Higher Sister Chromatid Exchange Frequency Research Articles

Intellectual disability and abnormal cortical neuron phenotypes in patients with Bloom syndrome.

Bloom syndrome (BS) is a rare autosomal recessive disorder characterized by genomic instability that leads to various complications, including cancer. Given the low prevalence of BS in Japan, we conducted a nationwide survey. We recruited eight patients with BS, three of whom exhibited intellectual disability. The 631delCAA mutation in the BLM gene was detected in 9 out of 16 alleles. To investigate neuronal development in patients with BS, we generated induced pluripotent stem cells derived from one of these patients (BS-iPSCs). We examined the phenotypes of the induced cortical neurons derived from the generated BS-iPSCs using a previously reported protocol; the generated BS-iPSCs showed an approximately 10-times higher frequency of sister-chromatid exchange (SCE) than the control iPSCs. Immunocytochemistry revealed shorter axons and higher proliferative potential in BS-iPSC-derived cortical neurons compared with control iPSCs. To our knowledge, our study is the first to clarify the abnormality of the cortical neuron phenotypes derived from patients with BS. Our findings may help identify the pathogenesis of neuronal differentiation in BS and aid in the development of novel therapeutic agents.

Valuating of sister chromatid exchange (SCE) in patients with type 2 diabetes mellitus

This study was established to test the cytogenetic parameter of sister chromatid exchange (SCE) in type 2 diabetic patients for its close relationship with mutations. In this study, cytogenetic analyses were done on peripheral blood lymphocytes obtained from 25 type 2 DM patients using short-term lymphocyte culture .Human lymphocytes have long been used to assess the gene damage occurring in vivo as well as in vitro. Results showed significant high frequencies of SCEs were scored in type 2 DM patients [2.25±0.08SCE/cell] compared with control [1.28±0.04SCE/cell] (P<0.01). We concluded that the DM patients have significantly more genetic damage (high SCE frequency), and there are no significant differences in diabetic patients in relation with demographic characteristics (age and gender).

The formation of SCEs as an effect of occupational exposure to formaldehyde

Formaldehyde (FA) is a ubiquitous toxic chemical employed worldwide due to its disinfectant and preservative properties. Despite being classified as a human carcinogen, FA is still employed as formalin in pathology wards as standard fixative. We evaluated its relationship with the formation of sister-chromatid exchanges (SCEs) in cultured peripheral blood lymphocytes on 57 pathologists and 48 controls and the risk/protective role played by several genetic polymorphisms. All subjects were assessed for SCEs and genotyped for the most common cancer-associated gene polymorphisms: CYP1A1 exon 7 (A > G), CYP1A1*2A (T > C), CYP2C19*2 (G > A), GSTT1 (presence/absence), GSTM1 (presence/absence), GSTP1 (A > G), XRCC1 (G399A), XRCC1 (C194T), XRCC1 (A280G), XPC exon 15 (A939C), XPC exon 9 (C499T), TNFα − 308 G > A), IL10 − 1082 (G > A), and IL6 − 174 (G > C). Air-FA concentration was assessed through passive personal samplers. Pathologists, exposed to 55.2 μg/m3 of air-FA, showed a significantly higher SCEs frequency than controls, exposed, respectively, to 18.4 μg/m3. Air-FA was directly correlated with SCEs frequency and inversely with the replication index (RI). Regression models showed FA exposure as a significant predictor in developing SCEs, while did not highlight any role of the selected polymorphisms. Our study confirms the role of low air-FA levels as genotoxicity inductor, highlighting the importance to define exposure limits that could be safer for exposed workers.

Cellular consequences of small supernumerary marker chromosome derived from chromosome 12: mosaicism in daughter and father.

Constitutional genomic imbalances are known to cause malformations, disabilities, neurodevelopmental delay, and dysmorphia and can lead to dysfunctions in the cell cycle. In extremely rare genetic conditions such as small supernumerary marker chromosomes (sSMC), it is important to understand the cellular consequences of this extra marker, as well the factors that contribute to their maintenance or elimination through successive cell cycles and phenotypic impact. The study of chromosomal mosaicism provides a natural model to characterize the effect of aneuploidy on genome stability and compare cells with the same genetic background and environment exposure, but differing in the presence of sSMC. Here, we report the functional characterization of different cell lines from two familial patients with mosaic sSMC derived from chromosome 12. We performed studies of proliferation dynamics, stability, and variability of these cells using fluorescent in situ hybridization (FISH), sister chromatid exchanges (SCE), and conventional staining. We also quantified the telomere-related genomic instability of sSMC cells using 3D telomeric profile analysis by quantitative-FISH. sSMC cells exhibited differences in the cell cycle dynamics compared to normal cells. First, the sSMC cells exhibited lower proliferation index and higher frequency of SCE than normal cells, associated with a higher level of chromosomal instability. Second, sSMC cells exhibited more telomeric-related genomic instability. Lastly, the differences of sSMC cells distribution among tissues could explain different phenotypic repercussions observed in patients. These results will help in our understanding of the sSMC stability, maintenance during cell cycle, and the cell cycle variables involved in the different phenotypic manifestations.

Carbon Disulfide (CS2) Induced Chromosomal Alterations and Apoptosis in Circulated Blood Lymphocytes of Personnel Working in Viscose Industry

Background and objective: Carbon disulfide (CS2) is a naturally occurring chemical substance in the environment and also an important endogenous substance in the human body. This study was done to collect data on the effects and to find a possible relationship between in-vivo CS2 induced apoptosis and genotoxic effects.Material and method: Circulated blood lymphocytes (PBL) of 41 workers occupationally exposed to Carbon disulfide (CS2) in viscose industry were investigated. The participants involved three groups. The first group included 41 participants exposed to CS2 together with various confounding factors; the second group comprised of 41 participants who were inhabitant of viscose industry and were partially exposed to CS2 in long periods; and third group consisting 41 participants as control group who were not exposed to any kind of chemicals and radiation hazards. Ambient air concentrations of CS2 were measured in different workplaces. Measures of genotoxicity included the determination of the frequencies of chromosomal aberrations (CA), sister-chromatid exchange (SCE), HPRT mutations (variant frequency, VF), and measurement of UV-induced unscheduled DNA-repair synthesis (UDS). The percentages of premature centromere division (PCD) and of cells with a high frequency of SCE (HF/SCE) were also scored. Apoptosis and c l proliferation were determined by flow cytometry.Results: In both CS2 exposed groups, the apoptotic activity and the CA levels in PBLs were significantly higher than in controls. CA was mostly breaks of the chromatid type. In group II, CA was slightly lower in comparison with group I, which can be attributed to a different rate of elimination of damaged lymphocytes as a consequence of CS2 induced apoptotic activity.Conclusion: The results demonstrate that exposure to CS2 induced apoptosis and CA, indicating an excess cancer risk among participants occupationally exposed to CS2. The results also emphasized the importance of the measurement of occupationally exposed pollutants such as CS2 in order to avoid genotoxic effects in the workers.

Bromodeoxyuridine does not contribute to sister chromatid exchange events in normal or Bloom syndrome cells.

Sister chromatid exchanges (SCEs) are considered sensitive indicators of genome instability. Detection of SCEs typically requires cells to incorporate bromodeoxyuridine (BrdU) during two rounds of DNA synthesis. Previous studies have suggested that SCEs are induced by DNA replication over BrdU-substituted DNA and that BrdU incorporation alone could be responsible for the high number of SCE events observed in cells from patients with Bloom syndrome (BS), a rare genetic disorder characterized by marked genome instability and high SCE frequency. Here we show using Strand-seq, a single cell DNA template strand sequencing technique, that the presence of variable BrdU concentrations in the cell culture medium and in DNA template strands has no effect on SCE frequency in either normal or BS cells. We conclude that BrdU does not induce SCEs and that SCEs detected in either normal or BS cells reflect DNA repair events that occur spontaneously.

Association of CYP2E1 and CYP1A1m2 (BsrD1) polymorphisms with cytogenetic biomarkers in petrol pump workers

Petrol pump workers are occupationally exposed to benzene through their contact with gasoline vapors. The toxicity of benzene has been related to its metabolism. This study investigated the association of CYP2E1 and CYP1A1m2 with sister chromatid exchanges (SCE) and tail moment (TM) value in workers occupationally exposed to gasoline fumes. Blood and urine samples were collected from 50 petrol pump workers and 50 control individuals matched with respect to age and other confounding factors except for exposure to benzene through gasoline vapors. To determine the benzene exposure, hydroquinone level was analyzed in urinary samples of exposed and control individuals. Urinary mean hydroquinone level was found to be significantly high (p < 0.05) in exposed workers. Our results showed that mean SCE frequency and TM value were significantly higher (p < 0.05) in exposed workers (5.56 ± 0.80 and 19.50 ± 2.16 μm, respectively) than control individuals (2.83 ± 0.39 and 1.00 ± 0.00 μm, respectively). Regarding the effect of CYP2E1 polymorphism, it was found that mutant genotypes (homozygous and heterozygous) showed significant high mean frequency of SCE (6.11 ± 0.51 and 5.98 ± 0.54, respectively) and TM (16.13 ± 4.36 μm and 13.24 ± 2.24 μm, respectively) value in exposed individuals (p < 0.05). With regard to the CYP1A1m2 polymorphism, it was observed that mutant genotypes (homozygous and heterozygous) had higher but nonsignificant mean value of SCE frequency (5.86 ± 1.07 and 5.86 ± 1.07, respectively) and significantly higher TM value (14.97 ± 3.74 μm and 13.93 ± 2.23 μm, respectively) in exposed individuals.

Biomarkers of genotoxicity measured in human lymphocytes exposed to benzo[a]pyrene: Aneugenic effect, and involvement multiple primary DNA lesions

Benzo-a-pyrene (B[a]P) is a polycyclic aromatic hydrocarbon classified as carcinogenic to human. Its metabolic activation leads to production of metabolites forming adducts with DNA, being at origin of B[a]P-induced DNA damages, mutagenesis and carcinogenesis. Human blood lymphocytes cultures established from 25 subjects aged 20 to 30 years old, living in Montreal (Quebec, Canada) were exposed to B[a]P (0.4, 4, 20 and 40 µM) for 24 h, then washed and cultivated without B[a]P for an additional 24 h. B[a]P-DNA adducts, DNA single-strand breaks (SSBs), sister chromatid exchanges (SCEs), chromosomal aberrations (CAs) and micronuclei (MN) were analysed. Fluorescent in situ hybridization (FISH) analysis of MN using a pancentromeric probe was also done to assess MN content. Significantly increased formation of B[a]P-DNA adducts, CAs, MN and SCEs were observed starting at [B[a]P]=0.4 µM (p<0.01), with a significant decrease of B[a]P-DNA adducts and MN after exposure to 20 µM B[a]P. For DNA SSBs, no significant increase was observed in all conditions. Besides, FISH analysis showed that B[a]P-induced MN mostly contain centromeres (77.1% vs 68.5% for the control, p<0.01), and specifically three or more centromeres (p<0.01). This study suggests an aneugenic effect of B[a]P in human lymphocytes. Finally, statistical analysis by multiple linear regression showed that two variables (B[a]P exposure level and B[a]P-DNA adducts) significantly explained 53% of observed variability in SCE test, while the percentage of cell presenting a high frequency of SCE (% HFC) was the only variable significantly explaining the observed variability in CA and MN test (34% and 12%, respectively). These observations indicate that DNA breaks, in addition to B[a]P-DNA adducts, contributed to SCEs formation.

Relationship between carbon monoxide intoxication and sister chromatid exchange in lymphocytes

Carbon monoxide (CO) intoxication can be serious and is reported to be the cause of more than half of all fatal intoxications. In this study, we aimed to identify its genotoxic effects based on sister chromatid exchange (SCE). CO-poisoned patients presented to the emergency services department were identified. Their demographic characteristics, vital findings, laboratory markers, source of CO gas, risk factors, and smoking habits were recorded. The genotoxic effect was assessed using the SCE method. A total of 38 patients were recruited. Their ages ranged from 16-64years (mean: 29.79±10.92years). In all the cases, the source of CO gas was a flash heater. The mean carboxyhemoglobin (COHb) level was 25.05±7.15%. Of all the patients, 12 (31.6%) had a the Glasgow Coma Scale (GCS) scores of less than 15, and an important negative correlation was found between the GCS and COHb level (r=-0.825; p<0.001). Genotoxicity investigations revealed a significantly higher SCE frequency among patients with high COHb levels compared with that of control subjects with physiological COHb levels (p<0.001). However, no correlation between increased SCE frequency and COHb level was found (r=0.16; p=0.34). CO poisoning was shown to result in genotoxicity via an increase in the frequency of SCE. This study is the first to demonstrate a genotoxic effect of CO independent of other chemicals.

DNA Damage and Susceptibility Assessment in Industrial Workers Exposed to Styrene

Styrene is a widely used chemical in the manufacture of synthetic rubber, resins, polyesters, and plastics. The highest levels of human exposure to styrene occur during the production of reinforced plastic products. The objective of this study was to examine occupational exposure to styrene in a multistage approach, in order to integrate the following endpoints: styrene in workplace air, mandelic and phenylglyoxylic acids (MA + PGA) in urine, sister chromatid exchanges (SCE), micronuclei (MN), DNA damage (comet assay), and genetic polymorphisms of metabolizing enzymes (CYP2E1, EPHX1, GSTM1, GSTT1, and GSTP1). Seventy-five workers from a fiberglass-reinforced plastics factory and 77 unexposed controls took part in the study. The mean air concentration of styrene in the breathing zone of workers (30.4 ppm) and the mean concentration of urinary metabolites (MA + PGA = 443 ± 44 mg/g creatinine) exceeded the threshold limit value (TLV) and the biological exposure index (BEI). Significantly higher SCE frequency rate and DNA damage were observed in exposed workers, but MN frequency was not markedly modified by exposure. With respect to the effect of genetic polymorphisms on different exposure and effect biomarkers studied, an increase in SCE levels with elevated microsomal epoxide hydrolase activity was noted in exposed workers, suggesting a possible exposure–genotype interaction.

Aberrant chromosome morphology in human cells defective for Holliday junction resolution

In somatic cells, Holliday junctions can be formed between sister chromatids during the recombinational repair of DNA breaks or after replication fork demise. A variety of processes act upon Holliday junctions to remove them from DNA, in events that are critical for proper chromosome segregation. In human cells, the BLM protein, inactivated in individuals with Bloom's syndrome, acts in combination with topoisomerase IIIα, RMI1 and RMI2 (BTR complex) to promote the dissolution of double Holliday junctions. Cells defective for BLM exhibit elevated levels of sister chromatid exchanges (SCEs) and patients with Bloom's syndrome develop a broad spectrum of early-onset cancers caused by chromosome instability. MUS81-EME1 (refs 4-7), SLX1-SLX4 (refs 8-11) and GEN1 (refs 12, 13) also process Holliday junctions but, in contrast to the BTR complex, do so by endonucleolytic cleavage. Here we deplete these nucleases from Bloom's syndrome cells to analyse human cells compromised for the known Holliday junction dissolution/resolution pathways. We show that depletion of MUS81 and GEN1, or SLX4 and GEN1, from Bloom's syndrome cells results in severe chromosome abnormalities, such that sister chromatids remain interlinked in a side-by-side arrangement and the chromosomes are elongated and segmented. Our results indicate that normally replicating human cells require Holliday junction processing activities to prevent sister chromatid entanglements and thereby ensure accurate chromosome condensation. This phenotype was not apparent when both MUS81 and SLX4 were depleted from Bloom's syndrome cells, suggesting that GEN1 can compensate for their absence. Additionally, we show that depletion of MUS81 or SLX4 reduces the high frequency of SCEs in Bloom's syndrome cells, indicating that MUS81 and SLX4 promote SCE formation, in events that may ultimately drive the chromosome instabilities that underpin early-onset cancers associated with Bloom's syndrome.

Formaldehyde-induced chromosomal aberrations and apoptosis in peripheral blood lymphocytes of personnel working in pathology departments

Peripheral blood lymphocytes (PBL) of 37 formaldehyde-exposed women from four pathology departments in Hungary were investigated to collect data on the effects of occupational exposures to formaldehyde and to find a possible relationship between in vivo formaldehyde-induced apoptosis and genotoxic effects. The subjects were divided into two groups: 16 donors exposed to formaldehyde together with various organic solvents, and 21 subjects exposed mainly to formaldehyde. The results were compared with 37 controls (all women) without known occupational exposure. Ambient air concentrations of formaldehyde were measured in three work places, and ranged from 0.23 to 1.21mg/m(3) (mean 0.9mg/m(3)). Measures of genotoxicity included the determination of the frequencies of chromosomal aberrations (CA), sister-chromatid exchange (SCE), HPRT mutations (variant frequency, VF) and the measurement of UV-induced unscheduled DNA-repair synthesis (UDS). The percentages of premature centromere division (PCD) and of cells with a high frequency of SCE (HF/SCE) were also scored. Apoptosis and cell proliferation were determined by flow cytometry. In both formaldehyde-exposed groups, the apoptotic activity and the CA levels in PBLs were significantly higher than in controls. The CA were mostly breaks of the chromatid type. In the second group, which was mainly exposed to formaldehyde, CA were slightly lower in comparison with the group exposed to formaldehyde and solvents, which may be attributed to a different rate of elimination of damaged lymphocytes as a consequence of formaldehyde-induced apoptotic activity. In the second group, a significant decrease of VF and a non-significant increase in HF/SCE were found compared with the control and the other group. In conclusion, the results demonstrate that exposure to formaldehyde induces apoptosis and CA, indicating an excess cancer risk among subjects occupationally exposed to formaldehyde. The results also emphasize the importance of the measurement of occupational air pollutants, such as formaldehyde, in order to avoid genotoxic effects in the workers.

Alteration of sister chromatid exchange frequencies in gastric cancer and chronic atrophic gastritis patients with and without H. pylori infection.

To determine, by counting sister chromatid exchange (SCE) frequencies, whether genetic impairment and DNA damage have an effect on the pathogenesis of gastric cancer (GC). Analysis of SCE is a cytogenetic technique used to show DNA damage as a result of an exchange of DNA fragments between sister chromatids. We analyzed SCE frequency in 24 patients with GC, 26 patients with chronic atrophic gastritis (CAG), and 15 normal controls. The presence of H. pylori was confirmed by urease test, toluidine-blue stain and hematoxylin-eosin stain. SCE was significantly increased in H. pylori-negative GC patients, and in H. pylori-negative CAG patients compared with controls (7.41 +/- 1.36 and 6.92 +/- 1.20, respectively, vs 5.54 +/- 0.8, P < 0.001). There was no difference in the SCE frequency between H. pylori-negative GC patients and H. pylori-negative CAG patients (P > 0.05). On other hand, the SCE frequencies in H. pylori-positive GC patients were higher than those in H. pylori-positive CAG patients (9.20 +/- 0.94 vs 7.93 +/- 0.81, P < 0.01). Furthermore, H. pylori-positive GC patients had a higher SCE frequency than H. pylori-negative GC patients (9.20 +/- 0.94 vs 7.41 +/- 1.36, P < 0.001). Similarly, a significant difference was detected between H. pylori-positive CAG patients and H. pylori-negative CAG patients (7.93 +/- 0.81 vs 6.92 +/- 1.20, P < 0.05). We suggest the increased SCE in patients reflects a genomic instability that may be operative in gastric carcinogenesis.

Elevated sister chromatid exchange frequencies in New Zealand Vietnam War veterans

From July 1965 until November 1971, New Zealand Defence Force Personnel fought in the Vietnam War. During this time more than 76,500,000 litres of phenoxylic herbicides were sprayed over parts of Southern Vietnam and Laos, the most common being known as ‘Agent Orange’. The current study aimed to ascertain whether or not New Zealand Vietnam War veterans show evidence of genetic disturbance arising as a consequence of their now confirmed exposure to these defoliants. A sample group of 24 New Zealand Vietnam War veterans and 23 control volunteers were compared using an SCE (sister chromatid exchange) analysis. The results from the SCE study show a highly significant difference (P < 0.001) between the mean of the experimental group (11.05) and the mean of a matched control group (8.18). The experimental group also has an exceptionally high proportion of HFCs (cells with high SCE frequencies) above the 95th percentile compared to the controls (11.0 and 0.07%, respectively). We conclude that the New Zealand Vietnam War veterans studied here were exposed to a clastogenic substance(s) which continues to exert an observable genetic effect today, and suggest that this is attributable to their service in Vietnam.

Lack of genotoxic effect in workers exposed to very low doses of 1,3-butadiene

1,3-Butadiene (BD), a probable carcinogen to humans, has been shown to have an ill-defined genotoxicity in occupationally exposed workers. In the present study, the influence of exposure to very low doses of BD and to cigarette smoking was investigated on some cytogenetic endpoints, namely, sister chromatid exchanges (SCE), chromosomal aberrations (CA) and cells with a high frequency of SCE (HFC), in peripheral blood lymphocytes. Twenty-seven male workers employed in a petrochemical plant and 26 matched controls were included in the study. As regards the airborne BD values, there was a significant difference between exposed (median BD value 1.5, min-max 0.2-69.0 microg/m3) and non-exposed workers (median BD value 0.4, min-max <0.1-3.8 microg/m3). Genotoxic biomarkers were not able to distinguish between the two groups. The frequency of SCE was higher in smokers than in non-smokers (p=0.001), with a positive correlation between the number of cigarettes smoked per day and both SCE (r=0.4; p=0.004) and HFC frequency (r=0.3; p=0.04). Multiple regression analysis confirmed the influence of cigarette smoking on the level of SCE and HFC, while these parameters were not affected by personal exposure to BD. Overall, the biomarkers of genotoxic effect investigated in our study were not able to discriminate between workers with a very low exposure to BD and controls, while it was possible to distinguish between smokers and non-smokers on the basis of SCE.

Cytogenetic analysis of nasal mucosa cells and lymphocytes from high-level long-term formaldehyde exposed workers and low-level short-term exposed waiters

The evidence for genotoxic potential of formaldehyde (FA) in humans is insufficient and conflicting. We previously reported a higher frequency of micronuclei in nasal and oral exfoliative cells from students exposed to formaldehyde vapor for short-term. To further evaluate the genetic effects of long-term occupational exposure to FA and short-term exposure to FA of indoor sources, the frequencies of micronuclei (MN) in nasal mucosa cells, sister chromatid exchanges (SCEs) of peripheral lymphocytes, and the lymphocyte subsets were evaluated in 18 non-smoking workers (mean exposure duration was 8.6 years) in an FA factory and 16 non-smoking waiters exposed to FA for 12 weeks in a ballroom. A non-smoking student group without occupational exposure ( n = 23) to FA was used as control. The 8 h time-weighted average (TWA) concentrations of formaldehyde was 0.985 ± 0.286 mg/m 3 with the ceiling exposure concentration of 1.694 mg/m 3 in the workshop, and 0.107 ± 0.067 mg/m 3 in the ballroom (5 h TWA). Higher frequencies of micronuclei per thousand cells in nasal mucosa cells of workers versus control (2.70 ± 1.50 versus 1.25 ± 0.65, p < 0.05) and higher frequency of SCEs in peripheral lymphocytes of workers group (8.24 ± 0.89 versus 6.38 ± 0.41, p < 0.05) were observed. Increased frequency of micronuclei in nasal mucosa cells or SCE in peripheral lymphocytes was not found among waiters group. The results suggest that the genotoxic potential of high level FA exposure may have occupational risks in long-term exposure groups.

Recql5 and Blm RecQ DNA helicases have nonredundant roles in suppressing crossovers.

In eukaryotes, crossovers in mitotic cells can have deleterious consequences and therefore must be suppressed. Mutations in BLM give rise to Bloom syndrome, a disease that is characterized by an elevated rate of crossovers and increased cancer susceptibility. However, simple eukaryotes such as Saccharomyces cerevisiae have multiple pathways for suppressing crossovers, suggesting that mammals also have multiple pathways for controlling crossovers in their mitotic cells. We show here that in mouse embryonic stem (ES) cells, mutations in either the Bloom syndrome homologue (Blm) or the Recql5 genes result in a significant increase in the frequency of sister chromatid exchange (SCE), whereas deleting both Blm and Recql5 lead to an even higher frequency of SCE. These data indicate that Blm and Recql5 have nonredundant roles in suppressing crossovers in mouse ES cells. Furthermore, we show that mouse embryonic fibroblasts derived from Recql5 knockout mice also exhibit a significantly increased frequency of SCE compared with the corresponding wild-type control. Thus, this study identifies a previously unknown Recql5-dependent, Blm-independent pathway for suppressing crossovers during mitosis in mice.

Spontaneous and γ-ray-induced sister chromatid exchanges in patients with carcinoma of cervix uteri

The aim was to investigate whether there are differences in the spontaneous and γ-ray-induced genomic instability in peripheral blood lymphocytes between untreated cervical cancer patients and healthy women using the sister chromatid exchange (SCE) assay as an indicator of chromosomal instability. Lymphocyte cultures from whole venous blood of 10 patients with cervical neoplasia and 10 healthy female volunteers were cultivated in vitro and irradiated using a 60Co-gamma source. Slides were prepared using the standard air-drying procedure and stained by the fluorescence-plus Giemsa (FPG) technique. The number of SCE and the number of chromosomes were assessed in second-division metaphases. A radiation dose-dependent increase of SCE/cell and SCE/chromosome values were found in healthy women as well as in patients, while statistical analysis has shown significantly higher SCE frequencies in healthy women as compared with patients. Cellular kinetics expressed as replication indices (RI) calculated from the frequency of cells in first cell division (M1), second cell division (M2) and third cell division (M3) were also significantly different, while observed RI were higher for patients than for control individuals. The results suggest that patients with carcinoma of the cervix uteri have chromosomal stability changes reflected in statistically different levels of spontaneous and induced SCE in comparison with healthy individuals. Despite the unknown mechanisms of SCE formation, it is felt that the changed SCE frequency, especially after mutagen treatment, may be used as a marker of increased cancer risk.

Clastogenicity of selective serotonin-reuptake inhibitors

Objective: Selective serotonin-reuptake inhibitors (SSRIs) are used in the treatment of various forms of psychiatric disorders. Preclinical studies in laboratory animals have indicated that SSRIs were not genotoxic, but clear results from in vitro testing of SSRIs in a human cell system are currently scarce. The purpose of this study was to investigate whether SSRIs might be genotoxic. Sertraline was chosen as model SSRI, since it appears to be at least as well-tolerated as other SSRIs and may even have a more favourable side-effect profile. Unlike fluoxetine, fluvoxamine and paroxetine, sertraline has low potential for pharmacokinetic drug interactions. So, sertraline would be considered first in the treatment of psychiatric disorders requiring SSRI therapy in the future. We therefore examined peripheral lymphocytes from sertraline-treated patients for both sister chromatid exchanges (SCEs), cells with a high frequency of SCEs (HFC) and chromosome aberrations (CA) to evaluate the clastogenicity of SSRIs. Method: Ten sertraline-treated patients meeting ‘Structured Clinical Interview for DSM-IV’ criteria for both generalized anxiety disorder and major depression were compared with 18 healthy volunteers and 18 non-treated patients with similar psychopathology. Sertraline hydrochloride was administered orally at 50 mg daily for 10 months to 1 year. The participants were selected on the basis of similar responses to a questionnaire assessing risk of genotoxicity related to other aspects of life. All participants had very similar lifestyles, medical histories, biological and dietary factors. All subjects were non-smokers. Result: A statistically significant difference between patients with both generalized anxiety disorder and major depression (sertraline-treated or non-treated) and healthy volunteer groups was found by both SCE frequencies and HFC percentages. Both patient groups showed higher frequencies of SCEs than the healthy controls. No statistically significant difference was found between SCE frequencies or HFC percentages observed in sertraline-treated and non-treated patient groups. No statistical difference was found between groups with respect to the frequency of CA. Conclusion: There are no adequate studies analysing the clastogenicity of SSRIs, in particular of sertraline. The SCE frequency, the percentage HFC and the frequency of CA in patients with both generalized anxiety disorder and major depression exposed to daily doses of sertraline do not indicate a possible clastogenic hazard. The increased SCE frequencies in patients with both generalized anxiety disorder and major depression in our study—irrespective of sertraline treatment—indicate a possible genotoxic effect. However, our observations were based on a limited number of patients; the results may be explained by psychogenic stress.

A new cytogenetic approach for the evaluation of mutagenic potential of chemicals that induce cell cycle arrest in the G2 phase.

The aim of the present study was to develop and standardize a cytogenetic approach for evaluation of the mutagenic potential of chemicals that induce cell cycle arrest in the G2 phase. Even though cytogenetic end-points such as sister chromatid exchange (SCE) have been extensively used to indirectly assess the DNA-damaging potential of various chemicals, they are based on metaphase chromosome analysis. Cells delayed in G2 phase after chemical exposure are not included in conventional SCE analysis. The yield of SCEs obtained, therefore, can be biased, since predominantly undamaged cells proceed to metaphase without delay. To overcome this shortcoming of conventional SCE analysis, the use of a new cytogenetic approach for genotoxic studies is presented that enables the analysis of SCEs directly in G2 phase using drug-induced premature chromosome condensation in cultured peripheral blood lymphocytes. By means of this method, firstly, the possibility that SCE analysis in metaphase chromosomes underestimates the mutagenic potential of various chemicals was tested. Secondly, whether the genotoxic potential of suspected carcinogens could be evaluated using SCE analysis in G2 phase, even at exposures that arrest cells in G2 phase, was examined. Thirdly, whether an important part of the background variation in SCE frequency among individuals is due to the delay of affected cells in G2 phase, rather than to a true biological variation in the cytogenetic end-point used, was tested. The results showed that a higher SCE frequency was scored in G2 phase than in metaphase. Subsequently, the mutagenic potential of chemicals that temporarily arrest cells in G2 phase could now be evaluated more accurately. In addition, it may be of interest to further examine the involvement of cell cycle kinetics in the baseline SCE variation among individuals since a lesser SCE variability was observed when the analysis was carried out in G2 phase rather than at metaphase.