Use of cytogenetic indicators in radiobiology

Effects of Whole Pelvic Radiotherapy on the Distribution of Lymphocyte Subpopulations in Prostate Cancer Patients

INTRODUCTION

In the current study, we have investigated the effects of the different modalities of treatment (volume of radiotherapy [RT], previous surgery) as well as the Gleason score of prostate cancer (PC) on the lymphocyte composition of PC patients undergoing RT.

METHODS

This is a monoinstitutional study that prospectively included PC patients that underwent RT from January 2016 until December 2017. To compare the different evaluations, the Wilcoxon signed-rank test was used among 2 times (Timepoint 0 to Timepoint 1). Percentage variation was calculated for all the lymphocyte subpopulation and was correlated with clinical parameters (previous surgery, Gleason score, and pelvic irradiation) with the χ2 test. The statistical analysis was repeated also on the stratified dataset according to the above parameters (previous surgery, Gleason score, and whole pelvic radiotherapy [WPRT]).

RESULTS

One hundred and eleven patients were included in the present analysis. All the lymphocyte subpopulations resulted significantly lower after RT. The modifications of several lymphocyte subpopulations correlated with previous surgery, Gleason score, and WPRT, although stratified analysis demonstrated that WPRT showed the greatest correlation.

CONCLUSION

Our results could be used to design a prospective trial in order to study the use of WPRT on the lymphocyte subpopulations.

The cytokinesis-block micronucleus assay for cryopreserved whole blood

PURPOSE

The cytokinesis-block micronucleus (MN) assay is a widely used technique in basic radiobiology research, human biomonitoring studies and in vitro radiosensitivity testing. Fresh whole blood cultures are commonly used for these purposes, but immediate processing of fresh samples can be logistically challenging. Therefore, we aimed at establishing a protocol for the MN assay on cryopreserved whole blood, followed by a thorough evaluation of the reliability of this assay for use in radiosensitivity assessment in patients.

MATERIALS AND METHODS

Whole blood samples of 20 healthy donors and 4 patients with a primary immunodeficiency disease (PID) were collected to compare the results obtained with the MN assay performed on fresh versus cryopreserved whole blood samples. MN yields were scored after irradiation with 220 kV X-rays (dose rate 3 Gy/min), with doses ranging from 0.5-2 Gy.

RESULTS

The application of the MN assay on cryopreserved blood samples was successful in all analyzed samples. The radiation-induced MN and NDI scores in fresh and cryopreserved blood cultures were found to be similar. Acceptable inter-individual and intra-individual variabilities in MN yields were observed. Repeated analysis of cryopreserved blood cultures originating from the same blood sample, thawed at different time points, revealed that MN values remain stable for cryopreservation periods up to one year. Finally, radiosensitive patients were successfully identified using the MN assay on cryopreserved samples.

CONCLUSIONS

To our knowledge, this study is the first report of the successful use of cryopreserved whole blood samples for application of the MN assay. The data presented here demonstrate that the MN assay performed on cryopreserved whole blood is reliable for radiosensitivity testing. Our results also support its wider use in epidemiological, biomonitoring and genotoxicity studies. The presented method of cryopreservation of blood samples might also benefit other assays.

Micronucleus Assay: The State of Art, and Future Directions

During almost 40 years of use, the micronucleus assay (MN) has become one of the most popular methods to assess genotoxicity of different chemical and physical factors, including ionizing radiation-induced DNA damage. In this minireview, we focus on the position of MN among the other genotoxicity tests, its usefulness in different applications and visibility by international organizations, such as International Atomic Energy Agency, Organization for Economic Co-operation and Development and International Organization for Standardization. In addition, the mechanism of micronuclei formation is discussed. Finally, foreseen directions of the MN development are pointed, such as automation, buccal cells MN and chromothripsis phenomenon.

CLINICAL APPLICATIONS OF BIOMARKERS OF RADIATION EXPOSURE: LIMITATIONS AND POSSIBLE SOLUTIONS THROUGH COORDINATED RESEARCH

Dosimetric biomarkers have been effectively and intensively used for a long time in the area of radiation protection. In contrast to that, no robust standards or widely accepted protocols for application of these end-points in radiotherapy, diagnostic and interventional radiology and nuclear medicine exist to date. The International Atomic Energy Agency (IAEA) organized the review of the available data on the possibilities of the use of dosimetric biomarkers in medical irradiation scenarios. The resultant Technical Report also contains a summary of identified problems, gaps in knowledge, limitations in methodology and recommendations for their overcoming. This work provided a conceptual background for the initiation of a new IAEA Coordinated Research Project E35010, MEDBIODOSE (2017-21), which is aimed specifically at the development and improvement of applications of biodosimetric markers in clinical practice.

Chromosomal abnormalities in roots of aquatic plant Elodea canadensis as a tool for testing genotoxicity of bottom sediments

Submersed freshwater macrophytes are considered as relevant indicators for use in bulk bottom sediment contact tests. The purpose of this study was to estimate the validity of endpoints of aquatic plant Elodea canadensis for laboratory genotoxicity testing of natural bottom sediments. The inherent level of chromosome abnormalities (on artificial sediments) in roots of E. canadensis under laboratory conditions was lower than the percentage of abnormal cells in bulk sediments from the Yenisei River. The percentage of abnormal cells in roots of E. canadensis was more sensitive to the presence of genotoxic agents in laboratory contact tests than in the natural population of the plant. The spectra of chromosomal abnormalities that occur in roots of E. canadensis under natural conditions in the Yenisei River and in laboratory contact tests on the bulk bottom sediments from the Yenisei River were similar. Hence, chromosome abnormalities in roots of E. canadensis can be used as a relevant and sensitive genotoxicity endpoint in bottom sediment-contact tests.

Use of the aquatic plant Elodea canadensis to assess toxicity and genotoxicity of Yenisei River sediments

The toxicity, cytotoxicity, and genotoxicity of bulk sediments from the Yenisei River (Siberia, Russia) were estimated in laboratory bioassays based on several endpoints in the aquatic plant Elodea canadensis. The bottom sediment samples were collected in the Yenisei River upstream and downstream of the sources of chemical and radioactive contamination. The testing revealed different sensitivities of Elodea endpoints to the quality of the bottom sediment: weight of shoots < length of shoots < mitotic index < length of roots < percentage of abnormal cells. The response of the genotoxicity endpoint (percentage of cells with chromosome abnormalities in roots of Elodea) was the highest in sediments with chemical pollution, whereas the highest inhibition of toxicity endpoints (shoot and root length) occurred in sediments with the highest level of radioactive pollution. The extreme response of Elodea endpoints to the quality of certain sediment samples may be regarded as related to the possible presence of unknown toxicants. The results show that E. canadensis can be used as an indicator species in laboratory contact testing of bottom sediment. The responses of shoot and root length growth endpoints of Elodea can be recommended as basic sensitivity indicators of bottom sediment toxicity. Analysis of cells carrying abnormal chromosomes in the apical root meristem of Elodea can be performed optionally in the same test to assess the genotoxicity of sediments.

Inter-individual variability in the response of human peripheral blood lymphocytes to ionizing radiation: comparison of the dicentric and micronucleus assays

Ionizing radiation can induce a wide range of DNA damage that leads to chromosomal aberrations. Some of those aberrations (dicentrics and micronuclei) are applied in biodosimetry. Biological dosimetry assumes similar radiosensitivity of each donor, but it does not exclude inter-individual variations in radiation susceptibility. Therefore, for biological reasons, it is always challenging to investigate inter-individual variability in response to radiation. For mechanistic reasons, it is also interesting to investigate the correlation between dicentric and micronuclei formation in response to radiation. In this experiment, irradiated blood specimens from 14 healthy male and female donors have been used to evaluate inter-individual variability in response to the genotoxic effects of X-ray radiation, as well as the dose-response relationship and test sensitivity using two endpoints (dicentrics and micronuclei). The results showed similar patterns of cytogenetic biomarker distribution between donors, but differences in the response of some donors at some doses. Data also showed that responses of male donors were better detected using the dicentric test, while for females, micronucleus frequencies were higher in response to the same dose of radiation. No influence of smoking status or age on specific responses was observed. Group variability in response to radiation was evaluated using coefficient of variation for each group of individuals irradiated with the same doses; as the dose increases, group variability becomes substantially lower. Despite sporadic inter-individual variability, trend of radiation-induced changes was similar. Produced calibration curves for both types of damage revealed dicentrics as genetic damage more typical for radiation than micronuclei.

Gene expression as a biomarker for human radiation exposure

Accidental exposure to ionizing radiation can be unforeseen, rapid, and devastating. The detonation of a radiological device leading to such an exposure can be detrimental to the exposed population. The radiation-induced damage may manifest as acute effects that can be detected clinically or may be more subtle effects that can lead to long-term radiation-induced abnormalities. Accurate identification of the individuals exposed to radiation is challenging. The availability of a rapid and effective screening test that could be used as a biomarker of radiation exposure detection is mandatory. We tested the suitability of alterations in gene expression to serve as a biomarker of human radiation exposure. To develop a useful gene expression biomonitor, however, gene expression changes occurring in response to irradiation in vivo must be measured directly. Patients undergoing radiation therapy provide a suitable test population for this purpose. We examined the expression of CC3, MADH7, and SEC PRO in blood samples of these patients before and after radiotherapy to measure the in vivo response. The gene expression after ionizing radiation treatment varied among different patients, suggesting the complexity of the response. The expression of the SEC PRO gene was repressed in most of the patients. The MADH7 gene was found to be upregulated in most of the subjects and could serve as a molecular marker of radiation exposure.

Implementation of a dose-response curve for γ-radiation in the Portuguese population by use of the chromosomal aberration assay

An in vitro dose-response curve following exposure to γ-radiation was determined at the IST/ITN, by use of the chromosomal aberration assay. This is the first study of this kind carried out among the Portuguese population. Un-irradiated and γ-irradiated peripheral blood lymphocytes from 16 healthy donors were cultured. A total of 22,395 metaphases were analyzed for frequency and distribution of dicentrics and centric rings, as a function of the radiation dose. The dose-response data for dicentrics and dicentrics plus centric rings were fitted by use of a linear-quadratic model: Y(dic)=(0.0011±0.0006)+(0.0105±0.0035)D+(0.0480±0.0019)D(2) and Y(dic+rings)=(0.0011±0.0006)+(0.0095±0.0036)D+(0.0536±0.0020)D(2). Also, calibration curves related to age and gender were determined, but no significant differences were found. Following the establishment of the dose-response curves, a validation experiment was carried out with three individuals. Real and estimated doses, obtained with the dose-response curves, were in agreement. These results give us confidence to apply both dose-response calibration curves in future biological dosimetry requirements.

Whole mouse blood microRNA as biomarkers for exposure to γ-rays and (56)Fe ion

PURPOSE

Biomarkers of ionising radiation exposure are useful in a variety of scenarios, such as medical diagnostic imaging, occupational exposures, and spaceflight. This study investigates to what extent microRNA (miRNA) expression signatures in mouse peripheral blood can be used as biomarkers for exposures to radiation with low and high linear energy transfers.

MATERIALS AND METHODS

Mice were irradiated with doses of 0.5, 1.5, or 5.0 Gy γ-rays (dose rate of 0.0136 Gy/s) or with doses of 0.1 or 0.5 Gy (56)Fe ions (dose rate of 0.00208 Gy/s). Total RNA was isolated from whole blood at 6 h or 24 h after irradiation. Three animals per irradiation condition were used. Differentially expressed miRNA were determined by means of quantitative real-time polymerase chain reaction.

RESULTS

miRNA expression signatures were radiation type-specific and dose- and time-dependent. The differentially expressed miRNA were expressed in either one condition (71%) or multiple conditions (29%). Classifiers based on the differentially expressed miRNA predicted radiation type or dose with accuracies between 75% and 100%. Gene-ontology analyses show that miRNA induced by irradiation are involved in the control of several biological processes, such as mRNA transcription regulation, nucleic-acid metabolism, and development.

CONCLUSION

miRNA signatures induced by ionising radiation in mouse blood are radiation type- and radiation dose-specific. These findings underline the complexity of the radiation response and the importance of miRNA in it.

Current status of biodosimetry based on standard cytogenetic methods

Knowledge about dose levels in radiation protection is an important step for risk assessment. However, in most cases of real or suspected accidental exposures to ionizing radiation (IR), physical dosimetry cannot be performed for retrospective estimates. In such situations, biological dosimetry has been proposed as an alternative for investigation. Briefly, biodosimetry can be defined as individual dose evaluation based on biological endpoints induced by IR (so-called biomarkers). The relationship between biological endpoints and absorbed dose is not always straightforward: nausea, vomiting and diarrhoea, for example, are the most well-known biological effects of individual irradiation, but a precise correlation between those symptoms and absorbed dose is hardly achieved. The scoring of unstable chromosomal-type aberrations (such as dicentrics and rings) and micronuclei in mitogen-stimulated peripheral blood, up till today, has been the most extensively biodosimetry assay employed for such purposes. Dicentric assay is the gold standard in biodosimetry, since its presence is generally considered to be specific to radiation exposure; scoring of micronuclei (a kind of by-product of chromosomal damages) is easier and faster than that of dicentrics for dose assessment. In this context, the aim of this work is to present an overview on biodosimetry based on standard cytogenetic methods, highlighting its advantages and limitations as tool in monitoring of radiation workers' doses or investigation into accidental exposures. Recent advances and perspectives are also briefly presented.

The genotoxic effects in lymphocyte cultures of children treated with radiosynovectomy by using yttrium-90 citrate colloid

The aim of this study was to investigate the genotoxic effect on the peripheral blood lymphocytes potentially induced by yttrium-90 citrate colloid (Y-90) in children who were undergoing radiosynovectomy for hemophilic synovitis, using chromosomal aberration analysis (CA) and the micronuclei (MN) assay for detecting chromosomal aberrations, as well as the sister chromatid exchanges (SCE) technique for assessed DNA damage.

MATERIALS AND METHODS

Cytogenetic analyses were undertaken in 18 boys (mean age, 14.5 +/- 2.1 years) with hemophilic synovitis who underwent radiosynovectomy with Y-90. CA, MN, and SCE were evaluated just prior to, then at 2 and 90 days following radiosynovectomy from the peripheral lymphocytes of the children. An activity of 185 MBq of Y-90 was injected into the 18 knee joints under aseptic conditions. To check the possibility of leakage from the joint and its migration within the body, the patients underwent scanning under a dual-headed gamma camera at the hours 2 and 48 following the procedure.

RESULTS

The procedure was well tolerated in all the children, and there was no extra-articular activity owing to extra-articular leakage of radioactive material in whole-body imaging. The mean frequency of CA in lymphocytes determined prior to the onset of therapy (0.31 +/- 0.48/900 cells) was not significantly increased, in comparison to the control values obtained 2 (0.30 +/- 0.48/900 cells) and 90 days (0.15 +/- 0.37/900 cells) after radiosynovectomy (p = 1.0 and 0.625, respectively). We observed that MN frequency was mildly increased in lymphocytes 2 days after therapy (8.30 +/- 1.89 MN/1000 binucleated cells vs. 9.23 +/- 1.79 MN/1000 binucleated cells; p = 0.013). But there was no significant difference between the baseline and the day 90 control levels of MN (p = 0.196). In the analysis of SCE frequency, there were no significant differences between the baseline (8.11 +/- 0.77) and the control analysis performed 2 and 90 days following radiosynovectomy (8.18 +/- 0.77 and 8.07 +/- 0.74; p = 0.710 and 0.662, respectively).

CONCLUSIONS

The results of this study indicated that high radiation doses are not obtained by peripheral lymphocytes of children who undergo Y-90 radiosynovectomy and, therefore, they contradict a high cancer risk.

Monitoring the genotoxic effects of radiosynovectomy with Re-186 in paediatric age group undergoing therapy for haemophilic synovitis

PURPOSE

The aim of this study was to investigate the genotoxic effect on the peripheral blood lymphocytes potentially induced by Re-186 in paediatric age group undergoing radiosynovectomy for haemophilic synovitis, by using chromosomal aberration analysis (CA) and the micronuclei (MN) assay for detecting chromosomal aberrations, as well as the sister chromatid exchanges (SCE) technique for assessing DNA damage.

METHODS

Cytogenetic analyses were evaluated in 20 boys (mean age: 13.8 +/- 2.7 years) before, and 2 and 90 days after radiosynovectomy from the peripheral lymphocytes of the patients. Joint retention and extra-articular spread of the radionuclides were evaluated by using quantitative gamma camera imaging.

RESULTS

Imaging after radiosynovectomy revealed local lymph node visualization in 8 (40%) patients and hepatosplenic visualization in 3 (15%) patients due to extra-articular leakage of radioactive material. The mean frequency of chromosome aberrations (0.2 +/- 0.4/1000 cells) determined prior to the onset of therapy was not significantly increased in comparison with control values obtained 2 days (0.4 +/- 0.5/1000 cells) and 90 days (0.2 +/- 0.4/1000 cells) after therapy (P = 0.754 and P = 1.0). In the analysis of MN and SCE, when we compare the baseline levels, the mean MN and SCE frequencies were slightly higher in the control analyses performed 2 and 90 days after radiosynovectomy but there were no significant differences between baseline and control levels (chi(2) = 2.621, P = 0.270 and F = 0.573, P = 0.569, respectively).

CONCLUSION

The major finding of this study with relatively small sample is that, radiosynovectomy with Re-186 does not seem to induce early genotoxic effects on the peripheral blood lymphocytes in paediatric age group.