Showing papers on "Sister chromatid exchange published in 1986"

Cytotoxicity, DNA fragmentation and sister-chromatid exchange in Chinese hamster ovary cells exposed to the lipid peroxidation product 4-hydroxynonenal and homologous aldehydes

Abstract: The cytotoxic and genotoxic activities of 4-hydroxypentenal (HPE), 4-hydroxyhexenal (HHE), 4-hydroxyoctenal (HOE), 4-hydroxynonenal (HNE) and 4-hydroxyundecenal (HUE) were investigated in Chinese hamster ovary (CHO) cells. All five 4-hydroxyalkenals reduced plating efficiency in a concentration (ranging from 7 to 170 μM) lower than that producing a parallel reduction of trypan blue-excluding cells, but with both methods the increase in molarity needed to obtain a lethal effect was constantly rather small. With all five 4-hydroxyalkenals a significant amount of DNA fragmentation, as revealed either by the alkaline elution assay or by alkaline denaturation followed by chromatographic partition of single- and double-stranded DNA, was detected only after cell exposure to a cytotoxic concentration. HPE, HHE and HOE induced a clear-cut increase of sister-chromatid exchange (SCE) frequency, while that displayed by cells treated with HNE, and HUE was minimal, even if dose-dependent and statistically significant. Since 4-hydroxyalkenals have been shown to originate from biomembrane lipids peroxidation, these findings should be taken into consideration in the assessment of the genotoxic role of lipoperoxidation in humans.

Topoisomerase inhibitors can selectively interfere with different stages of simian virus 40 DNA replication.

Abstract: I have found that antineoplastic drugs which are known to be inhibitors of mammalian DNA topoisomerases have pronounced and selective effects on simian virus 40 DNA replication. Ellipticine, 4'-(9-acridinylamino)methanesulfon-m-aniside, and Adriamycin blocked decatenation of newly replicated simian virus 40 daughter chromosomes in vivo. The arrested decatenation intermediates produced by these drugs contained single-strand DNA breaks. Ellipticine in particular produced these catenated dimers rapidly and efficiently. Removal of the drug resulted in rapid reversal of the block and completion of decatenation. The demonstration that these drugs interfere with decatenation suggests that they may exert their cytotoxic and antineoplastic effects by preventing the separation of newly replicated cellular chromosomes. Camptothecin rapidly breaks replication forks in growing Cairns structures. It is likely that the target of camptothecin is the "swivel" topoisomerase required for DNA replication and that it is located at or very near the replication fork in vivo. Evidence is presented that many of the broken Cairns structures are in fact half-completed sister chromatid exchanges. One pathway for the resolution of these structures is completion of the sister chromatid exchange to produce a circular head-to-tail dimer.

Suppression of human DNA alkylation-repair defects by Escherichia coli DNA-repair genes

Abstract: The ada-alkB operon protects Escherichia coli against the effects of many alkylating agents. We have subcloned it into the pSV2 mammalian expression vector to yield pSV2ada-alkB, and this plasmid has been introduced into Mer- HeLa S3 cells, which are extremely sensitive to killing and induction of sister chromatid exchange by alkylating agents. One transformant (the S3-9 cell line) has several integrated copies of pSV2ada-alkB and was found to express a very high level of the ada gene product, the 39-kDa O6-methylguanine-DNA methyltransferase. S3-9 cells were found to have become resistant to killing and induction of sister chromatid exchange by two alkylating agents, N-methyl-N'-nitro-N-nitrosoguanidine and N,N'-bis(2-chloroethyl)-N-nitro-sourea. This shows that bacterial DNA alkylation-repair genes are able to suppress the alkylation-repair defects in human Mer- cells.

The effect of low-level 60-Hz electromagnetic fields on human lymphoid cells: II. Sister-chromatid exchanges in peripheral lymphocytes and lymphoblastoid cell lines

Abstract: Dividing human peripheral lymphocytes from 10 normal adults (5 males and 5 females) as well as lymphoid cell lines from patients with the chromosomal instability syndromes were exposed to low-level 60-Hz sinusoidal electromagnetic fields (EMF). The current density of the electrical field was 30 microA/cm2 while the strength of the magnetic field was either 1 or 2 gauss. The cytological endpoints measured included the frequency of sister-chromatid exchanges per chromosome; the distribution of first-, second-, and third-division cells and chromosome breakage (lymphoblastoid cells only). No statistically significant differences, indicative of EMF effects were observed between the treated and control cells regarding SCE frequency, cell cycle progression or chromosome breakage.

In vivo sister chromatid exchange and micronucleus induction studies with 1,3-butadiene in B6C3F1 mice and Sprague-Dawley rats.

Abstract: Male B6C3F1 mice and Sprague-Dawley rats were exposed for 2 days, 6 h/day to 1,3-butadiene (BD) by inhalation (nose only) and their bone marrow cells were evaluated for the induction of micronuclei (MN) and sister chromatid exchanges (SCEs). A significant dose-dependent increase in MN induction was observed in mice. At 100 p.p.m., the frequency of micronucleated polychromatic erythrocytes was 6-fold above control with a maximal induction of 38-fold at 10,000 p.p.m. A significant increase in SCEs was also observed in mouse bone marrow cells starting at 100 p.p.m. with a 4-fold increase over the control evident at 10,000 p.p.m. The highest tested no observed effect level for both endpoints was 50 p.p.m. In contrast, rat bone marrow cells did not exhibit significant increases in micronucleated polychromatic erythrocytes or SCEs. These results indicate that BD is genotoxic in the bone marrow of the mouse but not the rat. This paralleled the chronic bioassays which showed mice to be more susceptible than rats to BD carcinogenicity.

Prediction of Human Tumor Cell Chemosensitivity Using the Sister Chromatid Exchange Assay

Abstract: The sister chromatid exchange (SCE) assay has been used to predict the chemosensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea of various neoplastic cell subpopulations in eight cell lines derived from human brain tumors. Because the SCE assay is based on analysis of individual cells, data obtained can be plotted as frequency histograms of SCEs per chromosome, and the range of chemosensitivities of cell subpopulations can be identified easily. Results suggest that the SCE assay has predictive value as a clinical assay for drugs for which a strong correlation between cell kill and induction of SCEs has been established.

Inhibition of cyclophosphamide and mitomycin C-induced sister chromatid exchanges in mice by vitamin C.

Abstract: Ascorbic acid (vitamin C) is known to act as an antimutagen and anticarcinogen in several test systems. However, there is no report of its effect on carcinogen-induced chromosomal damage in vivo in animals. The present study was performed to determine whether or not ascorbic acid affects sister chromatid exchanges (SCEs) induced by cyclophosphamide (CPA) and mitomycin C (MMC) in bone marrow and spleen cells in mice. The results indicate that ascorbic acid per se did not cause a significant increase in SCEs in mice. However, increasing concentrations of ascorbic acid caused decreasing levels of CPA- and MMC-induced SCEs in both cell types in vivo. At the highest concentration of ascorbic acid, 6.68 g/kg, approximately 75 and 40% SCE inhibition in both cell types was noted for CPA and MMC, respectively. Likewise, under in vivo/in vitro conditions (exposure of animals to experimental chemicals followed by culturing of cells), ascorbic acid caused a dose-related decrease in CPA- and MMC-induced SCEs, up to a dose of 3.34 g/kg At this concentration, approximately 50% CPA- and MMC-induced SCE inhibition was observed in both cell types studied. Thus, ascorbic acid acts as an anti-SCE agent in both in vivo and in vivo/in vitro conditions in mice.

Sister chromatid exchange and chromosome aberration analyses in mice after in vivo exposure to acrylonitrile, styrene, or butadiene monoxide.

Abstract: The use of polymers in plastic and rubber products has generated concern that monomers potentially active in biological systems may be eluted from these substances. We have evaluated two such monomers, acrylonitrile and styrene, for the induction of chromosome damage in mice. Butadiene monoxide, a presumed metabolite of a third important monomer, 1,3-butadiene, was also tested. These chemicals were administered as a single intraperitoneal injection; sister chromatid exchanges and chromosome aberrations were analyzed in bone marrow cells. Acrylonitrile and styrene were largely negative for these endpoints when tested at doses ranging to 60 mg/kg and 1,000 mg/kg, respectively. Butadiene monoxide, which previously has not been tested in a mammalian system, was determined to be a very effective inducer of sister chromatid exchanges and chromosome aberrations. Both endpoints showed a clear dose response and a greater than ten-fold increase over control levels at high doses. These studies represent an initial step in our efforts to evaluate genetic risk associated with exposure to common polymeric chemicals.

Increased repair of O6-alkylguanine DNA adducts in glioma-derived human cells resistant to the cytotoxic and cytogenetic effects of 1, 3-bis(2-chloroethyl)-1-nitrosourea

Abstract: We investigated the cytotoxic and cytogenetic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) treatment on two cell lines derived from human glioma biopsy specimens. SF-188 cells are 3-fold more resistant to the cytotoxic effects of BCNU and 14-fold more resistant to sister chromatid exchange (SCE) induction caused by BCNU treatment than are SF-126 cells. After treatment with BCNU, 60% fewer DNA interstrand crosslinks were found in SF-188 than in SF-126 cells. The O6-methylguanine alkylation product was removed rapidly from DNA in SF-188 cells treated with [3H]methylnitrosourea, but very little repair of alkylation product occurred in SF-126 cells. These results suggest that one of the mechanisms responsible for cellular resistance to BCNU treatment is increased repair of O6-alkylguanine products in DNA, which reduces the number of crosslinks formed and thereby increases survival and reduces the number of SCEs induced in resistant cells.

Differential effects of pre- and posttreatment of sodium arsenite on the genotoxicity of methyl methanesulfonate in Chinese hamster ovary cells.

Abstract: Pretreatment of sodium arsenite reduces hypoxanthine-guanine phosphoribosyltransferase mutagenicity and overcomes the inhibition of mitosis and cell proliferation but has no apparent effect on the cytotoxicity and clastogenicity in methyl methanesulfonate (MMS)-treated Chinese hamster ovary cells. Posttreatment of sodium arsenite drastically increases the cytotoxicity, clastogenicity, hypoxanthine-guanine phosphoribosyltransferase mutagenicity, and inhibition of mitosis and cell proliferation induced by MMS. Sodium arsenite either pre- or posttreatment has no apparent effect on the MMS-induced sister chromatid exchanges. The present results indicate that pretreatment of sodium arsenite not only does no harm but may even benefit the MMS-treated cells. On the contrary, posttreatment of sodium arsenite is cogenotoxic.

Variation in sister-chromatid exchange among 106 members of the general U.K. population.

Abstract: SCE scores of lymphocytes from 106 people revealed that the majority of background variation in SCE was between cells within individuals. Highly significant differences existed between individuals. Lesser, but still highly significant differences also existed between replicate cultures. Inter-individual variation was contributed to by each person's sex and their smoking habits. SCE frequency was not influenced by any of the other factors considered, age, drinking habits and diagnostic X-ray exposure of persons or lymphocyte number and proliferation rate in cultures.

Chromosomal changes without DNA overproduction in hydroxyurea-treated mammalian cells: implications for gene amplification.

Abstract: It has been reported that a 6-h incubation of early S-phase Chinese hamster cells with hydroxyurea promotes DNA overproduction, i.e., replication of DNA a second time within a single cell cycle, and that this could be the basis for gene amplification in drug-treated mammalian cells. When we incubated methotrexate-resistant Chinese hamster cells that were approximately 2 h into the S phase with hydroxyurea for 6 h, DNA that had been replicated before the incubation with hydroxyurea (early S-phase DNA) was replicated again within 11 h after the hydroxyurea treatment. However, incubation with colchicine or Colcemid after hydroxyurea treatment virtually abolished this overreplication, as well as that of the amplified dihydrofolate reductase genes in these cells, indicating that the second replication had occurred in a second cell cycle. Cells collected in the first mitosis after incubation with hydroxyurea never contained overreplicated DNA but did contain abundant chromosome aberrations. Early S-phase DNA replicated again on schedule during the first few hours after mitosis. Asymmetric segregation of chromosome fragments or unequal sister chromatid exchange may be the actual basis for gene amplification in drug-treated mammalian cells.

Incidence and localization of sister chromatid exchanges induced by nickel and chromium compounds.

Abstract: Carcinogenic nickel compounds enhanced the incidence of sister chromatid exchanges (SCEs) in a concentration-dependent fashion in intact Chinese hamster ovary cells. There was a preferential induction of these exchanges in the heterochromatic regions of the chromosomes. CaCrO4 also caused a dose-dependent induction of SCEs. However, in contrast to NiCl2, the exchanges induced by CaCrO4 were not localized in any particular chromosomal region. The total incidence of exchanges was higher with CaCrO4 than with NiCl2. CaCrO4, crystalline NiS and NiCl2 enhanced the incidence of SCEs at concentrations below the threshold of DNA damage as detected by the technique of alkaline elution. Additionally, following treatment time intervals of 24-48 h, there was an increase in SCEs at concentrations of NiCl2 or CaCrO4 that produced little disruption of cell cycle progression. These results are consistent with the hypothesis that potently carcinogenic nickel compounds which are not very mutagenic exert selective effects on genetically inactive heterochromatin, while potently mutagenic and carcinogenic chromate do not appear to produce a similar predominance of SCEs in heterochromatic regions.

Determination of the baseline sister chromatid exchange frequency in human and mouse peripheral lymphocytes using monoclonal antibodies and very low doses of bromodeoxyuridine.

Abstract: We measured the frequency of sister chromatid exchanges (SCEs) in human and mouse peripheral lymphocytes using doses of bromodeoxyuridine (BrdU) ranging from 30 ΠM to 100 µ M (human)

Fecapentaene-12 causes DNA damage and mutations in human cells.

Abstract: Fecapentaenes are mutagens found in human feces and may play a role in the pathogenesis of colon carcinoma. However, the genotoxic effects of fecapentaenes have not been previously studied in mammalian cells. We now report that fecapentaene-12 (fec-12), a prototype for these compounds, causes DNA single strand breaks, sister chromatid exchanges and mutations in cultured human fibroblasts. These results indicate that fec-12 is a potent genotoxic agent in human cells.

Incorporated bromodeoxyuridine enhances the sister-chromatid exchange and chromosomal aberration frequencies in an EMS-sensitive Chinese hamster cell line.

Abstract: The mutant Chinese hamster cell line, EM9, is characterized by a high baselne sister-chromatid exchange (SCE) frequency, increased sensitivity to cell killing, and a defect in DNA strand-break repair. The molecular basis for this pleotrophic phenotype is not known. We examined, at the chromosomal level, the increased sensitivity of this mutant to incorporated BrdUrd. By varying the amount of BrdUrd in template DNA and measuring the frequency of SCEs and chromosomal aberrations, we demonstrated the enhanced sensitivity of EM9 to BrdUrd present in the template strand of DNA. Our results show that a 6-fold increase in SCEs occurs due to DNA replication over a BrdUrd-substituted template relative to a dThd-substituted template. With regard to aberration production in EM9, there is a significant enhancement of aberrations and a specific bias toward damage for the chromatid with Brdurd in the template strand. While these cells share some phenotypic properties with cells from patients with Bloom's syndrome, the genotypic similarities have not yet been established.

Influence of incorporated 5-bromodeoxyuridine on the frequencies of spontaneous and induced sister-chromatid exchanges, detected by immunological methods.

Abstract: We have utilized monoclonal antibody against BrdUrd to detect sister-chromatid exchanges in CHO cells. This technique allows detection of SCEs at very low levels of BrdUrd incorporation. At incorporation level of 5.0%, a frequency of about 2 SCEs/cell/cycle was found. In a UV-sensitive mutant (43-3B) which has an increased spontaneous frequency of SCEs, it is found that this increase is due to incorporated BrdUrd. In MMS- and MMC-treated cells, an influence of BrdUrd on the frequencies of induced SCEs was found only when high concentrations of mutagens were employed.

Relationships between the DNA adducts and the mutations and sister-chromatid exchanges produced in Chinese hamster ovary cells by N-hydroxy-2-aminofluorene, N-hydroxy-N'-acetylbenzidine and 1-nitrosopyrene.

Abstract: Chinese hamster ovary cells were exposed to N-hydroxy-2-aminofluorene, N-hydroxy-N'-acetylbenzidine and 1-nitrosopyrene, and the resulting DNA adducts, sister-chromatid exchanges (SCEs) and mutations at the hypoxanthine-guanine phosphoribosyl transferase locus were quantified. Each agent produced a major DNA adduct substituted through the C8 of deoxyguanosine. When the data from all three agents were combined, both mutation and SCE induction correlated strongly with the concentration of DNA adducts. However, significant differences were found in the relationships between adduct formation and the biological responses produced by the individual agents. While N-hydroxy-N'-acetylbenzidine induced the most mutations per adduct, N-hydroxy-2-aminofluorene caused the greatest number of SCEs per adduct. The data support the involvement of C8-deoxyguanosine adducts in mutation and SCE induction, and indicate that the structure of the group adducted to DNA may be an important factor in determining the magnitude of these biological responses. These findings also suggest that SCE and mutation induction are independent expressions of DNA damage.

Delayed DNA maturation, a possible cause of the elevated sister-chromatid exchange in Bloom's syndrome.

Abstract: Differences in behaviour between the 5-bromodeoxyuridine (BrdU)-substituted template strands in Bloom's syndrome (BS) and normal human fibroblasts have been investigated in order to elucidate the mechanism responsible for the elevated baseline sister-chromatid exchange (SCE) frequency in BS. Alkaline sucrose gradient analysis of the normal and BrdU-substituted DNA strands showed the former to be of higher mol. wt. and of mature size while the latter were of lower molecular size, resulting from breaks introduced during the repair of the BrdU with no differences discernible between BS and normal cells. The rates of removal of BrdU were similar in BS and normal cells, which indicates that the increased SCE level in BS is not due to different rates of repair of the BrdU. The maturation of newly synthesized DNA on a normal template is delayed in BS cells compared with normal cells although it is complete at 18 h, the time it is acting as a template for DNA synthesis. In the presence of a BrdU-substituted template the maturation although further delayed is complete in normal cells by 12 h but in BS cells is not complete even by 30 h, when the newly synthesized strand, due to cell cycle delay produced by the incorporation of BrdU, becomes a template in the next round of DNA synthesis. It is suggested that a similar delay in maturation probably occurs when a new strand containing BrdU is synthesized on a normal template in BS cells. When these strands act as a template they will contain two types of breaks--those due to BrdU repair and those due to delayed maturation. The latter will be responsible for the elevated SCEs in BS cells as the DNA replication forks move through them in a manner similar to that previously reported. The possible implications of differential delays in cell proliferation in BrdU, rates of BrdU removal and extent of DNA maturation in this syndrome are discussed.

Detection of bromodeoxyuridine incorporation in mammalian chromosomes by a bromodeoxyuridine antibody. II. Demonstration of sister chromatid exchanges.

Abstract: A commercially available bromodeoxyuridine (BrdUrd) antibody was used to demonstrate sister chromatid differentiation (SCD) and to evaluate sister chromatid exchanges (SCEs) in V79 Chinese hamster cells. V79 cells were cultivated for one cell cycle in the presence of BrdUrd, followed by a second cell cycle in the absence of BrdUrd. Chromosome preparations were stained by a common immunologic staining technique. The staining pattern observed is similar to that after FPG (fluorescent plus Giemsa) staining, though with reverse staining specificity. The sensitivity of BrdUrd detection is enhanced by a factor of 20 compared to the FPG technique and thus allows the evaluation of SCEs at very low BrdUrd concentrations. The application of the antibody technique gives information about the origin and localization of SCEs and produces further evidence for the spontaneous occurrence of SCEs.

Induction of sister chromatid exchanges by inhibitors of topoisomerases.

Abstract: To investigate the role of topoisomerases in the production of sister chromatid exchanges, the effects of inhibitors of type I and II topoisomerases on baseline and mutagen-induced sister chromatid exchanges were compared. V79 cells were treated with VM-26 and m-AMSA, known inhibitors of type II topoisomerase, or with camptothecin, the only known inhibitor of type I topoisomerase. We observed that inhibitors of both type I and II topoisomerases induced high levels of sister chromatid exchanges at 10−6 M, and that the dose-response curves of these drugs were very similar. A clear heterogeneity in the distribution patterns of exchanges induced by inhibitors of topoisomerases was observed. We believe that this heterogeneity in response to these compounds is due to variation in sensitivity within the cell cycle. We also studied interactions of these agents with mitomycin-C and with PUVA (8-methoxypsoralen + UVA), both cross-linking agents and potent sister chromatid exchange inducers, and with x-rays, an agent that induces high levels of DNA strand breaks. No significant change in exchange levels was observed in interactions between topoisomerase inhibition and the levels induced by the agents studied. We conclude that double-strand break prevalence, known to be increased through inhibition of type II topoisomerase, is not the primary mechanism for induction of sister chromatid exchanges. We further conclude that acute inhibition of type I and type II topoisomerases does not influence substantially the induction of exchanges by other agents.

Sister chromatid exchange induction and persistence in peripheral blood and spleen lymphocytes of mice treated with ethylnitrosourea

Abstract: The induction and persistence of sister chromatid exchanges (SCEs) were studied in peripheral blood and spleen lymphocytes of mice given a single i.p. injection of ethylnitrosourea (ENU) of 100, 350, or 600 muMoles ENU/kg. SCE frequencies were measured on days 1, 3, 5, and 7, and at seven additional times up to 172 days post-injection. SCEs were analyzed statistically by comparing the mean frequencies as well as the distribution of SCEs per cell at each time. The latter approach was based on a non-parametric method of identifying high frequency cells (HFCs). The SCE frequencies and proportion of HFCs in each dose and tissue remained elevated for up to 172 days following treatment, although the degree and statistical significance of the increase varied according to the tissue, dose, and statistical test employed. The SCE frequencies were found to oscillate during the first week. Following this, however, the return of the SCE frequencies to control levels was fit to a linear regression model with time as the only independent variable. The persistence of SCE-forming lesions was found to be dose-dependent for the spleen but not for blood. Within each dose the persistence of SCE-forming lesions was significantly greater for the blood relative to the spleen. The results emphasize that tissue, dose, and time since exposure are important factors to consider when quantifying SCEs in vivo; analysis of high frequency cells may be a more sensitive method of detecting exposure than the t-test; and a single determination of SCE frequencies may not be sufficient to quantitatively assess genotoxic damage in the first week following exposure.

Chinese hamster cells harbouring the Escherichia coli O6-alkylguanine alkyltransferase gene are less susceptible to sister chromatid exchange induction and chromosome damage by methylating agents.

Abstract: Clones of Chinese hamster V79 cells harbouring the Escherichia coli O6-alkylguanine (O6-AG) alkylphosphotriester (AP) alkyltransferase (ATase) gene (clone 8) or a subclone of it that codes only for O6-AG ATase activity (clone SB) have been exposed to increasing doses of N-methyl-N-nitrosourea (MNU) or methylmethanesulphonate (MMS) and the frequencies of induced sister chromatid exchanges (SCEs) measured. In control (clone 2) cells, SCE induction was almost linearly proportional to dose of MNU or MMS and at the highest doses used (15 or 80 micrograms/ml) SCE frequencies were 6 or 8 times background levels, respectively. Slightly lower levels of MMS-induced SCEs were seen in clone 8 and clone SB cells whilst, in contrast, MNU-induced SCE levels in these two clones were drastically reduced being less than twice background levels at 15 micrograms/ml. After treatment with N-butyl-N-nitrosourea, SCE frequency was similar in all three clones. At higher doses, MNU treatment produced less chromatid aberrations and micronuclei in clone SB than in clone 2 cells. These results suggest that ATase-repairable damage is involved in the induction of SCE, chromosome aberrations and micronuclei in V79 cells.

Comparison of S9 mix and hepatocytes as external metabolizing systems in mammalian cell cultures: cytogenetic effects of 7,12-dimethylbenzanthracene and aflatoxin B1.

Abstract: Two external metabolizing systems, S9 mix from Aroclor-induced rat livers and freshly isolated hepatocytes, were used for activation in cultures of human lymphocytes and V79 cells. 7, 12-dimethylbenzanthracene (DMBA) and aflatoxin B1 (AFB1) were employed as indirectly acting reference mutagens. Mutagenic effects were measured by induction of sister chromatid exchange (SCE). With DMBA, SCE-inducing effects were found to be quite similar after activation by S9 mix and activation by hepatocytes. In human lymphocytes nearly the same dose-effect relationships were found with both metabolizing systems; in V79 cells the hepatocyte-mediated induction of SCE was detectable at slightly lower concentrations than the S9-mediated SCE induction. In contrast with AFB1, S9 activation led to a stronger SCE induction than hepatocyte activation in both target cells. The induction of chromosomal aberrations by AFB1 after activation by the two metabolizing systems was also analysed in V79 cells. This experiment again revealed that AFB1 was more efficiently activated by S9 mix than by hepatocytes, and it appeared that AFB1 is a more potent inducer of chromosomal aberrations than of SCE. The different activation capacities of the two metabolizing systems for AFB1 may be due to the maintenance of inactivation mechanisms in hepatocytes or to the Aroclor induction of the S9 fraction. Our experiments have shown that the suitability of hepatocytes as an activation system is not restricted to microbial or eukaryotic point mutation assays, but that hepatocyte metabolism can also be successfully included in cytogenetic tests with short- and long-term cultures of mammalian target cells.

Chromosomal alterations as markers of exposure and effect.

Abstract: Structural changes in chromosomes were one of the first recognized forms of genetic injury resulting from exposure to physical and chemical agents. Depending on the lesions induced in the DNA, and therefore, on the nature of the genotoxic substances, damage to chromosomes falls into two categories, structural aberrations and sister chromatid exchange (SCE). Because these two end points respond differently to chromatin lesions, they are complementary in any study designed to identify potential exposure. The circulating lymphocyte in the human is an appropriate cell type in which to measure cytogenetic changes because it is readily accessible, carries genotoxic substances and their metabolites throughout the body, is long-lived, and can integrate exposure. In animal and human studies, it has been shown that both SCEs and aberrations can persist in the lymphocyte following acute or chronic exposure.