Intra- and inter-laboratory variation in the scoring of micronuclei and nucleoplasmic bridges in binucleated human lymphocytes. Results of an international slide-scoring exercise by the HUMN project

Exposure assessment and cytogenetic biomonitoring study of workers occupationally exposed to extremely low-frequency magnetic fields

Human cytogenetic biomonitoring (HCB) has long been used to evaluate the potential effects of work environments on the DNA integrity of workers. However, HCB studies on the genotoxic effects of occupational exposure to extremely low-frequency electromagnetic fields (ELF-MFs) were limited by the quality of the exposure assessment. More specifically, concerns were raised regarding the method of exposure assessment, the selection of exposure metrics, and the definition of exposure group. In this study, genotoxic effects of occupational exposure to ELF-MFs were assessed on peripheral blood lymphocytes of 88 workers from the electrical sector using the comet and cytokinesis-block micronucleus assay, considering workers' actual exposure over three consecutive days. Different methods were applied to define exposure groups. Overall, the summarized ELF-MF data indicated a low exposure level in the whole study population. It also showed that relying solely on job titles might misclassify 12 workers into exposure groups. We proposed combining hierarchical agglomerative clustering on personal exposure data and job titles to define exposure groups. The final results showed that occupational MF exposure did not significantly induce more genetic damage. Other factors such as age or past smoking rather than ELF-MF exposure could affect the cytogenetic test outcomes.

Multi-level toxicity assessment of the antidepressant venlafaxine in embryos/larvae and adults of zebrafish (Danio rerio)

The toxic effects of venlafaxine (VLX) on aquatic organisms have already been verified and therefore are a proven matter of concern. Herein, we evaluated zebrafish embryos/adults after acute exposure to VLX. Embryos/larvae were exposed to different concentrations of VLX (100-1000 mg/L; 1.33 as a dilution factor), to evaluate mortality/developmental changos and to analyze biomarkers (0.002-100 mg/L). For adults, mortality, genotoxicity, and biomarkers were assessed in five different concentrations of VLX (1-100 mg/L). The median lethal concentration (LC50-168h) was 274.1 mg/L for embryos/larvae, and >100 mg/L for adults (LC50-96h). VLX decreased the heart rate frequency and caused premature hatching and lack of equilibrium in embryos/larvae exposed to different concentrations ranging from 100 to 562.5 mg/L. The activity of acetylcholinesterase (AChE) was inhibited in larvae exposed to 1, 25 and 100 mg/L. Glutathione-S-transferase (GST) activity was reduced in both larvae and adults after exposure to different concentrations, mainly at 25 mg/L. For both larvae and adults, lactate dehydrogenase (LDH) activity increased after 100 mg/L of VLX exposure. No DNA damage was observed in peripheral erythrocytes. Exposure to VLX may cause adverse effects on zebrafish in their early and adult life stages, interfering with embryo-larval development, and can induce physiological disturbances in adults.

Short- and long-term reproducibility of the COMET assay for measuring DNA damage biomarkers in frozen blood samples of the EPIC-Heidelberg cohort

The comet assay is widely used for quantification of genomic damage in humans. Peripheral blood derived mononuclear cells (PBMCs) are the most often used cell type for this purpose. Since the comet assay can be performed in an enhanced throughput format, it can be applied to large sample collections such as biobanks. The European Prospective Investigation into Cancer and Nutrition (EPIC) study is one of the largest existing prospective cohort studies, and the German Cancer Research Institute (DKFZ) in Heidelberg is a participating center with 25.000 frozen blood samples stored from around 25 years ago, enabling retrospective assessment of disease risk factors. However, experience with decades long frozen samples in the comet assay is so far missing. In Heidelberg, 800 study participants were re-invited twice between 2010 and 2012 to donate further blood samples. Here, we analyzed 299 Heidelberg-EPIC samples, compiled from frozen PBMC and buffy coat preparations selected from the different sampling time points. In addition, 47 frozen PBMC samples from morbidly obese individuals were included. For buffy coat samples, we observed a poor correlation between DNA damage in the same donors assessed at two sampling time points. Additionally, no correlation between DNA damage in buffy coat samples and PBMCs was found. For PBMCs, a good correlation was observed between samples of the same donors at the two time points. DNA damage was not affected by age and smoking status, but high BMI (>30; obesity) was associated with increased DNA damage in PBMCs. There was no indication for a threshold of a certain BMI for increased DNA damage. In conclusion, while 25 year-long stored buffy coat preparations may require adaptation of certain experimental parameters such as cell density and electrophoresis conditions, frozen PBMC biobank samples can be analyzed in the comet assay even after a decade of storage.

Blue light induces DNA damage in normal human skin keratinocytes

BACKGROUND

The generation of DNA damage by ultra-violet radiations (UV) is well established, and both the nature of the DNA lesions and their respective DNA repair pathways have largely been described. Besides UV rays, visible light constitutes a very important part of the sun spectrum where blue light is considered a significant contributor to premature aging. However, blue light-induced DNA damage has not been deeply explored yet.

METHODS

In the present study, we assessed in human skin keratinocytes the DNA and chromosome damaging activities of blue light rays (415 nm) as well as their associated DNA repair mechanisms.

RESULTS

Our results demonstrated that blue light induced dose-dependent DNA damage in human keratinocytes. Both oxidative and cyclobutane-pyrimidine-dimer (CPD) DNA lesions were generated. They were repaired through base excision repair (BER) and nucleotide excision repair (NER) pathways, respectively. Moreover, by using the micronucleus assay we demonstrated, for the first time, that a blue wavelength exerted a clastogenic/aneugenic effect in human keratinocytes, leading to chromosome aberration.

CONCLUSION

We concluded that, in normal human keratinocytes, blue light creates genotoxic lesions which might accelerate or at least contribute to premature skin aging.

Recommendations and quality criteria for micronucleus studies with humans

Micronucleus (MN) analyses in peripheral blood lymphocytes and exfoliated cells from different organs (mouth, nose, bladder and cervix) are at present the most widely used approaches to detect damage of genetic material in humans. MN are extranuclear DNA-containing bodies, which can be identified microscopically. They reflect structural and numerical chromosomal aberrations and are formed as a consequence of exposure to occupational, environmental and lifestyle genotoxins. They are also induced as a consequence of inadequate intake of certain trace elements and vitamins. High MN rates are associated with increased risk of cancer and a range of non-cancer diseases in humans. Furthermore, evidence is accumulating that measurements of MN could be a useful tool for the diagnosis and prognosis of different forms of cancer and other diseases (inflammation, infections, metabolic disorders) and for the assessment of the therapeutic success of medical treatments. Recent reviews of the current state of knowledge suggest that many clinical studies have methodological shortcomings. This could lead to controversial findings and limits their usefulness in defining the impact of exposure concentrations of hazardous chemicals, for the judgment of remediation strategies, for the diagnosis of diseases and for the identification of protective or harmful dietary constituents. This article describes important quality criteria for human MN studies and contains recommendations for acceptable study designs. Important parameters that need more attention include sufficiently large group sizes, adequate duration of intervention studies, the exclusion of confounding factors which may affect the results (sex, age, body mass index, nutrition, etc.), the evaluation of appropriate cell numbers per sample according to established scoring criteria as well as the use of proper stains and adequate statistical analyses.

Use of micronucleus assays for the prediction and detection of cervical cancer: a meta-analysis

Cervical cancer (CC) is the fourth most common cancer in women; the survival rates depend strongly on its early detection. The Pap test is the most frequently used diagnostic tool, but due to its limited sensitivity/specificity, additional screening tests are needed. Therefore, we evaluated the use of micronucleus (MN) assays with cervical cells for the prediction and diagnosis of CC. MN reflects structural and numerical chromosomal aberrations. A search was performed in Pubmed, Scopus, Thomson ISI and Google Scholar. Subsequently, meta-analyses were performed for different grades of abnormal findings in smears and biopsies from patients which were diagnosed with CC. Results of 21 studies in which findings of MN experiments were compared with data from Pap tests show that higher MN frequencies were found in women with abnormal cells that are indicative for increased cancer risks. MN frequency ratios increased in the order inflammation (2.1) < ASC-US and ASC-H (3.3) < LGSIL (4.4) < HGSIL (8.4). Furthermore, results are available from 17 investigations in which MN were scored in smears from patients with neoplasia. MN rates increased with the degree of neoplasia [CIN 1 (4.6) < CIN 2 (6.5) and CIN 3 (10.8)] and were significantly higher (8.8) in CC patients. Our meta-analysis indicates that the MN assay, which is easy to perform in combination with Pap tests, may be useful for the detection/prediction of CC. However, standardization (including definition of the optimal cell numbers and stains) and further validation is necessary before the MN test can be implemented in routine screening.

Can a digital slide scanner and viewing technique assist the visual scoring for the cytokinesis-block micronucleus cytome assay?

The cytokinesis-block micronucleus cytome (CBMNcyt) assay is a comprehensive method to measure DNA damage, cytostasis and cytotoxicity caused by nutritional, radiation and chemical factors. A slide imaging technique has been identified as a new method to assist with the visual scoring of cells for the CBMNcyt assay. A NanoZoomer S60 Digital Pathology slide scanner was used to view WIL2-NS cells treated with hydrogen peroxide (H2O2) and measure CBMNcyt assay biomarkers using a high-definition desktop computer screen. The H2O2-treated WIL2-NS cells were also scored visually using a standard light microscope, and the two visual scoring methods were compared. Good agreement was found between the scoring methods for all DNA damage indices (micronuclei, nucleoplasmic bridges and nuclear buds) and nuclear division index with correlation R values ranging from 0.438 to 0.789, P < 0.05. Apoptotic and necrotic cell frequency was lower for the NanoZoomer scoring method, but necrotic frequency correlated well with the direct visual microscope method (R = 0.703, P < 0.0001). Considerable advantages of the NanoZoomer scoring method compared to direct visual microscopy includes reduced scoring time, improved ergonomics and a reduction in scorer fatigue. This study indicates that a digital slide scanning and viewing technique may assist with visual scoring for the CBMNcyt assay and provides similar results to conventional direct visual scoring.

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.

The in vitro micronucleus assay using imaging flow cytometry and deep learning

The in vitro micronucleus (MN) assay is a well-established assay for quantification of DNA damage, and is required by regulatory bodies worldwide to screen chemicals for genetic toxicity. The MN assay is performed in two variations: scoring MN in cytokinesis-blocked binucleated cells or directly in unblocked mononucleated cells. Several methods have been developed to score the MN assay, including manual and automated microscopy, and conventional flow cytometry, each with advantages and limitations. Previously, we applied imaging flow cytometry (IFC) using the ImageStream® to develop a rapid and automated MN assay based on high throughput image capture and feature-based image analysis in the IDEAS® software. However, the analysis strategy required rigorous optimization across chemicals and cell lines. To overcome the complexity and rigidity of feature-based image analysis, in this study we used the Amnis® AI software to develop a deep-learning method based on convolutional neural networks to score IFC data in both the cytokinesis-blocked and unblocked versions of the MN assay. We show that the use of the Amnis AI software to score imagery acquired using the ImageStream® compares well to manual microscopy and outperforms IDEAS® feature-based analysis, facilitating full automation of the MN assay.

Association between glycation biomarkers, hyperglycemia, and micronucleus frequency: A meta -analysis

Micronucleus assay has been used as a biomarker of DNA damage, chromosomal instability, cancer risk and accelerated aging. In this review, a meta-analysis was performed to assess the association between micronuclei (MNi) and diseases with increased advanced glycation end products (AGEs) and HbA1c. The review identified eight studies with 632 subjects with disease and 547 controls. The Mean Ratio (MRi) for AGE levels (MRi = 2.92, 95 %CI: 2.06-4.13, P < 0.00001) and HbA1c levels (MRi = 1.32, 95 %CI: 1.12-1.56, P = 0.001) were significantly higher in the disease group compared to healthy controls. The meta-analysis indicated that the overall estimates of MRi for MNi was 1.83 (95 %CI: 1.38-2.42, p < 0.0001) in subjects with disease compared to controls. Significant increases in MRi for MNi were also observed in the following sub-groups: subjects with disease for elevated AGEs (MRi = 1.62, 95 %CI: 1.12-2.35, P = 0.01), elevated HbA1c (MRi = 2.13, 95 %CI: 1.33-3.39, P = 0.002), lymphocytes MNi (MRi = 1.74, 95 %CI: 1.29-2.33, P = 0.0003), exfoliated buccal cells MNi (MRi = 2.86, 95 %CI: 1.19-6.87, P = 0.02), type 2 diabetes mellitus (T2DM) (MRi = 1.99, 95 %CI: 1.17-3.39, P = 0.01), chronic renal disease (MRi = 1.68, 95 %CI: 1.18-2.38, P = 0.004) and other disease groups (MRi = 2.52, 95 %CI: 1.28-4.96, P = 0.008). The results of this review suggest that MNi could be used as a biomarker of DNA damage and chromosomal instability in degenerative disease where increased AGEs and HbA1c are implicated. The lack of heterogeneity for MN frequency when considered either for all studies or subgroup strengthened the MRi of the meta-analysis. However, the lack of significant association between MRi for MNi and MRi for AGEs or HbA1c indicates that the case-control studies investigated may be confounded by other variables. Thus, larger studies with long term AGE exposure is warranted to further understand the role of MN formation in the initiation and progression of diseases caused by excessive glycation.

Lymphocyte micronuclei frequencies in skin, haematological, prostate, colorectal and esophageal cancer cases: A systematic review and meta-analysis

Micronucleus (MN) assay has been widely used as a biomarker of DNA damage, chromosomal instability, cancer risk and accelerated aging in many epidemiological studies. In this narrative review and meta-analysis we assessed the association between lymphocyte micronuclei (MNi) and cancers of the skin, blood, digestive tract, and prostate. The review identified nineteen studies with 717 disease subjects and 782 controls. Significant increases in MRi for MNi were observed in the following groups: subjects with blood cancer (MRi = 3.98; 95 % CI: 1.98-7.99; p = 0.000) and colorectal cancer (excluding IBD) (MRi = 2.69; 95 % CI: 1.82-3.98, p < 0.000). The results of this review suggest that lymphocyte MNi are a biomarker of DNA damage and chromosomal instability in people with haematological or colorectal cancers. However, the MRi for lymphocyte MNi in subjects with cancers of skin, prostate, esophagus was not significantly increased. More case-control and prospective studies are warranted to further verify the observed trends and to better understand the role of lymphocyte MNi as a biomarker of cancer risk in blood, skin, digestive tract and prostate.

Micronuclei and upper body cancers (head, neck, breast cancers) a systematic review and meta-analysis

A systematic review and a meta-analysis were performed on 19 studies on head and neck cancer (HNC) and 21 studies on breast cancer (BC) to evaluate the application of micronucleus (MN) assay as a predictive and prognostic test for cancer risk. In these studies the MN test was applied in peripheral lymphocytes and buccal cells of patients and healthy subjects with family history of cancer. The meta-analysis on MN applied in buccal cells of HNC patients was performed on two subgroups of studies. A significant increase of MN frequency in patients compared to healthy controls was observed for the subgroup on oral cancer (243 cases/370 controls, meta-MR = 4.71 95 %CI:2.75-8.06) and HNC (204 patients/163 controls metaMR=2.28 95 %CI:2.02-2.58). A metaMR = 3.27 (95 %CI:1.41-7.59) was obtained for MN applied in peripheral lymphocytes on HNC (160 cases/160 controls). For BC, the analysis of MN in peripheral lymphocytes showed significantly higher values in patients (n = 761) than in controls (n = 788) (meta-MR1.90 95 % CI:1.44-2.49). No statistically significant increase of baseline MN was detected in studies on groups of healthy subjects with BC family history (n = 224) or with BRCA1/2 mutations (n = 101) with respect to the controls. After ex-vivo challenge with ionizing radiation, the meta-analysis revealed a slightly statistically significant increase in MN only in BC patients (n = 614) compared to controls (n = 622)(meta-MR = 1.11 95 %CI:1.02-1.21); no increase was observed in healthy subjects with BC family history carrying or not BRCA1/2 mutations. Significant difference between BC patients (n = 183) and controls (n = 165) was observed by the meta-analysis of data on MN in buccal cells (MR = 3.89 95 %CI:1.54-9.78). The MN assay in buccal cells has some perspective of clinical application in HNC.

Integrated ecotoxicological assessment of the complex interactions between chlorpyrifos and glyphosate on a non-target species Cnesterodon decemmaculatus (Jenyns, 1842)

Pesticide mixtures are frequent in freshwaters systems around the world, threatening the biota exposed to these conditions. The aim of this study was to determine the single and joint effect of two widely used pesticides in southern South America on a widely distributed fish species. In a 96-h assay, individuals of Cnesterodon decemmaculatus were exposed to 0.84 nL/L and 8.4 nL/L of Clorfox and 0.2 mg/L and 2 mg/L of Roundup Max, commercial formulations of chlorpyrifos and glyphosate, respectively. Also, there were four mixture treatments with all the possible combinations of both pesticides. A multi-level approach was carried out to assess their effects covering the following relevant biomarkers: behavior (immobile time, line crossings and average speed), somatic conditions (Fulton condition factor and hepatosomatic index), serum parameters (cortisol levels, lactate dehydrogenase (LDH), and creatine phosphokinase activity (CPK)), brain and muscle acetylcholinesterase and cytological characteristics (micronuclei frequency and nuclear abnormalities in erythrocytes). Our results showed that Clorfox exposures affect behavioral parameters, serum cortisol, and nuclear characteristics of erythrocytes. Roundup Max affects only the cortisol levels whereas mixture treatments have an effect on behavioral parameters, cortisol levels, LDH and CPK activities, and nuclear characteristics of erythrocytes. Potentiation was the main interaction at the lowest concentrations of both pesticides whereas antagonism occurred at the highest concentrations of both pesticides. These results are highly significant since they arise from an integrated ecotoxicological assessment at several levels of biological organization but even more important is that the potentiated effects of the mixtures we registered are environmentally relevant concentrations.

Dietary and lifestyle factors effect erythrocyte PIG-A mutant frequency in humans

It is well understood that poor diet and lifestyle choices can increase the risk of cancer. It is also well documented that cancer is a disease of DNA mutations, with mutations in key genes driving carcinogenesis. Measuring these mutations in a minimally invasive way may be informative as to which exposures are harmful and thus allow us to introduce primary preventative measures, in a bid to reduce cancer incidences. Here, we have measured mutations in the phosphatidylinositol glycan class A (PIG-A) gene in erythrocytes from healthy volunteers (n = 156) and from non-cancer patients attending the local endoscopy department (n = 144). The X-linked PIG-A gene encodes an enzyme involved in glycosylphosphatidylinositol (GPI) anchor synthesis. A silencing mutation in which leads to the absence of GPI anchors on the extracellular surface which can be rapidly assessed using flow cytometry. The background level of PIG-A mutant erythrocytes was 2.95 (95% CI: 2.59-3.67) mutant cells (10-6). Older age increased mutant cell frequency (P < 0.001). There was no difference in mutant cell levels between males and females (P = 0.463) or smokers and non-smokers (P = 0.186). In the endoscopy group, aspirin users had lower mutant frequencies (P = 0.001). Further information on diet and exercise was available for the endoscopy patient group alone, where those with a higher health promotion index score had lower mutant frequencies (P = 0.011). Higher dietary intake of vegetables reduced mutant cell levels (P = 0.022). Participants who exercised for at least 1 h a week appeared to have reduced mutant frequencies than those who did not exercise, although this was not statistically significant (P = 0.099). This low background level of mutant erythrocytes in a population makes this assay an attractive tool to monitor exposures such as those associated with lifestyles and diet, as demonstrated here.

The genotoxicological assessment of a tobacco heating product relative to cigarette smoke using the in vitro micronucleus assay

In vitro studies have supported the toxicological evaluation of chemicals and complex mixtures including cigarette smoke and novel tobacco and nicotine products which include tobacco heating products (THP). This new environment requires faster testing, higher throughput and appropriate in vitro studies, to support product innovation and development. In this study, total particulate matter (TPM) from a commercially available THP and a reference cigarette (3R4F) were assessed up to 500 μg/mL using two in vitro micronucleus techniques. V79 and TK6 cells were assessed using conventional OECD 487 manual scoring techniques, whereas, CHO cells were assessed using contemporary, automated high content screening approaches (Cellomics ArrayScan® VTI). V79 cells gave the most consistent response with all three treatment conditions producing a clear positive genotoxic response. Human TK6 cells only produced dose-dependent response, indicative of a weak-positive response. CHO cells demonstrated a positive response with TPM using long (24 h) -S9 conditions. All three cell lines equally demonstrated a negative response with THP TPM up to 500 μg/mL. In conclusion, THP TPM did not increase micronuclei formation above control levels even at doses far exceeding that tested with reference cigarette smoke, in most cases up to 10x the dose delivered compared to that of cigarette smoke. This study supports the growing belief that THPs are less risky than conventional cigarettes and that 21st century screening techniques can be employed to support product design and decision making, as a potential 1st screen prior to more traditional assessments.

Association between occupational heat stress and DNA damage in lymphocytes of workers exposed to hot working environments in a steel industry in Southern India

Occupational heat stress apart from adverse heat-related health consequences also induces DNA damage in workers exposed to high working temperatures. We investigated the association between chronic heat exposures and Micronuclei (MN) frequency in lymphocytes of 120 workers employed in the steel industry. There was a significant increase in the MN-frequency in exposed workers compared to the unexposed workers (X² = 47.1; p < 0.0001). While exposed workers had higher risk of DNA damage (Adj. OR = 23.3, 95% CI 8.0-70.8) compared to the unexposed workers, among the exposed workers, the odds of DNA damage was much higher for the workers exposed to high-heat levels (Adj. OR = 81.4; 95% CI 21.3-310.1) even after adjusting for confounders. For exposed workers, years of exposure to heat also had a significant association with higher induction of MN (Adj. OR = 29.7; 95% CI 2.8-315.5). Exposures to chronic heat stress is a significant occupational health risk including damages in sub-cellular level, for workers. Developing protective interventions to reduce heat exposures is imperative in the rising temperature scenario to protect millions of workers across the globe.

Treatment with 3-Aminobenzamide Negates the Radiofrequency-Induced Adaptive Response in Two Cell Models

In previous investigations, we demonstrated that pre-exposure of different cell cultures to radiofrequency fields can reduce the damage induced by genotoxic agents, an effect resembling the so-called adaptive response. In this study, we pre-exposed human peripheral blood lymphocytes and Chinese hamster lung fibroblast cell line to 1950 MHz, UMTS (Universal Mobile Telecommunication System) signal, for 20 h, and then treated cultures with Mitomycin-C. After confirming the induction of an adaptive response in terms of the reduction of micronuclei formation, we observed that such a response was negated by treatments with 3-aminobenzamide. Since 3-aminobenzamide is an inhibitor of poly (ADP-ribose) polymerase enzyme, which is involved in DNA repair, these results support the possible involvement of DNA repair mechanisms in radiofrequency-induced adaptive response.

Opportunities for future therapeutic interventions for hyperoxaluria: targeting oxidative stress

INTRODUCTION

Oxalate is a toxic byproduct of metabolism and is normally produced in quantities easily removed from the body. However, under specific circumstances oxalate production is increased resulting in deposition of calcium oxalate (CaOx) crystals in the kidneys as well as other organs causing inflammation and injury. Excessive buildup of crystal deposits in the kidneys causes eventual loss of renal function requiring renal transplantation. Areas covered: Cellular exposure to CaOx crystals induces the production of reactive oxygen species (ROS) with the involvement of renin-angiotensin aldosterone system (RAAS), mitochondria, and NADPH oxidase. Inflammasomes are activated and pro-inflammatory cytokines, such as IL-1β and IL-18 are produced. We reviewed results of experimental and clinical studies of crystal renal epithelial cell interactions with emphasis on cellular injury and ROS production. Expert opinion: Treatment should depend upon the level of hyperoxaluria and whether it is associated with CaOx crystal deposition. Persistent low grade or intermittent hyperoxaluria can be treated with antioxidants, free radical scavengers. Hyperoxaluria associated with CaOx crystal deposition will require administration of angiotensin II receptor blockers, and NADPH oxidase or NLRP3 inflammasome inhibitors. DASH-style diet will be beneficial in both cases.

"Normal values" for the lymphocyte cytokinesis-block micronucleus cytome parameters: Repeatability and reproducibility in a healthy reference population

The micronucleus test in peripheral blood lymphocytes is the most widely validated technique to evaluate the DNA damage and chromosomal instability in human populations. The test is largely applied in monitoring environmental and occupational exposure to genotoxic agents. It was also proposed as a biomarker of risk/susceptibility for cancer and other degenerative diseases. The availability of "normal values" in healthy populations is a main requisite for the assay application in human biomonitoring. Age and gender-related ranges of micronucleated binucleated cells (MNBN) baseline values were established in a group of 103 healthy platelet donors (50 males and 53 females) not recently exposed to genotoxic agents and characterized for demographic, lifestyle and dietary factors. Repeatability of the test by the same scorer was evaluated. Reproducibility was estimated through analysis of repeated blood samples. High correlation between the results of the three blood samplings in two separate scoring sessions of MNBN/1000BN (R² values were 0.83, 0.74 and 0.68; P < 0.0001) and PI values (R² values were 0.69, 0.62 and 0.65; P < 0.0001) was detected. High consistency among the values obtained in three different samplings in the same individual was observed (Intraclass Correlation Coefficient (ICC) = 0.905, (95% CI = 0.868-0.933, P < 0.0001) The range of "normal" values predicted on the basis of the results of the present study appears to be sufficiently narrow to warrant application of the assay in the comparison of data obtained from groups of exposed or susceptible subjects, supporting its use in preventive programs. The large inter-individual variability predicted by the model used in the present study hampers a clinical application of the assay at individual level. The method applied in the present study represents a generally applicable model to derive "normal values" in any population, as an essential step before starting a biomonitoring study.

In situ genotoxicity assessment in freshwater zooplankton and sediments from different dams, ponds, and temporary rivers in Tunisia

Tunisia water resources are limited. The country currently has 29 large dams, more than 1000 hill lakes, and 220 small dams which are essential for economic and social development given their contribution to irrigation, drinking water consumption, flooding protection, production of electrical energy, groundwater recharge, and industrial uses. Given the scarcity of these resources, it is crucial to be able to ensure the quality of freshwater environments, particularly those intended for human consumption. In this study, we meant to assess the health status of various freshwater ecosystems in different regions of Tunisia (north and center west) in order to detect genotoxic components in sediments and their potential effect on zooplankton (cladocerans). Sediment and cladoceran species were collected from dams, ponds, and temporary rivers in Tunisia. For each collection site, micronucleus (MN) assay was performed, in triplicates, using a pool of ten specimens of the same cladoceran species. MN occurrence in cladocerans varied from one site to another and MN frequencies varied between 0.67 and 22‰, suggesting the presence of genotoxic substances in certain sites. Sediment genotoxicity and mutagenicity were assessed using the SOS Chromotest and the Ames test. Sediment results showed that genotoxicity varies from one site to another displaying a quantitative and a qualitative variation of pollutant among the sites. These results suggest an urgent need for continuous monitoring of freshwater environments in Tunisia, particularly those intended for drinking water.

Micronucleus Cytome Assays in Human Lymphocytes and Buccal Cells

The micronucleus (MN) assay, applied in different surrogate tissues, is one of the best validated cytogenetic techniques for evaluating chromosomal damage in humans. The cytokinesis-block micronucleus cytome assay in peripheral blood lymphocytes (L-CBMNcyt) is the most frequently used method in biomonitoring human populations to evaluate DNA damage caused by exposure to genotoxic agents, micronutrient deficiency or excess and genetic instability. Furthermore, recent scientific evidence suggests an association between an increased MN frequency in lymphocytes and risk of cancer and other age-related degenerative diseases. The micronucleus cytome assay applied in buccal exfoliated cells (BMNCyt), provides a complementary method for measuring DNA damage and cytotoxic effects in an easily accessible tissue not requiring ex vivo/in vitro culture. The protocol for L-CBMNcyt described here, refers to the use of ex vivo whole blood method, involving 72 h of culture with the block of cytokinesis starting at 44 h. BMNCyt protocol reports the established method for sample collection, processing, slide preparation and scoring.

Automation of the in vitro micronucleus assay using the Imagestream® imaging flow cytometer

The in vitro micronucleus (MN) assay is a well‐established test for evaluating genotoxicity and cytotoxicity. The use of manual microscopy to perform the assay can be laborious and often suffers from user subjectivity and interscorer variability. Automated methods including slide‐scanning microscopy and conventional flow cytometry have been developed to eliminate scorer bias and improve throughput. However, these methods possess several limitations such as lack of cytoplasmic visualization using slide‐scanning microscopy and the inability to visually confirm the legitimacy of MN or storage of image data for re‐evaluation using flow cytometry. The ImageStream^X® MK II (ISX) imaging flow cytometer has been demonstrated to overcome all of these limitations. The ISX combines the speed, statistical robustness, and rare event capture capability of conventional flow cytometry with high resolution fluorescent imagery of microscopy and possesses the ability to store all collected image data. This paper details the methodology developed to perform the in vitro MN assay in human lymphoblastoid TK6 cells on the ISX. High resolution images of micronucleated mono‐ and bi‐nucleated cells as well as polynucleated cells can be acquired at a high rate of capture. All images can then be automatically identified, categorized and enumerated in the data analysis software that accompanies the ImageStream, allowing for the scoring of both genotoxicity and cytotoxicity. The results demonstrate that statistically significant increases in MN frequency when compared with solvent controls can be detected at varying levels of cytotoxicity following exposure to well‐known aneugens and clastogens. This work demonstrates a fully automated method for performing the in vitro micronucleus assay on the ISX imaging flow cytometry platform. © 2018 The Author. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of ISAC.

The potential for complete automated scoring of the cytokinesis block micronucleus cytome assay using imaging flow cytometry

The lymphocyte Cytokinesis-Block Micronucleus (CBMN) assay was originally developed for the measurement of micronuclei (MN) exclusively in binucleated (BN) cells, which represent the population of cells that can express MN because they completed nuclear division. Recently the assay has evolved into a comprehensive cytome method to include biomarkers that measure chromosomal instability and cytotoxicity by quantification of nuclear buds (NBUDs), nucleoplasmic bridges (NPBs) and apoptotic/necrotic cells. Furthermore, enumeration of mono- and polynucleated cells allows for computation of the nuclear division index (NDI) to assess mitotic activity. Typically performed by manual microscopy, the CBMN cytome assay is laborious and subject to scorer bias and fatigue, leading to inter- and intra-scorer variability. Automated microscopy and conventional flow cytometry methods have been developed to automate scoring of the traditional and cytome versions of the assay. However, these methods have several limitations including the requirement to create high-quality microscope slides, lack of staining consistency and sub-optimal nuclear/cytoplasmic visualization. In the case of flow cytometry, stripping of the cytoplasmic membrane makes it impossible to measure MN in BN cells, calculate the NDI or to quantify apoptotic or necrotic cells. Moreover, the absence of cellular visualization using conventional flow cytometry, makes it impossible to quantify NBUDs and NPBs. In this review, we propose that imaging flow cytometry (IFC), which combines high resolution microscopy with flow cytometry, may overcome these limitations. We demonstrate that by using IFC, images from cells in suspension can be captured, removing the need for microscope slides and allowing visualization of intact cytoplasmic membranes and DNA content. Thus, mono-, bi- and polynucleated cells with and without MN can be rapidly and automatically identified and quantified. Finally, we present high-resolution cell images containing NBUDs and NPBs, illustrating that IFC possesses the potential for completely automated scoring of all components of the CBMN cytome assay.

Radio-adaptive response in peripheral blood lymphocytes of individuals residing in high-level natural radiation areas of Kerala in the southwest coast of India

The present study investigates whether the chronic low-dose radiation exposure induces an in vivo radio-adaptive response in individuals from high-level natural radiation areas (HLNRA) of the Kerala coast. Peripheral blood samples from 54 adult male individuals aged between 26 and 65 years were collected for the study with written informed consent. Each of the whole blood sample was divided into three, one was sham irradiated, second and third was exposed to challenging doses of 1.0 and 2.0 Gy gamma radiation, respectively. Cytokinesis-block micronucleus (CBMN) assay was employed to study the radio-adaptive response. Seventeen individuals were from normal-level natural radiation area (NLNRA ≤1.5 mGy/year) and 37 from HLNRA (> 1.5 mGy/year). Based on the annual dose received, individuals from HLNRA were further classified into low-dose group (LDG, 1.51-5.0 mGy/year, N = 19) and high-dose group (HDG >5.0 mGy/year, N = 18). Basal frequency of micronucleus (MN) was comparable across the three dose groups (NLNRA, LDG and HDG, P = 0.64). Age of the individuals showed a significant effect on the frequency of MN after challenging dose exposures. The mean frequency of MN was significantly lower in elder (>40 years) individuals from HDG of HLNRA as compared to the young (≤40 years) individuals after 1.0 Gy (P < 0.001) and 2.0 Gy (P = 0.002) of challenging doses. However, young and elder individuals within NLNRA and LDG of HLNRA showed similar frequency of MN after the challenging dose exposures. Thus, increased level of chronic low-dose radiation (>5.0 mGy/year) seems to act as a priming dose resulting in the induction of an in vivo radio-adaptive response in elder individuals of the Kerala coast.

Micronucleus frequencies in groups receiving external or internal radiation

OBJECTIVE

In the current study, we aimed to explore whether there is alteration between pre- and post-treatment micronucleus (MN) frequencies induced by internal and external ionizing radiation.

MATERIALS AND METHODS

The study enrolled a total of 67 patients including patients admitted to our hospital for treatment of hyperthyroidism (n = 17), scanning with low-dose I-131 (n = 15), and ablative therapy with high-dose I-131 (n = 15) at Department of Nuclear Medicine as well as patients with different diagnoses receiving external radiotherapy with various doses and durations at Department of Radiation Oncology (n = 20). Thirty-two patients who received radioactive iodine and returned for a follow-up visit at 1 month.

RESULTS

Considering both pre- and post-treatment MN frequencies of each group, lowest MN frequencies were detected for patients undergoing screening with low-dose I-131, and highest MN frequencies were found in radiotherapy patients. Comparison of pre- and post-treatment MN frequencies among hyperthyroidism, when pre- and post-treatment MN frequencies compared among hyperthyroidism, I-131 whole body scanning, ablation, and radiotherapy patient groups differences between MN frequencies were significant for each group (P < 0.05).

CONCLUSION

Our study showed that MN analysis might be of value in determining chromosome damage that could potentially occur in patients exposed to internal and external radiation.

Analysis of Genetic Damage in Lymphocytes of Former Uranium Processing Workers

The frequency of cells containing micronuclei (MN) and the presence of centromeres in these MN were analyzed in lymphocytes of 98 men from Southern Bohemia. Forty-six of them had worked at the uranium processing plant ‘MAPE Mydlovary' which was closed in 1991, and 52 men were controls from the same area. FISH using human pan-centromeric chromosome paint was employed to detect centromere-positive (CEN+) and -negative (CEN-) MN. A total of 1,000 binucleated cells (BNC) per participant were analyzed after cytochalasin B treatment. All BNC with MN (CEN+ or CEN-) were recorded. No differences were found between formerly exposed workers and the control group, neither in the total frequency of cells with MN per 1,000 BNC (mean levels ± SD, 9.1 ± 3.1 and 9.8 ± 2.5, respectively) nor in the percentage of CEN- MN, which were equal (50 ± 18 and 49 ± 17, respectively). Also, there was no difference between individuals living in the 3 villages closest to the uranium processing plant and those living further away. Considering the fact that effective doses of the workers at MAPE Mydlovary were overall similar to those of former uranium miners in whom higher frequencies of CEN- MN have been found more than 10 years after they had finished working underground, these results are somewhat surprising. A more detailed analysis of the exposures indicates that uranium miners received a greater percentage of their effective dose from the inhalation of radon and its daughters, whereas uranium processing workers received it from the incorporation of long-lived radioactive nuclides such as uranium. If, as has been suggested before, the higher level of DNA damage in miners is due to induced genomic instability, then this phenomenon may be related to radon exposure rather than exposure to uranium.

Biological monitoring of Italian soldiers deployed in Iraq. Results of the SIGNUM project

BACKGROUND

Leukemia/lymphoma cases reported in 2001 among United Nation soldiers or peacekeepers deployed to the Balkans aroused alert on the exposure to depleted uranium. Recent epidemiological studies carried out in different European countries among peacekeepers who served in the Balkans failed to demonstrate a higher than expected risk of all cancers but, mostly due to their limitations in size and follow up time, leave open the debate on health risk of depleted uranium. The aim of SIGNUM (Study of the Genotoxic Impact in Military Units) was to identify potential genotoxic risk associated with the exposure to depleted uranium or other pollutants in the Italian Army military personnel deployed in Iraq.

METHODS

Blood and urine samples were collected before and after the deployment from 981 Italian soldiers operating in Iraq in 2004-2005. As, Cd, Mo, Ni, Pb, U, V, W, and Zr were determined in urine and serum. DNA-adducts, 8-hydroxy-2'-deoxyguanine and micronuclei frequency were evaluated in blood lymphocytes. Three different genetic polymorphisms, GSTM1, XRCC1, OGG1 were analyzed.

RESULTS

Significant T0-T1 reduction in the total concentration of uranium, increases for Cd, Mo, Ni, Zr, and decreases for As, Pb, W, and V in urine and plasma were observed. Increases in oxidative alterations and in micronuclei frequency, included in the range of values of non-occupationally exposed populations, were observed at the end of the period of employment.

CONCLUSIONS

Our results did not detect any toxicologically relevant variation of DNA-damage biomarkers related to the deployment in the operational theater.

Low doses of ochratoxin A induce micronucleus formation and delay DNA repair in human lymphocytes

The contamination of food commodities by fungal toxins has attracted great interest because many of these mycotoxins are responsible for different diseases, including cancer and other chronic illnesses. Ochratoxin A (OTA) is a mycotoxin naturally present in food, and long-term exposure to food contaminated with low levels of OTA has been associated with renal cancer. In the present study, the cytotoxicity, cytostaticity, and genotoxicity of OTA (0.075-15 µM) in human lymphocytes were evaluated. A comet assay, a modified comet assay (DNA repair assay), which uses N-hydroxyurea (NHU) to detect non-repaired lesions produced by OTA, and a cytokinesis-blocked micronucleus assay were used. Treatments with OTA were not cytotoxic, but OTA caused a cytostatic effect in human lymphocytes at a concentration of 15 µM. OTA (0.075-5 µM) produced a slight increase in the percentage of DNA in the comets and a delay in the DNA repair capacity of the lymphocytes. Micronucleus (MN) induction was observed at OTA concentrations of 1.5 and 5 µM. Our results indicate that OTA induces DNA stable damage at low doses that are neither cytotoxic nor cytostatic, and OTA delays the DNA repair kinetics. These findings indicate that OTA affects two pivotal events in the carcinogenesis pathway.

An automated imaging system for radiation biodosimetry

We describe here an automated imaging system developed at the Center for High Throughput Minimally Invasive Radiation Biodosimetry. The imaging system is built around a fast, sensitive sCMOS camera and rapid switchable LED light source. It features complete automation of all the steps of the imaging process and contains built-in feedback loops to ensure proper operation. The imaging system is intended as a back end to the RABiT-a robotic platform for radiation biodosimetry. It is intended to automate image acquisition and analysis for four biodosimetry assays for which we have developed automated protocols: The Cytokinesis Blocked Micronucleus assay, the γ-H2AX assay, the Dicentric assay (using PNA or FISH probes) and the RABiT-BAND assay.

Ozone inhalation leads to a dose-dependent increase of cytogenetic damage in human lymphocytes

Ozone is an important constituent of ambient air pollution and represents a major public health concern. Oxidative injury due to ozone inhalation causes the generation of reactive oxygen species and can be genotoxic. To determine whether ozone exposure causes genetic damage in peripheral blood lymphocytes, we used a well-validated cytokinesis-block micronucleus Cytome assay. Frequencies of micronuclei (MN) and nucleoplasmic bridges (NB) were used as indicators of cytogenetic damage. Samples were obtained from 22 non-smoking healthy subjects immediately before and 24-hr after controlled 4-hr exposures to filtered air, 100 ppb, and 200 ppb ozone while exercising in a repeated-measure study design. Inhalation of ozone at different exposure levels was associated with a significant dose-dependent increase in MN frequency (P < 0.0001) and in the number of cells with more than one MN per cell (P <  .0005). Inhalation of ozone also caused an increase in the number of apoptotic cells (P = 0.002). Airway neutrophilia was associated with an increase in MN frequency (P = 0.033) independent of the direct effects of ozone exposure (P < 0.0001). We also observed significant increases in both MN and NB frequencies after exercise in filtered air, suggesting that physical activity is also an important inducer of oxidative stress. These results corroborate our previous findings that cytogenetic damage is associated with ozone exposure, and show that damage is dose-dependent. Further study of ozone-induced cytogenetic damage in airway epithelial cells could provide evidence for the role of oxidative injury in lung carcinogenesis, and help to address the potential public health implications of exposures to oxidant environments.

Toxicological and Genotoxicity Assessment of a Dihydroquercetin-Rich Dahurian Larch Tree (Larix gmelinii Rupr) Extract (Lavitol)

Safety assessment is reported of an orally ingested dihydroquercetin-rich extract (Lavitol) derived from the Dahurian larch tree, used as a food additive and as a dietary supplement ingredient. Dihydroquercetin, a potent antioxidant, is also known as taxifolin. The results of genotoxicity and toxicological tests (Comet assay, micronucleus test in human lymphocytes, chromosomal aberration test, subacute 7-day oral toxicity study, subchronic 90-day toxicology study with histopathologies, and, prenatal and postnatal developmental toxicity studies) on the extract provide further support for the safety of its consumption as a food supplement and food additive.

Micronucleus formation in human keratinocytes is dependent on radiation quality and tissue architecture

The cytokinesis-block micronucleus (MN) assay was used to assess the genotoxicity of low doses of different types of space radiation. Normal human primary keratinocytes and immortalized keratinocytes grown in 2D monolayers each were exposed to graded doses of 0.3 or 1.0 GeV/n silicon ions or similar energies of iron ions. The frequencies of induced MN were determined and compared to γ-ray data. RBE(max) values ranged from 1.6 to 3.9 for primary keratinocytes and from 2.4 to 6.3 for immortalized keratinocytes. At low radiation doses ≤ 0.4 Gy, 0.3 GeV/n iron ions were the most effective at inducing MN in normal keratinocytes. An "over-kill effect" was observed for 0.3 GeV/n iron ions at higher doses, wherein 1.0 GeV/n iron ions were most efficient in inducing MN. In immortalized keratinocytes, 0.3 GeV/n iron ions produced MN with greater frequency than 1.0 GeV/n iron ions, except at the highest dose tested. MN formation was higher in immortalized keratinocytes than in normal keratinocytes for all doses and radiation qualities investigated. MN induction was also assessed in human keratinocytes cultured in 3D to simulate the complex architecture of human skin. RBE values for MN formation in 3D were reduced for normal keratinocytes exposed to iron ions, but were elevated for immortalized keratinocytes. Overall, MN induction was significantly lower in keratinocytes cultured in 3D than in 2D. Together, the results suggest that tissue architecture and immortalization status modulate the genotoxic response to space radiation, perhaps via alterations in DNA repair fidelity.

Clinical application of micronucleus test: a case-control study on the prediction of breast cancer risk/susceptibility

The micronucleus test is a well-established DNA damage assay in human monitoring. The test was proposed as a promising marker of cancer risk/susceptibility mainly on the basis of studies on breast cancer. Our recent meta-analysis showed that the association between micronuclei frequency, either at baseline or after irradiation, and breast cancer risk or susceptibility, has been evaluated in few studies of small size, with inconsistent results. The aim of the present study is to investigate the role of micronucleus assay in evaluating individual breast cancer susceptibility. Two-hundred and twenty untreated breast cancer patients and 295 female controls were enrolled in the study. All women were characterized for cancer family history and 155 subjects were evaluated for the presence of BRCA mutations. Micronuclei frequency was evaluated at baseline and after irradiation with 1-Gy gamma rays from a 137Cs source. The results show a non significant increase of frequency of micronucleated binucleated lymphocytes in cancer patients compared with the controls at baseline (Mean (S.E.): 16.8 (0.7) vs 15.7 (0.5), but not after irradiation (Mean (S.E.): 145.8 (3.0) vs 154.0 (2.6)). Neither a family history of breast cancer nor the presence of a pathogenic mutation in BRCA1/2 genes were associated with an increased micronuclei frequency. Our results do not support a significant role of micronucleus frequency as a biomarker of breast cancer risk/susceptibility.

Cytogenetic analysis of oral mucosa cells, induced by chlorhexidine, essential oils in ethanolic solution and triclosan mouthwashes

OBJECTIVES

The aim of this study was to evaluate DNA damage and cytokinetic defects, proliferative potential and cell death caused by the frequent use of mouthrinses containing chlorhexidine, triclosan and essential oils in ethanolic solution, compared to a placebo mouthwash.

STUDY DESIGN

This double-blind, prospective, randomized clinical trial included 80 Caucasian patients. Subjects were divided into four groups: Group I used a mouthrinse, Triclosan; Group II used physiological saline; Group III used chlorhexidine; Group IV a mouthrinse with essential oils in ethanolic solution. All subjects used the mouthrinses for two weeks (15 ml, twice a day, rinsing for 30s). Two cell samples per subject were collected, before and after mouthrinse use (on day 0 and day 15). Samples were processed as follows: cell collection from cheeks with a cytobrush; cell centrifuge; slide preparation, fixation and staining; and fluorescent microscope analysis. 2000 exfoliated cells were screened for nuclear abnormalities, particularly the presence of micronuclei by means of cytome assay.

RESULTS

No significant differences between study times (before and after use of mouthwash) were identified for any of the variables studied (p>0.05). Differences between mouthrinse groups were also compared but no significant differences were found (p>0.05).

CONCLUSIONS

This study did not observe any genotoxic effect resulting from mouthrinse use.

Delayed mitogenic stimulation decreases DNA damage assessed by micronucleus assay in human peripheral blood lymphocytes after (60)co irradiation

While contradictory reports are available on the yield of dicentric chromosomes (DC) in blood samples stored at different temperature and stimulated to enter into cell cycle, various times gap followed by exposure, limited information is available on the micronucleus (MN) assay. As scoring the micronuclei frequency from the blood lymphocytes of exposed individuals is an alternative to the gold standard DC assay for triage applications, we examined radiation induced MN yield in delayed mitogenic stimulation after irradiation of in vitro. Peripheral blood lymphocytes (PBL) were exposed to low LET ((60)Co) radiation dose (0.1 to 5Gy) and incubated at 37°C for 2, 6 and 24 hours. The MN frequency obtained in blood samples stimulated 2 hours post-irradiation showed a dose dependent increase and used to construct the dose-response curve. Further, the results also showed that blood samples stimulated twenty four hours of post-irradiation, a significant reduction (p<0.05) in MN frequencies were obtained when compared to that of blood samples stimulated two hours and six hours after post-irradiation (0.5, 1, 3 and 5Gy). The observed result suggests that the prolonged PBL storage without mitogenic stimulation could lead to interphase cell death and a delayed blood sampling could results in underestimation of dose in biological dosimetry.

Delayed mitogenic stimulation decreases DNA damage assessed by micronucleus assay in human peripheral blood lymphocytes after (60)co irradiation

While contradictory reports are available on the yield of dicentric chromosomes (DC) in blood samples stored at different temperature and stimulated to enter into cell cycle, various times gap followed by exposure, limited information is available on the micronucleus (MN) assay. As scoring the micronuclei frequency from the blood lymphocytes of exposed individuals is an alternative to the gold standard DC assay for triage applications, we examined radiation induced MN yield in delayed mitogenic stimulation after irradiation of in vitro. Peripheral blood lymphocytes (PBL) were exposed to low LET ((60)Co) radiation dose (0.1 to 5Gy) and incubated at 37°C for 2, 6 and 24 hours. The MN frequency obtained in blood samples stimulated 2 hours post-irradiation showed a dose dependent increase and used to construct the dose-response curve. Further, the results also showed that blood samples stimulated twenty four hours of post-irradiation, a significant reduction (p<0.05) in MN frequencies were obtained when compared to that of blood samples stimulated two hours and six hours after post-irradiation (0.5, 1, 3 and 5Gy). The observed result suggests that the prolonged PBL storage without mitogenic stimulation could lead to interphase cell death and a delayed blood sampling could results in underestimation of dose in biological dosimetry.