Intra- and Inter-individual Variation of Background and Radiation-induced Micronucleus Frequencies in Human Lymphocytes

Improving Patients’ Life Quality after Radiotherapy Treatment by Predicting Late Toxicities

Simple Summary

Over 50% of patients with cancer will receive radiotherapy treatment. Five to ten percent of patients who received radiotherapy will develop side effects. Identifying these patients before treatment start would allow for treatment modification to minimize these effects and improve the life quality of these patients. Our team developed a test, which allows predicting these secondary effects before starting the treatment. This will help in proposing personalized treatments to improve the outcome. This review presents how this test is performed, its results, as well as its modification in order to be used in hospitals.

Abstract

Personalized treatment and precision medicine have become the new standard of care in oncology and radiotherapy. Because treatment outcomes have considerably improved over the last few years, permanent side-effects are becoming an increasingly significant issue for cancer survivors. Five to ten percent of patients will develop severe late toxicity after radiotherapy. Identifying these patients before treatment start would allow for treatment adaptation to minimize definitive side effects that could impair their long-term quality of life. Over the last decades, several tests and biomarkers have been developed to identify these patients. However, out of these, only the Radiation-Induced Lymphocyte Apoptosis (RILA) assay has been prospectively validated in multi-center cohorts. This test, based on a simple blood draught, has been shown to be correlated with late radiation-induced toxicity in breast, prostate, cervical and head and neck cancer. It could therefore greatly improve decision making in precision radiation oncology. This literature review summarizes the development and bases of this assay, as well as its clinical results and compares its results to the other available assays.

Influence of sample preparation optimization on the accuracy of dose assessment of an automatic non-fluorescent MN scoring system

PURPOSE

Automatizing the scoring of the cytokinesis-blocked micronucleus assay spares a lot of valuable time. The dose-effect relationship can be applied reliably for dose estimation if the quality of the slides is the same from the perspective of the used image processing algorithm. This aspect brings in additional requirements against the quality of the slides compared to the conventional visual scoring.

MATERIALS AND METHODS

An add-in software was created to the non-fluorescent RS-MN automatic MN scoring system which is capable of measuring quantitatively the degree of typical anomalies. The image processing is less reliable when the presence of these anomalies is more frequent. The behavior of the designed sample quality parameters (SQPs) was tested on in vitro irradiated peripheral blood samples (0, 1, and 2 Gy) obtained from a healthy donor and also on samples from patients undergoing low dose-rate brachytherapy.

RESULTS

We examined 20 different SQPs and identified two that are independent and correlate significantly with the error of the fully automatic MN frequency. One is related to the size of the cells and the other reflects the homogeneity of the environment. An equation was established which presents a connection between the error of the auto MN frequency and the SQPs. By adding a fourth cleaning step to the conventional sample preparation and changing the pre-dripping temperature of the slide, the SQP can be modified, and consequently, the sample quality can be improved. The gain in accuracy is 54 ± 10 MN per 1000 binucleated cells, which corresponds to the effects of 0.5 Gy. Around the lowest limit of detection (<0.5 Gy), it means a 50-100% drop in the error of dose, which is significant. With sample quality harmonization, the positive predictive value was raised to 80-93% depending on the dose.

CONCLUSIONS

With the technique described in this paper, the suitability for automated scoring of a micronucleus slide can be tested quantitatively and objectively. A method is presented with which in some cases the uncertainty of the assessed doses due to variance in sample quality can be decreased or if it is not possible its bias can be predicted. The proposed protocol leads to more reliable estimation of dose. The SQPs are designed in a way that they have the potential to be adapted to similar systems.

Prediction of the Acute or Late Radiation Toxicity Effects in Radiotherapy Patients Using Ex Vivo Induced Biodosimetric Markers: A Review

A search for effective methods for the assessment of patients' individual response to radiation is one of the important tasks of clinical radiobiology. This review summarizes available data on the use of ex vivo cytogenetic markers, typically used for biodosimetry, for the prediction of individual clinical radiosensitivity (normal tissue toxicity, NTT) in cells of cancer patients undergoing therapeutic irradiation. In approximately 50% of the relevant reports, selected for the analysis in peer-reviewed international journals, the average ex vivo induced yield of these biodosimetric markers was higher in patients with severe reactions than in patients with a lower grade of NTT. Also, a significant correlation was sometimes found between the biodosimetric marker yield and the severity of acute or late NTT reactions at an individual level, but this observation was not unequivocally proven. A similar controversy of published results was found regarding the attempts to apply G2- and γH2AX foci assays for NTT prediction. A correlation between ex vivo cytogenetic biomarker yields and NTT occurred most frequently when chromosome aberrations (not micronuclei) were measured in lymphocytes (not fibroblasts) irradiated to relatively high doses (4-6 Gy, not 2 Gy) in patients with various grades of late (not early) radiotherapy (RT) morbidity. The limitations of existing approaches are discussed, and recommendations on the improvement of the ex vivo cytogenetic testing for NTT prediction are provided. However, the efficiency of these methods still needs to be validated in properly organized clinical trials involving large and verified patient cohorts.

Analysis of oxidative stress status through MN test and serum MDA levels in PCOS women

Polycystic Ovary Syndrome (PCOS) is a multifactorial reproductive healthcare problem affecting 4-12% of women and a leading cause of female infertility worldwide. The potential genetic contributors of PCOS are unclear. However, over the past decade emerging evidence has shown that increased Oxidative Stress (OS) and decreased antioxidant status were often linked with PCOS. The present case-control study was aimed to assess the reactive oxygen species induced OS in women from South India. A total of 164 individuals comprising of 89 patients and 75 controls were enrolled in the present study. For all the subjects, the frequency of micronucleated cells (MNC) in epithelial samples and serum Malondialdehyde (MDA) levels were estimated to assess genomic instability and cytotoxicity respectively. A statistically significant difference between the groups were identified with respect to Body Mass Index, Waist to Hip Ratio, luteinizing hormone and prolactin levels (< 0.05), however the mean follicle stimulating hormone was not different between the groups (p = 0.055). The frequency of MN cells (5.89 ± 4.86 vs. 2.24 ± 2.01) and mean serum MDA (360.84 ± 87.08 vs. 301.70 ± 82.82) levels were considerably higher in patients than controls (p = < 0.0001), furthermore, a positive correlation was observed between MNC and MDA levels in patients (r = 0.349, p = 0.0008) and not in controls (r = 0.104, p = 0.37), suggest high OS in PCOS women. Therefore, MN assay and serum MDA levels may serve together or individually as biomarkers of OS in PCOS women.

[Radiosensitivity assays of normal tissues]

Radiotherapy allows locoregional control with systemic impact in some indications. Technologic advances decrease the dose received by normal tissues leading to a low crude number of late side effects near to 5%. Intrinsic radiosensitivity are still of interest in this context of high level of technology and optimized treatments. Assays of radiosensitivity are detailed in this article arguing the negative results but also the perspectives.

Chromosomal radiosensitivity and acute radiation side effects after radiotherapy in tumour patients--a follow-up study

Background

Radiotherapists are highly interested in optimizing doses especially for patients who tend to suffer from side effects of radiotherapy (RT). It seems to be helpful to identify radiosensitive individuals before RT.

Thus we examined aberrations in FISH painted chromosomes in in vitro irradiated blood samples of a group of patients suffering from breast cancer. In parallel, a follow-up of side effects in these patients was registered and compared to detected chromosome aberrations.

Methods

Blood samples (taken before radiotherapy) were irradiated in vitro with 3 Gy X-rays and analysed by FISH-painting to obtain aberration frequencies of first cycle metaphases for each patient. Aberration frequencies were analysed statistically to identify individuals with an elevated or reduced radiation response. Clinical data of patients have been recorded in parallel to gain knowledge on acute side effects of radiotherapy.

Results

Eight patients with a significantly elevated or reduced aberration yield were identified by use of a t-test criterion. A comparison with clinical side effects revealed that among patients with elevated aberration yields one exhibited a higher degree of acute toxicity and two patients a premature onset of skin reaction already after a cumulative dose of only 10 Gy. A significant relationship existed between translocations in vitro and the time dependent occurrence of side effects of the skin during the therapy period.

Conclusions

The results suggest that translocations can be used as a test to identify individuals with a potentially elevated radiosensitivity.

Chromosome aberrations in peripheral blood lymphocytes of Croatian hospital staff occupationally exposed to low levels of ionising radiation

Medical staff is an occupational group exposed to different agents suspected to induce genetic damage. Among them ionising radiation is the most studied. Cytogenetic analysis of human chromosomes in peripheral lymphocytes allows direct detection of mutation in somatic cells. This study investigated the cytogenetic effects of low-level ionising x-radiation in 48-hour peripheral blood lymphocyte cultures sampled from 765 hospital staff occupationally exposed to several agents known or suspected to induce chromosome damage and compared them with 200 control subjects. The exposed subjects were divided in eight (8) groups according to their specialties and job titles. The exposed groups manifested an increase in all types of chromosome aberrations. Acentric fragments were the most frequent chromosome-type aberration. Dicentric chromosomes were statistically significant only in urologists/gynaecologists. Age and smoking significantly influenced the incidence of dicentrics in the exposed groups. The frequency of ring chromosomes was low in all exposed groups (range: 0-2), and none were found in the control group. These findings indicate the importance of periodic medical checkups of hospital staff occupationally exposed to low doses of ionising radiation. The purpose is to create an individual cytogenetic register, where changes could evidence individual risks.

Cytogenetic radiosensitivity of g0-lymphocytes of breast and esophageal cancer patients as determined by micronucleus assay

Enhanced chromosomal radiosensitivity is a feature of many cancer predisposition conditions, indicative of the important role of chromosomal alterations in carcinogenesis. In this study the cytokinesis-blocked micronucleous assay was used to compare the radiosensitivity of blood lymphocytes obtained from Iranian breast or esophageal cancer patients (n = 50, n = 16; respectively) with that of control individuals (n = 40). For each sample, one thousand binucleate lymphocytes were analyzed before and after in vitro exposure to 3 Gy of gamma rays. The radiation-induced frequency of micronucleus was significantly higher in the breast cancer group (261/1,000 binucleated cells) than in esophageal cancer group (241/1,000 binucleated cells, P < 0.01) or in the control group (240/1,000 binucleated cells, P < 0.01). The results indicate that breast cancer patients are more radiosensitive compared to normal healthy individuals or esophageal cancer patients. Increased radiosensitivity could be due to defects in DNA repair genes involved in breast cancer formation. Since patients with esophageal cancer did not show elevated radiosensitivity, it is assumed that the contribution of radiosensitivity-related genes to the development of esophageal cancer may be smaller than the contribution of those genes to breast cancer.

Frequency of micronuclei in peripheral blood lymphocytes from subjects occupationally exposed to low levels of ionizing radiation

The aim of this study was to evaluate the genotoxic effect of low dose of occupational radiation exposure in Nuclear Medicine Department employees, by using cytokinesis-blocked micronucleus assay in peripheral blood lymphocytes. The study included 46 exposed individuals together with 27 from the same area without occupational exposure to radiation which served as controls. The results obtained were evaluated with respect to age, gender, smoking habits, pathological condition and the occupational exposure to radiation of the individuals. The frequency of micronuclei increased significantly with the age of the subjects (P = 0.007). However there were no significant differences in micronucleus frequency with gender, smoking habits and occupational exposure. The frequency of micronuclei was significantly higher in individuals with presence of pathological condition (P < 0.0001) in comparison to healthy population irrespective of their exposure status.

Effect of a low-dose ethinylestradiol and gestodene in combination on the frequency of micronuclei in human peripheral blood lymphocytes of healthy women in vivo

BACKGROUND

Since most oral hormonal contraceptives contain a fixed combination of ethinylestradiol and gestodene as an estrogenic/progestogenic component, we decided to evaluate the possible mutagenic effect of a low-dose contraceptive pills containing 20 microg ethinylestradiol and 75 microg gestodene.

METHODS

A total of 30 healthy women received hormonal contraception during six consecutive menstrual cycles. A single daily dose was 20 microg ethinylestradiol and 75 microg gestodene. The pills were taken orally in a monthly cycle of 3 weeks on and 1 week off. In the investigation of the mutagenic effect of these contraceptive pills in vivo, the cytokinesis block micronucleus (CBMN) test was used, and the frequency of micronuclei (MN) in peripheral blood lymphocytes was determined.

RESULTS

Average MN frequency in women before therapy was 7.40 +/- 0.75 MN/1000 analyzed cells, and after therapy was 7.37 +/- 0.59 MN/1000 analyzed cells (p > 0.05).

CONCLUSION

Our data suggest that oral contraception with 20 microg ethinylestradiol and 75 microg gestodene in combination during six consecutive menstrual cycles does not induce micronuclei in peripheral blood lymphocytes of women.

Ascorbic acid potentiates mitomycin C-induced micronuclei and sister chromatid exchanges in human peripheral blood lymphocytes in vitro

Vitamin C (l-ascorbic acid), an effective free radical scavenger present as ascorbate in most biological systems, is one of the most extensively studied antioxidant vitamins. Vitamin C acts as either a free radical scavenger or a pro-oxidant producing hydrogen peroxide and free radicals. The modulatory effect of L-ascorbic acid (AA) on Mitomycin C (MMC) induced chromosome damage has been evaluated in human peripheral blood lymphocytes in vitro. The effect of L-ascorbic acid, 200 microg/ml as 1- and 2-h pretreatment on the frequencies of the biomarkers micronuclei (MN), sister chromatid exchanges (SCEs), and chromosome aberrations (CA) induced by mitomycin C 0.1 and 0.2 microg/ml has been studied. AA pretreatment caused a statistically significant increase in MMC-induced MN and SCE frequencies for all treatment groups, but did not show an increase in induced chromosome aberrations compared to MMC treatment alone. Cell division delays caused by MMC was reversed in the presence of AA. Interindividual variability in MMC as well as AA plus MMC-induced MN, SCE, and CA frequencies were evident. Ascorbic acid potentiated MMC-induced chromosome damage in human lymphocytes in vitro. The potentiation observed has to be viewed in the light of metal ion catalysed autooxidation of AA in oxygenated media and the existence of an antioxidant system in vivo that inactivates oxyradicals before their interaction with DNA.

Mutagenic and cytotoxic effectiveness of diisopropyl xanthogen polysulphide in human lymphocyte cultures

The mutagenic and cytotoxic effectiveness of the new rubber vulcanisation accelerator diisopropyl xanthogen polysulphide (Robac AS 100) was tested in human lymphocyte cultures of four healthy probands. The concentrations of Robac AS 100 were 0.57, 5.7 and 57.0 microg/ml. Higher concentrations showed too high cytotoxicity to be evaluable. Without external activation, incubation time with Robac AS 100 was 21 h. In the presence of rat liver microsomes from aroclor-induced rats (2mg microsomal protein/ml), incubation of the test compound was 2h. Mutagenicity testing was performed by analysis of micronuclei (MN), structural chromosome aberrations (CAs) and sister chromatid exchanges (SCEs). The MN-rate was determined using the cytochalasin B (cyt B) block method. For evaluation of cytotoxicity, mitotic index (MI) and nuclear division index (NDI) were determined. The validity of the test methods was ascertained by positive controls: mitomycin C (MMC) and bleomycin (BLM) were used in experiments without exogenous activation and cyclophosphamide (CP) in experiments with exogenous activation. The presence of rat liver microsomes increased the mutagenic effect of Robac AS 100 in the SCE- and MN-test. But only the highest Robac AS 100-concentration (57.0 microg/ml) showed significantly increased mutagenic activity in all tests. However, cytotoxicity at this concentration was already substantial. Therefore, we consider the evidence for mutagenicity of Robac AS 100 as limited.

The micronucleus and G2-phase assays for human blood lymphocytes as biomarkers of individual sensitivity to ionizing radiation: limitations imposed by intraindividual variability

As part of a program to assess the applicability of the micronucleus (MN) and G2-phase assays as biomarkers of cancer susceptibility, we investigated the inter- and intraindividual variations of these end points. For the MN assay, unstimulated blood cultures from 14 healthy donors were exposed in vitro to 3.5 Gy 60Co gamma rays; for the G2-phase assay, PHA-stimulated cell cultures were irradiated with a dose of 0.4 Gy 60Co gamma rays in the G2 phase of the cell cycle. Two of the 14 volunteers were assayed 9 times over a period of 1 year. The repeat experiments revealed that the intraindividual variability was not significantly different from the interindividual variability for both the G2-phase and MN assays. Since the intraindividual variability determines the reproducibility of the assay, our results highlight the limitations of these end points in detecting reproducible differences in radiation sensitivity between individuals within a normal population. For example, one donor of the population was identified as being radiosensitive (based on the 90th percentile criterion) but turned out to be normal when the assay was repeated twice. We conclude that the determination of individual radiosensitivity with these two cytogenetic assays is unreliable when based on one blood sample.

The genotoxic risk of hospital, pharmacy and medical personnel occupationally exposed to cytostatic drugs--evaluation by the micronucleus assay

The aim of this study was to evaluate the genotoxicity of cytostatic drugs in hospital and pharmacy employees (n=100), occupationally exposed. The micronucleus assay was used to study lymphocytes in 247 peripheral blood samples. Samples were collected at "baseline level" without any cytostatic drugs exposure before recruiting or after at least 3 weeks without cytostatic drugs contact and at three times (cycle 1-3) post-exposure. Samples from 60 office employees served as controls. Furthermore, our results were compared to urinary analyses of cytostatic drugs (oxazaphosporines, anthracyclines, platinum) which were collected in parallel to the cytogenetic investigation. Statistical analyses were performed under consideration of age, gender and X-ray exposure. The frequency of micronuclei was significantly related to the age of the subjects (r(Spearman)=0.16; P<0.05). However, there were no significant differences in micronucleus rates between controls and exposed hospital workers. Similarly, micronucleus rates were not significantly different at the various sampling time points and there was no correlation between duration of employment and micronucleus rates. Furthermore, no correlation between current biomonitoring data of exposure (urine tests) and micronuclei frequency was found. Therefore, significantly increased genotoxic damage of the lymphocytes investigated in this study could not be demonstrated.

Mutagenic and cytotoxic effectiveness of zinc dimethyl and zinc diisononyldithiocarbamate in human lymphocyte cultures

The mutagenic and cytotoxic effectiveness of the vulcanisation accelerators zinc dimethyldithiocarbamate (ZDMC; ziram) and zinc diisononyldithiocarbamate (ZDINDC; arbestab Z) was tested in lymphocyte cultures of five healthy probands. ZDMC and ZDINDC (c=0.1, 1.0 and 10.0microg/ml) were studied in lymphocyte cultures without external metabolic activation. Additionally, incubation of the compounds (c=10.0microg/ml) was performed in the presence of liver microsomes from aroclor-induced rats (1 and 2h, 1 and 2mg microsomal protein). Genotoxicity testing was performed by analysis of chromosomal aberrations (CA), sister chromatid exchanges (SCEs) and micronuclei (MN). For evaluation of antiproliferative effects, mitotic index (MI) and cell cycle kinetics (CCK) were determined. In contrast to earlier investigations we found no significantly increased mutagenic or cytotoxic activity of ZDMC; ZDINDC also was inactive under these conditions.

Non-disjunction and chromosome loss in gamma-irradiated human lymphocytes: a fluorescence in situ hybridization analysis using centromere-specific probes

Centromere-specific DNA probes for chromosomes 4, 7 and 18 were used to simultaneously analyze chromosome loss, non-disjunction, breaks within the labeled region, and nucleoplasmic bridges induced by gamma rays in binucleated human lymphocytes. The doses used were 0, 1, 2 and 4 Gy, and approximately 1000 cells were scored per dose. Micronucleus frequency increased in a linear-quadratic fashion. For chromosome loss, significant increases were observed at 2 and 4 Gy, whereas for non-disjunction significant increases were observed at 1 Gy; thus non-disjunction allowed us to detect the effects of radiation at a lower dose than chromosome loss. The use of centromere-specific probes allowed discrimination between the clastogenic and aneugenic effects of ionizing radiation. The analysis of chromosome loss, not taking fragmented signals into account, ensures the detection of an aneugenic effect, which was not possible using pancentromeric probes. The frequency of chromosome breakage within the labeled regions was higher in nuclei than in micronuclei, suggesting an increase in the engulfment of chromosomal material by nuclei as a consequence of the presence of cytochalasin B in the cultures. Chromatin filaments connecting main nuclei, the so-called nucleoplasmic bridges, were observed in irradiated samples, and are a manifestation of rearranged chromosomes producing anaphase bridges.

Increased micronuclei frequencies in couples with reproductive failure

A higher incidence of chromosomal instability in the infertile population is widely recognized. An increased level of micronuclei has been shown to be a marker of chromosome damage. Therefore, micronuclei frequencies were assessed in cytokinesis-blocked lymphocytes of 130 patients (65 couples) with idiopathic infertility or with two or more spontaneous abortions, and 30 healthy fertile donors (15 couples). The frequency of micronucleated cells in the cohort with reproductive failure and healthy controls averaged 14.95+/-6.04 per 1000 and 10.60 +/-2.57 per 1000 (P<0.0001), respectively. When micronuclei frequency sums in particular couples (male + female) were analyzed in the same order, identical statistical significance was reached (P<0.0001). We found no effect of age or sex on micronuclei frequency. In summary, the cytokinesis-blocked micronuclei assay revealed increased micronucleus frequency in couples with infertility or two or more spontaneous abortions, suggesting a possible role of chromosomal instability in reproductive failure.

Assessment of the micronucleus assay as a biological dosimeter using cytokinesis-blocked lymphocytes from cancer patients receiving fractionated partial body-radiotherapy

PURPOSE

To assess the suitability of the cytokinesis block micronucleus assay as a biological dosimeter following in-vivo radiation using cancer patients undergoing radiotherapy.

METHODS

Blood from 4 healthy donors was irradiated in vitro with gamma-rays and the dose response of induced micronuclei in binucleate lymphocytes following cytokinesis block was determined. Micronucleus frequency was ascertained before and at intervals during radiotherapy treatment in 6 patients with various tumors in the pelvic region. Equivalent whole body doses (physical doses) at these times were calculated from radiation treatment plans and cumulative dose volume histograms.

RESULTS

Linear dose response relationships were found for induced micronucleus frequency in lymphocytes resulting from both in-vitro and in-vivo irradiation. Doses resulting from in-vivo irradiation (biological doses) were estimated by substitution of micronucleus frequency observed in radiotherapy patients into the dose response curve from in-vitro irradiation of blood. The relationship between the biologically estimated dose (BD) and the calculated equivalent whole body dose (PD) was BD = 0.868 (+/- 0.043)PD + 0.117 (+/- 0.075).

CONCLUSION

The micronucleus assay appears to offer a reliable and consistent method for equivalent whole body radiation dose estimation, although our findings should be confirmed using lymphocytes from radiotherapy patients with tumors at anatomical sites other than the pelvis. Except at doses lower than about ).4 Gy, the method yields dose estimates acceptably close to "true" physically determined doses. The assay can be performed relatively rapidly and can be used as a "first line" biological dosimeter in situations where accidental exposure to relatively high radiation doses has occurred.

Interindividual variation in cytogenetic response to X-ray and colchicine measured with the cytokinesis-block micronucleus assay

Interindividual variation in cytogenetic response to two different types of micronucleus (MN) inducer, X-rays (a clastogen) and colchicine (a spindle poison), was investigated in the peripheral blood lymphocytes of normal healthy donors by the cytokinesis-block MN method. The data for 124 donors between the ages of 19 and 80 years showed that the histogram of individual frequency of X-ray (2 Gy)-induced micronucleated cells followed the normal distribution (Shapiro Wilks W-test) with a significant interindividual variance (ANOVA, p < 0.001). This was, however, not the case for colchicine (0.03 microgram/ml)-induced micronucleated cells. Instead, a skewed distribution illustrating interindividual variation was evident (ANOVA, p < 0.001). Statistical analysis of the effect of age and sex on MN incidence by using the Kruskal-Wallis test indicated that age affected the baseline and colchicine-induced MN incidences strongly but not the X-ray-induced MN incidence. There was no effect of sex on the incidence of micronuclei induced by either agent. In order to avoid any possible effect of age on the MN index, data for young subjects aged less than 30 years old were analyzed separately. The results of this analysis again showed significant interindividual variations in baseline, X-ray-induced, and colchicine-induced micronucleated cell rates. Results of the correlation-coefficient analysis showed that neither X-ray-induced MN incidence nor colchicine-induced MN incidence was related to baseline MN incidence. No correlation between X-ray-induced and colchicine-induced MN incidences was also found by this analysis. These results suggest that interindividual variance in chromosomal response to mutagens in normal populations may be a real phenomenon, as is interindividual variance in baseline MN frequency, and that individual susceptibilities to the two different types of micronucleus inducers (X-ray and colchicine) are unrelated, and the baseline MN level is not of predictive value for the susceptibilities.

Induction of micronuclei in human, goat, rabbit peripheral blood lymphocytes and mouse splenic lymphocytes irradiated in vitro with gamma radiation

The frequencies of gamma-ray-induced micronuclei (MN) in cytokinesis-blocked (CB) lymphocytes at several doses were measured in three donors of four species (human, goat, rabbit, mouse). Measurements performed after irradiation showed a dose-related increases in MN frequency in each of the donors studied. The relative sensitivity of mouse in spleen lymphocytes (SLs), goat in peripheral blood lymphocytes (PBLs) and rabbit PBLs compared with human PBLs was estimated by best fitting linear-quadratic model based on the radiation-induced MN data over the range from 0 to 400 cGy. In the case of MN frequency with 0.2, the relative sensitivities of mouse SLs, goat PBLs and rabbit PBLs were 1.67, 0.98 and 0.39, respectively. These data indicate that the induction of MN in CB cells following irradiation is similar in human and goat PBLs, and PBLs from rabbit were much less sensitive to the MN induction effects of gamma-radiation than those from human. Compared with the radiation-induced MN formation in the PBLs of human, the SLs of mouse were more radiosensitive.

Sources of variability in the determination of micronuclei in irradiated peripheral blood lymphocytes

Following a dose of 4 Gy 250 kVp X-rays to the blood lymphocytes from three healthy donors the frequency of micronuclei was enumerated by three scorers. Eight slides were prepared from each blood sample with 1000 cytokinesis-blocked binucleate cells being scored for micronuclei and a recount undertaken 4 weeks later. Seven possible sources of variation were investigated: differences between donors, scorers, the four stages of sample preparation and time. A complete factorial analysis indicated that the major sources of variation were differences between donors and differences between scorers. One scorer identified fewer micronuclei than did the other two scorers in all slides of the irradiated blood samples and gave wide and inconsistent results for baseline counts. These results suggest that the performance of scorers should be screened before undertaking analysis of micronuclei. The most striking result, however, was the consistent performance of the scorers on the repeat counts compared with the very large differences between the scorers.

Micronuclei in cytokinesis-blocked lymphocytes may predict patient response to radiotherapy

We have applied the cytokinesis-block micronucleus assay to peripheral blood lymphocytes of patients undergoing radiotherapy in pelvic and pulmonary sites, in order to evaluate the individual cytogenetic response. Our cytogenetic data correlated with the equivalent whole-body dose are homogeneous and compare well with the data presented by other authors. We have used an exponential mathematical formula to calculate the attenuation of the cytogenetic effect with time. The k coefficient (cytogenetic recovery factor) in the formula expresses the degree of attenuation. In lymphocytes from patients after radiotherapy, the trend of the micronucleus frequency observed after 2 Gy of in vitro X-irradiation demonstrates that the cytogenetic effect obtained in vitro is added to that obtained in vivo. The k coefficient is inversely proportional to the micronucleus frequency observed after 2 Gy in vitro. The micronucleus assay and the cytogenetic recovery factor are proposed as suitable diagnostic tools for application in the field of radiotherapy.

Micronuclei in lymphocytes of children from the vicinity of Chernobyl before and after 131I therapy for thyroid cancer

The present study addresses the monitoring of children from the Belorussian and Ukrainian Republics exposed to the fall-out of the Chernobyl accident. Micronucleus analysis has been performed on 56 children from different areas. The micronucleus frequencies in individuals as well as in regional groups were comparable with controls, except for three donors. Such results had to be expected, taking into account that at least 7 years have passed since the accident. Most of the children whose micronucleus frequencies were determined are suffering from thyroid cancer and were treated by radioiodine (131I) therapy. We studied the effect of in vitro exposure with 131I on micronucleus induction and that proliferative ability of lymphocytes. The present investigation indicates that micronuclei can be usefully employed to detect individual exposures to the incorporated radionuclide within several days after the intake of the radionuclide in a dose range of around 65-390 mGy (effective dose).

Detection of centromeres in vinblastine- and radiation-induced micronuclei of human lymphocytes using FISH with an alpha satellite pancentromeric DNA probe

Fluorescence in situ hybridisation (FISH) with a human alphoid satellite pancentromeric DNA probe was used to detect centromeres in micronuclei of human lymphocytes induced by gamma irradiation and by Vinblastine sulfate. In a cytokinesis-block micro-nucleus assay a dose-dependent increase of micronuclei was detected for both agents. 72-89% of vinblastine-induced micronuclei, but only 7-48% of radiation-induced micronuclei showed centromere-positive fluorescence signals. Vinblastine treatment frequencies of centromere-negative micronuclei did not increase compared to control values, nor did frequencies of centromere-positive micronuclei in irradiated lymphocytes. Since FISH with an alpha satellite DNA probe allows the direct detection of centromeric DNA sequences the spindle damaging or clastogenic effectiveness of a compound can be easily and reliably examined in a cytokinesis-block micronucleus assay in human lymphocytes.

Flow cytometric analysis of micronuclei in the CD2+/- subpopulation of human lymphocytes enriched by magnetic separation

An improved flow cytometric method for the scoring of micronuclei in human lymphocytes irradiated in vitro is presented. Because, especially in cultivated human lymphocytes, unspecific DNA-containing debris from dying cells can influence the measured frequency of micronuclei, a preselection of CD2 + population was performed before preparation of the suspension of micronuclei and nuclei. Magnetic separation using anti-CD2 antibody-conjugated magnetic beads were used for this purpose. The results obtained by this improved flow cytometric technique were compared with results obtained by microscopic scoring using the CB technique. No correlation was found when the individual values in unirradiated controls were compared, due mainly to the presence of DNA-containing particles from fragmented cell nuclei and other unspecific debris. The averaged data from nine dose-effect curves simultaneously analysed by both techniques showed a linear-quadratic dose dependence with alpha and beta's that were similar for flow cytometry and for microscopic scoring. Only the constant term was higher for the flow cytometric results. A correlation between both techniques applied to individual data at doses > 0.2 Gy could also be demonstrated. It is concluded that a dose estimation of man exposed to low doses of ionizing radiation can at present not be improved by the flow cytometric technique.

Dose dependence of radiation-induced micronuclei in cytokinesis-blocked human lymphocytes

Following selection of appropriate culture conditions, various experiments were conducted to evaluate the suitability of the micronucleus assay in cytokinesis-blocked lymphocytes for biological dosimetry purposes. A dose-effect relationship was determined, based on the frequency of micronuclei induced by various doses of 60Co gamma-rays. The data were best fitted to a linear-quadratic model. To validate the system, an attempt was made to estimate unknown dose levels from the yield of micronuclei, by inverting the derived dose-response function. It was concluded that the assay provides a valid approach for dose assessment. The size of radiation-induced micronuclei was measured in relation to the dose. A significant difference in the proportion of large micronuclei between high and low doses was observed. The chromosomal composition of micronuclei, detected by immunofluorescent staining of kinetochores, showed that only a small proportion of micronuclei contains kinetochore. The possible contribution of various mechanisms for the formation of large radiation-induced micronuclei is discussed.

Checks for chromosomal instability in Gorlin and non-Gorlin basal-cell carcinoma patients

The naevoid basal-cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder with multiple basal-cell carcinomas, an increased risk for other neoplasms, and various malformations. Chromosome instability has been implicated in the pathogenesis of this syndrome, but these reports are somewhat contradictory. We have investigated five patients, two with confirmed NBCCS and three suspected. No evidence for chromosome instability was found in lymphocytes at three sample times after stimulation using metaphase aberration analysis, sister-chromatid exchange (SCE) in second division cells, or micronuclei. A significant lengthening of the cell cycle was found for the two confirmed NBCCS patients, but not for the suspected cases.

Dose-response relationships of micronuclei in human lymphocytes induced by fission neutrons and by low LET radiations

The induction of micronuclei in cytokinesis-blocked human lymphocytes of different donors has been measured after G0 irradiation in vitro with a mixed fission neutron-gamma-ray beam, 220 kV X-rays and 60Co gamma-rays. The dose-response relationships for the micronucleus yields were linear-quadratic for both types of low LET radiations. The linear model applied for neutron-induced micronuclei over the dose range 0-0.66 Gy. At higher doses a saturation effect became apparent. For neutron-induced micronucleus yields a limiting RBE value of 12.2 was derived from the ratio of the alpha coefficients of neutrons and 60Co gamma-rays.

Intrinsic radiosensitivity of adult and cord blood lymphocytes as determined by the micronucleus assay

Predictive radiosensitivity testing necessitates rapid and reliable assays of radiosensitivity. We assessed the lymphocyte micronucleus assay as such an assay. We performed repeated experiments on lymphocytes from 10 healthy donors. Levels of radiation-induced micronuclei were measured following exposures of up to 4 Gy X-rays. When measuring the slope of the dose-response, we have found more variation between individuals than between repeated experiments on the same individual (F value 12.31, P < 0.001). There is also greater interindividual variation in the data following a single dose of X-rays of 2 Gy (F value 3.54, P < 0.01) and of 4 Gy (F value 7.55, P < 0.005). We performed the micronucleus assay on five different samples of cord blood lymphocytes (CBLs). Their radiosensitivities were compared with the mean radiosensitivity of the lymphocytes from the normal group of donors. Comparing the level of micronuclei induced by 2 Gy, only CBL1 (P < 0.01) and CBL2 (P < 0.02) were more radiosensitive than the mean of the adult lymphocytes. At 4 Gy, CBL1 (P < 0.001), CBL2 (P < 0.05), CBL3 (P < 0.01) and CBL5 (P < 0.01) were more radiosensitive than the mean radiosensitivity of the adult lymphocytes. This was also shown when the slope of the dose-response curves were measured. We conclude that the lymphocyte micronucleus assay shows more variability when applied to lymphocytes from different individuals than when repeatedly applied to lymphocytes from the same individual, a requirement for the determination of individual radiosensitivity.

Radiation dose-dependent variations of micronuclei production in cytochalasin B-blocked human lymphocytes

Using the cytokinesis-block technique, lymphocytes from healthy volunteers (n = 9) were evaluated for 1) the radiation dose-response curve for micronuclei (MN) expression; 2) technique variables on the yield of MN; and 3) the shortest lymphocyte incubation time required for the MN assay. We found that the best fitting of relationships between increasing MN production and increasing irradiation dose (0-4.0 Gy) was the linear-quadratic model as expressed by the yield equation Y = C+alpha D+beta D2 (P = 0.0003). When lymphocytes were irradiated in vitro with 2.0 Gy and harvested at various time intervals, MN increased during the entire 84 hr culture time. The radiation caused a division delay in lymphocyte as indicated by an increased frequency of mononucleated cells and a decreased number of mitotic indices. The data showed that a shortened culture time (60 hr) for the MN assay is possible and that binucleated cells with > or = 3 MN were found only in cells irradiated at > or = 2.0 Gy. These findings suggest that scoring of MN in lymphocytes may be a practical biological dosimeter for the rapid screening of accidental radiation exposure victims, especially when their clinical manifestations are not obvious.

Micronucleus frequency in cultured lymphocytes of an urban population

The frequencies of micronuclei in cultured cytokinesis-blocked lymphocytes of an urban industrial population of 188 persons were determined. For the mean and SD, 16.0 +/- 7.3 per 1000 CB cells were obtained. A slight but definite age dependence--appr. 0.2/1000 increase per year on average--was indicated by thorough statistical analysis.