Radon alpha track counting on solid state nuclear track detector by an ImageJ-based software macro.

Radon (222Rn) is a radioactive gas emanating from geological materials. Inhalation of this gas is closely related to an increase in the probability of lung cancer if the levels are high. The usual methodology for the quantification of radon by passive methods is the use of etched solid-state nuclear track detectors, frequently in combination with optical microscopes or image scanning for image acquisition and software-based image processing for track counting. Currently available commercial instrumentation, as the Radosys microscopy system, is quite expensive, so the development of alternative methodologies is desirable. In this work, a simple, fast and low-cost image acquisition system for the determination of tracks in chemically etched CR-39 solid-state nuclear track detectors to quantify 222Rn alpha tracks has been proposed. The image of the detector surface is obtained by a conventional light stereoscopic microscope, transmitted by a CCD camera into the computer, and analyzed by the ImageJ open-source software. This methodology was employed to analyze 45 samples collected in dwellings and caves located in the region of Extremadura (Southwest Spain). Results show a good correlation coefficient of r2 = 0.98 between the reference and purposed methodology and excellent repeatability, demonstrating that the system enables routine counting tracks for radon measurement as an alternative to the Radosys microscopy instrument.

Telomere length modulates human radiation sensitivity in vitro.

The molecular basis of the interindividual differences of normal individuals to ionizing radiation is poorly understood. Several studies in telomerase KO mice with short telomeres have uncovered an inverse relationship between telomere length and radiation sensitivity. The present work aims to determine if chromosome radiosensitivity is correlated with telomere length in healthy individuals. With this purpose, individual radiosensitivity was determined by the micronucleus assay in peripheral blood lymphocytes from two groups of individuals of the same age but with highly heterogeneous telomere length, selected from a population of 181 individuals where we previously measured telomere length. Our study demonstrates that telomere length modulates chromosome in vitro radiosensitivity in healthy individuals as the group with short telomeres presented higher frequencies of ionizing radiation-induced micronuclei when compared to the long telomeres group. This result supports the conclusion that individual telomere length acts as biomarker of individual chromosome instability upon exposure to ionizing radiation.

Radiation-induced chromosome aberrations in human euchromatic (17cen-p53) and heterochromatic (1cen-1q12) regions.

The constitutively heterochromatic 1q12 band and the primarily euchromatic 17cen-p53 region comprise a similar size in terms of percentage of the total human genome but have a completely distinguishable chromatin structure. The aim of this study is to unravel whether this structural difference has an impact on the formation and processing of radiation-induced chromosome aberrations. To do so, we have analysed the initial induction and the long-term persistence of radiation-induced (3 Gy gamma-rays) chromosomal aberrations with breakpoints in either the 1q12 band or the 17cen-p53 region in comparison with the behaviour of the overall genome. The fusigenic potential of euchromatic and heterochromatic ends was also compared. This time course experiment was performed in a human lymphoblastoid cell line with sampling times at 1, 3, 7, 14 and 56 days after irradiation. The outcome of this study, with 68 000 metaphases studied by multicolour FISH, with centromeric (1cen and 17cen), paracentric (1q12) and locus specific (p53 gene) probes, revealed: (i) a similar radiosensitivity of all regions analysed irrespective of their chromatin configuration; (ii) a possible enhanced fusigenic potential of heterochromatic chromosome ends; (iii) a rapid decline of 1q12 translocations; and (iv) a similar long-term behaviour of translocations involving 1q12 and 17cen-p53. The implications of these findings in biomonitoring studies are discussed.

Induction, processing and persistence of radiation-induced chromosomal aberrations involving hamster euchromatin and heterochromatin.

Euchromatic and heterochromatic regions are easily distinguished in Chinese hamster sex chromosomes, hence offering the possibility of studying the role of chromatin structure in the induction, processing and persistence of radiation-induced chromosome damage. X-ray (4 Gy)-induced breaks in the euchromatic Xp and in the heterochromatic Xq were analysed immediately and 4h after irradiation by premature chromosome condensation (PCC) in combination with either FISH using chromosome arm-specific probes or Giemsa staining. The study, performed with female Chinese hamster splenocytes, was extended to a 34 h recovery followed by arm-specific FISH in metaphase. A significant over-involvement of the heterochromatic Xq in radiation-induced breakage was observed at all sampling times (p<0.001). However, the heterochromatic state had little effect on the processing of the induced lesions. In a second experiment, the persistence of radiation-induced chromosome aberrations (CAs) involving Xp, Xq and Y chromosome was studied with cultured Chinese hamster male splenocytes sampled 30, 56 and 96 h after irradiation (4 Gy). A higher involvement of the heterochromatic regions (Xq and Y) in radiation-induced CAs was again observed in the first sampling time (p<0.001), suggesting that Chinese hamster heterochromatin could be more radiosensitive than euchromatin. Cells with CAs involving heterochromatin were apparently less persistent than those with lesions involving euchromatin. This observation could be attributable to either the distribution of CA per cell or to the fraction of potentially stable exchanges.

Equal induction and persistence of chromosome aberrations involving chromosomes 1, 4 and 10 in thyroid cancer patients treated with radioactive iodine.

A number of in vitro studies have questioned the assumption of random distribution of breaks in radiation-induced chromosome aberrations. The therapeutic application of radioactive 131I in thyroid cancer patients offers a good opportunity to study the induction and persistence of cytogenetic damage involving different chromosomes in vivo. Using whole-chromosome painting probes and triple colour painting by fluorescence in situ hybridization (FISH), we have analysed the frequency of chromosomal aberrations (CAs) involving chromosomes 1, 4 and 10 in peripheral blood lymphocytes of 10 thyroid cancer patients sampled before and 1 week, 1 year and 3.5 years after therapeutic application of radioactive iodine in a self-controlled, longitudinal study. A highly significant 3.4-fold increase in the frequency of chromosome breaks was observed 1 week after treatment with a similar representation of all chromosomes analysed. Although a significant decrease in dicentrics was observed during the first year after treatment, the frequency of chromosome aberrations remained over control levels until the last sampling time, 41-47 months post-treatment. The same behaviour, in terms of induction and persistence, was observed for all three chromosomes, confirming our previous results in vitro and rejecting the reported suggestion that chromosome 10 is radiosensitive in vivo. Our finding that the dynamics of radiation-induced CA in vivo is independent on the chromosome of choice suggests that this variable is not important in retrospective studies.

Multicolour FISH detection of radioactive iodine-induced 17cen-p53 chromosomal breakage in buccal cells from therapeutically exposed patients.

Simultaneous labelling of 17cen and the p53 locus by multicolour FISH was used to monitor radioactive iodine-induced structural and numerical chromosome abnormalities in buccal cells from 29 hyperthyroidism and thyroid cancer patients sampled before and after therapeutic treatment. This novel methodology allowed the efficient detection of 17p deletions leading to p53 allelic deletions, 17p gains and whole chromosome 17 numerical abnormalities in epithelial cells. Highly significant increases in the frequency of cells with (i) 17p abnormalities (1.8-fold; P < 0.001), including p53 monoallelic deletions (2.1-fold; P < 0.001) and 17p gains (3.5-fold; P < 0.001); (ii) chromosome 17 numerical abnormalities (2-fold; P < 0.001); and (iii) simultaneous 17p breakage and chromosome 17 numerical abnormalities (2.3-fold; P < 0.001), were observed after radioactive iodine treatment. As expected, the major contribution to these increases was detected in hyperthyroidism patients compared with thyroid cancer patients who suffered thyroidectomy before radioactive iodine exposure and, therefore, experienced a rapid elimination of the radioisotope. Considering that both the genetic endpoints and the target tissue are extremely relevant in carcinogenesis, it is suggested that the observed genetic damage could contribute to the reported increase in cancer risk of people therapeutically or accidentally exposed to radioactive iodine.

Low persistence of radiation-induced centromere positive and negative micronuclei in cultured human cells.

The micronucleus (MN) assay is widely used both in genetic toxicology and in the biomonitoring of human populations. Lymphocytes, cell lines, and bone marrow and epithelial cells are usually employed as target systems in such studies. However, little effort has been done to assess the persistence of MN in highly proliferative cells. To study the behaviour of MN containing whole chromosomes or acentric fragments, we have performed a time course experiment on the persistence of gamma-ray (3 Gy) induced MN in a human lymphoblastoid cell line. The frequency and content of MN were analyzed 1, 3, 7, 14, and 56 days after irradiation by pancentromeric fluorescence in situ hybridization (FISH). We observed a clear induction of both centromere positive and negative MN at completion of the first mitotic division. The frequency of both types of MN drastically declined to basal levels 7 days after irradiation with an identical kinetics. We therefore conclude that centromere positive and negative MN are highly unstable upon cell division, indicating that the MN assay could not be a good biomarker of DNA damage induced by acute treatments in highly proliferative cells. The implication of our findings in biomonitoring and in genotoxicity studies is discussed.

Aneugenic activity in human cultured lymphocytes. An overall study with colchicine using the micronucleus assay and fluorescence in situ hybridization techniques.

The effects induced by aneugenic agents on chromosome segregation are manifold. The biological relevance of these effects has led to the development of assays specifically detecting aneugens. In this context, the micronucleus (MN) assay in binucleated human lymphocytes along with FISH has been considered a pertinent tool for detecting aneugenic and clastogenic activity. However, the MN assay is insensitive in detecting aneugenic effects other than chromosome loss. By using the aneugenic model compound colchicine and X chromosome centromere-specific FISH, we have shown that besides chromosome loss in binucleated cells, other effects such as MN in mononucleated cells, cells arrested at metaphase, polyploidy and non-disjunction are also consistently induced by aneugenic agents. A chromosome 1 centromeric probe was used simultaneously with X chromosome centromeric labeling in mononucleated cells in order to distinguish polysomy from polyploidy. It is concluded that all these effects should be considered for a comprehensive evaluation of aneugenic activity.

Clasificación de los rotavirus aislados de granjas porcícolas localizadas en el estado de Yucatán / Classification of rotaviruses isolated from pig farms in the state of Yucatan, Mexico

La diarrea infecciosa aguda (DIA) por rotavirus (RV) es un problema de salud que afecta a la industria porcina, causando porcentajes variables de morbilidad y mortalidad que repercuten en el crecimiento, en la ganancia de peso y en la conversión alimenticia de los lechones. En el estado de Yucatán un informe preliminar indica la presencia de un 8.8 por ciento de RV en el ganado porcino. El presente trabajo da a conocer la frecuencia y la clasificación de RV del ganado porcino en granjas ejidales y particulares. El diagnóstico se realizó por la técnica de electroforesis en geles de poliacrilamida y la determinación del subgrupo y serotipo por medio de la técnica de ELISA con anticuerpos monoclonales específicos. El 26 por ciento del total de las muestras examinadas fueron positivas; 84 por ciento en las granjas ejidales y 16 por ciento en granjas particulares. Se le determinó el subgrupo de RV a 24 muestras: el subgrupo I se observó en 95.84 por ciento y 4.16 fue para el subgrupo II. Se puede asignar serotipo a 8 muestras (4 fueron del serotipo 1 y 4 del 3). El patrón electroforético encontrado fue el largo y se observó el Grupo A en 69 muestras, el B en 3, el C en 1, infección mixta en 1. La frecuencia y la variedad de genogrupos demuestra la distribución de diversas cepas y grupos de RV que se encuentran circulando en el ganado porcino