Differences in the satellite association pattern in the human population

Lead-induced genotoxicity in lymphocytes from peripheral blood samples of humans: in vitro studies

Lead is a known toxicant that has been implicated in encephalopathy in children and may affect the gastrointestinal and hematopoietic and other systems in adults. In fact, lead has been shown to compete with calcium for entry into the synaptosome and induce toxic effects. The aim of the current study was to evaluate the cytotoxic and genotoxic effects of lead by using lymphocytes from human peripheral blood in vitro. The LC50 for lead nitrate as determined by Trypan blue dye exclusion technique was found to be 3.14 mM. Chromosomal aberration frequency at sublethal doses (1/10 of LC50) as determined by examining the metaphase chromosomes (karyotyping) did not show significant aberrations except for some aneuploidy and about 2-4% gaps, breaks (3-4%), and about 5% satellite associations. However, significant DNA damage was determined by SCGE (Comet assay). The comet tail length proportionately increased with increasing lead nitrate concentration. Thus, Pb can induce single-strand DNA breaks, possibly by competing with metal binding sites.

Effect of sulphur dioxide exposure on human chromosomes

The genotoxic effects of an average concentration of 41.7 mg/m3 of SO2 exposure on 42 workers of a fertilizer factory were investigated. Mitotic index (MI), chromosomal aberrations (CAs), sister-chromatid exchanges (SCEs) and satellite associations (SA) were observed. In SO2-exposed workers, a higher mitotic index (7.09) was recorded in comparison to controls (4.34). The MI, however, declined with duration of exposure. Satellite associations showed a two-fold increase (17.1) as compared to controls (8.11). Among chromosomes, D-G group associations were the highest (7.43%), while 3D type associations were the lowest (0.4%). There was a significant difference (p < 0.05) in the mean frequency of CAs per cell in the exposed workers (3.262%) and the controls (0.833%). The mean frequency of SCEs per cell increased from 3.32 +/- 0.1 in controls to 7.72 +/- 0.19 in the exposed group. The difference was significant (p < 0.05). In smokers, alcoholics and smoker-alcoholics, the frequency of CAs and SCEs per cell was significantly higher than the non-smokers and non-alcoholics, both in the controls and the SO2-exposed workers and showed a correlation with the duration of exposure. SO2 is therefore a clastogenic and genotoxic agent for which necessary precautions must be taken.

High degree of satellite association and decreased nucleolar organizer activity in cystic fibrosis subjects

The effect of colchicine at concentrations of 0.25 X 10(-6) M, 1.0 X 10(-6) M, and 2.0 X 10(-6) M on the degree of satellite association (SA) was estimated in phytohemagglutinin-stimulated lymphocytes of individuals in the following groups: cystic fibrosis (CF) children, obligatory CF heterozygotes, control children, and control adults. In all four groups increasing colchicine concentration caused a higher degree of SA. The degree of SA differed between the two control age groups (children vs adults) only at the lowest concentration. CF patients had a significantly higher degree of SA than CF heterozygotes and than control individuals at all colchicine concentrations; CF heterozygotes had a significantly higher degree of SA than control adults at the low and intermediate concentrations. There was a strong interaction between genotype and colchicine concentration: the differences between the CF patients and the control individuals were most distinct at the intermediate concentration and between the carriers and the control individuals at the low colchicine concentration. Colchicine had no effect on the activity of the nucleolar organizer regions (NORs), as measured by the frequency of the silver-stained NORs (AgNORs), while the frequency of AgNORs in CF patients was significantly lower as compared to control individuals. Yet, the increase in the degree of SA caused by the CF mutant allele involved specifically the satellited chromosomes carrying active NORs.

Evaluation of genotoxicity of ampicillin and carbenicillin on human lymphocytes in vitro: chromosome aberrations, mitotic index, cell cycle kinetics, satellite associations of acrocentric chromosomes and sister chromatid exchanges

A large number of drugs have been introduced into man's environment in recent years, many of which have been shown to have mutagenic, teratogenic and carcinogenic effects. Keeping in view the potential hazardous effects of drugs and chemicals, it is desirable to test new drugs for their genotoxic effects prior to widespread use. In the present investigation genetic effects of ampicillin and carbenicillin were studied in vitro in human lymphocytes using a number of end-points. These drugs were added at a range of concentrations and times during a 72h culture period. Concentrations corresponding to the plasma level after receiving therapeutic doses as well as concentrations higher than the plasma levels were examined. Neither drug affected the frequency of chromosome aberrations, satellite associations, mitotic index and cell turnover rate at plasma level concentrations. However, all these parameters were affected at higher concentrations. The frequency of SCEs was not increased with both the drugs irrespective of the concentrations or durations of treatment, suggesting that the mechanisms leading to the formation of SCEs and chromosome aberrations are different. Both ampicillin and carbenicillin were genetically non-toxic for the end points measured and non-clastogenic in vitro at therapeutic doses. However, previous studies have shown ampicillin to be clastogenic in vivo. For evaluation of genetic toxicity, drugs should be tested both in vitro and in vivo.

Cytogenetic effect of colistin on human lymphocytes in vitro: chromosome aberrations, sister chromatid exchanges, mitotic index, cell cycle kinetics, and acrocentric associations

Colistin, a peptide antibiotic, was tested at three different concentrations--71, 142, and 214 units/ml. One hundred forty-two units per milliliter corresponds to the plasma level after receiving therapeutic dose. There was a dose-dependent increase in the frequency of chromosome aberrations irrespective of the duration of treatment (T0, T24, T48). This antibiotic decreased the mitotic index and delayed the cell turn over rate indicating inhibition of DNA synthesis by it. Inhibition of DNA synthesis probably results in increase in the frequency of chromosome aberrations. Frequency of satellite associations of acrocentric chromosomes was increased with increasing concentration of the drug, but the differences at three concentrations were not significant compared to controls. There was no increase in the frequency of SCEs at any concentration or duration of treatment compared to controls. It appears that colistin induces the type of lesions that lead to chromosome aberrations and not to SCEs.

Relationships between satellite association and the occurrence of non-disjunction in man

It has been reported that there is an increased incidence of Down's syndrome among the children of parents who have been exposed to ionizing radiations for radiodiagnostic or radiotherapeutic reasons. Work with Drosophila, mice and human lymphocytes has shown that irradiation with X- or gamma-rays induces aneuploidy, presumably by non-disjunction. It has been suggested that in man the frequency of satellite association (s.a.) of acrocentric chromosomes may be involved in the causation of chromosomal non-disjunction. In the present work the effects of radiation on s.a. have, therefore, been investigated. The frequency of s.a. between acrocentric chromosomes was determined after the exposure of human blood from normal and chromosomally abnormal individuals to various small doses of Co-60 gamma-rays. The criteria of Zang and Back were used for the evaluation of s.a. complexes. No effects of radiation on the frequency of s.a. were apparent within the dose range investigated. The same result was obtained when s.a. was evaluated using the silver-staining technique in which physical connections between the associating satellites may be observed and the association complexes evaluated directly. The effects of other radiation sources have also been investigated.

Satellite associations of human acrocentric chromosomes identified by trypsin treatment at metaphase

In the present work 2526 metaphase plates were prepared from 28 normal adult individuals (12 male and 16 female) and then treated with the trypsin method in order to recognize the acrocentric chromosomes involved in the satellite associations. From our data it can be inferred that while the pattern of association of D--D, D--G and G--G groups seems to be random, there exists some preferential association, particularly between the pairs 13--14, 13--13, 13--21 and 21--21. This non-random participation of the acrocentric chromosomes could fit with the new concepts of interphase/metaphase organization of the chromatin fibre.

Distribution of human chromosomes on the metaphase plate using banding techniques

This study deals with the problem of distribution of the 46 centromeres on the human metaphase plate after treatment with colchicine and hypotonic shock. The location of the centromeres was recorded for 400 metaphases in which the chromosomes were identified by bands. A quantitative analysis of chromosome distribution ascertains the absence of proximities between homologous chromosomes. The already known ones between acrocentric chromosomes are found at a very high level. The nature and intensity of these proximities vary from one sample to another as is the case between heterologues. A three-dimensional graphic technique is proposed to summarize all of the interchromosome proximities.