Induction of dominant lethal mutations by combined X-ray-acrylamide treatment in male mice

Acrylamide carcinogenicity

The induction of cancer by chemicals is a multiple-stage process. Acrylamide is carcinogenic to experimental mice and rats, causing tumors at multiple organ sites in both species when given in drinking water or by other means. In mice, acrylamide increased the incidence and multiplicity of lung tumors and skin tumors. In two bioassays in rats, acrylamide administered in drinking water consistently induced mesotheliomas of the testes, thyroid tumors, and mammary gland tumors. In addition, brain tumors appeared to be increased. In one of the rat bioassays, pituitary tumors, pheochromocytomas, uterine tumors, and pituitary tumors were noted. The conversion of acrylamide metabolically to the reactive, mutagenic, and genotoxic product, glycidamide, can occur in both rodent and humans. Glycidamide and frequently acrylamide have been positive for mutagenicity and DNA reactivity in a number of in vitro and in vivo assays. The effects of chronic exposure of glycidamide to rodents have not been reported. Epidemiologic studies of workers for possible health effects from exposures to acrylamide have not shown a consistent increase in cancer risk. Although an increase in the risk for pancreatic cancer (almost double) was seen in highly exposed workers, no exposure response relationship could be determined. The mode of action remains unclear for acrylamide-induced rodent carcinogenicity, but support for a genotoxic mechanism based on in vitro and in vivo DNA reactivity assays cannot be ruled out. In addition, the pattern of tumor formation in the rat following chronic exposure supports a genotoxic mode of action but also suggests a potential role of endocrine modification.

Detection of induced male germline mutation: correlations and comparisons between traditional germline mutation assays, transgenic rodent assays and expanded simple tandem repeat instability assays

Several rodent assays are capable of monitoring germline mutation. These include traditional assays, such as the dominant lethal (DL) assay, the morphological specific locus (SL) test and the heritable translocation (HT) assay, and two assays that have been developed more recently--the expanded simple tandem repeat (ESTR) and transgenic rodent (TGR) mutation assays. In this paper, we have compiled the limited amount of experimental data that are currently available to make conclusions regarding the comparative ability of the more recently developed assays to detect germline mutations induced by chemical and radiological agents. The data suggest that ESTR and TGR assays are generally comparable with SL in detecting germline mutagenicity induced by alkylating agents and radiation, though TGR offered less sensitivity than ESTR in some cases. The DL and HT assays detect clastogenic events and are most susceptible to mutations arising in post-spermatogonial cells, and they may not provide the best comparisons with TGR and ESTR instability. The measurement of induced ESTR instability represents a relatively sensitive method of identifying agents causing germline mutation in rodents, and may also be useful for bio-monitoring exposed individuals in the human population. Any future use of the TGR and ESTR germline mutation assays in a regulatory testing context will entail more robust and extensive characterization of assay performance. This will require substantially more data, including experiments measuring multiple endpoints, a greatly expanded database of chemical agents and a focus on characterizing stage-specific activity of mutagens in these assays, preferably by sampling epididymal sperm exposed at defined pre-meiotic, meiotic and post-meiotic stages of development.

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.

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.

Mouse dominant lethal and sperm abnormality studies with combined exposure to X-rays and mitomycin C

The induction of dominant lethal effects and sperm abnormalities in Pzh:Swiss male mice after treatments with X-rays and mitomycin C (MMC) was investigated. Combinations of high (1.00 Gy + 5.25 mg/kg bw MMC) and low (0.25 Gy + 1.75 mg/kg bw MMC) doses of both agents were used. Exposure to high doses of X-rays + MMC induced an increased rate of dominant lethal mutations in spermatogonia and late spermatocytes. Combined treatment with low doses of X-rays and MMC was not mutagenic in any stage of spermatogenesis. MMC increased the frequency of abnormal spermatozoa after exposure alone and in combination with X-rays. Treatment with two high doses (1.00 Gy + 5.25 mg/kg bw MMC) induced 58.4% abnormal spermatozoa. After combined exposure to low doses of both agents 35.7% spermatozoa with malformations were observed.