Mechanisms of clastogen-induced chromosomal aberrations: A critical review and description of a model based on failures of tethering of DNA strand ends to strand-breaking enzymes

Safety assessment of high fructose corn syrup and fructose used as sweeteners in foods

High Fructose Corn Syrup (HFCS) and Fructose (FR) are widely used sweeteners in many foods and beverages. This study aimed at investigating the cytotoxic effects of HFCS (5%-30%) and FR (62.5-2000 μg/mL) using MTT assay in Human Hepatocellular Carcinoma (HepG2) cells, and genotoxic effects of using Chromosome Aberrations (CAs), Sister Chromatid Exchanges (SCEs), Micronuclei (MN) and comet assays in human lymphocytes. HFCS significantly reduced the cell viability in HepG2 cells at between 7.5% and 30% for 24 and 48 h. 30% HFCS caused a very significant toxic effect. FR had a cytotoxic effect in HepG2 cells at all treatments. However, as fructose concentration decreased, the cell viability decreased. HFCS (10%-20%) and FR (250-2000 μg/mL) decreased the mitotic index at higher concentrations. IC50 value was found to be a 15% for 48 h. IC50 value of FR was detected as 62.5 μg/mL for 24 h and 48 h. HFCS significantly increased CAs frequency at 15% and 20%. FR significantly increased the frequency of CAs at 250, 1000, and 2000 μg/mL for 48 h. Both sweeteners increased the frequency of SCEs at all concentrations. HFCS (15% and 20%) and FR (250, 1000, and 2000 μg/mL) induced MN frequency at higher concentrations. HFCS caused DNA damage in comet assay at 10% -30%. FR increased tail intensity and moment at 125-2000 μg/mL and tail length at 62.5, 250 and 500 μg/mL. Therefore, HFCS and FR are clearly seen to be cytotoxic and genotoxic, especially at higher concentrations.

AOP report: Development of an adverse outcome pathway for deposition of energy leading to cataracts

Cataracts are one of the leading causes of blindness, with an estimated 95 million people affected worldwide. A hallmark of cataract development is lens opacification, typically associated not only with aging but also radiation exposure as encountered by interventional radiologists and astronauts during the long-term space mission. To better understand radiation-induced cataracts, the adverse outcome pathway (AOP) framework was used to structure and evaluate knowledge across biological levels of organization (e.g., macromolecular, cell, tissue, organ, organism and population). AOPs identify a sequence of key events (KEs) causally connected by key event relationships (KERs) beginning with a molecular initiating event to an adverse outcome (AO) of relevance to regulatory decision-making. To construct the cataract AO and retrieve evidence to support it, a scoping review methodology was used to filter, screen, and review studies based on the modified Bradford Hill criteria. Eight KEs were identified that were moderately supported by empirical evidence (e.g., dose-, time-, incidence-concordance) across the adjacent (directly linked) relationships using well-established endpoints. Over half of the evidence to justify the KER linkages was derived from the evidence stream of biological plausibility. Early KEs of oxidative stress and protein modifications had strong linkages to downstream KEs and could be the focus of countermeasure development. Several identified knowledge gaps and inconsistencies related to the quantitative understanding of KERs which could be the basis of future research, most notably directed to experiments in the range of low or moderate doses and dose-rates, relevant to radiation workers and other occupational exposures.

2-Mercaptoethanol protects against DNA double-strand breaks after kidney ischemia and reperfusion injury through GPX4 upregulation

BACKGROUND

Kidney ischemia reperfusion injury (IRI) is characterized by tubular cell death. DNA double-strand breaks is one of the major sources of tubular cell death induced by IRI. 2-Mercaptoethanol (2-ME) is protective against DNA double-strand breaks derived from calf thymus and bovine embryo. Here, we sought to determine whether treatment with 2-ME attenuated DNA double-strand breaks, resulting in reduced kidney dysfunction and structural damage in IRI.

METHODS

Kidney IRI or sham-operation in mice was carried out. The mice were treated with 2-ME, Ras-selective lethal 3, or vehicle. Kidney function, tubular injury, DNA damage, antioxidant enzyme expression, and DNA damage response (DDR) kinases activation were assessed.

RESULTS

Treatment with 2-ME significantly attenuated kidney dysfunction, tubular injury, and DNA double-strand breaks after IRI. Among DDR kinases, IRI induced phosphorylation of ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3 related (ATR), but IRI reduced phosphorylation of other DDR kinases including ataxia telangiectasia and Rad3 related, checkpoint kinase 1 (Chk1), Chk2, and Chinese hamster cells 1 (XRCC1). Treatment with 2-ME enhanced phosphorylation of ATM and ATM-mediated effector kinases in IRI-subjected kidneys, suggesting that 2-ME activates ATM-mediated DDR signaling pathway. Furthermore, 2-ME dramatically upregulated glutathione peroxidase 4 (GPX4) in IRI-subjected kidneys. Inhibition of GPX4 augmented adverse IRI consequences including kidney dysfunction, tubular injury, DNA double-strand breaks, and inactivation of ATM-mediated DDR signaling pathway after IRI in 2-ME-treated kidneys.

CONCLUSIONS

We have demonstrated that exogenous 2-ME protects against DNA double-strand breaks after kidney IRI through GPX4 upregulation and ATM activation.

Exploring graphene-based materials' genotoxicity: inputs of a screening method

Graphene-based materials (GBMs) are promising nanomaterials, and several innovations depend on their use. However, the assessment of their potential hazard must be carefully explored before entering any market. GBMs are indeed well-known to induce various biological impacts, including oxidative stress, which can potentially lead to DNA damage. Genotoxicity is a major endpoint for hazard assessment and has been explored for GBMs, but the available literature shows conflicting results. In this study, we assessed the genotoxicity of 13 various GBMs, one carbon black and one amorphous silica through a DNA damage response assay (using a human respiratory cell model, BEAS-2B). Concurrently, oxidative stress was assessed through a ROS production quantification (DCFH-DA assay using a murine macrophage model, RAW 264.7). We also performed a full physicochemical characterization of our samples to explore potential structure-activity relationships involving genotoxicity. We observed that surface oxidation appears linked to genotoxicity response and were able to distinguish several groups within our studied GBMs showing different genotoxicity results. Our findings highlight the necessity to individually consider each nanoform of GBMs since the tested samples showed various results and modes of action. We propose this study as a genotoxicity assessment using a high-throughput screening method and suggest few hypotheses concerning the genotoxicity mode of action of GBMs.

DNA repair gene polymorphisms and chromosomal aberrations in healthy, nonsmoking population

Nonspecific structural chromosomal aberrations (CAs) can be found at around 1% of circulating lymphocytes from healthy individuals but the frequency may be higher after exposure to carcinogenic chemicals or radiation. The frequency of CAs has been measured in occupational monitoring and an increased frequency of CAs has also been associated with cancer risk. Alterations in DNA damage repair and telomere maintenance are thought to contribute to the formation of CAs, which include chromosome type of aberrations and chromatid type of aberrations. In the present study, we used the result of our published genome-wide association studies to extract data on 153 DNA repair genes from 866 nonsmoking persons who had no known occupational exposure to genotoxic substances. Considering an arbitrary cut-off level of P< 5 × 10^-3, single nucleotide polymorphisms (SNPs) tagging 22 DNA repair genes were significantly associated with CAs and they remained significant at P < 0.05 when adjustment for multiple comparisons was done by the Binomial Sequential Goodness of Fit test. Nucleotide excision repair pathway genes showed most associations with 6 genes. Among the associated genes were several in which mutations manifest CA phenotype, including Fanconi anemia, WRN, BLM and genes that are important in maintaining genome stability, as well as PARP2 and mismatch repair genes. RPA2 and RPA3 may participate in telomere maintenance through the synthesis of the C strand of telomeres. Errors in NHEJ1 function may lead to translocations. The present results show associations with some genes with known CA phenotype and suggest other pathways with mechanistic rationale for the formation of CAs in healthy nonsmoking population.

DNA Repair Gene Polymorphisms and Chromosomal Aberrations in Exposed Populations

DNA damage and unrepaired or insufficiently repaired DNA double-strand breaks as well as telomere shortening contribute to the formation of structural chromosomal aberrations (CAs). Non-specific CAs have been used in the monitoring of individuals exposed to potential carcinogenic chemicals and radiation. The frequency of CAs in peripheral blood lymphocytes (PBLs) has been associated with cancer risk and the association has also been found in incident cancer patients. CAs include chromosome-type aberrations (CSAs) and chromatid-type aberrations (CTAs) and their sum CAtot. In the present study, we used data from our published genome-wide association studies (GWASs) and extracted the results for 153 DNA repair genes for 607 persons who had occupational exposure to diverse harmful substances/radiation and/or personal exposure to tobacco smoking. The analyses were conducted using linear and logistic regression models to study the association of DNA repair gene polymorphisms with CAs. Considering an arbitrary cutoff level of 5 × 10^-3, 14 loci passed the threshold, and included 7 repair pathways for CTA, 4 for CSA, and 3 for CAtot; 10 SNPs were eQTLs influencing the expression of the target repair gene. For the base excision repair pathway, the implicated genes PARP1 and PARP2 encode poly(ADP-ribosyl) transferases with multiple regulatory functions. PARP1 and PARP2 have an important role in maintaining genome stability through diverse mechanisms. Other candidate genes with known roles for CSAs included GTF2H (general transcription factor IIH subunits 4 and 5), Fanconi anemia pathway genes, and PMS2, a mismatch repair gene. The present results suggest pathways with mechanistic rationale for the formation of CAs and emphasize the need to further develop techniques for measuring individual sensitivity to genotoxic exposure.

Evaluation of genotoxic potential of peptides used in nuclear medicine (PSMA -617 and -11, and ubiquicidine 29-41) using a flow-cytometric, semi-automated analysis of micronuclei frequency in cell cultures

Assays that rely on the assessment of frequency of micronuclei are important standard techniques currently used to quantify potential genotoxic damage after exposure to chemical or physical agents, such as ionizing radiation, or in pre-clinical studies, to assessment of the genotoxic potential of drugs or its components. The experiments are usually performed using conventional microscopy, but currently the protocols are being upgraded to automated approaches based on flow cytometry protocols based on the elimination of the plasma membrane by chemical agents, allowing quantification by flow cytometry. In this work, the genotoxic potential of peptides used as components of radiopharmaceuticals (PSMA-617 and 11 and Ubiquicidine) was evaluated exposing CHO-KI cells to a wide range of concentration (0.1X and 100X the maximum allowed concentration to human adults). Incubation with PSMA-11 or UBI29-41 did not induce genotoxicity. After 24 h of incubation, PSMA-617 induced genotoxicity only in non-practical concentration (100-fold). Results corroborate the safety of the pre-drugs and the wide detection range of technique.

The effects of DNA repair polymorphisms on chromosome aberrations in the population of Kazakhstan

Purpose: To analyze the effects of DNA repair polymorphism and other factors on the frequency chromosome aberrations in an irradiated cohort of subjects living around the Semipalatinsk nuclear test site and non-exposed group of subjects from ecologically favorable zones of Kazakhstan.Materials and methods: Blood samples were collected in the rural areas of the East Kazakhstan district around the Semipalatinsk nuclear test site and ecologically favorable zones of Almaty region of Kazakhstan. Chromosome aberrations in the fresh and cryopreserved peripheral blood lymphocyte cultures were analyzed by Giemsa staining. Single nucleotide polymorphisms at eight DNA repair genes (XRCC1 rs1799782, XRCC1 rs25487, XRCC3 rs861539, ATM rs1801516, XPD rs1799793, XPD rs13181, APEX1 rs1130409, and hOGG1 rs1052133) were determined by PCR-RFLP method.Results: The age of donors and smoking significantly affected the frequency of chromosome aberrations among the irradiated and control subjects. In the irradiated and control cohorts, the frequency of chromosome aberrations was significantly increased in the heterozygous ATM rs1801516 (1853 Asp/Asn) individuals; for the rest of the loci no significant associations between polymorphism and the frequency of chromosome aberrations were detected.Conclusions: The age of donors, smoking, and the ATM rs1801516 polymorphism significantly affect the frequency of chromosome aberrations among individuals inhabiting contaminated area around the Semipalatinsk nuclear weapon test site, as well as among those inhabiting ecologically favorable zones of Kazakhstan.

Genetic variation associated with chromosomal aberration frequency: A genome-wide association study

Chromosomal aberrations (CAs) in human peripheral blood lymphocytes (PBL) measured with the conventional cytogenetic assay have been used for human biomonitoring of genotoxic exposure for decades. CA frequency in peripheral blood is a marker of cancer susceptibility. Previous studies have shown associations between genetic variants in metabolic pathway, DNA repair and major mitotic checkpoint genes and CAs. We conducted a genome-wide association study on 576 individuals from the Czech Republic and Slovakia followed by a replication in two different sample sets of 482 (replication 1) and 1288 (replication 2) samples. To have a broad look at the genetic susceptibility associated with CA frequency, the sample sets composed of individuals either differentially exposed to smoking, occupational/environmental hazards, or they were untreated cancer patients. Phenotypes were divided into chromosome- and chromatid-type aberrations (CSAs and CTAs, respectively) and total chromosomal aberrations (CAtot). The arbitrary cutoff point between individuals with high and low CA frequency was 2% for CAtot and 1% for CSA and CTA. The data were analyzed using age, sex, occupation/cancer and smoking history as covariates. Altogether 11 loci reached the P-value of 10^-5 in the GWAS. Replication 1 supported the association of rs1383997 (8q13.3) and rs2824215 (21q21.1) in CAtot and rs983889 (5p15.1) in CTA analysis. These loci were found to be associated with genes involved in mitosis, response to environmental and chemical factors and genes involved in syndromes linked to chromosomal abnormalities. Identification of new genetic variants for the frequency of CAs offers prediction tools for cancer risk in future. Environ. Mol. Mutagen. 60:17-28, 2019. © 2018 Wiley Periodicals, Inc.

Mesotrione herbicide does not cause genotoxicity, but modulates the genotoxic effects of Atrazine when assessed in mixture using a plant test system (Allium cepa)

Mesotrione (MES) is an herbicide from the triketone family and has been used as an alternative to Atrazine (ATZ), which was banned in some countries due to its toxicity to non-target organisms. Despite being considered an eco-friendly herbicide, data from the literature about the harmful effects of MES in its pure form and/or in combination with other herbicides is still scarce. Aimed at assessing the potential of MES to induce cell death and DNA damage, seeds of Allium cepa (higher plant, monocotyledon) were exposed to this herbicide, pure and in mixture with ATZ, and the number of dividing cells (cytotoxicity), chromosomal aberrations (CA, genotoxicity) and micronuclei (MN, mutagenicity) were then quantified. The pure MES (1.8 to 460 μg/L) did not show either cytotoxicity or genotoxicity/mutagenicity under the tested conditions. The genotoxicity of ATZ (1.5 to 400 μg/L), previous reported in the literature, was confirmed herein. The assessment of MES + ATZ mixtures (1.8 + 1.5; 7 + 6.25; 30 + 25 μg/L, respectively) showed that MES, at low concentrations, enhance the genotoxicity of ATZ (potentiation), since the significant frequencies of CA and MN were greater than the ones expected in additive effects. Taking together, MES in its pure form seems to be a safe alternative to ATZ regarding the capacity to damage (at cellular and DNA levels) non-target plants (Monocots); however, MES in combination with ATZ appeared to act as a co-mutagen at low concentrations.

Genetic variation of acquired structural chromosomal aberrations

Human malignancies are often hallmarked with genomic instability, which itself is also considered a causative event in malignant transformation. Genomic instability may manifest itself as genetic changes in the nucleotide sequence of DNA, or as structural or numerical changes of chromosomes. Unrepaired or insufficiently repaired DNA double-strand breaks, as well as telomere shortening, are important contributors in the formation of structural chromosomal aberrations (CAs). In the present review, we discuss potential mechanisms behind the formation of CAs and their relation to cancer. Based on our own studies, we also illustrate how inherited genetic variation may modify the frequency and types of CAs occurring in humans. Recently, we published a series of studies on variations in genes relevant to maintaining genomic integrity, such as those encoding xenobiotic-metabolising enzymes, DNA repair, the tumour suppressor TP53, the spindle assembly checkpoint, and cyclin D1 (CCND1). While individually genetic variation in these genes exerted small modulating effects, in interactions they were associated with CA frequencies in peripheral blood lymphocytes of healthy volunteers. Moreover, we observed opposite associations between the CCND1 splice site polymorphism rs9344 G870A and the frequency of CAs compared to their association with translocation t(11,14). We discuss the functional consequences of the CCND1 gene in interplay with DNA damage response and DNA repair during malignant transformation. Our review summarizes existing evidence that gene variations in relevant cellular pathways modulate the frequency of CAs, predominantly in a complex interaction. More functional/mechanistic studies elucidating these observations are required. Several questions emerge, such as the role of CAs in malignancies with respect to a particular phenotype and heterogeneity, the formation of CAs during the process of malignant transformation, and the formation of CAs in individual types of lymphocytes in relation to the immune response.

Strong associations between chromosomal aberrations in blood lymphocytes and the risk of urothelial and squamous cell carcinoma of the bladder

Chromosomal aberrations (CAs) in blood lymphocytes have been shown to be associated with overall cancer risk and aging. However, their relationship to bladder cancer risk remains to be elucidated. In a case-control study of bladder cancer in Egypt, we examined the relationship between the increased frequency of CAs in blood lymphocytes and bladder cancer risk. High frequency of CAs was significantly associated with an increased risk of bladder cancer [adjusted odds ratios (OR) = 3.90, 95% confidence interval (CI) = 2.65-5.73]. The associations were somewhat stronger in squamous cell carcinomas (SCC, OR = 4.90) than in urothelial carcinomas (UC, OR = 3.62). We also identified chromosome specific CAs for chromosomes 3, 4, 5, 8, 9, 10, 11, 12, 17, 19 that were significantly associated with an increased risk of bladder cancer. We observed particularly strong associations between aberrations of chromosomes 12, 13, 17 and risk of SCC (OR = 7.06, 6.91 and 6.23, respectively).

CONCLUSION

increased frequency of chromosomal aberrations in blood lymphocytes was significantly associated with bladder cancer risk. Overall and chromosome specific aberrations in blood lymphocytes may be a unique set of biomarkers for risk assessments of SCC and UC.

DNA and chromosomal damage in medical workers exposed to anaesthetic gases assessed by the lymphocyte cytokinesis-block micronucleus (CBMN) assay. A critical review

The lymphocyte cytokinesis-block micronucleus (CBMN) assay has been applied in hundreds of in vivo biomonitoring studies of humans exposed either environmentally or occupationally to genotoxic chemicals. However, there is an emerging need to re-evaluate the use of MN and other biomarkers within the lymphocyte CBMN cytome assay as quantitative indicators of exposure to main classes of chemical genotoxins. The main aim of the present report is to systematically review published studies investigating the use of the lymphocyte CBMN assay to determine DNA damage in subjects exposed to anaesthetic gases. We also compared performance of the CBMN assay with other DNA damage assays employed and identified strengths and weaknesses of the published studies. We have retrieved 11 studies, published between 1996 and 2013, reporting MN associated with occupational exposures (operating room personnel). The individual job categories were often described (anaesthesiologists, technicians, radiologists) among cases, as well as duration of exposure. All studies reported the compounds present at the workplace and, in some instances, the exposure levels were measured. Controls were usually recruited among personnel at the hospital not exposed to anaesthetics or they were healthy unexposed subjects from general population. The number of investigated subjects, due to the character of the occupation, was relatively smaller than those investigated in other occupational monitoring settings. Overall, the majority of the studies were age- and gender- matched (or investigated only males or females) while less attention was given to lifestyle confounders. Appropriate measurement of exposure, available in approximately half of the studies only, was compromised by the lack of the personal dosimetry-based determinations. In all studies, higher MN frequencies were observed in exposed individuals. The meta-analysis of mean MN frequency of combined studies confirmed this tendency (log mean ratio=0.56 [0.34-0.77]; P=3.51×10^-7). Similar differences between the exposed and controls were also observed for other biomarkers.

Chromosomal aberrations in ovine lymphocytes exposed in vitro to tolylfluanid

Chromosomal aberrations have been used as important cytogenetic biomarkers to study the mutagenic effects of different chemicals in vivo and in vitro. Chromosomal aberrations were evaluated in cultures of sheep lymphocytes in vitro exposed to the fungicide tolylfluanid. Lymphocyte cultures from three donors were exposed to four different concentrations of fungicide (1.10(-4) M(.)L; 1.10(-5) M(.)L; 1.10(-6) M(.)L; 1 × 10(-7) M(.)L). Chromosomal analysis showed a significant (P = 0.018 and 0.038 respectively, Anova test, P < 0.05, Tukey test) increase in the frequency of aberrant cells (ABC) in cultures treated with the highest negative experimental concentrations of tolylfluanid (1.10(-4) M(.)L; 1.10(-5) M(.)L) compared to control. Significantly increased numbers of chromatid breaks (7.67 ± 0.58% against 1.67 ± 2.08%, P = 0.009, Anova test, P < 0.05, Tukey test) and chromatid gaps (7.67 ± 1.15% against 2.67 ± 0.58%, P = 0.003, Anova test, P < 0.05, Tukey test) were observed in ovine cultures treated with the highest experimental concentration of tolylfluanid (1.10(-4) M(.)L). Tolylfluanid induced also chromosomal exchanges (P = 0.038, and 0.016 respectively, Anova test, P < 0.05, Tukey test) in ovine cultures treated with the highest experimental concentrations of tolylfluanid (1.10(-4) M(.)L; 1.10(-5) M(.)L). The mitotic index has not shown any statistical differences between the various treatments and control groups. Our results suggest a significant genotoxic effect of tolylfluanid only at the highest concentration in sheep peripheral lymphocytes in vitro.

Chromosomal integrity and DNA damage in freeze-dried spermatozoa

Freeze-drying technology may one day be used to preserve mammalian spermatozoa indefinitely without cryopreservation. Freeze-dried mouse spermatozoa stored below 4°C for up to 1 year have maintained the ability to fertilize oocytes and support normal development. The maximum storage period for spermatozoa increases at lower storage temperatures. Freeze-drying, per se, may reduce the integrity of chromosomes in freeze-dried mouse spermatozoa, but induction of chromosomal damage is suppressed if spermatozoa are incubated with divalent cation chelating agents prior to freeze-drying. Nevertheless, chromosomal damage does accumulate in spermatozoa stored at temperatures above 4°C. Currently, no established methods or strategies can prevent or reduce damage accumulation, and damage accumulation during storage is a serious obstacle to advances in freeze-drying technology. Chromosomal integrity of freeze-dried human spermatozoa have roughly background levels of chromosomal damage after storage at 4°C for 1 month, but whether these spermatozoa can produce healthy newborns is unknown. The safety of using freeze-dried human spermatozoa must be evaluated based on the risks of heritable chromosome and DNA damage that accumulates during storage.

Cytogenetic study of the effect of Schistosoma mansoni infection on human peripheral blood lymphocytes and the role of β-carotene and vitamin E in modulating this effect

This study has been made to determine the potential genotoxicity of Schistosoma mansoni on lymphocytes of infected patients using different mutagenic end points. The protective role of antioxidants pro vitamin β-carotene and vitamin E in minimizing these genotoxic effect was also studied. The study focused on the effect of schistosomiasis on the induction of sister chromatid exchange (SCEs) and other chromosomal aberrations. This work was conducted on 24 Schistosoma mansoni infected patients and 10 healthy adults as a control group. Lymphocytes from peripheral blood of patients and control group were used for culture and subsequent cytogenetic studies. The results indicated that schistosomiasis was genotoxic in all examined tests. It induced a significant increase in the percentage of structural chromosomal aberrations and the frequency of SCEs. It also inhibited cell division and caused cell cycle delay. Lymphocyte cultures of S. mansoni patients treated with 10 μg/ml β-carotene or 20 mg/ml vitamin E showed a significant decrease in the percentage of structural chromosomal aberrations and the frequency of SCEs. Schistosomiasis has a genotoxic effect on peripheral blood lymphocytes. The use of the antioxidants β-carotene and vitamin E can be considered a promising approach not only toward inhibiting the genetic damage of schistosomiasis but also as prophylactic agents against infection with S mansoni. Furthermore, higher doses of antioxidant drugs, β-carotene and vitamin E, should be tried as an adjuvants to conventional therapy in a trial to improve treatment of schistosomiasis.