New approaches to mutagenicity studies in animals for carcinogenic and mutagenic agents. II. Clastogenic effects determined in transplacentally treated mouse embryos

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

Improvements in Clinical Trials Information Will Improve the Reproductive Health and Fertility of Cancer Patients

There are a number of barriers that result in cancer patients not being referred for oncofertility care, which include knowledge about reproductive risks of antineoplastic agents. Without this information, clinicians do not always make recommendations for oncofertility care. The objective of this study was to describe the level of reproductive information and recommendations that clinicians have available in clinical trial protocols regarding oncofertility management and follow-up, and the information that patients may receive in clinical trials patient information sheets or consent forms. A literature review of the 71 antineoplastic drugs included in the 68 clinical trial protocols showed that 68% of the antineoplastic drugs had gonadotoxic animal data, 32% had gonadotoxic human data, 83% had teratogenic animal data, and 32% had teratogenic human data. When the clinical trial protocols were reviewed, only 22% of the protocols reported the teratogenic risks and 32% of the protocols reported the gonadotoxic risk. Only 56% of phase 3 protocols had gonadotoxic information and 13% of phase 3 protocols had teratogenic information. Nine percent of the protocols provided fertility preservation recommendations and 4% provided reproductive information in the follow-up and survivorship period. Twenty-six percent had a section in the clinical trials protocol, which identified oncofertility information easily. When gonadotoxic and teratogenic effects of treatment were known, they were not consistently included in the clinical trial protocols and the lack of data for new drugs was not reported. Very few protocols gave recommendations for oncofertility management and follow-up following the completion of cancer treatment. The research team proposes a number of recommendations that should be required for clinicians and pharmaceutical companies developing new trials.

Alterations in CD4+, CD8+, Vgamma3, Vgammadelta, and/or Valpha betaT-lymphocyte expression in lymphoid tissues of progeny after in utero exposure to benzo(alpha)pyrene

That benzo alpha)pyrene (Balpha P) decreases both humoral and cell-mediated immunity, and leads to increases in progeny tumor development after in utero insult, suggests that T- and B-lymphocytes are made defective in exposed offspring. In the study here, C3H mice were injected once with Balpha P (150 microg/g BW) at day 12 of pregnancy and progeny lymphoid tissues were excised during gestation (day 18; GD18) or at 1 or 6 weeks post-partum. The isolated lymphoid cells were analyzed by flow cytometry/immunofluorescence or assessed for function. In Balpha P-exposed fetuses, thymic Thy1(+) cell levels were decreased (relative to levels in organs of corn oil-exposed dam progeny). In addition, for up to 6 weeks post-birth, CD4(+)CD8(+) (double positive; DP) cells were virtually absent and levels of CD4(-)CD8(-) (double negative; DN) cells were consistently at epsilon 90%. With regard to single positive (SP) cells, CD4(+) cell levels were also decreased in tissues at GD18 up through 6 weeks post-birth; CD8(+) cell levels were increased, but only in pups at 1-week and 6-weeks post-birth. In 1-week-old progeny, spleen CD8(+) cell levels were quantitatively unchanged, though CD4(+) levels were reduced 2-4-fold and CD4(-)CD8(-) DN levels significantly increased. With respect to TCRs, fetal levels of thymic CD3Vgamma(3)(+) and CD3Vgamma delta(+) cells were decreased; levels of CD3Valphabeta cells were only slightly depressed. The latter results contrast sharply with a strong reduction in CD3Valphabeta cells in the fetal livers of Balpha P-exposed progeny. Interestingly, these livers also strongly evidenced a presence of BalphaP-7,8-dihydrodiol-9,10-epoxide metabolite. When assessed for any change in function, the CD4(+), Thy1(+) cells isolated from Balpha P-exposed progeny tissues responded weakly (relative to controls) to ConA and in an allogeneic MLR. Taken in totality, the results here strengthen our original hypothesis that BalphaP can create a favorable milieu for tumor growth progression in progeny of exposed mothers by affecting development of sufficient numbers of functional lymphocytes in the offspring.

Presence of CD4(+) SP and DP (gammadelta, alphabeta) T-Cells Expressing BPDE-DNA Adducts in Progeny of Mouse Dams Exposed to Benzo(alpha) pyrene at Mid-Gestation

After one exposure of C3H/HeJ pregnant females (at mid-gestation) to B(alpha) P (at 150 mu g/g BW), their progeny evidenced suppression of both humoral and cell-mediated immunity, as well as quantitative deficiencies in the levels of Lyt1(+) and Lyt2(+)cells, and CD4(+) CD8(+), V(gamma 3)(+), V(gamma delta)(+), and V(alpha beta)(+)T-cells. We hypothesized that these conditions could be a result, in part, of covalent binding of BPDE to DNA within these cells. To test this, antiserum to BPDE-DNA was generated in rabbits; after multiple purification steps, an anti-BPDE-DNA (rendered approximately 99.5% specific for BPDE-DNA and did not react with free BPDE or DNA antigens at dilutions even of < 1:50) antiserum was isolated. Flow cytometry and immunofluorescence analyses showed the adduct was present in CD4(+) cells of progeny fetal and in both post-natal thymus and spleen tissues. Using a [(32)P]-post-labelling method, adduct was also detected in samples of fetal liver during the period from Day 15 to 18 gestation. Surprisingly, it was found that thymus cells from B(alpha)P-exposed mice not exhibiting the adduct could severely suppress allogeneic mixed lymphocyte responses, while those in which the adduct was detected caused had a more pronounced suppression. We suspect from the findings here that the presence of BPDE-DNA adducts in T-cells contributes to, but is not necessarily the causa sola for, the immunosuppression that develops in the offspring of pregnant mothers who are exposed to B(alpha)P (among many other agents) via smoking, ingestion, or inhalation of environmental pollution.

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.

Clastogenic effects of benzo[a]pyrene in postimplantation embryos with different genetic background

Certain strains of mice vary in their enzyme inducibility by polycyclic hydrocarbons, i.e., the strain C57 shows high and the strain DBA shows low inducibility of aryl hydrocarbon hydroxylase (AHH) by benzo[a]pyrene (BaP). The effect of this genetically determined difference on the clastogenic response to BaP was studied in 11 day old embryos after transplacental treatment. The four possible crosses, C57 and DBA inter se, C57 X DBA and DBA X C57, were used to determine the influence of the genetic background on the aberration yields in the embryos. Constitutive and induced AHH levels were measured in liver, bone marrow, and placenta of the pregnant females and in their embryos. Enzyme inducibility was high in tissues of C57 dams and in their homozygous or heterozygous embryos. In contrast, induction of AHH activity was low in tissues of DBA females and their homozygous embryos. The high BaP-induced AHH activity found in heterozygous embryos of DBA dams is in agreement with the dominant mode of inheritance for high AHH inducibility. The cytogenetic results showed that the clastogenic response was lowest in homozygous C57 embryos and highest in hybrid embryos independent of the genetic constitution of the dams. Homozygous DBA embryos showed an intermediate aberration yield. The AHH inducibility by BaP did not correlate quantitatively with the induced aberration rates. However, the data suggest that BaP activation in embryonic tissue on day 11 of pregnancy is sufficient to account for the clastogenicity in the fetuses. It is concluded that the genetic endpoint chromosomal breakage is not only determined by the formation of active BaP metabolites but also by genetically controlled detoxification of BaP, repair process, and the rate of transformation of primary DNA lesions into true DNA discontinuities.

Micronucleus formation by benzene, cyclophosphamide, benzo(a)pyrene, and benzidine in male, female, pregnant female, and fetal mice

Male, female, pregnant female, and fetal ICR mice were compared for their acute sensitivity to four single doses of model carcinogens, as measured by micronucleus formation in polychromatic erythrocytes 24 h after treatment in adult bone marrow and fetal liver at days 17-19 of gestation. Cyclophosphamide caused a dose-responsive increase in micronuclei in all groups, without a consistent difference based on gender or pregnancy. At doses of 50 and 75 mg/kg given orally to the pregnant female, the fetuses were three to six times as sensitive as was the mother. Benzo(a)pyrene showed a similarly increased sensitivity of the fetus relative to the other groups, although it is a much weaker clastogen. Benzidine did not cause an increase in micronuclei in any group, although it was thought that the fetal liver might have been sensitive enough to detect it, relative to adult bone marrow. Benzene caused much less response in females than in males and almost no response in pregnant females and their fetuses, even though pregnant females metabolized at least half as much of the total dose as did the males (as measured by the presence of urinary metabolites of benzene). No single metabolite of benzene in the urine was consistently correlated with micronucleus formation in the bone marrow. Several factors must be interacting in different ways for different chemicals to influence their clastogenicity.

A new method to reveal the genotoxic effects of N-nitrosodimethylamine in pregnant mice

DNA damage and repair in kidney and liver of mouse fetuses exposed to selected doses of N-nitrosodimethylamine (NDMA) (CAS No. 62.75.9) were studied using the alkaline elution technique. CD1 female mice (15 days pregnant) were treated i.p. with 2 and 10 mg/kg b.w. of NDMA; a slight increase in DNA damage was observed in their fetuses compared to untreated controls. A 2-fold higher extent of DNA damage was induced when mice were treated by intrafetal injections of a rat S9 activating fraction (S9) immediately before exposure to the same dose of NDMA by transplacental means. The DNA-strand breaks disappeared as a function of time in animals treated with NDMA alone. In contrast, a significant persistence of DNA damage was detected in the liver and lung of fetuses which were treated with S9 and NDMA in sequence. These experiments demonstrate the metabolic immaturity of unborn mice as far as the carcinogenic activation of NDMA is concerned and show the high susceptibility of fetal tissues to DNA-damaging agents. The alkaline elution applied in vivo by the transplacental route combined with the intrafetal injection of an exogenous activating microsomal fraction allow to extend our knowledge on the interaction of metabolism-dependent chemicals with fetal tissues.

Stage-related induction of chromosomal aberrations and SCE in mouse embryos treated transplacentally during organogenesis with MMC and DMBA

During organogenesis, mouse embryos were treated transplacentally with MMC and DMBA. The clastogenic and SCE-inducing effects of MMC and the clastogenic effects of DMBA were analyzed in metaphases from whole embryo suspensions. Positive effects were observed on all the days of pregnancy on which the embryos were analyzed, i.e., on days 10, 11, 12, and 13. Whereas the MMC-induced SCE-frequencies did not change significantly during the tested period, the clastogenic effects of MMC and DMBA varied drastically. Extremely high aberration rates were observed in embryos on day 11; on the other days the aberration rates were much lower. Factors that might have given rise to these stage-related effects are discussed.

Transplacental genetic and cytogenetic effects of alkylating agents in the mouse. II. Induction of chromosomal aberrations

Six monofunctional alkylating agents, trenimon, cyclophosphamide, and isoniazid were proven for transplacental cytogenetic activity in mouse embryos at day 10 of gestational age under the same conditions as used in the mammalian spot test. With the exception of isoniazid, all compounds led to an increase in the aberration frequencies in embryonal cells. The results were statistically not significant in the case of EMS, while all other chemicals showed a dose-dependent clastogenic activity. After treatment with monofunctional alkylants, chromatid breaks were dominating, while polyfunctional compounds also produced chromatid exchanges, especially in the case of trenimon. ENU and DMS showed a very early aberration maximum 6 hr after injection. For both compounds, very similar dose-response curves were found for induction of chromatid breaks in the dose range 10-75 mg/kg. There is no correlation between the Swain-Scott factors of monofunctional alkylants and their ability to induce chromosomal damage when compared in terms of pharmacological doses. A quantitative comparison of data found in the cytogenetic test in embryonal cells with those obtained in the mammalian spot test led to the conclusion that chromosomal mutations are of minor relevancy for the expression of recessive alleles in heterozygous mouse embryos. With this respect, the mammalian spot test must be considered as an in vivo test for the detection of gene mutations in somatic cells of the mouse.

Transplacental genetic and cytogenetic effects of alkylating agents in the mouse. I: Induction of somatic coat color mutations

Induction of somatic coat color mutations by the alkylating agents ENU, MNU, EMS, MMS, DES, DMS, and trenimon and by the tuberculostatic drug INH was investigated in the mammalian spot test. Positive results were obtained with EMS (100 mg/kg), ENU (20-60 mg/kg), and INH (100 mg/kg), while trenimon (100 micrograms/kg), DES (225 mg/kg), and MNU (2 mg/kg) yielded inconclusive data. No mutagenic activity was found for MMS (125 mg/kg) and DMS (50 mg/kg). The mutagenic potency of monofunctional alkylating agents at subtoxic doses decreases as follows ENU greater than EMS greater than DES greater than MMS = DMS. The hypothesis that somatic coat color mutations in the mouse are predominantly due to intragenic changes is discussed. Differences in the RS frequency between offspring of the crosses NMRI X DBA and C57 X T are due to differences in loci available for mutation induction. Mutations that uncover the recessive allele p contribute to a significant extent to the total RS frequency observed in the mammalian spot test.