Sister-chromatid exchanges in lymphocytes from infants with Down's syndrome

Cell-cycle kinetics of cell lines from patients with chromosomal mosaicism

Lymphocyte cultures from five patients with chromosomal mosaicism (two 47,XY,+21/46,XY, one 47,XX,+21/46,XX, one 45,X/46,XX, and one 47,XXY/46,XY) were studied using sister chromatid differential staining technique for cell kinetic evaluation. Aneuploid and normal cell lines were compared to identify changes in cellular proliferation in vitro that could be related to cellular selective advantage and cell-line-proportion changes occurring with age. Comparison of the percentage of cells in different cell generations in 48, 72, and 96 h-cultures shows no differences between the aneuploid and normal cell lines indicating that cell-cycle kinetics is similar in these cells in vitro.

Genomic instability in Down syndrome and Fanconi anemia assessed by micronucleus analysis and single-cell gel electrophoresis

Cytokinesis-block micronucleus (CB-MN) assay and single-cell gel electrophoresis (SCGE) were employed to analyze leukocytes from 14 Fanconi anemia (FA) patients, 30 Down syndrome (DS) patients, and 30 control individuals, to examine the sensitivity of these techniques to detect genomic instability in these 2 diseases. The DS patients presented increased DNA damage as measured by SCGE in relation to controls. The frequencies of micronuclei and dicentric bridges were similar to those of controls. Micronucleus frequency, dicentric bridge frequencies, and DNA damage were higher in FA patients than in controls. The high frequency of micronuclei observed in FA patients seems to be due to clastogenic events, because an increase in the frequency of dicentric bridges was also observed. Micronuclei are expressed mutations and need cell division to appear. The damage detected by SCGE is repairable, and does not require cell division. Under alkaline conditions, SCGE assesses double- and single-strand breaks and alkali-labile sites. The 2 methods are efficient for monitoring mutagenic events in exposed populations or in individuals with genetic instability. While the damage measured by micronucleus analysis is accumulated over a long period of time, DNA damage measured by SCGE reflects recent, unrepaired events.

Increased steady state mRNA levels of DNA-repair genes XRCC1, ERCC2 and ERCC3 in brain of patients with Down syndrome

Although deficient DNA-repair was proposed for neurodegenerative disorders including Down Syndrome (DS), repair genes for nucleotide excision repair or X-ray repair have not been studied in brain yet. As one of the hypotheses for the pathogenesis of brain damage in DS is oxidative stress and cells of patients with DS are more susceptible to ionizing irradiation, we decided to study ERCC2, ERCC3 and XRCC1, representatives of repair genes known to be involved in the repair of oxidative DNA-damage. mRNA steady state levels of ERCC2, ERCC3, XRCC1, a transcription activator (TAF-DBP) and an elongation factor (EF1A) were determined and normalized versus the housekeeping gene beta-actin in five individual brain regions of nine controls and nine DS patients. Although different in the individual regions, DNA-repair genes were consistently higher in temporal, parietal and occipital lobes of patients with DS accompanied by comparable changes of TFA-DBP and EF1A. Our results are the first to describe DNA-repair gene patterns in human brain regions providing the basis for further studies in this area. We showed that DNA-repair genes ERCC2 and ERCC3 (excision-repair-cross-complementing-) for nucleotide excision repair and XRCC1 (X-ray-repair-cross-complementing-) for X-ray-repair, were increased at the transcriptional level with the possible biological meaning that this increase may be compatible with permanent (oxidative?) DNA damage.

Cytogenetic effects of copper-containing intrauterine contraceptive device (IUCD) on blood lymphocytes

Forty women using the copper-containing intrauterine contraceptive device (IUCD) for various periods and 22 control women were studied. The copper and zinc levels were measured in the plasma of the IUCD users and the control group. Chromosomal analyses were performed on blood lymphocytes of the same groups. Results showed that plasma copper level was significantly higher in the IUCD users than in that of controls (1.25+/-0.14 microg/ml vs. 0.89+/-0.04 microg/ml, P<0. 05). A decline in plasma zinc level from 2.90+/-0.41 microg/ml to 1. 27+/-0.13 microg/ml, P<0.05, with a significant alteration in plasma copper/zinc ratio was also measured in the IUCD women (62% vs. 111%, P<0.05). Chromosomal aberrations (4.47+/-1.40 vs. 0.62+/-0.12/100 cell, P<0.01) and high frequencies of sister chromatid exchanges (8. 79+/-0.46 vs. 6.59+/-0.19 SCE/cell, P<0.01) were evident in the IUCD women especially in those using the IUCD for more than 24 months. The combination of high copper plasma level, chromosomal aberrations and the increased frequency of sister chromatid exchange may support the existence of a positive correlation between the long term use of the IUCDs and DNA damage in the host somatic cells.

Expression of DNA excision-repair-cross-complementing proteins p80 and p89 in brain of patients with Down Syndrome and Alzheimer's disease

Although deficient DNA repair was proposed for neurodegenerative disorders including Down syndrome (DS), repair proteins for nucleotide excision repair have not been studied in brain yet. As one of the hypotheses for the pathogenesis of brain damage in DS and Alzheimer's disease (AD), is oxidative stress, and cells of patients with DS were shown to be more susceptible to ionizing irradiation. We decided to study expression of excision repair-cross-complementing (ERCC) gene products, proteins 80 and 89, representatives of repair genes known to be involved in the repair of different types of DNA damage. ERCC2-protein 80 kDa and ERCC3-protein p89 were determined in five individual brain regions of controls, aged DS and AD patients. Although different in the individual regions, DNA repair proteins were consistently higher in temporal and frontal lobes of patients with DS and higher in all brain regions of patients with AD. Our results are the first to describe DNA repair gene protein patterns in human brain regions providing the basis for further studies in this area. We showed that DNA repair genes ERCC2 and ERCC3 (excision-repair-cross-complementing) for nucleotide excision repair were increased at the protein level with the possible biological meaning that this increase may be compatible with and indicate ongoing (oxidative?) DNA damage.

The in vitro effect of beta-carotene and mitomycin C on SCE frequency in Down's syndrome lymphocyte cultures

Down's syndrome (DS) has the highest incidence among chromosomal disorders and is a predisposing factor in acute leukemia pathogenesis. DS patients are sensitive to both physical and chemical inducers at the DNA level. Studies on beta-carotene, an antioxidant, suggested the there is a relationship between high beta-carotene diet and reduced tumor incidence in humans indicating that beta-carotene is a chemopreventive agent against cancer. Sister chromatid exchange (SCE) is known as a sensitive parameter among the genotoxicity tests. In this study, we aimed to investigate the in vitro effect of beta-carotene on SCE frequencies in 7 DS patients and 7 healthy controls aged between 0-16 years. A direct leukomogenic agent Mitomycin-C (MMC) was used as a powerful SCE inducer. Addition of MMC to the cultures alone resulted in a significant enhancement of SCE frequencies in both groups when compared to the spontaneous values. In the study, beta-carotene seemed to decrease MMC induced mean SCE/cell values, but did not have an effect on unstimulated cells. As this is a limited study, it is hard to conclude that beta-carotene is a chemopreventive agent in DS patients, although our results seem to support other investigators' reports.

Increased sister chromatid exchanges in peripheral lymphocytes of patients with Crohn's disease

A cytogenetic study was performed using Crohn's disease patients to determine whether the presence of chromosome instability is related to Crohn's disease, a chronic inflammatory bowel disease. Sister chromatid exchange (SCE) frequencies in peripheral blood lymphocyte cultures from 22 Crohn's disease patients and an equal number of healthy controls matched for sex and age were analyzed. The mean of SCE frequency in Crohn's disease patients was 11.64 +/- 0.42 (SEM) per cell, which was significantly higher than the value of 8.38 +/- 0.22 per cell in the matched controls (p < 0.0001). The Crohn's disease patients showed significantly increased high frequency cells (HFC) as compared to those among the matched controls. There was a significant correlation between HFC frequencies of the Crohn's disease patients and the severity of their disease as determined by the number of relapses per year and the degree of chronic activity after adjusting for the smoking status (r = 0.54, p = 0.011). In both smokers and non-smokers, the mean SCE and HFC frequencies of the patients were significantly higher than those of the controls. These results suggest that Crohn's disease is a condition with increased chromosome instability characterized by a high level of SCE frequencies which are associated with the inflammatory condition itself.

Chromosome sensitivity to bleomycin in G2 lymphocytes from Down syndrome patients

Several studies have demonstrated that lymphocytes from patients with Down syndrome (DS) exhibit an increased frequency of chromosome aberrations when they are exposed to ionizing radiation or to chemicals at the G0 or G1 phases of the cell cycle, but not at G2, when compared to normal subjects. To determine the susceptibility of DS lymphocytes at G2 phase, bleomycin, a radiomimetic agent, was used to induce DNA breaks in blood cultures from 24 Down syndrome patients. All the patients with DS showed free trisomy 21 (47,XX + 21 or 47,XY + 21). Individuals that showed an average number of chromatid breaks per cell higher than 0.8 were considered sensitive to the drug. No control child showed susceptibility to bleomycin, and among the 24 patients with DS, only one was sensitive to the drug. No significant difference was observed between the two groups, regarding chromatid break frequencies in treated G2 lymphocytes. The distribution of bleomycin-induced breaks in each group of chromosomes was similar for DS and controls. No significant difference was found in the response to bleomycin between male and female subjects. Probably, the main factor involved in chromosome sensitivity of lymphocytes from patients with DS is the phase of the cell cycle in which the cell is treated.

Cytogenetic biomonitoring of a population of children allegedly exposed to environmental pollutants. Phase 2: Results of a three-year longitudinal study

Our previous cytogenetic biomonitoring of a group of inhabitants in a village (Mellery, Belgium) where exposure to a mixture of toxic environmental pollutants, (probably originating from a neighbouring chemical waste disposal site) was suspected, showed that difference in the SCE and HFC bioassays was more pronounced for children. The results of follow-up study in 1992 confirmed this surprising conclusion by an even higher incidence. As very few studies have been performed on the levels of children's biomarkers, this group of exposed populations needed to be explored further. Do children residing in the vicinity of hazardous waste sites indeed represent a population at higher risk? In the present study, we compare the performance of various bioassays (SCE, HFC, SSB and MN) in extended exposed and reference children's groups. Simultaneously, in the exposed group, we followed variation in the lymphocyte SCE frequencies as a function of time. Reversibility of the latter biomarker was ascertained subsequent to a preliminary technical remediation of the disposal site. We compared these data with those obtained from a synchronous cross-sectional study on a group of children living near a similar chemical disposal site. The two exposed populations did not differ from the reference population regarding to the SCE and HFC mean levels. Comparisons of the mean levels of the two other biomarkers, SSB and MN, showed no difference between the Mellery exposed children and the reference group from Wavre whereas significant differences appeared when the Hensies group is compared either to the Mellery or to the Wavre reference group.

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.