Recommended procedures for testing genetic hazards from chemicals, based on the induction of dominant lethal mutations in mammals

Dominant lethal mutations induced in mouse spermatogonia by antineoplastic drugs

Male mice were treated with nitrogen mustard (2.25 mg/kg), procarbazine (100 mg/kg) or vincristine (0.67 mg/kg). 5 weeks later they were mated to untreated females and the dominant lethal mutant rate was determined in the offspring by an in vitro analysis. Nitrogen mustard and procarbazine induced dominant lethal mutations to significant levels. Mutations were expressed, throughout early development, especially as a failure to form a trophectoderm outgrowth and to differentiate and proliferate an inner cell mass. Variations in the dominant lethal mutant rate were found from one week to the next, suggesting that differentiated and stem cell spermatogonia have differential sensitivity to mutation induction and cell killing by each drug.

Elevated fetal chromosomal damage in malnourished pregnant rats

Cytogenetic studies in fetal cells from pregnant rats given a protein-restricted diet revealed a significant induction of structural chromosomal aberrations and sister chromatid exchanges.

Dominant lethal induction and testicular uptake of iodine-125 in mice

The mutagenic potential of 125I was studied using dominant lethal (DL) and testicular uptake studies. Dominant lethality (DL) represents embryonic death resulting from the chromosomal breakage in gametes of parents. When compared to controls, mice treated with different doses of 125I showed significant levels of induced DL. Significant pre-implantation losses were observed and variations in live implantations indicated total losses by the isotope. Dead implantations per pregnant female in the isotope treated groups showed a significant increase from controls indicating induced levels of post-implantation losses. All the stages of spermatogenesis, i.e., spermatozoa, spermatid, spermatocyte and spermatogonia were found to be sensitive to the induction of post-implantation losses, the spermatid stage being the most sensitive. Testicular uptake was measured from 1/2 hour to 72 hours after injection and maximum uptake was recorded at 1/2 hour, indicating the permeability of the blood/testis barrier.

Evaluation of the mutagenic effects of phenobarbital by dominant lethal assay in Swiss mice

Phenobarbital, a potent antiepileptic drug, was tested for the induction of dominant lethal mutations in male Swiss mice. The drug was administered in sterile distilled water at doses of 42, 84 or 126 mg/kg body weight by intubation over five consecutive days. Controls were given distilled water alone. The males were then mated for 1 wk sequentially with pairs of untreated virgin females for a total of 8 wk. The females were killed 17 days after presumed mating and the uterine contents were examined. There was a significant reduction in the total number of implantations and an increase in the number of dead implantations per pregnant female in the treated groups compared with the controls. The results from sequential matings showed that the pre-meiotic stages of spermatogenesis were more affected than the post-meiotic stages.

Dominant-lethal study of technical-grade hexachlorocyclohexane in Swiss mice

Male Swiss mice, 6-8 weeks old, were given a diet containing technical-grade hexachlorocyclohexane (BHC) at 500 ppm continuously for 4, 6 and 8 months. After the completion of the scheduled exposure period, the males were sequentially mated with 2-3 untreated virgin females at weekly intervals for 8 weeks. The females were autopsied at mid-term pregnancy for evaluation of dominant-lethal mutation. The number of dead implants, including deciduomas and dead embryos, showed a significant increase. Similarly, the percentage fertility and live embryos per female showed a decline when compared with the control

Comparison of dominant lethal and heritable translocation methodologies

Groups of male Alderly Park mice of proven fertility were dosed by gavage for 5 consecutive days per week for 8 weeks or 5 consecutive days only with 100 or 150 mg/kg body weight ethyl methanesulphonate (EMS) or by intraperitoneal injection once a week for 8 weeks or once only with 500 mg/kg shikimic acid. Animals dosed in this manner were compared in the dominant lethal and heritable translocation assays. Animals were mated for 2 consecutive weeks following the 8-week treatment and for 8 consecutive weeks after the 1-week treatment: regimes which were thus non-specific and specific respectively for the stages of spermatogenesis. An additional method of measuring dominant lethality involving counting uterine scars after weaning (Soares (1972) Mutation Res., 16, 425-427) was used and also compared with the conventional method. EMS was clearly confirmed as a mutagen but this was not the case for shikimic acid. For screening purposes the dominant lethal 8-week mating assay was much more efficient in return for the same effort for detecting mutagenic responses than an 8-week mating heritable translocation assay, since the induction of dominant lethal effects paralleled the induction of heritable translocations. 8-week treatment with EMS showed increased dominant lethality but severely reduced fertility and the small numbers of male offspring born made potential heritable effects difficult to assess. The 1-week treatment with EMS produced both dominant lethal and heritable effects. Soares' method can be useful for determining dominant lethal effects in a heritable translocation assay. The "sieving" method of mating to determine partial and total sterility questions the necessity for a negative control in a heritable translocation study.

Lack of induction of dominant lethal mutations in male mice by nalidixic acid

Nalidixic acid (NA) in single or in 5 consecutive daily doses of 100 or 1000 mg/kg produced no dominant lethal mutational effects in male ddY strain mice during an 8-week mating schedule. Ethylmethanesulfonate (EMS), used as a positive control, produced dominant lethal mutations in the first and second weeks.

Genetic effects of turmeric and curcumin in mice and rats

Incorporation of either turmeric (0.5%) or curcumin (0.015%) into diets of mice did not show significant effect on the incidence of micronucleated polychromatic erythrocytes, structural and numerical aberrations in bone-marrow chromosomes, pregnancy rate, number of live and dead embryos, total implants and mutagenic index. Also rats fed cooked diets containing turmeric (0.5 and 0.05%) did not show significant differences in the incidence of chromosomal aberrations in their bone marrow.

Mutagenicity studies of 4-(2-carboxyethyl) phenyl trans-4-aminomethylcyclohexane carboxylate hydrochloride (DV-1006). A new antiulcer drug

An antiulcer drug, 4-(2-carboxyethyl) phenyl trans 4-aminomethylcyclohexane carboxylate hydrochloride (DV-1006), was studied for mutagenicity using bacterial systems, in vitro and in vivo cytogenetics, and dominant lethal tests. No mutagenicity of DV-1006 was observed either in the rec-assay on Bacillus subtilis or in the Salmonella/microsome test (Ames test). In in vitro cytogenetics, DV-1006 had no effects on the chromosomes of chinese hamster cells at cytotoxic doses. Rats were treated singly or on 5 consecutive days orally with dose levels of 16, 160, or 1600 mg DV-1006/kg for detecting cytogenetic effects in vivo. As a result, no increase of the incidence of chromosomal aberrations in bone marrow cells was observed in any group of DV-1006. A single or 5 daily oral administration of DV-1006 (16 or 1600 mg/kg) to male mice and subsequent mating for 8 weeks produced no dominant lethal mutational effects. These results show that DV-1006 has no mutagenic potential.

Chronic methadone administration to male rats: tolerance to adverse effects on sires and their progeny

Previous studies have shown that acute administration of methadone to male rats prior to mating results in adverse effects on their progeny, particularly decreased birth weights and increased neonatal mortality. Rather than chronic administration accentuating these effects, results of the present study indicate that tolerance developed so that no adverse effects were found in offspring sired after 21--32 days of methadone administration. In the sire, maintenance of normal weights of accessory sex glands after 4 months of daily methadone suggests that tolerance developed to the CNS effect(s) responsible for the depressed serum LH and testosterone levels found after acute administration of narcotics. In contrast, tolerance did not develop to the inhibition of weight gain produced by methadone administration. No evidence for a dominant lethal effect could be found after chronic methadone administration, in contrast to suggestive evidence for this effect found in previous experiments after acute methadone administration.

Lack of genetic and cytogenetic effects in mice fed on irradiated wheat

Experiments were conducted to test the mutagenicity of wheat irradiated with 20 and 200 krad gamma-rays by feeding male and female mice for various periods starting from weaning time. The results obtained from dominant lethal tests, specific locus mutation test, studies on chromosome rearrangements in males and gonadal cell survival studies indicated no positive evidence for genetic and cytogenetic effects.

Detection of X-ray induced dominant lethal mutations in mice: an in vitro approach

The expression of dominant lethal mutations induced by 450 rad of X-radiation in the germ cells of male mice was detected by an in vitro analysis. Embryos sired by irradiated males had a higher incidence of developmental failures in early cleavage, at the late morula stage, and at the late blastocyst stage due to dominant lethal mutations than did control embryos. Dominant lethal mutations were induced most frequently in germ cells exposed as early spermatids and spermatocytes and next most frequently in germ cells exposed as sperm. A decrease in fertilizations, presumably reflecting cell killing, was found in irradiated spermatocytes. These observations indicate that in vitro analysis permits a more detailed description of mutations that are expressed as preimplantation failures than does in vivo analysis.

The dominant lethal effect of dietary triethylenemelamine

Triethylenemelamine (TEM) was administered in the diet to adult male mice at doses of 0.1, 0.3, 1, 10 or 50 mg/kg body weight for 45 days or at doses of 0.1 or 0.3 mg/kg b.w. for 10 days. As a comparison, male mice were treated intraperitoneally with 5 daily doses of 0.25 or 0.5 mg TEM/kg b.w. At the end of the treatment period, males were mated sequentially with 2 untreated virgin females each for 2 or 3 weeks. Near mid-pregnancy the number of implantation sites and fetal deaths were determined. TEM, administered in the diet at 10 or 50 mg/kg b.w. for 45 dyas, was lethal to male mice. Surviving males from the 1 mg/kg level failed to impregnate any females during the two matings. TEM, given in the diet at 0.1 or 0.3 mg/kg for 10 or 45 dyas, decreased fertility and increased dominant lethal mutations in a dose and time dependent manner. These results were comparable to those obtained from males treated i.p. with TEM at 0.25 or 0.5 mg/kg b.w.

System for the evaluation of the risk from chemical mutagens for man: basic principles and practical recommendations

A testing system is recommended that permits (1) reduction in cost and time requirements, (2) analysis of gene and chromosome mutations in germ and somatic cells, (3) evaluation of mutagenic effects of a chemical substance and its metabolites, (4) guarantee of the minimal variability between separate experiments and (5) evaluation of the dose--effect relationship. The testing scheme has two parts, a screening system and a complete test system. The screening system consists of two tests: (a) test on microorganisms with a metabolic activation in vitro (or test on Drosophila) and (b) cytogenetic analysis of mammalian bone marrow. The complete test system includes 4 tests: (a) test on microorganisms with a metabolic activation in vitro and in vivo (or test on Drosophila), (b) dominant-lethal test on mammals, (c) cytogenetic analysis of mammalian bone marrow and (d) cytogenetic analysis of the culture of human lymphocytes. The decision whether the selected chemical substance is to be tested according to the screening or complete test system is based on: its occurrence in the population, its economic (or medical) significance, and on information concerning its mutagenic, carcinogenic or teratogenic effects. The group of chemicals to be tested according to the screening system involves: industrial chemicals, organophosphate insecticides, drugs used by a limited group of patients. The group of chemicals to be tested according to the complete test system consists of pesticides, food additives, drugs in general use as well as chemicals of the former group, if at least one of the screening system tests detected some genetic effect. Genetic risk estimation should be governed by the following considerations. A positive effect identified in any test of the testing system must have a direct bearing on man. Quantitative evaluation of mutagenic risk from a chemical substance can be determined by the increased level of spontaneous mutations in the most sensitive test on the basis of an average dose of, and exposure to, the given chemical substance in the human population. Chemicals showing a mutagenic activity in any of recommended tests are subject to the quantitative evaluation, they are usually widespread and because of their social or economic value they cannot be replaced or excluded. Genetic aspects require that any substance with a mutagenic activity be considered dangerous and its use should be prohibited or it should be replaced by another non-mutagenic chemical, or at least the contact with it should be limited to persons of non-reproductive age. From the hygienic aspect it is recommended, as a temporary measure, to evaluate a chemical mutagen and to prohibit or limit its use if its average population dose produces a 0.1% or greater increase in the spontaneous level of mutations.

Genetic effects of feeding irradiated wheat to mice

The effects of feeding irradiated wheat in mice on bone marrow and testis chromosomes, germ cell numbers and dominant lethal mutations were investigated. Feeding of freshly irradiated wheat resulted in significantly increased incidence of polyploid cells in bone marrow, aneuploid cells in testis, reduction in number of spermatogonia of types A, B and resting primary spermatocytes as well as a higher mutagenic index. Such a response was not observed when mice were fed stored irradiated wheat. Also there was no difference between the mice fed un-irradiated wheat and stored irradiated wheat.

The mutagenicity of azathioprine in mice, Drosophila melanogaster and Neurospora crassa

The chemotherapeutic coumpound azathioprine was tested for possible mutagenicity in Swiss Albino mice, Drosophila melanogaster and Neurospora crassa. Utilizing the dominant-lethal assay it was found that acute oral doses of azathioprine (2 times 25 mg/kg body weight), induced dominant-lethal mutations in mouse spermatocytes. Chronic oral doses of azathioprine (2 times 25 mg/kg body weight/week for 10 weeks) resulted in a greater rate of dominant-lethality. This increase was not permanent, and by week 4 of gamete sampling there was no significant increase in dominant-lethal mutations. Histological sections showed that chronic treatment of male mice with azathioprine caused pyknosis of spermatocyte nuclei and depletion of the spermatid population. Both acute and chronic doses of azathioprine caused a temporary reduction in sperm viability. Oral treatment of male Canton-S, D. melanogaster with azathioprine caused an increase in dominant-lethality in broods assumed to correspond to spermatid and spermaotcyte stages. Azathioprine also increased the rate of non-disjunction of the X and Y chromosomes, loss of the long arm of the Y chromosome, and loss of the X or Y chromosome in treated male R(I)2, vf/BsYy+D. melanogaster. Since sex-ratio deviation did not occur in progeny from treated rod-X (yv/B2Yy+) male D. melanogaster, it was concluded that the observed sex-ration deviation in the treated ring-X stock was the result of induced ring-X lethality. Azathioprine induced recessive-lethal mutations in the ad-3 region of a N. crassa heterokaryon. In the host-mediated assay using this same heterokaryon and male Swiss Albino mice as host, the mutagenic activity of azathioprine did not appear to be potentiated or detoxified by the host. The results show that azathioprine has a deleterious effect on reproduction in mice and probably induces mutational events in mice, D. melanogaster and N. crassa.