Sister-chromatid exchanges induced in rabbit lymphocytes by 2-aminofluorene and 2-acetylaminofluorene after in vitro and in vivo metabolic activation

Dose-dependent genotoxic effects of styrene on human blood lymphocytes and the relationship to its oxidative and metabolic effects

Although the genotoxic potential of styrene is known, very limited information is available regarding its dose-dependent genotoxic response to human blood lymphocytes and how such response correlates with different metabolic events in whole blood lymphocytes. The present study was therefore carried out to study such a relationship using in vitro human blood lymphocytes from healthy volunteers. To study genotoxic response to styrene, sister chromatid exchanges (SCEs), cell cycle, and cell survival were analyzed. Lymphocytes were cultured for 72 hr in the presence of different concentrations of styrene (0-1,000 microM). Twenty-four hr before harvest, BrdU (5 micrograms/ml) was added to assess the increase in SCEs and cell cycle delay. Both the SCE frequency and the cell cycle length were increased linearly with increasing concentrations of styrene up to 200 microM, without addition of any exogenous metabolizing system. Above 200 microM, no further increase in genotoxic response occurred. The range of concentrations (10-200 microM) at which increase of cell cycle length due to styrene was observed did not impair the viability of the cells, suggesting that such cell cycle delay is a genotoxic-related event and not caused by cytotoxicity. In vitro metabolic transformation of styrene in whole-blood lymphocyte cultures without the presence of any exogenous metabolic activation system showed the formation of a reactive intermediate, styrene 7,8-oxide, to be capacity-limited, as verified from a nonlinear increase in the formation of styrene glycol. The value of such metabolic parameter reached a plateau above 200 microM styrene. The same phenomenon of saturation has also been observed with regard to other metabolic effects due to styrene in whole blood lymphocytes in culture, such as dose-dependent increase in lipid peroxidation and depletion of blood lymphocyte glutathione. Based on the relationship between the formation of different metabolic events and the genotoxicity of styrene, it may be possible that the genotoxic properties of styrene in human blood lymphocytes may be mediated initially not only by the formation of the presumably reactive styrene 7,8-oxide, but also by that of a reactive oxygen species as well. However, the present data are not sufficient enough to definitely identify the role of reactive oxygen species in such toxicity and therefore it warrants further study.

Promutagen activation by Vicia faba: an assay based on the induction of sister-chromatid exchanges in Chinese hamster ovary cells

Plant activation of promutagens was studied using Vicia faba S10 (in vitro activation) and the extracts prepared from promutagen-treated roots of Vicia faba (in vivo activation). The induction of sister-chromatid exchanges in Chinese hamster ovary cells was used as an endpoint to evaluate the cytogenetic effects of promutagens activated by Vicia faba. Cyclophosphamide and ethyl alcohol were activated both by Vicia S10 and by the Vicia extracts, and their activation resulted in an increase in SCEs. Benzo[a]pyrene, 2-aminofluorene, and maleic hydrazide were not activated. Aniline was activated, but without effect on the induction of SCEs. The activation capacity in vitro and in vivo of Vicia faba was not very pronounced, except for the activation of ethyl alcohol, when compared with that of rat-liver S9, and showed differences in activation for the 6 chemical agents tested.

Persistence of SCE-inducing lesions in lymphocytes of mice exposed to diaziquone

Male C57B1/6 mice were injected i.p. with either 1.25 or 5.0 mg/kg diaziquone (AZQ) and killed at various time intervals from 1 to 99 days post treatment for examination of sister chromatid exchange (SCE) persistence in the peripheral blood lymphocytes (PBLs) and splenocytes. SCE frequencies were found to decay steeply during the first week after exposure in both PBLs and splenocytes. This pattern was followed by a slower decline to baseline over the next week. However, high-frequency cell (HFC) analysis indicates that significant numbers of HFCs persist in the PBLs through day 28 and splenocytes at day 99 post exposure. Mathematical modeling of the time-response curves indicates that the average life span of the majority of AZQ-induced SCE-producing lesions in murine PBLs and splenocytes responsive to phytohemagglutinin is between 3 and 5 days.

Monitoring the exposure of rats to 2-acetylaminofluorene by the estimation of mutagenic activity in excreta, sister-chromatid exchanges in peripheral blood cells and DNA adducts in peripheral blood, liver and spleen

The sensitivity of various methods suitable for biomonitoring the exposure to genotoxicants was compared in an animal model. The results were related to the presence of genotoxic effects in the target organ. Groups of male Wistar rats were given one oral dose of 0, 0.1, 10 or 200 mg 2-acetylaminofluorene (2-AAF)/5 ml dimethyl sulphoxide/kg body weight. Peripheral blood cells, excreta, liver and spleen were collected at different time intervals after dosing. Mutagenicity in urine and extracts of faeces was determined using the Ames test with Salmonella typhimurium TA98 with and without S9 and with and without beta-glucuronidase. Genotoxic effects were studied by measuring DNA-adduct formation in lymphocytes, liver and spleen, and sister-chromatid exchanges (SCEs) in lymphocytes. DNA adducts were measured with immunochemical techniques and postlabelling methods. Mutagenicity in urine and faeces, collected during the first 24 h after treatment, was detected at 2-AAF doses of 1 mg/kg b.w. and higher. At these doses DNA adducts also became apparent in the liver, the main target organ for tumour induction by 2-AAF. The adduct detected appeared to be the N-(deoxyguanosin-8-yl)-2-AAF adduct. There was no evidence of the presence of any other types of DNA adducts. At doses of 1 and 10 mg/kg b.w. no mutagenicity was detected in excreta collected during the second and third day after dosing. The DNA-adduct level in liver cells of the 1 mg/kg b.w. group was maximal 24 h after dosing. At 200 mg/kg b.w. a delay in excretion of mutagenicity with urine and faeces was seen and at 10 and 200 mg/kg b.w. the amount of DNA adducts continued to increase with time after dosing. At 24 and 48 h after treatment with 10 mg, the adduct levels were of the same order of magnitude as those found after the 20-fold higher dose. This points to overloading of the metabolizing system which in combination with the enterohepatic circulation, may lead to an increased retention of 2-AAF in the body. A slightly increased incidence of SCEs of doubtful significance was seen in lymphocytes, but only at the very high dose of 200 mg/kg b.w. No DNA adducts could be detected in blood lymphocytes or spleen cells at any of the dose levels applied, either with the immunochemical or with the postlabelling method.(ABSTRACT TRUNCATED AT 400 WORDS)

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

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.

In vitro induction of sister chromatid exchanges and chromosomal aberrations in peripheral lymphocytes of the oyster toadfish and American eel

A series of experiments was conducted to characterize the proliferation of oyster toadfish lymphocytes in medium containing 5-bromodeoxyuridine (BrdUrd) and to determine the effectiveness of cytogenetic endpoints for assessing the genotoxic effects of in vitro exposure of toadfish and eel lymphocytes to known mammalian clastogens. Although the rate of proliferation of toadfish lymphocytes was low compared to that of mammalian lymphocytes, the effects of increasing BrdUrd concentrations were similar, in that proliferation exhibited a concentration-dependent inhibition for concentrations above 10 microM BrdUrd, and sister chromatid exchange (SCE) frequencies exhibited a concentration-dependent increase for concentrations above 100 microM BrdUrd. Mitomycin C (MMC) and ethylene dibromide (EDB) induced concentration-dependent increases in chromatid-type exchange and SCE frequencies with least effective concentrations (control SCE frequency divided by the slope of the least-squares line) for SCE induction by MMC (6.8 X 10(-9) M) and EDB (2.6 X 10(-4) M) that were comparable to or slightly lower than those that have been obtained with mammalian in vitro systems. In vitro exposure of toadfish lymphocytes to dimethoate (DIM) induced a concentration-dependent increase in SCE frequency with a least effective concentration of 2.8 X 10(-3) M that was much higher than that observed with mammalian in vitro systems. In vitro exposure of American eel lymphocytes to MMC also induced a concentration-dependent increase in the frequency of chromosomal aberrations and SCEs with a least effective concentration for SCE induction of 2.0 X 10(-9) M. These results indicate that cytogenetic endpoints can be effectively scored with cultured lymphocytes from these and perhaps other fish species with comparable karyotypes that contain an average of at least 0.07 pg DNA/chromosome.

Induction of sister-chromatid exchange (SCE) and cell-cycle inhibition in mouse peripheral blood B lymphocytes exposed to mutagenic carcinogens in vivo

To determine the sensitivity of the mouse peripheral blood lymphocyte (PBL) culture system, male B6C3f1 mice were injected i.p. with either 2-acetylaminofluorene (AAF) (20, 40, 80, 160 mg/kg), benzo[a]pyrene (BP) 25, 75, 150, 300 mg/kg), dichlorvos (DCV) (5, 15, 25, 35 mg/kg), ethyl methanesulfonate (EMS) (10, 30, 90, 180, 270 mg/kg), or N-nitrosomorpholine (NM) (37.5, 75, 150, 300 mg/kg) dissolved in either RPMI 1640 (DCV, EMS, NM) or sunflower oil (AAF, BP). 24 h later blood was removed by cardiac puncture, and the lymphocytes were cultured in the presence of lipopolysaccharide for analysis of SCE in B lymphocytes. All 4 mutagenic carcinogens (AAF, BP, EMS, NM) induced significant dose-related increases in SCE frequency. DCV, a potent neurotoxicant, caused no change in the baseline SCE frequency. At the highest concentration of each chemical examined, AAF caused a 1.6-fold increase, EMS a 1.8-fold increase, NM a 3.0-fold increase, and BP a 3.1-fold increase in SCE frequency compared to concurrent controls. A comparison of these results for PBLs with those reported in the literature for bone marrow cells indicates that PBLs offer a good quantitative and qualitative estimate of the SCE-inducing potential for these 5 compounds in bone marrow cells.

Sister-chromatid exchange induction by indirect mutagens/carcinogens, aryl hydrocarbon hydroxylase activity and benzo[alpha]pyrene metabolism in cultured human hepatoma cells

2 human hepatoma cell lines (C-HC-4 and C-HC-20), in which aryl hydrocarbon hydroxylase activity was induced with benz[alpha]anthracene in vitro to about 140- and 64-fold of the respective basal levels, yielded an increased frequency of sister-chromatid exchanges (SCEs) when exposed to benzo[alpha]pyrene (BP), 7,12-dimethylbenz[alpha]anthracene and 3-methylcholanthrene in vitro. Analysis of the metabolism of BP by these cells by high-pressure liquid chromatography revealed that both cell lines produced various BP metabolites including the proximate form BP-7,8-dihydrodiol which has been reported to be the most potent inducer of SCEs among the metabolites of BP. In addition, aflatoxin B1 and cyclophosphamide also induced SCEs in these cell lines. The above findings suggest that these cells may be capable of metabolizing a range of indirect mutagens/carcinogens into DNA-active forms. These cells may therefore serve as a useful test system in vitro for the detection of genotoxic agents, without the use of an exogenous activating system.

The induction of chromosomal damage in rat hepatocytes and lymphocytes. I. Time-dependent changes of the clastogenic effects of diethylnitrosamine, dimethylnitrosamine and ethyl methanesulfonate

Male Wistar rats received a single injection of diethylnitrosamine (DEN), dimethylnitrosamine (DMN) or ethyl methanesulfonate (EMS). After a number of time intervals (up to 56 days) liver cells were assayed for the presence of possible preclastogenic damage by performing partial hepatectomy and subsequent analysis of chromosomal damage (micronucleus formation) in isolated hepatocytes. Peripheral blood lymphocytes from the same animals were collected, stimulated to proliferate and assayed for the frequency of sister-chromatid exchanges (SCEs). Whereas all agents significantly increased frequencies of SCEs in lymphocytes up to at least 28 days (EMS) or 56 days (DMN, DEN) after injection, only the latter 2 compounds gave rise to significantly increased incidences of micronucleated hepatocytes. DMN-induced preclastogenic damage in hepatocytes was lost between 28 and 56 days after injection. After DEN, this type of damage was persistent over the entire experimental period (56 days). When rats treated with DEN did not undergo partial hepatectomy, the frequencies of micronuclei at different time intervals after treatment were at control level. This result, together with those from hepatectomized DEN-treated rats, suggests that it is the persistent character of the preclastogenic damage that is responsible for the occurrence of micronucleated hepatocytes at later time intervals after treatment with DEN, rather than the stability of micronuclei which might eventually have been formed soon after injection.

Sister chromatid exchange distributions in rabbit lymphocytes treated with streptonigrin

Streptonigrin (NSC-45383), a direct-acting clastogen which induces SCEs in vivo and chromosome aberrations both in vivo and in vitro, was evaluated for SCE induction in both G0 and stimulated rabbit lymphocytes. Determinations were made for 16 cultures from seven female rabbits. These included controls as well as cells exposed to 90 micrograms/kg in vivo, cells pulse-treated with 50 ng/ml in vitro, and a culture continuously exposed to 5 ng/ml in vitro. For all cultures the SCE/cell frequency was determined from 20 complete (44 chromosome) metaphases and, in selected cultures, SCEs on individual chromosomes (880 per culture from 20 cells) were enumerated to determine SCE/chromosome frequency and the chromosomal distribution of SCEs. Analysis of variance and least significant difference tests of the square root x transformed SCE/cell data show that cells exposed to streptonigrin while dividing have significantly higher (P less than 0.01) frequencies (over double the control 5.3 SCE/cell value) whereas treated G0 cells were not significantly different from the controls. Dispersion analysis of both SCE/cell and SCE/chromosome data confirms the adequacy of the Poisson distribution for spontaneous or baseline but not streptonigrin-induced SCEs.

SCE frequencies in rabbit lymphocytes as a function of time after an acute dose of cyclophosphamide

Following acute and chronic exposures to various chemicals in vivo, the average SCE frequency in human and rabbit lymphocytes has generally been shown to decrease with time posttreatment. The rate of this decline varies, however, and little data have been published pertaining to the decrease in SCEs soon after exposure. To gain more information about the immediate decline in SCEs with time, we injected rabbits with a single dose of 35 mg/kg cyclophosphamide (CP) and determined SCE levels in circulating lymphocytes at various times 5 h to 2 weeks after treatment. We observed a rapid decline in SCE frequencies within 5 days, and by 10 days post-exposure the SCE levels were back to control values. The distribution of SCEs among cells and the number of circulating lymphocytes were also analyzed at each time. Within 2-3 days posttreatment we observed a rapid loss of cells with high SCE levels concomitantly with a rapid decline in circulating lymphocytes and a decrease in the average SCE frequency. When the number of lymphocytes began to increase, the number of cells with normal SCE values also increased. By 10-11 days after CP, the lymphocyte count had recovered, the SCE frequency had returned to control levels, and the distribution of SCEs among cells was almost identical to the control distribution. These data, in addition to published information on rabbit lymphocyte lifespan, suggest that the decline in SCE levels with time posttreatment is a function of lymphocyte turnover.

SCE induction in human lymphocytes by combined treatment with aniline and norharman

In human lymphocytes, aniline was unable to induce an increase of SCEs in vitro with or without metabolic activation by S9 mix. p-Aminophenol, one of the C-hydroxylation metabolites of aniline in the body, however, increased the SCE frequencies of lymphocytes at a concentration of 10-4 M. The addition of norharman to aniline plus S9 mix increased the SCE frequencies. The increase, however, was due to the SCE-inducing activity of norharman. These data show that the addition of norharman, which enhances the sensitivity of the Salmonella/microsome test, does not produce an enhancement of the sensitivity of the SCE test.

Sister-chromatid exchanges: a report of the GENE-TOX program

The effects of a number of chemicals on sister-chromatid exchange (SCE) frequencies in in vivo and in vitro systems are reviewed. Standardized protocols for future SCE testing in important systems, as well as for evaluation of test results, are presented. Data reported thus far suggest that SCE analysis may prove useful, especially at a secondary level, as a test of mutagenic carcinogens. Strengths and limitations of SCE analysis are summarized as a guide for future evaluation and use of this procedure.

Cytogenetic effects of cis-platinum(II)diamminedichloride in vivo

The chemotherapeutic agent cis-platinum(II)diamminedichloride (cis-PDD) has been shown to be mutagenic, teratogenic, and carcinogenic. We determined the cytogenetic effects of cis-PDD on human and rabbit lymphocytes in vitro and on rabbit marrow cells, lymph node cells, and lymphocytes in vivo. Lymphocyte cultures from two humans and one rabbit were treated in vitro with cis-PDD. For in vivo studies, five New Zealand white rabbits were given iv injections of cis-PDD. Posttreatment blood samples were withdrawn for analysis and rabbits were sacrificed at either 6 or 24 hr for cytogenetic analysis of marrow and node cells. Sister chromatid exchange (SCE) analysis of human and rabbit metaphases from lymphocytes treated in vitro showed that rabbit lymphocytes are more sensitive to SCE induction by cis-PDD. Significant increases in SCE were observed in lymphocyte cultures obtained as early as 1 hr post treatment from injected rabbits. Analysis of node, marrow, and lymphocyte metaphases from injected rabbits showed a high number of chromosome aberrations in these cells with bone marrow showing a delayed response to treatment. These results indicate that cis-PDD is clastogenic in hematopoietic tissues in vivo and that SCE methodology may be useful in monitoring patients receiving cis-PDD therapy.

Characterization of a rat lymphocyte culture system for assessing sister chromatid exchange after in vivo exposure to genotoxic agents

Lymphocyte culture systems have the major advantage of permitting the analysis of in vivo cytogenetic damage with minimal injury to the animal under study. This paper describes a rat lymphocyte culture system designed for the study of sister chromatid exchange (SCE) induced by in vivo exposure to genotoxic agents. A standard protocol was established in which 1 to 2 ml of blood are removed from rats by cardiac puncture, washed three times with phosphate-buffered saline (pH 7.4), and grown in RPMI 1640. 5-Bromodeoxyuridine (BrdU) (1.0 microM) is added after 24 hr, and cells are harvested after 56 hr of culture. Critical steps for successful blast transformation include washing the blood in buffered saline and the adding of 2.0 to 4.0 microgram phytohemagglutinin/ml to the culture medium. The use of low concentrations of BrdU (less than or equal to 5.0 microM) is recommended to maintain low baseline SCE levels and to avoid cytotoxicity. The mutagenic carcinogen, ethyl methanesulfonate (EMS), was used as a positive control agent and at a dose of 300 mg/kg caused a fourfold increase in SCE frequency. Twenty-eight days after EMS administration (30, 100, 300 mg/kg), lymphocytes from treated animals still displayed SCE levels at least 50% above baseline. This system provides a reliable means of investigating chemically induced SCE in the rat.

Methods for analysis of the mutagenicity of indirect mutagens/carcinogens in eukaryotic cells

The review discusses the variety of methods for activation of indirect mutagens/carcinogens and testing them in cell cultures, especially in mammalian cell cultures. After the necessity for including metabolizing components in mutagenicity tests has been pointed out, the enzymes that transform foreign compounds metabolically, and the factors influencing them, are described. In the main section the various methods of activating indirect mutagens/carcinogens are presented. The methods of including in vivo metabolism in mutagenicity tests are: Analysis of cells from organisms contaminated with a chemical (III.l.a); body fluid-mediated mutagenesis (III.l.b); host-mediated assay (III.l.c). The following activation systems are suitable for including in vitro metabolism of test compounds in mutagenicity tests: Liver and lung perfusion (III.2.a.alpha); organ slices and homogenates (III.2.a.beta); subcellular fractions (III.2.a.gamma); cultivated cells (cell-mediated mutagenesis) (III.2.b); nonenzymatic activation systems (III.2.c). Finally the main factors that influence the metabolism of test substances are summarized. Two factors illustrate the mutagenicity tests with regard to the metabolism of mammalian livers and the methods of performing mutagenicity tests in man.

In vivo induction of sister-chromatid exchanges in liver and marrow cells by drugs requiring metabolic activation

A highly sensitive method for the detection of in vivo induction of sister-chromatid exchange (SCE) has been developed in mice subjected to partial hepatectomy. SCE induction by either acetylaminofluorene (AAF) or cyclophosphamide, drugs requiring metabolic activation, is significantly greater in both regenerating liver and bone-marrow cells of partial hepatectomized animals than in marrow cells of unhepatectomized mice. These experiments have confirmed the ability of AAF, a well known mutagen-carcinogen, to induce SCE formation, even though the cytogenic effects of this drug on non-hepatectomized mice is very small. The in vivo system described has demonstrated the influence of the liver on drug-induced damage to extra-hepatic tissues. The procedures developed should facilitate the detection of drug-induced cytogenic damage and permit the comparison of inter-tissue differences in SCE induction with tissue-specific differences in drug-activation pathways.

Sister-chromatid exchanges in human lymphocytes exposed during Go to four classes of DNA-damaging chemicals

Human lymphocytes were treated prior to mitogenic stimulation with varying concentrations of 6 cytostatic drugs representing 4 classes of DNA-damaging chemicals. Afterwards the cells were washed to remove residual chemical and cultured in the presence of bromodeoxyuridine for analysis of sister-chromatid exchanges (SCEs). A dose-related increase in SCEs was observed in cells exposed during Go to the alkylating chemicals mitomycin C, chlorambucil, and thiotepa, while significant increases in SCEs were not noted in cultures exposed to methotrexate, cytarabine, or bleomycin. These findings suggest that not all classes of clatogenic chemicals which induce SCEs in proliferative cells substituted with BUdR are capable of inducing long-lived lesions in the DNA of Go lymphocytes that can lead to SCE formation.