Mean Sister Chromatid Exchange Frequency Research Articles

Cell Cycle Kinetics and Sister Chromatid Exchange in Mosaic Turner Syndrome.

Turner syndrome (TS) is caused by a complete or partial absence of an X or Y chromosome, including chromosomal mosaicism, affecting 1 in 2500 female live births. Sister chromatid exchange (SCE) is used as a sensitive indicator of spontaneous chromosome instability. Cells from mosaic patients constitute useful material for SCE evaluations as they grow under the influence of the same genetic background and endogenous and exogenous factors. We evaluated the proliferation dynamics and SCE frequencies of 45,X and 46,XN cells of 17 mosaic TS patients. In two participants, the 45,X cells exhibited a proliferative disadvantage in relation to 46,XN cells after 72 h of cultivation. The analysis of the mean proliferation index (PI) showed a trend for a significant difference between the 45,X and 46,X+der(X)/der(Y) cell lineages; however, there were no intra-individual differences. On the other hand, mean SCE frequencies showed that 46,X+der(X) had the highest mean value and 46,XX the lowest, with 45,X occupying an intermediate position among the lineages found in at least three participants; moreover, there were intra-individual differences in five patients. Although 46,X+der(X)/der(Y) cell lineages, found in more than 70% of participants, were the most unstable, they had a slightly higher mean PI than the 45,X cell lineages in younger (≤17 years) mosaic TS participants. This suggests that cells with a karyotype distinct from 45,X may increase with time in mosaic TS children and adolescents.

Analysis of chromatin instability of somatic cells in sheep

Cytogenetic tests are highly reliable, sensitive indicators of the early effects of genomic instability. Their results provide information on the organism’s susceptibility to exogenous and endogenous factors and are measures of the degree of repair of DNA damage. Our study assessed spontaneously occurring damage in following four breeds of sheep: Polish Heath, Polish Lowland (Zelazna variety), Polish Blackhead, and Berrichon du Cher. Instability was identified using the following three different tests: a sister chromatid exchange (SCE) assay, identification of fragile sites, and the comet assay. The distribution of instabilities varied depending on the breed. The mean frequency of SCEs was 5.13 ± 1.58, whereas that of fragile sites was 3.30 ± 1.24. The mean level of DNA damage (% head DNA) was 96.52 ± 6.59. The most damage to genetic material was observed in the Berrichon du Cher sheep, and the least in the Polish Heath sheep. The tests used are reliable biomarkers of genome stability in animal breeds, as well as in individuals within breeds.

Genoprotective Effect of Melatonin Against to the Genotoxicity of Glyphosate on Human Blood Lymphocytes

Purpose: Glyphosate is a widely used non-selective herbicide. Previous studies have shown that glyphosate has genotoxicity, and that even low-doses of glyphosate can cause DNA damage. Melatonin is a hormone produced and secreted by the pineal gland that is known to be a potent anti-carcinogen, anti-oxidant, and genetic protector. This study was conducted to investigate the genoprotective effect of melatonin against glyphosate in human blood lymphocytes. Methods: Human peripheral blood was obtained from 15 young, healthy volunteers and cultured under four different toxicologic conditions. The four groups consisted of a control group, glyphosate only group (300 ng/mL), glyphosate with low level of melatonin group ($50{mu}M$), and glyphosate with high level of melatonin group ($200{mu}M$). The mean Sister Chromatid Exchange (SCE) frequency of each group was then analyzed. Results: Glyphosate exposed groups had a higher mean SCE frequency ($10.33{pm}2.50$) than the control group ($6.78{pm}2.31$, p<0.001). Interestingly, the group that received a low-level of melatonin had a lower mean SCE frequency ($8.67{pm}2.58$) than the glyphosate-only group, while the group that received a high level of melatonin had a much lower mean SCE frequency ($8.06{pm}2.50$) than the glyphosate-only group. There was statistical significance. Conclusion: Melatonin exerted a potent gene protective effect against the genotoxicity of glyphosate on human blood lymphocytes in a dose-dependent fashion.

In vitro Effects of Epigallocatechin Gallate on Sister Chromatid Exchange in the Lymphocytes Exposed to Glyphosate

Purpose: Green tea is known as a potent anti-oxidant, anti-carcinogen, and genetic protector. Glyphosate (N-phosphonomethyl glycine) is a widely used non-selective herbicide that causes DNA damage. The present study was conducted to investigate the protective effects of green tea in human blood lymphocytes exposed to glyphosate using the Sister Chromatid Exchange (SCE) frequency method. Methods: Peripheral blood was obtained from 10 volunteers and cultured through four different conditions. Four groups were divided into control, glyphosate only (300 ng/mL), glyphosate and low ($20{mu}m$) concentrations of epigallocatechin gallate (EGCG) and glyphosate and high ($100{mu}m$) concentrations of EGCG. Results: The glyphosate exposed groups had a higher mean SCE frequency ($10.33{pm}2.50$) than the control group ($6.38{pm}2.28$, p<0.001). The low concentrations of EGCG groups had a lower mean SCE frequency ($9.91{pm}1.93$) than the glyphosate-only group, although this difference was not significant (p=0.219). However, the high concentration group ($9.49{pm}1.85$) had a significantly lower SCE frequency than the glyphosate-only group (p=0.001). Conclusion: EGCG has a gene protective effect in human lymphocytes exposed to the genotoxicity of glyphosate in the case of high concentrations.

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.

Cytogenetic Finding of Breast Cancer Cases and in Their First-Degree Relatives

PurposeThe aim of this study was to evaluate and compare the rate of sister chromatid exchange (SCE), the occurrence of micronuclei, and the lymphocyte proliferation rate index (PRI) in patients with breast cancer, their first-degree relatives, and healthy volunteers.MethodsWe analyzed the frequency of SCE and micronuclei, and the PRI in the peripheral blood lymphocytes of 30 women with breast cancer, 22 of their female family members, and 20 age-matched healthy female volunteers.ResultsSCE occurred significantly more often in the lymphocytes of breast cancer patients (10.84±0.4 per metaphase), compared with their first-degree relatives (7.45±0.54) and controls (5.94±0.2) (p<0.001 for both). The mean SCE frequency was not statistically different between first-degree relatives and controls (p=0.071). Similarly, micronuclei occurred at a significantly higher rate in breast cancer patients (9.6±0.72), and in their first-degree relatives (7±0.64), compared to controls (3.85±0.4) (p<0.001 and p=0.001, respectively). There was also a significant difference between the occurrence of micronuclei in patients compared to their family members (p=0.021). The PRI was significantly lower in patients (1.61±0.1), compared with both their first-degree relatives (1.75±0.1), and controls (1.74±0.1) (p=0.001 and p=0.002, respectively).ConclusionIncreased SCE and the occurrence of micronuclei, as well as a reduced PRI are associated with breast cancer. Furthermore, increased SCE and the frequency of micronuclei in a first-degree relative suggest that they exhibit greater genetic instability than women of the same age.

Genotoxicity of pemetrexed in human peripheral blood lymphocytes

Pemetrexed (PMX) is an antineoplastic antifolate used in the treatment of non-small cell lung cancer, mesothelioma and several types of neoplasms. Its toxicity in tumor cells has been linked with the potent inhibition of thymidylate synthase, dihydrofolate reductase and glycinamide ribonucleotide formyl transferase, and subsequent depletion of both purine and pyrimidine nucleotides. However, cytogenetic toxicity of PMX in non-diseased cells has not been adequately studied; despite the increasing data on the DNA-damaging potential of antineoplastic agents on normal cells. In the present study, the genotoxic potential of PMX was evaluated in peripheral blood lymphocytes obtained from healthy human subjects using chromosome aberration (CA), sister chromatid exchange (SCE) and micronucleus (MN) assays as the cytogenetic damage markers. Human peripheral blood lymphocytes were exposed to four different concentrations (25, 50, 75 and 100μg/mL) of PMX for 24- and 48-h treatment periods. PMX significantly increased the formation of CA in 24-h treatment, but not in 48-h treatment. PMX did not increase the mean SCE frequency in 24- and 48-h treatment periods; however, there was a striking increase (although not statistically significant, p>0.05) in the number of SCEs at 25μg/mL (24- and 48-h treatment) and 50μg/mL (24-h treatment) due to an increase of SCE at the single-cell level. Interestingly, PMX did not induce MN formation in either 24- or 48-h treatment periods. PMX strongly decreased the mitotic index (MI), proliferation index (PI) and nuclear division index (NDI) in 24- and 48-h treatment periods. Our results suggest that PMX has a potent cytotoxic effect against human peripheral blood lymphocytes at concentrations which are reached in vivo in the blood plasma.

Increased Chromosome Fragility in Gastric Cancer Patients

Gastric cancer is one of the most common lethal malignancy in global and survival mainly depends on prognosis. Sister Chromatid Exchanges (SCEs) assay is a very sensitive method of detecting chromosome fragility. The aim of our study was to determine the chromosomal fragility of gastric cancer patients in vitro. Samples from 32 gastric cancer patients and 12 healthy donors were controlled. Cancer patients lymphocytes’ genome is highly fragile as treatment of the cell cultures with MMC caused a statistically significant increase of the mean SCEs frequency (p<0.01). Also, so simultaneous as MMC-induced SCEs frequency of gastric cancer patients was statistically significant (p<0.01) higher compared to the healthy donors. PRI and MI of treated with MMC and untreated lymphocytes of gastric cancer patients were significantly (p<0.01) lower than that of healthy donors. These results suggest that peripheral lymphocyte chromosomes of cancer patients are highly fragile and alkyliotic agents increase their fragility.

Phototherapy causes a transient DNA damage in jaundiced newborns

In this study, we aimed to clarify the following questions: 1) Does phototherapy (PT) cause genotoxicity in full-term newborn babies undergoing PT as a result of neonatal jaundice?, 2) if genotoxic effect occurs, is there any relationship between the duration of PT and genotoxicity?, and 3) is genotoxic effect temporary or not? The frequency of sister chromatid exchange (SCE) was determined in jaundiced newborns before, during, and after phototherapy, then determined again in childhood (approximately 3.5 years old). Mean frequency of SCE of 22 full-term jaundiced babies significantly increased during the PT procedure and in every single day, compared to the previous day, in comparison to the pre-PT basal value (6.20 ± 0.57;); mean SCE frequencies at 24, 48, 72, and 96 hours were 7.75± 0.40, 8.16 ± 0.47, 8.50 ± 0.40, and 9.36 ± 0.55, respectively (all P-values <0.01). In childhood, no significant difference was found between the mean SCE value (4.9 ± 0.9) of 20 of 22 children, who received PT in the neonatal period, and the mean SCE value (4.7 ± 0.6) of 20 coevaluated healthy children (P = 0.40). This study demonstrates that the negative effect of PT on SCE is a temporary effect.

Sister chromatid exchanges in smokers and smokers with alcohol habit

Aim:Sister chromatid exchange (SCE) test is a sensitive, biomarker of genotoxic substances. The present study was conducted to observe the frequency of SCEs in peripheral blood lymphocytes of 30 males with and without the habit of cigarette smoking and alcohol consumption.Materials and Methods:Subjects for this study were males aged between 25-50 years and were selected from the students, employees and the patients attending the outpatient department of Ragas dental college and Hospital, Chennai.Results:Controls, smokers, and smokers with alcohol habit were divided into two age groups as ≤30 years and ≥30 years. In controls the mean frequency of SCEs/cell in ≤30 years and ≥30 year's age group was 5.80 and 6.05, respectively. In Smokers SCEs/cell in ≤30 years and ≥30 year's age group was 7.7 and 8.8, respectively. In Smokers with alcohol habit SCEs/cell in ≤30 years and ≥30 years age group was 10.1 and 12.8, respectively.Conclusions:In this study, the duration of the smoking habit has shown a positive correlation with the mean SCE frequency. Whereas, frequency of the habit did not show any influence on the SCE levels. In smokers with alcohol habit, both the duration and frequency of their smoking habit has shown a significant effect on the SCE levels suggesting a synergistic effect of alcohol and smoking leading to excessive DNA damage.

Investigation of Arg399Gln and Arg194Trp Polymorphisms of the XRCC1 (X-Ray Cross-Complementing Group 1) Gene and Its Correlation to Sister Chromatid Exchange Frequency in Patients with Chronic Lymphocytic Leukemia

Polymorphisms of the x-ray repair cross-complementing group 1 (XRCC1) gene have been reported to be associated with various forms of cancer. We evaluated the possible effects of the Arg194Trp and the Arg399Gln polymorphisms on the risk for chronic lymphocytic leukemia (CLL) in 73 patients and 50 controls. We also analyzed their relation to frequency of sister chromatid exchange (SCE). With respect to codon 194, the allelic frequency of the Arg194Trp polymorphism did not significantly differ between the 2 groups. The proportion of individuals carrying the Arg194Trp polymorphism was not different in the 2 groups. With respect to codon 399, the proportion of the individuals carrying the Arg399Gln allele (90% vs 62%; p=0.000; odds ratio [OR], 5.779; 95% confidence interval [CI], 2.2-15.183) and the allelic frequency of the Arg399Gln polymorphism (56% vs 36%; p=0.002; OR, 2.278; 95% CI, 1.350-3.843) was significantly higher in the patient group. The frequency of the Arg/Gln genotype was significantly higher in the patient group (68.50% vs 52%; p=0.049; OR, 2.007; 95% CI, 0.955-4.217). The mean SCE frequency in the patient group was significantly higher (9.2±4 vs 7.5±2; p=0.02). When different compound genotypes were compared, the coexistence of Arg/Arg genotype in codon 194 with Arg/Arg genotype in codon 399 was significantly more frequent in the control group (30% vs 9%; p=0.004; OR, 0.247; 95% CI, 0.092-0.664). Within the patient group, SCE frequency did not differ between patients with various genotypes. The Arg399Gln polymorphism may be etiologically associated with CLL; however, it does not seem to increase SCE frequency.

Sister chromatid exchange in selected horse breeds (&amp;lt;i&amp;gt;Equus caballus&amp;lt;/i&amp;gt;)

Abstract. In studies of chromosome instability, the sister chromatid exchange (SCE) test is a particularly sensitive cytogenetic assay for detecting DNA damage. SCE tests of chromosome instability were performed in the group of 6 horse breeds (Pure-bred Arabian, Malapolski horse, Polish noble half-bred, Polish cold-blooded, Hucul and Polish Konik). The chromosome preparations were obtained from our in vitro culture of peripheral blood lymphocytes stained using the FPG technique. The mean number of SCEs/cell in the analysed population of horses was 5.14±1.44. The mean frequency of SCEs in the 6 analysed horse breeds varied depending on the breed. Statistically significant differences were observed between the horse breeds (P&lt;0.01). No statistically significant differences in the number of SCEs per cell were found between the males and females (5.10±1.34 and 5.20±1.52, respectively). The horses were also assessed for the number of SCEs/cell in relation to the age of the animals. The differences between the age groups were statistically significant (P&lt;0.01).

The genotoxic risk in health care workers occupationally exposed to cytotoxic drugs—A comprehensive evaluation by the SCE assay

Present study aimed at an integral assessment of sister chromatid exchange (SCE) frequencies in the health care workers occupationally exposed to cytostatics. The results of 500 individual analyses were evaluated. Drug handling practice was investigated in parallel and the results showed that cytostatics are mostly prepared outside hospital pharmacy (98%) and mainly handled by nurses (96%). Mean frequency of SCE was 5.63 ± 2.28, while HFC represented 9.65% of the cells analysed. Both values were higher compared to previously established control values for Croatian population. The duration of exposure, profession, age, gender, smoking habit, medical exposures, and simultaneous exposure to other occupational mutagens significantly contributed to SCE and HFC values. The usefulness both biomarkers in the assessment of cytogenetic damage is confirmed. Since current practice in Croatian hospitals does not include regular monitoring of workplaces, to ensure maximal occupational safety, a surveillance on exposed health care workers, including periodic biomonitoring, is recommended.

Analysis of Spontaneous and Streptonigrin-Induced Sister Chromatid Exchanges in Peripheral Lymphocytes of Aircrew Members of International Flights

In this work, we extend our previous studies concerning mutagen sensitivity in flight personnel from commercial airlines by analyzing the frequency of spontaneous and streptonigrin (SN)-induced sister chromatid exchanges (SCEs) in peripheral blood lymphocytes of 18 long-haul aircrew members from Argentina and of 18 control individuals. Statistical analysis revealed no significant differences between aircrew and controls in the background level of SCEs (p > 0.05), which suggests that chronic exposure to cosmic radiation and other occupational hazards does not affect SCEs frequency in peripheral lymphocytes of aircrews. The fact that almost no correlation was found between cumulative flight hours and the yield of spontaneous SCEs in aircrews adds further support to this assumption. Therefore, the background SCEs frequency cannot be use as a valid biomarker to determine the genotoxic effects of cosmic radiation or other occupational hazards exposure in aircrews. Following SN treatment, a significant increase in the mean frequency of SCEs was observed in the control group (p < 0.05) but not in the aircrew group (p > 0.05), suggesting that at the population level, aircrew are more resistant to the mutagenic effects of SN than controls. The reasons of this resistance remain to be determined. Since cosmic radiation had no effect on the background SCEs frequency and no relationship was found between cumulative flight hours and SCEs inducer effect by SN in aircrews, a direct effect of cosmic radiation on SN resistance should be discarded.

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

The aim of this study was to investigate the genotoxic effect on the peripheral blood lymphocytes potentially induced by Re-186 in paediatric age group undergoing radiosynovectomy for haemophilic synovitis, by using chromosomal aberration analysis (CA) and the micronuclei (MN) assay for detecting chromosomal aberrations, as well as the sister chromatid exchanges (SCE) technique for assessing DNA damage. Cytogenetic analyses were evaluated in 20 boys (mean age: 13.8 +/- 2.7 years) before, and 2 and 90 days after radiosynovectomy from the peripheral lymphocytes of the patients. Joint retention and extra-articular spread of the radionuclides were evaluated by using quantitative gamma camera imaging. Imaging after radiosynovectomy revealed local lymph node visualization in 8 (40%) patients and hepatosplenic visualization in 3 (15%) patients due to extra-articular leakage of radioactive material. The mean frequency of chromosome aberrations (0.2 +/- 0.4/1000 cells) determined prior to the onset of therapy was not significantly increased in comparison with control values obtained 2 days (0.4 +/- 0.5/1000 cells) and 90 days (0.2 +/- 0.4/1000 cells) after therapy (P = 0.754 and P = 1.0). In the analysis of MN and SCE, when we compare the baseline levels, the mean MN and SCE frequencies were slightly higher in the control analyses performed 2 and 90 days after radiosynovectomy but there were no significant differences between baseline and control levels (chi(2) = 2.621, P = 0.270 and F = 0.573, P = 0.569, respectively). The major finding of this study with relatively small sample is that, radiosynovectomy with Re-186 does not seem to induce early genotoxic effects on the peripheral blood lymphocytes in paediatric age group.

Increased sensitivity to mitomycin C‐induced sister chromatid exchange in lymphocytes from patients undergoing hyperbaric oxygen therapy

Treatment of cells with hyperbaric oxygen (HBO) results in the generation of reactive oxygen species and the induction of DNA damage. In the present study, we have evaluated the sister chromatid exchange (SCE) frequencies in lymphocytes from patients undergoing hyperbaric oxygen therapy (HBOT). In addition, we have determined the sensitivity of lymphocytes from those patients to SCE induction by 20 and 40 ng/ml mitomycin C (MMC). Patients undergoing HBOT for diabetic feet were exposed to 10 consecutive daily HBO treatments according to a routine therapy protocol. The study began with 12 patients; however, it was not possible to sample all of the patients at all HBOT sessions, and the number of patients gradually decreased towards the end of the HBOT. We observed a statistically significant induction in mean SCE/cell (P < 0.05; n = 11) immediately after the first session of HBOT. Relative to its frequency after the 1st treatment, the mean SCE frequency gradually decreased after the 5th and 10th HBOT sessions and reached baseline (pretherapy) levels 1 day after the last treatment in the four patients that were sampled. The mean MMC-induced SCE frequency was highest in lymphocytes sampled immediately after the first HBOT session, and significantly higher than the MMC-induced SCE frequency in cells sampled before HBOT. Unlike the case with untreated cells, MMC-induced SCE frequencies remained high in lymphocytes sampled at later stages of therapy and mean MMC-induced SCE frequencies were significantly higher (P < 0.05; n = 4) in lymphocytes sampled 1 day after the last session of HBOT than in lymphocytes sampled from these patients prior to beginning the therapy. The results indicate that HBOT induces SCE and that lymphocytes retain increased sensitivity to the genotoxicity of MMC one day after completing the HBOT.

Clastogenic activity of 2-chlorodeoxyadenosine in mammalian somatic cells

The base analogue 2-chlorodeoxyadenosine (2-CdA) used for therapy in chronic resistant and advanced lymphoproliferative disorders, is cytotoxic for both dividing and non-dividing lymphocytes. The present work evaluated the clastogenic potential of this drug in vitro in human lymphocytes in culture and in vivo in BALB/c mice bone marrow cells. In human lymphocytes, the clastogenic effect of 2-CdA was studied in G1, S and G2 phases of the cell cycle, using three different concentrations (10, 20 and 40 mg/mL). The endpoints analyzed included mitotic index (MI), proliferation index (PI), sister chromatid exchange (SCE), and chromosomal aberration (CA). Statistical analysis by a variance (ANOVA) test showed a significant increase (p < 0.05) in CA frequencies for cells treated during the S phase, but the MI did not vary. The concentrations tested did not produce a significant increase in the mean frequency of SCEs, nor did they change the cell PI in the G1 and S phases. The concentrations in vivo tested were 0.25, 0.375 and 0.5 mg/kg body weight. In this assay, alterations in CA frequencies and MI were not observed at the dose levels tested. Therefore, the results indicate a clastogenic effect of 2-CdA in human lymphocyte cultures.

Acute Wood or Coal Exposure with Carbon Monoxide Intoxication Induces Sister Chromatid Exchange

The object of this study was to investigate the genotoxic effect of acute overexposure to combustion products originating from coal or wood stoves in patients presenting with acute carbon monoxide intoxication. In a prospective study, we analyzed the frequency of sister chromatid exchange and the carboxyhemoglobin concentration in 20 consecutive patients without a history of smoking or drug use who had been treated in the Emergency Care Unit of Istanbul Medical Faculty due to acute carbon monoxide intoxication. All of these cases were domestic accidents due to dysfunctioning coal or wood stoves. The results were compared with a control group of 20 nonsmoking, nondrug-using healthy individuals matched for age, sex, and absence of other chemical exposure. The mean sister chromatid exchange frequency per metaphase was significantly higher in the study group compared to the control group: 8.11 +/- 2.39 vs. 6.33 +/- 1.60 (p = 0.008). We found that there was no positive correlation between the blood carboxyhemoglobin concentration and sister chromatid exchange frequency. These results suggest that acute exposure to combustion products of wood or coal is genotoxic to DNA. Potential causes of genotoxicity include known mutagenic compounds present in coal or wood smoke and ash, oxygen radicals formed during combustion, as well as hypoxic and reperfusion injury mechanisms initiated by carbon monoxide intoxication. Additional studies on separate carbon monoxide exposure from smoke and ash are needed to understand individual genotoxic contributions and mechanisms.

Polymorphisms in the DNA repair genes XRCC1 and ERCC2 and biomarkers of DNA damage in human blood mononuclear cells.

Polymorphisms in several DNA repair genes have recently been identified, but little is known about their phenotypic significance. To determine whether variation in DNA repair genes is related to host DNA damage, we studied the association between polymorphisms in XRCC1 (codon 399) and ERCC2 (codon 751) and two markers of DNA damage, sister chromatid exchange (SCE) frequencies (n = 76) and polyphenol DNA adducts (n = 61). SCE frequencies were determined using a modified fluorescence-Giemsa method and polyphenol DNA adducts were determined using a P1-enhanced (32)P-post-labeling procedure. XRCC1 and ERCC2 genotypes were identified using PCR-RFLP. Mean SCE frequencies among current smokers who were homozygous carriers of the 399Gln allele in XRCC1 were greater than those in 399Arg/Arg current smokers. We also observed a possible gene-dosage effect for XRCC1 399Gln and detectable DNA adducts, and significantly more adducts among older subjects who were carriers of the 399Gln allele than in younger subjects with the 399Arg/Arg genotype. The polymorphism in ERCC2 was unrelated to SCE frequency or DNA adduct level. Our results suggest that carriers of the polymorphic XRCC1 399Gln allele may be at greater risk for tobacco- and age-related DNA damage.

Genotoxicity of the anticonvulsant drug phenytoin (PHT): A follow-up study of PHT-untreated epileptic patients. I. Sister chromatid exchange (SCE) analysis

Phenytoin (PHT) is a widely prescribed antiepileptic drug. Its potential to interact with genetic material was investigated in a set of 30 epileptic patients (age 10-30 years) prior to and following the administration of PHT over a period of 9 months (grouped in a multiple of 3 months) and 40 control subjects in relation to age, sex, duration of drug therapy, and plasma concentration of PHT, using the sister chromatid exchange (SCE) frequency assay. Plasma levels of the phenytoin were measured by biochemical assay in epileptic patients before and after the PHT therapy. The peripheral blood lymphocytes were cultured and harvested at 72 h. The frequency of SCE was significantly higher (P < 0.001) in both age groups (10-20 and 21-30 years) for PHT-treated epileptics compared to PHT-untreated and control subjects. However, there were no considerable variations in SCE finding between the control and PHT-untreated patients. Between the two age groups, a significantly higher SCE frequency was observed in PHT-treated patients (P < 0.01) in the older age group (21-30 years). Mean SCE frequency did not differ between the male and female in the controls, PHT-untreated, or treated epileptics. Correlation between the plasma concentration of PHT and the incidence of SCE among 30 patients was insignificant. PHT monotherapy appears to have genotoxic effect as expressed by the induction of increased SCE rates in treated epileptics, while disease does not play any role in inducing genetic damage as shown by no difference in SCE frequencies between control subjects and PHT-untreated epileptic patients.