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

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.

Acrylamide Induced Toxicity and the Propensity of Phytochemicals in Amelioration: A Review

Acrylamide is widely found in baked and fried foods, produced in large amount in industries and is a prime component in toxicity. This review highlights various toxicities that are induced due to acrylamide, its proposed mode of action including oxidative stress cascades and ameliorative mechanisms using phytochemicals. Acrylamide formation, the mechanism of toxicity and the studies on the role of oxidative stress and mitochondrial dysfunctions are elaborated in this paper. The various types of toxicities caused by Acrylamide and the modulation studies using phytochemicals that are carried out on various type of toxicity like neurotoxicity, hepatotoxicity, cardiotoxicity, immune system, and skeletal system, as well as embryos have been explored. Lacunae of studies include the need to explore methods for reducing the formation of acrylamide in food while cooking and also better modulators for alleviating the toxicity and associated dysfunctions along with identifying its molecular mechanisms.

Herbicides and adjuvants: an evolving view

The present report examines the in vitro genotoxicity (micronucleus assay) of herbicides and adjuvants and reports on an in vivo human study on potential endocrine effects of pesticides, including herbicides. Adjuvants are used in conjunction with 2,4-dichlorophenoxy acetic acid (2,4-D) and other herbicides. Earlier pesticide applier survey results ( n = 709) show that 59% of the applicators used adjuvants, and the majority of this group used paraffinic oils and/or surfactant mixtures. As a beginning effort to explore the role of adjuvants and herbicides in hormonally based reproductive effects, a prospective, controlled study was performed to analyze blood specimens from three different exposure groups (applicators using herbicides only; applicators using both herbicides and insecticides; and applicators using fumigants in addition to herbicides and insecticides; and a control group composed of other agricultural workers including organic farmers). The applicators and controls were age- and smoking-matched. Study subjects ( n = 78) were tested before, during, and after completion of pesticide application season for the effects of pesticide products on hormone levels in the bloodstream. Of the applicator exposure groups examined, only the herbicide group showed significant endocrinologic differences from controls. Free testosterone levels were significantly elevated in post-season measurements ( p = 0.032), and follicle-stimulating hormone (FSH) was significantly decreased at the height of the season ( p = 0.016) and in the post-season ( p = 0.010) as compared to controls. These endocrinologic findings are discussed in terms of their possible relationship to potential endocrine effects of herbicides, herbicide contaminants, and adjuvants. In vitro genotoxicity examination compared four different commercially available surfactant mixtures with 12 different commercial herbicide products, including six different chlorophenoxy herbicides. Only one herbicide yielded a significant dose-response curve. All four adjuvants showed positive dose-response effects. These preliminary data suggest that adjuvants are not inert but are toxicologically active components added to herbicide mixtures. Whether adjuvant toxicant effects are additive or are independent of herbicide effects is poorly understood.

Effects of long term low dose acrylamide exposure on rat bone marrow polychromatic erythrocytes

I investigated whether long term low dose exposure to acrylamide increased micronucleus frequency in rat bone marrow polychromatic erythrocytes (PCEs). Twenty-five male and 25 female Wistar rats were used. Animals of each sex were segregated into two treatment groups and one control group. Each treatment group consisted of ten animals and each control group consisted of five animals. Acrylamide, 2 or 5 mg/kg/day, was administered to the treatment groups in their drinking water for 90 days. Twenty-four hours after the last treatment, bone marrow samples were obtained and analyzed for the frequency of micronucleated polychromatic erythrocytes (MNPCEs). The cytotoxic effect of acrylamide on bone marrow also was tested by assessing the polychromatic erythrocyte/normochromatic erythrocyte (PCE/NCE) ratio. Both doses of acrylamide significantly increased the frequency of MNPCEs in both male and female rats. Acrylamide also decreased the PCE/NCE ratio in both sexes compared to the control group. My study showed that chronic low dose exposure to acrylamide increased the formation of micronuclei in PCEs of male and female rat bone marrow.

Acrylamide genotoxicity in young versus adult gpt delta male rats

The recent discovery that the potent carcinogen acrylamide (AA) is present in a variety of fried and baked foods raises health concerns, particularly for children, because AA is relatively high in child-favoured foods such as potato chips and French fries. To compare the susceptibility to AA-induced genotoxicity of young versus adult animals, we treated 3- and 11-week-old male gpt delta transgenic F344 rats with 0, 20, 40 or 80 p.p.m. AA via drinking water for 4 weeks and then examined genotoxicity in the bone marrow, liver and testis. We also analysed the level of N7-(2-carbamoyl-2-hydroxyethyl)-guanine (N7-GA-Gua), the major DNA adduct induced by AA, in the liver, testis and mammary gland. At 40 and 80 p.p.m., both age groups yield similar results in the comet assay in liver; but at 80 p.p.m., the bone marrow micronucleus frequency and the gpt-mutant frequency in testis increased significantly only in the young rats, and N7-GA-Gua adducts in the testis was significantly higher in the young rats. These results imply that young rats are more susceptible than adult rats to AA-induced testicular genotoxicity.

Genotoxicity of acrylamide in vitro: Acrylamide is not metabolically activated in standard in vitro systems

The recent finding that acrylamide (AA), a genotoxic rodent carcinogen, is formed during the frying or baking of a variety of foods raises human health concerns. AA is known to be metabolized by cytochrome P450 2E1 (CYP2E1) to glycidamide (GA), which is responsible for AA's in vivo genotoxicity and probable carcinogenicity. In in-vitro mammalian cell tests, however, AA genotoxicity is not enhanced by rat liver S9 or a human liver microsomal fraction. In an attempt to demonstrate the in vitro expression of AA genotoxicity, we employed Salmonella strains and human cell lines that overexpress human CYP2E1. In the umu test, however, AA was not genotoxic in the CYP2E1-expressing Salmonella strain or its parental strain. Moreover, a transgenic human lymphoblastoid cell line overexpressing CYP2E1 (h2E1v2) and its parental cell line (AHH-1) both showed equally weak cytotoxic and genotoxic responses to high (>1 mM) AA concentrations. The DNA adduct N7-GA-Gua, which is detected in liver following AA treatment in vivo, was not substantially formed in the in vitro system. These results indicate that AA was not metabolically activated to GA in vitro. Thus, AA is not relevantly genotoxic in vitro, although its in vivo genotoxicity was clearly demonstrated.

Toxicity of acrylamide and evaluation of its exposure in baby foods

Contaminants are a vast subject area of food safety and quality and can be present in our food chain from raw materials to finished products. Acrylamide, an α,β-unsaturated (conjugated) reactive molecule, can be detected as a contaminant in several foodstuffs including baby foods and infant formulas. It is anticipated that children will generally have intakes that are two to three times those of adults when expressed on a body-weight basis. Though exposure to acrylamide is inevitable, it is necessary to protect infant and children from high exposure. The present review focuses on the several adverse health effects of acrylamide including mutagenicity, genotoxicity, carcinogenicity, neurotoxicity and reproductive toxicity, and the possible outcomes of childhood exposure from baby foods and infant formulas.

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.

Genotoxicity of acrylamide in human hepatoma G2 (HepG2) cells

The recent finding that acrylamide (AA), a carcinogen in animal experiments and a probable human carcinogen, is formed in foods during cooking raises human health concerns. The relevance of dietary exposure for humans is still under debate. The purpose of the study was to evaluate the possible genotoxicity of acrylamide in human hepatoma G2 (HepG2) cells, a cell line of great relevance to detect genotoxic/antigenotoxic substances, using single cell gel electrophoresis (SCGE) assay and micronucleus test (MNT). In order to clarify the underlying mechanism(s) we evaluated the intracellular generation of reactive oxygen species (ROS) and the level of oxidative DNA damage by immunocytochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG). The involvement of glutathione (GSH) in the AA-induced oxidative stress was examined through treatment with buthionine sulfoximine (BSO) to deplete GSH. The results indicate that AA caused DNA strand breaks and increase in frequency of MN in HepG2 cells in a dose-dependent manner. The possible mechanism underlies the increased levels of ROS, depletion of GSH and increase of 8-OHdG formation in HepG2 cells treated with AA. We conclude that AA exerts genotoxic effects in HepG2 cells, probably through oxidative DNA damage induced by intracellular ROS and depletion of GSH.

Lack of preventive effects of dietary fibers or chlorophyllin against acrylamide toxicity in rats

Dietary fibers and chlorophyllin have shown to exert anti-carcinogenic effects against co-administered carcinogens. To test the possibility of chemoprevention by such dietary supplements on subacutely induced acrylamide (ACR) toxicity, Sprague-Dawley male rats were administered 2.5% sodium alginate, 5% glucomannan, 5% digestion resistant maltodextrin, 2.5% chitin or 1% chlorophyllin in the diet, and starting one week later, co-administered 0.02% ACR in the drinking water for 4 weeks. For comparison, untreated control animals given basal diet and tap water were also included. Neurotoxicity was examined with reference to gait abnormalities and by quantitative assessment of histopathological changes in the sciatic and trigeminal nerves, as well as aberrant dot-like immunoreactivity for synaptophysin in the cerebellar molecular layer. Testicular toxicity was assessed by quantitation of seminiferous tubules with exfoliation of germ cells into the lumen and cell debris in the ducts of the epididymides. Development of testicular toxicity as well as neurotoxicity was evident with ACR-treatment, but was not suppressed by dietary addition of fibers or chlorophyllin, suggesting no apparent beneficial influence of these dietary supplements on experimentally induced subacute ACR toxicity.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

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.

Comparison of Germ Cell Mutagenicity in Male CYP2E1-Null and Wild-Type Mice Treated with Acrylamide: Evidence Supporting a Glycidamide-Mediated Effect

Acrylamide is an animal carcinogen and probable human carcinogen present in appreciable amounts in heated carbohydrate-rich foodstuffs. It is also a germ cell mutagen, inducing dominant lethal mutations and heritable chromosomal translocations in postmeiotic sperm of treated mice. Acrylamide's affinity for male germ cells has sometimes been overlooked in assessing its toxicity and defining human health risks. Previous investigations of acrylamide's germ cell activity in mice showed stronger effects after repeated administration of low doses compared with a single high dose, suggesting the possible involvement of a stable metabolite. A key oxidative metabolite of acrylamide is the epoxide glycidamide, generated by cytochrome P4502E1 (CYP2E1). To explore the role of CYP2E1 metabolism in the germ cell mutagenicity of acrylamide, CYP2E1-null and wild-type male mice were treated by intraperitoneal injection with 0, 12.5, 25, or 50 mg acrylamide (5 ml saline)(-1) kg(-1) day(-1) for 5 consecutive days. At defined times after exposure, males were mated to untreated B6C3F1 females. Females were killed in late gestation and uterine contents were examined. Dose-related increases in resorption moles (chromosomally aberrant embryos) and decreases in the numbers of pregnant females and the proportion of living fetuses were seen in females mated to acrylamide-treated wild-type mice. No changes in any fertility parameters were seen in females mated to acrylamide-treated CYP2E1-null mice. Our results constitute the first unequivocal demonstration that acrylamide-induced germ cell mutations in male mice require CYP2E1-mediated epoxidation of acrylamide. Thus, CYP2E1 polymorphisms in human populations, resulting in variable enzyme metabolic activities, may produce differential susceptibilities to acrylamide toxicities.

In vivo cytogenetics: mammalian germ cells

This chapter summarizes the most relevant methodologies available for evaluation of cytogenetic damage induced in vivo in mammalian germ cells. Protocols are provided for the following endpoints: numerical and structural chromosome aberrations in secondary oocytes or first-cleavage zygotes, reciprocal translocations in primary spermatocytes, chromosome counting in secondary spermatocytes, numerical and structural chromosome aberrations, and sister chromatid exchanges (SCE) in spermatogonia, micronuclei in early spermatids, aneuploidy in mature sperm. The significance of each methodology is discussed. The contribution of novel molecular cytogenetic approaches to the detection of chromosome damage in rodent germ cells is also considered.

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.

Synthesis report of the step project detection of germ cell mutagens

The project 'Detection of Germ Cell Mutagens' was designed with three major goals: (1) Detection and characterization of germ-cell mutagens; (2) standardization and validation of new germ-cell tests; and (3) development of a data base on germ-cell mutagenicity. All three goals were achieved. The classical germ-cell tests were applied to characterize the genetic effects of acrylamide (AA), 1,3-butadiene (BD), trophosphamide (TP) and urethane (UR). All but UR were found to cause heritable genetic damage. The experimental data obtained for AA and BD were the basis for genetic risk evaluations during the EC/US Workshop on Risk Assessment 'Human Genetic Risk from Exposure to Chemicals, Focusing on the Feasibility of the Parallelogram Approach'. Nine chemicals were employed to validate the spermatid micronucleus assay with mice and rats: AA, BD and its metabolites 1,2-epoxybutene-3 and 1,2:3,4-diepoxybutane, chlorambucil, mitomycin C, methylnitrosourea, TP and UR. The spermatid micronucleus test was combined with micronucleus tests in somatic cells such as bone marrow or peripheral blood erythrocytes, and splenocytes which allowed a comparison of effects in somatic and germinal cells. Improvements of the spermatid micronucleus test included BrdU-labelling of premeiotic S-phase for the determination of stage sensitivity and fluorescence in situ hybridization with pancentromeric DNA-probes to distinguish between clastogenic and aneugenic events. The results indicate that the spermatid micronucleus test with its improvements is an adequate procedure to detect germ-cell clastogenicity and to compare the activity of chemicals in different tissues and between species, i.e., rats and mice. Other germ cell methods under study were the flow cytometric measurement of testicular sperm DNA and the cytogenetic analysis of preimplantation embryos for chromosomal aberrations and micronuclei. The collection of a reliable germ-cell data base was accomplished through a critical evaluation of the literature and with the data obtained in the present project. Remarkable concordance between responses of germ cell tests to chemical mutagens was the most striking conclusion to be drawn from the present data base.

Stage-specific DNA synthesis of rat spermatogenesis as an indicator of genotoxic effects of vinblastine, mitomycin C and ionizing radiation on rat spermatogonia and spermatocytes

We have studied the effects of three known mutagens: vinblastine sulphate, mitomycin C and local irradiation of testes on the stage-specific DNA synthesis in the rat testis by using transillumination assisted microdissection of rat seminiferous tubules. It enables us to investigate the sensitivity of different types of spermatogonia and preleptotene spermatocytes to the genotoxic effects of these agents. According to our results, spermatogonia and preleptotene spermatocytes are quite resistant to the action of vinblastine at the treatment times and the doses used. After treatment with mitomycin C, type A2, A3 and A4 spermatogonia seem to be the first cell types affected, which shows itself as a reduction in the DNA synthesis at stages I, II-III, XIII-XIV of the epithelial cycle two and/or three days after the treatment. It also seems that they are mostly affected during the S-phase of their cell cycles. In addition, preleptotene spermatocytes are also sensitive to the action of mitomycin C when they are treated in the G1 phase of the cell cycle. The local irradiation of 3 Gy has severe effects on the spermatogonia of rat testis which can be seen already 18 h after the treatment and becomes more evident 42 and 66 h after the treatment as a reduction of DNA synthesis at stages XII-V. Type A spermatogonia (A1-A4) seem to be the most sensitive cell types to the action of irradiation. This study indicates that the novel method of stage-specific DNA synthesis in rat spermatogenesis allows detailed studies of sensitivities in differentiating spermatogonia to genotoxic agents.

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.

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.