Sister chromatid exchanges in cultured peripheral lymphocytes from twins

Atypically low spontaneous sister chromatid exchange formation in uveal melanoma

Uveal melanoma (UM) is the most common primary intraocular cancer of adults and is characterized by several well-established chromosomal changes. More recently, a specific mutation of guanine nucleotide binding protein Gq alpha subunit (GNAQ) has also been identified in a proportion of UM. Although some of these alterations have been suggested to be early changes, the genetic alterations responsible for the development of UM have yet to be clearly determined. Cancers are characterized by increased genetic instability, and analysis of established cancer cell lines and blood from cancer patients has universally been associated with an increased level of sister chromatid exchange (SCE). We have observed that the spontaneous frequency of SCE in primary cultures of UM and UM-derived cell lines is decreased below normal baseline levels, a phenomenon unique to UM when compared with multiple other cancers. This finding was specific to the tumor and not found in lymphocytes from the patients. Although we cannot exclude the possibility that low SCE (LSCE) is peculiar to the uveal melanocytes lineage, as it was consistently observed in all UM studied, regardless of other genetic defects, we propose that this phenomenon contributes to the molecular pathogenesis of UM.

Spontaneous sister chromatid exchange and chromosome aberration frequency in humans: the familial effect

The possible effects of environmental and genetic factors on spontaneous frequencies of sister chromatid exchanges (SCEs) and cells with chromosome aberrations (CAs) in human lymphocytes were investigated by analysing 177 completed families (mother, father and at least one child). After removing the effects of methodological, biological and life-style factors by the use of multifactor analysis of variance (MANOVA), SCEs and CAs residuals were analysed by simple correlation analysis and principal component analysis. SCEs and CAs inter-familiar variability was higher than that found within families. A significant correlation was found between the average SCE frequencies shared by parents (the so-called 'midpoint parents', or 'midparent') and offspring (linear slope b=0.26+/-0.07, p<0.05), but also between mother and father (b=0.23+/-0.11, p<0.05) suggesting the presence of an effective environmental factor. The midparent-offspring correlation was found to be sustained by the mother-offspring relationship (b=0.28+/-0.08, p<0.05), being the father-offspring correlation not significant (b=0.16+/-0.11, p0.05). Concerning CAs, no statistically significant correlation between parents was found, but the strong relationship between mother and offspring was confirmed (b=0.468+/-0.11, p<0.001). The SCEs correlation between mother vs. offspring disappeared for older offspring (over 23 years old). The obtained findings strongly showed that the genetic make-up is barely detectable in the presence of domestic environment factors which are shown to play the major role in determining the interfamilial variability of SCE and CA in a general population. These results strengthen the suitability of the use of SCEs and CAs analysis in human cytogenetic surveillance for the detection of effective environmental factors.

Sister chromatid exchange frequencies in a group of individuals with unfavorable reproductive health

Sister chromatid exchange (SCE) frequencies and other cytogenetic parameters were investigated in peripheral blood lymphocytes from 92 subjects comprising 44 parents of malformed offspring or repeated fetal wastage (Group I) and 48 controls, age and sex matched, having normal reproductive health (Group II). The karyotypes were normal and the mean mitotic indices were comparable in both groups. The mean frequency of SCE per metaphase in Group I (8.67 +/- 0.32) was significantly higher than the mean for group II (6.65 +/- 0.16), and the cellular replicative index in Group I (1.78 +/- 0.04) was significantly different from that of Group II (1.66 +/- 0.03). The results are discussed in the light of the present understanding of the etiology and mechanism of production of sister chromatid exchanges.

Increased UV-induced sister-chromatid exchange in cultured fibroblasts of first-degree relatives of melanoma patients

Cultured fibroblasts of 17 first-degree relatives of familial melanoma patients and six first-degree relatives of cutaneous melanoma (CMM) patients with multiple CMM primaries were tested for in vitro sensitivity to UV light. Fibroblasts of nine familial CMM patients with a known UV-sensitivity and 19 healthy probands served as a control. Sister chromatid exchange (SCE) was used as a parameter to detect UV-induced genotoxic damage. We found significantly (p less than 0.001) increased UV-induced SCE levels in familial melanoma patients, as well as in first-degree relatives of familial melanoma patients (p less than 0.001) after UV-A,B irradiation (375 J/m2), compared to the healthy probands without a family history of CMM. A significant (p less than 0.001) increase of UV-induced SCE was also observed in the relatives of CMM patients with multiple CMM primaries. In addition, the spontaneous SCE were significantly increased (p less than 0.05) in familial CMM patients. This study shows that increased UV sensitivity is a familial phenomenon. It is consistent with the concept of a genetic predisposition to CMM, which is based on increased UV sensitivity and may help to define groups with an elevated risk of developing cutaneous malignant melanoma.

Analysis of sister-chromatid exchanges (SCEs) in familial and sporadic multiple sclerosis

The levels of sister-chromatid exchanges (SCEs) were calculated in 17 multiple sclerosis (MS) patients (14 familial and 3 sporadic cases) and 16 healthy controls matched for sex and age. The SCEs were significantly increased for MS patients (p = 0.0002), while there was no statistically significant difference between men and women and between younger and older subjects in both groups. Such factors as familial occurrence and severity of MS, smoking habits, and distribution of lymphocyte subpopulations were discussed. Although there was a significant difference between the MS patients taking medication and the patients taking none (p = 0.038), the latter were still significantly different from the controls (p = 0.035), supporting the fact that the disease itself increases SCEs. Our study, done with 2 doses of BrdU, also shows that the increased SCEs in MS patients are not due to a hypersensitivity to this substance known to be an inducer of SCEs. Thus we suggest that the increased SCEs found are probably disease-related.

A study of multiple biological markers in twins

Genetic and environmental influences on the phenotypic expressions of several biological markers were studied in 18 monozygous (MZ) and 8 dizygous (DZ) twin pairs. Zygosity was determined using ABO, Rh, and HLA. The biomarkers studied included: T & B lymphocytes, suppressor and helper T lymphocytes (T gamma, T mu), T cell (PHA) mitogen activation (MA), serum immunoglobulins (IgA, IgM, and IgG), plasma carcinoembryonic antigen (CEA), aryl-hydrocarbon hydroxylase (AHH) and sister chromatid exchange (SCE) in lymphocytes. Temporal variation of markers over a 6-month period was not significant. The mean absolute differences between levels from first and second blood draws were less than one standard deviation. Variability associated with age was not significant. Females had higher levels of T lymphocytes than males. A gender related association was observed for the IgM immunoglobulin test: females had a higher mean level of IgM. Smoking was found to influence the levels of SCE, T helper lymphocytes and mitogen activation. The variability of these biomarkers within and between twin pairs was quantified. Immunoglobulin levels, particularly that of IgM, showed statistically greater similarity within MZ twins than within DZ twins. Several other markers suggested heritability.

Sister chromatid exchange with and without in vitro mutagen induction in cultured skin fibroblasts from patients with adenomatosis of the colon and rectum

Fibroblast cell strains were obtained from skin biopsies taken from patients with adenomatosis of the colon and rectum (ACR), and their relatives. A total of 50 different fibroblast strains were tested for their frequencies of sister chromatid exchange (SCE) in vitro. These strains included nine from patients with the Gardner syndrome, 21 from patients with non-Gardner ACR, and 20 cell strains from healthy relatives who were not at an increased risk for ACR. In 23 strains, the SCE frequencies after in vitro exposure to N-methyl-N'-nitro-N-nitroso-guanidine (MNNG) were also determined. Both with and without MNNG induction, SCE values in the Gardner strains were found to be significantly higher than in the control strains (p less than 0.02 and p less than 0.03, respectively). Non-Gardner ACR strains differed only slightly from controls, thus making the difference between the control group and the pooled Gardner + non-Gardner ACR group not significant. In all groups, there was a significant increase in SCE after MNNG exposure, and those strains which had low SCE values spontaneously, also tended to have relatively moderate SCE values after MNNG induction. There was no significant difference between the ratios of SCE values with and without MNNG exposure in the different groups.

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.

Sister chromatid exchange in the centromere and centromeric area

Central and peripheral sister chromatid exchanges (SCE) were evaluated separately in human phytohemagglutinin (PHA)-stimulated lymphocytes after culture for 72 h in 5-bromodeoxyuridine (BrdU) containing medium. At the same time, the length of chromosome No. 1 was measured in 10 metaphases per case and the mean value taken as a representative parameter for the contraction of chromosomes. The statistical analysis of regression revealed a close relationship between the percentage of SCE observed in the centromere and the contraction state of chromosomes (P less than or equal to 0.01). A statistically significant increase of central exchanges was seen in more condensed chromosomes, due to the difficulty in differentiating clearly between centric and pericentric exchanges. Consequently, if exchanges in the centromere are omitted from evaluation, this would lead to spuriously low SCE rates in more contracted chromosomes. In order to exclude the variable factor of chromosome contraction in SCE studies, we highly recommend inclusion of counts of central exchanges. Results obtained on chromosomes with twisted chromatids, a situation which tends to stimulate SCE, should be omitted.

Sister chromatid exchanges and structural chromosome aberrations in relation to age and sex

Sister chromatid exchanges (SCE) and structural chromosome aberrations were analyzed in peripheral blood lymphocytes of 100 individuals, and correlated to age and sex. No correlation was found between the frequency of SCE and age, but older individuals had significantly more structural aberrations than younger. Females had significantly more SCE as well as structural chromosome aberrations than males. The positive correlations of SCE and structural aberrations to age and sex were also significant when these factors, as well as smoking habits, were taken into consideration in an analysis of covariance.

Effects of age, sex and genes on sister chromatid exchange

Sister chromatid exchange (SCE) was studied in cultured lymphocytes from a limited series of 21 like-sexed twin pairs; 11 monozygotic (MZ) and 10 dizygotic (DZ) pairs. The 18 subjects, who were between 57 and 61 years old, had an SCE mean value (mean) of 8.0 whereas the 24 subjects between 33 and 39 years of age had a mean of 6.8. The difference was statistically significant (P less than 0.001). The effect of age appeared to be present in both sexes. No significant difference was found between females (mean = 7.3) and males (mean = 7.5), nor between smokers (mean = 7.3) and non-smokers (mean = 7.4). Drug users had a slightly higher mean (mean = 7.9) than non-users (mean = 7.0) (P less than 0.05). This trend was found in each age group. The within-pair variance was slightly higher in DZ than in MZ pairs. The difference was not significant. We conclude that genetic factors are probably not a major source of subject variation in SCE mean value.

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

Human B and T lymphocytes differ in the rate of cell proliferation and frequency of sister chromatid exchange (SCE) when cultured separately in short-term cultures. This difference could theoretically be responsible for part of the variation in the SCE-frequency previously observed among healthy subjects since there is individual variation in the proportion of B and T cells in the peripheral blood. We have therefore studied cell proliferation and SCE-frequency in conventional short-term cultures of lymphocytes from 28 healthy subjects with different proportions of B and T cells. The percentage of B or T lymphocytes did not correlate with the SCE-frequency, nor with the rate of cell proliferation in culture. However, a significantly higher SCE-frequency was found in slowly proliferating cultures than in cultures with a high rate of turn over. Thus, the rate of cell proliferation appears to be an important determinant of the SCE-frequency in conventional lymphocyte cultures. Although the data do not exclude attribution of the difference in SCE- frequency between rapidly and slowly growing cultures to differences in subpopulations of lymphocytes, it appears less likely that B and T cells constitute these tentative subpopulations.