Sister chromatid exchange in aged human lymphocytes. A brief note

A study of the sister chromatid exchange (SCE) frequency in peripheral lymphocytes from 26 human subjects, with in vivo age of the cels as the variable, demonstrated a significant increase in SCE frequency with increasing age of the subject (analysis of variance: p < 0.01). The cells were cultured in Eagle's basal medium with 5-bromodeoxyuridine added to a final concentration of 10 μM. These results are contradictive to the brunt of the literature which indicates that background SCE frequency does not change with age.     

Sister chromatid exchange distributions in rabbit lymphocytes treated with streptonigrin

Streptonigrin (NSC-45383), a direct-acting clastogen which induces SCEs in vivo and chromosome aberrations both in vivo and in vitro, was evaluated for SCE induction in both G₀ and stimulated rabbit lymphocytes. Determinations were made for 16 cultures from seven female rabbits. These included controls as well as cells exposed to 90 μg/kg in vivo, cells pulse-treated with 50 ng/ml in vitro, and a culture continuously exposed to 5 ng/ml in vitro. For all cultures the SCE/ cell frequency was determined from 20 complete (44 chromosome) metaphases and, in selected cultures, SCEs on individual chromosomes (880 per culture from 20 cells) were enumerated to determine SCE/chromosome frequency and the chromosomal distribution of SCEs. Analysis of variance and least significant difference tests of the √x transformed SCE/cell data show that cells exposed to Streptonigrin while dividing have significantly higher (P<0.01) frequencies (over double the control 5.3 SCE/cell value) whereas treated G₀ cells were not significantly different from the controls. Dispersion analysis of both SCE/cell and SCE/ chromosome data confirms the adequacy of the Poisson distribution for spontaneous or baseline but not streptonigrin-induced SCEs.     

Sister chromatid exchange in cancer

Sister chromatid exchange (SCE) techniques have been shown to have great potential for use in the in vitro screening of suspected mutagens and carcinogens. Application of these techniques to bone marrow cells and/or lymphocytes from patients with various hematologic malignancies has demonstrated significant abnormalities in SCE frequencies in some of these diseases, as well as showing drug treatment effects. Interpretation of abnormal SCE findings in cancer patients is currently hindered by the lack of a clear understanding of the basic molecular and biochemical mechanisms involved in SCE formation. The potential practical use of SCE techniques in the diagnosis and treatment of cancer can not adequately be appreciated until this basic understanding is achieved.     

Sister chromatid exchange in lymphocytes of agricultural workers exposed to pesticides

Sister chromatid exchange (SCE) was studied in the lymphocytes of 27 agricultural workers occupationally exposed to several pesticides and 28 matched controls from el Maresme, an agricultural area near Barcelona. Comparison between both groups with the t-test did not reveal significant differences. These negative findings suggest that, possibly, the exposure level is too low to increase SCE in human lymphocytes in vivo. Our results indicate that smokers, both the workers and the controls, had a higher SCE frequency than non-smokers, in agreement with previous data reported by different authors.     

Sister chromatid exchange in childhood malignancies

Sister chromatid exchange studies were conducted in 53 children with malignant diseases. Children with acute lymphoid leukemia in long remission, already off chemotherapy or on maintenance therapy, had normal SCE values, whereas those receiving intensive cytostatic therapy showed elevated levels. SCE values were primarily related to the time and dose of preceding cytostatic drug therapy, and the subsequent relapse might influence the SCE frequencies, independently from the cytostatic therapy.     

Sister chromatid exchange in aplastic anemia

The incidence of sister chromatid exchanges (SCE) in the lymphocytes of patients with aplastic anemia (AA) was determined before and after exposure to mitomycin C (MMC). The “baseline” SCE rate was significantly higher in AA, but MMC-induced SCE rate was not different compared to controls. It is suggested that some patients with AA may have an underlying DNA damage.     

Sister chromatid exchange in malignant lymphomas

Sister chromatid exchange (SCE) was evaluated in peripheral lymphocytes from 20 untreated patients with malignant lymphomas: 6 with Hodgkin's disease (HD), 14 with non-Hodgkin lymphoma (NHL), and 5 with lymphadenitis. The mean SCE frequency (+/- SE) was: 11.2 +/- 0.6, 11.0 +/- 0.6, and 7.2 +/- 0.3 for HD, NHL, and lymphadenitis patients, respectively, and 8.7 +/- 0.2 for the control group. No differences in SCE score were observed in HD and NHL. These results allowed us to consider both groups (HD and NHL) as a single neoplastic population (mean +/- SE, 11.0 +/- 0.4). No significant differences were found between the lymphadenitis and control groups. On the other hand, significantly higher SCE scores were seen in neoplastic populations than in the control and lymphadenitis groups (p less than 0.001 and p less than 0.01, respectively). When SCE was compared by chromosome number and group between neoplastic patients and controls, a higher SCE frequency was observed in chromosomes #1, #2, #3, and B, C + X, E, F chromosome groups than in controls. SCE levels were significantly higher in lymphoma patients in all chromosome numbers and groups mentioned than in patients with lymphadenitis. It is suggested that the high SCE rate in the malignant lymphoma population is possibly related to an increased chromosomal instability.     

Sister chromatid exchange frequency in breast cancer cases.

Sister chromatid exchange (SCE) were studied in 22 patients with breast cancer (i.e., four stage II; 12 stage III, six stage IV) and 10 normal healthy females as age-matched controls. The data obtained in these cases followed a Poisson distribution. An apparent increase in the average rate of SCE/cell was observed with the advancing stage of breast cancer.     

Heterozygote detection through bleomycin-induced G2 chromatid breakage in dyskeratosis congenita families.

We determined the mean number of chromatid breaks per cell (b/c) in the bleomycin-treated lymphocytes of 10 patients with dyskeratosis congenita (DC) and 26 of their relatives to ascertain whether bleomycin sensitivity would distinguish DC heterozygotes from normal individuals. We observed a significantly higher mean number of chromatid b/c in DC patients and obligate heterozygotes (patients versus controls, p less than 0.0001; heterozygotes versus controls, p = 0.0076, Mann-Whitney rank-sum test). Unequivocal heterozygote detection was not possible owing to overlap of the b/c values of patients, heterozygotes, and controls, but our findings provided strong evidence of a link between autosomal recessive as well as X-linked recessive DC mutations and bleomycin sensitivity in homozygous, hemizygous, and heterozygous individuals.     

Sister chromatid exchange and proliferation pattern in stimulated lymphocytes of cutaneous malignant melanoma patients

Sister chromatid exchange (SCE) and the proliferative pattern of phytohemagglutinin-stimulated lymphocytes were examined in 36 nonfamilial cutaneous malignant melanoma (CMM) patients. One close relative of each of 27 CMM patients was also examined. All the patients had undergone surgical treatment for the neoplasm, but had received no chemotherapy or radiotherapy. The SCE rates were found to be higher and more variable in a significant fraction of CMM patients, and in relatively fewer unaffected relatives, which is in contrast to findings in unrelated subjects taken as controls. Also, variable and higher proportions of cells in metaphase of the first cell cycle (M1), after 72-hr culture in the presence of bromodeoxyuridine, were more often found among the CMM patients than in the controls; however, no effect of clinical progression of the neoplastic disease on SCE rates or on the lymphoproliferative pattern was observed. The present study indicates heterogeneity among subjects who develop CMM and suggests that the peculiarities of SCE rates and of the lymphoproliferative patterns observed in some of the CMM patients and in a few of their close relatives may be connected with the mechanism of onset of the neoplasm.     

Sister chromatid exchange induction in two cell lines

Sister chromatid exchange (SCE) induction by the procarcinogen benzo (a)-pyrene (BP) was studied using two established cell lines. Chinese hamster ovary (CHO) and Chinese hamster lung (Don) cells were exposed to varying concentrations of BP in the presence and absence of a rat liver metabolizing system. Results showed a significant difference in the abilities of the two cell lines to induce SCE in the absence of liver homogenate. These experiments demonstrate that Don cells are capable of generating active metabolites from biologically inactive procarcinogens presumably due to an inherent metabolizing system which is deficient or absent in CHO cells.     

Sister chromatid exchange analysis in the Prader-Labhart-Willi syndrome

The number of sister chromatid exchanges (SCE) and cell kinetics in lymphocytes were investigated from 16 Prader-Labhart-Willi syndrome (PLWS) patients [8 with 15q12 deletion (4 females, 4 males; mean age = 12.9y with age range of 0.3 to 24y), and 8 non-deletion (2 females, 6 males; means age = 16.8y with age range of 5 to 26y)], 18 parents of PLWS patients and age-matched control individuals. The average SCE frequency and standard deviation in PLWS patients with and without the chromosome 15 deletion was 6.6 +/- 1.3 and 6.2 +/- 0.8, respectively. Therefore no significant difference in SCE frequency or replicative index was found between the two PLWS subgroups. There was also no significant difference in SCE frequency or replicative index between the 16 PLWS patients and age-matched control subjects. The average SCE frequency and standard deviation in 8 fathers who were previously identified to have donated the chromosome 15 with the deletion in the child was 7.5 +/- 1.2, which was not significantly different from 8.5 +/- 2.0 seen in age-matched control subjects. There was also no significant difference in the SCE frequency or replicative index of 18 parents of PLWS patients with and without the chromosome 15 deletion when compared with age-matched control subjects.     

Sister chromatid exchange and chromosome breakage in complete hydatidiform moles.

Women with complete hydatidiform moles (CHM) are at a 10% risk for developing persistent trophoblastic disease or choriocarcinoma. We studied sister chromatid exchange (SCE) as a prognostic indicator for malignancy in peripheral blood lymphocytes (PBL) from women with CHM and their husbands, but found no differences from normal control couples. SCE levels in cultured tissue derived from 11 CHM (avg. 7.9) and 2 choriocarcinomas (avg. 6.8) were not significantly different from those of 8 normal skin fibroblast cultures (avg. 7.8). These same tissues were then examined for chromosome breakage which was significantly higher for CHM (0.48/cell) and choriocarcinoma (0.87/cell) than normal fibroblasts (0.33/cell). Chromosome breaks occurred at 50-60% known fragile sites and at 50-55% of cancer breakpoints. Whereas SCE was only associated with 13% of breaks in the three tissues, half of these were at known fragile sites. Our results suggest that SCE is not an indicator of malignancy in PBL or cultured cells from CHM or choriocarcinoma and that the level of SCE is not elevated in CHM or choriocarcinoma. However, our results confirm the increased breakage seen in the latter two tissues which may represent general DNA instability predisposing to choriocarcinoma and its accompanying chromosomal rearrangements.     

Sister chromatid exchange levels and cell cycle time in human bone marrow cells and lymphocytes

The frequency of sister chromatid exchange (SCE) and the cell-cycle-specific pattern of mitoses were analyzed at the same time in normal bone marrow cells and lymphocytes of six healthy donors. The SCE frequency was found to be significantly higher in lymphocytes. The cell-cycle-specific pattern revealed significantly shorter cell cycle times for normal bone marrow cells as compared with those of phytohemagglutinin (PHA) stimulated lymphocytes. Chromosomes of bone marrow metaphases displayed a more contracted morphology.     

Sister chromatid exchange in human lymphocytes induced by propoxur following plant activation by Vicia faba

Because the carbamate insecticide propoxur induced sister chromatid exchanges (SCE) in Vicia faba but was ineffective in producing SCE in lymphocytes in culture, it was hardly suspected that plant metabolism was involved. Experiments were conducted in which metabolic activation was afforded by Vicia faba roots, and SCE in human lymphocytes in vitro was used to assess cytogenetic damage. Several concentrations of propoxur (250, 500, 1, 000, 1, 500, and 2, 000 ppm) were applied for 4 hr to the roots of Vicia faba. Extracts prepared from these treatments were added to the lymphocyte cultures and a significant increase of SCE frequencies with a concentration-response relationship could be detected. The lymphocyte proliferation kinetics and the proliferation rate index (PRI) were not affected (except in the highest concentration, of 2, 000 ppm). This general behavior was in agreement with the presence of an enzymatic system (SI0 fraction) in Vicia roots capable of metabolizing or activating the propoxur. With 2, 000 ppm, cell necrosis was produced in Vicia; therefore, this extract did not induce SCE in lymphocytes. However, lymphocyte proliferation kinetics were delayed and PRI was significantly decreased. Ethanol, a promutagen activated by this plant, was applied directly to the lymphocyte cultures as a positive control, and the response was negative. On the other hand, the extracts of roots treated with ethanol increased the SCE to more than twice that of the negative control, but the lymphocyte proliferation kinetics and PRI were not affected. © 1995 Wiley-Liss, Inc.     

Sister chromatid exchange and chromosome abnormalities in uremic patients

Chronic renal failure heightens the risk of malignancy. We therefore examined lymphocytes from 44 uremic patients and 24 normal controls for chromosome abnormalities and sister chromatid exchange (SCE) rate. This is the first report of SCE in uremia. Uremia was found to increase structurally abnormal chromosomes and elevate the rate of SCE. These cytogenetic changes in uremia may play a role in the heightened risk of cancer.     

Sister chromatid exchange in families with Angelman or Prader-Willi syndrome

Using estimation of numbers of sister chromatid exchanges arising in 15q 11 q 13 as a measure, comparisons of the stability of the Prader-Willi syndrome critical region have been made. The groups studied included probands with Prader-Willi or Angelman syndromes either with or without a cytogenetically visible deletion in 15q11q13, their parents, specifically those parents who had passed on the homologue which had become deleted, and a control group. No significant differences were found between any of the four groups, indicating that there was no increase in the instability of the PWSCR region as measured by sister chromatid exchange.     

Sister chromatid exchanges in lymphocytes of patients with oral carcinoma

Sister chromatid exchanges (SCEs) were studied in cultured peripheral lymphocytes of 22 untreated patients with squamous cell carcinoma of the oral cavity and 29 age- and sex-matched controls. The SCE rate in cancer patients was not significantly higher compared with that found in controls, but there was a significant correlation between the SCE rate in lymphocytes of the cancer patients and the size of the primary tumor.     

Sister chromatid exchange induction and persistence in peripheral blood and spleen lymphocytes of mice treated with ethylnitrosourea

The induction and persistence of sister chromatid exchanges (SCEs) were studied in peripheral blood and spleen lymphocytes of mice given a single i.p. injection of ethylnitrosourea (ENU) of 100, 350, or 600 muMoles ENU/kg. SCE frequencies were measured on days 1, 3, 5, and 7, and at seven additional times up to 172 days post-injection. SCEs were analyzed statistically by comparing the mean frequencies as well as the distribution of SCEs per cell at each time. The latter approach was based on a non-parametric method of identifying high frequency cells (HFCs). The SCE frequencies and proportion of HFCs in each dose and tissue remained elevated for up to 172 days following treatment, although the degree and statistical significance of the increase varied according to the tissue, dose, and statistical test employed. The SCE frequencies were found to oscillate during the first week. Following this, however, the return of the SCE frequencies to control levels was fit to a linear regression model with time as the only independent variable. The persistence of SCE-forming lesions was found to be dose-dependent for the spleen but not for blood. Within each dose the persistence of SCE-forming lesions was significantly greater for the blood relative to the spleen. The results emphasize that tissue, dose, and time since exposure are important factors to consider when quantifying SCEs in vivo; analysis of high frequency cells may be a more sensitive method of detecting exposure than the t-test; and a single determination of SCE frequencies may not be sufficient to quantitatively assess genotoxic damage in the first week following exposure.