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

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.

Sister chromatid exchange and cell cycle patterns of normal human bone marrow cells after in vitro exposure to cytostatic drugs

The effect of different cytostatic chemotherapeutic drugs on the frequency of sister chromatid exchanges and growth kinetics of the bone marrow cells in normal adults was studied by means of an in vitro bromodeoxyuridine chromosome labeling method. Cytosine arabinoside, harringtonine, methotrexate, vincristine, and 6-mercaptopurine were tested. Three of these agents induced significantly high frequency of sister chromatid exchange (p less than 0.01 or p less than 0.05). The sister chromatid exchange frequency induced by cytosine arabinoside and that induced by 6-mercaptopurine were higher than those of the control group. The increased frequency of sister chromatid exchange predominated in C and A group chromosomes. At the concentration adopted by the authors, the growth kinetics were little influenced by these drugs.

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.

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 exchange in normal and Ph1-positive leukemic cells after mitomycin-C treatment in vitro

The sister chromatid exchange (SCE) frequency was investigated in normal bone marrow and Ph1-positive cells of chronic myelocytic leukemia (CML) patients with and without mitomycin-C (MMC) treatment in vitro. Even though the spontaneous SCE frequency was found to be significantly lower in CML cells, the absolute SCE values after MMC treatment did not differ between leukemic and normal cells, and this seems to indicate an equilization of SCE rates. However, the fact that leukemic cells with lower spontaneous SCE rates need a further increase of SCE to reach values equal to those of normal cells might indicate a somewhat higher susceptibility of leukemic cells to DNA damage by MMC. This interpretation appears to be confirmed by the fact that the inhibition of cellular proliferation at higher MMC doses considerably reduced the number of leukemic cells that was able to divide twice during a given culture time.