Bleomycin effects on mouse meiotic chromosomes

The effects of a radiomimetic chemical, bleomycin (BLM), on meiotic chromosomes was evaluated in mice treated by intraperitoneal (i.p.) or intratesticular (i.t.) injection. Chromosome aberrations were analyzed at meiotic metaphase I, and damage to the synaptonemal complex (SC) was analyzed in meiotic prophase cells. In the metaphase aberration studies, an i.p. injection of 80 mg/kg BLM, timed to precede or coincide with pre-meiotic S phase, led to a significant increase in structural damage (P less than 0.01) in cells reaching metaphase I 12 days after treatment. However, no increases in clastogenic effects were observed at metaphase I after treatment of cells during various stages of prophase. SC analyses in pachytene cells following an i.p. or i.t. injection at S phase revealed various forms of synaptic errors and structural anomalies, including qualitative changes similar to those observed following irradiation. I.p. doses ranging from 25 to 100 mg/kg, and i.t. doses as low as 0.5 mg/kg, caused roughly 6-fold increases over control levels in the number of damaged cells. SC analyses in pachytene cells following BLM treatments 2 days earlier (at leptotene-zygotene) or 16 h earlier (at early-mid pachytene), also revealed induced structural and synaptic anomalies. Following the treatment at early-mid pachytene, there was some suggestion of interference with chiasma formation as evidenced by univalent-like configurations detected at diakinesis-metaphase. It was concluded that BLM is clastogenic for meiotic chromosomes; however, it does not reveal the strong S-independent clastogenic activity at meiosis that is characteristic of its activity at meiosis. SC analysis indicated that some damage is induced at meiotic prophase, although structurally aberrant cells are not recoverable at meiotic metaphase I. The results call forth various possible explanations for germ-line specific responses to BLM clastogenic activity.

Genotoxicity of inhibitors of DNA topoisomerases I (camptothecin) and II (m-AMSA) in vivo and in vitro

The present study was designed to determine and compare the clastogenicity of m-AMSA and camptothecin (CAMP) in vivo in mouse bone marrow and peripheral blood lymphocytes (PBLs), and in vitro in mouse lymphoma L5178Y cells. m-AMSA interferes with topoisomerase II to induce double-strand DNA breaks. CAMP interferes with topoisomerase I to induce single-strand DNA breaks. Thus, we expected the two drugs to induce different types of chromosomal aberrations (CAs). However, both drugs produced quantitatively and qualitatively similar numbers and types of aberrations under similar experimental conditions. In mouse bone marrow exposed over and 18-h period, both drugs (3 mg/kg) induced approximately 30 damaged cells, with an average of 0.4 chromatid breaks per cell (in 100 cells analyzed/mouse). In addition, both drugs induced only chromatid-type aberrations in mouse bone marrow in vivo when exposure occurred during G2. Cell cycle specificity was indicated by the absence of CAs when exposure to the drugs occurred in vivo in mouse PBLs during G0. In L5178Y cells, m-AMSA was considerably more potent for the induction of mutations and somewhat more potent for the induction of CAs than CAMP was. In contrast to the in vivo bone marrow results, the drugs induced high levels of both chromatid- and chromosome-type aberrations in vitro. The ultimate types of chromosomal damage induced by m-AMSA and CAMP result from a complex interaction of (i) cell cycle specific variations in topoisomerase enzyme levels, (ii) the abilities of these drugs to interfere with the orderly DNA breakage/reunion associated with topoisomerase activity, and (iii) the processing of the damage resulting from these interactions.

Micronuclei in epithelial cells from sputum of uranium workers

The cytogenetic effects of exposure to radon progeny and cigarette smoke were assessed with the exfoliated-cell micronucleus assay among 99 uranium workers. Cells with micronuclei were determined in one sputum specimen from each worker. Exposure to radon progeny and smoking habits were classified from interview data collected at the same time as the sputum specimens. Underground miners were considered exposed to radon progeny, and the other workers were considered unexposed. Neither radon progeny exposure nor cigarette smoking had any appreciable effect on the prevalence of cells with micronuclei; the crude prevalence ratios for the two groups were 1.0 (95% confidence interval 0.7-1.4) and 0.9 (95% confidence interval 0.6-1.3), respectively. The effects of radon and smoking were not confounded by each other or by age, nor were they synergistic. These findings cast doubt on the use of sputum-based micronucleus assay in epidemiologic studies of other populations exposed to occupational or environmental lung carcinogens.

Further evidence that dichloromethane does not induce chromosome damage

Dichloromethane (DCM) is a widely used industrial solvent that has been determined to be a carcinogen in rats and mice. In vitro and in vivo analyses of chromosome damage induced by this agent have provided conflicting results. In order to further investigate the clastogenic potential of DCM in vivo, we analyzed sister chromatid exchanges (SCEs) and chromosome aberrations (CAs) in mouse bone marrow cells following intraperitoneal exposures of 100-2000 mg kg-1 DCM. Dichloromethane failed to increase the frequencies of either SCEs or CAs.

Percutaneous double balloon valvotomy for severe rheumatic mitral stenosis

Percutaneous double balloon valvotomy for severe rheumatic mitral stenosis was successfully performed in 281 of 285 consecutive patients. The changes evoked were a decrease of the mean transvalvular gradient from 16 +/- 7 to 5 +/- 3 mm Hg, an increase in cardiac output from 3.8 +/- 1.0 liters/min to 5.4 +/- 1.5 liters/min and an increase in mitral valve area from 0.86 +/- 0.24 cm2 to 2.41 +/- 0.54 cm2. The mean pulmonary artery pressure decreased from 37 +/- 13 mm Hg to 27 +/- 12 mm Hg and the pulmonary vascular resistance decreased from 307 +/- 181 to 238 +/- 122 dynes/s/cm-5. Symptomatic improvement occurred in 272 of the 285 (95%) patients. There were 3 procedure-related deaths (1%). Postdilatation mitral regurgitation was not significant in most patients. Therefore, this procedure can be performed at a low risk with effective results and a fast recovery.

Effects of atenolol on left ventricular hypertrophy and early left ventricular function in essential hypertension

Echocardiographic studies of left ventricular (LV) hypertrophy indicate clinical benefits of antihypertensive therapy. Therefore, M-mode and Doppler techniques were used to assess changes in LV hypertrophy after 10, 30 and 50 weeks of atenolol therapy (50 or 100 mg once daily) in 19 patients with essential hypertension. After 50 weeks of atenolol treatment, the most notable changes were: for M-mode parameters, increases (p less than 0.05) in diastolic LV internal dimension, radius to thickness ratio and stroke volume, and decreases (p less than 0.01) in total wall thickness and heart rate; for Doppler parameters, increases (p less than 0.01) in slope and peripheral resistance, and decreases (p less than 0.01) in heart rate, stroke volume and cardiac output. The decreased total wall thickness and increased radius to thickness ratio suggest a trend toward regression of LV hypertrophy. These findings, along with improvements in blood pressure, pulse and exercise stress tests, indicate potential benefits of atenolol in managing patients with essential hypertension and LV hypertrophy.

Evidence for chromosomal replicons as units of sister chromatid exchanges

Chromosomal replicons have been described as the cytological counterpart of DNA replicon clusters and have previously been studied in vitro using premature chromosome condensation-sister chromatid differentiation (PCC-SCD) techniques. Chromosomal replicons are visualized as small SCD segments in S-phase cells, and measurement of these segments can provide estimates of relative chromosomal replicon size corresponding to DNA replicon clusters functioning coordinately in S-phase. Current hypotheses of sister chromatid exchange (SCE) formation postulate that sites of SCE induction are associated with active replicons or replicon clusters. We have applied the PCC-SCD technique to in vivo studies of mouse bone marrow cells that have been treated with cyclophosphamide (CP) for two cell cycles. We have been able to visualize chromosomal replicons, as well as SCEs which have been induced in vivo by CP treatment, simultaneously in the same cells. Chromosomal replicons visualized as small SCD segments were measured in PCC cells classified at early or late S-phase based on SCD segment size prevalence. Early S-phase (E/S) PCC cells contained 90% of the SCD segments measured clustered in a segment size range of 0.1 to 0.8 micron with a peak value around 0.3 to 0.6 micron regardless of CP treatment. As the cells progressed through S-phase, late S-phase (L/S) PCC cells were characterized by the appearance of larger SCD segments and even whole SCD chromosomes in addition to small SCD segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptonemal complex damage as a measure of genotoxicity at meiosis

Synaptonemal complex aberrations can provide a sensitive measure of chemical-specific alterations to meiotic chromosomes. Mitomycin C, cyclophosphamide, amsacrine, ellipticine, colchicine, vinblastine sulfate, and cis-platin exposures in mice have been shown to cause various patterns of synaptonemal complex structural damage and synaptic irregularity. These effects are suggestive of abnormal homologue pairing/synapsis/recombination effects which, theoretically, could be implicated in mechanisms leading to aneuploidy and other potentially heritable chromosomal disorders.

Synaptonemal complex damage induced by clastogenic and anti-mitotic chemicals: implications for non-disjunction and aneuploidy

Mice were treated with mitomycin C, cyclophosphamide, amsacrine, colchicine, or vinblastine sulfate, and meiotic prophase cells analyzed for synaptonemal complex (SC) damage. All test agents caused synaptonemal complex breakage and synapsis irregularities, although propensities for inducing specific types of damage at S-phase or prophase stages varied among the chemicals. The data indicate that SC analysis can reveal chemical-specific alterations to meiotic homologue pairing/synapsis which have not generally been recognized, and which theoretically may be implicated in non-disjunction.

A private inquiry into the circumstances surrounding the 1972 death of John Gomilla, Jr., who died after allegedly consuming ten hallucinogenic mushrooms while residing in Hawaii

In December 1972, an 18-year-old male apparently took an accidental overdose of heroin. After becoming ill, he attempted to receive treatment for his condition by being admitted to the emergency room of Wahiawa General Hospital. When confronted by attending physicians in the emergency room as to the nature of his illness, the youth stated that he had only eaten 10 hallucinogenic mushrooms (an average dose for Copelandia cyanescens, the mushroom in question) and nothing else. This story was most likely concocted either by the youth himself or by some of his friends, who probably thought that they could or would be prosecuted for the use of an illegal substance. It is not uncommon that when confronted by an overdose of drugs, many young people are afraid to report their illness to the proper medical authorities out of fear of prosecution due to their illegal activities (Young et al. 1982). The doctors who attempted to treat this young man should not be held liable for his death, even though their treatment of the patient was more supportive (i.e., the talk-down method) than pharmacological. They had no way of knowing that the patient had lied to them about his condition. While it is true that several doctors had diagnosed Gomilla as possibly suffering from muscarine poisoning, why was no atropine or scopolamine administered to the patient? And why was his stomach not pumped and specimens collected for a toxicologist to study for the presence of toxins?(ABSTRACT TRUNCATED AT 250 WORDS)

A cytogenetic comparison of the responses of mouse and human peripheral blood lymphocytes to 60Co gamma radiation

Experiments were conducted to compare the chromosome damaging effects of 60Co gamma radiation on mouse and human peripheral blood lymphocytes (PBLs). Either whole blood or isolated and pelleted mononuclear leucocytes (MNLs) were irradiated with a 60Co unit to yield exposures of 1, 2, 3, or 4 Gy. In addition, mice were whole-body irradiated in vivo with the same doses so that an in vitro-in vivo comparison could be made. The results indicate that mouse PBLs irradiated in whole blood, whether in vivo or in vitro, respond similarly to 60Co gamma rays as measured by dicentric chromosome formation. In addition, mouse and human PBLs showed a similar radiosensitivity, but because the mouse PBL data were best fitted to an exponential function and the human PBL data to a quadratic function, direct comparisons were difficult to make. Pelleted MNLs from mice were much less sensitive to the clastogenic effects of gamma radiation than whole blood. This is believed to be due to hypoxic conditions that developed during irradiation and transport. Human PBLs did not show a marked difference whether irradiated in whole blood or as pelleted MNLs in tissue culture medium.

Synaptonemal complex damage in relation to meiotic chromosome aberrations after exposure of male mice to cyclophosphamide

The genetic implications of induced synaptonemal complex (SC) damage are not known. However, on theoretical grounds, such aberrations could be involved in mechanisms leading to potentially heritable defects. Cyclophosphamide (CP), a chemical reported to cause structural and numerical chromosomal aberrations in the mouse, was used to determine if SC damage observed in meiotic prophase is related to subsequent metaphase chromosomal aberrations. Male mice were injected i.p. with CP. In some instances, mice were also injected simultaneously with tritiated thymidine to label DNA so that cells could be tracked autoradiographically through spermatogenesis. Prophase, primary metaphase (M1), and secondary metaphase (M2) samples were sequentially harvested at appropriate times from the same individual, and nuclei were examined for aberrations. Correlation coefficients between SC and metaphase chromosome aberrations were calculated. The inclusion of tritium labeling increased the number and significance of positive correlations. Positive correlations were found between (1) dose-dependent total SC damage and damage to M1, and to a lesser extent, M2 chromosomes; (2) SC breaks/fragments and M1 chains/rings as well as isochromatid breaks/fragments; (3) SC asynapsis and M1 chromatid breaks/fragments; (4) SC multi-axial configurations and M1 chains/rings as well as isochromatid and chromatid breaks/fragments; and (5) SC multi-axial configurations and M2 hyperploidy. These correlations do not define mechanistic or causal relationships between SC and chromosomal damage. However, taken together with the observation that induced SC damage is many times greater than ensuing metaphase chromosome damage, they substantiate SC analysis as a highly sensitive indicator of potentially heritable effects of this (and presumably other) genotoxic agents.

Mutagenic screening of marker grenade dyes by the Salmonella reversion assay, L5178Y/TK+/- mouse lymphoma assay, and in vivo sister chromatid exchange analysis in mice

Two dyes (C.I. Solvent Yellow No. 33 and a mixture of C.I. Solvent Yellow No. 33 and C.I. Solvent Green No. 3) were tested for mutagenicity in the Salmonella reversion assay and the L5178Y/TK+/- mouse lymphoma assay, and also for sister chromatid exchange (SCE) induction in vivo in C57B1/6J mice. In addition, a greater than 99.9% pure sample of the yellow dye [2-(2'-quinolyl)-1,3-indandione] was tested with and without exogenous activation in the Salmonella reversion assay and the L5178Y/TK+/- mouse lymphoma assay. Neither C.I. Solvent Yellow No. 33 nor the C.I. Solvent Yellow No. 33 and Solvent Green No. 3 mixture was positive for inducing SCEs in vivo. All three dyes were tested in the standard plate incorporation test in seven Salmonella strains TA98, TA100, TA102, TA104, TA1535, TA1537, and TA1538. The dyes were negative with and without exogenous activation in TA98, TA1535, and TA1538. One test with TA1537 was positive with the greater than 99.9% purified yellow dye. All three dyes gave weakly positive results (less than a twofold increase) with S-9 in TA100 and were clearly positive in TA102 and TA104 both with and without S-9. They also induced mutation at the thymidine kinase locus in mouse lymphoma cells, produced both large- and small-colony trifluorothymidine-resistant mutants, and were clastogenic. The purified yellow dye was further tested for SCE induction in mouse lymphoma cells and was determined to give a slightly positive response in the presence of S-9.

Relationships between benzo(a)pyrene-DNA adduct levels and genotoxic effects in mammalian cells

The effectiveness of benzo(a)pyrene [B(a)P]-DNA binding as an internal dosimeter was evaluated. Data were obtained from concurrent studies, measuring B(a)P induced genotoxic effects and DNA adducts in several short-term bioassay systems: cytotoxicity, gene mutation, and sister chromatid exchange in Chinese hamster V79 cells; cytotoxicity, gene mutation, and chromosome aberrations in mouse lymphoma L5178Y TK+/-; cytotoxicity and enhanced virus transformation in Syrian hamster embryo cells; and cytotoxicity and morphological transformation in C3H10T1/2CL8 mouse embryo fibroblasts. Both total B(a)P-DNA binding and specific B(a)P-DNA adducts were measured. N2-(10 beta-[7 beta,8 alpha,9 alpha-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]yl)deoxyguanosine [BPDE I-dGuo] was one of the major adducts identified in all bioassay systems. DNA binding and genotoxic responses varied significantly between bioassays. Each genetic end point was induced with a differing efficiency on a per adduct basis. However, the relationships between frequency of genetic effect or morphological transformation and B(a)P-DNA binding or BPDE I-dGuo were linear within a given assay. In order to compare biological end points of diverse frequencies in diverse biological systems, a doubling adduct level, expressed as the number of BPDE I-dGuo adducts per unit of DNA required to double the induced frequency of biological response, was applied to the data.

Results of in vitro and in vivo genetic toxicity tests on methyl isocyanate

Methyl isocyanate (MIC) was tested for genetic toxicity in a variety of in vitro and in vivo assays. Negative results were obtained in the Salmonella/mammalian microsome assay using five bacterial strains in a preincubation protocol. The Drosophila sex-linked recessive lethal test also gave negative results in studies that involved three routes of administration: inhalation, feeding, and injection. Positive results were obtained for three endpoints in cultured mammalian cells. Reproducible, dose-related increases in trifluorothymidine-resistant clones were induced in L5178Y mouse lymphoma cells, and the frequencies of both SCE and chromosomal aberrations increased in Chinese hamster ovary cells. These effects were independent of exogenous metabolism. In mice exposed to methyl isocyanate by inhalation, cytogenetic analyses were carried out on bone marrow, blood, and lung cells. A single, 2-hr exposure to concentrations of 0, 3, 10, and 30 ppm MIC produced no evidence of chromosomal effects in the bone marrow, although significant cell cycle delay was observed. In four experiments involving exposures on 4 consecutive days to 0, 1, 3, or 6 ppm, delays in bone marrow cell cycle were again observed. Increases in SCE and chromosomal aberrations were observed in bone marrow cells, and a dose-related increase in SCE occurred in lung cells but not in peripheral blood lymphocytes. A significant increase in micronucleated polychromatic erythrocytes in the peripheral blood was observed in male mice in one experiment. From these results, it appears that methyl isocyanate has the capacity to affect chromosome structure but not to induce gene mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Diaziquone-induced micronuclei in cytochalasin B-blocked mouse peripheral blood lymphocytes

A mouse peripheral blood lymphocyte (PBL) micronucleus (MN) test was developed using a modification of the technique for assessing MN in human PBLs described by Fenech and Morley (1985). Male C57Bl/6 mice (5/dose) were injected i.p. with either 0, 2.5, 5.0, 7.5, or 10.0 mg diaziquone (AZQ)/kg. After 24 h the mice were bled by cardiac puncture, PBLs were isolated on a Ficoll-density gradient and then cultured in RPMI 1640 medium using 8 micrograms phytohemagglutinin/ml. In some cultures cytochalasin B (CYB) was added at 21 h during the medium change to block cytokinesis. In other cultures, CYB was omitted to compare the sensitivity of analyzing MN in binucleate versus unblocked mononucleate cells. All doses of AZQ yielded significant increases in MN-containing binucleated PBLs. The use of CYB in the mouse PBL MN test increased the sensitivity approximately 3-fold. The MN test in mouse PBLs should be useful in comparative cytogenetic studies of mice and humans.

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.

Synaptonemal complex damage as a measure of chemical mutagen effects on mammalian germ cells

As heritable chromosome anomalies are implicated in a variety of human disabilities, their induction in germ cells by environmental chemicals is viewed as a threat to health (National Research Council, 1982; Hook, 1983). Synaptonemal complex (SC) analysis is a novel approach for the detection of germ-line chromosomal damage. This sensitive cytological procedure reveals induced structural damage and pairing abnormalities in SCs of meiotic prophase chromosomes, together with other germ-line toxic effects, in the testes of rodents treated with mitomycin C and cyclophosphamide. Our results demonstrate the effectiveness of SC analysis as a rapid and practical in vivo germ-line mutagen assay that lacks many of the short-comings of existing tests.

Tumorigenesis and genotoxicity of ethyl carbamate and vinyl carbamate in rodent cells

Vinyl carbamate (VC) is a suspect metabolic intermediate in ethyl carbamate (EC) carcinogenesis. In the present studies, EC and VC were evaluated for their relative abilities to induce adenomas and sister chromatid exchanges (SCEs) in lung cells of A/J, C3HeB/FeJ, and C57BL/6J strain mice. For both end points, animals were administered a single i.p. injection of the test chemical. Percentage of mice with adenomas and number of adenomas per mouse were compared among the three strains 24 weeks following exposure to EC or VC. Although the relative order of strain sensitivity was the same for both chemicals: A/J greater than C57BL/6J greater than C3HeB/FeJ, VC was much more potent than EC. For SCE analysis of primary lung cells cultured from treated animals, EC and VC showed potency differences similar to those observed for tumorigenesis. All three mouse strains revealed significant dose-dependent increases in SCE frequency. However, there was no strain specificity for this effect. SCE persistence over time was also compared in treated A/J and C57BL/6J mice. Although EC- and VC-induced SCE frequencies declined over a 2-week observation period, again, there was no strain specificity for this effect. VC was also tested for enhancement of SA7 virus transformation of Syrian hamster embryo cells. Significant concentration-dependent increases in cell transformation frequency were observed.

Sister chromatid exchange analysis in cultured primary lung, liver, and kidney cells of mice following in vivo exposure to vinyl carbamate

Methods are described for the short-term culture (48 to 56 h) of lung, liver, and kidney cells from C57B1/6 mice. With these techniques, mice can be exposed in vivo to test compounds and the cells grown on cover glasses in the presence of 5-bromo-2'-deoxyuridine (BrdUrd) (5 microM) for analysis of sister chromatid exchange (SCE) and cell cycle kinetics. Mice exposed to vinyl carbamate (VC) ((10 to 60 mg/kg) by i.p. injection were used in the initial examination of this system. Cultured lung and kidney cells from exposed animals (60 mg/kg) exhibited significant increases in SCE frequencies (approximately 3 to 5 times baseline); however, liver cells were much less responsive and showed less than a twofold increase over baseline SCE levels. Lung cultures initiated as long as 320 h after VC exposure (60 mg/kg) revealed a persistence of lesions leading to the formation of SCEs in vitro. This methodology permits analysis of cytogenetic damage in organs with very low mitotic activity after in vivo exposure to known or suspected genotoxicants.

Rat and hamster hepatocyte-mediated induction of SCEs and mutation in V79 cells and mutation of salmonella by aminofluorene and dimethylnitrosamine

Aminofluorene (AF) and dimethylnitrosamine (DMN) were examined for their ability to induce multiple genetic endpoints after rat and hamster hepatocyte metabolic activation. The endpoints measured included mutations at the Na+/K+-ATPase (ouabain resistance) and hypoxanthine-guanine-phosphoribosyltransferase (6-thioguanine resistance) loci, and sister-chromatid exchanges (SCEs) in Chinese hamster V79 cells, and mutation of Salmonella typhimurium strains TA98 and TA100. AF, with rat and hamster hepatocyte activation, induced only low levels of mutations at either loci in V79 cells but did induce SCEs. Mutation of Salmonella by AF after hepatocyte activation also occurred and was a sensitive endpoint for detecting this aromatic amine. DMN induced high levels of mutations at both loci in V79 cells in addition to SCEs in the presence of hepatocytes from both species. DMN was also mutagenic to Salmonella, but only with hamster hepatocytes. Salmonella did not respond as strongly to DMN as the V70 cells. Hamster hepatocytes were more active than rat hepatocytes in activating both carcinogens. The results indicate the variable sensitivity of the genetic endpoints and species differences in activation for two potent chemical carcinogens.

Genotoxicity studies of benz[l]aceanthrylene

The genotoxicity of the cyclopenta-fused polycyclic aromatic hydrocarbon, benz[l]aceanthrylene (B[l]A), was evaluated in vitro using the L5178Y/TK+/- mouse lymphoma assay and in vivo using the mouse peripheral blood lymphocyte (PBL) culture system. The mutagenicity and sister chromatid exchange (SCE) inducing potential of B[l]A was then compared to that of benzo[a]pyrene (B[a]P). B[l]A appeared to be slightly less mutagenic than B[a]P at the TK locus, and each compound produced both small and large colony mutants indicating that they are clastogenic as well as mutagenic. Gross chromosome aberration analysis of treated L5178Y/TK+/- mouse lymphoma cells confirmed the clastogenicity of B[l]A in vitro. In the mouse PBL system, after administration by gavage, B[l]A was more cytotoxic and produced a sharper elevation in SCE frequency than B[a]P.

Review of literature on chemical-induced aneuploidy in mammalian male germ cells

80 papers published between 1970 and 1984 were evaluated for results pertaining to chemical-induced aneuploidy in mammalian male germ cells. Diverse assays and end points were represented. The assays considered to involve direct measures of aneuploidy were based upon chromosome counts in premeiotic, meiotic, and embryonic cells, and the male pronucleus, or upon phenotypic expression of X-linked genetic markers. Assays in which indirect measures were interpreted as evidence for aneuploidy included those primarily assessing chiasma frequencies, univalent frequencies, and spermatid/sperm sex chromosome body counts. An initial screening to reject studies with insufficient data and those which did not involve a single chemical test agent led to the elimination of 39 papers from further review. The remaining 41 papers reported effects from 46 different chemicals. These papers were rigorously assessed for adequacy of experimental protocols, relevance of end points as direct measures of aneuploidy, and completeness of data presentation and statistical analysis. Criteria specific to each assay were also considered. 4 chemical tests were considered to provide reliable positive or negative aneuploidy data. Cyclophosphamide and chloral hydrate each caused metaphase II hyperploidy when injected into mice. Very limited analyses of trenimon and isoniazid provided negative results. Test findings for 44 chemicals were viewed as inconclusive. It was concluded that standardization of tests to evaluate chemical-induced aneuploidy in male germ cells and the application of these tests towards increasing the data base are badly needed.

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

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.

Sister chromatid exchanges in mammalian meiotic chromosomes

Meiotic cells have been, and remain, a relatively difficult tissue in which to study SCEs. Experimental evaluations have had to contend with various problems unique to germ cells, i.e., poor in vitro growth, unusual cytotoxicities (from BrdUrd), trying chromosome morphologies, and confusion between chromosome label patterns generated by SCEs, COs, and replication kinetics. Nevertheless, BrdUrd differential staining techniques in insects and rodents have progressed to the point where SCE frequencies can be reliably determined. In the described Armenian hamster system, SCEs may be directly resolved in selected primary spermatocyte bivalents and indirectly assessed in secondary spermatocyte cells. SCE frequencies determined from spermatogonial, primary spermatocyte, and secondary spermatocyte cells are in good agreement. The system should be applicable for studies of possible mechanistic similarities between SCE and CO exchange, and for evaluating genotoxic effects. Experimental evidence in Drosophila (33) argues against a very close molecular relationship between these forms of breakage and recombination. However, it is likely that new information can be gained from cells in which normal SCE and CO frequencies and distributions can be characterized, and from studies of the consequences to these events after various mutagenic perturbations to premeiotic and meiotic DNA.