Follow-up in the micronucleus frequencies and its subsets in human population with chronic low-dose gamma-irradiation exposure

Micronuclei in lymphocytes from currently active uranium miners

Micronuclei can be used as markers of past radiation exposure, but only few studies have dealt with uranium miners. In this paper, we report on micronuclei in lymphocytes from individuals currently working at Rožná, Czech Republic, the last functioning uranium mine in the European Union. A modified micronucleus-centromere test was applied to assess the occurrence of micronuclei in stimulated lymphocytes, as well as their content in terms of whole chromosomes or fragments. Compared with unexposed individuals, the miners had higher frequencies of micronucleus-containing lymphocytes and higher percentages of micronuclei without centromeres, and the differences were significant for both parameters (0.74 ± 0.60 vs. 0.50 ± 0.42, p = 0.017 and 49 ± 44 vs. 12 ± 21, p = 0.0002; means ± standard deviations). There were also significant correlations between one or other of these parameters on the one hand and various dose values on the other, in particular with a 'retrievable' dose, that is, a dose whose effect should still be recognisable in lymphocytes assuming a half-life of 3 years. The 'retrievable' dose at which a doubling of the micronucleus frequency was observed was around 35 mSv, corresponding to a total dose of 90 mSv received while working in the mines. Altogether, our data show that the micronucleus-centromere test is a valuable tool for the assessment of past radiation exposure in uranium miners. The scatter in the data is of course far too great to allow individual dosimetry, but for groups of a few dozen exposed individuals, the method can be used to monitor doses clearly below 100 mSv.

Increased frequency of micronuclei in lymphocytes of infertile males after exposure to gamma irradiation: a possible sign of genomic instability

PURPOSE

Induced chromosomal instability and micronucleus (MN) formation in blood lymphocytes of infertile men in comparison with fertile men exposed to gamma radiation was investigated.

METHODS

Blood samples of healthy and infertile donors were irradiated by 2 and 4 Gy Co-60 gamma-rays, then cultured in RPMI-1640 complete medium containing 1% phytoheamaglutinin (PHA) and incubated in a CO(2) incubator. Cytochalasin-B was added to the cultures at a final concentration of 4 μg/ml. Finally, harvesting, slide making, and analysis were performed according to standard procedures.

RESULTS

We observed a statistically significant difference between the frequencies of micronuclei in lymphocytes of infertile individuals, compared to healthy donors, before and after exposure to gamma rays. Although higher in azoospermia patients, the frequency of MN was not statistically different between infertile groups.

CONCLUSIONS

This study indicates that genomic instability in infertile men could probably contribute to the development of an impaired reproductive capacity.

Dynamics of micronuclei in rat skin fibroblasts after X irradiation

In a previous study, we demonstrated DNA damage, expressed as micronuclei, in binucleate dermal fibroblasts obtained from human skin 2-9 weeks after fractionated radiotherapy. Here we assessed micronuclei in X-irradiated skin fibroblasts from 9-14-week-old female Lewis rats as a function of time after a single dose of radiation to determine the lifetime of such damage in the skin. After irradiation with 5, 10, 15 and 18 Gy, formation of micronuclei at 1 day or 2 months postirradiation increased up to about 10 Gy, with evidence for a plateau at higher doses. The time course of micronuclei present in the skin fibroblasts demonstrated a plateau region (approximately 20 days after 18 Gy and about 2 months after 10 Gy) before the number of micronuclei started to decline. Residual micronuclei were observed for more than 1 year after irradiation. Monomicronucleated cells predominated in fibroblasts from nonirradiated skin, whereas in fibroblasts from irradiated skin, multimicronucleated cells predominated and persisted (together with monomicronucleated cells) in the residual levels of damage at late times. The results suggest that DNA damage in dermal fibroblasts can be assayed by the micronucleus assay in samples from irradiated skin up to 1 month after irradiation for doses up to at least 10 Gy. Further studies are needed to define the dose-response relationship in detail.

Induction of chromatid-type aberrations in peripheral lymphocytes of hospital workers exposed to very low doses of radiation

Radiological personnel represent workers exposed to low cumulative doses of radiation. As their surveillance is generally based on physical dosimetry, there is little or inconclusive information on biological effects due to radiation exposure at these doses. We aimed to explore the extent of chromosomal damage in circulating lymphocytes of hospital workers (technicians, nurses and physicians) chronically exposed to a very low level of radiation using conventional and molecular cytogenetic analyses (chromosome painting with chromosomes #2, #3 and #10 as probe cocktail). Compared with controls, exposed workers displayed a significant increase in the frequency of aberrant lymphocytes (1.26+/-0.11/100 cells versus 1.63+/-0.17/100 cells). In particular, exposed technicians showed significantly higher mean values than nurses or physicians (3.68+/-1.17/100 cells versus 1.36+/-0.18/100 cells and 1.36+/-0.09/100 cells, respectively). Interestingly, we found that the chromosomal damage was prevalently expressed as chromatid-type aberrations. Chromosome painting indicated that the frequency of chromosome rearrangements (CR; translocations and dicentrics pooled together) was approximately comparable between radiological workers and the control group. Moreover, we did not detect any significant difference due to radiation exposure when CR rates were considered separately for each of the three chromosomes in the probe cocktail.

Perspectives of micronuclear test in human lymphocytes cultivated in cytogenetic block conditions. Part 1: Cell proliferation

Cultivation of human blood lymphocytes under the conditions of cytokinetic block with cytochalasin B creates unique opportunity to analyze the total spectrum of the changes describing genome instability. The main task of the present publication is the analysis of a modern state, opportunities and outlooks of the micronuclear test on human blood lymphocytes. The special attention is given those directions of researches which are rather seldom present in the literature - to laws of cellular proliferation, to existence of physiological conditionality and genetic predisposition to development of effects of genome instability; to effects of emotional stress and the adaptive response to action of ionizing irradiation, etc. The material is presented in 2 consecutive publications. It is finished with discussion of methodical features of statement of culture, results of the microscopic analysis and ideology of creation of the conclusions of the study.

DNA damage in cytologically normal urothelial cells of patients with a history of urothelial cell carcinoma

In order to determine if patients with a history of previous urothelial cell carcinoma (UCC) but with current normal urinary cytology have DNA damage in urothelial cells, the single-cell gel electrophoresis (comet) assay was conducted with cells obtained by urinary bladder washings from 44 patients (28 with a history of previous UCC). Increased DNA damage was observed in cytologically "normal" urothelial cells of patients with a history of UCC when compared with referents with no similar history and after correcting the data for smoking status and age (P < 0.018). Increased DNA damage also correlated with the highest tumor grade, irrespective of time or course of the disease after clinical intervention (Kendall tau correlation, 0.37, P = 0.016). Moreover, aneuploidy, as assessed by DNA content ratio (DCR; 75th/25th percentile of total DNA fluorescence of 50 comets/patient) was unaltered by smoking status, but increased with UCC grade: 1.39 +/- 0.12 (median +/- 95% confidence interval; referents); 1.43 +/- 0.11 (Grade I UCC; P = 0.264, against referents); 1.49 +/- 0.16 (Grade II UCC; P = 0.057); 1.57 +/- 0.16 (Grade III UCC; P = 0.003). Micronucleated urothelial cells (MNC) were also scored on Giemsa-stained routine cytological smears and were found not to correlate with DNA damage or DCR. MNC frequencies were higher for patients with a history of UCC and/or smoking than referents with neither history, but there was no statistical difference between groups. Taken together, these results suggest that the normal-appearing urothelium of patients resected for UCC still harbor genetically unstable cells.