Kinetochore-staining of spermatid micronuclei: Studies of mice treated with X-radiation or acrylamide

Effect of sampling time on somatic and germ cell mutations induced by acrylamide in gpt delta mice

Background

Acrylamide (AA) is a rodent carcinogen and classified by the IARC into Group 2A (probable human carcinogen). AA has been reported to induce mutations in transgenic rodent gene mutation assays (TGR assays), the extent of which is presumed to depend on exposure length and the duration of expression after exposure. In particular, it is not clear in germ cells. To investigate mutagenicity with AA in somatic and germ cells at different sampling times, we conducted TGR assays using gpt delta transgenic mice.

Results

The male gpt delta mice at 8 weeks of age were treated with AA at 7.5, 15 and 30 mg/kg/day by gavage for 28 days. Peripheral blood was sampled on the last day of the treatment for micronucleus tests and tissues were sampled for gene mutation assays at day 31 and day 77, those being 3 and 49 days after the final treatment (28 + 3d and 28 + 49d), respectively. Another group of mice was treated with N-Ethyl-N-nitrosourea (ENU) at 50 mg/kg/day by intraperitoneal administration for 5 consecutive days and tissues were sampled at the day 31 and day 77 (5 + 26d and 5 + 72d). Frequencies of micronucleated erythrocytes in the peripheral blood significantly increased at AA doses of 15 and 30 mg/kg/day. Two- to three-fold increases in gpt mutation frequencies (MFs) compared to vehicle control were observed in the testes and lung treated with 30 mg/kg/day of AA at both sampling time. In the sperm, the gpt MFs and G:C to T:A transversions were significantly increased at 28 + 3d, but not at 28 + 49d. ENU induced gpt mutations in these tissues were examined at both 5 + 26d and 5 + 72d. A higher mutant frequency in the ENU-treated sperm was observed at 5 + 72d than that at 5 + 26d.

Conclusions

The gpt MFs in the testes, sperm and lung of the AA-treated mice were determined and compared between different sampling times (3 days or 49 days following 28 day-treatment). These results suggest that spermatogonial stem cells are less sensitive to AA mutagenicity under the experimental condition. Prolonged expression time after exposure to AA to detect mutagenicity may be effective in somatic cells but not in germ cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41021-021-00175-5.

Risks of aneuploidy induction from chemical exposure: Twenty years of collaborative research in Europe from basic science to regulatory implications

Although Theodor Boveri linked abnormal chromosome numbers and disease more than a century ago, an in-depth understanding of the impact of mitotic and meiotic chromosome segregation errors on cell proliferation and diseases is still lacking. This review reflects on the efforts and results of a large European research network that, from the 1980's until 2004, focused on protection against aneuploidy-inducing factors and tackled the following problems: 1) the origin and consequences of chromosome imbalance in somatic and germ cells; 2) aneuploidy as a result of environmental factors; 3) dose-effect relationships; 4) the need for validated assays to identify aneugenic factors and classify them according to their modes of action; 5) the need for reliable, quantitative data suitable for regulating exposure and preventing aneuploidy induction; 6) the need for mechanistic insight into the consequences of aneuploidy for human health. This activity brought together a consortium of experts from basic science and applied genetic toxicology to prepare the basis for defining guidelines and to encourage regulatory activities for the prevention of induced aneuploidy. Major strengths of the EU research programmes on aneuploidy were having a valuable scientific approach based on well-selected compounds and accurate methods that allow the determination of precise dose-effect relationships, reproducibility and inter-laboratory comparisons. The work was conducted by experienced scientists stimulated by a fascination with the complex scientific issues surrounding aneuploidy; a key strength was asking the right questions at the right time. The strength of the data permitted evaluation at the regulatory level. Finally, the entire enterprise benefited from a solid partnership under the lead of an inspired and stimulating coordinator. The research programme elucidated the major modes of action of aneugens, developed scientifically sound assays to assess aneugens in different tissues, and achieved the international validation of relevant assays with the goal of protecting human populations from aneugenic chemicals. The role of aneuploidy in tumorigenesis will require additional research, and the study of effects of exposure to multiple agents should become a priority. It is hoped that these reflections will stimulate the implementation of aneuploidy testing in national and OECD guidelines.

Combined action of X-rays and nonylphenol on mouse sperm

The aim of this study was to assess the effects of 2-weeks’ X-ray and/or nonylphenol (NP) exposure on male mice’s sperm count and quality. Pzh:SFIS mice were exposed to X-rays (0.05 Gy, 0.10 Gy, 0.20 Gy) or to nonylphenol (25 mg/kg bw, 50 mg/kg bw, 100 mg/kg bw) or to both agents (0.05 Gy + 25 mg/kg bw NP, 0.10 Gy + 50 mg/kg bw NP). At 24 h and 5 weeks after the end of exposure the sperm count, morphology and frequency of DNA damage in the male germ cells were estimated. Each agent alone diminished sperm count and morphology. The dose of 0.05 Gy of X-rays decreased the frequency of DNA damage. Combined exposure to lower doses of both agents significantly improved sperm morphology and decreased the level of DNA damage compared to one agent alone. Combined exposure to higher doses reduced the frequency of DNA damage compared to the effect of the appropriate dose of NP. Results of combined exposure to low doses of both agents suggest that 0.05 Gy of X-rays stimulate the DNA damagecontrol system and in consequence repair of DNA caused by X-rays and NP. It may be correlated with increased antioxidant capacity.

The carcinogenicity of dietary acrylamide intake: a comparative discussion of epidemiological and experimental animal research

Since 2002, it is known that the probable human carcinogen acrylamide is present in commonly consumed carbohydrate-rich foods, such as French fries and potato chips. In this review, the authors discuss the body of evidence on acrylamide carcinogenicity from both epidemiological and rodent studies, including variability, strengths and weaknesses, how both types of evidence relate, and possible reasons for discrepancies. In both rats and humans, increased incidences of various cancer types were observed. In rats, increased incidences of mammary gland, thyroid tumors and scrotal mesothelioma were observed in both studies that were performed. In humans, increased risks of ovarian and endometrial cancers, renal cell cancer, estrogen (and progesterone) receptor-positive breast cancer, and oral cavity cancer (the latter in non-smoking women) were observed. Some cancer types were found in both rats and humans, e.g., endometrial cancer (observed in one of the two rat studies), but there are also some inconsistencies. Interestingly, in humans, some indications for inverse associations were observed for lung and bladder cancers in women, and prostate and oro- and hypopharynx cancers in men. These latter observations indicate that genotoxicity may not be the only mechanism by which acrylamide causes cancer. The estimated risks based on the epidemiological studies for the sites for which a positive association was observed were considerably higher than those based on extrapolations from the rat studies. The observed pattern of increased risks in the rat and epidemiological studies and the decreased risks in the epidemiological studies suggests that acrylamide might influence hormonal systems, for which rodents may not be good models.

Mutagenicity of acrylamide and glycidamide in the testes of big blue mice

Acrylamide (AA) is an industrial chemical, a by-product of fried starchy foods, and a mutagen and rodent carcinogen. It can also cause damage during spermatogenesis. In this study, we investigated whether AA and its metabolite glycidamide (GA) induce mutagenic effects in the germ cells of male mice. Male Big Blue transgenic mice were administered 1.4 or 7.0mM of AA or GA in the drinking water for up to 4 weeks. Testicular cII mutant frequency (MF) was determined 3 weeks after the last treatment, and the types of the mutations in the cII gene were analyzed by DNA sequencing. The testes cII MFs in mice treated with either the low or high exposure concentrations of AA and GA were increased significantly. There was no significant difference in the cII MFs between AA and GA at the low exposure concentration. The mutation spectra in mice treated with AA (1.4mM) or GA (both 1.4 and 7.0mM) differed significantly from those of controls, but there were no significant differences in mutation patterns between AA and GA treatments. Comparison of the mutation spectra between testes and livers showed that the spectra differed significantly between the two tissues following treatment with AA or GA, whereas the mutation spectra in the two tissues from control mice were similar. These results suggest that AA possesses mutagenic effects on testes by virtue of its metabolism to GA, possibly targeting spermatogonial stem cells, but possibly via different pathways when compared mutations in liver.

Cytogenetic damage in preimplantation mouse embryos generated after paternal and parental gamma-irradiation and the influence of vitamin C

Cytogenetic damage expressed as micronuclei (MN) in 4-8-cell embryos generated after irradiation of male or male and female mice in the absence and presence of vitamin C was investigated. Male NMRI mice were whole body exposed to 4 Gy gamma-rays and mated with non-irradiated superovulated female mice in 6 successive weeks after irradiation in a weekly interval. In experiments involving irradiation of both male and female mice, irradiated male mice for 6 weeks post irradiation were mated with female mice irradiated after induction of superovulation. Effect of 100 mg/kg vitamin C (ascorbic acid) on the frequency of MN was also studied. Pregnant animals were euthanized and embryos flushed from the oviducts and fixed on slides. The rate of MN observed in embryos generated from irradiated male compared with control group dramatically increased (P<0.01). Frequency of MN in this group decreased dramatically after vitamin C treatment (P<0.01). Frequency of MN in embryos generated by mating both male and female irradiated mice was higher than that observed for those embryos generated by irradiated male mice alone. However, a considerable modifying effect of vitamin C was observed for this group too (P<0.05). Results indicate that irradiation of gonads during spermatogenesis and preovulatory stage oocytes may lead to unstable chromosomal aberrations and probably stable chromosomal abnormalities affecting pairing and disjunction of chromosomes in successive preimplantation embryos expressed as MN. The way vitamin C reduces clastogenic effects of radiation on germ cells leading to reduced frequency of MN in pre-embryos might be due to its antioxidation and radical scavenging properties.

A review of the toxicology of acrylamide

Acrylamide (ACR) is a chemical used in many industries around the world and more recently was found to form naturally in foods cooked at high temperatures. Acrylamide was shown to be a neurotoxicant, reproductive toxicant, and carcinogen in animal species. Only the neurotoxic effects were observed in humans and only at high levels of exposure in occupational settings. The mechanism underlying neurotoxic effects of ACR may be basic to the other toxic effects seen in animals. This mechanism involves interference with the kinesin-related motor proteins in nerve cells or with fusion proteins in the formation of vesicles at the nerve terminus and eventual cell death. Neurotoxicity and resulting behavioral changes can affect reproductive performance of ACR-exposed laboratory animals with resulting decreased reproductive performance. Further, the kinesin motor proteins are important in sperm motility, which could alter reproduction parameters. Effects on kinesin proteins could also explain some of the genotoxic effects on ACR. These proteins form the spindle fibers in the nucleus that function in the separation of chromosomes during cell division. This could explain the clastogenic effects of the chemical noted in a number of tests for genotoxicity and assays for germ cell damage. Other mechanisms underlying ACR-induced carcinogenesis or nerve toxicity are likely related to an affinity for sulfhydryl groups on proteins. Binding of the sulfhydryl groups could inactive proteins/enzymes involved in DNA repair and other critical cell functions. Direct interaction with DNA may or may not be a major mechanism for cancer induction in animals. The DNA adducts that form do not correlate with tumor sites and ACR is mostly negative in gene mutation assays except at high doses that may not be achievable in the diet. All epidemiologic studies fail to show any increased risk of cancer from either high-level occupational exposure or the low levels found in the diet. In fact, two of the epidemiologic studies show a decrease in cancer of the large bowel. A number of risk assessment studies were performed to estimate increased cancer risk. The results of these studies are highly variable depending on the model. There is universal consensus among international food safety groups in all countries that examined the issue of ACR in the diet that not enough information is available at this time to make informed decisions on which to base any regulatory action. Too little is known about levels of this chemical in different foods and the potential risk from dietary exposure. Avoidance of foods containing ACR would result in worse health issues from an unbalanced diet or pathogens from under cooked foods. There is some consensus that low levels of ACR in the diet are not a concern for neurotoxicity or reproductive toxicity in humans, although further research is need to study the long-term, low-level cumulative effects on the nervous system. Any relationship to cancer risk from dietary exposure is hypothetical at this point and awaits more definitive studies.

Dose–response modeling of in vivo genotoxicity data for use in risk assessment: some approaches illustrated by an analysis of acrylamide

Methods for dose-response modeling of in vivo genotoxicity data are introduced and applied to a case study of acrylamide. Genetic toxicity results are typically summarized as being either positive or negative, with no further consideration of the dose-response patterns that can be estimated from such studies. This analysis explores the use of three modeling approaches: Poisson regression of counts of genetic effects per cell; dynamic modeling of the time-course of micronucleus production and loss as a function of exposure; and categorical regression of sets of genetic toxicity experiments, the results of which are recoded in terms of severities of response. Estimates derived from these models (benchmark doses and predictions of response rates for predetermined doses of interest) are then used to assess the relevance and role of the genetic toxicity results in a risk assessment. With respect to the acrylamide data base, the results suggest that the genetic damage studies do not appear to be consistent or congruent with the thyroid tumor endpoints observed in two long-term bioassays in rats. This suggests that acrylamide's mechanism of action with respect to production of such tumors may not be genotoxic, and that a cancer risk assessment that applied a linear, no-threshold approach to such endpoints might be inappropriate. Benchmark doses derived from the genetic toxicity data base do not appear to be the critical ones for acrylamide risk assessment. Dose metric and modeling issues associated with the proposed dose-response approach to evaluation of genetic toxicity data are explored, and it is recommended that further advancements of the methodology be developed and employed for optimal use of such data for risk assessment purposes.

Micronucleus formation induced by the combination of low doses of X-rays and antineoplastic drugs in bone marrow of male mice

People are widely exposed during their lifetime to many biological, chemical, and physical agents in the environment and at work. In this paper the effects of combined exposures of nonmutagenic doses of X-rays and anticancer agents (cyclophosphamide, mitomycin C, and vinblastine) have been investigated on the induction of micronuclei in the bone marrow of laboratory mice. The combination of X-rays and anticancer drugs enhanced the frequency of micronuclei in some cases. The strongest effects were found after the combination of X-rays and cyclophosphamide at 24 h and 72 h. The combined treatment of X-rays and mitomycin C enhanced the mutagenic effect at 72 h. The combination of X-rays + vinblastine slightly potentiated the mutagenic effect at 24 h and 48 h.

In vivo rodent erythrocyte micronucleus assay. II. Some aspects of protocol design including repeated treatments, integration with toxicity testing, and automated scoring

An expert working group on the in vivo micronucleus assay, formed as part of the International Workshop on Genotoxicity Test Procedures (IWGTP), discussed protocols for the conduct of established and proposed micronucleus assays at a meeting held March 25-26, 1999 in Washington, DC, in conjunction with the annual meeting of the Environmental Mutagen Society. The working group reached consensus on a number issues, including: (1) protocols using repeated dosing in mice and rats; (2) integration of the (rodent erythrocyte) micronucleus assay into general toxicology studies; (3) the possible omission of concurrently-treated positive control animals from the assay; (4) automation of micronucleus scoring by flow cytometry or image analysis; (5) criteria for regulatory acceptance; (6) detection of aneuploidy induction in the micronucleus assay; and (7) micronucleus assays in tissues (germ cells, other organs, neonatal tissue) other than bone marrow. This report summarizes the discussions and recommendations of this working group. In the classic rodent erythrocyte assay, treatment schedules using repeated dosing of mice or rats, and integration of assays using such schedules into short-term toxicology studies, were considered acceptable as long as certain study criteria were met. When the micronucleus assay is integrated into ongoing toxicology studies, relatively short-term repeated-dose studies should be used preferentially because there is not yet sufficient data to demonstrate that conservative dose selection in longer term studies (longer than 1 month) does not reduce the sensitivity of the assay. Additional validation data are needed to resolve this point. In studies with mice, either bone marrow or blood was considered acceptable as the tissue for assessing micronucleus induction, provided that the absence of spleen function has been verified in the animal strains used. In studies with rats, the principal endpoint should be the frequency of micronucleated immature erythrocytes in bone marrow, although scoring of peripheral blood samples gives important supplementary data about the time course of micronucleus induction. When dose concentration and stability are verified appropriately, concurrent treatment with a positive control agent is not necessary. Control of staining and scoring procedures can be obtained by including appropriate reference samples that have been obtained from a separate experiment. For studies in rats or mice, treatment/sampling regimens should include treatment at intervals of no more than 24 hr (unless the test article has a half-life of more than 24 hr) with sampling of bone marrow or blood, respectively, within 24 or 40 hr after the last treatment. The use of a DNA specific stain is recommended for the identification of micronuclei, especially for studies in the rat. In the case of a negative assay result with a non-toxic test article, it is desirable that systemic exposure to the test article is demonstrated. The group concluded that successful application of automated scoring by both flow cytometry and image analysis had been achieved, and defined criteria that should be met if automated scoring is employed. It was not felt appropriate to attempt to define specific recommended protocols for automated scoring at the present time. Other issues reviewed and discussed by the working group included micronucleus assays that have been developed in a number of tissues other than bone marrow. The group felt that these assays were useful research tools that could also be used to elucidate mechanisms in certain regulatory situations, but that these assays had not yet been standardized and validated for routine regulatory application.

Acrylamide causes preimplantation abnormalities in embryos and induces chromatin-adducts in male germ cells of mice

Acrylamide, a known male postmeiotic germ cell mutagen, caused a dose-dependent increase in the frequency of morphologic abnormalities in preimplantation embryos. Single-cell eggs, growth retardation, and blastomere lysis were detected after paternal treatment with acrylamide (10 to 50 mg/kg, 5 d). The major effects were seen at weeks 1 to 3 after male treatment, with the highest level of abnormalities at the first week (> 90% vs. 5% in control). The frequency of abnormal four-day embryos was similar to preimplantation loss assessed at 15 to 16 d p.c. A > 100-fold elevation of chromatin adducts in sperm was observed during 1st and 2nd week after treatment, after which adduct levels decreased to baseline level. However, morphologic defects in embryos are not fully explained by the spermatid adduct curve. These findings demonstrate the effects of paternal exposure to acrylamide on preimplantation development and indicate a potential risk to the offspring of men exposed to acrylamide.

Micronuclei and developmental abnormalities in 4-day mouse embryos after paternal treatment with acrylamide

The developmental consequences of paternal exposure to acrylamide (50 mg/kg i.p. for 5 days) were assessed in preimplantation embryos. There was a significant increase in the proportion of morphologically abnormal embryos after postmeiotic treatment during spermatogenesis (88.7% vs. 14.8% in control). Abnormal embryos had an average of 1.8 +/- 3.5 cells and > 80% had at least one fragmented nucleus. In addition, morphologically normal embryos were significantly delayed (34.3 +/- 12.8 cells per embryo vs. 57.6 +/- 15.7 in control, P < 0.001). Acrylamide caused 10- and 20-fold increases in frequencies of cells with micronuclei (MN) in morphologically normal and abnormal embryos, respectively (41 and 93 MN per 1,000 cells). Both centromere-negative (MN-) and centromere-positive (MN+) were induced. Nuclei of abnormal embryos were significantly larger (900 microm2 vs. 250 microm2) than controls. In addition, MN of abnormal embryos were larger than those of normal embryos (21.2 microm2 vs. 6.5 microm2, P < 0.01). Among control embryos, MN+ were significantly larger than MN- (P < 0.05). These findings suggest that the preimplantation embryo is a sensitive indicator of paternally transmitted effects on early development. Multiple mechanisms appear to be involved, including cytogenetic damage, proliferation arrest/delay, and fertilization failure. Future studies are needed to establish how induced cytological defects in preimplantation embryos contribute to birth defects and other postimplantation abnormalities.

Spermatid micronucleus analysis of aging effects in hamsters

Spermatid micronuclei (MN) from Armenian hamsters in different age groups were compared with regard to frequencies and kinetochore status (presence or absence) as determined with immunofluorescent staining. Six thousand cells analyzed from each of fifteen young animals (3 months) revealed a group mean frequency of 0.45 MN/1000 spermatids; kinetochore staining was uniformly negative. Six thousand cells scored from each of fifteen older animals (2 years) revealed a group mean frequency of 1.00 MN/1000 spermatids. Most of the MN in these animals were negative for kinetochore staining, although a significant representation of MN with positive kinetochore staining was also observed. The results indicate that frequencies of spermatid MN increase with advancing age, and suggest that the increase is due to significant elevations in both chromosome breakage and chromosome loss.

Induction of hypoploidy and cell cycle delay by acrylamide in somatic and germinal cells of male mice

Monomeric acrylamide was tested for its potential to induce aneuploidy in spermatocytes and bone marrow cells of mice. For this purpose, chromosomes from metaphase spreads were counted semi-automatically. In both test systems, cell proliferation was monitored, determining the meiotic index of spermatocytes and the average generation time of bone marrow cells after BrdU incorporation, respectively. No indications could be seen for different sensitivity of somatic and germinal cells towards acrylamide. With a dose of 120 mg/kg, the chemical caused cell cycle delay in both germ line and somatic cells. There was diverging response with respect to the balance of hypo- and hyperploidy. While the percentage of chromosome loss was significantly elevated in both test systems, acrylamide treatment did not increase the frequency of hyperploid cells. Interpreting these results on the basis of conventional test protocols, acrylamide should not be considered as an aneugen. The conservative approach, however, may be inadequate for the detection of aneugenic mechanisms different from non-disjunction.

Micronuclei induced in round spermatids of mice after stem-cell treatment with chloral hydrate: evaluations with centromeric DNA probes and kinetochore antibodies

The chromosomal effects of chloral hydrate (CH) on germ cells of male mice were investigated using two methods to detect and characterize spermatid micronuclei (SMN); (a) anti-kinetochore immunofluorescence (SMN-CREST) and (b) multicolor fluorescence in situ hybridization with DNA probes for centromeric DNA and repetitive sequences on chromosome X (SMN-FISH). B6C3F1 mice received single intraperitoneal (i.p.) injections of 82.7, 165.4, or 413.5 mg/kg and round spermatids were sampled at three time intervals representing cells treated in late meiosis, early meiosis, or as spermatogonial stem cells. No increases in the frequencies of SMN were detected for cells treated during meiosis using either SMN-CREST or SMN-FISH methods. After spermatogonial stem-cell treatment, however, elevated frequencies of SMN were detected by both methods. With SMN-FISH, dose trends were observed both in the frequencies of spermatids containing micronuclei and in the frequency of spermatids carrying centromeric label. These findings corroborate the recent report by Allen and colleagues [Allen JW et al.(1994): Mutat. Res. 323:81-88] that CH treatment of spermatogenic stem cells induced SMN. Furthermore, our findings suggest that chromosomal malsegregation or loss may occur in spermatids long after CH treatment of stem cells. Further studies are needed to understand the mechanism of action of the CH effect on stem cells and to determine whether similar effects are induced in human males treated with CH.

Aneuploidies and micronuclei in the germ cells of male mice of advanced age

The objective of this research was to determine whether the frequencies of chromosomally defective germ cells increased with age in male laboratory mice. Two types of chromosomal abnormalities were characterized: (1) testicular spermatid aneuploidy (TSA) as measured by a new method of multi-color fluorescence in situ hybridization (FISH) with DNA probes specific for mouse chromosomes X, Y and 8, and (2) spermatid micronucleus (SMN) analyses using anti-kinetochore antibodies. B6C3F1 mice (aged 22.5 to 30.5 months, heavier than controls but otherwise in good health) showed significant approximately 2.0 fold increases in the aneuploidy phenotypes X-X-8, Y-Y-8, 8-8-X and 8-8-Y with the greatest effects appearing in animals aged greater than 28 months. No age effect was observed, however, in X-Y-8 hyperhaploidy. Major age-related increases were seen in Y-Y-8 and X-X-8 hyperhaploidies suggesting that advanced paternal age is associated primarily with meiosis II rather than meiosis I disjunction errors. A approximately 5 fold increase was also found in the frequency of micronucleated spermatids in aged mice when compared with young controls. All micronuclei detected in the aged animals lacked kinetochore labeling, suggesting that they either did not contain intact chromosomes or the chromosomes lacked detectable kinetochores. The findings of the TSA and SMN assays are consistent with meiotic or premeiotic effects of advanced age on germ cell chromosomes, but there were differences in the age dependencies of aneuploidy and micronuclei. In summary, advanced paternal age may be a risk factor for chromosomal abnormalities (both aneuploidy and structural abnormalities) in male germ cells.

Acrylamide: a review of its genotoxicity and an assessment of heritable genetic risk

An updated review of the genotoxicity studies with acrylamide is provided. Then, using data from the studies generating quantitative information concerning heritability of genetic effects, an assessment of the heritable genetic risk presented by acrylamide is presented. The review offers a discussion of the reactions and possible mechanisms of genotoxic action by acrylamide and its epoxide metabolite glycidamide. Several genetic risk approaches are discussed, including the parallelogram, direct (actually a modified direct), and doubling dose approaches. Using data from the specific-locus and heritable translocation assays, the modified direct and doubling dose approaches are utilized to quantitate genetic risk. Exposures of male parents to acrylamide via inhalation, ingestion, and dermal routes are also quantitated. With these approaches and measurements and their underlying assumptions concerning extrapolation factors (including germ cell stage specificity, DNA repair variability, locus specificity), number of human loci associated with dominant disease alleles, and spontaneous mutation rates, an assessment of heritable genetic risk for humans is calculated for the three exposure scenarios. The calculated estimates for offspring from fathers exposed to acrylamide via drinking water are up to three offspring potentially affected with induced genetic disease per 10(8) offspring. Estimates for inhalation or dermal exposures suggest higher risks for induced genetic disease in offspring from fathers exposed in occupational settings.

Increased frequencies of micronuclei in early spermatids of rats following exposure of young primary spermatocytes to acrylamide

The 'suspension method' for detection of micronuclei in early spermatids (Golgi phase 1 + 2) of rats was used to study induction of chromosomal damage in spermatocytes exposed to single (50 and 100 mg/kg) or fractionated (4 x 50 mg/kg; 24-h intervals) doses of acrylamide. Animals were killed at different time intervals after treatment to measure induction of damage in different stages of spermatocyte development. A statistically significant enhancement of micronucleus frequencies was found after exposure of pre-leptotene spermatocytes to a single dose of 100 mg/kg (days 18 and 20 after treatment) or a fractionated dose of 4 x 50 mg/kg (day 19). In the latter case there was also a significant effect in zygotene spermatocytes that were sampled 15 days after treatment. Comparative studies indicated that the original 'suspension method' can be simplified by omitting enzyme treatments for the release of germ cells from the seminiferous tubules. In the present acrylamide study the old and new procedures gave similar results.

The spermatid micronucleus test with the dissection technique detects the germ cell mutagenicity of acrylamide in rat meiotic cells

As a part of the development and validation of the spermatid micronucleus test (SMNT) in the project 'Detection of Germ Cell Mutagens' sponsored by the CEC we studied the mutagenicity of acrylamide (AA) and mitomycin C (MMC). Of two alternative techniques, we used the 'dissection technique' based on microdissection of seminiferous tubules offering a narrow window for evaluation of cell stage sensitivity, and including DNA-specific staining and scoring. AA given as a single injection of 50 or 100 mg/kg did not significantly increase MN frequencies. When a subchronic treatment (4 x 50 mg/kg) was given, a significant increase over background was observed 18 and 19 days after the last injection, indicating genotoxic activity in preleptotene spermatocytes and late spermatogonial stages. MMC given as single injections of 0.5 or 1.0 mg/kg increased MN frequencies significantly 17, 18, 19 and 20 days after treatment as a result of clastogenicity in S phase cells. DNA flow cytometry did not show cytotoxicity of AA to preleptotene spermatocytes, but a small decrease in the numbers of stem cells. If spindle disturbances are caused by AA, as suggested, they were not detectable by induction of spermatid MN in vivo 1 or 3 days after treatment or by treatment with AA of cultured segments of seminiferous tubules undergoing meiotic divisions in vitro. In conclusion, the SMNT with the dissection technique is able to show the germ cell clastogenicity of AA and MMC. AA was observed to have a much weaker MN inducing potency than MMC.

Weak genotoxicity of acrylamide on premeiotic and somatic cells of the mouse

The effects of acrylamide (AA) were evaluated, under the EEC/STEP project 'Detection of Germ Cell Mutagens', by carrying out several cytogenetic assays on mouse germ and somatic cells. The spermatid micronucleus (MN) test was applied after treatment of meiotically dividing or premeiotic S phase cells. Acute treatments (50 and 100 mg/kg i.p.) as well as subchronic exposure to AA (4 x 50 mg/kg, 4 i.p. injections at 24-h intervals) were performed. A weak increase of MN was induced only by treatment with AA of cells in S phase. Sister-chromatid exchange (SCE) analysis in differentiating spermatogonia treated i.p. with 50 and 100 mg/kg confirmed the weak genotoxicity of AA in the premeiotic stages of spermatogenesis. The application of the MN test in peripheral blood reticulocytes of the same animals used for the spermatid MN assay indicated that the cytogenetic effects induced by AA in the somatic and the germ cell lines are comparable in magnitude. The results obtained in this study by applying the spermatid micronucleus assay are in very good agreement with those reported by two other laboratories with the same technique.

Spermatid micronucleus analyses of trichloroethylene and chloral hydrate effects in mice

Mice were exposed by inhalation to trichloroethylene (TCE) or by i.p. injection to the TCE metabolite, chloral hydrate (CH). Early spermatids were analyzed for micronucleus (MN) frequency and the presence or absence of kinetochore(s) using fluorochrome-labeled anti-kinetochore antibodies. It was determined that 5 consecutive days of exposure to 5, 50 or 500 ppm TCE during preleptotene through early pachytene stages of meiotic cell development do not result in increased frequencies of spermatid MN. CH at 41, 83 or 165 mg/kg was positive for spermatid MN induction when treatments corresponded to spermatogonial stem cell or preleptotene spermatocyte stages of development; negative results were obtained after treatments of leptotene-zygotene or diakinesis-metaphase stages. The significantly increased levels of MN observed were invariably of the kinetochore-negative type.