Sister Chromatid Exchange Formation Research Articles

Characterization of new transgenic Big Blue� mouse and rat primary fibroblast cell strains for use in molecular toxicology studies

We have established and characterized primary mouse and rat cell strains for studies designed to complement in vivo gene mutation assays using the Big Blue(R) mouse or rat. Primary fibroblast cell strains, designated BBM1 and BBR1, were derived from a transgenic male Big Blue(R) B6C3F1 mouse and from a male Big Blue(R) Fischer-344 rat, respectively. Both BBM1 and BBR1 are genetically stable and mostly diploid. Both cell strains have low spontaneous frequencies of mutation at the lacI and cII loci as well as low frequencies of sister chromatid exchange and micronuclei formation. In addition, N-ethyl-N-nitrosourea (ENU) induces mutations at the cII locus in both BBM1 and BBR1 cells. These new primary Big Blue(R) mouse (BBM1) and rat (BBR1) fibroblast cell strains represent useful new models for molecular toxicology studies. Environ. Mol. Mutagen. 34:90-96, 1999 Published 1999 Wiley-Liss, Inc.

Critical steps in alkylation-induced aberration formation

The process leading to chromosomal aberrations as a consequence of DNA damage is probably best understood for simple alkylating agents. Various functions have been identified which are involved in the conversion of critical primary lesions to aberrations. O 6-methylguanine is considered to be an important critical preclastogenic DNA lesion, which is converted to aberrations in conjunction with faulty mismatch repair. It operates at sites of O 6-methylguanine-thymine mispairing, leading to not yet defined secondary lesions. It is proposed that these secondary lesions cause DNA replication inhibition, which triggers recombination (sister-chromatid exchange formation) and is a critical event involved in aberration production in the second post-treatment replication cycle. For N-alkylations, DNA replication inhibition may result from depurinations and base excision repair intermediates causing a block of replication. In consequence, sister-chromatid exchanges as well as chromosomal aberrations are formed in the first post-treatment replication cycle. Data are available to show that DNA replication inhibition and aberration production in the first post-treatment replication cycle are interrelated.

A high yield of translocations parallels the high yield of sister chromatid exchanges in the CHO mutant EM9

The fluorescence plus Giemsa (FPG) and fluorescence in situ hybridization (FISH) techniques have been used to determine, respectively, the frequencies of sister chromatid exchanges (SCEs) and stable chromosome aberrations (translocations) induced by different concentrations of BrdU in the Chinese hamster ovary cell mutant EM9 and its parental line AA8. The results indicate that BrdU induced a high frequency of SCEs and translocations in EM9 as compared with AA8, and that the translocation/dicentric ratio was also higher in the mutant cell line than in the parental cell line in both untreated and BrdU-treated cultures. These observations may indicate a possible relationship between the molecular mechanisms involved in the formation of SCEs and translocations.

Chromosomal instability, reproductive cell death and apoptosis induced by O6-methylguanine in Mex −, Mex + and methylation-tolerant mismatch repair compromised cells: facts and models

O 6-Methylguanine ( O 6-MeG) is induced in DNA by methylating environmental carcinogens and various cytostatic drugs. It is repaired by O 6-methylguanine-DNA methyltransferase (MGMT). If not repaired prior to replication, the lesion generates gene mutations and leads to cell death, sister chromatid exchanges (SCEs), chromosomal aberrations and malignant transformation. To address the question of how O 6-MeG is transformed into genotoxic effects, isogenic Chinese hamster cell lines either not expressing MGMT (phenotypically Mex −), expressing MGMT (Mex +) or exhibiting the tolerance phenotype (Mex −, methylation resistant) were compared as to their clastogenic response. Mex − cells were more sensitive than Mex + cells to N-methyl- N′-nitro- N-nitrosoguanidine (MNNG)-induced chromosomal breakage, with marked differences in sensitivity depending on recovery time. At early recovery time, when cells out of the first post-treatment mitosis were scored, aberration frequency was about 40% reduced in Mex + as compared to Mex − cells. At later stages of recovery when cells out of the second post-treatment mitosis were analyzed, the frequency of aberrations increased strongly in Mex − cells whereas it dropped to nearly control level in Mex + cells. From this we conclude that, in the first post-treatment replication cycle of Mex − cells, only a minor part of aberrations (<40%) was due to O 6-MeG whereas, in the second post-treatment replication cycle, the major part of aberrations (>90%) was caused by the lesion. Thus, O 6-MeG is a potent clastogenic DNA damage that needs two DNA replication cycles in order to be transformed with high efficiency into aberrations. The same holds true for sister chromatid exchanges (SCEs). MNNG is highly potent in inducing SCEs in Mex − cells in the second replication cycle after alkylation. Under these conditions, SCE induction is nearly completely prevented by the expression of MGMT. This is opposed to SCE induction in the first post-treatment replication cycle, where higher doses of MNNG were required to induce SCEs and no protective effect of MGMT was observed. This indicates that SCEs induced in the first replication cycle after alkylation are due to other lesions than O 6-MeG. In methylation tolerant cells, which are characterized by impaired G–T mismatch binding and MSH2 expression, aberration frequency induced by MNNG was weakly reduced in the first and strongly reduced in the second post-treatment mitoses, as compared to CHO wild-type cells. The results indicate that mismatch repair of O 6-MeG–T mispairs is decisively involved in O 6-MeG born chromosomal instability and recombination. We also show that Mex + and methylation tolerant cells are more resistant than Mex − cells with regard to induction of apoptosis, indicating O 6-MeG to be also an apoptosis-inducing lesion. The data are discussed as to the mechanism of cytotoxicity, aberration and SCE formation in cells treated with a methylating agent.

Effects of ICRF-193, a catalytic inhibitor of DNA topoisomerase II, on sister chromatid exchange.

To investigate whether mammalian DNA topoisomerase II is directly involved in recombination events, the effects of ICRF-193, a specific catalytic inhibitor on sister chromatid exchange (SCE), were examined in MR-6 cells. ICRF-193 only slightly elevated SCE formation after 3 or 44 h treatments, while VP-16, a cleavable complex forming type of topoisomerase II inhibitor, caused significant enhancement. ICRF-193 had no effect on N-methyl-N'-nitro-N-nitrosoguanidine-induced SCE formation. It would thus appear that the inhibition of topoisomerase II does not affect recombinational repair, and that topoisomerase II inhibitors such as VP-16 and 4'-(9-acridinyl amino) methane sulfon-m-anisidide induce SCE through production of DNA strand breaks, rather than by inhibiting the enzyme activity.

Comparison of Different Genotoxic Tests for Biological Monitoring of Coke Oven Workers. Preliminary Results

ABSTRACT Chemical by-products of coke production are classified by IARC as carcinogenic in humans. Polycylic aromatic hydrocarbons (PAH) are the main compounds involved in carcinogenic and mutagenic activities of coke oven smokes, but many other compounds are present in emissions and could be involved in these activities. PAH analysis of the atmosphere indicated external contamination, but is not sufficient to evaluate the risk for exposed workers. The aim of this study was to evaluate relationship between atmospheric analysis of PAH and genotoxic markers in coke oven workers'white cells compared to controls. One hundred fifty-five exposed workers'samples were analyzed. They were selected in 5 coke production sites using a complete questionnaire allowing one to exclude all confounding factors. Two equal groups of smokers and nonsmokers were analysed. Analysis of chromosomal aberrations (CA), sister chromatid exchange (SCE), micronucleus (MN) and DNA-adduct formation using 32P-postlabelling were performed on leucocytes. Each worker was equiped with an individual pump during the shift, for analysis of 16 PAH. All markers were strongly modified by smoking habits. In smokers, CA, SCE and MN were not influenced by exposure to PAH. The number of DNA-adducts was increased with PAH concentration. In non smokers, we have observed an increaseof breaks / cells and of the percentage of cells with aberrations. Number of MN and SCE were unchanged. The number and the amount of DNA-adducts were strongly increased in exposed workers. DNA-adducts appear to be the best marker for genotoxic risk assessment.

On the importance of DNA strand breaks as the first event to initiate sister chromatid exchange (SCE): experiments with restriction endonuclease BglI.

The exact molecular mechanism of sister chromatid exchange (SCE) is still unknown, despite the many reports dealing with this cytogenetic end point published in the last 40 years. One point to be investigated is the nature of the original lesion(s) in DNA leading to the production of SCE. Whereas, for chromosomal aberrations, the importance of DNA double-strand breaks has been well established, there is still controversy about the relative importance of strand breaks and base modifications for triggering the process of SCE formation. In the present paper, we have taken advantage of the ability of the restriction endonuclease BglI to induce SCE and have exploited the fact that preincubation with 2,3-butanedione results in the loss of BgiI ability to cut DNA, while it is still able to recognize its sequence in DNA and bind to it, to see whether this alone is enough to initiate SCE formation, or if a physical DNA double-strand break is required. Our results seem to support the necessity of DNA breaks for SCE production.

In vivo studies on genotoxicity and cogenotoxicity of ingested UICC anthophyllite asbestos.

Early cytogenetic action of oral exposure to UICC anthophyllite, an amphibole type of asbestos, was studied in Fischer-344 rats. The animals were gavaged with a suspension of untreated fibres (50 mg/kg) and fibres which had been allowed to adsorb benzo[alpha]pyrene molecules from aqueous solutions of 0.25-2.5 micrograms/ml. HPLC measurements indicated effective adsorption of the benzo[alpha]pyrene molecules on the fibres. The authors consider this system a suitable model for the drinking of water containing asbestos fibres and organic micropollutants. The formation of micronuclei and sister chromatid exchanges was studied in bone marrow samples taken from animals 24 h after oral administration of suspensions. Whereas anthophyllite fibres failed to induce cytogenetic alterations, fibres pretreated with the polycyclic aromatic solutions caused dose-dependent increase in the sister chromatid exchange frequencies. The observed cytogenetic impact can be explained by a local action of carcinogen molecules accumulated and subsequently transported. The results support the hypothesis that epidemiological evidence of carcinogenicity of asbestos in potable water may rather be explained by cogenotoxic action of the asbestos fibres and biologically active organic micropollutants adsorbed on their surface.

The diplochromosome of endoreduplicated cells: a new approach to highlight the mechanism of sister chromatid exchange.

Chinese hamster lung embryonic cells (CL1) were treated with colchicine in order to induce endoreduplication and subsequently with mitomycin-C (MMC) to induce exchanges within the diplochromosome. The use of chromosomal differential staining through incorporation of 5-bromodeoxyuridine, resulting in only one stained chromatid, has allowed the analysis of all classes of exchanges among the four chromatids of the diplochromosome. Three classes of exchanges may occur: intradiplochromatid exchanges (ICEs) between the two inner chromatids, cousin chromatid exchanges (CCEs) between one inner and one outer chromatid, and sister chromatid exchanges (SCEs) between the two sister chromatids of the diplochromosome. The results show that MMC treatment, in the last cell cycle of endoreduplication, as expected, significantly increases only the frequency of SCEs, whereas the frequency of ICEs and CCEs remains unchanged. This result supports replication models of formation of SCEs. Furthermore the fact that the number of ICEs does not increase means that the molecular mechanism of somatic crossing over is not related to that of SCE formation, or very rarely. The results also indicate a statistically significant lower induction of SCEs in endoreduplicated metaphases as compared with diploid ones both in control and MMC-treated cells. Such a result may be due to structural restrictions within the diplochromosome.

Sister chromatid exchange analysis in workers exposed to noise and vibration

Workers chronically exposed to whole-body vibration and noise are known to develop pathophysiological and psychological disturbances. The frequencies of sister chromatid exchanges (SCEs) and of cells with high frequencies of SCEs (HFCs) were analyzed in lymphocytes of 50 workers occupationally exposed to vibration and noise and of 34 controls. The exposed group included: individuals operating hand-vibrating tools (group 1), ‘test-cell operators’ (group 2) and ‘run-up’ operators (group 3) from an air base and helicopter pilots (group 4). The statistical analysis of the mean SCE count per cell was carried out by multiple regression analysis, comparing various predictor variables: exposure group, duration of exposure, age and cigarette consumption. Only cigarette consumption and exposure group were found to be significantly correlated with the mean SCE frequency. After allowing for the effects of smoking, the analysis indicates that: (1) there was no significant difference between group 1 and controls ( p > 0.05); (2) the differences between group 2 and group 0, group 3 and group 0 and group 4 and group 0 were all highly significant ( p < 0.001); (3) there was no significant difference between groups 2 and 3 ( p > 0.05), nor between groups 2 and 3 combined and group 4 ( p > 0.05); (4) exposure groups 2, 3 and 4 combined, had a significantly elevated mean SCE frequency compared to the control group ( p < 0.0001). Statistical analysis of the proportion of HFCs was consistent with these results. Our data suggest that chronic exposure to whole-body vibration and noise may lead to an increase in the level of SCEs in man. The observed effects may not reflect a direct action of these physical agents on DNA. Alternative explanations may include some of the whole-body vibration and noise-induced or stress-induced pathophysiological alterations which may indirectly induce SCE formation.

Chromosome Aberrations, Sister Chromatid Exchange and Micronuclei Formation Analysis in Mice after in vivo Exposure to Bacoside A and B.

Bacopa monniera L. (Brahmi) is an annual creeping plant has been extensive1y used in the Indian Ayurvedic medicine as a nerve tonic. A mixture of two saponins Bacoside A and B, which are the active constituents of B. monniera has been evaluated for its genotoxic activities in mice with three cytogenetic end points i.e. chromosome aberrations (CA), sister chromatid exchange (SCE) and micronuclei formation (MN). No significant differences were observed in a11 the three end points tested when compared with negative controls. Thus the overall results indicate that Bacoside A and B is not genotoxic and is safe for medicinal use.

Targeting of O6-methylguanine-DNA methyltransferase (MGMT) activity by antimessenger oligonucleotide sensitizes CHO/Mex+ transfected cells to mitozolomide

The targeting of mRNA with antisense oligonucleotides is increasingly employed to inhibit the expression of gene function. Since the level of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is decisive in protection of cells against damage produced by alkylating agents, including cytostatic drugs, the targeted inhibition of this repair activity might be of importance for therapeutic approaches. In order to investigate whether antisense targeted MGMT depletion is feasible to transiently modify the sensitivity of cells to anticancer drugs, we studied the expression of MGMT and cellular sensitivity upon inhibitor and antisense treatment using CHO transfectants expressing human MGMT. It was shown by polymerase chain reaction that antisense oligonucleotides specifically inhibited MGMT mRNA level. Nevertheless, MGMT protein was found not to be reduced significantly, as demonstrated by Western blotting. Correspondingly, no significant decrease in MGMT activity was observed, as measured 36 h after MGMT antisense oligonucleotide administration. Given together with the MGMT depleting agent O6-methylguanine, reduction in MGMT protein as well as activity was found. MGMT antisense oligonucleotide enhanced the sensitivity of cells to the tumor therapeutic drug mitozolomide, as measured by sister chromatid exchange formation. This sensitization was further enhanced by combined treatment with antisense oligonucleotide and O6-methylguanine, indicating that MGMT antisense can be supportive in sensitization of cells to an alkylating drug.

Delayed chromosomal instability induced by DNA damage.

DNA damage induced by ionizing radiation can result in gene mutation, gene amplification, chromosome rearrangements, cellular transformation, and cell death. Although many of these changes may be induced directly by the radiation, there is accumulating evidence for delayed genomic instability following X-ray exposure. We have investigated this phenomenon by studying delayed chromosomal instability in a hamster-human hybrid cell line by means of fluorescence in situ hybridization. We examined populations of metaphase cells several generations after expanding single-cell colonies that had survived 5 or 10 Gy of X rays. Delayed chromosomal instability, manifested as multiple rearrangements of human chromosome 4 in a background of hamster chromosomes, was observed in 29% of colonies surviving 5 Gy and in 62% of colonies surviving 10 Gy. A correlation of delayed chromosomal instability with delayed reproductive cell death, manifested as reduced plating efficiency in surviving clones, suggests a role for chromosome rearrangements in cytotoxicity. There were small differences in chromosome destabilization and plating efficiencies between cells irradiated with 5 or 10 Gy of X rays after a previous exposure to 10 Gy and cells irradiated only once. Cell clones showing delayed chromosomal instability had normal frequencies of sister chromatid exchange formation, indicating that at this cytogenetic endpoint the chromosomal instability was not apparent. The types of chromosomal rearrangements observed suggest that chromosome fusion, followed by bridge breakage and refusion, contributes to the observed delayed chromosomal instability.

Delayed chromosomal instability induced by DNA damage.

DNA damage induced by ionizing radiation can result in gene mutation, gene amplification, chromosome rearrangements, cellular transformation, and cell death. Although many of these changes may be induced directly by the radiation, there is accumulating evidence for delayed genomic instability following X-ray exposure. We have investigated this phenomenon by studying delayed chromosomal instability in a hamster-human hybrid cell line by means of fluorescence in situ hybridization. We examined populations of metaphase cells several generations after expanding single-cell colonies that had survived 5 or 10 Gy of X rays. Delayed chromosomal instability, manifested as multiple rearrangements of human chromosome 4 in a background of hamster chromosomes, was observed in 29% of colonies surviving 5 Gy and in 62% of colonies surviving 10 Gy. A correlation of delayed chromosomal instability with delayed reproductive cell death, manifested as reduced plating efficiency in surviving clones, suggests a role for chromosome rearrangements in cytotoxicity. There were small differences in chromosome destabilization and plating efficiencies between cells irradiated with 5 or 10 Gy of X rays after a previous exposure to 10 Gy and cells irradiated only once. Cell clones showing delayed chromosomal instability had normal frequencies of sister chromatid exchange formation, indicating that at this cytogenetic endpoint the chromosomal instability was not apparent. The types of chromosomal rearrangements observed suggest that chromosome fusion, followed by bridge breakage and refusion, contributes to the observed delayed chromosomal instability.

Okadaic acid, a ptotein phosphatase inhibitor, induces sister-chromatid exchanges depending on the presence of bromodeoxyuridine

Okadaic acid (OA), a potent tumor promoter and an inhibitor of protein phosphatase 1 and 2A, induced sister-chromatid exchanges (SCEs) in human lymphoblastoid cells and Chinese hamster ovary cells at low concentrations of 2–10 nM, when the cells were grown for two cell cycles in the presence of OA and bromodeoxyuridine (BrdUrd). Prolonged treatment with OA prior to addition of BrdUrd did not induce SCEs, indicating an essential role of BrdUrd. A similar important role of BrdUrd in SCE induction has been reported in the cases of benzamide (BA) (Natarajan et al., 1981) and camptothecin (CPT) (Zhao et al., 1992), which are inhibitors of poly(ADP-ribose)polymerase and DNA topoisomerase I (topo I), respectively. Unlike many DNA-damaging agents, they are required to be present during S phase along with BrdUrd in the medium and/or in the parental DNA as BrdUMP. Thus OA, like BA and CPT, is a new type of SCE inducer. Exposing cells to a combined treatment with OA, BA and CPT, a significantly higher level of SCEs was induced than that expected if the numbers of SCE caused by these three inhibitors were additive, while no such synergistic increase was seen in every combination of two agents. Since both phosphorylation and poly(ADP-ribosyl)ation have been known to modify topo I activity, the results suggest a common involvement of topo I for SCE formation by OA, BA and CPT. In addition to SCE induction, OA resulted in an increase of mitotic cells which were characterized by a marked chromosome condensation. OA also induced chromosome fragmentation/pulverization in human lymphoblastoid cells and fragmented nuclei in Chinese hamster cells.

Restriction endonucleases do induce sister-chromatid exchanges in Chinese hamster ovary cells

Restriction endonucleases (REs) AluI, EcoRi, MspI, PvuII and SmaI were introduced into exponentially growing Chinese hamster ovary (CHO) cells permeabilised by the bacterial cytotoxin, streptolysin O (SLO). Sister-chromatid exchanges (SCEs) were scored in posttreatment metaphases following recovery times of 20 and 24 h. At both fixation times, all five REs tested were found to increase the frequencies of SCEs compared with that of SLO-treated controls. Among the REs used, AluI and PvuII were found to be most effective, inducing on average a 2–3-fold increase, with a proportion of cells exhibiting more than 80 SCEs. These results confirm the earlier findings of Natarajan et al. (1985) and tend to suggest that double-strand breaks (DSBs) induced by REs are involved in the formation of SCEs.

Contribution of O6‐alkylguanine and N‐alkylpurines to the formation of sister chromatid exchanges, chromosomal aberrations, and gene mutations: New insights gained from studies of genetically engineered mammalian cell lines

O6-methyl- and O6-ethylguanine are the major premutagenic and precarcinogenic lesions induced in DNA by monofunctional alkylating agents, albeit formed in minor amounts. The involvement of these lesions in SCE and aberration formation is less clear. We have analyzed the contribution of O6-alkylguanine to SCE and aberration formation, as well as its toxic and point mutation inducing effect in transgenic Chinese hamster ovary (CHO) cell lines that express variable amounts of human O6-methylguanine-DNA methyltransferase (MGMT). Cells that overexpress MGMT (or the bacterial Ada protein) gained resistance to the formation of alkylation-induced SCEs and aberrations, as compared to MGMT deficient cells. A correlation was apparent between the level of protection for SCEs and cell killing, indicating that both phenomena are interrelated. The protective effects were dependent on the level of MGMT expression, the agent used for alkylation, and cell cycle progression. Our data suggest that at least 2 kinds of lesions are responsible for SCE and aberration formation, namely, O6-alkylguanine and one or various N-alkylation products. The probability that O6-methylguanine is converted into cytogenetic effects has been estimated to be about 1:30 for SCEs, and 1:147,000 and 1:22,000 for chromosomal aberrations in the first and second post-treatment mitosis, respectively. The induction of SCEs and likely also of aberrations by O6-methylguanine requires two replication cycles and is supposed to involve the formation of secondary DNA lesions. Increased repair of 3-methyladenine and 7-methylguanine in CHO cells that overexpress the N-methylpurine-DNA glycosylase (MPG) after transfection with the human MPG-cDNA did not give rise to protection against methylation-induced SCEs and aberrations, probably because of incomplete excision repair. MPG overexpressing cells reacted even more sensitively to methylating agents, suggesting apurinic sites formed as a result of MPG action to be SCE and aberration-inducing lesions.

Molecular epidemiology of lung cancer and the modulation of markers of chronic carcinogen exposure by chemopreventive agents.

Chronic inhalation exposure to environmental carcinogens such as polycyclic aromatic hydrocarbons (PAHs), cigarette smoke, 4-aminobiphenyl (4-ABP), ethylene oxide, and styrene is associated with elevations in biomarkers such as DNA adducts, protein adducts, sister chromatid exchanges (SCEs), chromosomal aberrations, gene mutation, and/or oncogene activation. These biomarkers indicate an increased cancer risk for the exposed population, although quantitative estimates cannot be made with certainty. There is convincing epidemiological evidence that the antioxidant and free radical-scavenging vitamins C and E and beta-carotene (beta-C) protect against cancer of the lung and other epithelial tissues, with somewhat weaker evidence for retinol. Experimental studies demonstrate that these micronutrients are capable of blocking or reducing tumor formation caused by diverse carcinogens. A variety of mechanisms appear to be involved, including suppression of carcinogen activation, enhancement of carcinogen detoxification, induction of cellular differentiation, inhibition of mutagenesis, enhancement of immunologic function, and/or reduction of the formation of carcinogen-DNA adducts, SCEs, micronuclei, and other markers of genotoxic damage. Therefore, we have recently investigated the possible modifying effect of serum vitamins C and E, beta-C, and retinol on a number of such biomarkers in a case-control study of lung cancer, and in a cross-sectional study of heavy smokers. Preliminary results indicate an inhibitory effect of certain vitamins on DNA adduct formation. A significant number of human intervention trials are ongoing involving these vitamins. It appears that biomarkers can provide useful intermediate endpoints for assessment of both the mechanisms and the efficacy of chemopreventive agents.

Induction of a BrdU-enhanceable fragile site-like lesion and sister chromatid exchanges at 11q23.1 in EBV-transformed lymphoblastoid cell lines.

We examined the expression of a fragile site-like lesion and induction of sister chromatid exchanges (SCEs) at 11q23.1 in EBV-transformed lymphoblastoid cell lines derived from carriers of distamycin A-inducible fragile sites and ataxia telangiectasia patients. The fragile site-like lesion at 11q23.1 was found to be BrdU-enhanceable in all cell lines examined, and the expression frequencies increased linearly with the rates of BrdU substitution in replicated DNA. In addition, an increased frequency of SCEs was observed at 11q23.1 on the expressed chromosome. Thus, the BrdU-enhanceable fragile site-like lesion at 11q23.1 is a "hot spot" for the formation of SCEs, as has been reported for other rare and common fragile sites.

Lack of sensitivity of sister-chromatid exchange for lymphocyte chromosomal damage detection caused by antichagasic treatment

No studies exist on sister-chromatid exchange (SCE) formation in chagasic patients therapeutically exposed to nifurtimox (NFX) or benznidazol (BZ). In the present study SCE was analyzed in cultures of peripheral lymphocytes of patients aged 11 months to 11 years treated with NFX 12–15 mg/kg/d for 60 days or with BZ 5 mg/kg/d for 30 days. Chagasic patients before treatment constituted a control group. A mean of 30 metaphases were examined for each individual. All treated patients compared with untreated controls did not show a significant increase in SCE frequency. Compared with the percentage of chromosomal aberrations in these patients and others belonging to the same epidemic protocol, SCE seems to be less sensitive in the detection of lymphocyte chromosomal damage caused by NFX or BZ.