The lymphocyte cytokinesis-block micronucleus cytome assay and its application in radiation biodosimetry

Application of dosimetry systems and cytogenetic status of the child population exposed to diagnostic X-rays by use of the cytokinesis-block micronucleus cytome assay

Low-dose ionizing radiation used for medical purposes is one of the definite risk factors for cancer development, and children exposed to ionizing radiation are at a relatively greater cancer risk as they have more rapidly dividing cells than adults and have longer life expectancy. Since cytokinesis-block micronucleus cytome (CBMN Cyt) assay has become one of the standard endpoints for radiation biological dosimetry, we used that assay in the present work for the assessment of different types of chromosomal damage in children exposed to diagnostic X-ray procedures. Twenty children all with pulmonary diseases between the ages of 4 and 14 years (11.30 ± 2.74) were evaluated. Absorbed dose measurements were conducted for posterior-anterior projection on the forehead, thyroid gland, gonads, chest and back. Doses were measured using thermoluminescence and radiophotoluminescent dosimetry systems. It was shown that, after diagnostic X-rays, the mean total number of CBMN Cyt assay parameters (micronucleus, nucleoplasmic bridges and nuclear buds) was significantly higher than prior to diagnostic procedure and that interindividual differences existed for each monitored child. For the nuclear division index counted prior and after examination, no significant differences were noted among mean group values. These data suggest that even low-dose diagnostic X-ray exposure may induce damaging effect in the somatic DNA of exposed children, indicating that immense care should be given in both minimizing and optimizing radiation exposure to diminish the radiation burden, especially in the youngest population.

Reflections on the development of micronucleus assays

These are personal reflections on the development of methods to use micronuclei as a measure of genetic damage and their use in research and in toxicology by four people who have been intimately involved with this work, a personal rather than a comprehensive history. About 6000 papers have been published using such methods in many tissues in vivo or in cultured cells of many organisms from plants to humans, but the majority of the work has been on mammalian erythrocytes and human lymphocytes, the areas in which we have worked primarily. Although this is by no means a complete history, those working in the field may be interested in some of the personal events that lie behind the development and acceptance of methods that are now standard.

Ionizing radiation or mitomycin-induced micronuclei in lymphocytes of BRCA1 or BRCA2 mutation carriers

BRCA1 and BRCA2 genes are essential in preserving the integrity of genome, and it is not unambiguously clear whether the heterozygosity status may affect BRCA1 or BRCA2 functions. This may have implications for the clinical management of BRCA1 and BRCA2 mutation carriers both in breast cancer (BC) screening modality and in cancer treatment based on DNA-damaging or DNA-repair-inhibiting drugs. We investigated whether lymphocytes carrying BRCA1 or BRCA2 mutations displayed an increased sensitivity to radiation or mitomycin C (MMC) in vitro treatments. Peripheral blood from 21 BRCA1 mutation carriers (12 with BC and 9 healthy), 24 BRCA2 carriers (13 with BC and 11 healthy), 15 familial BC patients without detected mutation in BRCA1 or BRCA2 and 16 controls without familial history of cancer (5 with BC and 11 healthy) were irradiated or treated with MMC. Chromosomal damage was measured using the cytokinesis-block micronucleus assay. We evaluated micronuclei (MN) and nucleoplasmic bridges (NPBs). The BRCA2 mutation carriers and familial BC patients without detected mutation in BRCA1 or BRCA2 showed less basal NPB than BRCA1 carriers and controls. The BRCA1 (+/-) or BRCA2 (+/-) lymphocytes did not have increased frequencies of MN or NPB after irradiation. In contrast, BRCA2 (+/-) lymphocytes presented higher levels of MN after MMC exposure than BRCA1 carriers and controls. The monoallelic BRCA1 or BRCA2 pathogenic mutations seem not to be associated with an enhanced radiosensitivity. The mutation of one BRCA2 allele conferred an increased sensitivity to MMC, presumably because of the role of this gene in the repair of MMC-induced DNA damage. This finding indicates that the MMC-induced MN analysis could be useful in identifying functional deficiencies of BRCA2 or genes related to BRCA2. Since MMC can be used as an anti-cancer drug, these data may be relevant for the management and follow-up of BRCA2 mutation carriers.

A critical assessment of biodosimetry methods for large-scale incidents

Recognition is growing regarding the possibility that terrorism or large-scale accidents could result in potential radiation exposure of hundreds of thousands of people and that the present guidelines for evaluation after such an event are seriously deficient. Therefore, there is a great and urgent need for after-the-fact biodosimetric methods to estimate radiation dose. To accomplish this goal, the dose estimates must be at the individual level, timely, accurate, and plausibly obtained in large-scale disasters. This paper evaluates current biodosimetry methods, focusing on their strengths and weaknesses in estimating human radiation exposure in large-scale disasters at three stages. First, the authors evaluate biodosimetry's ability to determine which individuals did not receive a significant exposure so they can be removed from the acute response system. Second, biodosimetry's capacity to classify those initially assessed as needing further evaluation into treatment-level categories is assessed. Third, we review biodosimetry's ability to guide treatment, both short- and long-term, is reviewed. The authors compare biodosimetric methods that are based on physical vs. biological parameters and evaluate the features of current dosimeters (capacity, speed and ease of getting information, and accuracy) to determine which are most useful in meeting patients' needs at each of the different stages. Results indicate that the biodosimetry methods differ in their applicability to the three different stages, and that combining physical and biological techniques may sometimes be most effective. In conclusion, biodosimetry techniques have different properties, and knowledge of their properties for meeting the different needs for different stages will result in their most effective use in a nuclear disaster mass-casualty event.