Relation between sister chromatid exchange, cell proliferation and proportion of B and T cells in human lymphocyte cultures

Differential DNA damage induced by H2O2 and bleomycin in subpopulations of human white blood cells

The purpose of this study was to characterize the differential sensitivities of various subpopulations of human white blood cells after exposure to H2O2 (an oxidant agent) and bleomycin (a radiomimetic glycopeptide), in vitro, using single-cell gel electrophoresis (SCGE). Human peripheral blood was fractionated into mononuclear cells, which were further separated into monocytes, CD4+ T-cells, CD8+ T-cells, B-cells and natural killer cells (NK cells). The separated fractions were exposed to different doses of H2O2 and bleomycin, and then used to measure levels of induced and basal DNA damage. There was a significant increase in the amount of DNA damage in CD4+ T-cells, CD8+ T-cells, NK cells and B-cells when treated with H2O2 and bleomycin, whereas monocytes had the lowest sensitivity to H2O2 compared with the other cell fractions, but no lower sensitivity to bleomycin. Furthermore, CD4+ T-cells and CD8+ T-cells had the highest levels of basal DNA damage. When basal DNA damage was taken into account, NK cells tended to show a higher sensitivity to H2O2 than CD4+ T-cells, CD8+ T-cells and monocytes. In addition, B-cells, which showed lower sensitivity to H2O2 than CD4+ T-cells, CD8+ T-cells and NK cells when exposed to lower doses of H2O2 (<10 microM), showed higher sensitivity to H2O2 at higher doses (>20 microM). On the other hand, B-cells showed the highest sensitivity to bleomycin.

Spontaneous rate of sister chromatid exchanges (SCEs) and BrdU dose-response relationships in mitotic chromosomes of goat (Capra hircus L.)

The spontaneous level of sister chromatid exchange (SCEs) in the goat, estimated by exposing peripheral blood lymphocytes to 0.1 microgram/ml of 5-bromodeoxyuridine (BrdU), was 3.28 +/- 1.71 SCE/cell, 1.64 SCE/cell generation and 0.027 SCE/chromosome. The dose-response curve of SCE/cell, observed by exposing the cells to 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 micrograms/ml of BrdU, rose rapidly from 0.1 to 0.5 microgram/ml, remained fairly stable from 0.5 to 1.0 microgram/ml and rose less rapidly from 1.0 to 5.0 micrograms/ml of BrdU. The frequency distribution of sister chromatid exchanges/cell and that of chromosomes showing various number of exchanges followed the Poisson probability at all BrdU levels; only at 5.0 micrograms/ml of BrdU was the fit found on the border of the 5% probability level. The usefulness of determining the spontaneous level of SCE/cell in domestic animals is discussed in relation to its possible application for a more precise evaluation of the genotoxic effects of environmental pollutants.

Spontaneous rate of sister chromatid exchanges (SCEs) in mitotic chromosomes of sheep (Ovis aries L.) and comparison with cattle (Bos taurus L.), goat (Capra hircus L.) and river buffalo (Bubalus bubalis L.)

The spontaneous level of sister chromatid exchanges (SCEs) in the sheep, estimated by exposing peripheral blood lymphocytes in 0.1 microgram/ml of 5'-bromodeoxyuridine (BrdU), was 4.08 +/- 2.47 SCE/cell, 2.04 SCE/cell cycle, 0.038 SCE/chromosome. The dose-response relationships, observed by exposing the cells to 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 micrograms/ml of BrdU, rose rapidly from 0.1 to 0.25 microgram/ml, and less rapidly at higher concentrations, thus reaching a saturation level. The analysis of variance, performed on the square root transformed data at 0.1 and 5 micrograms/ml of BrdU, indicated significant differences (P < 0.001) among the four donors tested. The distribution of the SCE/cell frequencies in the cell population of the four donors followed the Poisson 'mixture' probability function, thus confirming previous findings. The spontaneous rate of SCE/cell of sheep is compared with those previously reported for cattle, goat and river buffalo. The theoretical and practical implications of the spontaneous sister chromatid exchanges are discussed in relation to their possible use in animal production for (a) better genetic evaluation of the breeding animals under selection, (b) more precise monitoring of the genotoxic effects of environmental pollutants.

Effects of a phytopreparation from Helleborus niger on immunocompetent cells in vitro

Extracts of Helleborus species are used as phytopreparations with immunostimulatory properties in Romanian traditional medicine. In Germany, Helleborus niger is used in homeopathy and as an adjuvant therapy in the treatment of tumor patients in anthroposophical medicine. In vitro application of an aqueous extract from Helleborus niger resulted in a slight induction of sister chromatid exchanges (SCE) in cultured peripheral blood mononuclear cells (PBMC) from healthy individuals, an effect associated with a slight increase of the [3H]thymidine uptake in the DNA of isolated lymphocytes. Since the cytokines interleukin (IL)-2 and tumor necrosis factor (TNF)-alpha were reported to increase the number of SCE, we measured the concentrations of these cytokines in the supernatants of cultured PBMC treated with the plant extract. Here, no significant changes were observed as compared with the controls, but a trend to higher supernatant concentrations of TNF-alpha in six out of ten individuals was noted. Compared with lymphocytes treated with the alkylating substance, cyclophosphamide, the increase of the SCE levels induced by the plant extract is weak. The relevance of this DNA destabilizing property remains to be clarified.

Sister-chromatid exchanges in cattle: breed, sex and BrdU dose effects

The spontaneous incidence of sister-chromatid exchanges (SCE) was investigated in a group of cattle, composed of 21 animals of both sexes and from two different breeds (Fleckvieh and Pirenaica). Peripheral lymphocytes of these animals were cultured in three different bromodeoxyuridine (BrdU) concentrations: 5, 15 and 30 micrograms/ml. The work was carried out following a randomized block design. Among the analyzed sources of variability, group, breed and BrdU dose factors had significant effects on the SCE frequency. No differences between sexes were found. Comparisons of the BdrU doses showed that the 5 micrograms/ml dose differed from both the 15 and 30 micrograms/ml doses, whereas the 15 and 30 micrograms/ml doses did not differ from each other. The results indicate that the breed of cattle as well as the BrdU dose chosen for the analysis must be considered when the SCE test is used for the biomonitoring of environmental mutagens.

SCE analysis in human lymphocytes of a Spanish control population

SCE (sister-chromatid exchanges), HFC (high frequency cells) and PRI (proliferative rate index) were studied in the peripheral blood lymphocytes of 154 healthy male volunteers, from Barcelona (Spain). SCE, HFC and PRI variability between and/or within individuals was estimated by means of a mixed linear model. This model allows a determination of the relationship between confounding factors (demographics, life style, work exposure and medical history) and the cytogenetic and cytokinetic parameters analyzed. The results obtained indicate the existence of an important intra-individual heterogeneity in SCE rates, as well as in HFC and PRI values. Although age did not seem to affect either the SCE frequency or the HFC percentage, it showed a significant positive association with the presence of cells with higher SCE frequencies. With respect to the confounding factors, only cigarette smoking increased the SCE rates and the HFC values. On the other hand, PRI mean showed significant differences dependent on age and was inversely correlated with alcohol consumption and X-ray exposure.

The genotoxic and cytotoxic activities of inorganic fluoride in cultured rat bone marrow cells

The effects of sodium and potassium fluoride (NaF and KF) at concentrations ranging from 10(-7) to 10(-2) M for 12, 24, or 36 h on cultured rat bone marrow cells have been studied with respect to cytotoxicity and induction of sister-chromatid exchanges (SCE). At the three exposure times, cell survival progressively decreased with increasing concentrations. Treatment with 10(-2) M fluoride resulted in a statistically significant death (62-65%) of cells. Similarly, no dividing cells were encountered at concentrations of 10(-3) M and 10(-2) M, and significant reductions in mitotic index (MI) were calculated at 10(-4) M. In contrast, cell kinetics, expressed as cell proliferation index (CPI), revealed no significant inhibitory effect of fluoride on cell proliferation. Furthermore, the mean SCE score reached a maximum (7.64 SCE/cell) in the 24-h-treated cultures. This value was not significantly different from that observed in sodium chloride (NaCl) at 10(-2) M (5.42 SCE/cell) and distilled water (4.86 SCE/cell) controls. In comparison, mitomycin-C (MMC, positive control) at 5 x 10(-8) M caused an average of 22.13 SCE/cell. These results indicated an inhibition of cell division and death of cells with high doses of fluoride with no effect on SCE frequencies.

Viscum album L. extracts reduce sister chromatid exchanges in cultured peripheral blood mononuclear cells

Increasing concentrations of Viscum album L. extracts were shown to significantly reduce sister chromatid exchange (SCE) frequency of phytohaemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC) of healthy individuals. This decrease of SCE could not be explained either by changes in lymphocyte subpopulations, by cytostatic effects of the drug or by accelerated proliferation of PHA-stimulated PBMC. Currently, no other cells tested have shown this effect. One therapeutic effect of these anti-mutagenic drugs could be a stabilisation of mononuclear blood cell DNA.

An analysis of gamma-ray-induced DNA damage in human blood leukocytes, lymphocytes and granulocytes

Lymphocytes and granulocytes were separated from human peripheral blood and irradiated with low doses of gamma-rays (0.05-0.5 Gy) from a 137Cs source. The magnitude and intercellular distribution of DNA damage, i.e., single-strand breaks and alkali-labile lesions, were compared with those obtained in unfractionated leukocytes irradiated in whole blood, using the alkaline single-cell gel-electrophoresis technique. Based on the extent of DNA migration, irradiation resulted in a linear and dose-dependent increase in DNA damage in all 3 cell populations, with a significant increase being detected at 0.05 Gy. The dose-dependent increase for DNA migration was not significantly different between separated lymphocytes and granulocytes, but their responses were significantly elevated over that obtained for leukocytes irradiated in whole blood. Based on an analysis of the ratio of the range to the standard deviation for each cell population at each dose of radiation, the distribution of damage among cells was relatively homogeneous and independent of dose and cell population. These results are consistent with a hypothesis that irradiation of leukocytes in whole blood partially protects against radical-induced DNA damage.

Sister-chromatid exchanges induced by chloramphenicol on bovine lymphocytes

The induction of sister-chromatid exchanges (SCE) was studied in bovine lymphocyte cultures treated with chloramphenicol (CAP), an antibiotic agent in wide use in human and animal therapy. A total of six individuals, matched for sex, race, age and environmental conditions, were used for the analysis. Chloramphenicol was tested at four different concentrations (5, 10, 20 and 40 micrograms/ml) and acted for the last 24 h of the culture. Each experiment included two animals, each of which was exposed to all chloramphenicol doses, for a total of three repetitions. The results of the corresponding analysis of variance showed that this chemical had a small but statistically significant effect on the SCE frequency. In addition, the lymphocyte cultures responded strangely to this chemical: the highest SCE induction was produced by the lowest dose. However, the study of high frequency cells did not show the presence of this kind of cell which could explain this chloramphenicol response. In addition, chloramphenicol induced a high delay in the cell cycle.

Sister chromatid exchange in Waldenström's macroglobulinemia

Results on sister chromatid exchange (SCE) frequency and interchromosomal distribution in bone marrow and peripheral blood cultures from patients with Waldenström's macroglobulinemia are reported. PHA-stimulated bone marrow cultures showed increased SCE frequencies in all 12 patients examined. The increase was particularly high in two cases (17.07 and 16.77 SCE/cell, respectively) and, in one of them, a very high SCE level was found in PHA-stimulated peripheral blood culture (40.81 SCE/cell). In LPS-stimulated cultures, increased SCE levels were observed in some patients. Comparison between SCE frequency in bone marrow cell cultures with either mitogen showed a significant increase in PHA-stimulated cultures. Analysis of the interchromosomal SCE distribution revealed significant differences with respect to the control values; however, these differences were variable in the different patients. In pooled data of PHA-stimulated bone marrow cultures, there were differences between expected and observed SCEs in chromosomes 1 and 2 and in B, E, F, and G chromosome groups. Results of cell cycle modifications are also reported.

Sister-chromatid exchange in highly purified human CD4+ and CD8+ lymphocytes

Sister-chromatid exchange (SCE) frequencies were determined in human peripheral blood CD4+ and CD8+ T lymphocyte subpopulations which were rapidly and highly purified from pooled T lymphocytes by immunological methods. The purified lymphocytes were stimulated with phytohemagglutinin (PHA) for 4 days. CD4+ lymphocytes showed significantly higher SCE frequencies than autologous CD8+ lymphocytes when measured simultaneously after identical bromodeoxyuridine (BrdU) incubation times. Differences in SCE frequencies between CD4+ and CD8+ lymphocytes were also detected when mitomycin C (MMC) was added to the cultures. Higher SCE frequencies in CD4+ lymphocytes were associated with lower proliferating rate indices (PRI) as compared to autologous CD8+ lymphocytes. Abnormalities in CD4+ T lymphocyte function and number in peripheral blood have been observed in several diseases characterized by immunological disorders. Thus, our data may suggest a link between some immunological disturbances and abnormal SCE frequencies in T lymphocyte subsets.

Cytogenetic study in peripheral blood lymphocytes from asthmatic patients receiving continued therapy with theophylline

Possible cytogenetic effects of theophylline have been investigated in asthmatic patients undergoing continuous therapy with this drug. Sister-chromatid exchanges (SCE), chromosome aberrations (CA) and proliferating rate indices (PRI) were evaluated in cultured peripheral blood lymphocytes from patients receiving theophylline alone, theophylline plus inhaled beta 2 adrenergic drugs or theophylline in combination with beta 2 adrenergic agents and corticoids. Two samples from each individual were obtained in order to perform a prospective study: before the theophylline medication (sample A) and at a time after the beginning of treatment (sample B). After treatment (66.3 +/- 37.8 days), an increase in SCE was observed without modifications either in PRI or in CA. Patients receiving beta 2 adrenergics or beta 2 adrenergics plus glucocorticoids before and during theophylline treatment, did not respond differently than those on theophylline alone.

Clastogenic effects of bleomycin, cyclophosphamide, and ethyl methanesulfonate on resting and proliferating human B- and T-lymphocytes

The effects of bleomycin (BM), cyclophosphamide (CP), and ethyl methanesulfonate (EMS) on the frequencies of chromosomal aberrations were tested in mitogen-stimulated highly purified human B- and T-lymphocytes. In unstimulated G0/G1 B- and T-lymphocytes the clastogen induction of chromosome fragments was investigated in prematurely condensed chromosomes (PCC) induced by cell fusion with xenogenic mitotic cells. BM, CP (with metabolic activation), and EMS induced a significant increase in chromosome aberrations in proliferating human B- and T-lymphocytes. There were no significant differences in the BM-induced aberration rates between the cell populations. CP and EMS induced more aberrations in T- than in B-lymphocytes. In the PCC tests, BM-exposed G0/G1 lymphocytes showed dose-dependent high yields of chromosome fragments. No significant differences between B- and T-lymphocytes were observed. CP and EMS induced no clear increase in fragments in either cell population.

Sister-chromatid exchange in human B- and T-lymphocytes exposed to bleomycin, cyclophosphamide, and ethyl methanesulfonate

Sister-chromatid exchange (SCE) frequencies were investigated in mitogen-stimulated cultures of highly purified human peripheral blood B- and T-lymphocytes exposed to bleomycin (BM), cyclophosphamide (CP), or ethyl methanesulfonate (EMS). In untreated controls, T-lymphocytes showed twice as many SCEs as B-lymphocytes. CP (with metabolic activation) and EMS significantly increased the SCE frequencies. EMS induced a similar, dose-dependent SCE increase in both cell populations, whereas CP induced more SCEs in T- than in B-lymphocytes. No clear SCE increase was found in B- and T-lymphocytes treated with BM.

Modulation of SCE induction and cell proliferation by 2-mercaptoethanol in phytohemagglutinin-stimulated rat lymphocytes

2-Mercaptoethanol (2-ME) is used as a medium supplement to enhance the proliferation of lymphocytes cultured in vitro. In this study, we have examined the effects of 2-ME on cell growth and on SCE induction in cultures of unstimulated and phytohemagglutinin (PHA)-stimulated Fischer 344 rat lymphocytes. There were virtually no metaphases detected in cells cultured without PHA. In PHA-stimulated cultures, 2-ME decreased SCE frequency but it enhanced SCE frequency in the presence of 5 to 12.5 microM bromodeoxyuridine (BRdU). Both mitotic and replication indices were increased in the PHA/2-ME system. The levels of incorporated exogenous thymidine, in the presence of 2-ME, were relatively low in unstimulated cells, suggesting that 2-ME is not mitogenic for T-cells. However, 2-ME enhanced PHA-induced response of T-cells as evidenced by increased levels of thymidine incorporation into cellular DNA. The growth-promoting effects and the decrease in SCE frequency caused by 2-ME upon PHA stimulation indicate that 2-ME may alter the nature of interaction between PHA and cellular activating properties or the replicative processes.

Spontaneous sister-chromatid exchange frequencies in human B and T lymphocytes at BrdU borderline concentrations for sister-chromatid differentiation

Human peripheral blood B and T lymphocytes, highly purified by immunologic methods, were supplemented with gamma-irradiated unseparated autologous mononuclear cells to restore helper functions and stimulated with pokeweed mitogen and phytohemagglutinin, respectively. Spontaneous sister-chromatid exchange (SCE) frequencies were investigated in proliferating B and T lymphocyte cultures labeled with the cell-type-specific borderline concentrations of 5-bromodeoxyuridine (BrdU) for sister-chromatid differentiation (SCD). B lymphocytes from 6 different donors showed mean values of 3.28-3.72 SCE events/cell. In T lymphocytes, mean values of 6.30-7.28 SCEs/cell were observed. The differences between the SCE distributions of the cell populations are highly significant. The results show that the differences in the spontaneous SCE frequencies between human B and T lymphocytes were not due to a difference in the uptake of BrdU.

Repair of sister-chromatid exchange-inducing lesions in mutagen-treated cultures of human whole blood and purified fresh or frozen lymphocytes

Repair of mutagen-induced lesions that result in sister-chromatid exchanges was evaluated in 10 normal individuals. The mutagens used were mitomycin C (MMC), 4-nitroquinoline 1-oxide (4NQO), and N-methyl-N'nitro-N-nitrosoguanidine (MNNG). Cultures of whole blood, freshly purified lymphocytes, or purified lymphocytes cryopreserved for 6 months were analyzed after the mutagen treatments. All 3 mutagens induced reparable damage as evaluated by comparison of sister-chromatid exchanges between cultures that were given time to repair induced damage before 5-bromo-2'-deoxyuridine (BrdUrd) was added to the culture medium with those where BrdUrd was added immediately after the administration of the mutagens (MMC or 4NQO) or at culture initiation (MNNG). Repair of mutagen-induced DNA damage was detected in all 3 culture types; thus cryopreservation did not appear to alter the capacity of lymphocytes to repair mutagen-induced lesions. Quantitative differences in apparent repair capabilities were observed among individuals. Variability also existed among the different culture types within an individual, suggesting that caution should be exercised in interpreting these apparent differences.

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.

SCE variability in lymphocytes and fibroblasts. A controlled study

To determine whether the sister chromatid exchange (SCE) distributions obtained in lymphocytes and fibroblasts from different individuals are comparable, a controlled study was set up. Peripheral blood and skin biopsies were taken on the same day from five individuals living for years under the same environmental conditions. All samples were treated in the same fashion, and the SCEs were scored in 50 metaphases of peripheral blood lymphocytes and of skin fibroblasts in an early and in a late passage. A repeat blood sample was taken from the same five individuals 1 year later. Based on the results obtained in this first part of the study, five randomly chosen healthy blood donors were sampled at different times and studied in the same fashion. Each chromosome was identified, and the SCE scores were tabulated per chromosome over 50 metaphases. The statistical analysis consisted of fitting log linear models to these scores and examining the best fit by determining the exceedance probabilities (observed significance level). For lymphocytes, the results indicated that the SCE distributions depended only on the chromosome examined, and not on BrdU-exposure time, individuals, or time of sampling. Treatment with ethyl methane sulfonate (EMS) increased the number of SCEs proportionally on all chromosomes. Analysis of the SCE scores on lymphocytes and fibroblasts of the five individuals and on their low and high passage fibroblast cultures revealed the necessity of including higher order interactions in order to fit a suitable model to the data. Therefore comparison of the SCE scores of lymphocytes with those of fibroblasts or comparison of scores on fibroblasts from different individuals could not be done. In practice, to compare samples or individuals, it suffices to score the SCE on a limited number of chromosomes (e.G., the A group) of 50 metaphases.

Lymphocytes proliferation kinetics and SCE variation after rubella vaccination

The effect of anti-rubella vaccination on lymphocyte proliferation kinetics in vitro and on SCE frequency was studied in three young women. The studies were carried out by taking blood samples before vaccination (day 0) and subsequently on days 7, 14, 28 and 42. The mitotic index (MI) shows a decrease at day 14 and 28 followed at day 42 by an increase above day 0 levels. The average cell cycle (ACC) shows a decrease at day 14 followed by an increase at day 28. Complex variations were also found in the percentage distribution of cells in the various division classes. The SCE frequency showed variations inverse to the MI. The whole picture seems to indicate the existence of changes in the lymphocyte population which can be correlated with immune response.

Factors that influence formation of sister chromatid exchanges in human blood lymphocytes

Sister chromatid exchange (SCE) reflects an interchange of DNA sequences between helices in a replicating chromosome. This was initially accomplished by Taylor and colleagues (1957) using tritiated thymidine incorporation followed by autoradiography. The development of an elegant technique for differential staining of sister chromatids by incorporating a thymidine analog, 5-bromodeoxyuridine (BrdU) has greatly simplified the detection of SCEs in metaphase chromosomes. In recent years, the analysis of SCE has been considered to be a highly sensitive and additional (i.e., with chromosome aberrations) end point for measuring mutagenic/carcinogenic potential of various environmental agents and is increasingly being used to detect and differentiate among chromosome fragility human diseases that predispose to neoplasia. Attention has been focused to see if the induction of SCEs in lymphocyte cultures can be used as a reliable "biological dosimeter" for genetic risk assessment and to monitor the exposed populations. Several physical or preparatory as well as biological factors that modify the response and formation of SCEs make the monitoring difficult. The purpose of this article is to review and analyze these factors to facilitate an effective development of a standard protocol for SCE testing and for appropriate evaluation of test results. This may also provide clues to understand the yet unknown molecular mechanism(s) and biological significance of SCE formation.

Lymphocyte micronuclei and sister chromatid exchanges among Canadian federal laboratory employees

Blood lymphocytes from 59 federally employed Canadian laboratory workers, 137 nearby office employees, and 11 workers with a mixed employment history were examined for the presence of sister-chromatid exchanges and micronuclei. These laboratory workers were exposed routinely to a host of organic solvents and had previously voiced complaints regarding the adequacy of the ventilation system in their building. Overall, no relationship between laboratory work and either cytogenetic endpoint was observed. The two tests were only weakly correlated, but in a multivariate analysis, both were associated with recent and past smoking. Within-person variation was measured for the sister-chromatid exchange assay, and it and other possible sources of variation are discussed.

Proliferation kinetics of human B- and T-lymphocytes

Human peripheral blood B- and T-lymphocytes, highly purified by immunological methods, were supplemented with gamma-irradiated unseparated autologous mononuclear cells to restore helper functions and stimulated with pokeweed mitogen and phytohaemagglutinin, respectively. Proliferation kinetics of the cell populations were investigated using 5-bromodeoxyuridine (BrdU) labelling of the cell cultures and chromosome preparation at different times after stimulation. The percentages of metaphase cells having replicated for one, two or three generations in the presence of BrdU were determined following sister chromatid differential staining. In all donors, the changes in these percentages were faster in B- than in T-lymphocytes, indicating a longer cell cycle time in the latter population.

Sister-chromatid exchange and cell proliferation in cultured lymphocytes of passively and actively smoking restaurant personnel

Sister-chromatid exchange frequencies were measured in peripheral lymphocytes of 12 cigarette smokers, 20 passive smokers, and 14 non-smokers with no regular exposure to tobacco smoke. All active and passive smokers worked as waiters and waitresses in restaurants. The passive smokers showed neither an increased mean SCE value nor an increased number of high SCE frequency cells (HFCs) when compared to non-exposed non-smokers. The incidence of SCEs and HFCs was observed to be elevated (P less than 0.01; P less than 0.05, resp.) among the active smokers. The proliferation rate of lymphocytes in whole blood cultures from the different exposure groups was also studied. The proportion of cells in first mitosis was lower and the mean replication index (RI) higher among the smokers than among non-smoker controls. However, no significant correlation was observed between the individual mean SCE and the replication index.

CHROMOSOME BREAKAGE AND SISTER CHROMATID EXCHANGE ANALYSIS IN COMPUTER OPERATORS

Chromosome breakage analysis with Mitomycin C (MMC) and sister chromatid exchanges (SCE) were obtained on 10 computer operators with computer exposure for a minimum of 3 hours per day for 4 years and 10 control subjects matched for age and personal lifestyle. No difference was found between the two groups in the total number of chromatid and chromosome aberrations in cells grown at 48 and/or 96 hours in Mitomycin C (20 or 50 ng/ml-final concentration). The average number of SCE per cell in approximately 30 cells from each person was 6.4 ± 1.1 (mean ± standard deviation) for the computer operators and 9.2 ± 1.6 for the controls. This difference was significant (p <.001). The replicative index was significantly higher (p<.01) in computer operators than in control subjects. The number of SCE appeared not to be influenced by the years of computer exposure. Additional studies with larger sample sizes will be needed to identify if significant differences exist in cell kinetics and sister chromatid exchanges in individuals employed as computer operators.

In vitro SCE discrepancy between embryonic and extraembryonic mouse tissues

In vitro sister-chromatid exchange (SCE) background levels and cytokinetics were compared in embryonic (whole embryo cell suspensions) and extraembryonic (yolk sac and amnion, placenta) cells of inbred and outbred strains at various gestational stages (days 12-17). Results indicate a tissue origin (embryonal, extraembryonal) related variation in the formation of baseline SCE frequencies and cytokinetics. The significant higher SCE levels in extraembryonic tissues (maximum increase of 2 X the background values of the embryo cells) were independent of mouse strain and gestational stage. An average of 4-5 SCEs/cell in embryo cells is contrasted by 7-9 SCEs/cell in extraembryo cells. Mitotic index was generally lower and average generation time longer (by 2-3 h) in extraembryonic tissue cells. No significant differences in SCE frequencies and no changes in cytokinetics were detected at the BrdU concentrations used (1.2-4.8 micrograms/ml). The reason for the inter-tissue differences in baseline SCE is still not clear.

Very low sister-chromatid exchange rate in Seventh-Day Adventists

42 Seventh-Day Adventists (SDAs) and 42 controls matched for sex, age and occupation had their sister-chromatid exchange (SCE) examined in peripheral blood lymphocytes. This was done to examine if the SCE frequency was lower in this group of people, who are known to have a decreased cancer risk compared to the general population. The average SCE/cell in 30 cells from each person was 5.54 +/- 0.07 (mean +/- standard error of the mean) for the SDAs and 8.00 +/- 0.15 for the controls, the difference being statistically significant (p less than 0.00001). No difference in SCE frequency was found between SDAs eating only an ovo-lacto-vegetarian diet and those eating some fish or meat. The mitotic index (MI) was significantly higher and the replication index (RI) was significantly lower in SDAs than in controls. No correlation was found between gamma (a statistical transformation of SCEs/cell) and MI or RI within the groups of SDAs or controls. In the pooled data there was a negative correlation of gamma and MI and a positive correlation of gamma and RI. Of the interpersonal variation in gamma 8% and 14% could be explained by MI and RI. The finding of a lower SCE frequency in a group of SDAs who have a low risk of cancer might indirectly indicate a relation between SCE and cancer and encourages further studies of SCE and diet.

Variation in sister-chromatid exchange among 106 members of the general U.K. population

SCE scores of lymphocytes from 106 people revealed that the majority of background variation in SCE was between cells within individuals. Highly significant differences existed between individuals. Lesser, but still highly significant differences also existed between replicate cultures. Inter-individual variation was contributed to by each person's sex and their smoking habits. SCE frequency was not influenced by any of the other factors considered, age, drinking habits and diagnostic X-ray exposure of persons or lymphocyte number and proliferation rate in cultures.

Different baseline sister chromatid exchange levels in density fractionated human lymphocytes

Different activation states of B and T lymphocytes, as manifested by differences in cell density, were obtained by Percoll density centrifugation of unstimulated human lymphocytes. Four different density fractions were defined: B cells with low (1.043 g/ml) and high (1.056) density, and T cells with low (1.067) and high (1.077) density, respectively. Sister chromatid exchange (SCE) conditions and proliferation rates were determined. Total B cells, stimulated by the bacterial mitogen Branhamella, had 4.6 SCE per cell, the lowest mean baseline SCE level recorded among lymphocytes. The growth rate was intermediate between that of low and high density T cells. The two T cell fractions stimulated by phytohemagglutinin (PHA) had different baseline SCE frequencies and different growth characteristics: the low density cells had 5.7 SCEs per cell and a short cell cycle, whereas high density cells had 12.5 SCEs per cell and a longer cell cycle. The differences in baseline SCE frequency and growth characteristics between the two T cell fractions seem to be correlated with the differences in the activation state as reflected by the cell density. Both high and low density T cells are G0 populations which supposedly differ with respect to previous history in vivo such as age and contact with antigens. The reason why these cells react differently to bromodeoxyuridine (BrdU) is unknown, but differences in intracellular DNA precursor pools and enzyme activities might play a role.

Sister chromatid exchange in immature haemopoietic cells, T- and B-lymphocytes

T-lymphocytes, B-lymphocytes, and cells derived from human haemopoietic progenitor cells were analysed for their sister chromatid exchange (SCE) rate. T- and B-lymphocytes were separated and stimulated with phytohaemagglutinin (PHA) and Epstein Barr (EB) virus respectively, while the progenitor cells were cultured in the mixed colony assay. B-lymphocytes had a significantly lower SCE rate than either the T-lymphocytes or cells derived from progenitor cells.

Sister-chromatid exchanges and cell-cycle kinetics in human lymphocyte cultures exposed to alkylating mutagens: apparent deformity in dose-response relationships

Experiments have been carried out using human whole-blood cultures to determine the effects of sampling times and of the duration of 5-bromodeoxyuridine (BrdUrd) treatment before fixation on sister-chromatid exchange (SCE) frequencies following exposure to mitomycin C (MMC). Cells were pulse treated for 1 h with 3 X 10(-6) M MMC at G1, and then sampled at 4-h intervals up to 88 h after stimulation of cultures with phytohemagglutinin (PHA). Results showed that this MMC treatment induced a 5-6 h proliferation delay per cell cycle, and that SCE frequencies first increased with time of fixation, peaking at 68 h, and then decreased. When cells were similarly treated with MMC, but subsequently exposed to BrdUrd for various times before fixation of cultures at 72 h, the SCE frequencies markedly increased with increasing durations of BrdUrd incubation times. These data indicate that, in mutagen-treated cultures, lymphocytes having relatively longer cell-cycle times show a higher mean frequency of SCEs. In a subsequent experiment, cells were treated for 1 h with increasing doses of MMC or 4-nitroquinoline 1-oxide (4NQO) at 0, 24, or 48 h, and then fixed at 72 h after PHA stimulation. Results showed that the optimal treatment times at which the agents could most efficiently produce SCEs were different for MMC and 4NQO, and that the dose-response curves tended to 'bend down' at very high doses; that is, treatments with very high doses induced smaller than expected numbers of SCEs. However, cells similarly treated with very high doses showed a higher, expected frequency of SCEs when sampled at 84 h, but again had a lower than expected SCE frequency when fixed at 96 h. The results indicate that there is an optimal time for sampling at which one can observe the maximum increase in SCE frequencies following mutagen exposure, and strongly suggest that the higher the dose, the later the optimal sampling time. Because of the apparent deformity of dose-response curves obtained after various treatments and sampling times, it seems necessary that extra fixation-time points be included in test protocols so as to avoid false negatives or confirm possible positives.

Changes in spontaneous SCE frequencies as a function of sampling time in lymphocytes from normal donors and cancer patients

Spontaneous SCE frequencies were measured in cells undergoing their second mitosis at 54, 68, 72, 78 or 90 h after PHA stimulation of whole blood cultures from 7 normal donors. A consistent pattern of fluctuation of SCE levels was observed between 54 and 78 h. The magnitude of change in SCE frequency between consecutive fixation times was as high as 80% for some donors. These observations support the hypothesis of Snope and Rary (1979) that there are subpopulations of lymphocytes with different spontaneous SCE levels and different proliferation rates. In untreated cancer patients the patterns of change in SCE frequency with time were different from that seen in normal donors. This may be because of quantitative changes in T-lymphocyte sub-populations which have been observed in cancer patients. Changes in SCE frequency of less than about a factor of two, observed at a single sampling time may not be indicative of genotoxic events or genetic instability but simply represent changes in the composition of lymphocyte sub-populations and/or in their rates of proliferation in vitro.

Sister-chromatid exchange in cultured lymphocytes of ewes and their newborn lambs

The incidence of sister-chromatid exchange (SCE) in cultured lymphocytes of ewes and their newborn lambs was determined using the BrdU-Giemsa technique. In all ewe-lamb pairs, the SCE rate in the lambs was less than that of the ewes. The mean SCE frequencies per chromosome of the ewes after lambing and of the newborn lambs were 0.1909 and 0.1581, respectively. The statistical analysis shows that a significant difference exists between SCE in the adult female sheep and their lambs. At the same time, a negative correlation was observed between SCE rate and cell proliferation. The results of this study are compared with those of previous reports on age-dependency of SCE.

Persistence of chromosome rearrangements in peripheral lymphocytes from patients treated with melphalan for ovarian carcinoma

Chromosome aberrations were studied in peripheral lymphocytes from 50 patients treated with melphalan against ovarian carcinoma. The chromosome analyses were carried out 4-132 months (mean 57 months) after the end of melphalan therapy. Most of the patients were studied several times during four years. The mean frequency of cells with chromosome and chromatid aberrations was 5.4% in the patients and 2.3% in an untreated control group. The highest aberration frequency (average 18%) was found in a patient who later developed gastric carcinoma. The dominating types of aberrations in the patients were chromosome exchanges occurring as single marker chromosomes or as multiple chromosome rearrangements. These types of aberrations were found in only 0.3% of the control cells as compared to 3.8% of the patient cells. Patients with a high total dose of melphalan (above 420 mg) and a long duration of the therapy (average 22.5 months) had a higher frequency of cells with aberrations (6.3%) than patients with a lower total dose (below 420 mg) and a shorter therapy (12 months) (4.2%). No additive effect of radiation therapy was observed on the aberration frequency.

The current state of research with peripheral tissues in Huntington disease

Huntington disease is a neurological autosomal dominant disease of unknown origin and the search for a suitable diagnostic marker has been extended to the peripheral tissues. It is generally believed that a membrane defect exists in Huntington disease although the evidence is controversial. It is the aim of this review to examine the validity of these claims for each of the peripheral tissues and techniques involved, and it is not intended to include all other aspects of research into Huntington disease.

The effect of storage of blood on the yield of X-ray-induced chromosome aberrations and spontaneous sister chromatid exchanges

Heparinized whole blood of man and muntjac (Indian barking deer) was stored at 5, 22 and 37 degrees C for varying durations up to 168 hours and then exposed to 2.0 or 3.0 Gy of X-rays. The yield of dicentrics and other aberrations scored in first post-irradiation metaphases from lymphocytes of both man and muntjac did not vary significantly. However, a marked increase in the proportion of first division metaphases at a given sampling time due to delay in cell cycle progression was noticed in lymphocyte cultures set up from stored blood. There was a relatively higher proportion of first division metaphases in cultures of blood stored at the frequency of spontaneous SCEs was observed in lymphocyte cultures set up from stored and fresh blood.

Sister chromatid exchanges and chromosome aberrations in rubber workers

Sister chromatid exchanges and chromosomal aberrations were studied in peripheral blood lymphocytes of 55 rubber workers (from two different plants) and 35 controls mainly employed in office jobs. In both plants an increased frequency of SCEs (P less than 0.05 for plant A and P less than 0.01 for plant B) was detected in nonsmoking rubber workers as compared with nonsmoking referents. When the SCEs of worker groups belonging to the different job categories were compared with referents, the only groups showing statistically significant increases in SCEs were the smoking workers from the weighing and mixing departments of factory A and the nonsmoking weighers of factory B. A slight increase in the SCE frequencies was seen especially among smoking workers employed in the chemical mixing departments. The frequency of structural chromosome aberrations was not significantly increased in the occupational groups studied, the only exception being the small group of nonsmoking weighers in plant B. Among both the exposed workers and the controls, smokers had a higher mean SCE frequency than nonsmoking referents. This difference was significant between the exposed smokers and nonsmokers of plant A (P less than 0.01) and between smoking and nonsmoking controls for plant B (P less than 0.001). In addition, the chromosome aberration frequency of smoking controls of plant A was significantly higher (P less than 0.01 when gaps excluded and P less than 0.05 when gaps included) than that of nonsmoking referents. Also, smokers among controls for plant B had an increased frequency of aberrations in their cultured blood lymphocytes when compared with nonsmokers. This difference was significant (P less than 0.05) when gaps were excluded.

Development of rodent peripheral blood lymphocyte culture systems to detect cytogenetic damage in vivo

Peripheral blood lymphocytes (PBLs) offer many advantages for in vivo cytogenetic studies. They can be removed nonlethally from the animal allowing a subject to serve as its own control, permitting the analysis of cytogenetic damage over time. Furthermore, mature PBLs normally do not divide, and some populations are long-lived. Thus, they have the potential to accumulate DNA lesions during chronic exposures to genotoxicants. We have developed standard methodologies for the whole blood culture of rat and mouse PBLs to serve as models for determining the sensitivity of PBLs to cytogenetic damage. The cultures obtained with these protocols give reproducible results with high mitotic indices, stable baseline sister chromatid exchange (SCE) frequencies, and ample numbers of first-and second-division methaphases for scoring both chromosomal aberrations and SCEs. The methodologies have been especially useful for examining cytogenetic damage after inhalation exposures to toxicants such as ethylene oxide, formaldehyde, benzene, and nitrobenzene. Of these compounds, only benzene and ethylene oxide were found to induce significant dose-dependent increases in SCEs in PBLs. Also, dose-response curves have been obtained for several carcinogens administered by ip injection. These studies show that PBLs are sensitive indicators of the genotoxic effects of the carcinogens benzo (a)pyrene, 2-acetylaminofluorene, cyclophosphamide (CP), N-nitrosomorpholine, and ethylmethanesulfonate (EMS). In addition, because subpopulations of lymphocytes can be stimulated to divide using different mitogens, it has been possible to compare the sensitivity of murine B and T lymphocytes following in vitro and in vivo cyclophosphamide exposure. Once the sensitivity and selectivity of rodent lymphocyte cultures are determined, these assays should be valuable not only as a means for predicting which environmental agents could lead to increases in human cytogenetic damage, but also as a way to corroborate human cytogenetic studies.

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.

The SCE test as a tool for cytogenetic monitoring of human exposure to occupational and environmental mutagens

The sister chromatid exchange (SCE) test system using human peripheral lymphocytes is proposed as a valuable tool for the cytogenetic monitoring of exposure to potential chemical mutagens in the occupational environment. We examined the SCE frequencies in organic solvent-exposed workers and reviewed the effects of occupational and environmental chemicals on SCE frequencies. The results obtained in these exposed populations are rather contradictory, which may be related to confounding factors, such as personal life style (smoking, drinking, and drugs) of the examinees, tissue culture conditions and the number of subjects examined. We discussed some practical problems for exposure estimation and sample size determination and are led to the following conclusions. 1) The possible combined effects of potential mutagens and cigarette smoking should be taken into consideration when using the SCE test system. 2) Cell cycle kinetic analysis by differential chromatid staining would provide valuable information as a biological indicator for the monitoring of the workers exposed to xenobiotics. 3) By appropriately setting the number of examinees, monitoring would become more efficient in detecting an increased SCE frequency in the exposed populations. Further studies are also required to enhance the sensitivity of the SCE test system for monitoring purposes.

Effects of temperature on the frequency of sister chromatid exchanges (SCEs) in peripheral blood lymphocytes of man and muntjac

The incidence of sister chromatid exchanges (SCEs) and cell proliferation kinetics have been studied in peripheral blood lymphocytes of man and muntjac grown at 33 to 44 degrees C to gain insight into SCE formation. The frequency of SCEs increased as a function of growth temperature. At a given temperature, however, the frequency of SCEs varied with the sampling times; the early sampled cells showed fewer SCEs than did those harvested late. At 33 degrees C the frequency of SCEs was lowest and there was a marked delay in cell-cycle progression. The number of SCEs was maximum at 40 degrees C in human and 42 degrees C in muntjac. Cell proliferation was markedly affected at higher temperature and 44 degrees C was found to be intolerable for lymphocytes of both the species. It is proposed that certain temperature-dependent enzyme(s) associated with DNA replication kinetics may be involved in the formation of SCEs.

Spontaneous and mutagen induced sister chromatid exchange in multiple sclerosis

Spontaneous and mutagen induced sister chromatid exchange (SCE) frequencies have been studied in nine patients with multiple sclerosis and in nine age and sex matched healthy controls. The incidence of spontaneous SCE in lymphocytes of the MS patients was significantly greater, by about 50%, than in those of the control subjects. When exposed to mitomycin C (MMC) or ethyl methane sulfonate (EMS) in vitro, cells from both groups showed typical dose dependent increases in SCE frequency, with yields from MS patients slightly higher than from controls. The higher SCE yields in mutagen treated MS cells relative to controls is considered to reflect initial basal differences between the cell types, so that MS cells are not intrinsically hypersensitive to mutagen treatment.

Reduced frequency of baseline sister chromatid exchanges in lymphocytes grown in antibiotics and serum-excluded culture medium

Peripheral venous blood from man, muntjac, and cattle were grown in medium (1) containing different serum (human AB+/FCS/autologous), (2) without serum or antibiotics (penicillin and streptomycin), or (3) without both serum and antibiotics to investigate to what extent certain essential culture components used in in vitro mammalian cell cultures affect the incidence of spontaneous sister chromatid exchanges (SCEs). The observation that exclusion of only serum from culture medium enhanced the frequency of SCEs whereas exclusion of both serum and antibiotics, which influence the cell cycle kinetics to a great extent, exhibited the lowest frequency of SCEs reported so far for lymphocyte cultures, indicates that the frequency of so-called spontaneous SCEs usually observed in normal lymphocyte cultures grown in medium supplemented with serum and antibiotics is in fact an elevated frequency.

The stimulation of human B and T lymphocytes by various lectins

The response of human peripheral blood lymphocytes to different lectins was tested in vitro by monitoring DNA synthesis, blast transformation, and mitotic activity. One group of lectins - RCA, VGA, HPA, PNA, and UEA - showed no stimulating effects at all. WGA and VVA induced DNA synthesis and blast transformation but failed in stimulating mitosis. The mitogens PHA, ConA, LCA, and PWM showed peaks of mitotic activity at 50-60 hours for PHA, 70 hours for ConA, 80 hours for LCA, and between days 4 and 5 for PWM. The stimulation of different subpopulations of lymphocytes was investigated by immunological methods for the detection of B- and T-cell-specific surface structures during the whole incubation period. PHA proved to be a predominantly T cell stimulating agent, whereas ConA seemed to activate a higher proportion of B cells than yet known. PWM and the so-called T cell mitogen LCA turned up to stimulate a large number of B cells, but lead also to a T cell activation. The analysis of SCE events in stimulation experiments with these two lectins showed the early proliferation of a cell population with low SCE frequencies and the late propagation of a cell population with higher SCE rates. It could be assumed that the first population is represented by B- and the second by T-cells.

Cell kinetics and sister-chromatid-exchange frequency in human lymphocytes

Repeated cultures from 5 healthy donors were set up in 3 tissue-culture media: TC109, TC199 and TC1640. For each donor, 3 blood samples were taken at 1-week intervals, making a total of 5 x 3 x 3 = 45 cultures. Our results show a large variability in the individual SCE base-line frequency. This variability can be partly attributed to the different tissue-culture media or to the donors themselves. Our results, however, stress the importance of the proliferating rate of the culture in determining the SCE frequency.

Analyses of sister-chromatid exchange and cell-cycle kinetics in mouse T- and B-lymphocytes from peripheral blood cultures

A reliable mouse peripheral blood lymphocyte culture assay has been developed for sister-chromatid exchange analysis. Crucial aspects for optimal mitogenesis include: (1) the addition of 5 X 10(5) leucocytes/ml culture; (2) the use of animals with leucocyte counts from 5 to 7 X 10(6)/ml; and (3) the addition of 6% mouse plasma for the first 24 h of a total 54-h incubation. When 7 micrograms phytohemagglutinin/ml were used to stimulate T-lymphocytes, the mitotic index was 3.4 +/- 0.3%, 28 +/- 2.3% of the metaphases were in first-division, and the SCE frequency/metaphase was 7.3 +/- 0.2 (n = 14 mice). When B-lymphocytes were stimulated with 60 micrograms lipopolysaccharide/ml, the mitotic index was 4.5 +/- 0.3%, 64 +/- 3.3% of the metaphases were in first-division, and the SCE frequency/metaphase was 4.6 +/- 0.1 (n = 7 mice). This culture method consistently yields sufficient numbers of metaphases from both B- and T-lymphocytes for SCE and chromosome-breakage studies.