A survey on the cytogenetic status of the Croatian general population by use of the cytokinesis-block micronucleus assay

Exploring cytokinesis block micronucleus assay in Croatia: A journey through the past, present, and future in biomonitoring of the general population

In this study, we used the cytokinesis-block micronucleus (CBMN) assay to evaluate the background frequency of cytogenetic damage in peripheral blood lymphocytes of the general population concerning different anthropometric data and lifestyle factors. The background frequency of CBMN assay parameters was analysed in 850 healthy, occupationally non-exposed male and female subjects (average age, 38±11 years) gathered from the general Croatian population from 2000 to 2023. The mean background values for micronuclei (MNi) in the whole population were 5.3±4.3 per 1000 binucleated cells, while the mean frequency of nucleoplasmic bridges (NPBs) was 0.7±1.3 and of nuclear buds (NBUDs) 3.1±3.2. The cut-off value, which corresponds to the 95th percentile of the distribution of 850 individual values, was 14 MNi, 3 NPBs, and 9 NBUDs. Results from our database also showed an association of the tested genomic instability parameters with age and sex but also with other lifestyle factors. These findings underscore the importance of considering several anthropometric and lifestyle factors when conducting biomonitoring studies. Overall, the normal and cut-off values attained here present normal values for the general population that can later serve as baseline values for further human biomonitoring studies either in Croatia or worldwide.

Re-evaluation of CBMN test reference values of persons continuously occupationally exposed to low doses of ionizing radiation in Serbia

When established, cytokinesis-block micronucleus (CBMN) test reference values should be periodically evaluated according to the recommendations of reference documents. The biodosimetry cytogenetic laboratory of the Serbian Institute of Occupational Health established the CBMN test reference range for people occupationally exposed to ionizing radiation in 2016. Since then, new occupationally exposed persons have been subjected to micronucleus testing, resulting in the need for re-evaluation of existing CBMN test values. The examined population comprised 608 occupationally exposed subjects - 201 from the previous laboratory database and 407 newly examined. Comparison of groups based on gender, age and cigarette consumption did not show significant differences, although certain CBMN values differed significantly between the old and new groups. Duration of occupational exposure, gender, age and smoking habit influenced micronuclei frequency in all three analyzed groups, while no relation was found between type of work and micronucleus test parameters. Since the mean values of all tested parameters in the new group of examinees are within previously established reference ranges, existing values can be used in further research.

"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.

Cytokinesis-block micronucleus cytome assay parameters in peripheral blood lymphocytes of the general population: Contribution of age, sex, seasonal variations and lifestyle factors

The cytokinesis-block micronucleus cytome (CBMN Cyt) assay was used to evaluate the baseline frequency of cytogenetic damage in peripheral blood lymphocytes of the general population (average age, 38.28 ± 12.83 years) in relation to age, sex, body mass index, seasonal variations (season of sampling, period of sampling and different meteorological parameters) and lifestyle factors (smoking habit, alcohol consumption, exposure to medications and diagnostic radiation, physical activity, and family history of cancer). The background frequency of micronuclei (MNi) for the 200 subjects assayed was 5.06 ± 3.11 per 1000 binucleated cells, while the mean frequency of nucleoplasmic bridges (NPBs) was 1.21 ± 1.46 and of nuclear buds (NBUDs) 3.48 ± 2.14. The background frequency of apoptosis and necrosis was 1.58 ± 1.50 and 1.39 ± 1.56, respectively, while the mean nuclear division index (NDI) was 1.99 ± 0.14. The cut-off value, which corresponds to the 95th percentile of the distribution of 200 individual values, was 11 MNi, 4 NPBs and 7 NBUDs. The study also confirmed an association of the above mentioned parameters with age, sex and several lifestyle factors. Moreover, significant confounders based on our results are also sampling season, sampling period and different meteorological parameters that were dependent on the CBMN Cyt assay parameters. In line with the above mentioned, several factors should be taken into account when it comes to the monitoring of exposed populations using cytogenetic biomarkers. Moreover, the normal and cut-off values obtained in this study present background data for the general population, and can later serve as baseline values for further biomonitoring studies.

Assessment of the genotoxicity and cytotoxicity in environmentally exposed human populations to heavy metals using the cytokinesis-block micronucleus cytome assay

The cytokinesis-block micronucleus cytome (CBMN-Cyt) assay was developed as a system for evaluating DNA damage, cytostasis, and cytotoxicity. The aim of the present study was to estimate levels of micronuclei (MNi), nucleoplasmic bridges (NPBs), nuclear buds (NBUDs), cell death (apoptosis/necrosis), nuclear division index, and nuclear division cytotoxicity index values in the peripheral blood lymphocytes of environmentally exposed subjects to heavy metals from five Bosnian regions, characterized by different exposure to heavy metals. The study was performed using CBMN-Cyt assay, considering factors, such as age, gender and smoking habits and their possible effects on analyzed parameters. In total, 104 healthy subjects were selected (49.04% females and 50.96% males; average age, 35.41 years; 51.92% smokers and 48.08% nonsmokers). There was significant difference between the frequency of NBUDs in Tuzla as compared to the control group. Furthermore, there was observed a statistically significant difference for the frequency of NPBs between Zenica, Olovo, and Kakanj when compared with the controls. Males showed a significantly higher number of apoptotic cells than females in controls. There were significant differences between smokers and nonsmokers in the frequency of NPBs in controls (higher in nonsmokers) and necrotic cells in Olovo (higher in nonsmokers). The pack years of smoking significantly influenced the number of necrotic cells in controls and the frequency of NBUDs in the overall sample. The results of the present study provide evidence of significantly increased frequency of NPBs and NBUDs in exposed subjects, suggesting that these endpoints are highly sensitive markers for measuring genotoxicity.

Aging and DNA damage in humans: a meta‐analysis study

Age-related DNA damage is regarded as one of the possible explanations of aging. Although a generalized idea about the accumulation of DNA damage with age exists, results found in the literature are inconsistent. To better understand the question of age-related DNA damage in humans and to identify possible moderator variables, a meta-analysis was conducted.

Electronic databases and bibliographies for studies published since 2004 were searched. Summary odds ratios (ORs) and 95% confidence intervals (CIs) for age-related DNA damage were calculated in a random-effects model.

A total of 76 correlations from 36 studies with 4676 participants were included. Based on our analysis, a correlation between age and DNA damage was found (r = 0.230, p = 0.000; 95% confidence interval = 0.111 - 0.342). The test for heterogeneity of variance indicates that the study´s results are significantly high (Q (75) = 1754.831, p = 0.000). Moderator variables such as smoking habits, technique used, and the tissue/sample analyzed, are shown to influence age-related DNA damage (p=0.026; p=0.000; p=0.000, respectively). Nevertheless, sex did not show any influence on this relation (p=0.114).

In conclusion, this meta-analysis showed an association between age and DNA damage in humans. It was also found that smoking habits, the technique used, and tissue/sample analyzed, are important moderator variables in age-related DNA damage.

Cytogenetic status of healthy children assessed with the alkaline comet assay and the cytokinesis-block micronucleus cytome assay

In the present study the alkaline comet assay and the cytokinesis-block micronucleus cytome (CBMN Cyt) assay were used to evaluate the baseline frequency of cytogenetic damage in peripheral blood lymphocytes (PBLs) of 50 healthy children from the general population in Croatia (age, 11.62±1.81 years). Mean values of tail length, tail intensity and tail moment, as comet assay parameters, were 12.92±0.10, 0.73±0.06 and 0.08±0.01, respectively. The mean frequency of micronuclei (MN) for all subjects was 2.32±0.28 per 1000 bi-nucleated cells, while the mean frequency of nucleoplasmic bridges (NPBs) was 1.72±0.24 and of nuclear buds (NBUDs) 1.44±0.19. The mean nuclear division index (NDI) was 1.70±0.05. When comet-assay parameters were considered, higher mean values for all three were found for the female population. According to the Mann-Whitney U test applied on the results of the comet assay, the only statistically significant difference between the male and female populations was found for tail length. Similar to the results obtained by the comet assay, girls showed higher mean values of all three measured parameters of the CBMN Cyt assay. This difference was statistically significant for total number of NPBs only. In the case of the NDI, a higher mean value was also obtained in girls, but this difference was not statistically significant. The results obtained present background data that could be considered as normal values for healthy children living in urban areas, and can later on serve as baseline values for further toxicological monitoring. Additionally, the usefulness of both techniques in measuring cytogenetic damage during bio-monitoring of children is confirmed.

Micronucleus evaluation in mitogen-stimulated lymphocytes of patients with acromegaly

Acromegaly is a syndrome characterized by a sustained elevation of circulating growth hormone and insulin-like growth factor-1 (IGF-1). Insulin-like growth factor-1 is a potent mitogen and has a role in the transformation of normal cells to malignant cells. This study aims to evaluate the spontaneous micronucleus (MN) frequency by using the cytokinesis-block MN assay to determine genetic damage in the lymphocytes of patients with acromegaly. The study was carried out in 20 patients who had active acromegaly and in 20 age- and sex-matched healthy controls. The MN values were measured in binucleated cells obtained from mitogen-stimulated lymphocytes of patients and control subjects. The distribution of binucleated cells with 1, 2, 3, or more MNs was also measured. We found significantly higher MN frequency values in the lymphocytes of acromegalic patients than in those of the control subjects (2.23 ± 0.68 vs 1.03 ± 0.54, P = .001). The MN frequency increased with increasing IGF-1 levels of acromegalic patients (P = .036, R = 0.47). We observed that the number of binucleated cells with 2 MNs was higher for the majority of patients with acromegaly than for control subjects. Furthermore, the receiver operating characteristic curve (area under the curve = 0.914, P < .0001) was calculated to assess the discriminative power of the MN frequency. Our results indicate that increased MN frequency in the lymphocytes of patients with acromegaly may reflect genomic instability and this increased MN frequency may be associated with elevated levels of circulating growth hormone and IGF-1.

Frequencies of micronuclei (MNi), nucleoplasmic bridges (NPBs), and nuclear buds (NBUDs) in farmers exposed to pesticides in Çanakkale, Turkey

This study aimed to determine the incidence of micronuclei (MNi), nucleoplasmic bridges (NPBs), and nuclear buds (NBUDs) in peripheral blood lymphocytes due to direct exposure to pesticides among 46 farmers in Çanakkale, Turkey. 48 non-exposed individuals living in the same socioeconomic conditions were chosen as control. In addition, a cytokinesis-block proliferation index (CBPI) was calculated. MNi and NBUDs frequencies were significantly higher among the farmers (p < 0.05). Although the NPB frequency of the farmers was higher than the controls, there was no statistical difference. Multiple linear regression analysis showed that apart from gender, no significant effects of various confounding factors were observed. Regarding CBPI, data obtained for the controls were higher than that of the farmers; however, there was no statistically significant difference.

Normal and Cut-Off Values of the Cytokinesis-Block Micronucleus Assay on Peripheral Blood Lymphocytes in the Croatian General Population

Mikronukleus (MN) test na limfocitima periferne krvi jedna je od najvažnijih metoda koje se primjenjuju u citogenetičkom nadzoru. Osnovni preduvjet za primjenu nekog testa u svrhu nadzora profesionalno izloženih populacija jest poznavanje normalnih vrijednosti promatranoga biološkog pokazatelja (biomarkera) u kontrolnoj populaciji. Baze podataka na razini opće populacije moraju se redovito obnavljati novim podacima. Cilj ovog istraživanja bio je utvrditi normalne i granične vrijednosti MN-testa na limfocitima periferne krvi 200 zdravih ispitanika obaju spolova iz opće populacije Republike Hrvatske te ispitati koji čimbenici pridonose spontanom nastanku MN. Na razini istražene populacije utvrđeno je prosječno (6,90±3,32) MN (medijan 7 MN), dok je raspon pojedinačnih vrijednosti iznosio 0 do 18 MN u 1000 binuklearnih stanica. Gornja granična vrijednost dobivena izračunavanjem 95. percentila za cjelokupnu promatranu populaciju iznosi 12,5 MN na 1000 limfocita. Utvrđeno je da na spontani nastanak MN utječu spol, dob i navika pušenja. Žene u prosjeku imaju više vrijednosti svih parametara MN-testa od muškaraca, a u njih je bio i naglašeniji porast vrijednosti citogenetičkog nalaza zbog navike pušenja. Kako su literaturni podaci o utjecaju pušenja cigareta na nastanak MN kontradiktorni, planiran je nastavak istraživanja radi razjašnjavanja utjecaja dnevno utrošenog broja cigareta i ukupnog trajanja pušačkog staža na vrijednosti parametara MN-testa. Usporedba rezultata s literaturnim podacima potvrdila je da su dobivene vrijednosti u skladu s vrijednostima MN-testa zabilježenim na općoj populaciji u drugim svjetskim laboratorijima. Normalne i granične vrijednosti MN-testa utvrđene u ovome istraživanju poslužit će kao osnova za usporedbu i tumačenje nalaza MN-testa u ispitanika izloženih populacija te daljnju nadogradnju laboratorijske baze podataka.

Cytogenetic status in newborns and their parents in Madrid: the BioMadrid study

Monitoring cytogenetic damage is frequently used to assess population exposure to environmental mutagens. The cytokinesis-block micronucleus assay is one of the most widely used methods employed in these studies. In the present study we used this assay to assess the baseline frequency of micronuclei in a healthy population of father-pregnant woman-newborn trios drawn from two Madrid areas. We also investigated the association between micronucleus frequency and specific socioeconomic, environmental, and demographic factors collected by questionnaire. Mercury, arsenic, lead, and cadmium blood levels were measured by atomic absorption spectrometry. The association between micronucleated cell frequency and the variables collected by questionnaire, as well as, the risk associated with the presence of elevated levels of metals in blood, was estimated using Poisson models, taking the number of micronucleated cells in 1,000 binucleated cells (MNBCs) as the dependent variable. Separate analyses were conducted for the 110 newborns, 136 pregnant women, and 134 fathers in whom micronuclei could be assessed. The mean number of micronucleated cells per 1,000 binucleated cells was 3.9, 6.5, and 6.1 respectively. Our results show a statistically significant correlation in MNBC frequency between fathers and mothers, and between parents and newborns. Elevated blood mercury levels in fathers were associated with significantly higher MNBC frequency, compared with fathers who had normal mercury levels (RR:1.21; 95%CI:1.02-1.43). This last result suggests the need to implement greater control over populations which, by reason of their occupation or life style, are among those most exposed to this metal.

Polymorphisms of GSTT1 and GSTM1 and increased micronucleus frequencies in peripheral blood lymphocytes in residents at an e-waste dismantling site in China

In the present study, we investigated whether genetic polymorphisms of metabolic enzymes in an exposed population were associated with genotoxic effects of the pollutants from e-waste in 58 subjects (the exposed) resided in a typical e-waste recycling site and 80 subjects (the controls) from a village away from the recycling site. Effects of genetic polymorphisms of glutathione S-transferases (GSTs) (GSTT1 and GSTM1) on the frequency of micronucleated binucleated cells (MNed BNC) in peripheral blood lymphocytes were evaluated. GSTM1 and GSTT1 were typed using PCR-restriction fragment length polymorphism methods. Cytogenetic alterations were evaluated using the cytokinesis-block micronucleus assay. The MNed BNC frequency was significantly higher in the exposed group (median: 4.0 per thousand, IQR: 2.0-7.0 per thousand) than in the control group (median: 1.0 per thousand, IQR: 0.0-2.0 per thousand, P < 0.01 for both comparisons); sera GST activities were also higher in the exposed subjects with either non-null GSTT1 (mean +/- SD: 20.27 +/- 6.43) or non-null GSTM1 (mean +/- SD: 19.71 +/- 4.89) than in the controls (mean +/- SD: 18.79 +/- 4.91 and 19.34 +/- 6.42, respectively, P < 0.05 for both). Although the increased MNed BNC frequencies among the exposed group may be associated with the co-exposure of various chemical pollutants in the environment, there was no statistical evidence of an association between GSTs genotypes and frequencies of micronuclei in the study population. Because this study size was small, the mechanism of genotoxic effects caused by exposure to e-waste needs to be further validated in larger studies.

Genome damage in oropharyngeal cancer patients treated by radiotherapy

AIM

To estimate genome damage in oropharyngeal cancer patients before, during, and after radiotherapy and to measure the persistence of caused genome damage relevant in the evaluation of secondary cancer risk.

METHODS

DNA damage was evaluated in peripheral blood lymphocytes of 10 oropharyngeal cancer patients using alkaline comet assay, analysis of structural chromosome aberrations, and micronucleus assay. Blood samples were taken 2 hours before irradiation on day 1 of the first radiotherapy cycle, 2 hours after the application of the first dose, in the middle of the radiotherapy cycle, within 2 hours after the last received radiotherapy dose, and after 6 and 12 months after radiotherapy.

RESULTS

In most participants, the highest level of primary DNA damage was recorded in blood samples collected after the administration of first radiation dose (mean tail length 25.04+/-6.23 mum). Most patients also had increased frequency of comets with long tail-nucleus (LTN comets) after the administration of the first radiation dose (mean, 10.50+/-7.71 per 100 comets), which remained increased in the middle of radiotherapy (mean, 18.30+/-27.62 per 100 comets). Later on, the levels of primary DNA damage as recorded by the comet assay, slightly diminished. The frequency of structural chromosome aberrations in lymphocytes gradually increased during the radiation cycle (26.50+/-27.72 per 100 metaphases at the end of the therapy), as well as the frequency of micronuclei (mean total number of micronuclei 167.20+/-35.69 per 1000 binuclear cells).

CONCLUSION

Oropharyngeal cancer patients had relatively high levels of primary DNA damage in their peripheral blood lymphocytes even before therapy. The frequency of complex structural chromosome aberrations and the frequency of micronuclei increased with the progression of the radiation cycle and the doses delivered. As the frequency of chromosomal aberrations a year after radiotherapy mostly did not return to pre-therapy values, it represents an important risk factor related to the onset of second cancer.