Methyl isocyanate: an evaluation of in vivo cytogenetic activity

The ability of inhaled methyl isocyanate (MIC) to induce genotoxic and cytotoxic damage in vivo was evaluated by assessing the induction of chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) in bone marrow metaphase cells, the induction of micronuclei in polychromatic erythrocytes (MN-PCEs), and the inhibition of bone marrow cellular proliferation and erythropoiesis. B6C3F1 mice were exposed to MIC by two exposure regiments: in two experiments, male mice only were exposed to 3, 10, and 30 ppm for 2 hr; in four experiments, male and female mice were exposed to 1 and 3 ppm (in one experiment, to 6 ppm, also), 6 hr per day for 4 consecutive days. The various cytogenetic endpoints were analyzed in bone marrow and peripheral blood (4-day exposure regimen only) samples taken from bromodeoxyuridine tablet-implanted animals killed 11 to 22 hr after cessation of the exposure to MIC. Exposure to MIC for 2 hr induced a significant delay in cellular proliferation but did not induce a significant increase in CAs, SCEs (evaluated at 3 and 10 ppm, only) or in bone marrow MN-PCEs. Also, this exposure regimen did not inhibit the rate of erythropoiesis. Following exposure to MIC for 4 days, a weak but significant increase in CAs and SCEs was observed in male (in one experiment) and in female (in two experiments) mice. The induction was especially apparent in the single experiment in which mice were exposed to 6 ppm MIC. At this concentration, a significant increase in MN-PCEs in peripheral blood was observed in male but not female mice. Delay in bone marrow cell proliferation was observed in male mice beginning at 3 ppm and in female mice at 6 ppm. The 4-day exposure regimen resulted also in a depressed rate of erythropoiesis, with male mice appearing to exhibit greater depression than female mice. The results demonstrate that exposure to MIC by inhalation results in bone marrow damage, indicating the systemic genotoxic/cytotoxic activity of MIC and/or reactive metabolites.     

Cytogenetic analyses of mice exposed to dichloromethane

Chromosome damage was studied in female B6C3F1 mice exposed to dichloromethane (DCM) by subcutaneous or inhalation treatments. No increase in the frequency of either sister chromatid exchanges (SCEs) or chromosome aberrations (CAs) in bone marrow cells was observed after a single subcutaneous injection of 2,500 or 5,000 mg/kg DCM. Inhalation exposure to DCM for 10 days at concentrations of 4,000 or 8,000 ppm resulted in significant increases in frequencies of SCEs in lung cells and peripheral blood lymphocytes, CAs in lung and bone marrow cells, and micronuclei (MN) in peripheral blood erythrocytes. Lung cell CAs and blood erythrocyte MN reached frequencies of approximately two times control levels. Following a 3-month inhalation exposure to 2,000 ppm DCM, mice showed small but significant increases in lung cell SCEs and peripheral blood erythrocyte MN. These findings suggest that genotoxicity may play a role in the carcinogenicity of DCM in the lungs of B6C3F1 female mice.     

Sister chromatid exchange analysis in lung and peripheral blood lymphocytes of mice exposed to methyl isocyanate by inhalation

Mice were exposed to 1, 3, or 6 ppm methyl isocyanate (MIC) for 6 hr/day for four consecutive days. Lung cells and peripheral blood lymphocytes (PBLs) were removed and cultured for analysis of sister chromatid exchange (SCE) and cell cycle kinetics. MIC caused a small but significant increase in SCE frequency of cultured lung cells from mice exposed to 1, 3, or 6 ppm MIC. MIC did not significantly increase SCE levels in PBLs of mice exposed to concentrations as high as 6 ppm. In cultured PBLs, MIC had a stimulatory effect on cell cycling rates as measured by the replicative index, and it caused a significant reduction in mononuclear leucocyte counts and the mitotic indices.     

Induction of sister chromatid exchange in spleen and bone marrow cells of rats exposed by inhalation to different dose rates of ethylene oxide

We investigated the effects of dose rate on the frequency of sister chromatid exchange (SCE) in bone marrow and spleen cells of rats exposed to ethylene oxide (EtO). Four groups (18/group) of male Fischer 344 rats were exposed to EtO by inhalation. The exposures consisted of 100 ppm for 6 hr/day, 300 ppm for 2 hr/day, 600 ppm for 1 hr/day, and clean air control. All EtO treated rats were given a total exposure dose of 600 ppm-hr daily, 5 days/week for 3, 6, or 9 months. Six rats per group were sacrificed at each time point, and SCEs were measured in cultured spleen and bone marrow cells. A statistically significant increase was found in SCEs in both bone marrow and spleen cells for all treated groups and at each time point when compared to the control, except at the 3-month exposure for the middle and high dose-rate groups in bone marrow cells. In the spleen, the increases in SCEs were similar among the three experimental groups. In bone marrow, the lowest dose rate (100 ppm) resulted in higher SCE frequencies than the medium and high dose-rate group after 3 and 6 month exposures. The overall frequencies of SCEs in the spleen cells were higher than in the bone marrow cells. The increase in SCE frequencies and decrease in the replicative index in spleen cells were also dependent on the duration of exposure. These results indicate that (1) EtO, by inhalation, can cause SCEs both in spleen and bone marrow cells of Fischer 344 rats, (2) spleen cells are more sensitive to EtO than bone marrow cells, and (3) in bone marrow cells the lowest dose-rate (longest) exposure causes more SCEs than the highest dose-rate (shortest) exposures. © 1993 Wiley-Liss, Inc.     

cytogenetic and germ cell effects of phosphine inhalation by rodents: II. subacute exposures to rats and mice

Phosphine (PH₃) is a highly toxic grain fumigant to which there is significant human workplace exposure. To determine the in vivo cytogenetic effects of inhalation of PH₃, male F344/N rats and B6C3F1 mice were exposed to target concentrations of 0, 1.25, 2.5, or 5 ppm PH₃ for 6 hr/day for 9 days over an 11 -day period. Approximately 20 hr after the termination of exposures, blood was removed from the mice and rats by cardiac puncture and the lymphocytes cultured for analyses of sister chromatid exchanges and chromosome aberrations in rats and mice, and micronuclei (MN) in cytochalasin B-induced binucleated lymphocytes from mice. In addition, bone marrow (rats) and peripheral blood (mice) smears were made for the analysis of MN in polychromatic and normochromatic erythrocytes. No significant increase in any of the cytogenetic endpoints was found at any of the concentrations examined. These results indicate that concentrations of PH₃ up to 5 ppm are not genotoxic to rodents when administered by inhalation for 9 days during an 11 -day period as measured by several cytogenetic assays. To evaluate the effects of PH₃ on male germ cells, a dominant lethal test was conducted in male mice exposed to 5 ppm PH₃ for 10 days over a 12-day period and mated to groups of untreated females (2 females/male) on each of 6 consecutive 4-day mating intervals. None of the 6 groups of females exhibited a significant increase in percent resorptions. These results indicate that exposure to 5 ppm PH₃ by inhalation does not induce dominant lethality in male mouse germ cells at steps in spermatogenesis ranging from late differentiating spermatogonia/early primary spermatocytes through mature sperm. © 1994 Wiley-Liss, Inc.     

Sister chromatid exchanges induced in rabbit lymphocytes by ethylene oxide after inhalation exposure

Ethylene oxide, which is the simplest epoxide and an extremely important commercial compound, has been used by many investigators as a model compound to study mutagenicity by alkylation of DNA. Knowledge of in vivo dose-effect relations under experimental conditions may provide further insight into the dynamics of the sister chromatid exchange (SCE) response. It may also provide information on temporal aspects of sampling design for human worker populations. Groups of four male New Zealand white rabbits were exposed in inhalation chambers to 0, 10, 50, and 250 parts per million (ppm) ethylene oxide for 6 hr a day, 5 days a week, for 12 weeks. Peripheral blood samples were taken before the start of exposure, at intervals during exposure, and up to 15 weeks after the end of exposure to measure SCE rates in peripheral lymphocytes as well as standard hematological endpoints. Additionally, the level of reduced glutathione (GSH) in liver and blood was measured in a set of concurrently exposed animals at the end of the 12-week exposure. Results show that exposure to 10 ppm does not cause a detectable increase in SCE rates. However, exposure to 50 and 250 ppm does cause an increase in SCEs that decreases after exposure ends, but still remains above baseline levels 15 weeks after exposure. Hematological and GSH measurements did not differ between control and exposed groups. These results indicate that inhalation exposure to the mutagenic alkylating agent ethylene oxide results in a dose-related SCE effect, and that SCE is a more sensitive indicator of exposure than either standard hematological end points or GSH levels.     

Assessment of 1,2-dimethylhydrazine in bone marrow micronucleus assay: variations in protocol and response.

The effect of variations in experimental protocol on the assessment of the genotoxicity of 1,2-dimethylhydrazine (DMH) in the bone marrow micronucleus assay was determined. The incidence of micronuclei (MN) in the bone marrow of CBA mice treated with DMH (either intraperitoneally (i.p.) or orally) was found to be significantly greater than that observed in C57B1/6J mice using the same dose and dosing regimen. With i.p. injection, DMH, at doses of 20 and 50 mg/kg, was found to be positive in the bone marrow MN test in CBA mice only. In C57B1/6J mice, DMH (i.p.) was found to be positive at only the 50 mg/kg dose. With oral administration, DMH was positive in the MN test only at the 50 mg/kg dose and only in CBA mice. No significant difference in the percentage of MN was observed when 300, 500, or 1,000 polychromatic erythrocytes (PCEs) were scored following a single treatment of DMH. Cyclophosphamide (CY) was found to induce a dose-dependent increase in the percentage of MN observed in the bone marrow of C57B1/6J mice. DMH tested positive in the colon nuclear aberration (NA) assay in both strains of mice using both i.p. and oral routes of administration, although C57B1/6J mice were found to be more sensitive than CBA mice. No significant difference was observed regarding the percentage of NAs observed in the colon between mice injected i.p. or orally gavaged.     

Cytogenetic effects of phosphine inhalation by rodents. I: Acute 6-hour exposure of mice

Phosphine (PH₃) is a highly toxic grain fumigant that can be produced from the reaction of metal phosphides with water. To determine the in vivo cytogenetic effects of inhalation of PH₃, male CD-1 mice were exposed to either 0, 5, 10, or 15 ppm target concentrations of PH₃ for 6 hr. Twenty hours after the termination of exposure, the spleens of the mice were removed, macerated, and the splenocytes cultured for analyses of sister chromatid exchanges, chromosome aberrations, and micronuclei in cytochalasin B-in-duced binucleated cells. In addition, bone marrow smears were made for the analysis of micronuclei in polychromatic erythrocytes. No increase in any of the cytogenetic endpoints was found at any of the concentrations examined. The only statistically significant response was a concentration-related slowing of the cell cycle in the splenocytes. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Micronuclei in mouse skin cells following in vivo exposure to benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene, chrysene, pyrene and urethane

Detection of micronuclei (MN) in skin cells from HRA/Skh hairless mice treated with chemical or physical agents may prove informative in qualitative and quantitative studies of skin carcinogenesis. MN induction and cell survival were estimated in cytokinesis-blocked keratinocytes, cultured for 4 days in vitro, after a single topical dose of various organic compounds. Treatment with 2.56 micrograms (10 nmol) 7,12-dimethylbenz[a] anthracene (DMBA) resulted in maximal MN induction in cells removed from skin 12-24 hr after topical administration (79-88 MN/1,000 cells compared with 10-16 MN/1,000 cells in acetone-treated controls). Even in cells removed only 1 hr after DMBA treatment, a significant increase in MN was evident. However, to allow sufficient time for metabolic activation, a sampling time for of 24 hr was adopted for all test substances. Dose-dependent increases in MN were observed with DMBA, benzo[a]pyrene, chrysene, and urethane. Increased numbers of micronucleated cells were detected at the lowest doses administered in the present study (0.128, 0.5, 50, and 50 micrograms, respectively). Although reduced cell recovery occurred following exposure of mice to acetone, pyrene, and other chemicals, there was no evidence that cytotoxicity contributed to MN scored in keratinocytes. Moreover, the probable noncarcinogen, pyrene, failed to induce MN at doses from 2.5 micrograms to 2.5 mg/mouse. These results show that it is possible to assess chemical exposure in skin by measuring cell survival and skin genotoxicity by measuring MN induction in cultured keratinocytes. The available data suggest that MN induction may be a useful indicator of the carcinogenic potential of chemicals applied to the skin.     

DNA content determination of micronucleated polychromatic erythrocytes induced by clastogens and spindle poisons in mouse bone marrow and peripheral blood

The frequencies and DNA distributions of micronuclei (MN) inpolychromatic erthrocytes (PCEs) from bone marrow (BM) and peripheralblood (PB) of mice after four different treatments were determinedby flow cytometry. PCEs were differentiated from normochromaticerythrocytes (NCEs) using the fluorescent RNA stain Thiazoleorange, while MN in erythrocytes were detected with the DNAstain Hoechst 33342. The treatments were X-irradiation (1 Gy)cyclophosphamide (CPA; 30 mg/kg) vincristine sulphate (VCR;0.08 mg/kg) and cholchicine (COL; 1 mg/kg). All treatments showedincreased frequencies of micronucleated PCEs at 30 h after treatmenthi BM and at 50 h in PB. The clastogens(X-irradiation and CPA)and the spindle poisons (VCR and COL) could be grouped accordingto the fluorescent characteristics of the induced MN as wellas the relative frequency of small (0.5—2% of the diploidDNA content) and large (2—10%) MN. In PB the relativefrequency of large MN was lower than in BM indicating that theywere partly eliminated before entrance into the peripheral circulation. ³To whom correspondence should be addressed     

Negative dose-response relationship for radiation-induced micronuclei in polychromatic erythrocytes of mice

Micronuclei were assessed among the bone marrow PCEs of mice 28 hr after exposures to 1 to 8 Gy of X-rays and at 6-hr intervals from 12-60 hr after exposures to 2 or 6 Gy. At 28 hr, the frequency of micronuclei declined as the exposure level increased from 1 to 8 Gy. The peak proportion of micronucleated PCEs appeared much later following 6 Gy than after 2 Gy exposures, implicating cell cycle delay as the cause of the negative dose-response relationship.     

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.     

Micronucleus assay for mouse alveolar Type II and Clara cells

The objective of our study was to develop a micronucleus (MN) assay for detecting genotoxic damage after inhalation exposure in mouse alveolar Type II and Clara cells, potential target cells for lung carcinogens. Ten male C57BL/6J mice were exposed to ethylene oxide (630 mg/m³) for 4 hr via inhalation; 10 unexposed mice serving as controls. 72 hr after the exposure, Clara cells and alveolar Type II cells were isolated using two different methods. Method 1 included a 15‐min trypsin lavage and a 2‐hr incubation of cell suspension. Method 2 involved a 30‐min trypsin lavage, Percoll gradient centrifugation, and a 48‐hr incubation for cell attachment. Nitro blue tetrazolium (NBT) ‐staining was applied to distinguish Clara cells. The frequency of micronuclei (MNi) was scored in NBT‐negative cells (defined as Type II cells in Method 2) and NBT‐positive cells (Clara cells). To detect possible differences between the techniques, MNi in Clara cells were analyzed from samples prepared by both methods. With Method 2, a clear increase in the mean frequency of micronucleated cells was seen in the exposed mice as compared with the controls, for both alveolar Type II and Clara cells. However, no significant increase in MN frequency was seen in Clara cells analyzed from samples prepared by Method 1. Based on our findings, mouse alveolar Type II and Clara cells seem to be suitable for MN analysis in studies aimed at identifying genotoxic lung carcinogens. Both alveolar Type II and Clara cells can be isolated using Method 2. Environ. Mol. Mutagen. 2010. © 2009 Wiley‐Liss, Inc.     

Comparative cytogenetic analysis of bone marrow damage induced in male B6C3F1 mice by multiple exposures to gaseous 1,3-butadiene

Groups of male B6C3F1 mice (N = 12) were exposed to ambient air or to gaseous 1,3-butadiene (BD) at 6.25, 62.5, and 625 ppm for 10 exposure days (6 hr + T90/day). Exposure to BD induced in bone marrow: 1) a significant increase in the frequency of chromosomal aberrations (CA); 2) a significant elevation in the frequency of sister chromatid exchanges (SCE); 3) a significant lengthening of the average generation time (AGT); 4) a significant depression in the mitotic index (MI); and, as measured in the peripheral blood, 5) a significant increase in the proportion of circulating polychromatic erythrocytes (%PCE), and 6) a significant increase in the level of micronucleated PCE (MN-PCE) and micronucleated normochromatic erythrocytes (MN-NCE). The most sensitive indicator of genotoxic damage was the frequency of SCE (significant at 6.25 ppm), followed by MN-PCE levels (significant at 62.5 ppm), and then by CA and MN-NCE frequencies (significant at 625 ppm). The most sensitive measure of cytotoxic damage was AGT (significant at 62.5 ppm), followed by %PCE (significant at 625 ppm), and then by MI (significant by trend test only). Because each cytogenetic endpoint was evaluated in every animal, a correlation analysis was conducted to evaluate the degree of concordance among the various indicators of genotoxic and cytotoxic damage. The extent of concordance ranged from a very good correlation between the induction of MN-PCE and the induction of SCE (correlation coefficient r = 0.9562) to the lack of a significant correlation between the depression in the MI and any other endpoint (r less than 0.37).     

Evaluation of the mutagenicity of the anti-inflammatory drug salicylazosulfapyridine (SASP)

Salicylazosulfapyridine, commonly known as sulfasalazine or SASP, is an anti-inflammatory drug that is widely used in the treatment of diseases such as ulcerative colitis and Crohn's disease. Increases in sister chromatid exchanges (SCE) and micronuclei (MN) frequencies have been reported in lymphocytes of patients maintained on SASP therapy for up to 21 months. We have tested SASP for its ability to induce chromosome aberrations (ABS) and SCE in cultured Chinese hamster ovary (CHO) cells, ABS in mouse bone marrow cells, and MN in erythrocytes from both bone marrow and peripheral blood of mice. In vitro assays for ABS and SCE were negative. In vivo, SASP administered by single gavage at doses up to 1000 mg/kg did not increase ABS in bone marrow cells of male B6C3F1 mice; however, increases in MN were observed in the peripheral blood erythrocytes of male and female B6C3F1 mice administered 675, 1350 or 2700 mg/kg SASP by gavage for 90 days. Weak but significant dose-related increases in MN were also observed in the bone marrow cells of male B6C3F1 mice administered 500, 1000 and 2000 mg/kg SASP for 3 days. These positive findings in mice support the role of SASP in the induction of MN and SCE in humans, and suggest the need for further evaluation of possible adverse human health effects associated with SASP therapy.     

Effect of O6‐chloroethylguanine DNA lesions on the kinetics and mechanism of micronucleus induction in vivo

The aim of this work was to determine the kinetics of micronucleus production because of an increase in O⁶‐chloroethyl guanine (O6‐ChlEt‐G) DNA lesions in murine bone marrow cells in vivo. We increased the frequency of O6‐ChlEt‐G lesions by pretreatment with an inhibitor of O⁶‐methylguanine‐DNA methyltransferase (MGMT), O⁶‐benzylguanine (O6BG), and subsequent treatment with bis‐chloroethylnitrosourea (BCNU). The kinetics of micronucleated‐polychromatic erythrocyte (MN‐PCE) induction was established by scoring the frequency of MN‐PCEs per 2000 PCEs in peripheral blood at 8‐hr intervals from immediately prior to treatment to 72‐hr post‐treatment. We examined groups of five mice treated with (i) dimethylsulfoxide (DMSO), (ii) O6BG in DMSO, (iii) BCNU, or (iv) O6BG in DMSO plus BCNU. The data indicate that O6BG pretreatment causes: (i) ían increase in MN‐PCEs induced by BCNU, (ii) a delay in the time of maximal MN‐PCE induction produced by the different BCNU doses, and (iii) an increase in cytotoxicity. These data confirm that O6‐ChlEt‐G is a lesion involved in DNA break induction and in the subsequent production of micronuclei, and also that these lesions seem to be stoichiometrically reduced by MGMT. These data also show that induction of MN‐PCEs by BCNU is delayed by pretreatment with O6BG for more than 6 hr, perhaps due to the time required for repair of crosslinks derived from O6‐ChlEt‐G and/or for DNA duplication, which is required for adduct transformation into crosslinks. Environ. Mol. Mutagen. 2010. © 2009 Wiley‐Liss, Inc.     

Ethylene oxide dose and dose-rate effects in the mouse dominant-lethal test

In the dose-response study, male mice were exposed by inhalation to ethylene oxide (EtO) for 4 consecutive days. Mice were exposed for 6 hr per day to 300 ppm, 400 ppm, or 500 ppm EtO for a daily total of 1,800, 2,400, or 3,000 ppm X hr (total exposures of 7,200, 9,600 and 12,000 ppm X hr), respectively. In the dose-rate study, mice were given a total exposure of 1,800 ppm X hr per day, also for 4 consecutive days, delivered either at 300 ppm in 6 hr, 600 ppm in 3 hr, or 1,200 ppm in 1.5 hr. Quantitation of dominant-lethal responses was made on matings involving sperm exposed as late spermatids and early spermatozoa, the most sensitive stages to EtO. In the dose-response study, a dose-related increase in dominant-lethal mutations was observed, the dose-response curve proved to be nonlinear. In the dose-rate study, increasing the exposure concentrations resulted in increased dominant-lethal responses.     

Micronuclei in binucleated lymphocytes of mice following exposure to gamma radiation

Experiments were designed to investigate the induction of micronuclei (MN) in mouse peripheral blood lymphocytes (PBLs) after in vitro or in vivo exposure to 60Co gamma radiation. For the in vitro experiments, 4 ml of blood from male C57BL/6J mice were either irradiated in 6 ml Falcon culture tubes as whole blood or isolated to obtain mononuclear leukocytes (MNLs) that were pelleted by centrifugation and then irradiated in RPMI 1640. For the in vivo analysis, mice received whole body irradiation, blood was obtained by cardiac puncture, and the MNLs were isolated for each mouse. Exposures were at a rate of 0.82 to 0.90 Gy/min to yield doses of 0.5, 1, 2, 3, or 4 Gy. MNLs were cultured using cytochalasin B for MN analysis in binucleated PBLs. There was a significant dose-dependent increase in MN observed at all doses. Dose-response curves for the in vivo and in vitro whole blood experiment were not significantly different. However, for isolated pelleted MNLs irradiated in vitro, the MN frequency at 4 Gy was less than one-half that seen in the in vivo experiment. The large difference in MN response is thought to be due to the radioprotective effect of hypoxia.     

Micronucleus induction in cytokinesis-blocked mouse bone marrow cells in vitro following in vivo exposure to x-irradiation and cyclophosphamide

A cytokinesis-block micronucleus (MN) method for the simultaneous but separate measurement of chromosome damage in erythroid and myeloid bone marrow cells is described. MN induction in cytokinesis-blocked mouse bone marrow cells in vitro following in vivo exposure to x-ray or cyclophosphamide (CP) was investigated. Immediately after whole body irradiation with acute doses of either 0, 1, 2 or 4 Gy x-rays, or 2 hr after treatment with either 0, 12.5, 25, or 50 mg CP/kg body weight, bone marrow cells were collected and then cultured in medium supplemented with 3.0 μ/ml cytochalasin B for 24 hr. The binucleated cells were scored in erythroid, myeloid, lymphoid and other cells. The myeloid/erythroid (M/E) ratio was decreased by x-irradiation or CP treatment in a dose-dependent manner. The dividing index (DI; binucleated cells/binucleated + mononucleated cells; %) was decreased in both eryth-roid and myeloid cells in the same manner. Dose-dependent increases in MN frequency were observed following x-irradiation in both erythroid and myeloid cells. A similar dose-dependent MN induction was observed with CP. The MN frequency in myeloid cells was much greater than in erythroid cells (about 4-fold following 4 Gy exposure, and more than 10-fold after 50 mg/kg CP). Lymphoid and other cells were not suitable for scoring DI and MN frequency because of insufficient numbers of binucleated cells. These results suggest that micronuclei can be identified in both myeloid and erythroid cells and that myeloid cells are more susceptible to x-ray or CP-induced chromosomal damage than erythroid cells as expressed by MN induction. © 1994 Wiley-Liss, Inc.     

Transplacental genotoxicity of triethylenemelamine, benzene, and vinblastine in mice.

Transplacental cytogenetic effects of triethylenemelamine (TEM), benzene, and vinblastine on maternal mice and their fetuses have been investigated using micronucleus and sister chromatid exchange (SCE) as genetic endpoints. CD-1 mice were treated on day 14 and 15 of gestation with TEM (0.125, 0.25, and 0.5 mg/kg), benzene (439,878, and 1,318 mg/kg), and vinblastine (0.5, 1, and 2 mg/kg) by intraperitoneal injection at 24 hr intervals, and sacrificed 40 hr after the first injection. Erythrocytic precursor cells in maternal bone marrow and fetal livers (2-4) from each pregnant mouse were used for the micronucleus and/or the SCE analyses. Significant dose-related increases in both micronuclei and SCE were found in maternal bone marrow and fetal liver following TEM treatment. Benzene at the highest dose (1,318 mg/kg) also caused a significant increase in micronuclei and SCE in both maternal bone marrow and fetal liver cells. The embryonic genotoxic effect of TEM was much higher than that of benzene for both genetic endpoints, and the frequency of micronuclei induced by benzene was higher in fetal liver than in maternal bone marrow cells. Vinblastine, a spindle poison, induced micronuclei but not SCE. Micronuclei induction by vinblastine was 7 fold greater in maternal bone marrow than in fetal liver cells. All three chemicals were cytotoxic in maternal bone marrow cells, but not in fetal liver cells except for TEM, which showed a weak cytotoxicity in fetal liver cells in the micronucleus assay. These results indicate that TEM, benzene, and vinblastine are transplacental genotoxicants in mice.