Which exposure stage (gestation or lactation) is more vulnerable to atrazine toxicity? Studies on mouse dams and their pups

Either during gestation or lactation, the experimental mouse dams received one of the following treatments: (a) diet free of pesticide; (b) diet enriched with atrazine (ATZ); 31.0 μg kg⁻¹; (c) diet free of pesticide + oral vitamin E (α-tocopherol; 200 mg kg⁻¹ per mouse); and (d) diet enriched with ATZ (31.0 μg kg⁻¹) + oral vitamin E (200 mg kg⁻¹ per mouse). At the weaning, pups and dams were killed and selected organs and blood samples were collected for analyses. Compared with the control results, ATZ induced alteration in a number of biochemical and histopathological parameters either in the dams or their offspring. The ameliorative effect of vitamin E, based on estimating the “Ameliorative Index; AI” to malondialdehyde (MDA) and superoxide dismutase (SOD) ranged between 0.95 and 1.06 (≈1.0) for the dams and the pups either in gestational or lactational exposure routes. In general, the mouse pups were more vulnerable to ATZ toxicity than their mothers and exposure during gestation was suggested to be more effective than during lactation. The findings may support the need to further investigating the adverse effects of exposure to low doses of commonly used pesticides, especially during pregnancy and breast-feeding as well as effects on newborn child.

The enhancement of the subacute repeat dose toxicity test OECD TG 407 for the detection of endocrine active chemicals: comparison with toxicity tests of longer duration

The OECD conventional 28-day repeat dose toxicity test (OECD TG 407) is widely employed in the initial hazard identification and characterization for commercial chemicals. The OECD has recently undertaken an international effort to "enhance" the conventional 28-day repeat dose toxicity test (OECD TG 407) in order to ensure that chemicals acting through (anti)estrogenic, (anti)androgenic, and (anti)thyroid mechanisms are identified. The enhancements include additional parameters based on the respective target organs from the male and female reproductive tracts, the thyroid, and circulating hormone levels. Ten chemicals with known endocrine modes of action and different potencies were administered using the "enhanced TG 407" test protocol to investigate the performance of this procedure. In the present evaluation, these "enhanced TG 407" protocol results, drawn from a report of the OECD validation studies, are compared to studies of the same or similar chemicals with longer and/or in utero exposures in order to evaluate the capability of the this "enhanced TG 407" in identifying the chemicals' mode of action. The major conclusions that can be drawn from these comparisons are: 1. The "enhanced TG 407" will reliably identify chemicals with a strong to moderate potential to act through endocrine modes of action on the gonads and the thyroid. In addition, this test method gives a first indication for the dose-related potency. 2. Substances with a low potency for an endocrine mode of action, i.e., having only marginal effects in the most comprehensive in vivo studies such as multi-generation studies, may not elicit clear endocrine-related effects in the "enhanced TG 407". In these cases, the primary or principal effects observed will be driven by other toxic actions of the test materials in the "enhanced TG 407". 3. It may be concluded from the present database that prolongation of exposure from 28 days up to 90 days is unlikely to improve the chance of detecting an endocrine-mediated effect 4. A number of higher tier studies with in utero and pubertal exposure show that prenatally exposed rats may be more sensitive to exposures to compounds with very low estrogenic or antiandrogenic potential in some cases than young adult rats as used in the "enhanced TG 407". 5. Overall, these comparisons support the use of the "enhanced TG407" for the detection of endocrine active chemicals. It is therefore recommended to fully accept the enhancements and include them in the test method for toxicological and regulatory use.

A repeated 28-day oral dose toxicity study of nonylphenol in rats, based on the 'Enhanced OECD Test Guideline 407' for screening of endocrine-disrupting chemicals

A 28-day repeated oral dose toxicity study of nonylphenol (NP) was performed for an international validation of the 'Enhanced OECD Test Guideline 407' paying particular attention to the sensitivity of individual endocrine-related parameters. Sprague-Dawley rats, each group consisting of ten males and ten females, were administered NP once daily by gavage at doses of 0 (control), 10, 50, or 250 mg/kg body weight. At 250 mg/kg, three females died or became moribund during the experiment. At this dose, hepatic and renal toxicity was evident in both sexes with increase of relative liver and kidney weights as well as histopathological changes, such as centrilobular liver cell hypertrophy and a variety of renal tubular lesions, and alteration of serum biochemical parameters, some of them being evident from 50 mg/kg in females (glucose and inorganic phosphates). Hematologically, development of anemia was evident at 250 mg/kg in both sexes. Regarding endocrine-related effects, increase of thyroid weight in males was detected from 50 mg/kg. At 250 mg/kg, males exhibited reduction of relative weights of the ventral prostate and seminal vesicles, and females developed irregular estrous cyclicity and vaginal mucosal hyperplasia. Although changes in serum hormone levels were detected in both sexes, magnitude of the changes was small to be regarded as a low toxicological significance. In summary, repeated oral doses of NP to rats for 28 days resulted in hepato-renal toxicity from 50 mg/kg and anemia at 250 mg/kg. Effects on the endocrine system were observed from 50 mg/kg, and assessment of weights and histopathology of endocrine-related organs and estrous cyclicity may be valid in a battery for detecting endocrine effects of NP. The no-observed-adverse-effect level of NP was estimated to be 10 mg/kg per day.

17α-Methyltestosterone: 28-day oral toxicity study in the rat based on the “Enhanced OECD Test Guideline 407” to detect endocrine effects

A 28-day oral gavage toxicity study in the rat with 17alpha-methyltestosterone was conducted as part of the international validation exercise on the modified Enhanced OECD Test Guideline 407 (Organisation for Economic Co-operation and Development, Paris). Special emphasis was placed on the endocrine mediated effects exerted by 17alpha-methyltestosterone, a potent androgen agonist. The test compound was administered daily by oral gavage for at least 28 days to groups of 7-week-old-Wistar rats. Dose levels were 0, 10, 40 and 200 mg/kg body weight per day for males and 0, 10, 100 and 600 mg/kg body weight per day for females. In addition, and outside the remit of the enhanced protocol, testosterone levels in males, oestradiol levels in females and luteinizing hormone (LH) levels in both sexes were measured, to provide a broader profile on the hormonally mediated effects of 17alpha-methyltestosterone. Furthermore, stage-specific quantification of Terminal deoxynucleotidyl transferase-mediated dUTP Nick-End Labeling (TUNEL)-labeled germ cells (apoptotic germ cells) in the seminiferous tubules was also performed, in an effort to demonstrate the precise stages in the spermatogenic cycle 17alpha-methyltestosterone exerts its effect. In this study, the most critical additional parameters contained in the Enhanced OECD Test Guideline 407 for the detection of endocrine disruption were considered to be the histopathological assessment and organ weight data of endocrine-related tissues. Beyond the scope of this validation exercise, an increase in apoptosis in specific germ cell types was detected using the TUNEL assay in male rats treated at 200 and 40 mg/kg.