The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings may not have been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. For more information, see the Explanation of Levels of Evidence for Developmental Toxicity. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Ethylene glycol, a widely used industrial chemical, was evaluated for toxic and teratogenic effects in timed-pregnant mice. EG (O, 750, 1500, and 3000 mg/kg/day, po) in distilled water was administered in a volume of 10 ml per kilogram of body weight on gestational days 6 through 15. Females were weighed and observed during daily treatment for clinical signs of toxicity. At sacrifice on gd 17, a total of 23-25 dams (i.e., confirmed-pregnant females) per treatment group were evaluated. The gravid uterus of each dam was weighed, and the status of uterine implantation sites were recorded (i.e., number of resorptions, dead fetuses, and live fetuses). All live fetuses were weighed, sexed, and examined for external, visceral, and skeletal malformations.
No unscheduled maternal deaths occurred during this investigation, nor were any distinctive clinical signs associated with EG treatment other than piloerection and maternal body weight loss. Maternal body weight on gd O and 6 (i.e., prior to the initiation of treatment) did not differ significantly among treatment groups. On gd 11, 15, and 17, maternal body weight was decreased across treatment groups in a dose-related manner, and both the mid-and high-dose groups were significantly below vehicle controls. Maternal weight gain during the treatment period, as well as maternal weight gain for the entire gestational period, was negatively associated with dose (i.e., weight gain decreased with increasing dose) and was significantly below vehicle controls for both the mid-and high-dose EG groups. When gravid uterine weight was subtracted from total gestational weight gain, none of the EG-treated groups were significantly different from vehicle controls with regard to absolute maternal weight gain, but a dose-related downward trend in absolute weight gain was observed as dosage increased. A significant dose-related reduction in gravid uterine weight was observed, which was significantly below vehicle controls for both the mid-and high-dose groups, and appeared to account for the corresponding reductions in maternal body weight on gd 17. Maternal liver weight (g) displayed a statistically significant dose-related decrease, and both the mid- and high-dose groups were significantly below vehicle controls by pairwise comparison. No significant differences among dose groups were observed for relative maternal liver weight (% body weight).
Indices of reproductive competence prior to the initiation of treatment on gd 6 revealed a preexisting difference among dose groups; i.e., statistically significant differences were observed for the number of corpora lutea per dam and number of implantation sites per dam, but not for percent preimplantation loss. Specifically, dams in the mid-dose group (1500 mg/kg/day EG) had a lower average number of corpora lutea and a corresponding decrease in the number of implantation sites per litter as compared to vehicle control dams. Viability of implanted embryos was significantly affected in the high-dose group (19.86% resorptions per litter) when compared to vehicle controls (8.74% resorptions per litter). A significant dose-related trend toward an increased proportion of litters with one or more resorptions per litter was also observed. The incidence of "dead" fetuses (i.e., fetuses weighing greater than 0.3 g, having discernible digits and exhibiting no vital signs at uterine dissection on gd 17) was decreased in dose-related manner and the mid- and high-dose EG groups were significantly below vehicle controls on this measure. The proportion of litters with one or more dead fetuses was significantly below vehicle controls for the mid-dose group. In summarizing post-implantation mortality (i.e., resorptions plus dead fetuses), the percent nonlive implants per litter exhibited a dose-related increase as dosage increased, but none of the individual treatment groups were significantly different from vehicle control by pairwise comparison. Similarly, the proportion of litters with one or more nonlive implants exhibited a dose-related upward trend as dosage increased, but no significant differences were observed between individual treatment groups and vehicle control. When the outcome of pregnancy was considered as a whole (i.e., accounting for all resorp-tions, dead fetuses and malformed live fetuses from all confirmed-pregnant dams), there was a significant increase in the percent of conceptuses per litter which were adversely affected during the post-implantation phase of gestation; this increase reached statistical significance for both the mid- and high-dose groups. The percent of adversely affected implants per litter exhibited a significant dose-relate trend and occurred with the following incidence for the vehicle control through high-dose groups, respectively: 11.17%, 19.65%, 50.67%, and 64.41%. The percent of litters containing one or more affected implants also increased with dose, i.e., 72.0%, 83.3%, 95.7%, and 100.0%, respectively; the increases for this parameter were statistically higher than vehicle controls for both the mid-and the high-dose groups.
Statistical evaluation of litters containing at least one live fetus (herein referred to as "live litters"), revealed a significant dose-relate reduction in the number of live fetuses per live litter which was significantly below vehicle controls at the highest dose of EG (3000 mg/kg/day). No treatment-relate effect was observed on the percentage of live male fetuses per litter. Average live fetal body weight per live litter was negatively associated with dose and was statistically below vehicle controls for all doses tested, with males and females being equally affected on this measure. The percentage of malformed live fetuses per live litter was positively associated with dose and displayed the following incidence for the vehicle control through high-dose groups, respectively: 0.25%, 10.00%, 37.77%, and 56.54%. The percentage of malformed live fetuses per live litter was statistically higher than vehicle controls for all EG-treated groups. When incidence of malformations was analyzed by fetal sex, male fetuses exhibited an increased incidence of malformations at all EG doses, but female fetuses exhibited an increase only in the mid-and high-dose groups. However, the absence of a significant dose x sex interaction in a dose (4) x replicate (2) x sex (2) ANOVA design with sex as a repeated measure, indicated that no robust sex-selective effect was observed with regard to the incidence of malformed live fetuses. The proportion of live litters containing at least one malformed live fetus also increased with dose and displayed an incidence of 4.00%, 66.67%, 81. 82%, and 95.65% in the vehicle control through high-dose respectively. The proportion of live litters with malformed live fetuses was significantly elevated in all EG-treated groups relative to the vehicle control group. A diversity of gross, visceral, and skeletal malformations were observed with the most characteristic malformations involving craniofacial and skeletal dysmorphogenesis.