not differ from control subjects. It corresponded to the distribution of DNA content among selected chromosomes indicating randomness of DNA damage. A good translocation yield correlation within years spent in pesticide production indicates that multiple pesticide exposure may pose a risk to genome integrity. However, for more accurate health risk assessments, the use of probes for some other groups of chromosomes should be considered.

Spontaneous abortions in female populations occupationally exposed to ionizing radiation.

OBJECTIVE: Exposure to radioisotopes of metals and halogen elements occurring in medical practice may cause spontaneous abortions. The potential role of occupational exposure to X-rays and internal radioisotopes on pregnancy outcome in childbearing age women employed in hospital departments were analyzed in order to estimate miscarriage risk. METHODS: Over a period of 16 years, the occurrence of miscarriages in 61 women exposed to radioisotopes was compared to that reported in 170 X-ray exposed women. Chromosomal aberrations (CA) were measured in both radiation-exposed groups and in 53 non-exposed women. RESULTS: Women exposed to radioisotopes experienced at least a threefold higher rate of spontaneous abortions than those exposed to X-ray (OR = 3.68, 95% CI = 1.39-9.74, P < 0.01). Although X-ray and radioisotopes exposed women had significantly higher levels of chromosome type frequency (0.51 +/- 0.82, and 0.63 +/- 0.99, respectively) than referents (0.17 +/- 0.34), there was no clear difference between radiation-exposed women. CONCLUSIONS: For exposure levels within standard recommended guidelines, radioisotopes are far more likely to play a role in the occurrence of spontaneous abortions than X-rays. Such biological effect is not detectable by deviations in CA frequency.

An efficient chemical method to generate repetitive sequences depleted DNA probes.

We describe an efficient method to remove repetitive sequences from DNA of microdissected whole chromosomes, chromosome arms, locus specific probes, and specific bands. The chemical approach described removes human repetitive DNA sequences from a source DNA, eliminating the need for blocking such sequences when the source DNA used as a probe is hybridized with a target DNA. It employs subtracting hybridized biotin-labeled repetitive-sequence DNA complex with phenol and chloroform after incubation of hybridized products with avidin. The method produces unique products that are formed after such repetitive sequences have been removed from the DNA. We have applied our newly designed subtraction strategy to microdissected chromosomes in generating whole chromosome painting (e.g., chromosome 4), chromosome arm (e.g., 1q and 15q), and band (e.g., 3q26) specific probes, and we have demonstrated its utility using flow-sorted chromosome. FISH analyses using these probes show consistent strong signals with no cross-hybridization, and optimal hybridization results can be obtained relatively quickly.

Distinct profiles of critically short telomeres are a key determinant of different chromosome aberrations in immortalized human cells: whole-genome evidence from multiple cell lines.

Chromosomal aberrations are common in cancers. However, the search for chromosomal aberrations leading to development of specific solid tumors has been severely hindered because the majority of solid tumors have complex chromosomal aberrations that differ within the same tumor types. A similar phenomenon exists in immortalized cell lines. The underlying mechanisms driving these diverse aberrations are largely unknown. Telomeres play crucial roles in protecting the integrity of eucaryotic chromosomes and maintaining genomic stability of human cells. Telomere lengths on individual chromosomes in normal human somatic cells are heterogeneous and undergo progressive shortening with aging process. In this study, for the first time, a molecular cytogenetic method using sequential telomere quantitative fluorescence in situ hybridization and spectral karyotyping on the same human metaphases was applied successfully to examine the dynamic profiles of individual telomere shortening and their relationship to chromosome aberrations in multiple human cell lines undergoing immortalization. Human ovarian surface epithelial cells and esophageal epithelial cells were immortalized by the expression of HPV16 E6 and E7, which drive cells to proliferate by inactivating p53 and Rb genes. In these cell lines, we consistently detected large-scale differences in telomere signal intensities not only among nonhomologous chromosome arms but also between some homologous chromosome arms. The cell lines derived from different donors had different profiles of critically short telomeres (lacking telomere signals). Strikingly, the different profiles of chromosomal structural aberrations in multiple immortalized cell lines were highly significantly associated with the distinct distributions of critically short telomeres in whole-genome. Since cellular immortalization is one of the hallmarks of cancer, our findings suggest that distinct profiles of critically short telomeres in different human individuals might play an essential role in determining the complex and individual-specific chromosomal structural aberrations in human solid tumors.

Role of short telomeres in inducing preferential chromosomal aberrations in human ovarian surface epithelial cells: A combined telomere quantitative fluorescence in situ hybridization and whole-chromosome painting study.

It is well established that specific cancers and immortalized cells have nonrandom chromosome aberrations. However, little is understood about the underlying mechanism that initiates these aberrations in human cells. To examine whether human chromosomes with the shortest telomeres initiate the preferential chromosomal aberrations before cellular immortalization, we simultaneously applied telomere quantitative fluorescence in situ hybridization and specific whole-chromosome painting on chromosomes 1, 5, 8, 17, 19, and 20 in human ovarian surface epithelial (HOSE 6-3) cells expressing human papilloma viral oncogenes (HPV16 E6E7). The HPV16 E6E7-expressing cells, with extended in vitro life span and telomerase-negative status, were previously identified as having nonrandom chromosomal imbalances and high frequencies of dicentrics. Our analyses showed that among six pairs of targeted chromosomes, chromosomes 8 and 20 showed critically short telomeres with an undetectable telomere signal in more than 50% of cells analyzed. These chromosomes with the critically short telomeres were preferentially involved in various types of chromosomal aberrations including dicentrics, translocations, breaks, insertions, and losses or gains of chromosomal elements. Our findings suggest that nonrandom chromosome aberrations in HOSE cells occurring before cellular immortalization could be caused by the telomere length heterogeneity.

A new method for improving metaphase chromosome spreading.

BACKGROUND: The success of complex molecular cytogenetic studies depends on having properly spread chromosomes. However, inconsistency of optimum chromosome spreading remains a major problem in cytogenetic studies. METHODS: The metaphase spreading process was carefully timed to identify the most critical phase of chromosome spreading. The effects of dropping height of cell suspension, slide condition, drying time, fixative ratio, and relative humidity on the quality of metaphase spreads were studied by quantitative examination of metaphase chromosome spreads. Normal and immortalized human epithelial ovarian cells, neuroblastoma cells, and normal lymphocytes were tested. RESULTS: Humidity over the slide was the most important variable affecting the quality of chromosome spreads. Consistent improvement in chromosome spreading (larger metaphase area, less chromosome overlaps, or lower frequencies of broken metaphases) was obtained for all cell types if dynamic cell rehydration, occurring as fixative absorbs moisture from air, was made to coincide with the prompt fixation of spread chromosomes to the slide. This was achieved by dropping cells on dry glass slides placed in a shallow metal tray and then quickly lowering the tray into a covered 50 degrees C water bath for slide drying. CONCLUSIONS: A new and simple method for improving metaphase chromosome spreading was developed based on our study on the characteristics of chromosome spreading.